Structure and material designs of stretchable electrochromic devices

Abstract

Electrochromic materials are a significant class of optoelectronic functional materials that can change colour by adjusting the voltage periodically. In recent years, there has been rapid development in electrochromic technology. However, current research predominantly focuses on traditional rigid electrochromic devices (ECDs), typically using conductive glass substrates such as indium tin oxide. These rigid colour-changing devices face significant challenges, including large thickness, low mechanical strength, and high cost, which hinder the advancement and commercialisation of electrochromic technology. With the rise of wearable devices and electronic skins, among other future technologies, flexible ECDs have garnered much attention due to their foldability, wearability, and even embeddability. They have emerged as a research hotspot in the field of electrochromism. As a further development direction of flexible ECDs, achieving stretchability poses higher difficulties as it requires maintaining high performance under large strains and even distortions. This article provides an overview of the latest advances in stretchable electrochromic devices (SECDs) from the perspectives of structural and material design. Regarding structural design, the ‘island-bridge’ structure, the ‘longitudinal wave’ structure, and core-shell structures are discussed. In terms of material design, the design schemes of substrate, conductive layer, electrochromic layer and electrolyte layer are mainly introduced, with particular emphasis on the introduction of gel electrolyte. Finally, the challenges and difficulties faced by the development of SECDs are briefly analysed.