Highly Stable Transparent Conductive Silver Grid/PEDOT:PSS Electrodes for Integrated Bifunctional Flexible Electrochromic Supercapacitors

Abstract

theoretical and practical aspects of supercapacitors in recent years. [4][5][6] Still, supercapacitors with more functionality and novel features are being sought to extend their application range. For example, fl exible, stretchable, and wearable supercapacitors have been developed to meet the requirements of portable and wearable electronics. [7][8][9][10] It would be highly attractive to integrate both an energy-storage and an electrochromism functionality into one device for multiple applications. Such device could be used not only for energy-storage smart windows, which can store energy by charging the window and adjusting the lighting and heating of the building, [ 11,12 ] but also for sensing variations in the level of stored energy and being able to respond to the variations in a noticeable and predictable manner. [13][14][15][16] As a key component of these smart devices, the transparent electrodes used not only need to be highly transparent but also highly conductive to simultaneously meet the needs of charging/discharging under high current density conditions and that of fast coloration switching speeds. However, the most commonly used transparent conducting electrodes are indium tin oxide (ITO)-coated glass, [ 11,16 ] fl uorine doped tin oxide (FTO)-coated glass, [ 13,15 ] poly(3,4-ethylenedioxythiophene)poly(styrene sulfonate) (PEDOT:PSS), [ 12 ] and carbon nanotubes. [ 14 ] The sheet resistance of these transparent conducting electrodes is in the range of tens to hundreds of Ω per square, which could hinder the device charging/discharging process and may lead to the color changes lagging behind the changes in the stored energy, especially under high current densities. In addition, ITO and FTO as transparent electrodes are unsuitable for fl exible electronics applications because of their brittleness and high cost of the preparation procedure. [17][18][19] Therefore, it is very important to design an electrode with a low electrical resistance and a high optical transmittance for smart energystorage device applications.A variety of fl exible transparent electrodes have been investigated as low-cost ITO substitutes, including conducting polymers, [ 20 ] carbon nanotubes (CNTs), [ 21 ] graphene, [ 22 ] metal nanowires, [ 23,24 ] and metal grids. [25][26][27] Among these fl exible Silver grids are attractive for replacing indium tin oxide as fl exible transparent conductors. This work aims to improve the electrochemical stability of silverbased transparent conductors. A silver grid/PEDOT:PSS hybrid fi lm with high conductivity and excellent stability is successfully fabricated. Its functionality for fl exible electrochromic applications is demonstrated by coating one layer of WO 3 nanoparticles on the silver grid/PEDOT:PSS hybrid fi lm. This hybrid structure presents a large optical modulation of 81.9% at 633 nm, fast switching, and high coloration effi ciency (124.5 cm 2 C −1 ). More importantly, an excellent electrochemical cycling stability (sustaining 79.1% of their initial transmittance modulation a...

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