Symposium Organizers
Yabing Qi, Okinawa Institute of Science and Technology
Jinsong Huang, University of North Carolina-Chapel Hill
Annamaria Petrozza, Istituto Italiano di Tecnologia
Huanping Zhou, Peking University
Symposium Support
Applied Physics Letters | AIP Publishing
Nature Energy | Springer Nature
Science | AAAS
Sustainable Energy &
Fuels | The Royal Society of Chemistry
ES01.01: Commercialization, Synthesis, Large Area, Stability, Tandem and LED
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 3, Ballroom B
8:00 AM - ES01.01.01
The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non-Stoichiometric Precursor Mixtures
Pablo Docampo 1
1 , Newcastle University, Newcastle upon Tyne United Kingdom
Show AbstractWe investigated the influence of moisture on methylammonium lead iodide perovskite (MAPbI3) films and solar cells derived from non-stoichiometric precursor mixtures. We followed both the structural changes under controlled air humidity through in situ X-ray diffraction, and the electronic behavior of devices prepared from these films. A small PbI2 excess in the films improved the stability of the perovskite compared to stoichiometric samples. We assign this to excess PbI2 layers at the perovskite grain boundaries or to the termination of the perovskite crystals with Pb and I. In contrast, the MAI-excess films composed of smaller perovskite crystals showed increased electronic disorder and reduced device performance owing to poor charge collection. Upon exposure to moisture followed by dehydration (so-called solvent annealing), these films recrystallized to form larger, highly oriented crystals with fewer electronic defects and a remarkable improvement in photocurrent and photovoltaic efficiency.
8:15 AM - ES01.01.02
Selection Principles for Stable Multicomponent Perovskites
Michael Saliba 1
1 , EPFL, Lausanne Switzerland
Show AbstractPerovskites have emerged as low-cost, high efficiency photovoltaics with certified efficiencies of 22.1% approaching already established technologies. The perovskites used for solar cells have an ABX3 structure where the cation A is methylammonium (MA), formamidinium (FA), or cesium (Cs); the metal B is Pb or Sn; and the halide X is Cl, Br or I. Unfortunately, single-cation perovskites often suffer from phase, temperature or humidity instabilities exhibiting “yellow phase” impurites instead of the more desired photoactive “black phase”.
Recently, double-cation perovskites (using MA, FA or Cs, FA) were shown to have a stable “black phase” at room temperature.(1,2) These perovskites also exhibit unexpected, novel properties. For example, Cs/FA mixtures supress halide segregation enabling band gaps for perovskite/silicon or perovskite/perovskite tandems.(3) In general, adding more components increases entropy that can stabilize unstable materials (such as the “yellow phase” of FAPbI3 that can be avoided using the also unstable CsPbI3). Here, we take the mixing approach further to investigate triple cation (with Cs, MA, FA) perovskites resulting in significantly improved reproducibality and stability.(4) We then use multiple cation engineering as a strategy to integrate the seemingly too small rubidium (Rb) (that never shows a black phase as a single-cation perovskite) to study novel multication perovskites.(5)
One composition containing Rb, Cs, MA and FA resulted in a stabilized efficiency of 21.6% and an electroluminescence of 3.8%. The Voc of 1.24 V at a band gap of 1.63 eV leads to a very small loss-in-potential of 0.39 V, one of the lowest measured on any PV material indicating the almost recombination-free nature of the novel compound. Polymer-coated cells maintained 95% of their initial performance at 85°C for 500 hours under full illumination and maximum power point tracking. This is a crucial step towards industrialisation of perovskite solar cells.
Lastly, to explore the theme of multicomponent perovskites further, molecular cations were revaluated using a globularity factor. With this, we calculated that ethylammonium (EA) has been misclassified as too large. Using the multication strategy, we studied an EA-containing compound that yielded an open-circuit voltage of 1.59 V, one of the highest to date. Moreover, using EA, we demonstrate a continuous fine-tuning for perovskites in the "green gap" which is highly relevant for lasers and display technology.
(1) Jeon et al. Nature (2015)
(2) Lee et al. Advanced Energy Materials (2015)
(3) McMeekin et al. Science (2016)
(4) Saliba et al., Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. Energy & Environmental Science (2016)
(5) Saliba et al., Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance. Science (2016).
8:30 AM - *ES01.01.03
High Performance of Perovskite Solar Cells—From Cells to Module
Liyuan Han 1 , Xudong Yang 2
1 , National Institute for Materials Science (NIMS), Tsukuba Japan, 2 State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai China
Show AbstractPerovskite solar cells (PSC) are widely interesting in recent years due to its excellent photovoltaic performance and simple solution processing method. Here I will introduce our main achievements in scaling up the area of efficient and stable PSCs. The first recorded efficiency of perovskite solar cells was obtained by using heavily doped inorganic charge extraction layers with high conductivity. We also developed new inverted-structure with a perovskite-fullerene graded heterojunction (GHJ) to improve the electron collection and reduce recombination loss because unbalanced carrier diffusion length at the invert structure with Formamidinium based perovskites. Combining with additive engineering, a certified efficiency 19.2% with cells size of > 1cm2 was achieved.
For further enlarge the cell to large area module, the big challenge is to develop new deposition methods suitable for fabricating large-area perovskite films with low defects density. We proposed a soft-cover deposition method which enable the fabrication of large-area and uniform perovskite films with large grains. The uniform perovskite film with an area of 51cm2 was successfully obtained. We recently synthesized a new non-solvent perovskite precursor and modified the soft-cover method by loading pressure before peeling off the polyimide film to control the thickness of films. The combination of this new precursor and deposition method led to the successful fabrication of perovskite module with aperture area of 6 x 6 cm2, and an efficiency of 12.1% was certified at AIST, which was the first perovskite module efficiency record. Furthermore, I will also talk the cost analysis and stability issue of PSCs.
W. Chen, L. Han, et al. Science, 350, 944(2015).
Y. Wu, L. Han, et al. Nature, Energy, 1 16148(2016).
Y. Wu, L. Han, et al. Adv. Mater. 2017, 1701073.
F. Ye, L. Han, et al. Energy Environ. Sci., 9, 2295(2016).
H. Chen, L. Han, et al. Nature, 2017, DOI :10.1038nature23877
M. Cai, L. Han, et al. Advanced Science, 2016, 1600269.
E. Bi, L. Han, et al. Nat. Commun., 2017, DOI: 10.1038/ncomms15330
9:00 AM - *ES01.01.04
Next-Generation Light-Emitting Materials—Metal Halide Perovskites
Himchan Cho 1 3 4 , Young-Hoon Kim 1 3 4 , Hong-Kyu Seo 2 , Su-Hun Jeong 2 , Min-Ho Park 2 , Hobeom Kim 2 , Jinwoo Byun 2 , Tae-Woo Lee 1 3 4
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 3 Research Institute of Advanced Materials, Seoul National University, Seoul Korea (the Republic of), 4 BK21 PLUS SNU Materials Division for Educating Creative Global Leaders, Seoul National University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show AbstractMetal halide perovskites are emerging high color-purity emitters with low material cost. However, low electroluminescence (EL) efficiency at room temperature is a challenge that should be overcome. Here, we present efficient perovskite light-emitting diodes (PeLEDs) using various strategies to overcome the EL efficiency limitations where the perovskite layers are in forms of (1) 3D crystal structures, (2) quasi-2D crystal structures and (3) nanoparticles (NPs). First, to improve EL efficiency of PeLEDs, we introduced a self-organized buffer hole injection layer to reduce the hole injection barrier and block the exciton quenching at the interface. The high-efficiency methylammonium lead bromide (MAPbBr3) and CsPbBr3 PeLEDs were realized based on the buffer hole injection layer and the temperature dependence of EL in the CsPbBr3 PeLEDs was systematically investigated and correlated with ion migration, EL quenching pathways, and electron-phonon coupling. Furthermore, we found that the formation of metallic lead atoms causes strong exciton quenching, and it was prevented by finely increasing the molar proportion of MABr in MAPbBr3 solution. Also, we suggest that the efficiency in PeLEDs can be increased by decreasing MAPbBr3 grain sizes and consequently improving uniformity and coverage of MAPbBr3 layers. Using these strategies, a high-efficiency PeLEDs was realized (current efficiency = 42.9 cd/A). High-efficiency flexible MAPbBr3 PeLEDs based on graphene anode were also developed for the first time. Chemically inert graphene avoids quenching of excitons by diffused metal atom species from indium tin oxide. Second, quasi-2D perovskites were employed in PeLEDs because of the advantages of quasi-2D perovskites such as the enhancement of film quality, exciton confinement, and reduced trap density, and the devices showed higher efficiency and brightness compared with pure 3D and 2D perovskite counterparts. Finally, perovskite NPs were also synthesized because they can show very high photoluminescence quantum efficiency due to improved exciton binding energy, efficient exciton confinement in their small dimension, and passivation of surface traps by surface-ligands. We fabricated high-efficiency PeLEDs based on MAPbBr3 and formaminidium lead bromide (FAPbBr3) NPs by ligand engineering methods.
9:30 AM - ES01.01.05
Record Operational Stability for Highly Efficient Perovskite Solar Cells Based on Inorganic Charge Extraction Layers
M. Ibrahim Dar 1 , Neha Arora 1 , Shaik Mohammed Zakeeruddin 1 , Michael Graetzel 1
1 Laboratory of Photonics and Interfaces, Department of Chemistry and Chemical Engineering, Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractPerovskite solar cells (PSC) hold the potential to become a credible low-cost photovoltaic technology. However, so far efficiencies over 20% have only been realized with prohibitively expensive organic hole transporting materials (HTM), which could affect adversely the long term operational stability of the PSCs. Therefore, developing efficient PSCs using cheap and stable inorganic HTMs is indispensable to realize large-scale deployment of PSC. In my presentation, I will discuss PSCs exhibiting stabilized power conversion efficiency (PCE) of 20.2%, using the low-cost inorganic compounds CuSCN and TiO2 as hole and electron extraction layer, respectively. We introduce a new method for the solution deposition of compact, 60 nm thin and highly conformal CuSCN layers that afford fast carrier extraction and collection even in the absence of any dopants or additives. The devices show record operational stability, retaining over 95% of initial efficiency after aging at a maximum power point under full-sun illumination at 60 °C for 1000 h. We believe that such a high efficiency together with a remarkable operational stability will pave the way for the large-scale deployment of PSC based technology.
References
Perovskite solar cells with CuSCN hole extraction layers yield stabilized efficiencies greater than 20%. Science 28 September 2017. DOI: 10.1126/science.aam5655.
Electronic and defect structures of CuSCN. J. Phys. Chem. C 114, 9111–9117 (2010).
10:15 AM - *ES01.01.06
Nanomaterials and Interfacial Engineering for Facilitating Commercialization of Perovskite Solar Cells
Hyun Suk Jung 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractAll solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 22% and further improvements are expected up to 25%. These novel organometal halide perovskite absorbers which possess exceptionally strong and broad light absorption enable to approach the performances of the best thin film technologies. To commercialize these great solar cells, there are many bottlenecks such as long term stability, large scale fabrication process, and environmental issues.
In this presentation, we introduce our recent efforts to facilitate commercialization of perovskite solar cells.1-5 For examples, we introduce a recycling technology of perovskite solar cells, which will facilitate the commercialization as well as solve the environmental issues of perovskite solar cells.4 Moreover, Br-concentration gradient perovskite materials were realized by using HBr treatment of perovskite materials.5 The enhancement in hole extraction was verified from measurement of photoluminescence spectroscopy. Also, we are going to discuss about stability issue of perovskite materials regarding charge generation and extraction.
(1) B. J. Kim, D.H. Kim, Y.-Y. Lee, H.-W. Shin, G. S. Han, J. S. Hong, K. Mahmood, T. Ahn, Y.-C. Joo, K. S. Hong, N.-G. Park, S. Lee and H. S, Jung, Energy Environ. Sci., 2015, 8, 916.
(2) M.-C. Kim, B. J. Kim, J. Yoon, J.-W. Lee, D. Suh, N.-G. Park, M. Choi and H. S. Jung, Nanoscale , 2015, 7, 20725.
(3) S. Jang, J. Yoon, K. Ha, M.-C. Kim, D. H. Kim, S. M. Kim, S. M. Kang, S. J. Park, H. S. Jung, and M. Choi, Nano Energy, 2016, 22, 499.
(4) B. J. Kim, D. H. Kim, S. L. Kwon, S. Y. Park, Z. Li, K. Zhu and H. S. Jung, Nature Communications, 2016, 7, 11735.
(5) M.-C Kim, B. Jo Kim, D.-Y. Son, N.-G. Park, H. S. Jung, and M. Choi, Nano Lett., 2016, 16, 5756.
10:45 AM - *ES01.01.07
Fully Evaporated High Efficiency Single Junction and Tandem Perovskite Based Solar Cells
Jorge Avila 1 , Christina Momblona 1 , Benedikt Daenekamp 1 , Lidon Gil-Escrig 1 , Daniel Perez-del-Rey 1 , Pablo Boix 1 , Michele Sessolo 1 , Henk Bolink 1
1 , University of Valencia, Paterna Spain
Show AbstractPerovskite based solar cells, mostly employ solution processed perovskite layers. Evaporated methylammonium lead iodide perovskite layers have also been reported and been employed in solar cells. Our group has developed several perovskite based solar cells, using vacuum based perovskite preparation methods. These metal oxide free p-i-n type perovskite cells exhibit high power-conversion efficiencies. We have extended this work to fully evaporated perovskite devices reaching power conversion efficiencies as high as 20 % in a planar single junction device and similar performance in tandem devices. Avenues to further increase the device performance by using multiple cation perovskite prepared via sublimation will also be presented.
11:15 AM - ES01.01.08
Optical Bandgap Energy of CH3NH3PbI3 Studied by Photoconductivity and Reflectance Spectroscopy
Wei Huang 1 2 , Yu Liu 1 2 , Shizhong Yue 1 2 , Peng Jin 1 2 , Zhijie Wang 1 2 , Yonghai Chen 1 2
1 Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing China, 2 College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing China
Show AbstractOver the past several years, methylammonium lead halide CH3NH3PbX3 (MAPbX3, X = I, Br, and Cl) have attracted global attention as a promising light-energy conversion device because of their low fabrication cost, process simplicity, and robust nature. Especially the efficiency of solar cell based on solution-processed hybrid halide perovskite is 22.1%. However, the real optical band gap of perovskite MAPbI3 is still disputed. To comprehend the intrinsic characteristics in this materials, we studied the near-band-edge optical responses of solution-processed MAPbI3 thin films and single crystals by photoconductivity and reflectance spectroscopy at room temperature. These spectra of MAPbI3 thin film all show a significant absorption edge about 1.58 eV. Surprisingly, we observe an extra absorption edge (1.47 eV) in MAPbI3 single crystal. To explain the reason why this low energy structure of polycrystalline MAPbI3 have disappeared, we established a simple kinetic model of charge annihilation processes. It is noteworthy that this low energy absorption edge of MAPbI3 single crystal is the first report on an organic-inorganic hybrid perovskite. Therefore, the MAPbI3 single crystal exhibits a relatively wide absorption which makes it as a promising candidate for photoelectric applications.
11:30 AM - ES01.01.09
Determination of Unique Power Conversion Efficiency of Perovskite Solar Cell Showing Hysteresis in the I-V Curve under Various Light Intensities
Satoshi Uchida 1 , Ludmila Cojocaru 1 , P.V.V. Jayaweera 2 , Shoji Kaneko 2 , Jotaro Nakazaki 1 , Takaya Kubo 1 , Hiroshi Segawa 1
1 , The University of Tokyo, Tokyo Japan, 2 , SPD Laboratory, Inc., Hamamatsu Japan
Show AbstractPhotovoltaic response of solar cells under weak irradiation intensity is very useful and attractive topic for understanding of power generation at real use. To achieve the ultimate low light intensity (10-4 mWcm-2 range) we started experiments from the construction of LED solar simulator itself and carefully calibrated with specific spectrometer. Surprisingly, we found very interesting I-V behavior, especially for dye sensitized solar cells (DSC) and perovskite solar cells (PSC). Under the light intensity below 10-2 mWcm-2, unlike reference c-Si solar cell, both DSC and PSC showed constant current resulting in a conversion efficiency of over 100% for PSC and over 10% for DSC. This is not by error of machine, not by mistake for operation because the reference c-Si solar cell works well. We spent almost two years to solve this problem and finally understood well as follows.
Constant open circuit voltage and short circuit current in the conventional I-V measurement for PSC and DSC at such an ultra-low light intensity are originated from internal capacitance, which gives small amount of current, so called capacitive current. Having constant capacitive current at low light intensity, we found these different values for DSC, PSC and c-Si and described in the article. Moreover the difference in capacitance values can be directly related to the gap of hysteresis in I-V measurement.
In order to avoid the above over/under estimation of performance of capacitive solar cell such as PSC and DSC, we again constructed specialized machine for tracking maximum power point (MPP), which gives correct power efficiencies at low current, single nano-ampere range.
11:45 AM - ES01.01.10
Colloidal APbX3 Nanocrystals [A=Cs+, CH3NH3+, CH(NH2)2+, X=Cl, Br, I] with Bright Photoluminescence Spanning from Ultraviolet to Near-Infrared Spectral Regions
Maksym Kovalenko 1 2
1 , ETH Zurich, Zurich Switzerland, 2 , Empa–Swiss Federal Laboratories for Materials Science and Technology, Duebendorf Switzerland
Show AbstractChemically synthesized inorganic nanocrystals (NCs) are considered to be promising building blocks for a broad spectrum of applications including electronic, thermoelectric, and photovoltaic devices. We have synthesized monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X=Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors [1]. Their bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 NCs is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90% and also low thresholds for stimulated emission [2]. Post-synthestic chemical transformations of colloidal NCs, such as ion-exchange reactions, provide an avenue to compositional fine tuning or to otherwise inaccessible materials and morphologies [3]. Similar synthesis methodologies are well suited also for hybrid perovskite nanocrystals based on methylammonium (MA) and formamidinium cations (FA): MAPbX3 [4], FAPbBr3 [5], Cs1-xFAxPbI3 and FAPbI3 [6]. In particular, Cs- and FA-based NCs are highly promising for luminescence downconversion-based LCD television displays (bright and narrow emission at 530 and 640 nm), for infrared light-emitting diodes and as precursors/inks for perovskite solar cells. In this talk, we will discuss the synthesis methodologies and optical properties of these novel APbX3 NCs.
L. Protesescu et al. Nano Letters 2015, 15, 3692–3696
G. Nedelcu et al. Nano Letters 2015, 15, 5635–5640
S. Yakunin et al. Nature Communications 2015, 9, 8056.
O. Vybornyi et al. Nanoscale 2016, 8, 6278-6283
L. Protesescu et al. J. Am. Chem. Soc. 2016, 138, 14202–14205
L. Protesescu et al. ACS Nano 2017, 11, 3119–3134
ES01.02: Commercialization, Synthesis, Large Area, Stability and Tandem
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 3, Ballroom B
1:30 PM - *ES01.02.01
Solution Chemistry Engineering towards Large-Scale High-Performance Perovskite Solar Cells and Modules
Kai Zhu 1
1 , National Renewable Energy Laboratory, Lakewood, Colorado, United States
Show AbstractOrganic-inorganic hybrid halide perovskites have recently emerged as a new class of light absorbers with a rapid progress and impressive efficiencies (>22%) for solar conversion applications. However, there is a significant processing gap between the lab-scale spin coating and scalable deposition methods toward future roll-to-roll manufacturing. In this presentation, I will discuss the upscaling challenges associated with the sensitivity of perovskite crystallization and film formation in different processing conditions. I will show our recent studies toward a better understanding and control of perovskite nucleation, grain growth, and microstructure evolution using solution processing. The precursor chemistry and growth conditions are found to affect significantly the structural and electro-optical properties of perovskite thin films. We also find that the solvent and coordination chemistry of perovskite precursor is critical for scalable deposition. We discuss a rational design of perovskite precursor film formation to achieve highly specular films using scalable deposition methods. Using these high quality perovskite films, we have achieved high-efficiency perovskite solar modules as well as lab-scale devices with efficiencies approaching the values obtained by spin coating. The challenges associated with perovskite solar module fabrication will also be discussed. These results demonstrate a promising path towards commercialization of the perovskite photovoltaic technology.
2:00 PM - *ES01.02.02
The Application of 2D Materials in Perovskite Solar Cells
Feng Yan 1
1 , Hong Kong Polytechnic University, Hong Kong China
Show AbstractGraphene has shown promising applications in photovoltaic devices for its high carrier mobility and conductivity, high transparency, excellent mechanical flexibility and ultrathin thickness, and has been used in solar cells as transparent electrodes or interfacial layers. Other 2-dimensional (2-D) materials also show some fascinating physical properties due to the 2-dimensional nature. In this talk, I will introduce our recent work on the applications of graphene and other 2-D material in perovskite solar cells as follows. (1) Semitransparent perovskite solar cells are prepared by laminating graphene transparent electrodes on the top for the first time. The device performance is optimized by improving the conductivity of the graphene electrodes and the contact between the graphene and the perovskite active layers during the lamination process. The devices show high power conversion efficiencies when they are illuminated from both sides. (2) Solution-exfoliated few layers black phosphorus (BP) and MoS2 flakes are served as effective charge transport layers in perovskite solar cells, which can improve the device performance due to the passivation of grain boundaries of perovskite active layers and the enhancement of charge transfer. (3) Ultrathin flexible perovskite solar cells were prepared by introducing graphene transparent electrodes. The devices show excellent bending stability and high power output per weight. All of the works demonstrate promising applications of 2-D materials in perovskite solar cells and pave a way for improving perovskite solar cells as well as other types of photovoltaic devices by utilizing novel 2-D materials.
2:30 PM - ES01.02.03
Novel Microfabrication-Free Solution-Based Approach for Forming Periodically Nanostructured Perovskite for Photovoltaic and LED Applications
Wallace Choy 1 , Jian Mao 1
1 , University of Hong Kong, Hong Kong China
Show AbstractOrganic-inorganic hybrid perovskite has attracted extensive attention in recent years for its wide applications in various optoelectronic devices such as solar cells, light emitting diodes (LEDs), lasers, transistors, and photodetectors. However, it is still challenging to directly pattern perovskite thin films because perovskite is very sensitive to polar solvents and high temperature environment. In this work, we demonstrate our novel approach to fabricate high-quality perovskite grating and its potential applications in optoelectronic devices through the study of the performances of grating patterned light emitting diode.
Our results show that (1) different from typical imprint method to form nanograting, we report for the first time to utilize methylamine gas (MA) to fabricate CH3NH3PbI3 (MAPbI3) periodic nanostructures via MA induced phase transition under ambient condition (the MA induced intermediate is liquid under room temperature). This approach is quite different from traditional nanoimprinting which use high pressure to press the rigid mold and completely different from most used photo-lithography or electron beam lithography technique which needs solvent to etch the sample. (2) our direct nano-patterning approach is suitable for fabrication of large-area perovskite pattern. As a proof of concept in lab scale, 15 mm*15 mm periodic nanostructures have been demonstrated. (3) Our direct nano-patterning approach can not only fabricate periodic nanostructures in different perovskite materials such as MAPbI3 and HC(NH2)2PbI3 (FAPbI3) but also improve the crystallinity, light absorption and emission of perovskite for solar cell and LED applications. It should be noted that some works reported by others also demonstrate the fabrication of perovskite grating, however most of them lead to reduced crystallinity and PL. Consequently, our approach opens up a simple way to nano-engineering perovskite. The nano-patterned perovskite can be used in different perovskite optoelectronic devices.
2:45 PM - ES01.02.04
Accidents Happen—Perovskite Solar Cells in a Fire
Bert Conings 1 , Aslihan Babayigit 1 , Hans-Gerd Boyen 1
1 , Hasselt University, Diepenbeek Belgium
Show AbstractIn the past 5 years, metal halide perovskites have become the prodigy of photovoltaic technology.[1] A tremendous surge of research in the topic has led to an unprecedented rise in power conversion efficiency up to values that rival CIGS and Si solar cells, and remarkable improvements have been made in terms of environmental and thermal stability as well. Arguably the remaining Achilles heel of the technology is that the desirable properties of metal halide perovskites for application in photovoltaics so far have only been achieved with lead (Pb), (and to a lesser extent tin (Sn)) as the metal cation. Consequently, the associated toxicological hazard in case of unintentional liberation of heavy metal containing chemicals into the environment raises concerns in view of the large-scale applicability of perovskite photovoltaics.[2] On the other hand, what has not been sufficiently considered so far is that in real-world applications the large-area perovskite devices are always thoroughly encapsulated, so accidental spillage of heavy metals is unlikely. A scenario that should not be overlooked, however, is that of fire. Not only can the module encapsulation be severely compromised in such event, possibly setting free toxic compounds in the immediate environment, an additional hazard lies in the exhaust of toxic airborne particles that may travel longer distances. To gain insight in the severity of the danger involved, we have conducted fire simulations on Si-perovskite tandem mini-modules, fabricated according to industry standards. A post-fire chemical analysis is presented of the module as well as downstream fumes. The results of these experiments allow to come closer to an objective assessment of the—hitherto alleged—inherent danger associated with perovskite-based solar panels in the case of fire.
[1] M. Saliba, J.-P. Correa Baena, M. Grätzel, A. Hagfeldt, A. Abate, Angew. Chem. Int. Ed., 2017, DOI: 10.1002/anie.201703226.
[2] A. Babayigit, A. Ethirajan, M. Muller, B. Conings, Nat. Mater. 15, 2016, 247-251.
3:30 PM - *ES01.02.05
Progress in Making Stable and Efficient Perovskite Tandem Solar Cells
Michael McGehee 1 , Zhengshan Yu 2 , Mathieu Boccard 2 , Tomas Leijtens 1 , Rongrong Cheacharoen 1 , Zachary Holman 2 , Stacey Bent 1 , Kevin Bush 1 , Rohit Prasanna 1
1 , Stanford University, Stanford, California, United States, 2 , Arizona State University, Tempe, Arizona, United States
Show AbstractWe have perovskite on silicon tandem solar cells with efficiency greater than 25 %. We have also made all-perovskite tandems using a new ABX3 perovskite composition containing a mixture of tin and lead on the B site that have greater than 20% efficiency. With solar cells packaged between two sheets of glass with rubber edge seals, we have passed the industry standard 1000 hour 85°C 85% humidity damp heat test as well as 200 cycles between 85°C and -40°C. One of the keys to obtaining high efficiency and stability was optimizing the composition of cesium and formamidinium on the A site and iodine and bromine on the X site. We will show how light -induced phase separation occurs when there is too much bromine in the films. Another crucial step towards improving stability is the use of atomic layer deposition to deposit a tin oxide buffer layer on the perovskite that enables the sputter deposition of an indium tin oxide transparent electrode. ITO is less reactive with perovskites than the metals that are typically used in perovskite solar cells. The ALD layer has minimal parasitic absorption and prevents shunting. Our progress towards achieving 30% power conversion efficiency and passing even more aggressive stability tests will be presented.
4:00 PM - ES01.02.06
Efficient All-Perovskite Tandem Solar Cells with Effective Interconnecting Layer
Dewei Zhao 1 , Yue Yu 1 , Changlei Wang 1 , Weiqiang Liao 1 2 , Corey R. Grice 1 , Lei Guan 1 , Kai Zhu 3 , Ren-Gen Xiong 2 , Yanfa Yan 1
1 Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, University of Toledo, Toledo, Ohio, United States, 2 Ordered Matter Science Research Center, Southeast University, Nanjing, Jiangsu, China, 3 Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractTandem solar cells using all metal-halide perovskite thin films are an attractive choice for next-generation solar cells in terms of reduced cost and high efficiency.[1-4] However, the progress in developing efficient all-perovskite tandem solar cells has been hindered by the lack of high-performance low-bandgap perovskite solar cells. We have reported efficient mixed tin-lead iodide low-bandgap (~1.25 eV) perovskite solar cells with a maximum power conversion efficiency of 17.6% and a certified efficiency of 17.01% with a negligible current-voltage hysteresis, indicating it is suitable for bottom cell applications in all-perovskite tandem solar cells.[5] When mechanically stacked with a ~1.58 eV bandgap perovskite top cell, our best all-perovskite 4-terminal tandem solar cell shows a steady-state efficiency of 21.0%. Moreover, we have recently demonstrated high-performance wide bandgap (1.75 eV) perovskite solar cells with a stabilized PCE of 17.18%.[6] Hereby, we will demonstrate the fabrication of efficient all-perovskite monolithic tandem solar cells. Careful optimization of novel interconnecting layer has been completed to realize the electrical and optical connection of wide-bandgap and low-bandgap sub cells, leading to current matching in both sub cells and high-efficiency all-perovskite monolithic tandem solar cells. Our results suggest that tandem architecture is promising to further enhance the performance of perovskite solar cells and move forward the commercialization of the emerging perovskite solar cell technology.
References
[1] D. Forgács, L. Gil-Escrig, D. Pérez-Del-Rey, C. Momblona, J. Werner, B. Niesen, C. Ballif, M. Sessolo, H. J. Bolink, Adv. Energy Mater. 2017, 7, 1602121.
[2] G. E. Eperon, T. Leijtens, K. A. Bush, R. Prasanna, T. Green, J. T.-W. Wang, D. P. McMeekin, G. Volonakis, R. L. Milot, R. May, A. Palmstrom, D. J. Slotcavage, R. A. Belisle, J. B. Patel, E. S. Parrott, R. J. Sutton, W. Ma, F. Moghadam, B. Conings, A. Babayigit, H.-G. Boyen, S. Bent, F. Giustino, L. M. Herz, M. B. Johnston, M. D. McGehee, H. J. Snaith, Science 2016, 354, 861.
[3] B. Chen, Y. Bai, Z. Yu, T. Li, X. Zheng, Q. Dong, L. Shen, M. Boccard, A. Gruverman, Z. Holman, J. Huang, Adv. Energy Mater. 2016, 6, 1601128.
[4] N. N. Lal, Y. Dkhissi, W. Li, Q. Hou, Y.-B. Cheng, U. Bach, Adv. Energy Mater. 2017, DOI: 10.1002/aenm.201602761.
[5] D. Zhao, Y. Yu, C. Wang, W. Liao, N. Shrestha, C. R. Grice, A. J. Cimaroli, L. Guan, R. J. Ellingson, K. Zhu, X. Zhao, R.-G. Xiong, Y. Yan, Nat. Energy 2017, 2, 17018.
[6] Y. Yu, C. Wang, C. R. Grice, N. Shrestha, D. Zhao, W. Liao, L. Guan, R. A. Awni, W. Meng, A. J. Cimaroli, K. Zhu, R. J. Ellingson, Y. Yan, ACS Energy Letters 2017, 1177.
4:15 PM - ES01.02.07
Work-Function Modification of FTO in Perovskite Solar Cells
Federico Pulvirenti 1 , Berthold Wegner 2 4 , Jay Patel 3 , Nakita Noel 3 , Grey Christoforo 3 , Moritz Riede 3 , Henry Snaith 3 , Laura Herz 3 , Norbert Koch 4 , Seth Marder 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , Helmholtz-Zentrum Berlin, Berlin Germany, 4 , Humboldt-Universität zu Berlin, Berlin Germany, 3 , University of Oxford, Oxford United Kingdom
Show AbstractMinimization of electron-collection losses at the interface between fluorinated tin oxide (FTO) and the electron-transporting layer (ETL) in perovskite solar cells can be achieved by decreasing the work-function (WF) of the electrode so that it is lower than the electron affinity of the ETL. The WF of FTO can be decreased by more than 1 eV by vacuum-depositing layers of a relatively air-stable organometallic dimer on the electrode surface. Such large changes in WF are associated with electron transfer from the dimer to the FTO substrate. Ultraviolet photoelectron spectoscopy data shows that when vacuum-depositing the ETL on the dimer-modified FTO, the WF of the electrode is pinned to the LUMO of the electron-transporting layer. Since x-ray photoelectron spectroscopy (XPS) data reveals the presence of unreacted dimer on FTO, XPS was used to investigate whether doping of the ETL takes place upon annealing. Two classes of organic semiconductors with similar electron affinities are compared for their use as efficient n-type compact layer in perovskite solar cells. While higher stabilized power outputs (SPO) are obtained for devices using a fullerene instead of a perylene derivative as ETL, WF-modification of the electrode leads to an increase in SPO, which is consistent with the minimization of the electron-collection barrier between FTO and the ETL. Moreover, the organometallic dimer, which acts as a strong molecular reductant, can also be solution-processed and its use as a WF-modifier is compared to the use of a cheaper metal-free reducing agent. Devices were fabricated and interesting results pave the way to WF-tuning of several relevant electrode materials, and the adoption of such WF-modifiers in the industrial production of perovskite solar cells.
4:30 PM - ES01.02.08
Open Circuit Potential Build-Up in Perovskite Solar Cells from Dark Conditions to 1 Sun
Laxman Gouda 1 , Ronen Gottesman 1 , Adam Ginsgurg 1 , David Keller 1 , Eynav Haltzi 1 , Jiangang Hu 1 , Shay Tirosh 1 , Pablo P. Boix 1 2 , Arie Zaban 1
1 , Bar-Ilan University, Ramat-Gan Israel, 2 , Nanyang Technological University, Singapore Singapore
Show AbstractThe high open-circuit potential (Voc) achieved by perovskite solar cells (PSCs) is one of the keys to their success. The Voc analysis is essential to understand their working mechanisms. A large number of CH3NH3PbI3−xClx PSCs were fabricated on single large-area substrates and their Voc dependencies on illumination intensity, I0, were measured showing three distinctive regions. Similar results obtained in Al2O3 based PSCs relate the effect to the compact TiO2 rather than the mesoporous oxide. We propose that two working mechanisms control the Voc in PSCs. The rise of Voc at low I0 is determined by the employed semiconductor n-type contact (TiO2 or MgO coated TiO2). In contrast, at I0 close to AM1.5G, the employed oxide does not affect the achieved voltage. Thus, a change of regime from an oxide-dominated EFn (as in the dye sensitized solar cells) to an EFn, directly determined by the CH3NH3PbI3−xClx absorber is suggested.
4:45 PM - ES01.02.09
A Facile Lead Removal Process from Waste Products of Perovskite Solar Cells Using Magnetic Hydroxyapatite Composites
So Yeon Park 1 , Donghoe Kim 2 , Hyun Suk Jung 1
1 School of Advanced Materials Science and Engineering, Sungkyunkwan Univ, Suwon Korea (the Republic of), 2 Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractHybrid organic-inorganic perovskite solar cells (PSCs) have emerged as one of representative candidates for next generation photovoltaic industry field. However, some challenges such as lead issues and expensive novel materials should be overcome for commercialization. Especially lead issue seems to be the utmost problem although the amount of lead contained in Perovskite solar cells is controversially lower than those in paints and batteries. The lead waste yielded from manufacturing PSCs may significantly impact environment. Many researchers have addressed the recycling strategies to solve this problem. So far, these methods have been restricted only to recycling PSCs themselves. The recycling byproducts such as Pb-contained solvent is also important.
In this study, we synthesized the multi-functional magnetic hydroxyapatite (Fe/HAP) composite as a lead adsorbent agent by using a two-step procedure: 1) formation of IONP/HAP composites by attaching iron oxide nanoparticles (IONPs) on surface of hollow-structured HAP using hydrogen bonding 2) Fe/HAP composites fabricated by annealing at 500 °C in forming gas (95% N2 + 5% H2, reducing) for eliminating polymers and improving magnetic properties. The efficient lead-absorption properties of Fe/HAP were confirmed in both water and aprotic polar solvents, which are used for fabrication of PSCs. The lead concentration in solvents after Fe/HAP treatment was below 15 ppb. Moreover, we discovered that the lead adsorption mechanism in aprotic polar solvents is different from that in water, given by analysis using Brunauer–Emmett–Teller (BET) surface area, Zeta-potentials, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We believe that this lead removal process will be solution to relieve the environmental issues of Perovskite solar cells.
ES01.03: Poster Session I
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - ES01.03.01
Direct Evidence of Ion Diffusion for the Silver-Electrode-Induced Thermal Degradation of Inverted Perovskite Solar Cells
Jiangwei Li 1 , Qingshun Dong 1 , Nan Li 1 , Liduo Wang 1
1 Chemistry, Tsinghua University, Beijing China
Show AbstractPerovskite solar cells (PSCs) are widely acknowledged as promising photovoltaic devices. However, the state-of-art PSCs have long suffered from the thermal instability during the standard damp heat test at 85 °C, thus hindering their commercialization. So far, no thorough investigation on the thermal degradation mechanism has been reported for PSCs with the inverted structure, which is widely adopted due to the promising application of the thin-film technology. The poor understanding of the thermal degradation mechanism has long caused the lack of experimental supports for most researchers to improve the thermal stability of PSCs.
Herein, we provide direct evidence for the thermal degradation mechanism of the inverted structure PSCs. We find that the undesirable efficiency degradation is strongly associated with the introduction of silver electrodes during the thermal treatment. Elemental depth profiles directly expose that during thermal treatment, iodide (I-) and methylammonium (MA+) ions from the perovskite layer diffuse through the PCBM layer and accumulate at the Ag inner surface. The driving force of forming AgI then facilitates the extraction of ions, and further causes the decomposition of the MAPbI3. We demonstrate that the loss of ions mainly occurred at the perovskite grain boundaries (GBs), leading to the reconstruction of GBs (with an interesting phenomenon of GB "fusing" and crystal grain enlargement) and forming thick PbI2 gaps between crystal grains. Therefore, the deteriorated MAPbI3 thin film, the poor electron extraction and the generation of AgI barrier result in the degradation of efficiencies.
These direct evidence provide an in-depth understanding of the effect of thermal stress on the planar devices, offering both experimental support and theoretical guidance for the further improvement of the thermal stability of the PSCs.
8:00 PM - ES01.03.02
Thin-Film Hybrid Halide Perovskite Crystallization—Approaching Single Crystal Mobilities
Pablo Docampo 1
1 , Newcastle University, Newcastle upon Tyne United Kingdom
Show AbstractHybrid halide perovskites combine top-notch optoelectronic properties with solution-deposition. This unprecedented combination has led to the development of solar cells approaching power conversion efficiencies achieved by industry staples such as poly-Si. The road towards these achievements has been marked by a constant improvement of perovskite deposition techniques fuelled by our increasing understanding of the crystallization processes. In particular, the choice of deposition technique and the composition of the precursor species have a big influence on the crystallization kinetics and ultimately on the quality of the final perovskite film. Regardless of the approach, all results converge on the idea that in order to maximize performance, the disorder in the perovskite film must be minimised, generally by targeting larger crystals. Here, I will show a new approach based on the stabilisation of an intermediate lead-acetate phase, which results in extremely highly ordered perovskite films, both in terms of crystal orientation and size. Our results show that with this new approach, mobility values approaching those found in single crystals can be achieved.
8:00 PM - ES01.03.03
Enhanced Light Absorption of Thin Perovskite Solar Cells Using Textured Substrates
Biao Shi 1 , Bofei Liu 1 , Jingshan Luo 2 , Yuelong Li 1 , CuiCui Zheng 1 , Xin Yao 1 , Lin Fan 1 , Junhui Liang 1 , Yi Ding 1 , Changchun Wei 1 , Dekun Zhang 1 , Ying Zhao 1 , Xiaodan Zhang 1
1 , Institute of Photoelectronic Thin Film Devices and Technology of Nankai University, Tianjin China, 2 , Laboratory of Photonics and Interfaces, Institution of Chemical Sciences and Engineering, Lausanne Switzerland
Show AbstractThin perovskite layers are crucial for fabricating semitransparent perovskite solar cells and tandem devices. However, this will reduce the light absorption of the device, resulting in low efficiency. To overcome this dilemma, we use textured fluorine doped SnO2 (FTO) substrates to trap light and enhance light absorption in thin perovskite solar cells. Both optical simulation and experimental demonstration show the successful application of this new strategy in enhancing the efficiency. In the meantime, the transmittance of the full cell beyond the perovskite absorption range is not sacrificed, which is pivotal for fabricating semitransparent perovskite solar cells and tandem devices. The textured substrates not only enhance the light absorption of the device, but also induce the growth of perovskite films with large crystal grain size, which are both beneficial for the efficiency improvement. As a result, we successfully fabricated thin PSC based on textured substrate with short circuit current density and efficiency enhanced 14.5% and 22% compared with smooth substrate.
8:00 PM - ES01.03.04
Molecular Design Enabled Reduction of Interface Trap Density for Highly Efficient and Stable Perovskite Solar Cells
Xiangyue Meng 1 2
1 , Beijing University of Chemical Technology, Beijing China, 2 Department of Chemistry, Hong Kong University of Science and Technology, Hong Kong China
Show AbstractAdvancing perovskite solar cell (PVSC) technologies toward its theoretical power conversion efficiency (PCE) and optimum stability requires stringent control over the trap densities in the devices. By introducing PPDIN6 as a new interlayer material at the PCBM/Ag interface for planar p-i-n PVSCs, we succeeded in significantly reducing the trap density, and thus facilitating electron injection and suppressing electron recombination at the PCBM/Ag interface. Thus a PCE of 20.43% was achieved with an impressive fill factor of 83.4%. Moreover, since the amine groups in PPDIN6 can neutralize the migrating iodide ions and inhibit the formation of the insulating Ag-I bonds on the surface of the Ag electrode. As a consequence, we realized long-term stability for PPDIN6 based PVSCs, which maintained 90% of their initial performance after continuous operation at their maximum power point for 200 hours under 1-sun illumination in air with a relative humidity of 30%-50%.
8:00 PM - ES01.03.05
Effect of Interfacial Molecular Orientation on Power Conversion Efficiency of Perovskite Solar Cells
Minyu Xiao 1 , Zhan Chen 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractAs more and more high-performance planar heterojunction solar cells have been developed, understanding buried interfacial molecular structure and the interfacial structure-function correlation becomes increasingly important, because a wide variety of charge carrier dynamics (transportation, separation, extraction etc.) happen at interfaces in a planar heterojunction solar cell. However,, currently widely used characterization techniques for surfaces and thin films such as X-ray diffraction, cross-section SEM, UV-Visible absorption spectroscopy etc. could not provide the needed structural information at buried interfaces. In this research, by controlling the structure of the hole transport layer (HTL) in a perovskite solar cell and by applying a surface/interface sensitive non-linear vibrational spectroscopic technique (Sum Frequency Generation vibrational spectroscopy or SFG), we successfully probed the molecular structure at the buried interface and correlated the structural information of the buried interfaces to solar cell performance. Here, an edge on polythiophene (PT) interfacial molecular orientation at the buried perovskite (photoactive layer)/PT (HTL) interface showed more than 2 times higher power conversion efficiency (PCE) verses a lying down PT interfacial orientation. The interfacial molecular structural difference was achieved by altering alkyl sidechain length of the PT derivatives, where PT with a shorter alkyl side chain showed an edged on interfacial orientation with a higher PCE, compared to PT with a longer alkyl side chain. With similar bandgap alignment and bulk structure in the PT layer, it is believed that the interfacial molecular structural difference (i.e., the orientation difference) of the different PT derivatives is the major cause of the perovskite solar cell PCE difference.
8:00 PM - ES01.03.06
Development of Highly Efficient Monolithic Perovskite-Perovskite Tandem Solar Cells
Adharsh Rajagopal 1 , Zhibin Yang 1 , Alex Jen 1
1 , University of Washington, Seattle, Washington, United States
Show AbstractPower conversion efficiencies (PCEs) for perovskite single junction solar cells are inching closer to the corresponding Shockley-Queisser limit. To further improve PCE, it is highly desirable to develop all perovskite tandem solar cells, which possess merits of solution processability and low-cost, large-scale manufacturing capability inherent to hybrid perovskites. However, severe photovoltage loss (Voc,loss) in individual subcells are currently limiting the performance of perovskite tandem solar cells.
By utilizing an integrated process, compositional, interfacial, optical, and device engineering we successfully minimized the overall Voc,loss and have achieved a record high PCE of 18.5% for monolithic (2-terminal) perovskite-perovskite tandem solar cells. Mitigation of non-radiative recombination centers arising from improper interfacial energetics and poor optoelectronic characteristics of absorber materials were pivotal in realization of enhanced quasi-fermi level splitting and thus improved open-circuit voltage (Voc) for individual subcells. Ultimately, the tandem solar cell possesses a high Voc of 1.98 V, which is approaching an impressive 80% of the theoretical limit and by far the best for all perovskite based monolithic tandem solar cells. The talk will be centered around this recent exciting development to highlight prospects of using perovskite-perovskite tandems for solar energy generation, provide a blueprint for further improvement and discuss the path for realizing PCEs around 25%.
References:
A. Rajagopal, Z. Yang, and A. Jen et al., Adv. Mater. 2017, DOI: adma.201702140.
Z. Yang,# A. Rajagopal,# and A. Jen et al., Nano Lett. 2016, 16, 7739.
Z. Yang, A. Rajagopal, and A. Jen et al., Adv. Mater. 2016, 28, 8990.
8:00 PM - ES01.03.08
Toward Industrialization—High Performance Flexible Perovskite Solar Cells via Blade Coating under Ambient Conditions
Jishu Gao 1 , Jiabang Chen 1 , Deng Wang 1 , Hang Hu 1 , Baomin Xu 1
1 , Southern University of Science and Technology, Shenzhen China
Show AbstractPerovskite solar cells (PSCs) as one of the promising photovoltaic technologies has attracted great research interest among the world. Due to their advantages of solution processing ability, low cost and remarkable power conversion efficiencies, PSCs enjoy huge potential for the industrialization. The state-of-art researches about PSCs mainly focus on the spinning coating process; however, this is not suitable for the large scale production of electronic devices1. In order to find an alternative approach to fabricate PSCs, research communities have developed many methods, including spray deposition, blade coating, and slot-die coating2. In our research, blade coating rather than spin coating is adopted since lots of raw materials could be saved, resulting in a low cost on the materials. Moreover, this method is compatible with the roll-to-roll process, which aims to the mass production. In the experiment, we use PEN/ITO as the substrate, PEDOT: PSS as the hole transportation layer (HTL) material, the lead acetate as the lead source of the perovskite, PCBM as the electron transportation layer (ETL) material. The Ag electrode is prepared via thermal evaporation, while all the rest layers, namely HTL, perovskite layer and ETL, are fabricated by the blade coating method under the ambient condition, with a relative humidity higher than 35%. It is found that the thickness of the perovskite layer can greatly affect the performance of the solar cells. The thickness of the perovskite layer is finely controlled by adjusting the distance between the blade and the substrate, or the height of the blade in other words. The best height of the blade is determined to be 70μm. To improve the quantity of the perovskite film, the annealing temperature and annealing time were both investigated, and the optimal film in this system was annealed at 90 degree Celsius for 12 min. As the result, the champion device has achieved the PCE of 8.95%, with Jsc=17.4 mA cm-2, Voc=0.83V, FF=0.62. To our best knowledge, it is the highest PCE of the fully printable flexible PSCs fabricated under ambient condition, especially for the ones with such high relative humility. This work provides a pathway toward the large scale industrial production of the perovskite solar cells, and can promote the commercialization of the PSCs.
Reference:
1：Wu, H., Zhang, C., Ding, K., Wang, L., Gao, Y., & Yang, J. (2017). Efficient planar heterojunction perovskite solar cells fabricated by in-situ, thermal-annealing doctor blading in ambient condition. Organic Electronics.
2：Zheng, J., Zhang, M., Lau, C. F. J., Deng, X., Kim, J., & Ma, Q., et al. (2017). Spin-coating free fabrication for highly efficient perovskite solar cells. Solar Energy Materials & Solar Cells, 168, 165-171.
8:00 PM - ES01.03.09
Tailoring Interfaces to Enable > 1000 Hr Unencapsulated Perovskite Solar Cell Stability
Jeffrey Christians 1 , Philip Schulz 1 , Jonathan Tinkham 2 , Tracy Schloemer 2 , Bertrand Tremolet de Villers 1 , Steven Harvey 1 , Alan Sellinger 2 1 , Joseph Berry 1 , Joseph Luther 1 , Zhen Li 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Chemistry and Geochemistry Department, Colorado School of Mines, Golden, Colorado, United States
Show AbstractThe efficiency of halide perovskite solar cells has reached parity with commercially available thin film photovoltaic absorbers. Because of this, their future commercial prospects appear to hinge upon their long-term operational stability. Recent work has provided insight into the moisture instability, thermal instability, phase instability, and phase segregation of the halide perovskite absorbers themselves. This work has translated into much improved device-level operational stability, yet the combined effects of light (including UV-light), oxygen, and moisture remain problematic.
In this work, we investigate the performance of n-i-p perovskite solar cells which are held, unencapsulated, under continual simulated solar illumination in ambient conditions. We demonstrate that degradation is driven by the heterointerfaces in the device stack and systematically engineer the interfaces in the device to improve operational stability. Replacing the Li+-containing spiro-OMeTAD with a Li+-free hole transport material (HTM), EH44, we achieve comparable power conversion efficiency and a factor of 4 better operational stability. Using Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) of devices at various stages of degradation, we observe an irreversible redistribution of components in the perovskite layer when TiO2 is used as the electron transport layer (ETL) which correlates to the initial burn-in which the devices exhibit under illumination. We find that this redistribution and the burn-in which the devices experience is driven by the TiO2/perovskite interface and can be significantly reduced by the use of a nanoparticle SnO2 ETL in place of TiO2. By utilizing MoOx/Al electrodes in place of Au, which can migrate into the device stack, we develop a SnO2/perovskite/EH44/MoOx/Al device stack with very promising stability. This systematic approach to stability results in a device which retains 94% of its peak power conversion efficiency despite 1000 hrs of continual, unencapsulated operation in ambient conditions. This represents a >3 order of magnitude improvement over standard TiO2/perovskite/spiro-OMeTAD/Au devices with the same perovskite absorber layer. This dramatic improvement in stability, despite the combined stresses of UV-light, oxygen, and moisture, demonstrates the importance of carefully designed interfaces for realizing true long-term perovskite solar cell stability.
8:00 PM - ES01.03.10
Structural Engineering of Two-Dimensional Organometal Halide Perovskites for Efficient and Eco-Friendly Planar Solar Cells
Yani Chen 1 , Yong Sun 1 , Kaibo Zheng 2 , Tõnu Pullerits 2 , Ziqi Liang 1
1 , Fudan University, Shanghai China, 2 , Lund University, Lund Sweden
Show AbstractThe inherent instability of three-dimensional (3D) organic–inorganic halide perovskites remains a crucial challenge before their realization of commercialization. Two-dimensional (2D) Ruddlesden−Popper perovskites have recently been shown to exhibit significantly improved environmental stability. Derived from their 3D analogues, 2D perovskites are formed by inserting bulky alkylammonium cations in-between the anionic layers. However, these insulating organic spacer cations also hinder charge transport. Herein, such a 2D perovskite, (iso-BA)2(MA)3Pb4I13, that contains short branched-chain spacer cations (iso-BA+) and shows a remarkable increase of optical absorption and crystallinity in comparison to the conventional linear one, n-BA+, is designed. After applying the hot-casting (HC) technique, all these properties are further improved. The HC (iso-BA)2(MA)3Pb4I13 sample exhibits the best ambient stability by maintaining its initial optical absorption after storage of 840 h in an environmental chamber at 20 °C with a relative humidity of 60% without encapsulation. More importantly, the out-of-plane crystal orientation of (iso-BA)2(MA)3Pb4I13 film is notably enhanced, which increases cross-plane charge mobility. As a result, the highest power conversion efficiencies (PCEs) measured from reverse scanned J-V curves afford 8.82% and 10.63% for room-temperature and HC-processed 2D perovskites based planar solar cells, respectively. However, the corresponding steady-state PCEs are remarkably lower, which is presumably due to the significant hysteresis phenomena caused by low charge extraction efficiency at interfaces of C60/2D perovskites.
Another issue limiting further industrialization of perovskites is the environmental toxicity of lead. Investigation of eco-friendly tin (Sn)-based organic-inorganic halide perovskites has recently attracted considerable interest. However, Sn-perovskites inevitably suffer from oxidation and morphological issues. More recently, we developed Pb-Sn alloyed 2D perovskites, (BA)2(MA)3Pb4-xSnxI13, for planar solar cell applications, which combine each advantage of both three-dimensional Sn-based and 2D perovskites. Smooth film with high surface coverage are readily formed without any additive owing to the self-assembly characteristic of 2D perovskites. It is found that Sn plays a significant role in improving the crystallization and crystal orientation while narrowing the bandgap of Pb–Sn 2D perovskites. Moreover, Sn can aid to suppress bimolecular recombination in device. As a consequence, (BA)2(MA)3Pb3SnI13 based regular planar solar cells yield the best PCE of 3.57%.
Reference
[1] Y. Chen, Y. Sun, J. Peng, W. Zhang, X. Su, K. Zheng, T. Pullerits, Z. Liang, Tailoring Organic Cation of Two-Dimensional Air-Stable Organometal Halide Perovskites for Highly Efficient Planar Solar Cells. Adv. Energy Mater. 2017, 1700162.
[2] Y. Chen, Y. Sun, J. Peng, Z. Liang, Pb-Sn Alloyed Two-Dimensional Perovskite Solar Cells. (Submitted)
8:00 PM - ES01.03.11
Enhanced Efficiency and Stability of Inverted Perovskite Solar Cells by Interfacial Engineering with Alkyl Bisphosphonic Molecules
Nan Li 1 , Hainan Wei 1 , Hongbin Liu 2 , Xiaosong Li 2 , Changmei Cheng 1 , Liduo Wang 1
1 , Department of Chemistry, Tsinghua University, Beijing China, 2 , Department of Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractThe moisture instability of perovskites materials especially under illumination has engendered severe hindrance toward future industrial applications for high-efficiency and stable perovskite solar cells. Here, we designed and synthesized a series of hydrophobic alkyl bisphosphonic molecules which served as interfacial layers between perovskite and PC61BM to improve the moisure and light-stability of the inverted PVSCs. The steric arrangement of the bisphosphonic molecules suppressed the infiltration of moisture and oxygen inside the perovskite film under humidity and continuous illumination, decreased the loss of halide and methylammonium ions as revealed by the less PbI2 and Pb0 in the film. When exposed to 50~60%RH and continuous AM1.5G illumination, devices with the interfacial treatment remained 70% of the initial power conversion efficiency, while the control device totally died, suggesting markedly improved moisture and light-stability by the interfacial engineering. Moreover, the treated devices showed almost no degradation after stored in ambient atmosphere for 300 h.
8:00 PM - ES01.03.12
AACVD of Methylammonium Lead Triiodide for Photovoltaic Applications
Sinclair Ratnasingham 1 , Joe Briscoe 1 2 , Russell Binions 1 2
1 , Queen Mary University of London, London United Kingdom, 2 Materials Research Institute, Queen Mary University, London United Kingdom
Show AbstractOrgano-metal halide perovskites are promising solar cell materials and research in this area has progressed rapidly, with devices reaching over 20% efficiency1. Currently solution processing techniques are widely used within the research community, and therefore scalable synthesis routes still need to be developed. We investigate the growth of films via the use of aerosol assisted chemical vapour deposition (AACVD) and electric field-AACVD (EFAACVD). AACVD is a scalable deposition process and one advantage of this of this method compared to conventional CVD is the fact that the precursors do not need to be vaporized. This allows for lower operating temperature, less complex equipment, and therefore lower overall cost.2
Methylammonium lead triiodide (MAPI) films were deposited using a 2-Step AACVD technique on titanium dioxide coated substrates. The first step involves nebulizing a lead iodide (PbI2) in dimethylformamide solution, via an ultrasonic mister. The mist was carried by nitrogen gas into a reaction chamber containing a heated substrate at 70°C, producing a film of PbI2 on the substrate. In the second step, a methylammonium iodide (MAI) solution in methanol was passed into the reaction chamber, converting the film into MAPI. EFAACVD was accomplished by applying a potential between the FTO layer and a counter electrode placed above the substrate, investigating the effect of both positive and negative DC fields and AC fields.
Films were analyzed using SEM, XRD and UV/vis spectroscopy. XRD measurements confirm the composition as MAPI. UV/vis absorbance measurements further validated the film composition, with a characteristic absorption onset at 800 nm; bandgap values derived from Tauc plots gave a value of ~ 1.54 eV. SEM images of AACVD samples revealed a porous film with a rough surface and varying grain size (~ 0.2-2 µm). SEM images of EFAACVD reveal that field type and direction affect the topography. Negative field shows a more even surface with notably larger grain sizes (2-3 µm). Furthermore, non-electric field samples had thickness between 3-4 µm, but with the application of an AC field this was reduced to 1 µm. Moreover, the UV/vis absorption spectra of EFAACVD samples revealed higher light absorption for AC samples, indicating that the thinner films are also denser. Thus, EFAACVD allowed films to be produced with thicknesses approaching optimal values for device applications. These films were therefore used to fabricate working photovoltaic devices in the n-i-p structure.
In conclusion, we have demonstrated successful synthesis of MAPI using AACVD. We have also shown that the application of an electric field during deposition can alter both morphology and film thickness. Moving forward, we intend to improve the solar cell efficiency by further reducing the thickness and improving the morphology of the AACVD films.
8:00 PM - ES01.03.13
Critical Environmental Stability Analysis of Material Tuning in Perovskite Thin Films and Solar Cells
Sebastian Pont 1 , Chieh-Ting Lin 1 , Nicholas Aristidou 1 , Daniel Bryant 3 , Saif Haque 1 , James Durrant 1 2
1 , Imperial College London, London United Kingdom, 3 , King Abdullah University of Science and Technology, Saudia Arabia (KAUST), Thuwal Saudi Arabia, 2 SPECIFIC, Swansea University, Swansea United Kingdom
Show AbstractThe operating stability of perovskite solar cells is currently a major barrier to realizing the immense potential of perovskite photovoltaic technologies. Understanding the stress factor limiting the long term performance of these materials is key to developing strategies to overcome them. A methodology for maximising the power conversion efficiency has been the tunability of ions in the ABX perovskite structure, optimizing the impressive optoelectrical properties. However the effect of material tuning on environmental stability has not been critically examined in much detail. Here we look into examples of the tunability of perovskite stability through mixed ions, and separately by comparing device architecture.
In the example of tuning stability with mixed ions, we investigate the degradation of methyl ammonium lead iodide/bromide (MAP(IxBrx-1)3, x = 0 - 1) under controlled environmental conditions. For MAPI, two principal extrinsic degradation mechanisms that have been identified thus far, firstly involving sensitivity to humidity and secondly exposure to light + oxygen.[1] Using image analysis and XRD we show higher bromine ratio improves MAP(IxBrx-1)3 stability to humid conditions, but a more complex effect is seen under light + oxygen. In light and oxygen x<0.75 films degrade rapidly whereas MAPBr shows very promising stability.[2] Superoxide analysis, transient absorption spectroscopy and morphological studies are used to investigate the difference between MAPI and MAPBr. Development of stable interlayers can enable fully stable MAPBr perovskite solar cells for high voltage applications and 4-terminal tandem solar cells.
References
[1] D. Bryant, N. Aristidou and S. Pont, et al. , Energy Environ. Sci., 2016, 9(5), 1655–1660
[2] S. Pont, C.T. Lin, N. Aristidou1, S. Wheeler, D Bryant, S. Haque, J. Durrant, Journal of Materials Chemistry A (2017) 5, 9553 – 9560
8:00 PM - ES01.03.14
Inkjet-Printing of Methylammonium Lead Trihalide Perovskite as Active Layers for Optoelectronic Devices
Charles Trudeau 1 2 , Martin Bolduc 1 , Patrick Beaupre 1 , Jaime Benavides-Guerrero 2 , Sylvain Cloutier 2
1 , INO, Montreal, Quebec, Canada, 2 Electrical Engineering, Ecole de Technologie Superieure, Montreal, Quebec, Canada
Show AbstractNew routes in additive devices fabrication techniques and advances in printable materials are required to meet the ever increasing demands for low-cost and large-area flexible electronics. In particular, perovskite-based materials have gained an appeal due to their unique optoelectronics and ferroelectrics properties, which may replace p-n junction in semiconductor devices. Metal-organic Methylammonium Lead Trihalide Perovskite formulations have been extensively studied in the last few years as promising materials for use in printed electronics, which do not require high temperatures or vacuum environment, contrary to conventional semiconductor fabrication techniques.
In this work, digital inkjet-printing is proposed as a deposition pathway for the fabrication of perovskite active layers in photodetector and thin-film photovoltaic device architectures. A major portion is dedicated to optimizing jetting and printing parameters of the perovskite solution. Additive fabrication parameters such as jetting waveforms, drops spacing, solution temperatures, as well as substrate temperatures are some examples of key characteristics in printing homogeneous layers having the desired properties. The device architecture containing the printed perovskite active layer sandwiched between CNT-doped TiO2 and Spiro-OMeTAD as electron and hole transport layers, respectively, as well as layer-on-layer fabrication are presented. The photocurrent response of the perovskite-based device is also presented, demonstrating strong dependence to the printing optimization of the perovskite active layer.
8:00 PM - ES01.03.15
Boosting the Efficiency of Perovskite Solar Cell with Cesium Modification
Ji-Youn Seo 1 , Shaik Mohammed Zakeeruddin 1 , Michael Graetzel 1
1 , École Polytechnique Fédérale de Lausanne, Lausanne Switzerland
Show AbstractThe organic-inorganic perovskites used for photovoltaics (PV) have an AMX3 formula that is comprised of a monovalent cation, A = (methylammonium (MA+) CH3NH3+; formamidinium (FA+) CH3(NH2)2+); a divalent metal M = (Pb2+; Sn2+); and an anion X = (Cl-, Br-; I-), which can cumulate functions of light absorption, n-type conduction and p-type conduction. Perovskite solar cells (PSCs) generally employ mesoscopic and planar architectures consisting of FTO/compact-TiO2 (cp-TiO2)/mesoporous-TiO2 (mp-TiO2)/perovskite/hole transport layer (HTM)/Au and FTO/cp-TiO2/ perovskite /hole transport layer (HTM)/Au, respectively. There have been many studies on perovskite materials such as compositional engineering to achieve high power conversion efficiency (PCE) or stability of perovskite solar cells (PSCs), resulting in certified PCEs to 22.1%.
Among them, cesium remarkably has opened opportunity breakthrough for enhancing stability and efficiency by modification of mixed halide and cation perovskite, FA1-xMAxPbI3-yBry. The cesium is kind of alkali metal with similar atomic size as enable to intercalate photo active perovskite phase, APbX3. Here we show that Cs ions in combination with MA facilitate greatly the rapid room temperature crystallization of perovskites and explore its role in enhancing crystal formation. The device with optimized A-cation composition of FA0.8MA0.1Cs0.1 showed a solar to electric power conversion efficiency (PCE) of 18.1% (stabilized at 17.7%). Our method provides an attractive path to room temperature fabrication of PSCs by low-cost, large-scale manufacturing such as the roll-to-roll process.
8:00 PM - ES01.03.16
Perovskite Solar Cells Fabricated by Aqueous Precursor Solutions to Enable Humidity Tolerance During Fabrication in Air
Dianyi Liu 1 , Christopher Traverse 1 , Richard Lunt 1 , Pei Chen 1 , Mark Elinski 1 , Chenchen Yang 1 , Lili Wang 1 , Margaret Young 1
1 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Show AbstractPerovskite solar cells have emerged as competitive candidates for photovoltaic applications due to the high efficiency, low cost and ease of fabrication. To achieve high performance, perovskite device fabrication is generally been carried out on under dry atmosphere with anhydrous solvents to protect the perovskite precursors and films. A key challenge moving forward is to address the moisture sensitivity of perovskite films. In this work, we describe a breakthrough in developing aqueous perovskite precursor methods to successfully fabricate efficient perovskite solar cells with over 20% power conversion efficiency. This work not only shows that an excess of water (> 20 vol%) does not necessarily have an adverse impact on the device performance, but it can actually enhance the performance, reproducibility, and device stability. Moreover, our work enables the fabrication of efficient perovskite devices with water-containing solvents and high humidity conditions (~ 60%) that lead to a reduction in moisture sensitivity for perovskite devices and, surprisingly, longer lifetimes. Since water is an economical and green solvent, this work also paves a way to reducing the negative influence of the solvent system while easing the strict air- and moisture-free fabrication requirements.
8:00 PM - ES01.03.17
A New Type of Inorganic Perovskite Quantum Dot-Based Optical Oxygen Sensor
Shanshan Wu 1 , Weichuan Wang 1 , Siying Wu 1 , Hongting Fan 1 , Yanqing Tian 1
1 , Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen China
Show AbstractOxygen sensors have incomparable application values in oceanography, meteorology, environmental science, biology and life science. Up to now, various types of oxygen sensors based on pressure, electrochemistry, and fluorescence quenching have been realized for accurate quantitative determination of oxygen [1]. On the other hand, for sensing, colorimetric method provides high accuracy, sensitivity, easy use and observation even by eyes. Herein, we explored the use of the perovskite QDs as oxygen insensitive internal reference for colorimetric and ratiometric oxygen sensors. To the best of our knowledge, it is the first time that perovskite QD was used in the research field of oxygen sensing.
Fully inorganic perovskite QDs, CsPbX3 (X = Cl, Br, I), with narrow size distribution, broad absorption coupled with narrow emission, high photoluminescence quantum yield, short radiative lifetimes, color tunability, as well as simple synthetic procedures have already become one of the fast moving and exciting research directions in optoelectronics and photonics. The instability of perovskite QDs was still one major issue that obstructs their practical applications[2], limiting its wide use.
In detail, CsPbBr3 perovskite QDs were embedded in 50 micro-meter thin film in polystyrene or poly(methyl methacrylate) films to achieve high stable QD-containing polymer films. The films were prepared by thermal polymerization of polystyrene, SR454, PEGDMA. [meso-tetrakis(pentafluorophenyl)-porphyrinato]platinum(II) (PtTFPP), an excellent sensor because of its good response to oxygen concentrations and high photostability, was polymerized into the 25 micro-meter polymer composite film, which was deposited above the CsPbBr3 perovskite QDs polymerization film by using the same method. This layer by layer perovskite QDs-based oxygen sensing film had good oxygen permeability and photo-stability. Liner Stern-Volmer response to gaseous oxygen was observed. By taking the advantage of the green emission color of the QDs and the red emission of the oxygen probe, distinct color change from red to green with increasing oxygen concentration was observed. The color changes can be easily recorded by a charge-coupled device (CCD) camera or cell phone. While, without the green background emitted by the layer of QDs, the naked eye had low resolution towards the fluorescence intensity change of PtTFPP. The ratios of fluorescence intensities and O2 concentrations showed a perfect linear regression relationship when the O2 concentrations changed, but the fluorescence intensities of CsPbBr3 perovskite QDs still kept unchanged. We believe this CsPbBr3 perovskite QDs based colorimetric O2 film sensor will make great contributions to oxygen related applications.
8:00 PM - ES01.03.18
Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films
Qing Sun 1 2 , Paul Faßl 1 2 , David Becker-Koch 1 2 , Alexandra Bausch 1 2 , Sai Bai 3 4 , Paul E. Hopkinson 1 2 , Henry Snaith 3 , Yana Vaynzof 1 2
1 Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg Germany, 2 Centre for Advanced Materials, Ruprecht-Karls-Universität Heidelberg, Heidelberg Germany, 3 Clarendon Laboratory, Department of Physics, University of Oxford, Oxford United Kingdom, 4 Biomolecular and Organic Electronics, IFM, Linköping University, Linköping Sweden
Show AbstractWe investigate the role of microstructure on the degradation rate of methylammonium lead triiodide (MAPbI3) perovskite films upon exposure to light and oxygen. We compare perovskite films of different microstructure fabricated using either a lead acetate trihydrate precursor (PbAc2) or a solvent engineering technique (sol-eng). The PbAc2 method results in large and more uniform grains of higher electronic quality, while films deposited using the sol-eng technique exhibit smaller, more irregular grains. We characterise the effect of degradation on the optical, compositional and microstructural properties of the perovskite layers and correlate these to the loss of performance of photovoltaic devices. We find that films made by sol-eng technique degrade significantly more rapidly than those made using PbAc2 method, demonstrating that improved microstructure results in not only improved performance, but also enhanced device stability. We show that oxygen induced degradation is initiated at the layer surface and grain boundaries, explaining why films with large and uniform grains exhibit enhanced stability. Additionally, we find that under illumination, irreversible degradation can occur at oxygen levels as low as 1%, suggesting that this process can commence already during the device fabrication stage. To summarise, our work demonstrates that active layers consisting of large uniform grains with a low density of defects are required to achieve enhanced stability of perovskite photovoltaic devices. [1]
[1] Q. Sun, P. Fassl, D. Becker-Koch, A. Bausch, B. Rivkin, S. Bai, P. E. Hopkinson, H. Snaith and Y. Vaynzof, “Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films”, Adv. Energy Mater., Advance Article.
8:00 PM - ES01.03.20
Spatial Atomic Layer Deposition of Impermeable Tin Oxide Electron Extraction Layers—Towards Roll-to-Roll Manufacturing of Temperature Stable Perovskite Solar Cells
Kai Brinkmann 1 , Lukas Hoffmann 1 , Jessica Malerczyk 1 , Tim Becker 1 , Detlef Theirich 1 , Thomas Riedl 1
1 , Bergische Universitat Wuppertal, Wuppertal Germany
Show AbstractWhile perovskite solar cells (PSCs) have reached efficiencies beyond 20%, concerns about their stability are still linked to the topic.[1] Thermally activated decomposition of the perovskite and secondary effects like corrosion of the top electrode by halide compounds may hinder market introduction.[2]
Recently we have introduced impermeable tin oxide (SnOx)[3] deposited by atomic layer deposition (ALD) as electron extraction layers in inverted PSCs. Thereby we sealed decomposition products inside the device and successfully suppressed perovskite decomposition. At the same time, the sensitive metal electrode was protected against corrosion.[4] A major drawback of classical vacuum based ALD (V-ALD) is its inherent limit regarding throughput and its high manufacturing costs. Therefore, spatial ALD (S-ALD) has been introduced, which can operate under atmospheric pressure and offers roll-to-roll compatibility.(5)
Here, we demonstrate for the first time S-ALD of SnOx (at 80°C) at atmospheric pressure. We unravel the critical role of deposition temperature, as well as the role of substrate speed and gas flows as requirement for roll to roll processing. We show, that up to a web speed of 2.4 m/min, we can combine the benefits of continuous processing without sacrificing the excellent electrical and barrier properties of ALD deposited SnOx. In inverted PSCs, the S-ALD SnOx layers afford characteristics comparable to that based on established V-ALD. An outstanding long time stability beyond 3000 hours at elevated temperatures is achieved.
[1] W. S. Yang et al., Science 2015, 348, 1234.
[2] Y. Kato et al., Adv. Mater. Interf. 2015, 2, 1500195.
[3] A. Behrendt et al., Adv. Mater. 2015, 27, 5961.
[4] K. Brinkmann et al., Nat. Commun. 2017, 8, 13938.
[5] L. Hoffmann et al., ACS Appl. Mater. Interf. 2017, 9, 4171.
8:00 PM - ES01.03.21
Highly Efficient and Stable Perovskite Solar Cells via Engineering the Interface Perovskite/Hole Transporting Material
Kyung Taek Cho 1 , Mohammad Nazeeruddin 1
1 , EPFL, Sion Switzerland
Show AbstractA high power conversion efficiency (PCE) of metal halide perovskite solar cells (PSCs), 22.1%, is contributed by the relatively large open-circuit voltage (VOC) of PSCs, generally over 1.0 V, which is outstanding compared to other photovoltaic technologies such as organic- or silicon based solar cells. However, considering the bandgap energy (Eg) of the best optimized perovskite, such as 1.6 eV, the VOC could increase more by reducing the energy loss to theoritical value, 250mV. Thus, there are still some gains to achieve a higher PCE by further improving VOC.
To enhance VOC, various surface passivating methods have been explored in solar cells. By reducing charge carrier recombination at heterojunction interfaces, the passivating effects can improve VOC without sacrificing short circuit current (JSC) and the fill factor (FF) in the photovoltaic performance. To employ the surface passivation, we developed a new method engineering a composition of perovskite at the rear interface between the perovskite film and the hole transporting layer (HTL).
Via constructing an additional perovskite layer on top of the pristine perovskite ([FAPbI3]0.85[MAPbBr3]0.15 or Cs0.1FA0.74MA0.13PbI2.48Br0.39) film, the band offset can be generated inside perovskite films. As a result, the higher conduction energy level of the newly formed perovskite layer causes to block the charge recombination at the interface of perovskite/HTL under illumination and the VOC is improved. In addition, we found this method can improve the stability of PSCs by protecting perovskite films from HTM degradation and UV light of decomposition. Consequently, the PCE is acheived to 20% and the 90% of initial PCE are maintained after maximum power point tracking of 800 hours under one sun simulated illumination at 50oC. Our results shed light on the importance of the interfacial engineering on the perovskite layers and address an innovative approach that will further boost the PSC efficiency and stability.
8:00 PM - ES01.03.22
Extrinsic Ion Migration in Perovskite Solar Cells
Zhen Li 1 , Chuanxiao Xiao 2 , Ye Yang 1 , Steven Harvey 1 , Kai Zhu 1
1 , National Renewable Energy Laboratory, Lakewood, Colorado, United States, 2 , Colorado School of Mines, Golden, Colorado, United States
Show AbstractOrganic-inorganic hybrid perovskite is a promising candidate for next generation photovoltaics with its superior performance and low-cost processing. One unique feature of perovskite materials comparing to traditional photovoltaic materials (Si, CdTe, CIGS, etc.) is easy migration of its ion constitute under operation conditions. Large current-voltage (J-V) hysteresis is believed to be one major consequence of ion migration in the PSCs. Ion migrations also can lead to accelerated degradation, defects formation and redistribution in the PSCs. Here we demonstrate that not only the intrinsic ions (e.g. CH3NH3+, I-), extrinsic ions such as Li+, Na+ and H+ can also migrate through the perovskite layer and strongly impact the operation of PSCs. Using evidences from time-of-flight secondary-ion mass spectrometry, time-resolved photoluminescence, Kelvin probe force microscopy, we show that Li+ ions can migrate from spiro-OMeTAD to the TiO2 electron transport layer and enhance charge separation at the TiO2/perovskite interface. The migration of Li+ ions also introduces larger J-V hysteresis in the PSCs. Similar modulation effects can be seen with other extrinsic ions such as H+ and Na+. These results demonstrate the important roles of extrinsic ion migration in PSCs, especially to the origins of hysteresis. We will also show that extrinsic ion migration can be used as a tool for modulating the electrical and optoelectronic properties of perovskite materials, which leads to novel device applications.
Reference
[1] Li, Z. et al. Extrinsic ion migration in perovskite solar cells. Energy Environ. Sci. 2017, 10, 1234
8:00 PM - ES01.03.23
Melt Processing of Hybrid Organic-Inorganic Lead Iodide Perovskites
Tianyang Li 1 , Wiley Dunlap-Shohl 1 , Qiwei Han 1 , David Mitzi 1
1 , Duke University, Durham, North Carolina, United States
Show AbstractHybrid organic-inorganic perovskites have been widely studied, yielding interesting structural motifs, exciting optical and electronic properties and implementation into applications such as solar cells, field-effect transistors and light emitting diodes. Current thin film preparation and device fabrication techniques for the important family of lead halide perovskites heavily rely on solution-based approaches, which have some inherent drawbacks, including the use of toxic solvents, requirement of additional post-annealing steps, and challenges in adapting laboratory fabrication methods to industrial scale. Here we demonstrate that organic cation selection and targeted modification can be employed to tune the melting temperature of two-dimensional lead iodide perovskites and that, using this approach, highly crystalline films can be conveniently prepared in ambient air using melt processing. This observation is expected to open up new avenues for creating low-cost high-performance optoelectronic devices.
8:00 PM - ES01.03.24
Highly Stable Low-Temperature Solution-Processed Low-Dimensional Perovskite Solar Cells
Deepak Thrithamarassery Gangadharan 1 , Qingzhe Zhang 1 , Ricardo Izquierdo 2 , Dongling Ma 1
1 Institut National de la recherche Scientifique (INRS), Université du Québec, Varennes, Quebec, Canada, 2 , École de technologie supérieure, Université du Québec, Montreal, Quebec, Canada
Show AbstractRecent photovoltaic research has mainly been dominated by the hybrid organic-inorganic perovskites because of their remarkable photophysical and optoelectronic properties as well as their broad tunability in material properties, highly relying on the nature and content of inorganic and organic components. Within a few years of development, an impressive certified power conversion efficiency (PCE) of 22.1% has been achieved by perovskite solar cells, challenging the matured inorganic semiconductor technologies. Unfortunately, the poor chemical stability of perovskite hinders the commercialization prospect of this exciting new technology. For instance, moisture and heat exposure can cause rapid decomposition of three-dimensional (3D) perovskite films. On an attempt to resolve the stability issue of perovskite, multilayered or two-dimensional (2D) perovskite has been explored as a solar absorber. 2D perovskites are an extended family member of 3D perovskites, where large organic cations separate the perovskite layers. Excitonic nature of charge carrier and higher absorption onset in 2D perovskite limit the power conversion efficiency of solar cells. In this work, the photovoltaic properties of 2D perovskites were explored. By optimizing the number of perovskite layers, device fabrication technique and 2D perovskite film thickness we improved crystallinity and absorbance of the 2D perovskite film and got high photovoltaic performance. In particular, the 2D perovskite device demonstrates excellent moisture, thermal and photostability, superior to what has been reported in the literature. Furthermore, a proof of concept for plasmonic 2D perovskite solar cells is realized for the first time. It opens a new avenue towards high-efficiency and stable plasmonic 2D perovskite solar cells.
8:00 PM - ES01.03.25
Direct Correlation between Crystallinity, Structure and Photovoltaic Performance and Photo-Stability of Hybrid Perovskite Devices
Wanyi Nie 1 , Hsinhan Tsai 1 2 , Jean-Christophe Blancon 1 , Amanda Neukirch 1 , Claudine Katan 3 , Jacky Even 4 , Sergei Tretiak 1 , Aditya Mohite 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , Rice University, Houston, Texas, United States, 3 , Université de Rennes, Rennes France, 4 , Centre National de la Recherche Scientifique (CNRS), Rennes France
Show AbstractHybrid perovskite are on a trajectory towards realizing the most efficient single-junction devices using low-temperature processing schemes. However, a critical issue is the limited understanding of how the structure and crystalline quality of the perovskite thin-films affects its opto-electronic properties and the stability. In my talk, I will focus on two aspect: crystal structure of hybrid perovskite thin film and the impact towards device performance and stability.
We first studied in detail of the hybrid perovskite thin film crystal structure by hot-casting method. We found methyl ammonium lead triiodide (MAPbI3) perovskite thin-films grown on Lithium doped nickel oxide surface by hot-casting method leads to a high quality crystalline thin film. The crystallinity is greatly enhanced as revealed by sharp peaks in X-ray diffraction spectrums, which exhibits a characteristic peak splitting observed only in single-crystals and are indicative of a stabilized tetragonal phase. We further study the composition by alloying formamidinium with methyl ammonium in hybrid perovskite structure doped by cesium (FAxMAyCs5PbI3). The obtained thin film crystal structure transitioned from tetragonal phase (MA) to cubic phase (FA). We fabricate planar photovoltaic device using the alloy film for characterization and found a direct correlation between the degree of crystallinity and achieving high-efficiency, photo-stable and reliable photovoltaic devices. The FA-MA alloy compound based device reaches peak efficiency over 19% with long term photo-stability (>800 hours constant 1-Sun illumination) because of the replacement of MA molecules. This high efficiency is mainly from high short circuit current due to reduced optical band gap and high open circuit voltage (~1.08V). The alloy film yields a high photoluminescence quantum efficiency as well as high electro-luminescence quantum efficiency, which explains the high open circuit voltage value.
8:00 PM - ES01.03.26
Ambient-Processed Efficient and Stable Printable Mesoscopic Perovskite Solar Cells
Yaoguang Rong 1 , Mi Xu 1 , Yue Hu 1 , Xiong Li 1 , Hongwei Han 1 , Guangda Niu 1
1 , Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan China
Show AbstractMesoscopic perovskite solar cells (MPSCs) have captured intensive attention in the field of energy conversion due to the advantages of low material cost, simple fabrication process and high power conversion efficiency. Benefiting from the optimization of perovskite absorber deposition approaches, the design of new material systems, and the diversity of device concepts, the efficiency of MPSCs have increased from 2.19% in 2006 to a certified 22.1% in 2016. Such extremely fast increasing efficiency enables this photovoltaic technology challenge the current commercialized solar cells. However, typical perovskites of methylammonium lead halides (CH3NH3PbX3, X = Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. We demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO2/ZrO2/Carbon to fabricate printable MPSCs. An additive of ammonium chloride (NH4Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH3NH3X-NH4PbX3(H2O)2 (X = I or Cl) enables high-quality perovskite CH3NH3PbI3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH3NH3PbI3 achieve an efficiency of 15.6% and a lifetime of over 130 days in ambient condition with 30% relative humidity. This ambient-processed printable perovskite solar cell provides a promising prospect for mass-production, and will promote the development of perovskite-based photovoltaics.
8:00 PM - ES01.03.27
Stability of Perokvsikte Absorbers and Solar Cells upon Illumination
O. Shargaieva 1 , Felix Lang 1 , Victor Brus 1 , Joerg Rappich 1 , Norbert Nickel 1
1 , Helmholtz Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany
Show AbstractFor some years organic-inorganic perovskites have attracted great interest due to their outstanding electrical and optical properties. Because of their large absorption coefficient, high carrier mobility, and long carrier diffusion length this class of materials is very attractive for opto-electronic applications. In particular, perovskite solar cells show a remarkable development in recent years reaching power conversion efficiencies beyond 22 %. However, the major drawback of these devices is the long-term stability.
Our paper describes an extensive spectroscopic investigation of photodegradation mechanisms of methylammonium (CH3NH3+ - MA) and formamidinium (HC(NH2)2+ - FA) lead iodide perovskite films and solar cells. The employed characterization methods includ FT-IR, PL, Raman, effusion and UV-vis absorption. We revisited the light-induced degradation of MAPbI3 in the presence of oxygen. Illumination in O2 atmosphere results in a swift degradation. Isotope experiments clearly show that O2 acts as a catalyst decomposing MA ions into CH3NH2 and hydrogen. In case of FAPbI3 perovskites illumination in the presence of O2 results in a more complex reaction; decomposition of the FA ions occurs at the N - C - N bonds and as a result CO2 and C = O molecules are formed that rapidly diffuse out of the crystalline lattice.
In addition, we present experimental evidence of a fundamental degradation mechanism of MAPbI3 and FMPbI3 perovskite layers due to exposure to visible and ultra violet light in vacuum, nitrogen, and argon atmosphere. This degradation mechanism does not require the presence of oxygen or other constituents. Prolonged illumination causes the dissociation of MA ions into molecular hydrogen and CH3NH2. Interestingly, FM ions also decompose into CH3NH2. The resulting molecules are highly mobile at room temperature and diffuse out of the perovskite layer.
The degradation experiments were extended to fully functional solar cells. In-oparando spectroscopic experiments reveal a hitherto hidden number of reactions in the various layers of the devices. We show for the first time that prolonged illumination of perovskite solar cells results in structural and electronic changes of the hole- and electron transport layers. Also, the dissociation of MA ions into molecular H2 and CH3NH3 is observed. Based on the data new pathways will be proposed to yielding stable perovskites.
8:00 PM - ES01.03.28
High-Efficiency Solution-Processed Polycrystalline Perovskite Light-Emitting Diodes Based on Cesium and Formamidinium Cations
Himchan Cho 1 5 6 , Joo Sung Kim 1 , Christoph Wolf 4 , Hyung Joong Yun 2 , Young-Hoon Kim 1 5 6 , Jong Seong Bae 3 , Hobeom Kim 4 , Jung-Min Heo 1 , Soyeong Ahn 4 , Tae-Woo Lee 1 5 6
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 5 Research Institute of Advanced Materials, Seoul National University, Seoul Korea (the Republic of), 6 BK21 PLUS SNU Materials Division for Educating Creative Global Leaders, Seoul National University, Seoul Korea (the Republic of), 4 Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 Advance Nano Research Group, Korea Basic Science Institute (KBSI), Daejeon Korea (the Republic of), 3 Division of Analysis & Research, Korea Basic Science Institute (KBSI), Busan Korea (the Republic of)
Show AbstractMetal halide perovskites based on formamidinium (FA) and cesium (Cs) cations have shown a great potential as stable perovskite emitters, but the electroluminescence (EL) efficiency of FA- and Cs-based perovskite light-emitting diodes (PeLEDs) is still much poorer than the efficiency of methylammonium-based PeLEDs. We report highly-bright and efficient CsPbBr3 and FA1-xCsxPbBr3 polycrystalline perovskite light-emitting diodes (PeLEDs) fabricated by simple one-step spin-coating of uniform perovskite polycrystalline layers on a self-organized conducting polymers and stoichiometry-controlled perovskite precursor solutions. The influence of chemical composition on morphology, crystal structure, photoluminescence (PL), chemical bonding status and energy levels were systematically investigated. We found that the incorporation of Cs+ cations to FAPbBr3 can significantly reduce the average grain size and that the ionization energy was minimized at an optimized FA:Cs molar proportion. Also, the Cs inclusion leaded to the increase in PL lifetime and suppressed thermally-induced PL quenching, which may be attributed to the reduction of trap density. With these strategies and advantages, we realized high-efficiency CsPbBr3 PeLEDs that have the best EL efficiency among the pure CsPbBr3 polycrystalline PeLEDs with very narrow EL spectral width (~16.5 nm). Also, the FA1-xCsxPbBr3 PeLEDs showed the highest EL efficiency among FA-Cs-based PeLEDs reported to date. Furthermore, we investigated the origin of current hysteresis in CsPbBr3 PeLEDs, which can be ascribed to migration of Br- anions. Temperature dependence of the EL spectrum was measured and the origins of decreased spectrum area, spectral blue-shift, and linewidth broadening were analysed systematically with the activation energies, and were correlated with Br- anion migration, thermal dissociation of excitons, thermal expansion, and electron-phonon interaction. Our work provides simple ways to improve the efficiency and brightness of FA- and Cs-based polycrystalline PeLEDs.
8:00 PM - ES01.03.29
Improved Efficiency and Stability of Perovskite Solar Cells with Submicron Barrier Films Deposited in Air
Nicholas Rolston 1 , Adam Printz 1 , Florian Hilt 1 , Michael Hovish 1 , Brian Watson 1 , Reinhold Dauskardt 1
1 , Stanford University, Stanford, California, United States
Show AbstractOrganometal halide perovskites exhibit remarkable optoelectronic properties with a high tolerance for defects, enabling low-cost, high efficiency, solution-processable photovoltaic devices. However, photoactive perovskites suffer from three main degradation pathways: (1) moisture ingress, which decomposes the perovskite; (2) thermally induced volatility of the organic cation; and (3) corrosion of metal electrodes from halide reactions.
We address all three of these degradation pathways with submicron barrier films produced rapidly in open air by a one-step scalable spray plasma process that improves the efficiency and stability of perovskite solar cells using an organosilane (hexamethyldisiloxane, HMDSO) and a fluorinated organic (trifluorotoluene, TFT) precursor. By varying the precursor ratio, we found a large effect on the morphology and chemistry of the films, ranging from rough, hydrophobic coatings for 1-25% TFT to extremely smooth, hydrophilic coatings for 50-90% TFT. The plasma is at sufficiently low temperature to prevent harm to the underlying layers, and oxidizing species and heat from the plasma improve device performance by improving the conductivity of the hole transporting layer. The thickness of the barrier is highly tunable and transparent over the entire visible spectrum, showing promise for applications in traditional as well as semitransparent and tandem solar cells. Devices with sub-micron coatings exhibited significant improvements in stability, maintaining 94% of their initial PCE in dry heat (85 °C, 25% RH) after 2,000 hours while also being resistant to degradation under simulated operational conditions of continuous exposure to light, heat, and moisture. The coatings were ~100 nm in thickness, enabling compatibility with flexible, lightweight devices on plastic substrates. Optical microscope images revealed the barrier film did not crack or deform after 5,000 cycles with a bending radius of 1 cm, indicating the robust mechanical properties of the ultrathin barrier film.
The spray plasma configuration produces uniform coatings on lengths approaching a meter, enabling a deposition method more suitable for scale-up and industrial applications than conventional spin coating. This process is particularly desirable for future encapsulation efforts on flexible electronic and perovskite devices based on the scalability and thickness control at the nanometer scale.
8:00 PM - ES01.03.30
Fabrication of Large Scale PSCs via Fully Blade Coating under Air Ambient
Hang Hu 1 , Jishu Gao 1 , Jiabang Chen 1 , Deng Wang 1 , Baomin Xu 1
1 Material Science and Engineering, Southern University of Science and Technology, Shenzhen China
Show AbstractAs one of the most potential solar cells with power conversion efficiency exceeding 20% within several years, perovskite solar cells(PSCs) have attracted much attention from the whole world. However, due to its sensitivity and instability under moist and oxygen condition, it is difficult to achieve high efficiency under atmospheric environment which restricts the industrialization of PSCs.
In our work, we applied one-step process to fabricate perovskite layer on glass/FTO substrate with lead acetate as lead source. PEDOT/PSS and PCBM are used as holes transport layer(HTL) and electrons transport layer(ETL) respectively. Except depositing Ag electrodes via thermal evaporation, HTL, perovskite layer and ETL are all prepared by blade coating under fully air ambient with relative humidity about 40%. As the results, the PCE of large area cells(1.2cm2) achieved 5.96% with Jsc=12.42mA/cm2, Voc=0.954V and FF=50.30%. As for small efficient area(0.1cm2), the highest efficient got 11.21% with Jsc=21.31 mA/cm2, Voc=0.85V and FF=61.89%. For blade coating, it is possible to achieve large scale preparation under air ambient and to be transferred on flexible substrate to achieve roll-to-roll process. To our acknowledgment, the fully blade coating process under fully ambient air would provide a potential method to realize industrial production for PSCs.
8:00 PM - ES01.03.31
Bandgap Mapping of Ternary Mixed Halide Perovskite, CH3NH3Pb(Br1-x-yClxIy)3 (0≤x≤1 and 0≤y≤1)
Se-Yun Kim 1 , Ho-Chang Lee 1 , Seunghak Shin 1 , Sihong Lee 1 , Jeong-Joo Kim 1 , Joon-Hyung Lee 1 , Chul-Hong Park 2 , Sangwook Lee 1 , Young-Woo Heo 1
1 , Kyungpook National University, Daegu Korea (the Republic of), 2 , Busan National University, Busan Korea (the Republic of)
Show AbstractHalide based perovskite materials have emerged as an important optoelectronic material due to their marvelous characteristic, such as long charge lifetime, high absorption coefficient, direct bandgap structure, ease of band tuning, flexibility and solution processability at low temperature. Especially, a complete band gap tuning characteristic of mixed halide perovskite was attractive enough to lead to investigations about tandem solar cell and LED as well as single-junction solar cell. Despite of many unprecedented results, there are still remained the critical problem such as environmental issues and long term instability. Among the various strategies to solve these problems, we focused on the development of a new composition and conducted the following research as first step. Herein, we report a phase diagram of MAPb(Br1-x-yClxIy)3 with bandgap of each composition, 0≤x≤1 and 0≤y≤1. Optical absorption, photoluminescence, and crystallographic structure of MAPb(Br1-x-yClxIy)3 are investigated in the forms of bulk powder which were synthesized via a simple solid-state reaction process. As the results, the ternary phase diagram having the vertex of MAPbI3, MAPbBr3 and MAPbCl3 was obtained with the maps of lattice constant, energy bandgap, and photoluminescence intensity. It was found that a certain bandgap value, in the range of 1.55 - 2.9 eV, can be built up from various combinatorial compositions. These interesting results could be understood based on the first principles calculation, from the view point of smooth orbital mixing among the Pb-halogen bondings.
8:00 PM - ES01.03.32
Charge Transport Properties and Their Limiting Factors in Hybrid Perovskite Photovoltaic Devices Studied via Time-of-Flight Experiments
Irene Grill 1 2 , Meltem Aygüler 1 2 , Nadja Giesbrecht 1 2 , Thomas Bein 1 2 , Pablo Docampo 1 3 , Nicolai Hartmann 1 , Matthias Handloser 1 , Achim Hartschuh 1 2
1 Department of Chemistry and CeNS, LMU Munich, Munich Germany, 2 , Nanosystems Initiative Munich (NIM), Munich Germany, 3 School of Electrical and Electronic Engineering, Newcastle University, Newcastle upon Tyne United Kingdom
Show AbstractOrganolead halide perovskites represent one of the most promising absorber materials for solar energy conversion due to facile solution processing and the achieved high photoconversion efficiency values (PCE) [1]. To date, fundamental physical properties including dynamics and transport of photogenerated charge carriers, crucial for optimum device performance, are not fully explored and are at the focus of intense research.
In this work, we investigate the influence of the individual layers incorporated in typical perovskite based solar cells on the overall charge transport characteristics and identify their limiting factors via detailed Time-of-Flight (ToF) studies. We determine the transport times of photoinduced charge carriers (electrons and holes separately) in the respective perovskite absorber layer in a lateral architecture upon pulsed laser excitation and observe effective charge carrier mobilities ranging from 4 up to 30 cm2/Vs, depending on the fabrication protocol. The results of the single film measurements are further discussed in terms of material composition, crystal size and orientation.
To gain deeper insights into the effect of different charge selective materials on the charge transport properties in working devices, we investigate perovskite thin films in the aforementioned lateral architecture additionally coated with different hole or electron transport layers on top.
We correlate the obtained results to the respective device efficiencies, allowing for a detailed investigation of limiting factors for charge transport and efficiency in PSCs (low mobility sheets, etc.). Our results are beneficial for the optimization of fabrication techniques [2,3] as well as the choice of the best suited materials in order to improve the PCE of future devices.
References:
[1] M. Saliba, et al., Energy Environ. Sci. 9, 1989-1997 (2016).
[2] I. Grill, K. Handloser, et al., Sol. Energ. Mat. Sol. Cells 166, 269-275 (2017).
[3] A. Binek, I. Grill, et al., Chem. Asian J. 11, 1199-1204 (2016).
8:00 PM - ES01.03.33
In Situ Defect Passivation in Organic-Inorganic Halide Perovskite Thin Films for High-Performance Solar Cells
Yi Zhang 1 2
1 School of Engineering, Brown University, Providence, Rhode Island, United States, 2 Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, Lausanne Switzerland
Show AbstractPassivation of defects in the organic-inorganic halide perovskite (OIHP) thin films is of vital importance for achieving high-performance perovskite solar cells (PSCs). Here, we present a new, facile method for passivating the OIHP thin films. In this method, methylammonium lead iodide thin films that are doped/incorporated with large organic-cations such as imidazolium and guanidinium are first solution-processed. Then, a fumigation step with methylamine gas is followed, which results into in situ deprotonation of the large organic cations to form their corresponding neutral organic species. These neutral organic species are found to have a profound effect on passivating the defects in the OIHP films. The underlying mechanisms are discussed in detail. The PSCs made using this method shows power conversion efficiency up to 20.2 % that are very stable upon continuous illumination. This study points out a new direction in engineering OIHPs/PSCs through a combination of doping and methylamine-gas-fumigation approaches.
8:00 PM - ES01.03.34
Crystal Facets—Do They Matter?
Nadja Giesbrecht 1 , Eline Hutter 2 , Irene Grill 1 , Johannes Schlipf 3 , Achim Hartschuh 1 , Tom Savenije 2 , Pablo Docampo 4
1 , LMU Munich, Munich Germany, 2 , TU Delft, Delft Netherlands, 3 , TU Munich, Munich Germany, 4 , Newcastle University, Newcastle United Kingdom
Show Abstract
Tunable crystal orientations in perovskite thin films open up a new playground to investigate charge transport and charge transfer at interfaces. In order to push device performance further, understanding of interfacial charge transfer is important. Here, we introduce an approach to selectively expose a particular crystal face to the charge extraction layers without significant changes to the morphology. This allows a like-to-like comparison of the optoelectronic properties.
Our films with differently exposed crystal facets revealed a significant anisotropy of hole- and electron injection in Time-Resolved Microwave Conductivity measurements (TRMC). The same trend was confirmed in photovoltaic devices with different architectures. Thus, the power conversion efficiencies improved for a well matched interfacial stacking from 15 to 18 %. Additionally, Time of Flight measurements (TOF) disclosed a correlation between crystal alignment and charge carrier mobility within the perovskite film. The charge carrier mobility was increased dramatically with an increased degree of crystal orientation. The ability to tailor perovskite crystal alignment and match facets to charge transport layers opens a new route to further improve perovskite-based device properties.
8:00 PM - ES01.03.35
The Effect of Light on the Ionic Conduction of Hybrid Organic-Inorganic Lead Halides Perovskite
Gee Yeong Kim 1 , Alessandro Senocrate 1 , Igor Moudrakovski 1 , Tae–Youl Yang 1 , Giuliano Gregori 1 , Michael Graetzel 2 , Joachim Maier 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , Swiss Federal Institute of Technology Station, Lausanne Switzerland
Show AbstractMethylammonium lead halide perovskite (MAPbI3) solar cells have become a key light harvesting element in the field of energy conversion showing fabulous high conversion efficiency. To explain key features responsible for such performances, not only electronic but also ionic transport properties need to be considered. Ionic transport properties can in a straightforward way explain the origin of the anomalous capacitive behavior, the hysteresis in current-voltage sweep and the high effective dielectric constant at low frequencies. Our group firstly confirmed that MAPbI3 is a mixed (electronic and ionic) conductor, using stoichiometric polarization measurement [1]. Using a multitude of experiment techniques, we could show at least under dark conditions iodine vacancies are the responsible carriers and could give upper limit for the contribution of MA+ and Pb2+ [2]. One of the critical remaining questions to be clarified is the ionic conduction in MAPbI3 under illumination. In this study, we carried out electrochemical measurement such as galvanostatic d.c. polarization, a.c. impedance, emf cell, Hall effect measurement under dark and light. The results showed that both electronic and ionic conductivities are greatly increased under light. The same is true for the chemical capacitance. We discuss the origin of this striking result in the context of recent experiments of our group. In addition, we analyze the impact of oxygen which is weak under dark conditions, but strong under illumination.
8:00 PM - ES01.03.36
In Situ Study—Elucidation of Different Perovskite Solvate Systems and Their Roles
Sehyun Lee 1 , Ming-Chun Tang 3 , Rahim Munir 3 , Dounya Barrit 3 , Rira Kang 2 , Jin-Mun Yun 2 , Jong-Jin Park 1 , Dongseong Yang 1 , Youn-Jung Heo 1 , Detlef Smilgies 4 , Aram Amassian 3 , Dong-Yu Kim 1
1 , Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 , King Abdullah University of Science and Technology, Saudia Arabia (KAUST), Thuwal Saudi Arabia, 2 Radiation Research Division for Industry and Environment, Korea Atomic Energy Research Institute (KAERI), Jeongeup-si Korea (the Republic of), 4 , Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, New York, United States
Show AbstractSince the organic/inorganic hybrid perovskite materials suggested as a light absorber in 2009, tremendous researches have been conducted various approaches such as characteristics of materials, high efficiency, stability, and even printing technique. Although the best efficiency of perovskite solar cells (PeSCs) has been achieved as high as 22.1 %, the film formation mechanism and role of solvate systems were not clearly revealed yet during spin-coating. Amassian et al investigated the existence of perovskite:solvent solvate phase by spin-coating method from in-situ GIWAXS (grazing incidence wide angle X-ray scattering) analysis and discussed the solvate phase had a crucial role to form the perovskite morphology and device performances. In this work, we implemented the in-situ GIWAXS of CH3NH3PbI3 perovskite materials, which was a representative perovskite material, based on various additive systems in order to adjust the unbalanced crystal growth rate of CH3NH3I and PbI2. The behaviors of solvate phase were strikingly mediated by various additives as we expected and one of additives highly retarded the PbI2 solvate phase during one step spin-coating, so overcome the troublesome unbalanced crystal growth rate of perovskite films. Consequently, the well-controlled perovskite films not only had a good film morphology and also highest photovoltaic performances with an excellent reproducibility.
8:00 PM - ES01.03.37
Low Cost, High Yield Synthesis of High Performance Triazatruxene Hole Transport Material for Perovskite Solar Cells
Arthur Connell 1 , Peter Holliman 1 , Henry Snaith 2 , Zhiping Wang 2
1 , Swansea University, St Asaph United Kingdom, 2 , University of Oxford, Oxford United Kingdom
Show AbstractIn this work, we have reported a champion device η of 20.3% and 19.4% for devices with stabilised η and minimal hysteresis respectively, using a novel triazatruxene hole transport material with a formadinium lead iodide perovskite. To the best of our knowledge, this is the highest η reported for a triazatruxene hole transport material in perovskite solar cells. Furthermore, it is amongst the highest η reported for perovskite devices to date. This HTM can be synthesised at less than half the cost of the most widely used HTM spiro-OMeTAD. There are four papers reporting triazatruxene HTMs in perovskite solar cells [1-4]. The highest η reported is 18.8% using triazatruxene SP-12 that contains anisole as a donor ligand to tune the electronic and morphological properties [2]. Anisole was attached to the triazatruxene using anisole boronic acid as a precursor. A palladium catalyzed suzuki coupling reaction requiring carefully controlled oxygen free conditions was used to attach two solid reactants together forming a solid product which required purification using time consuming and solvent intensive column chromatography. In this work, we have used tertiary butoxy styrene (TBS) as the donor ligand; this offers several advantages over using anisole. TBS is ten times cheaper costing £1 g-1 c.f. £10 g-1 for anisole boronic acid. Furthermore, TBS is a liquid which is attached to triazatruxene using a heck coupling reaction which is less sensitive to oxygen by comparison to the suzuki coupling reaction. The heck coupling reaction is completed in a higher yield i.e. 95% by comparison to 86% for the suzuki coupling reaction and the solid product can be purified from the excess liquid TBS using a simple silica plug followed by the quick and less solvent exhaustive technique of precipitation/ recrystallisation. To the best of our knowledge, this is the first time that tertiary butoxy styrene has been used as a donor ligand in HTMs. We hope that this result encourages the development of HTMs using cheap and readily available molecules rather than relying on very specific and costly materials mainly used in the organic molecular electronics industry.we calculate that purified TAT-tBuSty can be produced for (£52.77 g-1) 35% the cost of spiro-OMeTAD (ca. over £85 g-1) and 24% cheaper than the next best performing triazatruxene SP12 (£72.83 g-1). This is important for the scaled manufacture of all HTM-containing solar cell devices.
8:00 PM - ES01.03.38
Development of a Physical Analytics Pipeline (PAL) to Optimize Solution Processing of Hybrid Inorganic-Organic Perovskites for a Chosen Performance Characteristic
Henry Herbol 1 , Weici Hu 1 , Matthias Poloczek 1 2 , Paulette Clancy 1
1 , Cornell University, Ithaca, New York, United States, 2 , University of Arizona (current affiliation), Tucson, Arizona, United States
Show AbstractHybrid Organic-Inorganic Perovskites (HOIPs) are a class of materials that have taken the materials community by storm. In 2017, these perovskites surpassed the best performing multicrystalline silicon solar cells. However, this impressive lab performance rarely translates to large-scale manufacturing processes. One important roadblock is that little is known about the fundamentals governing the solution processing of HOIPs into thin-film products. Gaining that knowledge is complicated by the sheer size of the underlying combinatorial space: HOIP lattices are composed of a metal ion (typically Pb, but sometimes mixed with Sn), three halides (often a combination of Cl, Br, and I), and a chaperone cation (methylammonium, formamidinium, or Cs) that are formed in a bath solvent (invariably a blend of solvents in some ratio). For example, even if we restrict our solvent choices to a conservative choice of DMSO, DMF, THTO, GBL, and NMP, and only consider pure solvents, there is a large compositional space to search for optimal performance (as judged by some appropriate metric): (1 metal ion) * (3 halide choices) * (3 chaperone cation choices) * (1 of 5 pure solvents) = 150 options. Exploring the entire 150 combinations in an experimental lab is simply infeasible in terms of materials, time and effort. It is also extremely time-intensive on the computational side since ab initio calculations are likely to be involved. Even these 150 combinations constitute a significantly reduced conformational space than in experiments, given the tendency to explore solvent, halide, and cation blends. If we are to rationally design better HOIP materials in the future, some means to “down-select” among HOIP compositions must be developed.
We have attacked this problem by developing what we call a Physical Analytics pipeline, which rapidly searches for suitable HOIP combinations, maximizing some objective function, typically a physical property and/or order parameter. This software suite merges data analytics techniques and physical science knowledge to predict high-performing HOIP compositions for a chosen objective. In a proof of concept, our codebase computes the objective value of a chosen HOIP composition (MX3A and solvent, where M is a metal, X is a mix of 3 halides, and A is a chaperone cation). Currently, two objective functions are supported: solvent binding energies (Ebind), and the Unsaturated Mayer Bond Order (UMBO) [Stevenson et al., Chem. Mat. 2016]. Based on this functionality, we implemented a Bayesian search method that recommends HOIP compositions that are likely to have a high objective value, with subsequent compositions based on previous evaluations. Ongoing work is geared towards developing a robust order parameter for mixed solvents of varying concentrations, considering intersolvent interactions both within the presence of the HOIP monomer and in vacuum.
8:00 PM - ES01.03.39
Towards an Understanding of the Role of Oxygen in Halide Perovskite Materials
Alessandro Senocrate 1 2 , Tae-Youl Yang 3 , Gee Yeong Kim 1 , Michael Graetzel 2 1 , Joachim Maier 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , École Polytechnique Fédérale de Lausanne, Lausanne Switzerland, 3 , Korean Research Institute of Chemical Technology, Daejeon Korea (the Republic of)
Show AbstractOxygen is an extremely common contaminant in perovskite solar cells (PSCs), which can be introduced in the halide perovskite layer both during the synthesis and during device operation through simple exposure to air. Curiously, the effect of oxygen has been reported to be both beneficial for the optical properties of halide perovskites[1, 2] and detrimental for device performance and stability.[3-5] Considering the ubiquity of O2 and the severe influence it appears to have on the properties of halide perovskites and relative devices, the understanding of O2 interaction with these materials is of utmost importance. Yet, as of today, this topic only received a modest attention. In this contribution, we study the effect of oxygen on the electrical and optical properties of MAPbI3, both in dark and under illumination, showing that O2 exposure can significantly enhance both material conductivity and photoluminescence. In addition, we study the diffusion of oxygen in the MAPbI3 lattice using 18O tracer diffusion techniques. Notably, we show that oxygen incorporation in MAPbI3 is modest under dark conditions, but strongly enhanced under illumination. Interestingly, this improved O2 uptake is coupled with an increased instability of the halide perovskite material. As a final point, we complement our material characterisation by studying the influence of O2 on the photovoltaic properties and stability of PSCs. The peculiar interplay of ionic and electronic charge carriers with the oxygen in the gas phase, both in dark and under illumination, is discussed in detail paying particular attention to the nature of the degradation processes involved.
[1] Y. Tian, M. Peter, E. Unger et al., Phys. Chem. Chem. Phys. 2015, 17, 24978.
[2] J. F. Galisteo-López, M. Anaya, M. E. Calvo et al., J. Phys. Chem. Lett. 2015, 2200.
[3] N. Aristidou, I. Sanchez-Molina, T. Chotchuangchutchaval et al., Angew. Chemie 2015, 54, 8208.
[4] N. Aristidou, C. Eames, I. Sanchez-Molina et al., Nat. Commun. 2017, 8, 1–40.
[5] A. J. Pearson, G. E. Eperon, P. E. Hopkinson et al., Adv. Energy Mater. 2016, 6, 1600014.
Symposium Organizers
Yabing Qi, Okinawa Institute of Science and Technology Graduate University
Jinsong Huang, University of North Carolina-Chapel Hill
Annamaria Petrozza, Istituto Italiano di Tecnologia
Huanping Zhou, Peking University
Symposium Support
Applied Physics Letters | AIP Publishing
Nature Energy | Springer Nature
Science | AAAS
Sustainable Energy &
Fuels | The Royal Society of Chemistry
ES01.04: Interface Engineering, Hysteresis, Ion Migration, Polaron and Lattice Dynamics
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 3, Ballroom B
8:00 AM - ES01.04.01
Interfacial Engineering and Charge Transport Investigation for Perovskite Solar Cells
Qingbo Meng 1 , Jiangjian Shi 1 , Dongmei Li 1 , Yanhong Luo 1
1 , Institute of Physics, Chinese Academy of Sciences, Beijing China
Show AbstractRecently, perovskite-based solar cells, has attracted worldwide interest due to their easy fabrication and outstanding photovoltaic performance. In our lab, we focus our interest in investigating the interface engineering and charge transport properties of solar cell to increase of the performance and stability.[1-9] Firstly, by improving the film deposition quality, an efficient single p-n heterojunction cell without the usage of an organic hole transport material layer is achieved with an efficiency of about 10.5%. [2-3] It has been found that the charge transfer properties of this type of cell can be well described by an ideal heterojunction model. The junction nature of this cell is systematically studied. The hole concentration of the perovskite absorber and junction properties can be controlled [1, 4, 5] Based on the understandings of the charge transport and junction nature of the perovskite solar cell, controlling the charge transport properties of the cell by engineering the boundary conditions has also been applied as an effective approach to enhance the cell performance. [6-8] Aside from the fast electron transport, we are also interested in the slow ion transport in this cell. By developing an in-situ modulated electrical transient method, the microscopic charge transport and recombination behind the photoelectric hysteresis have also been investigated, which demonstrates the critical role that the heterojunction electric field plays in determining the charge processes in this cell.[9-15] Deeper investigations found that the interfacial doping and defect caused by the ion migration and accumulation may be the physical origins for the wide-concerned hysteresis in this cell.
References：
1. J. J. Shi, Q.-B. Meng et al, Small, 2015, 11, 2472.
2. J. Shi, J. Dong, Q. B. Meng, et al., Appl. Phys. Lett. 2014, 104, 063901.
3. J. Shi, Y. Luo, Q. Meng et al, ACS Appl. Mater. Interfaces 2014, 6, 9711.
4. J.-J. Shi, Q.-B. Meng et al, Chemphyschem 2015, 16, 842.
5. J. Dong, Qingbo Meng et al, Chem. Commun., 2014, 50, 13381.
6. J. Dong, J. Shi, Q. Meng, et al, Applied Physics Letters 2015, 107 (7), 073507.
7. J. Shi, Q. B. Meng, Q. Chen, Chin. Phys. Lett., 2013, 30, 128402.
8. H. Wei, J. Shi, Q. Meng et al, Phys. Chem. Chem. Phys. 2015, 17 (7), 4937-4944.
9. J. Shi, D. Li, Q. B. Meng, et al., Rev. Sci. Instrum. 2016, 87, 123107.
10. J. Shi, X. Xu, Q. B. Meng, et al, Appl. Phys. Lett. 2015, 107, 163901.
11. J. Shi, H. Zhang, Q. B. Meng, et al., Small 2016,12, 5288.
12. X. Xu, H. Zhang, Q. B. Meng, et al., Journal of Materials Chemistry A 2015, 3 (38), 19288-19293
13. H. Zhang, J. Shi, Q. Meng et al., J. Mater. Chem. A 2016, 4, 15383-15389.
14. L.Zhu, Y. Xu, J. Shi, Q. Meng et al., Rsc Advances 2016, 6 (85), 82282-82288.
15. X. Xu, K. Li, L. Gu, Z. Wu, Q. Meng, et al., Nano Research. 2017, 10(2), 483-490.
8:15 AM - ES01.04.02
Highly Efficient Perovskite Solar Cells with Large Area and High Stability
Xudong Yang 1 , Chen Han 1 , Liyuan Han 2
1 , Shanghai Jiao Tong University, Shanghai China, 2 , National Institute for Materials Science, Tsukuba Japan
Show AbstractOrganic-inorganic hybrid perovskite solar cells (PSCs) have attracted great attention owing to the low-cost manufacture and high energy conversion efficiency. However, the efficiency decreases dramatically with the increase in the area of active layer or the operation time.
Here I would like to introduce our recent approaches in achieving high efficiency PSCs with large area and high stability. First, we developed a low-temperature non-spin deposition method for the formation of uniform large-area perovskite thin films. By controlling the processing key factors like surface wettability, solution viscosity and thermal evaporation, we made scaling-up and pinhole-free perovskite films for efficient PCSs cells with working area of 5 cm2. Secondly, we suppressed the thermal degradation of perovskite films via controlling the iodide diffusion within PSCs. The iodide diffusion out of the perovskite films can be suppressed 3 times after we introduced graphene derivatives into fullerene based electron transport layer. We obtained efficient PSCs stable under 85 oC for 500 hours or under light soaking for 1000 hours.
[1] F. Ye, W. Tang, F. Xie, M. Yin, J. He, Y. Wang, H. Chen, Y. Qiang, X. Yang* and L. Han*, Advanced Materials, 2017, accepted.
[2] E. Bi, H. Chen, F. Xie, Y. Wu, W. Chen, Y. Su, A. Islam, M. Graetzel*, X. Yang* and L. Han*, Nature Comm., DOI: 10.1038/ncomms15330.
[3] H. Chen, F. Ye, W. Tang, J. He, M. Yin, Y. Wang, F. Xie, E. Bi, M. Graetzel*, X Yang*, Liyuan Han*, 2017, submitted.
8:30 AM - *ES01.04.03
Surface Polarization Effects in Perovskite Solar Cells
Juan Bisquert 1
1 Institute of Advanced Materials, University of Jaume I, Castelló Spain
Show AbstractThe development of organic-inorganic lead halide perovskites with very large efficiency requires us to understand the operation of the solar cell. This class of semiconductors presents remarkable bulk electronic and optical properties, but the contacts to the device are a key aspect of the operation and show important dynamic interactions. We provide an interpretation of capacitances as a function of frequency both in dark and under light, and we discuss the meaning of resistances and how they are primarily related to the operation of contacts in many cases. The capacitance reveals a very large charge accumulation at the electron contact, which has a great impact in the cell measurements, both in photovoltage decays, recombination, and hysteresis. We present the surface polarization model that gives insight and quantitative description of current-voltage dynamic hysteresis and impedance spectroscopy loops. We develop a global view of the formation of photovoltage and the kinetic processes governing the operation of the solar cell, providing a suitable unified explanation to the many strange observations reported in the last few years.
9:00 AM - *ES01.04.04
Crystalline Liquid Duality and Large Polaron Formation in Lead Halide Perovskites
Xiaoyang Zhu 1
1 Department of Chemistry, Columbia University, New York, New York, United States
Show AbstractThe feverish research activity on lead halide perovskites has been fueled by their exceptional optoelectronic properties, e.g., in solar cells and light-emitting devices. Hybrid lead halide perovskites exhibit exceptional defect tolerance despite static and dynamic disorder, but how carriers are protected from efficient scattering with charged defects and optical phonons is unknown. We have recently put forward the large polaron model to explain the carrier protection (J. Phys. Chem. Lett. 2015, 6, 4758). We find that nascent charge carriers are screened by “solvation” or large-polaron formation on sub-ps time scales, leading dramatic suppression of electron- LO phonon scattering. This explains long-lived energetic electrons (Science, 2016, 353, 1409; J. Am. Chem. Soc. 2016, 2016, 138, 15717) as well the defect tolerance and low recombination rates of bandedge carriers. Using femtosecond Kerr-effect spectroscopy, we directly probe large polaron formation by following the phonon response to above-gap optical excitations. A large polaron forms predominantly from the deformation of the PbX3- frameworks, irrespective of the cation type. The difference lies in the polaron formation time, which in CH3NH3PbBr3 (0.3 ps) is less than half of that in CsPbBr3 (0.7 ps) (Science Adv. 2017, in press). The understandings presented here suggest a new design principle for high performance and defect tolerant semiconductors from soft and hybrid materials with liquid-like dielectric functions.
9:30 AM - ES01.04.05
Measuring Phonon Lifetimes and Lattice Dynamics of Single-Crystal Methylammonium Lead Iodide with Neutron Triple-Axis Spectroscopy
Aryeh Gold-Parker 1 2 , Peter Gehring 3 , Ian Smith 2 , Dan Parshall 3 , Jarvist Frost 4 , Linda Hung 3 , Taner Yildirim 3 , Aron Walsh 4 , Hemamala Karunadasa 2 , Michael Toney 1
1 Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 2 Chemistry, Stanford University, Stanford, California, United States, 3 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 4 Materials, Imperial College London, London United Kingdom
Show AbstractHybrid organic-inorganic perovskite methylammonium lead iodide (CH3NH3PbI3, herein MAPbI3) shows significant promise as a photovoltaic absorber material. As device efficiencies continue to rise, there is growing interest in the fundamental physical properties of MAPbI3. The phonons are of particular interest because they provide information regarding two areas of active study: the dynamical coupling of electronic states to the lattice1, and the vibrational coupling between PbI6 octahedra and the MA+ cations.2 Both couplings influence the opto-electronic properties of MAPbI3. We report results from neutron inelastic scattering measurements on single-crystal MAPbI3 that were made to characterize the low-energy lattice dynamics.
To avoid the strong incoherent scattering cross-section of hydrogen, we synthesized large, fully-deuterated single crystals of CD3ND3PbI3 for this study. This enhances our ability to measure the coherent inelastic scattering arising from correlated motions, such as phonons, which are distinct from those reported in the neutron elastic and quasi-elastic scattering study of Chen et al. on powdered samples of MAPbI3, and which only provide information about the rotational dynamics of isolated MA+.3 We have measured the momentum-resolved transverse acoustic (TA) phonon dispersion and lifetimes in the orthorhombic, tetragonal, and cubic phases. The TA dispersion along the pseudocubic [010] direction is consistent with first-principles calculations and softens nearly 10% on heating into the tetragonal phase. The TA phonon becomes strongly damped with increasing wave vector, and on heating into the tetragonal phase the TA phonon lifetimes decrease by roughly a factor of two for wave vectors near the Brillouin zone boundary. The corresponding lifetimes vary from about 2.6 ps in the orthorhombic phase to 1.4 ps in the tetragonal and cubic phases. This has major implications for the carrier scattering and cooling processes.
In addition, we observe quasi-elastic scattering (QES) that increases in intensity upon heating into the tetragonal phase. This QES varies strongly with reduced wave vector and corresponds to the coupled dynamics of the MA+ cation and PbI6 octahedral distortions. This QES is due to nm-scale domains with correlated lattice distortions and lifetimes on a few picosecond timescale.
References
1. Wright, A. D. et al. Electron–phonon coupling in hybrid lead halide perovskites. Nat. Commun. 7, 11755 (2016).
2. Leguy, A. M. a et al. The dynamics of methylammonium ions in hybrid organic–inorganic perovskite solar cells. Nat. Commun. 6, 7124 (2015).
3. Chen, T. et al. Rotational dynamics of organic cations in the CH 3 NH 3 PbI 3 perovskite. Phys. Chem. Chem. Phys. 17, 31278–31286 (2015).
ES01.05: Interface Engineering, Ion Migration, Defects, Optical and Charge Transport
Session Chairs
Tuesday PM, November 28, 2017
Hynes, Level 3, Ballroom B
10:15 AM - *ES01.05.01
Rational Material, Interface, and Device Engineering for High-Performance and Stable Perovskite Solar Cells
Alex Jen 1 2
1 Department of Materials Science and Engineering, University of Washington, Seattle, Washington, United States, 2 Department of Materials Science, City University of Hong Kong, Kowloon Hong Kong
Show AbstractAdvances in controlled synthesis, processing, and tuning of the properties of peroskites have enabled significantly enhanced performance of hybrid perovskite solar cells. The performance of hybrid perovskite solar cells is strongly dependent on their efficiency in harvesting light, charge transport, and charge collection at the metal/organic/perovskite or the metal/metal oxide perovskite interfaces. In this talk, an integrated approach of combining material design, interface, and device engineering to significantly improve the performance and stability of organic and hybrid perovskite photovoltaic cells (PCE of >20%) will be discussed. At the end, several new device architectures and optical engineering strategies to make tandem cells and semitransparent solar cells will be discussed to explore the full promise of perovskite hybrid solar cells.
10:45 AM - ES01.05.02
Atomic-Scale Insights into Perovskite Solar Cells—Diffusion, Defects and Degradation
Saiful Islam 1 , Nicholas Aristidou 2 , Christopher Eames 1 , Saif Haque 2
1 , University of Bath, Bath United Kingdom, 2 , Imperial College London, London United Kingdom
Show AbstractHybrid lead halide perovskites are attracting intense interest as promising materials for next-generation solar cells, but serious issues related to long-term stability need to be addressed. Specifically, perovskite films based on CH3NH3PbI3 undergo oxygen- and light-induced degradation. However, the mechanism of such degradation is poorly understood. Here, we report new insights through the combined use of photoluminescence, secondary ion mass spectrometry and ab initio simulation techniques [1], extending our recent work on ion transport [2]. We find fast oxygen diffusion into CH3NH3PbI3 films is accompanied by photo-induced formation of reactive superoxide species. Ab initio simulations indicate that iodide vacancies are the preferred sites in mediating the formation of superoxide species. Thin-film passivation with iodide salts is shown to enhance film and device stability. The understanding of degradation phenomena gained from this study is important for the future design and optimisation of stable perovskite solar cells.
[1] N. Aristidou et al., Nature Commun. 8, 15218 (2017).
[2] C. Eames et al. Nature Commun. 6, 7497 (2015).
11:00 AM - ES01.05.03
High Internal and External Photoluminescence Quantum Efficiency in Organic-Inorganic Perovskite Thin Films—Approaching the Shockley-Queisser Radiative Limit
Dane deQuilettes 1 , Ian Braly 1 , Luis Pazos-Outon 2 , Sven Burke 1 , David Ginger 1 , Hugh Hillhouse 1
1 , University of Washington, Seattle, Washington, United States, 2 Electrical Engineering and Computer Science, The Lawrence Hall of Science (located at the University of California, Berkeley), Berkeley, California, United States
Show AbstractReducing non-radiative recombination in semiconducting materials is a prerequisite for achieving the highest performance in a host of light emitting and photovoltaic applications. Here we use a surface ligand treatment to significantly reduce non-radiative recombination and improve the photoluminescence quantum efficiency of hybrid perovskite (CH3NH3PbI3) thin films. With respect to material bandgap, these passivated films demonstrate quasi-Fermi level splittings comparable to the highest performing GaAs solar cells, reaching 96% of the Shockley-Queisser limit. Importantly, we report internal photoluminescence quantum efficiency values of 92.5% under one sun illumination intensity, which are the highest achieved to date. Next, we use fluorescence microscopy to track carriers on the microscale and show how surface treatments affect lateral carrier diffusion as well as carrier flux across grain boundaries. These surface passivation studies suggest that the material optoelectronic quality can be significantly enhanced and further increases in voltage and device efficiency will be obtained by integrating these types of schemes into charge carrier selective interfaces.
11:15 AM - ES01.05.04
Polarons in CH3NH3.PBI3—Formation, Transport and Recombination
Jarvist Frost 1 2 , Lucy Whalley 2 , Jonathan Skelton 1 , Scott McKechnie 3 , Pooya Azarhoosh 3 , Mark van Schilfgaarde 3 , Aron Walsh 2
1 , University of Bath, Bath United Kingdom, 2 Department of Materials, Imperial College London, London United Kingdom, 3 Department of Physics, King's College London, London United Kingdom
Show AbstractHybrid halide perovskites have rich solid state physics. A unique characteristic is their soft nature, with multiple response processes on timescales of many orders of magnitude[1]. We propose that unusually low energy optical phonon modes, and soft zone boundary acoustic modes, are responsible for carrier scattering and the modest mobility. We calculate the electron-phonon coupling of these soft modes with a novel method, solving the nuclear Schr\"odinger equation for a potential energy landscape recovered from following the phonon eigenvectors[2].
We solve the Feynman polaron state in a variational manner, providing an ab-initio temperature-dependent calculation of mobility[3].
A key question is how a solution processed (thus defective) material has such long minority carrier recombination times, enabling high photovoltaic performance.
We build a multi-scale model for the formation of the polaron, and its migration through the material, based on our prior Monte Carlo disorder model. We quantify the beneficial decrease in recombination rate due to segregation of electrons and holes in the 'ferroelectric highways', versus the detrimental decrease in mobility due to disorder. We quantify the contribution of short-range ferroelectric order on carrier stability and electron-hole recombination in this unique class of materials.
Reduced recombination can occur due to the spin-split indirect-gap. Local ferroelectric distortions generating a crystal field interacts with the high spin-orbit coupling of the lead and iodide atoms. We have directly calculated the reduction in recombination due to this band-structure effect[4].
[1] JM Frost et al. Acc.Chem.Res. 49 (3) pp 528–535 (2016).
[2] LD Whalley, JM Skelton, JM Frost, and A Walsh. Phys. Rev. B 94, 220301(R) (2016).
[3] JM Frost. ArXiv:1704.05404 (2017).
[4] P Azarhoosh et al. APL Materials 4 (9) (2016).
11:30 AM - ES01.05.05
Anomalous Photovoltaic Effect in Organic-Inorganic Hybrid Perovskite Solar Cells
Yongbo Yuan 1 2 , Tao Li 3 , Qi Wang 2 , Jie Xing 2 , Alexei Gruverman 3 , Jinsong Huang 2
1 School of Physics and Electronics, Central South University, Changsha, Hunan, China, 2 Department of Mechanical and Materials Engineering, University of Nebraska–Lincoln, Lincoln, Nebraska, United States, 3 Department of Physics and Astronomy, University of Nebraska–Lincoln, Lincoln, Nebraska, United States
Show AbstractOrganic-inorganic hybrid perovskites (OIHPs) have been proved to be highly successful for very-high-efficiency solar cells. So far, there is a consensus that OIHP materials are a family of soft materials with both high electronic and ionic conduction due to their relatively loosely bonded crystal structure, which closely related to many unusual observations such as giant switchable photovoltaics, current hysteresis, light induced phase separations and etc. In this presentation, we will disclose the room temperature observation of an anomalous photovoltaic (APV) effect in lateral structure OIHP devices.1 This APV is characterized as the device’s open-circuit voltage (VOC) is much larger than the bandgap of photoactive materials. So far, there are several semiquantitative or phenomenological models for the explanations of the APV effect, which are generally classified into two types: (i) the intrinsic noncentrosymmetry in crystal and (ii) the granularity of the polycrystalline materials. A very low conductivity in photovoltaic materials is principally required in the former type of APV mechanism, which is not required in the latter mechanism. However, the understanding of the latter mechanism is lagged, i.e. most proposed models for the granularity mechanism are speculative due to the insufficient experimental evidences for their formation mechanism. Hence, identifying the origins of the over-bandgap VOC is of great academic interest. In our study, the persistent large VOC increases with the electrode spacing, resembling that of ferroelectric photovoltaic devices. However, we demonstrated that the APV effect in OIHP devices is not contributed by ferroelectricity. The APV effect is explained by the formation of tunneling junctions randomly dispersed in the polycrystalline films, which leads to an accumulation of photovoltage at a macroscopic level. The in-situ formation of internal tunneling junctions as a result of ion migration is visualized with Kelvin probe force microscopy scanning. This observation deepened the understandings of ion migration effect in OIHP materials, and it provided a new method for the formation of large and tunable VOC that is not limited by the materials’ bandgap.
Reference
1 Y. Yuan, T. Li, Q. Wang, J. Xing, A. Gruverman, J. Huang, Anomalous photovoltaic effect in organic-inorganic hybrid perovskite solar cells. Sci. Adv. 3, e1602164 (2017).
11:45 AM - ES01.05.06
Real-Time Observation of Iodide Ion Migration and PCBM Passivation in Methylammonium Lead Halide Perovskites
Cheng Li 1 , Antonio Guerrero 2 , Yu Zhong 1 , Anna Gräser 1 , Carlos Andres Melo Luna 3 4 , Jürgen Köhler 3 , Juan Bisquert 2 , Richard Hildner 3 , Sven Huettner 1
1 Organic and Hybrid Electronics, Macromolecular Chemistry I, University of Bayreuth, Bayreuth Germany, 2 Institute of Advanced Materials (INAM), Universitat Jaume I, Castello Spain, 3 Experimental Physics IV and Bayreuth Institute of Macromolecular Research, University of Bayreuth, Bayreuth Germany, 4 Universidad del Valle, Centre for Bioinformatics and Photonics – CIBioFi, Calle 13 No. 100-00, Edificio 320 No. 1069 and Departamento de Fisica, Cali Colombia
Show AbstractOrganometal trihalide perovskite solar cells (PSC) have achieved power conversion efficiency (PCE) of 22.1%. However, PSCs are still suffering from the problem of hysteresis, that is, the discrepancy between two voltage-sweeping directions when performing a current-voltage (J-V) measurement. In this work we utilize correlated time-resolved photoluminescence (PL) microscopy and impedance spectroscopy (IS) on perovskite films to in-situ investigate both the spatial and temporal evolution of ion migration under external optical/electrical fields. We attribute the formation of PL inactive domains to the migration and accumulation of iodide ions under external electrical fields. Our approach, therefore, enables us to quantitatively characterize the kinetic processes and determine the mobility of these ions. Furthermore, we fabricate PSCs incorporating phenyl-C61-butyric acid methyl ester (PCBM) to investigate the influence of diffusion of PCBM molecules on the hysteretic behavior. By employing PL imaging microscopy, we in-situ visualize the diffusion of PCBM during thermal annealing process and its impact on ionic migration under external electrical field. Following that, the step-wise temperature dependent J-V curve measurement further confirms the reduction of ionic migration and increase of activation energy with the aid of PCBM molecules. Hence, it is proposed that the elimination/alleviation of J-V curve hysteresis is ascribed to the diffusion of PCBM molecules, which passivate the iodide related defects and form the PCBM-halide radical. This formation of radical significantly hinders the iodide ion migration, leading to the reduction of modulation in built-in field and interfacial barriers in devices.
References:
1. C. Li. et al. Iodine Migration and its Effect on Hysteresis in Perovskite Solar Cells. Adv. Mater. 28, 2446-2454 (2016).
2. C. Li et al. Emission Enhancement and Intermittency in Polycrystalline Organolead Halide Perovskite Films. Molecules 21, 1081 (2016)
3. C. Li, A. Guerrero, Y. Zhong, S. Huettner, Origins and Mechanisms of Hysteresis in Organometal Halide Perovskites, J. Phys.: Condens. Matter 29, 19 (2017)
4. M. L. Petrus, J. Schlipf, C. Li, T. P. Gujar, N. Giesbrecht, P. Müller-Buschbaum, M. Thelakkat, T. Bein, S. Hüttner, P. Docampo, Capturing the Sun: a Review of the Challenges and Perspectives of Perovskite Solar Cells, Adv. Energy. Mater. DOI: 10.1002/aenm.201700264. (2017) (Accepted)
5. C.Li, et al. Real-Time Observation of Iodide Ion Migration in Methylammonium Lead Halide Perovskites. Small. DOI: 10.1002/smll.201701711 (2017)
ES01.06: Pb-Free, Theoretical, Double-Perovskites, Mixed Composition and Stability
Session Chairs
Tuesday PM, November 28, 2017
Hynes, Level 3, Ballroom B
1:30 PM - *ES01.06.01
Hybrid Metal Halide Perovskites for PV—Optoelectronic Properties and Stability
Waqaas Rehman 1 , Rebecca Milot 1 , Elizabeth Parrott 1 , David McMeekin 1 , Giles Eperon 1 , Michael Johnston 1 , Henry Snaith 1 , Laura Herz 1
1 , University of Oxford, Oxford United Kingdom
Show AbstractHybrid metal halide perovskites (stoichiometry AMX3) have recently emerged as low-cost active materials in PV cells with power conversion efficiencies in excess of 21%. We discuss how parameters essential for photovoltaic operation, such as crystallinity, photostability, charge carrier mobility and diffusion lengths are altered with substitutions of the organic A cation (e.g. methylammonium versus formamidinium), the metal M cation (e.g. Pb2+ or Sn2+) and the halide X anion (I- versus Br-). We focus on two 3D perovskite systems that have attracted interest lately, lead-free ASnI3 (optical bandgap ~1.3 eV) and the mixed organic lead iodide/bromide system APb(BryI1-y)3 whose band gap can be tailored between ~1.5 eV (FAPbI3) and ~2.3 eV (FAPbBr3). We show that unintentional hole doping in tin iodide perovskites introduces fast recombination pathways that can be moderated by crystal structure [1] and introduces a radiative quasi-monomolecular charge recombination channel [2]. In addition, we demonstrate that charge-carrier diffusion and recombination in FA1-xCsxPb(BryI1-y)3 depends on a complex interplay between changes in morphology and electronic bandstructure with bromide fraction y [3,4,5].
References
[1] Parrott, Milot, Stergiopoulos, Snaith, Johnston, Herz, J. Phys. Chem. Lett. 7, 1321 (2016).
[2] Milot, Eperon, Green, Snaith, Johnston, Herz, J. Phys. Chem. Lett. 7, 4178 (2016).
[3] Rehman, Milot, Eperon, Wehrenfennig, Boland, Snaith, Johnston, Herz, Adv. Mater. 27, 7938 (2015).
[4] McMeekin, Sadoughi, Rehman, Eperon, Saliba, Hörantner, Haghighirad, Sakai, Korte, Rech, Johnston, Herz, Snaith, Science 351, 151 (2016).
[5] Rehman, McMeekin, Patel, Milot, Johnston, Snaith, Herz, Energy Environ. Sci. 10, 361 (2017).
2:00 PM - *ES01.06.02
From Lead Halide Perovskites to Lead-Free Metal Halide Perovskites and Double Perovskites—Insights from Density-Functional Theory
Yanfa Yan 1 , Zewen Xiao 1 , Weiwei Meng 1 2 , Feng Hong 1 , Wanjian Yin 1 , Tingting Shi 1 , Jianbo Wang 2 , David Mitzi 3
1 , University of Toledo, Toledo, Ohio, United States, 2 School of Physics and Technology, Center for Electron Microscopy, MOE Key Laboratory of Artificial Micro- and Nano-structures, and Institute for Advanced Studies,, Wuhan University, Wuhan China, 3 Department of Mechanical Engineering and Materials Science, and Department of Chemistry, Duke University, Durham, North Carolina, United States
Show AbstractDespite the demonstration of rapid improvement in record power conversion efficiency over the past few years, the ultimate commercialization of organic–inorganic lead (Pb) halide perovskite (ABX3) solar cell technology, where A is a relatively large inorganic or organic cation (e.g., Cs+, CH3NH3+), B = Pb and X = Cl, Br, I, is still facing serious challenges, most notably with regards to cell instability against moisture and temperature and the inclusion of toxic Pb. Extensive efforts have been paid to discover nontoxic or low-toxicity and air-stable metal halide perovskite-based solar cell materials. Substituting Pb by another divalent cation to form Pb-free perovskites or a combination of monovalent (BI) and trivalent (BIII) cations to form A2BIBIIIX6 halide double-B-cation perovskites has been considered one attractive approach for achieving this goal. In this talk, we review the effects of Pb substitution through density functional theory calculations, focusing on three critical issues: optical absorption; defect properties; and stability. Our results explain the challenges for realizing promising Pb-free halide absorbers for thin–film solar cell application via Pb substitution.
2:45 PM - ES01.06.04
Valence Band Dispersion Measurements of Perovskite Single Crystal with Angle-Resolved Photoemission Spectroscopy
Congcong Wang 1 , Benjamin Ecker 1 , Haotong Wei 2 , Jinsong Huang 2 , Jian-Qiao Meng 3 , Yongli Gao 1
1 , University of Rochester, Rochester, New York, United States, 2 , University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 3 , Central South University, Changsha China
Show AbstractThe electronic structure of the cleaved perovskite (CH3NH3PbBr3) single crystal was studied in an ultra-high vacuum (UHV) system by angle-resolved photoemission spectroscopy (ARPES) and inverse photoelectron spectroscopy (IPES). Highly reproducible dispersive features of the valence bands were observed with symmetry about the Brillouin zone center and boundaries. The largest dispersion width was found to be ~0.73 eV and ~0.98 eV along the ΓX and ΓM directions, respectively. The effective mass of the holes was estimated to be ~0.59 m0. The quality of the surface was verified by atomic force microscopy (AFM) and scanning electron microscope (SEM). The elemental composition was investigated by high resolution x-ray photoelectron spectroscopy (XPS). The experimental electronic structure shows a good agreement with the theoretical calculation.
3:30 PM - *ES01.06.05
Halide Perovskites—New High Performance Semiconductors
Mercouri Kanatzidis 1 , Konstantinos Stoumpos 1 , Chan Myae Myae Soe 1 , Lingling Mao 1 , Jacky Even 2 , Aditya Mohite 3
1 , Northwestern University, Evanston, Illinois, United States, 2 , Fonctions Optiques pour les Technologies de l’Information, Rennes France, 3 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractOrganic-inorganic hybrid perovskites are a special class of low cost semiconductors that have revolutionized the prospects for photovoltaic and optoelectronics technologies. The inorganic chemistry of this class of materials is fascinating. These compounds adopt the three-dimensional ABX3 perovskite structure, which consists of a network of corner-sharing BX6 octahedra, where the B atom is a divalent metal cation (typically Ge2+, Sn2+ or Pb2+) and X is a monovalent anion (typically Cl−, Br−, I−); the A cation is selected to balance the total charge and it can be a Cs+ or a small molecular species. Such perovskites afford several important features including excellent optical properties that are tunable by controlling the chemical compositions, they exhibit ambipolar charge transport with high mobilities. Some members exhibit long electron and hole diffusion lengths. The fundamental similarities and differences between MeNH3PbI3, MeNH3SnI3 and MeNH3GeI3 perovskites as well as other low dimensional materials will be discussed. Another class of materials gaining significance are the two-dimensional (2D) perovskites -a blend of perovskites with layered crystal structure- (Ruddlesden-Popper type) offer a greater synthetic versatility and allow for more specialized device implementation due to the directional nature of the crystal structure. A remarkable advantage of the 2D perovskites is that their functionality can be easily tuned by incorporating a wide array of organic cations into the 2D framework, in contrast to the 3D analogues which have limited scope for structural engineering.
4:00 PM - *ES01.06.06
Tuning Halide Double Perovskites for Sunlight Absorption
Adam Slavney 1 , Linn Leppert 2 5 , Davide Bartesaghi 3 , Aryeh Gold-Parker 1 4 , Michael Toney 4 , Tom Savenije 3 , Jeffrey Neaton 2 5 , Hemamala Karunadasa 1
1 , Stanford University, Stanford, California, United States, 2 , Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 , University of California, Berkeley, California, United States, 3 , Delft University of Technology, Delft Netherlands, 4 , SLAC National Accelerator Laboratory, Menlo Park, California, United States
Show AbstractThe AIBIIX3 (X = halide) perovskites are typically limited to containing divalent B-site metals, which greatly restricts substitution chemistry. In an effort to incorporate a greater range of metals and oxidations states, we recently developed double perovskites as less toxic analogs of lead-halide perovskite solar-cell absorbers.1 The double perovskite Cs2AgBiBr6 exhibits microsecond carrier recombination lifetime, which is very promising for charge extraction in a solar cell. It also displays greater stability to heat and moisture compared to the well-studied solar-cell absorber (CH3NH3)PbI3. However, the material's indirect bandgap of 1.95 eV affords weaker sunlight absorption than the lead-iodide perovskites. Although there has been great recent interest in halide double perovskites, all these materials have large bandgaps exceeding 1.95 eV. I will present the effects of dilute impurity alloying for tuning these materials for visible-light absorption. Notably, the impurities selectively modify the material's bandedges, without significantly changing the bulk material. Incorporation of less than 1 atom% Tl into Cs2AgBiBr6 affords a bandgap of 1.4 eV, which is close to ideal for a single-junction absorber. Importantly, the alloyed perovskite maintains long carrier lifetime of several microseconds. The alloyed material is the first double perovskite to be competitive with (CH3NH3)PbI3 with respect to bandgap energy and carrier lifetime. I will discuss our understanding of how energy- and symmetry-matched impurity orbitals, at very low concentrations, can dramatically alter the bandedges of these materials. These guidelines provide a potential pathway for double perovskites to compete with lead perovskite absorbers.
1. “A bismuth-halide double perovskite with long carrier recombination lifetime for photovoltaic applications” Slavney, A. H.; Hu, T.; Lindenberg, A. M.; Karunadasa, H. I. J. Am. Chem. Soc. 2016, 138, 2138.
2. “Defect-induced band-edge reconstruction of a bismuth-halide double perovskite for visible-light absorption” Slavney, A. H.; Leppert, L.; Bartesaghi, D.; Gold-Parker, A.; Toney, M. F.; Savenije, T. J.; Neaton, J. B.; Karunadasa, H. I. J. Am. Chem. Soc. 2017, 139, 5015.
4:30 PM - ES01.06.07
All Inorganic Sb-Based Perovskite Inspired Photoabsorbers for Solar Cell Applications
Juan-Pablo Correa-Baena 1 , Lea Nienhaus 1 , Seong Sik Shin 1 , Noor Titan Putri Hartono 1 , Sarah Wieghold 1 , Moungi Bawendi 1 , Tonio Buonassisi 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPerovskite solar cells (PSCs) have achieved certified power conversion efficiencies (PCEs) of 22.1% by low cost and low temperature solution processing. However, these materials are based on toxic lead and pose a threat to the commercialization efforts. Our efforts focus on screening criteria for defect-tolerant photovoltaic (PV) absorbers, identifying several classes of semiconducting compounds with band structures and dielectric constants similar to lead-halide perovskites. Further, we evaluate the carrier lifetimes of several Pb-free PV absorbers using a consistent combined experimental and theoretical approach. The carrier lifetimes of five candidate materials based on Sb exceed 1 ns, a threshold for promising PV device performance. We fabricate solar cells based on these compounds and provide extensive characterization of the materials and devices. Additional work is ongoing to add more complexity to our models to obtain Pb-free materials with high currents as they are currently limited due to low out-of-plane mobilities in these layered materials.
4:45 PM - ES01.06.08
Low-Temprature Synthesis of Perovskite Barium Stannate Photoelectrodes for Efficient and Stable Perovskite Solar Cells
Seong Sik Shin 1 2 , Jangwon Seo 1 , Jun Hong Noh 1 , Sang Il Seok 1 3
1 , Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of), 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractAlthough provskite solar cells (PSCs) exceeding a power conversion efficiency (PCE) of 20% have been demonstrated by using mesoporous titanium dioxide (mp-TiO2), they can have limited stability under ultraviolet (UV) irradiation because TiO2 can photocatalyze unwanted reactions in the perovskite layer. Therefore, development of new photoelectrodes is key issue to achieve long-term stability in PSCs. BaSnO3 perovskite would be an ideal replacement given its electron mobility and electronic structure, but BaSnO3 cannot be easily synthesized or crystallized below 500°C, which limits its application to PSCs. To overcome this problem, we develop a novel low temperature process to synthesize BaSnO3 below 500 °C, and investigate a possible synthesis mechanism. Employing the synthesized BaSnO3 as a photoelectrode in PSCs, BaSnO3-based PSCs show a steady-state power conversion efficiency of 21.2%, versus 19.7% for a mp-TiO2 device with great photo-stability under full-sun illumination including UV during 1000 hours.
ES01.07: Poster Session II
Session Chairs
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - ES01.07.01
Effect of Organic Cation Motion on Charge Mobility and Recombination Dynamics in CH3NH3PbI3
María Gélvez-Rueda 1 , Duyen Cao 2 , Konstantinos Stoumpos 2 , Sameer Patwardhan 2 , Joseph Hupp 2 , Tom Savenije 1 , Mercouri Kanatzidis 2 , Ferdinand Grozema 1
1 , Delft University of Technology, Delft Netherlands, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractWe have studied the mobility and lifetime of charge carriers in CH3NH3PbI3 by pulse radiolysis time-resolved microwave conductivity experiments. In this unique technique, we are able to generate a uniform concentration of charges with a known yield and measure the mobility and recombination kinetics of these charges. We have focused our research on the charge carrier recombination dynamics and the effect of CH3NH3PbI3 phase transitions at different temperatures. The latter is not so easy in more common photoconductivity measurements as both the yield of dissociation of excitons into free charge and their mobility may change as a function of temperature.
By varying the initial concentration of charge carriers, we show that the charge decay dynamics in this material can be described by second order recombination kinetics with the presence of a limited concentration of trap states. We have observed significant changes in the mobility and lifetime of the charges. A very abrupt change in the mobility and lifetime is observed on going through the transition from the tetragonal (β) to the orthorhombic (γ) phase. For moderate decreases in temperature a clear decrease in the mobility is observed. This gradual increase of the mobility before the phase transition is attributed to reduction of the lattice vibrations as the temperature decreases and can be fit with a norma phonon scattering relation (~T-1.5). However, an abrupt deviation from this behavior is observed after the β/γ phase transition. An even stronger deviation is observed in the lifetime of the charge carrier, recombination being an order of magnitude slower below the phase transition. This points to a clear change in the recombination mechanisms in CH3NH3PbI3 on going through the phase transition. It is known that the organic cation exhibits substantial rotational dynamics inside the perovskite crystal structure, leading to a high dielectric constant at room temperature. On going through the phase transition, these dynamics dramatically decrease, which is accompanied by a large drop in the dielectric constant. Our experimental results show that the dynamics of the organic cation strongly influences the mobility and recombination kinetics of charge in CH3NH3PbI3.
8:00 PM - ES01.07.02
Making Perovskite Solar Cells Ready for the Market—The Challenge of Stability and Scalability in Perovskite Solar Cells
Xiong Li 1 2 , Michael Graetzel 2
1 Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhon University of Science and Technology, Wuhan, Hubei, China, 2 Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, School of Basic Sciences, Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractMetal halide perovskite solar cells (PSCs) currently attract enormous research interest because of their high solar-to-electric power conversion efficiency (PCE) and low fabrication costs, but their practical development is hampered by difficulties in achieving long-term stability under operation and high performance with large-size devices.
In this presentation, starting from the fundamental understanding of the device equivalent circuit, I will firstly emphasize a universally useful idea of a simple vacuum flash–assisted solution processing method for film morphology control to prepare high-quality perovskite films of high electronic quality over large areas. This enabled us to fabricate solar cells with an aperture area exceeding 1 square centimeter a certified PCE of 19.6%.1 Then I will demonstrate that chemically decorating pervoskite grain surface or the mesoporous scaffold surface by bifunctional ammonium surfactants allows controlling the crystal growth and substantial enhancement in device performance and durability.2 Finally, I will introduce a strategy of using triple-layered architecture, which achieved a certified power conversion efficiency of 12.8% and was stable under outdoor tests in the hot desert climate and indoor long-term light soaking as well as heat exposure during 3 months at 80–85 0C.3,4 This innovative stable and low-cost architecture will enable the timely commercialization of perovskite solar cells.
References
1. Xiong Li, et al., Science, 2016, 353, 58-62.
2. Xiong Li, et al., Nature Chemistry, 2015, 7, 703-711.
3. Anyi. Mei‡, Xiong Li‡, et al., Science, 2015, 345, 295–298.
4. Xiong Li, et al., Energy Technology, 2015, 3, 551–555.
8:00 PM - ES01.07.03
Assessing Degradation and Improving Stability of Hybrid Perovskite Solar Cells Towards Commercialization
Rongrong Cheacharoen 1 , Kevin Bush 1 , Nicholas Rolston 1 , Duncan Harwood 2 , Reinhold Dauskardt 1 , Michael McGehee 1
1 , Stanford University, Stanford, California, United States, 2 , D2 Solar, San Jose, California, United States
Show AbstractOver the past five years, a great deal of research has brought organic-inorganic metal halide perovskite solar cells single junction efficiency from 12% to 22%. In addition, incorporating perovskites as a wide bandgap absorber in tandem with a silicon solar cell increased the efficiency to 26%, on par with solar cell technologies in the market. However, standardized stability according to the IEC 61646, which uses accelerated methods to identify potential problems inhibiting 25 years lifetime, have not been demonstrated. We study stability of single junction Cs0.17FA0.93Pb(Br0.17I0.83)3 perovskite solar cells, which make 23.6% efficient tandem on Si solar cells. We made three improvements on the solar cells for stability. First, we replaced Methylammonium with a bigger Formamidinium(FA) molecule to increase the sublimation temperature for thermal stability. Secondly, we completely removed TiO2 for UV stability. Thirdly, we sputtered a robust, dense, and non-reactive indium doped tin-oxide on the solar cells to prevent FA sublimation, moisture ingression, and metal-halide reaction. Afterwards, we packaged the cells between encapsulant layers and glass with an edge seal all around the sides to prevent lateral moisture ingress.
Following the IEC 61646 standard, we demonstrated for the first time that encapsulated perovskite solar cells can be stable for 1000 hours in 85°C-85%RH chamber in the dark. We used complementary mapping techniques including PL, EL, and dark lock-in thermography to elucidate any macroscopic changes leading to open circuit voltage improvement, thus resulting in 20% increase in efficiency. Moreover, encapsulated solar cells also retained 90% of their performance after 15 kWh/m2 of UV exposure in the 280-400 nm range. Further experiments comparing stability under UV and visible light of encapsulated perovskite solar cells held at maximum power point and open circuit are promising. We will discuss potential mechanism for light induced stabilization of solar cells after prolonged annealing and exposure of light. Mechanical stability is another concern for perovskite solar cells because each layer has a different thermal expansion coefficients and the perovskite has the lowest fracture energy of all solar cell technology. We demonstrated that nine encapsulated solar cells in ethylene vinyl acetate packages survived 200 temperature cycles between -40°C and 85°C, with no delamination and less than 10% decrease in performance. We used a double cantilever beam fracture test to identify PCBM as the weakest layer in the perovskite solar cells and show that the fracture energy is six times higher having encapsulant laminated on top of the solar cells. We will discuss encapsulation design criteria for environmental and mechanical stability of perovskite solar cells. Having passed many accelerated tests, perovskite solar cells are one step closer to commercialization.
8:00 PM - ES01.07.04
Single-Dot Spectroscopy of Perovskite FAPbBr3 Nanocrystals: Luminescence Blinking and Single Photon Emission
Naoki Yarita 1 , Hirokazu Tahara 1 , Masaki Saruyama 1 , Tokuhisa Kawawaki 1 , Ryota Sato 1 , Toshiharu Teranishi 1 , Yoshihiko Kanemitsu 1
1 , Institute for Chemical Research, Kyoto University, Kyoto Japan
Show AbstractMetal-halide perovskite semiconductors are one of the promising candidates for optoelectronic devices including solar cells, photodetectors, light-emitting diodes (LEDs), and lasers [1]. In addition to intensely studied thin films and single crystals, the nanocrystal (NC) counterparts are also gathering much attention due to their remarkable optical properties resulting from their unique size-effects combined with the perovskite structure [2]. Hybrid organic-inorganic formamidinium lead halide perovskite (CH(NH2)2PbX3 or FAPbX3, X = Cl, Br, I) NCs have recently shown excellent optical properties, such as high photoluminescence (PL) quantum yields (QY) of up to 85 % and tunable bandgap covering entire visible spectrum along with their high stability in air and high temperature [3,4]. However, the PL dynamics in NCs are complicated because of multiple carrier recombination processes. Particularly, nonradiative Auger recombination of biexcitons and charged excitons (trions), which causes PL blinking, is quite responsible for decrease in PL QY of perovskite NCs [5]. Therefore, it is necessary to understand the nature of biexcitons and trions in FAPbX3 NCs for their application in optoelectronic devices. In this study, we report detailed PL properties of FAPbBr3 perovskite NCs revealed by single-dot spectroscopy.
The samples used in this work were FAPbBr3 NCs spin-coated onto a cover glass with PMMA. Using single-dot luminescence spectroscopy, we measured the time trace of the PL spectrum, the PL intensity, and the PL lifetime. We found the correlation between the PL peak energy and the PL lifetime. Moreover, we measured the second-order photon correlation function g(2) of single NCs. From the area ratio between the central and the side peaks, which correspond to biexciton-cascade and single-exciton emissions, respectively, we conclude that a single photon is efficiently emitted from a single NC under weak pulse excitation. By analyzing the first photon emission at the central peak in g(2), we extracted PL dynamics of biexcitons in single FAPbBr3 NCs. From the excitation fluence dependence of the PL spectrum and dynamics, we discuss the formation and recombination dynamics of trions in single NCs.
Part of this work was supported by JST-CREST (JPMJCR16N3).
[1] Y. Kanemitsu, J. Mater. Chem. C 5, 3427 (2017).
[2] L. Protesescu et al., Nano Lett. 15, 3692 (2015).
[3] L. Protesescu et al., J. Am. Chem. Soc. 138, 1010 (2016).
[4] I. Levchuk et al., Nano Lett. 17, 2765 (2017).
[5] N. Yarita et al., J. Phys. Chem. Lett. 8, 1413 (2017).
8:00 PM - ES01.07.05
Insights into Inverted Organic-Inorganic Hybrid Perovskite Solar Cell Degradation
Christian Saiz 1 , Castro Edison 2 , Luis Martinez 1 , Sohan Hennadige 2 , Luis Echegoyen 2 , Hans van Tol 3 , Srinivasa Rao Singamaneni 1
1 Department of Physics, University of Texas at El Paso, El Paso, Texas, United States, 2 Chemistry, University of Texas at El Paso, El Paso, Texas, United States, 3 , National High Magnetic Field Laboratory, Tallahassee, Florida, United States
Show AbstractIn this presentation, we report on electron spin resonance (ESR) investigations carried out on three-layer inverted solar cell structure: PCBM/CH3NH2PbI/PDOT:PSS/Glass, where, the PCBM and PDOT:PSS act as electron and hole transport layers, respectively. ESR measurements were carried out on light (1 Sun) illuminated samples, moisturized samples, and the samples exposed through N2 gas. We find two distinct ESR spectra. First ESR spectra contains a signal with g = 4.2 (glassy pattern), found to be originated from Fe3+ located in the glass substrate. The intensity of this signal decreased drastically upon light illumination. Second ESR spectra contains a sharp, intense ESR signal at g = 2.005-2.008; and a weak, sharp ESR signal at g = 2.0022. The intensity of second set of ESR spectra also decreased upon illumination. The latter two signals were found to stem from silicon dangling bonds and oxygen vacancies, respectively. Our controlled measurements infer that these centers were generated during UV-Ozone treatment (30 min) –a necessary step to be performed before PDOT:PSS spin coating. We detected no new signals from our samples under external stimuli. This work signifies the importance in closely looking at the process-induced effects on solar cell substrates that might contribute to the performance degradation of over layers.
8:00 PM - ES01.07.06
A New, More Stable Structural Motif for Hybrid Halide Perovskites
Alex Ganose 1 2 , Christopher Savory 1 , David Scanlon 1 2
1 , University College London, London United Kingdom, 2 , Diamond Light Source, Harwell United Kingdom
Show AbstractIn the last 6 years, hybrid halide perovskites have emerged as a highly efficient class of solar absorbers, with efficiencies reaching 22.4 %, quickly surpassing other 3rd generation devices.[1] The highest performing hybrid perovskite is the cubic CH3NH3PbI3 (MAPI), which is made from earth-abundant elements and can be easily solution processed, dramatically reducing manufacturing costs. Unfortunately, chemical stability is a major concern for these materials and much effort has been devoted to increasing the stability of MAPI based devices.[2]
Recently, partial substitution of iodine with the pseudohalide ion, SCN–, to form the layered (CH3NH3)2Pb(SCN)2I2 (MAPSI), has been suggested as novel route to increase stability whilst retaining high efficiencies. In this work, we explain why MAPSI can still possess an ideal electronic structure for light absorption, despite the loss in connectivity when moving from a cubic to a layered structure.[3] We also explain, for the first time, why MAPSI is more stable than MAPI. Lastly, we demonstrate that MAPSI can act as a parent structure for a related family of materials whose optoelectronic properties can be fine-tuned for use in photovoltaic applications.[4] We further screen this extended family for their defect properties and suggest solar cell architectures likely to result in efficient devices.
References
[1] M. Grätzel, Nat. Mater. 13, 838–842 (2014)
[2] A. M. Ganose, C. N. Savory and D. O. Scanlon, Chem. Commun. 53, 20–44 (2017)
[3] A. M. Ganose, C. N. Savory and D. O. Scanlon, J. Phys. Chem. Lett. 6, 4594–4598 (2015)
[4] A. M. Ganose, C. N. Savory and D. O. Scanlon, J. Mater. Chem A 5, 7845–7853 (2017)
8:00 PM - ES01.07.08
Direct Recombination Behavior in Highly-Emissive CH3NH3PbI3 Perovskite Films
Sarthak Jariwala 1 , Dane deQuilettes 1 , David Ginger 1
1 , University of Washington, Seattle, Seattle, Washington, United States
Show AbstractConventionally, methylammonium lead iodide perovskites were considered direct bandgap semiconductors. More recently, both experimental and theoretical studies have proposed that the fundamental bandgap is weakly indirect arising from combinations of collective methylammonium cation rotations and/or spin-orbit effects. Experimentally, it has been difficult to differentiate between the direct and indirect nature of the bandgap due to the presence of shallow defects near the band-edge especially when measured at low carrier densities. We study methylammonium lead iodide, CH3NH3PbI3 prepared to achieve internal photoluminescence quantum efficiencies near unity. Under these optimized material conditions, we study the recombination kinetics at low fluences (~1x1014 cm-3) and find that the bimolecular electron-hole recombination becomes dominant and the slow recombination that has been previously reported under these conditions is no longer observed. We reconcile previous reports by comparing the recombination rate constants measured in films with both high, and low internal quantum efficiency and therefore isolate the inherent materials properties from defect-dominated behavior.
8:00 PM - ES01.07.09
High-Bandgap Mixed-Halide Hybrid Perovskites—Phase Segregation, Stability and the Intimate Connection between Carrier Transport and Radiative Efficiency
Ian Braly 1 , Ryan Stoddard 1 , Hugh Hillhouse 1
1 , University of Washington, Seattle, Washington, United States
Show AbstractMixed-halide hybrid perovskites are of significant interest since their bandgap can be tuned to be 1.70-1.75 eV and may be ideal candidates as a top-cell in tandem photovoltaics with silicon, CIGS, or CZTS as the bottom cell. However, they have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed several approaches to study and improve their stability and optoelectronic quality. The presentation will focus on: (i) Our development of a new method to simultaneously measure the absolute-intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of correlation between PLQY and diffusion length and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation [1]. (ii) The development of an improved solvent wash for high bandgap (FA,Cs)Pb(I,Br)3 that results in an enhancement of photoluminescence quantum yield (PLQY) of over an order-of-magnitude, an increased quasi-Fermi Level splitting (to 1.29 eV for a 1.75 eV bandgap material), an increase in diffusion length by a factor of 3.5 (to over 1 um), and enhanced open-circuit voltage and short-circuit current from photovoltaic devices. (iii) Elucidation of the mechanism of iodobromide HP phase segregation and its impact on tandem PV operation [2]. (iv) Device results from HP-CIGS tandems with over 18% efficiency [3].
[1] Stoddard, R.J., Eickemeyer, F.T., Katahara, J.K., Hillhouse, H.W., J. Chem. Phys. Lett. Accepted 6/14/2017, will add DOI.
[2] Braly, I.L., Stoddard R.J., Uhl, A., Hillhouse, H.W., Submitted. Will revised with article citation.
[3] Uhl, A.R., Yang, Z., Jen, A.K.-Y, Hillhouse, H.W., J. Mater. Chem. A 5, 3214-3220 (2017).
8:00 PM - ES01.07.10
Fast Force Reconstruction (F3R)-KPFM—Quantifying Local Ion Transport in Organic-Inorganic Perovskites with Micro-Second Time Resolution
Liam Collins 1 , Mahshid Ahmadi 2 , Ting Wu 2 , Bin Hu 2 , Sergei Kalinin 1 , Stephen Jesse 2
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Knoxville, Tennessee, United States
Show AbstractIn recent years, organometallic trihalide perovskites (OIHP) have attracted a lot of attention for high performance and low-cost applications in solar cells. At the same time, many factors remain if these materials are to be commercially viable. In particular, to improve stability and performance, a full understanding of the role ion migration plays in these hybrid perovskite devices needs to be fully established. This necessitates techniques capable of probing dynamic processes on the length scales of an interface, grain boundary, or single point defect. While scanning probe microscopy (SPM) techniques, such as Kelvin probe force microscopy (KPFM), have shown to be useful for mapping ionic and electronic processes across these length-scales, the slow detection speeds (>> ms) limits KPFM measurements to investigating static or quasi-static parameters. In this presentation I will introduce a fast (<20 µs) mode of KPFM, referred to as F3R-KPFM. I will briefly describe how F3R-KPFM utlilizes big data capture and analytics to extract information from the tip-sample interaction pertaining to ion migrations in OIHP materials.Finally I will use this F3R-KPFM apporach to quantify optical and electric field driven ion migration with <20 µs time resolution and sub-micrometer spatial resolution on range of OIHP thin films and devices.
This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
8:00 PM - ES01.07.11
Ionic Influences on Recombination in Perovskite Solar Cells
Adam Pockett 1 , Matthew Carnie 1
1 SPECIFIC, Swansea University, Swansea United Kingdom
Show AbstractDespite rapid progress in terms of the efficiencies of perovskite solar cells, the understanding of some of the observed behaviours in devices is still not fully developed. Of particular interest is the slow dynamic response that is seen in some devices, most commonly as hysteresis in the JV curve. It is also displayed in a range of other slow responses to stimuli, such as the slow Voc rise under illumination or a large capacitance apparent at low frequencies.1,2 Several hypotheses for this anomalous behaviour were initially suggested which included the presence of ferroelectric domains and high densities of surface defects.3 More recently there appears to be a growing consensus that ionic species within the perovskite can move towards interfaces and modify the electronic properties in that region, which impacts charge injection and recombination.4,5
In this work, we have studied the affect different contact materials have on interfacial recombination in the presence of mobile ions in planar perovskite devices. A range of different perovskite cell architectures were studied, including TiO2/Spiro-OMeTAD and “hysteresis-free” organic contact devices. By performing transient photovoltage (TPV) measurements over a period in which ions redistribute within the perovskite layer the dominant recombination mechanism, responsible for hysteresis and other slow dynamic processes, is found to occur at the TiO2/perovskite interface. Low temperature measurements are used to slow down the migration of ions and enable the subsequent variation in recombination behaviour to be studied in detail. We observe an anomalous negative transient upon firing the laser pulse, during the slow Voc rise from an equilibrium starting condition, which we attribute to interfacial recombination at the TiO2/perovskite interface. The impact of recombination at the perovskite/HTL interface is shown to be negligible by performing TPV measurements using different laser wavelengths to probe different depths into the perovskite layer, as well as by changing the type of HTL used.
This technique was further used, together with impedance spectroscopy, to study the improved interfacial properties of hole-conductor-free triple mesoporous architecture devices containing the modified perovskite, (5-AVA)x(MA)(1-x)PbI3.6 The additive, 5-ammoniumvaleric acid (5-AVA) iodide, is found to reduce interfacial recombination at the TiO2 interface and lead to a subsequent improvement in overall device performance, following an associated ‘burn-in’ period under illumination at short-circuit.
References
1. Pockett, A. et al., PCCP 19, 5959–5970 (2017).
2. Chen, B. et al., J. Phys. Chem. Lett. 6, 4693–4700 (2015).
3. Snaith, H. J. et al., J. Phys. Chem. Lett. 5, 1511–1515 (2014).
4. Van Reenen, S. et al., J. Phys. Chem. Lett. 6, 3808–3814 (2015).
5. Calado, P. et al., Nat. Comm. 7, 13831 (2016).
6. Mei, A. et al., Science 345, 295-298 (2014).
8:00 PM - ES01.07.12
Photoinduced Stark Effect in the Layered Perovskites—Monovalent Cation Dependence
Ravichandran Shivanna 1 , Johannes Richter 1 , Felix Deschler 1 , Richard Friend 1
1 Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge United Kingdom
Show AbstractThe two-dimensional analog of organic-inorganic perovskite exhibit strong excitonic character due to the dielectric confinement of electrons and holes between inorganic layer and organic spacers. We explore the photoinduced Stark effect in these self-assembled layered perovskites at ultrafast timescales [(BA)2(X)n-1Pb2I3n+1, where BA = CH3(CH2)3NH3+, X = Methylammonium (MA+)/ Formamidinium (FA+) or Cesium (Cs+)]. Particularly, monitoring monovalent cation dependence in the unit cell (i.e., n=2) consist of single monovalent cations. The oscillator strength, exciton binding energy and lifetime varies with different cation substitutions due to their size (crystal structure) and associated intrinsic dipole moments. The photoinduced Stark effect can be observed at earliest time as 150 fs and persist up to 100’s of ps. The transient signal from the linearly polarized pump and probe pulses resembles the second derivative of ground state absorption suggesting the highly localized bound excitons formation in this system. The electric field of pump pulse causes a shift in the absorption to lower and higher energy leading to two photoinduced absorption band on both the sides of the ground state bleach. The observed two photoinduced absorption(PIA) bands are attributed to the splitting of the excitonic band. The exciton lifetime for all the three systems measured using the transient grating technique reveals 10's of picosecond time scale. It is also observed that the PIA bands are spin selective when probed using circularly polarized pulses. The observed photoinduced Stark effect can be envisioned for ultrafast modulation of light for opto-spin logical applications in these room temperature solution processed layered perovskites.
8:00 PM - ES01.07.14
Direct Observation of Ion Migration in a Planar Perovskite Solar Cell with Low Hysteresis
Stefan Weber 1 3 , Ilka Hermes 1 , Victor Bergmann 1 , Wolfgang Tress 2 , Michael Graetzel 2 , Ruediger Berger 1
1 , Max Planck Institute, Mainz Germany, 3 Department of Physics, Johannes Gutenberg University, Mainz Germany, 2 , EPFL, Lausanne Switzerland
Show AbstractEfficient charge extraction within solar cells explicitly depends on the optimization of the internal interfaces. Potential barriers, unbalanced charge extraction or interfacial trap states can prevent cells from reaching high power conversion efficiencies. In the case of perovskite solar cells, slow processes happening on timescales of seconds cause hysteresis in the current-voltage characteristics. Recently, more and more evidence was found that hysteresis is directly connected to ion migration and trap-assisted recombination at the electrode interfaces. Furthermore, hysteresis could be mostly avoided by selection of suitable selective electrode materials. The exact mechanism behind hysteresis and the suppression thereof, however, is still not clear.
Here, we report on local and time-dependent potential measurements with a modified Kelvin probe force microscopy (KPFM) [1,2] method on cross sections of planar spiro/methylammonium:formamidinium lead iodide (MAPI:FAPI)/SnO solar cells. Due to the SnO contact, the cell had a very low hysteresis. By implementing a pointwise KPFM measurement approach, full potential maps across the device could be obtained with a time resolution of 0.5 ms. Our experiments revealed distinct differences in the charging dynamics at interfaces of the perovskite to adjacent layers. In particular, we found a strong reverse electric field of 4-5 kV/cm in the active layer for 100-200 ms after switching off of the illumination. This electric field is caused by space charge regions close to the interfaces that contain slowly moving charged species, i.e. migrating ions. Our observation clearly shows that the suppression of hysteresis is not connected to the suppression of ion migration. Therefore, the suppression of interfacial recombination is the crucial step for reducing hysteresis.
[1] Bergmann et al., Nat. Comm., 5, 5001 (2014).
[3] Bergmann et al., ACS AM&I, 8(30), 19402 (2016).
8:00 PM - ES01.07.15
Effect of Residual Charge Carrier Species on Light Stability of Perovskite Materials
Min-cheol Kim 1 2 , Young Un Jin 3 , Byeong Jo Kim 3 , Donghwa Lee 4 , Hyun Suk Jung 3 , Mansoo Choi 1 2
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Global Frontier Center for Multiscale Energy Systems, Seoul Korea (the Republic of), 3 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon Korea (the Republic of), 4 Department of Materials Science and Engineering, Pohang University of Science and Technology(POSTECH), Pohang Korea (the Republic of)
Show AbstractThough stability enhancement of organic-inorganic hybrid perovskite materials is fascinating recently, unveiling profound mechanisms of perovskite materials decomposition is the key to achieving the progress for the next level. Photo-generated charge carriers have been blamed for the destruction of perovskite materials according to recent researches. However, we do not understand how each the charge carrier species –electron or holes – influence the light stability. In the case of silicon solar cells, electron-hole pairs generated by means of breaking covalent Si-Si bonds. Such generated holes inside of crystalline structure contribute to weakening the bonding strength, therefore weaken the structural stability. Likewise, perovskite materials also can be differently affected depending on charge carrier species. In this report, we control the internal charge carrier species through introducing charge-selective transporting half devices. Absorbance, X-ray assisted measurements and scanning electron microscopic images clearly demonstrate that the presence of hole carriers inside the perovskite is harmful to the light-stability. Potential applied lateral perovskite device in order to fabricate polarized perovskite layer coherently tells us that hole carriers are detrimental to maintain structural durability. From the density function theory (DFT) calculation, the vulnerability of hole excess state inside the perovskite materials is obviously identified. This study highlights the importance of extracting residual hole carriers inside the perovskite devices for long-term endurable perovskite devices.
8:00 PM - ES01.07.16
Hybrid Perovskite Crystalline Grain Effects on Electronic and Ionic Conduction
Md Nadim Ferdous Hoque 1 , Zhaoyang Fan 1
1 Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock, Texas, United States
Show AbstractTo further improve the hybrid perovskite solar cell performance, including the power conversion efficiency and ion migration related stability, microscopic study of perovskite crystalline grain effect is necessary. In this study, perovskite solar cells with different grain size were assessed by several characterization methods, particularly conductive atomic force microscopy (c-AFM) and impedance spectroscopy. C-AFM study confirmed that the sample with larger grain size prepared under moderate humidity is superior to those with smaller grains prepared in dry condition. The passivation by annealing in humidity helped preventing the ion migration in the grain boundary resulting more current conduction through the grain inside, which ultimately resulted in better photovoltaic performance. Impedance spectroscopic study of different grain sizes revealed that the activation energy for ionic migration is increased with the grain size in both tetragonal and cubic phases. The findings in this work provide guidance on optimizing the crystalline structure of perovskite materials for better solar cell performance by minimizing ion migration and the related adverse effects.
8:00 PM - ES01.07.17
High-Throughput Generation and Analysis of Hybrid Organic-Inorganic Perovskites
Chiho Kim 1 , Huan Tran 1 , Sridevi Krishnan 1 , Rampi Ramprasad 1
1 , University of Connecticut, Storrs, Connecticut, United States
Show AbstractHybrid organic-inorganic perovskites (HOIPs) have been attracting a great deal of attention due to their versatility of electronic properties and fabrication methods. While methylammonium-containing perovskites are of primary interest, the hybrid perovskite family is significantly diverse in terms of both the possible organic cations [1] and the structural motifs [2]. We prepare a dataset of more than 2,000 HOIPs, which features 5 group-2 and 4 group-IV cations, 4 halide anions, and 16 organic cations [3]. Using a combination density functional theory calculations with the minima-hopping structure predictions method, the low-energy structure, the bandgap, the dielectric constant, and the relative energy of the HOIPs are uniformly prepared and validated by comparing with relevant experimental and/or theoretical data. It could be useful for future data-mining efforts that can explore possible structure-property relationships and phenomenological models. Progressive extension of the dataset is expected as new organic cations become appropriate within the HOIP framework, and as additional properties are calculated for the new compounds found.
[1] B. Saparov, and D. Mitzi, Chem. Rev. 116, 4558 (2016).
[2] T. D. Huan, V. N. Tuoc, and N. V. Minh, Phys. Rev. B 93, 094105 (2016).
[3] C. Kim et al., Sci. Data 4, 170057 (2017).
8:00 PM - ES01.07.18
Interface Electronic Structure at the Interface of ALD-Grown SnOx and MAPbI3 in In-Free Perovskite Solar Cells
Kai Brinkmann 1 , Ting Hu 1 2 , Tim Becker 1 , Neda Pourdavoud 1 , Jie Zhao 1 2 , Ralf Heiderhoff 1 , Tobias Gahlmann 1 , Selina Olthof 3 , Klaus Meerholz 3 , Daniel Toebbens 4 , Baochang Cheng 2 , Yiwang Chen 2 , Thomas Riedl 1
1 , Bergische Universitat Wuppertal, Wuppertal Germany, 2 , Nanchang University, Nanchang China, 3 , University of Cologne, Cologne Germany, 4 , Helmholtz-Zentrum Berlin, Berlin Germany
Show AbstractSemi-transparent electrodes based on metal nanowires or ultra-thin metal layers are considered as promising alternatives for ITO thin-film optoelectronic devices.[1] Unfortunately, these metal layers are extremely susceptible to corrosion by the halide precursors used to synthesize hybrid perovskites, such as MAPbI3.
Here, we study ALD grown SnOx in conventional perovskite solar cells (PSCs). The dense and impermeable SnOx affords the realization of In-free bottom electrodes based on semi-transparent ultra-thin silver layers. Specifically, the SnOx serves a twofold purpose: It shields the ultra-thin metal bottom electrode against halide species and it simultaneously functions as electron extraction / hole blocking layer. For the latter, we identify a strong influence of the choice of oxidant (water, ozone, O-plasma) used for the ALD process.[2] XPS and UPS studies unravel the formation of mostly PbI2 (thickness about 3 nm) between SnOx and MAPbI3. The energy line-up of SnOx/PbI2/MAPbI3 differs significantly for the different SnOx variants, which infers different electron extraction barriers and critically affects their selectivity. As a result, the Voc ranges from 1.03 V for water-SnOx to 1.186 V (PCE: 15.4%) for ozone-SnOx. The ultra-low voltage loss of only 0.36 V in the latter case is among the lowest values reported for PSCs and rivals that of commercial silicon cells. Photoelectron spectroscopy shows, that in case of ozone SnOx, the energy barrier for electron extraction is minimum and hole blocking is found most effective. Finally, we were able to realize indium free PSCs based on a SnOx/Ag/SnOx sandwich bottom electrode with a maximum processing temperature of only 100°C.
[1] K. Zilberberg et al., J. Mater. Chem. A 2016, 4, 14481.
[2] T. Hu et al., Adv. Mat. 2017, 1606656.
8:00 PM - ES01.07.19
Solution-Processed Organohalide Perovskite Image Sensor Array
Woongchan Lee 1 2 , Jongha Lee 1 2 , Huiwon Yun 1 2 , Hyung Joon Shim 1 2 , Jun-Kyul Song 1 2 , Dong Chan Kim 1 2 , Seungki Hong 1 2 , Dae-Hyeong Kim 1 2
1 , Institute of Basic Science, Seoul Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractAs organohalide perovskite materials show significant improvement in the field of optoelectronics, demand for commercialization of perovskite optoelectronics has increased. There are many obstacles to commercialize perovskite optoelectronics such as low stability, difficulty in large-scale fabrication, and so on. One of the obstacles for image sensor with perovskite photodiode is high-definition and high-resolution patterning for perovskite materials. However, perovskite materials are too vulnerable to pattern them with conventional lithographic solution (e.g., acetone, isopropanol, water). For this reason, patterned solution-processed perovskite thin films which have higher performance than any type of perovskite materials have not been successfully demonstrated although many researches on perovskite single crystal and perovskite nanowire tried to solve the problem before. In addition to patterning perovskite material, integration of patterned perovskite photodetecting units with other electronic components like transistor and blocking diode is another critical issue of commercialization. Because of low thermal stability of perovskite materials, perovskite optoelectronics should be manufactured on the top of the active components and especially, patterning perovskite materials based on wetting/dewetting behavior is highly affected by bottom structure. Here, we successfully demonstrated solution-processed organohalide perovskite image sensor array. For patterning perovskite materials, we manipulated surface energy of the electron transport layer or insulating layer with self-assembled monolayer and perovskite precursor solution was deposited on the area of hydrophilic region during spin-coating process. It was identified that there are several intermediate steps of patterning behavior through slow-motion video. Furthermore, to build up perovskite photodiode array on the top of blocking diode, we manipulated surface energy of insulating layer by changing length of self-assembled monolayer and fabricated solution-processed organohalide perovskite image sensor array. The reported solution-processed perovskite image sensor will show the possibility of commercial perovskite optoelectronics.
8:00 PM - ES01.07.20
Impact of Ultrathin Electron Extraction Layers on Perovskite Solar Cells
Dianyi Liu 1 , Qiong Wang 2 , Christopher Traverse 1 , Thomas Hamann 2 , Richard Lunt 1
1 Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States, 2 Department of Chemistry, Michigan State University, East Lansing, Michigan, United States
Show AbstractThe power conversion efficiency (PCE) of planar perovskite solar cells (PSC) has recently reached over 20% utilizing fullerenes optimized as top electron transport layers. However, the function of fullerenes in PSC is still not entirely clear. Previous work on solution processed PCBM has indicated that a sufficient thickness of fullerene layer > 20 nm is crucial for full surface coverage that can help efficiently extract electrons, passivate trap states, reduce hysteresis, and lead to high device performance. When the thickness of the fullerene layer is reduced to < 20 nm, the device performance has been shown to drop significantly. In this work, we demonstrate an efficient planar structure PSC with ultrathin (~ 1 nm) electron extraction layers and investigate the key electronic role of such thin layers. In particular, we find that the electron extraction efficiency is dramatically altered, even though the perovskite film is only partially covered. The PCE of corresponding device is over 18% with negligible hysteresis, while the absence of the ultrathin layer results in a PCE < 1%. The function of the ultrathin layer is studied by photoluminescence and impedance spectroscopy, which indicate that an incomplete monolayer can switch-on the perovskite device. This demonstration could aid the commercial scalability and simplify the manufacturing by essentially removing transport layers, minimizing the necessary amount of materials, reducing the impact of material variability without losing performance, and increasing the lifetime. This work allows us to rethink the role and need for any layers other than just the perovskite and electrodes.
8:00 PM - ES01.07.21
Relation of Charge-Carrier Dynamics to Structural Orientation in Ruddlesden-Popper Organic Metal Halides
Naveen Venkatesan 1 , John Labram 1 , Michael Chabinyc 1
1 , University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractHybrid-halide perovskite materials have recently been the subject of great research interest due to their ability to form high-efficiency photovoltaics while being low-cost and solution-processable. Two-dimensional layered perovskites represent an exciting subclass of materials that show increased material stability relative to three-dimensional materials, such as methylammonium lead iodide.1 These layered compounds are typically formed via two distinct strategies – partial halide substitution with pseudohalides such as thiocyanate (SCN-),2 and the use of mixed organic cations, leading to the formation of Ruddlesden-Popper (R-P) phases that have shown high power conversion efficiencies and stability.3 Yet, the electronic properties of compounds with the R-P structures are expected to be highly anisotropic and not well understood.
Using methylammonium (MA) along with an n-butylammonium (BA) cationic spacer, films of Ruddlesden-Popper phases of the form (BA)2(MA)n-1PbnI3n+1 were synthesized by spincoating, with lead iodide layer thicknesses of 1 to 4. Structural characterization by X-ray diffraction shows a gradual texture change; lead iodide sheets change from being parallel to the substrate to perpendicular as the layer thickness increases, also corroborated by distinct changes in SEM and AFM micrographs. Quantifying this texture change results in near-perfect parallel orientation of the sheets of lead-iodide octahedra in n = 1 and perpendicular alignment in n = 4. Optical measurements of absorbance and emission help to confirm the phase purity of the distinct phases. Measurements of transient photoconductance by time-resolved microwave conductivity (TRMC) reveal carrier mobilities and lifetimes, while elucidating the connection between exciton dynamics, carrier transport, and crystal orientation in these R-P thin films. We observe that charge transport in the in-plane and out-of-plane directions are comparable, suggesting the existence of transport pathways in all directions in our polycrystalline thin-films. Finally, two-dimensional images of X-ray scattering reveal structural disorder in these materials and the impact on the observed electronic properties will be discussed. The results of this work suggest that the interesting charge transport properties of these two-dimensional systems, along with their enhanced stability, give rise to a range of highly-stable, high-performance perovskite optoelectronic devices.
[1] Smith, I. C. et al., Angew. Chem. (2014).
[2] Labram, J. G., Venkatesan, N. R., et al., J. Mater. Chem. C (2017).
[3] Tsai, H., et al., Nature (2016).
8:00 PM - ES01.07.22
Quantum-Dots-in-Perovskite Hybrid Material for High Performance Optoelectronics
Xiwen Gong 1 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada
Show AbstractColloidal quantum dots (CQDs) are known as promising light emitting materials in view of their tunable luminescence, high quantum efficiency and solution processability. However, CQD thin films today still suffer a compromise between luminescence efficiency and charge transport, and this leads to unacceptably high power consumption. Perovskites have been discovered with excellent carrier transport properties, such as low defect density, high mobility and long diffusion length. The presentation will highlight our recent efforts in designing heteroepitaxial quantum-dot-in-perovskite (QDIP) solid material, and the study of photophysics interactions between the quantum dot and perovskite. The second part of the presentation will focus on a variety of applications of the QDIP in optoelectronics, such as solar cells, light emission diodes, and photodetectors.
References:
[1] Z. Ning*, X. Gong*, R. Comin*, G. Walters, F. Fan, O. Voznyy, E. Yassitepe, A. Buin, S. Hoogland, and E. H. Sargent, “Quantum-dot-in-perovskite solids,” Nature, vol. 523, no. 7560, pp. 324–328, 2015.
[2] X. Gong*, Z. Yang*, G. Walters, R. Comin, Z. Ning, E. Beauregard, V. Adinolfi, O. Voznyy, and E. H. Sargent, “Highly efficient quantum dot near-infrared light-emitting diodes,” Nat. Photonics, vol. 10, no. 4, pp. 253–257, Feb. 2016.
[3] F. P. Garcia de Arquer*, X. Gong*, R. P. Sabatini, M. Liu, G.-H. Kim, B. R. Sutherland, O. Voznyy, J. Xu, Y. Pang, S. Hoogland, D. Sinton, and E. Sargent, “Field-emission from quantum-dot-in-perovskite solids,” Nat. Commun., vol. 8, p. 14757, Mar. 2017.
[4] Z. Yang*, A. Janmohamed*, X. Lan, F. P. Garcia de Arquer, O. Voznyy, E. Yassitepe, G.-H. Kim, Z. Ning, X. Gong, and R. Comin, “Colloidal quantum dot photovoltaics enhanced by perovskite shelling,” Nano Lett., vol. 15, no. 11, pp. 7539–7543, 2015.
8:00 PM - ES01.07.23
Electron-Doped CH3NH3PbX3 (X = Br and I) Single Crystals—Fabrication and Optoelectronic Properties
Yasuhiro Yamada 1 , Mizuki Hoyano 1 , Ryo Akashi 1 , Kenichi Oto 1 , Yoshihiko Kanemitsu 2
1 , Chiba University, Chiba Japan, 2 Institute for Chemical Research, Kyoto University, Kyoto Japan
Show AbstractDoping semiconductors with carriers is one of the most essential techniques for materials science from the viewpoints of both fundamental physics and device applications. Halide perovskite semiconductors MAPbX3 (MA = CH3NH3+, X = Cl, Br, and I) are currently at the center of attention in the research field of solar cells and optoelectronic device applications. However, only a few studies have been reported on the chemical doping method and the carrier-doping effects in doped halide perovskites. Here we investigated the optical and electronic properties of n-type Bi-doped MAPbX3 [X = Br and I] single crystals by a combination of time-resolved laser spectroscopy and electronic transport measurements.
We fabricated Bi-doped MAPbX3 single crystals with different Bi concentrations by means of both inverse-temperature crystallization and antisolvent-vapor-assisted crystallization methods. The Bi/Pb ratio in the feed solution ranges from 0 to 5 mol%. We evaluated the Bi/Pb ratio in the single crystals by element analysis (ICP).
Reflectivity spectrum shows a broad peak at 1.6 eV for Bi-doped MAPbI3 and 2.3 eV for Bi-doped MAPbBr3, irrespective of Bi concentration. This clearly shows that the bandgap energy is unchanged by Bi doping. On the other hand, photoluminescence (PL) spectrum shows a significant blueshift with an increase of Bi concentration. These electron-density dependent optical properties are successfully explained in terms of photon recycling effects, a repeated emission and absorption of photons in crystals [1-5]. In undoped crystals, the PL peak shows redshift compared with the original band-edge PL because of the photon recycling (photon re-absorption) and carrier diffusion process. In Bi-doped samples, the photon recycling is suppressed. We can estimate the diffusion constant (or carrier mobility) of photocarriers from the detailed analysis of the PL dynamics [2,3].
In addition, we conducted the AC-Hall measurements to determine the carrier density and electron mobility in Bi-doped MAPbX3. Based on these experimental results, we will discuss the doping effects on optical and electronic properties in MAPbX3.
Part of this work was supported by JST-CREST (JPMJCR16N3), Collaborative Research Program of Institute for Chemical Research, Kyoto University (grant # 2017-15), and Iketani Science and Technology Foundation.
References
[1] Y. Yamada, et al., Appl. Phys. Express (2014), 7, 032302.
[2] Y. Yamada, et al., J. Am. Chem. Soc. (2015), 137, 10456-10459.
[3] T. Yamada, et al., Adv. Electron. Mater. (2016), 2, 1500290.
[4] T. Yamada, et al., Phys. Rev. Appl. (2017), 7, 014001.
[5] Y. Yamada et al., Bull. Chem. Soc. Jpn. (2017), in press.
8:00 PM - ES01.07.24
Highly Stablized Perovskite Solar Cells by Li+-Containing Fullerene Salt as Both Dopant and Anti-Oxidant
Hiroshi Ueno 1 , Il Jeon 2 , Seungju Seo 2 , Shigeo Maruyama 2 , Yutaka Matsuo 1 2 3
1 School of Chemistry, Northeast Normal University, Changchun, Jilin, China, 2 Department of Mechanical Engineering, The University of Tokyo, Tokyo, Tokyo, Japan, 3 Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei China
Show AbstractLead halide perovskite solar cells (PSCs) have drawn great attention as the promising solar energy source in recent years. Their certified power conversion efficiencies (PCEs) now reach more than 20%. Despite high PCE, low stability of PSCs has been the most serious drawback, which is in dire need of resolution. It has been found that light, oxygen, and water are the origins of the perovskite layer degradation. In particular, dopants used for 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobi-fluorene (spiro-MeOTAD) hole-transporting material are attributed for the low stability, due to their hygroscopic nature. Replacement of liquid electrolyte by spiro-MeOTAD was a breakthrough at the initial stage of PSC development, improving PCE substantially, owing to well-aligned energy band and amorphous nature of spiro-MeOTAD. However, because spiro-MeOTAD intrinsically has low mobility, a dopant must be present to improve the conductivity. Lithium bis(trifluoromethanesulfonyl)imide salt (Li+TFSI−) has been widely used as the p-dopant for spiro-MeOTAD. Li+TFSI− does not directly oxidize spiro-MeOTAD, but instead, promotes the oxidation of spiro-MeOTAD by oxygen at the presence of light or thermal excitation. Because doping spiro-MeOTAD with Li+TFSI− requires oxygen, it is difficult to control the amount of spiro-MeOTAD oxidation; the formation of oxidized spiro-MeOTAD has been shown to be reversible during device operation depending on ambient conditions and the sweep direction of current−voltage (J−V) measurement. Also, a number of factors, including light intensity, the concentrations of lithium ions and oxygen, has been shown to the amount of oxidized spiro-MeOTAD. Uncontrolled oxidized spiro-MeOTAD is unpredictable and leads to inconsistent reproducibility and instability of PSCs. In addition to this, as mentioned above, Li+ salt is extremely hygroscopic and induces moisture-based degradation of PSCs.
In this work, lithium-ion-encapsulated [60]fullerene bis(trifluoromethanesulfonyl)imide salt ([Li+@C60]TFSI−) was used in PSCs instead of Li+TFSI− as a solution aforementioned problems. C60 encapsulating Li+ changed the hydrophilic alkali salt to a hydrophobic species. Also, spiro-MeOTAD mixed with [Li+@C60]TFSI− produced cationic salt spiro-MeOTAD●+TFSI− and neutral Li+@C60●− by electron transfer from spiro-MeOTAD to Li+@C60. While spiro-MeOTAD●+TFSI− functioned as an effective hole transporting material Li+@C60●− functioned as an antioxidant, reacting with any intruding oxygen and moisture. spiro-MeOTAD●+TFSI− required no chemical additives nor oxidation as it was technically pre-oxidized spiro-MeOTAD. By preventing unnecessary oxidation in the device system, [Li+@C60]TFSI−-used devices showed approximately 10 times higher stability than the conventional Li+TFSI−-used devices.
8:00 PM - ES01.07.25
Interdomain Charge Transfer within Hybrid Organic Inorganic Mixed Cations, Mixed Halides Perovskites
Marine Bouduban 1 , Fabrizio Giordano 1 , Arnulf Rosspeintner 2 , Joël Teuscher 1 , Eric Vauthey 2 , Michael Graetzel 1 , Jacques-Edouard Moser 1
1 , Ecole Polytechnique Federale Lausanne, Lausanne Switzerland, 2 , University of Geneva, Geneva Switzerland
Show AbstractHybrid lead-halide perovskite solar cells (PSCs) have kept their promises and still appear as a thrilling newcomer in solar cell technologies, with power conversion efficiencies rising above 20%. At this point however, further developments require a more fundamental understanding of key features inherent to PSCs, such as the bulk dynamics of photocarriers within the perovskite layer. Indeed, the larger VOC of mixed perovskite devices, responsible in part for their enhanced performances, remains unexplained.
Herein, we aim at rationalizing the decreased amount of charge carrier recombination in a mixed perovskite material, namely MA1-yFAyPbI3-xBrx. In this respect, we use femtosecond transient absorbance spectroscopy (TAS), and focus on two different approaches. First, we perform lineshape analysis of a photoinduced electroabsorption signature, shedding light on the nature of the photogenerated carriers; and second, we resort to global analysis to highlight the various spectral population in presence as well as their dynamics. 1,2
We report the presence of charge-transfer excitons and corresponding domains in mixed perovskites. Those domains are assigned to chemical heterogeneities, and exhibit defined spectral signatures. In addition, we observe efficient interdomain charge transfer ensuring an efficient charge separation. This accounts for the reported higher VOC and alltogether better performance of mixed perovskite-based solar cells.
(1) Bouduban, M. F.; Burgos-Caminal, A.; Teuscher, J.; Moser, J. E. Unveiling the Nature of Charge Carrier Interactions by Electroabsorption Spectroscopy: an Illustration with Lead-Halide Perovskites. chimia (aarau) 2017, 71, 231–235.
(2) Bouduban, M. E. F.; Burgos-Caminal, A.; Ossola, R.; Teuscher, J.; Moser, J. E. Energy and Charge Transfer Cascade in Methylammonium Lead Bromide Perovskite Nanoparticle Aggregates. Chemical Science 2017, 00, 1–10.
8:00 PM - ES01.07.26
Control Over Self-Doping in High Bandgap Perovskite Films
Michael Kulbak 1 , Igal Levine 1 , Einav Barak-Kulbak 1 , Satyajit Gupta 1 , Doron Azulay 2 , Oded Millo 2 , Isaac Balberg 2 , Gary Hodes 1 , David Cahen 1
1 , Weizmann Inst of Science, Rehovot Israel, 2 , The Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractThe effects of different cations and anions on carrier diffusion lengths and formation of a junction in high bandgap halide perovskite (HaP) film-based solar cells is studied in detail. HaP cells are of interest as high bandgap ones in solar spectrum splitting for boosting solar to electrical energy conversion efficiency/area by adding them to c-Si photovoltaic cells and driving photo-electrochemical reactions for chemical energy storage. Resolving how the addition of cations and anions change the (unintentional) doping of the HaP is of great importance for understanding the film and device physics as well as for performance improvement. We study Pb-based, APbX3, HaP films, where A can be a mixture of formamidinium, methylammonium and cesium and X a mixture of bromine and chlorine, using a combination of Photoconductivity and Steady-State Photocarrier-Grating (SSPG) techniques [1]. This way we measure the effect of the different cation/anion compositions on the majority and minority carrier diffusion lengths. We also use Electron Beam Induced Current (EBIC), Contact Potential Difference (CPD) and Surface Photovoltage (SPV) [2] to identify the formation of the junction and built-in voltage and to track the position and size of the space charge region width following the changes in the HaP composition. We find mixed-cation HaP form a p-i-n junction with relatively long and ambipolar carrier diffusion lengths, in contrast to the single cation based bromide HaPs, who form a p-n junction and shorter diffusion lengths.
References
[1] I. Levine, et al., J. Phys. Chem. Lett. 2016, 7, 5219.
[2] N. Kedem, M. Kulbak, et al., Phys. Chem. Chem. Phys. 2017, 19, 5753.
8:00 PM - ES01.07.28
Enhanced Perovskite Electronic Properties via a Modified Lead(II) Chloride Acid-Base Adduct and Their Effect in High-Efficiency Perovskite Solar Cells
Ngoc Duy Pham 1
1 , Queensland University of Technology, Brisbane, Queensland, Australia
Show AbstractRecently perovskites based on organic-inorganic metal halides have been given enormous attention from solar community due to its promising material properties. Solar cells made from this material possess impressive certified power conversion efficiency exceeding 22% and can potentially compete with current market-dominant silicon solar cells. However, the best-performing perovskite solar cell (PSC) is still far below efficiency limit of ~31% for this material. In addition, the common current-voltage hysteresis in devices has posed challenges for an accurate determination of device performance. Suppression of recombination in bulk and at interfaces of perovskite layer is critical to achieve hysteresis-free high performance PSCs. We found that by simply incorporating lead chloride (PbCl2) into the methylammonium lead tri-iodide (MAPbI3) perovskite precursor through the Lewis acid-base approach, a large performance enhancement was achieved. The average efficiency was increased from 16.5% for pure MAPbI3 device to an average efficiency of 18.1% for PbCl2-additive device while hysteresis effect was also suppressed with PbCl2-additive, owing to an enhanced electronic properties of perovskite layer and interfaces. Our experimental results have shown that the optimal concentration of PbCl2 that helps increase grain size of MAPbI3 with introduction of the ideal amount secondary phases (lead iodide and methylammonium lead tri-chloride) is 2.5% (molar ratio, relative to lead iodide). Examination by photoluminescence and time-resolved photoluminescence has shown that devices based on MAPbI3-2.5% of PbCl2 facilitated longer charge carrier lifetime and electron-hole collection efficiency which is ascribed to reduced defects and concurrent improved material crystallinity. Electrochemical impedance spectra of corresponding PSCs have revealed that, compared to the pristine MAPbI3 perovskite film, the 2.5% PbCl2-additive increased the recombination resistance of the PSCs by 2.4-fold. Meanwhile, measurement of the surface potential of the perovskite films has indicated PbCl2-additive modifies the electronic property of the film, shifting the fermi-level of the MAPbI3 film by 90 meV, leading to a more favourable energetic band matching for charge transfer.1
1. N. D. Pham, V. T. Tiong, P. Chen, L. Wang, G. Wilson, J. M. Bell and H. Wang, Journal of Materials Chemistry A, 2017, DOI: 10.1039/C6TA11139D.
8:00 PM - ES01.07.29
Synthesis and XPS and TPD Quantification of Interfacial Br– Basicity on CsSnBr3 via Interactions with Adsorbed Boron Reagents of Varying Lewis Acidity
Weiran Gao 1 , Kenneth Zielinski 1 , Alexander Carl 1 , Ronald Grimm 1
1 , Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractCsSnBr3 is a lead-free, solar-relevant perovskite with a band gap that is ideal for the top absorber in a tandem-junction photovoltaic, however the Sn2+ species is unstable to oxidation in air and would require passivation. Motivated to understand the reactivity of CsSnBr3 towards organometallic ALD precursors, we studied the basicity of interfacial Br– sites on polycrystalline CsSnBr3 based reactions with a series of fluorinated Lewis acids. CsSnBr3 crystal synthesis followed both solution-cooling and high-temperature-melt methods. The series of Lewis acids include boron trihalides as well as triphenylboranes with varying halogen substituents of a broad degree of acidity and known pKa values. X-ray photoelectron spectroscopy (XPS) quantified interfacial oxidation states and fractional coverage of surface-adsorbed species. Temperature programmed desorption (TPD) quantified the strength of interactions between the BF3 adsorbate and the CsSnBr3 substrate. The results elucidated the Lewis basicity of interfacial Br– sites on CsSnBr3, and we discuss these results in the context of reactivity towards ALD-relevant precursors for ambient air passivation.
8:00 PM - ES01.07.30
Single-Walled Carbon Nanotube Films for Perovskite Solar Cells
Shigeo Maruyama 1 2 , Il Jeon 1 , Esko I. Kauppinen 3 , Yutaka Matsuo 4 1
1 , The University of Tokyo, Tokyo Japan, 2 Energy NanoEngineering, AIST, Tsukuba Japan, 3 Department of Applied Physics, Aalto University, Espoo Finland, 4 Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei China
Show AbstractA film of single-walled carbon nanotubes (SWNTs) can be a dual-functional as carrier-selection-layer and transparent-conductive electrode in various solar cells. Here, this dual functional application of SWNT film is demonstrated for organic-inorganic hybrid perovskite solar cells. Replacement of ITO in inverted-type perovskite solar cells, SWNTs/PEDOT:PSS/CH3NH3PbI3/PCBM/Al, is demonstrated by adjusting the surface energy of PEDOT:PSS [1]. The flexible application on polyethylene terephthalate (PET) is also demonstrated [1]. Furthermore, replacement of electron-blocking-layer and metal electrode in normal-type perovskite solar cells is demonstrated as well. They show high power conversion efficiency (PCE), cost-efficiency, and higher stability. Those devices can have comparable PCE as the conventional design with organic electron-blocking layer and top metal electrode. In addition to the expected lower cost and improved stability, these solar cells can be potentially semi-transparent when transparent SWNT films are used. This means that they can be illuminated from either cathode or anode side. The normal-type perovskite solar cell, composed of ITO/TiO2/CH3NH3PbI3/SWNTs, can achieve a PCE of 10 % without doping of SWNTs [2]. The PCE can be as high as 17 % with the preliminary doping of the film of SWNTs using Spiro-MeOTAD, which is the typical electron-blocking-layer used for the normal type perovskite solar cells. The PMMA layer on top of the film of SWNTs can also contribute as doping and protection layer. Furthermore, the modified structure with a perovskite layer sandwiched by C60 and SWNTs, i.e. ITO/C60/CH3NH3PbI3/SWNTs, can lead to the solar cells without hysteresis and with much improved air-stability [3]. The effective passivation of the degradation of perovskite material by moisture can be achieved with C60 and SWNTs [3]. This device show about 13 % PCE without hole-transporting layer and 17% with spiro-MeOTAD this far [3]. This can be a good candidate for scale-up demonstration of practical perovskite solar cells.
This work was supported by JSPS KAKENHI Grant Numbers JP25107002, JP15H05760, and IRENA Project by JST-EC DG RTD, Strategic International Collaborative Research Program, SICORP. Part of this work is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).
References
[1] I. Jeon, T. Chiba, C. Delacou, Y. Guo, A. Kaskela, O. Reynaud, E. I. Kauppinen, S. Maruyama, Y. Matsuo, Nano Lett. 15, 6665 (2015).
[2] T. Sakaguchi, I. Jeon, T. Chiba, A. Shawky, R. Xiang, S. Chiashi, E. I. Kauppinen, N.-G. Park, Y. Matsuo, S. Maruyama, to be submitted.
[3] N. Ahn, I. Jeon, J. Yoon, E. I. Kauppinen, Y. Matsuo, S. Maruyama, M. Choi, to be submitted.
8:00 PM - ES01.07.31
Understanding the Compositional Effect on the Band Structures of Lead-Free Halide Double Perovskites from First-Principles Calculations
Peng Zhang 1 , Su-Huai Wei 1
1 , Beijing Computational Science Research Center, Beijing China
Show AbstractThe past four years have witnessed an explosive emergence and development of a new class of solar cell based on the hybrid organic-inorganic halide perovskites which show dramatically boosted power conversion efficiencies (PCE) from initial value of 3.8% to currently 22.1%. The class of halide perovskites under investigations has a general formula ABX3, where A is a relatively large inorganic or organic cation, such as Cs+ and CH3NH3+, B is a metal cation (typically Sn2+ and Pb2+), and X is a halogen anion (e.g., Cl-, Br- and I-). Although the ABX3 perovskites exhibit a number of remarkable properties that make them ideal for optoelectronics applications, these materials suffer from the long-term instability issue, especially under the heat and humidity conditions, and the presence of toxic Pb may limit their widespread applications. Thus, to realize commercial applications of this technology, further development of Pb-free and air-stable halide perovskites with appropriate optoelectronics properties is still highly desired. Here, we use DFT calculations to systematically study a series of double perovskites to reveal the fundamental relationship between the composition and optoelectronic properties of these materials. We inspect these materials from the basic physical perspectives and analyze how different atomistic orbitals of their constituting ions would influence their band structures. The results indicate that when the CBM has a ns0 character (e.g. In 5s0), the double perovskites usually exhibit a direct bandgap at the Γ point, but the direct band edge transition is parity-forbidden. When the CBM has a np0 character (e.g. Bi 5p0), it usually occurs at the L point, and the VBM is determined by its character (e.g. np6 or nd10) together with the possible s-p-d coupling. Our studies provide a comprehensive understanding of the compositional effect on the band structures of halide double perovskites and may act as a guideline for the future design of novel halide double perovskites for optoelectronics applications.
8:00 PM - ES01.07.32
Effects of Oxygen, Water and Air Exposure on the Electronic Structure of CH3NH3PbI3-xClx Mixed Halide Perovskite Films
Maryline Ralaiarisoa 1 2 , Ingo Salzmann 1 3 , Fengshuo Zu 1 , Norbert Koch 1 2 4
1 Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin Germany, 2 , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin Germany, 3 Institute for Solid State Physics, University of Tokyo, Chiba Japan, 4 Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou China
Show AbstractPerovskite solar cells are confronted with air stability and reproducibility issues, which represent a serious obstacle for establishing reliable property-function relationships and long-term applications. Thus, the understanding of the processes underlying these issues is indispensable and it is equally important to gain information that best possibly reflects the perovskite material behavior in an actual device-operation environment.
Here, we investigated (i), the influence of pure oxygen and water exposure on the electronic structure of CH3NH3PbI3-xClx mixed halide perovskite film surfaces, and (ii), that of ambient air exposure, where both oxygen and water act in combination. To obtain insight into the surface electronic properties we employed photoelectron yield spectroscopy (PYS) in atmospheric conditions and photoelectron spectroscopy (PES) in ultrahigh vacuum (UHV).
Perovskite films that were kept in inert gas (nitrogen) atmosphere of a glove-box or UHV exhibit a pronounced n-type surface character mostly due to Pb-related defects [1], where the Fermi-level is within ca. 100 meV of the conduction band edge. Pure oxygen exposure leads to a shift of the Fermi-level towards a mid-gap position, i.e., the surface became significantly less n-type, while the ionization energy (IE) remains unchanged. Upon water vapor exposure, the pronounced n-type surface character was accentuated. This change is mostly reversible after mild heating in UHV. Finally, based on grazing-incidence X-ray diffraction (GIXRD) measurements, we discuss the impact of water on the perovskite thin films by monitoring structural changes in-situ at high relative humidity levels above 80 %. We find indications for the formation of an intermediate phase, similar to a reported monohydrate phase [2], before severe material degradation sets in.
Consequently, we face two competing effects of oxygen and water on the surface electronic properties in air. We consistently found that the IE measured in UHV by PES was 0.4 eV higher than that measured in ambient air by PYS. Such variations of the electronic structure of perovskite film surfaces will certainly affect the energy-level alignment at the interface between the perovskite and typical charge-transport materials, which will be investigated in future work.
8:00 PM - ES01.07.32
Effects of Oxygen, Water and Air Exposure on the Electronic Structure of CH3NH3PbI3-xClx Mixed Halide Perovskite Films
Maryline Ralaiarisoa 1 2 , Ingo Salzmann 1 3 , Fengshuo Zu 1 , Norbert Koch 1 2 4
1 Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin Germany, 2 , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin Germany, 3 Institute for Solid State Physics, University of Tokyo, Chiba Japan, 4 Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou China
Show AbstractPerovskite solar cells are confronted with air stability and reproducibility issues, which represent a serious obstacle for establishing reliable property-function relationships and long-term applications. Thus, the understanding of the processes underlying these issues is indispensable and it is equally important to gain information that best possibly reflects the perovskite material behavior in an actual device-operation environment.
Here, we investigated (i), the influence of pure oxygen and water exposure on the electronic structure of CH3NH3PbI3-xClx mixed halide perovskite film surfaces, and (ii), that of ambient air exposure, where both oxygen and water act in combination. To obtain insight into the surface electronic properties we employed photoelectron yield spectroscopy (PYS) in atmospheric conditions and photoelectron spectroscopy (PES) in ultrahigh vacuum (UHV).
Perovskite films that were kept in inert gas (nitrogen) atmosphere of a glove-box or UHV exhibit a pronounced n-type surface character mostly due to Pb-related defects [1], where the Fermi-level is within ca. 100 meV of the conduction band edge. Pure oxygen exposure leads to a shift of the Fermi-level towards a mid-gap position, i.e., the surface became significantly less n-type, while the ionization energy (IE) remains unchanged. Upon water vapor exposure, the pronounced n-type surface character was accentuated. This change is mostly reversible after mild heating in UHV. Finally, based on grazing-incidence X-ray diffraction (GIXRD) measurements, we discuss the impact of water on the perovskite thin films by monitoring structural changes in-situ at high relative humidity levels above 80 %. We find indications for the formation of an intermediate phase, similar to a reported monohydrate phase [2], before severe material degradation sets in.
Consequently, we face two competing effects of oxygen and water on the surface electronic properties in air. We consistently found that the IE measured in UHV by PES was 0.4 eV higher than that measured in ambient air by PYS. Such variations of the electronic structure of perovskite film surfaces will certainly affect the energy-level alignment at the interface between the perovskite and typical charge-transport materials, which will be investigated in future work.
8:00 PM - ES01.07.33
Low-Temperature Processed Flexible Perovskite Solar Cells Employing SnO2 Colloidal Nanocrystals
Miyeon Baek 1 , So Yeon Park 1 , Yeonkyeong Ju 1 , Hyun Suk Jung 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractThe rapid development in organic-inorganic metal halide perovskite solar cells (PSCs) has significantly attracted research attention for next generation photovoltaic (PV) industry filed due to their excellent electrochemical properties, large absorption coefficient, and long diffusion length. In PSC’s architecture, the electron transfer layer (ETL) is a key component in highly efficient planar PSCs. Most in common, TiO2 has been widely used for ETL materials up to now. Although it has been successfully used so far, there is a distinct disadvantage that TiO2 films require the high temperature sintering not only to achieve a comparatively dense layer, but also to be transformed into the crystalline structure. Thus, in order to overcome the drawback by using TiO2, the other metal oxides such as SnO2, ZnO, ArO2, Al2O3 and so on have been used as substitute. 1, 2 Especially, the research for SnO2 has emerged as the center of attention, since it has the wider band gap and higher mobility compared to than TiO2. 3 However, it is still sparse to research for formation of SnO2 ETL at very low-temperature being suitable for fabricating flexible and wearable PSCs.
In this study, we have fabricated stable and efficient PSCs by using SnO2 colloidal nanocrystals (NCs). A ~30nm of thin layer was densely deposited by spin-coting SnO2 colloidal NCs (≒3nm) solution onto the indium tin oxide (ITO) glass substrate and annealing at low-temperature to remove solvent residuals. The SnO2 ETL with colloidal NCs without high-temperature process showed a high crystallinity via the transmission electron microscopy (TEM) and X-ray diffraction (XRD) results. As a result, the enhanced morphology and crystallinity of SnO2 colloidal NCs contributed to reducing the number of defect traps on SnO2 ETL, which played a pivotal role forming smooth and pinhole-free perovskite films. Compared to amorphous SnOx films by sol-gel method, we focused on the enhanced influences of SnO2 films by colloidal NCs on electrical parameters, optical properties, and photovoltaic performances. Furthermore, we confirmed that a very dense and stable ETL with SnO2 colloidal NCs shows efficient charge extraction via photoluminescence spectrum result due to low trap density and reduced resistivity between ETL and perovskite layer. Moreover, flexible devices with SnO2 colloidal NCs showed stable and efficient performances without hysteresis. Ultimately, this study demonstrates that the formation of electron transfer layer with high crystalline SnO2 colloidal NCs at low-temperature contributes to reducing trap density and enhancing electron transfer, so the application onto flexible substrates indicates the potential toward commercialization of flexible PSCs.
References
[1] Dianyi Liu. et al.,Nature Photonics. 8,133-138 (2014)
[2] Anyi Mei. et al., Science. 345 (6194), 295-298 (2014)
[3] Juan Pablo Correa Baena. et al., Energy & Environmental Science. 8, 2928-2934 (2015)
8:00 PM - ES01.07.33
Low-Temperature Processed Flexible Perovskite Solar Cells Employing SnO2 Colloidal Nanocrystals
Miyeon Baek 1 , So Yeon Park 1 , Yeonkyeong Ju 1 , Hyun Suk Jung 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractThe rapid development in organic-inorganic metal halide perovskite solar cells (PSCs) has significantly attracted research attention for next generation photovoltaic (PV) industry filed due to their excellent electrochemical properties, large absorption coefficient, and long diffusion length. In PSC’s architecture, the electron transfer layer (ETL) is a key component in highly efficient planar PSCs. Most in common, TiO2 has been widely used for ETL materials up to now. Although it has been successfully used so far, there is a distinct disadvantage that TiO2 films require the high temperature sintering not only to achieve a comparatively dense layer, but also to be transformed into the crystalline structure. Thus, in order to overcome the drawback by using TiO2, the other metal oxides such as SnO2, ZnO, ArO2, Al2O3 and so on have been used as substitute. 1, 2 Especially, the research for SnO2 has emerged as the center of attention, since it has the wider band gap and higher mobility compared to than TiO2. 3 However, it is still sparse to research for formation of SnO2 ETL at very low-temperature being suitable for fabricating flexible and wearable PSCs.
In this study, we have fabricated stable and efficient PSCs by using SnO2 colloidal nanocrystals (NCs). A ~30nm of thin layer was densely deposited by spin-coting SnO2 colloidal NCs (≒3nm) solution onto the indium tin oxide (ITO) glass substrate and annealing at low-temperature to remove solvent residuals. The SnO2 ETL with colloidal NCs without high-temperature process showed a high crystallinity via the transmission electron microscopy (TEM) and X-ray diffraction (XRD) results. As a result, the enhanced morphology and crystallinity of SnO2 colloidal NCs contributed to reducing the number of defect traps on SnO2 ETL, which played a pivotal role forming smooth and pinhole-free perovskite films. Compared to amorphous SnOx films by sol-gel method, we focused on the enhanced influences of SnO2 films by colloidal NCs on electrical parameters, optical properties, and photovoltaic performances. Furthermore, we confirmed that a very dense and stable ETL with SnO2 colloidal NCs shows efficient charge extraction via photoluminescence spectrum result due to low trap density and reduced resistivity between ETL and perovskite layer. Moreover, flexible devices with SnO2 colloidal NCs showed stable and efficient performances without hysteresis. Ultimately, this study demonstrates that the formation of electron transfer layer with high crystalline SnO2 colloidal NCs at low-temperature contributes to reducing trap density and enhancing electron transfer, so the application onto flexible substrates indicates the potential toward commercialization of flexible PSCs.
References
[1] Dianyi Liu. et al.,Nature Photonics. 8,133-138 (2014)
[2] Anyi Mei. et al., Science. 345 (6194), 295-298 (2014)
[3] Juan Pablo Correa Baena. et al., Energy & Environmental Science. 8, 2928-2934 (2015)
8:00 PM - ES01.07.35
Reversible Chemistry at the TiO2/CH3NH3PbI3 and the Implications on Device and Material Property Characterization
Ross Kerner 1 , Barry Rand 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractMeasuring iodine gas sensing behavior of TiO2 and CH3NH3PbI3 (MAPbI3) thin film devices allows us to infer that reversible chemistry occurs at the TiO2/MAPbI3 interface. The chemisorption of I2 very strongly oxidizes TiO2, reducing its free electron concentration to a greater degree and much more rapidly than O2/superoxide chemistry. On the other hand, I2 chemisorption on MAPbI3 mainly acts to passivate surface defects. Both occur on a time scale of several to tens of seconds, the same time scale that perovskite photovoltaic parameter transients, such as Voc decay, are observed to follow. Electronic carriers are a main reactant involved in the proposed Faradaic reactions indicating that the steady state concentrations of chemical species associated with each material are voltage- and illumination-dependent. The chemical reactions reveal that perovskites on TiO2 may often be measured to be n-type due to an electrochemical redox mechanism rather than purely by work function difference. Furthermore, reversible interfacial chemistry can better explain why the nature of both capacitive and non-capacitive current-voltage hysteresis as well as ionic transport properties are highly interface dependent. We expect this work to lead to a systematic understanding of the chemical stability properties and optimization of device relevant perovskite interfaces including oxides, organics, and metals.
Reference: R. A. Kerner and B. P. Rand. “Linking Chemistry at the TiO2/CH3NH3PbI3 Interface to Current-Voltage Hysteresis.” J. Phys. Chem. Lett., 2017, 8, 2298–2303
8:00 PM - ES01.07.35
Reversible Chemistry at the TiO2/CH3NH3PbI3 and the Implications on Device and Material Property Characterization
Ross Kerner 1 , Barry Rand 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractMeasuring iodine gas sensing behavior of TiO2 and CH3NH3PbI3 (MAPbI3) thin film devices allows us to infer that reversible chemistry occurs at the TiO2/MAPbI3 interface. The chemisorption of I2 very strongly oxidizes TiO2, reducing its free electron concentration to a greater degree and much more rapidly than O2/superoxide chemistry. On the other hand, I2 chemisorption on MAPbI3 mainly acts to passivate surface defects. Both occur on a time scale of several to tens of seconds, the same time scale that perovskite photovoltaic parameter transients, such as Voc decay, are observed to follow. Electronic carriers are a main reactant involved in the proposed Faradaic reactions indicating that the steady state concentrations of chemical species associated with each material are voltage- and illumination-dependent. The chemical reactions reveal that perovskites on TiO2 may often be measured to be n-type due to an electrochemical redox mechanism rather than purely by work function difference. Furthermore, reversible interfacial chemistry can better explain why the nature of both capacitive and non-capacitive current-voltage hysteresis as well as ionic transport properties are highly interface dependent. We expect this work to lead to a systematic understanding of the chemical stability properties and optimization of device relevant perovskite interfaces including oxides, organics, and metals.
Reference: R. A. Kerner and B. P. Rand. “Linking Chemistry at the TiO2/CH3NH3PbI3 Interface to Current-Voltage Hysteresis.” J. Phys. Chem. Lett., 2017, 8, 2298–2303
8:00 PM - ES01.07.36
Halide Perovskite Heteroepitaxy—Bond Formation and Carrier Confinement at the PbS – CsPbBr3 Interface
Young-Kwang Jung 1 , Keith Butler 2 , Aron Walsh 1 3
1 , Yonsei University, Seoul Korea (the Republic of), 2 , University of Bath, Bath United Kingdom, 3 , Imperial College London, London United Kingdom
Show AbstractRecently, hybrid halide perovskites have been widely studied for photovoltaics [1-2], but their application range is extending to light-emitting diodes [3], solid-state memories [4], sensors [5], and battery electrodes [6]. Therefore, control of the energetic stability, transport, and confinement of charge carriers (electrons & holes) at interface is a key requirement for practical devices. We systematically investigate chemical and physical properties of the PbS – CsPbBr3 interface, where epitaxial growth is possible due to their similar lattice constants, by performing a first-principles density functional theory (DFT) calculations. Our results include: (i) insights into the surface chemistry of halide perovskites; (ii) what is the most favorable contact geometry; (iii) how bonding is formed between the two materials; (iv) which type of heterojunction occurs at interface. Moreover, we present a practical first-principles procedure for screening optimal interfaces for optoelectronic devices.
[1] L. D. Whalley, J. M. Frost, Y.-K. Jung, and A. Walsh, J. Chem. Phys. 146, 220901 (2017).
[2] P. Gao, M. Grätzel, and M. K. Nazeeruddin, Energy Environ. Sci. 7, 2448–2463 (2014).
[3] S. A. Veldhuis, P. P. Boix, N. Yantara, M. Li, T. C. Sum, N. Mathews, and S. G. Mhaisalkar, Adv. Mater. 28, 6804–6834 (2016).
[4] D. Liu, Q. Lin, Z. Zang, M. Wang, P. Wangyang, X. Tang, M. Zhou, and W. Hu, ACS Appl. Mater. Interfaces 9, 6171–6176 (2017).
[5] Y. Fang, Q. Dong, Y. Shao, Y. Yuan, and J. Huang, Nat. Photon. 9, 679–686 (2015).
[6] H.-R. Xia, W.-T. Sun, and L.-M. Peng, Chem. Commun. 51, 13787–13790 (2015).
8:00 PM - ES01.07.36
Halide Perovskite Heteroepitaxy—Bond Formation and Carrier Confinement at the PbS – CsPbBr3 Interface
Young-Kwang Jung 1 , Keith Butler 2 , Aron Walsh 1 3
1 , Yonsei University, Seoul Korea (the Republic of), 2 , University of Bath, Bath United Kingdom, 3 , Imperial College London, London United Kingdom
Show AbstractRecently, hybrid halide perovskites have been widely studied for photovoltaics [1-2], but their application range is extending to light-emitting diodes [3], solid-state memories [4], sensors [5], and battery electrodes [6]. Therefore, control of the energetic stability, transport, and confinement of charge carriers (electrons & holes) at interface is a key requirement for practical devices. We systematically investigate chemical and physical properties of the PbS – CsPbBr3 interface, where epitaxial growth is possible due to their similar lattice constants, by performing a first-principles density functional theory (DFT) calculations. Our results include: (i) insights into the surface chemistry of halide perovskites; (ii) what is the most favorable contact geometry; (iii) how bonding is formed between the two materials; (iv) which type of heterojunction occurs at interface. Moreover, we present a practical first-principles procedure for screening optimal interfaces for optoelectronic devices.
[1] L. D. Whalley, J. M. Frost, Y.-K. Jung, and A. Walsh, J. Chem. Phys. 146, 220901 (2017).
[2] P. Gao, M. Grätzel, and M. K. Nazeeruddin, Energy Environ. Sci. 7, 2448–2463 (2014).
[3] S. A. Veldhuis, P. P. Boix, N. Yantara, M. Li, T. C. Sum, N. Mathews, and S. G. Mhaisalkar, Adv. Mater. 28, 6804–6834 (2016).
[4] D. Liu, Q. Lin, Z. Zang, M. Wang, P. Wangyang, X. Tang, M. Zhou, and W. Hu, ACS Appl. Mater. Interfaces 9, 6171–6176 (2017).
[5] Y. Fang, Q. Dong, Y. Shao, Y. Yuan, and J. Huang, Nat. Photon. 9, 679–686 (2015).
[6] H.-R. Xia, W.-T. Sun, and L.-M. Peng, Chem. Commun. 51, 13787–13790 (2015).
8:00 PM - ES01.07.39
Functionalized poly(9-vinylcarbazole) as a Hole Transporting Material in Perovskite Solar Cells Having Improved Stability
Camille Geffroy 3 1 2 , Eftychia Grana 3 , Muhammad Mumtaz 3 , Ludmila Cojocaru 2 , Eric Cloutet 3 , Satoshi Uchida 2 , Hiroshi Segawa 2 , Thierry Toupance 1 , Georges Hadziioannou 3
3 , Laboratoire de Chimie des Polymères Organiques, Pessac France, 1 , Institut des Sciences Moléculaires, Talence France, 2 , Research Center for Advanced Science and Technology, Tokyo Japan
Show AbstractThe hole transporting material (HTM) is a key component in part ruling both performance and stability of perovskite solar cells (PSCs). The most studied and effective HTM reported so far is the spiro-OMeTAD. In addition to its tedious and relatively expensive fabrication, this HTM shows some stability issues. New HTMs have thus been investigated to replace spiro-OMeTAD, including carbazole-based materials. Among them, polyvinylcarbazoles show promises for organic electronics and optoelectronics applications due to their relatively high stability, hydrophobicity, hole mobility, easy processability that make them for instance good candidates for PSCs.
In this context, this paper would like to report on a newly designed functionalized-polyvinylcarbazole (F-PVK) as HTM in planar PSCs. Thermoanalytical and electro-optical measurements such as DSC, TGA, UV/Vis, thin-film conductivity, hole mobility, contact angles and photoelectron spectroscopy were carried out for further understanding this new material. Compared to spiro-OMeTAD in FTO/c-TiO2/CH3NH3PbI3-xClx/HTM/Au devices, similar average photovoltaic performances where achieved in F-PVK-based PSCs with a best PCE of 12.62% under 1 sun conditions. More importantly, the stability of the perovskite solar cells is significantly improved. After 10-day ageing, without encapsulation, in dry air conditions, F-PVK-based devices maintain their initial efficiency whereas the efficiency of spiro-OMeTAD devices had deteriorated from the second day. The improved stability can be attributed to a more hydrophobic behaviour and more homogeneous layers of the new HTM polymer as compare to spiro-OMeTAD.
Finally, the impact of the HTM polymer (e.g. influence of molecular weight) on hysteresis phenomena along with on interfaces in PSCs will also be presented.
Reference:
C. Geffroy, E. Grana, M. Mumtaz, L. Cojocaru, E. Cloutet, S. Uchida, T. Toupance, H. Segawa and G. Hadziioannou, J. Mater. Chem. A., 2017, submitted.
8:00 PM - ES01.07.39
Functionalized poly(9-vinylcarbazole) as a Hole Transporting Material in Perovskite Solar Cells Having Improved Stability
Camille Geffroy 3 1 2 , Eftychia Grana 3 , Muhammad Mumtaz 3 , Ludmila Cojocaru 2 , Eric Cloutet 3 , Satoshi Uchida 2 , Hiroshi Segawa 2 , Thierry Toupance 1 , Georges Hadziioannou 3
3 , Laboratoire de Chimie des Polymères Organiques, Pessac France, 1 , Institut des Sciences Moléculaires, Talence France, 2 , Research Center for Advanced Science and Technology, Tokyo Japan
Show AbstractThe hole transporting material (HTM) is a key component in part ruling both performance and stability of perovskite solar cells (PSCs). The most studied and effective HTM reported so far is the spiro-OMeTAD. In addition to its tedious and relatively expensive fabrication, this HTM shows some stability issues. New HTMs have thus been investigated to replace spiro-OMeTAD, including carbazole-based materials. Among them, polyvinylcarbazoles show promises for organic electronics and optoelectronics applications due to their relatively high stability, hydrophobicity, hole mobility, easy processability that make them for instance good candidates for PSCs.
In this context, this paper would like to report on a newly designed functionalized-polyvinylcarbazole (F-PVK) as HTM in planar PSCs. Thermoanalytical and electro-optical measurements such as DSC, TGA, UV/Vis, thin-film conductivity, hole mobility, contact angles and photoelectron spectroscopy were carried out for further understanding this new material. Compared to spiro-OMeTAD in FTO/c-TiO2/CH3NH3PbI3-xClx/HTM/Au devices, similar average photovoltaic performances where achieved in F-PVK-based PSCs with a best PCE of 12.62% under 1 sun conditions. More importantly, the stability of the perovskite solar cells is significantly improved. After 10-day ageing, without encapsulation, in dry air conditions, F-PVK-based devices maintain their initial efficiency whereas the efficiency of spiro-OMeTAD devices had deteriorated from the second day. The improved stability can be attributed to a more hydrophobic behaviour and more homogeneous layers of the new HTM polymer as compare to spiro-OMeTAD.
Finally, the impact of the HTM polymer (e.g. influence of molecular weight) on hysteresis phenomena along with on interfaces in PSCs will also be presented.
Reference:
C. Geffroy, E. Grana, M. Mumtaz, L. Cojocaru, E. Cloutet, S. Uchida, T. Toupance, H. Segawa and G. Hadziioannou, J. Mater. Chem. A., 2017, submitted.
8:00 PM - ES01.07.40
Contact Passivation for Efficient and Stable Low-Temperature-Processed Planar Perovskite Solar Cells
Hairen Tan 1 , Ankit Jain 1 , Oleksandr Voznyy 1 , Sjoerd Hoogland 1 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada
Show AbstractMetal halide perovskite solar cells (PSCs) have attracted extensive research interest for next-generation solution-processed photovoltaics because of their high solar-to-electric power conversion efficiency (PCE) and low fabrication costs. Planar perovskite solar cells made entirely via solution-processing at low temperatures (<150oC) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices. However, their power conversion efficiency and device operational stability are still inferior to those of their mesoscopic counterparts that rely on high-temperature (450-550oC) sintered TiO2 as electron selective layer. We reasoned that performance and stability loss in low-temperature planar PSCs could arise from imperfect interfaces and charge recombination between the selective contact at the illumination side and the perovskite film grown on top, since the perovskite active layers themselves have been demonstrated to possess excellent long-term photostability. Indeed, once the impressively long photocarrier diffusion lengths in perovskite films are achieved, attention must shift to perfecting the interface. We reasoned that deep trap states present at the perovskite/ESL interface could potentially be addressed by passivating the interface between the charge selective contact and the perovskite absorber. Here we report a contact passivation strategy that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. This enables us to fabricate solar cells with certified efficiencies of 20.1% and 19.5% for active areas of 0.049 and 1.1 cm2, respectively, achieved via low-temperature solution processing. The certified efficiencies are among the highest reported low-temperature planar perovskite solar cells. Solar cells with efficiency >20% retain 90% (97% after dark recovery) of their initial performance following 500 hours continuous room-temperature operation at their maximum power point under one-sun illumination.
8:00 PM - ES01.07.40
Contact Passivation for Efficient and Stable Low-Temperature-Processed Planar Perovskite Solar Cells
Hairen Tan 1 , Ankit Jain 1 , Oleksandr Voznyy 1 , Sjoerd Hoogland 1 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada
Show AbstractMetal halide perovskite solar cells (PSCs) have attracted extensive research interest for next-generation solution-processed photovoltaics because of their high solar-to-electric power conversion efficiency (PCE) and low fabrication costs. Planar perovskite solar cells made entirely via solution-processing at low temperatures (<150oC) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices. However, their power conversion efficiency and device operational stability are still inferior to those of their mesoscopic counterparts that rely on high-temperature (450-550oC) sintered TiO2 as electron selective layer. We reasoned that performance and stability loss in low-temperature planar PSCs could arise from imperfect interfaces and charge recombination between the selective contact at the illumination side and the perovskite film grown on top, since the perovskite active layers themselves have been demonstrated to possess excellent long-term photostability. Indeed, once the impressively long photocarrier diffusion lengths in perovskite films are achieved, attention must shift to perfecting the interface. We reasoned that deep trap states present at the perovskite/ESL interface could potentially be addressed by passivating the interface between the charge selective contact and the perovskite absorber. Here we report a contact passivation strategy that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. This enables us to fabricate solar cells with certified efficiencies of 20.1% and 19.5% for active areas of 0.049 and 1.1 cm2, respectively, achieved via low-temperature solution processing. The certified efficiencies are among the highest reported low-temperature planar perovskite solar cells. Solar cells with efficiency >20% retain 90% (97% after dark recovery) of their initial performance following 500 hours continuous room-temperature operation at their maximum power point under one-sun illumination.
8:00 PM - ES01.07.41
Interconversion Between Free Charges and Bound Excitons in 2D Hybrid Lead Halide Perovskites
María Gélvez-Rueda 1 , Eline Hutter 1 , Duyen Cao 2 , Nicolas Renaud 1 , Konstantinos Stoumpos 2 , Joseph Hupp 2 , Tom Savenije 1 , Mercouri Kanatzidis 2 , Ferdinand Grozema 1
1 , Delft University of Technology, Delft Netherlands, 2 , Northwestern University, Evanston, Illinois, United States
Show AbstractThe opto-electronic properties of hybrid perovskites can be easily tailored by varying their components. Specifically, mixing the common short organic cation (methyl ammonium (MA)) with a larger one (e.g. butyl ammonium (BA)) results in 2-dimensional perovskites with varying thicknesses of inorganic layers separated by the large organic cation. These materials, known as Ruddlesden-Popper phases, have proven to result in highly efficient, solution-processed and stable LEDs (EQE = 8.8%) and photovoltaic solar cells (PCE = 12.5%). In both of these applications a detailed understanding of the dissociation and recombination of electron-hole pairs is of prime importance. In this work we give a clear experimental demonstration of the interconversion between bound excitons and free charges as a function of temperature by combining microwave conductivity techniques with photoluminescence measurements. We demonstrate that the exciton binding energy varies strongly (between 80 meV and 370 meV) with the thickness of the inorganic layers. Additionally, we show that the mobility of charges increases with the layer thickness, in agreement with calculated effective masses from electronic structure calculations.
8:00 PM - ES01.07.42
What Limits Recombination for Metal-Halide Perovskites
Rebecca Belisle 1 , Rohit Prasanna 1 , Rongrong Cheacharoen 1 , Michael McGehee 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractMuch work has been done to characterize the exceptional optoelectronic performance of the perovskite material, methylammonium lead triodide (MAPI). Via improvements in processing and surface passivation, photoluminescence lifetimes for MAPI now exceed microseconds and internal photoluminescence quantum efficiencies exceed fifty percent. These advancements have established a picture that well-processed MAPI is of outstanding optoelectronic quality, has an incredible tolerance to intrinsic point defects in the bulk, and that the passivation of surface states is a promising pathway to improve to material quality and ultimately the solar cell efficiency. However, the majority of high-performing perovskite solar cells no longer employ MAPI as an absorber and it is not yet clear if all that we have learned about recombination dynamics can be translated from MAPI onto this next generation of materials. Of particular interest are the materials Cs0.17CH(NH2)20.83Pb(I(1-x)Br(x))0.17 and FA0.75Cs0.25Pb0.5Sn0.5I3, which have recently generated excitement for their use in tandem solar cell applications. In this talk we will discuss our recent progress in understanding the limiting recombination mechanisms in these novel perovskite materials. We explore the impacts of both intrinsic passivants (such as PbI2) as well as additional surface treatments (such as Lewis acids and bases) on recombination processes both in films and in devices, via steady-state and transient photoluminescence measurements as well as transient photocurrent and photovoltage measurements. Our results show, that although radiative recombination processes may appear similar for untreated samples across perovskite chemistries, their response to various post-processing treatments differs greatly. This suggests that strategies that may have been effective for improving the performance of MAPI are not immediately translatable, and a more complete understanding of how defect chemistry and resulting recombination processes vary with changing perovskite chemistry is needed.
8:00 PM - ES01.07.42
What Limits Recombination for Metal-Halide Perovskites
Rebecca Belisle 1 , Rohit Prasanna 1 , Rongrong Cheacharoen 1 , Michael McGehee 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractMuch work has been done to characterize the exceptional optoelectronic performance of the perovskite material, methylammonium lead triodide (MAPI). Via improvements in processing and surface passivation, photoluminescence lifetimes for MAPI now exceed microseconds and internal photoluminescence quantum efficiencies exceed fifty percent. These advancements have established a picture that well-processed MAPI is of outstanding optoelectronic quality, has an incredible tolerance to intrinsic point defects in the bulk, and that the passivation of surface states is a promising pathway to improve to material quality and ultimately the solar cell efficiency. However, the majority of high-performing perovskite solar cells no longer employ MAPI as an absorber and it is not yet clear if all that we have learned about recombination dynamics can be translated from MAPI onto this next generation of materials. Of particular interest are the materials Cs0.17CH(NH2)20.83Pb(I(1-x)Br(x))0.17 and FA0.75Cs0.25Pb0.5Sn0.5I3, which have recently generated excitement for their use in tandem solar cell applications. In this talk we will discuss our recent progress in understanding the limiting recombination mechanisms in these novel perovskite materials. We explore the impacts of both intrinsic passivants (such as PbI2) as well as additional surface treatments (such as Lewis acids and bases) on recombination processes both in films and in devices, via steady-state and transient photoluminescence measurements as well as transient photocurrent and photovoltage measurements. Our results show, that although radiative recombination processes may appear similar for untreated samples across perovskite chemistries, their response to various post-processing treatments differs greatly. This suggests that strategies that may have been effective for improving the performance of MAPI are not immediately translatable, and a more complete understanding of how defect chemistry and resulting recombination processes vary with changing perovskite chemistry is needed.
8:00 PM - ES01.07.43
High Efficient Perovskite Solar Cells Based on SnO2 Nanocrystals Electron Transfer Layer—Whole Preparation Progress Below 100 °C
Qingshun Dong 1 , Yantao Shi 2 , Chunyang Zhang 2 , Yukun Wu 1 , Liduo Wang 1
1 Chemistry, Tsinghua University, Beijing China, 2 Chemistry, Dalian University of Technology, Dalian China
Show AbstractAlthough high power conversion efficiencies (PCEs) up to 22.1% have been achieved to date by perovskite solar cells (PSCs), many scientific issues are still under intensive investigations. An important research topic focousing on PSCs is the fabrication of flexible devices, which need low-temperature fabrication of all functional layers. Electron transfer layer (ETL) as one of the key components in PSCs takes the responsibility of interfacial electron extraction, which are crucial to the final photovoltaic performance.
In conventional architecture PSCs, SnO2-ETLs has been accepted as a promising candidate in terms of high conductivity, appropriate energy level, superb chemical stability and UV resistance. Wet chemical routes are more popular as they are known with many advantages over vacuum deposition techniques, e.g. low-cost and facile processibility, which enable them to well accommodate future large-scale production. In fabrication of SnO2 electron transfer layer (ETL) via traditional solution routes, the strong dependence of film crystallization on high temperature annealling or rubost thermal treatment makes it challengeable to prepare crystallized SnO2 ETLs at low temperature (< 150 °C).
Here, we put forward a sol-gel route by which the whole fabrication process of crystallized SnO2 ETL below 80 °C is realized for the first time. In the new route, participation of atmosphere O2 and H2O by refluxing is curcial as it can greatly promote Sn2+ oxidation and controlled hydrolysis in SnCl2 2H2O alcohol solution, in trun opening up an energetically favorable pathway for SnO2 crystallizaiton at low temperature. Systematical investigations reveal that SnO2 ETLs have high conductivity and transmittance and appropriate energy band level, by which PSCs obtain superior photovotlaic performance, with a champion power conversion efficiency (PCE) and steady-state PCE of 19.20% and 18.48% achieved, respectively, much higher than that of the devices using high temperature annealed TiO2 ETLs (16.61% and 15.03%). The SnO2-ETL-based flexible PSCs also attain a high PCE up to 16.11% and among the highest records of flexible PSCs. Due to a larger band gap, SnO2-ETLs-based PSCs show superior UV resistance against high intensity UV light irradiation.
In addition to support the high PCE, ETLs in inverted architecture devices can direct influence the stability of PSCs. PCBM is ineffectiveness to prevent diffusion of iodide (I-) and methylammonium (MA+) ions from perovskite layer to react with mental electrode and permeation of oxygen and moisture into the perovskite film. And replacing PCBM by inorganic ETLs is a potential efficient way to improve the stablity of PSCs. We used our SnO2 as ETLs to replace the PCBM and gained the PCE over 2%, showing the feasible of this strategy. And further studies focusing on efficiency and stability improvement of all-inorganic-charge-transfer-layer-PSCs are in progress.
Symposium Organizers
Yabing Qi, Okinawa Institute of Science and Technology Graduate University
Jinsong Huang, University of North Carolina-Chapel Hill
Annamaria Petrozza, Istituto Italiano di Tecnologia
Huanping Zhou, Peking University
Symposium Support
Applied Physics Letters | AIP Publishing
Nature Energy | Springer Nature
Science | AAAS
Sustainable Energy &
Fuels | The Royal Society of Chemistry
ES01.08: Low-Dimensional, Ferroelectric, Grain Boundary, Passivation and Hole Transport Material
Session Chairs
Tsutomu Miyasaka
Annamaria Petrozza
Wednesday AM, November 29, 2017
Hynes, Level 3, Ballroom B
8:00 AM - ES01.08.01
Grain Boundary Engineering in Hybrid Perovskite Thin Films for Efficient, Stable Solar Cells
Yuanyuan Zhou 1 , Yingxia Zong 1 , Lin Zhang 1 , Shuping Pang 2 , Nitin Padture 1
1 School of Engineering, Brown University, Providence, Rhode Island, United States, 2 Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao China
Show AbstractGrain boundary (GB) is one of the most prominent microstructure features in solution-processed hybrid organic-inorganic perovskite (HOIP) thin films. There is significant evidence showing the nature of the GBs in these truly hybrid materials is unprecedented and they have profound effects on the optoelectronic properties and stability of HOIPs. Here, we have introduced two general strategies for engineering GBs in HOIP thin films. First, we have incorporated additives with tailored volatility in the HOIP crystallization process, which tunes the GB-migration dynamics and construct GB network that is favorable for charge transport and thermal/light/moisture tolerance in HOIPs. Second, we have invented a new chemical approach of 'self-assembly' to form HOIP thin films with new-type GB regions that are homogenously, continuously decorated with second phases in HOIPs. The decorated GB regions with optimized thickness boost the stability of the HOIP thin films under thermal/light/moisture stress, and also show benign effects on the optoelectronic properties of HOIPs. Micro-/nanoscopic characterization experiments are performed to confirm these engineered GB structures. The mechanisms responsible for the GB dynamics and stabilization are elucidated. Highly efficient an stable perovskite solar cells are fabricated based on two strategies. This study opens up a new research direction for achieving more efficient, stable perovskite solar cells via GB engineering.
8:15 AM - ES01.08.02
A Novel Strategy in Design of Polymeric Hole Transporting Materials for Highly Efficient, Dopant-Free Perovskite Solar Cells with High Stability
Taiho Park 1
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractSpiro-OMeTAD as hole transporting material (HTM) has been widely employed up to PCE = 22.1 %, but it is only processed in chlorinated or harmful solvents such as chlorobenzene (CB), dichlorobenzene (DCB), or toluene, despite of its low molecular weight relative to polymeric HTMs. Therefore, it is necessity to replace it to green solvent processable HTM. Here, we report a green solvent processable, polymeric HTM consisting of benzodithiazole and benzo[1,2-b:4,5:b’]dithiophene. We design a novel D (e-donor) – A (e-acceptor) type conducting polymer to obtain its proper highest occupied energy level (HOMO) easily and to achieve its high mh as we demonstrated, allowing effective hole extraction from perovskites to HTM and then hole transportation through HTM without Li-TFSI and t-BP, respectively. The resulting novel polymeric HTM is not only soluble in the various halogenated or harmful solvents but also highly soluble in a green solvent. In this talk, I will present a design strategy for a green solvent processable HTM and why it exhibits a highly stable device with a highest PCE in the absence of the dopants.
References
1) YS Kwon, J Lim, H-J Yun, Y-H Kim, T Park, Energy Environ. Sci. 2014, 7, 1454.
2) G-W Kim, J Kim, G-Y Lee, G Kang, J Lee, T Park, Adv. Energy Mater. 2015, 5, 1500471.
3) G-W Kim, G Kang, J Kim, G-Y Lee, H Kim, L Pyeon, J Lee, T Park, Energy Environ. Sci. 2016, 9, 2326.
8:30 AM - *ES01.08.03
Up-Scaling of Organic-Inorganic Hybrid Perovskite Solar Cells and Modules
Luis Ono 1 , Matthew Leyden 1 , Sonia Raga 1 , Yan Jiang 1 , Mikas Remeika 1 , Emilio Juarez-Perez 1 , Shenghao Wang 1 , Yabing Qi 1
1 , Okinawa Institute of Science and Technology, Okinawa Japan
Show AbstractIn organic-inorganic hybrid perovskite solar cells, development of up-scaling processes with high solar energy power conversion efficiency (PCE) and stability is important for moving forward this technology towards commercialization. At OIST, a team of researchers in the Energy Materials and Surface Sciences Unit has been making concerted efforts to develop processes aiming at high PCE, high-throughput, and minimum batch-to-batch variation, and compatible with large-area perovskite solar cells and modules. In this talk, we will present our progress to use chemical vapor deposition CVD [1-4] and spray coating [5] to fabricate perovskite solar cells and modules. Also, we will introduce a novel methylamine (CH3NH2) gas induced crystallization process [6, 7], which provides valuable insight into the formation of perovskite films.
[1] L.K. Ono, M.R. Leyden, S. Wang, and Y.B. Qi*, Organometal Halide Perovskite Thin Films and Solar Cells by Vapor Deposition. J. Mater. Chem. A 4 (2016) 6693-6713.
[2] M.R. Leyden, Y. Jiang, and Y.B. Qi*, Chemical Vapor Deposition Grown Formamidinium Perovskite Solar Modules with High Steady State Power and Thermal Stability. J. Mater. Chem. A 4 (2016) 13125-13132.
[3] M.R. Leyden, M.V. Lee, S.R. Raga, and Y.B. Qi*, Large Formamidinium Lead Trihalide Perovskite Solar Cells Using Chemical Vapor Deposition with High Reproducibility and Tunable Chlorine Concentrations. J. Mater. Chem. A 3 (2015) 16097-16103.
[4] M.R. Leyden, L.K. Ono, S.R. Raga, Y. Kato, S. Wang, and Y.B. Qi*, High Performance Perovskite Solar Cells by Hybrid Chemical Vapor Deposition. J. Mater. Chem. A 2 (2014) 18742-18745.
[5] M. Remeika, S.R. Raga, S. Zhang, and Y.B. Qi*, Transferrable Optimization of Spray-Coated PbI2 Films for Perovskite Solar Cell Fabrication. J. Mater. Chem. A 5 (2017) 5709-5718.
[6] S.R. Raga, L.K. Ono, and Y.B. Qi*, Rapid Perovskite Formation by CH3NH2 Gas-Induced Intercalation and Reaction of PbI2. J. Mater. Chem. A 4 (2016) 2494-2500.
[7] Y. Jiang, E.J. Juarez-Perez, Q. Ge, S. Wang, M.R. Leyden, L.K. Ono, S.R. Raga, J. Hu, and Y.B. Qi*, Post-Annealing of MAPbI3 Perovskite Films with Methylamine for Efficient Perovskite Solar Cells. Mater. Horiz. 3 (2016) 548-555.
9:00 AM - *ES01.08.04
Processing Approaches for High-Performance and Versatile Halide Perovskite Semiconductor Films and Devices
David Mitzi 1
1 , Duke University, Durham, North Carolina, United States
Show AbstractHalide-based perovskite semiconductors (e.g., CH3NH3PbI3) have attracted substantial recent interest for photovoltaics (PV) and other optoelectronic applications, due to large optical absorption coefficients, high carrier mobilities, long minority carrier lifetimes, and relatively benign defects and grain boundaries achieved within these materials. Coupled with the demonstrated high performance of associated devices, the ability to employ a diverse array of simple and low-temperature film deposition approaches provides an opportunity for very low processing costs and wide-ranging substrate form factors (e.g., flexible, light weight, curved surface). This talk will explore recent advances in thin-film deposition, considering interfacial reactivity, precursor additive engineering and new deposition pathways for 2-D and 3-D perovskite films. Advances in film deposition and control offer promise of enhanced device performance, improved operational stability and greater device form factor flexibility.
9:30 AM - ES01.08.05
Defect Passivation in Hybrid Perovskite Solar Cells Using Quaternary Ammonium Halides Anions and Cations
Xiaopeng Zheng 1 , Jinsong Huang 1 2
1 Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, North Carolina, United States
Show AbstractThe ionic defects at the surfaces and grain boundaries of organic-inorganic halide perovskites films are detrimental to both the efficiency and stability of perovskite solar cells. Here, we show that quaternary ammonium halides, can effectively passivate ionic defects in several different types of hybrid perovskites with their negative- and positive-charged components. The efficient defect passivation reduces the charge trap density and elongates the carrier recombination lifetime, which is supported by density-function-theory calculation. The defect passivation reduces open-circuit-voltage deficit of the p-i-n structured device to 0.39 V, and boosts the efficiency to a certified value of 20.59±0.45%. Moreover, the defect healing also significantly enhances the stability of films in ambient conditions. Our findings provide an avenue for defects passivation to further improve both the efficiency and stability of solar cells.
10:15 AM - *ES01.08.06
Strategies for Achieving Efficient and Stable Large Area Perovskite Solar Cells
Yongzhen Wu 1 2 , Liyuan Han 2
1 School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai China, 2 , National Institute for Materials Science, Tsukuba Japan
Show AbstractPerovskite (PSC) solar cells have achieved extremely high power conversion efficiencies (PCEs) of over 20%, but practical application of this photovoltaic technology requires further advancements on both long-term stability and large area devices. In this presentation, we would like to introduce some of our latest results on the development of efficient and stable large area PSCs in the past few years. An additive engineering strategy is developed to realize a facile and convenient fabrication method of large-area uniform perovskite films composed of large crystal size and low defects density. The high crystalline quality of perovskite is found to simultaneously enhance the PCE and durability of PSCs. By using the simple and widely used methylammonium lead iodide (MAPbI3), a certified PCE of 19.19% is achieved for devices with an aperture area of 1.025 cm2, and the high-performing devices can sustain over 80% of the initial PCE after 500 hours of thermal aging at 85 oC, which are among the best results of MAPbI3 based PSCs so far.
10:45 AM - *ES01.08.07
Congeneric Incorporation of Perovskite Nanocrystals in Hybrid Perovskite Heterojunction for Photovoltaic Efficiency Enhancement
Qi Chen 1
1 MSE, Beijing Institute of Technology, Beijing, Beijing, China
Show AbstractOrganic-inorganic hybrid perovskite materials have received remarkable success in photovoltaics due to their superior optoelectronic properties and compositional abundance. Most advancements focus on the improvement of heterojunction, whereas non-perovskite materials are employed at the pertaining interfaces. Herein we demonstrate the incorporation of the perovksite nanocrystals which is congeneric to the hybrid perovskite absorber. A graded heterojunction was constructed, which resulted in the significant improvement in the photovoltaic performance in the corresponding devices. In addition, thermal stability of the device is improved. It suggests a different strategy for further improvement of the perovskite heterojunction by using congeneric materials.
11:15 AM - ES01.08.08
High Performance Nanorod Perovskite-Based Solar Cells
Changwen Liu 1 , Ruixue Zhu 2 , Annie Ng 1 , Zhiwei Ren 1 , Sin Hang Cheung 3 , Lili Du 2 , Shu Kong So 3 , Juan Antonio Zapien 4 , Aleksandra Djurisic 2 , David Lee Phillips 2 , Charles Surya 1
1 , Hong Kong Polytechnic University, Hong Kong China, 2 , The University of Hong Kong, Hong Kong Hong Kong, 3 , Hong Kong Baptist University, Hong Kong Hong Kong, 4 , City University of Hong Kong, Hong Kong Hong Kong
Show AbstractIn this paper, systematic investigations on the fabrication and characterization of high performance TiO2 nanorod array perovskite solar cells (NAPSCs) are reported. The TiO2 nanorods, of length around 350-400 nm, were grown by solvothermal technique directly on glass/FTO substrates which were cleaned by ultrasonication sequentially in acetone, 2-propanol, and deionized water. The substrates were then dried by nitrogen gas and exposed to UV-ozone for 30 min. For the growth of TiO2-NA typically, 20 mL of deionized water was mixed with 20 mL hydrochloric acid (37%, Sigma Aldrich) in a teflon-lined stainless steel autoclave, in which the patterned FTO substrate had been suspended in advance. Then, 0.6 mL titanium isopropoxide (TTIP, Sigma Aldrich) was added into the autoclave, followed by an ultrasonic treatment for 5 min. The solvothermal synthesis was conducted at 180°C for 50 min. From the scanning transmission electron microscopy we demonstrate that excellent crystallinity for the TiO2 nanorods can be produced using the technique. Precursor consisting of a mixture of PbI2, CH3NH3I (MAI) and CH3NH3Cl (MACl) was used for the growth of perovskite thin films on the glass/FTO/TiO2 nanorod array (TiO2-NA) substrates. It is found that the morphology and quality of the perovskite layer depend strongly on the concentration of MACl in the precursor. Experimental studies on femtosecond transient absorption (fs-TA) indicate that the incorporation of TiO2-NA greatly enhances the collection efficiency of the photo-generated carriers due to substantial reduction in their diffusion distance. It is shown to be the key factor that the proposed technique facilitates the use of a thicker perovskite absorber layer (~500 nm) without compromising on the series resistance. Detailed J-V characterization shows that the NAPSCs exhibit negligible hysteresis with a power conversion efficiency >19% for the champion device which a high fill factor of ~78%. Electrochemical impedance spectroscopy was used to investigate study the charge transport dynamics in the completed devices. The experimental data demonstrate marked decrease in the selective contact resistance coupled with substantial increase in the recombination resistance. The results stipulates significant enhancements in the transport and reduction in the recombination rate of the carriers in the perovskite layer.
11:30 AM - ES01.08.09
Dopant Compensation in Alloyed CH3NH3PbBr3-xClx Perovskite Single Crystals for Gamma-Ray Spectroscopy
Haotong Wei 1 2 , Jinsong Huang 1 2
1 , University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 , University of Nebraska–Lincoln, Lincoln, Nebraska, United States
Show AbstractOrganic-inorganic halide perovskites (OIHPs) bring an unprecedented opportunity for radiation detection with their defect-tolerance nature, large mobility-lifetime product, and simple crystal growth from solution. Here we report a dopant compensation in alloyed OIHP single crystals to overcome limitations of device noise and charge collection, enabling γ-ray spectrum collection at room temperature. CH3NH3PbBr3 and CH3NH3PbCl3 are found to be p-type and n-type doped, respectively, whereas dopant-compensated CH3NH3PbBr2.94Cl0.06 alloy has over ten-folds improved bulk resistivity of 3.6×109 Ω cm. Alloying also increases the hole mobility to 560 cm2 V-1 s-1, yielding a high mobility-lifetime product of 1.8×10-2 cm2 V-1. The use of a guard ring electrode in the detector reduces the crystal surface leakage current and device dark current. A distinguishable 137Cs energy spectrum with higher resolution than standard scintillator detectors is collected under a small electric field of 1.8 V mm-1 at room temperature.
11:45 AM - ES01.08.10
Real-Time Mapping of Perovskite Intragrain Instabilities at the Nanoscale
Elizabeth Tennyson 1 2 , Joseph Garrett 2 3 , Jeremy Munday 2 4 , Marina Leite 1 2
1 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland, United States, 3 Department of Physics, University of Maryland, College Park, Maryland, United States, 4 Department of Electrical and Computer Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractPerovskite solar cells have stirred up a great amount of attention in the solar energy research field, as their power-conversion efficiency of >22% approaches that of large-market Silicon photovoltaics. However, the high performance is unstable and degrades with time, often within a matter of minutes or seconds. The instabilities have previously been observed to occur due to exposure to either light and/or air moisture. In order to investigate how these degradation mechanisms affect the local electrical performance of the perovskite material in real-time, we utilize fast-Kelvin probe force microscopy (KPFM), a nanoscale spatial resolution functional imaging method based on an atomic force microscope (AFM) [1, 2]. During the KPFM experiments on perovskites, the AFM chamber is connected to a dry-air system to maintain the humidity <15%, thus, minimizing one perovskite instability variable. Further, to capture the degradation at relevant time-scales, we perform fast-KPFM scans, mapping a 1 x 1 µm2 area in 16 seconds [3]. For the first time, we observe that after an illumination treatment of 1-sun at 532 nm, it takes ~9 minutes for the voltage response of the perovskite solar cell to return to its original dark equilibrium voltage value. Surprisingly, we distinguish two separate electrical responses within a single perovskite grain, one in which the voltage returns immediately back to equilibrium, and another region that experiences a ‘residual voltage’ signal. We attribute this lingering electrical behavior to ion migration and explain the phenomenon using the diode equation with an additional time-dependent current variable. We further resolve the local Voc response of Cs-containing triple cation perovskites through spectrally dependent KPFM, which shows uniform voltage distribution when compared to pure perovskite compounds (containing iodine and bromine). The real-time nanoscale Voc imaging method demonstrated here shows that light-induced reversible ion-migration could be the cause of the transient behavior of the power-conversion efficiency observed in most perovskite photovoltaics. Our approach can be used as a universal tool to probe any solar cell material, including lead-free perovskites, accelerating the design of stable, non-toxic, and higher-efficiency photovoltaics.
[1] E.M. Tennyson et al., ACS Energy Letters, 2, 1825 (2017) Invited Perspective
[2] E.M. Tennyson et al., Adv. Energy Mater., 5, 1501142 (2015) Front Cover
[3] J.L. Garrett, E.M. Tennyson, et al., Nano Lett., 17, 2554 (2017)
ES01.09: Two-Dimensional, Electrodes, Pb-Free and LED
Session Chairs
Wednesday PM, November 29, 2017
Hynes, Level 3, Ballroom B
1:30 PM - *ES01.09.01
Tolerance of Polymer HTM-Based Perovskite Solar Cells against High Temperatures and High Energy Irradiations
Tsutomu Miyasaka 1 , Masashi Ikegami 1 , Youhei Numata 1 , Yu Miyazawa 2
1 , Toin University of Yokohama, Yokohama Japan, 2 , Japan Aerospace Exploration Agency (JAXA), Yokohama Japan
Show AbstractFast progress in efficiency of perovskite solar cells now faces examination of long term stability and robust durability of the device towards commercialization. Apart from the environmental issue to develop non-lead perovskite materials, lead halide perovskites that guarantee high performance need to explore robust carrier transporting materials as partners in order to ensure durability against impacts of high temperatures and intense irradiation. As hole transporting material (HTM), the most popular spiro-OMeTAD cannot be accepted in terms of thermal instability in addition to high cost. We recently clarified a significant morphological change of this HTM thermally caused at 100oC [1], indicating necessity of replacing it with a heat tolerant material. We chose a polymer, P3HT (thickness <50 nm, Tg>110 C), as an alternative HTM. Perovskite composition is also subjected to basic improvement. We employed FA/Cs double cation (non-MA) perovskite that has high stability to heat and moisture, sustaining high performance. Uniform FA/Cs perovskite absorber was prepared on thin TiO2 mesoporous scaffold by improved solution processes to fabricate perovskite solar cells with P3HT as HTM. Although our FA/Cs perovskite cells made with spiro-OMeTAD worked at stable high efficiency >18% [2], the P3HT-based FA/Cs perovskite exhibited lower efficiency <15%. The latter however demonstrated high durability under long time exposure to 100 C, which significantly degraded both of MA perovskite solar cells and spiro-OMeTD-based solar cells. The FA/Cs P3HT perovskite device was subjected to tolerance tests by exposure to high energy irradiation including electron irradiation (1 MeV) and proton irradiation (50 KeV) in JAXA Energy Research Center. The cell exhibited no big drops in I-V performance and in EQE action spectrum against these irradiations at high fluence. The result indicates sufficiently high tolerance of the perovskite solar cell for use in space environment.
In connection to heat-resistant perovskite devices, we will also report our recent challenge to fabricate the high-performing device by using low temperature process applied to metal oxide layers, which includes combinations of ZnO with FA perovskite [3] and FA/MA/Cs triple cation perovskite [4].
References
[1] A. Jena, M. Ikegami, T. Miyasaka, submitted.
[2] Y. Numata, Y. Sanehira, T. Miyasaka, submitted.
[3] J. Song, W. Hu, X.-F. Wang, G. Chen, W. Tian, T. Miyasaka, J. Mater. Chem. A, 2016. 4, 8435-8443.
[4] J. Song, L. Liu, X.-F. Wang, G. Chen, W. Tian, T. Miyasaka, J. Mater. Chem. A, 2017. DOI: 10.1039/C7TA03331A.
2:00 PM - ES01.09.02
Perovskite Solar Cells Using Carbon Nanotubes as Both Electrodes
Il Jeon 1 , Esko I. Kauppinen 2 , Shigeo Maruyama 1 , Yutaka Matsuo 1
1 , The University of Tokyo, Minato-ku Japan, 2 , Aalto School of Science, Aalto Finland
Show AbstractIn recent years, metal halide organic-inorganic perovskite solar cells (PSCs) have gained ground, reaching certified power conversion efficiencies (PCEs) of over 22%. Such high performance is now leading many groups to consider commercialization of PSCs, because of their low-cost solution processability and flexible applicability. Indeed, the forte of the solution-processed solar cells, such as PSCs, is the prospective of low-cost module processing via high throughput printing with large area coverage compared with wafer-based silicon solar cells. While the problem of high-temperature processing can be avoided by adopting inverted planar heterojunction architecture, there are still several shortcomings which hinder their commercialization. First, finite indium tin oxide (ITO) and costly metal electrodes are thermally deposited under vacuum undermines the scalability in maximizing their low-cost potential. In addition, the production of solution-processed photovoltaic devices to date has been done in non-continuous sheet-to-sheet or roll-to-roll processes, which incurs physical and electrostatic damage during the process and increases set-up and running costs.
A smart approach to overcoming above limitations is the use of both-carbon electrodes and entirely solution-based inner materials. Carbon has been proven to show comparable device performance to those of ITO and metal electrodes. Also, it is possible to construct PSCs using entirely solution-processable layers, with only a minor loss of PCE. Using carbon electrodes and entirely solution processed structure will lead to a dramatic reduction in the processing costs via compatibility to a continuous roll-to-product (R2P) process as opposed to roll-to-roll (R2R) or sheet-to-sheet (S2S). In this work, we fabricated all carbon nanotube (CNT) electrode-based PSCs that employ fully solution-processed layers. At the heart of this work, there are two important technologies: demonstrating of CNT films as both anode and cathode and devising an entirely solution-processed configuration with a rational cost analysis for the fabrication process. We demonstrated that [6,6]- phenyl C61-butyric acid methyl ester (PC61BM)-soaked CNTs can function as the cathode, via n-type doping, and also that poly(3-hexylthiophene-2,5-diyl) (P3HT)-soaked CNTs can function as an anode, which played a role in energy alignment. Our flexible all-CNT electrode and fully solution-processed PSCs, with a configuration of CNT-P3HT/poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) /CH3NH3PbI3 (MAPbI3)/CNT-PC61BM, gave a PCE of 7.32% and showed superior mechanical flexibility. Such structure displayed a material cost of 33% to that of conventional devices, according to cost analysis. The total fabrication cost can be decreased even further if we consider set-up costs, maintenance costs, and reduced processing time.
2:15 PM - ES01.09.03
Predicting and Optimising the Energy Yield of Perovskite-on-Silicon Tandem Solar Cells under Real World Conditions
Maximilian Hoerantner 1 , Henry Snaith 2
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Physics, University of Oxford, Oxford United Kingdom
Show AbstractMetal halide perovskite absorber materials have emerged as a potential new technology for
large-scale low-cost photovoltaic solar power. One great advantage lies in the ability to tune
their light absorption band across the visible to near infrared spectral regions, making it an
ideal candidate for tandem solar cell applications, in combination with traditional crystalline
silicon. For a multi-junction solar cell to operate at peak efficiency, the current generation in
all junctions must closely match, especially for monolithically integrated tandem architectures.
It is feasible to achieve such matching under a standardized solar spectrum with direct
illumination. However, under real world conditions, the spectrum of sunlight and the fraction
of diffuse to direct sunlight varies considerably depending on the location and weather
conditions. Hence, it is not directly obvious how much more efficient a multi-junction solar
cell needs to be, in comparison to a single junction cell, before it will produce more electrical
power under real world conditions. Here, we introduce a rigorous optical and device simulation
to optimize perovskite-on-silicon tandem solar cells and identify the feasibility of various
optimization parameters to achieve the highest possible efficiencies. Firstly, we determine that
the ideal bandgap for a perovskite “top-cell” is 1.65eV, which will deliver up to 32% efficiency
when combined with a silicon rear cell. Furthermore, we calculate the annual energy yield
under hourly spectrum changes at different locations and optimize the stack to show that
tandem solar cells are yielding up to 30 % more energy output than the single junction silicon.
Most critically, the standardized air mass 1.5 efficiency measurement improvements observed
for the tandems cells, translate almost entirely to the same fractional improvement in energy
yield. Hence, the efficiency of the tandem cell is not significantly “de-rated” by real world
spectral variations. We do observe, however, that tandem solar cell stacks can deliver further
improvements by optimizing differently depending on the location of installation. Our results
justify the drive towards monolithically integrated multi-junction solar cells and will enable
guidance to design the ideal perovskite tandem device and allow estimations for energy yield
and hence the levelized cost of electricity.
3:30 PM - *ES01.09.04
Theoretical Investigation of Stable Pb-Free Halide Perovskite Materials for Solar Cell Applications
Su-Huai Wei 1
1 , Beijing Computational Science Research Center, Beijing China
Show AbstractHalide perovskites such as CH3NH3PbI3 have recently emerged as promising materials for low-cost, high-efficiency solar cells. The efficiency of perovskite-based solar cells has increased rapidly, from 3.8% in 2009 to more than 22.1% recently by modifying material compositions and engineering cell architectures. The emergence of high efficiency perovskite solar cells can be attributed to the intrinsic properties that distinguish them from conventional semiconducting solar cell absorber materials. However, despite the enormous progress of the perovskites in solar cell applications, challenges are still standing in their way to large-scale commercial applications, including their poor long-term stability, especially under heat and humidity conditions, which could be partially attributed to the intrinsic thermodynamic instability of CH3NH3PbI3 and related materials, and the toxicity of Pb, currently used in halide perovskite based solar cells with high power conversion efficiencies. Recently, various approaches have been proposed to overcome these bottlenecks in achieving high efficiency, stable, Pb free perovskite solar cells, including elimination of the organic molecules, alloying on anion and/or cation sites, and atomic transmutation. In this talk, I will discuss our recent theoretical investigations into these strategies in relation to their applications in solar cells along with theoretical insights and possible solutions.
4:00 PM - ES01.09.05
Combined Experimental and Theoretical Investigation of the Valence and Conduction Band Energy Levels in n=1 Two-Dimensional Perovskites
Scott Silver 1 , Jun Yin 2 , Hong Li 3 , Jean-Luc Bredas 3 , Antoine Kahn 1
1 , Princeton University, Princeton, New Jersey, United States, 2 Solar Center, King Abdullah University of Science and Technology, Saudia Arabia (KAUST), Thuwal Saudi Arabia, 3 Chemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractLow-dimensional layered metal halide perovskites have garnered an increasing amount of attention in the on-going effort to develop solution processed perovskite solar cells and LEDs with marketable lifetimes. However, the energetics of these 2D materials are not yet well understood. Their large exciton binding energies and natural quantum well structure have made their band gap and density of states of high interest and a necessity in the development of optimized devices, yet evasive in determination. We present here the results of a combined experimental and theoretical study of a pair of 2D metal halide perovskites. Ultraviolet and inverse photoemission spectroscopy (UPS, IPES) are performed on solution-processed thin films of n=1 layered perovskite BA2PbI4 and BA2PbBr4 characterized by optical absorption and XRD, to determine values for their transport gap and exciton binding energy, and understand in more detail their valence and conduction density of states. We report the electron affinity (EA) and ionization energy (IE) of BA2PbI4 and BA2PbBr4 to be 3.1 eV and 5.8 eV, and 3.1 eV and 6.5 eV, respectively. The electron spectroscopy results are compared with the calculated density of states determined by density functional theory (DFT). The remarkable agreement between experiment and simulation enables a detailed identification and analysis of the organic and inorganic contributions in the valence and conduction bands of the two materials. In contrast to the 3D lead iodide and bromide perovskites that show large energy dispersion leading to a low density of states near the band edges [1], the n=1 2D materials exhibit significantly less dispersion and a density of states that allows a more conventional determination of the band edges in electron spectroscopy. The effects of using various organic ligands are discussed.
[1] J. Endres et al., J. Phys. Chem. Lett. 7, 2722 (2016)
4:15 PM - ES01.09.06
Efficient Perovskite Solar Cells and Light-Emitting Diodes
Jingbi You 1
1 Institute of Semiconductors, Chinese Academy of Sciences, Beijing China
Show AbstractPlanar structures for halide perovskite solar cells have recently garnered attention, due to their simple and low-temperature device fabrication processing. Unfortunately, planar structures typically show I–V hysteresis and lower stable device efficiency compared with mesoporous structures, especially for TiO2-based n-i-p devices. SnO2, which has a deeper conduction band and higher electron mobility compared with traditional TiO2, could enhance charge transfer from perovskite to electron transport layers, and reduce charge accumulation at the interface. Here we report low-temperature solution-processed SnO2 nanoparticles as an efficient electron transport layer for perovskite solar cells. Our SnO2-based devices are almost free of hysteresis, which we propose is due to the enhancement of electron extraction1. According to optimization, a 20.9% certificated planar structure perovskite solar cells was achieved.
In addition the application of solar cells, perovskite materials exhibit high photoluminescence quantum yield (PLQY, greater than 90% in solution for nanocrystals) and high color purity with narrow emission line-widths less than 20 nm, which make them promising candidates as new materials for light-emitting diodes (LEDs). According to interface and composition engineering, we have achieved inorganic perovskite light-emitting diodes with the brightness of 91000 cd/m2 and external quantum efficiency of 10.4%2.
References
1. Q. Jiang, J. You* et al., Enhanced Electron Extraction Using SnO2 for High-Efficiency Planar-Structure HC(NH2)2PbI3-based Perovskite Solar Cells. Nature Energy, 2, 16177 (2016).
2. L. Zhang, J. You* et al., Ultra-Bright and Highly Efficient Inorganic Based Perovskite Light-Emitting Diodes. Nature Communications, 8, 15640 (2017).
4:30 PM - ES01.09.07
Extremely Efficient Internal Exciton Dissociation through Edge-States in Layered 2D Perovskites for High-Efficiency Optoelectronic Devices
Jean-Christophe Blancon 1 , Hsinhan Tsai 2 , Wanyi Nie 1 , Stier Andreas 1 , Konstantinos Stoumpos 3 , Michael Kepenekian 4 , Sergei Tretiak 1 , Claudine Katan 4 , Mercouri Kanatzidis 3 , Scott Crooker 1 , Jacky Even 5 , Jared Crochet 1 , Aditya Mohite 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , Rice University, Houston, Texas, United States, 3 , Northwestern University, Chicago, Illinois, United States, 4 , Université de Rennes, Rennes France, 5 , INSA Rennes, Rennes France
Show AbstractUnderstanding and controlling charge and energy flow in state-of-the-art semiconductor quantum-wells has enabled high-efficiency optoelectronic devices. Two-dimensional Ruddlesden-Popper layered perovskites (RPPs) have recently emerged as an alternative to the classic bulk organic-inorganic hybrid perovskites, mainly due to significantly improved photo- and chemical-stability in optoelectronic devices [1][2]. Few recent encouraging developments in optoelectronic applications, notably in energy harvesting and light emitting [2][3], have already been demonstrated in these two-dimensional layered perovskites. RPPs are solution-processed quantum-wells wherein the band gap can be tuned by varying the perovskite layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photo-generated electrons and holes are strongly bound by Coulomb interactions or excitons, the photo-physics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite crystal-units (>1.3 nanometers) is dominated by lower energy states associated with the local intrinsic electronic structure of the edges of the perovskite layers [4]. These states provide a direct pathway for dissociating excitons into longer-lived free-carriers that significantly improve the performance of optoelectronic devices.
References
[1] I. C. Smith, E. T. Hoke, D. Solis-Iberra, M. D. McGehee, H. I. Karunadasa, Angew. Chem. Int. Ed. (2014), 53, 11232-11235.
[2] Tsai et al., Nature (2016), 536, 312-316.
[3] M. Yuan et al., Nat. Nanotechnol. (2016), 11, 872-877.
[4] Blancon et al., Science (2017), 355, 1288-1292.
4:30 PM - ES01.09.07
Extremely Efficient Internal Exciton Dissociation through Edge-States in Layered 2D Perovskites for High-Efficiency Optoelectronic Devices
Jean-Christophe Blancon 1 , Hsinhan Tsai 2 , Wanyi Nie 1 , Stier Andreas 1 , Konstantinos Stoumpos 3 , Michael Kepenekian 4 , Sergei Tretiak 1 , Claudine Katan 4 , Mercouri Kanatzidis 3 , Scott Crooker 1 , Jacky Even 5 , Jared Crochet 1 , Aditya Mohite 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , Rice University, Houston, Texas, United States, 3 , Northwestern University, Chicago, Illinois, United States, 4 , Université de Rennes, Rennes France, 5 , INSA Rennes, Rennes France
Show AbstractUnderstanding and controlling charge and energy flow in state-of-the-art semiconductor quantum-wells has enabled high-efficiency optoelectronic devices. Two-dimensional Ruddlesden-Popper layered perovskites (RPPs) have recently emerged as an alternative to the classic bulk organic-inorganic hybrid perovskites, mainly due to significantly improved photo- and chemical-stability in optoelectronic devices [1][2]. Few recent encouraging developments in optoelectronic applications, notably in energy harvesting and light emitting [2][3], have already been demonstrated in these two-dimensional layered perovskites. RPPs are solution-processed quantum-wells wherein the band gap can be tuned by varying the perovskite layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photo-generated electrons and holes are strongly bound by Coulomb interactions or excitons, the photo-physics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite crystal-units (>1.3 nanometers) is dominated by lower energy states associated with the local intrinsic electronic structure of the edges of the perovskite layers [4]. These states provide a direct pathway for dissociating excitons into longer-lived free-carriers that significantly improve the performance of optoelectronic devices.
References
[1] I. C. Smith, E. T. Hoke, D. Solis-Iberra, M. D. McGehee, H. I. Karunadasa, Angew. Chem. Int. Ed. (2014), 53, 11232-11235.
[2] Tsai et al., Nature (2016), 536, 312-316.
[3] M. Yuan et al., Nat. Nanotechnol. (2016), 11, 872-877.
[4] Blancon et al., Science (2017), 355, 1288-1292.
4:45 PM - ES01.09.08
Evidence of Ultrafast Photo-Induced Mixing of Excitonic Spin States in Two-Dimensional Lead Halide Perovskites
Stefanie Neutzner 1 4 , Félix Thouin 2 , Daniele Cortecchia 3 , Vlad Alexandru Dragomir 2 , Cesare Soci 3 , Annamaria Petrozza 1 , Srinivasa Maruthi Ajay Ram Srimath Kandada 1 2 , Carlos Silva 2
1 , Center for Nanoscience and Technology, Istituto Italiano di Tecnologia, Milan Italy, 4 Dipartimento di Fisica, Politecnico di Milano, Milan Italy, 2 Département de Physique, Université de Montréal, Montréal, Quebec, Canada, 3 Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore Singapore
Show Abstract
Two dimensional hybrid lead halide perovskites, often referred to as self-assembling organic-inorganic quantum well structures exhibit a narrow and well defined excitonic transition both in their optical absorption and emission spectra, a desirable characteristic for lasing applications [1]. A pronounced fine structure with peaks separated by approximately 35-40 meV appears on top of the primary excitonic transition at lower temperatures, origin of which is under debate recently [2].
Here, we elucidate a possible mechanism via comprehensive spectroscopic investigation of (PEA)2PbI4, one of the widely used 2D perovskites. Combining optical and structural probes, we associate the appearance of these features to a structural phase transition, which breaks the inversion symmetry of the lattice and along with the large spin orbit coupling in the system, leads to mixing of the excitonic spin states via Rashba-Dresselhaus mechanism. Further, using two-dimensional electronic spectroscopy, we observe similar mixing under photo-excitation even at room temperature. We unambiguously observe the re-distribution of oscillator strength among the excitonic sub-states within 200 fs.
We hypothesize that a dynamic Jahn-Teller like lattice re-organization process breaks the inversion symmetry upon photo-excitation leading to the observed mixing. Our findings stress the intrinsic role of lattice distortions, both steady-state and dynamic in the optical properties of these materials.
[1] Lanty, G., Zhang, S., Lauret, J. S., Deleporte, E., Audebert, P., Bouchoule, S. , Lafosse, X., Zuñiga-Pérez, J., Semond, F., Lagarde, D., Médard, F., Leymarie, J., Phys. Rev. B, 2011, 84, 195449
[2] Straus, D.B., Hurtado Parra, S., Iotov, N., Gebhardt, J., Rappe, A.M., Subotnik, J.E., Kikkawa, J.M. and Kagan, C.R., J. Am. Chem. Soc., 2016, 138 (42), 13798-13801
4:45 PM - ES01.09.08
Evidence of Ultrafast Photo-Induced Mixing of Excitonic Spin States in Two-Dimensional Lead Halide Perovskites
Stefanie Neutzner 1 4 , Félix Thouin 2 , Daniele Cortecchia 3 , Vlad Alexandru Dragomir 2 , Cesare Soci 3 , Annamaria Petrozza 1 , Srinivasa Maruthi Ajay Ram Srimath Kandada 1 2 , Carlos Silva 2
1 , Center for Nanoscience and Technology, Istituto Italiano di Tecnologia, Milan Italy, 4 Dipartimento di Fisica, Politecnico di Milano, Milan Italy, 2 Département de Physique, Université de Montréal, Montréal, Quebec, Canada, 3 Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore Singapore
Show Abstract
Two dimensional hybrid lead halide perovskites, often referred to as self-assembling organic-inorganic quantum well structures exhibit a narrow and well defined excitonic transition both in their optical absorption and emission spectra, a desirable characteristic for lasing applications [1]. A pronounced fine structure with peaks separated by approximately 35-40 meV appears on top of the primary excitonic transition at lower temperatures, origin of which is under debate recently [2].
Here, we elucidate a possible mechanism via comprehensive spectroscopic investigation of (PEA)2PbI4, one of the widely used 2D perovskites. Combining optical and structural probes, we associate the appearance of these features to a structural phase transition, which breaks the inversion symmetry of the lattice and along with the large spin orbit coupling in the system, leads to mixing of the excitonic spin states via Rashba-Dresselhaus mechanism. Further, using two-dimensional electronic spectroscopy, we observe similar mixing under photo-excitation even at room temperature. We unambiguously observe the re-distribution of oscillator strength among the excitonic sub-states within 200 fs.
We hypothesize that a dynamic Jahn-Teller like lattice re-organization process breaks the inversion symmetry upon photo-excitation leading to the observed mixing. Our findings stress the intrinsic role of lattice distortions, both steady-state and dynamic in the optical properties of these materials.
[1] Lanty, G., Zhang, S., Lauret, J. S., Deleporte, E., Audebert, P., Bouchoule, S. , Lafosse, X., Zuñiga-Pérez, J., Semond, F., Lagarde, D., Médard, F., Leymarie, J., Phys. Rev. B, 2011, 84, 195449
[2] Straus, D.B., Hurtado Parra, S., Iotov, N., Gebhardt, J., Rappe, A.M., Subotnik, J.E., Kikkawa, J.M. and Kagan, C.R., J. Am. Chem. Soc., 2016, 138 (42), 13798-13801
ES01.10: Poster Session III
Session Chairs
Thursday AM, November 30, 2017
Hynes, Level 1, Hall B
8:00 PM - ES01.10.01
Novel PV Power Analyzing System with Maximum Power Point Tracking Technique—Towards the Solution for Evaluation Challenges of Perovskite Solar Cells Due to Hysteresis in I-V Measurements
P.V.V. Jayaweera 1 , Shoji Kaneko 1 , Ludmila Cojocaru 2 , Satoshi Uchida 2 , Hiroshi Segawa 2
1 , SPD Laboratory, Inc., Hamamatsu Japan, 2 , The University of Tokyo, Tokyo Japan
Show AbstractPerovskite solar cells are clearly the new frontier in solar energy conversion with reported high conversion efficiencies over 20%. It is well known that planar perovskite solar cells shows huge hysteresis in forward and reverse I-V curves which cause difficulties in evaluating proper conversion efficiency. In this talk, we will present the construction of new photovoltaic power analyzing system that uses a Maximum Power Point Tracking (MPPT) technique to evaluate true performance of perovskite solar cells. Unlike c-Si solar cells, most of the organic and organic-inorganic hybrid solar cell shows I-V curves which depend on the scan direction, speed, and starting value. Maximum power output (Pmax) obtained from I-V characteristic curve is no longer representing a unique value for these types of solar cells. During an I-V scan, the voltage of the cell changes from few hundred millivolts above the open circuit voltage (negative current) to negative few hundred millivolts. Capacitive behavior of perovskite solar cell shows charge accumulation and discharging phenomena during I-V scanning which lead to overestimate or underestimate output current values of the cell. Instead of scanning full I-V curve, maintaining cell near Pmax position and plotting Pmax vs. time solves the issue and provides trustworthy unique evaluation results. Also, I-V behavior of planar perovskite solar cell with hysteresis was successfully modeled with a double diode-capacitor equivalent circuit and confirmed by a practical device assembled using standard electronic components. Several long-lasting challenges faced by the perovskite research community are resolved in this study.
References:
1.Ludmila Cojocaru, Satoshi Uchida, Piyankarage V. V. Jayaweera, Shoji Kaneko, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Chemistry Letters, 44, (12), 1750-1752 (2015).
2.Ludmila Cojocaru, Satoshi Uchida, Piyankarage V. V. Jayaweera, Shoji Kaneko, Yasutake Toyoshima, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Applied Physics Express, 10, (2), 025701 (2017).
Ludmila Cojocaru, Satoshi Uchida, Koichi Tamaki, Piyankarage V. V. Jayaweera, Shoji Kaneko, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Scientific Reports, 7: 11790 (2017).
Ludmila Cojocaru, Satoshi Uchida, Piyankarage V. V. Jayaweera, Shoji Kaneko, Haibin Wang, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Energy Technology, 5, 1-5 (2017).
8:00 PM - ES01.10.01
Novel PV Power Analyzing System with Maximum Power Point Tracking Technique—Towards the Solution for Evaluation Challenges of Perovskite Solar Cells Due to Hysteresis in I-V Measurements
P.V.V. Jayaweera 1 , Shoji Kaneko 1 , Ludmila Cojocaru 2 , Satoshi Uchida 2 , Hiroshi Segawa 2
1 , SPD Laboratory, Inc., Hamamatsu Japan, 2 , The University of Tokyo, Tokyo Japan
Show AbstractPerovskite solar cells are clearly the new frontier in solar energy conversion with reported high conversion efficiencies over 20%. It is well known that planar perovskite solar cells shows huge hysteresis in forward and reverse I-V curves which cause difficulties in evaluating proper conversion efficiency. In this talk, we will present the construction of new photovoltaic power analyzing system that uses a Maximum Power Point Tracking (MPPT) technique to evaluate true performance of perovskite solar cells. Unlike c-Si solar cells, most of the organic and organic-inorganic hybrid solar cell shows I-V curves which depend on the scan direction, speed, and starting value. Maximum power output (Pmax) obtained from I-V characteristic curve is no longer representing a unique value for these types of solar cells. During an I-V scan, the voltage of the cell changes from few hundred millivolts above the open circuit voltage (negative current) to negative few hundred millivolts. Capacitive behavior of perovskite solar cell shows charge accumulation and discharging phenomena during I-V scanning which lead to overestimate or underestimate output current values of the cell. Instead of scanning full I-V curve, maintaining cell near Pmax position and plotting Pmax vs. time solves the issue and provides trustworthy unique evaluation results. Also, I-V behavior of planar perovskite solar cell with hysteresis was successfully modeled with a double diode-capacitor equivalent circuit and confirmed by a practical device assembled using standard electronic components. Several long-lasting challenges faced by the perovskite research community are resolved in this study.
References:
1.Ludmila Cojocaru, Satoshi Uchida, Piyankarage V. V. Jayaweera, Shoji Kaneko, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Chemistry Letters, 44, (12), 1750-1752 (2015).
2.Ludmila Cojocaru, Satoshi Uchida, Piyankarage V. V. Jayaweera, Shoji Kaneko, Yasutake Toyoshima, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Applied Physics Express, 10, (2), 025701 (2017).
Ludmila Cojocaru, Satoshi Uchida, Koichi Tamaki, Piyankarage V. V. Jayaweera, Shoji Kaneko, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Scientific Reports, 7: 11790 (2017).
Ludmila Cojocaru, Satoshi Uchida, Piyankarage V. V. Jayaweera, Shoji Kaneko, Haibin Wang, Jotaro Nakazaki, Takaya Kubo, and Hiroshi Segawa, Energy Technology, 5, 1-5 (2017).
8:00 PM - ES01.10.02
Photo-Induced Dark States in Metal Halide Perovskites Probed via Two-Dimensional Spectroscopy
Srinivasa Maruthi Ajay Ram Srimath Kandada 1 2 , Félix Thouin 2 , Pascal Gregoire 2 , Quinten Akkerman 3 , Liberato Manna 3 , Annamaria Petrozza 1 , Carlos Silva 2
1 Center for Nano Science and Technology, Istituto Italiano di Tecnologia, Milano Italy, 2 Department of Physics, Université de Montréal, Montreal, Quebec, Canada, 3 Nanochemistry Department, Istituto Italiano di Tecnologia, Genova Italy
Show AbstractHybrid lead halide perovskites have emerged as promising materials for efficient opto-electronic technologies. Colloidal nanocrystals of these systems have shown remarkably high photoluminescence(PL) quantum yields, reaching upto 90% and have recently been proposed as inks to achieve high quality thin films [1]. Being virtually defect-free [2], these nanocrystals offer an ideal scenario to address some of the key issues in the photo-physical processes in these novel materials. Here, we use two dimensional photoluminescence excitation spectroscopy (2D-PLE) [3] and 2D coherent electronic spectroscopy (2D-ES) [4] to investigate coherent non-linear interactions in colloidal suspensions of CsPb(Br:I)3 nanocrystals. In the case of 2D-ES measurements, which are performed at relatively high exciation density ( ~ 1), we find evidence for the formation of photo-induced transitions in about 100 fs that are inaccessible from the ground state and into which the photo-excited population is transferred. We propose that such dark states are a consequence of Rashba splitting of the carrier bands induced by photo-induced lattice deformations[5] combined with the large spin-orbit coupling in the system. These results also rationalize the ultrafast loss of carrier population and thus photo-luminescence observed previously in excitation correlation measurements[2]. Remarkably, such effects are absent at low exciation densities ( ~ 0.01), where the coherent non-linear response is detected via PL. These investigations shed light on the intrinsic non-radiative path ways that open up in metal halide perovskites as a consequence of the deformity of the lattice.
References
[1] Q. A. Akkerman, V. D’Innocenzo, S. Accornero, A. Scarpellini, A. Petrozza, M. Prato, and L. Manna, J. Am. Chem. Soc. 137, 10276 (2015).
[2] A. R. Srimath Kandada, S. Neutzner, V. D’Innocenzo, F. Tassone, M. Gandini, Q. A. Akkerman, M. Prato, L. Manna, A. Petrozza, and G. Lanzani, J. Am. Chem. Soc. 138, 13604 (2016).
[3] P. F. Tekavec, G. A. Lott and A. H. Marcus, J. Chem. Phys. 127, 214307 (2007).
[4] G. Moody, I. A. Akimov, H. Li, R. Singh, D. R. Yakovlev, G. Karczewski, M. Wiater, T. Wojtowicz, M. Bayer and S. T. Cundiff, Phys. Rev. Lett. 112, 097401 (2014).
[5] G. Batignani, G. Fumero, A. R. Srimath Kandada, G. Cerullo, M. Gandini, C. Ferrante, A. Petrozza and T. Scopigno, ArXiv ID: 1705.08687 (2017).
8:00 PM - ES01.10.02
Photo-Induced Dark States in Metal Halide Perovskites Probed via Two-Dimensional Spectroscopy
Srinivasa Maruthi Ajay Ram Srimath Kandada 1 2 , Félix Thouin 2 , Pascal Gregoire 2 , Quinten Akkerman 3 , Liberato Manna 3 , Annamaria Petrozza 1 , Carlos Silva 2
1 Center for Nano Science and Technology, Istituto Italiano di Tecnologia, Milano Italy, 2 Department of Physics, Université de Montréal, Montreal, Quebec, Canada, 3 Nanochemistry Department, Istituto Italiano di Tecnologia, Genova Italy
Show AbstractHybrid lead halide perovskites have emerged as promising materials for efficient opto-electronic technologies. Colloidal nanocrystals of these systems have shown remarkably high photoluminescence(PL) quantum yields, reaching upto 90% and have recently been proposed as inks to achieve high quality thin films [1]. Being virtually defect-free [2], these nanocrystals offer an ideal scenario to address some of the key issues in the photo-physical processes in these novel materials. Here, we use two dimensional photoluminescence excitation spectroscopy (2D-PLE) [3] and 2D coherent electronic spectroscopy (2D-ES) [4] to investigate coherent non-linear interactions in colloidal suspensions of CsPb(Br:I)3 nanocrystals. In the case of 2D-ES measurements, which are performed at relatively high exciation density ( ~ 1), we find evidence for the formation of photo-induced transitions in about 100 fs that are inaccessible from the ground state and into which the photo-excited population is transferred. We propose that such dark states are a consequence of Rashba splitting of the carrier bands induced by photo-induced lattice deformations[5] combined with the large spin-orbit coupling in the system. These results also rationalize the ultrafast loss of carrier population and thus photo-luminescence observed previously in excitation correlation measurements[2]. Remarkably, such effects are absent at low exciation densities ( ~ 0.01), where the coherent non-linear response is detected via PL. These investigations shed light on the intrinsic non-radiative path ways that open up in metal halide perovskites as a consequence of the deformity of the lattice.
References
[1] Q. A. Akkerman, V. D’Innocenzo, S. Accornero, A. Scarpellini, A. Petrozza, M. Prato, and L. Manna, J. Am. Chem. Soc. 137, 10276 (2015).
[2] A. R. Srimath Kandada, S. Neutzner, V. D’Innocenzo, F. Tassone, M. Gandini, Q. A. Akkerman, M. Prato, L. Manna, A. Petrozza, and G. Lanzani, J. Am. Chem. Soc. 138, 13604 (2016).
[3] P. F. Tekavec, G. A. Lott and A. H. Marcus, J. Chem. Phys. 127, 214307 (2007).
[4] G. Moody, I. A. Akimov, H. Li, R. Singh, D. R. Yakovlev, G. Karczewski, M. Wiater, T. Wojtowicz, M. Bayer and S. T. Cundiff, Phys. Rev. Lett. 112, 097401 (2014).
[5] G. Batignani, G. Fumero, A. R. Srimath Kandada, G. Cerullo, M. Gandini, C. Ferrante, A. Petrozza and T. Scopigno, ArXiv ID: 1705.08687 (2017).
8:00 PM - ES01.10.03
Exploring Spin-Orbital Coupling Effects on Photovoltaic Actions in Sn and Pb Based Perovskite Solar Cells
Jia Zhang 1 2 , Ting Wu 1 , Jiashun Duan 2 , Mahshid Ahmadi 1 , Fangyuan Jiang 2 , Yinhua Zhou 2 , Bin Hu 1 2 3
1 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 , Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei, China, 3 , College of Science, Beijing Jiaotong University, Beijing, Beijing, China
Show AbstractOrgano-metal halide perovskites, as emerging photovoltaic materials, have demonstrated interesting spin states due to spin-orbital coupling (SOC) effects. However, replacing the Pb with the Sn can inevitably affect the SOC and consequently changes the internal photovoltaic processes in the development of environmentally friendly perovskite devices. Here, by operating the spin states with circularly polarized photoexcitation we report that the spin-dependent photocurrent (Jsc) becomes much more prominent upon replacing Pb with Sn, increasing the spin dependence from 0.25% to 1.25% by switching the photoexcitation from linear to circular polarization. Essentially, the spin-dependent Jsc is determined by the spin relaxation time, changing with the SOC strength, as compared to the charge dissociation time. On the other hand, our magneto-photocurrent (magneto-Jsc) results show that the internal magnetic parameter decreases from 281 mT to 41 mT upon Sn-Pb replacement, providing an evidence that the SOC is indeed weakened from Pb to Sn based solar cells. Furthermore, the spin-dependent photoluminescence (PL) indicates that weakening the SOC upon the Sn-Pb replacement leads to more antiparallel spin states (singlets) available for PL but less parallel spin states (triplets) available for photovoltaic action. Therefore, SOC plays an important role in the development of photovoltaic actions in Sn-based perovskite solar cells.
8:00 PM - ES01.10.05
Analysis of Effects of Additive-Based Nanocrystal Pinning Process for Perovskite LEDs
Min-Ho Park 1 , Su-Hun Jeong 1 , Hong-Kyu Seo 1 , Christoph Wolf 1 , Young-Hoon Kim 2 , Hobeom Kim 1 , Joo Sung Kim 2 , Himchan Cho 2 , Tae-Woo Lee 2
1 , POSTECH, Pohang Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractOrganometal halide perovskite light emitting diode (PeLED) as a narrow band emitter is an emerging research field. In this work, we noted conventional inherent limitations of PeLEDs to have low efficiency and suggested effective approaches to overcome the PeLED efficiency limitation, and thus we focused on fundamental issues for high electroluminescence efficiency by unravelling the role of additive-based nanocrystal pinning (A-NCP) process using the carefully controlled electron-transporting small molecule solutions diluted in a volatile nonpolar solvent. Our work suggests the mechanism of perovskite film formation during A-NCP process, and we found that without affecting the intrinsic crystal structure, A-NCP improved the radiative recombination rate by reducing effective defect density at grain boundaries due to the defect healing effect. Moreover, it induced the improved electron-hole balance in the dominantly p-type CH3NH3PbBr3 based PeLEDs, leading to the highest efficiency of 8.79% ever reported to date among pure green PeLEDs. Therefore, our findings provide a practical way to effectively overcome limited PeLED efficiency.
8:00 PM - ES01.10.06
Comparison of Bulk, Surface and Interfacial Properties in Hybrid Halide Perovskite for Photovoltaic Applications
Rabi Khanal 1 , Sheila Briggs 1 , Nicholas Ayers 1 , Taufique Mohammad 2 , Soumik Banerjee 2 , Samrat Choudhury 1
1 Chemical and Materials Engineering, University of Idaho, Moscow, Idaho, United States, 2 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show AbstractHybrid halide perovskite-based photovoltaic cells have received significant attention in the photovoltaic community due to their drastic improvement in the power conversion efficiency (3.8% to 21%) within the last five years. Although the structural and electronic properties of bulk perovskite have been well studied, the properties of the surface of the carrier generating perovskite layers and their interface with the electron transport layer are still not fully understood. In this work, we have used electronic structure calculations to determine the atomic structure, electronic, and transport properties at the interface between the hybrid halide perovskite and the electron transport layer. Later, these calculated interfacial properties are compared with the calculated electronic and transport properties within the bulk and surface layer of the hybrid halide perovskite. As a model system, we use CH3NH3PbI3 as the hybrid halide perovskite and phenyl-C61-butyric acid methyl ester (PCBM) as the electron transport layer. Our results reveal that the band gap of the perovskite decreases continuously from the bulk to the surface layer of the perovskite. Further, for the same (110) surface termination, band gap is sensitive to the surface terminating groups (CH3NH3I vs. PbI2) of the perovskite. Defects, particularly those resulting in deep trap states such as the Pb-I antisite defects, are known to play an important role in determining the performance of these solar cells. Our calculations indicate that the formation energy of Pb-I antisite defects is lower at the perovskite surface compared to that within the bulk perovskite. Furthermore, unlike the bulk, Pb-I antisite atomic defect at the surface also creates deep electronic states within the band gap. Finally, we observed that the calculated band gap and interatomic distance at the interface are significantly different compared to corresponding values within the bulk and surface layers of the hybrid halide perovskite.
8:00 PM - ES01.10.07
Dielectric Response—Answer to Many Questions in the Methylammonium Lead Halide Solar Cell Absorbers
Doru Lupascu 1 , Irina Anusca 1 , Sergejus Balciunas 2 , Pascale Gemeiner 3 , Šarunas Svirskas 2 , Mehmet Sanlialp 1 , Gerhard Lackner 1 , Christian Fettkenhauer 1 , Jaroslavas Belovickis 2 , Vytautas Samulionis 2 , Maksim Ivanov 2 , Brahim Dkhil 3 , Juras Banys 2 , Vladimir V. Shvartsman 1
1 , Univ of Duisburg-Essen, Essen Germany, 2 , Vilnius University, Vilnius Lithuania, 3 Laboratoire Structures, Propriétés et Modélisation des Solides, CentraleSupélec, Grande Voie des Vignes, Châtenay-Malabry France
Show AbstractDue to the unprecedented rapid increase of their power conversion efficiency, hybrid organic–inorganic perovskites CH3NH3PbX3 (X = I, Br, Cl) can potentially revolutionize the world of solar cells. However, despite tremendous research activity, the origin of the exceptionally large diffusion length of their photogenerated charge carriers, that is, their low recombination rate, remains elusive. Using frequency and temperature-dependent dielectric measurements across the entire frequency spectrum, it is shown that the dielectric constant conserves very high values (>27) for frequencies below 1 THz in all three halides. This efficiently prevents photocarrier trapping and their recombination owing to the strong screening of charged entities. By combining ultrasonic and Raman spectroscopy with dielectric analysis, similarly large contributions to the dielectric constant are attributed to the dipolar disorder of the CH3NH3+ cations as well as lattice dynamics in the gigahertz range yielding dielectric constants of εstat = 62 for the iodide, 58 for the bromide, and about 45 for the chloride below 1 GHz at room temperature. Disorder continuously reduces for decreasing temperature. Dipole dynamics prevail in the intermediate tetragonal phase. The low-temperature orthorhombic state is antipolar. No indications of ferroelectricity are found.
8:00 PM - ES01.10.07
Dielectric Response—Answer to Many Questions in the Methylammonium Lead Halide Solar Cell Absorbers
Doru Lupascu 1 , Irina Anusca 1 , Sergejus Balciunas 2 , Pascale Gemeiner 3 , Šarunas Svirskas 2 , Mehmet Sanlialp 1 , Gerhard Lackner 1 , Christian Fettkenhauer 1 , Jaroslavas Belovickis 2 , Vytautas Samulionis 2 , Maksim Ivanov 2 , Brahim Dkhil 3 , Juras Banys 2 , Vladimir V. Shvartsman 1
1 , Univ of Duisburg-Essen, Essen Germany, 2 , Vilnius University, Vilnius Lithuania, 3 Laboratoire Structures, Propriétés et Modélisation des Solides, CentraleSupélec, Grande Voie des Vignes, Châtenay-Malabry France
Show AbstractDue to the unprecedented rapid increase of their power conversion efficiency, hybrid organic–inorganic perovskites CH3NH3PbX3 (X = I, Br, Cl) can potentially revolutionize the world of solar cells. However, despite tremendous research activity, the origin of the exceptionally large diffusion length of their photogenerated charge carriers, that is, their low recombination rate, remains elusive. Using frequency and temperature-dependent dielectric measurements across the entire frequency spectrum, it is shown that the dielectric constant conserves very high values (>27) for frequencies below 1 THz in all three halides. This efficiently prevents photocarrier trapping and their recombination owing to the strong screening of charged entities. By combining ultrasonic and Raman spectroscopy with dielectric analysis, similarly large contributions to the dielectric constant are attributed to the dipolar disorder of the CH3NH3+ cations as well as lattice dynamics in the gigahertz range yielding dielectric constants of εstat = 62 for the iodide, 58 for the bromide, and about 45 for the chloride below 1 GHz at room temperature. Disorder continuously reduces for decreasing temperature. Dipole dynamics prevail in the intermediate tetragonal phase. The low-temperature orthorhombic state is antipolar. No indications of ferroelectricity are found.
8:00 PM - ES01.10.08
Transition Metal Carbides and Nitrides for Regeneration of Light Absorbers in Mesoscopic and Perovskite Solar Cells
Myeong Jae Lee 1 2 3 , Jin Soo Kang 1 2 , Jin Kim 1 2 , Yoon Jun Son 1 2 , Juwon Jeong 1 2 , Yung-Eun Sung 1 2
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Center for Nanoparticle Research, Institute for Basic Science, Seoul Korea (the Republic of), 3 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show AbstractOrganic/inorganic hybrid solar cells, namely mesoscopic and perovskite solar cells, have been under intensive investigations due to a steep increase in performances. Though the hybrid cells manifest high power conversion efficiencies even comparable to the conventional silicon and thin film photovoltaics, reliability in long-term operations and economical feasibility of mesoscopic and perovskite solar cells are yet to reach at sufficient levels for practical utilizations. Various carbonaceous and polymeric materials were introduced to the organic/inorganic hybrid solar cells for enhanced stability and lower production cost, but further improvements are still required.
Recently, transition metal compounds have been introduced for regeneration of light absorbers in organic/inorganic hybrid solar cells, but current approaches are often based on complicated nano-architecturing/deposition processes. In this presentation, we introduce facile procedures for the preparations of carbides and nitrides for applications in mesoscopic and perovskite solar cells. Based on facile synthesizing procedures, nanostructured carbide and nitride electrodes were produced, and various physicochemical characterizations including synchrotron X-ray analyses were performed in order to confirm complete carburization and nitridation by our facile procedures. The prepared films manifested excellent electrochemical properties, and high performance up to 15.0%, which is one of the best results based on inorganic materials, was achieved.
8:00 PM - ES01.10.08
Transition Metal Carbides and Nitrides for Regeneration of Light Absorbers in Mesoscopic and Perovskite Solar Cells
Myeong Jae Lee 1 2 3 , Jin Soo Kang 1 2 , Jin Kim 1 2 , Yoon Jun Son 1 2 , Juwon Jeong 1 2 , Yung-Eun Sung 1 2
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Center for Nanoparticle Research, Institute for Basic Science, Seoul Korea (the Republic of), 3 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show AbstractOrganic/inorganic hybrid solar cells, namely mesoscopic and perovskite solar cells, have been under intensive investigations due to a steep increase in performances. Though the hybrid cells manifest high power conversion efficiencies even comparable to the conventional silicon and thin film photovoltaics, reliability in long-term operations and economical feasibility of mesoscopic and perovskite solar cells are yet to reach at sufficient levels for practical utilizations. Various carbonaceous and polymeric materials were introduced to the organic/inorganic hybrid solar cells for enhanced stability and lower production cost, but further improvements are still required.
Recently, transition metal compounds have been introduced for regeneration of light absorbers in organic/inorganic hybrid solar cells, but current approaches are often based on complicated nano-architecturing/deposition processes. In this presentation, we introduce facile procedures for the preparations of carbides and nitrides for applications in mesoscopic and perovskite solar cells. Based on facile synthesizing procedures, nanostructured carbide and nitride electrodes were produced, and various physicochemical characterizations including synchrotron X-ray analyses were performed in order to confirm complete carburization and nitridation by our facile procedures. The prepared films manifested excellent electrochemical properties, and high performance up to 15.0%, which is one of the best results based on inorganic materials, was achieved.
8:00 PM - ES01.10.09
Effect of Thermal and Structural Disorder on Electronic Structure in Methylammonium Lead Halide Perovskites
Cheng Li 1 , Shivam Singh 2 , K. L. Narasimhan 2 , Fabian Panzer 3 , Yu Zhong 1 , Anna Gräser 1 , Tanaji Gujar 4 , Mukundan Thelakkat 4 , Anna Koehler 3 , Dinesh Kabra 2 , Sven Huettner 1
1 Organic and Hybrid Electronics, Macromolecular Chemistry I, University of Bayreuth, Bayreuth Germany, 2 , Indian Institute of Technology Bombay, Mumbai India, 3 Experimentalphysik II, University of Bayreuth, Bayreuth Germany, 4 Applied Functional Polymers, Macromolecular Chemistry I, University of Bayreuth, Bayreuth Germany
Show AbstractOrganometal trihalide perovskite solar cells (PSC), e.g. methylamonimum lead iodide (MAPbI3=CH3NH3PbI3), have achieved power conversion efficiency (PCE) of 22.1% in <4 years' intensive investigation. In this work, in order to understand the structure of this material, we investigate the temperature dependence of optical properties, both UV-Vis and photoluminescence (PL) spectra, of perovskite film from room temperature (300K) to 6K. By using Elliott's theory, we can fit the temperature dependent UV-Vis absorption spectra, distinguishing the contribution from (1) band-band transition and (2) exciton absorption. Unlike many inorganic semiconductors, in both tetragonal (T>163K) and orthorhombic (T<163K) phases of MAPbI3, the band gap decreases with decreasing temperature. We indicate that this temperature dependent behaviour is governed by the lattice expansion term instead of the electron-phonon interaction. Then the exciton linewidth is observed to homogeneously broaden in both phases. The absorption, at the low energy edge of the exciton absorption, increases exponentially with energy, i.e reminiscent of Urbach tail absorption. The Urbach energy which is used to characterize order of structure, is modelled using thermal and static disorder for both phases separately. The static disorder component is small, which agrees with the homogeneous broadening of the exciton with temperature. Similarly, temperature dependent PL measurements also allow to observe the effect of static and thermal disorder. This quantitative work provides important insights to the electronic and structural properties of MAPbI3 based perovskites, and this method is transferable to many related organometal halide perovskites.
References:
1. S. Singh, C. Li, F. Panzer, K. L. Narasimhan, A. Graeser, T. P. Gujar, A. Köhler, M. Thelakkat, S. Huettner, D. Kabra, J. Phys. Chem. Lett. 7, 3014 (2016)
2. F. Panzer, C. Li, T. Meier, A. Köhler, S. Huettner. Adv. Energy. Mater. 7, 1700286 (2017)
8:00 PM - ES01.10.09
Effect of Thermal and Structural Disorder on Electronic Structure in Methylammonium Lead Halide Perovskites
Cheng Li 1 , Shivam Singh 2 , K. L. Narasimhan 2 , Fabian Panzer 3 , Yu Zhong 1 , Anna Gräser 1 , Tanaji Gujar 4 , Mukundan Thelakkat 4 , Anna Koehler 3 , Dinesh Kabra 2 , Sven Huettner 1
1 Organic and Hybrid Electronics, Macromolecular Chemistry I, University of Bayreuth, Bayreuth Germany, 2 , Indian Institute of Technology Bombay, Mumbai India, 3 Experimentalphysik II, University of Bayreuth, Bayreuth Germany, 4 Applied Functional Polymers, Macromolecular Chemistry I, University of Bayreuth, Bayreuth Germany
Show AbstractOrganometal trihalide perovskite solar cells (PSC), e.g. methylamonimum lead iodide (MAPbI3=CH3NH3PbI3), have achieved power conversion efficiency (PCE) of 22.1% in <4 years' intensive investigation. In this work, in order to understand the structure of this material, we investigate the temperature dependence of optical properties, both UV-Vis and photoluminescence (PL) spectra, of perovskite film from room temperature (300K) to 6K. By using Elliott's theory, we can fit the temperature dependent UV-Vis absorption spectra, distinguishing the contribution from (1) band-band transition and (2) exciton absorption. Unlike many inorganic semiconductors, in both tetragonal (T>163K) and orthorhombic (T<163K) phases of MAPbI3, the band gap decreases with decreasing temperature. We indicate that this temperature dependent behaviour is governed by the lattice expansion term instead of the electron-phonon interaction. Then the exciton linewidth is observed to homogeneously broaden in both phases. The absorption, at the low energy edge of the exciton absorption, increases exponentially with energy, i.e reminiscent of Urbach tail absorption. The Urbach energy which is used to characterize order of structure, is modelled using thermal and static disorder for both phases separately. The static disorder component is small, which agrees with the homogeneous broadening of the exciton with temperature. Similarly, temperature dependent PL measurements also allow to observe the effect of static and thermal disorder. This quantitative work provides important insights to the electronic and structural properties of MAPbI3 based perovskites, and this method is transferable to many related organometal halide perovskites.
References:
1. S. Singh, C. Li, F. Panzer, K. L. Narasimhan, A. Graeser, T. P. Gujar, A. Köhler, M. Thelakkat, S. Huettner, D. Kabra, J. Phys. Chem. Lett. 7, 3014 (2016)
2. F. Panzer, C. Li, T. Meier, A. Köhler, S. Huettner. Adv. Energy. Mater. 7, 1700286 (2017)
8:00 PM - ES01.10.10
Carbon Nanotubes versus Graphene as Flexible Transparent Electrodes in Perovskite Solar Cells
Il Jeon 1 , Jungjin Yoon 2 , Namyoung Ahn 2 , Mohamed Atwa 3 , Esko I. Kauppinen 4 , Mansoo Choi 2 , Shigeo Maruyama 1 , Yutaka Matsuo 1
1 , The University of Tokyo, Minato-ku Japan, 2 , Seoul National University, Seoul Korea (the Republic of), 3 , OIST, Okinawa Japan, 4 , Aalto University, Aalto Finland
Show AbstractIn the past seven years, organohalide lead perovskite solar cells (PSCs) have shown remarkable progress in terms of their power conversion efficiency (PCE) and showed the potential for flexible applications. Their PCEs have been reported to reach over 20% by several groups around the world to date. To maximize the full potential of PSCs, it is necessary to replace indium tin oxide (ITO) electrode. This is because ITO has numerous limitations of finite indium, inflexibility, and degradation by poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Among the viable alternatives, earth-abundant and mechanically resilient carbon electrodes, carbon nanotube (CNT) and graphene, have demonstrated good performance as electrodes in PSCs.
Since Iijima reported the first CNT, concentric cylindrical shaped CNTs have shown the potential for the electrode applications in electronics. This is owing to their high electrical conductivity and optical transparency, arising from their network of infinitely conjugated double bonds. Recently, Esko and colleagues have reported aerosol-synthesized single-walled carbon nanotube (SWNT) films that show high electrical conductivity and transparency, at the same time capable of direct and dry transfer onto any substrates.
Graphene, which is another carbon-based electrode, was only the hypothetical material until it was realized by a research group in Manchester, England in 2004. Despite being a late runner, one-atom thick graphene also manifested superb conductivity and transparency to those of CNTs. Graphene films, which are mostly wet-transferred, have also been outstanding in replacing conventional electrodes in photovoltaics as well.
In this work, we fabricated flexible indium-free inverted PSCs by substituting ITO by SWNTs and graphene, and compared their feasibility as the flexible transparent electrodes in both photovoltaic and mechanical perspectives. Thus far, there has not been a direct comparison between CNT and graphene electrodes within the best of our knowledge. For this study, we used stable MoOx for the choice of doping. Through this work, we found that graphene gives higher efficiency when used as the transparent electrode in inverted PSCs compared to those using SWNTs, due to the better surface morphology and higher transparency. Meanwhile, both SWNT- and graphene-based PSCs showed similar mechanical properties, albeit SWNTs manifested greater latent mechanical resilience against bending and stretching compared with graphene, according to Raman spectroscopy.
8:00 PM - ES01.10.10
Carbon Nanotubes versus Graphene as Flexible Transparent Electrodes in Perovskite Solar Cells
Il Jeon 1 , Jungjin Yoon 2 , Namyoung Ahn 2 , Mohamed Atwa 3 , Esko I. Kauppinen 4 , Mansoo Choi 2 , Shigeo Maruyama 1 , Yutaka Matsuo 1
1 , The University of Tokyo, Minato-ku Japan, 2 , Seoul National University, Seoul Korea (the Republic of), 3 , OIST, Okinawa Japan, 4 , Aalto University, Aalto Finland
Show AbstractIn the past seven years, organohalide lead perovskite solar cells (PSCs) have shown remarkable progress in terms of their power conversion efficiency (PCE) and showed the potential for flexible applications. Their PCEs have been reported to reach over 20% by several groups around the world to date. To maximize the full potential of PSCs, it is necessary to replace indium tin oxide (ITO) electrode. This is because ITO has numerous limitations of finite indium, inflexibility, and degradation by poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Among the viable alternatives, earth-abundant and mechanically resilient carbon electrodes, carbon nanotube (CNT) and graphene, have demonstrated good performance as electrodes in PSCs.
Since Iijima reported the first CNT, concentric cylindrical shaped CNTs have shown the potential for the electrode applications in electronics. This is owing to their high electrical conductivity and optical transparency, arising from their network of infinitely conjugated double bonds. Recently, Esko and colleagues have reported aerosol-synthesized single-walled carbon nanotube (SWNT) films that show high electrical conductivity and transparency, at the same time capable of direct and dry transfer onto any substrates.
Graphene, which is another carbon-based electrode, was only the hypothetical material until it was realized by a research group in Manchester, England in 2004. Despite being a late runner, one-atom thick graphene also manifested superb conductivity and transparency to those of CNTs. Graphene films, which are mostly wet-transferred, have also been outstanding in replacing conventional electrodes in photovoltaics as well.
In this work, we fabricated flexible indium-free inverted PSCs by substituting ITO by SWNTs and graphene, and compared their feasibility as the flexible transparent electrodes in both photovoltaic and mechanical perspectives. Thus far, there has not been a direct comparison between CNT and graphene electrodes within the best of our knowledge. For this study, we used stable MoOx for the choice of doping. Through this work, we found that graphene gives higher efficiency when used as the transparent electrode in inverted PSCs compared to those using SWNTs, due to the better surface morphology and higher transparency. Meanwhile, both SWNT- and graphene-based PSCs showed similar mechanical properties, albeit SWNTs manifested greater latent mechanical resilience against bending and stretching compared with graphene, according to Raman spectroscopy.
8:00 PM - ES01.10.11
Utilization of Fullerene Derivatives for Creation of New Perovskite Solar Cells
Yutaka Matsuo 1 2 , Il Jeon 2 , Hiroshi Ueno 3 , Esko I. Kauppinen 4 , Shigeo Maruyama 2
1 , University of Science and Technology China, Hefei China, 2 Department of Mechanical Engineering, The University of Tokyo, Tokyo Japan, 3 , Northeast Normal University, Changchun China, 4 , Aalto University, Aalto Finland
Show AbstractIn this presentation, we discuss the use of C60 and fullerene derivatives for improvement of performance in perovskite solar cells (PVSCs). C60 and a fullerene derivative, PCBM are generally used as electron transport layers (ETLs) in inverted PVSCs. In our research, we used C60 as an ELT in normal structure PVSCs, where a perovskite layer was sandwiched by an electron-collecting C60 ELT and a hole-collecting single-walled carbon nanotubes (SWCNTs) electrode. The SWCNTs electrode was modified with various small molecule organic semiconductors or semiconductive polymers to enhance hole-transporting ability and barrier property. These carbon-sandwiched PVSCs showed 17% PCE, when P3HT was applied to SWCNTs films. On the other hand, when we used spiro-MeOTAD instead, long-lived PVSCs were realized.
Methano-indene-fullerene (MIF, C60(CH2)Ind) was used as an ELT in inverted PVSCs.[1] The planar p–i–n device with a NiO-diethanolamine/CH3NH3PbI3/MIF structure showed 18.1% PCE with high open-circuit voltage (VOC) of 1.13 V and fill factor (FF) of 0.80. This high performance is attributed to high-lying LUMO level and small volume of the indeno group that can provide short fullerene–fullerene contact distance for high electron mobility.
A fullerene derivatives, PCBM was interpenetrated into SWCNTs film network to create a SWCNTs cathode. This is contrast to the fact that SWCNTs are usually hole-collecting anode with p-doping. We fabricated both-carbon PVSCs with a structure of substrate/CNT:P3HT/PEDOT:PSS/CH3NH3PbI3/CNT:PCBM by using both P3HT-wrapping SWCNTs and PCBM-penetrating SWCNTs films as anode and cathode, respectively. The both-carbon PVSCs are flexible and can be used entirely without vacuum process, which is advantageous cost-effective production.
Finally, we utilized lithium-ion-containing [60]fullerene, Li+@C60 TFSI (NTf2; bis(trifluoromethanesulfonyl)imide) salt as a dopant to spiro-MeOTAD in PVSCs. We demonstrated 10 times higher stability than the conventional devices with commonly used LiTFSI. We ascribe this improvement to hydrophobicity of the fullerene cage and oxygen-capture ability of the neutral Li@C60 that forms electron transfer from spiro-MeOTAD to [Li+@C60]TFSI– in the doping process.
8:00 PM - ES01.10.11
Utilization of Fullerene Derivatives for Creation of New Perovskite Solar Cells
Yutaka Matsuo 1 2 , Il Jeon 2 , Hiroshi Ueno 3 , Esko I. Kauppinen 4 , Shigeo Maruyama 2
1 , University of Science and Technology China, Hefei China, 2 Department of Mechanical Engineering, The University of Tokyo, Tokyo Japan, 3 , Northeast Normal University, Changchun China, 4 , Aalto University, Aalto Finland
Show AbstractIn this presentation, we discuss the use of C60 and fullerene derivatives for improvement of performance in perovskite solar cells (PVSCs). C60 and a fullerene derivative, PCBM are generally used as electron transport layers (ETLs) in inverted PVSCs. In our research, we used C60 as an ELT in normal structure PVSCs, where a perovskite layer was sandwiched by an electron-collecting C60 ELT and a hole-collecting single-walled carbon nanotubes (SWCNTs) electrode. The SWCNTs electrode was modified with various small molecule organic semiconductors or semiconductive polymers to enhance hole-transporting ability and barrier property. These carbon-sandwiched PVSCs showed 17% PCE, when P3HT was applied to SWCNTs films. On the other hand, when we used spiro-MeOTAD instead, long-lived PVSCs were realized.
Methano-indene-fullerene (MIF, C60(CH2)Ind) was used as an ELT in inverted PVSCs.[1] The planar p–i–n device with a NiO-diethanolamine/CH3NH3PbI3/MIF structure showed 18.1% PCE with high open-circuit voltage (VOC) of 1.13 V and fill factor (FF) of 0.80. This high performance is attributed to high-lying LUMO level and small volume of the indeno group that can provide short fullerene–fullerene contact distance for high electron mobility.
A fullerene derivatives, PCBM was interpenetrated into SWCNTs film network to create a SWCNTs cathode. This is contrast to the fact that SWCNTs are usually hole-collecting anode with p-doping. We fabricated both-carbon PVSCs with a structure of substrate/CNT:P3HT/PEDOT:PSS/CH3NH3PbI3/CNT:PCBM by using both P3HT-wrapping SWCNTs and PCBM-penetrating SWCNTs films as anode and cathode, respectively. The both-carbon PVSCs are flexible and can be used entirely without vacuum process, which is advantageous cost-effective production.
Finally, we utilized lithium-ion-containing [60]fullerene, Li+@C60 TFSI (NTf2; bis(trifluoromethanesulfonyl)imide) salt as a dopant to spiro-MeOTAD in PVSCs. We demonstrated 10 times higher stability than the conventional devices with commonly used LiTFSI. We ascribe this improvement to hydrophobicity of the fullerene cage and oxygen-capture ability of the neutral Li@C60 that forms electron transfer from spiro-MeOTAD to [Li+@C60]TFSI– in the doping process.
8:00 PM - ES01.10.12
Resonant Multiphoton Excitation Processes Induce Multiple Exciton Generation in CsPbBr3 Nanocubes
Aurora Manzi 1 2 , Yu Tong 1 2 , Lakshminarayana Polavarapu 1 2 , Alexander Urban 1 2 , Jochen Feldmann 1 2
1 Chair for Photonics and Optoelectronics, Ludwig-Maximilians-Universität, Munich Germany, 2 , Nanosystems Initiative Munich (NIM), Munich Germany
Show AbstractMulti-photon excitation (MPE) represents a route to access low-energy photons in semiconductor-based solar energy converting devices. On the other side, multiple exciton generation (MEG) is considered a very promising way to convert the excess energy of photogenerated carriers into usable electric energy for above band-gap photons, showing reasonable efficiencies in quantum-confined nanocrystals.
Here, we have investigated the combined action of both MPE and MEG in the interband photoluminescence of CsPbBr3 nanocubes [1] for a wide-range of optical excitation wavelengths below the band-gap. We have observed that the excitation with four photons whose total energy equals the energy necessary to generate three excitons produces an enhanced signal in the photoluminescence excitation spectrum. Analogously, we have detected similar effects for a three photon absorption process whose energy matches the creation of two excitons. Further intensity dependent experiments support the interpretation that the observation of such resonances can be ascribed to the resonant creation of multiple excitons through MPE. [2] This may open up new pathways for the efficient conversion of below band-gap solar energy also for other semiconducting materials.
1) Y. Tong, E. Bladt, M. Ayguler, A. Manzi, K. Z. Milowska, V. A. Hintermayr, P. Docampo, S. Bals, A. S. Urban, L. Polavarapu, J. Feldmann, Angewandte Chemie 44, 13887 (2016)
2) A. Manzi, Y. Tong, L. Polavarapu, A. S. Urban, J. Feldmann, manuscript submitted, (2017)
8:00 PM - ES01.10.12
Resonant Multiphoton Excitation Processes Induce Multiple Exciton Generation in CsPbBr3 Nanocubes
Aurora Manzi 1 2 , Yu Tong 1 2 , Lakshminarayana Polavarapu 1 2 , Alexander Urban 1 2 , Jochen Feldmann 1 2
1 Chair for Photonics and Optoelectronics, Ludwig-Maximilians-Universität, Munich Germany, 2 , Nanosystems Initiative Munich (NIM), Munich Germany
Show AbstractMulti-photon excitation (MPE) represents a route to access low-energy photons in semiconductor-based solar energy converting devices. On the other side, multiple exciton generation (MEG) is considered a very promising way to convert the excess energy of photogenerated carriers into usable electric energy for above band-gap photons, showing reasonable efficiencies in quantum-confined nanocrystals.
Here, we have investigated the combined action of both MPE and MEG in the interband photoluminescence of CsPbBr3 nanocubes [1] for a wide-range of optical excitation wavelengths below the band-gap. We have observed that the excitation with four photons whose total energy equals the energy necessary to generate three excitons produces an enhanced signal in the photoluminescence excitation spectrum. Analogously, we have detected similar effects for a three photon absorption process whose energy matches the creation of two excitons. Further intensity dependent experiments support the interpretation that the observation of such resonances can be ascribed to the resonant creation of multiple excitons through MPE. [2] This may open up new pathways for the efficient conversion of below band-gap solar energy also for other semiconducting materials.
1) Y. Tong, E. Bladt, M. Ayguler, A. Manzi, K. Z. Milowska, V. A. Hintermayr, P. Docampo, S. Bals, A. S. Urban, L. Polavarapu, J. Feldmann, Angewandte Chemie 44, 13887 (2016)
2) A. Manzi, Y. Tong, L. Polavarapu, A. S. Urban, J. Feldmann, manuscript submitted, (2017)
8:00 PM - ES01.10.13
The Sobering Reality of Perovskite/Si Tandem Solar Cells under Realistic Operating Conditions
Moritz Futscher 1 , Bruno Ehrler 1
1 , AMOLF, Amsterdam Netherlands
Show AbstractPerovskites have entered the research field of photovoltaics by storm, already reaching efficiencies close to highly optimized silicon solar cells. Perovskite/silicon tandem solar cells have been proposed as a promising candidate to surpass silicon efficiency records at low cost. Under laboratory conditions, perovskite/silicon tandem solar cells already outperform the silicon single junction. These results, however, do not necessarily transfer to solar cells under realistic operating conditions. We model the performance of realistic perovskite/silicon tandem solar cells under real-world climate conditions, by incorporating parasitic cell resistances, non-radiative recombination, and optical losses into the detailed-balance limit. Rather surprisingly, we find that even when using current record efficiency perovskite and silicon devices, tandem solar cells are hardly more efficient than the silicon cell alone. We show quantitatively that optimizing the device parameters in the perovskite top cell, perovskite/silicon tandem solar cells can reach an efficiency advantage of up to 14% absolute, even while leaving the silicon cell untouched. Despite the rapid efficiency increase of perovskite solar cells, our results emphasize the need for further material development, careful device design, and light management strategies, all necessary for highly efficient perovskite/silicon tandem solar cells.
8:00 PM - ES01.10.14
Toward-Wafer Scale Ionic Epitaxy of Halide Perovskite Single Crystalline Thin Film Carrying Hidden Carrier Dynamics
Yiping Wang 1 , Xin Sun 1 , Zhizhong Chen 1 , Toh-Ming Lu 1 , Jian Shi 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractHigh-temperature vapor phase epitaxy (VPE) has been proved ubiquitously powerful in enabling high-performance electro-optic devices in III-V semiconductor research and industrial community. A typical example is the successful growth of p-type GaN by VPE for blue light emitting diodes. VPE excels as it well controls the film defects such as point defects, grain boundary and interphase defects, thanks to its high-temperature processing condition and controllable deposition rate. In this report, for the first time, we have demonstrated single crystalline high-temperature VPE halide perovskite thin film – a unique platform on unveiling previously uncovered hidden carrier dynamics in inorganic halide perovskite materials. Towards wafer scale epitaxial and grain boundary-free film is grown with alkaline halides as substrates. We show the metal alkali halides could be used as a universal substrate for the VPE growth of perovskite due to their similar material chemistry and close crystal symmetry and lattice constant. With VPE, hot photoluminescence and nanoseconds photo Dember effect were revealed in inorganic halide perovskite. These two phenomena suggest that inorganic halide perovskite could be as compelling as its organic-inorganic counterpart in terms of optoelectronic properties and help explain the long carrier lifetime in halide perovskite. Our findings suggest a new avenue on developing high quality large scale single crystalline halide perovskite films requiring precise control of defects and morphology.
8:00 PM - ES01.10.15
High Efficiency Perovskite Solar Cell by Blade Coating in Air
Hong Chen 1 , Weiguang Kong 1 , Chun Cheng 1 , Guoliang Wang 1
1 , Southern University of Science and Technology, Shenzhen China
Show AbstractPerovskite solar cells have attracted great attention due to their low cost and high power conversion efficiency (PCE). However, most perovskite solar cells are fabricated under the protection of N2 or other inert gas because of the perovskite materials sensitive to water and oxygen. Particularly, the most common methods to obtain good perovskite polycrystalline thin films, such as spin-coating method and vapor deposition technique, are not compatible with the scalable processing technologies, e.g., Roll-to-Roll. Here we have used blade coating method to fabricate perovskite films in a clean room where the humidity and the temperature are precisely controlled to be around 45±5 % and 25±3°C, respectively. Blade coating matches well with the Roll-to-Roll process which is believed to be the most ideal method for the large-scale production of the perovskite solar cell panels. Our basic solar cell structure is ITO/PEDOT:PSS/Perovskite/PC61BM/BCP/Ag. By tuning the temperature of the substrate, the gap between blade and substrate and the coating speed, micro scale grain size and high crystallization quality have been obtained. No hysteresis is observed in the J-V curve measurement for the final perovskite solar cells, as we change the scanning mode, such as the scanning direction and the scanning speed. An average PCE of as high as 12% has been achieved. In addition, by optimizing the hole-transport-layer (HTL) and electron-transport-layer (ETL), the average PCE is further improved to 14.1%, and the best-performing devices can get a PCE of 16.39% (Voc=0.930V, Jsc=22.77mA/cm2, FF=77.4%). High PCE could be attributed to lower defect concentration and larger grain size in the blade coated perovskite films. Since the PCE has been comparable to that of the devices made by spin-coating in an inert gas-protected glove box, our next target is to improve the stability of the PSCs. The PSCs made by blade coating in air with high PCE and stability are meaningful for their commercial use in future.
8:00 PM - ES01.10.16
From 3D to 2D Structures—Insights into Mobility of Perovskite Materials and Their Solar Cell Metrics
Noor Titan Putri Hartono 1 , Rachel Kurchin 1 , Juan-Pablo Correa-Baena 1 , Shijing Sun 1 , Seong Sik Shin 1 , Tonio Buonassisi 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractMixed ion perovskite solar cells (PSCs) with ABX3 structure, have reached 22.1% efficiency. Recent studies have hinted at the shifting focus from 3D to 2D perovskite structures, because 2D structures, as lead-free perovskite-inspired photoabsorbers, are more stable for a longer period than the 3D. However, these 2D compounds tend to have low photocurrents, warranting deeper studies to understand the relationship between out-of-plane mobility and their solar cell metrics. One way to move from a 3D to a 2D structure is to increase the size of the A-site cation to force the structure to split into a layered compound. To understand this, we propose a detailed study where PbI2 is used as the backbone and A-site cations are alloyed with various combinations: methylammonium, iso-propylammonium, t-butylammonium, and dimethylammonium. We measure the PSC devices performance and characterize the solar absorber to understand the mobility. Finally, we compare these measured metrics with calculated and experimental perovskite mobilities.
8:00 PM - ES01.10.18
Mixing High and Low Bandgap Grains towards Enhancing Electroluminescence Actions in Perovskite Light-Emitting Diodes
Jiajun Qin 2 1 , Shengbo Ma 2 , Jia Zhang 2 , Miaosheng Wang 2 , Matthew Loyd 2 , Xiaoyuan Hou 1 , Bin Hu 2
2 Material Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 1 , Fudan University, Shanghai China
Show AbstractQuasi-2D perovskite is very attractive in light emitting diodes, due to high EQE and PLQY, where the idea of energy cascade between different perovskite units with different bandgaps is the possible mechanism. Revealing this idea in 3D poly-crystal materials is very challenging and it will provide a deep understanding for such energy cascade. On the other hand, charge transport and confinement are critical issues in developing high electroluminescence (EL) in perovskite light-emitting diodes, which is difficult to be combined together in one perovskite material. Here, we report a new strategy to mix two bandgaps in one perovskite layer based on one-step solution processing method, as well as balance the transport and confinement, by generating large and small grains with two well-defined low and high bandgaps mixed. We find that mixing large and small grains can largely enhance the EL efficiency with the turn-on voltage (2.0 V) lower than the bandgap (2.25 eV). Capacitance measurement indicates that grain boundary defects are decreased and non-radiative emission towards enhancing the PL quantum yield. Therefore, mixing low and high bandgap grains provides a new approach to enhance the EL efficiencies in perovskite light-emitting diodes upon balancing the charge transport and confinement. Furthermore, at dark condition, our capacitance-frequency characteristics show that an external bias can largely influence the surface polarization in the mixed low and high bandgap grains. This bias-induced surface polarization provides the necessary condition to obtain a turn-on voltage lower than the bandgap. Moreover, we find that mixed low and high bandgap grains show an extremely slow PL response, in the order of 20 seconds, to an external electric field in the device at the open-circuit condition. However, such slow PL response to an external field can be completely removed in the device at short-circuit condition. This slow PL response to an external field provides the evidence that the ion migration at grain boundaries initiate a slow EL in perovskite light-emitting diodes.
8:00 PM - ES01.10.19
Polarizations Effects and Crystallographic Structure of Hybrid Perovskites—A Key to Understand and Yield High-Efficiency Perovskite Solar Cells
Ting Wu 1 , Liam Collins 2 , Jiantao Li 1 , Yongtao Liu 1 , Bin Hu 1
1 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractHybrid perovskites have been insensitively studied in photovoltaic applications and achieved remarkable progress in power conversion efficiency over 20% in less than five years. To further advance the photovoltaic performance requisites in-depth understanding of the optical-electrical properties, crystal structure, and their correlations. Theoretical studies have suggested the “soft” character of hybrid perovskites; meanwhile, recent experimental studies have demonstrated the twining domain structure within individual grains of methylammonium lead triiodide perovskites. These findings bring out an important question on the relationship between structure and functions in perovskite solar cells. Our recent studies demonstrate photoinduced bulk polarizations in the efficient and hysteresis-free perovskite solar cells based on an anomalous signature observed in the photoexcitation-manipulated capacitance-voltage characteristics within the depletion region and intermediate frequency window, where surface polarization fails to response. This photoinduced bulk polarizations can be effectively enlarged by three times through suppressing charged defects, concurrently the photovoltaic performance shows to be improved from 12.41% to 18.19%. Such photoinduced bulk polarization phenomenon can be attributed to the “soft” nature of perovskite crystal structure and also shows to suppress charge recombination based on our bias-dependent photoluminescence and magneto-photocurrent measurements. Meanwhile, our studies show that the photovoltaic performance of perovskite solar cells strongly depends on the polarizations of photoexcitation in tetragonal phase. However, the light polarization dependence becomes dramatically reduced at tetragonal-to-cubic phase transition temperature, therefore can be correlated with the twin domain structure of hybrid perovskites. Clearly, the unique properties of perovskite crystal structure are highly associated with the polarization properties, consequently determining the photovoltaic processes in perovskite solar cells. This opens up new opportunities to further advance the photovoltaic performance for different types of perovskite solar cells by controlling domain orientation and improving film quality of hybrid perovskites.
8:00 PM - ES01.10.20
Impact of Cesium and Tin Doping in Phase and Device Stability of Hybrid Organic-Inorganic Perovskite Solar Cells
Gabriella Tosado 1 , Yi-Yu Lin 1 , Qiuming Yu 1
1 Chemical Engineering, University of Washington, Seattle, Washington, United States
Show AbstractHybrid organic-inorganic perovskite (HOIP) solar cells are becoming both a cost and energy efficient alternative to conventional silicon solar cells. Recently, HOIP solar cells have been demonstrated the fastest advances in performance to a record power conversion efficiency (PCE) of 22.1%, and are able to be manufactured through solution-processing, making low energy fabrication feasible. Despite of these tremendous progresses, the thermal phase instability of the photovoltaically active HOIP materials proves to be a bottleneck towards commercialization. Both organic cation based perovskites, methylammonium lead iodide (MAPbI3) and formamidinium lead iodide (FAPbI3), undergo a phase change to a photovoltaically inactive orthorhombic structure upon temperature increase, which increases trap states and exciton recombination, and hinders electron transport and stability. Replacing these organic cations with inorganic cesium improves the device stability in ambient conditions but also creates a blue shift in the band gap and allows a room temperature phase change due to its low cubic Goldschmidt tolerance factor of 0.8. Although the ionic radius of cesium (1.8 Å) is smaller than both formamidinium (2.53 Å) and methylammonium (2.16 Å) resulting in a less cubic perovskite, this can be mitigated with the replacement of lead with tin because of the smaller ionic radius of tin (1.1 Å) compared to lead (1.33 Å). As a result, a smaller transition metal-halide cage allows the cesium to fill more of the cubic cavity, creating a more cubic tolerance factor. Through tuning the Goldschmidt tolerance factor with additional tin doping with the perovskite composition Csx(MA0.17FA0.83)1-xPb1-ySny(I0.83Br0.17)3, we are able to synthesize cesium and tin doped cubic perovskite thin films that are stable at room temperature using a one-step solution technique with x and y ranging from 0 to 75%. The surface morphologies, optical properties, crystalline structures and optical band gaps were investigated using AFM, SEM, XRD, and UV-Vis absorption and photoluminescence spectroscopies. Photovoltaic devices were fabricated with the structure of glass/ITO/ poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/ Csx(MA0.17FA0.83)1-xPb1-ySny(I0.83Br0.17)3/ Phenyl-C60-butyric acid methyl ester (PC60BM)/C60/bathocuproine (BCP)/Ag. The current density-voltage characteristics of devices under dark and illuminated conditions were measured to determine the correlation between the cesium and tin doping to photovoltaic performance. The current density-voltage characteristics were also measured with devices exposed to air over time to determine increased stability with cesium doping. The knowledge gained from this study could be generally applied to the development of phase stable, lead-free perovskites for the commercialization of perovskite solar cells.
8:00 PM - ES01.10.21
High-Performance and Low-Cost Hole-Transporting Materials for Perovskite Solar Cells
Xiang Deng 1 , Jianchang Wu 1 2 , Chang Liu 1 , Yanqing Tian 1 , Baomin Xu 1
1 Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, China, 2 School of Advanced Materials, Peking University Shenzhen Graduate School, Shenzhen, Guangdong, China
Show AbstractIn recent years, the efficiency of organic-inorganic metal halide perovskite-based solar cells (PSCs) have been improved rapidly, which possess the prospect of becoming the next-generation large-scale commercial solar cells. Hole transporting materials (HTMs) play an important role to the PSCs in charge extraction and interface modification, so HTMs can improve the performance of PSCs device.[1] However, the most extensively studied and applied HTM for perovskite devices,[2-4] 2,2’,7,7’-tetrakis(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene (Spiro-OMeTAD), is too expensive because of its high-cost synthesis and purification process. The development of PSCs is hindered due to the high-cost HTM, so here we synthesize a novel low-cost HTM to replace Spiro-OMeTAD.
We synthesize two HTMs by connecting the arylamine side groups to the both sides of thiophene and benzene respectively, in which the synthesis procedures are short and simple. When applied in the PSCs device, the thiophene-based and benzene-based HTMs show short circuit photocurrent densities (Jscs) of 21.08 mA cm-2 and 15.83 mA cm-2 , open circuit voltages (Vocs) of 1.01 V and 0.79 V and fill factors (FFs) of 0.59 and 0.46 respectively. And they show an average power conversion efficiencies (PCEs) of 13.7% and 6.4 % with best PCEs of 14.7% and 7.5% while Spiro-OMeTAD shows a best PCE of 15.8% under the similar device preparation method and measurement condition, which means the thiophene-based HTM has a comparable performance to the Spiro-OMeTAD. So, the novel thiophene-based HTM is both performance and cost competitive compared with Spiro-OMeTAD and has the prospect of replacing the Spiro-OMeTAD to be applied in PSCs commercially.
Reference
1. Calió, L.; Kazim, S.; Grätzel, M.; Ahmad, S., Angew. Chem. Int. Ed. 2016, 55, 14522-14545.
2. Ding, I. K.; Tétreault, N.; Brillet, J.; Hardin, B. E.; Smith, E. H.; Rosenthal, S. J.; Sauvage, F.; Grätzel, M.; McGehee, M. D., Adv. Funct. Mater. 2009, 19, 2431-2436.
3. Journal Of The American Chemical SocietyJeon, N. J.; Lee, H. G.; Kim, Y. C.; Seo, J.; Noh, J. H.; Lee, J.; Seok, S. I., J. Am. Chem. Soc. 2014, 136, 7837-40.
4. Liu, D.; Kelly, T. L., Nat. Photon. 2014, 8, 133-138.
8:00 PM - ES01.10.22
Dielectric Screening and Excitonic Effects in CH3NH3PbI3 from First Principles
Andre Schleife 1 , Joshua Leveillee 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractDue to a remarkable increase of photo-conversion efficiency over merely a few years and cost-efficient production techniques, hybrid organic-inorganic perovskites are very promising materials for next-generation solar cells. Practical problems that need to be addressed include stability, environmentally friendly constituents, and increased efficiency. This has triggered enormous research efforts that lead to a wealth of experimental and theoretical data for these materials, also rendering them an ideal test bed for exploring fundamental science.
In particular, the combination of organic and inorganic constituents leads to interesting properties of the dielectric screening: Static (lattice) and static electronic dielectric constants differ by about a factor of 3-5 for these materials and, in addition, exciton-binding energies and longitudinal-optical phonon frequencies are of the same order of magnitude (10-20 meV). This begs the question of the strength and origin of the dielectric screening of the electron-hole interaction, which has important implications on the exciton binding energy.
In this talk, we report results from first-principles calculations of electronic and optical properties of CH3NH3PbI3 using many-body perturbation theory. We compute electronic band structures using Hedin’s GW approximation for the electronic self-energy. Optical properties, including excitonic effects, are computed by solving the Bethe-Salpeter equation for the optical polarization function. This allows us to study the influence of dielectric screening on excitonic effects. We show that a large lattice polarizability contributes to dielectric screening and can explain small exciton-binding energies observed in experiment. We further quantify the influence of free-carrier contributions to dielectric screening, that become important in unintentionally doped material. Our results are directly compared, qualitatively and quantitatively, to experiment.
8:00 PM - ES01.10.23
Nanoscale Back Contact Perovskite Solar Cell Design for Improved Tandem Efficiency
Gede Adhyaksa 1 , Eric Johlin 1 , Erik Garnett 1
1 Center for Nanophotonics, AMOLF, Amsterdam Netherlands
Show AbstractTandem photovoltaics, combining absorber layers with two distinct band gap energies into a single device, provide a practical solution to reduce thermalization losses in solar-energy-conversion. Traditionally, tandem devices have been assembled using two-terminal (2-T) or four-terminal (4-T) configurations; the 2-T limits the tandem performance due to its series connection requiring current matching, while the standard 4-T configuration requires at least three transparent electrical contacts, which reduce the total collected power due to unavoidable parasitic absorption. Here, we introduce a novel architecture based on a nanoscale back-contact for a thin-film top cell in a three terminal (3-T) configuration. Using coupled optical-electrical modelling, we optimize this architecture for a planar perovskite-silicon tandem, highlighting the roles of nanoscale contacts to reduce the required perovskite electronic quality. For example, with an 18% planar silicon base cell, the 3-T back contact design can reach a 32.9% tandem efficiency with a 10 μm diffusion length perovskite material. Using the same perovskite quality, the 4-T and 2-T configurations only reach 30.2% and 24.8%, respectively. We also confirm that the same 3-T efficiency advantage applies when using 25% efficient textured silicon base cells, where the tandems reach 35.2% and 32.8% efficiency for the 3-T, and 4-T configurations, respectively. Furthermore, since our design is based on the individual sub-cells being back contacted, further improvements can be readily made by optimizing the front surface, which is left free for additional anti-reflective coating, light trapping, surface passivation, and photoluminescence outcoupling enhancements.
8:00 PM - ES01.10.24
Controlled Grain Sizes on Thin Film CH3NH3PbBr3—Statistical Correlation on Carrier Recombination Lifetime and Diffusion Length
Gede Adhyaksa 1 , Sarah Brittman 1 , Haralds Abolins 1 , Teodor Duevski 1 , Andries Lof 1 , Erik Garnett 1
1 Center for Nanophotonics, AMOLF, Amsterdam Netherlands
Show AbstractTrap-assisted recombination centers in polycrystalline semiconductors occur in the bulk, at surfaces, and at grain-boundaries but separating each of these contributions is challenging. Part of this difficulty stems from the lack of techniques available to map the grain size and orientation in halide perovskite thin-films. In traditional thin-film materials, crystallographic information is easily obtained by electron backscatter diffraction (EBSD), but degradation under the electron beam renders standard EBSD useless for halide perovskite thin-films. Instead, groups have so far used morphological and topographical features in scanning electron microscope (SEM) or optical images to infer the grain size, which is known to be problematic. Here, we use a new type of solid-state EBSD detector with much higher sensitivity than the traditional camera and phosphor screen to collect EBSD maps of grain size and orientation in halide perovskite thin-films. We show that the average grain size measured from EBSD is substantially different (more than factor 2) from what is inferred from optical and SEM images and further correlate the correct values with carrier recombination lifetimes and minority carrier diffusion lengths. We developed a thin film deposition protocol to decouple nucleation and crystal growth regimes that allows us to control the resulting average grain size over a large range between less than 1 and more than 20 microns. Using the time-correlated single photon counting (TCSPC) method, we will present the result of how the radiative and non-radiative recombination coefficient depends on the grain size, and next quantify the correlation with their ambipolar carrier diffusion lengths obtained from a steady-state photocarrier grating (SSPG) technique.
8:00 PM - ES01.10.25
Rapid Plasma-Annealed Single and Double Cation Perovskite Thin Films
Michael Hovish 1 , Florian Hilt 1 , Nicholas Rolston 2 , Reinhold Dauskardt 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Applied Physics, Stanford University, Stanford, California, United States
Show AbstractWe have developed a highly scalable and rapid plasma-annealing method for the formation of mechanically tough and photoactive single and double cation perovskite thin films in ambient conditions. A synergistic combination of heat, light, and chemical potential distribute energy quickly and effectively to an ultrasonically sprayed perovskite precursor solvate, forming quality MAPbI3 and (CsxFA1-x)Pb(BryI1-y)3 thin films at deposition rates in excess of 4 cm/s. We observe a high density of grains when compared to the spin-coated control, both in the plane of the film and through the thickness of the film. The unique microstructure leads to a ten-fold enhancement in fracture toughness, and despite the high density of grain boundaries, optoelectronic properties are not compromised. When incorporated into an inverted perovskite solar cell, plasma-annealed single and double cation devices consistently have greater open-circuit voltages than optimized spin-coated controls. Power conversion efficiencies of 13% are obtained, (avg. 11.0% ± 1.0%), among the highest achieved for open-air deposition.
We investigate and rationalize how the thermal, photonic, and chemical potential is disseminated to the rapidly formed perovskite film, and their subsequent influence on material properties and device performance. Briefly, reactive plasma species generated in the discharge have internal energies well above the background gas, and can readily thermalize and remove solvent, leading to the fast formation of the film. Additionally, incident photons generated in the plasma are absorbed by the growing semiconductor particle, exciting electrons to the conduction band and charging the surface. The electrical energy stored in this capacitive structure lowers the interfacial energy between the growing particle and surrounding solvate, and therefore the barrier to nucleation. The net effect is that plasma illumination can stabilize particles well below the critical radius. We propose the plasma-annealing process as an emerging and viable candidate for the commercialization of perovskite solar cells, particularly given the outstanding fracture toughness which will prove vital in the manufacturing setting.
8:00 PM - ES01.10.26
Tunable Conductivity of MAPbI3 via Surface Doping from Small Molecules
Erin Perry 1 , John Labram 1 , Naveen Venkatesan 1 , Michael Chabinyc 1
1 , University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractLead halide perovskites have gained enormous attention as a low-cost and solution-processable active material for solar cells. Currently, the highest PCE for methylammonium lead iodide (MAPbI3)-based solar cells is in excess of 22%;1 higher that of polycrystalline silicon. The performance of hybrid-halide solar cells is critically dependent on the nature of interfaces in the solar cell structure. Organic hole and electron transport materials are often employed as electron- and hole-blocking layers. In order to optimize charge-extraction in the device, these organic layers can be doped using organic small molecules. However, to date there has been little work carried out on the details of doping at these interfaces. Due to the similar energy levels, and undercoordinated Pb2+ ions on the perovskite surface, it is possible for charge transfer to take place from small molecule n-type dopants to MAPbI3. Here we study the change in electrical properties of MAPbI3 forming a bilayer structure with an organometallic dopant molecule: cobaltocene. By varying the amount of cobaltocene deposited, the conductivity of thin films of MAPbI3 are observed to be tunable over several orders of magnitude; with a peak conductivity three order of magnitude higher than that of neat films. The increased conductivity is attributed to charge transfer between MAPbI3 and cobaltacene. We observe a tunable shift in the Fermi level up to 0.7 eV upon doping by ultraviolet photoemission, illustrating that charge transfer doping allows for control over the Fermi level at the interface. These studies of surface doping suggest routes to control the electronic properties of interfaces in perovskite solar cells, LEDs and devices.
(1) Green, M. A.; Emery, K.; Hishikawa, Y.; Warta, W.; Dunlop, E. D.; Levi, D. H.; Ho-Baillie, A. W. Y. Solar Cell Efficiency Tables (Version 49). Prog. Photovolt. Res. Appl. 2017, 25 (1), 3–13.
8:00 PM - ES01.10.27
Parameters Controlling Photo-Induced Interfacial Charge Separation and Recombination Dynamics in Perovskite Solar Cells
Maning Liu 1 , Yasuhiro Tachibana 1 2
1 , RMIT University, Bundoora, Victoria, Australia, 2 , Osaka University, Osaka Japan
Show AbstractPerovskite solar cells have been recognized as a newly emerging solar cell with the potential of achieving high efficiency with a low cost fabrication process. In particular, facile solution processed cell fabrication facilitated rapid development of optimum cell structure and composition. Over the last few years, the cell efficiency has rapidly been improved to 22%.
A typical perovskite solar cell employs a perovskite layer sandwiched by p-type semiconductor (such as spiro-OMeTAD, PEDOT or NiO) and n-type semiconductor (such as TiO2, ZnO or PCBM) layers. Following light absorption, an electron and a hole are separated at the perovskite film interface, and will be collected at the back electrodes. Based on this simple configuration, it is clear that the perovskite interface controls the cell performance and stability. We previously reported a role of a TiO2 nanocrystalline film acting as an electron acceptor [1]. The electron injection rate (~10 ns) is relatively slow compared to dye or QD sensitised films [2,3], however it is sufficiently fast compared to the excited state lifetime (~200 ns), confirming high charge transfer quantum yield. In this presentation, we will present parameters controlling charge separation and recombination dynamics at the perovskite interfaces employing a series of transient absorption and emission spectroscopies. Nanosecond transient emission spectroscopy (Vis-ns-TES) clarifies charge separation processes, while Vis-NIR submicrosecond-millisecond transient absorption spectroscopies (VisNIR-smm-TAS) identify charge separation efficiency and charge recombination rates. Correlation of the dynamics results with the solar cell performance will be discussed [4].
This work was financially supported by the JST PRESTO program (Photoenergy Conversion Systems and Materials for the Next Generation Solar Cells) and partly by JSPS KAKENHI Grant Number JP16K05885. The author also acknowledges Australian Research Council (ARC) LIEF grant (LE170100235) and the Office for Industry-University Co-Creation, Osaka University, for the financial supports.
References
[1] S. Makuta, M. Liu, M. Endo, H. Nishimura, A. Wakamiya, Y. Tachibana, Chem. Commun., 52, 673 - 676 (2016).
[2] R. Nakamura, S. Makuta, Y. Tachibana, J. Phys. Chem. C, 119(35) 20357-20362 (2015).
[3] Y. Tachibana, J. E. Moser, M. Grätzel, D. R. Klug, J. R. Durrant, J. Phys. Chem., 100(51), 20056-20062 (1996).
[4] M. Liu, M. Endo, A. Shimazaki, A. Wakamiya, Y. Tachibana, J. Photopolym. Sci. Technol., 30 (2017) accepted.
8:00 PM - ES01.10.28
Band-Tail States of Lead-Halide Perovskite Single Crystals Evaluated by Two-Photon Excited Photoluminescence Spectroscopy
Takumi Yamada 1 , Tomoko Aharen 1 , Atsushi Wakamiya 1 , Yoshihiko Kanemitsu 1
1 , Kyoto University, Kyoto Japan
Show AbstractOrganic-inorganic perovskites MAPbX3 (MA = CH3NH3, X = I, Br, and Cl) have attracted much attention as a new class of photonic device materials. In particular, the power conversion efficiencies of thin-film solar cells based on MAPbI3 have rapidly grown and already exceed 22%. The wide band-gap perovskites MAPbBr3 and MAPbCl3 are also important for developing new perovskite photonic devices in the green and blue spectral region. Throughout understanding of the fundamental optical properties of MAPbX3 is needed to improve the performance of perovskite photonic devices [1]. Sharp optical absorption edge and high-efficient band-to-band light emission with no essential Stokes shift produce unique optical phenomena of perovskites such as photon recycling and radiative cooling [2-5]. To understand the near-band-edge optical properties of perovskites is important and the sophisticated optical experiments on single crystals are useful to reveal intrinsic material properties.
In this study, photoluminescence (PL) and PL excitation (PLE) measurements were conducted under one- and two-photon excitation to investigate the near-band-edge optical properties of MAPbX3 single crystals. Right below the band-gap excitation, the peak of one-photon-excited PL (1-PL) was redshifted because the photocarriers are created at a deeper position with longer penetration depth and the emission from the interior region should be reabsorbed strongly. On the other hand, the peak of two-photon-excited PL (2-PL) was significantly lower than that of 1-PL due to strong reabsorption. However, the shape of 2-PL did not change with excitation energy because the carriers were excited homogeneously from the surface to the back with any excitation energy. The one-photon excited PLE (1-PLE) spectrum shows a distinct exciton peak in MAPbBr3 and MAPbCl3, while there is no clear peak structure in MAPbI3. On the other hand, the two-photon PLE (2-PLE) shows no peak and its intensity increased gradually with excitation energy from the band gap. By considering reabsorption effect, we calculate absorption spectra from 1-PLE, and the obtained absorption spectra have small Urbach energy. The nature of band-tail states and near-band-edge PL properties will be discussed.
Part of this work was supported by JST-CREST (JPMJCR16N3) and JSPS Research Fellowships for Young Scientists (17J07890).
[1] Y. Kanemitsu, J. Mater. Chem. C 5, 3427-3437 (2017).
[2] Y. Yamada et al., J. Am. Chem. Soc. 137, 10456–10459 (2015).
[3] T. Yamada et al., Adv. Electron. Mater. 2, 1500290 (2016).
[4] T. Yamada et al., Phys. Rev. Applied. 7, 014001 (2017).
[5] S.-T. Ha et al., Nat. Photonics 10, 115-121 (2016).
8:00 PM - ES01.10.29
Air-Stable Cesium Lead Iodide Perovskites for Resistive Switching Memory
Ji Su Han 1 , Jaeho Choi 1 , Ho Won Jang 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractThe organometallic halide perovskites (OHP), ABX3 where A is organic cation, CH3NH3 (MA), B is metal cation and X is halide anion, Cl, Br and I, is a unique semiconducting material having the intrinsic properties like tunable bandgap, fast ion migration, mechanical and compositional flexibility. The great success of OHP in solar cells brought about a paradigm shift and lots of subsequent research. According to this trend, many optoelectronic and electronic devices such as photodetectors, light-emitting diodes, field effect transistors, memristors, and lasers have been rapidly investigated with OHP.
As the beginning of big data and Internet of things times, the volume of data is expected to extremely increase at even a faster rate despite already huge data size. This indicates that development in the memory storage technology is consistently demanded for the next generation data technology. Resistive switching random-access memory (ReRAM) which can be applied to memristors and neuromorphic technology has been considered to be a promising nonvolatile memory device due to its low power consumption, fast switching speed, and high integration density. Many ReRAM devices with OHP have been reported, however, the OHP have an inevitable limits such as extreme sensitivity to oxygen and moisture, photo and thermal instability originating from organic groups. The stability can be improved by replacing the organic groups by inorganic cations such as Cesium while maintaining the optical and electrical perovskites properties.
Herein, we successfully fabricated air-stable all-inorganic 200-nm-thick CsPbI3 perovskites resistive switching memory devices by all-solution process under low temperature for the first time. Adding additive to the perovskite precursor solution, we can attain the CsPbI3 perovskites-phase stabilization. The Ag/CsPbI3/Pt/Ti/SiO2/Si devices exhibited resistive switching behavior such as ultralow operating voltage (<0.2 V), high ON/OFF ratio (>106), pulse voltage operation in 640µs pulse width, multilevel data storage by regulating current compliance. The simple solution-based process also has the possibility to flexible and large area devices. This research suggests the future non-volatile memory devices and also contributes to better understanding on the resistive switching mechanisms about the halide perovskites.
8:00 PM - ES01.10.30
Multiphoton Absorption Coefficients of Organic-Inorganic Lead Halide Perovskites CH3NH3PbX3 (X = Cl, Br, I)
Joon Jang 1 , Felix Saouma 2 , Dae Young Park 3 , Mun Seok Jeong 3
1 Physics, Sogang University, Seoul Korea (the Republic of), 2 Physics, Binghamton University, State University of New York, Binghamton, New York, United States, 3 Energy Science, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractHybrid organic-inorganic lead halide perovskites have recorded unprecedented improvement in efficiency as fourth-generation photovoltaic materials. Recently, they have attracted enormous interest in nonlinear optics stemming basically from their excellent optoelectronic properties. Here, we investigate multiphoton absorption (MPA) in high-quality MAPbX3 (MA = CH3NH3 and X = Cl, Br, I) bulk single crystals synthesized by an inverse-temperature crystallization (ITC) method. The two-photon absorption (2PA) coefficients under picosecond pulse excitation are determined to be β = 23±2 cm/GW and 9±1 cm/GW for MAPbI3 and MAPbBr3 at λ = 1064 nm, and 13±2 cm/GW for MAPbCl3 at λ = 532 nm. The 2PA coefficients are comparable to those of conventional semiconductors having similar bandgaps and can be explained by a two-band model. Furthermore, we characterize the three-photon absorption behavior of MAPbCl3 at λ = 1064 nm, yielding γ = 0.05±0.01 cm3/GW2. The polarization dependence of MPA is also probed to experimentally estimate the degree of anisotropy. The hybrid perovskites are promising materials for nonlinear optical applications due to polarization-dependent MPA response and subsequent strong photoluminescence emission, especially for the Br- and I-containing compounds.
8:00 PM - ES01.10.31
One-Step Surface Modification of Perovskite Thin Films via Impurity Cation Doping, A-Site Cation Exchange and Ostwald Ripening
Yen-An Lu 1 , Ting-Hsiang Chang 1 , Hsin-Chun Lu 2 , Kuo-Chuan Ho 1 3
1 , Department of Chemical Engineering, National Taiwan University, Taipei Taiwan, 2 , Department of Chemical and Materials Engineering, Chang Gung University, Taoyuan City Taiwan, 3 , Institute of Polymer Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractIn recent years, perovskite solar cells (PSCs) have been considered as a new generation of solar cells with low-cost and high power conversion efficiency compared with silicon solar cells. However, PSCs are known to suffer from poor long-term stability. Researchers have focused on material modifications and fabrication methods to improve cell efficiency and stability. Among all fabrication methods, solvent engineering process is considered as a promising approach to fabricate high-efficiency PSCs, but it still has the problems of generating undesired pinholes on thin films and poor reproducibility. Our work aims at developing a facile post-treatment to modify the surface of methylammonium lead iodide (MAPbI3) perovskite thin films after solvent engineering process, which is expected to heal the pinholes and further improve the photovoltaic properties and the long-term stability of PSCs. Herein, a facile post-treatment is demonstrated, combining Ostwald ripening, impurity cation doping, and A-site cation exchange (e.g., Cs+ and FA+) in one single step. Not only does this post-treatment enhance the photovoltaic performances of PSCs but also improves the reproducibility and reliability. An appropriate solvent which slightly dissolves the perovskites thin film is utilized to induce Ostwald ripening; large grains and dense perovskite thin films can be obtained via Ostwald ripening, which are beneficial to eliminating the carrier recombination sites at the grain boundaries. In addition, an optimized temperature and time for annealing is used to exchange MA+ with other kinds of A-site cation. It is expected that the moisture and thermal resistance would be improved by A-site cation exchange and result in better long-term stability. Furthermore, a specific amount of impurity cation doping can reduce the defects at the grain boundaries and improve the roughness of perovskites thin film, thus resulting in better interface at the perovskite film/hole-transport layer and eliminating the hysteresis effect. The as-prepared PSCs show the significant improvement of grain size from nanoscale to microscale and the power conversion efficiency from 15 to 18%. The combined effect of these approaches will be addressed.
8:00 PM - ES01.10.32
All-Solution-Processed Copper-Nickel Core-Shell Nanowire Network Based Bottom Electrode for Hybrid Perovskite Solar Cells
Kyungmi Kim 1 , Eunsong Lee 1 , Sunihl Ma 1 , Hyeok-Chan Kwon 1 , Jooho Moon 1
1 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractOrganometal trihalide perovskites have attracted tremendous interest as promising materials for solar energy conversion, due to their low-cost, easy processability, and high photovoltaic performance. For the past 5 years, the maximum power conversion efficiency (PCE) of perovskite-based solar cells has quickly exceeded 20%. As a bottom electrode in perovskite solar cells, indium tin oxide (ITO) is the most commonly used. However, ITO is undesirable because indium is high-cost rare metal and it is deposited via vacuum sputtering process, which limits the commercialization of perovskite solar cells (PSCs). A key challenge that can unlock the potential of new generation photovoltaics is to develop new transparent conductive electrodes (TCEs) that can replace ITO. With these considerations, copper nanowire (CuNW) can be one of the promising candidates as an alternative for the application as a bottom electrode in PSCs. However, CuNW electrodes degrade abruptly during perovskite absorber production, caused by the formation of insulating copper iodide phase. In addition, the solution processed electron transport metal oxide layer (e.g., zinc oxide) cannot be applied on top of CuNW layer owing to poor chemical/thermal stability of copper. Herein, we developed solution-processed nickel coating layer around CuNW network as a passivation layer to improve thermal/chemical resistance against the two-fold formations of copper oxide and copper iodide. Copper-nickel core-shell nanowires (Cu@Ni NWs) network electrodes were formed by simple deposition of CuNW electrodes (20 Ω/sq with a transmittance of 88.7% at 550 nm), followed by electroless plating of Ni. Thermal and chemical robustness of Cu@Ni NWs were evaluated by oxidation test and iodide formation test. The Cu@Ni NWs did not show an increase in sheet resistances when exposed to 85oC for over 100 minutes, whereas bare CuNWs revealed a large increase in sheet resistance due to oxidation. In addition, when the perovskite layer was directly coated on top of the Cu@Ni NWs, the variation of sheet resistance was nearly unchanged unlikely to bare CuNWs. The Cu@Ni NWs derived TCEs (45 Ω/sq with a transmittance of 81.3% at 550 nm) were applied to PSCs, exhibiting a PCE of nearly 10%, comparable to the conventional sputtered FTO electrode based PSCs (PCE of ~ 13%). These findings clearly suggest that our all-solution-processed indium-free noble-metal-free Cu@Ni NWs derived electrodes have the great potential as a bottom electrode for low-cost perovskite solar cells.
8:00 PM - ES01.10.33
Improving Power Conversion Efficiency of Perovskite Solar Cells Using Sol-Gel Derived Crater Like TiO2 as an Electron Transfer Bilayer
Sunihl Ma 1 , Eunsong Lee 1 , Hyeok-Chan Kwon 1 , Kyungmi Kim 1 , Jooho Moon 1
1 , Yonsei University, Seoul, SE, Korea (the Republic of)
Show AbstractRecently, an astoundingly high power conversion efficiency (PCE) of over 20% has been realized in perovskite solar cells (PSCs) based on mesoporous structures, with an aid of not only desirable inherent properties of the perovskite material itself, but also developments of film crystal control, and interface engineering. Until now, TiO2 based mesoporous structures were successfully adopted, showing high efficiency and stable power output for perovskite solar cells. Although these high efficient devices have reached their achievable limits, there is still room for further improved performance through optical design. Maximizing solar energy absorption by optical engineering is expected one of the promising approach to boost PCE. A number of approaches have been tried to improving light harvest were investigated such as embedding light scattering particles or plasmonic particles into the scaffold layer. However, since these optical modulation studies have been focused on mesoporous structures, pre-synthesis steps for scaffolds and additional steps for optical tuning inevitably increased process time and complexity, which may thereby pose a hurdle towards the commercialization of PSCs. As a different architecture, a simple planar-structure solar cells have been developed after the perovskite materials have been found to have micrometer range charge carrier diffusion length and ambipolar properties. TiO2 is also commonly used electron transport layer (ETL) in planar structure, due to its excellent ability to prevent shunting and leakage current under reverse bias. However, it has been reported that TiO2 causes a reduction in transmittance due to its high reflectance, suggesting that ETL with lower refractive index is necessary for allowing more light transmission with reduced reflection. Therefore, tuning the optical properties of TiO2 ETL is the promising way to advance to higher efficiency of planar PSCs. Herein, we present a facile method for modulating optical properties of TiO2 ETL without additional complicate processes through sol-gel chemistry. The resulting TiO2 layer has a crater-like porous structure with a diameter of 100 - 300 nm and a depth of 50 nm, which was observed by scanning electron microscopy (SEM). Surface profile and roughness were also analyzed and calculated using atomic-force microscopy (AFM) image analysis. Introducing this crater-like porous TiO2 layer increased transmitted light due to less reflection on the porous film. In addition to the optical modification effect, a significant increase in external quantum efficiency (EQE) was observed due to an improved charge extraction. To analysis electrical properties of crater like TiO2 layer and discern charge transfer characteristic during the cell operation, electrochemical impedance spectroscopy (EIS) was used. As compared to dense TiO2 involved planar structure, the planar PSCs with crater-like porous TiO2 ETL improved the photocurrent density by ~14.5% and PCE by ~19.5%.
8:00 PM - ES01.10.34
High Mobility Fullerene Derivatives for Interface Modification on Compact-TiOx in Planar Perovskite Solar Cells
Md Shahiduzzaman 1 , Makoto Karakawa 1 , Kohei Yamamoto 1 , Kyosuke Yonezawa 1 , Takayuki Kuwabara 1 , Kohshin Takahashi 1 , Tetsuya Taima 1
1 , Kanazawa University, Kanazawa Japan
Show AbstractA precise control of the morphology and crystallization of perovskite thin-films is well-correlated to higher perovskite solar cells performances. The efficiency of perovskite solar cells can be enhanced by interfacial engineering of electron collecting layer (ECL) compact-TiOx by a thin-layer of low-cost organic material. Commonly used PCBM is still expensive material. Herein, a noble, higher potential of [60]fulleropyrrolidine derivatives named as N-phenyl[60]fulleropyrrolidines (PNP) is presented as an interfacial modification of ECL compact-TiOx layer to replace the commonly used PCBM in planar perovskite solar cells. Compared with PCBM, this PNP features a higher hydrophobicity, and higher electronic mobility. The higher crystallinity of TiOx/PNP/ CH3NH3PbI3 was observed owing to the better crystallinity of PNP material, while the unchanged crystallinity of TiOx/PCBM/CH3NH3PbI3 was observed due to amorphous PCBM, as evident from XRD pattern. The enhanced crystallization enhances charge-carrier mobility with PNP modified perovskite than that of PCBM. PNP devices exhibited higher twofold (0.14 cm2V1S1) electron mobility from that of the PCBM device of 0.067 cm2V1S1. The devices were optimized with varying PNP thickness. The highest solar cell performance was found at an optimum PNP thickness of 10 nm. The incorporation of the PNP interfacial layer caused an increase in short-circuit current density (Jsc) from 11.90 mA/cm2 to 21.44 mA/cm2, while the value is limited to 13.47 mA/cm2 with the PCBM interfacial layer. The enhancement of Jsc of 21.44 mA/cm2 was obtained owing to higher electron mobility of PNP led to more efficient electron transport and charge extraction in the resulting solar cells performances. The UV-vis spectra revealed that the enhancements of Jsc and the IPCE peak of the solar cell with a PNP interfacial layer are caused by improved charge carrier separation between the CH3NH3PbI3 and PNP layers and increased exciton generation in the PNP layer induced by higher light absorption. The power conversion efficiency increases significantly from 5.12 to 8.23%, when 10 nm PNP interfacial layer is inserted between the CH3NH3PbI3 and compact-TiOx layers. We observed that the surface energy and morphology of PNP layer employed an impact on the resulting device performance. The surface energy of the compact-TiOx layer can be modified in the range of 41 to 46.5 mJ/m2, with the introduction of PNP interfacial layer. Therefore, we assume that surface energy control might give further insight to enhance performance of perovskite solar cells. Our finding may attract attention in the aspects to the new low-cost production perovskite solar cells.
Keywords: Perovskite solar cells; High mobility; Interfacial modification layer; N-phenyl[60]fulleropyrrolidines (PNP); Amorphous compact-TiOx.
8:00 PM - ES01.10.35
Two-Dimensional Organo-Halide Perovskite for Wafer-Scale Reliable Resistive Switching
Ja-Young Seo 1 , Jaeho Choi 2 , Ho Won Jang 2 , Nam-Gyu Park 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractOrganic-inorganic perovskite material has been populated for application in resistive memory because of low operating voltage, high on/off ratio as well as flexibility and low-cost fabrication via solution method. Active reports were published about the 3-dimensional MAPbI3 resistive memory, however, the switching speed and reliability were still poor. Here, we focused on the relation between the performance of resistive memory and the dimension of material. We report on the resistive memory based on the (CH3(CH2)3NH3)2MAn-1PbnI3n+1 (n=1,2,3 and ∞) and compared its characteristics. The clear dependency of characteristics on dimension was found and it was related to the properties such as low energy consumption, the magnitude of resistance at high resistance state (HRS), on/off ratio and endurance. 2-dimensional (CH3(CH2)3NH3)2PbI4 is superior to 3-dimensional MAPbI3 as resistive memory material and it also showed enhanced thermal stability, good reproducibility even in the 4-inch scale thin film. It is believed that 2-dimensional perovskite is a promising material for resistive memory with merit-of-figure.
8:00 PM - ES01.10.36
Excitonic Properties of CH3NH3PbBr3 Single Crystals Revealed by Temperature-Dependent Photocurrent Excitation and Photoluminescence Excitation Spectroscopy
Le Phuong 1 , Takumi Yamada 1 , Tomoko Aharen 1 , Yasuhiro Yamada 2 , Atsushi Wakamiya 1 , Yoshihiko Kanemitsu 1
1 , Kyoto University, Kyoto Japan, 2 , Chiba University, Inage Japan
Show AbstractMethylammonium lead halide perovskites (MAPbX3, X = I, Br and Cl) provide a potential class of materials for high-efficiency and cost-effective optoelectronic applications including solar cells, light-emitting diodes, lasers, and photodetectors [1]. The operating efficiencies of these perovskite-based devices correlate strongly to the predominant type of excitations, i.e., charge carriers or excitons, in perovskite thin films. Therefore, understanding the nature of excitations and their fundamental photoelectrical properties in MAPbX3 perovskites is of importance. In spite of diligent efforts done in the last few years, the exciton binding energy in MAPbBr3 has not been well determined yet. Thus far, the reported binding energy of excitons in MAPbBr3 varies in a wide range, from 15 to 60 meV [2], causing inconsistent opinions on the nature of excitation in MAPbBr3. Further work is needed to resolve this conflict, and using different spectroscopic techniques simultaneously and single crystals gives a powerful tool to reveal precisely optoelectronic properties in organic-inorganic lead halide perovskites [3].
In this work, we investigated the excitonic properties of MAPbBr3 single crystals using a combination of temperature-dependent photocurrent excitation (PCE) and photoluminescence excitation (PLE) spectroscopy. A sharp emission band located at 2.247 eV was observed in the photoluminescence (PL) spectra of MAPbBr3 at 16 K. Meanwhile, multiple peak structures were detected in both PCE and PLE spectra, in which the energy position of the lowest peak coincides with that of the sharp PL band. We assigned the sharp PL band to the emission of the free excitons at the ground state, and the high-energy peak structures in the PCE spectra to the excited states of the free excitons. The exciton binding energy in MAPbBr3 then was evaluated to be about 20 meV at low temperatures. The temperature dependence of the exciton binding energy in MAPbBr3 will be discussed.
Part of this work was supported by JST-CREST (JPMJCR16N3) and JSPS KAKENHI (16F017).
[1] W. S. Yang et al., Science 348, 1234 (2015); H. Zhu et al., Nat. Mater. 14, 636 (2015); Q. Lin et al., Nat. Photon. 9, 687 (2014).
[2] Y. Yamada et al., Bull. Chem. Soc. Jpn (2017) in press.
[3] Y. Yamada et al., J. Am. Chem. Soc. 137, 10456 (2015); L. Q. Phuong et al., J. Phys. Chem. Lett. 7, 2316 (2016).
8:00 PM - ES01.10.37
Patterning Hybrid Perovskites at the Nanoscale for Distributed Feedback Lasers
Sarah Brittman 1 , Stefan Schünemann 2 , Kun Chen 2 , Ke Guo 1 , Femius Koenderink 1 , Harun Tüysüz 2 , Erik Garnett 1
1 , AMOLF, Amsterdam Netherlands, 2 , Max-Planck-Institut für Kohlenforschung, Mülheim Germany
Show AbstractHybrid perovskites are promising materials for optoelectronics, as demonstrated by their high efficiencies in photovoltaics and applications in light emission. Both of these fields can benefit from nanophotonic patterning to improve performance and create new functionality. We apply two techniques to mold hybrid perovskites into periodic nanophotonic structures: imprinting with silicone polymer stamps and back-filling self-assembled polystyrene opals. Controlling the crystallization of the perovskite film is essential to produce high quality structures. The nanophotonic patterns engineer the emission of the perovskite both spectrally and angularly and produce distributed feedback lasers. These patterning approaches open up possibilities for nanophotonic solution-processed optoelectronics.
8:00 PM - ES01.10.38
Reliable Operation of Hybrid Perovskite-Based Broadband Photodetectors by Suppression of Ion Migration
Kootak Hong 1 , Ki Chang Kwon 1 , Junmin Suh 1 , Ho Won Jang 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractHybrid perovskites have attracted extensive attention as active layer materials for optoelectronics and electronic devices recently, because of their high charge carrier mobility, high photoconversion effi ciencies, low cost, and simple fabrication methodology. Despite rapid progress in hybrid perovskite-based optoelectronics, the current–voltage (I–V) hysteresis behavior of hybrid perovskites makes it difficult to obtain reliable device performance, an issue that has not been intensively studied. In this respect, careful investigation of the migration of unintentionally formed defects in hybrid perovskites films and of methods for inhibtion defects and ion migration should be carried out to obtain reliable performance of hybrid perovskites-based optoelectronics.
Here, we report reliable CH3NH3PbI3 (MAPbI3) broadband photodetectors with a buffer-layer-free simple lateral structure and a high on/off ratio (Ion/Ioff = 104 under 0.05 sun conditions). Due to the migration of defect ions in MAPbI3 films, the I–V characteristics of photodetectors clearly exhibit sweep rate-dependent hysteresis, especially in the dark. The migration of defect ions is generated
by external bias, and it more severely affects dark current behavior as the external bias increases. Thus, photodetectors show poor on/off ratios due to the increasing of dark currents and spikes of photo currents at high external bias. We show that the proposed
photodetector exhibits high on/off ratios and reliable operation at low voltages where the migration of defect ions is suprressed. More interestingly, it is revealed that the electrical history of the device such as poling significantly affects device performance and should be controlled for reliable operation.
8:00 PM - ES01.10.39
Structural and Property Reversibility of Organic-Inorganic 2D-Perovskites in Presence of NH3 Gas
Sayantan Sasmal 2 , Raj Pala 1 , Sri Sivakumar 1 , Suresh Valiyaveettil 2
2 Chemistry, NUS, Singapore Singapore, 1 Chemical, IITK, Kanpur India
Show AbstractOrganic-inorganic hybrid halide perovskites have emerged as one of the high performance materials for the next generation photovoltaics. Despite achieving excellent energy conversion efficiencies, performance of perovskite materials is affected by various environmental conditions such as heat, humidity and presence of polar gases such as ammonia. Short exposure of ammonia (NH3) induces drastic changes in opto-electronic properties of MAPbI3 film and completely transformed MAPbI3 to NH4PbI3. Recently we investigated the mechanism of interaction between hybrid halide perovskites with NH3 using a series of alkyl perovskites prepared from different amines and investigating the changes in both structure and properties. The two dimensional (2D) hybrid perovskite materials developed using long chain aliphatic amines showed higher stability, good reversibility and fast response, which could be used for the development of new materials in the future.
8:00 PM - ES01.10.40
Origin of Band Gap Bowing in Mixed Lead-Tin Hybrid Perovskite Alloys
Anuj Goyal 1 2 , Scott McKechnie 3 , Dimitar Pashov 3 , William Tumas 2 , Mark Schilfgaarde 3 , Vladan Stevanovic 1 2
1 , Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 , King's College London, London United Kingdom
Show AbstractMixed lead-tin hybrid perovskite alloys, MA(Pb1-xSnx)I3, have lately attracted much attention from the photovoltaic (PV) community due to their possible application in all-perovskite tandem solar cells. The main reason is the experimentally observed lowering of the band gap below both end-compounds (band gap bowing) to the values around 1.1 eV. To investigate the origins of the band gap bowing in lead-tin hybrid halide perovskite alloys we employ both the standard and advanced schemes within first-principles electronic structure calculations. These include standard semilocal functionals (such as generalized gradient approximation), hybrid functionals and quasiparticle self-consistent GW (QSGW) approach with spin-orbit coupling included, in combination with the special quasi-random structure representation of the random alloy in the quasi-cubic perovskite structure. All levels of theory show bowing of the band gap in MA(Pb1-xSnx)I3 alloys with the magnitude comparable to experimental findings and the minimal band gap value in the composition range between x = 0.5 and 0.75. Contrary to the current opinion, we find that band gap bowing exists both with and without spin-orbit coupling and without any phase transformation. Furthermore, we find that the main reason behind the band gap bowing is the relative positions (offsets) of the individual band-edge energies of end compounds determined by position of the Sn(5s) and Pb(6p) atomic orbitals.
8:00 PM - ES01.10.41
Uranium Oxide Compact Layer for Perovskite Solar Cellš—Promising Novel Electron Transfer Material?
Alexander Möllmann 1 , Jennifer Leduc 1 , Maximilian Steinhorst 2 , Sanjay Mathur 1 , Thomas Kirchartz 2
1 , University of Cologne, Cologne Germany, 2 IEK-5, Forschungszentrum Jülich GmbH, Jülich Germany
Show AbstractPerovskite solar cell efficiencies are rapidly increasing for the last five years. The improvements are based on the better understanding and higher investigation of the perovskite absorber material and electron/hole transfer material. New metal oxides besides titanium oxide and aluminium oxide are tested as electron transfer material to improve efficiencies and open more possibilities for different perovskite absorber materials. Uranium (oxide) is known and studied well in the nuclear power plant sector and the problem of produced uranium waste is also not just an economic and ecological but also a political issue. Uranium applications besides the usage in nuclear power plants are investigated poorly yet because of the risk and the image of using uranium.
In this work, we present a possible application for depleted uranium waste by transforming it into an usable precursor and depositing it with PE-CVD and spin-coating to be used as a compact layer in perovskite solar cells. The difficulty of determining the crystal structure, modification, band edges and band gap is reduced by previous experiments and experience using it in PEC water splitting application. We already showed that it can rather work as electron transfer materials than absorber material which could be beneficial for perovskite solar cell performance. Furthermore the limits and understanding of uranium oxide is broadened.
8:00 PM - ES01.10.42
Tantalum Oxide as an Electron Transporting Material for Photostable Perovskite Solar Cell
Meenal Deo 1 , Alexander Möllmann 1 , Sanjay Mathur 1
1 Institute of Inorganic Chemistry, University of Cologne, Cologne Germany
Show AbstractHighly efficient organic-inorganic hybrid perovskite solar cells have emerged recently as very promising future for harvesting solar power. In a typical perovskite solar cell, organic-inorganic trihalide layer with a thickness of several hundred nanometers is sandwiched between the electron-transporting layer (ETL) and the hole-transporting layers (HTLs). A mesoporous electron transporting layer is usually considered beneficial because of its high surface area. However, similar to dye-sensitized solar cells (DSSCs), perovskite solar cells with mesoscopic ETLs suffer from a loss in open-circuit voltage (Voc), which compromises the overall efficiency. One direct approach to improving Voc in solid-state sensitized solar cells is to reduce the band offset between the sensitizer and the ETL/HTL. It is important to note here that most of the efforts of improving the Voc have been focusing on improving or replacing the hole transporting layer.
TiO2 is one of the most sought after material for electron transporting layer as well as mesoporous layer in organic-inorganic hybrid perovskite solar cell. However, it has been recently shown that TiO2 layer faces problem with charge injection because of its conduction band misalignment with the perovskite material, CH3NH3PbI3. Under such circumstances, Tantalum oxide (Ta2O5), which has ~ 120 meV deeper conduction band and shows proper band alignment with CH3NH3PbI3, can be explored as an alternative material for electron transport layer in the perovskite solar cells. In addition, Ta2O5 has a very high dielectric constant, which helps to reduce charge recombination at the interface and improve the device performance, mainly open circuit voltage.
In this work, we have explored tantalum oxide (Ta2O5) for the first time as an electron transport material in perovskite solar cells. Perovskite solar cells with Ta2O5 nanoparticles as a mesoporous layer show fill factor enhancement by ~10% compared to that of using TiO2 mesoporous layer. We found that the nanoparticles size and the thickness of the mesoporous layer play important role in determining the solar cell performance. Our findings show that tantalum oxide is a competitive candidate as electron transporting layer in perovskite solar cells.
8:00 PM - ES01.10.44
First-Principles-Based Novel Materials Design for Pb-Free Perovskite Solar Cell
Kyung-yeon Doh 1 , Seong Hun Kim 1 , Donghwa Lee 1
1 , POSTECH, Gyeongbuk Korea (the Republic of)
Show AbstractDepletion of fossil fuel and the following environmental impact has increased the importance of developing new energy source. In particular, there is a pressing need to develop new energy sources that are efficient, conservative and carbon-neutral to ensure minimal environmental impact. Solar, water and wind-based energy generation are widely considered to be some of the most promising technologies that can meet these requirements. Among these, solar cell has received wide attention from many scientists and engineers since it has several advantages such as environmentally friendly and non-depleting and long-term durability. Although the silicon-based solar cell devices show good energy efficiency (>20%), complexity of manufacturing system and high production cost have limited its wide range applications. Recently, hybrid perovskite solar cell, which uses (CH3NH3)PbI3 as a photoactive layer, is receiving extensive attention because high energy efficiency has been achieved without complex manufacturing process. However, the inclusion of toxic lead has increased the necessity of developing Pb-free photoactive materials. Thus, we have searched alternative perovskite materials that can replace conventional (CH3NH3)PbI3. Especially, we have employed First-Principles-based novel materials design technique to reduce time and cost required for synthesis and characterization of traditional experimental approaches. We have extensively studied on ABX4, A2BX4, A3B2X9 backbone structures to find alternative materials for perovsktie solar cell. Our study has identified a couple of candidate materials which are suitable for photoactive layer based on bandgap and energy level alignment. In addition, analysis on electronic structure has led the understanding of the relationship between constituent elements and bandgap.
8:00 PM - ES01.10.46
Resistive Switching Memory Operated by Two Kinds of Conducting Paths in Guanidinium Lead Iodide Perovskite Memory Cell
Young-Hoon Kim 1 , Seongrok Seo 1 , Yongjae In 1 , Changdeuck Bae 1 , Hyunjung Shin 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractRecently, organo-lead halide perovskite materials have received attention for use as resistive switching materials. For example, methylammonium lead iodide (MAPbI3) has been reported as good resistive switching layer operating at 0.15V with on/off ratio higher than 106. However, reset processes (LRS → HRS) of MAPbI3 based resistive memory cells were not perfectly operated in many times in our experiments. Moreover, its mechanism has not been clearly proven even though there are two conducting filament theories: filaments consist of iodide vacancies or silver. Here, we firstly report guanidinium lead iodide (GAPbI3) based resistive memory device. In a Ag/GAPbI3/Pt cell, we found out that two kinds of high resistance states co-existed (HRS1 and HRS2). By varying ac pulse width and amplitude with a proper interface engineering, we could separate type1 (LRS↔HRS1) and type2 (LRS↔HRS2). It can be explained that silver filaments and iodide vacancies filaments are both involved in the process. In addition, it has better stability than MAPbI3 under humid environment because GA ions at grain boundaries interact with humidity first. In a stability test, it maintained stable resistive switching behavior during 7 days under ambient conditions. Therefore, we suggest that GAPbI3 material is highly promising as multi-level resistive memory devices. In addition, this result will help to understand the behavior of organo-lead halide perovskite resistive memory and develop improved devices in the future.
8:00 PM - ES01.10.48
A Photon Ratchet Route to High-Efficiency Halide Perovskite Intermediate Band Solar Cells
Jarvist Frost 1 3 , Pooya Azarhoosh 2 , Scott McKechnie 2 , Mark van Schilfgaarde 2 , Aron Walsh 1
1 Department of Materials, Imperial College London, London United Kingdom, 3 Chemistry, University of Bath, London United Kingdom, 2 Department of Physics, King's College London, London United Kingdom
Show AbstractRecently[1] we suggested that the spin-orbit split band structure of hybrid halide perovskite can form a reciprocal space realisation of an intermediate band solar cell (IBSC). Local disorder in the material generates a crystal field, which interacts with the large spin-orbit coupling to displace the band extrema (a Rashba effect). This leads to a spin-split indirect-gap, which operates as a photon ratchet. This is the same process which we propose leads to the long minority carrier lifetimes in the material when operated as a single gap solar cell[2].
To show that the material can operate as an IBSC, we must demonstrate that the intermediate and conduction bands can develop independent quasi-Fermi levels. We do this by inspection of the quasi-particle self-consistent GW electronic band structure[3].
To calculate the potential performance of the material we need to calculate quantitative rates for the excitation and recombination processes. This requires custom codes to calculate the optical response as the function of an out-of-equilibrium electron population.
We build a rate-equation device model with parameters directly from electronic structure, to infer the performance limits of this system with ideal contacts.
An interesting finding is that the large spin-orbit-coupling is an essential component of this proposed IBSC mechanism. This (i) renormalises otherwise degenerate orbitals to form the intermediate band, (ii) allows for otherwise forbidden optical transitions between these bands, (iii) is the origin of the Rashba effect producing the photon ratchet.
We present initial work looking beyond hybrid halide perovskites for similar spin-orbit coupling derived IBSC features.
[1] JM Frost, P Azarhoosh, S McKechnie, M van Schilfgaarde, A Walsh. ArXiv:1611.09786, 29 Nov 2016.
[2] P Azarhoosh, JM Frost, S McKechnie, A Walsh, M van Schilfgaarde. APL Materials 4,9 (2016).
[3] F Brivio, KT Butler, A Walsh, M van Schilfgaarde. Phys. Rev. B 89, 155204 (2014).
8:00 PM - ES01.10.49
Negative Electron Affinity Photocathode Based on Cesium Lead Halide Perovskites
Fangze Liu 2 , Vitaly Pavlenko 1 , Mark Hoffbauer 3 , Wanyi Nie 2 , Hsinhan Tsai 2 4 , Jean-Christophe Blancon 5 , Nathan Moody 1 , Aditya Mohite 2
2 Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 1 Accelerator Operations and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Materials Science and Nano-engineering, Rice University, Houston, Texas, United States, 5 Physical Chemistry and Applied Spectroscopy Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractNegative electron affinity (NEA) photocathodes are electron beam source for many applications including electron accelerators, photomultipliers, image intensifiers, and electron beam lithography. Among the advantages of NEA photocathodes are very high quantum efficiency (QE), prompt response time and very low thermal emittance. The NEA condition is established by deposition of a few monolayers of cesium and a strong oxidizer (oxygen) on the surface of photocathode material, namely III-V semiconductors. The strong dipole created near the surface lowers the vacuum level below the conduction band minimum. Hence, the minimum photon energy required for generating photoelectrons is reduced to the band gap of the material and the QE is greatly enhanced. Although conventional NEA photocathodes have been studied for a few decades, the inability of conventional materials to meet increasingly stringent emittance requirements has motivated a growing investigation of new classes of designer materials for potential use in photo-emission applications.
In the past few years, halide perovskites have attracted enormous attention as high performance solution-processed semiconductors for applications such as solar cells, light emitting devices, lasers and radiation detectors. However, the stability issue of hybrid organic-inorganic perovskites has become the major bottle neck for their applications. Inorganic perovskites, for example, cesium lead halide (CsPbX3, X=Cl, Br or I) perovskites exhibit higher stability than their organic analogues, especially at elevated temperature. Here we report the first demonstration of NEA photocathodes based on solution-processed CsPbX3 thin films with QE exceeding 0.1%. Intrinsic cesium lead halide perovskites have electron affinity between 3 and 4 eV. By activation of NEA condition, the cesium lead halide photocathodes are able to generate photoelectrons using visible to near-infrared light. Moreover, the solution process is more suitable for large-area production compared with conventional III-V semiconductors, giving these materials great potential as a new class of photocathode materials.
8:00 PM - ES01.10.50
Characterisation and Optimisation of Processing Time for Perovskite Solar Cells
Katherine Hooper 1 , Benjamin Smith 1 , Joel Troughton 1 , Trystan Watson 1
1 , SPECIFIC, Swansea University, Swansea United Kingdom
Show AbstractPerovskite solar cells (PSCs) have quickly become a very promising candidate for low cost thin film photovoltaics, due to their rapid rise in efficiency and improvements in manufacturability over the last 5 years. However to improve commercial viability it is critical to focus research on the potential bottlenecks to large scale industrial manufacture such as the deposition and heating processes. One of the highest performing PSC architectures involves over 2 hours of heating time in order to sinter the compact and mesoporous TiO2 layers, and anneal the perovskite [1]. This is very energy and time intensive which reduces the feasibility of manufacturing these devices commercially.
Near infrared (NIR) radiation is a technique that has previously been used to significantly reduce the annealing time of perovskite [2] in PSCs and mesoporous TiO2 [3] in dye-sensitised solar cells. It utilises the high infrared absorption of FTO glass to achieve temperatures exceeding 500°C in seconds. We characterise the NIR heated TiO2 and perovskite layers in detail using cyclic voltammetry, XRD, Raman spectroscopy and SEM. For the first time we also fabricate PSCs with both the TiO2 and perovskite layers heated rapidly. NIR heating enabled the fabrication of perovskite solar cells based on mesoporous TiO2 with a total heating time of only 14.6 seconds compared with 2 hours for a standard device. The best device achieved an efficiency of 15.5% (14.8% stabilised), which although lower than that of the best standard hot plate heated cell 18.3% (17% stabilised), was impressive for Cs0.05(MA0.17FA0.83)(1-0.05)Pb(I0.83Br0.17)3 perovskite which requires slow heating times on a hot plate. Devices with perovskite films which were annealed for only 10 min on the hot plate were less efficient than the 2.1 s near infrared annealed films and displayed greater hysteresis which further cements the usefulness of NIR to reduce fabrication times. The significant time and energy saving of this method should help improve the viability of this architecture for large scale production.
[1] M. Saliba, T. Matsui, J.-Y. Seo, K. Domanski, J.-P. Correa-Baena, M. K. Nazeeruddin, S. M. Zakeeruddin, W. Tress, A. Abate, A. Hagfeldt, M. Grätzel, Energy Environ. Sci. 2016, 9, 1989
[2] J. Troughton, C. Charbonnaeu, M.J. Carnie, M.L. Davies, D.A. Worsley, T.M. Watson, J. Mater. Chem. A 2015, 3, 9123
[3] K. Hooper, M. Carnie, C. Charbonneau, T. Watson, Int. J. Photoenergy 2014, 1-8
8:00 PM - ES01.10.51
Exploring Anomalous Polarization Dynamics in Organometallic Halide Perovskites
Mahshid Ahmadi 1 , Liam Collins 2 , Alexander Puretzky 2 , Jia Zhang 1 , Sergei Kalinin 2 , Bin Hu 1
1 , Institute for Advanced Materials, Department of Materials Science, University of Tennessee, Knoxville, Tennessee, United States, 2 , Center for Nanophase Materials, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractOrganometallic halide perovskites (OMHPs) have attracted broad attention as perspective materials for optoelectronic applications. Among many anomalous properties of these materials, of special interest are the ferroelectric properties including both classical and relaxor-like components, as potential origin of slow dynamics, field enhancement, and anomalous mobilities. Here we explore ferroelectric properties of the three representative OMHP including FAPbxSn1-xI3 (x=0, x=0.85) and FA0.85MA0.15PbI3 using band excitation Piezoresponse Force Microscopy and contact mode Kelvin Probe Force Microscopy, providing the insight into long- and short-range dipole and charge dynamics in these materials and probing ferroelectric density of states. In addition, we observe second-harmonic generation in thin films of OMHPs, providing a direct evidence for the material’s non-centrosymmetry. Overall, this data provides strong evidence for the presence of ferroelectric domains in these systems; however, the domain dynamics is completely suppressed by fast ionic dynamics. These materials hence present the limit of ferroelectric materials with spontaneous polarization dynamically screened by ionic and electronic carriers.
8:00 PM - ES01.10.52
Environmental Effects on Ionic and Electronic Conductivity in Single Crystals of Organic-Inorganic Halide Perovskites
Mahshid Ahmadi 1 , Eric Muckley 2 , Ilia Ivanov 2 , Eric Lukosi 3 , Jeremy Tisdale 1 , Sergei Kalinin 2 , Bin Hu 1 , Liam Collins 2
1 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 , Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Nuclear Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractOrganometallic halide perovskites (OMHP) have recently emerged as highly efficient optoelectronic materials and are being intensively investigated and developed for thin film solar cells, light emitting diodes and photodetectors1-4. More recently, single crystals of the same materials are established as superior candidates for detector applications from low energy light sensors to high energy radiation sensors5-7. These applications have stimulated an extensive effort towards understanding of the properties of these materials, including electronic and ionic charge transport. Correspondingly, observed behaviors contain contributions from electrodes, internal interfaces, surfaces, and bulk, as well as chemical and phase inhomogeneities. Here, we report the transport behavior and origins of the gas sensitivity in the MAPbBr3 single crystals grown via an inverse temperature crystallization method8. We demonstrate the strong dependence of the electronic conductivity on gas atmosphere using classical I-V and current relaxation measurements. The observed changes in conductivity was attributed to multiple mechanisms, including ionic conduction of surficial water layers, water intercalation in crystal bulk, or changes in bulk electronic and ionic concentrations. We further explore the frequency dependence transport in these materials using impedance spectroscopy to decouple bulk and interface behaviors via determining the equivalent lumped circuit and establish the nature of the gas-sensitive elements. Finally, we proceed to explore the non-linear transport properties of these materials using fast Kelvin Probe Force Microscopy (KPFM) on a lateral device configuration. G-Mode KPFM is used to explore spatio-temporal charge dynamics at the perovskite/electrode interface with <20 µs time resolution and ~10s nm spatial resolution. Based on these observations, we argue that the transport behavior of these materials is considerably more complex than previously argued. While instrumental for understanding the device characteristics of these materials, it also opens significant opportunities in new chemical sensors and radiation detectors.
This material is based upon work supported by the U.S. Department of Homeland Security under grant no. 2016-DN-077-ARI01.
1. T. M. Brenner, et al., Nature Reviews Materials 16011 (2016).
2. Z.-K. Tan, et al., Nat Nano 9 (9), 687-692 (2014).
3. L. Dou, et al., Nat Commun 5 (2014).
4. N.-G. Park, Materials Today 18 (2), 65-72 (2015).
5. S. Yakunin, et al., Nat Photon 10 (9), 585-589 (2016).
6. H. Wei, et al., Nat Photon 10 (5), 333-339 (2016).
7. Y. Fang, et al., Nat Photon 9 (10), 679-686 (2015).
8. M. I. Saidaminov et al, Nat Commun 6, 7586 (2015)
8:00 PM - ES01.10.53
TiO2 Annealing Effect on Its Stoichiometry and the Impacts on Perovskite Solar Cells
Yuche Ho 1 , Md Nadim Ferdous Hoque 1 , Zhaoyang Fan 1
1 Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock, Texas, United States
Show AbstractTiO2 thin films, formed by solution coating followed by thermal annealing, have been commonly used as the electron transport layer in the hybrid perovskite solar cells. They play critical roles in determining electron extraction efficiency from the perovskite photo absorber and particularly the hysteresis phenomenon commonly observed in this category of solar cells. Studies of TiO2 stoichiometry effect on perovskite solar cells could provide useful information for further improvement of their efficiency and stability. Here we report a systematic annealing study of TiO2 thin films by controlling the gas environment and annealing duration, the resulted stoichiometry, and the impact on perovskite solar cell performance. Surprisingly, the PCE was improved from 13.6 % to 15.9 % by simply optimizing TiO2 annealing condition. From a variety of material and device characterizations, it was found with a reduction of oxygen vacancy defects has a dramatic effect on solar cell performance. The electron recombination and carrier transport kinetics were particularly investigated to interpret the observed phenomena.
8:00 PM - ES01.10.54
Van der Waals Epitaxy and Electron-Phonon Coupling of Two-Dimensional Ruddlesdon-Popper Hybrid Perovskite
Zhizhong Chen 1 , Yiping Wang 1 , Xin Sun 1 , Toh-Ming Lu 1 , Jian Shi 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractAs a two-dimensional limit of Ruddlesdon-Popper (R-P) phase perovskites, the alternative organic/inorganic stacking in (C4H9NH3)2PbI4 not only gives rise to huge exciton binding energy and unique carrier dynamics, but also induces interesting phononic properties. While efforts have been paid to fundamental studies and device fabrication for years, the perovskite crystals/films were mainly synthesized from solution methods. For crystals with reduced concentrations of metastable defects and better compatibility with current semiconductor processing techniques, high temperature vapor based synthesis methods may still be needed. Here we report the first van der Waals epitaxy of single crystalline (C4H9NH3)2PbI4 sheets on muscovite mica. By temperature dependent, time-resolved photoluminescence studies of (C4H9NH3)2PbI4 sheets on different substrates, the role of van der Waals interactions from substrates were identified, providing evidence for possible inter matter electron-phonon couplings. The impacts of dielectric environment on exciton behaviors were also characterized. Our finds may shed new lights on excitonic and phononic properties of layered materials and potential device fabrications.
8:00 PM - ES01.10.55
Shining (X-Ray) Light on Perovskite Solar Cell Structure and Stability via Nano-Diffraction
Xueying Li 1 , Yanqi Luo 1 , Martin Holt 2 , Zhonghou Cai 2 , David Fenning 1
1 Nanoengineering, University of California, San Diego, La Jolla, California, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractEven with their cost-efficient fabrication and exceptional optoelectronic properties, the most efficient perovskite solar cells are slowed on the path toward commercialization by their low stability. Detailed understanding of the kinetics of perovskite degradation is required to establish more stable perovskite solar cells and modules. In this study, we use synchrotron-based X-ray nano-diffraction with 50 nm spatial resolution to analyze degradation kinetics of the local crystal structure in methylammonium lead bromide (MAPbBr3) and cesium lead bromide (CsPbBr3) thin film crystals. In Bragg nano-diffraction, we raster scan a focused X-ray nanoprobe across the sample surface to detect variations in scattering intensity and angle, offering a powerful window into local disorder, including strain and lattice distortion. The perovskite crystals we investigate appear as single-crystals in electron backscatter diffraction, but significant structural defects are revealed in the nanodiffraction measurement in both hybrid and inorganic crystals.
After assessing these baseline heterogeneities in the crystal structure, we analyze the kinetics of crystal degradation as a function of extended X-ray dosing. Because the high energy X-ray irradiation generates core holes that thermalize into a high concentration of band edge carriers, X-ray nano-diffraction presents an opportunity to investigate the dynamics of irradiation-induced degradation, commonly observed in photo-induced degradation and E-beam degradation. Mapping the nano-diffraction of the crystal in two spatial dimensions, we link crystallinity, crystallite size, and surface geometry to the degradation rate. Slower degradation of the crystal lattice of CsPbBr3 relative to MAPbBr3 is observed at the nanoscale, in alignment with the enhanced operational stability of CsPbBr3 devices. Establishing quantitative bounds on the X-ray induced degradation of perovskites paves the way for detailed in situ study of degradation factors such as humidity and temperature that will deepen understanding of perovskite destabilization mechanisms.
8:00 PM - ES01.10.57
Slow Electron-Hole Recombination in Lead Iodide Perovskites Does Not Require a Molecular Cation
Subham Dastidar 1 , Siming Li 1 , Sergey Smolin 1 , Jason Baxter 1 , Aaron Fafarman 1
1 , Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractIn methylammonium lead iodide the bi-molecular electron-hole recombination rate is extremely low, defying the Langevin limit for the capture rate between two freely diffusing, oppositely charged species by five orders of magnitude.[1] One common theory to explain this remarkable property is that motion of the molecular cation plays a critical role, electrostatically screening the charges from each other. Herein transient absorption and transient terahertz spectroscopies are applied to thin films of the all-inorganic, perovskite-phase cesium lead iodide (CsPbI3). In this study the recombination kinetics of photoexcited carriers in CsPbI3 are systematically studied as a function of the initial photo-induced carrier concentration and excitation wavelength. A kinetic model is developed and applied to these results consisting of mono- bi- and tri-molecular recombination processes along with carrier diffusion, given an initial carrier concentration profile determined by the wavelength dependent absorption coefficient, measured experimentally. The bi-molecular rate constant is of particular interest as it is a fundamental property of the material that governs optoelectronic device performance. The combination of wavelength- and fluence-dependent data allow for an accurate determination of this rate, revealing a value of 10-10 cm3s-1, on par with hybrid perovskites. The similarity of all of the rate constants as well as the charge-carrier mobility, measured herein, to values reported for the hybrids strongly suggest that the organic cation does not offer a fundamental advantage. Coupled with recent reports that the otherwise unstable perovskite phase of CsPbI3 can be made more stable through nanostructuring, this argues for a greater role for this material in future photovoltaic applications.[2-4]
References
[1] C. Wehrenfennig et al Adv. Mater. (2014), 26, 1584–1589
[2] G.E. Eperon, et al J. Mater. Chem. A (2015), 3, 19688–19695
[3] S. Dastidar et al Nano Lett. (2016), 16, 3563–3570
[4] P. Luo et al J. Phys. Chem. Lett. (2016), 7, 3603–3608
8:00 PM - ES01.10.58
Air-processed Highly Efficient Perovskite Solar Cells on Moisture Repelling Organic Interlayers
Yuanhang Cheng 1 2 , Ho-Wa LI 1 2 , Franky So 3 , Sai Wing Tsang 1 2
1 , City University of Hong Kong, Kowloon Hong Kong, 2 , City University of Hong Kong Shenzhen Research Institute, Shenzhen China, 3 Material Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractComparing with the conventional hydrophilic PEDOT:PSS hole transport materials (HTMs), the moisture repelling organic HTMs have great potential in enhancing the stability of air-processed perovskite solar cells (PVSCs) by opposing moisture ingress. To solve the intrinsic severe non-wetting issue of the organic HTMs, a facile ultraviolet-ozone (UVO) modification method is demonstrated to overcome this issue. When we applied the UVO method to the air-processed PVSCs, it is found that, besides the general wisdom of the effect of moisture, oxygen in air has severe impact on the quality of the solution-deposited perovskite films. Interestingly, different from moisture that induces fast crystallization of PbI2 upon deposition, oxygen exacerbates the wetting of the PbI2 solution on substrates. To weaken the impact of oxygen and moisture on the formation of PbI2, we preheat the substrate and PbI2 solution to build up a shield of organic vapor from the solvent during PbI2 film formation. Using this simple method, an air-processed PVSC made under a humid atmosphere of 70% RH has a record PCE of 18.11%. Our work not only reveals the origin of the detrimental effects on perovskite film formation in ambient air, but also provides a simple practical strategy to develop air-processed high-efficiency PVSCs for future commercialization.
Reference:
[1]Cheng et al., J. Power Sources, 2017, 360, 157-165.
[2]Cheng et al., Solar RRL, submitted.
8:00 PM - ES01.10.59
Pressure-Dependent Phase Transition and Bandgap Tuning of Methylammonium Lead Iodide Perovskite
Shaojie Jiang 1 , Fang Yanan 2 , Tim White 2 , Tom Baikie 2 , Jiye Fang 1
1 , SUNY-Binghamton, Binghamton, New York, United States, 2 , Nanyang Technological University, Singapore Singapore
Show AbstractWe report pressure-induced structural transitions and optical behavior of MAPbI3 (MA = methylammonium) determined using in-situ synchrotron X-ray diffraction and laser-excited photoluminescence (PL) spectroscopic methods. At ambient pressure, the existing phase is confirmed as I4/mcm tetragonal polymorph with octahedral tilting about c axis. Upon compression at 0.3 GPa, MAPbI3 transforms to Im-3 phase and maintains in this phase up to 2.3 GPa. The Im-3 phase corresponds to a ReO3-type cubic supercell with a doubled lattice parameter in regard to its ambient pressure analogue and octahedral tilt of equal magnitude about all three axes (Glazer notation a+a+a+). Further compression to 2.7 GPa leads to a conversion from the cubic polymorph to a putative orthorhombic phase, which is an Immm polymorph with a+b+c+ PbI6 tilting. Beyond 4.7 GPa it starts to lose long range order and becomes partially amorphous with no further change in X-ray scattering character up to 6.4 GPa. Upon decompression, the phase-mixed material goes through discrete restoration pathways towards the original tetragonal phase depending on the peak pressure. When using 6.4 GPa as the peak pressure, the partially amorphous phase restores Im-3 phase at 0.58 GPa and I4/mcm at 0.55 GPa, without an appearance of the putative Immm phase; whereas using 3.5 GPa as the peak pressure, the Immm structure is favored at 2.8 GPa and Im-3 polymorph is recovered at 0.9 GPa. In-situ pressure PL investigation demonstrates a progressive red shift of I4/mcm structure up to 0.3 GPa. With increasing PbI6 octahedral tilt angles, the transition to the Im-3 polymorph at 0.4 GPa and further compression to 1.95 GPa lead to a blue shift PL spectra, indicating an increase of the band gap from 1.64 eV to 1.69 eV. The PL signal weakens beyond 2.0 GPa and vanishes at 2.7 GPa with the transition from Im-3 phase to Immm phase.
8:00 PM - ES01.10.60
On the Reversibility of MAPI Solar Cell Parameters with Pressure
Mariana Bertoni 1 , David Fenning 2 , Maria Chan 3
1 , Arizona State University, Tempe, Arizona, United States, 2 , University of California, San Diego, La Jolla, California, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractIt is well known that the archetypal hybrid perovskite for solar cells, methylammonium lead iodide (MAPI), readily degrades in ambient atmosphere under standard operating conditions. Understanding the origin and effects of this degradation can pave the way to better engineer the solar devices and the perovskite material itself. Herein we present the effects of atmospheric pressure on the electrical performance of MAPI solar cells. Solar cell parameters, especially open circuit voltage, are significantly affected by the total ambient pressure and present an unexpected reversible behavior upon pressure cycling. We complement photoluminescence studies as a function of ambient atmosphere and temperature with first-principles DFT calculations. Photoluminescence measurements in varying relative humidity indicate a stark blueshift when water is present, indicating a change in the material that leads to a larger band gap. DFT calculations provide evidence that partial water hydration of the film is associated with an increase in band gap due to increased Pb-I bond distance. The calculations also demonstrate that water release at high vacuum is thermodynamically favorable. Our observations suggest that the solar cell parameter changes are due to changes in water partial pressure in the ambient and stress the importance of conducting and reporting ambient conditions when characterizing devices.
8:00 PM - ES01.10.61
Electron-Phonon Coupling in Lead-Free Tin-Triiodide Perovskites—Temperature Dependence of the Photoluminescence Spectrum
Taketo Handa 1 , Tomoko Aharen 1 , Atsushi Wakamiya 1 , Yoshihiko Kanemitsu 1
1 , Kyoto University, Uji Japan
Show AbstractLead-halide perovskites have attracted great interest due to their advanced features for solar cell applications, although the toxicity of lead is problematic for their widespread utilization. Accordingly, in recent years, tin-halide perovskites have been investigated actively to realize lead-free perovskite solar cells [1]. There has been great progress on the fabrication method of tin-halide perovskite films and devices [2], but fundamental optical properties of these materials remain still unclear. It is partly because these materials can be easily oxidized and tin-deficient perovskite [2], which might obscure the intrinsic material properties. Especially, the tin-halide perovskites usually exhibit very broad emission width, but the report on the spectral broadening mechanism, which is strongly related to the carrier-scattering process, is limited. For both fundamental physics and practical application viewpoints, it is required to clarify the origin of such a broad emission width. Here, we investigated the temperature-dependence of photoluminescence (PL) line width for CH3NH3SnI3 (MASnI3) high-quality thin films and discussed the effect of phonons and impurities on the carrier-scattering processes.
We prepared the MASnI3 thin films with and without 20 mol% SnF2 additive, which is well-known for suppressing the formation of tin vacancy and leading to better film quality [2]. The film with SnF2 showed PL peak at ~1.26 eV with full-width half-maximum of ~90 meV at room temperature, which is narrower than the film without SnF2 and previously reported values. It is considered due to the suppression of the inhomogeneous broadening by unintentionally doped impurities and/or defects. From the temperature-dependent PL, we found that the PL width shows superlinear dependence above the phase transition temperature of 110 K, which clearly indicates the longitudinal optical (LO) phonon scattering is the dominant broadening process in MASnI3 thin film with SnF2 near room temperature. This result is similar to the recent reports for the lead-triiodide perovskites [3]. Furthermore, we found that an abrupt change in the PL spectrum occurs below 110 K and its temperature dependence is quite different depending on the existence of SnF2 additive; the film with SnF2 showed PL spectra consisting of two different peaks, while the film without SnF2 exhibited only one broader emission peak. The observed difference in PL properties between the samples with and without SnF2 is discussed considering the different doped hole concentration.
Part of this work was supported by JST-CREST (JPMJCR16N3) and JSPS (17J09650).
References
[1] F. Hao et al., Nat. Photon. 8, 489 (2014).
[2] M. Kumar et al., Adv. Mater. 26, 7122 (2014); W. Liao et al., Adv. Mater. 28, 9333 (2016).
[3] L. Phuong et al., J. Phys. Chem. Lett. 7, 4905 (2016); S. Singh et al., J. Phys. Chem. Lett. 7, 3014 (2016).
8:00 PM - ES01.10.62
Stable and Size-Controllable Organometal Trihalide Perovskite Nanocrystals/Polymer Film
Wonhee Cha 2 , Hae-Jin Kim 3 , Jiwon Kim 1
2 Department of Chemistry, Yonsei University, Seoul Korea (the Republic of), 3 Department of Mechanical Engineering, University of Houston, Houston, Texas, United States, 1 School of Integrated Technology, Yonsei University, Incheon Korea (the Republic of)
Show AbstractOrganometal trihalide perovskite (OTP) materials have recently attracted much attention mainly due to their rapid advances in power conversion efficiencies (PCEs) for solar cells. OTP materials can also be used in light emitting diodes (LEDs) because of their superior optical properties and ease of fabrication. Focus has now been directed to the fabrication of perovskites as nanocrystals (NCs) in order to enhance their photoluminescence quantum yields (PLQYs) since the confinement effect in NCs promotes radiative recombination. Although previous studies have demonstrated PLQYs for MAPbBr3 NCs as high as 93%, its stability was limited to about one month. Also, a precise control of the perovskite NCs’ size is quite challenging.
In this work, we introduce the preparation of OTP-NCs/PDMS films using a polymer with precise control of NC’s size, high stability, and maintaining their photophysical properties. The OTP (MAPbX3, X= Cl, Br, and I)-NCs/PDMS films were prepared by using porous PDMS (p-PDMS) as a template for perovskite NCs’ growth. In this method, a film comprising gold nanoparticles (AuNPs) and PDMS was prepared at first by blending AuNPs with the PDMS polymer. Then, the AuNPs in the composite film are selectively etched by aqua regia, leaving the p-PDMS template for perovskite NCs’ growth. Then, the p-PDMS template was immersed in the perovskite precursor solution (1.0 M). To demonstrate the size control of MAPbBr3 NCs within the OTP-NCs/PDMS film, three sizes of AuNPs were synthesized. As the smaller the AuNPs used, the greater the blue shift of absorption and PL peak of MAPbBr3 NCs/PDMS film were observed. These indicate that smaller perovskite NCs were synthesized when the smaller AuNPs were used. The PL peaks are also quite narrow, with full width at half maximum (FWHM) values of about 20 nm, indicating that the sizes of OTP-NCs within the films are very uniform. The MAPbBr3 NCs/PDMS films showed PLQYs of about 10% at maximum, compared to the bulk film showing PLQY of about 2%. Using crystallographic analysis, X-ray diffraction peaks from the MAPbBr3 NCs/PDMS film at 15.0° and 21.3° which can be indexed to the (100) and (110). These correspond to the cubic structure of MAPbBr3 perovskite materials. To note, we have observed the crystalline structure and PLQYs of MAPbBr3 NCs/PDMS films remained almost the same even after several months which proves our film is stable over time.
In sum, we have successfully synthesized OHP-NCs/PDMS films using p-PDMS as a template. By this template-based method, we can not only precisely control the size of NCs without any capping ligands, but also enhance the stability of perovskite materials by blocking contact with the ambient environment. Furthermore, we are currently working on to utilize conducting polymer instead of PDMS which will further broaden the range of applications.
8:00 PM - ES01.10.63
Morphological Control of Gravure Printed Perovskite Films
Matt McPhail 1 , Vivek Subramanian 1
1 Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, California, United States
Show AbstractPerovskite materials show tremendous promise as a third-generation solar material, owing to their long carrier lifetimes, high absorption coefficient, and their ability to be solution processed. For perovskite materials to transition from the lab to commercial scale, an industrially viable method of processing needs to be shown. The processing of perovskites has been previously explored via spin coating, blade coating, spray casting, slot-die coating, and thermal evaporation- none of which offer high speed, large area, low energy processing and patterning capabilities. Gravure printing offers extremely high processing speeds (>1 m/s), low energy requirements, and is fully compatible with other roll-to-roll techniques. In this work, we explore the key factors to controlling the thickness and roughness of gravure printed active layers in a perovskite solar cell.
Gravure printing of perovskite active layers presents several challenges; namely ink design and the control of printing induced non-idealities, such as the need for film leveling and the reduction of surface roughness of the printed layer. The choice of solvent, concentration, and roller pattern depth are shown to be key factors in producing leveled films with uniform thickness. The effect of solvent choice and solvent annealing on the roughness of the film is also explored. The grain morphology is found to be strongly dependent on the ink solvent, with the use of higher boiling point solvents leading to larger but rougher grains. Solvent annealing is found to be essential to lower the roughness of the perovskite films. Using gravure printed active layers, we have reached 3.5% PCE. This work marks a key step towards high speed and low cost fabrication of perovskite solar cells.
8:00 PM - ES01.10.64
Composition Dependence of Trion Recombination Dynamics in CsPb(Br1-xIx)3 Nanocrystals
Satoshi Nakahara 1 , Hirokazu Tahara 1 , Go Yumoto 1 , Tokuhisa Kawawaki 1 , Masaki Saruyama 1 , Ryota Sato 1 , Toshiharu Teranishi 1 , Yoshihiko Kanemitsu 1
1 , Kyoto University, Uji Japan
Show AbstractAll-inorganic cesium lead halide perovskite nanocrystals (NCs) have attracted great attentions for application in low-cost and high-performance optoelectronic devices owing to their high luminescence efficiencies [1]. Our previous studies have reported that trions in these NCs cause the nonradiative recombination and blinking phenomenon, leading to the reduction in luminescence yield of NCs [2]. However, the generation and relaxation processes of trions in perovskite NCs have not fully been clarified yet. The understanding and control of the trion-generation is of great importance for further improvement of the luminescence efficiency in the application to light-emitting diodes and lasers. Since trions are a charged state of excitons, it is expected that the iconicity and band-gap energies of perovskite halides should influence on the trion-creating process. Therefore, in this work, to clarify the impact of halide substitution on the trion-generation and relaxation dynamics, we performed time-resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopies on CsPbX3 (X = Br, I) NCs dispersed in hexane at room temperature.
The CsPbX3 NCs used in this experiment were synthesized from parent CsPbBr3 NCs by halide exchange. We analyzed the excitation-power dependent TRPL and TA results on the basis of the absorption photon number, which allowed us to extract the exciton, trion, and biexciton components. In low-excitation conditions, the exciton-generation process was dominant, while in high-excitation regime the trion- and biexciton- generation processes were comparable. The lifetimes of excitons, trions, and biexcitons were obtained to be a few ns, hundred ps, and ten ps, respectively, meaning that these lifetimes are not sensitive to the halide composition. In contrast, the generation efficiencies of excitons, trions, and biexcitons are strongly related to the halide composition. From the excitation-power dependence of the TRPL and TA signals, we discuss the composition dependence of the generation and recombination dynamics of exciton complexes.
Part of this work was supported by JST-CREST (JPMJCR16N3).
[1] L. Protesescu et al., Nano Lett., 2015, 15, 3692.
[2] N. Yarita et al., J. Phys. Chem. Lett., 2017, 8, 1413.
8:00 PM - ES01.10.65
Efficient Search Methods for Perovskite Compositions
Paulette Clancy 2 , Peter Frazier 2 , Henry Herbol 2 , Weici Hu 2 , Matthias Poloczek 1
2 , Cornell University, Ithaca, New York, United States, 1 , University of Arizona, Tuscon, Arizona, United States
Show AbstractWhen optimizing functional materials, the sheer number of combinations that we may choose from rules out exhaustive search and often prevents us from obtaining an optimal solution in practice. To tame the complexity, we employ ideas from machine learning.
In this talk, we will propose an efficient search method. It is based on a novel Bayesian statistical model that is tailored for combinatorial search spaces, as they often arise in materials informatics.
To demonstrate the value of this approach, we implement it to search for a perovskite composition with maximum solvent binding energy, computed via ab initio calculations. Here a composition is determined by a combination of three halides (X) and one out of three cations (A), comprising our perovskite monomer (PbX3A), and one out of eight solvents. Our approach correctly identifies the overall best composition after a small number of probes.
We present extensions of our method that allow us to exploit the exploitation of low fidelity estimates of the maximum binding energy and how to leverage the ability of taking several probes simultaneously.
8:00 PM - ES01.10.66
The Quantum-Confined Stark Effect in Layered Hybrid Perovskites
Grant Walters 1 , Mingyang Wei 1 , Oleksandr Voznyy 1 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada
Show AbstractThe quantum-confined Stark effect is an efficient optical modulation mechanism. However, the best-performing modulators rely on multiple quantum well structures made from compound semiconductors that require costly epitaxial growth incompatible with silicon photonics and electronics. Layered hybrid perovskites, recently attracting attention as top-performing light-emitting materials, offer self-assembled and solution-processed quantum well structures. Here, we report large modulation amplitudes for the QCSE in layered hybrid perovskites and anomalous behavior associated with the orientational polarizability of dipolar cations. The extraordinary oscillator strengths and exciton binding energies for these materials lead to absorption coefficient modulation amplitudes of 70 cm-1 for 10 kV/cm electric fields. These are the largest amplitudes amongst solution-processed materials at room temperature. They can further be realized as either red or blue-shifts, adding flexibility to modulator design. When methylammonium cations are incorporated into the perovskite layers, we observe anomalous blue-shifts of the exciton resonances in electroabsorption spectra. This contrasts cesium-incorporated perovskites that exhibit typical red-shifts. Through density functional theory calculations we show that an extraordinary decrease in the exciton binding energy occurs as a result of the orientational response of the methylammonium cations. This decrease accounts for the energetic changes necessary to effectuate a blue-shift. The orientational polarizability of the confined dipoles represents a new modulation mechanism that can be realized in solution-processed materials.
8:00 PM - ES01.10.67
Hot Exciton Luminescence from CsPbI3 Nanocrystals
Go Yumoto 1 , Hirokazu Tahara 1 , Tokuhisa Kawawaki 1 , Masaki Saruyama 1 , Ryota Sato 1 , Toshiharu Teranishi 1 , Yoshihiko Kanemitsu 1
1 , Institute for Chemical Research, Kyoto University, Kyoto Japan
Show AbstractSlowing down hot carrier cooling is key to realizing hot-carrier solar cells with high conversion efficiencies beyond the Shockley-Queisser limit [1]. The retardation of hot carrier relaxation has been observed in thin films of organic-inorganic hybrid lead halide perovskites due to hot phonon bottleneck effect [2]. In nanocrystals, quantized electronic states are formed, and the mismatch between the phonon energies and the energy separation of the quantized states appears. Such a phonon bottleneck effect might cause the slow energy relaxation. Recently, in methylammonium lead tribromide perovskite nanocrystals, the hot carrier cooling has found to be two orders of magnitude slower than their bulk-film counterparts [3]. In contrast to such intensive studies in organic-inorganic hybrid perovskites, less is known about the confinement effect on the hot carrier dynamics in their all-inorganic versions, cesium lead halide perovskites. To elucidate how the confinement effect modifies hot carrier dynamics in cesium lead halide perovskites, we investigated optical responses of hot carriers in cesium lead triiodide (CsPbI3) nanocrystals.
We performed transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopy on CsPbI3 nanocrystals in hexane at room temperature. In TA experiments with 350-nm-wavelength pump pulses, we observed an absorption bleaching signal around the band edge of CsPbI3 nanocrystals. From the time evolution of high energy tail of the bleaching signal as a function of pump-probe delay time, we observed hot carrier relaxation and estimated its decay time to be ~20 ps. The TRPL measurements also revealed the PL emission from the hot carriers at 350-nm-wavelength-excitation. The PL intensity spectra exhibit hot PL emission with decay time of ~20 ps, which agrees well with the value estimated by TA signals. In addition to the near-band-edge hot PL, we observed PL emission from a higher energy state. In this talk, we will discuss the detail of the hot PL from CsPbI3 nanocrystals.
Part of this work was supported by JST-CREST (JPMJCR16N3).
[1] R. T. Ross et al., J. Appl. Phys. 53, 3813 (1982).
[2] Y. Yang et al., Nat. Photonics 10, 53 (2016).
[3] M. Li et al., Nat. Commun. 8, 14350 (2017).
8:00 PM - ES01.10.68
Scanning Force Microscopy on Perovskites
Ilka Hermes 1 , Victor Bergmann 1 , Dan Li 1 , Ruediger Berger 1 , Stefan Weber 1 2
1 , Max-Planck-Inst, Mainz Germany, 2 Department of Physics, Johannes Gutenberg University, Mainz Germany
Show AbstractScanning force microscopy (SFM) is a versatile tool for studying nano- and sub-nanoscale surface structures. Using advanced SFM methods, morphological features can be correlated with a vast number of material properties, such as mechanical or electrical properties. This information is of particular interest in the field of novel photovoltaic materials such as perovskites, where the nanoscale structure of the materials has a huge impact on the device performance. Additional to topographic information, electrical SFM methods can map various surface properties on a nanometer length scale. The accessible surface properties include electric potential, electric fields and charge carrier distribution by Kelvin probe force microscopy, (KPFM) or electromechanical coupling in piezoresponse force microscopy (PFM). Additionally, our newly developed time resolved KPFM can map charge carrier dynamics caused by migrating ions with a temporal resolution of 500 µs.
This poster provides an overview on our activities in studying the electrical properties of perovskite films and solar cells. We used KPFM to map the potential distribution on cross sections of perovskite solar cell devices in dark and under illumination, revealing distinct differences in the charging dynamics at different interfaces [1,2]. With PFM on micron-sized perovskite grains we observed a periodically alternating structure reminiscent of ferroelastic domain patterns [3]. Using a SFM under controlled humidity, the effects of reversible hydration in perovskite films on the morphology were studied [4]. Such experiments provide valuable information for the optimization of the light harvesting abilities in these materials and the fabrication processes.
[1] Nat. Commun. 2014, 5, 5001. [2] ACS Appl. Mater. Interfaces, 2016, 8 (30), 19402. [3] J. Phys. Chem. C (2016), 120, 5724. [4] J. Phys. Chem. C, 2016, 120 (12), 6363.
8:00 PM - ES01.10.69
Environment vs Sustainable Energy? The Case of Lead Halide Perovskitebased Solar Cells
Aslihan Babayigit 1 , Hans-Gerd Boyen 1 , Bert Conings 1
1 Institute for Materials Research, Hasselt University, Diepenbeek Belgium
Show AbstractLead halide perovskites have caused a paradigm shift in state-of-the-art photovoltaic technology half a decade ago, and have gained tremendous momentum ever since. Given their seemingly imminent commercialization, rigorous scrutiny regarding their potential environmental hazard is without doubt becoming increasingly relevant. In light of the current need for sustainable energy resources, several start-up and spin-off companies have been established, already promising modules on the market by the end of 2017.1 On the down side, Lead (Pb) representing approximately one third by weight of the absorber layer in such photovoltaic devices is enough reason to become wary about the potential environmental impact of their large-scale implementation.2 Whilst many have wondered were the acceptable boundaries lie regarding Pb consumption, it remains a focal point in many discussions, as it seems almost unattainable to ban Pb usage from our society. Currently enlisted as one of the 10 chemicals of major health concerns by the World Health Organisation, the magnitude of misgivings expands even more as recent works also demonstrate promising application of Pb halide perovskites in light emitting diodes, lasers and photodetectors. Hence, there is no doubt that a discussion should be commenced on how to assess and handle the impact of Pb content in a new technology of such high potential.
By reflecting on historical experiences obtained from anthropogenic Pb poisoning and consumption, this work investigates and carefully scrutinises the protection offered by current legislation for the exploitation of Pb halide perovskites in opto-electronic applications. We discuss the European “Restriction of Hazardous Substances” directive (RoSH) (2002/95/EC) that based on heath and environmental criteria on the one hand allows up to only 1 ‰ Pb per weight in homogenous materials while on the other hand it legally permits the use of unlimited amounts of Pb in photovoltaic panels. Apropos, we also focus on other worldwide directives and point out relevant considerations and ambiguity in these regulations. We will address “if” and “how” the recent and unprecedented Pb halide perovskites can enter the consumer market.
[1] (2013). Oxford Photovoltaics (2013) "Oxford PV reveals breakthrough in efficiency of new class of solar cell" (12/07/2017), from https://http://www.oxfordpv.com/News/20130610-Oxford-PV-reveals-breakthrough-in-efficiency-of-new-class-of-solar-cell.
[2] Babayigit, A., A. Ethirajan, M. Muller and B. Conings Nature Materials (2016), 15(3): 247-251.
Symposium Organizers
Yabing Qi, Okinawa Institute of Science and Technology Graduate University
Jinsong Huang, University of North Carolina-Chapel Hill
Annamaria Petrozza, Istituto Italiano di Tecnologia
Huanping Zhou, Peking University
Symposium Support
Applied Physics Letters | AIP Publishing
Nature Energy | Springer Nature
Science | AAAS
Sustainable Energy &
Fuels | The Royal Society of Chemistry
ES01.11: Interface, Passivation and Device Engineering
Session Chairs
Yongbo Yuan
Huanping Zhou
Thursday AM, November 30, 2017
Hynes, Level 3, Ballroom B
8:00 AM - ES01.11.01
Active Materials and Interfaces for Stable Perovskite Solar Cells
Antonio Abate 1
1 , Helmholtz-Zentrum Berlin, Berlin Germany
Show AbstractOrganic-inorganic perovskites are quickly overrunning research activities in new materials for cost-effective and high-efficiency photovoltaic technologies. Since the first demonstration from Kojima and co-workers in 2009, several perovskite-based solar cells have been reported and certified with rapidly improving power conversion efficiency. Recent reports demonstrate that perovskites can compete with the most efficient inorganic materials, while they still allow processing from solution as a potential advantage to deliver a cost-effective solar technology.
Compare to the impressive progress in power conversion efficiency, stability studies are rather poor and often controversial. An intrinsic complication comes from the fact that the stability of perovskite solar cells is strongly affected by any small difference in the device architecture, preparation procedure, materials composition and testing procedure.
In the present talk, we will focus on the stability of perovskite solar cells in working condition. We will discuss a measuring protocol to extract reliable and reproducible ageing data. We will present new materials and preparation procedures which improve the device lifetime without giving up on high power conversion efficiency.
8:15 AM - ES01.11.02
Passivation Routes toward Eliminating Non-Radiative Losses and Ion Migration in Metal Halide Perovskites
Mojtaba Abdi-Jalebi 1 , Zahra Andaji-Garmaroudi 1 , Stefania Cacovich 2 , Camille Stavrakas 1 , Eline Hutter 3 , Tom Savenije 3 , Giorgio Divitini 2 , Richard Friend 1 , Samuel Stranks 1
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 Department of Materials, University of Cambridge, Cambridge United Kingdom, 3 Optoelectronic Materials Section, Delft TU, Delft Netherlands
Show AbstractMetal halide perovskites are generating enormous interest for their use in solar photovoltaic and light-emission applications. One property linking the high performance of these devices is a high radiative efficiency of the materials; indeed, a prerequisite for these devices to reach their theoretical efficiency limits is the elimination of all non-radiative decay. However, there still exists substantial parasitic non-radiative losses and ionic migration in the materials, both of which lead to performance limitations and instabilities.
Here, we will detail several new and promising passivation approaches through additives aimed at eliminating these problematic processes in triple cation (MA,FA,Cs)Pb(I0.8Br0.2)3 thin films. We find internal photoluminescence quantum efficiencies over 90% along with the removal of transient photo-induced ion migration processes. We use time-resolved microwave conductivity measurements to reveal mobilities exceeding 40 cm2/V/s. STEM-EDX measurements on film cross-sections reveal that the passivation treatments facilitate the presence of minimal halide vacancies (defects) by acting as a source of excess halide while also immobilizing the surplus halides into benign chemical products.
Our work reveals promising approaches to fabricate metal halide thin films with the highest optoelectronic quality. The work also provides further evidence that non-radiative decay and ionic motion are intimately related, generalizing the conjecture that there are common solutions to both problems.
8:30 AM - *ES01.11.03
Impacts of Interfacial and Interstitial Engineering in Perovskite Solar Cells
Nam-Gyu Park 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractSince the first report on solid-state perovskite solar cell with power conversion efficiency (PCE) of 9.7% in 2012 reported by Park et al, perovskite solar cell related publications increase exponentially. As a result, more than 2,000 peer-reviewed research papers were published in 2016. Technologically, PCE was improved in a very short period and reached over 22%, indicating that organic-inorganic halide perovskite is very promising photovoltaic material. Nevertheless, hysteresis and stability are critical issues to be solved. In this talk, methodologies to eliminate hysteresis and/or improve stability will be introduced based on interfacial and interstitial nanoengineering. We developed a universal method to get rid of I-V hysteresis, where a severe current-voltage hysteresis observed usually in normal structure with TiO2 electron transporting layer was completely removed by interstitial doping to MAPbI3, FAPbI3 and mixed cation-anion perovskites. Interfacial nanoenginnering was found to be effective method to improve stability and reduce hysteresis as well. Manipulation of grain boundary of 3D perovskite with 2D perovskite led to significant increase in stability along with substantial reduction in hysteresis. In addition, insertion of 2D layer in HTL/perovskite interface using molecular engineering process resulted in simultaneous improvement of stability and reduction of hysteresis. Besides perovskite material engineering, interfacial and interstitial engineering is suggested here to be equally or even more important.
9:00 AM - *ES01.11.04
Light Engineering of Perovskite Solar Cells
Liguo Gao 2 , Chu Zhang 2 , Zhanglin Guo 2 , Tingli Ma 1 2
2 Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Fukuoka Japan, 1 School of Petroleum and Chemical Engineering, Dalian University of Technology, Panjin China
Show AbstractPerovskite solar cells (PSCs) have attracted much attention due to their high-energy conversion efficiency and low production cost. Our group focuses on the studies on development of new materials for compact layer, active layer, hole transfer layer, as well as back electrodes.
Recently, we tried to do the light engineering of PSCs to improve the PCE. We designed and fabricated a bifacial transparent perovskite solar cell (BTPSC) in order to harvest more solar energy. We found that the light engineering can improve the performance of devices. It is observed that the reflecting-light intensity and illumination angle are the key factors to affect the PCEs of BTPSCs.
In addition, an integrative electrode of compact layer and mesoporous layer has been in situ fabricated on Ti subtract. The integrative electrode showed high conductivity and good stability. High PCEs for PSCs based on Ti electrodes have been achieved due to the light engineering of the back electrodes.
References:
[1] J. T.-W. Wang, J. M. Ball, E. M. Barea, A. Abate, J. A. Alexander-Webber, J. Huang, M. Saliba, I. Mora-Sero, J. Bisquert, H. J. Snaith, R. J. Nicholas, Nano Lett. 2014, 14, 724.
[2] K. Wang, Y. Shi, Y. Li, S. Wang, X. Yu, M. Wu, T. Ma, Adv. Mater 2016. 28, 1891–1897
9:30 AM - ES01.11.05
Investigation of Atomic Structures and Electronic Properties of Mixed Perovskites MAPb(Br)x(Cl)y(I)z, by Scanning Tunneling Microscopy and Photoelectron Spectroscopy
Jeremy Hieulle 1 , Xiaoming Wang 2 , Collin Stecker 1 , Robin Ohmann 1 , Luis Ono 1 , Yanfa Yan 2 , Yabing Qi 1
1 Energy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology Graduate University (OIST), Okinawa Japan, 2 Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, University of Toledo, Toledo, Ohio, United States
Show AbstractOrganic-inorganic perovskite solar cells are currently under the spotlight. But the commercialization is hampered by drawbacks such as device degradation and hysteresis effects. Atomic-scale effects for example doping, defect sites, ion migration and the mixing of different-halide are under intensive investigation. The use of mixed perovskites has recently demonstrated to be a promising strategy to further increase the device performance and stability. [1-4] However, a fundamental understanding remains largely elusive regarding the correlation between the structure of the mixed-perovskites and their electronic properties at the atomic level.
In this work, we show the first low-temperature scanning tunneling microscopy (STM) study of mixed-halide perovskite (CH3NH3Pb(Br)x(Cl)y(I)z). Topographic images reveal the atomic-structure of the perovskite surface. By combining STM imaging and density functional theory (DFT), we are able to determine the energetically favorable configuration of Cl and I ions in perovskite. In addition, we perform photoelectron spectroscopy (PES) to correlate the atomic arrangement of the mixed-halide perovskites with their electronic properties. Understanding how halide substitution affects electronic properties of perovskite provides valuable insight for the design of future photovoltaic devices.
References:
[1] Bischak, C. G.; Hetherington, C. L.; Wu, H.; Aloni, S.; Ogletree, D. F.; Limmer, D. T.; Ginsberg, N. S., Origin of Reversible Photoinduced Phase Separation in Hybrid Perovskites. Nano Letters 2017, 17 (2), 1028-1033.
[2] Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I., Chemical Management for Colorful, Efficient, and Stable Inorganic–Organic Hybrid Nanostructured Solar Cells. Nano Letters 2013, 13 (4), 1764-1769.
[3] Sadhanala, A.; Ahmad, S.; Zhao, B.; Giesbrecht, N.; Pearce, P. M.; Deschler, F.; Hoye, R. L. Z.; Gödel, K. C.; Bein, T.; Docampo, P.; Dutton, S. E.; De Volder, M. F. L.; Friend, R. H., Blue-Green Color Tunable Solution Processable Organolead Chloride–Bromide Mixed Halide Perovskites for Optoelectronic Applications. Nano Letters 2015, 15 (9), 6095-6101.
[4] National Renewable Energy Laboratory (NREL). http://www.nrel.gov/ncpv/images/efficiency_chart.jpg.
10:15 AM - *ES01.11.06
SnPb Mixed Metal Perovskite Solar Cell with Low Voc Loss and 16% Efficiency
Yuhei Ogomi 1 , Qing Shen 2 , Taro Toyoda 2 , Kenji Yoshino 3 , Takashi Minemoto 4 , Shuzi Hayase 1
1 , Kyushu National Institute of Technology, Kitakyushu Japan, 2 , The University of Electrocommunication, Tokyo Japan, 3 , Miyazaki University, Miyazaki Japan, 4 , Ritumeikan University, Shiga Japan
Show AbstractWe have already reported that the interface between TiO2 / perovskite (MAPbI3: Pb-PVK) are composed of Ti-O-Pb linkages which passivates the hetero-interface traps acting as charge recombination centers (1-5). In addition, passivation of other hereto-interface (Pb-PVK/SPIRO(p-semiconductor)) was also effective. We have proved that insertion of thin passivation layer (Trifluoro,ammonium propane cation: (F1)) increased the efficiency of the Pb-PVK solar cells (6). These results were applied for enhancing the efficiency of SnPb mixed metal perovskite solar cells. The SnPb PVK has a potential to possess ideal band gap (about 1.4eV), which is better than that of MAPbI3 (around 1.55eV) (1). We focused on the Voc loss for the evaluation of these hetero-interfaces. In the composition of TCO/c-TiO2/mp-TiO2/SnPb-PVK/SPIRO/Au (A), the Voc loss was about 0.9eV, which is larger than that of conventional MAPbI3 (0.4 eV). We found that Ti-O-Sn linkages are present at the hetero-interface between TiO2 and SnPb PVK and create new traps (charge recombination center). In order to remove the hetero-interface, inversion structure (TCO/PEDOT-PSS/SnPb-PVK/C60/Au)(B) was made. The Voc loss for (B) decreased to 0.5 eV which was lower than 0.9 eV for the common structure (A). In addition, the insertion of F1 was also effective for enhancing the efficiency. Finally, the Voc loss decreased to 0.45 eV and 16% efficiency was obtained. It was proved that hetero-interface for SnPb mixed metal PVK is much more serious than that for Pb-PVK solar cells.
1. Y. Ogomi, et al., J. Phys. Chem. Lett. 2014, 5, 1004-1011; 2. S. Nakabayashi, et al., J. Photonics for Energy; 2015, 5, 057410; 3. Y. Ogomi, et al., J. Phys. Chem. C, 2014, 118, 16651-16659; 4. Q. Shen, et al., Phys. Chem. Chem. Phys. 2014, 19984-19992; 5. Y. Ogomi, et al., Chem. Phys. Chem. 2014, 15, 1062-1069; 6. H. Moriya, et al., ChemSusChem., 2016, 9, 2634-2639.
10:45 AM - *ES01.11.07
Nature of Structural Fluctuations and Photophysics of Lead Halide Perovskites
Andrew Rappe 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractThe lead halide perovskites have recently attracted much attention because of their large and growing photovoltaic power conversion efficiencies. However, questions remain regarding the temporal and spatial correlations of the structural fluctuations, and how they affect electronic and photovoltaic properties. To address these questions, we apply the tools of molecular dynamics, density functional theory, and multiscale modelling. We report on the discovery of local polar fluctuations in CsPbBr3 and MAPbBr3, involving the head-to-head motion of A-site Cs/MA cations. These findings show that structural fluctuations in lead-halide perovskites are more general than rotation of polar organic cations. Furthermore, we show that the cubic-tetragonal phase transition is driven by effective interactions between organic cations beyond the dipole-dipole level, explaining the critical exponents of this phase transition and its proximity to a tricritical transition.
We describe how these structural properties are manifested in the photophysics of the lead halide perovskites. After photo-excitation, the evolution of pair distribution functions indicates an activation of preferential sublattice motions over fully thermal motions, as supported by our molecular dynamics simulations and ultrafast electron diffraction experiments. Following our initial proposal of the dynamical Rashba effect as a mechanism for increasing carrier lifetimes, we have discovered new manifestations of the Rashba effect in experiments. These include a splitting of exciton peaks at low magnetic fields, and the anisotropic relaxation of carriers at picosecond time scales. Finally, we discuss how the bulk photovoltaic effect can be sharply enhanced by inducing a topological phase transition of CsPbI3 under pressure.
11:15 AM - ES01.11.08
Interface Defects in Organic Inorganic Lead Halide Perovskites Solar Cells
Philip Schulz 1 , Joseph Berry 1
1 , National Renewable Energy Laboratory, Lakewood, Colorado, United States
Show AbstractFor hybrid organic/inorganic perovskite solar cells the role of interfaces between perovskite absorber and adjacent charge transport layers has been singled out as a primary factor for the optoelectronic performance of the photovoltaic stack. For example, we reported that the type and doping characteristic of the underlying oxide substrate and the respective energetic alignment at the interface influence the Fermi level position in the perovskite thin-film on top [1].
While the alignment of the electronic energy levels remains a key figure, our results indicate that the device performance is dominated by defect formation and band bending at the interface. Here, we use photoemission spectroscopy to determine electronic and chemical changes at the interface between oxide charge extraction layers deposited on top of methylammonium lead iodide (MAPbI3) perovskite films. These results are linked to the performance characteristics for respective solar cell geometries. In one case, we find that the direct contact between a high work function MoO3 charge extraction layer and MAPbI3 leads to a chemical reaction and band bending in the perovskite absorber diminishing device functionality. Introducing an ultrathin spiro-MeOTAD buffer layer prevents the reaction, yet the band bending remains and leads to a decrease in device performance [2].
In our recent work we investigate the impact of a broad range of transparent conductive oxides from n-type TiO2 to p-type NiO from pulsed laser deposition and atomic layer deposition techniques on top of a set of different perovskite absorber layers. Our findings show that the formation of a specific defect at the interface leads to poor charge transfer from absorber film to transport layer and eventually results in critical device failure. However, we demonstrate that adjustments in the processing methods of the interlayers can prevent this detrimental behavior and lead up to new device layouts with oxide interlayer integration.
[1] Schulz P.; Whittaker-Brooks L. L.; MacLeod B. A.; Olson D. C.; Loo Y.-L.; Kahn A. Adv. Mater. Interfaces 2015, 2, 1400532
[2] Schulz P.; Tiepelt J.O.; Christians J. A,; Levine I.; Edri E.; Sanehira E. M.; Hodes G.; Cahen D.; Kahn A. ACS Appl. Mater. & Interfaces 2016, 8, 31491-31499
11:30 AM - ES01.11.09
Engineering Interface Structure to Improve Efficiency and Stability of Perovskite Solar Cells
Longbin Qiu 1 , Luis Ono 1 , Yan Jiang 1 , Matthew Leyden 1 , Sonia Raga 1 , Shenghao Wang 1 , Yabing Qi 1
1 , Okinawa Institute of Science and Technology Graduate University, Okinawa Japan
Show AbstractThe rapid rise of power conversion efficiency of low cost perovskite solar cells suggests that these cells are a promising alternative to conventional photovoltaic technology. However, anomalous hysteresis and unsatisfactory stability hinder the industrialization of perovskite solar cells [1-2]. Interface engineering is of importance for the fabrication of highly stable and hysteresis free perovskite solar cells [3-5]. Here we report that a surface modification of the widely used TiO2 compact layer can give insight into interface interaction in perovskite solar cells [6]. In this work, we propose to coat the TiO2 surface with an interfacial layer to prevent the direct contact between TiO2 and CH3NH3PbI3 [6]. This strategy indeed leads to significantly improved stability of our devices.
[1] L.K. Ono, S.R. Raga, S. Wang, Y. Kato, Y.B. Qi*, J. Mater. Chem. A 3 (2015) 9074.
[2] S. Wang, Y. Jiang, E.J. Juarez-Perez, L.K. Ono, Y.B. Qi*, Nat. Energy 2 (2016) 16195.
[3] Z. Hawash, L.K. Ono, S.R. Raga, M.V. Lee, Y.B. Qi*, Chem. Mater. 27 (2015) 562.
[4] L.K. Ono, S.R. Raga, M. Remeika, A.J. Winchester, A. Gabe, Y.B. Qi*, J. Mater. Chem. A 3 (2015) 15451.
[5] M.C. Jung, S.R. Raga, L.K. Ono, Y.B. Qi*, Sci. Rep. 5 (2015) 9863.
[6] L. Qiu, L.K. Ono, Y. Jiang, M.R. Leyden, S.R. Raga, S. Wang, Y.B. Qi*, J. Phys. Chem. B (2017) DOI: 10.1021/acs.jpcb.7b03921.
11:45 AM - ES01.11.10
Photo-Induced Structural Dynamics in Lead-Halide Perovskites—Creation and Passivation of Defects
Silvia Motti 1 2 , Marina Gandini 1 , Alex Barker 1 , James Ball 1 , Ajay Kandada 1 , Annamaria Petrozza 1
1 , Istituto Italiano di Tecnologia, Milan Italy, 2 , Politecnico di Milano, Milan Italy
Show AbstractThe recombination dynamics and photoluminescence (PL) efficiencies of lead halide perovskites are strongly affected by a high defect density, inevitable in solution processed materials. Moreover, the photophysical properties of these materials have been known to display atmosphere sensitivity and instabilities still not completely understood. We combine steady state and time resolved PL and transient absorption measurements to investigate the underlying mechanism of such instabilities, which comprise distinct competing mechanisms.
Under illumination in inert environment we observe two opposite processes: The photoinduced generation of defects, resulting in quenching of PL, and also a competing self-healing of trap states, which has a positive contribution to PL efficiency. When the sample is exposed to oxygen, on the other hand, we observe an additional process that results in decrease of trap density, suggesting defect passivation. A series of experimental parameters influence these processes and determine the resulting effect observed as decrease or increase of PL quantum yields and transformation of the recombination dynamics. It was also observed for the first time a broad sub band gap PL at room temperature, originating from long lived trap states. The processes reported were observed on lead halide perovskites of different chemical compositions and morphologies, revealing intrinsic instabilities of great relevance for optoelectronic device application. By analyzing the factors that influence the dynamics of photo-induced trap formation and passivation and the interplay of defect population and band-to-band carrier recombination, we propose possible mechanisms for such processes and possible methods to overcome its detrimental effects and improve device performance and stability.
ES01.12: Synthesis, Large Area, In Situ Monitoring, Interface Engineering and Preferred Crystal Orientation
Session Chairs
Thursday PM, November 30, 2017
Hynes, Level 3, Ballroom B
1:30 PM - *ES01.12.01
Enabling High Stability in Perovskite Solar Cells
Henry Snaith 1
1 Department of Physics, Clarendon Laboratory, University of Oxford, Oxford United Kingdom
Show AbstractSince the outset, perovskite solar cells have demonstrated high efficiency, and an obvious clear path to increase this efficiency towards the very highest levels exists. However, a key concern and a key question remains around long term operational stability: For useful solar power generation, perovskite modules must be able to last for at least 25 years operation outdoors. In this talk I will present our work on increasing the stability of perovskite absorber layers and solar cells under external stressing, and identify the basic mechanisms and influencing factors driving (in)stability. Our progress indicates a promising future for the long term operational stability of perovskite solar modules.
2:00 PM - ES01.12.02
Polymer-Templated Nucleation and Crystal Growth of Perovskite Films for Solar Cells with Efficiency Greater Than 21%
Dongqin Bi 1
1 , EPFL, Lausanne Switzerland
Show Abstract
The past several years have witnessed the rapid emergence of a new class of solar cells based on mixed organic-inorganic halide perovskites. Today’s state of the art pervoskite solar cells (PSCs) cells employ various methods to enhance nucleation and improve the smoothness of the perovskite films formed via solution processing. However, the lack of precise control over the crystallization process creates a risk of forming unwanted defects, e.g. pin holes and grain boundaries. Here, we introduce a new approach to prepare perovskite films of high electronic quality by using poly(methyl methacrylate) (PMMA) as a template to control nucleation and crystal growth. We obtain shiny smooth perovskite films of excellent electronic quality, as manifested by a remarkably long photoluminescence lifetime. We realize stable PSCs with excellent reproducibility showing a power conversion efficiency (PCE) of up to 21.6% and a certified PCE of 21.02% under standard AM 1.5 reporting conditions.
2:15 PM - ES01.12.03
Synergistic Effects of Lead Thiocyanate Additive and Solvent Annealing on the Performance of Wide-Bandgap Perovskite Solar Cells
Yue Yu 1 , Changlei Wang 1 , Corey R. Grice 1 , Niraj Shrestha 1 , Dewei Zhao 1 , Weiqiang Liao 1 , Lei Guan 1 , Rasha Awni 1 , Weiwei Meng 1 , Alexander J. Cimaroli 1 , Kai Zhu 2 , Randy Ellingson 2 , Yanfa Yan 2
1 , University of Toledo, Toledo, Ohio, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractRecently, organic-inorganic mixed-cation lead (Pb) mixed-halide perovskites have shown their great potential for top cell application in tandem solar cells. By varying the ratio of bromine (Br) to iodine (I), the bandgap (Eg) value of Pb perovskites is tunable from 1.58 to 2.20 eV1. More importantly, the open-circuit voltage (Voc) deficit does not significantly increase as the Eg value increases. While efficient tandem solar cells have been fabricated by combining wide-bandgap perovskite top cells with silicon (Si), copper indium gallium diselenide (CIGS), polymer, and perovskite low-bandgap bottom cells, further improvements on the performance of wide bandgap perovskite solar cells are still needed in order to produce efficient tandem solar cells.
Here in this work, we show that by combining lead thiocyanate additive and solvent annealing process, the grain size of the mixed-cation Pb mixed-halide wide-bandgap perovskite thin films can be effectively increased while avoiding excess lead iodide formation. As a result, the average grain size of the perovskite thin films increases from 66 ± 24 nm to 1036 ± 111 nm, and the mean carrier lifetime shows a more than 3-fold increase, from 330 ns to over 1000 ns. Consequently, the average Voc of the wide-bandgap perovskite solar cells increases by 80 (70) mV and the average power conversion efficiency (PCE) increases from 13.44 ± 0.48 (11.75 ± 0.34) % to 17.68 ± 0.36 (15.58 ± 0.55) % when measured under reverse (forward) voltage scans. The best-performing wide-bandgap perovskite solar cell registers a stabilized PCE of 17.18 %, with an Voc of 1.25 eV, the state-of-the-art Voc among those perovskite solar cells with a similar Eg value of 1.75 eV2. Our approach of the combined lead thiocyanate additive and solvent annealing process shines light on further improvements of wide-bandgap perovskite solar cells, and is therefore of great importance for fabricating efficient tandem solar cells.
References
(1) McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Hörantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B., et al. Science 2016, 351, 151-155.
(2) Yu, Y.; Wang, C.; Grice, C. R.; Shrestha, N.; Zhao, D.; Liao, W.; Guan, L.; Awni, R. A.; Meng, W.; Cimaroli, A. J., et al. ACS Energy Lett. 2017, 2, 1177-1182.
2:30 PM - ES01.12.04
Perovskite Thin Film Formation—An In Situ Investigation of Blade Coating to Consistently Produce High Quality, Pin Hole-Free Films
Yufei Zhong 1 , Rahim Munir 1 , Jianbo Li 3 , Ming-Chun Tang 1 , Muhammad Niazi 1 , Ruipeng Li 2 , Detlef Smilgies 2 , Kui Zhao 3 , Aram Amassian 1
1 , King Abdullah University of Science and Technology, Thuwal-Jeddah Saudi Arabia, 3 School of Materials Science and Engineering , Shaanxi Normal University, Xi’an China, 2 CHESS, Cornell University, Ithaca, New York, United States
Show AbstractOrganic-inorganic hybrid lead halide perovskite semiconductors have attracted a great deal of attention because of their remarkable optoelectronic properties which make them potentially suitable as active materials in photovoltaics, light emission, and photodetection. The key reason for its popularity is that it can yield good semiconductor properties despite being solution processed in ambient conditions and requires no vacuum or excessive heating. To date, the most efficient perovskite solar cells have been fabricated using spin coating, for which several ink and solvent engineering methods have been developed and perfected. However, this is a wasteful process which cannot be easily scaled up to continuous large area fabrication, where existing solvent engineering methods, such as anti-solvent dripping, are also unlikely to work. Here we compare the ink solidification and film formation mechanisms of CH3NH3PbI3 in DMF by spin-coating versus blade-coating using in-situ time-resolved optical metrology and x-ray scattering. We show significant differences in the process kinetics and formation of complex intermediate phases between the two processes at room and intermediate temperatures. To overcome these challenges in the context of blade coating, the sample is heated during deposition. We observe high-quality film formation for T > 100oC, namely in conditions which inhibit the formation of the crystalline intermediate complex phases. In doing so, we achieve fast and direct formation of the perovskite phase with solar cells yielding PCE > 17%.
2:45 PM - ES01.12.05
Optimization of Solution-Processable, Low-Temperature Planar p-i-n Perovskite Solar Cells
Brandon Dunham 1 , Drake Bal 1 , Christos Dimitrakopoulos 1
1 Chemical Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractSolution-processable organic-inorganic perovskites have emerged as one of the most promising technologies for the future of photovoltaics due to their exceptional intrinsic optoelectronic properties. Perovskite solar cells achieving over 20% power conversion efficiency (PCE) often adopt an n-i-p architecture with TiO2 scaffolds requiring processing at T > 450 ○C, which render the devices incompatible with flexible substrates and roll-to-roll manufacturing. Alternatively, organic materials have been used in p-i-n perovskite solar cells as the hole and electron transport layers. Despite their lower PCE compared to TiO2-containing devices, p-i-n devices demonstrate low hysteresis, low processing temperatures, and compatibility with flexible substrates. In an effort to make p-i-n devices more competitive with their n-i-p counterparts, we have taken steps to understand the origins of their relatively lower PCE, and have developed optimized processing schemes to improve their performance and stability. We do this without any compositional or interfacial engineering, which improve charge transport or mitigate the poor ohmic contact at the electrode interfaces, an approach investigated separately[i].
Whereas denser, larger-grained perovskite films can be easily grown on crystalline surfaces like TiO2, those grown on amorphous surfaces like PEDOT:PSS show numerous pinholes and poor surface coverage, a main reason for lower PCE in p-i-n devices. To combat this disparity, we developed an evaporation-induced self-assembly processing technique that yields pin-hole free lead iodide (PbI2) complex intermediate films with excellent surface coverage on PEDOT:PSS surfaces. These qualities were maintained upon further conversion of the intermediate film to the desired methylammonium lead iodide (MAPbI3) perovskite, and thick films with crystal grain sizes of up to 1 μm were produced. Incorporating this higher quality perovskite film into a completed solar cell led to PCE up to 16.72%, compared to a PCE up to ~11% for our control devices made with a standard sequential deposition process.
In an effort to prolong the ambient lifetime of our perovskite devices, we developed a process to transfer large-area graphene cap layers on top of the PCBM layers of our p-i-n perovskite devices to encapsulate the device. It is well known that solar cells comprising ABX3 perovskite active layers exhibit very poor moisture stability. However, due to its inherent barrier properties and conductivity, graphene effectively prevents water from penetrating our devices while simultaneously allowing for electron transfer to the top electrode. The incorporation of the graphene barrier avoids the need for expensive, post-processing encapsulation, and represents a key step towards the realization of low temperature roll-to-roll manufacturing of stable, efficient, and flexible perovskite solar cells.
[i] Duzhko, et al. ACS Energy Lett., (2017), 2, 957–963.
3:30 PM - ES01.12.06
Interfacial Modification of Perovskite Solar Cells Using an Ultrathin MAI Layer Leads to Enhanced Energy Level Alignment, Efficiencies and Reproducibility
Zafer Hawash 1 , Sonia Raga 1 , Dae-Yong Son 2 , Luis Ono 1 , Nam-Gyu Park 2 , Yabing Qi 1
1 Energy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology Graduate University (OIST), Onna-son Japan, 2 School of Chemical Engineering and Department of Energy Science, Sungkyunkwan University (SKKU), Suwon Korea (the Republic of)
Show AbstractOrganic and inorganic hybrid perovskites (PVSK) have demonstrated exceptional potential for optoelectronic devices in the past few years. Outstanding performance has been achieved for perovskite solar cells (PSCs). However, sensitive dependence on fabrication conditions is often a concern and affects the performance and reproducibility. Using x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), we have investigated the influence of excess methyl ammonium iodide (MAI) in PSCs by introducing an ultrathin MAI layer on purpose. Our experimental result helped to identify the key role of excess MAI in the perovskite layer. Our XPS and UPS measurements suggest that excess MAI leads to an efficient interfacial energy level tuning of methyl ammonium lead iodide (MAPI) PVSK films. We have found that excess MAI leads to an efficient interfacial energy level tuning of the MAPI PVSK films. We implemented our findings in fabrication of PSCs and achieved high reproducibility and performance. The fabricated PSCs with interfacial modification show an average steady state power conversion efficiency (PCE) of 17.2%, which is 19% higher than that of the reference cells (14.5%). In addition, the device steady state PCE shows much less spreading with a PCE standard deviation (σ) of 0.4% as compared with 1.9% for reference cells, suggesting significantly improved device reproducibility.
Reference:
Hawash, Z.; Raga, S. R.; Son, D. Y.; Ono, L. K.; Park, N. G.;* Qi, Y. B.,* Interfacial Modification of Perovskite Solar Cells Using an Ultrathin MAI Layer Leads to Enhanced Energy Level Alignment, Efficiencies, and Reproducibility. J. Phys. Chem. Lett. 2017, 8 (17), 3947.
3:45 PM - ES01.12.07
Two-Step Fabrication Hybrid Perovskite Solar Cells—In Situ Investigation of PbI2 Precursor Film Formation and Its Subsequent Conversion to Mixed Cation Perovskite Semiconductors
Dounya Barrit 1 , Buyi Yan 1 , Ming-Chun Tang 1 , Rahim Munir 1 , Detlef Smilgies 2 , Ruipeng Li 2 , Aram Amassian 1
1 KAUST Solar Center (KSC), Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900 Saudi Arabia, 2 Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, 14850, New York, United States
Show AbstractPerovskite solar cells have garnered significant interest thanks to the meteoric rise of their efficiency over the last few years to a power conversion efficiency (PCE) of 22.1% despite being processable using cheap and potentially high-throughput solution coating techniques. Currently, the two-step process employed to produce hybrid organic-inorganic perovskite films by first depositing PbI2 and subsequently converting it to CH3NH3PbI3 (MAPI) through exposure to CH3NH3I (MAI) is responsible for the world record PCE. However, a one-step spin-coating process has emerged as a more popular option thanks to its ability to produce films of different compositions, including mixed cation and mixed halide perovskites, which can stabilize the perovskite phase and produce phases with desired band gap. There is significant need and opportunity to adopt the two-step process toward mixed cation and mixed halide perovskites, but this requires deeper understanding of the two-step conversion process, for instance when using different cations and mixtures thereof, to produce high quality perovskite films with uniform composition. In this work, we demonstrate using in situ investigations that the conversion of PbI2 to perovskite is largely dictated by the state of the PbI2 precursor film in terms of its solvated state. Using time-resolved grazing incidence wide-angle x-ray scattering (GIWAXS) measurements during spin coating of PbI2 from a DMF solution we show the film formation to be a sol-gel process involving three PbI2-DMF solvate complexes: disordered precursor (P0), ordered precursor (P1, P2) prior to PbI2 formation at room temperature after 5 minutes. The ordered solvates are highly metastable and eventually disappear, but we show that performing conversion from P0, P1, P2 or PbI2 can lead to very different conversion behaviors and outcomes. We compare conversion behaviors by using MAI, FAI and mixtures of these cations, and show that conversion can occur spontaneously and quite rapidly at room temperature without requiring further thermal annealing. We confirm this by demonstrating improvements in the morphology and microstructure of the resulting perovskite films, as well as their impact on the PCE of solar cells.
4:00 PM - ES01.12.08
Tunable and Wide Bandgap MAPbBr3-xClx Hybrid Perovskite Semiconductors
Ming-Chun Tang 1 , Sehyun Lee 3 , Rahim Munir 1 , Ruipeng Li 2 , Detlef Smilgies 2 , Aram Amassian 1
1 , King Abdullah University of Science and Technology, Thuwal Saudi Arabia, 3 School of Materials Science and Engineering, Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of), 2 , Cornell High Energy Synchrotron Source (CHESS), Ithaca, New York, United States
Show AbstractOrganic-inorganic lead-based halide perovskites have attracted tremendous attention because of their remarkable optoelectronic properties and photovoltaic performance while being solution processable materials. Beyond the low bandgap workhorse of perovskite photovoltaics, namely MAPbI3, the high bandgap MAPbBr3-xClx hybrid perovskite is shown to achieve a wide and tunable bandgap ranging from 2.3 eV to 3.1 eV for x=0 to 3, making it suitable for semitransparent and transparent photovoltaics, as well as blue and ultraviolet light emitting diode and photodetector applications. However, the vast majority of perovskite film processing know-how has been developed for MAPbI3, where solvent engineering approaches help manage the formation of intermediate ordered precursor solvate phases, as revealed by in situ diagnostics (Munir et al., Adv. Mater. 29, 1604113, 2017). In this contribution, we compare and contrast the solidification and growth behaviors of tunable bandgap MAPbBr3-xClx to MAPbI3 using the one-step spin coating approach. We utilize a multi-probe in situ diagnostics approach consisting in grazing incidence wide angle x-ray scattering (GIWAXS) and UV-vis absorbance complemented with ex situ characterizations of thin film morphology, microstructure, optical and electronic properties and solar cell power conversion efficiency. We reveal that the wide-bandgap lead-based hybrid perovskite phase (MAPbBr3-xClx) forms directly during solution processing, while MAPbI3 forms intermediate ordered phases. We use this insight to develop a solvent engineering protocol suitable for depositing pin-hole-free MAPbBr3-xClx films and demonstrate working single junction solar cells with high open circuit voltage > 1.6 V and great potential for transparent photovoltaics.
4:15 PM - ES01.12.09
Low-Threshold Distributed Feedback Lasers Based on Thermally Imprinted MAPbBr3
Neda Pourdavoud 1 , Andre Mayer 1 , Maximilian Buchmüller 1 , Kai Brinkmann 1 , Tobias Häger 1 , Ting Hu 2 , Ralf Heiderhoff 1 , Ivan Shutsko 1 , Patrick Goerrn 1 , Yiwang Chen 2 , Hella-Christin Scheer 1 , Thomas Riedl 1
1 , Bergische University of Wuppertal, Wuppertal Germany, 2 , Nanchang University, Nanchang China
Show AbstractHybrid halide perovskites have attracted tremendous attention in the field of optoelectronics, as they can be prepared by facile low-temperature deposition methods. In a waveguide laser, the resulting layers are poly-crystalline and their roughness infers substantial propagation losses for guided optical modes. A further issue is the difficulty to pattern photonic nanostructures into these perovskites by standard lithography.
Among the structural weaknesses of hybrid perovskite materials, it is important to consider that unlike conventional inorganic semiconductors, crystal binding in these materials has been found to include significant contributions of van der Waals interactions among the halide atoms as well as Hydrogen bonding, endowing these perovskites with “soft matter” properties.[1] Very recently, we have demonstrated the direct thermal nanoimprint lithography (NIL) of Bragg diffraction gratings into MAPbI3 at temperatures as low as 100°C and a concomitant pressure of 100 bar.[2]
Beyond MAPbI3 with its emission on the NIR, distributed feedback (DFB) lasers based on gain media with a larger bandgap (like MAPbBr3) and an emission in the visible spectral range have not been reported, as of yet. Aiming for thermal imprint of MAPbBr3, it has to be noted that DFT calculations suggest an increasing formation enthalpy per unit cell ranging from 0.1eV to 0.25 eV when going from MAPbI3 to MAPbBr3 suggesting a higher thermal stability of the MAPbBr3 perovskite.[3]
Here, we present the first thermally imprinted DFB lasers based on MAPbBr3. The imprinted linear gratings with a periodicity of 300 nm form a second order DFB resonator, which upon optical excitation supports lasing which can be tuned in the spectral region of 543.3-557.4 nm. A very low lasing threshold of 3.4 µJ/cm2 has been achieved, which is indicative of the outstanding material quality of the imprinted MAPbBr3 layer. In a control experiment using a flat stamp for the imprint process, we clearly evidence the re-crystallization of the MAPbBr3 from an initially rough, polycrystalline thin film (rms roughness: 46 nm) to a layer consisting of extended single crystals with lateral dimensions on the order of 10 µm and a roughness that is on the order of only 0.6 nm (rms), limited by the roughness of the flat stamp. This smooth morphology is the essential key to unlock low waveguide losses and is thus affords low lasing thresholds.
[1] D. A. Egger, L. Kronik, The Journal of Physical Chemistry Letters 2014, 5, 2728.
[2] N. Pourdavoud, S. Wang, A. Mayer, T. Hu, Y. Chen, A. Marianovich, W. Kowalsky, R. Heiderhoff, H.-C. Scheer, T. Riedl, Adv Mater 2017, 29, 1605003.
[3] A. Buin, R. Comin, J. Xu, A. H. Ip, E. H. Sargent, Chem Mater 2015, 27, 4405.
4:30 PM - ES01.12.10
300% Enhancement of Carrier Mobility in Uniaxial-Oriented Perovskite Films Formed by Topotactic-Oriented Attachment
Donghoe Kim 1 , Jaehong Park 1 , Zhen Li 1 , Mengjin Yang 1 , Joseph Berry 1 , Garry Rumbles 1 , Kai Zhu 1
1 , National Renewable Energy Laboratory, Lakewood, Colorado, United States
Show AbstractOrganic-inorganic perovskites with intriguing optical and electrical properties, such as excellent absorption coefficient, long carrier diffusion length, and unique defect physics, have attracted significant research interests due to their excellent performance in optoelectronic devices. Recent efforts on preparing uniform and large-grain (micrometer-sized) polycrystalline perovskite film have led to enhanced carrier lifetime up to several μs. However, the mobility (10–45 cm2V–1s–1) and trap density (1015–1016 cm-3) of polycrystalline perovskite films which are closely related to device characteristics are still significantly less than the values (~ 105–165 cm2V–1s–1 and 1010 –1011 cm-3, respectively) of their single-crystal counterparts. We recently showed for perovskite films with a grain size beyond 400 nm there is little if any correlation with grain size and carrier mobility. This suggests that the details of materials processing could limit the transport properties within the bulk rather than at the boundaries. This motivates the development of strategies for reducing trap density in the bulk to further enhance the electrical properties of polycrystalline perovskites films for various optoelectronic applications. In addition, controlling crystalline orientation in polycrystalline films can also enhance charge transport over their randomly oriented counterparts by reducing structural disorder. Oriented attachment involving spontaneous self-organization along a common crystallographic orientation between neighboring particles is one of the most well-known mechanisms for synthesizing oriented nanocrystals with improved crystallinity and reduced defect density, but it has never been adopted, so far, for perovskite growth.
Here, we demonstrate a facile topotactic transformation with oriented attachment (we called this process as a topotactic-oriented attachment, TOA) to grow highly oriented perovskite films, featuring strong uniaxial-crystallographic texture, micron-grain morphology, high crystallinity, and low trap density (~4×1014 cm-3). These uniaxial-oriented TOA-perovskite films exhibit unprecedented 9-GHz charge-carrier mobility of 71 cm2V–1s–1 that approaches the reported mobilities for CH3NH3PbI3 single crystals (115±15 cm2V–1s–1). TOA-perovskite based n–i–p planar solar cells show minimal discrepancies between stabilized efficiency (19.0%) and reverse-scan efficiency (19.7%). The reverse-scan efficiencies exhibit no dependence on the scan delay time. We also demonstrate the versatility of the TOA process for growing other state-of-the-art perovskite alloys, including triple-cation and wide-bandgap perovskites.
4:45 PM - ES01.12.11
Transformation Kinetics from a One-Dimensional Crystalline Precursor to PbCl2 Derived MAPbI3
Aryeh Gold-Parker 1 2 , Kevin Stone 2 , Vanessa Pool 2 , Eva Unger 3 , Andrea Bowring 4 , Michael McGehee 4 , Michael Toney 2 , Christopher Tassone 2
1 Chemistry, Stanford University, Stanford, California, United States, 2 Materials Science, SSRL, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 3 Chemical Physics, Lund University, Lund Sweden, 4 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractHalide perovskites offer the promise of low cost photovoltaics via solution processing, but a great deal remains unknown regarding the chemistry of perovskite formation from solution. In addition to the remarkably high power conversion efficiencies achievable from perovskite solar cells, these materials are characterized by the wide array of chemistries which seemingly lead to the same final structure. Most preparation methods of MAPbI3 are a variation on the solid state conversion of MAI and PbI2 into MAPbI3. One exception to this is films derived from PbCl2 and an excess of MAI, which have achieved some of the longest carrier lifetimes among perovskite films [1]. This method does not involve the solid state transformation of the two precursor materials directly into the final perovskite structure, but rather forms a crystalline precursor phase immediately after spin casting which in turn undergoes the transformation into the nearly chlorine-free perovskite phase [2,3].
Using a number of in-situ synchrotron X-ray techniques, we have identified the precursor phase and followed the transformation kinetics during film annealing. We have also tracked the loss of chlorine from the film and determined this to be a distinct yet key mechanism of the transformation into the perovskite film. Here, we demonstrate that the as-spun film is composed of 1) amorphous MACl, and 2) crystalline MA2PbI3Cl, composed of one-dimensional chains of lead halide octahedra. Furthermore, we show that the evolution of MACl is the rate-determining step in the conversion of the precursor to perovskite, effectively delaying perovskite formation until the amorphous MACl has sublimed. This approach provides a complete picture of the chemical and structural pathways from the as-deposited film to perovskite. This also provides a template for studying other perovskite conversion mechanisms, toward improving perovskite devices via tuning of the precursor chemistry.
References
[1] Tress, Wolfgang. "Perovskite Solar Cells on the Way to Their Radiative Efficiency Limit - Insights Into a Success Story of High Open-Circuit Voltage and Low Recombination." Advanced Energy Materials (2017).
[2] Unger, Eva L., et al. "Chloride in lead chloride-derived organo-metal halides for perovskite-absorber solar cells." Chemistry of Materials 26.24 (2014): 7158-7165.
[3] Pool, Vanessa L., et al. "Chlorine in PbCl 2-Derived Hybrid-Perovskite Solar Absorbers." Chemistry of Materials 27.21 (2015).
ES01.13: Poster Session IV
Session Chairs
Friday AM, December 01, 2017
Hynes, Level 1, Hall B
8:00 PM - ES01.13.01
High-Performance Perovskite Solar Cells with Carbazole-Cored Hole Transport Material through Reduced-Cost and Facile Synthesis
Lei Guan 1 2 , Xinxing Yin 3 , Dewei Zhao 1 , Changlei Wang 1 , Niraj Shrestha 1 , Yue Yu 1 , Corey R. Grice 1 , Rasha Awni 1 , Jiangsheng Yu 3 , Yingbin Han 3 , Baojing Zhou 3 , Weihua Tang 3 , Jianbo Wang 2 4 , Randy Ellingson 1 , Yanfa Yan 1
1 Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, University of Toledo, Toledo, Ohio, United States, 2 School of Physics and Technology, Center for Electron Microscopy, MOE Key Laboratory of Artificial Micro- and Nano-structures, and Institute for Advanced Studies, Wuhan University, Wuhan, Hubei, China, 3 Key Laboratory of Soft Chemistry and Functional Materials (Ministry of Education of China), Nanjing University of Science and Technology, Nanjing, Jiangsu, China, 4 Science and Technology on High Strength Structural Materials Laboratory, Central South University, Changsha, Hunan, China
Show AbstractOrganic-inorganic hybrid metal-halide perovskite solar cells (PVSCs) have drawn intensive attention due to low-cost, light-weight, facile solution processability, and superior photovoltaic performance. High-efficiency PVSCs are achieved by sandwiching the perovskite film between electron selective layers (ESLs, n-type) and hole selective layers (HSLs, p-type), to improve the selective blocking and extracting of charges into the electrodes and external circuits. Many efforts have been made on HSLs in pursuing better PVSCs performance. Here we demonstrate an efficient MA0.7FA0.3PbI3(MA = methylammonium and FA = formamidinium) based perovskite solar cells with newly synthesized HSL (i.e. 4,4',4'',4'''(9-Octylcarbazole-1,3,6,8-tetrayl)-tetrakis(N,N-bis(4-methoxyphenyl)aniline) (CZ-TA)). The uniform and thin CZ-TA HSL (~50 nm) coated device shows fast charge transfer properties without any space charge limitation. The champion device achieves a maximum power conversion efficiency of 18.33% with a Voc of 1.044 V, a Jsc of 21.66 mA/cm2, and a FF of 81.0% under reverse voltage scan. Our work sheds light on commercialization of perovskite solar cells with cheaper HSLs and relatively good performances.
8:00 PM - ES01.13.02
Fabrication and Application of Formamidine Based Quasi Two-Dimensional Perovskites
Ryuki Hamaguchi 1 , Masahiro Yoshizawa-Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 , Sophia University, Tokyo Japan
Show AbstractTo solve instability of perovskite solar cells, quasi two-dimensional (q-2D) perovskite compounds, whose general formula is A2Bn-1PbX3n+1 have attracted attention because of their long-term robustness provided by hydrophobic alkylamine group in the structure. Recently, our group reported photovoltaic application of q-2D perovskites whose B site cation is formamidine (FA) [1]. We confirmed that FA-based q-2D perovskite had higher photovoltaic properties than other homologous methylamine or caesium based q-2D compounds. Although FA-based q-2D perovskite shows promising possibilities, circumstantial properties of these compounds are still unclear. Here, we report optical, structural, and photovoltaic properties of FA-based q-2D perovskites in detail. FA-based perovskites (A2FAPb2I7) were synthesized by the reaction of stoichiometric formamidine hydroiodide and PbI2 with A-site cation hydroiodides as spin-coated films. We tried to introduce ethylamine (EA), butylamine (BA), hexylamine (HA), octylamine (OA), decylamine (DA), dodecylamine (DDA), iso-butylamine (iso-BA), tert-butylamine (t-BA), phenethylamine (PEA), and 1,6-diaminohexane (HDA) as A-site cations. These spin-coated films were investigated by UV-vis absorption spectroscopy and XRD measurements. Formation of pure q-2D perovskite structure was confirmed when BA, HA, OA, DA were introduced as A site cations. We also investigated the orientation of crystalline growth by in-plane XRD measurements. A diffraction peak at 2θ = 3 ~ 4° originated from the d-spacing value of 20 ~ 30 Å was observed in all pure q-2D perovskites. Especially, HA2FAPb2I7 showed stronger diffraction peak with 4-fold intensity than others. The d-spacing values are equal to the interlayer distance of q-2D perovskite structure. This indicates crystalline growth partly perpendicular to the film. This perpendicular crystalline growth is well-suited to photovoltaic applications, as it allows charges to migrate within the perovskite layers without disturbance. Photovoltaic properties of pure q-2D perovskites were investigated by introducing to mesoscopic cells.
[1] R. Hamaguchi, M. Yoshizawa-Fujita, T. Miyasaka, H. Kunugita, K. Ema, Y. Takeoka, M. Rikukawa, Chem. Commun., 2017, 53, 4366.
8:00 PM - ES01.13.03
Enhanced Stabilization of Inorganic Cesium Lead Triiodide (CsPbI3) Perovskite Quantum Dots with Tri-Octylphosphine
Chang Lu 1 , Hui Li 1 , Kathy Kolodziejski 1 , Chaochao Dun 1 , Wenxiao Huang 1 , David Carroll 1 , Scott Geyer 1
1 , Wake Forest University, Winston Salem, North Carolina, United States
Show AbstractSignificant attention has focused on perovskite materials in recent years for optoelectronic applications. Among them, lead triiodide based perovskites (such as CsPbI3, MAPbI3, and FAPbI3) have shown superb optoelectronic properties. Enhancing the stability of this class of materials is an essential step towards developing large-scale applications. In our work, recently accepted as an article in Nano Research, we show that by simply adding tri-octylphosphine (TOP) as part of the post synthesis treatment, the stability of CsPbI3 QDs in the solution phase can be dramatically enhanced to weeks, which otherwise degrade rapidly in hours. For CsPbI3 QDs treated by TOP, the absorption and photoluminescence emission properties are unchanged over the course of weeks, and the quantum yield remains almost constant at 30% even after a month. Moreover, the thermal stability of the treated QDs is also enhanced, maintaining the spectral features at 80 °C, while the untreated QDs rapidly decay below 80 °C. The morphologies of both treated and untreated QDs are cubic initially, however the treated QDs largely maintain the initial size and shape while the untreated ones lose size uniformity, which is a sign of degradation. Infrared spectroscopy and X-ray photoelectron spectroscopy confirm the phosphorus presence in the TOP treated QDs. We hope the idea of utilizing a ligand post-treatment can bring new insight into this field solve the intrinsic instability issue of triiodide perovskite materials and devices.
8:00 PM - ES01.13.04
Microfluidic Growth of Single-Crystal Perovskite Thin Films for High-Performance Solar Cells
Tianpeng Xiong 1 , Zhifang Shi 1 , Qixi Mi 1
1 School of Physical Science and Technology, Shanghaitech University, ShangHai China
Show AbstractPerovskite solar cells are typically based on a spin-coated polycrystalline active layer, where grain boundaries are prone to charge-carrier recombination and chemical decomposition, and one solution to these issues is to use single-crystal perovskite material. Unlike crystalline Si solar cells that are hundreds of microns thick, the optimum thickness for a perovskite active layer is on the order of microns, predicted from the charge-carrier diffusion length of perovskite single crystals. Herein, we demonstrate a microfluidics-based strategy to grow single-crystal perovskite thin films in a confined space. By flowing a growth solution through the micron-sized gap between two glass electrodes, and by precise control of the flow rate and temperature for crystal nucleation and growth, we were able to produce single-crystal MAPbBr3 domains 5×5 mm2 in size. Scanning electron microscopy (SEM) reveals a uniform thickness adjustable between 3–10 μm, in addition to smooth surfaces and cross sections without obvious grain boundaries. X-ray diffraction (XRD) identifies a specific crystal alignment such that the (100) facet contacts the glass electrodes. For prototype solar cells having an ITO/TiO2/sc-MAPbBr3/Au/ITO architecture, where the single-crystal MAPbBr3 active layer is 6 μm thick, photocurrent measurements showed an external quantum efficiency curve that is flat from 380 to 545 nm, before abruptly dropping near the absorption edge at 550 nm, which resembles bulk MAPbBr3 crystals but is red-shifted by ~20 nm from that of spin-coated polycrystalline films. We have also successfully grown single-crystal thin films of FA0.85MA0.15PbI3, one of the favorite materials for high-efficiency perovskite solar cells. By optimizing the transport layer materials, we anticipate that this facile technique will provide a low-cost and scalable fabrication of single-crystal perovskite solar cells that significantly outperform spin-coated ones, in terms of both efficiency and stability.
8:00 PM - ES01.13.05
Profiling the Organic Cation-Dependent Degradation of Organolead Halide Perovskite Solar Cells
Teng Zhang 1 , Yang Bai 1 , Shuang Xiao 1 , Shihe Yang 1
1 , The Hong Kong University of Science and Technology, Hong Kong Hong Kong
Show AbstractThe operational stability is one of the main obstacles that may hold back the commercialization of perovskite solar cells (PVSCs). In this paper, we provide a detailed account for the ion migration accelerated PVSCs degradation by comparatively studying perovskite materials with two different organic cations (MA+ and FA+). Using Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), we have uncovered the ion migration accelerated degradation of PVSCs. Not only mobile iodide (I-) ions from the perovskite layer out-diffused, Ag atoms/ions from the metal electrode also diffused into the perovskite layer, which resulted in severe device degradation. Besides, we identified I- species in the hole transport material (HTM) layer for even freshly prepared PVSC devices, which was responsible for the degradation of devices kept in the inert condition. Compared with MAPbI3, the ion migration process can be slow down in FAPbI3 devices which account for a better stability of FAPbI3 devices. This work underscores the impact of organic cation substitution on the PVSCs degradation and provides solid evidence for the mobile ion migration in perovskite materials and the consequent degradation in specific device settings such as the n-i-p type perovskite solar cells.
8:00 PM - ES01.13.06
Effects of PbI2 Film Pre-Heating for Photovoltaic Performance of Perovskite Solar Cells
HsinYu Shih 1
1 , Graduate School of Pure and Applied Sciences, Tsukuba Japan
Show AbstractPerovskite solar cells (PSCs) show amazing characteristics for converting light into electricity. Perovskite solar cells were firstly reported in 2009. The efficiency of perovskite solar cells is already over 22% in 2017. The morphology of perovskite layer, such as thickness, roughness and the particle size have effects on photovoltaic performances. We focused on the preparation process of perovskite active layer, especially pre-heating temperature of PbI2 film before the conversion to CH3NH3PbI3. The pre-heating temperature affected on the particle size of CH3NH3PbI3, which resulted in the different solar cell performance.
PSCs are composed of metal electrodes, hole transport layer (HTL), perovskite active layer (CH3NH3PbI3), electron transport layer (ETL) and FTO glass. For the electron transport layer, it is composed of TiO2 compact and porous layer. Titanium diisopropoxide bis(acetylacetonate) solution and TiO2 paste were spin-coated on FTO glass, and the TiO2 films were sintered at 500°C for 15 min. For the perovskite active layer, PbI2 solution was spin-coated on TiO2 porous layer, and then, annealed at 80°C for 10 min. The PbI2 films were pre-heated at different temperature of RT, 40°C, 60°C, 80°C and 100°C, and then, they were dipped in CH3NH3I solution to convert to CH3NH3PbI3. As a hole transport layer, spiro-OMeTAD solution was spin-coated on CH3NH3PbI3 layer. At last, Ag films were deposited on the hole transport layer as electrodes.
We measured the photovoltaic performance of the prepared solar cells using simulated sun light calibrated to AM 1.5, 100 mW/cm2. Moreover, the CH3NH3PbI3 films were evaluated by XRD, SEM and UV-Vis. As a result, the pre-heated cells at 60°C - 80°C showed better performance compared with other pre-heating temperature. This indicates that the PbI2 film pre-heating temperature is very important factor to determine the cell performances. The CH3NH3PbI3 particles were well-grown at 60°C and 80°C, which resulted in the improved performances.
8:00 PM - ES01.13.07
Enhanced Efficiency and Air-Stability of Inverted Planar Perovskite Solar Cells via PCBM Electron Transporting Layer Modification with Triton X–100
Kisu Lee 1 , Jyongsik Jang 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractPerovskite solar cells (PSCs) based on organometallic tri-halide absorber materials have shown impressive progresses in recent years and attracted much attention as one of the most promising third-generation photovoltaic technologies. The power conversion efficiency (PCE) of PSCs has dramatically increased from 3.8% to 21% within the past five years, exceeding that of both organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs). Generally, there are two major types of device architectures in PSCs: n−i−p or p−i−n structure, depending on the position of the electron and hole transporting layers. In contrast to conventional n-i-p structure, p-i-n structured PSCs, the so-called “inverted” PSCs, do not require sintering process for TiO2 at about 500 °C and can be fabricated at relatively low temperature (<150 °C). Thus, inverted PSCs would shorten the fabrication procedures and cut the overall manufacturing cost, and also have the potential for tandem and flexible substrate applications.
For the state-of-the-art inverted PSCs, phenyl-C61-butyric acid methyl ester (PCBM) is generally used as electron transporting material (ETM) due to high electron mobility and solubility in non-polar solvents. Electron transporting layer (ETL) of inverted PSCs plays an important role in extracting electrons from a perovskite layer and blocking the recombination of electrons in the perovskite and holes in the metal electrode. However, it is difficult to form a defect-free and uniform PCBM film on the perovskite layer due to limited solubility of PCBM and low viscosity of PCBM solution. Moreover, the aggregation behavior of PCBM could lead to a poor surface morphology. These result in uncovered perovskite film surfaces by PCBM ETL, inducing the undesirable charge recombination by the contact of perovskite and metal electrode. To avoid this undesirable recombination, many studies inserted an interlayer (e.g., Ca, LiF, organic functional molecules, and metal oxide nanoparticles) between the ETL and metal electrode. However, it demands additional processing of thermal evaporation or spin coating, and may suffer from instability and bad reproducibility. As an alternative, PCBM modification with additive has been studied to improve the morphological and electrical property. Previously, several polymers such as poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyethylenimine were used as an additive, but so far the use of organic small molecules is quite limited.
In this work, we modified PCBM using Triton X–100 for use as a stable, efficient ETL in inverted PSCs. Triton X–100, a polymeric surfactant, was added to PCBM solution to improve interfacial properties by producing a thick and extremely smooth PCBM layer. The PSC using modified PCBM achieved an enhanced PCE of 16.08%, in comparison to 11.53% for the reference device. Moreover, PSCs using modified PCBM showed good air-stability, retaining 83.8% of its initial performance after 800-h exposure in ambient condition.
8:00 PM - ES01.13.08
STM and DFT Study of Atomic Structures and Stability Trends of Mixed Perovskites
Collin Stecker 1 , Jeremy Hieulle 1 , Xiaoming Wang 2 , Robin Ohmann 1 , Luis Ono 1 , Yanfa Yan 2 , Yabing Qi 1
1 Energy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan, 2 Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo 43606, Ohio, United States
Show AbstractOrganic-inorganic perovskites (OHP) are under intense investigation due to their application as light absorbers in thin film solar cells. Although achievable efficiencies are approaching those of commercially available Si-based cells [1], practical implementation of these devices is hindered by stability issues that prevent them from being economically viable. Mixed halide perovskites allow for bandgap tuning and have been shown to confer benefits in device stability and performance. [2] The role and actual incorporation of Cl in mixed OHP films, however, remains an active debate. [3,4] Clarification of the effect of halide substitution on stability from a fundamental perspective is needed, as is an understanding of how halides incorporate into the perovskite crystal lattice.
Here we present the first real-space imaging of the surface of mixed-halide perovskites (CH3NH3Pb(Br)3-x(Cl)x and CH3NH3Pb(Br)3-y(I)y) via low-temperature scanning tunneling microscopy (STM). Density functional theory (DFT) calculations are used to corroborate topographic images of the mixed perovskite surface and to calculate the energies of halide substitution. Comparing energy values obtained, we correlate halide substitution to stability with respect to thermal degradation. A thorough understanding of how stability can be optimized via halide substitution will provide guidelines for improving device performance and marketability.
References:
[1] National Renewable Energy Laboratory (NREL). http://www.nrel.gov/ncpv/images/efficiency_chart.jpg.
[2] Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I. Chemical Management for Colorful, Efficient, and Stable Inorganic–Organic Hybrid Nanostructured Solar Cells. Nano Letters 2013, 13, 1764-1769.
[3] Luo, S.; Daoud, W.A. Crystal Structure of CH3NH3PbIxCl3-x Perovskite. Materials 2016, 9, 123.
[4] Pool, V. L.; Gold-Parker, A.; McGehee, M.D.; Toney, M.F. Chemistry of Materials. 2015, 27, 7240−7243.
8:00 PM - ES01.13.09
Investigation of the Nature of Ion Conduction in Methylammonium Lead Iodide through a Multi-Method Approach
Alessandro Senocrate 1 , Gee Yeong Kim 1 , Igor Moudrakovski 1 , Tae-Youl Yang 1 , Giuliano Gregori 1 , Michael Graetzel 2 , Joachim Maier 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , Swiss Federal Institute of Technology, Lausanne Switzerland
Show AbstractIonic conductivity in CH3NH3PbI3 and related compounds has been initially invoked to explain the anomalous hysteresis in current-voltage sweeps observed in perovskite solar cells under operation, and the unusually high dielectric constant values measured at low a.c. frequencies in these devices [1-3]. Such significant polarization phenomena can be directly linked to the presence of a substantial ionic conductivity in these compounds[3], and have the potential to severely affect both charge transport in the bulk of the material and charge extraction at the interfaces. More pressingly, ion migration has been linked to detrimental electrode reactions [4] and poor stability [5] in perovskite solar cells. As a consequence, a thorough understanding of the nature of ionic and electronic charge carriers in these compounds is key to understand and potentially improve halide-perovskite based solar cell devices. In this study [6,7], we measure the electrical transport properties of CH3NH3PbI3 by means of d.c. galvanostatic polarization, a.c. impedance spectroscopy and open circuit voltage measurements in electrochemical cells, detecting a significant ionic contribution to the conductivity under equilibrium conditions. We follow-up these characterizations with NMR/NQR measurements and electrochemical reaction cells, unambiguously showing that the ionic conductivity is due to iodine ions. Moreover, by measuring the changes in ionic and electronic conductivity as a function of doping and iodine partial pressure (stoichiometry variation), we identify the nature of the electronic and ionic charge carriers in CH3NH3PbI3, that are electron holes and iodine vacancies.
8:00 PM - ES01.13.10
Efficient Photo- and Electroluminescence in Perovskite Nanocrystals Thin Films
Laura Martínez-Sarti 1 , Henk Bolink 1 , Subodh Mhaisalkar 2 3
1 Instituto de Ciencia Molecular, Universidad de Valencia, Valencia, Valencia, Spain, 2 Energy Research Institute, Nanyang Technological University (ERI@N), Singapore Singapore, 3 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractOrganic-inorganic (hybrid) perovskites have become one of the most studied semiconducting materials thanks to their exceptional photovoltaic performance. This is a consequence of their unique properties, such as the high absorption coefficient, high carrier mobility and long range carrier diffusion, which allows an efficient photocurrent generation with minimal non-radiative losses. More recently, perovskites have been investigated for applications in lasers and light-emitting diodes (LEDs). Their application in LEDs requires a precise control over their morphology, since this strongly influences their optical and electronic properties. In particular, perovskites with high photoluminescent quantum yield (PLQY) are desirable for the preparation of efficient LEDs, as they would lead to enhanced external quantum efficiency for electroluminescence. One of the most successful strategies to control the morphology and enhance the photoluminescence of perovskites is the preparation of nanostructured materials, such as colloidal nanocrystals. However, the current preparation methods for perovskite nanocrystals are rather complexes, and the PLQY typically diminishes when they are deposited in thin film, limiting the electroluminescence efficiency.
In this work, we will discuss the preparation as well as the structural and optical properties of luminescent films consisting of organic-inorganic halide perovskite nanocrystals. Upon dispersion in toluene, the nanocrystals show a remarkable PLQY of about 80%. Importantly, they can be easily processed into homogeneous thin films which retain a high PLQY, exceeding 50%. We will discuss the application of these nanostructured perovskite films in bright LEDs employing organic and inorganic charge transport layers. This opens a path for the simple and inexpensive preparation of efficient multilayer light-emitting devices.
8:00 PM - ES01.13.11
Understanding and Eliminating Hysteresis for Highly Efficient Planar Perovskite Solar Cells
Changlei Wang 1 3 , Chuanxiao Xiao 2 , Yue Yu 1 , Dewei Zhao 1 , Rasha Awni 1 , Corey R. Grice 1 , Kiran Ghimire 1 , Danae Constantinou 4 , Weiqiang Liao 1 , Alexander J. Cimaroli 1 , Pei Liu 3 , Jing Chen 5 , Nikolas Podraza 1 , Chun-Sheng Jiang 2 , Mowafak Al-Jassim 2 , Xingzhong Zhao 3 , Yanfa Yan 1
1 , University of Toledo, Toledo, Ohio, United States, 3 School of Physics and Technology, Wuhan University, Wuhan, Hubei, China, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 4 , University of Heidelberg, Heidelberg Germany, 5 , Southeast University, Nanjing China
Show AbstractThrough detailed device characterization using cross-sectional Kelvin probe force microscopy (KPFM) and trap density of states measurements, we identify that the J–V hysteresis seen in planar organic-inorganic hybrid perovskite solar cells (PVSCs) using SnO2 electron selective layers (ESLs) synthesized by low-temperature atomic-layer deposition (ALD) method is mainly caused by the imbalanced charge transportation between the ESL/perovskite and the hole selective layer (HSL)/perovskite interfaces. We find that this charge transportation imbalance is originated from the poor electrical conductivity of the low-temperature ALD SnO2 ESL. We further discovered that a facile low-temperature thermal annealing of SnO2 ESLs can effectively improve the electrical mobility of low-temperature ALD SnO2 ESLs and consequently significantly reduce or even eliminate the J–V hysteresis. With the reduction of J–V hysteresis and optimization of deposition process, planar PVSCs with stabilized output powers up to 20.3% are achieved. Our results provide insights for further enhancing the efficiency of planar PVSCs.
8:00 PM - ES01.13.12
Realization of High NTSC LCD Using Green and Red Perovskite Quantum Dot Films and Blue LED
Hyelim Kang 1 , Sohee Kim 1 , Yun Jae Eo 1
1 , Kookmin University, Seoul Korea (the Republic of)
Show AbstractIn this study, we synthesized narrow-band emitting green and red perovskite quantum dots (QDs) using hot injection colloidal method and fabricated QDs films with NOA, UV curable polymer, for use of a color-by-blue QD emissive liquid crystal displays (LCDs) with high National Television System Committee (NTSC). To realize efficient and monochromatic emissions from color-by-blue green and red QD films, we inserted a light-recycling filter(LRF) between blue LED and QD films in order to enhance the efficiency by recycling backward emission from QD films and capped a long-wavelength-pass dichroic filter (LPDF) on the QD films in order to prevent color mixing and realize monochromatic green and red emission by reflecting blue light from blue excitation source. We measured green and red QD films with LRF and LPDF as a function of QD concentration to find optimum condition of QD films. The LCD system using LRF/LPDF-sandwiched perovskite QD films shows a high NTSC over 100%. Also, we find eight levels of blue, green and red emission grayscale from LCD system.
8:00 PM - ES01.13.13
Efficient Perovskite Solar Cell with Enhanced Environment Stability
Peng Zhang 1 , Yafei Wang 1 , Ting Zhang 1 , Detao Liu 1 , Shibin Li 1
1 , University of Electronic Science and Technology of China, ChengDu China
Show AbstractPerovskite solar cells (PSCs) have attracted wide attention in recent years, and because of its simple structure, planar PSCs are regarded as a good alternative for traditional solar cells. However, the environmental instability of PSCs restrict its further development. In this paper, we passivated the electron transport layer, which reduced the surface defect density and suppress the decomposition induced by photocatalysis. And because of the surface passivation, the initial performance and long term stability of PSCs in atmospheric environment under continuous illumination are effectively improved. The efficiency just dropped from 17.2% to 15.03% after 250 h continuous exposure under full spectrum simulated sunlight in air. Fabrication of highly efficient planar PSCs with improved stability provides a pathway for commercialization of PSCs.
8:00 PM - ES01.13.14
Understanding Surface and Bulk Properties in Hybrid Perovskites
Jonathan Ngiam 1 2 , Natalie Stingelin 1 2 , David Payne 1 , Martyn McLachlan 1 2
1 Materials, Imperial College London, London United Kingdom, 2 Centre for Plastic Electronics, Imperial College London, London United Kingdom
Show AbstractThe novel group of organic-inorganic hybrid materials with a perovskite crystal structure have shown great promise in semiconducting applications, particularly photovoltaics. There have been a substantial number of published works, not only on device physics and device optimisation but also on fundamental material research on pure-halide, mixed-halide, and non-stoichiometric perovskites. Despite their tremendous promise in the field of photovoltaics one of the largest challenges for perovskite devices is improving their stability. Their poor stability can be partly attributed to low defect formation energies and non-stoichiometry within the material, causing ionic migration/diffusion. This has been supported by theoretical and experimental studies; often using photophysical techniques such as photoluminescence, electroluminescence, and other variants, which usually do not provide surface information and have limited-spatial resolution. Using time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) and low-energy ion scattering (LEIS), the vertical composition and surface composition of various compositions of methyl ammonium lead iodide (MAPI) films has been probed with a view to better understand ion migration and ultimately improve stability. Additionally X-ray photoelectron spectroscopy (XPS) has been carried out on simple MAPI films and MAPI films sandwiched between various functional/charge-selective interlayers to deduce the degree of ionic migration. This strategy is also extended to non-stoichiometric perovskites to better understand the effect of PbI2-rich or MAI-rich compositions on ion migration.
8:00 PM - ES01.13.15
Dual-Source Co-Evaporation of Perovskite Absorbers and Determination of the Acoustic Impedance Ratio of the Deposited Single Precursors
Sascha Wolter 1 , Verena Steckenreiter 1 , Marta Christine Tatarzyn 1 , Marvin Diederich 1 , Raphael Niepelt 1 , Sarah Kajari-Schröder 1
1 Photovoltaics, Institute for Solar Energy Research Hamelin, Emmerthal Germany
Show AbstractThe combination of the high-efficiency1 and low cost2 silicon solar cell technology with an epitaxy-free top cell technology in a tandem configuration is a promising approach for further lowering the levelized cost of electricity of photovoltaics. Halide organic perovskites are in the focus of recent research as top absorbers due to their convenient and adjustable band gap as well as the wide range of suitable non-epitaxial deposition technologies, e.g. spray coating3, spin coating4 and thermal dual-source co-evaporation5,6. The thermal dual-source co-evaporation of perovskite absorbers facilitates the conformal deposition5,6 with accurate thickness and stoichiometry control. Nevertheless, the co-evaporation process is technologically complex and several material parameters of the precursors and the geometry of the evaporation tool are important for a controlled evaporation. Special attention must be paid on the acoustic impedance ratio of the deposited single precursors and the oscillating quartz crystal, the so-called Z-factor. Especially during the evaporation of methylammonium iodide (MAI) an inaccurate Z-factor will lead to incorrect deposition rate measurements, non-constant deposition rates and inaccurate layer thicknesses.
In this work, we systematically determine the crucial material parameters of the source materials (Z-factor and density) for co-evaporation of perovskite solar cell absorbers to enhance the accuracy of the measured deposition rate. The precursors used here for the deposition of methylammonium lead triiodide are MAI and lead(II) iodide. We use a model with a one-dimensional acoustical composite resonator for the correct determination of the Z-factor7. We measure the thickness of the deposited layers by SEM cross sections and monitor the frequency change of the quartz crystal. Then, we determine the Z-factor by a least square fit of the one-dimensional acoustical composite resonator to the experimental data. We generalize this approach to be applicable to other materials, such as formamidinium iodide or lead(II) bromide. We use the resulting material properties to deposit a uniform layer of methylammonium lead triiodide with an accurately controlled thickness and characterize it by energy resolved photoluminescence, XRD and SEM. We document an increasing band gap with an increasing excess of methylammonium iodide, confirming the importance of exact deposition parameters for controllable evaporation conditions.
1. Yoshikawa, K. et al., Nat. Energy 2, 17032 (2017).
2. International Technology Roadmap for Photovoltaic (ITRPV), 2016 Results. (2017).
3. Barrows, A. T. et al., Energy Environ. Sci. 7, 2944 (2014).
4. You, J. et al., Nat. Nanotechnol. 11, 1–8 (2015).
5. Liu, M., Johnston, M. B. & Snaith, H. J., Nature 501, 395–398 (2013).
6. Momblona, C. et al., APL Mater. 2, (2014).
7. Lu, C. S. & Lewis, O., J. Appl. Phys. 43, 4385–4390 (1972).
8:00 PM - ES01.13.16
On the Thermodynamics of Halide Perovskites
Alessandro Senocrate 1 2 , Gisela Siegle 1 , Reinhard Kremer 1 , Gee Yeong Kim 1 , Michael Graetzel 2 1 , Joachim Maier 1
1 , Max Planck Institut for Solid State Research, Stuttgart Germany, 2 , École Polytechnique Fédérale de Lausanne, Lausanne Switzerland
Show AbstractLead-based halide perovskites materials have been widely studied in recent years due to their potential as light-harvester in solar cells. The efficiencies of such devices are outstanding (> 22 %), posing no limitation to a future commercial application of these compounds. However, stability of halide perovskites still presents a significant challenge to be overcome prior to commercialization. One of the questions that should be answered is whether these compounds are intrinsically thermodynamically stable. The fact that these perovskites material spontaneously form at low temperatures upon drying a solution of the precursors, along with the possibility of obtaining them through a manual mechano-synthetic approach speak for a negative Gibbs free energy of formation. However, recent calorimetric studies report that some halide perovskites (specifically MAPbI3 and MAPbBr3) have distinct positive formation enthalpies, suggesting that they are intrinsically unstable.[1] Moreover, it is widely known how such compounds easily degrade under even moderate thermal stress.[2] DFT studies have also reported about an intrinsic instability of halide perovskites, and of MAPbI3 in particular.[3, 4] This contribution discusses the interplay of intrinsic stability with environmental and light effects influencing the durability of the materials. In this respect we present and compare heat capacity data of several different halide perovskites (MAPbI3, MAPbBr3, MAPbCl3, CsPbI3, CsPbBr3). Electrochemical cell experiments, from which we expect results on both enthalpy and entropy, are underway.
8:00 PM - ES01.13.17
In Situ Observation of of CH3NH3PbI3-XClX Perovskite Thin Films During Annealing Process
Seunghak Shin 1 , Changhyun Ko 2 , Yeonghun Yun 1 , Heesu Jeong 1 , Se-Yun Kim 1 , Young-Woo Heo 1 , Joon-Hyung Lee 1 , Sangwook Lee 1
1 School of Materials Science and Engineering, Kyungpook National University, Daegu Korea (the Republic of), 2 Department of Applied Physics, College of Engineering, Sookmyung Women's University, Seoul Korea (the Republic of)
Show AbstractOrganic-Inorganic perovskite solar cells (PSCs) have been attracted great attention because of their high power conversion efficiency (PCE) , low production cost, and high flexibility. The most intensively studied light absorbing material is perovskite-structured CH3NH3PbI3 (MALI). Interestingly, it is reported that a small amount of chlorine incorporation into MALI increases charge carrier diffusion lengths (from 129 nm to 1069 nm), which enables planar structured PSCs with high PCEs. However, whether chlorine exists at the final perovskite film is under debate. Some studies report negligible amount or absence of chlorine in the final film, while others report detection of chlorine from the final film. In this study, we observed microstructure and chlorine content of Cl-incorporated MALI thin films with increasing temperature, using an in-situ nano-Auger spectroscopy and an in-situ scanning electron microscopy system. Precipitates begin to appear at the surface of Cl-incorporated MALI films, from lower temperatures compared to the MALI thin films. Moreover, grains of Cl-incorporated MALI films grow faster than those of MALI films. Local concentrations of chlorine at intragrain and the vicinity of grain boundary were analyzed to understand the microstructural evolution of the perovskite films.
8:00 PM - ES01.13.18
Materials Design for Perovskite Solar Cell
Omar Allam 1 , Colin Holmes 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractAlthough perovskite has been intensively studied as a promising material for solar cell technology due to its high power conversion efficiency, its stability should be improved for real applications. In this study, we have developed a protocol for discovery/design of new materials in perovskite solar cells. In this protocol, first, we explore the crystal ionic radii for all elements and select possible stable perovskites possessing cubic structure. A Goldschmidt tolerance factor of 0.95 and an Octahedral factor of 0.5-0.7 are used to filter only cubic perovskites that are stable at room temperature. After removing rare or radioactively unstable elements, quantum mechanical density functional theory (DFT) calculations are performed on remaining perovskites to assess whether their electronic properties are suitable for solar cell applications. Dielectric breakdown strength, band structure, band gap energy, energy density, and stability are all assessed using these calculations. Similar calculations are performed on Ruddlesden-Popper (from n=1 to n=50) and Double Perovskite phases of remaining perovskites with suitable properties. All calculation results are compared to that obtained from a reference system, methylammonium lead iodide.
8:00 PM - ES01.13.19
Investigation of Vacuum Deposited NiOx P-Type Oxide Semiconductor for Planar Structured Perovskite Solar Cells Application
Hyunmo Koo 1 , WooIl Jung 1 , Jungseok Oh 1 , Dukjoon Cha 1 , DaSeul Hyeon 2 , Wonbae Ko 2 , Jinpyo Hong 2 , JungYup Yang 1
1 Physics, Kunsan National University, GunsanSi Korea (the Republic of), 2 Physics, Hanyang University, Seoul Korea (the Republic of)
Show AbstractA vacuum deposited NiOx thin films were used as the hole transport layer of a planar structured perovskite solar cells. The NiOx thin films, which were deposited by reactive sputtering from a Ni target in a mixture of oxygen and argon gases, can transport holes and block electrons efficiently, without any post-treatment process. The influences of process parameters including sputtering power, O2/Ar gas ratio, and working pressure on the film properties such as crystallographic structure, preferred orientation, transmittance, and resistivity were investigated. The photovoltaic properties of planar structured perovskite solar cells with NiOx hole transport thin films were also investigated. The results present that NiOx thin films have two preferred orientation with (200) or (111) diffraction peak depending on sputtering conditions. In addition, the planar structured perovskite solar cells with (200) or (111) orientated NiOx films showed different photovoltaic properties. The vacuum deposited NiOx thin films had efficiently hole transport and electron blocking property, thus providing a good hole contact for planar structured perovskite solar cells.
8:00 PM - ES01.13.21
Dynamics of Charged Excitons in Perovskite CsPbBr3 Nanocrystals Reveled by Femtosecond Transient Absorption and Single Dot Spectroscopies
Naoki Yarita 1 , Hirokazu Tahara 1 , Toshiyuki Ihara 1 , Tokuhisa Kawawaki 1 , Ryota Sato 1 , Masaki Saruyama 1 , Toshiharu Teranishi 1 , Yoshihiko Kanemitsu 1
1 , Kyoto University, Uji Japan
Show AbstractRecently, metal halide perovskite semiconductors have attracted much attention as a new class of functional materials for solar cells, photodetectors, light-emitting diodes (LEDs), and lasers. All-inorganic cesium lead halide perovskite nanocrystals (NCs) have shown fascinating optical properties resulting from unique size-effects of NCs [1]. It is well known that for NCs their unique optical processes appear due to the presence of excitons, trions (charged excitons) and biexcitons. In particular, the nonradiative Auger recombination of trions and biexcitons strongly affect the radiative recombination of carriers and the performances of the NC devices such as LEDs, solar cells, and single photon emitters. Thus, it is crucial to understand the behaviors of trions and biexcitons for the device application of perovskite NCs. In this work, we study the generation and recombination dynamics of trions in cesium lead bromide (CsPbBr3) all-inorganic perovskite NCs using femtosecond transient-absorption and single-dot spectroscopies.
The samples used in this work were CsPbBr3 NCs dispersed in hexane (solution) for femtosecond transient absorption (TA) spectroscopy and CsPbBr3 NCs/PMMA thin films for single dot spectroscopy. We observed the three components in the TA decay curves: their lifetimes are about 40 ps, 200 ps, and 6 ns for 7 nm size NCs [2]. In single-dot second-order photon correlation g(2) spectra, we detected the weak signals originating from the biexciton−exciton cascade emission. Because the first photon emission at the central peak in the g(2) spectrum is caused by the biexciton decays, the biexciton lifetime is determined by the decay curve of the first emitted photons [3]. Combining the results obtained using femtosecond TA and single-dot g(2) spectroscopies, we clarified the recombination dynamics of excitons, trions, and biexcitons. Trions are formed efficiently in CsPbBr3 perovskite NCs. We will discuss the impact of trions on the optical responses of perovskite nanostructures.
Part of this work was supported by JST, CREST (JPMJCR16N3).
[1] L. Protesescu et al., Nano Lett. 15, 3692 (2015).
[2] N. Yarita et al., J. Phys. Chem. Lett. 8, 1413 (2017).
[3] N. Hiroshige et al., J. Phys. Chem. Lett. 8, 1961 (2017).
8:00 PM - ES01.13.22
High-Efficiency Perovskite Quantum-Dot Light-Emitting Devices by Effective Washing Process and Interfacial Energy Level Alignment
Keigo Hoshi 1 , Takayuki Chiba 1 2 3 , Yong-Jin Pu 1 2 3 , Yuya Takeda 1 , Yukihiro Hayashi 1 , Satoru Ohisa 1 2 3 , So Kawata 1 , Junji Kido 1 2 3
1 , Graduate School of Organic Materials Science, Yamagata University, Yonezawa Japan, 2 , Research Center for Organic Electronics, Yamagata University, Yonezawa Japan, 3 , Frontier Center for Organic Materials, Yamagata University, Yonezawa Japan
Show AbstractPerovskite quantum dots (PeQDs) are receiving a lot of attention by their unique properties, such as narrow emission spectra, color tunability and solution processing to apply for PeQDs light-emitting devices (PeQD-LEDs) [1-3].
We fabricated low-driving-voltage and high-efficiency PeQD-LEDs using a PeQDs washing process with an ester solvent of butyl acetate (AcOBu) to remove excess ligands from the PeQDs. The CsPbBr3 film washed with AcOBu exhibited a photoluminescence quantum yield (PLQY) of 42%, and a narrow PL emission with a full width at half-maximum of 19 nm. We also demonstrated energy level alignment of the PeQD-LEDs in order to achieve effective hole injection into PeQDs, exhibited a maximum power efficiency of 31.7 lm W-1 and external quantum efficiency (EQE) of 8.73%[4]. Control of the interfacial PeQDs through ligand removal and energy level alignment in the device structure are promising methods for achieving high PLQY in film state and high efficiency of the PeQDs-LED.
Reference: [1] L. Protesescu et al., Nano Lett. 2015, 15, 3692. [2] J. Pan et al.,Adv. Mater. 2016, 28, 8718. [3] J. Li et al., Adv. Mater. 2017, 29, 1603885. [4] T. Chiba et al., ACS Appl. Mater. Interfaces, 2017, 9, 18054.
8:00 PM - ES01.13.23
Low-Temperature Annealing and Stable Inorganic Cesium Lead Bromide Perovskite Solar Cells
Kai Chi Tang 1 , Peng You 1 , Feng Yan 1
1 , The Hong Kong Polytechnic University, Hong Kong Hong Kong
Show AbstractHybrid organic-inorganic perovskite solar cells have achieved higher than 20% power conversion efficiency (PCE) to date but they usually suffer from instability of organic cation in the perovskite under ambient air. Inorganic perovskite material cesium lead bromide (CsPbBr3) is a potential candidate to solve the unstable problem. However, the crystallization of the perovskite CsPbBr3 traditionally requires a high-temperature (250°C) annealing process which is not favorable to fabrication because of high fabrication cost and complexity. In this work, pyridine (Py) vapor-assisted treatment is utilized in two-step fabrication of the CsPbBr3 to lower the annealing temperature to 160°C and a comparable PCE 6.05% is obtained comparing to the device without pyridine. Pyridine is supposed to form an intermediate state with lead bromide (PbBr2) film so that the activation energy required to establish the perovskite CsPbBr3 can be decreased. Meanwhile, the CsPbBr3 possesses a high stability under atmosphere without encapsulation which is beneficial to commercialization. This work helps us take a step further on long-term stable and low-temperature annealing perovskite solar cells.
8:00 PM - ES01.13.24
Suppression of Rashba Couplings by Recovery of Inversion Symmetry in Mesoscale APbBr3 Perovskite
Yung Ji Choi 1 , Nam-Gyu Park 2 , Dongho Kim 1
1 , Yonsei University, Seoul Korea (the Republic of), 2 , Sungkyunkwan University Advanced Institute of NanoTechnology, Suwon-si Korea (the Republic of)
Show AbstractLead halide perovskite (APbX3) has emerged as an efficient light emitter in light-emitting devices (LEDs) as well as an absorber for photovoltaic devices, because of its high color purity and tunability, and low fabrication cost. Although lead halide perovskite has been successfully applied to LEDs in recent studies, there is a lack of understandings of the fundamental mechanism on its optoelectronic properties. In this work, we evaluated the effect of reducing the size of APbBr3 crystalline on the photophysical properties with regard to the spin-orbit coupling, Rashba splitting, and ferroelectricity. APbBr3 (A = MA+ or Cs+) thin films were synthesized by stoichiometric and non-stoichiometric synthetic approaches, composed of bulks or mesoscale crystalline with average crystalline sizes of >100 or 15 nm, respectively. The mesoscale APbBr3 film exhibits much brighter green PL emission under UV light exposure than bulk one irrespective of A cation species, which is corresponding to a drastic increase in PL quantum yield. Moreover, radiative recombination pathway, distinct from well-known non-geminate recombination in bulk perovskite, became prominent only in mesoscale film.
Through crystallographic analyses, XRD and TEM, we evaluated the impact of crystalline size on the resultant crystal structures. As the crystalline size decreased from bulk to mesoscale, the crystal structure was transformed from tetragonal (P4mm) to cubic (Pm-3m) structure, thus resulting in a recovery of centrosymmetry. The recovery of centrosymmetry can effectively diminish the effect of Rashba splitting, or a mismatch of spin texture and momentum near the band gap, which is caused by the strong spin-orbit coupling of heavy atoms (Pb and Br). We demonstrated computationally that the consequential recovery of centrosymmetry leads to spin- and momentum-allowed carrier recombination, which leads to accelerated radiative recombination and improved PL quantum yield in mesoscale perovskite crystalline. To the best of our knowledge, this work is the first comprehensive investigation on the relationship between the morphology of APbBr3 and its optoelectronic properties from a crystallographic perspective. Thus, this study will provide a general strategy that could be useful for modulating the photophysical properties of perovskite thin film to design the active layer of LEDs
8:00 PM - ES01.13.25
Solution-Processed Stable Cesium Lead Halide Perovskite Photodetectors for UV Light
Ting Zhang 1
1 , University of Electronic Science and Technology, Chengdu China
Show AbstractOrganic-inorganic halide perovskites have drawn great attention and been very promising candidate for opto-electronic applications due to low cost and high throughput solution process, mainly focusing on photovoltaics (PVs) device. However, it has been recognised that these hybrid materials show both environmental and thermal instability. In order to overcome these critical issues, researches have been moving towards fully inorganic perovskites. CsPbCl3 seems to be attracted less interest up to now, despite it is suitable for UV detectors due to its favourable band-gap (3.0 eV). This work has focussed on preparing CsPbCl3 thin films with a one-step s simple solution process and UV detection devices. CsPbCl3 layers have been prepared via one solution process, spin-coated and then annealed at temperatures in the range 47 – 70°C in an inert atmosphere. Our results confirm that this inorganic perovskite is thermally stable, and the devices show a detectivity of up to 104 at 1V under 365nm illumination. This technique offer a novel detection for UV applications.
8:00 PM - ES01.13.26
Enhanced Electrons Transport of Spin-Coated SnO2 Nanoparticles in Flexible Perovskite Solar Cells via Interfacial Modification with Fullerene
Detao Liu 1 , Shibin Li 1 , Yafei Wang 1 , Peng Zhang 1 , Rui Zhang 1 , Hualin Zheng 1 , Zhi Chen 1 2 , Jiang Wu 3
1 , University of Electronic Science and Technology of China, Chengdu China, 2 , University of Kentucky, Lexington, Kentucky, United States, 3 , University College London, London United Kingdom
Show AbstractPerovskite solar cells (PSCs) have been developed rapidly recently and regarded as the most promising alternative to the Si solar cells. And the flexibility of the solar cells is one of the most important tendencies for the PSCs. Flexible solar cells have advantages in fabrication, application and transportation. Flexible solar cells can be fabricated by roll-to-roll and it can be applied in portable device. The flexible solar cells also have a light weight due to thin substrate layers. However, the fabrication of flexible PSCs is limited because the flexible substrate couldn’t be processed under high-temperature condition (>150 degree centigrade). So the low temperature process of ETL is important for the fabrication of flexible PSCs.
It has been demonstrated that the fullerene could modify the ETL and enhance the performance of the photoelectric devices, for instance, organic light-emitting diode and PSCs. In this study, we deposited the pre-crystalized tin dioxide (SnO2) nanoparticles as the ETL in flexible PSCs at low temperature (150 degree centigrade) and then spin-coated a ultrathin fullerene film on the SnO2 film before the deposition of the perovskite film. It showed that the film deposited with SnO2 nanoparticles could cover the surface of the ITO completely and transport electrons efficiently. After modified with fullerene film, the ETL could extract electrons much more efficiently compared with the pristine SnO2 film. Flexible PSCs with a structure of ITO/SnO2 or fullerene-modified SnO2/perovskite/spiro-OMeTAD/gold have been fabricated. compared with the flexible PSCs with pristine SnO2, the performance of the flexible PSCs with fullerene-modified SnO2 has been enhanced, and the hysteresis also has been suppressed dramatically.
8:00 PM - ES01.13.27
W-Doped In2O3 Electrodes Prepared by Vertical Type Ion Plating System for High Performance Flexible CH3NH3PbI3 Perovskite Solar Cells
Jae-Gyeong Kim 1 , Hyeong-Jin Seo 1 , Hae-Jun Seok 1 , Ju-Yeoul Baek 2 , Kyung-Jun Ahn 2 , Yong-Jin Noh 3 , Seok-In Na 3 , Han-Ki Kim 1
1 Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yoning-si Korea (the Republic of), 2 , SNTEK Co., Ltd, Suwon-Si Korea (the Republic of), 3 , Chonbuk National University, Jeonju-si Korea (the Republic of)
Show AbstractWe report the electrical, optical, mechanical, structural and morphological properties of high mobility W-doped In2O3 (IWO) films prepared by using a vertical type ion plating system on a PET substrate to replace the conventional sputtered ITO electrodes. Due to high ion energy input during ion plating process, the 100 nm-thick IWO film showed a sheet resistance (Rsh) of 36.39 Ohm/square and an optical transmittance (T) of 89.4% at 550 nm even though it was deposited at room temperature. Low sheet resistance of the ion-plated IWO film comparable to sputtered crystalline ITO film could be attributed to higher mobility (59 cm2/V-s) of the ion-plated IWO films than that (32.5 cm2/V-s) of sputtered ITO films. In particular, the ion-plated IWO film showed high optical transmittance in near IR wavelength region, which is beneficial of high mobility IWO electrode. Until outer bending radius of 6 mm and inner bending radius of 3mm, the ion-plated IWO film showed a constant a resistance change. In addition, dynamic outer and inner bending fatigue tests of the ion-plated IWO film showed no change in resistance (ΔR) even after 10,000 bending cycles, demonstrating the flexibility of the ion-plated IWO film. To investigate the feasibility of the ion-plated IWO electrodes, we fabricated flexible perovskite solar cells on ion-plated IWO/PET and sputtered ITO/PET, respectively. Due to lower sheet resistance and higher optical transmittance of the ion-plated IWO electrode, the flexible CH3CH3PbI3 perovskite solar cells with IWO anode showed higher power conversion efficiency of 8.964% than the sputtered ITO-based flexible perovskite solar cells (2.573 %). High PCE of flexible perovskite solar cells with ion-plated IWO anode indicates the possibility of the ion-plating IWO electrode as replacement of conventional sputtered ITO films for high performance flexible perovskite solar cells.
8:00 PM - ES01.13.28
Quantum-Dot TiO2 Hole-Blocking Layer for n-i-p Planar Perovskite Solar Cell
Rui Cheng 1 , Peng Zhai 2 1 , Hyeonseok Lee 1 , Shien Ping Feng 1 3
1 , The University of Hong Kong, Hong Kong Hong Kong, 2 , Northwestern Polytechnical University, Xi'an China, 3 , The University of Hong Kong-Zhejiang Institute of Research and Innovation (HKU-ZIRI), Hangzhou, Zhejiang, China
Show AbstractA solution-based synthesis for the preparation of quantum dots (QDs) TiO2 nanoparticles (NPs) with the size of 2 to 5 nm is developed to use as an effective hole blocking layer (HBL) for n-i-p planar perovskite solar cell (PSC). The TiO2-QDs smoothen FTO surface, of which the root-mean-square roughness was reduced from 41.9 nm to 21.2 nm. XRD shows a better crystallinity of TiO2-QDs HBL as compared to the commonly used titanium diisopropoxide bis(acetylacetonate) (TiAcAc) based TiO2 HBL. TiO2-QDsbased PSC exhibits weaker photoluminescence (PL) intensity than TiAcAc-TiO2 based PSC, indicating stronger electron extraction ability. The time-resolved photoluminescence (TRPL) provides evidence of a longer charged carrier lifetime for TiO2-QDs based PSC as compared to TiAcAc-TiO2 based PSC. TiO2-QDs based PSC achieves high energy conversion efficiency of 16.4% with Jsc of 19.85 mA/cm2, Voc of 1.09 V, and fill factor of 0.76, which outperforms TiAcAc-TiO2 based PSC.
8:00 PM - ES01.13.29
The Dual Roles of MoS2 in Enhancing the Performance of Perovskite Solar Cells
Tang Guanqi 1 , Peng You 1 , Shenghuang Lin 1 , Feng Yan 1
1 , The Hong Kong Polytechnic University, Hong Kong Hong Kong
Show AbstractMolybdenum disulfide (MoS2) is potentially superior hole-transporting material due to its high carrier mobility and less defects density. The effect of solution processed MoS2 flake on the growth of perovskite film has not been investigated in the perovskite solar cells (PSCs). Here, we introduce the MoS2 as interfacial layer between Poly(bis(4-phenyl) (2,4,6-trimethylphenyl) amine) (PTAA) and perovskite layers to study its influence on both the growth of perovskite and the performance of PSCs. SEM measurement indicates that the grain size of perovskite increases along with the rising of flake size of MoS2. The grain size of perovskite has been increased from 200-300 nm to 400-600 nm. Due to the enlarging grain size and higher crystallinity, the traps density of state of perovskite film is decreased by half. The recombination lifetime of the device has been significantly prolonged. Photoluminescence measurement demonstrates the insertion of MoS2 between PTAA and perovskite could increase the hole extraction rate and alleviate the charge accumulation at the interface. With the modification of MoS2, the power conversion efficiency (PCE) is boosted from 17.49 to 19.28%. This work paves a way for preparing high performance PSCs as well as other devices by using 2D materials.
8:00 PM - ES01.13.30
Highly Flexible ITO Anode Prepared by Ion Plating System for High-Performance Flexible CH3NH3PbI3 Perovskite Solar Cells
Han-Ki Kim 1 , Jae-Gyeong Kim 1 , Ju-Yeoul Baek 2 , Kyung-Jun Ahn 2
1 Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yoning-si Korea (the Republic of), 2 , SNTEK Co., Ltd, Suwon-Si Korea (the Republic of)
Show AbstractWe fabricated high-performance flexible CH3NH3PbI3 (MAPbI3) perovskite solar cells with a power conversion efficiency of 16.8% on transparent and flexible ITO electrode prepared by specially designed ion plating system. The vertical-type ion plating system was employed to fabricate high-quality ITO electrodes on PET substrate at room temperature. The electrical, optical, and mechanical properties of ion-plated ITO electrodes were investigated as a function of film thickness to determine optimal ITO electrode thickness. The ion plated ITO films on PET substrate showed a lower sheet resistance and higher optical transmittance than conventional sputtered ITO films because the high energy input into a growing ITO film led to densification of the growing film during ion plating process. At optimal coating condition, the ion-plated ITO film with a thickness of 100 nm showed a sheet resistance of 15.75 Ohm/square and an optical transmittance of 84%, which are better than those of sputtered ITO film. Outer and inner bending tests demonstrated that the mechanical flexibility of the ion plated ITO film was superior to that of the conventional sputtered ITO film due to better adhesion between ion plated ITO and PET substrate. Flexible perovskite solar cells with the structure of Au/PTAA/MAPbI3/ZnO/ITO/PET showed a higher power conversion efficiency of 16.8% than sputtered ITO-based flexible perovskite solar cells (15.4%) due to lower sheet resistance and higher optical transmittance. The successful operation of these flexible perovskite solar cells on ion-plated ITO electrode indicated that the ion-plating is a promising technique to prepare high quality ITO anode for high performance flexible perovskite solar cells.
8:00 PM - ES01.13.31
Characteristics of P-Type Li-Doped Cu2O Hole-Transport Layer for Semi-Transparent Perovskite Solar Cell
Hyeong-Jin Seo 1 , Yong-Jin Noh 2 , Seok-In Na 2 , Han-Ki Kim 1
1 , Kyung Hee University, Yongin-si Korea (the Republic of), 2 , Chonbuk National University, Jeonju-si Korea (the Republic of)
Show AbstractWe investigated characteristics of RF sputtered Li-doped Cu2O (LCO) film to use as p-type buffer layer for semi-transparent perovskite solar cells. The p-type properties and optical transmittance of the RF sputtered LCO films were measured using Hall measurement and U/visible spectrometer as a function of oxygen gas flow rate. At optimized Ar/O2 flow rate (20/3 SCCM), the LCO film showed a stable p-type conductive with a carrier concentration of 5.81x1020 cm-3 and a mobility of 5.1x10-1 cm2/V-s. In addition the p-type LCO films showed an optical transmittance of 53.83 %. The work function of RF sputtered LCO films was measured by Kelvin prove force microscopy as a function of Ar/O2 flow ratio. Based on optimized p-type LCO layer, we fabricated p-type LCO buffer graded ITO anode for semi-transparent perovskite solar cells. Graded sputtering of the p-type LCO buffer layer on top of the ITO layer produced p-LCO graded ITO anodes with a sheet resistance of 53.46 Ω/square, a resistivity of 8.01x10-4 Ohm-cm, and an optical transmittance of 68.3% %, all of which were comparable to a conventional crystalline ITO anode. In addition, the p-type LCO graded ITO electrode showed a greater work function of 4.85 eV than that (4.6 eV) of a ITO anode, which is beneficial for hole extraction from a perovskite active layer. Due to the high work function of p-LCO graded ITO electrodes, the semi-transparent perovskite solar cells fabricated on the p-LCO graded ITO electrode exhibited a power conversion efficiency 8.5 % greater than reference perovskite solar cells (7.0 %) with solution process p-type NiO buffer layer. The successful operation of semi-transparent perovskite solar cells on the p-LCO graded ITO electrode indicates simpler fabrication steps to remove the solution coating of p-type buffer layer for cost-effective perovskite solar cells.
8:00 PM - ES01.13.32
Forming Lead Iodide Perovskite Thin Films in Seconds
Hanaa AlMaghamsi 1 , Iulia Salaoru 1 , Shashi Paul 1 , Krishna Manjunatha 1
1 Emerging Technologies Research Centre, De Montfort University, Leicester United Kingdom
Show AbstractOrgano-lead tri-halide perovskite thin-films have been emerged recently as a novel absorber material for efficient and low-cost photovoltaic applications [1], [2]. The stability of the perovskite thin films based photovoltaic cells upon the illumination for long periods of time strongly depends on the quality of the active layer and hence by the deposition conditions. Here, we are looking to fabricate a dense organo-lead tri-halide perovskite thin-film free of defects (pinholes) via developing novel synthesis approach with an overall aim to improve the performance of the solar cell.
In this work, the methyl-ammonium lead tri-iodide perovskite film was deposited on a glass substrate via spin-coating technique. The solution was prepared by mixing CH3NH3I and PbI2 powders by a molar ratio of (3:1) followed by dissolving this mixture in DMF. Isopropyl alcohol (IPA) was used as a crystallization agent on the film’s surface that leads to dense and cohesive non-porous layer. The IPA effect on the morphology, surface coverage, and quality of thin films were investigated. The fabricated perovskite thin films showed average thickness of 400 nm. Additionally, the optical properties of the grown film were studied via UV-VIS spectroscopy. The as-grown perovskite film showed an optical band gap of 1.5 eV. Furthermore, the current-voltage (I-V) characteristics of the lead iodide tri-halide perovskite film was measured in dark and under illumination via Hewlett-Packard (HP) HP4140B picoammeter. The experimental results revealed that the photocurrent is increased by three orders of magnitudes, demonstrating the ability of thin film, synthesized by a novel method, as a potential candidate for solar cell application.
References
[1] H. Kim, C. Lee, J. Im, K. Lee, T. Moehl, A. Marchioro, S. Moon, R. Humphry-Baker, J. Yum and J. E. Moser, Scientific reports, vol 2, pp. 591, 2012.
[2] M. M. Lee, J. Teuscher, T. Miyasaka, T. N. Murakami and H. J. Snaith, Science (New York, N.Y.), vol 338, no 6107, pp. 643-647, Nov 2 2012.
8:00 PM - ES01.13.33
Highly Efficient Plasmon Enhanced Organic and Perovskite Solar Cells via Incorporation of Gold Nanostars
Riski Titian Ginting 1 , Jae-Wook Kang 1
1 Department of Flexible and Printed Electronics, Chonbuk National University, Jeonju Korea (the Republic of)
Show AbstractAmong other methods to improve the power conversion efficiency (PCE) of organic solar cells (OSCs) and perovskite solar cells (PSCs), the incorporation of metal nanoparticles with plasmonic effects is an efficient way to enhance the light absorption and management of charge carrier dynamics. Herein, we report for the systematic synthesis of gold nanostar (Au NSs) and utilize it to investigate the role of plasmonic effect in active layer of OSCs and hole transporting layer of PSCs. Based on the current-voltage (J-V) characteristics, the results demonstrated that Au NSs significantly increased the PCE from 8.30 to 8.78 % for OSCs and 12.49 to 13.97 % for PSCs, owing to the improvement of short-circuit current density and fill-factor. The reason behind the plasmonic enhancement of Au NSs was investigated based on the combination of reflectance measurement, incident photon-to-current efficiency, photoluminescence, and impedance spectroscopy. The results indicate that localized surface plasmon resonance (LSPR) and backscattering gives rise to the improved light absorption and efficient charge separation/transfer, followed by effective charge transport in the presence of Au NSs. This work provides a novel strategy for high performance optoelectronic devices by employing Au NSs.
8:00 PM - ES01.13.34
Using a Brief Recrystallization Process, Synthesis Bulk State of Highly Luminescent CsPbBr3 Perovskite
Jae Young Noh 1 , Joong-Pil Park 1 , Sang-Wook Kim 1
1 Nano Material Laboratory, Ajou University, Suwon-si Korea (the Republic of)
Show AbstractJae-Young Noh1, Joong-pil Park2 Sang-Wook Kim*1
1Department of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea
Recently, ABX3 perovskites have enormous interest due to the good optoelectronic materials such as photovoltaics and LED display. Here we introduce a bulk state of all inorganic CsPbBr3 perovskite synthesized by adding a PbBr2-DMF solution to CsBr bulk. CsBr is a matrix of CsPbBr3 perovskite. The final product has a narrow full width at half maximum(FWHM) with strong green emission. This synthetic method is very fast, and suitable for mass synthesizing and large area coating. Product particle sizes are about more than hundreds of nanometers, and have orthorhombic crystal structures. Interestingly, this product shows a good photoluminescence (PL) emission at room temperature (RT).
Through this study, we found a recrystallization method about novel synthesis of highly luminescent perovskite-CsPbBr3 materials. As a result, we achieve film application and scalable mass production.
8:00 PM - ES01.13.35
Crystal Growth Control of PbI2 Thin Film by Thermal Treatment for Planar Perovskite Solar Cells Fabricated by Two-Step Coating Method
Kohei Yamamoto 1 , Keitaro Hamada 2 , Md Shahiduzzaman 3 , Kyosuke Yonezawa 1 , Makoto Karakawa 1 3 , Takayuki Kuwabara 1 , Kohshin Takahashi 1 , Tetsuya Taima 1 3
1 Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa Japan, 2 , Japan Advanced Institute of Science and Technology, Nomi Japan, 3 Institute for Frontier Science Initiative (InFiniti), Kanazawa University, Kanazawa Japan
Show AbstractOrganometallic halide perovskite (PSCs) has recently emerged as promising cost-effective and highly efficient nanostructured solar cells. The efficiency of PSC solar with the power conversion efficiency (PCE) of 3.81% was first reported by Kojima et al. At present, typical PCE value of perovskite solar cells are over 20% far higher than that of organic thin-film solar cells. CH3NH3I molecule intercalates into PbI2 film, in terms of formation of CH3NH3PbI3 (MAPbI3) perovskite crystal. Controlled crystal growth of PbI2 is important for precise intercalation to yield efficient perovskite film and resulting solar cells. Higher solar cells performance would be owing to better intercalation control of MAPbI3 film. The PbI2 assumes different crystal phases depending on temperature, which may result in the changing crystallinity, and morphology by thermal annealing. Herein, we attempt to control the crystal growth of PbI2 by varying annealing temperature of 70, 150, and 250 oC for 1, 5, 10, and 30 min using two-step spin-coating method for precise intercalation to yield efficient, perovskite thin-film and solar cells. We also investigate the effect of crystallinity of PbI2 on the performance of resulting MAPbI3 solar cells. X-ray diffraction (XRD) was used to evaluate the structural properties of PbI2 and MAPbI3 films by using full-width at half maximum (FWHM) of the (110) primary peak. The lower FWHM has a correlation with higher crystallinity of film. In terms of annealing temperature of PbI2 thin-film for 1 min, the FWHM of PbI2 yielded MAPbI3 film was decreased by higher annealing temperature. The optimized annealing temperature was found at 250 oC for the resulting devices fabrication. The resulting PCE is increased considerably in the average range of 2.38±1.52% to 5.65±1.18%, while changing the annealing time from 1 to 30 min. The best control and highest reproducibility performance were obtained with the controlled crystal growth of PbI2 film annealed with 30 min, which leads to an enhanced charge dissociation and transport efficiency and reduction in recombination events in the solar cells. Our results highlight that the controlled growth of PbI2 significantly affected to precise intercalate to yielding efficient perovskite film and resulting in solar cells performance.
8:00 PM - ES01.13.36
Metal Thin Film Based ITO-Free Semitransparent Perovskite Solar Cells
Se-Phin Cho 1 , Seok-In Na 1 , Seok-Soon Kim 2
1 , Chonbuk University, Jeonju-si Korea (the Republic of), 2 , Kunsan University, Gunsan-si Korea (the Republic of)
Show AbstractIn parallel with tremendous attention to perovskite solar cells (PeSCs) as next generation photovoltaics owing to their excellent power conversion efficiency (PCE), semitransparent PeSCs have emerged as promising approach for multi-functional device such as highly efficient tandem cell and power generating windows. General planar heterojunction (PHJ) PeSCs are composed of perovskite/PCBM bilayer sandwiched between ITO transparent electrode and top metal electrode. However, because commonly used ITO has several disadvantages such as high cost and poor mechanical property, development of alternative electrode is a crucial issue for realization of PeSCs.
In this work, we investigate ITO-free semitransparent PeSCs by using thermally evaporated thin metal layer as ITO alternative. Thermal evaporation is suitable with roll-to-roll based mass production and thin metal layer has excellent conductivity and flexibility. For that reason, thin metal films can be considered as a potential transparent electrodes for PeSCs. By optimizing metal layers and each interfacial layer, highly efficient ITO-free semitransparent PeSCs showing PCE of ~ 10 % (Average transmittance of ~ 30 %) was demonstrated. More significantly, the resulting devices showed excellent ambient stability. Characterization of various metal layers and their effect on the performance of devices will be discussed.
8:00 PM - ES01.13.37
Interface Engineering for Efficient Electron Extraction in Planar Perovskite Solar Cells
Gyeongho Kang 1 , Seulki Song 1 , Chaesung Lim 1 , Taiho Park 1
1 , POSTECH, Pohang Korea (the Republic of)
Show AbstractUnderstanding and controlling interfacial charge transfer at heterojunction of electronic and optoelectronic devices are currently receiving extensive interest. The parameters that can influence the electron extraction in planar perovskite solar cells (P-PSCs) were studied in this work. We find that a large free energy difference value between the electron transport layer (ETL) and perovskites plays a more important role in electron extraction than the high electron mobility of the ETL. It has also been proven that physical contact is crucial for achieving improved electron extraction. By introducing a bilayered ETL consisting of SnO2 (~30 nm) and anodized TiO2 (a-TiO2, ~10 nm), SnO2@a-TiO2, a large free energy difference as well as defect-free physical contact can be achieved in the ETL. The resulting P-PSC employing a SnO2@a-TiO2 ETL exhibits a 21.1% J–V scan efficiency and a 20.2% maximum power point (MPP) efficiency with reduced hysteresis.
8:00 PM - ES01.13.40
Preparation of Quality Transparent Conductive Oxides for Next Generation Solar Cells through a Spray Pyrolysis Deposition
Shun-ichi Ohta 1 , P.V.V. Jayaweera 1 , Shoji Kaneko 1
1 , SPD Laboratory, Inc., Hamamatsu Japan
Show AbstractTransparent conductive oxide (TCO) has essentially been applied for dye-sensitized and perovskite solar cell studies as working electrodes, which are continuing to request the supply of their quality products for their performance improvement.
A spray pyrolysis deposition (SPD) is chemical thin film formation or surface coating on a substrate from liquid phase. SPD is carried out using double fluids of raw solution and compressed air at room temperature under an atmospheric pressure, resulting in tailored thin films from atomized raw material solutions using simple apparatus with easy operation. The spraying operation here is carried out not consecutively but intermittently for suppressing remarkable reduction of a prescribed substrate temperature between 200 and 600 °C, and the component and composition of thin film deposited coincide with those of starting solution [1-3].
The coating of 150 mm squared FTO with a visible light transmittance 81.4% and a sheet resistance 7.4 Ω/sq was achieved from an ethanol solution including di-butyl tin(IV) di-acetate and ammonium fluoride on a glass substrate by the above-mentioned SPD. High quality of the FTO was assured also from small numerical deviations of transmittance and sheet resistance data measured at 36 divided locations. Also, we could obtain better specifications of a transmittance 83.4% and a sheet resistance 4.6 Ω/sq with small deviation in ITO deposited from an ethanol solution including indium(III) chloride tetra-hydrates and tin(II) chloride di-hydrates. It has been proved that our spray pyrolysis deposition is suitable for the preparation of quality TCO. The surface roughness and electronic properties of TCO will be discussed from AFM observation and electrical measurements, respectively.
[1] I. Yagi and S. Kaneko, Chem. Lett., 1991, 156-59.
[2] K. Murakami et al., J. Am. Ceram. Soc., 79 (1996) 2557-62.
[3] E. V. A. Premalal et al., Thin Solid Films, 520 (2012) 6813-17.
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Ultrafast X-Ray (Synchrotron) Study of Perovskite Cage Towards Increasing Thermal Stability
Eurig Jones 1 , Peter Holliman 1 , Arthur Connell 1 , Leo Furnell 1 , Rosie Anthony 1 , Chris Kershaw 1
1 College of Engineering, Swansea University, Swansea United Kingdom
Show AbstractHerein, we report studies of the formation and increased thermal stability of the perovskite cage measured by ultra-fast X-ray diffraction using the synchrotron at the Diamond Lightsource. These data have been correlated with Raman spectroscopy.
Our data show that by close pairing of the perovskite material to a suitable metal oxide scaffold (Al2O3) [1], the initial stability of the perovskite stack can be greatly enhanced, allowing the perovskite to be synthesized entirely under ambient conditions. In an additional benefit, our data also show that the perovskite material produced using this method also retains its structural integrity and colour over time. Furthermore, these benefits are achieved using a ball milling process to create perovskite inks in terpineol; thus, entirely avoiding the need for any toxic solvents during perovskite processing which can also be retained within the structure [2, 3].
In order to further understand the nature of the perovskite cage, we will also report a multi-user analysis of the deposited perovskites to compare the one-step, solution-based spin coating approach. Here the deposited perovskites have been re-dissolved and the constituent materials analyzed by absorption and NMR spectroscopy. The data confirm the importance of the equipment used and the surrounding conditions (e.g. RH, temperature) which highlighting the highly sensitive nature of the perovskite material set. During the ultra-fast measurements, in order to minimize these inherent variations, synthesized perovskite crystals were suspended in a suitable medium and cast down; avoiding re-crystallization and complex solvent issues.
References
1. E. W. Jones, P. J. Holliman, A. Connell, M. L. Davies, J. Baker, R. J. Hobbs, S. Ghosh, L. Furnell, R. Anthony and C. Pleydell-Pearce, Chem. Commun., 2016, 52, 4301-4304. DOI:10.1039/C5CC09859A
2. A.E. Williams, P.J. Holliman, M.J. Carnie, M.L. Davies, D.A. Worsley, T.M. Watson, J. Mater. Chem. A, 2014, 2, 19338-19346.
3. P.J. Holliman, A. Connell, E.W. Jones, S. Ghosh, L. Furnell, R.J. Hobbs, Materials Research Innovations, 2015, 19, 508-511. DOI: 10.1080/14328917.2015.1121317.
8:00 PM - ES01.13.42
Cs Oleate Passivation of Perovskite for Stable and Efficient Photovoltaics
Xintong Guo 1 2 , Tech Ming Koh 1 , Subodh Mhaisalkar 1 3 , Nripan Mathews 1 3 , Xiaodong Chen 3
1 Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Singapore Singapore, 2 Interdisciplinary Graduate School, Nanyang Technological University, Singpaore Singapore, 3 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractOver the last few years, tremendous development in organic-metal halide perovskites have led to solar cells with high power conversion efficiency, showing promising potential for low cost and efficient photovoltaic application. However, poor stability is one of the most serious obstacles that prevents their commercial applications. Here, we show an improved moisture stability of triple cation perovskite solar cells, Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3, using Cs oleate to modify perovskite/HTM interface. Devices with Cs oleate passivation are able to maintain more than 85% of initial power conversion efficiency after 400 hours at RH~40%, while that of control devices drop to 67%. The Cs oleate layer does not sacrifice the high power conversion efficiency of 16.8%. It maintains the high Jsc and improves the Voc. The oleate tails coated on perovskites provide hydrophobicity, which protect the film from degradation in ambient environment. The improved hydrophobicity of perovskite film after Cs oleate passivation is confirmed by measuring the water contact angle, which increases dramatically from 60 degree to over 100 degree.
8:00 PM - ES01.13.43
High Performance, Fast Response and Air-Processed CH3NH3PbI3-xClx Based MSM Photodetector with Broad Spectral Response
Vishwa Bhatt 1 , Manjeet Kumar 1 , Eunji Song 1 , Jieun Park 1 , Ju-Hyung Yun 1
1 Department of Electrical Engineering, Incheon National University, Incheon, Seoul, Korea (the Republic of)
Show Abstract
In recent years, hybrid perovskites such as MAX3 where X: Cl, Br, I have been emerged as one of the most promising candidate for the fabrication of Photovoltaic (PV) and Optoelectronic (OE) devices due to its captivating optical and electrical properties[1]. Tremendous light sensitivity, broad-band light absorption, and high carrier mobility has been the reason of its emergence as one of the key technological materials for light sensitive devices[2]. The advantages of fabrication process are its ease of processibility, simple synthesis roots and easy techniques. This can lead to overall reduction in fabrication cost of device. Based on such encouraging properties and recent advancements in research and developments, MAX3 have been an emerging field of interest. For example, the band gap of CH3NH3PbI3-xClx is 1.55 eV which suggests that it exhibits broad-band photoresponse from visible to UV region[3]. The basic structure consists of the photo absorbing material deposited with contact electrodes. Many researchers have incorporated hole transport material (HTM) and electron transport material (ETM) to enhance the collection efficiency of the photodetector by improving the charge transport taking place across the junctions but overall cost of device increases and complicate fabrication processes.
Despite of such advancements, there is a scope of study to investigate photodetection properties with a low dark current and high photoresponse along with fast transient conditions. In present study, a simple MSM photodetector by using CH3NH3PbI3-xClx has been fabricated over Si/SiO2(100nm) using Au contact electrodes. The device has been investigated over a broad spectrum suggesting that device is very useful for light detection in a visible range. The device shows a symmetric response in forward and reverse bias directions behaving as two diodes connected in a back to back manner and exhibiting a schottky junction across the barrier and gives a dark current as low as 2.6mA/m2 without introducing any HTL or ETL. In addition, due to very low dark current, sensitivity and ON/OFF ratio are nearly similar and obtained to be 23.2 and 25.4 at 505nm. The photoresponse has been observed to be 4 mA/m2 at 2V with an incident power of 0.6W/m2 at 505nm. The transient response has been observed to be 2.7ms (rise time) and 11ms (fall time). The highest detectivity and spectral responsivity are obtained to be 16.2×1012 Jones and 0.11A/W at 505nm respectively.
Reference
Liu, Jingying, et al. ACS nano 10.3 (2016): 3536-3542.
Gao, Liang, et al. Nano Letters 16.12 (2016): 7446-7454.
Vishwa Bhatt et al. RSC Advances 6, 113 (2016): 111942-111949.
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Domain Size Dependence of Photodegradation in MAPbI3
Jose Castaneda 1 , Yong Zhang 1 , JeongHyeok Im 2 , Nam-Gyu Park 2 , Yucheng Liu 3 , Shengzhong Liu 3
1 , University of North Carolina at Charlotte, Charlotte, North Carolina, United States, 2 , Sungkyunkwan University, Suwon Korea (the Republic of), 3 , Shaanxi Normal University, Xi'an China
Show AbstractOrganic-inorganic perovskites have gathered much attention as a cost-effective and efficient photovoltaic material. Methylammonium lead triiodide (MAPbI3) devices have already reached power conversion efficiencies above 20%, but long-term stability concerns restrict the practical application of this fast-growing technology. Lead iodide (PbI2) is often left over from degradation, which can be induced upon incident light due to low photo and thermal stabilities. Through Raman spectroscopy the structural changes within MAPbI3 were monitored to provide information on the degradation process. Our study has indicated that the intrinsic Raman spectrum of MAPbI3 essentially has no clearly identifiable feature in the spectral range related to the Pb-I cluster, and the Pb-I related modes become progressively more apparent and resolvable in the degradation stages closer to PbI2 [1]. In this work, we investigate the correlation between the polycrystalline domain size and the ease of photodegradation. A set of samples with respective average domain sizes of 100, 200, and 400 nm were studied, and compared with a single large crystal. Raman measurements were carried out in both a continued and pulsed excitation mode, using a 532 nm laser with excitation densities varying from 0.6 – 45 kW/cm2. We find that the photodegradation process is accelerated as domain sizes decrease where spectral features from the PbI2 degradation product are more pronounced, and display a faster rate of transformation. This trend follows throughout different excitation conditions, except at lower excitation densities where photodegradation is only seen in the smallest domain size probed (100 nm). These results suggest that film domain size should also be considered under a set of experimental conditions just the same as parameters such as excitation power and illumination time. The possible mechanisms for the observed domain size dependence could include such phenomena as surface effects and variation in thermal conductivity. Slight heating (e.g., to 60 °C) is found to accelerate the photodegradation in the more stable single crystal sample, which is consistent to the theoretical prediction that this material has a small thermal dissociation energy (Gibbs free energy) from MAPbI3 → MAI + PbI2 [2].
[1] Q. Chen et al., PRX 6, 031042 (2016); 7, 019902 (2017).
[2] Y. Zhang et al., arXiv:1506.01301 (2015); E. Tenuta et al., Sci. Rep. 6, 37654 (2016).
8:00 PM - ES01.13.44
Domain Size Dependence of Photodegradation in MAPbI3
Jose Castaneda 1 , Yong Zhang 1 , JeongHyeok Im 2 , Nam-Gyu Park 2 , Yucheng Liu 3 , Shengzhong Liu 3
1 , University of North Carolina at Charlotte, Charlotte, North Carolina, United States, 2 , Sungkyunkwan University, Suwon Korea (the Republic of), 3 , Shaanxi Normal University, Xi'an China
Show AbstractOrganic-inorganic perovskites have gathered much attention as a cost-effective and efficient photovoltaic material. Methylammonium lead triiodide (MAPbI3) devices have already reached power conversion efficiencies above 20%, but long-term stability concerns restrict the practical application of this fast-growing technology. Lead iodide (PbI2) is often left over from degradation, which can be induced upon incident light due to low photo and thermal stabilities. Through Raman spectroscopy the structural changes within MAPbI3 were monitored to provide information on the degradation process. Our study has indicated that the intrinsic Raman spectrum of MAPbI3 essentially has no clearly identifiable feature in the spectral range related to the Pb-I cluster, and the Pb-I related modes become progressively more apparent and resolvable in the degradation stages closer to PbI2 [1]. In this work, we investigate the correlation between the polycrystalline domain size and the ease of photodegradation. A set of samples with respective average domain sizes of 100, 200, and 400 nm were studied, and compared with a single large crystal. Raman measurements were carried out in both a continued and pulsed excitation mode, using a 532 nm laser with excitation densities varying from 0.6 – 45 kW/cm2. We find that the photodegradation process is accelerated as domain sizes decrease where spectral features from the PbI2 degradation product are more pronounced, and display a faster rate of transformation. This trend follows throughout different excitation conditions, except at lower excitation densities where photodegradation is only seen in the smallest domain size probed (100 nm). These results suggest that film domain size should also be considered under a set of experimental conditions just the same as parameters such as excitation power and illumination time. The possible mechanisms for the observed domain size dependence could include such phenomena as surface effects and variation in thermal conductivity. Slight heating (e.g., to 60 °C) is found to accelerate the photodegradation in the more stable single crystal sample, which is consistent to the theoretical prediction that this material has a small thermal dissociation energy (Gibbs free energy) from MAPbI3 → MAI + PbI2 [2].
[1] Q. Chen et al., PRX 6, 031042 (2016); 7, 019902 (2017).
[2] Y. Zhang et al., arXiv:1506.01301 (2015); E. Tenuta et al., Sci. Rep. 6, 37654 (2016).
8:00 PM - ES01.13.45
CsSnBr3 as a Lead-Free, All-Inorganic Perovskite Semiconductor for High-Performance Optoelectronics
Binghan Li 1
1 School of Physical Science and Technology, Shanghaitech University, Shanghai, Shanghai, China
Show AbstractAbstract
Organic lead triiodide perovskite materials, MAPbI3 in particular, are currently being intensely studied as the active-layer material for solar cells, photodetectors, and light-emitting diodes. To replace the toxic Pb2+ in these materials, metal cations with an s2 electronic configuration (e.g., Ge2+, Sn2+, Sb3+, and Bi3+) have been considered, and Sn2+ stands out from other candidates in terms of performance, cost, and sustainability. Among the known Sn2+-based perovskite materials, CsSnBr3 is unique for being all-inorganic and semiconducting. Althought it is unclear whether the dynamic MA+ cation in MAPbI3 is responsible for its large dielectric constant (ε = 60) and hence small exciton binding energy, herein we report that the dielectric constant of CsSnBr3 is even greater: ε(100 kHz) = 70 and ε(1 kHz) = 140. Challenges in fabricating CsSnBr3 devices orginate largely from Sn4+ defects on surfaces and in the bulk. To address this issue, we grew shiny CsSnBr3 single crystals up to 6×6×3 mm3 in size, using surfactants under an inert atmosphere. Transimission spectroscopy show a steep absorption edge at ~740 nm, and no sub-bandgap absorption attributable to defect states. The CsSnBr3 single crystals were further made into plates of thicknesses between 0.3 and 2.5 mm, and then into metal–perovskite photodiodes. These photodiodes generate an open-circuit voltage of 0.40–0.43 V under simulated sunlight, higher than that of spin-coated CsSnBr3 solar cells reported so far. By measuring the external quantum efficiencies (EQEs) of Ga/CsSnBr3/Au photodiodes toward 650 nm excitation as a function of plate thickness, we estimate the charge carrier diffusion length of single-crystal CsSnBr3 to be on the order of 101–102 μm, similar to that of MAPbI3. All the above characterization results suggest that CsSnBr3, especially in the form of single crystals, is a promising lead-free substitute for MAPbI3 as a high-performace optoelectronic material.
8:00 PM - ES01.13.46
All Inorganic Lead-Free Perovskite Films Obtained through Controlled Crystallization
JeongHyeok Im 1 , M. Ibrahim Dar 1 , Michael Graetzel 1
1 Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Switzerland, Lausanne Switzerland
Show AbstractOrganic-inorganic halide perovskite materials have attracted unprecedented interest in recent years as promising photovoltaic materials because of their desired optical and electronic properties. Most of the high-efficiency perovskite solar cell are based on lead (Pb) which is highly toxic material. Therefore, to realize theire practical application, it is important to replace the Pb metal with a benign material. Recently, inorganic lead-free perovskite solar cells have been reported but their performances are still low because the deposition of high-quality perovskite layer is a big challenge. The lead-free alkali metal halide is insoluble in aprotic solvents to dissolve the metal halide materials. Hence, most lead-free perovskite layers are fabricated using low concentration of the solution, leading to the poor quality perovskite layer [1]. Here, we present sequential deposition method to deposit high-quality cesium tin bromide (CsSnBr3) based on all inorganic lead-free. In the second step fabrication process, alkali metal halide materials were dissolved in the isopropanol-water mixture. We found out that the thickness of the inorganic lead-free perovskite film can be controlled by the concentration of a solution in this step. It is beneficial for making good device because the thickness of the perovskite layer has a correlation with crystallinity and conductivity. And we confirm that the inorganic lead-free material is thermally highly stable.
[1] Tze-Bin Song et al., J. AM. Chem. Soc. 2017, 139, 836-842
8:00 PM - ES01.13.47
Pulsed Laser Deposition of Methyl Ammonium Lead Iodide Thin Films for Vis-Near Infrared Photodetectors
Nagabhushan Patel 1 , Sandra Dias 1 , Venkat Daramalla 1 , S.B. Krupanidhi 1
1 , Indian Institute of Science, Bengalore, KA, India
Show AbstractPerovskite halide materials are considered as promising candidates for emerging thin-film photodetectors. In this work we discussed the application of the CH3NH3PbI3 thin films by pulsed laser deposition for photo detection applications. With this method we obtained high perovskite film coverage on FTO substrate and observed well formed grains. The films did not show any sign of degradation over months together.
We investigated the surface morphology and surface roughness of the films by field emission scanning electron microscope and atomic force microscope. We studied the optical responses of the films. Photoluminescence (PL) spectra was observed for all films which were grown at different deposition and annealing time durations, and the PL peak was found at 1.61 eV, 1.61eV, 1.6 eV and 1.62 eV respectively. Also, UV-Visible spectra was observed for all the samples and the band gaps were found at 1.55 eV, 1.52 eV, 1.57 eV and 1.6 eV respectively. From the time resolved PL spectrum, the decay time constant was increasing with the film thickness.
We carried out a study on the solar and infrared photodetection of CH3NH3PbI3 thin films. The values of the responsivity, sensitivity, external quantum efficiency and specific detectivity under 1 sun illumination and 0.7 V bias were 105.4 A/W, 1.9, 238% and 1.5 × 1012 Jones respectively.
8:00 PM - ES01.13.48
Photoinduced Anion Exchange of Cesium Lead Halide Perovskite Nanocrystals and Photoinduced Patterning
David Parobek 1 , Dong Hee Son 1 , Yitong Dong 1
1 , Texas A&M University, College Station, Texas, United States
Show AbstractRecently, inorganic cesium lead halide (CsPbX3) perovskite nanocrystals (NCs) were developed exhibiting photoluminescence quantum yields greater than 90% with band gap tunability throughout the visible spectrum via anion exchange. The labile nature of the perovskite NC allows for the exchange of the halide anions without damaging the host lattice by using reactive alkyl halide precursors. The use of chemical precursors makes it difficult to control the extent of the anion exchange, limiting the ability to tune the band gap energy precisely. In this work, CsPbX3 perovskite NCs undergo light-triggered anion exchange, in the presence of unreactive dihalomethane solvents. The irradiation of CsPbX3 perovskite NCs above the bandgap prompts the interfacial electron transfer from the surface of NC to the dihalomethane solvent molecules resulting in the reductive dissociation of the halide ion. The halide ions photogenerated near the NC surface subsequently undergoes anion exchange, allowing for the fine control of the extent of anion exchange by varying either the photon dose or wavelength of the excitation light. In particular, a targeted extent of exchange could be readily achieved via self-limiting behavior of the photoinduced anion exchange when an appropriate wavelength is chosen. Multiphoton excitation-induced anion exchange was also performed successfully demonstrating the possible photopatterning in 2 or 3-dimensional space when limiting the diffusion of free anions in the medium. In summary, photoinduced anion exchange allows for selective tuning of the band gap with high precision and provides a route towards patterning specific areas of a substrate.
8:00 PM - ES01.13.50
Strontium Based Perovskites for Solar Cell Applications
Thomas Christian 1 , Fiona Teevan-Kamhawi 1 , Carl Bonner 1
1 , Norfolk State University, Norfolk, Virginia, United States
Show AbstractThis perovskite research studies the replacement of Lead with the alkaline- earth metal Strontium using ratios of 1:1 and 3:1 and 5:1 (Strontium to Lead). These are studies with the goal of increasing the efficiency of solar energy conversion to electricity using a perovskite solar cell. Organic/ inorganic perovskite solar cells exhibit over 17% efficiency for solar to electrical power conversion. Organic/ inorganic methylamine strontium lead iodide perovskites act as both a light harvester and an exciton producer. Although the methylamine lead iodide perovskite has shown the ability to directly convert solar energy into electricity, a major concern exists because of lead’s toxicity to humans this is why the replacement of lead with strontium is being used. Our results indicate that the absorption intensity decreases as the strontium concentration increases, the absorption spectrums reveal a wavelength transition shift as the concentration of strontium increases and strontium increases the intensity of the emission from fluorescence.
8:00 PM - ES01.13.51
Investigation the Role of Chlorine in Lead Free Mixed Halide Perovskites (Cs2SnI6-xClx)
Weiguang Zhu 1 , Jie Lian 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractOrganic-inorganic perovskite (CH3NH3PbI3) experiences significantly environmental instability under ambient moist air and presents a toxicity issue of lead (Pb). To overcome these challenges, we synthesize lead-free hybrid inorganic perovskites with a general formula Cs2SnI6-xClx and explore their potentials for photovoltaic applications. Due to the high oxidation state of Sn, Cs2SnI6-xClx is considered to be more stable in air and moisture than CH3NH3PbI3. The presence of Cl- is essential to improve the material stability and enhance the perovskite crystallization. By changing the ratio of I/Cl, the optical absorption can be fine-tuned and with Cl- a longer charge diffusion length has been observed, which is very important for photovoltaic applications. A unique phase behavior was also observed in which the binary Cs2SnI6-xClx separates into two different phases with chlorine and iodine-enriched compositions, and the phase separation significantly affects the optical properties and stability of the inorganic perovskite. To investigate the role of chlorine, thin films were fabricated with optimized deposition parameters. The film conformity and crystal structures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The optical and transport properties were studied by photoluminescence (PL) and Hall effect measurement to decipher the role of chlorine in the hybrid all-inorganic perovskites (Cs2SnI6-xClx). Moreover, the solar cell performance and currently limiting efficiency will be discussed to provide guidelines for further development and optimization of lead-free inorganic perovskites.
8:00 PM - ES01.13.52
Effects of Hole Transport Layer on the Crystallinity, Local Morphologies of Organometal Halide Perovskite Films and Carrier Transport Properties in Inverted Perovskite Solar Cells
Hironori Ogata 1 , Toshiya Kobayashi 1 , Kazunori Ito 1 , Tomoko Onaka 1 , Hiroya Kiuchi 1 , Takamasa Takeuchi 1 , Yuki Fukazawa 1
1 , Hosei University, Tokyo Japan
Show AbstractOrganometal halideperovskite solar cells based on an n–i–p architecture have recently been reported to be highly efficient, giving an overall power conversion efficiency exceeding 20%. In the n–i–p architecture, the hole transport layer is usually made of spiro-OMeTAD with mixed additives to improve the conductivity of itself. However, spiro-OMeTAD is expensive and precision control of cell fabrication is difficult because additives used in spiro-OMeTAD dissolve the organometal halide perovskite layer. For these reasons, mass production of perovskite solar cells using spiro-OMeTAD is considered to be difficult. In order to avoid these problems, inverted organometal halide perovskite solar cells based on p–i–n architectures have recently been proposed and reported.
In the hole transport layer materials of inverted organometal halide perovskite solar cells, there are several requirements as follows. (1)Limit interfacial energy barriers between the perovskite layer and the electrodes and block recombinations at the interfaces, (2) HOMO level maching between hole transport layer and perovskite, (3)high hole mobility, (4)high optical transmittance, and (5)compatibility with adjacent components and solution processability.
Currently, PEDOT-PSS, poly TPD, Cu: NiOx, graphene oxide, carbon nanotubes etc. are reported as hole transporting layer meterials of inverted organometal halide perovskite solar cells satisfying these conditions.
To take full advantage of the characteristics of inverted organometal halide perovskite solar cell, it is essential to improve the highly crystalline, pin-hole free and planar perovskite film. However, detailed relationship between the hole transport layer and the crystallinity and local morphologie of perovskite film and their photovoltaic performance has not fully unknown. Here, we have employed the several kinds of hole transport layer films and investigated the relationship between their crystallinity and transport properties of perovskite films and their cell performances systematically.
In this presentation, detailed results of crystallinity of perovskite layers, surface morphologies and photovoltaic properties of inverted organometal halide perovskite solar cells prepared systematically by changing the hole transporting layers will be presented.
References
1) P. Docampo, J. M. Ball, M. Darwich, G. E. Eperon and H. J. Snaith, Nat. Commun., 2013, 4, 2761.
2) J. You, L. Meng, T. B. Song, T. F. Guo, Y. M. Yang, W. H. Chang,
Z. Hong, H. Chen, H. Zhou, Q. Chen, Y. Liu, N. De Marco and
Y. Yang, Nat. Nanotechnol., 2016, 11, 75.
3) Y. Shao, Y. Yuan and J. Huang, Nat. Energy, 2016, 1, 15001.
4)Esmaiel Nouri, Mohammad Reza Mohammadi and Panagiotis Lianos, Chem. Commun., 2017,
53, 1630.
8:00 PM - ES01.13.53
Photo Assisted Poling Effect in Organic-Inorganic Hybrid Perovskite and Its Application for Self-Powered Tactile Sensors
Rohit Saraf 1 , Long Pu 1 , Vivek Maheshwari 1
1 , University of Waterloo, Waterloo, Ontario, Canada
Show AbstractOrganometallic trihalide perovskite materials have drawn substantial interest due to their outstanding performance in solar energy conversion and optoelectronic applications, especially tetragonal methylammonium lead tri-iodide (MAPbI3). We have investigated the anomalous photovoltaic (APV) response in MAPbI3 symmetric lateral structure cell configuration when electrically poled at different voltages. The effect is characterized by its open-circuit voltage (Voc), short-circuit current (Jsc) and its transient decay. We specifically observe a significant difference in the stability of APV (and also other parameters) based on poling under dark and under one sun illumination. The effect is also shown to be dependent on the phase of the perovskite with difference between the α phase and the β phase. To further investigate its coupling to a typical solar cell, we have fabricated a lateral non-symmetric structure of Au/MAPbI3/ZnO, and characterized its performance, effect of poling and phase transition. This study provides new insights for understanding MAPbI3 properties and provides a simple photo-assisted method for manipulating the electric properties of MAPbI3 film.
8:00 PM - ES01.13.54
Impact of Ultra-Low Thermal Conductivity on Perovskite Solar Cells
Aron Walsh 1 , Lucy Whalley 1 , Jarvist Frost 1
1 , Imperial College London, London United Kingdom
Show AbstractAnharmonicity in the lattice vibrations of hybrid halide perovskites results in short phonon lifetimes and ultra-low thermal conductivity1,2. There are important consequences for the physical and chemical properties of halide perovskites, which can explain many anomalies in reported device measurements and behaviour. These include: (i) inefficient hot-carrier cooling in operating solar cells; (ii) slow non-radiative electron-hole recombination rates; (iii) enhanced ion transport due to heat gradients; (iv) accelerated chemical degradation due to local heating. The microscopic driving forces for these phenomena will be shown, as well as approaches to overcome them.
1. Whalley, L. D., Frost, J. M., Jung, Y.-K. & Walsh, A. Perspective: Theory and simulation of hybrid halide perovskites. J. Chem. Phys. 146, 220901 (2017).
2. Whalley, L. D., Skelton, J. M., Frost, J. M. & Walsh, A. Phonon anharmonicity, lifetimes, and thermal transport in CH3NH3PbI3 from many-body perturbation theory. Phys. Rev. B 94, 220301(R) (2016).
8:00 PM - ES01.13.55
Synthesis of Large Hybrid Perovskite Single Crystals with Continuous-Mass Transport Process
Wenzhen Wang 1 , Jiang Cai 1 , Hua Meng 1 , Linjun Wang 1 , Run Xu 1 , Fei Xu 2 3
1 School of Materials Science and Engineering, Shanghai University, Shanghai China, 2 SHU-Solare Research and Development Laboratory, Department of Physics, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai China, 3 State Key Laboratory of Surface Physics and Department of Physics, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai China
Show AbstractOrganic–inorganic hybrid perovskites such as methylammonium lead halide (MAPbX3, MA= CH3NH3+, X=I-, Br-, Cl-) attract more and more attention due to excellent optoelectronic properties, such as high carrier mobility, long-range balanced electron and hole diffusion lengths, long carrier lifetime, strong absorption in the whole visible range. In particular, optical and electrical properties can be considerably enhanced in single crystalline perovskites, compared to their polycrystalline thin film. However, perovskite single crystals with small size can generally be observed in a single perovskite growth process as previously reported by solution-based methods. Single crystals with large size should be grown by several repeated processes upon exposure to environment.
In this work, we reported a new approach to synthesize MAPbX3 single crystals with size larger than 10cm. This approach was based on continuous-mass transport process (CMTP). Firstly, a perovskite seed obtained by inverse temperature crystallization was transferred to a specially designed equipment with circulating solution in two flasks, one for crystal growth and the other for the raw materials. The continuous growth of single crystals with good crystallinity was controlled by the temperatures of two flasks. This growth method of single crystals can uninterruptedly provide raw materials through mass transport, so that single crystal with large size can be achieved continuously. The size of crystal is only limited by the diameter size of the growth flask. Notably, both the size and shape of the crystals can be controlled by manipulating different crystallization parameters through this approach. We demonstrate that 1 cm solution-grown perovskites single crystals can serve as solid-state gamma-detecting materials. The Energy-resolved sensing at room temperature is presented using MAPbI3 SCs and an 241Am source at low bias.
8:00 PM - ES01.13.56
Effect of Preparation Methods of Metal Oxide Layers on the Carrier Transport Properties of Perovskite Solar Cells
Takamasa Takeuchi 1 , Hiroya Kiuchi 1 , Masato Gocho 1 , Kazunori Ito 1 , Toshiya Kobayashi 1 , Tomoko Onaka 1 , Yuki Fukazawa 1 , Hironori Ogata 1
1 , Hosei University, Tokyo Japan
Show AbstractPerovskite solar cells are an important photovoltaic technology with high efficiencies exceeding 20% due to their optimal band gap, large absorption coefficient, and high charge mobilities. We focused on the electron transport layer (ETL) in perovskite solar cells, which is an important part for high performing perovskite solar cells. Here, the ETL is referred to as a mesoporous and a compact metal oxide layers. The compact layer acts as hole-blocking layer, which could avoid the heavy recombination of the holes which were generated in perovskite layer and the electrons, which were existed in both perovskite layer and the HTL at the surface of the FTO layer. In this study, titanium oxide, zinc oxide and tin oxide were used as the mesoporous layer oxide layers, and we investigated the influence of the fabrication method of mesoporous layer on the interface structure, charge transport properties and the performances of perovskite solar cells systematically. We have adopted the sol-gel method, chemical bath deposition method and electrodeposition method as fabrication method of mesoporous layers and clarified the difference of interface structure, charge transport properties and solar cell characteristics by the preparation method.
We have also investigated the effect of fabrication parameters (electrodeposition time, applied current) for electrodeposition method on the film thickness, morphologies, crystallinities and defect structures of mesoporous layers. Detailed experiment results will be presented.
8:00 PM - ES01.13.57
Fabrication and Electronic Properties of Doped Tin Oxides as Electron Transporting Layers for Efficient Perovskite Solar Cells
Hiroya Kiuchi 1 , Takamasa Takeuchi 1 , Masato Gocho 1 , Kazunori Ito 1 , Toshiya Kobayashi 1 , Tomoko Onaka 1 , Yuki Fukazawa 1 , Hironori Ogata 1
1 , Hosei University, Tokyo Japan
Show AbstractHalogenated lead perovskite materials are the most promising candidates for high efficient next- generation solar cells because their excellent optoelectronic properties including high absorption coefficient, high carrier mobilities. The power conversion efficiency (PCE) of perovskite solar cells has increased to over 20% in the past few years. In the process of manufacturing perovskite solar cells,
the electron transport layers prepared by low-temperature process are essential for large-scale production of perovskite solar cells. In general perovskite solar cells, titanium oxide is widely used as the electron transport layer(both compact layer and mesoporous layer).
However, high temperature treatment is necessary for the fabrication of TiO2 . On the other hand, SnO2 can be fabricated at lower temperature than TiO2. In addition, SnO2 has a wide band gap, high electric mobility and is considered to be a promising electron transport layer. Perovskite solar cells using SnO2 as electron transport layer have been reported, their power However, the conversion efficiency is lower than those using TiO2. Doping the SnO2 layer is expected to further improve solar cell characteristics.
In this study, we have fabricated perovskite solar cells using several types of metal oxide nanoparticles as hole blocking layer and using doped SnO2 as an electron transporting layer and and investigated the effect of metal oxide layer on their charge transport properties and solar cell performances systematically. Detailed experiment results will be presented.
8:00 PM - ES01.13.58
Monolithic Perovskite/Silicon-Homojunction Tandem Solar Cell with Over 22% Efficiency
Yiliang Wu 1 , Di Yan 1 , The Duong 1 , Jun Peng 1 , Yimao Wan 1 , Pheng Phang 1 , Heping Shen 1 , Sachin Surve 1 , Chog Barugkin 1 , Dale Grant 1 , Thomas White 1 , Kylie Catchpole 1 , Klaus Weber 1
1 , Australia National University, Acton, Australian Capital Territory, Australia
Show AbstractCrystalline silicon (c-Si) solar cells featuring a high-temperature processed homojunction have dominated the photovoltaic industry for decades, with a global market share of around 93%. Integrating commercially available crystalline silicon solar cells with high-efficiency perovskite solar cells is a viable pathway to increase the power conversion efficiency, and hence achieve low levelized electricity costs for the photovoltaic systems. However, the fabrication process for this type of cell is challenging due to the many, and often conflicting, material processing requirements and limitations. Here, we present an innovative design for a monolithic perovskite/silicon tandem solar cell, featuring a mesoscopic perovskite top subcell and a high-temperature tolerant homojunction c-Si bottom subcell. The improved temperature tolerance of the c-Si bottom cell permits significantly increased flexibility in the design and fabrication of the perovskite cell. We demonstrate an efficiency of 22.5% (steady-state) and a Voc of 1.75 V on a 1-cm2 cell. The method developed in this work opens up new possibilities in designing, fabricating and commercialising low-cost high-efficiency perovskite/c-Si tandem solar cells.
8:00 PM - ES01.13.59
Optical and Electrical Properties of Wide Bandgap Perovskites
Aida Torabi 1 , Timothy Siegler 2 , Brian Korgel 2 , Taylor Harvey 1
1 , Texas A&M-Central Texas, Killeen, Texas, United States, 2 , The University of Texas at Austin, Austin, Texas, United States
Show AbstractRecently introduced Organic-inorganic hybrid perovskite solar cells CH3NH3PbX3 (x = halogen) have attracted considerable attention due to the demonstrated high power conversion efficiency (exceeding 22%). In this class of materials, wide-bandgap perovskite based on I and Br-mixed halide are considered promising candidates for tandem photovoltaics. Herein we present our study on the optical and electrical properties of these materials using cathodoluminescence (CL), Electron beam-induced current (EBIC), and energy dispersive X-ray spectroscopy (EDS) measured with scanning electron microscopy (SEM). The minority carrier properties and micro composition of the layers were studied to determine spatial distribution of physical and electrical properties. In addition, the carrier transport and recombination characteristics were studied via in situ photoimpedance spectroscopy. The results of the wide band gap perovskites are presented in comparison to other photovoltaic absorbers such as Copper indium gallium selenide (CIGS) and Cadmium Telluride (CdTe).
8:00 PM - ES01.13.60
What is at the Surface of Methylammonium Lead Iodide?
Kenneth Zielinski 1 , Ronald Grimm 1
1 , Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractWe utilized a series of wet-chemical reactions and subsequent surface science characterization to elucidate the chemical species present at the (100) and (110) faces of methylammonium lead iodide. Wet functionalization reagents included the Lewis acid BF3 for its ability to form adducts with a Lewis base, p-trifluoromethylanilinium chloride to probe the possible substitution with interfacial cations, and bis-4,4’-trifluoromethyl-2,2’-bipyridine that would ligate to interfacial metal species. Following photoelectron spectra that indicated the absence of lead oxide species, the BF3, p-trifluoromethylanilinium chloride, and derivatized bipyridine uniquely probe the presence of interfacial iodide, methylammonium, and lead species. Photoelectron spectroscopy and temperature programmed desorption quantified surface coverages and adsorbate interaction strengths. On the (100) face, adsorbed BF3 demonstrated a coverage of 45 ± 5% and a desorption energy of 210 ± 20 kJ mol–1 that we ascribe to the formation of a adduct bond with interfacial iodide. On p-trifluoromethylanilinium-functionalized surfaces, photoelectron spectra showed no residual chloride species that indicates a solution-phase substitution with interfacial methylammonium species, resulting in a surface in which p-trifluoromethylanilinium has substituted for interfacial methylammonium species. These results demonstrate the viability of covalent contacts at interfacial iodide, as well as the viability of interactions with ammonium species from some contacting phase. We discuss the implications for both the passivation and formation of intimate electrical contacts at perovskite semiconductors.
8:00 PM - ES01.13.61
High Stability of MAPbI3 Perovskite Solar Cells Showing no Degradation over 1000 Hours of Continuous Power Generation
M. Bodiul Islam 1 , Yasuhiro Shirai 1 , Masatoshi Yanagida 1 , Kenjiro Miyano 1
1 , National Institute for Materials Science, Tsukuba Japan
Show AbstractWe present high stability of methyl ammonium (MA) lead triiodide perovskite (MAPbI3) solar cells with sputter–deposited polycrystalline NiOx hole transport layer (HTL) and indium tin oxide (ITO) for both top and bottom electrodes. Previously, we demonstrated high thermal stability of the MAPbI3 perovskite devices with the NiOx HTL and glass encapsulations, showing no performance degradation at 85°C over 1000 hours in dark. However, they still degraded gradually under 1 sun illumination for continuous power generation at maximum power point (MPP). Here, we demonstrate that the combination of the NiOx HTL and the ITO electrode for both top and bottom electrodes of the perovskite solar cells resulted in the highly stable semitransparent devices with the average visible light transmittance (AVT) above 16% and the power conversion efficiency (PCE) of 12.5%, showing no performance degradation over 1000 hours of continuous operation under 1 sun illumination at MPP. Although the use of poly[bis(4-phenyl)(2,4,6-trimethylphenyl) (PTAA) HTL resulted in the semitransparent devices with higher PCE of 13.6%, their device stabilities were much inferior to the NiOx HTL based devices. These results indicated that a rather classical MA based perovskite, MAPbI3, is indeed a stable photovoltaic material with the proper choice of the interface layers and electrode materials, and the use of the sputter–deposited NiOx HTL together with the ITO for both top and bottom electrodes are the key elements to overcome the stability problem in the lead halide perovskite solar cells.
8:00 PM - ES01.13.62
Degradation of Encapsulated Perovskite Solar Cells Driven by Deep Trap States and Interfacial Deterioration
Dhruba Khadka 1 2 , Yasuhiro Shirai 1 , Masatoshi Yanagida 1 , Kenjiro Miyano 1
1 , National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan, 2 International Center for Young Scientist, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan
Show AbstractThe degradation of encapsulated perovskite device has been investigated by optoelectronic characterizations. The device performances with aging were found to be influenced by both interface recombination and deep trap assisted recombination in the bulk. The analysis of temperature dependent current-voltage characteristics and capacitance spectra revealed that decrease in activation energy of interface recombination, deep defect levels and reducing diffusion potential of devices led to deterioration of device parameters with aging. The degradation of our encapsulated devices might be governed by dissociation and migration of constituent ions which induces deeper defect level in perovskite layer and worsens the interfacial layer with aging. Our study implicates that the intrinsically stable perovskite layer and passivation of interfacial layer’s deterioration could be crucial aspects for device stability.
8:00 PM - ES01.13.63
Enhancing Perovskite Solar Cell Performance by Doping Barium in Methylammonium Lead Halide
Shun-Hsiang Chan 1 , Ming-Chung Wu 1 , Wei-Fang Su 2
1 Department of Chemical and Materials Engineering, Chang Gung University, Taoyuan City Taiwan, 2 Department of Materials Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractThe organic-inorganic lead halide perovskite solar cell is considered as one of the most promising technology for future photovoltaics because it shows high power conversion efficiency and can be fabricated through a simple solution process. The typical structure of organic-inorganic lead halide perovskite is APbX3, where A is an organic cation and X is a halide. However, long-term contact to lead can cause severe nerve and brain damage. The toxicity issue of lead drags the commercialization of PSC. Non-toxic alkaline earth metal cations are suitable candidates to replace toxic lead in perovskite because they meet tolerance factor of Goldschmidt’s rule and maintain the charge balance in perovskite. Thus, we partially replace the lead by alkaline earth ions to have a structure of CH3NH3M1-xPbxI3-yCly, where M are alkaline earth ions (Mg2+, Ca2+, Sr2+ and Ba2+). After the systematic study, the Ba2+-doped perovskite (i.e., CH3NH3Ba1-xPbxI3-yCly) exhibits the best photovoltaic performance. We investigated the crystal structure, absorption behavior and surface morphology of various Ba2+-doped perovskite active layers with different doping levels, and determined the correlation between the optoelectronic properties and Ba2+ doping levels. The charge carrier dynamics of Ba2+-doped perovskite active layers with different doping concentrations are also explored by time-resolved photoluminescence (TRPL) measurements. At the optimal 3.0 mol% Ba2+ replacement, the average power conversion efficiency of perovskite solar cells is increased from 11.8 to 14.0%, and the champion power conversion efficiency is as high as 14.9%.
8:00 PM - ES01.13.64
Highly Efficient and Uniform 1 cm2 Perovskite Solar Cells with an Electrochemically Deposited NiOx Hole-Extraction Layer
Ik Jae Park 1 , Jin Young Kim 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractGiven that the highest certified conversion efficiency of the organic-inorganic perovskite solar cell (PSC) is already over 22%, which is even higher than that of the polycrystalline silicon solar cell, the significance of new scalable processes that can be utilized for preparing large-area devices and their commercialization is rapidly increasing. From this perspective, the electrodeposition method is one of the mostly suitable processes for preparing large-area devices, because it is an already commercialized process with proven controllability and scalability. Here, we report highly uniform NiOx layer prepared by the electrochemical deposition process as an efficient hole-extraction layer of a p–i–n type planar PSC with a large active area of > 1 cm2. We demonstrate that the increased surface roughness of the NiOx layer, achieved by controlling the deposition current density, facilitates the hole extraction at the interface between perovskite and NiOx, and thus increases the fill factor and the conversion efficiency. The electrochemically deposited NiOx layer also exhibits extremely uniform thickness and morphology, leading to the highly efficient and uniform large-area PSCs. As a result, the p–i–n type planar PSC with an area of 1.084 cm2 exhibits a stable conversion efficiency of 17.0% (19.2% for 0.1 cm2) without showing hysteresis effect.
8:00 PM - ES01.13.66
Environmental Stability Studies of Triple-Cation Perovskite Materials of Csx(FA0.83MA0.17)1-xPb(I0.83Br0.17)3
Sheng-Yuan Chen 2 , Sheng-Chih Huang 2 , Sun-Tang Chang 1 , Chia-Hsin Wang 1 , Yaw-Wen Yang 1 2
2 Department of Chemistry, National Tsing Hua University, Hsinchu Taiwan, 1 , National Synchrotron Radiation Research Center, Hsinchu Taiwan
Show AbstractThe rapid advancement of hybrid perovskite solar cell research has been a remarkable success with the device performance reaching a commerical threshold in a short few years. However, one important problem related to device stability remains to be solved. A recent finding that the incorporaion of three types of cations into perovskite unit cell can significantly increase the device stability is worth noting. The three cations included cesium, methyl ammonium (MA), formamidinium (FA) ions and the device showed an unabated performance after running at 85 °C for 500 h. To shed ligh on why the triple-cation perovskite yields an imporved device stability, we set up to investigate the changes of material properties of Csx(FA0.83MA0.17)1-xPb(I0.83Br0.17)3 when exposed to different gas ambients in conjuction with AM1.5 light illumination with the overall treatments administered in an environmental control box. The three gas ambients are N2 mixed with water vapor (80% RH), dry O2, and O2 with water vapor (80% RH) and the treatments usually lasted 6 h long. The chemical composition and the electronic property of perovskites are monitored by means of SR-XPS and UPS. SEM and XRD were employed to address the struture issues. The perovskites exposed to gas ambients and illuminated with light can exhibit a large downward Fermi level shift up to 0.9 eV. XPS data show that light illumination is more effective than gas exposure in causing the loss of both Br and I ions in the perovskites. The creation of halide vacancies exerts a hole doping effect, corroborating the finding of downward EF shift. The observation of various reaction products resulting from the exposure to diffent gas ambients and the plausible reaction pathways will be presented. The potent effect of cesium ion in enhancing the environmental stability of the perovskite will be discussed as well.
8:00 PM - ES01.13.67
Flexible All-Inorganic Perovskite CsPbBr3 Non-Volatile Memory Device
Wei Hu 1 , Xiaosheng Tang 1
1 College of Optoelectronic Engineering, Chongqing University, Chongqing China
Show AbstractAll-inorganic perovskite CsPbX3 (X = Cl, Br, I) were widely used in a variety of photoelectric devices such as solar cell, light-emitting diode, laser and photodetector. However, studies to understand the flexible CsPbX3 electrical application relatively scarce, mainly due to the limitation of low-temperature fabricating process. In this study, all-inorganic perovskite CsPbBr3 films were successfully fabricated at the temperature of 75 oC through a two-step method. And, the high-crystallized films were firstly employed as a resistive switching layer in the Al/CsPbBr3/PEDOT:PSS/ITO/PET structure for flexible non-volatile memory application. The resistive switching operations and endurance performance demonstrated the as-prepared flexible ReRAM devices possess reproducible and reliable memory characteristics. Electrical reliability and mechanical stability of the non-volatile device were further testified by the robust current-voltage curves under different bending angles and consecutive flexing cycles. Moreover, the model of the formation and rupture of filaments through the CsPbBr3 layer was proposed to explain the resistive switching effect. It is believed that the study will offer a new playground to understand and design all-inorganic perovskite materials for future stable flexible electronic devices.
8:00 PM - ES01.13.68
Exploring Ferroelectricity of Hybrid Organic-Inorganic Perovskites
Yongtao Liu 1 , Mahshid Ahmadi 1 , Sabine Neumayer 3 , Anton Ievlev 2 , Stephen Jesse 2 , Kai Xiao 2 , Scott Retterer 2 , Sergei Kalinin 2 , Bin Hu 1 , Olga Ovchinnikova 2
1 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 3 School of Physics, University College Dublin, Dublin, Belfield, Ireland, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractHybrid organic-inorganic perovskites (HOIPs) have attracted considerable attention in recent years due to their rapid development for optoelectronics, such as photovoltaics, light emitting diodes, and photodetectors. Nevertheless, performance reproducibility and device stability are still big issues in the applications of HOIPs-based optoelectronics. Ferroelectric polarization has been suggested as one of the possible origins of anomalous behavior in this class of semiconductors. Thus, understanding polarization mechanisms and ferroelectricity are critical to develop HOIPs-based optoelectronics. Our previous study shows that ferromagnetic surface can effectively interact HOIPs surface, and consequently generate a magneto-dielectric function at room temperature. However, it is still a lack of solid understanding on either ferroelectric polarization of MAPbI3 itself or ferroelectric/ferromagnetic coupling at the interface between HOIPs and ferromagnetic system. Here, we combine nickel patterns and HOIPs to explore ferroelectric/ferromagnetic coupling created by nickel and HOIPs. In this work, we study MAPbI3 on both indium tin oxide (ITO) (reference sample) and nickel patterned ITO substrates (coupled sample).
During sample preparation, we fabricate patterned nickel cylinders on ITO substrates using electron beam lithography and conventional metal lift-off processing. MAPbI3 was deposited on both nickel patterned substrates (coupled sample) and normal ITO substrate (reference sample) using two-step deposition when PbI2 spin coated first following by MAI deposition and subsequent annealing. X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy were used to confirm the quality of MAPbI3 film. Interestingly, two domains within one grain were observed by SEM. To the best of our knowledge, this is the first time that different domains within one grain were observed by SEM in HOIPs. The ferroelectric and charge trapping properties of these materials and devices were explored by contact mode Kelvin Probe Force Microscopy. This technique explores the coupled ferroelectric and ionic density of states and its evolution with bias pulses. We present the results of cKPFM studies and analyze its spatial variability. Furthermore, we analyze ion distribution and interaction through Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and corresponded chemical properties through nano-IR.
8:00 PM - ES01.13.70
Growth of Perovskite Nanorods from PbS Quantum Dots
Jose Maria Silva Filho 1 , Francisco Marques 1
1 , University of Campinas, Campinas Brazil
Show AbstractOrganolead iodide perovskite, CH3NH3PbI3, have attracted the attention of researchers around the world due to their impressive optical and electrical properties. Their main characteristics include, direct band-gap (1.4 to 3.0 eV), high absorption coefficient, long carrier diffusion length and ambipolar charge transport. Aside that, perovskite thin films have a low-cost production and are compatible with large-scale manufacture. Perovskite thin films have been synthesised mainly by spin-coating technique and thermal evaporation, which can be executed in one or two steps. Aiming increase the light absorption, nanostructured perovskite thin films also are under intense study, since the nanostructures can absorb more light than a flat film. Thus, in this work, we reported the synthesis of perovskite (CH3NH3PbI3) nanorods by means of conversion of Lead Sulphide quantum dots (PbSQD). The perovskite nanorods were grown by exposing the PbSQD to a highly concentrate iodine atmosphere and then dipping the film in methylammonium iodide (CH3NH3I) solution. The first step converts completely the PbSQD into Lead Iodide (PbI2) nanorods, ~200 nm diameter, through substitution of sulphur by iodine atoms and subsequent aggregation of particles. The later step converts the PbI2 nanorods in perovskite nonorods (~400 nm diameter). The perovskite nanorods present a regular geometry along all its length. A preferential alignment of nanorods to the substrate plane was observed. The preliminary results show that we can control the size of nanorods through exposition time of PbSQD to iodine, which change the size of PbI2 nanorod as well. The conversion process was studied by X-ray diffraction, optical absorption, infrared spectroscopy, photoluminescence and scanning electron microscopy.
8:00 PM - ES01.13.71
Stitching Triple Cation Perovskite by a Mixed Anti-Solvent Process for High Performance Perovskite Solar Cells
Yafei Wang 1 , Jiang Wu 3 , Peng Zhang 1 , Detao Liu 1 , Ting Zhang 1 , Long Ji 1 , Zhi Chen 2 , Shibin Li 1
1 , University of Electronic Science and Technology, Chengdu China, 3 , University College London, London United Kingdom, 2 , University of Kentucky, Kentucky, Kentucky, United States
Show AbstractIn this study, the mixed solvent of isopropanol (IPA) and chlorobenzene (MCB) was employed as the anti-solvent in the deposition process of triple cations perovskite films. We investigated eight different ratios between MCB and IPA (1:0, 1:0.01, 1:0.02, 1:0.04, 1:0.06, 1:0.08, 1:0.1, 0:1) to find a proper one which could ensure the best effect of controlling the interface morphology and grain size of perovskite films. IPA (polarity=4.3) has a stronger polarity than MCB (polarity= 2.7), and also has a lower boiling point. Perovskite solar cells (PSCs) were fabricated and J-V curves of PSCs were measured to screen out the optimal ratio of IPA and MCB and found the ratio MCB: IPA= 1:6% is the best one. Then using SEM, AFM, XRD and UV-Vis absorption measurements, we found the existence of IPA could efficiently enhance the grain size of perovskite and modify the surface morphology of perovskite films. A “stitching effect” is proposed here which shows IPA could stitch different perovskite domains via its solvent properties. Fourier transform infrared (FTIR) spectroscopies of unannealed perovskite films based MCB, mixed solvent (MCB: IPA= 1:6%) and MCB washing processes reveal that IPA could remove the residual MCB quickly in the formation of perovskite films. The unannealed perovskite films exhibited dramatically different textures as seen by metallographic microscope. Without any anti-solvent treatment, the composite perovskite film shows a colorful surface covered with distributed needle-like crystals indicating a very inhomogeneous nucleation kinetic. After treatment by anti-solvent process (MCB, mixed anti-solvent and IPA), radial needle shaped crystals grew in the relative uniform surface having different needle density. The differences in crystal size and crystal density further confirm the “stitching effect” of IPA in mixed anti-solvent. Solar cells fabricated using the anti-solvent process exhibit the best efficiency of 19.2%. Our results show that solvent and solvent additives dramatically influenced the formation and crystallization process for perovskite materials with their different coordination and extraction capabilities. This method presents a new way for controlling the growth and morphology of perovskite films.
8:00 PM - ES01.13.73
The Critical Roles of SnF2 in the Structural and Optoelectronic Properties of Lead-Free Tin Perovskites
Satyajit Gupta 1 , Tatyana Bendikov 1 , Gary Hodes 1 , David Cahen 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel, Israel
Show AbstractLead (Pb)-based ‘halide perovskites’ (HaPs), have demonstrated exceptionally high power conversion efficiencies in recent years. Structural tolerance allows incorporation of multiple cations and anions in the perovskite lattice, leading to >21% solar cell efficiencies, which made it a game changer in photovoltaics. However, the toxicity of lead (Pb), which is used in the most studied cells, and especially the public’s perception of this toxicity, , may affect its large-scale uses. Hence we explore completely Pb-free HaPs such as CsSnBr3, for optoelectronic applications. Addition of SnF2 was observed to have major beneficial effects on several performance parameters of CsSnBr3-based cells and in this study we focus on these effects.
Cell efficiency was reported to increase up to ~200 times when SnF2 was added to the perovskite deposition solution compared to what is achieved without SnF2, possibly due to 1) filling of Sn2+ vacancies, 2) minimizing Sn2+ à Sn4+ oxidation or, 3) removal of trap states. To understand the effect of SnF2 concentration on PV parameters, different concentrations of SnF2 were added during CsSnBr3 preparation and 20 mol% was found be optimal to achieve improved device parameters such as short circuit current (JSC), open circuit potential (VOC) and fill factor (FF). To understand the role of SnF2 on the energetics (work function-WF and top of the valence band-EVBM) of the HaP (with and without SnF2 addition), Ultraviolet Photoelectron Spectroscopy (UPS) was monitored on titania (TiO2) and gold (Au) substrates. SnF2 addition was found to aid in the alignment of the bands with some selective contacts in a solar cell, which can explain at least some of the improvement in the PV parameters. Furthermore, continuous X-irradiation was found to be detrimental for pristine CsSnBr3, and resulted in zerovalent tin (Sn0) formation. However, addition of SnF2 protected the halide perovskite from beam damage, possibly because of a SnF2-induced change in the Sn2+ electrochemical potential that makes the reaction to form Sn0, energetically less probable.
8:00 PM - ES01.13.74
Photoactive Polymer Assisted Formation of High Quality Perovskite Layer for Efficient Solar Cell Application
Yuchen Zhou 1 , Zhenhua Yang 1 , Likun Wang 1 , Chang-Yong Nam 2 , Miriam Rafailovich 1
1 Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York, United States, 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractThe organic-inorganic hybrid perovskites solar cells (PSCs) with remarkable power conversion efficiency (PCE) have been unprecedentedly popular in the research community in past several years. The simple film fabrication, panchromatic light absorption, optimal carrier diffusion length, as well as tunable electronic band gap of perovskites materials make the PSCs highly competitive as the next generation of power conversion device. The state-of-art PSCs usually requires a high-quality perovskite layer with pinhole-free coverage and smooth surface. It has been proved that key characters of high-quality perovskites can be obtained through optimizing the kinetics of nucleation and growth of its crystals. Despite of several successful practices of manipulating the crystal formation process, the lack of precise controls on the structural level makes these methods less repeatable. In this study, we introduce the photoactive polymer of Poly(3-hexylthiophene-2,5-diyl) (P3HT) into the perovskite layer as a dopant. We creatively modify the widely applied solvent engineering technique by dissolving the P3HT in the anti-solvent (toluene or chlorobenzene) and dripping the P3HT-dissolved chlorobenzene onto the forming film of perovskite during the spin casting process. The P3HT polymer, therefore, can be evenly distributed and diffuse into the perovskite layer when the solvent extraction takes place. In structure and performance perspectives, the benefits of doping P3HT polymer are summarized in three folds: 1) the P3HT additive serves as uniform heterogenous nucleus for preferential formation and growth of perovskite crystals in 2D direction. With the support of P3HT polymer, the average grain size of crystals is increased and the roughness of the surface is maintained below 10nm; 2) The structural defects and grain boundaries have been effectively reduced after the addition of P3HT as nucleus; 3) Apart from the structural merits, the doped P3HT promotes the carrier diffusion and mobility within the perovskite layer. As a p-type semiconductor, the presence of P3HT largely facilitates the carriers (hole) diffusion at P3HT/perovskite interfaces, which further suppresses the non-radioactive recombination and minimizes the charge carrier losses. Such structural and electronic advances, consequently, endow the novel photoactive polymer doped PSCs with superior PCE as compared with traditional polymer-free PSCs. (This work was supported by the NSF, Inspire #1344267.)
8:00 PM - ES01.13.75
Energy Level Engineering of Hole-Transporting Material For Perovskite Solar Cells to Extract High Photovoltage
Neha Arora 1 , M. Ibrahim Dar 1 , Shaik Mohammed Zakeeruddin 1 , Michael Graetzel 1
1 , Ecole Polytechnique Federale de Lausanne,, Lausanne Switzerland
Show AbstractA new and simple hole-transporting material (HTM) has been designed and employed successfully in the fabrication of bromide perovskite solar cells yielding high open-circuit voltage (VOC). Detailed characterization of the new hole-transporting material was carried out using electrochemical techniques, and steady state absorption and emission spectroscopy. While retaining the mesoporous TiO2 based architecture, the fabrication of FAPbBr3 devices yielding an impressive photovoltage of above 1.5 V and a power conversion efficiency of 8% was realized. The current−voltage curves exhibited negligible hysteresis, and the performance showed good reproducibility. Spectro-electrochemical measurements revealed a high oxidation potential for new hole-transporting material, which rationalizes the higher VOC obtained. Techniques like transient photovoltage analysis, time-integrated and time-resolved photoluminescence were employed to further investigate the various photophysical processes occurring within the perovskite films and across various interfaces in the complete device. Importantly, the solar cells based on the new HTM demonstrated stable photovoltaic performance for more than 100 h under full-sun illumination at a maximum power point. In addition to the studies bringing out the role of the perovskite light harvester and HTM in determining the VOC, results of stability measurements will be presented.
8:00 PM - ES01.13.76
Inorganic Charge Transporting Layers for High Effecient Pervoskite Solar Cells
Hoang Dang 1
1 Solar Center, King Abdullah University of Science and Technology (KAUST), Jeddah Saudi Arabia
Show AbstractIn this poster, we will present our works regarding to charge transporting (both electron and hole) inorganic layers for perovskite-based devices. We specifically investigated the effect of doping metal oxides (as electron transporting layers) and CuSCN (as a hole transporting layer) on achieving high-efficiency, hysteresis-free devices. Energy alignments and long-term stability of the corresponding devices will be also discussed in details. Given the exciting progress in perovskite solar cells, we believe that our findings will contribute to the better understanding of the roles of charge transporting materials toward efficient perovskite top-cells in either 4-termial or 2-terminal configurations.
8:00 PM - ES01.13.77
Improved Morphology and Efficiency of n-i-p Planar Perovskite Solar Cells by Processing with Glycol Ether Additives
Esma Ugur 1 , Jafar Khan 1 , Arif Sheikh 1 , Rahim Munir 1 , Erkki Alarousu 1 , Dounya Barrit 1 , Aram Amassian 1 , Frederic Laquai 1
1 , King Abdullah University of Science and Technology, Jeddah Saudi Arabia
Show AbstractMetal halide perovskite solar cells have now reached power conversion efficiencies (PCE) of more than 22%. To date, the highest device efficiencies for perovskite solar cells have been demonstrated for mesoporous charge transport layers, which require a high temperature (≥ 500 °C) annealing step. In contrast, the planar device architecture offers significant advantages in terms of large scale processing, potential use of flexible substrates, and applicability to tandem device structures; yet, the efficiency of planar perovskite photovoltaic devices lacks behind that of conventional mesoporous devices. Here, we report a modified sequential (two-step) interdiffusion deposition protocol suitable to prepare pin-hole free perovskite films with largely improved morphology. This is achieved by simply adding glycol ethers, either 2-methoxyethanol, 2-ethoxyethanol, or 2-propoxyethanol, to the methylammonium iodide (MAI) solution. We found that the addition leads to more compact perovskite layers, better reproducibility, enhanced absorption, and improved conversion of lead iodide (PbI2) to perovskite (MAPbI3). Specifically, the addition of 2-methoxyethanol to the precursor solution resulted in improved perovskite crystal growth with average grain sizes exceeding 1 µm and, more importantly, crystals which were free of grain boundaries across the vertical direction of the photoactive layer. Consequently, we observed a considerable enhancement of the photovoltaic performance from 14.3% to 16.7% and largely improved reproducibility. We attribute this enhancement in device performance to the high quality of the perovskite films showing enlarged grain size, vertical orientation of crystals in the perovskite layer plus enhanced conversion of PbI2 to MAPbI3. Our conclusions are supported by in-situ UV-Vis absorption experiments and GIWAXS experiments showing improved PbI2 to MAPbI3 conversion during spin-coating and after annealing, ultimately leading to compact and pin-hole free perovskite films. Finally, time-resolved photoluminescence (TR-PL) and ultrafast transient absorption (TA) experiments demonstrated largely reduced carrier trapping and increased charge carrier lifetime compared to conventional MAPbI3 perovskite films.
References:
E. Ugur, A. D. Sheikh, R. Munir, J. I. Khan, D. Barrit, A. Amassian, F. Laquai, ACS Energy Lett. 2017, submitted.
8:00 PM - ES01.13.79
High Performance Resistive Switching Memory by Using Hybrid Organic-Inorganic Perovskite and RbPbI3 Blend Active Layer
SangMyeong Lee 1 , Jaeho Choi 2 , Jae Bum Jeon 1 , Ho Won Jang 2 , Hyun Suk Jung 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractHybrid organic-inorganic perovskite layer has been conceived as emerging materials for resistive random-access memory applications. This resistive random-access memory based MAPbI3 have high performance resistive properties, i.e. low operation voltage and high ON/OFF ratio1, which are beneficial to fast information storage and low energy consumption. However, memory devices based perovskite halide materials have poor endurance properties.2 In order to enhance endurance, composition engineering has been undertaken.3
In this presentation, we demonstrate the effect of Rb addition to MAPbI3 perovskite on ON/OFF ratio and endurance properties. We found that XX mol % addition of Rb yielded a mixture of MAPbI3 perovskite and RbPbI3, which exhibited the enhanced resistive ON/OFF ratio and endurance properties in comparison with other pure of MAPbI3 and RbPbI3 phases. The poor endurance property of MAPbI3 was overcome due to uniform distribution of stable RbPbI3 phase. This mixture composition is expected to be another alternative to active materials for resistive switching memories.
Reference.
1. E. Yoo, M. Lyu, J.H. Yun, C. Kang, Y. Choi and L.Z. Wang: Bifunctional resistive switching behavior in an organolead halide perovskite based Ag/CH3NH3PbI3-xClx/FTO structure. Journal of Materials Chemistry C 4, 7824 (2016).
2. J. Choi, S. Park, J. Lee, K. Hong, D.H. Kim, C.W. Moon, G.D. Park, J. Suh, J. Hwang, S.Y. Kim, H.S. Jung, N.G. Park, S. Han, K.T. Nam and H.W. Jang: Organolead Halide Perovskites for Low Operating Voltage Multilevel Resistive Switching. Advanced Materials 28, 6562 (2016).
3. B.H. Hwang, C.W. Gu, D.H. Lee and J.S. Lee: Effect of halide-mixing on the switching behaviors of organic-inorganic hybrid perovskite memory. Scientific Reports 7 (2017).
8:00 PM - ES01.13.80
The Role of Ion Migration in the Optical and Electronic Properties of Organic-Inorganic Perovskite Materials
Olivia Hentz 1 , Zhibo Zhao 1 , Paul Rekemeyer 1 , Silvija Gradecak 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractOrganic-inorganic perovskite materials have become one of the most promising photovoltaic materials for solar cell applications due to their incredible rise to >22% power conversion efficiency in less than a decade. However, some of the major barriers to commercialization of the perovskite solar cells is their long-term instability and hysteresis in the current-voltage measurements. In this work, we show that ion migration has major effects on the optical and electronic properties of perovskite materials, and thus is a likely contributor to the instability of the perovskite materials and the resulting device hysteresis.
We first use spatially-resolved cathodoluminescence to show that changes in local composition are directly correlated with nanoscale spatial variations of both the intensity and wavelength of luminescence. This result suggests that ion migration directly modifies optical properties of the perovskite material. We then study local electronic properties of full perovskite solar cell devices using electron beam induced current measurements in scanning electron microscopy. Specifically, we compare local charge extraction efficiency on a micron scale before and after applying a bias across the device. Based on timescales of the current decay observed after the bias is removed, temporarily modified device performance can be attributed to ionic and electronic migration interactions. Finally, to understand the nature of the species migrating under applied bias, we have mapped photoluminescence across laterally biased perovskite films. We observe a clear rise in photoluminescence between lateral electrodes under low-voltage biasing when the film is protected from moisture and air, strongly suggesting defect mediated migration. From this work, we have demonstrated the importance of ion migration on material quality, developed an understanding of the underlying ionic and electronic processes that modify device performance under biasing, and found evidence that the observed migration is mediated by defects intrinsic to the perovskite film.
8:00 PM - ES01.13.81
Two-Step Annealing Process for Planar Heterojunction Perovskite Solar Cells
Vishal Yeddu 1 , Gijun Seo 1 , Do Young Kim 1
1 , Oklahoma State University, Tulsa, Oklahoma, United States
Show AbstractOrganic/inorganic hybrid perovskite solar cells are a rising star in the photovoltaic community due to its remarkable performance and rapid progress in the past five years. Recently, lead acetate has been widely used as a lead precursor salt for planar heterojunction perovskite solar cells due to its relatively short processing time. CH3NH3PbI3 perovskite film has been deposited by spin coating a lead acetate precursor solution with a single-step post-annealing process at a constant temperature (80oC-100oC). In this work, however, we investigated a two-step post-annealing process for further enhancing device performance in perovskite solar cells. A planar heterojunction perovskite solar cell was fabricated with the following structure: ITO/PEDOT:PSS/Perovskite/PCBM/C60/Bphen/Ag. Spin-coated lead acetate precursor films were first annealed at a lower temperature (30oC-60oC) and then annealed at a higher temperature (80oC-100oC). While the open circuit voltage (VOC) decreases slightly, the fill factor (FF) and the short circuit current (JSC) increase with the two-step annealing process compared to the conventional single-step annealing process. Finally, the perovskite solar cells with the power conversion efficiency (PCE) of over 17 % were fabricated with the two-step annealing process. A systematic study of these devices with different two-step post-annealing conditions will be presented.
8:00 PM - ES01.13.82
Tuning the Optical Bandgap of Organometal Halide Perovskites—Ternary and Quaternary Compounds
Fatemeh Rahimi 1 , Andrew Hoff 1
1 , University of South Florida, Tampa, Florida, United States
Show AbstractRecently, organometal halide perovskites have been a subject of great scrutiny owing to their non-exitonic dynamics. Smarter devices are to be realized using these emerging technology of semiconductors. The optical bandgap of the solution-processed perovskite structures can be tuned using various methods. In this work, ternary and quaternary structures of methylammonium lead halides were developed and characterized. Utilization of these compounds is substantial in fabrication of smart optoelectronic devices such as photodetectors. The optical bandgap of the structures are measured using their cutoff frequency. The bandgaps vary from 1.1-2.0 eV. The study indicates the superior absorption of iodide ions compared with bromide and chloride. Selective absorption in electromagnetic spectrum translates directly to lower dissipation in material level and elimination of optical accessories such as filters and lenses in device level. The ternary and quaternary compounds were further tuned using a macro molecule namely methylene blue. Our study shows the presence of the macro molecule in the compound narrows the absorption to a certain wavelength (bandwidth of less than 150nm), desired for image sensing technology.
8:00 PM - ES01.13.83
Light-Induced Trap Healing Effect in Perovskite Solar Cells
Hui-Seon Kim 1 , Anders Hagfeldt 1
1 , Ecole Polytechnique Federale Lausanne, Lausanne Switzerland
Show AbstractThe light soaking of the inverted perovskite solar cells employing NiO and PCBM induced a certain increase in the power conversion efficiency. Under illumination, the current density was steadily increased at the maximum power point and reached the saturation point, which should be considered apart from the current-voltage hysteresis because the voltage sweeps in short-term period still resulted in the hysteresis-free characteristics of the inverted device. The capacitance observed with 0.1 kHz perturbation corresponded to the peak of trap density in the perovskite. The calculated trap density was gradually released by light soaking and become constant while it was invariable by applying bias voltage in dark. Furthermore, the reduced trap influenced on the recombination resistance, leading to the efficient charge collection in the perovskite solar cells.
8:00 PM - ES01.13.84
Solar Inks—Toward Ink-Jet Printed Perovskite Solar Arrays
Anna Osherov 1 , Yi Song 1 , Joel Jean 1 , Richard Swartwout 1 , Jing Kong 1 , Vladimir Bulovic 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractHigh power conversion efficiency coupled with an abundance of the precursor materials and low-temperature solution processability fosters hybrid organic-inorganic metal halide perovskites as an attractive alternative for low-cost next-generation photovoltaics. As of today, the mainstream of perovskite PVs in research reports are fabricated by a combination of spin coating, dip coating, and thermal evaporation. These techniques are not easily scalable hindering the commercialization outlook of perovskite technology. In order to realize large-scale deployment of emerging thin-film technologies, low-cost, high-throughput manufacturing techniques with marginal power conversion efficiency losses must be developed.
Inkjet printing of hybrid organic-inorganic perovskites (e.g., CH3NH3PbI3) offers a promising approach for economical, scalable manufacturing of future thin-film solar cells. In this work, we develop a process for ink-jet printing perovskite mini-modules from a single source inks on various flexible substrate/electrode systems and correlate the influence of precursor solution chemistries and the key printing parameters with the film formation on a larger scale and the corresponding photovoltaic performances.
Symposium Organizers
Yabing Qi, Okinawa Institute of Science and Technology Graduate University
Jinsong Huang, University of North Carolina-Chapel Hill
Annamaria Petrozza, Istituto Italiano di Tecnologia
Huanping Zhou, Peking University
Symposium Support
Applied Physics Letters | AIP Publishing
Nature Energy | Springer Nature
Science | AAAS
Sustainable Energy &
Fuels | The Royal Society of Chemistry
ES01.14: Fundamental Aspects, Optical, LED, Solar Cells and Photophysics
Session Chairs
Bert Conings
Michael Saliba
Friday AM, December 01, 2017
Hynes, Level 3, Ballroom B
8:00 AM - ES01.14.01
Moisture Stable Orange Emitting Mn-Doped CsPbCl3 Perovskite Film for White LED Application
Won Bin Kim 1 , Young Hyun Song 2 , Jae Myeong Lee 1 , Gi Joo Bang 1 , Hyun Suk Jung 1
1 , Sungkyunkwan University, Suwon-si Korea (the Republic of), 2 , Sejong University, Seoul Korea (the Republic of)
Show AbstractPerovskite nanocrystals have been under active research due to their bright luminescence , narrow emission wavelength full width half maximum(FWHM), color tunability and wide color gamut area1. CsPbX3 (X = I, Br, Cl) inorganic perovskite nanocrystals possess better stability than organic-inorganic hybrid perovskite nanocrystals such as CH3NH3PbX32. Despite of better stability, CsPbX3 nanocrystals have suffered from long term stability especially under moisture ambiance.
In this study, we fabricated Mn-doped CsPbCl3 nanocrystals with wide orange emission wavelength around 585 nm through the energy transfer from CsPbCl3 to Mn2+ ions3. We compared optical properties such as absorption, PL (photoluminescence) emission, PLQY (photoluminescence quantum yield) and crystallinity of synthesized perovskite nanocrystals with various ratio of Mn precursor.
Moreover, we fabricated Mn-doped CsPbCl3 perovskite film by mixing nanocrystal solution dispersed in toluene with NOA. 63 (Norland Optical Adhesive 63) UV curing photopolymer and measured film’s PL intensity change by immersing in water for the test of moisture stability4. The PL intensity of the perovskite film remained above 85% of the initial value after 36 hours. As a result, we expect that the Mn-doped CsPbCl3 perovskite can be applied as a white LED due to the comparable anti-moisture stability
Reference
1. Y. Bekenstein, B.A. Koscher, S.W. Eaton, P.D. Yang and A.P. Alivisatos: Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies. Journal of the American Chemical Society 137, 16008 (2015).
2. K.F. Wu, G.J. Liang, Q.Y. Shane, Y.P. Ren, D.G. Kong and T.Q. Lian: Ultrafast Interfacial Electron and Hole Transfer from CsPbBr3 Perovskite Quantum Dots. Journal of the American Chemical Society 137, 12792 (2015).
3. D. Parobek, B.J. Roman, Y.T. Dong, H. Jin, E. Lee, M. Sheldon and D.H. Son: Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals. Nano Letters 16, 7376 (2016).
4. R.T. Ginting, M.K. Jeon, K.J. Lee, W.Y. Jin, T.W. Kim and J.W. Kang: Degradation mechanism of planar-perovskite solar cells: correlating evolution of iodine distribution and photocurrent hysteresis. J Mater Chem A 5, 4527 (2017).
8:15 AM - ES01.14.02
Photoluminescence Quantum Yield Exceeding 80% in Low Dimensional Perovskite Thin Films by Passivation Control
Maria Grazia La Placa 1 , Giulia Longo 1 , Azin Babaei 1 , Laura Martínez-Sarti 1 , Michele Sessolo 1 , Henk Bolink 1
1 , Institute of Molecular Science (ICMol) - University of Valencia, Paterna Spain
Show AbstractOrganic-inorganic (hybrid) perovskites are interesting semiconductors materials for optoelectronics devices. Beside their application in photovoltaics, perovskites are emerging as promising components of light-emitting diodes (LEDs). In electroluminescent devices, a high photoluminescence quantum yield (PLQY) is desirable in order to efficiently convert the injected charges into photons. As for inorganic semiconductors, one way to substantially enhance the luminescence of perovskites is the preparation of nanostructured materials. Perovskites with reduced dimensionality have been prepared using templates or by direct synthesis of perovskite nanoparticles. In the former case, the use of scaffolds inhibit the connectivity needed for efficient charge transport in electroluminescent devices. On the other hand, while efficient LEDs employing perovskites nanoparticles are being demonstrated, there are still difficulties to deposit homogeneous thin-films. It has been widely shown that the size of the crystallites in perovskite layers can be substantially reduced by controlling the crystallization rate from solution via the use of co-solvents or processing additives. Among these, long chain ammonium cations are of particular interest since they can lead to the formation of 2D and quasi-2D perovskites. In this work, we studied the effect of the processing condition during the deposition of quasi-2D lead bromide perovskites, employing methylammonium (MA) and butylammonium (BA) as the small and large cations, respectively, in an effort to increase the PLQY. By varying the ratio between the BA and MA cations, and by adjusting the solution-processing parameters, we were able to tune the grain size as well as the overall perovskite film morphology. Importantly, with the addition of an organic semiconductor with electron donating properties to the non-solvent as passivating agent, we obtained films with a PLQY exceeding 80% even when measured at very low excitation intensity. These materials have been applied in LEDs that exhibit by high brightness and current efficiencies. Recent advances in the fabrication of vacuum-deposited 3D and quasi-2D perovskites for electroluminescence applications will also be presented.
8:30 AM - ES01.14.03
Structural Origins of Broadband Emission from Two-Dimensional Layered Lead-Bromide Perovskites
Matthew Smith 1 , Adam Jaffe 1 , Emma Dohner 1 , Aaron Lindenberg 2 , Hemamala Karunadasa 1
1 , Department of Chemistry, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractTwo-dimensional (2D) layered lead-bromide perovskites are direct-gap, highly excitonic semiconductors with potential applications in luminescence. The large phase space of 2D perovskites afforded by the choice of organic cation allows for the synthesis of a variety of inorganic layer topologies with different connectivities and structural distortions. The photoluminescence (PL) from the flat inorganic sheets in (001) lead-bromide perovskites is primarily free-excitonic and narrow at room temperature. In contrast, we recently discovered that the corrugated inorganic sheets in (110) lead-bromide perovskites emit broadband PL that appears as white light. I will discuss how broadband PL is accessible from the more common (001) Pb–Br perovskites using a combination of structural and optical studies. Through a series of temperature- and power-dependent PL measurements on a representative member of the (001) perovskites, we find that this broadband emission appears intrinsic to these materials. We ascribe it to the radiative recombination of self-trapped excitons in analogy with our proposed mechanism for white-light emission in (110) perovskites. Self-trapped excitons can be considered an excited-state defect, wherein photogenerated carriers induce distortions of the inorganic sheets mediated by carrier-lattice coupling. Importantly, the relative intensity of the broadband emission strongly correlates with increasing distortion of the Pb–(μ-Br)–Pb angle in the inorganic sheets. This structural correlation also provides indirect evidence for the highly localized nature of the self-trapped excited state. The design rules we posit here suggest a rational route to optimizing white-light emission in layered hybrid perovskites.
References
Smith, M. D.; Jaffe, A.; Dohner, E. R.; Lindenberg, A. M.; Karunadasa, H. I. Structural Origins of Broadband Emission from Layered Pb–Br Hybrid Perovskites. Chem. Sci. 2017, 8, 4497-4504.
Hu, T.; Smith, M. D.; Dohner, E. R.; Sher, M.-J.; Wu, X.; Trinh, M. T.; Fisher, A.; Corbett, J.; Zhu, X.-Y.; Karunadasa, H. I.; Lindenberg, A. M. Mechanism For Broadband White-Light Emission from Two-Dimensional (110) Hybrid Perovskites. J. Phys. Chem. Lett. 2016, 7, 2258-2263.
Dohner, E. R.; Hoke, E. T.; Karunadasa, H. I. Self-Assembly of Broadband White-Light Emitters. J. Am. Chem. Soc. 2014, 136, 1718-1721.
8:45 AM - ES01.14.04
Highly Robust, Efficient and Flexible Perovskite Light Emitting Devices with an External Quantum Efficiency of 13%
Lianfeng Zhao 1 , Nicholas Rolston 2 , Kyung Min Lee 1 , Reinhold Dauskardt 2 , Barry Rand 1
1 , Princeton University, Princeton, New Jersey, United States, 2 , Stanford University, Stanford, California, United States
Show AbstractOrganic-inorganic hybrid perovskites have recently attracted considerable attention for light emitting device (LED) applications because of their tunable bandgap, narrow emission bandwidth, and low material cost. Recently, substantial improvements have been achieved to improve the efficiency of perovskite LEDs. However, today’s best perovskite LEDs have been demonstrated on rigid substrates with indium tin oxide (ITO) anodes, a brittle and expensive layer not favorable for large area, low cost flexible devices. Furthermore, the perovskite layer is also brittle, limiting the mechanical stability and flexibility of perovskite devices.
Here, we report improved mechanical stability of the CH3NH3PbI3 (MAPbI3) perovskite films by introducing 20 mol % of bulky organoammonium halide additives into the perovskite, achieving an average fracture energy as high as 1.11 J/m2, which is roughly a two-fold enhancement compared to native perovskite films without additives.
Furthermore, using silver nanowire (Ag NW) transparent electrodes on a polymer substrate, we demonstrate highly efficient and flexible perovskite LEDs with external quantum efficiency (EQE) up to ~13% based on perovskite films with the bulky organoammonium halide additives. Notably, the EQE of these flexible devices is higher than the ITO-based controls. We attribute the high performance to better electron/hole balance and improved light outcoupling by replacing ITO with Ag NW. The flexibility of these LEDs was studied through a bending test, which shows nearly no device degradation upon bending for 10000 cycles at a radius of 2 mm.
9:00 AM - ES01.14.05
Highly Efficient Light-Emitting Diodes Based on Ligand-Engineered Colloidal Organic-Inorganic Hybrid Perovskite Nanoparticles beyond Quantum Size
Young-Hoon Kim 1 2 3 , Christoph Wolf 4 , Young Tae Kim 4 , Geon-Hui Lee 4 , Himchan Cho 1 2 3 , Aditya Sadhanala 5 , Chan-Gyung Park 4 , Richard Friend 5 , Tae-Woo Lee 1 2 3
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Research Institute of Advanced Materials, Seoul National University, Seoul Korea (the Republic of), 3 BK21 PLUS SNU Materials Division for Educating Creative Global Leaders, Seoul National University, Seoul Korea (the Republic of), 4 Department of Materials Science and Engineering, Pohang University of Science and Engineering, Pohang Korea (the Republic of), 5 Cavendish Laboratory, University of Cambridge, London United Kingdom
Show AbstractColloidal organic-inorganic hybrid perovskite nanoparticles (NPs) emerged as promising light emitters due to their high photoluminescence quantum efficiency (PLQE), spectrally-narrow emitting light, easy color tuning and simple synthesis process. However, light-emitting diodes (LEDs) based on perovskite NP films showed much lower electroluminescence efficiencies than did polycrystalline perovskite bulk-film based LEDs possibly due to the insulating ligands on the surface of NPs.
Here, we report ligand-engineered perovskite NPs based on methylammonium (MA) and formamidinium (FA) cations beyond quantum size and highly efficient perovskite NP LEDs by fabricating uniform perovskite NP film on a buffer hole injection layer (Buf-HIL). We found that we can effectively control the dimension of MAPbBr3 NPs and FAPbBr3 NPs by tuning the concentration of carboxylic acid ligands and length of amine ligands, respectively. Using these simple ligand-engineering methods, we can synthesize perovskite NPs with a dimension larger than exciton Bohr diameter (regime beyond quantum size), which have emitting light with size-insensitively high color-purity and constant wavelength. Ligand-engineered perovskite NPs can maximize the PLQE by preventing the non-radiative recombination of charge carriers at surface traps and inside the NPs, and also improve the charge injection/transport capability in perovskite NP films because insulating hydrocarbon chain in organic ligands hinders the charge injection and transport in NP films. Also, Buf-HIL prevented the aggregation of NPs in films and thus induced uniform perovskite NP layers with full coverage. With these strategies, we demonstrated highly efficient perovskite NP LEDs (15.5 cd/A for MAPbBr3 NP LEDs and 9.156 cd/A for FAPbBr3 NP LEDs) which are the highest values in MAPbBr3 NP LEDs and FAPbBr3 NP LEDs, respectively, to date. The effects of ligand engineering on photoluminescence (PL), PLQE, PL lifetime, exciton binding energy and surface-chemical properties of perovskite NPs, and EL efficiencies of NP LEDs were also systematically studied. Our works reported here provide very simple and primitive ways to improve the luminescence efficiency of perovskite NP LEDs.
9:15 AM - ES01.14.06
Efficient Perovskite Light-Emitting Diodes Featuring Self-Assembled Nanometer-Sized Crystallites
Zhengguo Xiao 1 , Ross Kerner 1 , Lianfeng Zhao 1 , Kyung Min Lee 1 , Barry Rand 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractOrganic-inorganic hybrid perovskites are very promising for LEDs due to their high color purity, low non-radiative recombination rates, and tunable emission wavelength. Nevertheless, the small electron-hole binding energy in three-dimensional (3D) perovskite materials result in small electron-hole capture rates for radiative recombination. Ultrathin perovskite emission layers, and/or small perovskite grain size have been employed to spatially confine the electrons and holes to best enable bimolecular radiative recombination. However, the grain sizes of solution-processed perovskite thin films are generally around hundreds of nanometers from both one-step and two-step solution processes, with a resulting large surface roughness.
In this talk, we will report highly efficient perovskite LEDs enabled through the formation of self-assembled, nanometer-sized crystallites. The addition of large-group ammonium halides such as n-butylammonium halides to the stoichiometric three-dimensional perovskite precursor solution act as a surfactant that dramatically constrains the growth of three-dimensional perovskite grains during film formation, producing crystallites with dimensions as low as 10 nm, and decreasing film roughness to less than 1 nm. These nanometer-sized perovskite grains coated with longer-chain organic cations allow for significant gains in emissivity. Incorporating such films within LEDs allows us to demonstrate external quantum efficiency of 10.4% for CH3NH3PbI3 and 9.3% for CH3NH3PbBr3 as emitters.[1] Additionally, the n-butylammonium halide-incorporated perovskite LEDs exhibit significantly improved shelf stability with no degradation after storage in the glove box for more than 10 months.
Finally, we will talk about our recent work on mixed-halide (mixed iodine and bromine) perovskite based LEDs and solar cells. Mixed-halide perovskites suffer from phase separation to I-and Br-rich domains under light illumination, which has precluded stable bandgap tuning of mixed-halide perovskites. We show that the addition of large-group ammonium halides suppress halide redistribution. Using the stable mixed-halide perovskite films, we are able to fabricate efficient and wavelength-tunable perovskite LEDs from infrared to green with high external quantum efficiencies of up to 5%, as well as linearly tuned VOC from 1.05 V to 1.45 V in solar cells.
References:
[1] Xiao, Z. et al. Efficient perovskite light-emitting diodes featuring nanometre-sized crystallites. Nat. Photonics 11, 108-115 (2017).
9:30 AM - ES01.14.07
Molecularly Engineered Organic-Inorganic Hybrid Perovskite with Multiple Quantum Well Structure for Multicolored Light-Emitting Diodes
Hongwei Hu 1 , Yeng Ming Lam 1
1 School of Materials Science and Technology, Nanyang Technological University, Singapore Singapore
Show AbstractOrganic-inorganic hybrid perovskite is an interesting class of materials because of their unique molecular structure whereby organic molecules are incorporated into inorganic crystals. In recent years, numerous studies have shown the viability of this material system in functional devices due to their exceptional optical and electrical properties, including high charge mobility, tunable band structure and high luminance efficiency1. On top of these functional properties, the solution processability of these hybrid perovskites also enables them to be promising candidates for the next-generation low-cost optoelectronic devices suitable for large-scale production. Recently, room-temperature infrared and green electroluminescence from the 3D hybrid perovskites have been reported confirming their potential for highly efficient, low-cost LED devices2. The performance of 3D perovskite LEDs has been dramatically improved through controlled film formation and employing nano-sized crystals to confine the exciton diffusion length. Perovskite LEDs with a high current efficiency were demonstrated and this reinforces the belief that they have strong potential to compete as a new material in light-emission devices.
Despite recent rigorous explorations of 3D perovskites, the first perovskite-based LED demonstrated in 1994 was in fact based on layered hybrid perovskite, which inherently possessed a two-dimensional (2D) quantum well structure. Within those quantum wells, electrons and holes are strongly confined in two dimensions rendering a large exciton binding energy and hence high luminescence yield. However at that time, the efficient electroluminescence from those 2D perovskite LEDs could only be preserved at cryogenic temperature possibly due to exciton quenching at room temperature.
Extending the pioneering work on both 3D and 2D perovskites, herein we report the first demonstration of room-temperature light-emitting devices based on layered perovskites possessing multiple quantum well (MQW) structure. The quantum well thickness was adjusted by combining the 3D and 2D perovskites at molecular level, resulting in tunable light emission due to the quantum confinement effect. Red perovskite LED with high color purity was obtained with a maximum external quantum efficiency of 2.29%. Green and blue LEDs based on MQW perovskite were also demonstrated for a solution-processed full-color perovskite display.3
Reference
1. Xing, G.C. et al. Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science 342, 344-347 (2013).
2. Cho, H.C. et al. Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes. Science 350, 1222-1225 (2015).
3. Hu, Hongwei, et al. "Molecularly Engineered Organic-Inorganic Hybrid Perovskite with Multiple Quantum Well Structure for Multicolored Light-Emitting Diodes." Scientific Reports 6 (2016).
10:15 AM - ES01.14.08
Carbon Perovskite Solar Cells—The Route to Low-Cost Module Manufacture
Trystan Watson 1 , Jenny Baker 1 , David Worsley 1 , Katherine Hooper 1 , Simone Meroni 1 , Francesca De Rossi 1 , Daniel Williams 1
1 , SPECIFIC, Swansea University, Swansea United Kingdom
Show AbstractThe “hole-conductor free” fully printable perovskite solar cell or triple mesoscopic carbon perovskite solar cell (C-PSC) as it is sometimes known is an exciting leap forward in the pursuit of industrial deployment of perovskite technology with recent reports demonstrating 10,000 hours of continuous light soaking data. This triple layered device structure comprising mesoporous TiO2, ZrO2 and carbon deposited by screen printing and sintered sequentially is likely to be one of the forerunners for early commercial adoption because the manufacturing method used requires low capital investment and delivers uniform large area deposition using inexpensive materials. This paper will present the recent challenges overcome in the transition to C-PSC modules; from patterning of the glass to the screen printing of multiple layers to infiltration of the perovskite into the device stack.
The current fabrication process for a C-PSC is a manual and time consuming batch process, this paper will demonstrate two new approaches to both increasing throughput and mechanising manufacture.
Typically each layer of a C-PSC requires a long heating step of at least 400°C following printing, to achieve the necessary porosity. These heating steps are very energy and time intensive which reduces the feasibility of manufacturing these devices commercially. Near infrared (NIR) radiation is a technique that has previously been used to significantly reduce the annealing time of perovskite in PSCs. Layers such as FTO and carbon that absorb in the NIR region rapidly heat up upon exposure to NIR producing enough thermal energy to burn off binder and sinter particles together in seconds rather than minutes.
Using NIR heating it is possible to reduce the high temperature heating steps associated with the compact TiO2 layer and the three printed mesoporous layers from 2 h to 30 s, this means that a complete device from substrate to final functioning solar cell can be achieved in less than 5 minutes. NIR heated C-PSCs were fabricated with a stabilised efficiency of 11%, identical to the performance of those heated in hours.
Secondly, the infiltration of the perovskite precursor is usually performed by manually dropping microlitre drops into the mesoscopic stack. This labour intensive process does not lend itself to module size devices. A novel method that enables large area, instantaneous and homogeneous deposition of droplets on a selected surface has been developed to increase speed and reproducibility of infiltration. Defined as ‘robotic mesh’ (RbM) infiltration, RbM allows the deposition of the liquid on a selected area with the aid of a mesh, which controls the permeation of the liquid. Cells manufactured with this method have comparable performance to those manufactured with a manual dropping technique.
The paper will conclude by discussing the trials and tribulations of a recent pilot scale manufacturing trial of C-PSC modules at the SPECIFIC facility in Swansea University.
10:30 AM - ES01.14.09
Device Engineering Concepts for Perovskite Photovoltaics
Stelios Choulis 1
1 , Cyprus University of Technology, Limassol Cyprus
Show AbstractAs one of the top ten science breakthroughs of 2013, Perovskite solar cells are a breath of fresh air in the emerging photovoltaic (PV) technology landscape. They have amazed with an incredibly fast power conversion efficiency (PCE) improvement, going from below 10% in 2009 [1] to over 20 % in 2017 [2]. However, these cells are facing issues towards commercialization, such as the need to achieve long-term stability and the development of a low cost environmental friendly electrodes for the reproducible fabrication of high-performance devices. The Presentation aims in covering a range of engineering and underpinning scientific issues needed to bring perovskite solar cells [3-5] to commercial viability in terms of efficiency [3], lifetime[4] and reliability [5]. A systematic understanding of the relationship between device interlayers, processing and device performance relevant to Perovskite photovoltaics product development targets will be presented.
AKNOWLEDGEMENTS: Funding from the ERC (H2020-ERC-2014-GoG project number 647311) is gratefully acknowledged.
[1] Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T., Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. Journal of the American Chemical Society 2009, 131 (17), 6050-6051.
[2] Saliba, M.; Matsui, T.; Seo, J.-Y.; Domanski, K.; Correa-Baena, J.-P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, W.; Abate, A.; Hagfeldt, A.; Grätzel, M., Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. Energy Environ. Sci. 2016, 9 (6), 1989-1997.
[3] Saliba M, Matsui T, Seo J-Y, Domanski K, Correa-Baena J-P, Nazeeruddin MK, Zakeeruddin SM, Tress W, Abate A, Hagfeldt A, Grätzel M. Energy and Environmental Science, 2016. DOI: 10.1039/C5EE03874J
[4] Savva,A., Burgués-Ceballos, I. ,Choulis, S.A. Advanced Energy Materials, 2016, DOI: 10.1002/aenm.201600285
[5] Galatopoulos, F, Savva, A., Papadas I. and Choulis, S.A “, APL Materials, 2017.
10:45 AM - ES01.14.10
Built-In Voltage of CsPbI2Br and CH3NH3PbI3 Heterostructures with N- and P-Type Silicon Wafers
Silvia Mariotti 1 , Ken Durose 1
1 , University of Liverpool, Liverpool United Kingdom
Show AbstractMost solar cell devices containing perovskite absorbers are fabricated on thin film TiO2. However, since the perovskites have relatively high bandgaps compared to silicon (i.e. CH3NH3PbI3 - 'MAPI' 1.6 eV and CsPbI2Br 1.9 eV compared to 1.1 eV) they are of interest for use in tandem solar cells. Nevertheless, there is very little reported work on the direct combination of these materials in heterostructures on wafer silicon itself. In this work we explore the built-in voltages (Vbi) obtained from simple heterostructures of both CsPbI2Br and MAPI in combination with n- and p- silicon. Additionally we compare the results to those from a 9.08% efficient CsPbI2Br/TiO2 device.
One-step spin-coating was used to form films of both MAPI and CsPbI2Br from DMF/DMSO solvents with annealing at 100°C (MAPI) or 350°C (CsPbI2Br). Both n- and p-type silicon wafers were cleaned using solvent and RCA-1 processes followed by HF etching. The contacts to the perovskites were gold and aluminium was used on the silicon. Comparison was made with the performance of a CsPbI2Br device prepared using compact TiO2 and Spiro-OMeTAD. Both JV and CV data were collected. For the CV, the frequency dependence of the capacitance was checked, and the depth density curves and Vbi were extracted using frequencies from the linear region.
A summary of the preliminary results of built-in voltage and carrier concentrations from C-V measurements of perovskite heterostructures is presented:
CsPbI2Br/n-Si: Vbi 0.41 V, carrier concentration 1.50 E15 cm-3;
CsPbI2Br/p-Si: Vbi 0.03 V, carrier concentration 1.41 E15 cm-3;
MAPI/n-Si: Vbi 1.09 – 1.32 V, carrier concentration 1.14 – 1.31 E15 cm-3;
MAPI/p-Si: Vbi 0.72 – 1.07 V, carrier concentration 2.22 – 4.66 E13 cm-3;
CsPbI2Br device: Vbi 0.78 V, carrier concentration 1.03 – 1.64 E16 cm-3;
For the case of MAPI the Vbi was in the range 1.09 - 1.32 V on n-type, and 0.72 – 1.07 V on p-type silicon. However, very much lower voltages were obtained for CsPbI2Br. Hence, silicon/MAPI heterostructures are a better choice in order to make potential heterojunction silicon wafer solar cells than the CsPbI2Br. In order to explore the potential of CsPbI2Br in more conventional structures, solar cells with the following layer sequence were fabricated: glass/ITO/TiO2/CsPbI2Br/Spiro-OMeTAD/Au. The highest efficiency device we measured had η = 9.08%, Voc = 1.05 mV, Jsc = 12.68 mA.cm-2 and FF = 68.42%. For this structure Vbi was measured as 0.78 V.
The work is ongoing: Vbi will be measured for perovskites on other semiconductor wafers e.g. GaAs and InP and solar cell results for heterostructures grown on wafer semiconductors will be presented.
11:00 AM - ES01.14.11
Terahertz Emission from Hybrid Perovskites Driven by Ultrafast Charge Separation and Strong Electron-Phonon Coupling
Burak Guzelturk 2 1 , Rebecca Belisle 1 , Matthew Smith 3 , Karsten Bruening 4 , Rohit Prasanna 1 , Christopher Tassone 4 , Hemamala Karunadasa 3 , Michael McGehee 1 , Aaron Lindenberg 1 2 5
2 SIMES, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 1 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Department of Chemistry, Stanford University, Stanford, California, United States, 4 SSRL Materials Science Division, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 5 Department of Photon Science, Stanford University, Stanford, California, United States
Show AbstractIn recent years, hybrid organic – inorganic perovskites have attracted great interest thanks to their exceptional performance in optoelectronic devices. This has been primarily enabled by their unusual photophysical properties such as slow carrier recombination and high defect tolerance, which has puzzled the community concerning the nature of charge carriers in the hybrid perovskites. These discussions have underlined the importance of understanding the initial steps in charge separation and carrier-lattice coupling. However, this has proven difficult using conventional ultrafast techniques.
Here, we observe, for the first time, strong terahertz (THz) emission from hybrid perovskites upon resonant or above-gap excitation. The emitted THz transients encode essential information on the initial out-of-plane charge separation and carrier-lattice coupling, empowering a real-time probe under 1-sun equivalent excitation conditions. We show that the initial charge separation in the hybrid perovskites is driven by diffusion and not by surface fields or intrinsic ferroelectricity. In MAPbI3 by resolving the radiated THz fields, we find that hot electron diffusivity (Dn = 9.1 cm2/s) is faster than that of hot holes (Dp = 7.9 cm2/s), whereas under resonant excitation, the hole mobility (µp = 15.1 cm2/V.s) is found to be larger than that of electrons (µn = 9.9 cm2/V.s). Moreover, we find that hot carriers are separated by ~8 nm within the first 500 fs following the photo-excitation due to the large difference in their diffusivities. Finally, analysis of the emitted THz amplitude spectra shows enhanced emission at the THz frequencies associated with vibrational modes of the inorganic sub-lattice as well as coupled organic-inorganic modes, indicative of a strong carrier – lattice coupling in the hybrid perovskites.
11:15 AM - ES01.14.12
Unravelling the Temperature-Dependent Urbach Energies of Organic-Inorganic Halide Perovskites
Martin Ledinsky 1 , Jakub Holovský 1 2 , Bjoern Niesen 3 , Jeremie Werner 3 , Zdenka Hájková 1 , Lucie Abelová 2 , Neda Neyková 1 , Tereza Schonfeldová 1 , Ha Stuchlíková 1 , Jan Kočka 1 , Stefaan De Wolf 4 , Christophe Ballif 3 , Antonín Fejfar 1
1 Laboratory of Nanostructures and Nanomaterials, Institute of Physics, ASCR, Prague Czechia, 2 Faculty of Electrical Engineering, Czech Technical University in Prague, Prague Czechia, 3 Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Neuchatel Switzerland, 4 KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal Saudi Arabia
Show AbstractSolar cells based on organometallic halide perovskite absorber layers have become a topic of intense research for high-performance photovoltaics. Since the first report [1] on perovskite-based solar cells, their efficiency has already increased above 22%. Following this rapid surge, the attention of research is now shifting to increase the understanding how the stability of perovskites and perovskite solar cells can be improved. To tackle such a task improved physical knowledge about this exceptional material is needed.
We probed the temperature dependence of methylammonium lead iodide (MALI) absorption spectra in detail, using Fourier-transform photocurrent spectroscopy (FTPS) directly connected with a cooling stage for this purpose. The FTPS technique was previously used to demonstrate the high material quality of MALI [2] as evidenced by its very sharp optical absorption edge. The exponential absorption decrease at the band gap edge is described by the Urbach energy, which is directly correlated with material quality/order and the maximal open-circuit voltage (VOC) reachable with an optimized cell using this absorber layer. We have found a strong decrease in Urbach energy when the sample was cooled. At room temperature, its value was 15 meV, in agreement with [2]. At 150 K the Urbach energy fell to 8 meV. At the same time the optical band gap energy slowly decreased due to the high temperature expansion coefficient of MALI. The combination of these two effects, i.e., the sharpening of the optical edge and the decrease of the optical band gap energy, leads to a phenomenon known as Urbach focus [3] – all absorption curves measured at different temperatures intersect at one point (1.52 eV in this case). This value is a general limit for the optical band gap in this material as well as for the VOC accessible with this MALI film.
Temperature dependence of Urbach energy allow us to separate absorption edge broadening given by static (defects in the crystalline lattice) and dynamic (phonon based) contributions. Extrapolated value of Urbach energy to 0 K is on the level of GaAs, proving very high ordering of MALI structure comparable with bulk crystalline materials.
[1] A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka: J. Am. Chem. Soc. 131 (2009) 6050.
[2] S. De Wolf et al.: J. Phys. Chem. Lett. 5 (2014) 1035.
[3] S. Singh et al.: J. Phys. Chem. Lett. 7 (2016) 3014.
11:30 AM - ES01.14.13
Matching Charge Extraction Contact for Wide Bandgap Perovskite Solar Cells
Yuze Lin 1 , Jinsong Huang 1
1 Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractEfficient wide-bandgap (WBG) perovskite solar cells are needed to boost the efficiency of silicon solar cells to beyond Schottky-Queisser limit, but they suffer from a larger open circuit voltage (VOC) deficit than narrower bandgap ones. Here we show that one major limitation of VOC in WBG perovskite solar cells comes from the non-matched energy levels of charge transport layers. Indene C60 bisadduct (ICBA) with higher-lying lowest-unoccupied-molecular-orbital is needed for WBG perovskite solar cells, while its energy-disorder needs to be minimized before a larger VOC can be observed. A simple method is applied to reduce the energy-disorder by isolating isomer ICBA-tran3 from the as-synthesized ICBA-mixture. WBG perovskite solar cells with ICBA-tran3 show enhanced VOC by 60 mV, reduced VOC deficit of 0.5 V, and then a stabilized power conversion efficiency of 18.5%. This work points out the importance of matching the charge transport layers in perovskite solar cells when the perovskites have a different composition and energy levels.
11:45 AM - ES01.14.14
Indirect to Direct Bandgap Transition in Methylammonium Lead Halide Perovskite
Tianyi Wang 1 , Benjamin Daiber 1 , Jarvist Frost 2 , Sander Mann 1 , Erik Garnett 1 , Aron Walsh 2 , Bruno Ehrler 1
1 Center for Nanophotonics, AMOLF, Amsterdam Netherlands, 2 Department of materials, Imperial College London, London United Kingdom
Show AbstractSolar cells based on organic-inorganic hybrid perovskites have reached an efficiency of 22%. For a long time, the prototype material in this family, methylammonium lead iodide perovskite (MAPI) has been considered a direct bandgap semiconductor. However, theoretical calculations have predicted a slight indirect bandgap for MAPI as a consequence of spin-orbit coupling resulting in Rashba-splitting of the conduction band. Currently there is limited experimental evidence to support this theoretical prediction.
Using pressure-dependent absorption and emission measurements, we show that a weakly indirect bandgap around 60 meV below the direct bandgap transition is present. The indirect transition arises from Rashba splitting of the conduction band. The splitting occurs due to the local electric field generated by the absence of inversion symmetry around the Pb site, which acts on the 6p orbitals of the lead-atom where most of the conduction band minimum is located. Under hydrostatic pressure from ambient to 325 MPa, Rashba splitting is reduced due to a pressure-induced reduction in electric field around the Pb atom. The indirect nature of the bandgap is suppressed, leading to five times faster charge carrier recombination, and a two-fold increase of the radiative efficiency. At hydrostatic pressures above 325 MPa, a reversible phase transition of MAPI occurs, resulting in a purely direct bandgap semiconductor.
The finding of an indirect bandgap in MAPI sheds light on the apparent contradiction of strong absorption and long charge carrier lifetime. Novel epitaxial and synthetic routes to solar cells with higher open-circuit voltage might be developed based on the pressure-induced changes we observe.
ES01.15: Pb-Free, Charge Transport and Stability
Session Chairs
Friday PM, December 01, 2017
Hynes, Level 3, Ballroom B
1:30 PM - ES01.15.01
Towards Lead-Free Perovskite Solar Cells—A Case for In-Based Double Perovskites
George Volonakis 1 , Amir Abbas Haghighirad 2 , Henry Snaith 2 , Feliciano Giustino 1
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 Department of Physics, University of Oxford, Oxford United Kingdom
Show AbstractSince their discovery, hybrid lead halide perovskites have emerged as a very promising low-cost photovoltaic technology, achieving remarkable power conversion efficiencies of more than 22%. Yet, solar cells based on lead halide perovskites are known to degrade upon exposure to moisture, air and/or heat. At the same time, the presence of lead in these photovoltaic devices, raises concerns about their potential environmental impact. Up-to-date, the quest for a stable efficient lead-free halide perovskite has proven particularly challenging, with the obvious one-to-one substitution of Pb2+ with other +2 cations, either suffering from stability issues or failing to retain the optoelectronic properties of the Pb-based compounds. Among the lead-free alternatives, A2B3+B’+X6 halide double perovskites have attracted considerable attention1, and within just a year, four inorganic and three hybrid halide double perovskites have been successfully synthesized and were found to be more stable than MAPbI3 2,3,4. Unfortunately, the electronic structure of these compounds is not ideal for opto-electronic applications, due to either the indirect nature of their band gaps, their non-dispersive bands or the presence of toxic Tl. Here we combine state-of-the-art first-principles calculations with experiments to design non-toxic double perovskites with direct band gaps. The calculated electronic band gaps of the Cs2InAgX6, with X = Cl,Br,I range from the ultraviolet for chloride to within the visible for the iodide. We further report on the synthesis of Cs2InAgCl6, a double perovskite with a Fm-3m space group and a measured band gap of 3.3 eV. The compound is prone to the formation of defects and shows a photo-sensitive behaviour which we attribute to the presence of In and Ag d-states at the top of the valence band. Finally, we discover a set of design rules to make an ideal lead-free double perovskite absorber5. We employ these rules and show that the main candidates for the B3+ site are Sb and Bi, and for B’+ the main option is In. We perform a thorough ab initio study of their phase stability and propose a way to overcome the problematic oxidation of In+ to In3+. The successful synthesis of these direct band gap compounds that absorb light in the visible will open the way to the development of a stable and environmental-friendly perovskite technology.
[1] Giustino F. and Snaith H. J., ACS Energy Lett., 1 1233 (2016)
[2] Volonakis G. et al., J. Phys. Chem., Lett. 7 1254 (2016)
[3] Volonakis G. et al., J. Phys. Chem., Lett. 8 772 (2017)
[4] Kamat P. V. et al., ACS Energy Lett., 2 904 (2017)
[5] Volonakis G. et al., J. Phys. Chem., Lett. 8 3917 (2017
1:45 PM - ES01.15.02
Carrier Recombination and Transport Dynamics in Long-Term Stable Lead-Free CH3NH3SnI3 Solar Cells
Taketo Handa 1 , Takumi Yamada 1 , Hirofumi Kubota 2 , Shogo Ise 2 , Yoshihiro Miyamoto 2 , Yoshihiko Kanemitsu 1
1 , Kyoto University, Uji Japan, 2 , CEREBA, Tsukuba, Ibaraki, Japan
Show AbstractMetal-halide perovskites are one class of promising materials for photovoltaic and optoelectronic applications. Although lead-halide perovskite solar cells exhibit high conversion efficiencies exceeding 20% [1], the toxicity of lead is problematic for their widespread implementation. Thus, fabrication of lead-free tin-halide perovskite solar cells has been conducted intensively in the last four years [2]. It has been revealed that the performance of tin-halide perovskite devices improves drastically by using SnF2 as an additive, due to the improvement of the film morphology as well as the suppression of the oxidation of Sn2+ to Sn4+ [3]. However, the impact of the SnF2 addition on the fundamental optical properties still remains unclear. In order to improve the currently limited conversion efficiencies of perovskite solar cells, in-depth understanding of the optical and transport properties is required [4]. Here, we report on optical responses as well as the SnF2’s effect in lead-free CH3NH3SnI3 (MASnI3) solar cells using various optical spectroscopic techniques.
We prepared the MASnI3 solar cells (FTO/compact-TiO2/mesoporous TiO2/MASnI3/PTAA/Au) with and without 20 mol% SnF2 additive, via one-step spin-coating process with anti-solvent dripping. All the samples were encapsulated in an inert condition, and the solar cell showed remarkable long-term stability over 500 hours under continuous 1-sun illumination. While the MASnI3 thin film prepared with SnF2 exhibited a steep absorption onset at 1.25 eV, a significant blueshift of the absorption edge appeared in the film prepared without SnF2. Independent of the presence of the SnF2, the photoluminescence (PL) peak energy showed almost no shift. These results indicate that the sample prepared without the SnF2 experienced a blueshift of the absorption onset due to large number of unintentionally doped holes. In addition, the resonantly excited PL spectra evidenced that the PL emission width is independent of the excitation energy, suggesting that the broad spectrum from MASnI3 is determined by the intrinsic broadening due to strong electron-phonon interactions. Furthermore, it became clear that by adding SnF2, the photocarrier lifetime increases by an order of magnitude, leading to the improvement in the efficiency of carrier extraction to the transport layer up to 80%. We discuss the optoelectronic properties of long-term stable MASnI3 solar cells.
Part of this work was supported by JST-CREST (JPMJCR16N3), NEDO, and JSPS (17J09650).
References
[1] W. S. Yang et al., Science 348, 1234 (2015). [2] F. Hao et al., Nat. Photon. 8, 489 (2014).
[3] M. H. Kumar et al., Adv. Mater. 26, 7122 (2014); W. Liao et al., Adv. Mater. 28, 9333 (2016).
[4] T. Handa et al., Opt. Express 24, A917 (2016); T. Handa et al., J. Phys. Chem. Lett. 8, 954 (2017); Y. Kanemitsu, J. Mater. Chem. C 5, 3427 (2017).
2:00 PM - ES01.15.03
Defect-Induced Band-Edge Reconstruction of a Bismuth-Halide Double Perovskite
Adam Slavney 1 , Linn Leppert 2 3 , Davide Bartesaghi 4 5 , Aryeh Gold-Parker 1 6 , Michael Toney 6 , Tom Savenije 4 , Jeffrey Neaton 2 3 7 , Hemamala Karunadasa 1
1 Chemistry, Stanford University, Stanford, California, United States, 2 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Physics, University of California, Berkeley, California, United States, 4 Chemical Engineering, Delft University of Technology, Delft Netherlands, 5 , Materials Innovation Institute, Delft Netherlands, 6 , SLAC National Accelerator Laboratory, Menlo Park, California, United States, 7 , Kavli Energy NanoScience Institute at Berkeley, Berkeley, California, United States
Show AbstractWe have recently begun exploring halide double perovskites, A2BB′X6 (A = monovalent cation, B/B′ = monovalent and trivalent cations, X = halide), as possible non-toxic alternatives to the ubiquitous lead halide perovskites.1 The ability to incorporate mono- and trivalent metals into the perovskite framework is a powerful materials design tool; however, to date all known double perovskite materials have large and/or indirect bandgaps making them unsuitable replacements for the lead perovskites. I will show that low levels of Tl incorporation have large effects on the optical properties of the double perovskite Cs2AgBiBr6.2 This culminates in a reduction of the apparent bandgap of Cs2AgBiBr6 down to 1.4 eV placing the material in the ideal range for single-junction photovoltaics. Carrier lifetimes for the doped material remain in the microsecond regime as determined by time-resolved microwavex conductivity measurements (TRMC). I will explain the electronic origin of these dramatic optical changes using a combination of experimental and theoretical tools. Additionally, I will discuss how other dopants which may display similar effects can be identified. These results demonstrate that low levels of carefully selected dopants permit large-scale changes to the electronic structure of the double perovskite host and opens a pathway to double perovskite materials which are competitive with lead halide perovskites.
References:
(1) Slavney, A. H.; Hu, T.; Lindenberg, A. M.; Karunadasa, H. I. J. Am. Chem. Soc. 2016, 138, 2138.
(2) Slavney, A. H.; Leppert, L.; Bartesaghi, D.; Gold-Parker, A.; Toney, M. F.; Savenije, T. J.; Neaton, J. B.; Karunadasa, H. I. J. Am. Chem. Soc. 2017, 139, 5015.
2:15 PM - ES01.15.04
Effect of SnCl2 on Lead-Free Halide Perovskite Thin Films and Solar Cell Devices
Tomoko Aharen 1 , Taketo Handa 1 , Atsushi Wakamiya 1 , Yoshihiko Kanemitsu 1
1 , Kyoto University, ICR, Uji Japan
Show AbstractTin halide Perovskite is the first alternative material presented as possible environmentally friendly alternative for lead halide perovskites [1]. However it has been suffered from the material instability and resulting lower photovoltaic performance compared to methylammonium lead tri-iodide, MAPbI3, a good contender for silicon based solar cells. As for performance improvement, Sn2+ excess condition has been proven to reduce tin vacancy during the formation of the perovskite [2]. To date, SnF2 is accepted as the best additive to overcome the instability partially and improve the performance of tin based devices. Moreover, a recent study on tin iodide excess condition in reducing atmosphere provides variation for excess Sn2+ source [3]. Besides, SnCl2 can be another option as dual functioned additive: moderate reducing agent and creating tin rich environment similar to SnF2. Additionally, Cl- inclusion has been demonstrated to improve film morphology and crystal growth on lead halide perovskite [4]. Therefore it is natural to examine the effect of Cl- inclusion on the tin halide perovskite formation process and their optical properties. This examination allows us to obtain further insight into the advantages/drawbacks in off-stoichiometric condition, the targeted perovskite phase coexisting with impurity phases, for the formation and material properties of the tin halide perovskites. We study the phase formation with X-ray powder diffraction, film morphology and microstructures using scanning electron microscopy, photocarrier lifetime by optical measurements, along with device fabrication. In addition, considering Cl- inclusion effect only, it can be achieved using methylaamonium chloride (MACl) or formamidinium chloride (FACl). This control examination works to extract chloride effect on film fabrication and material properties.
One-step method was employed in this study for film fabrication as is widely used in the device fabrication. DMSO and DMF/DMSO solvent mixture were used as solvent(s) in order to keep the better film coverage on various substrates. A remarkable change in film formation has been observed compared to tin fluoride additive. In addition, the control experiments using FACl or MACl has indicated positive contribution on film morphology and preliminary optical measurements. We will present further study on optical responses and device fabrication.
Part of this work was supported by JST, CREST (JPMJCR16N3) and Integrated Research Consortium on Chemical Sciences（IRCCS）
[1] N. K. Noel et al, Energy Environ. Sci., , 7, 3061 (2014)
[2] M. H. Kumar. et al, Adv. Mater., 26: 7122–7127 (2014): C.C. Stoumpos et al, Nat. Photon.,
8, 489−494 (2014)
[3] Tze-Bin Song et al, ACS Energy Lett., 2, 897−903 (2017)
[4]Zhang, W. et al. Nature Commun. 6, 6142 (2015) : Tidhar, Y. et al.. J. Am. Chem. Soc. 136, 13249–13256 (2014) :Williams, S. T. et al.. ACS Nano 8, 10640–10654 (2014) :Moore, D. T. et al.. J. Am. Chem. Soc. 137, 2350–2358 (2015)
2:30 PM - ES01.15.05
Improving Ambient Stability of BiI3 Based Perovskites Using Different Phosphoniums as the Organic Cation
Diana Garcia-Gutierrez 1 , Diego González-Quijano 1 , Jesus Lopez-Lopez 1 , Simon Flores-Armendariz 1 , Itzel Abarca-Villarreal 1 , Sofia Galindo-Garza 1 , Domingo Garcia-Gutierrez 2 , Eduardo Sánchez-Cervantes 1
1 Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León , San Nicolás de los Garza Mexico, 2 Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, Mexico
Show AbstractPbI3 : Organic Cation perovskites have gained a lot of attention in recent years, due to the impressive efficiencies attained by photovoltaic devices fabricated with this material as the absorbing layer. However, one of the major drawbacks displayed by this type of materials is their low stability at ambient and operating conditions. One of the options explored by different research groups to improve this ambient stability is to replace the Pb atoms for Bi atoms, and using as the organic cation different types of phosphoniums. In this work, BiI3 : Phosphonium perovskites were synthesized by the spin coating methodology, using different types of phosphoniums (ethylphosphonium, butylphosphonium, hexylphosphonium and octylphosphonium), to assess the stability at ambient conditions displayed by the synthesized pervoskites. Afterwards, they were characterized in order to study their morphology and crystal structure, as well as their optical and electrical properties. Different thermal treatments were performed on the synthesized perovskites in order to study their effect on their ambient stability, morphology, crystallinity and optical and electrical properties. Finally, photovoltaic devices were fabricated based on the thin films perovskites which displayed optimum characteristics.
2:45 PM - ES01.15.06
Transition Metal Perovskite Chalcogenides—Visible Luminescence to Anisotropic Infrared Absorption
Shanyuan Niu 1 , Huan Zhao 1 , Graham Joe 2 , Huaixun Huyan 1 , Rehan Kapadia 1 , David Singh 3 , Mikhail Kats 2 , Han Wang 1 , Jayakanth Ravichandran 1
1 , University of Southern California, Los Angeles, California, United States, 2 , University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 , University of Missouri, Columbia, Missouri, United States
Show AbstractTransition metal perovskite chalcogenides (TMPC) are a new class of highly absorptive semiconductors based on early transition metals such as Ti, Zr. They are composed of abundant, non-toxic elements and hence, can lead sustainable opto-electronic applications. Past experiments have shown that Zr containing perovskites with orthorhombic structure show optical gap in the visible range, and can be useful for photovoltaic energy conversion. We have shown that such materials can posses large visible luminescence with high quantum efficiencies in the first generation materials. On the other hand, theoretical studies have predicted that the Ti containing perovskites that crystallizes in hexagonal structure can show absorption in the infrared regime. We prepared single crystals of Ti containing perovksites using the halogen assisted vapor transport growth. Two different varients of crystals such as plates and wires were obtained. The infrared absorption characteristics of these crystals show that the absorption onset is drastically different along the c-axis and the perpendicular direction to c-axis. Further studies are underway to understand this anisotropy in these materials. These materials can find application as infrared detectors and infrared light emitting devices. Overall, we hope that these materials will find unique optoelectronic applications similar to the well known cousin, the perovskite halides.
ES01.16: Preferred Crystal Orientation, Single Crystals and Quantum Dots
Session Chairs
Friday PM, December 01, 2017
Hynes, Level 3, Ballroom B
3:30 PM - ES01.16.01
Investigating Charge Carrier Dynamics of Vertically Aligned One-Dimensional Nanostructured Hybrid Perovskites as a Function of Aspect Ratio
Hyeok-Chan Kwon 1 , Eunsong Lee 1 , Sunihl Ma 1 , Kyungmi Kim 1 , Jooho Moon 1
1 , Yonsei Univ, Seoul, SE, Korea (the Republic of)
Show AbstractOrganic-inorganic hybrid perovskite solar cells have demonstrated huge potential as next generation solar cells with low cost and high efficient performance due to solution processability and excellent photovoltaic characteristics. Several nanostructures such as planar heterojunction, mesoporous metal oxides, or one-dimensional (1-D) semiconductor nanorod array have been studied to enhance efficiencies of the solar cells, and various analysis techniques revealed that different charge carrier behaviors of perovskite phase in nanostructured electron transport materials were shown. However, studies depending on nanostructures of perovskite layer itself have been rarely performed, since the structuring of perovskite is difficult due to its easy dissolution in polar solvents. Recently, we successfully fabricated vertically aligned 1-D nanostructured perovskite (CH3NH3PbI3-XClX) solar cells using anodized aluminum oxide (AAO) layers as scaffolds. Since the pore size of AAO template was easy to control, perovskite structures with various aspect ratios was readily fabricated, allowing us better understanding of 1-D effects on perovskite phase.
Four samples with aspect ratios of 0 (planar), 3.03, 4.17, and 6.67 were chosen to compare characteristics. In order to observe the physical properties of the perovskite layer as a function of the aspect ratio, the area specific series resistance extracted from the J-V curve was compared. It was found that the resistance value becomes smaller with the increasing aspect ratio. Impedance spectroscopy measurements under also show reduced resistance value at high frequency region. This observation implies that 1-D structured perovskite has better photocarrier transport properties. To gain a better understanding of charge carrier dynamics, intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) analyses were performed. The electronic transport time obtained from the IMPS analysis is lowered as the increasing aspect ratio of the perovskite, implying that the photocarriers are able to be readily mobile and extractable as the aspect ratio increases. Interestingly, however, the electronic lifetime obtained by IMVS analysis was found to be larger as the increasing aspect ratio, and it declined again as the aspect ratio increased beyond 4.17. This phenomenon is presumed to be due to defects at the interface between the AAO wall and the perovskite, which are in a good agreement with defect density analysis by temperature dependent admittance spectroscopy. In the term of electronic transport time and lifetime, the charge collection efficiency can be maximized when the AAO of 44 nm pore size is utilized as a scaffold by which 1-D perovskite with an aspect ratio of 4.17 is produced. Our studies could provide insights of photo-carrier dynamics depending on the 1-D nanostructured perovskites, enabling us to design efficient nanostructures for enhanced photovoltaic device performances.
3:45 PM - ES01.16.02
Controlling the Crystal Orientation and Anisotropy in Metal-Halide Single Crystals with Solvent Hydrostatic Pressure and Temperature
Sehmus Ozden 1 , Fangze Liu 1 , Yoosuf Ameen M 1 2 , Noelia Devesa Canicoba 1 3 , Jean-Christophe Blancon 1 , Aditya Mohite 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Physics, National Institute of Technology, Kerala India, 3 , University of Rennes , Rennes France
Show AbstractMetal halide hybrid perovskites have attracted a great deal of attention because of their remarkable optoelectronic properties. The ability to control the crystal orientation is critical for a wide range of optoelectronic devices, which rely on achieving directional high mobility of charge carriers in the direction of the electrodes. However, despite the relative ease of growing high quality single crystals using several methods, it is challenging to control the anisotropy during crystal growth. In this study we used a new method for synthesis of large area single-crystals of hybrid lead-halide perovskites using a closed system, which allows for controlling the thermodynamic state variables of pressure, temperature, volume and concentration to achieve a strong anisotropy of certain planes in the resultant single-crystals. We investigate how the different variables and driving forces effect the crystallinity, morphology and correlate these with the charge mobility and trap density of perovskite single crystals thus validating our synthesis approach. We anticipate that this method could be applicable as a general method for the growth of single crystals with any combination of the compounds (cations, divalent metals and halides) that otherwise may be limited kinetically and will also allow for tuning their crystalline orientation based on the desired device functionalities.
4:00 PM - ES01.16.03
Observation of Solid State Rydberg Exciton Polariton and Its Condensate in a Single Crystal Perovskite
Xiaoze Liu 1 , Wei Bao 1 , Fan Zheng 2 , Yang Xia 1 , Mervin Zhao 1 , Jeongmin Kim 1 , Sui Yang 1 , Ying Wang 1 , Yuan Wang 1 , Lin-Wang Wang 2 , Xiang Zhang 1 2
1 , University of California, Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractGaseous Rydberg atoms are one of the primary building blocks for realization of quantum information processing due to their long range coherent dipole-dipole interactions. A solid-state platform is desired for quantum applications and on-chip integration, making the Rydberg excitons found in semiconductors attractive solid-state candidates. However, quantum manipulation in Rydberg excitons has been difficult due to its fast decoherence rate. Here, we address this critical challenge by coherent coupling between Rydberg excitons and photons in an optical cavity, and demonstrate the first solid state Rydberg exciton polaritons (REPs) with a single crystal inorganic perovskite, CsPbBr3. Such REPs exhibit strong nonlinear behavior, enabling an anomalous dynamic process that leads to a coherent polariton condensate. Furthermore, we discovered the first anisotropic REP with large extinction ratio over 50, arising from the perovskite’s asymmetric orthorhombic crystal structure. Our observation not only sheds light on the importance of coherent many-body Rydberg interactions in solid state systems, but also enables new possibilities to coherently manipulate Rydberg excitons for quantum information processing.
4:15 PM - ES01.16.04
Impact of White Light Illumination on the Electronic and Chemical Properties of Mixed Halide and Single Crystal Perovskites
Fengshuo Zu 1 , Patrick Amsalem 1 , Ingo Salzmann 1 3 , Rongbin Wang 1 2 , Maryline Ralaiarisoa 1 , Stefan Kowarik 1 , Steffen Duhm 2 , Norbert Koch 1
1 Institut für Physik, Humboldt-Universität zu Berlin, Berlin Germany, 3 Institute for Solid State Physics, The University of Tokyo, Tokyo Japan, 2 FUNSOM, Soochow University, Suzhou, Jiangsu, China
Show AbstractLarge variations with respect to the electronic structure and interface energetics of perovskites used in solar cells have been reported by the pertinent community. The experimentally observed n-type character of perovskite film surfaces is intriguing, since these materials are expected to be bipolar. In the present study, to explore the underlying physics of the n-type character, we investigate the effect of white-light illumination on the electronic structure of mixed halide perovskite thin films and of CH3NH3PbI3 single crystals using X-ray and ultraviolet photoelectron spectroscopy, as well as UV-Vis absorption spectroscopy. Our sample surfaces are found to be strongly n-type in the dark, i.e., the Fermi level is close to the conduction band edge. However, upon illumination the Fermi level shifts by up to 0.7 eV towards mid-gap due to surface photovoltage. We show this to be correlated with initial surface band bending due to the presence of donor-levels, likely consisting of reduced lead (Pb0) acting as surface traps. Upon short-time illumination, the Fermi level shift is found to be partially reversible; for prolonged illumination, however, a high concentration of metallic Pb0 is generated, inducing strong Fermi level pinning and quenching of the surface photovoltage.1 This is accompanied by the formation of PbI2 defects within the film and a deficiency of iodine in the surface region. Similar experiments performed on CH3NH3PbI3 single crystals reveal the presence of a relatively high concentration of reduced (metallic) Pb0 at the sample surface already after cleaving and without light treatment; likewise, strongly pinning of the Fermi level even under high intensity (comparable to 1 sun) illumination.
1. F.-S. Zu, P. Amsalem, I. Salzmann, R.-B. Wang, M. Ralaiarisoa, S. Kowarik, S. Duhm, N. Koch. Adv. Optical Mater. 5 (2017) 1700139
4:30 PM - ES01.16.05
Growing Methylammonium Lead Iodide Single Crystals with Controlled Exposed Facets
Meng-Huan Jao 1 , Chun-Fu Lu 1 , Pao-Yi Tai 1 , Wei-Fang Su 1
1 , National Taiwan University, Taipei Taiwan
Show AbstractHigh quality polycrystalline thin films of organic-inorganic hybrid perovskites can be fabricated by low cost and low temperature solution process. The materials exhibit appealing properties of high absorption coefficient, broad absorption range, outstanding charge carrier mobility and long diffusion length. They have found potential applications in solar cells, photodetectors, light emitting diodes, lasers, spintronics, etc. The hybrid perovskite solar cells have progressed rapidly in the last decade, and their efficiency now has reached the same level as cadmium telluride and silicon based solar cells. Despite the remarkable achievement for hybrid perovskite solar cells, there are still some uncertainties or debating issues. In order to further promote their application in high performance devices, in-depth study on the intrinsic material properties should be carried out.
Single crystal is one of the best platforms to study the intrinsic properties of materials. There are lots of methods to synthesize the single crystal of hybrid perovskite. However, seldom of them reported possible ability to control the exposed facets during crystal growth, which may hinder the opportunities to study the effect of exposed facet on the performance of devices. Here in our research, we focus on the crystal growth strategy of methylammonium lead iodide (MAPbI3) to obtain the single crystal with specific exposed facets. In most reports, the exposed facets for the single crystal of MAPbI3 are (100) and (112). We developed a facile approach to manipulate the exposed facets and were able to obtain single crystals with exposed facets of (002) and (110). The new structures were verified by X-ray diffraction and quantum calculation. In additional, by our crystal growth strategy, the ratio of (100) and (112) to (002) and (110) could be carefully controlled. The properties of newly exposed (002) and (110) were thoroughly studied. We fabricated photodetectors based on different facets and offered the first insight on the facet-dependent device performance. The results of this work open a new pathway to understand the hybrid perovskite and lead to better device performance.
4:45 PM - ES01.16.06
Confining Metal-Halide Perovskites in Nanoporous Thin Films
Stepan Demchyshyn 1 , Janina Roemer 2 , Heiko Groiss 1 , Herwig Heilbrunner 1 , Christoph Ulbricht 1 , Dogukan Apaydin 1 , Anton Böhm 2 , Uta Ruett 3 , Florian Bertram 3 , Günter Hesser 1 , Markus Scharber 1 , Niyazi Serdar Sariciftci 1 , Bert Nickel 2 , Siegfried Bauer 1 , Eric Glowacki 4 , Martin Kaltenbrunner 1
1 , Johannes Kepler University, Linz Austria, 2 Faculty of Physics, Ludwig-Maximilians-Universität München, Munich Germany, 3 , DESY Photon Science, Hamburg Germany, 4 , Linköpings Universitet, Linköping Sweden
Show AbstractControlling size and shape of semiconducting nanocrystals advances nanoelectronics and photonics. Quantum confined, inexpensive, solution derived metal halide perovskites offer narrow band, color pure emitters as integral parts of next-generation displays and optoelectronic devices. We here employ nanoporous silicon and alumina thin films as templates for the growth of perovskite nanocrystallites directly within device-relevant architectures without the use of colloidal stabilization[1]. We find significantly blue shifted photoluminescence emission by reducing the pore size; normally infrared-emitting materials become visibly red, green-emitting materials cyan and blue. Confining perovskite nanocrystals within porous oxide thin films drastically increases photoluminescence stability as the templates auspiciously serve as encapsulation. We quantify the template-induced size of the perovskite crystals in nanoporous silicon with microfocus high-energy X-ray depth profiling in transmission geometry, verifying the growth of perovskite nanocrystals throughout the entire thickness of the nanoporous films. Low-voltage electroluminescent diodes with narrow, blue-shifted emission fabricated from nanocrystalline perovskites grown in embedded nanoporous alumina thin films substantiate our general concept for next generation photonic devices.
[1] S. Demchyshyn, J. Roemer, H. Groiss, H. Heilbrunner, C. Ulbricht, D. Apaydin, A. Böhm, U. Ruett, F. Bertram, G. Hesser, M. Scharber, S. Sariciftci, B. Nickel, S. Bauer, E. Glowacki, M. Kaltenbrunner, Science Advances 2017:e1700738, accepted for publication.