Insight into the structure–activity relationship in electrochromism of WO3 with rational internal cavities for broadband tunable smart windows

Tungsten trioxide (WO 3 )-based electrochromic devices have attracted great interest in smart windows, low-power displays, and other cutting-edge fields. The electrochromic behavior of WO 3 is strongly dominated by both electron conduction and ion diffusion process. Nevertheless, the structure–activity relationship of the WO 3 in the electrochromism has not been well elucidated so far. Herein, we systematically studied the relationship between the crystal structure composed of the fundamental units of typical WO 3 and the electron conduction/ion diffusion processes at a sub-nanoscale level. Our theoretical results unveil that the h-WO 3 with appropriate band gap by piling up the WO 6 octahedral molecular units along c axis profit electron conduction, and the continuous three-, six-ring tunnels along ab plane built by the units are conducive to ion diffusion. Therefore, the h-WO 3 film exhibits large optical modulation (up to 86% at 633 nm and 90% at 1000 nm), excellent cycling stability (86.4% of retention over 3000 cycles), and fast switching speed (1.9 s of bleaching time at 633 nm). Moreover, we provide unique insights between H + adsorption/desorption and the electrochromic response in the near-infrared region. We believe that this study lays a foundation for the design and construction of high-performance electrochromic nanomaterials and broadband tunable smart windows.