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.

We report in this communication on the synthesis, purification and use of silver or copper nanowires to fabricate flexible transparent electrodes.[1]
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. [4]
[1] 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.
[2] 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
[3] 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.
[4] 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

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.

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.

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.

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.

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 [1] 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) [2] 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.
[1] 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).
[2] 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).

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% .

Nowadays, there is an increasing demand for transparent conductive electrodes (TCE) for application in optoelectronic devices [1], 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 [4]. 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.

[1] Ginley, D. S., Hosono, H. & Paine, D. C. Handbook of Transparent Conductors. Springer (2010).
[2] Kim S, Lee J-L. Design of dielectric/metal/dielectric transparent electrodes for flexible electronics. J Photon Energy 2:021215 (2012).
[3] 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).
[4] 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).

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.[1] 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.
Reference
[1] Jin et al., Energy & Environmental Science, 2013, 6, 1811-1817

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.

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.
References
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.

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 200^oC 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 200-500^oC 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 200^oC 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 400^oC. 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 - 300^oC. 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 SiO_x at the ZnO-Si interface.

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.
Acknowledgement
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).

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.

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.

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.

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.

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.

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.

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.

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 MoO_3</