Conventional Indium Tin Oxide Electrode Research Articles

A Polymeric Two-in-One Electron Transport Layer and Transparent Electrode for Efficient Indoor All-Organic Solar Cells.

Transparent electrodes (TEs) are vital in optoelectronic devices, enabling the interaction of light and charges. While indium tin oxide (ITO) has traditionally served as a benchmark TE, its high cost prompts the exploration of alternatives to optimize electrode characteristics and improve device efficiencies. Conducting polymers, which combine polymer advantages with metal-like conductivity, emerge as a promising solution for TEs. This work introduces a two-in-one electron transport layer (ETL) and TE based on films of polyethylenimine ethoxylated (PEIE)-modified poly(benzodifurandione) (PBFDO). These PEIE-modified PBFDO layers exhibit a unique combination of properties, including low sheet resistance (130 Ω sq-1), low work function (4.2 eV), and high optical transparency (>85% in the UV-vis-NIR range). In contrast to commonly used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the doping level of PBFDO remains unaffected by the PEIE treatment, as verified through UV-vis-NIR absorption and X-ray photoelectron spectroscopy measurements. When employed as a two-in-one ETL/TE in organic solar cells, the PEIE-modified PBFDO electrode exhibits performance comparable to conventional ITO electrodes. Moreover, this work demonstrates all-organic solar cells with record-high power conversion efficiencies of >15.1% under indoor lighting conditions. These findings hold promise for the development of fully printed, all-organic optoelectronic devices.

A Graphene-Based Polymer-Dispersed Liquid Crystal Device Enabled through a Water-Induced Interface Cleaning Process.

We report the use of four-layer graphene (4LG) as a highly reliable transparent conductive electrode (TCE) for polymer-dispersed liquid crystal (PDLC)-based smart window devices. The adhesion between 4LG and the substrate was successfully improved through a water-induced interface-cleaning (WIIC) process. We compared the performance of a device with a WIIC-processed 4LG electrode with that of devices with a conventional indium tin oxide (ITO) electrode and a 4LG electrode without a WIIC. With the application of the WIIC process, the PDLC smart window with a 4LG electrode exhibited reduced turn-on voltage and haze compared to 4LG without the WIIC process and characteristics comparable to those of the ITO electrode. The WIIC-processed 4LG electrode demonstrated enhanced electrical properties and better optical performance, leading to improved device efficiency and reliability. Furthermore, our study revealed that the WIIC process not only improved the adhesion between 4LG and the substrate but also enhanced the compatibility and interfacial interactions, resulting in the superior performance of the smart window device. These findings suggest that 4LG with WIIC holds great promise as a transparent conductive electrode for flexible smart windows, offering a cost-effective and efficient alternative to conventional ITO electrodes.

Anomalous Optoelectric Properties of an Ultrathin Ruthenium Film with a Surface Oxide Layer for Flexible Transparent Conducting Electrodes

AbstractThe growing industrial demand for flexible optoelectric devices has led to intensive researches on highly flexible transparent electrode materials such as graphene, reduced graphene‐oxide (r‐GO), Ag‐nanowire, and 2D metal oxides. However, except Ag‐nanowire, transparent electrode materials having optoelectric properties comparable to that of indium–tin–oxide (ITO) have not yet been developed. In this study, an ultrathin ruthenium film with a ruthenium oxide (RuO2) subsurface layer has been introduced as a flexible transparent electrode. The metallic Ru thin film is fabricated from a RuO2 nanosheet using a layer‐by‐layer coating technique, followed by thermal reduction. The thin film (≈6 nm) reveals comparable sheet resistance and transmittance as that of conventional ITO electrodes. The high transmittance (≈79%) of the metal thin film in the visible range is attributed to the presence of an oxide subsurface layer which acts as antireflection. The Ru film (with oxide subsurface layer) with figure‐of‐merit ≈3.4 × 10−4 Ω−1 shows the best performance among the thin films fabricated using a wet‐chemistry process with 2D nanosheets including graphene, r‐GO, and other metal oxides. In addition, the high mechanical flexibility of Ru thin film makes it next‐generation flexible transparent conducting electrodes, beyond graphene, r‐GO, and 2D metal oxides.

Polyimide-free liquid crystal devices with carbon nanotube-based electrodes

A novel type of polyimide-free liquid crystal (LC) device has been fabricated using layer-by-layer (LBL) deposition of carbon nanotube-based electrodes and in situ formation of self-aligning amphiphilic graft copolymer layer. The LBL-processed organic electrodes showed high transparency comparable to indium tin oxide (ITO) and the self-aligned layer of amphiphilic graft copolymer on organic electrodes provided a stable vertical alignment of LCs. Moreover, the proposed LC device resulted in voltage-dependent driving characteristics suitable for display application. This functional organic electrode layer has potential for application in a flexible display to replace conventional ITO electrode and polyimide alignment layer.

High-Performance Transparent Copper Grid Electrodes Fabricated by Microcontact Lithography for Organic Photovoltaics

We report high-performance transparent copper grid electrodes on glass and plastic substrates that offer a higher Haacke figure-of-merit than conventional indium tin oxide electrodes and are well-matched to the requirements for organic photovoltaics (OPVs). The electrode is fabricated using microcontact lithography with a combination of molecular resist and low toxicity etchant, namely, hexadecanethiol and aqueous ammonium persulfate. This approach to electrode fabrication is much faster than conventional lithography because it takes 20 times narrower than is possible using conventional metal printing methods and so a grid pitch <30 μm is easily achieved without increasing metal coverage. The very small grid-line spacing relaxes the requirement to use highly conductive films to span the gaps between grid lines, reducing parasitic absorption losses. This is demonstrated using an extremely thin (10 nm) poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer. Additionally, we present evidence that it is not always necessarily to embed the metal grid into the substrate or to planarize with a charge-transport layer, to avoid leakage current across the OPV device.

Fabrication of Highly Flat, Flexible Mesh Electrode for Use in Photovoltaics

Metal mesh-based flexible transparent conductive electrodes have attracted much interest as one alternative to conventional indium tin oxide electrodes. In addition to ongoing efforts to develop scalable and cost-effective fabrication processes for high-resolution mesh patterns, the high surface roughness of the mesh which can cause short circuiting and current leakage in optoelectronic devices must be solved. Herein, high-resolution (below ~ 10 μm) mesh patterns with various thicknesses are fabricated by scalable, selective transfer printing and then stably and sufficiently sintered under delicately controlled flash irradiation. A polyethylene terephthalate (PET) film is laminated on the patterns overlaid with a UV-curable resin and then peeled off after UV curing, which produces mesh patterns strongly bonded to the cured resin to be separated in a fully embedded form. The final, highly flat, flexible mesh with a low sheet resistance of 1.7 Ω sq−1, a high optical transparency of 88.6%, excellent mechanical flexibility, and strong adhesion to the substrate is successfully implemented in a flexible perovskite solar cell with a high power conversion efficiency (PCE) of 14.92%.

High-Performance Oxide TFTs With Co-Sputtered Indium Tin Oxide and Indium-Gallium-Zinc Oxide at Source and Drain Contacts

Amorphous indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs) have shown significant potential for applicationin transparent and flexible electronicdevices. However, the source and drain (S/D) electrodesof IGZO TFTs with indium tin oxide (ITO) thin films can cause Schottkylike behavior in the output characteristics owing to the formation of a potential barrier between the IGZO and ITO thin films. In this study, we designed and fabricated TFTs by applying a novel ITO S/D electrode layer (375 nm) with co-sputtered IGZO and ITO thin films (125 nm) deposited at room temperature. The proposed TFT exhibits superior electric characteristics (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> = 35.4 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs) compared to those of TFTs with conventional ITO electrodes (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> = 9.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs) owing to its lower contact and channel resistance and the generation of a surface reaction between S/D and channel layers, creating additional oxygen vacancies at the IGZO channel region. The proposed S/D electrode could be fabricated on a glass substrate at low temperatures (below 200 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C). The excellent electrical properties of the proposed IGZO TFT are expected to promote the application of TFTs in advanced displays.

Solution Processable, Flexible, and Transparent Hybrid Electrodes Using Tungsten Oxide Buffer Layer on Silver Nanowires.

In this study, we fabricate solution processable, flexible, and transparent hybrid electrodes. The hybrid electrodes are designed by depositing a tungsten trioxide (WO3) buffer layer on silver nanowires. The fabrication method is solution based, and the electrodes can be fabricated directly on a flexible substrate at low temperatures. This fabrication method is cost-effective and scalable. The hybrid electrodes show high flexibility, transparency, and conductivity. In addition, since the thickness of the WO3 buffer layer can be controlled, the transparency, conductivity, and surface roughness of the hybrid electrodes can be tailored. These hybrid electrodes are potential alternatives to conventional indium tin oxide electrodes for flexible electronic devices.

Flexible Transparent Electrodes Based on Silver Nanowires: Material Synthesis, Fabrication, Performance, and Applications

AbstractOwing to their compatibility with biology and large deformation, flexible electronics meet the demands for a wide range of applications that lie outside the capabilities of conventional rigid wafer‐based electronics. Devices such as solar cells, light‐emitting devices, touch screens, and wearable sensors have significantly advanced in recent years and changed human life. Flexible transparent electrodes are one of the most important components in flexible optoelectronic devices, collecting charges and transmitting light. Such electrodes based on silver nanowires (AgNWs), which exhibit superior mechanical flexibility, electrical and thermal conductivity, and optical transparency, are regarded as the most promising alternative to conventional indium tin oxide electrodes. However, some technical challenges, such as the uniformity and stability of AgNW networks, still exist and hinder the large‐scale commercialization of AgNW electrodes. Great efforts have been made in this field. A comprehensive survey of recent progress in flexible transparent AgNW electrodes in terms of performance criteria, material synthesis, fabrication process, performance enhancement, and future applications is provided. Finally, technical challenges and future trends are presented for the application of flexible transparent AgNW electrodes in flexible electronics.

Fabrication of New Liquid Crystal Device Using Layer-by-Layer Thin Film Process

Indium tin oxide (ITO) transparent electrodes are troubled with high cost and poor mechanical stability. In this study, layer-by-layer (LBL)-processed thin films with single-walled carbon nanotubes (SWNTs) exhibited high transparency and electrical conductivity as a candidate for ITO replacement. The repetitive deposition of polycations and stabilized SWNTs with a negative surfactant exhibits sufficiently linear film growth and high optoelectronic performance to be used as transparent electrodes for vertically aligned (VA) liquid crystal display (LCD) cells. The LC molecules were uniformly aligned on the all of the prepared LBL electrodes. VA LCD cells with SWNT LBL electrodes exhibited voltage-transmittance (V-T) characteristics similar to those with the conventional ITO electrodes. Although the response speeds were slower than the LCD cell with the ITO electrode, as the SWNT layers increased, the display performance was closer to the LCD cells with conventional ITO electrode. This work demonstrated the good optoelectronic performance and alignment compatibility with LC molecules of the SWNT LBL assemblies, which are potential alternatives to ITO films as transparent electrodes for LCDs.

Polyaniline/Carbon Nanotubes Composite Modified Anode via Graft Polymerization and Self-Assembling for Microbial Fuel Cells.

Microbial fuel cells (MFCs) are promising devices for sustainable energy production, wastewater treatment and biosensors. Anode materials directly interact with electricigens and accept electrons between cells, playing an important role in determining the performance of MFCs. In this study, a novel carbon nanotubes (CNTs) and polyaniline (PANI) nanocomposite film modified Indium-tin oxide (ITO) anode was fabricated through graft polymerization of PANI after the modification of γ-aminopropyltriethoxysilane (APTES) on ITO substrate, which was followed by layer-by-layer (LBL) self-assembling of CNTs and PANI alternatively on its surface. (CNTs/PANI)n/APTES/ITO electrode with low charge transfer resistance showed better electrochemical behavior compared to the bare ITO electrode. Twelve layers of CNTs/PANI decorated ITO electrode with an optimal nanoporous network exhibited superior biocatalytic properties with a maximal current density of 6.98 µA/cm2, which is 26-fold higher than that of conventional ITO electrode in Shewanella loihica PV-4 bioelectrochemical system. MFCs with (CNTs/PANI)12/APTES/ITO as the anode harvested a maximum output power density of 34.51 mW/m2, which is 7.5-fold higher than that of the unmodified ITO electrode. These results demonstrate that (CNTs/PANI)12/APTES/ITO electrode has superior electrochemical and electrocatalytic properties compared to the bare ITO electrode, while the cellular toxicity of CNTs has an effect on the performance of MFC with (CNTs/PANI)n/APTES/ITO electrode.

Optical properties of conductive silver-nanowire films with different nanowire lengths

Transparent electrodes made of silver nanowires (Ag NWs) exhibit a higher flexibility than conventional indium tin oxide electrodes. For this reason, Ag NWs may find applications in future flexible electronic and optoelectronic devices. However, different optoelectronic devices have different specific requirements for Ag NWs. For example, the optical transmittance haze is an important but rarely studied aspect of Ag NW films. In this study, the optical transmittance and optical scattering of long (5–50 μm, L-NWs) and short (1–20 μm, S-NWs) Ag NW films were investigated. The L-NWs exhibited better optical transmission than the S-NWs, whereas the S-NWs exhibited better light-scattering properties than the L-NWs. Our results indicate that the L-NWs are suitable for touch-screen displays, whereas the S-NWs are better suited as transparent conductive films for solar cells. We analyzed the scattering ratio of forward-scattered light to backscattered light for both the L-NWs and S-NWs and discovered that the mesh size affected the scattering ratio. For longer wavelengths, a larger mesh yielded a higher backscattering ratio, whereas a smaller mesh yielded a lower backscattering ratio. We formulated an equation for calculating the reflection haze using the total reflection (Ag NWs/glass), R and the reflection of glass, R 0. The reflection haze of the S-NWs and L-NWs exhibited different trends in the visible–near-infrared region. An omnidirectional scattering model for the Ag NWs was used to evaluate the Ag NW scattering properties. The results of this study have great significance for the evaluation of the performance of Ag NWs in optoelectronic devices.

Electro-optical Properties of Twisted Nematic Liquid Crystal Cell with Silver Nanowire Network Electrodes

This paper introduces liquid crystal (LC) alignment and its electro-optical properties in the LC cells with silver nanowire (AgNW) networks. The AgNW network was used as an electrode of LC cell as a substitute for an indium-tin-oxide (ITO) film. LC alignment characteristics in the LC cell using AgNW networks, which have two different sheet resistances of 60 Ω/㎡ and 80 Ω/㎡, were observed. The LC alignment characteristics including pretilt angle, LC alignment state, and thermal stability are similar irrespective of sheet resistance of AgNW network. However, twisted-nematic (TN)-LC cell normally operated when using AgNW network with sheet resistance of 80 Ω/㎡. Electrooptical properties of TN-LC cell exhibited competitive performance compared to those of TN-LC cell based on conventional ITO electrode, which allow new approaches to replace conventional ITO electrode in display technology.

Effects of the Ag Layer Embedded in NIZO Layers as Transparent Conducting Electrodes for Liquid Crystal Displays

In the present work, a Ni-doped indium zinc oxide (NIZO) film and its multilayers with Ag layers were investigated as transparent conducting electrodes for liquid crystal display (LCD) applications, as a substitute for indium tin oxide (ITO) electrodes. By interposing the Ag layer between the NIZO layers, the loss of the optical transmittance occurred; however, the Ag layer brought enhancement of electrical sheet resistance to the NIZO/Ag/NIZO multilayer electrode. The twisted nematic cell based on the NIZO/Ag/NIZO multilayer electrode exhibited superior electro-optical characteristics than those based on single NIZO electrode and was competitive compared to those based on the conventional ITO electrode. An LCD-based NIZO/Ag/NIZO multilayer electrode may allow new approaches to conventional ITO electrodes in display technology.

Flexible transparent electrodes for organic light-emitting diodes

The use of flexible organic light-emitting diodes (OLEDs) for the next-generation displays and solid-state lightings has been considered, but the widely used transparent conducting electrode (TCE), indium–tin-oxide (ITO), should be replaced by flexible electrodes due to its brittleness and increasing cost. Therefore, many kinds of alternative TCEs have been increasingly studied. In this paper, the properties and applications of the candidate transparent flexible electrodes classified into four categories (conducting polymer, silver nanowire, carbon nanotube and graphene) are described. This paper finally suggests how to develop alternative TCEs for replacing the conventional ITO electrode.

Effect of geometric lattice design on optical/electrical properties of transparent silver grid for organic solar cells.

Silver (Ag) grid transparent electrode is one of the most promising transparent conducting electrodes (TCEs) to replace conventional indium tin oxide (ITO). We systematically investigate an effect of geometric lattice modifications on optical and electrical properties of Ag grid electrode. The reference Ag grid with 5 μm width and 100 μm pitch (duty of 0.05) prepared by conventional photo-lithography and lift-off processes shows the sheet resistance of 13.27 Ω/sq, transmittance of 81.1%, and resultant figure of merit (FOM) of 129.05. Three different modified Ag grid electrodes with stripe added-mesh (SAM), triangle-added mesh (TAM), and diagonal-added mesh (DAM) are suggested to improve optical and electrical properties. Although all three of SAM, TAM, and DAM Ag grid electrodes exhibit the lower transmittance values of about 72 - 77%, they showed much decreased sheet resistance of 6 - 8 Ω/sq. As a result, all of the lattice-modified Ag grid electrodes display significant improvement of FOM and the highest value of 171.14 is obtained from DAM Ag grid, which is comparable to that of conventional ITO electrode (175.46). Also, the feasibility of DAM Ag gird electrode for use in organic solar cell is confirmed by finite difference time domain (FDTD) simulations. Unlike a conventional ITO electrode, DAM Ag grid electrode can induce light scattering and trapping due to the diffuse transmission that compensates for the loss in optical transparency, resulting in comparable light absorption in the photo active layer of poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₀BM). P3HT:PC₆₀BM based OSCs with the DAM Ag grid electrode were fabricated, which also showed the potential for ITO-free transparent electrode.

Optical and electrical properties of transparent conducting gallium-doped ZnO electrodes prepared by atomic layer deposition for application in organic solar cells

Transparent and conducting gallium-doped ZnO electrodes were fabricated by means of atomic layer deposition. The electrode showed the lowest resistivity of 7.19×10−4Ωcm at a 5% cyclic layer deposition ratio of Trimethyl-gallium and Diethyl-zinc chemicals. The electrodes showed minimum resistivity when deposited at a temperature of 250°C. The electrode also showed optical transmittance of about 82%–89% with film thicknesses between 100nm and 300nm. An organic solar cell made with a 300-nm-thick gallium-doped ZnO electrode exhibited 2.5% power conversion efficiency, and an efficiency equivalent to that of cells made with conventional indium tin oxide electrodes.

Improved performance of flexible amorphous silicon solar cells with silver nanowires

A novel hybrid electrode structure using Ag nanowires (NWs) to create surface plasmons to enhance light trapping is designed and applied on the front surface of hydrogenated amorphous silicon (a-Si:H) solar cells on steel substrates, targeting broad-band absorption enhancements. Ag NWs were synthesized using a soft and self-seeding process. The produced Ag NWs were deposited on indium tin oxide (ITO) glass substrates or the ITO layers of the as-prepared flexible a-Si:H solar cells to form Ag NW-ITO hybrid electrodes. The Ag NW-ITO hybrid electrodes were optimized to achieve maximum optical enhancement using surface plasmons and obtain good electrical contacts in cells. Finite-element electromagnetic simulations confirmed that the presence of the Ag NWs resulted in increased electromagnetic fields within the a-Si:H layer. Compared to the cell with conventional ITO electrode, the measured quantum efficiency of the best performing a-Si:H cell shows an obvious enhancement in the wavelength range from 330 nm to 600 nm. The cell based on the optimized Ag NW-ITO demonstrates an increase about 4% in short-circuit current density and over 6% in power conversion efficiency under AM 1.5 illumination.

Light-trapping design of graphene transparent electrodes for efficient thin-film silicon solar cells

In this paper, the performance of solar cells with graphene transparent electrodes is compared with cells using conventional indium tin oxide (ITO) electrodes, and it is demonstrated the optical absorption of solar cells with bare graphene structure is worse than that of bare ITO structure because of the higher refractive index of graphene. To enhance the light trapping of graphene-based thin-film solar cells, a simple two-layer SiO(2)/SiC structure is proposed as antireflection coatings deposited on top of graphene transparent electrodes, and the thickness of each layer is optimized by differential evolution in order to enhance the optical absorption of a-Si:H thin-film solar cells to the greatest degree. The optimization results demonstrate the optimal SiO(2)/SiC/graphene structure can obtain 37.30% enhancement with respect to bare ITO structure, which has obviously exceeded the light-trapping enhancement of 34.15% for the optimal SiO(2)/SiC/ITO structure. Therefore, with the aid of the light-trapping structure, the graphene films are a very promising indium-free transparent electrode substitute for the conventional ITO electrode for use in cost-efficient thin-film silicon solar cells.

Highly clear conductive polymer electrode films hybridized with gold nanoparticles

Improved conductive poly(3,4-ethylenedioxy thiophene) (PEDOT) electrode films were made through hybridization with charged gold nanoparticles. The conductivity of these hybrid films increased more than seven times than the value for the PEDOT alone. The optimized films show a sheet resistance value down to 85 ohm·sq−1 at 85% transparency when PEDOT was hybridized with gold particles of 12 nm diameter, and the organic light-emitting diode devices deposited on these electrodes show a performance equivalent to that of devices based on a conventional indium tin oxide electrode.