An overview of recent progress in the development of flexible electrochromic devices

Electrochromic materials are capable of reversibly switching their colors or optical properties through redox reactions under applied voltages, which have shown great potential applications including smart windows, non-emissive displays, optical filters, among others. Although the current rigid electrochromic devices have shown emerging interest and developed rapidly, many applications (e.g., wearable/deformable optoelectronics) are blocked due to their inflexible features. Herein, the adaption of rigid electrochromic devices to flexible ones is of particular interest for the new era of smart optoelectronics. In this review, the current state-of-the-art achievements of flexible electrochromic devices (FECDs) are highlighted, along with their design strategies and the choice of electrochromic materials. The recent research progress of FECDs is reviewed in detail, and the challenges and corresponding solutions for real-world applications of FECDs are discussed. Furthermore, we summarize the basic fabrication strategies of FECDs and their potential applications. In addition, the development trend, the perspectives, and the outlook of FECDs are discussed at the end of this Review, which may provide recommendations and potential directions to advance the practical applications of FECDs.