Recent progress in transmissive and reflective electrochromic devices for multi-color modulation

Multi-color electrochromic devices (M-ECDs), which dynamically and reversibly regulate the visible optical properties of the objects, have received significant interest in various fields such as displays, flexible intelligent electronics, smart windows and military camouflage. This review provides comprehensive summaries of the latest advances in inorganic electrochromic materials and M-ECDs. We discuss the basic principles for achieving M-ECDs, from the intrinsic multicolor characteristics of materials to a combination with optical structures. The progress on the construction of multicolor electrochromic thin-films and associated devices are unfolded in detail based on their transmissive or reflective working scenarios. Moreover, the limitations and challenges are also outlined for consideration for the future development of M-ECDs.