High-performance Transparent Conductive Electrodes Research Articles

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.

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.

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.

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.

Rapid fabrication of high-performance transparent electrodes by electrospinning of reactive silver ink containing nanofibers

All-solution processable fabrication of high performance transparent conductive electrodes is vital for next-generation optoelectronics applications. In this study, rapid and versatile fabrication of high-performance transparent electrodes by synergetic integration of electrospun nanofibers and particle-free reactive silver inks is reported. Direct electrospinning of reactive silver ink containing polymer blend solution followed by a swift thermal annealing enables fabrication of transparent conductive electrodes (TCEs) with a sheet resistance of ∼1.9Ω/sq with 90% transmission. The high-performance TCEs were fabricated within couple of minutes including the electrospinning and thermal annealing duration. The key aspects of our strategy are the use of a polymer blend consisting of poly(ethylene oxide) (PEO) and polyvinylpyrrolidone (PVP) and particle-free nature of reactive silver inks. Practical utility of the fabricated transparent electrodes in Joule heaters that work at temperatures as high as 300°C is presented. The simple, versatile, inexpensive, and rapid fabrication of transparent conductive electrodes can enable broad range of applications.

Fast microwave-assisted synthesis of copper nanowires as reusable high-performance transparent conductive electrode

We report the microwave synthesis of copper nanowires (CuNWs) by using alkylamine-mediated approach. The aspect ratio of CuNWs of this study was two–fold compared to the previous microwave-assisted synthesis study. In addition, we showed that microwave synthesis could produce high aspect ratio CuNWs in a much shorter time compared to conventional method. Purification process of CuNWs was done via a simple and fast centrifugation method using water-hydrophobic organic solvent system. We also show the importance of purification process on the performance of the fabricated transparent conductive electrode (TCE) films. Purified CuNWs TCE showed a low sheet resistance of 35 Ω/sq with high transparency of 81% (at λ550 nm). Furthermore, we demonstrated how the retreatment of acetic acid was able to assist CuNWs to regain its high conductivity even after five cycles of repetitive continuous oxidation process.

Hydrogen reduced graphene oxide/metal grid hybrid film: towards high performance transparent conductive electrode for flexible electrochromic devices

The metal grid and reduced graphene oxide (RGO) are both promising transparent conductive materials for replacing the indium tin oxide (ITO) in flexible optoelectronics. However, the large empty area that exists in the grid together with the relatively high sheet resistance of RGO hinder both the materials for practical applications. In this work, we report for the first time a novel strategy for efficient combination of the metal grid and RGO by using a newly developed room-temperature reduction technique. The obtained RGO/metal grid hybrid films not only overcome the shortcomings of individual components but exhibit enhanced optical and electrical performances (Rs=18Ωsq−1 and T=80%) and excellent flexural endurance. With this hybrid film as the window electrode, a highly flexible electrochromic device with excellent stability and ultra-fast response shorter than 60ms has been successfully fabricated. Considering its high efficiency, high quality, low cost and large area, the strategy would be particularly useful for economically fabricating various metal grid/RGO films which are quite promising high performance transparent and conductive materials for next generation optoelectronic devices.

Optimization of ZnO:Al/Ag/ZnO:Al structures for ultra-thin high-performance transparent conductive electrodes

Al-doped ZnO (AZO)/Ag/AZO multilayer coatings (50–70nm thick) were grown at room temperature on glass substrates with different silver layer thickness, from 3 to 19nm, by using radio frequency magnetron sputtering. Thermal stability of the compositional, optical and electrical properties of the AZO/Ag/AZO structures were investigated up to 400°C and as a function of Ag film thickness. An AZO film as thin as 20nm is an excellent barrier to Ag diffusion. The inclusion of 9.5nm thin silver layer within the transparent conductive oxide (TCO) material leads to a maximum enhancement of the electro-optical characteristics. The excellent measured properties of low resistance, high transmittance in the visible spectral range and thermal stability allow these ultra-thin AZO/Ag/AZO structures to compete with the 1μm thick TCO layer currently used in thin film solar cells.

Transfer of Large-Area Graphene Films for High-Performance Transparent Conductive Electrodes

Graphene, a two-dimensional monolayer of sp(2)-bonded carbon atoms, has been attracting great interest due to its unique transport properties. One of the promising applications of graphene is as a transparent conductive electrode owing to its high optical transmittance and conductivity. In this paper, we report on an improved transfer process of large-area graphene grown on Cu foils by chemical vapor deposition. The transferred graphene films have high electrical conductivity and high optical transmittance that make them suitable for transparent conductive electrode applications. The improved transfer processes will also be of great value for the fabrication of electronic devices such as field effect transistor and bilayer pseudospin field effect transistor devices.