Transparent Electrode Material Research Articles

Zinc Grid Based Transparent Electrodes for Organic Photovoltaics

AbstractZinc is the fifth most electrically conductive metal and is available at a fraction of the cost of the most widely used transparent electrode materials; silver, indium‐tin oxide, and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate, but has been surprisingly overlooked as a current carrying element in organic photovoltaics. Here, a transparent flexible electrode based on an embedded zinc grid with ≈1 µm linewidth is reported and its utility as a drop‐in replacement for indium‐tin oxide coated glass electrodes in model organic photovoltaic devices is demonstrated. The zinc grids are fabricated using the unconventional approach of condensation coefficient modulation, using a micro‐contact printed patterned layer of poly(perfluorooctylmethylmethacrylate) to resist zinc condensation in the gaps between grid lines, together with a copper acetylacetonate seed layer to nucleate zinc condensation where grid lines are required. Density functional theory calculations of the strength of the interaction between zinc atoms and this fluorinated polymer provide fundamental insight into why the latter is so effective at resisting zinc condensation. The resulting zinc grid is embedded in a flexible polymer support and transferred to a flexible plastic substrate by delamination, which enables recovery and reuse of the fluorinated polymer.

Preparation and Optoelectrical Property of Silver Nanowire Transparent Conductive Film via Slot Die Coating

Silver nanowire transparent conductive films (AgNW TCFs), as the novel transparent electrode materials replacing ITO, are anticipated to be applied in numerous optoelectronic devices, and slot-die coating is currently acknowledged as the most suitable method for the mass production of large-sized AgNW TCFs. In this study, sodium carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA), as film-forming aids, and AgNWs, as conductive materials, were utilized to prepare a specialized AgNW ink, and a slot-die coating is employed to print and prepare AgNW TCFs. The optoelectrical properties of AgNW TCFs are optimized by adjusting the compositions of AgNW ink and the process parameters of slot-die coating. The suitable compositions of AgNW ink and the optimal parameters of slot-die coating are a CMC type of V, a PVA volume of 1 mL, a AgNW volume of 1.5 mL, a volume ratio of 30 and 45 nm AgNWs (2:1), and a coating height of 400 μm. The resultant AgNW TCFs achieve excellent comprehensive optoelectronic performance, with a sheet resistance of less than 50 Ω/sq, a visible light transmittance exceeding 92%, and a haze below 1.8%. This research provides a valuable approach to producing AgNW TCFs on a large scale via the slot-die coating.

Exploring new dimensions beyond ITO: a comprehensive study of transparent conductive materials using a novel figure of merit for photovoltaics

The field of photovoltaics faces a challenge in selecting transparent conductive electrode materials, especially due to limitations of commonly used Indium Tin Oxide (ITO) in terms of cost and brittleness. To address this, a comprehensive Figure of Merit ( FOM ) has been derived, incorporating mechanical, electrical, and optical properties of the materials. This novel FOM equation, denoted as ‘FOM (CoMEO)’, guides the evaluation of transparent conductive materials. Systematic simulations and sensitivity analyses explore the trade-offs among different parameters. Remarkably, our findings reveal that Silver Nanowires (AgNWs) exhibit the highest FOM value at 688 × 10−6 m3/Ω. Zinc Oxide doped with Aluminium (ZnO:AI) also demonstrates promising performance with an FOM of 295.4 × 10−6 m3/Ω. Even the traditional ITO stands out at 36.16 × 10−6 m3/Ω. These results make AgNWs, ZnO:AI, and ITO promising candidates for high-efficiency photovoltaic devices. This study not only addresses the urgent need for optimised transparent conductive electrodes but also lays the foundation for a new era of photovoltaic materials that are efficient, cost-effective, and mechanically robust.

Bimodal functionality of highly conductive nanostructured silver film towards improved performance of photosystem I-based graphene photocathode

We present the novel design of photosystem I (PSI)-based biosolar cell, whereby conductive transparent electrode materials, such as ITO or FTO, are replaced with glass covered with silver island film. This nanostructured metallic layer combines high electric conductance with enhancing the absorption efficiency of the PSI biocatalyst via the plasmonic effect. We demonstrate strong enhancement of the photocurrent generated in the biohybrid electrode composed of oriented layers of PSI reaction centers due to plasmonic interactions of the PSI fluorophores and redox centres with the conductive silver island film.

Directed crystallization of a poly(3,4-ethylenedioxythiophene) film by an iron(III) dodecyl sulfate lamellar superstructure

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), a successfully commercialized polymeric semiconductor material, has potential as a transparent electrode in flexible electronic devices, yet has insufficient conductivity. We present the synthesis, properties, and directed crystallization of the PEDOT:dodecyl sulfate (PEDOT:DS) film. Iron(III) dodecyl sulfate (Fe(DS)3) multi-lamellar vesicles (MLVs), a new growth template, are used to synthesize and direct the growth of the PEDOT:DS film via vapor-phase polymerization of 3,4-ethylenedioxythiophene to form huge PEDOT:DS co-crystal domains within the MLV superstructure. The polycrystalline film has metallic conductivity (avg. ~1.0 × 104 S cm−1), is highly transparent and mechanically durable yet flexible, and suitable for next-generation flexible electronics. These noteworthy properties are conferred by the MLV lamellar superstructure of Fe(DS)3, a selective oxidant and an efficient in situ dopant that enhances the film hydrophobicity and durability. Sophisticated MLV-type oxidants are foreseen to enable the synthesis of more conductive, transparent, robust, flexible, and water-stable polymer electrode materials in future.

Highly Transmittance, Mechanical, Thermally Stable Silver Nanowires Network Using ZnO Nanoparticles.

This research addresses challenges with silver nanowires (Ag NWs) as transparent conductive electrodes (TCEs) and heaters in commercial devices. Here, zinc oxide nanoparticles (ZnO NPs) are first reported as a protective layer for Ag NWs. Multi-physics simulations confirm enhanced thermal stability due to improved heat dissipation, temperature distribution, and thermal conductivity from ZnO. When Ag NWs are surrounded by air, heat transfers mainly through convection and radiation because of air's low conduction coefficient. Encasing Ag NWs in ZnO enhances heat transfer to the ZnO surface, accelerating cooling and dissipating more heat into the atmosphere via convection. The results show composite's efficiency in the Joule effect, maintaining a consistent temperature of 78°C for 700s after 500 bending cycles, a significant improvement over Ag NWs operating for only 5s at 80°C. Additionally, the composite film exhibited exceptional performance, including a sheet resistance of 9.8Ωsq-1 and an optical transmittance of 96.96 %, outperforming Ag NWs, which have a sheet resistance of 12Ωsq-1 and a transmittance of 94.11%. The combination of enhanced electrical, thermal, and mechanical stability, along with impressive optical properties, makes Ag NWs/ZnO NPs a promising candidate for transparent conductive electrode materials in various applications.

Carbon-doped ZnO thin films: A transparent conductive oxide for application in solar-blind photodetectors

Transparent conductive oxide (TCO) films are crucial in optoelectronic devices, such as photodetectors, due to their unique blend of transparency and electrical conductivity. ZnO is a top choice for TCOs owing to its excellent properties, non-toxicity, and cost-effectiveness. In this work, we explore the potential of carbon doping to enhance the electrical properties of ZnO films for transparent conductive applications. Our findings reveal that C-doped ZnO (ZnO:C) films retain the pristine high quality and surface morphology despite an increase in defects with higher C doping. Notably, C doping does not compromise the visible light transmittance of ZnO films, while inducing a gradual increase in optical bandgap, indicative of the typical Burstein–Moss effect. As carbon doping increases, the ZnO:C films exhibit improved carrier concentration, lower resistivity, and sustained high mobility, achieving optimal performance with an electron concentration of 3.73 × 1019 cm−3, resistivity of 3.69 × 10−3 Ω cm, and mobility of 46.08 cm2 V−1 s−1. Finally, we utilized ZnO:C films as a transparent electrode material in ε-Ga2O3-based photodetector, achieving the development of transparent device and attaining high-performance solar-blind detection capabilities. This work provides a strategy for developing a transparent conductive oxide, with ZnO:C emerging as a promising rival to IIIA-doped ZnO for optoelectronic applications.

ZnO nanoarrays/Cu nanowires composite films with high haze value

In this work, we worked on compositing Cu nanowires (NWs) with ZnO nanoarrays (NAs) to enhance the light trapping abilities of transparent conductive films. A well-dispersed, crosslinked network of Cu NWs with appropriate light trapping ability was formed on the surface of the ZnO NAs, and the ZnO NAs/Cu NWs composite structures were obtained ultimately. The Cu NWs on the surface of the composite structures maintained excellent transparency and conductivity while preventing agglomeration phenomena. The ZnO NAs/Cu NWs composite films exhibited low average sheet resistance (59 Ω/sq) and high haze value (0.53) at 550 nm with uniform conductivity and exceptional light trapping performance. The composite films not only demonstrate enhanced light trapping abilities, but also exhibit improved electrical properties, making it an outstanding candidate for transparent front electrode materials in solar cell applications.

Indirect Liftoff Mechanism for High‐Throughput, Single‐Source Laser Scribing for Perovskite Solar Modules

AbstractA high‐throughput, single‐source laser scribing method exploiting a transparent conducting oxide (TCO) indirect liftoff mechanism is developed to produce serially interconnected perovskite solar modules. The TCO‐based indirect liftoff mechanism relies solely on laser absorption in the front transparent electrode material reducing thermal damage to the overlying layers and allowing for fast scribing speeds with low‐cost μs‐pulse duration fiber laser systems. Minimal resistive power losses are observed with the method compared to conventional ablative laser scribes, maintaining the power conversion efficiencies of small‐area devices (≈0.2 cm2) across significantly larger deposition areas (≈1 cm2). Demonstrating > 3 m s−1 processing speeds, TCO‐based liftoff provides the highest throughput laser scribing method for thin‐film photovoltaic devices produced on glass/TCO substrates, capable of processing large‐area perovskite solar modules at a manufacturing scale.

Stretchable Substrates with 3D Wave Patterned Surface for Enhanced Mechanical Stability of Indium Tin Oxide Electrodes

AbstractFlexible electronic devices have promising applications in many future technologies such as wearables, implantables, robotics, and displays. Among the distinct types of mechanical flexibility, stretchability stands as a significant challenge. A particularly demanding objective is the realization of a high‐performance transparent electrode that endures stretching and can be mass produced, all while avoiding additional restrictions on device density. In this work, it is demonstrated that a 3D wave patterned surface provides a threefold improved strain performance of deposited indium tin oxide electrodes, in a statistical comparison of 3D wave patterned and planar surfaces, where indium tin oxide electrodes are stretched to electrical failure. Moreover, this platform alleviates residual thin film stress, allowing for easier handling of the substrates. This study demonstrates the feasibility of attaining stretchability for upcoming electronic devices using a scalable platform that incorporates high‐performance transparent electrode materials using only conventional materials and fabrication steps.

ELECTRICAL, OPTICAL, AND CHEMICAL PROPERTIES OF GRAPHENE THIN FILMS FABRICATED BY VACUUM FILTRATION TECHNIQUE

There has been considerable interest in graphene as a transparent electrode material because of its extraordinary features, such as high optical transmittance, high electrical conductivity, excellent thermal conductivity, exceptional mechanical strength, and remarkable electrochemical capacity. In addition, transparent conductors’ graphene thin films have been considered a promising candidate to replace currently utilized indium tin oxide films, which are unlikely to meet future demands because of their rising cost. In this study, a vacuum filtration process along with isopropyl alcohol (IPA)-assisted with direct transfer (IDT) technique is used to prepare wide-area highly conductive graphene thin films on different substrates including (glass, and PET). The graphene thin films' optical, structural, and electrical properties are studied. The graphene sheets are deposited homogeneously on the substrate, and the distribution of small graphene sheets is observed in SEM images. XPS analysis revealed that the amount of oxygen in graphene decreases significantly with annealing at 500°C and treated with HNO3. Furthermore, the graphene transparent conductive films prepared by the adjusted vacuum filtration method show low sheet resistances of 12.2, 1.41, 1.18, and 0.8 kΩ/sq with transmittances of 81%, 70%, 64.3%, and 46.4% respectively after being annealing at 500°C and treated with HNO3.

Photoelectrochemical Enzyme Biosensor for Malate Using Quantum Dots on Indium Tin Oxide/Plastics as a Sensing Surface.

A photoelectrochemical biosensor for malate was developed using an indium tin oxide (ITO) layer deposited on a poly(ethylene terephthalate) plastic sheet as a transparent electrode material for the immobilization of malate dehydrogenase together with CdTe quantum dots. Different approaches were compared for the construction of the bioactive layer; the highest response was achieved by depositing malate dehydrogenase together with CdTe nanoparticles and covering it with a Nafion/water (1:1) mixture. The amperometric signal of this biosensor was recorded during irradiation with a near-UV LED in the flow-through mode. The limit of detection was 0.28 mmol/L, which is adequate for analyzing malic acid levels in drinks such as white wines and fruit juices. The results confirm that the cheap ITO layer deposited on the plastic sheet after cutting into rectangular electrodes allows for the economic production of photoelectrochemical (bio)sensors. The combination of NAD+-dependent malate dehydrogenase with quantum dots was also compatible with such an ITO surface.

Beyond Flexibility: Transparent Silver Nanowire Electrodes on Patterned Surfaces for Reconfigurable Devices

Silver nanowire (AgNW) emerges as a next‐generation transparent electrode material, offering enhanced flexibility and ease of fabrication compared to traditional transparent electrode materials, such as metallic oxides. In the previous research, the uniform deposition of AgNWs on flat surfaces is demonstrated, exhibiting high conductivity, flexibility, and excellent transmittance. However, the evolution of nano‐electronics technology necessitates the fabrication of transparent electrodes on non‐flat surfaces, such as those found in zenithal bistable devices and reconfigurable Fresnel lenses. In this study, a method is proposed to deposit AgNW material on uneven surfaces using the Mylar‐bar‐coating method, with a polyvinyl chloride (PVC)‐based Fresnel lens serving as the target surface. Additionally, the impact of varying AgNW suspension concentrations on transmittance and sheet resistance is investigated. To further reduce sheet resistance, a layer of conductive polymer, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is deposited on the AgNWs. The measurements reveal that a 2 mg mL−1 sample exhibits a sheet resistance of 187.83 W W−1 with 87.4% transmittance at 550 nm. After the PEDOT:PSS process, the sheet resistance decreases to 122.84 W W−1 with 84.4% transmittance. In this research, a solution is offered for the uniform deposition of AgNWs on patterned surfaces, paving the way for the next generation of optical devices.

Conductive Nanofiber Web Film with Polydimethylsiloxane Sidewalls Selectively Coated through a Plasma Process for High Performance Flexible Transparent Electrodes.

Transparent electrodes are commonly used in various applications, such as solar cells, touch screens, smart windows, wearable electronic devices, and rollable flexible displays. Currently, indium tin oxide (ITO) is widely used as a transparent electrode material. However, ITO is not suitable for next-generation transparent electrodes that require flexibility; therefore, alternative nanomaterials, such as carbon nanotubes, conductive polymers, and metal nanowires, are being studied. However, these nanomaterials have poor mechanical strength and limited substrate availability. In this study, we developed a high-performance transparent electrode web film fabrication process based on conductive nanofibers, in which metal nanofibers are semiembedded in polydimethylsiloxane (PDMS). The mechanical strength of the conductive nanofibers was improved through the PDMS coating on the entire surface of the film, and the semiembedded structure of the nanofibers was realized using the reactive ion etching (RIE) process. In this study, we confirmed through transparency/conductivity analysis and bending, cycle, and taping tests that the transparent electrode fabricated using our approach has excellent mechanical strength and conductivity. Finally, the transparent electrode fabricated using our method can be widely applied as a next-generation transparent electrode because the process is easy and simple and requires inexpensive equipment and materials.

Graphene as advanced applied material in flexible display applications

Flexible display technology has grown in popularity as a study area in the electronics industry as a result of the quick development of flexible electronics technology. Transparent electrodes, the main element of flexible display technology, are crucial for high resolution, high brightness, low power consumption, and interference resistance. A new kind of transparent electrode material is urgently required because conventional applied transparent electrode materials have issues like expensive cost, difficult preparation, and low dependability. Due to its exceptional performance in terms of transparency, electrical conductivity, and flexible bendability, graphene has gained a much interest as an emerging material. In order to provide guidance on the future development of cutting-edge materials for flexible display applications, this paper investigates the use of graphene in flexible displays. It examines graphene's use as a transparent electrode material and a thin film transistor material in flexible displays, as well as its application prospects and development trends. It is found that graphene has a high transparency of 97.7% and high conductivity, which outperforms the generally used indium tin oxide and copper materials. However, further advancements in the mass production of graphene is necessary for the industrialization of graphene in flexible display applications.

Flexible Quantum-Dot Light-Emitting Diodes Using Embedded Silver Mesh Transparent Electrodes Manufactured by an Ultraprecise Deposition Method.

Transparent conductive electrodes (TCEs) fabricated onto flexible substrates are crucial parts of organic-light-emitting diodes (OLEDs), which are vastly utilized for display and lightning applications. Indium tin oxide (ITO), which is so far the most popular material for transparent and conductive electrodes, is found to be an unsuitable candidate for flexible devices mostly due to its brittleness. Here, we present a novel approach for the fabrication of transparent, conductive, and flexible electrodes for optoelectronic applications made of silver metal mesh by an ultraprecise deposition (UPD) method. The fabricated mesh exhibits an 80% (λ = 550 nm) optical transmittance and a sheet resistance of 11 Ω/sq. The Ag-mesh embedded into the polymer is implemented as an anode for a quantum-dot light-emitting diode (QLED) in order to assess its performance. The fabricated QLED is characterized by the maximum external quantum efficiency (EQE) of 2% and a current efficiency (CE) of 6 cd/A, reaching the maximum luminance (L) of 3200 cd/m2 at a current density of 100 mA/cm2. This method shows a fast and relatively simple approach to fabricate optoelectronic devices without the need for special treatment and sophisticated equipment.

Flexible, Transparent, and Cytocompatible Nanostructured Indium Tin Oxide Thin Films for Bio-optoelectronic Applications.

Electrical stimulation has been used successfully for several decades for the treatment of neurodegenerative disorders, including motor disorders, pain, and psychiatric disorders. These technologies typically rely on the modulation of neural activity through the focused delivery of electrical pulses. Recent research, however, has shown that electrically triggered neuromodulation can be further enhanced when coupled with optical stimulation, an approach that can benefit from the development of novel electrode materials that combine transparency with excellent electrochemical and biological performance. In this study, we describe an electrochemically modified, nanostructured indium tin oxide/poly(ethylene terephthalate) (ITO/PET) surface as a flexible, transparent, and cytocompatible electrode material. Electrochemical oxidation and reduction of ITO/PET electrodes in the presence of an ionic liquid based on d-glucopyranoside and bistriflamide units were performed, and the electrochemical behavior, conductivity, capacitance, charge transport processes, surface morphology, optical properties, and cytocompatibility were assessed in vitro. It has been shown that under selected conditions, electrochemically modified ITO/PET films remained transparent and highly conductive and were able to enhance neural cell survival and neurite outgrowth. Consequently, electrochemical modification of ITO/PET electrodes in the presence of an ionic liquid is introduced as an effective approach for tailoring the properties of ITO for advanced bio-optoelectronic applications.

Ultrathin transparent carbon nanotube/LiMn2O4 and carbon nanotube/MoS2 film electrodes for Li-ion full batteries

The increasing demands for wearable devices have significantly facilitated the development of transparent electronics. Serving as key components of fully integrated transparent devices, transparent batteries are urgently needed yet their development is largely hindered by the difficulties of fabricating transparent electrode materials. Here, we successfully designed the transparent cathodes and anodes through combining transparent single-walled carbon nanotubes (SWNTs) films with lithium manganate (CNT/LMO) and molybdenum disulfide (CNT/MoS2), respectively. We found that the fabricated cathode and anode composite films exhibit excellent transmittances of 75% and 80%, respectively. Also, the interconnected SWNT networks in the composite films provide an efficient channel for fast electron transport that significantly contribute to their electrochemical performance. Specifically, when employed as battery electrodes, the highly transparent CNT/LMO cathode and CNT/MoS2 anode show initial areal capacities of 13 and 66 μAh cm−2 at current densities of 0.05 and 0.2 mA cm−2, respectively. More impressively, a full cell, which is constructed with transparent CNT/LMO and CNT/MoS2 composite films as electrodes, shows the capacity retention up to 90% after 100 cycles. The demonstration of transparent electrodes in this study provides a promising strategy to realize the fabrication of fully transparent wearable devices.

Amorphous Transparent Cu(S,I) Thin Films with Very High Hole Conductivity.

Amorphous transparent conductors (a-TCs) are key materials for flexible and transparent electronics but still suffer from poor p-type conductivity. By developing an amorphous Cu(S,I) material system, record high hole conductivities of 103-104 S cm-1 have been achieved in p-type a-TCs. These high conductivities are comparable with commercial n-type TCs made of indium tin oxide and are 100 times greater than any previously reported p-type a-TCs. Responsible for the high hole conduction is the overlap of large p-orbitals of I- and S2- anions, which provide a hole transport pathway insensitive to structural disorder. In addition, the bandgap of amorphous Cu(S,I) can be modulated from 2.6 to 2.9 eV by increasing the iodine content. These unique properties demonstrate that the Cu(S,I) system holds great potential as a promising p-type amorphous transparent electrode material for optoelectronics.

Fabrication of submicron linewidth silver grid/ionogel hybrid films for highly stable flexible transparent electrodes via asymmetric wettability template-assisted self-assembly

High-performance flexible transparent electrodes are the basis for the continuous upgrading of optoelectronic devices. Silver grids are attractive for replacing traditional indium tin oxide (ITO) as the premier transparent electrode materials, due to their high transmittance, excellent conductivity, and low cost. However, large linewidth and oxidation of silver grids are limiting the practical application of the resulting optoelectronic devices. Here, we report an effective and scalable solution-based method to prepare highly stable flexible transparent silver grid electrodes with submicron linewidth by the asymmetric wettability template-assisted self-assembly of silver nanoparticles (AgNPs), which is then encapsulated by a thin transparent conductive ionogel as protective layer. It is demonstrated that the linewidth of silver grids can be precisely controlled by the concentration of the AgNP dispersion. Wrapping with the ionogel nanolayer have no deterioration for conductivity and transmittance of the grid electrodes. The optimized hybrid grid electrodes exhibit low sheet resistance of 24.6 Ω sq−1 and high transparency of 99%. More importantly, the introduction of the iongel nanolayer endows the hybrid grid electrodes with excellent mechanical flexibility and thermal, electrical, and chemical stability. As a proof of concept demonstration, the submicron linewidth silver grid/ionogel hybrid films are successfully used to fabricate flexible smart windows and transparent touch panel. We envision that this work will shed new light on the development of next-generation optoelectronic applications which need ultrahigh resolution displays.