Enhanced Electrochromic Properties of WO3 Nanotree-like Structures Synthesized via a Two-Step Solvothermal Process Showing Promise for Electrochromic Window Application

Hierarchical WO3 nanotree-like structures grown from nanowires were prepared by a two-step nonseeded solvothermal approach using a fluorine-doped tin oxide coated glass substrate. The nanotrunks formed in the first step before the nanobranches grew in the second step. The trunks were orientated along the (002) plane of hexagonal phase WO3, while the branches were orientated along the (100) and (200) planes. An electrochromic film prepared with WO3 nanotrees had a large active surface area, which enabled a large optical modulation of 74.7% at 630 nm at a low potential of 0.2 V versus Ag/AgCl, shorter response times of 2.64 s for bleaching and 7.28 s for coloration, and a high coloration efficiency of 75.35 cm(2) Thus, such structures are of interest for electrochromic window application.