Review on recent progress in WO 3 -based electrochromic films: preparation methods and performance enhancement strategies.

Transition metal oxides have drawn tremendous interest due to their unique physical and chemical properties. As one of the most promising electrochromic (EC) materials, tungsten trioxide (WO 3 ) has attracted great attention due to its exceptional EC characteristics. This review summarizes the background and general concept of EC devices, and key criteria for evaluation of WO 3 -based EC materials. Special focus is placed on preparation techniques and performance enhancement of WO 3 EC films. Specifically, four methods - nanostructuring, regulating crystallinity, fabricating hybrid films, and preparing multilayer composite structures - have been developed to enhance the EC performance of WO 3 films. Finally, we offer some important recommendations and perspectives on potential research directions for further study.