High-performance Transparent Electrodes Research Articles

High-performance composite transparent electrode composed of ultra-long silver nanowires and antimony-doped tin oxide nanoparticles

Composite transparent conductive electrodes (TCEs) consisting of silver nanowires (AgNWs) and conductive metal oxides are very promising for flexible optoelectronic devices due to their smooth surface morphology and high chemical stability. However, it is still challenging to ensure high optoelectronic performance and long-term stability in practical applications. Here, we solved these problems by coating antimony-doped tin oxide (ATO) nanoparticles dispersion on ultra-long AgNWs network using waterborne polyurethane (WPU) binder. Ultra-long nanowires occupy less wire-wire junctions and space than short nanowires, thus increasing the optoelectronic performance and flexibility of the composite TCE. WPU improves the adhesion and stability of ATO nanoparticles to the substrate and AgNWs network. The fabricated composite TCE showed a low sheet resistance of 11.9 Ω sq−1, good optical transmittance of 83% at 550 nm and a figure of merit (FOM) of 162 compared to PET/ITO electrode. It also showed excellent mechanical flexibility, adhesion to the substrate and solvent stability. Furthermore, the long-term conductivity was maintained under ambient conditions for 60 days.

Size-Optimized Silver Nanowires with Graphene Oxide for High-Performance Transparent Electrodes

Silver nanowires (AgNWs)-based transparent electrode is one critical component for many modern electronic devices, however, preparation of high-performance AgNWs-based transparent electrode with appealing light transmittance and long-term stability is still challenging. Herein, by combining the size-optimized AgNWs with graphene oxide (GO), the composite AgNWs/GO film electrode with high light-transmittance and appealing stability is prepared. For the size-controlled preparation of AgNWs, well-defined one-dimensional structure (average diameter = 62 nm) is obtained by elaborately adjusting the Br− concentration (0.05 mM), Cl− concentration (1 mM), ratio of PVP/AgNO3 (5:1) and PVP-type selection (PVP1300k: PVP58k = 2:1), contributing to a high light transmittance of 84% for the corresponding AgNWs-based electrode. After further introducing the GO, the film electrode presents much enhanced stability and increased film-substrate adhesive strength, namely only 3.6% increase in resistance after 1000 cycles of bending and being stable even under ultrasonic vibration. The results can provide new insights for designing electrode with ultrastability and high light transmittance.

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.

Tailoring Optoelectronic Properties of ZnO Films Through Synergistic Mg and B Co-Doping for Unprecedented High-Performance Transparent Electrode Applications

The quest for indium-free transparent conductive electrodes with enhanced optical band gaps and superior electrical conductivity is imperative for the advancement of flexible electrochromic devices. This study presents a groundbreaking approach wherein composite ZnO films, incorporating Mg and/or B dopants through a facile sol–gel spin coating method, are meticulously crafted and systematically scrutinized for their optoelectrical properties. Our findings reveal that Mg doping primarily influences the optical band gap, while B doping facilitates the augmentation of free electrons by modulating morphology and electronic defect states. Optimal performance is achieved with pure Mg doping at an atomic molar concentration of 0.2, resulting in a ZnMgO film boasting an exceptional average transmittance of 98.79% and an impressively low electrical resistivity of 15.3 Ω·cm. Although pure B doping compromises the crystalline quality, it significantly reduces electrical resistivity. Intriguingly, co-doping with Mg at an atomic molar concentration of 0.2 introduces challenges to crystalline quality but enriches the composite film with additional charge carriers, leading to a reduction in bandgap and a remarkable drop in resistance to 6.2 Ω·cm. This innovative work not only sheds light on the delicate balance between Mg and B doping in ZnO films but also paves the way for unparalleled opportunities in the development of high-performance transparent conductive electrodes for flexible electrochromic devices.

Optimization of photoelectric properties of transparent conductive B and Ga co-doped ZnO films for electrochromic applications

To improve the performance of electrochromic devices, it is urgently necessary to develop transparent indium-free conductive electrodes with high conductivity and transparency. In this study, thin films of Ga-doped ZnO (GZO) and B–Ga co-doped ZnO (BGZO) were prepared on glass substrates using the plasma-assisted atomic layer deposition (PEALD) technique, and their structural and optoelectronic properties were characterized. It is found that all thin films were consistent with hexagonal fibrous ZnO structure, and the surface morphology of the membrane was homogenous at nanoscale. UV spectroscopy analysis showed that the doping of B and Ga elements could increase the transparency of ZnO films. The electrical properties can be remarkably enhanced by doping with B and Ga elements. Further more, tungsten oxide (WO3) was deposited on the as-prepared BGZO films using magnetron sputtering method. We activated the sample by applying voltage and observed a color transition from transparent to dark blue. It has a modulation range of 65 % in the 633 nm spectrum and a coloring efficiency of 37.8 cm2C-1. This work opens up remarkable new opportunities for developing high-performance transparent conductive electrode in electrochromic devices.

Smooth, Chemically Altered Nucleating Platform for Abrupt Performance Enhancement of Ultrathin Cu-Layer-Based Transparent Electrodes.

Rapid advances in flexible optoelectronic devices necessitate the concomitant development of high-performance, cost-efficient, and flexible transparent conductive electrodes (TCEs). This Letter reports an abrupt enhancement in the optoelectronic characteristics of ultrathin Cu-layer-based TCEs via Ar+-mediated modulation of the chemical and physical states of a ZnO support surface. This approach strongly regulates the growth mode for the subsequently deposited Cu layer, in addition to marked alteration to the ZnO/Cu interface states, resulting in exceptional TCE performance in the form of ZnO/Cu/ZnO TCEs. The resultant Haacke figure of merit (T10/Rs) of 0.063 Ω-1, 53% greater than that of the unaltered, otherwise identical structure, corresponds to a record-high value for Cu-layer-based TCEs. Moreover, the enhanced TCE performance in this approach is shown to be highly sustainable under severe simultaneous loadings of electrical, thermal, and mechanical stresses.

Free-standing ultra-thin film with semi-embedded metal nanofiber web for high-performance flexible transparent electrodes

We develop a novel manufacturing process for freestanding conductive nanofiber web films in which metal nanofibers are semi-embedded in polydimethylsiloxane (PDMS) to realize high-performance flexible transparent electrode films. This concept utilizes a sacrificial layer to induce a very thin, free-standing film, and the semi-embedded structure maintains the nanofiber web structure. The excellent adhesion properties of PDMS as well as improved mechanical strength mean that it can be applied to large area devices. In this study, we demonstrate that our approach has improved mechanical strength and excellent conductivity through transparency/conductivity analysis and bending, cycle, and taping tests.

High Performance Transparent Silver Grid Electrodes for Organic Photovoltaics Fabricated by Selective Metal Condensation.

We report silver grid electrodes on glass and flexible plastic substrates with performance that exceeds that of commercial indium-tin oxide (ITO) coated glass and show their suitability as a drop-in replacement for ITO glass in solution processed organic photovoltaics (OPVs). When supported on flexible plastic substrates these electrodes are stable towards repeated bending through a small radius of curvature over tens of thousands of cycles. The grid electrodes are fabricated by the unconventional approach of condensation coefficient modulation using a perfluorinated polymer shown to be far superior to the other compounds used for this purpose to date. The very narrow line-width and small grid pitch that can be achieved also opens the door to the possibility of using grid electrodes in OPVs without a conducting PEDOT:PSS layer to span the gaps between grid-lines. This article is protected by copyright. All rights reserved.

High work function thermally stable OMO-based transparent electrode for optoelectronic applications

Ultrathin metal films (UTMFs) have emerged as a potential contender as a transparent electrode (TE) in various optoelectronic applications. Oxide-metal-oxide (OMO) based TEs incorporating UTMFs are the new state-of-the-art approach towards fabricating high-performance indium-free TEs. Here, we have demonstrated an OMO-based indium-free TE utilizing nickel oxide (NiO) and silver (Ag) as oxide and metal films respectively. Optical constants of NiO and Ag obtained from spectroscopic ellipsometry have been utilized in determining the optimum thickness of alternate layers in the OMO stack using a MATLAB code based on the transfer matrix method. To minimize the reflection losses, 40 nm of NiO as films was deposited on either side of the Ag film. A highly transparent NiO/Ag/NiO (NAN) electrode has been obtained by the physical vapor deposition technique. The fabricated TE shows high transmittance >82% in the visible region along with a low sheet resistance below 6 Ω/□. To analyze the thermal stability of NAN-TE, it has been treated at different elevated temperatures. It was observed that NAN-TE shows better thermal stability in comparison to commercially available ITO-TE. The incorporation of NiO as an overcoat layer results in enhancing the work function to 5.35 eV as measured by Kelvin Probe Force Microscopy (KPFM). The high average visible transmittance, high work function, low sheet resistance, and high-temperature tolerance make the developed TE compatible with optoelectronic devices where high-temperature processing is necessary. To verify the same a bifacial perovskite solar cell is fabricated incorporating the NAN-TE as top TE and a power conversion efficiency (PCE) of 3.51% and 2.56% is obtained by illuminating the fabricated device from FTO and NAN side.

Micro–nano dual-scale embedded graphene/Ag architectures for flexible low-voltage-driven transparent electrothermal films

Micro–nano dual-scale embedded graphene/Ag architectures are designed for fabricating high-performance flexible transparent electrodes, thus realizing low-voltage-driven transparent electrothermal films.

Effect of the Blade-Coating Conditions on the Electrical and Optical Properties of Transparent Ag Nanowire Electrodes.

Optimizing the coating conditions for a doctor blading system is important when seeking to improve the performance of Ag nanowire electrodes. In this study, the effect of the blading height and speed on the optical and electrical properties of Ag nanowire electrodes was investigated. Ag nanowires were first spread on a PET substrate using a doctor blade with differing heights at a fixed blading speed. An increase in the blading height resulted in the degradation of the optical transmittance and stronger haze due to the higher probability of Ag nanowire agglomeration arising from the greater wet thickness. When the blading speed was varied, the optical transmittance and haze were unaffected up until 20 mm/s, followed by minor degradation of the optical properties at blading speeds over 25 mm/s. The higher speeds hindered the spread of the Ag nanowire solution, which also increased the probability of Ag nanowire agglomeration. However, this degradation was less serious compared to that observed with a change in the blading height. Therefore, optimizing the blading height was confirmed to be the priority for the production of high-performance transparent Ag nanowire electrodes. Our study thus provides practical guidance for the fabrication of Ag nanowire electrodes using doctor blading systems.

Synthesis of oxidation-resistance copper nanowires-formate for high-performance transparent conductive electrodes

In this study, high-aspect-ratio (~1250) curved copper nanowires (CuNWs) composed of formate (FA) as the surface passivation layer were synthesized by the solvothermal method using sodium formate (HCOONa). Experimental data and density functional theory (DFT) simulations suggest that the growth of CuNWs-FA was due to the high chemisorption energy of FA on the [100] plane of Cu. The relative resistance ratio of CuNWs-FA increased by 1.67 and 1.72 after aging at 25 °C for 60 days and 60 °C for 5 days, showing FA passivation greatly improved the oxidation resistance of CuNWs. The transparent conductive electrodes (TCEs) fabricated from CuNWs-FA showed high transmittance (89.19%), low sheet resistance (Rs = 44.54 Ω sq−1), and excellent mechanical stability against 10,000 bending cycles. The TCEs-based transparent flexible heaters (TFHs) exerted a fast heating rate and a uniform temperature distribution within the 20 s response time, which is a testament to the CuNWs-FA in applications such as electrochromic and optoelectronic devices. This passivation approach sheds light on solving the major drawback of CuNWs oxidation and promotes its use in flexible electronic devices.

PDMS micro-dewy spider-web-like metal nanofiber films for fabrication of high-performance transparent flexible electrode with improved mechanical strength

Research to develop next-generation flexible transparent electrode materials using various nanomaterials is being actively pursued, and nanomaterials with sufficient conductivity and transparency for replacing ITO have been realized. However, because numerous nanomaterials are in contact physically and overlap with each other to form a wide conductive two-dimensional space, the mechanical strength of an electrode film composed of nanomaterials and the adhesion to the substrate are limited significantly. In this study, we develop a new fabrication process for microsized polydimethylsiloxane (PDMS) droplet-coated conductive nanofiber web films to achieve high-performance flexible transparent electrode films. This concept is inspired by the structure of a spider web with dew, and PDMS microdroplets with transparency and elasticity mimicking the dew of a spider web are introduced into the film. These PDMS microdroplets can improve the mechanical strength to maintain the nanofiber web structure, as well as improve adhesion with various substrates and films owing to the excellent adhesive properties of PDMS. In this study, we confirm the superiority of our approach via transparency/conductivity analysis as well as bending, cycle, wind resistance, and immersion tests. Because this approach involves an extremely short process time of less than 5 min as well as inexpensive equipment and materials, it is expected to be widely applied to various next-generation optoelectronic devices such as flexible displays and wearable devices.

Highly conductive and stretching-insensitive transparent electrodes based on CuNWs

Flexible transparent electrode is attracting a lot of attention for various applications due to their versatile ability. However, it is still challenging to apply transparent electrode in stretchable application, because the conductivity will be degraded even lost when the electrode is stretched. Here, a high-performance transparent electrode with stretching-insensitivity is reported. The electrode is obtained by embedding copper nanowires into wrinkled polydimethylsiloxane elastomers via using simple sol–gel transition. The resulting electrode exhibits low sheet resistance of 16 Ω/sq. at an acceptable transmittance of ∼ 74% at visible region, and tensile stability under below 210% strain. In particular, the resistance is almost unchanged after 2500 stretching cycles with a strain of 70%, indicating excellent stretching-insensitively.

Tailoring of structual, optical, and electrical properties of Cu films by sputtering power and deposition atmosphere

In order to effectively modify the structure and optical-electric properties of Cu films and thus provide guidance for the development of high-performance transparent electrodes based on ultrathin Cu films, different thicknesses of Cu films were prepared by magnetron sputtering under three different sputtering powers and atmospheres (34 W and Ar, 136 W and Ar, and 34 W and Ar + H2). The results show that both increasing the sputtering power and introducing H2 into the sputtering atmosphere can improve film crystallinity, electrically conductive properties, and transparency of the film. Increasing the sputtering power can increase deposition rate, decrease surface roughness, improve stability in air, and help the formation of continuous films, but introducing H2 into the sputtering atmosphere can decrease deposition rate, increase surface roughness, degrade stability in the air, and hinder the formation of continuous films. In addition, the mechanisms of increasing the sputtering power or introducing H2 to affect the crystallinity, surface roughness, and the formation of continuous films are discussed.

Fabrication of high-quality flexible transparent conductive thin films with a Nb2O5/AgNWs/Nb2O5 sandwich structure

Different sandwich structures of flexible transparent conductive thin film (TCFs) composed of Nb2O5 layers and Ag nanowires (AgNWs) have been prepared onto flexible polyethylene terephthalate (PET) substrate at room temperature to develop an indium-free TCF. The AgNWs are synthesized by a modified polyol method and inserted into the Nb2O5 layers that are prepared by radio frequency magnetron sputtering. The optical and electrical properties can be modified by changing the number of spin-coating cycle of AgNW suspension. At optimized condition, we achieve a flexible Nb2O5/AgNWs/Nb2O5 sandwich thin film with a low sheet resistance of 9.61 Ω/square and a high optical transmittance of 84.3%. Meanwhile, the resistance remains nearly constant after 30 tape tests, suggesting a strong adhesion to the PET substrate. The sandwich thin films show high long-term stability to oxidation, humid heat, and chemicals compared with that of AgNW networks, which can be attributed to the effective covering of Nb2O5 layer on the AgNWs. In addition, the Nb2O5/AgNWs/Nb2O5 sandwich thin films show good stability after repeated bending. This Nb2O5/AgNWs/Nb2O5 sandwich thin film can therefore serve as a high-performance transparent conductive electrode for numerous flexible electronic devices.

Solution process formation of high performance, stable nanostructured transparent metal electrodes via displacement-diffusion-etch process

Transparent electrodes (TEs) with high chemical stability and excellent flexibility are critical for flexible optoelectronic devices, such as photodetectors, solar cells, and light-emitting diodes. Ultrathin metal electrode (thickness less than 20 nm) has been a promising TE candidate, but the fabrication can only be realized by vacuum-based technologies to date, and require tedious surface engineering of the substrates, which are neither ideal for polymeric based flexible applications nor suitable for roll-to-roll large-scale manufacture. This paper presents high-performance nanostructured transparent metal electrodes formation via displacement–diffusion-etch (DDE) process, which enables the solution-processed sub-20-nm-thick ultrathin gold electrodes (UTAuEs) on a wide variety of hard and soft substrates. UTAuEs fabricated on flexible polyethylene terephthalate (PET) substrates show a high chemical/environmental stability and superior bendability to commercial flexible indium–tin-oxide (ITO) electrodes. Moreover, flexible organic solar cells made with UTAuEs show similar power conversion efficiency but much enhanced flexibility, in comparison to that of ITO-based devices.

High performance transparent electrodes combining graphene with Joule-heated welded silver nanowires

Various low-dimensional materials are widely used in many fields, such as electroluminescent devices, sensors, solar cells and so on. Among these candidates, silver nanowire-based electrodes stand out due to their excellent optoelectronic properties. In this paper, silver nanowire composite electrodes were welded by Joule-heating to prepare transparent conductive electrodes with high-quality graphene. When the concentration of silver nanowires is 3 mg/ml, the FoM of the composite electrode is at a maximum of more than 100. Joule heat welding can effectively and accurately solve the knotting problem of silver nanowires and greatly improve the conductivity of the films. Subsequently, high-quality graphene was grown by chemical vapor deposition method. The graphene layer improved the conductivity and effectively prevented the formation of AgO or Ag2O. Furthermore, the heat dissipation capability of graphene/silver nanowires electrodes is significantly better than that of ITO electrodes.

High-performance silver nanowires transparent conductive electrodes fabricated using manufacturing-ready high-speed photonic sinterization solutions

On the long road towards low-cost flexible hybrid electronics, integration and printable solar energy harvesting solutions, there is an urgent need for high-performance transparent conductive electrodes produced using manufacturing-ready techniques and equipment. In recent years, randomly-distributed metallic nanowire-based transparent mesh electrodes have proven highly-promising as they offer a superb compromise between high performances and low fabrication costs. Unfortunately, these high figure-of-merit transparent mesh electrodes usually rely heavily on extensive post-deposition processing. While conventional thermal annealing yields good performances, it is especially ill-suited for deposition on low-temperature substrates or for high-throughput manufacturing solutions. Similarly, laser-induced annealing severely limits the processing time for electrodes covering large surfaces. In this paper, we report the fabrication of ultra high-performance silver nanowires-based transparent conductive electrodes fabricated using optimized manufacturing-ready ultrafast photonic curing solutions. Using conventional indium tin oxide (ITO) as our benchmark for transparent electrodes, we demonstrate a 2.6–2.7 times performance gain using two different figure-of-merit indicators. Based on these results, we believe this research provides an ideal manufacturing-ready approach for the large-scale and low-cost fabrication of ultra high-performance transparent electrodes for flexible hybrid electronics and solar-energy harvesting applications.

Effect of vacuum annealing on the optical and electrical properties of sputtered silicon doped indium oxide thin films

Silicon doped indium oxide (SIO) thin-films were deposited on Corning glass substrates using radio frequency magnetron sputtering at room temperature. The deposited SIO thin-films were post annealed under vacuum conditions (∼3.9 × 10−4 Pa) at 100–500 °C, respectively. The XRD analysis confirmed presence of polycrystalline indium oxide (In2O3) with preferred orientation in the (400) plane. Atomic force microscopy images show root mean square roughness ranging between ∼6 and 10 nm. The SIO thin-film post annealed at 400 °C had shown the electrical resistivity, mobility carrier concentration and sheet resistance values of 3.7 × 10−4 Ω-cm, 40 cm2/V.s, 4.2 × 1020 cm−3 and 4.96 Ω/□, respectively. The average transmittance of 76.2%, in the visible region (380–750 nm) was observed for SIO thin-film post annealed at 400 °C. The obtained results confirm that SIO thin films can be used for further development of high-performance transparent electrodes by sputtering technique.