Robert Abbel, Holst Centre - TNO
Maikel van Hest, National Renewable Energy Laboratory
Shlomo Magdassi, The Hebrew University of Jerusalem
Katsuaki Suganuma, Osaka University
LL3: Metal Nanowire Networks - Preparation
Maikel van Hest
Tuesday PM, April 22, 2014
Moscone West, Level 3, Room 3009
2:30 AM - *LL3.01
A Wet Chemical Method for In-Situ Preparation of Metal Nanowire Films on Surfaces for Transparent Electrodes
Gil Markovich 1 Daniel Azulai 1 Elad Cohen 1 Einat Tirosh 1
1Tel Aviv University Tel Aviv IsraelShow Abstract
We have developed a wet chemical technique that is based on self-assembly from an aqueous solution to produce ultra-thin gold-silver nanowire films at the substrate-solution interface. The nanowire films can be used as transparent electrodes, with the advantage of a single step preparation directly on a substrate of choice, even on conducting polymer films. The deposition occurs at ambient conditions and the films do not require any high temperature annealing steps. The process starts with small metal seed particles that are mixed with the growth solution. The seed concentration determines the morphology of the nanowire film. The process is compatible with photolithographic patterning and with various printing techniques.
3:00 AM - LL3.02
Flexible Transparent Electrodes Based on Copper and Silver Nanowires: Integration into Functional Devices
Jean-Pierre Simonato 1
1CEA Grenoble FranceShow Abstract
We report in this communication on the synthesis, purification and use of silver or copper nanowires to fabricate flexible transparent electrodes.
We will present results on the synthesis and specific purification processes for both metals. The metallic nanowires are then used as flexible transparent electrodes through the fabrication of random networks of nanowires, either by spin-coating or spray-coating.[2-3] The performances of these electrodes are excellent, typically ~20-30 ohm/sq at 90 % transparency.
This solution-processable technique appears as a really promising alternative to ITO, with in addition the possibility to realize highly flexible electrodes (even crumpling was demonstrated on a 1.3 µm thick film with our silver nanowire based electrodes). Comparison of the stability of the electrodes will be discussed.
These electrodes have been integrated in various optoelectronic devices.
We will show that it affords a large area, low-cost deposition method, with good performances in devices such as organic photovoltaic cells, flexible touch sensors, and organic photodiodes.
We will also present results dealing with the use of such electrodes to realize transparent film heaters (TFH), with very good performances. 
 Flexible transparent conductive materials based on silver nanowire networks: A review. Langley D., Giusti G., Mayousse C., Celle C., Bellet D., Simonato J.P., Nanotechnology, 2013, in press.
 Improvements in Purification of Silver Nanowires by Decantation and Fabrication of Flexible Transparent Electrodes. Application to Capacitive Touch Sensors. Mayousse C., Celle C., Moreau E., Mainguet J.-F., Carella A., Simonato J.P. Nanotechnology, 2013, 24, 215501
 Synthesis and purification of long copper nanowires. Application to high performance Flexible Transparent Electrodes with and without PEDOT:PSS. Mayousse C., Celle C., Carella A., Simonato J.P., submitted.
 Highly Flexible Transparent Film Heaters Based on Random Networks of Silver Nanowires. Celle C., Mayousse C., Moreau E., Basti H., Carella A., Simonato J.P. Nano Research, 2012, 5(6): 427-33
3:15 AM - LL3.03
Performance Enhancement of Metal Nanowire Transparent Conducting Electrodes by Mesoscale Metal Wires
Po-Chun Hsu 1 Shuang Wang 2 Hui Wu 1 Vijay Kris Narasimhan 1 Desheng Kong 1 Hye Ryoung Lee 2 Yi Cui 1 3
1Stanford University Stanford USA2Stanford University Stanford USA3Stanford Institute for Materials and Energy Sciences Stanford USAShow Abstract
For transparent conducting electrodes in optoelectronic devices, electrical sheet resistance and optical transmittance are two of the main criteria. Recently, metal nanowires have been demonstrated to be a promising type of transparent conducting electrode because of low sheet resistance and high transmittance. Here we incorporate a mesoscale metal wire (1-5 micrometer in diameter) into metal nanowire transparent conducting electrodes and demonstrate at least a one order of magnitude reduction in sheet resistance at a given transmittance. We realize experimentally a hybrid of mesoscale and nanoscale metal nanowires with high performance, including a sheet resistance of 0.36 Ohm/sq and transmittance of 92%. In addition, the mesoscale metal wires are applied to a wide range of transparent conducting electrodes including conducting polymers and oxides with improvement up to several orders of magnitude. The metal mesowires can be synthesized by electrospinning methods and their general applicability opens up opportunities for many transparent conducting electrode applications.
3:30 AM - *LL3.04
ITO-Free OLED and OPV Devices with a Transparent Silver Nanowire Electrode
Florian Pschenitzka 1
1Cambrios Technologies Sunnyvale USAShow Abstract
Cambrios has developed a transparent conductor material based on silver nanowires to replace the ITO layer in organic photovoltaics (OPV) device and in organic light-emitting devices (OLED).
After being deposited from a liquid suspension by conventional coating or printing methods onto a transparent substrate, these nanowires form a transparent conducting network. The sheet resistance of the resulting film is determined by the density of the nanostructures and can thus be easily controlled during the coating process.
The elimination of the ITO layer also results in a reduced microcavity effect and thus has a positive impact on the optical performance for OLED lighting devices.
The talk will focus on the use of this material as an ITO replacement for OLED devices for lighting applications and for OPV devices. We will report in detail on the fabrication and characterization of the nanowire film. The performance of ITO-free OPV and OLED devices with a nanowire anode will be discussed. We also will present the optical performance data of OLED lighting devices which show the implications of a reduced microcavity effect. In addition, we will show lifetime data for these devices which demonstrate the viability of this technology.
LL4: Thin Dielectric-Metal-Dielectric Films
Maikel van Hest
Tuesday PM, April 22, 2014
Moscone West, Level 3, Room 3009
4:30 AM - *LL4.01
Novel Flexible Polymer/Metal/Polymer TC with Superior Performance to ITO
Clark I Bright 1 2
1Bright Thin Film Solutions Tucson USA23M Corporate Research Process Laboratory, Retired Tucson USAShow Abstract
Performance demands on transparent conductors (TC) for transparent electrodes in current carrying and large area applications such as OLED displays, photovoltaic solar cells and solid-state lighting, continue to increase. Transparent conductive oxides (TCO) such as indium tin oxide (ITO), when deposited on heated glass (~ 200 °C) have useful electrical and optical (E-O) performance (~ 10 Ohm/sq - 88%T) for these applications. However, when ITO or another TCO, are vacuum deposited at low substrate temperature on plastic film to allow roll-to-roll processing, the E-O performance is much worse (~ 50 Ohms/sq - 85%T). Novel TC based on antireflected very thin metallic films in Polymer/Metal/Polymer (PMP) designs, were developed to address these performance limitations, yet be compatible with high speed, roll-to-roll, vacuum deposition on temperature-sensitive plastic film. The antireflection layers were high index polymers (P) rather than traditional brittle inorganic oxides, e.g., ITO or TiO2, to enable applications requiring flexible transparent electrodes. The fundamental optical limitation in using metallic thin films is the transmission loss, which occurs because of absorption in the metal. Because absorption is exponentially proportional to the product of the film thickness and its absorption coefficient; to mitigate absorption very thin metallic layers were used. However, if a metallic layer becomes too thin the absorption increases (anomalous absorption) because very thin metals tend to agglomerate forming an island type structure, which becomes discontinuous and non-conductive. To inhibit island formation various metal oxides were evaluated experimentally as a nucleating and bonding agent for the silver based thin film. First sputter depositing zinc oxide nanoclusters, “seeds”, enabled much thinner silver based layers without their becoming nonconductive, unstable or exhibiting significant absorption. Polymer/Metal/Polymer TC (P/M/P-TC) deposited by this method, have a combined E-O performance, which far exceeds the typical performance of single layer ITO films deposited with low substrate temperature, and is equal or better than high temperature processed ITO. For example, by adjusting the metal thickness, E-O performance from ~ 10 Ohms/sq - 87%T to < 40 Ohms/sq - ge; 90%T was achieved. The P/M/P-TC flexing/bending capability is superior to commercially available ITO and oxide-metal-oxide based TC on plastic substrates. P/M/P-TC demonstrated up to 50% extension without loss of conductivity and bending around a 3 mm radius of curvature without degradation. Additionally, its environmental durability, e.g., ge; 72 hours @ 65°C/95% RH, is also superior. The P/M/P-TC environmental durability, i.e., corrosion resistance, was further enhanced by adding anti-corrosion additives to the polymers, thin tin oxide nanoclusters, and/or using a silver/gold alloy metallic layer.
5:00 AM - LL4.02
Improving Environmental Stability of Single and Multilayer Ga Doped ZnO Films
Thanaporn Tohsophon 1 Monica Morales Mesis 1 Christophe Ballif 1
1Ecole Polytechnique Famp;#233;damp;#233;rale de Lausanne (EPFL) Neuchamp;#226;tel SwitzerlandShow Abstract
Transparent conductive oxides can be used for a wide range of electronics application ranging from touch screen to photovoltaic panels. The goal of this work is the design and realization of transparent conductive materials with enhanced stability under adverse environmental conditions while maintaining high conductive and optical transmittance characteristics.
We investigated heavily gallium (10wt%) doped ZnO (GZO) single layers and GZO/Ag/GZO trilayers, prepared by rf magnetron sputtering on glass substrate at room temperature. The best as-deposited GZO layer shows high transmittance (>85%) in the wavelength range of 400-1100 nm, and low resistivity (5 x10-4 #8486;cm) corresponding to a sheet resistance of 50 #8486;/square for 120 nm thick films. The trilayers fabricated with different GZO layer thickness (total thickness of 60-90 nm) exhibit excellent conductivity (5-8x10-5 #8486;cm), with sheet resistance of 7-9 #8486;/square and high transmittance (>80%), with the average absorptance of 10% in the visible region.
The long term stability of the films to moisture was tested by damp heat exposure (DH) at relative humidity of 85 % and 85 °C over 1000 h. The electrical, optical and morphological properties of the films before and after DH as functions of different GZO layer thickness were analyzed, in order to assess the optimal trilayer structure. After DH, a small degradation (< 5 %) of GZO single layer is observed. An increase in resistivity of trilayers is also occurred, related to the thickness of GZO and Ag layer.
We demonstrate here the trilayer structure with high optical transmittance, excellent conductivity and enhanced stability. Possible physical mechanisms responsible for a retarded degradation of the films will be discussed.
5:15 AM - LL4.03
Alternative Transparent Electrode Technologies for Organic Optoelectronic Devices
Lars Mueller-Meskamp 1 Sylvio Schubert 1 Christoph Sachse 1 YongHyun Kim 1 2 Ludwig Bormann 1 Franz Selzer 1 Tobias Schwab 1 Simone Hofmann 1 Malte C. Gather 1 3 Karl Leo 1
1TU Dresden Dresden Germany2University of Minnesota Minnesota USA3University of St Andrews St Andrews United KingdomShow Abstract
Alternative transparent electrodes for optoelectronic applications on flexible substrates are an actual topic in research and application. We have investigated a wide variety of electrodes, such as record conductivity PEDOT:PSS, high-performance silver and cost-efficient copper nanowire networks, state of the art carbon nanotube layers for top and bottom electrodes, doped small molecules and ultra-thin metal films. All of these technologies were successfully incorporated into highly efficient pin-type vacuum deposited organic solar cells.
Within this presentation we will give a short overview on our recent results, showing highly promising alternative electrode technologies and their successful integration into organic optoelectronic devices. Then we will focus on recent investigations on super-transparent dielectric/metal/dielectric thin-film electrodes. These can be deposited by vacuum deposition, just as our OLED or OPV devices, which makes them suitable as top or bottom electrodes.
By optimizing the growth and microstructure of thin metal films, we were able to improve the thin-film properties and the device performance significantly. We boosted the device lifetime by using a stabilizing metal oxide sandwich structure  and we were able to improve the silver thin-film electrode performance to the ITO-like range (Rs=19 Omega; /sq. and T= 83% at 580 nm)  by introducing seed layers, controlling the growth of the thin. Recently we modified the ultrathin film by co-evaporation, generating a microstructured thin-film-electrode with extraordinarily high transmittance of 84.3 % (93.0 % after substrate correction) in the visible wavelength regime combined with a low sheet resistance of 27.3 Omega; /sq. (figure of merit σopt/σdc of 186.7). The application of these high performance metal thin-film electrodes for efficient OLED and OPV devices is demonstrated.
 Schubert, S., Hermenau, M., Meiss, J., Müller-Meskamp, L. & Leo, K. Oxide Sandwiched Metal Thin-Film Electrodes for Long-Term Stable Organic Solar Cells. Adv. Funct. Mater. 22, 4993-4999 (2012).
 Schubert, S., Meiss, J., Müller-Meskamp, L. & Leo, K. Improvement of Transparent Metal Top Electrodes for Organic Solar Cells by Introducing a High Surface Energy Seed Layer. Adv. Energy Mater. 3, 438-443 (2013).
5:30 AM - LL4.04
Flexible Transparent Organic/Ag/Metal Oxide Electrode for Organic Solar Cells
Juyoung Ham 1 Jong-Lam Lee 1
1PSOTECH Pohang Republic of KoreaShow Abstract
Flexible organic solar cells have been promising as next generation renewable energy because of ease of processing, light-weight portability and a competitive price. Although their potentials were investigated over the past decade, sufficient power generation has not yet been realized to the industry fields due to the natural phenomenon, varying the angle of incidence depending on the sun&’s coming up over a full day. Therefore, the light harvesting at a wide range of incident angles is a key issue for solar cells. Several approaches, multilayer antireflection coatings or surface texturing structures have been previously used to reduce the surface reflection and enhance the absorption efficiency. However, thermal mismatch, instability of the thin film stacks and complicated fabrication process still remain major obstacles in developing the angle-independent solar cells with broadband wavelength.
Hereby, we present a novel way of preparing an omnidirectional electrodes with excellent transparency. Ormoclear/Ag/WO3 (OoMDi) was designed not only for an alternative to ITO but also for an omnidirectional layer independent of incident angle of lights. Employing the ormoclear with low refractive index (n = 1.45) as an outer organic (Oo) layer, insensitivity to the angles of incidence (0 ~ 90o) was acheived in the OoMDi structures. Moreover, oxygen plasma treatment on Ormoclear prior to deposition of 10-nm-thick Ag, surface plasmon coupling at the Ormoclear/Ag interface could be greatly suppressed. As a result, an optimized structure of Ormoclear/Ag/WO3 shows an high optical transmission of > 91%, low sheet resistance of ~5.2 ohm sq-1. Employing the OoMDi electrode as an anode to the PTB7:PCBM organic solar cell resulted in the significantly improvement in the power conversion efficiency up to 10 %, from 7.1% using ITO anode to 7.7% .
5:45 AM - LL4.05
Laser Irradiation of High-Performance AZO/Ag/AZO Transparent Electrodes
Antonio Terrasi 1 2 Isodiana Crupi 2 Stefano Boscarino 1 2 Giacomo Torrisi 1 Giorgia Scapellato 2 1 Salvatore Mirabella 2 Giovanni Piccitto 1 Francesca Simone 1
1University of Catania Catania Italy2CNR-IMM MATIS Catania ItalyShow Abstract
Nowadays, there is an increasing demand for transparent conductive electrodes (TCE) for application in optoelectronic devices , as flat-panel displays, organic light emitting diodes and photovoltaic cells, to name a few. In this context, dielectric-metal-dielectric (DMD) multilayer structures are promising candidates for next-generation flexible transparent electrodes [2, 3]. Compared to standard TCEs, DMD electrodes show enhanced conductivity, higher transmission of visible light, lower temperature process, reduced thickness and, consequently, significant cost reduction and improved mechanical flexibility. However, at present, DMD multilayer structures are still far from being implemented on thin film photovoltaic device technology. A crucial aspect is the TCE film patterning (scribing) for electrical isolation. This process, performed with a laser wavelength of 1064 nm, requires relatively high laser fluences and multipulse irradiation to segment the thick, typically 0.7 to 1 mu;m, ZnO:Al (AZO) front contact in the solar cell.
We demonstrate how the energy density threshold for the scribing of the transparent electrodes can be significantly reduced by replacing the standard AZO single layer with a 10 times thinner AZO/Ag/AZO multilayer structure with better electrical and optical properties . Thin films of 40 nm of AZO, 10 nm of Ag and 40 nm of AZO are sequentially deposited on conventional soda lime glass substrates by RF magnetron sputtering at room temperature in argon atmosphere. Laser treatments are performed in air by a single pulsed (12 ns) Nd:YAG laser operating with an infrared (at 1064 nm), Gaussian-shaped (FWHM = 1 mm) beam. The laser power is varied to obtain fluences in the range from 1.15 to 4.6 J/cm2. Our experimental results, supported by a computer simulation of the thermal behaviour under laser irradiation, provide clear evidences of the key role played by the silver interlayer by increasing the maximum temperature reached in the structure and fastening the cool down process. These evidences can promote the use of ultra-thin AZO/Ag/AZO electrode in large-area products, such as for solar modules.
 Ginley, D. S., Hosono, H. & Paine, D. C. Handbook of Transparent Conductors. Springer (2010).
 Kim S, Lee J-L. Design of dielectric/metal/dielectric transparent electrodes for flexible electronics. J Photon Energy 2:021215 (2012).
 Crupi I, Boscarino S, Strano V, Mirabella S, Simone F, Terrasi A, Optimization of ZnO:Al/Ag/ZnO:Al structures for ultra-thin high-performance transparent conductive electrodes. Thin Solid Films 520, 4432 (2012).
 Crupi I, Boscarino S, Torrisi G, Scapellato G, Mirabella S, Piccitto G, Simone F, Terrasi A, Laser irradiation of ZnO:Al/Ag/ZnO:Al multilayers for electrical isolation in thin film photovoltaics. Nanoscale Res Lett 8:392 (2013).
LL5: Poster Session: Transparent Electrodes
Maikel van Hest
Tuesday PM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 8-9
9:00 AM - LL5.01
High-Performance Conducting Hybrid Composite Film: A Robust Transparent Electrode Platform for Flexible Thin-Film Optoelectronics
Jungho Jin 1 3 Jaemin Lee 2 3 Seonju Jeong 2 3 SeungCheol Yang 1 3 Ji-Hoon Ko 1 3 Hyeon-Gyun Im 1 3 Se-Woong Baek 2 3 Jung-Yong Lee 2 3 Byeong-Soo Bae 1 3
1KAIST Daejeon Republic of Korea2KAIST Daejeon Republic of Korea3KAIST Daejeon Republic of KoreaShow Abstract
Herein, we report a novel flexible transparent conducting hybrid composite film that can be utilized as a robust transparent electrode platform for thin-film optoelectronic devices. This hybrid composite film (AgNW-GFRHybrimer film) is composed of a glass-fabric reinforced transparent composite film and silver nanowire (AgNW) networks which are monolithically buried on the film surface as the electrode. The resulting monolithic hybrid structure of the AgNW-GFRHybrimer film simultaneously offers an exceptionally smooth AgNW electrode topography (<2nm) and excellent thermo-mechanical performance, both of which are the most critical factors for the viable implementation of AgNW-based transparent electrode system.
In this study, we discuss the fabrication and basic feature characteristics of the AgNW-GFRHybrimer film, and demonstrate a flexible inverted organic solar cell with a ~6% efficiency (AM 1.5G at 100mWcm-2) using AgNW-GFRHybrimer film as the all-in-one substrate/electrode platform.
 Jin et al., Energy & Environmental Science, 2013, 6, 1811-1817
9:00 AM - LL5.02
Copper and Silver Nanowire Arrays for Transparent Electrodes
Tongchuan Gao 1 Paul W Leu 1
1University of Pittsburgh Pittsburgh USAShow Abstract
Metallic nanowires have demonstrated high optical transmission and electrical conductivity with potential for application as transparent electrodes that may be used in flexible devices. We systematically investigated the electrical and optical properties of 1D and 2D copper and silver nanowire (Cu and Ag NW) arrays as a function of diameter and pitch and compared their performance to that of Cu and Ag thin films. NWs exhibit enhanced transmission over thin films due to propagating resonance modes between NWs. For the same geometry, the transmission of Cu NW arrays is about the same as that of Ag NW arrays since the dispersion relation of propagating modes in metal nanowire arrays are independent of the metal permittivity. The sheet resistance is also comparable since the conductivity of Cu is about the same as that of Ag. Just as in Ag NWs, larger Cu NW diameters and pitches are favored for achieving higher solar transmission at a particular sheet resistance. Cu NW arrays may achieve solar transmission >90% with sheet resistances <10 Omega;/sq and figure of merit σDC/σop > 1000. The physics of the optical behaviors of NW arrays are revealed by the study of the contour plots and electric field profiles.
One of the primary concerns with the use of Cu is oxidation and we also investigated the impact of a nickel (Ni) coating, which can serve as an anti-oxidation layer, on the electrical and optical properties. A better performance is demonstrated with ordered Cu nanowires than other nanomaterials such as carbon nanotubes, graphene, and random metal nanowire networks.
9:00 AM - LL5.03
Transparent Conductive ZnO: Al/Ag/ ZnO: Al Multilayer Electrodes for Photovoltaic Applications Grown by RF Magnetron Sputtering
Milenis Acosta 1 Ines Riech 1 Victor Rejon 2 Juan Luis Pena 2
1University of Yucatan Merida Mexico2CINVESTAV- IPN Merida Merida MexicoShow Abstract
With the development of optoelectronic devices, such as photovoltaic solar cells, light emitting diodes, flat panel devices, etc., transparent conductive oxide (TCO) coatings becoming more and more attractive. Traditionally indium tin oxide has been used as TCO because its high optical transparency, and good electrical properties, but it is a scarce element and expensive. Therefore new TCO materials are extensively investigated. Aluminum doped zinc oxide (AZO) is a promising alternative, which is non-toxic, low cost and environmentally friendly. To decreased the resistivity of AZO films a multilayer structure using a thin metallic film have been proposed by various authors [1-3].
In this study we report on transparent and highly conductive multilayer AZO/Ag/AZO structures grown by RF sputtering at room temperatures on glass substrates. The multilayer films were prepared by RF sputtering of ZnO:2% at. Al2O3 and silver targets, varying the total pressure, the ratio Ar/O2 and the Ag film thickness. We study the morphological and optoelectronic properties of the multilayer structure as a function of the growth parameters. The AZO/Ag/AZO electrodes exhibited superior square resistance and optical properties compared to AZO films grown at the same conditions. Furthermore, results of a CdTe solar cell using an optimized AZO/Ag/AZO as TCO are reported.
1-Anna Sytchkova, Maria Luisa Grilli, Antonio Rinaldi, Sylvain Vedraine, Philippe Torchio, Angela Piegari and Franccedil;ois Flory, J. Appl. Phys. 114 (2013) 094509.
2- Sebastian Wilken, Thomas Hoffman, Elizabeth von Hauff, Holger Borchert, Jurgen Parisi, Solar Energy Materials & Solar Cells 96 (2012) 141-147.
3- Jin-He Qi, Ying Li, Thanh-Tung Duong, Hyung-Jin Choi, Soon-Gil Yoon, Journal of Alloys and Compounds 556 (2013) 121-126.
9:00 AM - LL5.04
Electronic Properties of the ZnO:Al/Si(100), (110) and (111) Interface
Per Lindberg 1 Kristin Bergum 1 Bengt Svensson 1 Eduard Monakhov 1
1University of Oslo Oslo NorwayShow Abstract
Al-doped ZnO (AZO) is presently considered as probably the most promising transparent conductive oxide that can potentially replace indium-tin oxide. The application of ZnO to Si-based electronics and photovoltaics motivates studies of the ZnO-Si interface. Recently, we have reported on investigations of the interface between nominally undoped ZnO and moderately doped p- and n-type (100) Si (Quemener et al., J. Phys. D: Appl. Phys. 45 (2012) 315101). In the present work we have studied electrical properties of the interface between AZO and n-type Si with different crystalline orientations.
100-nm thick AZO has been deposited on (100), (110) and (111) n-type Si with a resistivity of 2-10 Ohm-cm and on a fused silica substrate by Atomic Layer Deposition (ALD) at 200oC using trimethylaluminum, diethylzinc and water as the precursors. A 200-nm thick Al film has been e-beam evaporated on top of AZO. Circular contacts with a diameter of 400 mu;m have been defined by photolithography and etching of the exposed Al and AZO. Post processing heat treatments have been performed in the temperature range 200-500oC for 30 min in air. The structures have been electrically characterized by current-voltage measurements and by Deep Level Transient Spectroscopy (DLTS). Hall measurements, performed for AZO deposited on fused silica, reveal the resistivity of the as-deposited film to be around 1.8x10-3 Ohm-cm.
It is found that the AZO films form Schottky diodes for all of the studied Si orientations. The as-deposited structures show significant non-systematic variations in the diode behavior between different contacts on the same sample. However, after an initial heat treatment at 200oC in air, no significant variations between the contacts occur. The general trend for all samples, regardless of crystallographic orientations, is that the leakage current is reduced after heat treatments, and the diode characteristics improve after annealing up to 400oC. Annealing beyond this point reduces the rectification by limiting the forward current. For all samples the ideality factor is close to unity after annealing at 200 - 300oC. Annealing at higher temperatures increases the ideality factors, suggesting an increased recombination in the space charge region. AZO on (110)Si exhibits the highest rectification. DLTS measurements reveal formation and annealing of electronic states after the heat treatments. The origin of these states is attributed to formation of SiOx at the ZnO-Si interface.
9:00 AM - LL5.05
Ultra-Fine Pattern Printing of Metal Mesh for Single-Layer Touch Screen Sensors Using Ag Nanoparticle Ink
Kwang Young Kim 1 Young-Man Choi 1 Eon-Seok Lee 1
1Korea Institute of Machinery and Materials Daejeon Republic of KoreaShow Abstract
We demonstrate thin metal mesh patterns for flexible devices especially for touch screen sensors. For transparent applications, the metal meshes should be composed of very fine lines whose width are less than 10 micrometers. In this paper, the ultra-fine pattern is fabricated by the reverse-offset printing method using Ag nanoparticle ink instead of photolithography. A whole conductive layer including active sensing area and routing electrodes is printed at one time. By controlling ink adhesion and cohesion, the printing quality is determined in reverse-offset printing. Also we found that the thickness of metal mesh affects the printing quality. For 100% transfer and sharp edge definition, printing process parameters like printing speed, printing pressure are optimized. The printing quality is verified using the optical transmittance. The optimized metal mesh shows an excellent agreement with the theoretical transmittance of the designed pattern. Finally, a single-layer metal mesh 5-inches touch screen sensor is fabricated on a transparent flexible plastic substrate.
This research was financially supported by the “Sensitivity touch platform development and new industrialization support program” through the Ministry of Trade, Industry & Energy(MOTIE) and Korea Institute for Advancement of Technology(KIAT).
9:00 AM - LL5.07
First Principles Study on Microscopic Origin of Visible Light Absorption in Amorphous Transparent Conducting Oxides
Youngho Kang 1 Seungwu Han 1
1Seoul National University Seoul Republic of KoreaShow Abstract
There have been growing interests in transparent conducting oxides (TCOs) such as ZnO, In2O3, SnO2 and its compound structure due to their superior optical transparency and electrical conductivity, which leads to various optoelectronic applications. Interestingly, their metallic conductivities are also well maintained even in a form of amorphous phase, which have attracted a great deal of interests for the industrial application since the cost of fabrication of the device can be reduced. However, previous studies on amorphous TCOs reported that they absorb the light with the smaller frequency than their optical band gaps (~3 eV) and that causes the change of the device properties unintentionally. Furthermore, the device instability worsens in the case of absorbing the photon with the higher energy than 2.8 eV corresponding to blue and near UV light. In recent, the tail state from the band edge receives attention as the important source for visible light absorption because it can vary the electrical property of amorphous TCOs by leading the formation of peroxide. However, the amount of the tail states and the energy ranges of the light they can absorb remain unresolved.
In this study, we perform the first principles calculation based on the density functional theory (DFT) to investigate the optical absorption coefficient and the band gap of amorphous IGZO which is one of the representative TCOs. We model the 10 different supercells with 14 formula units of InGaZnO4 for the statistical analysis and carry out the GW calculation for the quasiparticle band structure. We find out that even though the tail states are smeared out from both of the valence and conduction band edge, the states close to the valence band edge are more extended energetically and spatially localized than conduction band edge. Microscopically, the anti-bonding between two oxygen ions that are located close together induces the valence band tail state. It is noted that the transition of the electrons between each tail state can be started from 2.3 eV that corresponds to green light. In addition, the theoretical absorption spectrum in the vicinity of blue light region agrees well with the experimental data implying that the tail states plays a critical role to the device instability under the visible light illumination stress.
9:00 AM - LL5.09
Scalable, Printable, Surfactant-Free Graphene Ink Directly from Graphite
Xiaogang Han 1 Yu-Chen Chen 1 Jiayu Wan 1 Liangbing Hu 1
1University of Maryland, College Park College Park USAShow Abstract
We developed printable graphene ink through a solvent-exchange method. Printable graphene ink in ethanol and water free of any surfactant is dependent on matching the surface tension of the cross-solvent with the graphene surface energy. Percolative transport behavior is observed for films made of this printable ink. Optical conductivity is then calculated based on sheet resistance, optical transmittance, and thickness. Upon analyzing the ratio of dc/optical conductivity vs. flake size/layer number, we report that our dc/optical conductivity is among the highest of films based on direct deposited graphene ink. This is the first demonstration of scalable, printable, surfactant-free graphene ink derived directly from graphite.
9:00 AM - LL5.10
Laser-Assisted Processing of Current and Next Generation Transparent Electrodes for Flexible Optoelectronic Device Applications
David Jen Hwang 1 Pyung-cho Han 1 Hwan Lee 1 Andrew Mann 1 Tao Zhang 1
1State University of New York at Stony Brook Stony Brook USAShow Abstract
Transparent electrode is a critical component to realize modern optoelectronic devices including display, touchpad, and solar cells. While the most commonly used transparent electrode up to date is thin metal oxide film as Indium Tin Oxide (ITO) due to its superior optical transparency and electrical conductance, its brittleness and lithographic difficulty have posed major challenges in manufacturing cost-effective flexible optoelectronic devices.
In this study, we firstly attempt to address the aforementioned issues via optimization of direct lithographic step of current generation ITO and conducting polymer films on flexible polymer substrate by direct laser scribing processes. Through rigorous parametric examination of various short pulsed lasers and commercially popular film configurations, optimized performance is demonstrated in terms of electrical isolation, minimal substrate damage, excellent visuality and low degree of film delamination for long-term stability. Additionally, thin coating layer of nanomaterials such as silver nanowires and carbon nanotubes as emerging alternative transparent electrodes, we will also report our recent progress on the order of magnitude improvement in the electrical performance by enhancing local connectivity within nanomaterials network utilizing a unique enhancement mechanism of laser field in the nanomaterials system. Based on advanced in-situ and ex-situ characterization results by optical and electron microscopic techniques, key improvement mechanisms are also discussed.
9:00 AM - LL5.11
Submicron Metal Lines for Transparent Electrode Using Shadow Mask Printed by Electrohydrodynamic (EHD) Process
Youngsup Song 1 Jiwon Kim 2 Sung Mook Choi 1 Kyu Hwan Lee 1 Doyon Chang 1 Jae-Hong Lim 1 Nosang V. Myung 2 Dong Chan Lim 1 Joo-Yul Lee 1
1Korea Institute of Materials Science Gyeongnam Republic of Korea2University of Californica Riverside Riverside USAShow Abstract
Transparent electrodes have been studied actively for various potential applications including touch panels, light-emitting diodes, solar cells, liquid crystal displays, etc. Indium tin oxide (ITO), the most widely used material in this area, has low resistivity and high transparency; however, researchers have tried to replace ITO due to its rarity and high cost. Metal mesh electrodes, one of the ITO substitutes, have shown promising properties comparable to those of ITO. Among many fabrication methods of metal meshes such as imprinting, photolithography, and ink-jet printing, etc., electrohydrodynamic (EHD) jet printing have been attracting attention because the techniques has many advantages including simple process, high resolution, and the ability to control the optical and electrical properties by adjusting metal-grid pitch and width. However, its resolution is still limited to a few microns. Also, due to EHD printing utilizes inks with metal nanoparticles, printed lines need high-temperature sintering process, and the lines with nanoparticles have worse electrical conductivity than that of lines deposited by vacuum process. Here, we developed a novel fabrication method of submicron metal lines by the combination of vacuum and EHD processes. The shadow masks are prepared by EHD process with viscous solutions such as glycerol, diffusion pump oil, and photoresist on top of glass substrate. High viscosity is important for stable jetting of shadow mask, and low vapor pressure is required not to be evaporated at the following vacuum process. Metals like Cu, Ag are then deposited by evaporation or sputtering process followed by the removal of shadow masks with a proper etchant for used materials. Nano gaps between shadows masks are formed and controlled by nano stage. The pitch and width of polymer-based lines defines width and gap of metal lines, respectively. It is expected that our method could be widely adopted for applications, which need high transparency and electrical conductivity.
9:00 AM - LL5.13
Nanostructured Metallic Thin-Film Transparent Conductor
Wei Wu 1 Nancy Tassi 1
1DuPont Wilmington USAShow Abstract
Transparent conductors can be applied into a myriad of applications, ranging from touch screens, to thin-film PVs. Currently the vast majority of the market is dominated by ITO, which has developed for decades with a good tradeoff of optical transmittance and electrical conductance. However, with the increasing demands of TCs, the use of ITO will have several limitations, such as the scarce indium supply, the high cost, and brittleness. A lot of alternative TCs have been proposed and developed, such as carbon nanotubes, silver nanowires and nanoparticles, copper nanowires and nano-fibers, conductive polymers, metal meshes and recently graphene. In this talk, we will present using nanostructured thin metallic film as a transparent conductor structure. We&’ll show how we optimize the optical transmission and sheet resistance of the structure using 3D optical and electrical modeling methods. We&’ll also compare the results with other high performance transparent conductors, and indicate the possible enhancement mechanism from our nanostructure design.
9:00 AM - LL5.14
Transparent Conducting TiNx/TiO2 Hybrid Film Deposited by Atmospheric Plasma on Plastics
Siming Dong 1 Makoto Watanabe 1 2 Reinhold H. Dauskardt 1
1Stanford University Stanford USA2High Temperature Materials Unit, National Institute for Materials Science Ibaraki JapanShow Abstract
We report on the successful deposition of transparent TiNx/ TiO2 hybrid conductive thin films on polycarbonate (PC) using atmospheric plasma. A specialized high-temperature precursor delivery system was employed using a titanium ethoxide precursor, helium delivery and primary plasma gas, and a nitrogen secondary plasma gas. The hybrid film chemical composition, deposition rate, optical and electrical properties as well as adhesion energy with the polycarbonate substrate were investigated as a function of plasma power and gas flow rate. The film deposited was a hybrid of amorphous TiNx and a Rutile phase of TiO2. The TiNx content increased with higher plasma power and nitrogen flow rate. The visible transmittance varied from 71% to 83% and increased as either the plasma power decreased or nitrogen flow rate decreased. The hybrid thin film resistivity was in the range of 101-105 ohm cm and a lowest 8.5×101 ohm cm resistivity was achieved without annealing. The adhesion energy on the polycarbonate ranged from 1.2 J/m2 to 8.5 J/m2 with increasing plasma power and decreasing nitrogen flow rate. We further demonstrated that annealing and adding of H2 into the primary plasma gas had a significant influence on the composition and resistivity of the hybrid film. After annealing, the resistivity of the thin film decreased to 6.1×10-1 ohm cm. Processing conditions for the optimum combination of the high optical transmittance TiO2 phase and the high electrical conductivity of the TiNx was determined. The study reveals a promising new way to fabricate transparent conductive thin film with low cost.
9:00 AM - LL5.15
Buffer and Anode Integrated Ta-Doped In2O3 Electrodes Prepared by Co-Sputtering for PEDOT: PSS-Free Organic Solar Cells
Hye-Min Lee 1 Da-young Cho 1 Ki-Won Seo 1 Hyo-Jung Kim 1 Yong-Jin Noh 2 Seok-In Na 2 Kwun-Bum Chung 3 Han-Ki Kim 1
1Kyung Hee University Yongin Republic of Korea2Chonbuk National University Jeonju Republic of Korea3Dankook University Cheonan Republic of KoreaShow Abstract
We developed poly (3,4-ethylene dioxylene thiophene):poly (styrene sulfonic acid) (PEDOT:PSS)-free organic solar cells (OSCs) using buffer and anode integrated Ta-doped In2O3 (ITaO) electrodes. To optimize the ITaO electrodes, we investigated the effect of Ta2O5 doping power on the electrical, optical, morphological, and structural properties of the co-sputtered ITaO films. In addition, optical properties and electronic structure for as-deposited and annealed ITaO films prepared at optimized doping power were measured by spectroscopic ellipsometer and X-ray absorption spectroscopy. The optimized ITaO film doped with 20W Ta2O5 radio frequency power showed sheet resistance of 17.11 Ohm/square, a transmittance of 93.45 %, and a work function of 4.9 eV, all of which are comparable to the value of conventional ITO electrodes. The conventional bulk heterojunction OSC with ITaO anode showed a power conversion efficiency (PCE) of 3.348 % similar to the OSCs (3.541%) with an ITO anode. In addition, OSCs fabricated on an ITaO electrode successfully operated without an acidic PEDOT:PSS buffer layer and showed a PCE of 2.634 %, which was much higher than the comparable no buffer OSC with an ITO anode. Therefore, co-sputtered ITaO electrodes simultaneously acting as a buffer and an anode layer can be considered promising transparent electrodes for cost-efficient and reliable OSCs because they can eliminate the use of an acidic PEDOT:PSS buffer layer.
9:00 AM - LL5.16
Transparent MoO3 Graded ITO Films for Use As HIL and Anode Integrated Electrodes for Phosphorescent Organic Light Emitting Diodes
Hye-Min Lee 1 Da-Young Cho 1 Ki-Won Seo 1 Hyo-Jung Kim 1 Han-Ki Kim 1
1Kyung Hee University Yongin Republic of KoreaShow Abstract
We investigated characteristics of MoO3-graded ITO films for use as hole injection layer (HIL) and anode integrated electrode for organic light emitting diodes (OLEDs). By combining a high work function of MoO3 (6.2-6.6 eV) and highly conductive ITO, we fabricated high work function MoO3-ITO multicomponents electrodes acting as HIL and anode simultaneously in OLEDs. Thin MoO3 layer co-sputtered on the ITO films with graded content showed a low sheet resistance and a high transmittance as well as high work function acceptable values in fabrication of OLEDs. In particular, effect of MoO3 thickness on the electrical, optical, morphological, and structural properties of MoO3 graded ITO anodes was investigated in detail to optimize the MoO3 graded layer. At optimized co-sputtering conditions, we obtained MoO3 graded ITO electrodes with a low sheet resistance of 13 Ohm/square and a high optical transmittance of 83%, comparable to conventional ITO films. Due to the existence of MoO3 on the ITO film, we can fabricate phosphorescent OLEDs without a HIL. The OLEDs fabricated on MoO3 graded ITO electrodes showed an identical current density-voltage-luminance and efficiencies to OLEDs with HIL and ITO anode due to the low sheet resistance, high transmittance, and high work function of MoO3 graded ITO films. This indicates that the MoO3 graded ITO films fabricated by co-sputtering is a promising integrated electrode to remove the use of HIL in the OLEDs.
9:00 AM - LL5.17
Self-Formed Cu/C Core/Shell Electrospun Nanofibers for Oxidation-Resistant Transparent Electrode
Dae-Hyun Nam 1 Ji-Hoon Lee 1 Na-Rae Kim 1 Yoo-Yong Lee 1 Han-Wool Yeon 1 So-Yeon Lee 1 Young-Chang Joo 1
1Seoul National University Seoul Republic of KoreaShow Abstract
Demand for transparent electrodes with high electrical conductivity and transmittance has been recently increased. 1-D nanostructured metals have drawn great attention as a replacement of sputtered ITO. Among them, Cu nanofiber formed by electrospinning is expected to be most suitable for transparent electrode due to its high electrical performance and cost-efficiency. However, high oxidation tendency of Cu hinders the application as nanostructured form whose surface to volume ratio is high. There were previous attempts to enhance oxidation stability of Cu nanostructures by coating outer shell with ALD or plating. The limit of these approaches was that additive materials and inefficient process were needed after electrospinning and calcination.
We developed a novel method of self-forming outer protective carbon shell to prevent oxidation of electrospun Cu nanofiber. It can be realized with the atomic diffusion of original components by controlling oxygen partial pressure(PO2) during calcination without any additional materials and processing. Electrospinning proceeded with the solution composed of copper acetate(CuAc) as metal precursor and polyvinyl alcohol(PVA) as polymer matrix. After electrospinning, calcination of as-spun nanofibers proceeded at 700°C by modulating PO2 with the insertion of oxygen gas. Phase transformation of Cu and quantitative degree of C decomposition were analyzed by XRD and XPS.
Systematic categorization about the effect of PO2 on calcination was established from the principle that C has higher oxidation tendency than Cu. Especially, calcination under specific PO2 range between them induced simultaneous oxidation of C and reduction of Cu. Pressure between 1.0×10-2 and 1.0×10-1 Torr was suitable for this phenomenon called selective oxidation. In this range, Cu phase without oxide was observed unlike calcination under air which induces oxidation of Cu. Also, weight percent of C in nanofiber decreased with the increase of PO2. It proves that C is decomposed by oxidation based combustion, not pyrolysis. In selective oxidation, various Cu/C nanostructures can be formed by inducing the growth of void inside nanofiber according to the degree of C decomposition. At the lowest PO2, structure with small Cu agglomerates outside nanofiber was obtained. However, Cu/C core/shell was self-formed at 2.5×10-2 Torr by the formation of void and inner diffusion of Cu. As PO2 increased further, thickness of C shell gradually decreased to form hollow C nanofiber with outward Cu diffusion and agglomeration. Nanostructures dominantly affected electrical properties that core/shell structure showed electrical conductivity with sheet resistance(Rs) as 250Omega;/sq with 65% transmittance. Oxidation resistance of self-formed Cu/C core/shell nanofiber was demonstrated by within 10% increase of Rs during 28 days in atmosphere. Oxidation resistivity under high temperature and humidity condition is discussed.
9:00 AM - LL5.18
Surface Roughness and Electrical Stability of Silver Nanowire Transparent Electrodes
Hadi Hosseinzadeh Khaligh 1 Irene A Goldthorpe 1
1University of Waterloo Waterloo CanadaShow Abstract
We have fabricated silver nanowire transparent and flexible electrodes with a sheet resistance of 9 Omega;/sq at a transparency of 90%. Although these resistance and transparency values match that of ITO and are superior to most other alternative materials, there are issues that need to be addressed before the widespread use of silver nanowire electrodes in devices. In this presentation, two important issues will be discussed: surface roughness and the stability of the electrode under current flow.
When a film of silver nanowires is dispersed on a substrate and then annealed, the maximum peak-to-valley roughness can be 300 nm or more. This can cause shorting in organic optoelectronic devices where the thickness of the active layers deposited on the electrode are very thin. We will introduce a simple method to reduce maximum peak-to-valley heights to less than 15 nm, and the root-mean-square roughness to below 7 nm. Unlike other methods to reduce surface roughness, an additional material such as a polymer is not required.
I will then present the first study of the stability of nanowire electrodes during their use (i.e. when they are conducting current) . In contrast to ITO where current conducts throughout the entire area of the film, in nanowire electrodes, transport occurs only through the metal wire pathways. Because of this, current densities in the nanowires can be very high. We will show that when silver nanowire electrodes conduct current at levels typically encountered in organic solar cells, the electrodes can fail in as little as 2 days. Suggestions to improve the stability of the electrodes will be given.
 H.H. Khaligh and I.A. Goldthorpe, Nanoscale Res. Lett. 8:235 (2013).
9:00 AM - LL5.19
Fabrication of Transparent Electrodes with Silver Nanowires and PPT Gel for Organic Optoelectronic Devices
Ming-Chih Tsai 1 2 Yu-Hsuan Chen 1 3 Yu-Hsuan Ho 1 Shang-Jung Yang 1 3 Pei-Kuen Wei 1 2 3
1Academia Sinica Taipei Taiwan2National Yang-Ming University Taipei Taiwan3National Taiwan Ocean University Keelung TaiwanShow Abstract
We have developed a low cost and convenient approach to fabricate ITO-comparable transparent electrodes by using solution process of silver nanowires mixed with poly peroxotitanium acid (PPT) gels. The PPT gel is applied to connect the dispersed silver nanowires to preserve its high conductivity while remaining transparency and reducing surface roughness of the transparent electrode. The silver nanowires were synthesized via a modified polyol method, and the PPT gels were prepared by sol-gel method in appropriate concentrations. After applying the PPT gels, the sheet resistance of the transparent electrodes was improved from 192 Omega;/square to 44.7 Omega;/square with a transmittance of 81 %. And the roughness (RMS) was decreased from 106.3 nm to 48.1 nm. The PPT gel also improved the reliability of the proposed electrodes, which the conductivity was remained after general atmospheric storage of 6 months. We also demonstrate an Alq3 based OLED with the proposed transparent electrodes.
9:00 AM - LL5.20
High Haze Transparent Conducting Al-Doped ZnO: Towards Nanoscale Design of Flexible Scattering Electrodes
Paolo Gondoni 1 Piero Mazzolini 1 2 Valeria Russo 1 Annamaria Petrozza 2 Matteo Amati 3 Luca Gregoratti 3 Andrea Li Bassi 1 2 Carlo Spartaco Casari 1 2
1Politecnico di Milano Milano Italy2Istituto Italiano di Tecnologia Milano Italy3ELETTRA - Sincrotrone Trieste Trieste ItalyShow Abstract
New generation photovoltaic devices require indium-free transparent electrodes synthesizable at room temperature with multiple functional properties, including large surface area, mechanical flexibility and effective light management. Aluminum doped zinc oxide (AZO) has been identified as a promising low cost material to address these requirements.
To combine these properties while maintaining a fine control of optical transparency, electrical conductivity and morphology we exploit the versatility of Pulsed Laser Deposition (PLD) at room temperature. By varying the background O2 pressure during deposition it is possible to tailor nano- and mesoscale morphology and stoichiometry, obtaining compact transparent conductors with state of the art functional properties (ρ < 5x10-4 Omega; cm, visible T>85%) or hierarchically assembled mesoporous structures with tunable light scattering (haze factor >80%, with T>85%). The compatibility with flexible devices, ensured by room temperature deposition, has been tested by performing the depositions also on ethylene-tetrafluoroethylene (ETFE) substrates.
The goal of combining all the properties of interest into a multiply functionalized material is pursued by achieving separate control of mesoscale morphology and defect (Zn interstitial, O vacancy) concentration. One way to attempt this is chemically based, by performing depositions in a mixed Ar:O2 atmosphere to permit clustering and hierarchical assembly (Ar partial pressure) and, simultaneously, stoichiometry control (O2 partial pressure). This kind of approach, together with investigation of thermal treatments in vacuum, air or inert atmosphere, allows to study the role of oxygen vacancies and dopants (intentional and unintentional) in determining functional properties. With respect to this approach, the nanostructures were also characterized by Scanning Photo Electron Microscopy with synchrotron radiation in order to investigate preferential electron transport properties in the cross-plane direction, and how they are related with elemental (Al, Zn, O) distribution and local chemical bonding: the vertical conductivity along the nanotrees was studied through the charge induced shift of the core levels, and a significant Al concentration at the top of the structures (i.e., on the film surface) was discovered, almost irrespectively of deposition conditions.
Another approach consists in the synthesis of graded architectures consisting of a porous layer evolving into a compact layer, which can be obtained in a single deposition process by varying the background pressure during film growth. Optimized graded AZO films have a resistivity of the order of 10-3 Omega; cm, a mean visible transparency of 80%, with a haze over 40%. The benefits of haze for application in photovoltaic devices have been tested by measuring a 100% increase in the absorption of a low bandgap polymer employed in organic photovoltaics (PCPDTBT) in the spectral regions where haze is maximum.
9:00 AM - LL5.21
High Performance Flexible Transparent Conductive Film with Silver Nanowires on Various Substrates
Hanleem Lee 1 Hyoyoung Lee 1 2 3 Youghun Shin 1 Heejoun Yoo 1 Yeoheung Yoon 1 Doyoung Kim 1 Shahbaz Khan 1
1Sungkyunkwan University Suwon Republic of Korea2Sungkyunkwan University Suwon Republic of Korea3Sungkyunkwan University Suwon Republic of KoreaShow Abstract
Recently, silver nanowires (AgNWs) have intensively studied as an ITO substitute in the field of touch screen, light emitting device, solar cell, and flexible displays. In spite of their numerous advantages such as high conductivity, flexibility, low percolation thresholds, several issues still remain unresolved. a) Effective passivation and b) ohmic contact on junction side is considered the influential factor to produce high performance AgNWs based application.
Firstly, effective passivation using protecting layer is essential on AgNWs based film because of their poor oxidative stability by humidity, light, heat, or acidic gases. Polymer composite (ex) PEDOT:PSS, Teflon), which is one of the most well-known protecting materials, can passivate conductive nanowires. However, the problem is that protecting layer increase resistivity by openning the gap between two nanowires. In here, we propose a new approach to prepare novel AgNW transparent conductive film using aqueous graphene oxide (GO) nanosheets as a protecting layer. Hydrophilic, ultrathin, highly dispersible GO can have strong adhesion to the oxygen plasma treated PET owing to hydrophilic-hydrophilic interaction and it results to low sheet resistance, high uniformity, high transmittance, and strong mechanical stability.
Secondly, ohmic contact on junction side should be obtained. Resistivity of AgNWs&’ network mainly depends on number of junction and/or state of junction. If AgNWs are incorporated in the substrate or laid on attractive substrate, there is no problem. Junction of nanowire will be close enough so that resistivity, transmittance, mechanical property of film will be enhanced. In case of PDMS, however, it is hard to fabricate uniform and stable thin electrode on account of hydrophobic nature of that. So, we focus on modifying PDMS surface with various silane compounds to facilitate the realization of highly stretchable transparent electrode. As a result, well ordered and high density coordination-type bond between functional group of silane on PDMS surface and AgNW prevents self-healing ability of PDMS and leading to low resistivity with high transparency and good strechability.
9:00 AM - LL5.22
Optical and Electronic Properties of Two-Dimensional Ti3C2 Epitaxial Thin Films
Joseph Halim 1 2 3 Maria Lukatskaya 1 2 Kevin Cook 1 2 Jun Lu 3 Cole Smith 1 Lars-Ake Naeslund 3 Steve May 1 Lars Hultman 3 Yury Gogotsi 1 2 Per Eklund 3 Michel Barsoum 1
1Drexel University Philadelphia USA2Drexel University Philadelphia USA3Linkamp;#246;ping University Linkamp;#246;ping SwedenShow Abstract
Two-dimensional (2D) materials receive growing interest because of their unique properties as compared to their bulk counterparts. Although graphene has garnered the lion&’s share of this attention, other 2D materials beyond MoS2 and BN are being sought out. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2C, Ti3C2, Ti3CN, V2C, Nb2C, Ta4C3 and more) known as MXenes has been discovered. Herein we show the fabrication of a 2D epitaxial Ti3C2 thin film, formed by the selective etching of Al from magnetron sputter-grown Ti3AlC2. The etching was carried out at room temperature and using two different aqueous etchants: hydrofluoric acid and ammonium hydrogen difluoride. Morphological, chemical and phase characterization for these films were carried out using XRD, XPS, TEM, and SEM. The optical transmittance, electrical resistivity, and magnetoresistance of the films were also measured. These data show that the films are up to ~ 90% transparent in the visible to infrared range, and that metallic-like conductive behavior is exhibited down to ~ 100 K. At temperatures below 100 K, resistivity of the films increased with decreasing temperature and magnetoresistance proved to be negative, due to a weak localization phenomenon characteristic of 2D films. These results illustrate the potential for the use of Ti3C2 thin films as transparent conductive electrodes, as well as in electrical, photonic and sensing applications.
9:00 AM - LL5.23
Effects of UV Illumination and Thermal Treatment in Hydrogen on Electrical Conductivity of Solution-Processed ZnO Film
JeongSoo Hong 1 Hajime Wagata 2 Naoki Ohashi 3 Ken-ichi Katsumata 1 Kiyoshi Okada 1 Nobuhiro Matsushita 1
1Tokyo Institute of Technology Yokohama Japan2Shinshu University Nagano Japan3National Institute for Materials Science Tsukuba JapanShow Abstract
Functional transparent conductive oxide (TCO) films have been used for various applications. Among the TCO materials, zinc oxide (ZnO) is one of superior candidates as alternative materials for ITO due to their several merits such as low cost of raw material and wide band gap energy (~ 3.7 eV).
We succeeded in preparing ZnO films by environmentally friendly solution process named “Spin-Spray”. Spin-spray method enables us to deposit a high-quality crystallized ZnO films at low substrate temperature (< 100oC) without seed layer. As-deposited ZnO films had a high transmittance above 80 % and good film adhesion. Also, they could exhibit a high conductivity after UV illumination due to the doping of C and H which were generated by decomposing organic substance.
In this study, the effects of thermal treatment in hydrogen to the electrical conductivity of ZnO films were investigated. After UV illumination, as-deposited ZnO films indicated a very low (#8786; 1 cm2 V-1 s-1) which carrier concentration (> 1019 cm-3) was high. To improve the mobility, as-deposited ZnO films were thermally treated in hydrogen atmosphere before or after UV illumination.
The source solution was prepared dissolving 10 mM of Zn(NO3)26H2O in 1 L of de-ionized water and the reaction solution was prepared dissolving NH3 and 4 mM C6H5Na3O7 in the same amount of de-ionizes water. ZnO films were deposited by spraying these solutions onto heated glass substrates at 95oC. As-deposited ZnO films were subjected thermal treatment in hydrogen atmosphere at 100oC for treatment time of 0.5, 1, and 2, 3 h and UV illumination by black-light-blue lamp for 24 h. The two kinds of post treatments were done in the different order as follows
P1) UV illumination → Thermal treatment, P2) Thermal treatment → UV illumination
After two kinds of processes, there were not noticeable changes in structural properties and ZnO films still exhibited a high transmittance above 80 % regardless of thermal treatment. In case of resistivity, the mobility of P1) increased, but the resistivity was increased (11 Omega;cm) due to the drastic decrease of carrier concentration (~1017 cm-3). On the other hand, the resistivity of P2) decreased to ~10-3 Omega;cm due to the increase of mobility (#8786; 8 cm2 V-1 s-1) keeping the carrier concentration about ~1019 cm-3. These improved results seemed to be attributed to the reduction of the electron trap density at grain boundary.
9:00 AM - LL5.24
The Effects of Thickness of Al and Ga Co-Doped ZnO Films Grown by Linear Facing Target Sputtering for GaN-Light Emitting Diodes
Ki-won Seo 1 Da-Young Cho 1 Hye-Min Lee 1 Hyo-Jung Kim 1 Kwon-Bum Chung 2 Han-Ki Kim 1
1Kyung Hee university Yongin-si Republic of Korea2Dankook University Chenan Republic of KoreaShow Abstract
We investigated the effects of thickness on the electrical, optical, structural, and morphological properties of Al and Ga co-doped ZnO films (AGZO) grown by Linear Facing Target Sputtering (LFTS) for use as a transparent electrode in GaN-light emitting diodes (LEDs). Below a critical thickness of 200 nm, the resistivity and optical transmittance of the AGZO films were significantly affected by the thickness of the AGZO films. However, above a thickness of 200 nm, the AGZO films had similar resistivities and optical transmittances due to the stable columnar structure, which developed at a thickness of 200 nm. Due to the change of the growth mode with increasing thickness, the microstructure and surface morphology were also affected by the film thickness. Based on the figure of merit values, we determined that the optimized thickness of the LFTS-grown AGZO film was 200 nm, which was applied in a GaN-LED as a transparent anode. Successful operation of GaN-LEDs with an optimized AGZO film without plasma damage indicates that the LFTS-grown AGZO film is promising plasma damage-free anode for use in GaN-LEDs.
9:00 AM - LL5.25
Transparent TIO/Ag NW/TIO Hybrid Electrode Grown on PET for Flexible Organic Solar Cell
Ki-won Seo 1 Da-Young Cho 1 Hye-Min Lee 1 Hyo-Jung Kim 1 Han-Ki Kim 1
1Kyung Hee university Yongin-si Republic of KoreaShow Abstract
We fabricated highly transparent Ti doped In2O3 (TIO)/Ag nanowire(NW)/TIO (TAT) multilayer electrodes by Linear Facing Target Sputtering (LFTS) and brush-painting for used as anode flexible organic solar cells(FOSCs). And we investigated the TAT transparent anode as a function of number of brush-painting cycles. We achieved highly flexible TAT multilayer electrodes with a low sheet resistance of 9.01 Omega;/square and a high diffusive transmittance more than 80 % in visible region as well as superior mechanical stability. The effective embedment of the Ag NW network between top and bottom TIO films led to a metallic conductivity, high transparency. Due to the inserting Ag NW between TIO layers, we increased mechanical stability and confirmed by structural properties by FE-SEM, HRTEM, XRD analysis. Based on the figure of merit values, we determined that the optimized cycle of brush painting, which was applied in FOSCs. Successful operation of FOSCs with efficiency of 3.01 % indicates that TAT hybrid electrode is a promising alternative to conventional ITO electrode for high performance FOSCs.
9:00 AM - LL5.26
Investigating Critical Factors for Improving Charge Carrier Transport Across Interfaces between a Hybrid Transparent Conductive Electrode (TCE) and Organic Materials in Flexible Organic Light Emitting Diodes (f-OLED)
Huanyu Zhou 1 Ross E. Triambulo 1 Jin-Woo Park 1
1Yonsei Seoul Republic of KoreaShow Abstract
With increasing need for flexible organic electronics, efforts are made to develop new TCE that are highly flexible and have functional properties better than indium tin oxide (ITO). Among various candidates, graphene and nanowire random networks have shown most promising properties on flexible substrates. However, electric short and nonuniform functional properties over large areas due to structural discontinuities delay their successful integration in flexible organic devices. Alternatively, we studied hybrid TCE (h-TCE) of nanowires and transparent conductive oxides (TCO). TCO coated between and over nanowires improve the nonuniform properties of nanowires, and the nanowires reinforce functional and mechanical properties. But, there is little understanding about the characteristics of charge carriers and transport mechanism of h-TCE interfacing with organic materials that are essential for designing h-TCE and interfaces in real devices. Here, we investigated the charge carriers and transport in h-TCE of Ag nanowires (AgNWs)-ITO integrated in f-OLED and compared them with those in ITO. On polyethylene terephthalate (PET) substrates, we fabricated 100 nm ITO films and Ag nanowires (AgNWs)-ITO h-TCE. In h-TCE, 30 nm-thick ITO was sputtered on AgNWs-coated PET. The wire density and degree of crystallinity of ITO were varied by controlling processing conditions. TCE is used as an anode in f-OLED. As a hole transport layer (HTL) on top of TCE, we spin-coated PEDOT:PSS. Using Hall measurement, the carrier density and mobility in ITO and h-TCE were analyzed. Chemical reaction and diffusion on the surface and across interfaces between TCE and HTL and the changes in energy structures with variations of ITO crystallinity and wire densities were investigated by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), respectively. Analysis results showed that the carrier density in TCE is a dominant factor for device performance when others are fixed, which is determined by the ITO crystallinity. The degree of crystallinity increases with wire density as AgNWs act as crystalline seeds. Thus, h-TCE showed superior electrical properties to ITO. XPS and UPS results revealed that diffusion of In and Sn into HTL and chemical reactions at interfaces are reduced with crystallinity as adhesion between ITO and AgNWs and the cohesion strength of ITO on the surface increase with crystallinity. Overall, the carrier density, mobility, and carrier transport are significantly affected by the microstructure of ITO matrix and surface morphology of h-TCE, which provides great possibilities of further improvement in the electrical properties of TCEs by controlling deposition processes, the density and alignment of AgNWs. We also successfully fabricated h-TCE making f-OLED perform significantly better than with ITO.
9:00 AM - LL5.27
Highly Flexible Metal-Oxide Hybrid Transparent Electrodes (TCE) for Application in Flexible Organic Light-Emitting Diodes (f-OLED)
Hahn-Gil Cheong 1 Ross E. Triambulo 1 Jin-Woo Park 1
1Yonsei University Seoul Republic of KoreaShow Abstract
As electrical interconnections in various photovoltaic devices, indium tin oxide (ITO) is the most extensively used transparent conductive oxide (TCO). However, increasing cost and brittleness of ITO must be constantly addressed, with new TCE materials needed to replace ITO for the applications in flexible electronics. Among the new TCEs developed for ITO replacements, Ag nanowire networks (AgNWs) not only exhibit improved functional properties but also greater flexibility than ITO. In addition, AgNWs can be coated onto large-area flexible polymer substrates using new solution coating technologies. However, AgNWs have drawbacks such as electrical shorts at the ends of disconnected wires and nonuniform functional properties over large areas. We propose a hybrid TCE (h-TCE) using AgNWs and TCO. For the TCO and polymer substrate, we selected ITO and polyethylene terephthalate (PET), respectively, because commercial roll-type PET substrates with ITO are available as reference materials. ITO was sputtered atop the AgNWs coated PET. In AgNWs-ITO h-TCE, ITO thickness was less than a third of the commercial ITO on PET. According to our microstructural analysis, uniform ITO coatings over and between AgNWs were obtained. ITO atop the AgNWs grew into perfectly crystalline ITO (c-ITO) with AgNWs acting as crystalline seeds, and the degree of crystallinity between and over the AgNWs could be controlled by sputtering conditions. The degree of ITO crystallinity determined the functional properties and flexibility of h-TCE based on our 4-point probe station and bending test measurements. The nonuniform functional properties over large areas was significantly reduced and the electrical conductivity of h-TCE was comparable to that of AgNWs without ITO. Increasing ITO crystallinity and thickness, conductivity of h-TCE improved further, which confirmed that properly welding junctions between AgNWs by ITO reduced the local disconnections in the network, which is the critical factor for improving conductivity through networks. Like AgNWs without ITO, decrease in conductivity of h-TCE under tension at the bending radius (r) down to 5 mm was negligible. Below 5 mm, the degree of ITO crystallinity significantly affected the bending stability of h-TCEs. The cohesion strength of ITO and the adhesion between AgNWs and ITO increased with ITO crystallinity. Therefore, at a critical stress, largely amorphous ITO delaminated from interfaces with AgNWs, and AgNWs become free of the stress, which resulted in a gradual decrease in conductivity with further decreases in r below 5 mm. In contrast, AgNWs were broken with c-ITO without delamination at interfaces. Hence, conductivity abruptly decreased at a critical r when the matrix was c-ITO. We successfully fabricated f-OLEDs on h-TCE with significantly better performance than on ITO. The performance was well maintained under bending, while that on the homogeneous ITO was significantly degraded by ITO cracking.
9:00 AM - LL5.28
Indium Tin Oxide Thin Films Deposited at Low Temperature Using Dual Ion Beam Sputtering
Wilhelmus J Geerts 1 Nelson A Simpson 1 Alan D Woodall 1 Maclyn Stuart Compton 1
1Texas State University San Marcos USAShow Abstract
Indium Tin Oxide (ITO) is a transparent conducting oxide that is used in flat panel displays and optoelectronics. Highly conductive and transparent ITO films are normally produced by heating the substrate to 300 degrees Celsius during deposition excluding plastics to be used as a substrate material. We investigated whether high quality ITO films can be sputtered at room temperature by using atomic oxygen instead of molecular oxygen during sputter deposition. The films were deposited by dual ion beam sputtering (DIBS) in a vacuum chamber with a background pressure less than 1.3 E-7 Torr. A high energy RF ion beam source with focused dual grid ion optics operating at 850 volts was used to create an argon beam incident at 45 degrees on the target material (RF-power: 80 Watt, 15 sccm Ar, 60 mA screen grid). During deposition, the substrate was exposed to either atomic or molecular oxygen. The atomic oxygen was created with a HD25 radical atom source of Oxford Applied Research (RF power: 200 Watt). A high voltage deflector was used to deflect the ions, so the substrate would only be exposed to neutral atoms (ratio of atomic oxygen to molecular oxygen = 0.6 ). Samples were made as a function of the oxygen flow rate (1-5 sccm). Glass microscope slides and (100) silicon wafers were used as substrates. All substrates were covered with a thin layer of SiO2 before depositing the ITO films and were rotated during deposition. The depositions were done at room temperature.
AFM measurements revealed that the samples had an rms roughness below 3 nm. XRD 2-theta scans showed no diffraction peaks, indicating that the crystals in our films were very small. The optical properties were measured by an M2000 Woollam spectroscopic ellipsometer and are best described by the combination of a Tauc-Lorentz contribution, a Gaussian contribution, and a Drude contribution. Film thickness and absorption spectra were calculated from the measured optical data. A lower absorption was observed in films sputtered at larger oxygen flow rates and films sputtered with atomic oxygen.
The electrical properties of the ITO films were measured by linear four point probe using a Jandel 4pp setup employing silicon carbide electrodes, high input resistance, and low bias current buffer amplifiers. The resistivity of the samples sputtered with atomic oxygen appeared to be consistently lower than the resistivity for the samples made with molecular oxygen, achieving a minimum value of 2.67E-3 Ohm cm. This value is comparable to what has been obtained by others using ion beam sputtering.
The figure of merit (FOM), i.e. the ratio of the conductivity and the average optical absorption coefficient (400-800 nm), was calculated from the optical and electric properties and appeared to be 1.2 to 5 times higher for the samples sputtered with atomic oxygen. The largest value obtained for the FOM was 0.08 reciprocal Ohms.
 Oxford Applied Research fact-sheet HD25.
9:00 AM - LL5.29
Characterization of AZO/Silver Nanowire/AZO Multilayer as Transparent Conductive Thin Films by Varying the Content of Ag Nanowire
Hak-jun Chung 1 Ju Hwan Choi 1 So-Ra Jang 1 Jin-Koog Shin 1 Won-Jong Choi 2 Sang-Hoon Lee 2
1Korea Electronics Technology Institute Jeonju Republic of Korea2Nanopyxis Jeonju Republic of KoreaShow Abstract
Transparent conductive thin film (TCF) is at the center of attention between various layers of materials that make up electronic devices such as Display and Solar cell. Especially, The Indium Tin Oxide (ITO) layer has been applied to variety of display and electronics components such as flexible displays, smart windows, touch panels, solar cells, etc.
However, ITO films cannot meet the requirements for low cost electronics device due to its expensive raw materials. In recent years, several candidates to replace ITO films has heavily been investigated for transparent conductive material with surface resistance 100Omega;/square or less and more than 85% transmission.
In this study, we have investigated the possibilities of conductive oxide and Silver nanowire multilayer as transparent conductive thin films for replacing ITO film and simultaneous satisfying requirements for flexible electronic devices. These multilayer structured TCF were fabricated that consists of the multiple AZO conductive oxide layers and inserted silver nanowires, in which sliver nanowire was coated with dispersion of sliver nanowire.
At first, AZO(ZnO 97 wt% : Al2O3 3wt%) layer was deposited by RF plasma sputtering of about 50 nm on the substrate . On top of the conductive oxide layer, silver nanowires layer was coated by printing method. Finally, the 50nm AZO(ZnO 97 wt% : Al2O3 3wt%) film deposited on top of the silver nanowires layer to form multilayer transparent conductive thin films. The properties of this multilayered TFC have shown large variation by changing content of silver nanowires at 0.5, 1.0, 2.0 wt%
Characterizations of multilayer transparent conductive thin films were analyzed by surface resistivity and transmittance, surface flatness using 4-point probe, UV-Vis, SPM, SEM.
Acknowledgement : This research was financially supported by the Ministry of Trade, Industry & Energy(MOTIE), Korea Institute for Advancement Of Technology(KIAT) (project No. R0002275)
 I. Crupi, S. Boscarino, V. Strano, S. Mirabella, F. Simone, A. Terrasi, Thin Solid Films 520(2012), 2012, 2, pp.4432-4435.
 Jong-Wook Lim, Da-YoungCho, Jihoon-Kim, Seok-InNa, Han-KiKim, Solar Energy Materials & Solar Cells 107 (2012),
2012, 8, pp.348-354.
 Hong-Chol Chae, Chang-Hyun Baeg, and Joo-Wha Hong, Kor. J. Met. Mater., Vol. 49, No. 2, pp. 192~196
 Liangbing Hu, Han Sun Kim, Jung-Yong Lee, Peter Peumans, and Yi Cui, ACS Nano 2010, 4, 11, pp.2955-2963
 Ya-Jun Zhang, Hong-Bea Kim, and Sang-Yeol Lee, J. KIEEME, Vol. 26, No. 7, July 2013, pp. 510-514.
9:00 AM - LL5.30
Fabrication of Highly Bendable Organic Solar Cells Using Silver Nanomesh Electrodes on Plastic Substrates
Dong-Ho Kim 1 Myungkwan Song 1 Dae-Geun Choi 2
1Korea Institute of Materials Science Changwon Republic of Korea2Korea Institute of Machinery and Materials Daejeon Republic of KoreaShow Abstract
Transparent conducting electrode (TCE) is one of key materials for optoelectronic devices such as flat panel displays and thin film solar cells. Although metal oxide (ITO or Al, Ga-doped ZnO) thin films are currently adopted in those industries, the issues of cost and flexibility drive to develop alternatives. In this purpose, carbon-based nanomaterials such as CNT and graphene attracted much attention. Recently, Ag nanowire is emerging as a prominent material as TCE. There are many papers reporting successful fabrications of electronic devices adopting Ag NWs electrodes. We have also successfully demonstrated flexible organic solar cells using Ag NWs [M. Song et al, Adv. Funct. Mater. 2013, 23, 4177]. The results were quite promising to show the potential of OPV devices as next generation solar cells, being cost-effective and flexible. Further enhancement of solar cell efficiency can be expected with the design of electrode and the incorporation of plasmonic effects. In this analogy, we are trying to use metallic nanomesh as TCE for OPV devices. Several types of Ag nanomesh were designed and prepared on PES substrates by transfer printing method. Our preliminary results show that Ag nanomesh with a line width of 150 nm and line spacing of 1.6 mu;m has a good performance as TCE comparable to ITO and Ag NWs. The inverted-type OPV cells using a low band gap polymer (PTB7/PC71BM) blend exhibit a power conversion efficiency of 7.2%. More scientific analysis including plasmonic effects will be given at the presentation.
9:00 AM - LL5.31
Centrifuge Coating for Solution Processing of Nanostructured Transparent Electrodes
Yan Yan Shery Huang 1 Eugene Terentjev 2
1University of Cambridge Cambridge United Kingdom2University of Cambridge Cambridge United KingdomShow Abstract
We demonstrate a new solution-based coating process, centrifuge coating, for the fabrication of nanostructured conductive layers over large areas. This coating procedure can be applied to 1-dimensional nano- filaments as well as 2-dimensional nano-layers, with the added benefit of minimizing materials wastes resulting from particle re-aggregation. Alongside with fabrication improvement, a theoretical model is developed to account for the sheet resistance exhibited by layered random-network coatings such as nano-filaments and graphene; in particular, it allows the correlation of the commonly observed scaling regimes to the coating microstructure. We also show a refined setup which allows the determination of curvature- dependent sheet resistance. This simple setup can be used to minimize the discrepancy in the measured electromechanical performance for flexible electronics.
9:00 AM - LL5.32
Nanostructured, ITO-Free Electrodes for OLED Emission Control
Arfat Pradana 1 Christian Kluge 1 Martina Gerken 1
1Christian-Albrechts-Universitamp;#228;t zu Kiel Kiel GermanyShow Abstract
Nanostructuring the thin-film layer stack of an organic light-emitting diode (OLED) is a promising approach for emission control. Emission efficiency may be improved and light may be guided to specific emission angles using a periodic grating nanostructure. The most common approach in fabricating nanostructured OLEDs is nanostructuring the indium tin oxide (ITO) layer. The refractive index contrast between ITO and the subsequent organic layers allows for efficient grating scattering. Due to the mechanical rigidity of ITO, other transparent electrode materials need to be considered for mechanically flexible, nanostructured OLEDs. Here, we present a flexible, nanostructured OLED employing a nanostructured composite organic-inorganic base layer in combination with a conductive polymer layer.
TiO2 nanoparticles were blended into a nanoimprint polymer resist. This yields an inorganic-organic composite material suitable for nanoimprint lithography with an increased optical refractive index up to n=1.86 at a wavelength of 500 nm. The composite material was spin-coated onto flexible polycarbonate (PC) substrates and imprinted with a 460-nm period grating using UV nanoimprint lithography. Subsequently, a PEDOT:PSS conductive, transparent polymer layer was processed on this base layer. The nanostructure transfers to the conductive polymer. To demonstrate the functionality of this nanostructured, flexible electrode an organic emission layer (PPV-derivative “Super Yellow”) and a metal cathode (LiF/Al) were deposited. OLED operation is demonstrated for different bending radii. The emission spectrum is characterized as a function of emission angle using a goniophotometer. The extraction of waveguide modes is observed both in electroluminescence and photoluminescence emission spectra. The waveguide mode extraction angle is demonstrated to vary with bending radius of the flexible OLED device.
The combination of an inorganic-organic composite material with a conductive polymer transparent electrode is a promising approach for improving the performance of ITO-free, flexible OLEDs. The conductive polymer provides the electrical conductivity, while the composite material may be nanostructured and provides the high refractive index necessary for emission control. Thus, the combination of the two materials may be used to replace nanostructured ITO layers.
9:00 AM - LL5.33
Sheet Resistance and Stability of Graphene Chemically Doped by Layer-by-Layer Method
Sooyeoun Oh 1 Jihyun Kim 1
1Korea University Seoul Republic of KoreaShow Abstract
Indium tin oxide (ITO) has been used as a transparent conductive electrode in liquid crystal display, solar cells, light-emitting diodes and so on, as it has excellent electrical conductivity and transparency. However, ITO suffers from high cost, limited resource, poor flexibility and complex fabrication process. Because of these limitations, many studies have been focused on carbon materials such as carbon nanotube and graphene because graphene is suitable for a transparent conductive electrode due to its high transparency, carrier mobility, flexibility and scale-ability. But its low sheet resistance compared to that of ITO needs to be improved.
We used two layered graphene grown by chemical vapor deposition method on Cu-foil. A technique of layer by layer AuCl3 (20mM) doping was previously reported to be an effective method to lower sheet resistance and maintain the stability. We investigated the doping effects on graphene with various configurations. 4-point probe, transmittance measurement, scanning electron microscopy and micro-Raman spectroscopy were performed to study optical and the electrical characteristics of the doped graphenes. We observed that the simple top-doping process is preferred because the defects may be introduced during the complex layer-by-layer doping process. The details of the results will be presented at the conference.
9:00 AM - LL5.34
Metal Embedded Grid Transparent Conductive Films for Organic Solar Cell
Jeongdai Jo 1 Jong Su Yu 1 Seong Man Yoon 1 Kwang-Young Kim 1
1Korea Institute of Machinery and Materials(KIMM) DaeJeon Republic of KoreaShow Abstract
In this paper, we report a method to fabricate roll printed and thermal roll imprinted transparent conductive films (TCFs) using Ag metal grids and embedded grids with conductive polymer. We were development a highly TCF having a roll-to-roll printability on flexible substrates. First, a gravure-offset printing method was used to fabricate Ag electrode grid layers and a electro-spray coating method was also used to form thin polymer layers with a cell structure of substrate/ Ag grids/ PEDOT:PSS. The optical transmittance and sheet resistance of Ag grid were controlled in the range of 80 ~ 83 % and 20 ~ 100 Ohm/Sq., respectively, by controlling the line width and pitch of Ag grid (30 cm x 20 cm). Second, to fabricate a high resolution imprinted TCFs, the following steps were performed: the manufacture of an electroforming stamp mold, the fabrication of thermal roll imprint (TRI) patterned plastic substrates, patterned plastic substrates filled Ag paste using a doctor blade coating, and coated with a thin film layer of conductive polymer. As a result of measuring line widths and channel lengths of a TRI grid patterns, the linearity and uniformity characteristics for deviation and variation was good obtained. After the Ag paste was used to fill part of the patterned film with conductive polymer coating, the following parameters were obtained: a sheet resistance of 5 ~ 20 Ohm/Sq., transmittance ratio was 83 ~ 86 % at a wavelength of 550 nm (30 cm x 30 cm). We were fabrication the large area polymer solar cells by roll-to-roll compatible slot die coating and screen printing on embedded Ag grids substrates. Printed and coated polymer solar cells with a cell structure of plastic substrate/ Ag grids/ PEDOT:PSS/ ZnO/ P3HT:PCBM/ PEDOT:PSS/ Ag grids obtained the power conversion efficiency (PCE) of between 0.79 % and 1.84 % for large area devices (30 cm2).
9:00 AM - LL5.35
Promoting the Formation of Twinned Silver Seeds and Their Growth into Nanowires by a Heat-Up Process for Flexible Organic Device Applications
Guh-Hwan Lim 1 Seong Jun Lee 2 Insung Han 1 Shingyu Bok 1 Hwansu Sim 1 Jeong Ho Cho 2 3 Byungkwon Lim 1
1Sungkyunkwan University Suwon-si, Gyunggi-do Republic of Korea2Sungkyunkwan University Suwon-si, Gyunggi-do Republic of Korea3Sungkyunkwan University Suwon-si, Gyunggi-do Republic of KoreaShow Abstract
The polyol reduction of AgNO3 has been a preferred method of synthesizing silver (Ag) nanostructures and is typically conducted by using a hot-injection process, where the Ag precursor is rapidly injected to a preheated, ethylene glycol solution containing polymeric stabilizers such as poly(vinyl pyrrolidone) and other additives. However, it is often difficult to control the crystallinity of seeds, which plays an important role in determining the morphology of the final products. Here we report that long Ag nanowires with an average length of about 20 mu;m can be synthesized in high yields by applying a heat-up process in the polyol synthesis. Electron microscopy studies revealed that multiple-twinned Ag seeds were generated preferentially during the heat-up procedure, and then grew into nanowires. We also demonstrate that these Ag nanowires can be applied as electrode materials for the fabrication of flexible and transparent organic field-effect transistors with a high hole-mobility.
9:00 AM - LL5.38
Resistance and Transparency Tunable Ag-Inserted Transparent Ag-In-O (IAO) Films for Organic Solar Cells
Da-Young Cho 1 Hye-Min Lee 1 Ki-Won Seo 1 Hyo-Jung Kim 1 Kwun-Bum Chung 2 Han-Ki Kim 1
1Kyung Hee University Youngin Republic of Korea2Dankook University Cheonan Republic of KoreaShow Abstract
We have investigated sheet resistance and transparency tunable Ag-doped In2O3 (IAO) films through the insertion of a nano-size Ag layer for use as transparent electrodes for organic solar cells (OSCs). Due to the high conductivity of a nano-size Ag layer, the optimized IAO/Ag/IAO film showed the lowest resistivity of 3.988×10-5 Ohm-cm, even though it was sputtered at room temperature. Furthermore, effective antireflection of the IAO/Ag/IAO at optimized Ag thickness (10 nm) led to high optical transmittance of 84.78 %, which is higher than that of conventional ITO films. Using optimized IAO/Ag/IAO with sheet resistance of 4.988 Ohm/square and optical transmittance of 84.78 % prepared on a glass substrate, we successfully demonstrated OSCs. The successful operation of OSCs with IAO/Ag/IAO multilayer electrodes indicates that the IAO/Ag/IAO multilayer is a promising transparent electrode for large-area OSCs due to its low sheet resistance and high transparency when it is very thin. In addition, we investigated the effect of Ag thickness in the IAO/Ag/IAO electrodes on the performance of OSCs to correlate the Ag thickness and performance of OSCs.
9:00 AM - LL5.40
Ruthenium Dioxide Ultrathin Films on Optical Substrates: A New TCO with UV to Microwave Broadband Transparency and Unique Charge-Carrier Characteristics
Irina Pala 1 Christopher N. Chervin 1 Jeffrey W. Long 1 Debra R. Rolison 1 Jeffrey C. Owrutsky 1 Michael S. Osofsky 2 Frederic J. Rachford 2 Joseph S. Melinger 3
1Naval Research Laboratory Washington USA2Naval Research Laboratory Washington USA3Naval Research Laboratory Washington USAShow Abstract
Indium-doped tin oxide (ITO) has been the preferred transparent conductor (TC) for laboratory studies and commercial applications because of its electrical conductivity and transparency in the visible range of the spectrum. However, thin film fabrication of ITO requires high-vacuum deposition techniques and the resulting film is absorbing strongly in the ultraviolet (UV) and infrared (IR) regions of the spectrum, restricting its application space. In attempting to provide a design strategy for a viable alternative to ITO, we study a nontraditional transparent conductive oxide (TCO) material, namely ultrathin ruthenium dioxide films (~10 nm), deposited from solution phase onto optical substrates using an easy, bench-top, self-limiting process . The resulting nanoscale skins of RuO2 are broadband transparent over an uncommonly wide spectral range for an oxide, from UV to microwave, far surpassing the range of ITO . Also, the deposition protocol allows for conformal, non-line-of-sight coating of structured 3D substrates and the resulting films are intrinsically conductive, exhibiting a unique combination of high carrier concentration and low carrier mobility. In this presentation, we will provide an overview of the synthetic methods and the optical, electrical and spectroelectrochemical properties of RuO2 ultrathin films as a broadband TCO.
 C.N. Chervin, A.M. Lubers, K.A. Pettigrew, J.W. Long, M.A. Westgate, J.J. Fontanella, D.R. Rolison, Nano Lett.9 (2009) 2316-2321.
 J.W. Long, J.C. Owrutsky, C.N. Chervin, D.R. Rolison, J.S. Melinger, U.S. Patent Application 20110091723.
9:00 AM - LL5.41
Highly Conductive Reduced Graphene Oxide via Pressure-Assisted Reduction at Low Temperature for Flexible and Transparent Electrodes
Kyoung-Hwan Shin 1 Choon Woo Lim 2 Sung Hyun Kim 1
1Seoul National University Seoul Republic of Korea2Kyung Hee University YoungIn Republic of KoreaShow Abstract
Reduced graphene oxide (rGO) thin films are fabricated as gate electrodes for organic thin film transistors (OTFTs) by an alternative method combining chemical and subsequent pressure-assisted thermal reduction at relatively low temperature on flexible plastic substrates. The reduction process uses a hot press to squeeze the two bodies, the chemically reduced graphene oxide (CRGO) film and the substrate, maximizing the area of direct contact. Heat flow which induced by the contact area in the reduction transfers sufficient energy to dissociate functional groups from the exfoliated graphene oxide layers. The pressure-assisted thermally reduced graphene oxide (PRGO) thin film has lower sheet resistance (~100 k#8486;/sq), lower root-mean-square (RMS) roughness (1.61 nm), higher restoration of the conjugated π-orbital system (C/O atomic ratio of 10), and smaller interlayer spacing (0.364 nm) at about 78% optical transparency compared to CRGO and thermally reduced graphene oxide (TRGO) thin films. The PRGO thin film-gated OTFT exhibits a field-effect mobility of 0.18 ± 0.04 cm2 Vminus;1 sminus;1, a threshold voltage of minus;18.18 V, and an on/off current ratio of 6.94 × 10^4.
9:00 AM - LL5.43
Properties of IZO/Ag/IZO Films Prepared by Sputtering Under Various Conditions
Midori Kawamura 1 Yuzuru Matsumura 1 Yoshihisa Kudo 1 Ziyang Zhang 1 Yoshio Abe 1 Kyung Ho Kim 1
1Kitami Institute of Technology Kitami JapanShow Abstract
Among various transparent conductive oxides, indium zinc oxide (IZO) is known for its higher work function than ITO, which seems preferable for the use as anode of organic light emitting diodes. IZO film is not indium-free unlike aluminum zinc oxide (AZO) film, but it is known that indium consumption can be reduced by the use of metal interlayer in the middle of IZO film. We have investigated electrical and optical properties of IZO/Ag/IZO structures prepared by magnetron sputtering under various conditions.
First, single layer of IZO (70 nm in thickness) sputtered in Ar atmosphere had electrical resistivity of 4 x 10^-4 Omega;cm, n-type conduction. That deposited in mixtures of Ar and O2 (O2 ratio:0-100%) showed high resistivity of 10^1 -10^4 Omega;cm with the increase of O2 ratios.
Then, we have fabricated multilayer structure of IZO/Ag/IZO film by sputtering. Ag thickness was mainly 10 nm. Then thickness of IZO was 30 or 40 nm each. When the IZO layer was sputtered in Ar, a multilayer with a resistivity of 5 x 10^-5 Omega;cm was obtained. Optical transmittance at a wavelength of 550 nm was 81 % and its figure of merit (FOM) was 26 x 10^-3 Omega;^-1. On the other hand, when the IZO layer was sputtered in O2, a resistivity of the multilayer was also high as 10^4 Omega;cm.
It has been reported that a multilayer consists of high resistivity oxide layer and metal interlayer showed a high conductivity. However, in our results, it is found that conductivity of a multilayer depends not only on property of metal interlayer but also on that of oxide layers.
9:00 AM - LL5.44
Flexible Transparent Conducting Composite Film Using Surface-Embedded Metal Nanowires with Robust Performance Stability
Hyeon-Gyun Im 1 Jungho Jin 1 Jaemin Lee 2 Su-Ho Jung 1 Jung-Yong Lee 2 Il-Doo Kim 1 Byeong-Soo Bae 1
1Korea Advanced Institute of Science and Technology Daejeon Republic of Korea2Korea Advanced Institute of Science and Technology Daejeon Republic of KoreaShow Abstract
Transparent conducting electrodes (TCEs) are an essential component for modern opto-electric devices such as solar cells, organic light emitting diodes (OLEDs), liquid crystal displays (LCSs), and touch screen panels (TSPs). Especially, random networks of metal nanowires (metalNW) are considered the most promising TCE material for the viable replacement of indium tin oxide (ITO) due to their tempting advantages of excellent opto-electrical property, good flexibility, and compatibility with low-cost solution process. In this work, we demonstrate flexible transparent conducting plastic films with surface-embedded silver or copper nanowire (metalNW-GFRHybrimer film). This film can be used as a high-performance flexible TCE platform for opto-electric devices. MetalNW-GFRHybrimer film is composed of a glass-fabric reinforced transparent composite (GFRHybrimer) film as the basal substrate and random networks of AgNW or CuNW that are monolithically buried on the film surface as the TCE. The resulting hybrid structure of the metalNW-GFRHybrimer film represents exceptionally smooth surface topology, good thermo-mechanical performance, and excellent opto-electrical performance. With the embedment of the metalNWs in thermally and chemically resistant resin matrix, excellent stability against heat, thermal oxidation, and wet chemicals was established, which is not commonly achieved with standard metalNW TCE systems on glass.  The electrical and optical performances of the metalNW-GFRHybrimer film were found to be strongly durable even during long-term high-temperature annealing. The chemical stability was confirmed by an extended duration time in the K2S corrosion test. The metalNW-GFRHybrimer film can be a promising platform for high-performance flexible opto-electric devices.
Key Words: Transparent conducting electrode, Metal nanowires, Glass-fabric reinforced transparent composite
 H. G. Im, J. Jin, J. H. Ko, J. Lee, J. Y. Lee and B. S. Bae “Flexible Transparent Conducting Composite Film Using Monolithically Embedded AgNW Electrode with Robust Performance Stability” Nanoscale accepted
9:00 AM - LL5.45
Selective Patterning of Graphene on Flexible Transparent Substrates by near Infrared LASER
Taejun Choi 1 Yuna Kim 1 Byung Hee Hong 1
1Seoul National University Seoul Republic of KoreaShow Abstract
Flexibility and transparency has become crucial requirements for emerging electronics including bendable and rollable displays, and flexible sensors. Graphene, a two-dimensional monolayer of sp2-bonded carbon atoms, is being considered as a future transparent and flexible electrode for those emerging frontiers due to its high optical transmittance, flexibility, and conductivity. However, the difficulty of large-area production has been the major obstacle to apply graphene at industrial production level. The roll-to-roll production by chemical vapor deposition (CVD) and transfer process provided a practical solution to large-area graphene sheet production. However, the patterning of graphene on a desired substrate is still limited, although it is an essential process for graphene device fabrication. Previously, various graphene patterning methods have been developed, including electron beam lithography, scanning probe lithography, plasma etching, catalytic etching, and nanoimprint lithography. However, these methods are costly and hardly scalable. Other lithographical methods also require complicated pre-defined masking and wet chemical etching processes. Here we present a selective pattering of graphene on flexible transparent substrates using direct near infrared (NIR) nano second pulse laser (1064nm) without using any masking and lift-off processes. We found that the polyethylene terephthalate (PET) film is totally transparent to the NIR laser, while the graphene layer absorbs the laser beam by ~2.3%, resulting in the selective removal of graphene from the irradiated region. Compared to other conventional patterning methods, the NIR pattering of graphene is expected to be more practical for applications to industrial production by enabling fast patterning of graphene on transparent flexible substrates without using complicated lithographic methods.
9:00 AM - LL5.46
Aluminium Doped Zn1minus;xMgxO - A Transparent Conducting Oxide with Tunable Optical and Electrical Properties
Karsten Fleischer 1 Elisabetta Arca 1 Christopher Smith 1 Igor Shvets 1
1Trinity College Dublin Dublin IrelandShow Abstract
A ternary mixed oxide Zn1minus;xMgxO has been successfully doped with aluminium to create a range of transparent
conducting oxides (TCOs) with tunable refractive index as well as work function. Conductive material
was synthesised up to a magnesium concentration of x=0.45, although the conductivity is reduced compared
to standard ZnO:Al. The changes in band gap, work function and conductivity have been attributed to a
modified band structure and energetic position of the aluminium induced donor state.
9:00 AM - LL5.47
Electrolessly Deposited Metal Electrospun Nanowire Transparent Electrodes
Po-Chun Hsu 1 Desheng Kong 1 Shuang Wang 2 Haotian Wang 3 Alex J Welch 1 Hui Wu 1 Yi Cui 1 4
1Stanford University Stanford USA2Stanford University Stanford USA3Stanford University Stanford USA4SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Metal nanowire transparent conducting electrodes (TCEs) have been widely developed for their promising sheet resistance-transmittance performance, excellent mechanical flexibility, and facile synthesis method. How to lower the junction resistance without compromising optical transmittance has become the key issue in enhancing the performance. Here we have combined electrospinning and electroless deposition to synthesize interconnected, ultra-long metal nanowire networks. For both silver and copper nanowire networks, the sheet resistance-transmittance performances reach around (10 Omega;/sq, 90%), which is by far the best performance among all wet-chemistry synthesized metal nanowire TCEs. The bending tests suggest our electrolessly desposited metal nanowire TCEs are high flexible, and we also synthesize a 11-cm large sample to demonstrate it scalability. This approach opens new opportunities for flexible electronics and roll-to-roll large-scale manufacturing of transparent electrodes.
9:00 AM - LL5.49
Low Work Function Transparent Electrodes for Inverted Type Photosensitive Devices
Grzegorz Luka 1 Krzysztof Goscinski 1 Vitalii Ivanov 1 Bartlomiej S Witkowski 1 Lukasz Wachnicki 1 Marek Godlewski 1 2
1Institute of Physics Polish Academy of Sciences Warsaw Poland2Cardinal S. Wyszynski University Warsaw PolandShow Abstract
Electrode work functions greatly influence the performance of organic heterojunction (planar as well as bulk) solar cells. In such devices, a proper adjustment of the electrodes with respect to their work functions can improve the power conversion efficiencies. New low work function electrodes are highly desirable since so far widely used metals like Mg, Ca, Li or their alloys are chemically reactive and very sensitive to oxygen, upon which they easily oxidize. In case of organic electronic devices in the so-called inverted architecture, a low work function contact is placed on the bottom of the device. The bottom electrode is usually the one which is transparent. The most commonly used indium tin oxide (ITO) material for transparent electrode applications typically has work function of 4.2 - 4.8 eV or even higher. Transparent conducting aluminum-doped zinc oxide (ZnO:Al, AZO) films have the work function of 4.1 eV, which promotes their use as transparent electrodes in inverted organic solar cell devices. Additionally, by introducing magnesium into AZO films, a further decrease of the work function can be achieved due to the modification of the ZnMgO:Al band structure.
We obtained, using atomic layer deposition, AZO films with a very thin (a few nm thick) Zn1-xMgxO:Al (0 < x < 0.4) layers grown on the top of the AZO films. Here, we combine the highly conducting state ensured by the AZO layer and the low work function due to magnesium presence at the AZO surface. An additional advantage of the proposed electrode architecture is almost unchanged ZnMgO:Al film morphology, comparing to ZnO:Al surface. We test the so-obtained layers as electron injecting/hole blocking contacts to organic single layer devices as well as ZnO/organic hybrid heterojunction diodes. Based on the current-voltage and capacitance measurements we indicate the possible mechanisms of the charge injection and transport phenomena in those devices.
This work was partially supported by the Polish National Science Centre (NCN) under decision No. DEC-2012/07/D/ST3/02145, and by the European Union within the European Regional Development Fund, through the Innovative Economy grant (POIG.01.01.02-00-108/09).
9:00 AM - LL5.50
A Comparative Study of Annealing Effects on Al and Si Doped ZnO
Ramon Schifano 1 Heine Nygard Riise 1 Augustinas Galeckas 1 Alexander Azarov 1 Edouard Monakhov 1 Bengt Gunnar Svensson 1
1University of Oslo Oslo NorwayShow Abstract
ZnO and ZnO based alloys are among the most promising candidates as Transparent Conductive Oxides (TCOs) for large scale applications such as windows films/active layers for solar cells and displays.1 However, despite the wide research on these materials and that most of the CuIn1-xGaxSe2 (CIS and CIGS) based photovoltaic modules are already based on ZnO as a conducting front contact,2 the role of commonly used dopant impurities (at extremely high concentrations suitable for TCOs applications) on the materials properties and stability are not fully clarified and still under investigation.
As an example, it has been shown that Al introduces non-equilibrium defects into ZnO films.3 Similarly, the thermally induced conductivity degradation of Ga doped ZnO has been attributed to the Ga atoms instability that relax to octahedral coordination after air annealing at already relatively low temperatures (~420 °C).4
We have recently shown that Si acts similarly as Al with respect to the electrical and structural properties of ZnO.5 Here, we present a comparative study of the annealing effects on magnetron sputtered thin films of ZnO nominally undoped and doped with Si to ~1.5 at.% and Al to ~2 at.%, as measured by Rutherford Backscattering Spectrometry (RBS) and corresponding to a resistivity of ~2 x10-3 #8486; x cm as extracted from room temperature Hall measurements (RTH). The films were prepared on quartz substrates by RF co-sputtering at 400 °C and subsequently annealed in air for 1 h in the 550 °C -1050 °C range. The comparison between the structural characteristics of the annealed films clearly indicate that Al and Si inhibit the increase in the grain size as extracted from X-ray diffraction (XRD) measurements. Photoluminescence Spectroscopy (PL) confirmed these findings indicating that Si and Al are retarding a substantial onset of the near band edge emission at annealing temperatures above ~800 °C. However, RTH measurements reveal that the films experience a dramatic increase in resistivity of ~4 orders of magnitude already after the 550 °C annealing step possibly due to chemisorption of Oxygen at the grain boundaries and/or increase in the number of compensating Zinc vacancies (VZn).6,7
1) K. Ellmer, A. Klein, and B. Rech, Transparent Conductive Zinc Oxide (Springer-Verlag Berlin Heidelberg, 2008).
2) F. J. Pern, R. Noufi, B. To, C. DeHart, X. Li, and S. H. Glick (2008), Conference Paper NREL/CP-520-42792.
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9:00 AM - LL5.51
Direct Patterning of Metal Nanowire Percolation Network Transparent Conductor by Selective Laser Ablation
Sukjoon Hong 1 Junyeob Yeo 1 Jinhwan Lee 2 Habeom Lee 1 Young Duk Suh 1 Seungyong Han 2 Jinhyeong Kwon 2 Hu Seung Lee 2 Seung Hwan Ko 1
1Seoul National University Seoul Republic of Korea2KAIST Daejeon Republic of KoreaShow Abstract
Because of the increasing demands in large-area optoelectronic devices such as organic light emitting diodes, touch screen panels and thin film solar cells, novel transparent conductors are being extensively studied in order to replace wide band gap transparent conductive oxides (TCO), indium tin oxide (ITO) in particular, which suffers from various problems including its scarcity, huge waste of target material and fragile nature. The potential alternatives of ITO include conducting polymers and carbon-based materials such as PEDOT:PSS, graphene and CNT, however, their performance highly depends on the preparation and often does not meet the requirements for many applications in terms of conductivity and stability. On the other hand, metal NW transparent conductor, or metal NW percolation network, has become a markedly mature technology in terms of material synthesis and fabrication process, yet very little work has been done on developing patterning techniques for such metal NW based transparent conductors.
In this study, we demonstrate a simple patterning method for metal NW percolation network by using 355 nm nanosecond (ns) pulsed laser ablation. This method is basically conducted in ambient condition without using any conventional patterning processes such as photolithography or chemical etching, which are considered as time consuming, multistep and expensive. Pulsed laser ablation has long been utilized as a facile and handy tool for direct patterning, and we confirmed that metal NW also can be effectively ablated by ns pulsed laser ablation at low threshold fluence even at a single shot. Being a direct writing method, no premade mask is needed to create an arbitrary pattern, while the processing speed has been increased significantly in this study by using galvanometer mirror to obtain a rapid scanning (>100 mm/s) of focused laser beam. By scanning the focused laser spot at low (1 KHz) or high pulse repetition (20 KHz) rates, a microhole array with ~15 mu;m hole diameter or a continuous ablation line at 5~50 mu;m width is readily produced on the metal NW percolation network to tune the properties of the resultant percolation network or create a desired pattern at micro-scale. It is also found that metal NW based electrode line prepared by the ablation process substantiates that the general relation for a conducting thin film fails at a narrow width, which should be considered for the applications that requires a high resolution patterns. Finally, through a simple capacitive touch sensor demonstration, it is confirmed that the selective laser ablation can be directly applied for the device fabrication which requires a patterned transparent conductor.
9:00 AM - LL5.52
MoO3 Intergraded InZnO Films for Use as a Transparent Anode in Organic Solar Cells
Hyo Jung Kim 1 Sin-Bi Kang 1 Hye-Min Lee 1 Da-Young Cho 1 Ki-Won Seo 1 Kwun-Bum Chung 2 Han-Ki Kim 1
1Khung Hee university Yongin-si Republic of Korea2Dankook University Chenan Republic of KoreaShow Abstract
We reported on transparent MoO3-Zn doped In2O3 (IZO) electrodes fabricated by co-sputtering for use as an anode in organic solar cells (OSCs). By adjusting RF and DC power of MoO3 and IZO targets during co-sputtering, we fabricated the MoO3-IZO electrode with graded content of the MoO3 on the IZO films. In particular, we investigated the thickness effect of graded MoO3 layer on the electrical, optical, structural and morphological properties of MoO3-IZO multicomponent electrodes. At optimized MoO3 thickness of 20 nm, the MoO3 graded IZO electrode showed a sheet resistance of 40.22 Ohm/square and optical transmittance of 70.1 %. Without degradation of electrical and optical properties of IZO films, we obtained MoO3 graded IZO films for use as an anode for OSCs. To investigate the feasibility of MoO3 graded IZO films, we fabricated conventional P3HT:PCBM based OSCs with MoO3 graded IZO as a function of MoO3 thickness. The OSC fabricated on the MoO3 graded IZO anode showed a fill factor of 66.53 %, a short circuit current of 8.121 mA/cm2, an open circuit voltage of 0.592 V, and a power conversion efficiency of 3.2 % comparable to OSC fabricated on ITO anode. We correlated the performance of OSCs with a MoO3 thickness on the IZO film and suggested a possible mechanism to explain the effect of MoO3 graded layer.
9:00 AM - LL5.53
Highly Transparent and Low Resistance ITO/Ag-Pd-Cu/ITO Multilayer Electrodes for Organic Solar Cells
Hyo Jung Kim 1 Sin-Bi Kang 1 Hye-Min Lee 1 Da-Young Cho 1 Ki-Won Seo 1 Han-Ki Kim 1
1Khung Hee university Yongin-si Republic of KoreaShow Abstract
We investigated characteristics of ITO/Ag-Pd-Cu (APC)/ITO multilayer electrodes prepared by direct current magnetron sputtering for use as an anode in organic solar cells (OSCs). To optimize the sheet resistance and optical transmittance of ITO/APC/ITO multilayer, we fabricated the ITO/APC/ITO multilayer at a fixed ITO thickness of 30 nm as a function of APC thickness. At optimized APC thickness of 12 nm, the ITO/APC/ITO multilayer exhibited a sheet resistance of 6 Omega;/square and optical transmittance of 84.15 % at a wavelength of 550 nm which is comparable to conventional ITO/Ag/ITO multilayer. However, the APC-based ITO multilayer showed a higher average transmittance in a visible region than the Ag-based ITO multilayer. The higher average transmittance of ITO/APC/ITO multilayer indicated the multilayer is suitable anode for organic solar cells with P3HT:PCBM active layer. OSCs fabricated on the optimized ITO/ACP/ITO multilayer exhibited a better performance with a fill factor of 64.815 %, a short circuit current of 8.107 mA/cm2, an open circuit voltage of 0.59 V, and power conversion efficiency (3.101 %) than OSC with ITO/Ag/ITO multilayer. Therefore, ITO/APC/ITO multilayer can replace Ag-based ITO/Ag/ITO multilayer in fabrication of OSCs due to its high optical transmittance in a wide range wavelength and low sheet resistance.
9:00 AM - LL5.55
High-Mobility Thin-Film Transistor with Polycrystalline In-Ga-O Fabricated by Rf-Magnetron Sputtering
Kwang-Min Jo 1 Se-yun Kim 1 Ho-Chang Lee 1 Myeong-Eon Kim 1 Joon-Hyung Lee 1 Jeong-Joo Kim 1 Young-Woo Heo 1
1Kyungpook National University Daegu Republic of KoreaShow Abstract
Oxide thin film transistors (TFTs) have attracted considerable interest for gate diver and pixel switching devices of the active matrix (AM) liquid crystal display (LCD) and organic light emitting diode (OLED) display because of their high field effect mobility, transparency in visible light region, and low temperature processing below 300oC. Recently, oxide TFTs with polycrystalline In-Ga-O(IGO) channel layer reported by Ebata. et. al. showed a amazing field effect mobility of 39.1 cm2/Vs. The reason having high field effect mobility of IGO TFTs is because In2O3 has a bixbyite structure in which linear chains of edge sharing InO6 octahedral are isotropic.
In this work, we investigated the characteristics and the effects of oxygen partial pressure significantly changed the IGO thin-films and IGO TFTs transfer characteristics. IGO thin-film were fabricated by rf-magnetron sputtering with different oxygen partial pressure (O2/(Ar+O2), Opp)ratios. IGO thin film Varies depending on the oxygen partial pressure of 0.1%, 1%, 3%, 5%, 10% have been some significant changes in the electrical characteristics. Also the IGO TFTs VTH value conspicuously shifted in the positive direction, from -8 to 11V as the Opp increased from 1% to 10%. At Opp was 5%, IGO TFTs showed a high drain current on/off ratio of ~10^8, a field-effect mobility of 84cm2/Vs, a threshold voltage of 1.5V, and a subthreshold slpe(SS) of 0.2V/decade from log(IDS) vs VGS.
9:00 AM - LL5.56
MoO3/Au/MoO3-PEDOT: PSS Transparent Composite Electrodes for ITO-Free Bulk-Heterojunction Organic Solar Cells
Md. Maniruzzaman 1 Kyunghoon Jeong 1 Mohammad Arifur Rahman 1 Jaegab Lee 1 Abdur Rahim 1
1Kookmin University Seoul Republic of KoreaShow Abstract
Indium tin oxide (ITO)-free organic solar cells were fabricated with highly conductive and transparent MoO3/Au/MoO3-PEDOT:PSS composite electrode. The solution process MoO3-PEDOT:PSS composite film on MoO3/Au enhance both the of transmittance and conductivity of the electrode. The transmittance of anodes and power conversion efficiency, (PCEs) were optimized with thickness of MoO3-PEDOT:PSS composite film. Transmittance was maximized at 80% at 550 nm wavelength using 30 nm bottom MoO3 layer and solution process 30 nm top MoO3-PEDOT:PSS composite layer of a 12 nm Au layer. The MoO3-PEDOT:PSS composite film characterized with Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). Power conversion efficiency was maximized at 2.81% which is comparable to that of ITO based conventional organic solar cell, PCE (2.89%). The improvement of PCEs due to the incorporation composite in multilayer electrode is attributed to the smooth surface, high reflectance index (2.45), lower work function of the electrode (4.9 eV) close to ITO (4.7 eV) and high conductivity. The MoO3/Au/MoO3-PEDOT:PSS electrode was shown to be a promising replacement of ITO for use in low-cost optoelectronic devices.
9:00 AM - LL5.57
Development of Hybrid Transparent Electrode with Copper Grid and Graphene Film
Junseong Eom 1
1Korea Advanced Insitute of Science and Technology Daejeon Republic of KoreaShow Abstract
As the market of transparent electrode is growing, researchers developed transparent electrodes with new materials and fabrication process. Many materials and processes to make a highly transparent and highly conductive transparent electrode are introduced but they all have their own pros and cons. Metal-based films are researched well and the new material, graphene is uprising for next-generation transparent electrode material. Metallic nanostructure has very low surface resistance, while it has big hole for transparency. Graphene flake film is easily fabricated by solution-based process and has good uniformity but has very low electric conductivity. With these two materials, this paper suggests a hybrid-type transparent electrode with copper grid and graphene film.
Copper grid is fabricated by two processes; lift-off process and PDMS nano-imprinting transfer pro-cess while PDMS process was not very successful. Graphene flake film is fabricated by vacuum filtration process with AAO filter and Teflon filter. Teflon filter filtration process was not stabled. With these two ma-terials and processes, hybrid transparent electrode was developed. It has 75% transparency and 40Omega;/sq sur-face resistance. This result is not very effective in comparison with pre-existed ITO film (with >85% trans-parency and <20Omega;/sq surface resistance). This paper shows its possibility to be a flexible transparent elec-trode with high performance over than ITO film.
Keywords: transparent electrode, metal grid, graphene, touch screen, solar cell
LL1: Metal Nanowire Networks - Processing
Tuesday AM, April 22, 2014
Moscone West, Level 3, Room 3009
9:15 AM - LL1.01
Deposition and Post Processing Techniques for Silver Nanowire Based Transparent Conductive Electrodes
M. Greyson Christoforo 1 Saahil Mehra 2 Zach M. Beiley 2 Peter Peumans 3 Alberto Salleo 2 Michael D. McGehee 2
1Stanford University Stanford USA2Stanford University Stanford USA3IMEC Leuven BelgiumShow Abstract
Silver nanowire based transparent electrodes hold several important advantages over traditional transparent conductive oxides such as indium tin oxide. They are more compatible with flexible substrates and can be deposited at ambient temperatures and pressures. Here, we will discuss a computer controlled spray deposition technique we have developed and optimized for room temperature deposition. This technique has allowed us to deposit a transparent conductor with good performance (14 ohm/sq and peak light transmission of 93%) directly onto a sensitive organic solar cell with no heating steps. This process has enabled us to produce semi-transparent solar cells suitable for inclusion into a hybrid tandem photovoltaic device stack.
Lifting the low temperature deposition restriction allows for significantly improved electrode performance. By re-tuning our spray deposition system for a heated glass substrate (100°C) and adding an additional laser based post processing step, we are able to deposit uniform large area films which pass over 92% of incident light while maintaining a low sheet resistance of 6.3 ohm/sq, surpassing the highest performing solution processed transparent conductors reported in literature today.
9:30 AM - LL1.02
Passivation Coating on Electrospun Copper Nanowires for Stable Transparent Electrodes
Po-Chun Hsu 1 Hui Wu 1 Thomas J Carney 1 Matthew T McDowell 1 Yuan Yang 1 Erik C Garnett 1 Michael Li 1 Liangbing Hu 1 Yi Cui 1 2
1Stanford University Stanford USA2SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Copper nanowire (CuNW) networks are one of the most promising candidates to replace indium tin oxide films as the premier transparent conducting electrode (TCEs) due to its high sheet resistance(Rs) -transmittance(T) performance, superior mechanical flexibility and low lost. However, the chemical activity of CuNWs causes a substantial increase in the Rs after thermal oxidation or chemical corrosion, which may undermine its applicability. In this work, we utilize atomic layer deposition(ALD) to coat a passivation layer onto electrospun copper nanowires and remarkably enhance their durability. The passivation layer is composed of 20-nm-thick aluminum-doped zinc oxide (AZO) for the inner layer and 1-nm-thick aluminum oxide for the outer layer. Without changing the optical transmittance, the passivated CuNW TCE shows an resistance increase of only 10% after thermal oxidation at 160 °C in dry air and 80 °C in humid air with 80% relative humidity, whereas the bare CuNWs quickly become insulating. In addition, the coating and baking of the acidic PEDOT:PSS layer increases the Rs of bare CuNW by 6 orders of magnitude, while the passivated CuNWs show an 18% increase. Our work demonstrates that this ALD method can greatly enhance the reliability of CuNW TCE and thus provide a practical solution for the degradation problem of metal nanowire TCEs.
9:45 AM - LL1.03
Silicon/Organic Heterojunction Photovoltaic Cell with 12.7% Efficiency by Use of Spray-Coated Nanowire Transparent Conductor
Ken Alfred Nagamatsu 1 2 Joshua A. Spechler 3 2 Sushobhan Avasthi 2 Craig B. Arnold 3 2 James C. Sturm 1 2
1Princeton University Princeton USA2Princeton University Princeton USA3Princeton University Princeton USAShow Abstract
Hybrid photovoltaic devices incorporating inorganic and organic materials are receiving great interest as an approach to next-generation photovoltaics. These technologies aim to combine the advantages of different material systems to provide better efficiency, more cost efficient manufacturing, or both. Silicon/Organic Heterojunctions (SOH) are attractive because these heterojunctions can be fabricated at temperatures < 100°C, without p-n junctions in the silicon, using simple methods such as spin-coating [1,2]. In comparison, conventional crystalline silicon solar cells require p-n junctions that are fabricated at temperatures higher than 800°C . In this abstract we report a record 12.7% AM1.5 power efficiency for this type of cell, enabled in our work by a spray-coated nanowire-enhanced transparent conductor, with a sheet resistance as low as 10Omega;/square.
The basic cell structure consists of the conducting organic layer PEDOT:PSS spin-coated on a p-type silicon (100)wafer. A sparse metal contact (to admit light) and a uniform ohmic back contact complete the structure. The field from the SOH separates electron-hole pairs created in the silicon, and the high LUMO (- 3.3 eV) blocks electrons from entering the PEDOT from the silicon, leading to high open circuit voltages (~ 0.59V). To lower the series resistance from the PEDOT, a silver nanowire mesh is applied on top before a minimal metal contact (<1% contact pad). Silver nanowire meshes are increasingly of interest as a flexible transparent conductor for organic PV (5-7). Deposition of AgNW networks has been demonstrated via spin-coating, drop-casting, or spray deposition on top of a polymer film . The networks typically must utilize some process to join AgNW junctions to enhance conductivity such as thermal annealing, , pressure, or laser fusing.
In this work, Ag NW networks were applied via spray coating for silicon-organic heterojunction PV. First, we demonstrate the performance of the spray deposited AgNW films (with any subsequent annealing) is comparable or better than the, spin-cast laser-fused  or thermally-annealed AgNW films . The conduction and transmission properties of these films are are typically 10 Omega;/square sheet resistance for a wire density yielding 75% transmission at 600nm wavelength, vs 100 Ohms/sq for the PEDOT:PSS alone. Without any thermal/laser process, any degradation of the polymer layer is avoided. Spray deposition has recently been shown to provide a “fusing” effect simply due to the kinetic energy of the AgNWs during the deposition process .. Second, utilizing spray-coated AgNW films, we report a Si/PEDOT:PSS solar cell with an AM1.5 power conversion efficiency of 12.7%. The high conductivity of the nanowires allows both sparse metal contact coverage while maintaining a very high fill factor of 72.6% and allowing an Isc of 29.6 mA/cm2.
10:00 AM - LL1.04
Highly Reliable Copper Nanowires/Nanoparticles Film on the Flexible Polymer Substrate via Flash Light Sintering under Repeatable Bending Fatigue for Printed Electronics
Sung-Jun Joo 1 Sung-Hyeon Park 1 Chang-Jin Moon 1 Hak-Sung Kim 1 2
1Hanyang University Seoul Republic of Korea2Hanyang University Seoul Republic of KoreaShow Abstract
The printed electronics has obtained enormous attention over the last few decades due to its low cost, and various applications such as flexible display, organic solar cells, wearable display, and flexible battery. Since these printed electronics use flexible substrates that have low-melting point, flexibility, and low cost, solution-based noble metallic nanoparticles (Au, Ag, etc) inks are widely employed. However, these noble metals are very expensive to be commercialized. Therefore, copper nanoparticles are recently proposed as an alternative for high electrical conductivity and low cost. However, it is difficult to sinter the Cu nanoparticles because it is easily oxidized in the room temperature. Therefore, a flash light sintering method with poly(N-vinylpyrrolidone) (PVP) coated Cu nanoparticles has been investigated. The oxide shells of the copper nanoparticles can be eliminated by combinational function of flash light and PVP evaporation in the room temperature and ambient condition. Meanwhile, the flexible electrical devices fabricated on the polymer flexible substrates via printed electronics should maintain their electrical functions under severe mechanical bending and twisting and stretching conditions. To satisfy these needs, several studies have been conducted to increase reliability of sintered silver nanoparticles thin film by mixing various materials such as CNT, graphene, and nanowires. However, there is no study result to increase a reliability of the sintered Cu nanoparticles thin film. Therefore, in this study, Cu nanowires were added in Cu nanoparticles-ink to improve reliability and electrical conductivity under the mechanical fatigue loading. The Cu nanowires (NW) /nanoparticles (NP)-ink was printed on the polyimide substrates and sintered by flash light irradiation in the room temperature and ambient condition. The reliability of the flash light sintered Cu NW/NP thin film was investigated by measuring resistance variation during outer-bending fatigue tests varying the bending radius, the weight fraction of Cu NW and the flash light irradiation conditions. It was found that the flash light sintered Cu NW/NP thin film showed much higher reliability by adding only 5 wt% of Cu NW (The resistance change (ΔR/R0) of the Cu NW/NP film was 4.196 while that of the Cu NP film was 92.751 at 103 cycles under the 7 mm of the bending fatigue radius). X-ray diffraction, scanning electron microscope, and in-situ sheet resistance measurement were conducted to study deeply the mechanism of reliability improvement of sintered Cu nanowires/nanoparticles thin film.
10:15 AM - *LL1.05
Nanowire Network as Next Generation of Transparent Electrodes
Yi Cui 1
1Stanford University Stanford USAShow Abstract
Transparent electrodes are important for solar cells, display, touch screen and solid state lighting. Indium tin oxides are the dominating transparent electrode technology although the scarcity of indium and the sputtering processing can limit their future application. I will present novel metal nanowire networks as transparent conducting electrodes to replace the existing indium tin oxides. Metal nanowires with diameters smaller than and with separations larger than the wavelength of the light can allow the sunlight pass through without significant reflection or scattering back. We show that these metal nanowire networks provide very competitive optical transmittance at very low sheet resistance. The low cost processing makes them attractive for future large area optoelectronic applicat