Symposium Organizers
Jian Li Arizona State University
Chung-Chih Wu National Taiwan University
Jian-Bin Xu The Chinese University of Hong Kong
NoraS. Radu E. I. DuPont de Nemours and Co., Inc.
AssangaB. Padmaperuma Pacific Northwest National Laboratory
OO10: Poster Session: OLED and Organic Solar Cells
Session Chairs
Wednesday PM, April 27, 2011
Salons 7-9 (Marriott)
1:00 AM - OO10: Poster
OO10.20 Transferred to OO1.5
Show Abstract1:00 AM - OO10: Poster
OO10.67 Transferred to OO17.12
Show Abstract9:00 PM - OO10.1
Incorporation of Furan into Low Band-gap Polymers for Efficient Solar Cells.
Claire Woo 1 2 , Pierre Beaujuge 1 2 , Thomas Holcombe 1 , Olivia Lee 1 , Jean Frechet 1 2
1 College of Chemistry, University of California, Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractA survey of state-of-the-art organic solar cells reveals that all high performance polymers reported so far rely on thiophene or thiophene-based heterocycles. In contrast, there has been a scarcity of studies examining polymer backbones containing furans. This is surprising given that furans exhibit similar energy levels and a comparable degree of aromaticity relative to their thiophene counterparts. Here, we present the design, synthesis, and characterization of the first examples of furan-containing low band-gap polymers. We found that inserting furan moieties in the backbone of the conjugated polymers enables the use of relatively small solubilizing side chains because of the significant contribution of the furan rings to overall polymer solubility in common organic solvents. These low band-gap furan-containing polymers exhibit similar optical and electronic properties as their thiophene analogs, and they achieve up to 5% power conversion efficiencies in bulk heterojunction solar cells with soluble fullerene derivatives. These results demonstrate the potential of furans as thiophene alternatives in the design of high performing OPV materials.
9:00 PM - OO10.10
Multi-layer Blade Coating for Organic Light-emitting Diode and Solar Cell.
Meng Hsin-Fei 1 , Zan Hsiao Wen 1
1 , National Chiao Tung University Institute of Physics, Hsinchu Taiwan
Show AbstractMultilayer organic light-emitting diodes are fabricated by blade coating without dissolution. A soluble polymer is used for hole transport layer. Both Ir complex with alkyl side chain and dendrimer are used the emitter. Efficient electron injection is realized by coating a small-molecule electron transport layer combined with the relatively stable evaporated LiF/Al cathode. The efficiency is 12 cd/A for blue emission, 45 cd/A for green, 20 cd/A for orange, and 17 cd/A for red. Large area OLED with brightness up to 8000 cd/m2 is made with blade coating. For solar cell blade coating is applied polymer blend in toluene. Power conversion efficiency of 4.6 % is achieved. Top-emitting OLED on metal substrate is made by blade coating. Silver with chemical modification to increase the workfunction is used as anode. Cathode can also be deposited without vacuum by printing chemically modified aluminum from epoxy mold.
9:00 PM - OO10.12
Charge Transport Enhancement via Air-mediated Self-organization in Polymer Semiconductors.
Takashi Kushida 1 , Takashi Nagase 2 3 , Hiroyoshi Naito 2 3
1 Integrative Technology Research Institute, Teijin Limited, Hino, Tokyo, Japan, 2 Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka, Japan, 3 The Research Institute for Molecular Electronic Devices, Osaka Prefecture University, Sakai, Osaka, Japan
Show AbstractOrganic field-effect transistors (OFETs) fabricated on the basis of soluble organic semiconductors are attracting considerable attention as a key device for realizing printed electronics. In recent years, there has been a remarkable increase in the charge mobility in soluble organic semiconductors as a result of the improvements in intermolecular coupling utilizing self-organizing behaviour on hydrophobic, low-energy surfaces. In this study, we report a significant enhancement in the self-organization of soluble organic semiconductors in OFETs fabricated by microcontact printing (μCP) using polydimethylsiloxane (PDMS) exhibiting varying surface energy. The field-effect mobility measurement of a printed poly(3-hexylthiophene) (P3HT) thin film reveals a large difference between the microscopic structures of the P3HT thin film at the interfaces with air and with substrate; in addition, it was found that efficient charge transport through the microstructure was formed at the air interface. The charge mobility of P3HT FETs fabricated on bare SiO2 substrates by air-mediated self-organization is more than 100 times higher than that of P3HT FETs fabricated by spin coating. The charge mobility of P3HT FETs can be improved by enhancing the molecular ordering of P3HT molecules in a very thin layer at the air/P3HT interface that is responsible for superhydrophobic air. This improvement is also observed in the charge mobility of other organic semiconductor films prepared from solution processes. Thus, we conclude that the enhancement in the self-organization at the air/P3HT interface generally occurs in solution-processed organic semiconductors.Moreover, we investigated the influence of semiconductor film thickness on charge mobilities at the air/P3HT interface. When the film thickness is less than 50 nm, the charge mobilities decrease as the surface energy of PDMS stamps are increased. This implies that air-mediated self-organization is affected by the surface energy of the substrate in the P3HT films that thickness is less than 50 nm, suggesting that the driving force of air-mediated self-organization is weaker than that of substrate-mediated self-organization. The use of air-mediated self-organization is advantageous for fabricating high-performance printed OFETs on conventional organic gate dielectrics and for understanding the interfacial effect of solution-processed OFETs. Air-mediated self-organization can help distinguish between the self-organization effect and the dielectric surface effect. In the case of P3HT films, charge (hole) mobility is strongly influenced by molecular ordering and weakly influenced by hydroxyl groups present at the dielectric surface. On the other hand, in the case of poly[(9,9′-dioctylfluorenyl-2,7-diyl)-(2,2′-bithiophene-5,5′-diyl)] (F8T2) film, hole mobility is influenced by both the molecular ordering and the hydroxyl groups at the dielectric surfaces.
9:00 PM - OO10.13
Efficient Polymer Phosphorescent Light-emitting Diodes Based on Silver Nanowire Electrodes.
Lu Li 1 2 , Zhibin Yu 1 , Qingwu Zhang 1 , Qibing Pei 1
1 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 State Key Laboratory of Electronic Thin Films and Integrated Devices, Department of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu, Sichuan, China
Show AbstractPolymer light-emitting diodes (PLED) are promising candidates for flat panel displays and solid state lighting. Both applications require large-area, low cost transparent electrodes to replace indium-tin oxide. We will present recent progress in achieving efficient blue and white PLED employing silver nanowire electrodes. High device performance has been obtained using a host polymer with a high triplet energy level, blue, green, and red phosphorescent dopants. The balance of opposite charge carrier injections and transport are obtained in the PLED devices having a simple device architecture of Al/CsF/Polymer host and dopants/PEDOT/silver nanowire electrode/polymer substrate. The device performance is comparable to control devices on ITO/glass substrate. The PLED devices are high flexible.
9:00 PM - OO10.14
Saturated Deep-blue Solid-state Light-emitting Electrochemical Cells.
Chih-Teng Liao 1 , Hsiao-Fan Chen 2 , Te-Chuan Chen 1 , Hai-Ching Su 1 , Ken-Tsung Wong 2
1 Institute of Lighting and Energy Photonics, National Chiao Tung University, Tainan Taiwan, 2 Department of Chemistry, National Taiwan University, Taipei Taiwan
Show AbstractLight-emitting electrochemical cells (LEC’s) in general have several advantages over conventional organic light-emitting diodes (OLEDs), such as the simple single-layer configuration, solution-processing and low operation voltages with air-stable electrodes. However, saturated deep-blue emission, which is essential for full-color display, can not be easily obtained from commonly used LEC materials, e.g. cationic transition metal complexes (CTMCs) and conducting polymers. Reported high-gap Ir-based CTMCs used in LECs have mainly exhibited electroluminescence (EL) in the blue-green region. The difficulty in color-tuning toward the deep-blue region through molecular design of Ir-based CTMCs is mainly due to the intrinsically narrower energy gaps in such cationic complexes relative to those of neutral ones. On the other hand, the EL of LECs based on polyfluorenes (PFs) usually contains significant green emission due to the interchain aggregation, deteriorating color saturation of blue emission coming from PFs. In this work, we report the utilization of an ionic small-molecule fluorene derivative (Fan13) to achieve saturated deep-blue EL from LEC devices. Photoluminescence measurements show highly retained photoluminescence quantum yields of Fan13 in neat films (0.76) as compared to those in solutions (1.00), indicating insignificant self-quenching in condensed phase and thus suitable use as an emissive material of single-layer LECs. Device 1 (neat film) and Device 2 (with 10 wt.% 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+(PF6)-) to accelerates device response) provided saturated deep-blue EL centered at 424 nm with Commission Internationale de l’Eclairage (CIE) coordinates (x, y) of (0.151, 0.122) and (0.159, 0.115), respectively, extremely close to the blue standard (0.14, 0.08) of the National Television System Committee (NTSC) color gamut. Atomic force microscopy shows no significant difference in film morphologies of Fan13 with and without BMIM+(PF6)-, thus indicating good mixing compatibility of Fan13 and ionic liquids. Device 1 at 3.4 V showed a peak external quantum efficiency (EQE) and a peak power efficiency of 1.04 % and 0.63 lm/W, respectively. Addition of BMIM+(PF6)- (Device 2) improved the carrier balance and decreased the operating voltage and, therefore, increased the EQE and the power efficiency relative to those of the parent neat-film device (Device 1). Device 2 under 3.2 V exhibited a peak EQE and a peak power efficiency of 1.14 % and 1.24 lm/W, respectively. These results successfully demonstrate the bluest EL emissions ever obtained from LECs and suggest that ionic small-molecule fluorene derivatives are promising candidates for saturated deep-blue solid state LECs.
9:00 PM - OO10.16
Comprehensive Investigation of Transient Electroluminescence (EL) Spikes in Small Molecular Organic Light-emitting Diodes (SMOLEDs).
Rui Liu 1 2 , Zhengqing Gan 1 2 , Ruth Shinar 3 4 , Joseph Shinar 1 2
1 Ames Laboratory - USDOE, Iowa State University, Ames, Iowa, United States, 2 Physics & Astronomy, Iowa State University, Ames, Iowa, United States, 3 Microelectronics Research Center, Iowa State University, Ames, Iowa, United States, 4 Electrical and Computer Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractA comprehensive study of transient EL spikes and tails following a bias pulse in guest-host SMOLEDs, which elucidates carrier and exciton dynamics, is presented. This study is important due to the pulsed-mode operation of SMOLEDs in active matrix displays. The transient EL is dependent on device materials and structure. At low temperatures, all measured devices, with the exception of Pt octaethylporphyrin (PtOEP)-doped tris(8-hydroxyquinoline) Al (Alq3), exhibit the spikes at ~70-300 ns. At room temperature, however, only those with a hole injection barrier, carrier-trapping emitting layer, and no strong electron-transporting and hole-blocking layer exhibit spikes. These narrow and appear earlier under post-pulse reverse bias. To elucidate the spikes’ origin, we monitored their dependence on the bias width and voltage, the doped layer thickness, and its location in the OLED. The characteristics of the microsecond-long tails were also evaluated via the effect of the post-pulse voltage. A model based on the recombination of correlated charge pairs (CCPs) and charge detrapping, which agrees with experiment, is presented. The results suggest that reduced electric field-induced dissociative quenching of CCPs and singlet excitons is responsible for the spikes’ amplitude exceeding the on-pulse EL. The tails are attributed to recombination of charges detrapped from a distribution of shallow sites, reminiscent of the thermally stimulated luminescence of such materials. In addition to systems with charge trapping on the guest, the PtOEP:Alq3 system, where energy transfer dominates, and the triplet exciton emission extends to ~0.1 ms, was also studied, revealing no spike even at low temperature. Hence, the transient EL can distinguish between efficient energy transfer and charge trapping in guest-host OLEDs.*Ames Laboratory is operated by Iowa State University for the US Department of Energy (USDOE) under Contract No. DE-AC 02-07CH11358. This work was supported by the Director for Energy Research, Office of Basic Energy Sciences, USDOE.
9:00 PM - OO10.18
Contact Resistance of P3HT: PCBM Heterojunction Solar Cells.
Yang Shen 1 , Kejia Li 1 , Nabanita Majumdar 1 , Joe Campbell 1 , Mool Gupta 1
1 Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractIn this paper, the series resistance of poly (3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic solar cells has been studied. The series resistance of thermal annealed and un-annealed devices with different active layer thickness was measured. The series resistance of the organic solar cells consists of the bulk resistance of the active layer itself and the specific contact resistance between the active layer and the electrode. The bulk resistance and contact resistance were extracted from the measured series resistance using the vertical transmission line model (TLM) method. By fabricating solar cell devices with different active layer thickness, a relationship of the series resistance with thickness was established from which bulk and the contact resistance was derived. We have also found that the thermal annealing helps reduce both contact resistance and bulk resistance significantly, the contact resistance dropped by a factor of 2, while the bulk resistance decreased by a factor of 10. Results have shown that for an annealed P3HT:PCBM devices which have an active layer thickness of 85 nm (optimum thickness for high efficiency), 17% of the total series resistance was due to contact resistance and bulk resistance contributed the rest 83%. The bulk resistance value for thermal annealed organic solar cell device with an active area of 0.1 cm2 was found to be 150 Ω, and the measured specific contact resistance was 3.1 Ωcm2. The measured bulk and contact resistance values are much higher than compared to the high efficiency silicon solar cells. Bulk resistance and contact resistance need to be further decreased in order to achieve higher organic solar cell efficiency.
9:00 PM - OO10.19
Syntheses of Conjugated Polymers for Solar Cells Using New Electron Deficient Moiety.
Hongsuk Suh 1 , Suhee Song 1 , Joo Young Shim 1 , Youngeup Jin 2 , Sung Heum Park 3 , Kwanghee Lee 3
1 Department of Chemistry, Pusan National University, Busan Korea (the Republic of), 2 Department of Industrial Chemistry, Pukyong National University, Busan Korea (the Republic of), 3 Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractUtilization of 2,2-dialkyl-2H-benzimidazole has received strong attention as the electron deficient unit for the generation of electron donor material for organic photovoltaic cells (OPVs). This novel dialkyl-2H-benzimidazole unit has two alkyl groups which can supply higher solubility as compared to that of the BT series. The thin film of new polymer, with dimethyl-2H¬-benzimidazole unit, shows two broad absorption bands with maxima at 400 and 636 nm. The device with PCDTMBI:PC71BM blend demonstrated the efficiency of 3.12%. New other polymers, utilizing dihexyl-2H-benzimidazole, were synthesized using Stille coupling reaction. Even with two bithiophene units in the copolymers to facilitate absorption at the longer wavelength, the incorporation of dihexyl-substituent on 2H-benzimidazole enables the polymers to have good solubility. The device with PEHOPBBTHBI:PC71BM blend demonstrated an open-circuit voltage (VOC) of 0.59 V, a short-circuit current (JSC) of 6.43 mA/cm2, and a fill factor (FF) of 0.39, leading to the efficiency of 1.46%.
9:00 PM - OO10.21
Importance of Molecular Alignment for Opto-electronic Devices.
Roy Vellaisamy 1 , Zong-Xiang Xu 1
1 Physics and Materials Science, City University of Hong kong, Hong Kong Hong Kong
Show AbstractThe search for new classes of organic and metal-organic compounds for molecular electronics is of immense current interest due to the relative low-cost and potential applications in electronic logic circuits. The development of molecular materials represents a new frontier in preparation of high performance opto-electronic devices. In addition, the structural tailorability and multifunctionality of molecules attract huge attention and it is feasible to develop such self-assembly molecules for the incorporation in opto-electronic devices. In this work, we focus on various self-assembled organic/organo-metallic molecular materials and their molecular alignment for the construction of electronic and opto-electronic devices.
9:00 PM - OO10.22
Self-assembly of a Fullerene Poly(3-hexylthiophene) Dyad.
Mingfeng Wang 1 2 3 , Fred Wudl 1 2 3
1 Department of Chemistry and Biochemistry, University of California, Santa Barbara, California, United States, 2 Center for Polymers and Organic Solids, University of California, Santa Barbara, California, United States, 3 Materials Research Laboratory, University of California, Santa Barbara, California, United States
Show AbstractWe report the self-assembly of a C60-capped P3HT dyad molecule (PCB-P3HT) that serves as a “surfactant” to enhance the solubility of fullerenes in poor solvents such as THF, a selective good solvent for P3HT. The phase separation of PCB-P3HT in thin films leads to well-defined nanostructures. Here the solvent plays a vital role in determining the morphology and the structure of these self-assembling structures. PCB-P3HT from THF solution tends to form spherical aggregates in which the methanofullerene (PCB) moieties form a micelle core stabilized by P3HT chains that extend to the solvent medium. In contrast, PCB-P3HT from o-DCB solution forms fibrous structures with a uniform diameter of 15-20 nm and varying lengths up to micrometers. We rationalize that in these fibrous structures the P3HT chains crystallize to form the core, surrounded by a monolayer of C60 moieties. We expect that these different self-assembled structures of PCB-P3HT dyads could be interesting nanoscale model systems for study of photoinduced charge transfer. For example, in the spherical self-assemblies formed from THF solution, photoinduced electrons after the exciton dissociation at PCB/P3HT interfaces would be localized in the micellar core, while photoinduced holes would be localized in the corona. Nevertheless, in the elongated one-dimensional fibrous self-assemblies, we could imagine both holes and electrons tend to be delocalized in the P3HT phase and in the methanofullerene sheath, respectively.
9:00 PM - OO10.23
Simplified Phosphorescent Organic Light Emitting Diode with High Efficiency and Small Efficiency Roll-off.
Zhibin Wang 1 , Michael Helander 1 , Jacky Qiu 1 , Danny Puzzo 1 , Mark Greiner 1 , Zhiwei Liu 1 , Zhenghong Lu 1
1 Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada
Show AbstractOrganic light emitting diodes (OLEDs) are considered the next generation of technology for flexible flat panel displays and low cost solid state lighting. In particular, phosphorescent organic light emitting diodes (PHOLEDs) that have the potential to achieve an internal quantum efficiency close to 100% have attracted considerable research interest. Much research effort has been devoted to synthesizing new materials and to developing new device architectures to achieve high efficiency. Although high efficiency has been realized at low luminance (e.g., < 100 cd/m2), it is still a significant challenge to obtain a similarly high efficiency at high luminance (e.g., > 5000 cd/m2). The long triplet lifetimes and diffusion lengths result in the notorious efficiency roll-off problem common to all phosphorescent devices at high luminance. In addition to achieving high efficiency, a minimization of efficiency roll-off is also critical for applications that require high brightness, such as solid state lighting. Many different structures have been proposed in literature, such as double emission layers and the incorporation of different blocking layers, to improve the PHOLEDs performance. However, from the practical point of view, a complex device structure with a multuplet of layers will increase the complexity and cost of manufacturing. As will be shown here, all these additional layers are not necessarily needed to achieve high performance PHOLEDs. In this work, a green phosphorescent organic light emitting device that concurrently satisfies: i) a simple structure, ii) a high efficiency and iii) a low efficiency roll-off has been demonstrated. In particular, the external quantum efficiency (EQE) drops < 1 % from 100 cd/m2 to 5000 cd/m2 and reaches ~20% at 10,000 cd/m2. The EQE can be further boosted up to > 50 % at 10000 cd/m2 by employing our optical out-coupling technique, i.e. an innovative development of optical out-coupling without using the high-index glass substrate.
9:00 PM - OO10.24
Toward Predictive Modeling of 3D Bulk Heterojunction in Organic Solar Cells.
Olga Wodo 2 , Baskar Ganapathysubramanian 2 1
2 Mechanical Engineering Department, Iowa State University, Ames, Iowa, United States, 1 Electrical and Computer Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractThe past decade has witnessed considerable advances in organic photovoltaic technology both from the perspective of understanding the physical aspects of the underlying processes, as well as concurrent improvement in efficiencies. This improvement was made possible through a three pronged approach: (a) new materials development (e.g. PTB systems); (b) new device designs (e.g. tandem cells); and (c) morphology control during manufacturing process. Despite these significant improvements in both fundamental understanding as well as device enhancements, there still remain several potential issues that thwart wide-spread use and profitable commercial production of OSC. One major challenge is the weak control over manufacturing process to get tailored morphologies. Current state-of-the-art approaches to understanding morphology evolution and tailoring manufacturing process for high efficiency OSCs are either limited to combinatorial trial-and-error based experimental investigation or single scale analysis. Experimental techniques, however, provide limited data for analysis (limited to final morphology and mostly to lateral cross sections). The main reasons for that are mostly related to the difficulty of attaining high spatial resolution and the requirement of good contrast between components. These challenges hinder our ability to understand and subsequently control the interaction of multiple factors affecting morphology evolution. These challenges serve as a rational for developing a computational framework that can be used to analyze morphology evolution thus significantly augmenting experimental analysis and opening up new possibility of data-driven knowledge discovery.In our approach we use a phase field approach to develop a predictive theory for the evolution of morphology during solvent-based fabrication of organic solar cells. We model evaporation-induced phase-separation in ternary systems, which consist of conjugated polymer, fullerene derivative and solvent. The model takes into account both thermodynamic (e.g. interaction parameters between components) and kinetic parameters (e.g. diffusion coefficient). To enable quantitative prediction we equip the model in material-specific parameters obtained via molecular dynamic simulation. Additionally to augment the device scale simulation we develop an efficient, multiscale computational framework to model evolution of three dimensional bulk heterojunction structures. We showcase the framework by investigating the effect of fabrication parameters (e.g. evaporation rate) and system parameters (e.g. type of solvent, blend ratio) on the morphology during two currently competitive solvent based fabrication techniques: spin coating and drop casting.
9:00 PM - OO10.25
Tacticity Directed Solution Self-assembly in Small Molecule Organic Semiconductor – Polymer Blends.
Stephen Yeates 1 , Marie-Beatrice Madec 1
1 Chemistry, University of Manchester, Manchester United Kingdom
Show AbstractThe role of polystyrene as a structural scaffold in the nucleation and self assembly of solution processable small molecule organic semiconductors is demonstrated. The nature of the tacticity of polystyrene is found to influence the nature of the solution aggregation behaviour of 6,13 triisopropylsilyletynylpentacene (TIPS-pentacene) with small molecule and polymer matrix interaction being dominated by van der Waals dispersion forces between the π orbitals favouring a parallel (S shape) or perpendicular (T shape) contact. Fluorescence spectroscopy reveals that TIPS-pentacene forms supramolecular clusters well below the solubility limit, with a small monomer signal being observed at very high dilution decaying rapidly with increased concentration. Clusters in the form of dimer or higher organised structure are influenced by addition of a polymer matrix which enhances the emission and shifts the maximum free dimer and monomer concentration in solution depending upon tacticity. Neutron scattering analysis exhibits a dramatic difference between the TIPS-pentacene and the polystyrene interaction dependent upon its tacticity.Isotactic polystyrene demonstrates synergistic pi-pi stacking interactions with TIPS-pentacene, resulting in longer range crystalline order of the semiconductor when deposited from solution when compared with the semiconductor on its own. This is manifested as higher organic thin film transistor performance and improved discrete device to device performance [1,2].1. Thermo-mechanical stabilisation of a crystalline organic semiconductor for robust large area electronics. Organic Electronics. M. M. Ibrahim, A. C. Maciel, C. P. Watson, M.-B. Madec, S. G. Yeates and D.M. Taylor, Organic electronics (2010), 11, 1234-1241.2. Organic field effect transistors from ambient solution processed low molar mass semiconductor-insulator blends. Madec, Marie-Beatrice; Crouch, David; Llorente, Gonzalo Rincon; Whittle, Tracie J.; Geoghegan, Mark; Yeates, Stephen George. Journal of Materials Chemistry (2008), 18(27), 3230-3236.
9:00 PM - OO10.28
Narrow-bandgap Copolymer Based on Diketo-Pyrrolo-Pyrrole /Cyclopentadithiophene for Polymer Solar Cells.
Kanpitcha Jiramitmongkon 1 , Phimwipha Piyakulawat 1 , Anusit Keawprajak 1 , Michael Forster 2 , Udom Asawapirom 1
1 , National Nanotechnology Center, Pathumthani Thailand, 2 Macromolecular Chemistry, University of Wuppertal, Wuppertal Germany
Show AbstractThe electroactive conjugated polymers have been extensively used for photovoltaic cells [1-2]. The key attributes of the polymer contributing to high power conversion efficiency (PCE) have been identified to include high hole mobility and good miscibility with the acceptor material to maximize the bulk-heterojuntion area [3-5]. Moreover, the important parameter for optimization of polymer photovoltaic cells is the bandgap of the donor materials. For single junction cells, using [60] PCBM as acceptor, a bandgap lower than 2.0 eV is expected to be optimal, provided that the HOMO and LUMO levels are correctly positioned with respect to the levels of the electron acceptor.[6] In this study, we have synthesized a new low band gap copolymer based on diketo-pyrrolo-pyrrole and cyclopentadithiophene for using as donor material. The polymer was polymerized through a Stille cross-coupling reaction via Palladium complex catalyzed and confirmed the chemical structure by NMR. The obtained copolymer absorbs light in wide range from 300 to 750 nm. The energy band gap was estimated by UV-vis and electrochemical studies. Photovoltaic cells were fabricated via spin-coating method by using the blend of the obtained copolymer and PCBM in various ratios as an active layer. The best device performance was achieved at the copolymer/PCBM weight ration of 1:3 under the illumination of A.M. 1.5, 100mw/cm2.
9:00 PM - OO10.3
Bimolecular Recombination and Energetic Disorder in Low-gap Polymer Solar Cells.
Song Chen 1 , Jegadesan Subbiah 1 , Chad Amb 2 , John Reynolds 2 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 The George and Josephine Butler Polymer Research Laboratory, Department of Chemistry, Center for Macromolecular Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractLow-gap polymer poly ((4, 4- dioctyldithieno (3,2-b:2',3'-d) silole) -2,6- diyl-alt- (2,1,3- benzothiadiazole) -4,7-diyl) (DTS-BTD) is a promising material for donor-acceptor bulk heterojunction solar cell applications with a wide-absorption band and excellent transport. While the solar cell short-circuit current exceed 15 mA/cm2, its power conversion efficiency is limited by its fill factor as well as external quantum efficiency. In order to study the loss mechanism of photo-current, we carried out transient photo-voltage (TPV) experiments to probe the bimolecular recombination of photo-carriers under open circuit condition. Together with photo-CELIV (carrier extraction by linearly increasing voltage) data, we will present a device model explaining the loss mechanism in this type of donor-acceptor photovoltaic system.Solar cells were fabricated with the following structure: ITO/ ZnO/ DTS-BTD:PCBM/ MoO3/ Ag. TPV measurements were carried out directly on the solar cell by using two light sources. A solar simulator provides a constant light bias to the device while the sample is modulated by a pulsed laser with durations of 5 ns. The photo-carriers lifetime was extracted by probing the decay of the photo-generated carriers. Our results show the polymer: fullerene system (DTS-BTD: PCBM) has a photo-carrier lifetime of 400 ns at open circuit condition, which corresponds to a k/kL ratio (kL is the Langevin mode recombination coefficient) over 10-1. In contrast, conjugated polymer: fullerene system (poly-3(hexylthiophene) (P3HT): PCBM) has a lifetime of 8 μs with a k/kL ratio < 10-2. The difference in lifetime between the two systems is consistent with the device performance data. Thus, the recombination at open circuit condition is a strong limiting factor for DTS-BTD: PCBM. Finally, we will correlate the photo-carrier lifetime with the degree of energetic disorder (diagonal disorder) of the polymer materials. Based on the Marcus theory small polaron model, the bound electron-hole pair lifetime is limited due to a large population of tail states in the HOMO band. Our mobility data that the DTS-BTD: fullerene system shows much higher energetic disorder than P3HT: PCBM are consistent with the small polaron model.
9:00 PM - OO10.30
A Facile Transferring Method to Fabricate a Light Harvesting System for Polymer Solar Cells.
Yu-Sheng Hsiao 1 , ChiungWen Kuo 1 , Chih-Wei Chu 1 , Peilin Chen 1
1 Research Center for Applied Sciences, Academia Sinica, Taipei Taiwan
Show AbstractA simple light harvesting system with two-dimensional (2D) periodic granular-like electrodes was fabricated using transferring process for polymer solar cells (PSCs). This transferring technique, which was based on nanosphere lithography, could be used to fabricate periodic nanostructures on both photoactive layers and Al electrodes in the normal PSC device configuration (ITO glass/PEDOT:PSS/photoactive layer/Al). The properties of the PSC devices with periodic nanostructures in the photoactive layers have been investigated by several techniques, including reflection UV-vis spectra, external quantum efficiency (EQE), photocurrent–voltage characteristics. In addition, the electromagnetic field distribution for devices as evaluated by numerical simulation. It has been demonstrated that the light trapping efficiency in the PSCs with periodic nanostructures has been enhanced due to light scattering and localized surface plasmon resonance (LSPR). When compared to conventional devices with flat geometry, the power conversion efficiency (PCE) of the small thickness of photoactive layer (ca. 150 nm) of P3HT/C70 bi-layer devices with periodic nanostructures has been increased by 90%. Furthermore, when the bulk heterojunction (BHJ) devices with low absorption coefficient photoactive layer (PTPTBT:PC70BM) were engineered with periodic nanostructures, 20% enhancement in photocurrent has been observed, which suggested that this facile light harvesting system be suitable for both small thickness or low bandgap polymer solar cell applications.
9:00 PM - OO10.31
Effects of Substituted Side Chains on the Optical and Electrical Properties of D-A Conjugated Copolymers.
Shinuk Cho 1 , Sangkyu Lee 2 , Minghong Tong 3 , Jung Hwa Seo 3 , Hongsuk Suh 4 , Alan Heeger 3
1 Department of Physics, University of Ulsan, Ulsan Korea (the Republic of), 2 Energy Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon Korea (the Republic of), 3 Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California, United States, 4 Department of Chemistry, Pusan National University, Busan Korea (the Republic of)
Show AbstractBecause of the low band-gap property together with relatively high hole mobilities, conjugated copolymers containing electron donor–acceptor (D-A) repeating units have drawn considerable attention for use as active materials in organic electronic devices, such as bulk heterojunction (BHJ) photovoltaic (PV) cells and polymer field-effect transistors (FETs). Although the conjugated core units of D-A conjugated copolymers convey solubility, D-A copolymers have relatively low solubility if they have a high molecular weight (Mw). As a simple way to improve the solubility of high molecular weight D-A copolymers, alkyl or alkoxy side chains may be introduced at the thiophene unit. Substitution of side chains in conventional conjugated polymers, however, often alters the configuration of the conjugated chain, thereby affecting the electronic properties. In this presentation, the effects of several substituted side chains (alkyl or alkoxy) on the optical and electrical properties of D-A conjugated copolymers will be presented. The substituted alkyl or alkoxy side chains significantly altered the optical and electrical properties of D-A conjugated copolymers due to steric hindrance. In addition, the effects of the position of substituted side chains (alkyl) on the optical and electrical properties of D-A conjugated copolymers also will be dicsessued. The intrinsic properties of the copolymers were significantly altered by perturbations of the intramolecular charge transfer (ICT) between the donor and acceptor segments.
9:00 PM - OO10.32
Synthesis of Novel Double Spiro Core Structure and Efficiency Improvement of Green Phosphorescent Organic Light Emitting Diodes Using Double Spiro Based Hole Transport Materials.
Yong Joo Cho 1 , Chang Woo Seo 1 , Oh Young Kim 1 , Jun Yeob Lee 1
1 Polymer Science and Engineering, Dankook University, Yongin-si, Gyeonggi-do Korea (the Republic of)
Show AbstractA novel double spiro structure was designed and synthesized as the core structure of hole transport materials for green phosphorescent organic light-emitting diodes. The double spiro core structure was prepared by one step or two step ring closing methods to functionalize the double spiro core at different positions. Two hole transport materials, double spiro compound with two diphenylamines at different fluorene moiety (DSPN1) and double spiro compound with two diphenylamines at the same fluorene moiety (DSPN2), were effectively synthesized by the two step and one step ring closing methods, respectively. The triplet energies of the DSPN1 and DSPN2 were calculated to be 2.53 eV and 2.40 eV, respectively. The quantum efficiency of green phosphorescent organic light-emitting diodes was improved by more than three times using the DSPN1 and DSPN2 instead of common N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine hole transport material. Maximum quantum efficiency of the DSPN1 device was 19.2 %. The double spiro structure was effective as the core structure of hole transport material and can be used as the core of host or electron transport materials due to thermal stability and high triplet energy.
9:00 PM - OO10.33
Effect of Tert Butyl Group in Asymmetric Stilbene Based Compounds on the Performance of Blue Organic Light Emitting Diodes.
Kyoung Soon Choi 1 , Hyunjong Jo 1 , Kwangyong Park 1 , Soo Young Kim 1 , Bon Hyeong Koo 2 , Kihyon Hong 2 , Jong-Lam Lee 2
1 School of Chemical Engineering and Materials Science, Chung-Ang University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractThe effect of derivatives in asymmetric stilbene based compounds on the performance of blue organic light emitting diodes (OLEDs) was investigated. Organic compounds were synthesized with respect to number and location of methyl and tert butyl groups. Red shift in photoluminescence (PL) spectra and decrease of difference in PL main peak between solid state and solution state were observed as the number of tert butyl in organic compounds is decreased, indicating that tert butyl group prohibit the formation of planar structure, reducing chromophoric phi-phi interaction followed by reducing fluorescence quenching. Luminance value of OLEDs used in tert butyl-tert butyl functional group as an active layer was the highest value due to reduction of fluorescence quenching. Therefore, it is considered that tert butyl group is very efficient in stilbene based compound to prohibit fluorescence quenching. [Acknowledgements]This research was supported in part by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(2010-0011590) and in part by Seoul R&BD program (ST10004M093171).
9:00 PM - OO10.34
High Molecular Weight Donor-acceptor Copolymers based on Benzo[1,2-b:4,5-b']dithiophene.
Robert Coffin 1 , Christopher MacNeill 2 , Eric Peterson 1 , Wanyi Nie 1 , Gregory Smith 1 , Ronald Noftle 2 , David Carroll 1
1 Physics, Wake Forest University, Winston-Salem, North Carolina, United States, 2 Chemistry, Wake Forest Univeristy, Winston-Salem, North Carolina, United States
Show AbstractThere have been many reports of high efficiency organic solar cells comprised of BDT copolymers, which prompted us to investigate these materials. We were particularly interested in a copolymer of BDT with benzothiadiazole (BT). This repeat unit structure, bearing bearing dodecyloxy chains at the 4 and 8-positions of the BDT monomer, had been previously reported, and shown to have attractive HOMO and LUMO levels for organic solar cell applications. Upon synthesizing this copolymer in our lab, we found the majority of the isolated material was insoluble, while the chloroform soluble fraction had an Mn less than 5 kDa. Not unexpectedly this resulted in poor device performance. To improve molecular weight we altered the side chain to undecan-6-yloxy (1-pentylhexyl), a large branched chain which had not been previously used in BDT copolymers. This resulted in a freely soluble, high molecular weight (> 30 kDa), BDT-BT copolymer. With this new BDT monomer in hand we investigated copolymers of BDT with several other acceptor monomers including benzoxadiazole (BO) and benzoselenadiazole (BS). The chloroform soluble fractions of all our copolymers show similarly high Mn’s allowing for valid comparisons between elements of the repeat unit structure, and the physical properties and device performance of the materials. We find that not only can large changes in LUMO levels and bandgap be achieved through varying the acceptor comonomer, but contrary to conventional wisdom we also see large changes in HOMO levels. Despite the bulky side chains increasing pi-pi stacking distances to greater than 3.8 Å as determined by powder XRD (compared with ~3.6 Å, for the dodecyloxy analogs), higher power conversion efficiencies can be obtained from the 4,8-bis(undecan-6-yloxy)BDT copolymers, indicating the benefits of high molecular weight outweigh those of close inter-chain spacing.
9:00 PM - OO10.36
High-performance Multilayered Blue Phosphorescent Organic Light-emitting Diodes Achieved by Sequential Solution-processing Method.
Taeshik Earmme 1 , Eilaf Ahmed 2 , Samson Jenekhe 1 2
1 Chemical Engineering, University of Washington, Seattle, Washington, United States, 2 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractWe report high-performance multilayered polymer-based blue phosphorescent organic light-emitting diodes (PhOLEDs) achieved by a new electron-transport material, TQB (1,3,5-tris(4-phenylquinolin-2-yl)benzene) with sequential solution-processing method. Current high-performance blue PhOLEDs have mainly focused on using vacuum deposited small organic molecules, involving thermal evaporation processes to obtain multilayered device structures, which severely affect the device fabrication cost. Solution processed PhOLEDs provide an attractive alternative to those processed by vacuum deposition. Using a solution-processable electron-transport layer (ETL), we observe a large improvement of the device performance compared to vacuum deposited ETL. By virtue of the high electron affinity (3.42 eV) and a deep HOMO energy level (-6.82 eV), TQB serves as an efficient electron-transport layer (ETL) and a good hole-blocking layer (HBL). The unique TQB ETL surface formed by solution-processing enables the high quality TQB/Al interface formation, resulting in efficient electron-injection/transport into the devices. We expect the solution-processing approach demonstrated here for high performance blue PhOLEDs to be also applicable to different colors of OLEDs / PhOLEDs as well as other solution-processed multilayered organic electronic devices.
9:00 PM - OO10.37
Materials for Hole-injection/Transport Layers of Organic Light-emitting Diodes Fabricated by Solution Processing.
Shigeaki Funyu 1 , Kenichi Ishitsuka 1 , Yosuke Hoshi 1
1 , Hitachi Chemical, Tsukuba-shi Ibaraki Japan
Show AbstractOrganic light-emitting diodes (OLEDs) have attracted considerable attention because of their potential application to solid-state lighting and display.Efficient OLED devices composed of multilayer structures are generally manufactured by using vacuum vapor deposition or solution processing. As compared to vacuum vapor deposition under strict manufacturing conditions, a multilayer coating technique using solution processing affords a lower cost of production and is easy to magnify the area of layers. However, a serious drawback of this method is the erosion of the bottom layer by a solvent used in a subsequent step. One of the development targets in the field of OLEDs, therefore, is to utilize orthogonal solvents or cross-linkable materials to overcome this problem; many research groups are working to achieve this. Here, we report a series of hole-injection/transporting polymers having cross-linkable substituents for solution processing. The developed polymers have four fundamental features: They are (1) soluble in common organic solvents such as toluene, chlorobenzene, chloroform, and tetrahydrofuran, (2) easily spin-coatable from corresponding solutions on ITO or PEDOT-PSS layers, (3) curable at 120 °C or a lower temperature, and (4) curable in short periods. The resultant polymer layers are thermally cross-linked with initiators and are insoluble in common solvents; thus, these layers can exhibit excellent properties when used as a bottom layer. One of the most important achievements of this study is the successful control of the energy level of the conjugated system. In fact, our new concepts regarding structural design and synthetic technique have made it possible to obtain wider band gaps (BGs) at the bottom layer and adjust the level of ionization potentials (IPs) for hole-injection/transportation. For example, a device with a configuration of ITO/hole-injecting polymer/αNPD/αNPD:Ir(piq)3(5:1)/Balq/Alq3/LiF/Al achieved a long lifetime greater than 5000 h at 1000 cd/m2. The device lifetime was 6 times greater than that of a reference device, which had PEDOT-PSS as the hole-injection layer. Thus, a device having the configuration of ITO/PEDOT-PSS/hole-transporting polymer/yellowish green fluorescent polymer/Ba/Al has a luminous efficiency and device lifetime that are twice and ten times that of a reference device without the hole-transporting polymer.
9:00 PM - OO10.38
Early-effect like Behavior in Space Charge Regions of Organic Bulk-heterojunction Photodiodes.
Ali Guvenc 1 , Emre Yengel 1 , Guoping Wang 1 , Cengiz Ozkan 2 3 , Mihrimah Ozkan 1
1 Electrical Engineering, University of California, Riverside, Riverside, California, United States, 2 Mechanical Engineering, University of California, Riverside, Riverside, California, United States, 3 Materials Science and Engineering, University of California, Riverside, Riverside, California, United States
Show AbstractThe space charge region width of the Schottky barrier that forms on the interface between aluminum and organic semiconductor polymer of bulk-heterojunction organic photodiodes has been investigated according to reverse voltage bias over the device and the capacitance-voltage characteristics. Here, we investigated the space charge region widths according to incident light power. Comparison of the mathematical models and experimental data measured under different light power indicate that effect of light on the space charge region of photodiodes is similar to the effect of base-emitter voltage on the space charge region of base-emitter junction in bipolar junction transistors.
9:00 PM - OO10.39
Diketopyrrolopyrrole-based Donor-acceptor Alternating Copolymer for Electronic and Optoelectronic Applications.
Jae Seung Ha 1 , Tae Wan Lee 1 , Kyung Hwan Kim 1 , Dong Hoon Choi 1
1 Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractSubstantial progress has been made in the exploration of organic semiconductors as active elements in electronic devices such as light-emitting diodes, field-effect transistors (FETs), and solar cells. Semiconducting conjugated polymers containing diketopyrrolopyrrole (DPP) in the repeating group were well known as low bandgap polymers for various electronic and optoelectronic applications. DPP unit with two fused electron-deficient lactams was recognized as an efficient building block combining with p-type ones for designing the low bandgap alternating copolymer, In the study, we synthesized new low bandgap alternating copolymers containing DPP and aromatic or fused heteroaromatic ring monomers and characterized their physical and photophysical properties. Thermal analaysis, cyclic voltammetry, absorption spectroscopy and photoluminescence spectroscopy were employed to investigate their intrinsic materials properties. Eventually, we fabricated thin film transistors to study their semiconducting property and polymer solar cells with well-known PCBM as a reference of bulk heterojucntion device of P3HT and PCBM.
9:00 PM - OO10.4
New Blue Polymer LEDs (PLEDs) Based on Electron Transporting Poly(arylenevinylene)s Containing Benzobisoxazole and Fluorene Moieties.
Min Cai 1 2 , Teng Xiao 1 2 , Rui Liu 1 2 , Jeremy Intemann 3 , Jared Mike 3 , Malika Jeffries-El 3 , Joseph Shinar 1 2 , Ruth Shinar 4 5
1 Ames Laboratory - USDOE, Iowa State University, Ames, Iowa, United States, 2 Physics & Astronomy Department, Iowa State University, Ames, Iowa, United States, 3 Chemistry Department, Iowa State University, Ames, Iowa, United States, 4 Microelectronics Research Center, Iowa State University, Ames, Iowa, United States, 5 Electrical and Computer Engineering Department, Iowa State University, Ames, Iowa, United States
Show AbstractPromising new electron-transporting blue PLEDs based on poly[(9,9-di-n-octylfluorene-2,7-vinylene)-2,6-diyl-benzo[1,2-d;5,4-d’]bisoxazole] (cis-NO-PFVBBO) (HOMO energy -5.76 eV, LUMO energy -3.27 eV) doped into poly (N-vinyl carbazole) (PVK) hosts are described. Electron transporting 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and hole transporting N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)-[l,l'biphenyl]-4,4'-diamine (TPD) were doped simultaneously into the host to improve the transport balance of the charge carriers, and 4,7-diphenyl-1,10-phenanthroline (BPhen) was added as an electron transport layer and buffer to prevent exciton quenching by the metal cathode. By optimizing the concentration of the cis-NO-PFVBBO in the blend and the thickness of BPhen layer, the device exhibited a luminous efficiency as high as 1.93 Cd/A at a current density of 0.14 mA/cm2, with the electroluminescence (EL) peaking at ~470 nm. Transient EL measurements indicate strong energy transfer from PVK to cis-NO-PFVBBO rather than charge trapping on this guest polymer. Ames Laboratory is operated by Iowa State University for the US Department of Energy (USDOE) under Contract No. DE-AC 02-07CH11358. This work was supported by the Director for Energy Research, Office of Basic Energy Sciences, USDOE.
9:00 PM - OO10.41
Synthesis and Characterization of Azatetrabenzoporphyrins Based Materials for Photovoltaic Applications.
Liang Huang 1 , Tyler Fleetham 1 , Xiaochun Hnag 1 , Jian Li 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractThe development of new organic semiconducting materials for photovoltaic applications has been the focus of considerable research in the past several years. One of the most investigated materials is phthalocyanine because of its low energy gap, high extinction coefficient and high hole mobility. Azatetrabenzoporphyrins, isoelectonic isomers of phthalocyanine (6-aza-13,20,27-triphenyltetrabenzoporphyrin, 6,13-diaza-20,27-diphenyltetrabenzoporphyrin, 20-diaza-13,27-diphenyltetrabenzoporphyrin, 6,13,27-triaza-20-phenyltetrabenzoporphyrin), in which some of the carbon atoms at 6, 13, 20,27position in the phthalocyanine ring are replaced by nitrogrn atoms, are expected to have good solubility, broad and strong absorption, and high hole mobility, making them promising candidates for organic photovoltaic applications. However, azatetrabenzoporphyrins are not fully characterized because there was no well established method to obtain reasonable reaction yield of pure azatetrabenzoporphyrins. In this presentation, we will introduce our modified reaction condition, by which we can produce pure azatetrabenzoporphyrins isomers in good yield. All four Azatetrabenzoporphyrins isomers have been synthesized and characterized. The slight difference in the structure of the four azatetrabenzoporphyrins isomers leads to significantly different absorption spectra. Also, the modified method enables us to add different ionic atoms to azatetrabenzoporphyrins to get different materials for variety of applications. Organic solar cells devices utilizing some azatetrabenzoporphyrins materials as donors will also be discussed.
9:00 PM - OO10.42
Organic-inorganic Interfaces at Fullerene-based Solar Cells: Role of the Buffer Layers for Tunable Functionality.
Gyoung Seok Hwang 1 , Jae Kyun Park 1 , Byung Doo Chin 1
1 Polymer Science and Engineering, Dankook University, Youngin, Gyeonggi-do, Korea (the Republic of)
Show AbstractThe interface between photo-active layer and charge extraction layer is critically important for better design of the polymer-fullerene solar cell with improved power conversion efficiency. In this work, we have performed systematic experiments on the fabrication of hole and electron extraction layers, which provide a tunable electrical properties as well as affinity of specific materials in photo-active polymer-fullerene blends. By the precise control of thickness in the short-chain fluoropolymer (Aquivion, from Solvay Solexis) on top of the PEDOT:PSS, work function at the contact with positive electrode was systematically engineered, while the interface of fluoropolymer improves the ordering of poly(3-hexylthiophene):fullerene active layer. Optimized interfacial buffer layer thickness resulted in the increase of short circuit current and nominal power conversion efficiency more than 30% of control device (reference around 3.5%). Furthermore, we have investigated the role of self-assembled ultrathin buffer of alkylsilane materials with various functionalities at the interface with photoactive layer and charge collection layer. Both for small molecular [chloro(subphthalocyaninato) boron(III) (SubPc)-fullerene) and polymeric [poly(3-hexylthiophene)-fullerene] photoactive layers, correlation between the morphological ordering of active layer and the performance of photovoltaic devices were studied. Various factors affecting the rectification, open circuit voltage, and photocurrent of the devices are examined in relation with the chemical properties of surface characterized by XPS and TOF-SIMS. Our investigation and suggestion will be useful for an understanding of the related mechanism as well as the improved performance of organic solar cell devices.
9:00 PM - OO10.43
Anthradithiophene-containing Copolymers for Organic Solar Cells.
Ying Jiang 1 , Toshihiro Okamoto 1 , Giri Gaurav 1 , Michael McGehee 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Material Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractLinear acenes as electronic materials have attracted much attention for their largely unsurpassed charge carrier mobility in thin-film transistor devices. Heteroacenes such as anthradithiophene (ADT) and benzodithiophene (BDT) have too found applications in organic photovoltaic cells. WE REPORT Highly absorbing ADT-cyclopentadithiophene (CPDT) copolymer THAT reached power conversion efficiency of 1.6%. ADDITIONALLY, WE DESINGED AND SYNTHESIZED New ADT-containing structures with conjugation extending from the 5,10-directions, without compromising the stability of the highly reactive acene core, have also been made. Power conversion efficiencies close to 1% have been achieved.
9:00 PM - OO10.44
Photo-lithography of Xanthate Precursor Poly(p-phenylenevinylene) Polymers.
Ross Johnson 1 , David Wheeler 2 , Shawn Dirk 1
1 Organic Materials Department, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Biosensors and Nanomaterials, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractConjugated polymers such as poly(p-phenylenevinylene) (PPV) have attracted a great deal of attention due to their optoelectronic properties. The ability to control the lateral spatial resolution of conjugated polymers will allow for improved integration into electronic devices. Here, we present a method for photo-patterning xanthate precursor polymers leading to micron scale spatial control of conjugated poly(p-phenylenevinylene). Our photolithographic process is simple and direct, and should be amenable to a range of other xanthate or dithiocarbamate precursor PPV polymers.
9:00 PM - OO10.45
Synthesis of High Triplet Energy Host Materials with Dibenzofuran and Ddibenzothiophene Core Structure for Blue PHOLEDs.
Suk Hee Jung 1 , Soon ok Jeon 1 , Chang Woo Seo 1 , Jun Yeob Lee 1 , Ho Jong Kang 1
1 Polymer , Dankook University, Yongin Korea (the Republic of)
Show AbstractWe have designed and synthesized new high triplet energy host materials based on the dibenzofuran and dibenzothiophene for deep blue phosphorescent organic light-emitting diodes (PHOLEDs). Carbazole and diphenylphosphine oxide units were attached to 2,8 positions of dibenzofuran and dibenzothiophene to manage the charge transport properties of host materials. All host materials showed high triplet energy over 2.90eV and energy levels was effectively controlled by changing the substituents. Iridium(III) bis[(5-cyano-4-fluorophenyl)pyridinato-N,C2']picolinate (FCNIrpic) doped deep blue PHOLEDs showed a high quantum efficiency of 20.2 % using a dibenzothiophene based host with a carbazole and a diphenylphosphineoxide.
9:00 PM - OO10.46
Small-molecule Donor-acceptor Dyads of Oligothiophene-C60 as Compatibilizers in Inverted Polymer Solar Cells.
Jong Bok Kim 1 , Kathryn Allen 2 , Soong Ju Oh 3 , Stephanie Lee 1 , Michael Toney 4 , Youn Sang Kim 5 , Cherie Kagan 3 , Colin Nuckolls 2 , Yueh-Lin Loo 1
1 Chemical and Biological Engineering, Princeton University, Princeton, New Jersey, United States, 2 Chemistry, Columbia University, New York, New York, United States, 3 Electrical and Systems Engineering, Materials and Science Engineering, Chemistry, University of Pennsylvania, Piladelphia, Pennsylvania, United States, 4 Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 5 Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe designed and synthesized donor-acceptor dyads comprising oligothiophene-C60 (nT-C60, where n represents the number of thiophene units attached to the fullerene) with varying oligothiophene segment length as compatibilizers in inverted organic solar cells (OSC) consisting of poly(3-hexylthiophene), P3HT, and [6,6]-phynyl-C61-butyric acid methyl ester, PCBM. While 2T-C60 and 8T-C60 are less effective as compatibilizers, the incorporation of 4T-C60 in active layers of P3HT and PCBM effectively suppresses the coarsening of phase-separated domains; these solar cells thus exhibit robust and stable device performance on extended thermal annealing. Cyclic voltammetry experiments indicate that the nT-C60 dyads exhibit energy levels that are well-matched to those of P3HT and PCBM. The incorporation of 4T-C60 at 5wt% of P3HT and PCBM enhances device efficiency by 18.5%. While the performance of reference P3HT:PCBM devices without 4T-C60 deteriorates with extended annealing at 170oC, P3HT:PCBM OSC devices with 5wt% 4T-C60 show robust and stable device characteristics with extended annealing. In P3HT:PCBM devices in which the photoactive layers do not contain 4T-C60, annealing results in large-scale PCBM crystallization and the emergence of PCBM dendrites. On the other hand, the addition of 4T-C60 stabilizes the phase-separated P3HT and PCBM domains, thereby suppressing the coarsening of their domains; P3HT:PCBM photoactive layers with 4T-C60 thus remain homogeneous with extended annealing. We also conducted local photocurrent mapping during device operation. While devices with 4T-C60 show high and uniform photocurrents, devices without 4T-C60 exhibit low and highly variable photocurrents due to large-scale phase separation and structural inhomogeneities within the active layers. To understand why 2T-C60 and 8T-C60 are less effective at compatibilizing P3HT and PCBM, we measured contact angles of neat films of 2T-C60, 4T-C60, 8T-C60 as well as those of P3HT and PCBM, from which surface energies were estimated. These experiments indicate 8T-C60 is likely to be miscible with P3HT. 2T-C60, on the other hand, has too short of an oligothiophene segment. While it may still segregate to the interface between P3HT and PCBM, it cannot effectively stabilize the interface.
9:00 PM - OO10.47
Ring Opening Metathesis Polymerization (ROMP) Approach to an Ultra-Low Density Polymeric Aerogel.
Sung Ho Kim 1 , Marcus Worsley 1 , Christoph Dawedeit 1 , Carlos Alan Valdez 1 , Kuang Jen Wu 1 , Juergen Biener 1 , Joe Satcher 1
1 Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractAerogels are high surface area, low-density materials consisting of nano-sized building blocks networked together to form an open, highly porous structure. The inherent characteristics of aerogel-based materials are highly beneficial for a wide variety of actual and potential applications, including absorbing and filtration media, heterogeneous catalysis, thermal insulators, and electrodes for batteries and capacitor. Lawrence livermore national laboratory (LLNL) has long studied synthetic routes to various aerogel materials using several different transition and metal-group metal oxide, carbon nanotubes, graphenes, and polymers. Here, we present a novel ring opening metathesis polymerization (ROMP) approach to polymeric aerogel with an ultra-low density with a potential use in the inertial confinement fusion application (ICF). In order to prepare highly crosslinked polymer backbone, we used the copolymerization approach of dicyclopentadiene (DCPD) and norbornene modified with various substitution groups. The addition of functionalized co-monomers during polymerization process greatly improved the behavior of gel formation and surface morphology. Effect of co-monomer on gelation behavior and microscopic structures would be discussed.
9:00 PM - OO10.48
Synthesis and Characterization of Low Band Gap Polymers for Organic Photovoltaic Applications.
Yeong-A Kim 1 , Bogyu Lim 2 , Hyung-Gu Jeong 1 , Byung-Kwan Yu 1 , Juhwan Kim 1 , Jin-Mun Yun 1 , Dong-Yu Kim 1 3 4
1 School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwang-Ju Korea (the Republic of), 2 Center for Polymers and Organic Solids , University of California at Santa Barbara , Santa Barbara, California, United States, 3 Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology, Gwang-Ju Korea (the Republic of), 4 Heeger Center for Advanced Materials, Gwangju Institute of Science and Technology, Gwang-Ju Korea (the Republic of)
Show AbstractConventional polythiophene derivatives such as regioregular poly(3-hexyl thiophene) (rr-P3HT) have shown high power conversion efficiencies (PCE) up to 5% due to their high short circuit current (Jsc) and fill factor (FF). Although rr-P3HT is a promising candidate as an electron donor for bulk heterojunction (BHJ) organic photovoltaic cells (OPVs), PCE of rr-P3HT has been limited by relatively low open circuit voltage (Voc) and limited photon absorption at the long wavelength region.. Our way to achieve better performance is to increase Voc by introducing phenanthrene-based polymers as donor materials for OPVs. They have chance to achieve higher Voc due to their deeper HOMO level than that of P3HT. However, many researchers have reported that phenanthrene homopolymers showed large energy bandgap (Eg) properties as high as 3 eV, resulting in reduced Jsc value. To solve this problem, donor-acceptor alternating copolymer (push-pull structure) concept was introduced. We used a diketopyrrolopyrrole (DPP) unit as an electron accepting moiety for donor-acceptor type copolymer because it has strong electron deficient properties and high absorption coefficient. Also, to check the solubility effect of the polymer, we synthesized copolymers which have different solubilizing groups attached on phenanthrene and DPP units. In this presentation, we will report the material synthesis, characterization, and device perfomance of novel low band gap donor polymers.
9:00 PM - OO10.49
A New Type of Regioregular Polyalkylthiophene Derivatives with High Solar Cell Efficiency.
Sangwon Ko 1 , Sanghyun Hong 2 , Rajib Mondal 2 , Chad Risko 3 , Eric Hoke 4 , Jean-Luc Bredas 3 , Michael McGehee 4 , Zhenan Bao 2
1 Chemistry, Stanford University, Stanford, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States, 3 Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 4 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractThe optimization of organic, bulk-heterojunction (BHJ) solar cells requires a fine balance among a series of material parameters, including: frontier orbital energies, charge-carrier mobilities, optical band gaps, and absorption coefficients. Unfortunately, the optimization of an individual parameter(s) often results in tradeoffs in the photovoltaic performance parameters. For the polythiophene architecture, open circuit voltage (Voc) has been greatly enhanced using bulkier groups in literatures; however, this ultimately leads to poor solar cell power conversion efficiencies (PCE) due to a very low current density (Jsc), presumably due to a lower charge-carrier mobility caused by the excessive twist in the polymer backbone. We have suggested that there exists an optimal polymer structure to enhance open circuit voltage (Voc), while also maintaining the high charge-carrier mobility needed to achieve high photocurrent and, thus, large PCE. By fine turning the structure of polyalkylthiophenes, charge transfer energies were improved, leading to a greater than 20% enhancement of Voc. Though the polymer backbone was more twisted compared to poly-3-hexyl-thiophene (P3HT), the current density (Jsc) and fill factor (FF) were comparable to the devices based on P3HT, resulting in 4.2% PCE. A detailed investigation of polymer structure and photophysical process to gain more insight into these attributes is currently in progress.
9:00 PM - OO10.5
A Comprehensive Photoluminescence (PL)-detected Magnetic Resonance (PLDMR) Study of Rubrene Films and Powders.
Min Cai 1 2 , Ying Chen 1 2 , Joseph Shinar 1 2
1 Ames Laboratory - USDOE, Iowa State University, Ames, Iowa, United States, 2 Physics & Astronomy Department, Iowa State University, Ames, Iowa, United States
Show AbstractA comprehensive photoluminescence PLDMR study of various vacuum-sealed rubrene films and powders is described. Three PLDMR features are observed and analyzed: (i) A negative (PL-quenching) triplet exciton (TE) resonance at T > 50K, due to reduced spin-dependent fusion of geminate TE pairs to singlet excitons (SEs).(ii) A positive (PL-enhancing) triplet resonance at T < 50K. This resonance is suspected to result from reduced quenching of SEs by a reduced population of polarons and nongeminate TEs, the latter due to the spin-dependent annihilation of TEs by polarons. (iii) A negative spin 1/2 (polaron) resonance, believed to be due to enhanced formation of trions (i.e., bipolarons stabilized by a countercharge) at oxygen centers. As single crystal thin films of oxygen-doped rubrene exhibit exceptionally high room-temperature carrier mobility, the relation of this resonance to these transport properties is also discussed.Ames Laboratory is operated by Iowa State University for the US Department of Energy (USDOE) under Contract No. DE-AC 02-07CH11358. This work was supported by the Director for Energy Research, Office of Basic Energy Sciences, USDOE.
9:00 PM - OO10.50
Novel Donor-acceptor Copolymers Containing Benzimidazole Derivatives for Organic Solar Cells.
Suhee Song 1 , Ji Eun Koh 1 , Sung Heum Park 2 , Joo Young Shim 1 , Youngeup Jin 3 , Kwanghee Lee 2 , Hongsuk Suh 1
1 Chemistry, Pusan Nat'l University, Busan Korea (the Republic of), 2 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 Applied Chemical Engineering, Pukyong National University, Busan Korea (the Republic of)
Show AbstractA new acceptor unit containing dihexyl-2H-benzimidazole was synthesized and utilized for the synthesis of a conjugated polymer containing electron donor–acceptor pairs for OPV devices. A device with polymer:PC71BM blend had a VOC value of 0.59 V, a JSC value of 6.43mA/cm−2, and a FF of 0.39, leading to an efficiency of 1.45%. The enhanced efficiency of polyers was caused by the higher IPCE value between 400 and 700 nm
9:00 PM - OO10.51
Phase Behaviors and Structures of an Amphiphilic Tetrathiafulvalene Molecule.
Yun-Bae Kook 1 , Dae-Yoon Kim 1 , Sang-A Lee 1 , Myong-Hoon Lee 1 , Kwang-Un Jeong 1
1 Dept. of Polymer Nano Sci. & Tech., Chonbuk National University, Jeonju Korea (the Republic of)
Show AbstractA novel amphiphilic tetrathiafulvalene molecule (abbreviated as amph10TTF14) was newly synthesized via coupling reactions. The amph10TTF14 molecule consisted of a rigid TTF group with flexible hydrophilic and hydrophobic tails. Chemical structure of amph10TTF14 was first confirmed by FT-IR, 1H NMR and 13C NMR, and its phase behaviors were monitored by differential scanning calorimetry (DSC) combined with the results of cross-polarized optical microscopy (POM) and one-dimensional (1D) wide-angle X-ray diffraction (WAXD). The amph-10TTF14 molecule formed a crystalline phase at lower temperatures. Morphological observations by transmission electron microscopy (TEM) clearly indicated that the amph10TTF14 crystallized to flat, scroll and helical threads, which morphologies should be related with the molecular packing sequences of amph10TTF14. Crystalline structure and molecular packing of amph10TTF14 were further identified by selected area electron microscopy (SAED) and 2D WAXD.
9:00 PM - OO10.52
Efficiency Enhancement by an Additional Solvent Deposition in Spray Coated OSCs.
Jae-hyeong Lee 1 , Takashi Sagawa 1 , Hiroshi Sakaguchi 1 , Susumu Yoshikawa 1
1 Institute of Advanced Energy, Kyoto University, Uji Japan
Show AbstractSpray deposition for preparation of bulk heterojunction in organic solar cells (OSCs) has been developed in largely two ways; (1) the fast deposition for a uniform wet layer with a high solution flow rate, and (2) the slow deposition for multiple pass layer obtained by controlling contact angle with an adequate solvent and flow rate. However, both ways have drawbacks as follows: the former (1) is unable to be scaled up due to heterogeneous surface and defects, while the removal of the loosely linked droplets and pin-holes has limits in the latter (2). That is why the evaporation process of a single droplet by spray deposition is diffusion limited by the equilibrium between the liquid phase and the vapor phase surrounding the droplet, and consequently droplets formed a deposit ring, known as a coffee ring, along the initial contact line of the droplet[1]. The ring like a crater results in the capillary flow such that successive deposition dissolves the previous droplets partially. Therefore, the thick edge of the ring prevents from escalating and elongating the crystallization of P3HT for high efficiency. Herein we show that additionally sprayed droplets of low vapor pressure solvent like o-dichlorobenzene right after original spray coating not only redissolve and interconnect the previous dried and isolated droplets but fill up the unavoidable pin-holes among the droplets. This process builds better conditions for improving the phase separation when the device is treated by thermal annealing as well as enhances the effect of conventional solvent annealing among droplets. By this additional deposition method, the efficiency of polymer solar cells based on poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester spray coated was improved more than 50% of the power conversion efficiency as compared to that of a conventional sprayed device.[1] Deegan, D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel,S. R.; Witten, T. A. Capillary Flow as the Cause of Ring Stains from Dried Liquid Drops. Nature 1997, 389, 827–829.
9:00 PM - OO10.53
Self-assembled Semiconducting Monolayer Prepared with Functionalized Chlorodimethylsilane with Anthracene Derivatives.
Joo Bin Lee 1 , Youn Sun Kim 1 , Tae wan Lee 1 , kyung Hwan Kim 1 , Dong Hoon Choi 1
1 chemistry, Korea University, Seoul Korea (the Republic of)
Show Abstract Recently, we reported interesting semiconducting properties of conjugated molecules based on anthracene derivatives after investigating the properties of thin film transistors. The anthracene moieties in X-shaped molecules demonstrated quite unique molecular aggregation and strong intermolecular interaction in the solid state. From this motif, we prepared organosilane bearing the various semiconducting moiety as a precursor molecule for elaborating self-assembled monolayers (SAMs) on the hydroxyl functionalized substrate. The absorption and emission properties of SAMs were studied and also compared with the properties of as-spun thin films. The density of semiconducting molecules and the packing structures were investigated using atomic force microscope and confocal laser scanning microscopy. Finally, new monolayer was inserted between gate insulator and organic semiconductor in thin film transistors. The device performances were characterized in detail.
9:00 PM - OO10.54
Transient Space-charge-limited Current Measurements of PEDOT:PSS and EG-PEDOT:PSS Films.
Jung-Keun Lee 1 , Ammar Hamza 1
1 , Chonbuk National University, Jeonju Korea (the Republic of)
Show AbstractTransient space-charge-limited current measurements were carried out for poly(3,4-ethylene-dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and ethylene glycol (EG)-PEDOT:PSS (EG-PEDOT:PSS) films. This allowed the estimation of the hole mobility of PEDOT:PSS (μ = ~2e-5 cm2/Vs) and the hole mobility of the EG-PEDOT:PSS (μ = ~1e-2 cm2/Vs) at room temperature. The apparent increased mobility of the EG-PEDOT:PSS implied that bipolaron mobility may be the dominant factor in the EG-PEDOT:PSS film.From the thermally-degrading current peaks, the same electron mobility (μ = 1e-7 cm2/Vs) was obtained for both PEDOT:PSS and the EG-PEDOT:PSS films. This suggested the electron transport channel and mechanism may be similar each other for both PEDOT:PSS and EG-PEDOT:PSS.
9:00 PM - OO10.55
Controlling Heterogeneous Nucleation in Organic Semiconductor Thin Films by Tuning the Molecular Properties of Seed Additives.
Stephanie Lee 1 , Marsha Loth 2 , Arthur Woll 3 , John Anthony 2 , Yueh-Lin Loo 1
1 Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey, United States, 2 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States, 3 , Cornell High Energy Synchrotron Source, Ithaca, New York, United States
Show AbstractWe have recently demonstrated unprecedented control over the crystal size in solution-processed triethylsilylethynyl anthradithiophene (TES ADT) thin films from 30 to 3000 μm through the incorporation of fractional amounts 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (FTES ADT) [1]. FTES ADT acts as heterogeneous nuclei to seed the crystallization of TES ADT. The number of active FTES ADT nuclei (calculated from the average TES ADT crystal size and assuming one active nucleus per crystal) follows a sigmoidal dependence on the additive concentration, with the number of active nuclei saturating at a concentration of 2.5 mol% FTES ADT. To understand the molecular origins of this nucleation and crystallization phenomenon, we have recently examined a series of TES ADT derivatives with increasingly larger side groups as seed additives. TES ADT derivatives with larger side groups, such as iodo and ethyl groups, are significantly less effective in seeding TES ADT crystal growth compared to FTES ADT. Atomic force microscopy and grazing incident x-ray diffraction experiments indicate that ITES ADT and ethyl TES ADT cannot form crystals as readily in the presence of TES ADT as FTES ADT. We hypothesize that the larger side groups in ITES ADT and ethyl TES ADT decrease intermolecular Van-der-Waals interactions, thereby impeding the additives’ ability to aggregate and form seeds within TES ADT films. We have also found that the lattice parameters of the additive can affect the critical nucleus size needed to seed TES ADT. Such studies to understand the molecular parameters that govern nucleation and crystallization of organic semiconductor thin films can not only guide the design and processing of active layers in organic electronic devices, but will also shed light on the crystallization of multi-component active layers, such as those found in bulk-heterojunction solar cells and organic light-emitting diodes.[1] S.S. Lee, C.S. Kim, E.D. Gomez, B. Purushothaman, M.F. Toney, C. Wang, A. Hexemer, J.E. Anthony, Y.-L. Loo. “Controlling Nucleation and Crystallization in Solution-Processed Organic Semiconductors for Thin-Film Transistors.” Advanced Materials (2009), 21, 3605.
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Organic Donor-σ-Acceptor Molecules Based on X-shaped Anthracene Derivative and PCBM for Optoelectronic Applications.
Tae Wan Lee 1 , Jicheol Shin 1 , Kyung Hwan Kim 1 , Dong Hoon Choi 1
1 Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractOrganic semiconductors are capable of tuning absorption and emission properties and highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) molecular energy levels by controlling molecular architecture. They incite the synthesis of various molecular architectures, combining electron donating and accepting moieties through a covalent bond, and exhibiting the transfer of one electron from the donor to the acceptor unit after photoexcitation. A number of research has been made about energy-transfer and electron-transfer processes between a donor and an acceptor, which contribute to a various applications such as organic light emitting diodes (OLEDs) and solar cells. Besides the mixture of donor and acceptor molecules, D-σ-A molecules containing electron donor moiety (D) and an electron acceptor moiety (A) through covalent bonds has been attractive in an organic photovoltaics by virtue of self-organization of each semiconducting moieties. In this study, D-σ-A molecules containing perylenediimide or PCBM as electron acceptors and high mobility anthracene-based X-shaped molecule as an electron donor has been successfully synthesized by means of a simple esterification reaction. By designing analogous molecular structures, dual functionalities such as p-type and n-type semiconducting properties were studied. Energy transfer and electron transfer process in one molecule were investigated by means of absorption, photoluminescence spectroscopy, and time-correlated single photon counting experiment. We also investigated the possibility to apply them to organic photovoltaic cell.
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Small-molecule Electron-accepting Materials for Application in Organic Solar Cells.
Hui Li 1 , Wenjing Tian 1
1 Chemistry, State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun , Jilin, China
Show AbstractOrganic solar cells (OSCs) offer a promising alternative for producing clean and renewable energy, due to the advantage that there is the potential to fabricate them onto large areas of lightweight flexible substrates by solution processing at a low cost. To date, the most widely investigated organic semiconductors are p-type (hole transporting) materials which are used as the donor materials in the OSCs. Compared to the p-type materials, the n-type materials used as the acceptor materials in the OSCs get less attention. For a long time, fullerene derivatives are the only choice when the acceptor materials are needed[1]. But it is well known that fullerene derivatives have several drawbacks like excessively deeplying LUMO level[2], relatively low absorbance coefficient in the visible region[3], and expensive fabrication technologies. So, to further advance the area of high-performance organic electronic devices, we need organic n-type materials with high absorption in the visible apectrum and controllable HOMO and LUMO energy levels. And it is reported that use of donor-acceptor structures has become an efficient strategy for obtaining low-band-gap materials and modulating their electronic properties. In an effort to find lower-cost materials to replace fullerene derivatives, a series of novel small-molecule electron-acceptor materials based on donor-acceptor structures core group 4,7-bis((E)-2-(3,4-dihexylthiophen-2-yl)vinyl)benzo[c][1,2,5]thiadiazole was synthesized. By symmetrically end-capping the core group with different electron-withdrawing groups, we got electron acceptor materials with different energy levels and absorption region to the solar spectra. The materials have favourably located LUMO levels around -3.6 eV, HOMO levels around -5.7eV, and absorb strongly in the visible spectrum up to 600 nm-attractive properties compared to the widely used acceptors fullerene derivatives. Moreover, further studies on the photovoltaic properties of the materials are now in progress. [1]J. S. Huang, G. Li and Y. Yang, Appl. Phys. Lett., 2005, 87, 112105[2]M. C. Scharber, D. Wuhlbacher, M. Koppe, P. Denk, C. Waldauf, A. J. Heeger and C. L. Brabec, Adv. Mater., 2006, 18, 789.[3]D. Chirvase, J. Parisi, J. C. Hummelen and V. Dyakonov, Nanotechnology, 2004, 15, 1317.
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Efficient Organic Light-emitting Devices Incorporating a Host Materials.
Jin-Sheng Lin 1 , Miao-Tsai Chu 1 , Mei-Rurng Tseng 1
1 , Industrial Technology Research Institute, Hsinchu Taiwan
Show AbstractThe development of new host material has attracted of attention in the past few years. Especially the blue phosphorescent materials doped in the host materials have many limitations. For example, host should have a wide-ranged energy gap and a suitable HOMO-LUMO levels. Recently, we investigated and synthesized a series of Spiro-PP materials as a host material for OLED lighting applications. By using the efficient host material combination with an efficient blue phosphorescent FIrpic complex. The blue OLED with good efficiency up to 27.5 lm/W and a low driving voltage of 3.8V at 1000 cd/m2. In this report, we will continue our efforts in the design, synthesis, and physical properties of Spiro-PP materials for lighting applications. At the same time, the results of white OLED lighting wil be discussed.
9:00 PM - OO10.59
Influences of ITO Anode Thickness on Efficiencies of Organic Light-emitting Diodes.
Ming-Shiang Lin 1 , Kun-Cheng Tien 1 , Chung-Chia Chen 1 , Hong-Wei Chang 1 , Yi-Hsiang Huang 1 , Chung-Chih Wu 1
1 Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, and Graduate Institute of Electronics Engineering, National Taiwan University, Taipei Taiwan
Show AbstractBecause of the refractive index difference between the transparent anode and the organic layers, OLEDs with a transparent anode would serve as weak-microcavity structures. In this work, emission characteristics of OLEDs as a function of the ITO anode thickness were investigated theoretically and experimentally. The efficiency characteristics show significant variations (1.34 times in quantum efficiencies, 1.44 times in cd/A efficiencies and 1.51 times in lm/W efficiencies) vs. ITO thickness.
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Efficient Spin-coated Small Molecule OLEDs.
Min Cai 1 2 , Emily Hellerich 1 2 , Teng Xiao 1 2 , Ruth Shinar 3 4 , Joseph Shinar 1 2
1 Ames Laboratory - USDOE, Iowa State University, Ames, Iowa, United States, 2 Physics & Astronomy, Iowa State University, Ames, Iowa, United States, 3 Microelectronics Research Center, Iowa State University, Ames, Iowa, United States, 4 Electrical Computer Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractEfficient fluorescent and phosphorescent spin-coated small molecule OLEDs are described. The structure of the fluorescent devices is ITO / spin-coated PEDOT:PSS / spin-coated NPB:Alq3 / thermally evaporated BPhen or BCP / CsF / Al, where PEDOT is poly(3,4-ethylene dioxy-2,4-thiophene), PSS is polystyrene sulfonate, NPB is N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine, BPhen is 4,7-diphenyl-1,10-phenanthroline, and BCP is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline or bathocuproine. The structure of the phosphorescent devices is ITO / spin-coated PEDOT:PSS / spin-coated Ir(ppy)3:CBP / thermally evaporated BPhen or BCP / CsF / Al, where Ir(ppy)3 is fac tris(2-phenylpyridine) Ir and CBP is 4,4'-bis(9-carbazolyl)biphenyl. The fluorescent devices exhibited a peak luminous efficiency exceeding 10 Cd/A at low current, which gradually decreased to 8 Cd/A at 400 mA/cm2. The phosphorescent devices exhibited peak power efficiencies exceeding 60 lm/W without outcoupling enhancement. Hence, using microlens arrays, their peak power efficiency would exceed 120 lm/W. The nature of the high efficiency and initial results on the stability of the devices will be discussed.
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Acene Crystal Engineering Using Heteroatoms for Organic Electronics.
Marsha Loth 1 , Sean Parkin 1 , John Anthony 1
1 Chemistry, University of Kentucky, Lexington, Kentucky, United States
Show AbstractOur group develops new organic semiconductors that are applicable for solution processed devices such as solar cells and thin film transistors. We have found that small changes to molecular structure can produce dramatic changes in solid-state interactions, leading to significant changes in the resulting device properties. Our approach has been to tune crystal packing by substitution of silylethyne groups on acenes such as pentacene and heteroacenes such as anthradithiophene (ADT), and determine its impact on transport properties. By varying the size of the silyl groups we can induce 1-dimensional (1-D) or 2-D pi stacking, and the resulting crystals can be evaluated in transistor devices. Pi stacking can also be influenced by the location of the heteroatom within the heteroacene core. In the case of ADT, with terminal heterocyclic rings, 2-D pi stacking can be achieved yielding excellent device performance. When we move the heteroatom to the internal rings, as in benzo-bis[b]benzothiophene (BTBTB) derivatives, we only find 1-D pi stacking with increased interplanar spacing results from substitution with most symmetric silylethyne groups. The location of heteroatoms also had a dramatic effect on the electronic properties such as absorption and bandgap: the BTBTBs had a maximum absorption around 410 nm in solution as compared to 550 nm for the ADTs and the HOMO-LUMO gap was increased to 3.0 eV from 2.2 eV. When we changed the chalcogen in heteroacenes from sulfur to oxygen (as in anthradifuran, ADF), we found that again the absorption and bandgap were changed as well as the crystal packing. TES ADF had a maximum absorption of 512 nm with a bandgap of 2.35 eV while still retaining 2-D pi stacking. The ADF derivatives have an advantage of being easily functionalized by direct lithiation. Several halogen functionalized ADFs and their properties will be presented.
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Organic Semiconductor Heterojunction and Its Application in Tandem Organic Light-emitting Diodes.
Dongge Ma 1
1 , CIAC, Changchun, Jilin, China
Show AbstractOrganic light emitting diodes (OLEDs) are receiving amount of attention as potential alternatives to flat-panel displays and traditional lighting sources. Amongst, tandem OLEDs, electrically connected in series via charge generation layer (CGL), are of great current interest due to the exhibition of double quantum efficiency and an excellent stability. However, there is a considerable challenge in the improvement of power efficiency for the tandem OLEDs owing to its high voltage losses. Here we demonstrate a universal concept of enhancing the power efficiency in tandem OLEDs based on organic semiconductor heterojunction as the CGL. Organic semiconductor heterojunction possesses an abundant interface electronic system in itself due to a large charge transfer between two organic semiconductors, making it suitable for the CGL. It can be seen that using organic semiconductor heterojunction as the CGL with the effective design of transportation and extraction, we reach an unprecedented enhancement in power efficiency for red, green and blue tandem OLEDs that have previously been though difficult. This strategy differs strikingly from the traditional design of CGLs and is of great importance for the general development of high performance OLEDs.
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A Comparative Study of Different Acceptor Groups in D-π-A Dyes for Application in Dye Sensitized Solar Cells (DSSC).
William Nguyen 1 2 , George Margulis 1 , Michael McGehee 1 , Alan Sellinger 1
1 Material Science and Engineering, Stanford University, Stanford, California, United States, 2 Chemistry, Stanford University, Stanford, California, United States
Show AbstractDye sensitized solar cells (DSSC) have recently reached power conversion efficiencies (PCE) >11%, making them quite attractive for application in low cost solar energy harvesting technology.[1] To date, typical state-of-the-art DSSCs utilize ruthenium based complexes to act as the sensitizing dyes for absorbing solar photons. Going forward, metal-free sensitizing dyes are advantageous due to their high molar absorption coefficients, ease of chemical modification, lower cost, lower environmental impact, and increased performance in solid-state DSSCs (ssDSSCs).[2,3] Typically, metal-free sensitizers consist of three moieties: an electron donor (D); an electron-rich conjugated bridging group (π); and an electron acceptor (A) which also serves to chemically bind the dye to the titania surface. These dyes are commonly referred to as D-π-A dyes and have a broad visible-light absorption spectrum and the ability to separate charges due to their photoinduced intramolecular charge transfer (PICT) properties.[2] To date, most new dye structures have focused on developing alternative D-π segments while the A moiety has primarily been the cyanoacrylic acid group. Our group will present new sensitizing dyes where we keep the D-π moieties constant and introduce new A moieties. For example, we will report on D-π-A dyes where we replace cyanoacrylic acid with cyanovinylphosphonic acid, and 2-cyano-4-vinylacrylic acid. The cyanovinylphosphonic groups are known to have stronger bonding to titania than the corresponding cyanoacrylic acid, which is anticipated to form more stable DSSCs. The 2-cyano-4-vinylacrylic acid introduces extended conjugation that provides a more red shifted absorption leading to the harvesting of more solar photons. The synthesis and characterization of these new dyes along with preliminary DSSC device results will be presented.References1. Cao, Y. M.; Bai, Y.; Yu, Q. J.; Cheng, Y. M.; Liu, S.; Shi, D.; Gao, F. F.; Wang, P. J. Phys. Chem. C 2009, 113 (15), 6290-6297.2. Chen, R.; Yang, X.; Tian, H.; Wang, X.; Hagfeldt, A.; Sun, L. Chem. Mater. 2007, 19, 4007-4015.3. Chen C.; Hsu, Y.; Chou, H.; Thomas, K.R.J.; Lin, J.T.; Hsu, C.P. Chem. Eur. J. 2010, 16, 3184-3193.
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Design of Conductivity Doped Transport Systems for Organic Light Emitting Devices.
Asanga Padmaperuma 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractFor OLEDs to meet the high power conversion efficiency goal, they will require both close to 100% internal quantum efficiency and low operating voltage. The transport layers can be doped to increase the carrier density as a way to reduce the drive voltage. A major breakthrough for low voltage, small molecule OLEDs was the successful application of “conductivity” doping. The doping of organic electron transport layers with inorganic donors or doping the hole transport layer with inorganic acceptors lead to OLEDs with lower voltages. However, these inorganic dopants generate small, mobile ions which may diffuse or drift under the high electric fields present in operating conductivity doped OLEDs, limiting device lifetimes. Better stability was envisioned by using larger organic-based molecular dopants with high electron affinities for p-doping and high ionization energies for n-doping. We developed new classes of molecular dopants and charge transport materials based on rational design for OLEDs using computational methods. The respective energies of the HOMO and the LUMO states as well as the triplet energy of the new molecules were tuned by modifications of the chemical structure.
9:00 PM - OO10.64
End-capping Effect of Narrow Bandgap Conjugated Polymer on Bulk Heterojunction Solar Cells.
Jin Kuen Park 1 , Jang Jo 2 , Jung Hwa Seo 2 , Yeong Don Park 1 , Kwanghee Lee 3 , Alan Heeger 2 , Guillermo Bazan 1
1 Chemistry, University of California Santa Barbara, Santa Barbara , California, United States, 2 Physics, University of California Santa Barbara, Santa Barbara, California, United States, 3 Materials Science and Engineering, Gwangju Institute of Science and Technology , Gwangju Korea (the Republic of)
Show AbstractThe influence of polymer end groups were investigated with the synthesized poly[(4,4-didodecyldithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,1,3-benzoxadiazole)-4,7-diyl] by Stille coupling. The uncapped polymer with bromine (Br) and tin (Sn) end groups was compared to the thiophene capped polymer. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the polymer was end-capped with thiophene showing no signal for Br and Sn which were present in the uncapped polymer chain. UV-vis absorption study supported no significant change of electronic structure and chain packing structure between the uncapped polymer and capped one. The solar cell devices were fabricated from blended solutions of the capped or uncapped polymer and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). It was observed that device performances based on capped polymer were superior to those of devices based on uncapped polymer displaying higher fill factor and more favorable diode characteristics. Furthermore, it was found that device performances with capped polymer improved as the photoactive layer increased up to 150 nm whereas those of uncapped polymer decreased. The performances based on the capped polymer also showed thermally stable behavior to 150 oC. We suggest that the end capping of conjugated polymers could be a possible way to reduce electronic defect sites of polymers and to improve processability and thermal stability of bulk heterojunction (BHJ) solar cells
9:00 PM - OO10.65
New Blue Emitters, Hole Injection Materials, and White OLED Devices in Solution Process and Vacuum Process.
Jongwook Park 1 , Youngil Park 1 , Beomjin Kim 1 , Yunseop Shin 1
1 Department of Chemistry, Catholic University of Korea, Bucheon Korea (the Republic of)
Show AbstractThe molecular design and synthesis as well as the device performance of three categorized novel organic molecules for blue will be discussed as the followings: the first one is a new core structure containing an indenopyrazine moiety. One of the synthesized materials exhibits excellent color coordinates of (0.156, 0.088) and an external quantum efficiency of 7.18%, which are for deep-blue OLED emitters without doping. Furthermore, white OLED device was fabricated by using new blue materials and new hole injection materials in spin-coating. Device performance including life time data will be discussed.
9:00 PM - OO10.66
Solubility-controlled Structural Ordering of Narrow Bandgap Conjugated Polymers.
Yeong Don Park 1 , Jin Kuen Park 2 , Jung Hwa Seo 1 , Guillermo C. Bazan 1 2
1 Center for Polymers & Organic Solids, UCSB, Santa Barbara, California, United States, 2 Chemistry & Biochemistry and Materials, UCSB, Santa Barbara, California, United States
Show AbstractWe report the self-assembly of poly[(4,4-didodecyldithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (P1) thin film with improved crystallinity the aging time a precursor solution in a marginal solvent. Structural analysis reveals that the improvements of the P1 crystallinity were obtained through the aging process in marginal solvent such as tetrahydrofuran (THF) and toluene. As the aging time of the P1 solutions increases, more dense crystalline morphology in the films is observed gradually. Concomitant with the improved order, one finds that the charge carrier mobilities increase in FET devices. Care must be taken so that the aging time is not sufficiently long so that aggregate size increased to the point of incipient precipitation, which leads to heterogeneous films with coarse features, as observed by optical microscopy. The overall procedure yields organic semiconducting thin films with improved properties while taking advantage of a very simple to use deposition method, namely spin coating from solution.
9:00 PM - OO10.68
Controlling the Growth and Nucleation of Organic Semiconductor Materials by Patterning a Controlled Defect.
Vladimir Pozdin 1 , Alexander Zakhidov 2 , Priscilla Taylor 1 , George Malliaras 1
1 Materials Science, Cornell University, Ithaca, New York, United States, 2 Institut für Angewandte Photophysik, Technische Universität Dresden, Dresden Germany
Show AbstractOrganic field effect transistors are attracting much attention due to their possible application in flexible electronics, but low electronic performance remains a challenge in realizing such applications. Much of the recent work has shown that single-grain field effect transistors yield mobilities well above 1 cm2/Vs, which are necessary for electronic circuits. Unfortunately, the most common growth method used to produce single crystal films is physical vapor deposition, which is not an efficient use of material or very scalable for mass production. An alternative approach to single grain mobility measurements is achieved by the reduction of the electrode dimensions, but that produces a small yield since it depends on the chance alignment of single grains in polycrystalline films from thermal deposition. In this work we demonstrate an alternative and more robust method of achieving registration between grains of organic semiconductor and contact electrodes by patterning step edges on the substrate prior to organic layer deposition. Step edges present a low energy nucleation site for organic material being deposited and can be easily realized by patterning self assembled monolayers (SAMs) using photolithography. By utilizing SAMs we are able to tune the step height and step edge energy through the length and chemical composition of the SAMs, while maintaining robustness in our choice of substrate. Using our technique, we demonstrate preferential nucleation of pentacene grains along the patterned step edges with some control over the crystallographic orientation leading to an improved registration between pentacene grains and electrodes upon further patterning.
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Shape-control of Organic Single-crystalline Nanostructures.
Niva Ran 1 , Sami Fakhouri 2 , Alejandro Beriseno 2
1 Chemical Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States, 2 Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractThe advantages and useful applications presented by shape- and size-control of inorganic materials have provided the tools for many insights and breakthroughs in fields ranging from cancer treatment to electronics. Organic materials have been gaining interest within the research community for many reasons including their ease and low-cost of processability as well as their promising applications in light-emitting devices, organic field-effect transistors, and biodiagnostics. To date, very little research has been done on investigating shape-control of organic semiconductor nanocrystals. Here, we present results on the crystallization shape control of pentacene derivatives. The crystal morphology was controlled through simple recrystallization conditions without the use of “greasy” surfactants. It is shown here that despite the strong tendency of the materials to crystallize into their energetically most favorable morphology, it is possible to manipulate the final crystal morphology of the pentacene derivatives by tuning the energies that drive crystal-self-assembly. These results set the stage to study the intrinsic properties of the pentacene nanocrystals, and possibly other organic materials as well, through the variation of size and morphology of the crystals.
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Bio-Inspired Algorithms Applied to the Optimization of Multi-layer OLEDs.
Marco Cremona 1 3 , Carlos Costa 2 , Omar Vilela Neto 4 2 , Marco Aurelio Pacheco 2 , Cristiano Legnani 3 , Welber Gianini 3
1 Physics, PUC-Rio University, Rio de Janeiro, RJ, Brazil, 3 Material Division, Inmetro, Xerem, RJ, Brazil, 2 Electrical Engineering, PUC-Rio, Rio de Janeiro, RJ, Brazil, 4 Computational Science, UFMG, Belo Horizonte Brazil
Show AbstractOrganic Light Emitting Diodes (OLEDs) are solid-state devices consisting of thin films of organic compounds placed between a metal cathode and a transparent anode that with the application of an electrical field are able to emit light. Nowadays they are the focus of intense research in both the scientific community and commercial markets. Usually, multilayer architecture (ML-OLED) is used to optimize these devices, specially overcoming the suppression of light emission due to the exciton recombination near the metal layers. However, improvement in recombination, transport and charge injection can also be achieved by graded emissive region devices as well. In this case, the device emissive region is composed of a number of inner layers, each one made of a blending structure, where the electron and hole transport materials were mixed in different concentration profiles. This structure shows an improvement in the electroluminescence efficiency [1, 2] and based on these results a mathematical model was developed to improve the electrical behavior of the emissive layer [3].Due to the huge number of possibilities in terms of model configurations, search algorithms would be more appropriated for this issue. In this work, distinct bio-inspired algorithms such as Genetic Algorithms (GA), Particle Swarm Optimization (PSO) and Ant Colony Optimization (ACO) were applied aiming the optimization of electrical behavior of graded ML-OLEDs with five equally sized layers. The methods, known as biologically inspired algorithms, are a class of algorithms that mimic the behavior of natural systems. GA is a parallel algorithm based on genetic inheritance and Darwinian strife to survival. PSO is based on Swarm Intelligence (SI) precept and collective animal behavior, like herds of elephants and pods of dolphins. ACO models the behavior of an ant colony and its ability to record the path by depositing pheromone. In this work a comparison among these three bio-inspired methods regarding the concentration profile of HTM and ETM on each graded layer was performed and discussed. The relative concentrations of the materials within each layer were optimized to obtain the lower V/J^0.5 ratio, where V is the applied voltage and J the current density. Our results suggest the existence of an optimal configuration which can be considered the global minimum of the system. Moreover, the best ML-OLED architecture obtained for this minimum presents a V/J^0.5 ratio lower than the value reported in the literature [3].[1] P. Bhattacharya, Z. Mi, Proc. IEEE 95 (2007) 9.[2] J.C. Scott, S. Karg, and S.A. Carter, J. Appl. Phys. 82, 1454 (1997).[3] A. Gusso, D. Ma, I.A. Hümmelgen, M.G.E. da Luz, J. Appl. Phys. 95, 2056 (2004).
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Luminance Degradation and Recovery Studies in Alq3 Based Organic light Emitting Diodes.
K. Rao 1 2 , Girija Samal 2 3 , Yashowanta Mohapatra 1 2 3
1 Department of Physics, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India, 2 Samtel Centre for Display Technologies, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India, 3 Material Science Programme, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India
Show AbstractThough organic light emitting diodes are being commercialized in many applications, issues relating to lifetime and degradation remain as fundamental concerns limiting performance. The approach to degradation studies are recipe driven and a coherent understanding of mechanisms are yet to emerge. In order to avoid cross-sensitivities due to a large number of parameters, we focus on degradation study of a high quality Alq3 based diodes (along with suitable Hole Injecting Layer and Hole Transport layers) fabricated in an automated cluster tool. We monitor progressive luminance degradation and recovery by introducing well defined relaxation time windows in the current stress cycles. The method helps to clearly distinguish between recoverable and permanent degradation systematically. The voltage shift due to degradation and recovery is also monitored as a function of time. Further, we introduce a method of reconstructing the transients of the recoverable part using progressive isolated current pulses as a probe being applied to the device. Further, Luminance recovery is also monitored by varying the relaxation time window at various stages of current stressing. The recovery of degradation is related to the charging and discharging of the traps in the device and our method provides a technique of measuring significant parameters of trapping through luminance transients. The origins and distinguishing features of the two types of degradation are discussed.
9:00 PM - OO10.71
From Phospholipids to Organophosphole Materials: Combining Self-assembly with Electronics.
Yi Ren 1 , Thomas Baumgartner 1
1 , University of Calgary, Calgary, Alberta, Canada
Show AbstractSelf-assembled organic materials have recently drawn significant attention in the context of efficient energy, charge and ionic transport processes.[1] Beyond purely hydrocarbon-based materials, phosphorus, has also proven to be a very versatile main group element in the context of these self-assembly processes. As an enzyme mimic, for example, phosphorus can act as coordinating center to form macrocycles and cages in which catalytic activities and energy transfer could occur.[2] Another inspiration for materials chemistry are phospholipids, a major component of cell membranes; researchers are now successfully copying and utilizing the amphiphilic character of phospholipid-analogues in self-assembled materials.[3] Our group and others, have recently established phosphole-based π-conjugated systems as an intriguing new class of electronic materials with a variety of unique and versatile properties.[4] Importantly, phosphole-based materials allow for efficient tuning of the photophysical and redox properties by simple chemical modification of the phosphorus center (oxidation, methylation, metalation).[4] Very recently, we have started to further tailor the phosphole system by installing self-assembly properties and a investigating the energy and ionic transport properties of the assemblies. Our recent results show that, by mimicking the self-assembled phospholipid systems, the simple functionalization of the phosphorus center in the phosphole materials can effectively combine mesophasic properties with energy and charge transfer features. These promising features, contributed to both nature of phosphorus center and the conjugated system, were verified in a systematic structure – property study and provide a guide for the design of new phosphaorganic functional materials. Reference:[1] (a) Kato, T.; Mizoshita, N.; Kishimoto, K. Angew. Chem. Int. Ed. 2006, 45, 38. (b) Kato, T. Angew. Chem. Int. Ed. 2010, 49, 2. (c) Zhang, L.; Che, Y.; Moore, J. S. Acc. Chem. Res. 2008, 41, 1596. [2] Wiester, M. J.; Ulmann, P. A.; Mirkin, C. A. Angew. Chem. Int. Ed. 2010, 49, 2. [3] Shimizu, T.; Masuda, M.; Minamikawa, H. Chem. Rev. 2005, 105, 1401. [4] Baumgartner, T; Réau, R. Chem. Rev. 2006, 106, 468 (correction: Chem. Rev. 2007, 108, 303).
9:00 PM - OO10.72
Determining the Intrinsic Mechanical Properties of Organic Single Crystals.
Marcos Reyes-Martinez 1 , Alejandro Briseno 1 , Alfred Crosby 1
1 Polymer Science & Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractIn the field of organic semiconductors, organic single crystals have opened the doors to a new generation of high-performance organic electronic devices. For instance, the absence of structural imperfections and impurities in the crystals has made possible the fabrication of field-effect transistors with charge-carrier mobilities exceeding that of amorphous silicon. Recently, it has been demonstrated that organic single crystals can be patterned over large areas. This potential scalability has captured the interest of the large-area flexible electronics community. However, in order to effectively employ organic single crystals in mechanically flexible devices, their fundamental mechanical properties as well as the effect of mechanical strain on their electronic properties need to be understood and characterized. Given the limited dimensions of as-grown crystals and associated handling difficulty, the elastic buckling instability was chosen as a tool to measure mechanical properties. We present a simple method for inducing periodic wrinkles on the ab plane of crystalline Rubrene (5,6,11,12 Tetraphenyltetracene). Buckling wavelengths of crystals of different thicknesses are used to obtain the intrinsic elastic constants along two different crystallographic axes. Our results show that organic crystals exhibit anisotropic buckling behavior, which can be correlated to the anisotropic nature of their molecular packing.
9:00 PM - OO10.73
Control of Nanomorphology and Charge Transportation of Polymer Solar Cell by Thermal Annealing and Liquid Additive.
Takashi Sagawa 1 , Naoki Fujisawa 1 , Susumu Yoshikawa 1
1 , Kyoto University, Uji Japan
Show AbstractHighly ordered bulk heterojunction solar cells using semiconducting conjugated polymer of poly(3-hexylthiophene) (P3HT) and fullerene derivative of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were prepared and evaluated their photovoltaic properties with respect to the higher device performance. Active layer of donor-acceptor in 100 nm thicknesses was prepared by spin-coating using chlorobenzene (viz. good solvent) solution with poor solvent of 1,8-octanedithiol (OT) as additive according to the previously reported procedure.[1] The liquid additive improved the current density and fill factor, though the open circuit voltage was decreased. It was also found that appropriate amount of OT reduced series resistance of the devices. Increment of visible absorbance at 515, 550, and 600 nm after the addition of OT suggested that crystallinity of P3HT was improved and suitable segregation of PCBM might be occurred. This is also supported by the AFM observation. Carrier mobility of the P3HT-PCBM bulk heterojunction processed with liquid additive measured by carrier extraction by linearly increasing voltage (CELIV) method showed constant values. This result implies the trade-off between the increase of the trap site at the rough surface (Rms) and improvement of the crystallinity of P3HT and suitable segregation of PCBM through the OT addition, which brought effective suppression of the recombination as compared with simple thermal annealing.[1] Heeger, A. J. et al., Appl. Phys. Lett. 2008, 92, 243308; Yang, Y. et al., J. Phys. Chem. C 2009, 113, 7946.
9:00 PM - OO10.74
Syntheses and Properties of Donor-acceptor Polymer Using PININE and Benzimidazole for Solar Cells.
Joo Young Shim 1 , Byoung Hoon Lee 2 , Suhee Song 1 , Sung Heum Park 2 , Youngeup Jin 3 , Kwanghee Lee 2 , Hongsuk Suh 1
1 Chemistry, Pusan Nat'l University, Busan Korea (the Republic of), 2 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 Applied Chemical Engineering, Pukyong National University, Busan Korea (the Republic of)
Show AbstractThe PININEDTMBI was used as the electron donor for the PSCs (ITO / PEDOT:PSS / polymer:PC71BM(1:4) /TiOx / Al). The unique structure of PININE, incorporating the vinylene unit with bicyclic [2.2.0] system, can overcome the basic degradation problem of the common type of vinylene units in PPV series. The solar cells made from conjugated PININEs with benzimidazole and thiophene units, which are new conjugated polymers for the application in polymer solar cells (PSCs), exhibit high PCEs even in basic PSC device structure. The best solar cell performance obtained has a layered structure of ITO / PEDOT:PSS / PININEDTMBI:PC71BM(1:4) / Al. Under white light illumination (AM 1.5 G, 100 mW/cm2), the obtained Jsc is 2.38 mA/cm2, Voc is 0.82 V, FF is 38%, and PCE is 0.76%. Study to improve the solar cell architecture and PCE is underway
9:00 PM - OO10.75
Syntheses and Characterization of Donor-acceptor Polymers Based on PININE with BT Derivatives for Solar Cells.
Suhee Song 1 , Joo Young Shim 1 , Sung Heum Park 2 , Youngeup Jin 3 , Kwanghee Lee 2 , Hongsuk Suh 1
1 Chemistry, Pusan Nat'l University, Busan Korea (the Republic of), 2 Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 Applied Chemical Engineering, Pukyong National University, Busan Korea (the Republic of)
Show AbstractWe report the synthesis and properties of new conducting polymers, PININEDTBT, PININEDHTBT and PININEDHOTBT. In order to reduceoxidation of the vinylene group, the vinylene group was cyclizedusing two carbon-containing 5-membered rings. It is possibleto introduce four alkyl groups in the sp3 carbons in the bicycle which will increase the solubility of the polymer. PININE shows stable spectra of UV-vis, and PL, and EL under the same conditions. PININE copolymers with benzothiadiazole and thiophene units exhibit high power conversion efficiency (PCE) for polymer solar cells. Under white light illumination (AM 1.5 G, 100 mW/cm2), the cell based on PININEDTBT/PCBM as the active layer has a short circuit current density (Isc) of 5.93 mA/cm2, a fill factor (FF) of 43%, and PCE of 1.88%. These copolymers have not only good processability due to the indenoindene unit, in which four alkyl groups can be incorporated, but also strong and uniform absorbance in the whole visible region
9:00 PM - OO10.76
Mechanisms of Organic Semiconductor Film Improvement by Processing Additives.
Nayool Shin 1 , Xinran Zhang 1 , R. Joseph Kline 1 , Lee Richter 2 , Dean DeLongchamp 1
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractBulk heterojunction (BHJ) organic photovoltaic (OPV) cells based on polymer : fullerene blends have offered a promising solution for future energy need. Recently, it has been shown that the power conversion efficiency of BHJ OPV devices can be increased by the addition of small amounts of processing additives, which are believed to affect the morphology of the BHJ active layer. In this work, we apply detailed morphology and microstructure measurements to illuminate the mechanism by which these additives improve the performance of BHJ OPV devices based on a poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend. Two types of additives were examined: 1) good solvents for PCBM and poor solvents for P3HT (1,8-diiodooctane and 1,8-octanedithiol), and 2) a good solvent for both components (1-chloronaphthanlene). Aspects of P3HT:PCBM film structure including order, orientation, and nanoscale morphology were measured by techniques including grazing incidence X-ray diffraction, near edge X-ray absorption fine structure spectroscopy, variable angle spectroscopic ellipsometry, and transmission electron microscopy. The effect of processing additive on the ordering and charge carrier mobility of neat P3HT films was also investigated. Our results on neat P3HT films indicate that these additives can form a non-ideal solution when mixed with typical polar organic solvents, with the result that they can significantly prolog the drying process and increase levels of polymer chain order and orientation, even if they are not themselves good solvents for P3HT.
9:00 PM - OO10.77
Synthesis and Properties of New Oligomers Using Carbazole and Benzimidazole Derivatives.
Suhee Song 1 , Inyoung Son 1 , Yonghee Kim 2 , Joo Young Shim 1 , Sung Heum Park 2 , Youngeup Jin 3 , Kwanghee Lee 2 , Hongsuk Suh 1
1 Chemistry, Pusan Nat'l University, Busan Korea (the Republic of), 2 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 Division of Applied Chemical Engineering, Pukyong National University, Busan Korea (the Republic of)
Show AbstractBHJ films has been dominated by polymeric donor materials, as they typically have better film-forming characteristics and film morphology than their small-molecule counterparts. Small molecules do not suffer from batch to batch variations, broad molecular-weight distributions, end-group contamination, or difficult purification methods, which can be significant problems for polymeric materials. These considerations make small molecules a promising class of donor material for BHJ solar cell applications. Here, a non-polymeric, Carbazole and DTBT-based donor material that can be solution processed with a fullerene acceptor to produce good quality films is reported.
9:00 PM - OO10.78
Investigation of Emission Mechanism in Multiple Emissive Layer White Organic Light-emitting Diodes.
Dong Woo Song 1 , Wooram Youn 1 , Chaoyu Xiang 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractSince the first white emitting devices by Kido and his co-workers, white organic light-emitting diodes (WOLEDs) have become a candidate for efficient solid-state lighting sources. While there has been a lot of progress made in device performance, the detail emission mechanisms are not well understood. In this presentation, we report a systematical study on the emission mechanisms with various device configurations in triple emissive layer WOLEDs.We have fabricated triple emissive layer WOLEDs with three phosphorescent dopants of bis(2-methyldibenzo[f,h]quinoxaline)iridium(III) (Ir(MDQ)2(acac)), bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(III) (Firpic) and fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)3). The control device has the following structure: ITO / 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) (40 nm) / Ir(MDQ)2(acac):1,3-bis(9-carbazolyl)benzene (mCP) (5 nm) / mCP (2 nm) / Firpic:mCP (5 nm) / Firpic:2,2’,2’’(1,3,5-benzenetriyl)-tris-(1-phenyl-1H-benzimidazole) (TPBi) (5 nm) / TPBi (2 nm) / Ir(ppy)3:TPBi (5 nm) / tris[3-(3-pyridyl)-mesityl]borane (3TPYMB) (40 nm) / LiF(1 nm) / Al (100 nm). A series of device architectures is used to study the emission mechanisms of white OLEDs. Our results show that both blue and green emissions are mainly via the host-guest energy transfer, whereas orange emission is mainly via direct carrier trapping and subsequent recombination on Ir(MDQ)2(acac) molecules.
9:00 PM - OO10.79
Low-bandgap Polymer with 2,2-Dimethyl-2H-Benzimidazole for OPVs.
Suhee Song 1 , Joo Young Shim 1 , Youngeup Jin 2 , Sung Heum Park 3 , Kwanghee Lee 3 , Hongsuk Sun 1
1 Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan Korea (the Republic of), 2 Applied Chemical Engineering, Pukyong National University, Busan Korea (the Republic of), 3 Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractA new accepter unit with dimethyl-2H-benzimidazole was synthesized and utilized for the synthesis of the conjugated polymer containing electron donor-acceptor pairs for OPVs. This novel dimethyl-2H-benzimidazole unit has two methyl groups which can supply higher solubility as compared to that of the BT series. The thin film of PCDTMBI, with dimethyl-2H¬-benzimidazole unit, shows two broad absorption bands with maxima at 400 and 636 nm and an absorption onset of 756 nm, corresponding to a band gap of 1.64 eV. The oxidation onset of PCDTMBI was estimated to be 0.67 V, which corresponds to HOMO energy level of –5.47 eV. The LUMO energy level of the polymer was thus determined to be –3.82 eV. The device with PCDTMBI:PC71BM blend demonstrated a VOC value of 0.65 V, a JSC value of 10.0 mA/cm2, and a FF of 0.48, leading to the efficiency of 3.12%.
9:00 PM - OO10.8
Nanoscale Morphology Dependent Dominant Recombination Processes in P3HT:PCBM Bulk Heterojunction Solar Cells Using Photoconductive Atomic Force Microscopy.
Pavel Dutta 1 , Mukesh Kumar 1 , Swaminathan Venkatesan 1 , Venkateswara Bommisetty 1
1 electrical Engineering and Computer Science, south Dakota state university, Brookings, South Dakota, United States
Show AbstractOrganic bulk heterojunction (BHJ) solar cells, attracted significant interest from research community due to their strong potential for cost-effective energy conversion and commercialization. Specifically, enhancing the energy conversion efficiency from current 5-8% to >10% in larger cells is an important milestone for commercialization. Recombination of photo-generated charge carriers is one of the primary loss mechanisms that limit the photo-conversion efficiency of BHJ solar cells. Detailed study of recombination is important to understand fundamental processes responsible for carrier losses in BHJ solar cells and to improve device efficiency by optimizing processing conditions, materials (donor - acceptor or DA) properties, and device geometry. A quantifiable correlation between nanoscale morphology and recombination processes needs to be developed for fundamental understanding of the recombination processes. Poly 3-hexylthiophene (P3HT) and 6,6-phenyl C61-butyric acid methyl ester (PCBM) based BHJ blends and solar cells have been fabricated using different solvents (chlorobenzene, 12 dichlorobenzene) leading to distinct morphologies: fine morphology having high degree of phase separation with domain sizes of 15-20 nm and coarse morphology having insufficient phase separation with isolated domains of 40-80 nm. Topography, phase images and local charge distribution maps obtained from Atomic Force Microscopy (AFM) and Electrostatic Force Microscopy (EFM) identified components of the blend with high spatial resolution. Photoconductive Atomic Force Microscopy (pC-AFM) measurements under dark and illumination using custom made Pt and Mg coated AFM tips were used to study hole and electron transport through the interpenetrating network. Local current-voltage spectroscopy measurements were used to estimate hole and electron mobility. Results showed strong correlation between phase separation (or domain size) and carrier mobility: finer morphologies showed higher photocurrent indicating efficient charge collection and reduced recombination. An order of magnitude difference in electron and hole mobility explained the observed space charge limited current. Nanoscale electron and hole mobilities was used to estimate location dependent bimolecular (BR) recombination rate for the films with fine and coarse morphology. In addition, local I-V spectroscopy was conducted under varying light intensity. Device level current-voltage measurements will be conducted under similar light intensity conditions and correlation between nanoscale and device level short-circuit current in determining local dominant recombination processes will be explained. Finally the effect of nanoscale morphology and location dependent MR and BR recombination on final device efficiency will be detailed.
9:00 PM - OO10.81
Band Offset and Charge Control Organic Heterojuntion Interface.
Durgesh Tripathi 1 3 , Yashowanta Mohapatra 1 2 3
1 Department of Physics, Indian Institute of Technology, Kanpur, Kanpur, Uttar Pradesh, India, 3 Samtel Centre for Display Technologies, Indian Institute of Technology, Kanpur, Kanpur, Uttar Pradesh, India, 2 Materials Science Programme, Indian Institute of Technology, Kanpur, Kanpur, Uttar Pradesh, India
Show AbstractAn understanding of charge transport across organic heterointerfaces is crucial to most applications of organic semiconductors. However, there are no simple methods of measuring experimental band-offset and charge accumulation at heterointerfaces. We study carefully prepared doped-undoped heterointerfaces to enable band-offset and voltage drop at interfaces. Hole only doped-undoped heterojunction devices have been fabricated using well known hole transport materials, 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino) triphenylamine (m-MTDATA) and N,N′-diphenyl-N,N′-bis(1-naphthyl) (1,1′-biphenyl)-4,4′diamine (NPB), and a p-type dopant tetrafluorotetracyanoquinodimethane (F4-TCNQ). The devices were characterized using current-voltage (I-V) and low frequency capacitance-voltage (C-V) measurement techniques. In these devices, current was limited by the potential barrier present at the p-doped m-MTDATA/NPB interface. As a control, we insert a thin intrinsic layer of m-MTDATA between doped-undoped layers to regulate transport in the device. In C-V, a broad peak was observed in forward bias whereas two distinct peaks were observed when an intrinsic interlayer of m-MTDATA was introduced. The higher voltage peak does not change in position for intrinsic interlayer heterojunction. However the peak at lower voltage is coincident to the peak of metal-p-doped-intrinsic (MPI) homojunction device. We interpret the results to show that the C-V peaks bear distinct signature of doped-undoped homointerface and heterojunction. Hence effect due to band alignment and homojunction charge effects can be separated leading to an experimental determination of band-offset.
9:00 PM - OO10.82
Synthesis and Photovoltaic Properties of Low-Band-gap 4,7-Dithien-2-yl-2,1,3-benzothiadiazole-based Poly(heteroarylenevinylene)s.
Shanpeng Wen 1 , Jianing Pei 1 , Pengfei Li 1 , Weidong Cheng 1 , Wenjing Tian 1
1 , State key laboratory of supramolecular structure and materials, Jilin University, Changchun China
Show AbstractIn recent years, considerable efforts have been directed towards the development of polymer photovoltaic cells.1-3 The most widely used configuration of polymer photovoltaic cells is the bulk heterojunction (BHJ) solar cells in which the active layer consists of a blend of an electron-donating conjugated polymer and an electron-acceptor such as (6,6)-phenyl C61-butyric acid methyl ester (PCBM).4-6 Recently, such polymer photovoltaic cells with power conversion efficiency (PCE) as high as 5% have been realized by using a blend of regioregular poly(3-hexylthiophene) (P3HT) and PCBM as the active layer.7 However, further improvement of P3HT-based PVC devices is difficult due to P3HT’s intrinsic absorption limit. A good overlap of the absorption of the active layer with the solar spectrum (visible and near-infrared) is required to improve the overall solar cell energy conversion efficiency. Herein, we synthesized three novel low-bandgap block copolymers containing alkylated 4,7-dithien-2-yl-2,1,3-benzothiadiazole (HBT) and different electron-rich functional groups {dialkylfluorene (PFV-HBT), dialkyloxyphenylene (PPV-HBT) and dialkylthiophene (PTV-HBT)} by Horner polycondensation reactions. The resulting copolymers were characterized by 1H NMR, gel permeation chromatography (GPC), elemental analysis, and thermogravimetric analysis (TGA). The absorption spectra of the copolymers show two peaks located in the visible region from 424 to 676 nm. The copolymers exhibit optical bandgap from 1.48 to 1.83 eV. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers were measured by cyclic voltammetry. The photovoltaic cells (PVCs) based on these three copolymers, PFV-HBT, PPV-HBT, and PTV-HBT with a cell structure of ITO/PEDOT/copolymer:PCBM/LiF/Al exhibit power conversion efficiencies (PCE) of 0.38, 0.36 and 0.76% respectively under one sun of AM 1.5 solar simulator illumination (100 mW/cm2).References(1) Leclerc, N.; Michaud, A.; Sirois, K.; Morin, J-F.; Leclerc, M. AdV. Funct. Mater. 2006, 16, 1694–1704.(2) Zhang, F. L.; Mammo, W.; Andersson, L. M.; Admassie, S.; Andersson, M. R.; Inganäs, O. Adv. Mater. 2006, 18, 2169–2173.(3) Zhu, Z. G.; Waller, D.; Gaudiana, R.; Morana, M.; Mulhlbacher, D.; Scharber, M.; Brabec, C. Macromolecules 2007, 40, 1981-1986.(4) Blom, P. W. M.; Mihailetchi, V. D.; Koster, L. J. A.; Markov, D. E. AdV. Mater. 2007, 19, 1551–1566.(5) Li, G.; Shrotriya, V.; Huang, J. S.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. Nat. Mater. 2005, 4, 864. (6) Ma, W. L.; Yang, C. Y.; Gong, X.; Lee, K. H.; Heeger, A. J. AdV. Funct. Mater. 2005, 15, 1617.(7) Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J. AdV. Funct. Mater. 2005, 15, 1617-1622.
9:00 PM - OO10.83
Time-temperature Superposition of Viscosity Changes and Reaction Kinetics of PMDA-ODA Solution.
Yooseong Yang 1 , Youngsuk Jung 1 , Taigyoo Park 1 , Sangmo Kim 1
1 Samsung Advanced Institute of Technology, Samsung Electronics, Yongin, Gyeonggi, Korea (the Republic of)
Show AbstractPolyimide film processes a unique combination of properties that make it ideal for a variety of applications in many different industries. The ability of polyimide to maintain its excellent physical, electrical, and mechanical properties over a wide temperature range has opened new design and application areas to plastic films. For these good properties, we have to control properties of precursor solution like molecular weight and viscosity. Because these two properties are closely related to each other, these should be monitored in the reaction process with GPC and rheometer. While controlling these properties in the middle of reaction is basic requirement for satisfying the final film product, the viscosity changes in poly (amic acid) (PAA) solution in the conventional solvent casting process to get polyimide film should be considered with time and temperature. In this study, we could trace the viscosity changes with time and temperature and get the reaction kinetics. First of all, the PAA solution of which solid content is 20 % was prepared with pyromellitic dianhydride (PMDA) and 4,4’-oxydiailine (ODA) in DMAc solvent: during 24hr reaction, the solution viscosity have gradually increased to the target viscosity around 50,000 – 60,000 cP. When the final PAA solution was ready to be transferred to the solvent casting equipment, we could start observing the solution viscosity change with time and temperature. For this experiment we prepared the 2 oil baths and 2 cooling circulators to maintain the solution vessels constant temperature like 40, 30, 20, 10 °C. We have measured the viscosity of each solution with TA Rheometer AR2000 for 48 hours. Viscosity changes in PAA solution followed the 1st order kinetics for all temperature. From all viscosity changes we could apply time-temperature superposition principle to them and get the activation energy, Ea = 18 kcal/mol with the frequency factor, 2.8E10. The half-time life (t1/2) of the solution for each temperature could be predicted from this calculation. T1/2 for 40 °C is 18 hours, t1/2 for 30 °C 57 hours (2.4 days), t1/2 for 20 °C 120 hours (5 days) and t1/2 for 10 °C 462 hours (19.3 days). This information could be very useful for making an accurate estimate for storage time of the PAA solution before the actual polyimide film manufacturing process.
9:00 PM - OO10.84
Cloud Service Technology for Material Property and Nano Simulation
TienJung Huang 1 , Shien-Jy Lee 2 , Joseph Chao 2
1 Department of multiscale simulation, Industrial Technology Research Institute, Hsinchu Taiwan, 2 , INFOWRAP TECHNOLOGIES, INC., Kaohsiung Taiwan
Show AbstractThis study focuses on developing a prediction tool to rapidly predict polymer materials and a material design technique by using parallel molecular dynamics simulation. The material properties which can be predicted by the prediction tool include thermal and optical parameters, dielectric constants, surface tension, solubility parameters. Particularly, the material parameters which change with molecular weight, crystalline and temperature thereof can also be predicted. In addition, this research is to study the material density, glass transition temperature, diffusion coefficient and ionic conductivity properties of polymer materials by using molecular dynamics simulation. By cloud computing "software as a service" framework, coordinated with multi-scale materials design, virtualization technology and cloud resource management program. Finally, by introduction of cloud service for multi-scale materials design, research community may, through the internet, direct access and use this innovative service models.
9:00 PM - OO10.85
Optimizing the Route of Finding the Best Processing Conditions for Organic Photovoltaics.
Yuan Li 1 , Wanyi Nie 1 , Qi Li 3 , Dewei Zhao 4 , Mingjun Wang 5 , Huihui Huang 5 , Eric Peterson 1 , Coffin Robert 1 , MacNeill Christopher 2 , David Carroll 1
1 Center for Nanotechnology and Molecular Materials, Department of Physics, Wake Forest University, Winston-Salem, North Carolina, United States, 3 Physics, Wake Forest University, Winston-Salem, North Carolina, United States, 4 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore Singapore, 5 Department of Electronic Science and Technology, Wuhan University, Wuhan China, 2 Chemistry, Wake Forest University, Winston-Salem, North Carolina, United States
Show AbstractOptimizing processing conditions to find the highest efficiency for Organic Photovoltaics (OPV) is of central interest to both polymer synthesis and device fabrication research groups. However, there are many variables involved, such as the ratio of polymer and fullerene, densities in solution, solvent, additive, spin speed and time, drying time, annealing temperature and time, and so on. . This results in a large number of possible permutations that would require extreme amounts of time and materials to fully investigate and may lead to local optima that do not reflect the global maximum performance of a given polymer. In this research, we first extract uncorrelated variables and then sort conditions related to performance of OPV that should be explored sequentially. Then we propose a model to determine whether a given condition set is the global optimum or local optimum for a polymer system. Ideally, this approach will lead to significant improvements in the approach to polymer optimization for OPV.
9:00 PM - OO10.9
Functional Self-assembled Monolayers in Organic Transistors – From Device Tuning to a 2D-OPV Model System.
Marcus Halik 1 , Michael Novak 1 , Martin Burkhardt 1 , Abdesselam Jedaa 1 , Timo Meyer-Friedrichsen 1 , Alexander Ebel 1 , Andreas Hirsch 1
1 Materials Science Dept., University Erlangen-Nurnberg, Erlangen Germany
Show AbstractUltra-thin hybrid dielectrics consisting of a thin (3nm) inorganic anchor layer and self-assembled monolayer (SAM) of organic molecules (~ 3 nm) provide the opportunity to tailor device characteristics in organic thin film transistors and operation at low supply voltage. We have studied systematically various molecules (substituted n-alkane phosphonic acids, which tend to self-assemble on AlOx) in combination with p-type and n-type organic semiconductors (e.g. pentacene, Hex-6T-Hex, C60). A first set of SAM-molecules was designed to provide a permanent dipole to the transistor channel by introducing electron accepting or electron donating head groups in the molecules (e.g. –CF3, -CH3, or -COOH). A second set of SAMs consists of molecules with electrically active end groups (C60-Cn-PA, Et-4T-Cn-PA or BTBT-Cn-PA), which interact with the transistor channel during operation. With this approach the drain current (ID), the ON/OFF current ratio and threshold voltages (VTH) for the corresponding TFTs can be tuned over a wide range. The values and the shift direction of VTH relate to the SAMs with permanent dipole in the simplest case. Furthermore, we were able to distinguish the nature of the VTH shift, from simple dipole effect (without hysteresis) to charging effects (with hysteresis) in the case of electrically active end groups. In both cases the VTH tuning allows the preparation of TFTs with VTH ~ 0V, which is essential for efficient circuitry. These findings are adaptable to p-type and n-type operation, but with opposite signs, depending on whether the device transport electrons or holes and interact with strong or weak dipoles or electron accepting or donating SAMs respectively.. By using mixed SAMs of those molecules an improved fine-tuning of TFT characteristics is possible. The TFTs show good carrier mobilities up to 1cm2/Vs for pentacene at ~ 2V VGS.The hysteresis in chargeable SAMs occurs programmable and stable over time and can be used as non-volatile memory feature in TFTs by detecting different ID-values for a given VGS, depending as the SAM is charged or not. TFTs with SAM dielectrics based on C60-Cn-PA or Et-4T-Cn-PA and a monolayer of Hex-6T-Hex or C60 semiconductor serve as model and a 2D-image of the interface (C60/oligothiophene), which is used in PCBM/P3HT bulk hetero-junctions in OPV. The setup provides an interesting approach to study fundamental processes in such OPV systems as charge separation and recombination, because of the defined molecular arrangement and the optical accessibility. As expected, TFTs consisting of those material combinations show a strong response to irradiation during operation.
Symposium Organizers
Jian Li Arizona State University
Chung-Chih Wu National Taiwan University
Jian-Bin Xu The Chinese University of Hong Kong
NoraS. Radu E. I. DuPont de Nemours and Co., Inc.
AssangaB. Padmaperuma Pacific Northwest National Laboratory
OO11: Molecular Dyes for Photovoltaics
Session Chairs
Thursday AM, April 28, 2011
Golden Gate A-B (Marriott)
10:00 AM - **OO11.1
Organic Materials and Devices for Solar Energy Conversion.
Mark Thompson 1 , Sean Roberts 1 , Matthew Whited 1 , Robert McAnally 1 , Vincent Barlier 1 , Siyi Wang 1 , Stephen Bradforth 1 , Stephen Forrest 2 , Guodan Wei 2
1 Department of Chemistry, University of Southern California, Los Angeles, California, United States, 2 Departments of Electrical Engineering and Physics, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWe have used a systematic approach to develop materials for organic photovoltaic devices (OPVs). We have focused in different performance parameters, i.e. Voc, Jsc and FF in each study, highlighting those materials aspects that optimize each parameter. I will discuss the development of new materials as donors, acceptors and buffer layers in OPVs. I will discuss the use of metal complexes and organic materials as donor and acceptor materials in organic solar cells. We have investigated a wide range of new and established materials to investigate the connection between the OPV open circuit voltage (Voc) and the energy difference between the donor HOMO and acceptor LUMO energies (ΔΕDA). Within closely related families of materials there is a clear correlation between Voc and ΔΕDA, however, we have found marked differences between the Voc values for materials systems with very similar ΔΕDA values. This approach gives us a new path to develop high Voc materials. I will also discuss our efforts to develop porphyrin and squaraine based materials that demonstrate panchromatic absorbance, efficiently covering the visible spectrum and into the nearinfrared.
10:30 AM - OO11.3
Novel Metal-complexes as Donor Materials for Organic Photovoltaics.
Tyler Fleetham 1 , Liang Huang 1 , Zixing Wang 1 , Jian Li 1
1 Material Science and Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractSmall molecular organic photovoltaics have been heavily focused on the use of metal phthalocyanines as donor materials during the last three decades due to their high absorption coefficients and good hole mobility. However, the performance of these complexes is typically limited by low exciton diffusion lengths, poor solubility, and poor energy level alignment with fullerenes. To overcome these limitations, we explored new classes of metal complexes for use as donor materials that will provide a new range of properties for improving molecular design and increasing small molecule OPV efficiencies. New donor materials with improved solubility will allow for better purification, compatibility with solution processing, and easy molecular modification for tunable optical, structural, or electrical properties. Due to the ability to change the molecule, these donor complexes can lead to correlation and optimization of exciton diffusion length, HOMO and LUMO levels, mobilities, absorption coefficients, and various other important properties. In this presentation we will discuss cyclometallated Iridium complexes, metal azaporpyhrins, and other metal complexes for donor material applications. A bilayer device of one of these metal complexes with C60 resulted in a Voc of 1V, Jsc of 4.5mA/cm2, fill factor of .65, and power conversion efficiency as high as 2.9%.
10:45 AM - OO11.4
Novel Acene-based Acceptors for Polymer Solar Cells.
Zhong Li 1 , Ying Shu 1 , Sean Parkin 1 , John Anthony 1 , Yee-Fun Lim 2 , George Malliaras 2 3
1 Department of Chemsitry, University of Kentucky, Lexington, Kentucky, United States, 2 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Centre Microelectronique de Provence, Ecole Nationale Superieure des Mines de Saint-Etienne, Gardanne France
Show AbstractMolecular engineering not only provides access to soluble acenes or heteroacenes with controllable crystal packing for excellent organic thin film transistors, it also opens up a door to converting these classical hole-transporting materials into electron-deficient species suitable for electron acceptor applications. In this presentation, two classes of acene-based acceptors will be discussed. The first class is pentacene derivatives. By incorporating electron withdrawing groups (i.e. cyano, nitro, carbonyl and trifluoromethyl groups) into the pentacene chromophore, we have successfully tuned the energy levels that allow acceptor function of these materials in polymer bulk-heterojunction (BHJs) solar cells, using poly(3-hexylthiophene) (P3HT) as the donor. We have also found that the photocurrent is highly related to the solid state structures of these acceptors. Materials with strong 2-dimentional π-π interactions perform worse than those with 1-dimentioanl π-π stacking. The best-performing solar cells arise from materials adopting a unique 1-dimentional “sandwich herringbone” packing in solid state, mainly due to the large improvement of short circuit current (Isc). Using these materials, we have achieved power conversion efficiency (PCE) of about 1.5%, which is among the highest performing non-fullerene polymer BHJs solar cells reported to-date. The second class of acceptors that will be discussed is anthradithiophene (ADT) derivatives. Compared to pentacenes, heteroacene ADTs are generally more soluble and also more stable. Similar molecular engineering strategies were applied to this material class. Initial screening for functional groups showed that: 1. Di-functionalization, compared to the mono-functionalization for pentacenes, is necessary for ADTs to match the energy level alignment with the other components in a ITO/PEDOT:PSS/P3HT-ADT/CsF/Al device; 2. Amide groups show impressive response in the open circuit voltage (Voc), which reaches as high as 1.1 V. Our initial results have shown that these ADT amides can reach PCE around 1% with only slight device optimization, even if in the case where a normal 1-dimentional packing but not the desired sandwich herringbone packing was observed. Another interesting result we found in ADT amides are their preferential isomerically-pure crystallization behavior. ADTs are mostly studied as a mixture of syn and anti isomers which are usually inseparable as a result of indiscriminative synthesis involved. However, ADT syn amide and anti amide were found to crystallize quite differently, which allowed us to isolate the isomers and study the isomerically-pure materials to correlate chemical structures, solid state structures and device performance.
11:00 AM - OO11: MDP
BREAK
OO12: N-type Semiconductor Materials
Session Chairs
Thursday PM, April 28, 2011
Golden Gate A-B (Marriott)
11:30 AM - OO12.1
Synthesis of Non–fullerene Based Electron Acceptors Bearing Diketopyrrolopyrrole and Dicyanoimidazole Moieties for Applications in Organic Photovoltaics.
Jason Bloking 1 , Xu Han 2 , Michael McGehee 1 , Alan Sellinger 1
1 Materials Science & Engineering, Stanford University, Stanford, California, United States, 2 , DuPont PV R&D Center, Shanghai China
Show AbstractOrganic photovoltaic devices (OPVs), which utilize organic small molecules and/or polymers to directly convert sunlight to electricity, are an attractive technology for sustainable, low cost, clean energy production. For example, solution-processed bulk heterojunction (BHJ) OPVs have attracted much attention because of their potential for flexible, light weight, large area and low-cost device fabrication. In particular, fullerene compounds have been the dominating electron acceptor/transport material in BHJ OPVs. However, fullerene compounds have some disadvantages, such as low absorption in the visible spectrum, low extinction coefficient, high-cost synthesis and purification, and a low lying LUMO which generally results in low open circuit voltages (Voc). In an attempt to solve these problems, reported here is a family of new electron acceptor materials from simple, minimal step, high yield, and inexpensive synthetic processes for application in OPVs. The new electron accepting molecules, based on diketopyrrolopyrrole and dicyanoimidazole moieties, are designed with extended π-conjugated systems that help contribute to significant absorption of the visible spectrum, and tunable chemistry to allow for varying of HOMO/LUMO levels and solubility. The synthesis, characterization, and initial solution processed OPV results using these new materials with selected electron donor materials will be reported.
11:45 AM - OO12.2
Influencing the Nanomorphology of Dicyanovinyl-oligothiophene Fullerene Blends for Use in Small Molecule Organic Solar Cells: A photoinduced Absorption Study.
Hannah Ziehlke 1 , Christian Koerner 1 , Roland Fitzner 2 , Egon Reinold 2 , Peter Baeuerle 2 , Karl Leo 1 , Moritz Riede 1
1 Insitute of Applied Photophysics, TU Dresden, Dresden Germany, 2 Institute of Organic Chemistry II and Advanced Materials, Ulm University, Ulm Germany
Show AbstractThe performance of organic solar cells crucially depends on the separation of the initially created excitons into free charge carriers. The specific nanomorpholgy of donor (D) and acceptor (A) molecules blended in a thin film sensitively influences the dissociation process. Closed percolation paths have to be present such that the created charges are able to leave the active layer, but also the crystallinity of the donor and the acceptor phase and the distance of D and A molecule influence exciton dissociation on a molecular scaleThe nanomorpholgy can on the one hand be influenced by adding functional side chains to the D- or A-molecule, on the other hand in-situ or post annealing processes are used to influence the phase separation of D and A molecules.We here characterize oligothiophenes endcapped with electron withdrawing dicyanovinyl groups (DCV2-nT) which have been proven to be excellent donor materials for small molecule organic solar cells [1]. Furthermore this material class provides the opportunity for systematic variations of the molecular structure. An increase of the number of thiophene rings in the molecule backbone results in a shift of the highest occupied molecular orbital (HOMO) from -6.3 eV(n=3) to -5.6 eV(n=6), as measured by ultraviolet photoelectron spectroscopy (UPS). Besides variations of the backbone length, variations of the side chains are easily accessible.To investigate changes in transfer processes between donor (D) and acceptor (A) molecules due to side chains variations, we use photoinduced absorption spectroscopy (PIA). PIA probes the long-living photoexcited species at the D-A interface: triplet excitons, cations, and anions.For a series of dicyanovinyl-terthiophenes with different alkyl side chains (methyl and butyl) and different number of side chains (0,2,4) PIA spectroscopy as well as linear absorption, atomic force microscopy, and UPS are performed. We find a strong influence of side chains on the film morphology in the neat layer. In mixtures with the acceptor C60, energy transfer occurs via the singlet and triplet manifold back to the triplet exciton on the terthiophene. The efficiency of this energy transfer is estimated using PIA by comparing neat and blend layers. In general the transfer efficiency decreases with longer side chains.For a series of dicyanovinyl-quinquethiophenes, the influence of different side chain substitution patterns and side chain lengths as well as the influence of deposition of films on heated substrates are investigated by PIA spectroscopy. Here, efficient charge separation occurs in blends with C60. Heating the substrate results in an increased lifetime of the donor cation due to a sufficiently large phase separation which on the other hand reduces the generation of cations. The PIA results are complemented by solar cell devices as well as morphological studies.[1] D. Wynands et al., Appl. Phys. Lett. 97, 073503 (2010)
12:00 PM - OO12.3
Synthesis and Processing of Perylene Diimide (PDI)-Based ``Nanofabric” Thin Films for Organic Photovoltaic Cells.
Yong Min 1 , Chi-Yueh Kao 1 , Lynetta Mier 1 , June Hyoung Park 2 , Austin Carter 2 , Arthur Epstein 2
1 Department of Chemistry, The Ohio State University, Columbus, Ohio, United States, 2 Department of Physics, The Ohio State University, Columbus, Ohio, United States
Show AbstractA series of Perylene Diimide (PDI) compounds and complexes have been synthesized through condensation reaction of 3,4,9,10-Perylenetetracarboxylic dianhydride with various amines. The material band gaps, charge transfer (CT) efficiencies, and processibilities can be modified through the selection of different amines (H2N-R), optimizing side-chains, controlling molecular weight changes from oligomer to polymer, and using different organic solvents. The molecular structure and corresponding CT mechanism were studied using ultrafast time-resolved infrared (IR) and Raman techniques. PDI and its modifications have earned a highly regarded reputation as exceptionally photostable compounds with broad absorption in the visible and near IR, intense fluorescence with the yield approaching unity, favorable carrier mobility, and redox properties which could be of use for applications in photovoltaics, light-emitting diodes, and field-effect transistors. Various PDI based nanofibers and thin films were fabericated through solution and vacuum deposition techniques. The materials were characterized using techniques including SEM, AFM, ESR, XRD, photoluminescence, UV/vis, FTIR, etc. These materials were blended with poly(3-hexylthiophene) to form nanofiberic networks. A solution-processible novel structure for organic photovoltaic cells with fast electron-transporting organic overlaping nanofibers forming a “nanofabric“ is constructed and investigated. The photovoltaic cell has nano fabric heterojunction (FHJ) of poly(3-hexylthiophene) and the electron transporting nanofabric. We have observed a significant improvement in power-conversion efficiency. Bis(octyl)-perylenediimide (PDI-C8) is the organic electron-transporting material, its field-effect electron mobility is measured to be as high as 0.08 cm2/Vs. The nanofabric improves power-conversion efficiency by expanding interfacial area as well as providing high mobility electron pathways to LiF/Al electrodes. The nanofabric also remove accumulated charges at the interfaces of bilayer to improve fill factors of photovoltaic cells. This work is supporting in part by OSU-IMR project.Keywards: Perylene Diimide (PDI), nanofiber, nanofabric, fabric heterojunction (FHJ), OPV.
12:15 PM - OO12.4
Rational Design and Systematic Study of Organic N-type Dopants for N-channel Semiconductors.
Peng Wei 1 , Jianguo Mei 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show Abstract Controlled electrical doping attracts more and more attentions for the beneficial effects such as the improvement of film conductivity and reduction of ohmic losses in organic devices such as OLEDs and OSCs.[1] In contrast to p-type doping, n-type dopants are rare for the requirement of high HOMO energy level on dopants, which makes such materials unstable in air against oxygen and moisture. We designed and synthesized a series of organic n-type dopants, which all show strong n-type doping effect so that they can effectively improve the conductivity of organic n-channel semiconductors by both vacuum deposition and solution process. High conductivity more than 1 S/cm of the doped C60 film was obtained by vacuum deposition. Moreover, the strength of doping can be tuned by different substitutions such as electron donating and withdrawing groups. We also utilized these n-type dopants for the first time to improve the air-stability of n-channel organic thin-film transistors, in which the doping can compensate for the electron traps. Our successful demonstration of n-type doping opens up new opportunities for the development of air-stable n-channel semiconductors. It is also potentially useful for application on solution-processed organic light-emitting diodes and organic photovoltaics.[1] K. Walzer, B. Maennig, M. Pfeiffer, and K. Leo, Chem. Rev., 2009, 107, 1233
12:30 PM - OO12.5
Effect of Morphology on the Properties of an N-type Semiconductor for Organic Solar Cells and Field Effect Transistors.
Ke Gui 1 , , Paul Schwenn 1 , Karsten Krueger 1 , Karyn Mutkins 1 , Pascal Wolfer 2 , Natalie Stingelin Stutzmann 2 , Paul Meredith 1 , Paul Burn 1
1 Centre for Organic Photonics & Electronics, University of Qeensland, Brisbane, Queensland, Australia, 2 Department of Materials, ETH Zurich, CH-8093 Zurich Switzerland
Show AbstractThe majority of organic semiconductors developed are more easily oxidized (p-type) than reduced (n-type). However, n-type materials are important for a variety of applications including electron transport materials in organic light-emitting diodes, active channels in organic field effect transistors, and electron acceptors in organic photovoltaic devices. In this presentation we describe the preparation and properties of new n-type organic semiconductors that incorporate benzothiadiazole units. The presentation will focus on a small molecule n-type material, K12, that has the remarkable property in that it can be deposited from solution or under vacuum with the former route in some cases giving better performance. K12 exhibits a tendency to order, even at room temperature, and with mild heating the process can be accelerated. The extent of ordering in the films is correlated with the thermal properties and optoelectronic properties, which are revealed by Polarized Optical Microscopy, Atomic Force Microscopy, and X-ray Diffraction. K12 has been shown to be a good electron acceptor candidate for bulk heterojunction organic solar cells and as an active channel in organic field effect transistors. A 0.7% power conversion efficiency under AM1.5 light has already been achieved in a bulk heterojunction solar cell configuration with poly(3-n-hexylthiophene) as the donor. OFETs with K12 as the active channel have achieved field effect mobilities of 2 x 10-3 cm2/Vs.
OO13: Organic Thin Film II: Morphology, Transport and Characterization
Session Chairs
Thursday PM, April 28, 2011
Golden Gate A-B (Marriott)
2:30 PM - OO13.1
Probing Organic Optoelectronic Film Morphology with Neutrons.
Paul Burn 1 , Arthur Smith 1 , Ian Gentle 1 , Paul Meredith 1
1 , University of Queensland, Brisbane, Queensland, Australia
Show AbstractAdvances in organic optoelectronic materials design and manufacturing have brought the first organic light-emitting diodes (OLEDs) and photovoltaic devices (OPV) to market. For all the organic materials used as the active layers the morphology of the film plays an important role in controlling their opto-electronic and device properties. Neutron techniques such as neutron reflectometry (NR) and small angle neutron scattering are important methods for studying physical structures of (macro)molecules and their interactions in solution and/or the solid state. We have been using an in situ photoluminescence-NR measurement for elucidating the direct relationship between physical structure and emissive properties. For example, we have shown how this combined technique can be used to determine the structure of films comprised of phosphorescent iridium(III) complexes. OLEDs containing iridium(III) complexes are highly efficient but achieving this efficiency usually involves diluting the emissive complex in a host material such as 4,4’-bis(N-carbazolyl)biphenyl (CBP). We have found that not only is the concentration of complex in a blend important for the emissive properties of the film but also the morphological thermal stability. In addition, NR measurements can reveal how thermal annealing can cause the mixing of layers in multilayer device architectures. Finally, the combined photoluminescence-NR measurements can provide valuable insight into the effects of analyte diffusion in organic films that are used for sensing explosives. In this presentation we will report our important findings on how film morphology is revealed by neutron reflectometry and the implications for device perfomance.
2:45 PM - OO13.2
Control of Semiconducting Polymer Chain Orientation through Nanostructured Device Architectures.
Danvers Johnston 1 , Kevin Yager 1 , Htay Hlaing 2 3 , Xinhui Lu 2 , Benjamin Ocko 2 , Charles Black 1
1 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 2 Condensed Matter Physics & Materials Science Dept, Brookhaven National Laboratory, Upton, New York, United States, 3 Dept of Physics & Astronomy, Stony Brook University, Stony Brook, New York, United States
Show AbstractIn films of semiconducting polymers, the polymer chain packing orientation relative to a substrate surface can promote anisotropic charge transport. For example, poly(3-hexlythiophene) (P3HT), an important solution-processable conjugated polymer used in both photovoltaic devices and field-effect transistors, preferentially packs with the high-conductivity π–π stacking direction oriented parallel to the substrate plane, resulting in an in-plane charge carrier mobility several orders of magnitude higher than that in the transverse direction.We can control the chain packing orientation of semiconducting P3HT by confining the material within large-area nanostructured surfaces patterned using electron-beam lithography. In contrast to films formed on planar surfaces, P3HT and P3HT:Phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction blend films formed on nanostructured grating patterns with sub-50nm dimensions exhibit preferential parallel lamellar stacking, with π–π stacking rotated 90 degrees out of the substrate plane. We characterize the degree of chain re-orientation using grazing incidence x-ray diffraction (GIXRD) in order to measure the influence of the confining geometry dimensions.We understand the relationship between chain orientation and electronic function of pure P3HT and P3HT:PCBM blends by measuring the transverse current—voltage characteristics of the confined materials. For confining template dimensions inducing only a small degree of chain reorientation, P3HT:PCBM bulk heterojunction solar cells exhibit conversion efficiencies similar to unconfined films, indicating that the template structure itself does not adversely affect performance. A detailed understanding of the correlation between device electrical and optical properties and the material internal structure will inform design of higher performing solar cell architectures.
3:00 PM - OO13.3
Electrochemical Impedance Spectroscopy of Efficienct Dye-sensitized Solar Cells using a Series of Novel Organic Dyes.
Chih-Hung Tsai 1 , Tsung-Wei Huang 1 , Lun Hsieh 1 , Sui-Ying Hsu 1 , Yu-Tang Tsai 1 , Chung-Chih Wu 1 , Li-Yen Lin 2 , Chia-Hung Chen 2 , Shu-Hua Chou 2 , Ken-Tsung Wong 2
1 Electrical Engineering, Graduate Institute of Photonics and Optoelectronics and Graduate Institute of Electronics Engineering, National Taiwan University, Taipei Taiwan, 2 Chemistry, National Taiwan University, Taipei Taiwan
Show AbstractDye-sensitized solar cells (DSSCs) offer the advantages of simple structures, cost-effective manufacturing, and high efficiencies, thus emerging as one of the most promising solar cell technology. A typical DSSC consists of transparent conductive substrate, a porous thin-film electrode consisting of TiO2 nanoparticles, dye, electrolyte, and a platinum counter electrode. We had developed a series of novel push–pull organic dyes incorporating electron-deficient pyrimidine or coplanar diphenyl-substituted dithienosilole as the π-spacers. They were successfully applied to fabrication of DSSC devices, yielding conversion efficiency close to those achieved by the more expensive ruthenium-based dye sensitizers. Electrochemical impedance spectroscopy (EIS), a useful tool for characterizing various interfacial/bulk charge-transfer processes in DSSCs, was used for studying mechanisms of DSSCs adopting these novel organic dyes. It was found that the introduction of alkoxy chains on the donors effectively suppresses charge recombination at the TiO2/dye/electrolyte interface, leading to higher open-circuit voltage and efficiency of the solar cells.
3:15 PM - OO13.4
Characterization of Charge Transport in Organic Light-emitting Diodes.
Matthias Schober 1 , Merve Anderson 1 , Mauro Furno 1 , Bjoern Luessem 1 , Karl Leo 1
1 , Technische Universitaet Dresden, IAPP, Dresden Germany
Show AbstractOrganic light-emitting diodes (OLEDs) consist of a large number of different organic layers such as doped injection layers, blocking layers, and emitting layers. The large variety of organic materials along with unknown transport properties and interface effects makes the development of a new OLED a complex task: Usually, much optimization and testing is needed until a satisfying performance is obtained.In this contribution, we present a concept to simplify the characterization and optimization of OLEDs by taking advantage of a numerical charge transport model which has been designed especially for disordered organic semiconductors [1,2]. The model is based on the charge carrier density and electric field dependent mobility functions as obtained by Pasveer et al. [3] and comprises electrical doping, transport over interfaces, recombination, and various other characteristical processes in organic multilayer devices. For the example of a three-color white OLED with fluorescent blue and phosphorescent red and green emission, we will demonstrate how this concept can be applied to investigate and identify the transport properties of the single layers, interface effects, as well as non-radiative recombination paths which lead to loss in efficiency.[1] Schober et al., Appl. Phys. Lett. 97, 013303 (2010);[2] Coehoorn et al., Phys. Rev. B 80, 085302 (2009);[3] Pasveer et al., Phys. Rev. Lett. 94, 206601 (2005).
3:30 PM - OO13.5
The Effect of Disorder on Charge Transport in High Performance Semicrystalline Polymers.
Jonathan Rivnay 1 , John Northrup 2 , Rodrigo Noriega 1 , Alberto Salleo 1
1 , Stanford University, Stanford, California, United States, 2 , Palo Alto Research Center, Palo Alto, California, United States
Show AbstractThe high performing semicrystalline polymer pBTTT {poly[2,5-bis(3-alkylthiophen-2-yl)thieno(3,2-b)thiophene]}, with reported mobilities >1cm2/Vs, represents one of the top performing polymeric semiconductors to date. While its unique, terraced, microstructure and phenomenal texture out of the plane of the substrate have been attributed to side chain interdigitation and a generally more crystalline film, little has been done to understand the more relevant directions for fast charge transport (i.e. π-stacking and chain backbone directions). It has been suggested that the isotropic in-plane morphology of pBTTT consists of small 'grains', and that the ordered regions feature gradual or soft transitions from one in-plane orientation to another, however, the details of the degree of ordering and their potential to limit transport in these directions has not been explored. A better understanding of the bottlenecks for transport in such high performing materials will lead to potential design rules for future materials.In this work, we use advanced X-ray lineshape analysis with rigorous error propagation procedures to quantitatively extract the fluctuations in molecular spacing due specifically to static, cumulative disorder for the fast transport π-stacking direction in an aligned film of pBTTT. Even as one of the most microscopic- and macroscopically ordered films (an aligned ribbon phase film), the π-stacking shows 6.7% paracrystalline disorder (where <1% is considered highly crystalline, and 15% is considered amorphous). Through this analysis we also conclude that the high degree of disorder in this crystallographic direction suggests that the meaning of grain size is lost, and that therefore, interchain transport should be dominated by details related to disorder. By modeling the band structure of a collection of π-stacked pBTTT segments with different degrees of paracrystalline disorder, we show that, compared to the ideal completely ordered microstructure, the experimentally determined disorder introduces a tail of localized states which can act as traps for charge transport. These calculations provide physical justification for the mobility edge model, and are in agreement with experimental data.
3:45 PM - OO13.6
Nanoscopic Assembly of Organic Semiconductors for Organoelectronic Devices.
Benjamin Rancatore 1 2 3 , Clayton Mauldin 1 , Joe Strzalka 4 , Jean Frechet 1 3 , Ting Xu 1 2 3
1 Department of Chemistry, UC Berkeley, Berkeley, California, United States, 2 Department of Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 3 Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 4 X-Ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractOrganic small molecule semiconductors have many advantages over their polymer counterparts for fabricating organoelectronic devices, such as high purity and well-defined electronic properties. To this end, it is necessary to assemble them into nanoscopic features that can be macroscopically aligned normal to a substrate. To be compatible with solution processing, so as to reduce fabrication costs, requires the elimination of dewetting to ensure film uniformity. We recently developed a supramolecular approach in order to address the bottlenecks listed above (1). A quaterthiophene organic semiconductor with phenolic and alkyl moieties were hydrogen-bonded to the 4-vinylpyridine groups of either a block copolymer (BCP), poly(styrene)-b-poly(4-vinylpyridine) (PS-b-P4VP), or a homopolymer, P4VP. Uniform films of a quaterthiophene can be readily obtained with nanoscopic features aligned perpendicularly to a substrate while maintaining the charge mobility of the semiconductor. Since these polymers and organic semiconductors can be readily substituted for others, this supramolecular approach presents a viable method for the fabrication of functional, nanostructured semiconductor films using solution processing. It was shown that the resulting morphologies of the organic semiconductors depend on at least two competing assembly processes, i.e. crystallization of the semiconductor to ensure high charge mobility and ordering of the polymer for directing the nanoscopic assembly. A family of oligothiophenes with different melting temperatures was used to develop a systematic understanding of how the interplay between the two processes affect the device performances. Generally, a supramolecular approach requires asymmetrically functionalized small molecules which can be synthetically demanding. To overcome this limitation, we expanded this approach to blends of symmetric and asymmetric semiconductors and investigated the morphologies of the active layers as a function of mixing ratio and chemical structures of the organic semiconductor used. Our results showed that the favorable π-stacking interactions between the asymmetric and symmetric small molecules enable intercalation into supramolecular domains and morphological control can be achieved to obtain nanoscopic assemblies of organic semiconductors. These studies have led to some basic design principles to optimize morphologies of active layers toward the fabrication of small molecule-based optoelectronic devices. References:(1) Rancatore et al., ACS Nano 2010, 4, 2721.
4:00 PM - OO13: OTF II
BREAK