Dual-band electrochromic film based on mesoporous h-WO3/o-WO3·H2O/r-TiO2 for high performance smart windows

Porous three-dimensional electrochromic films composed of orthorhombic WO3·H2O, hexagonal WO3, and rutile TiO2 array (h-WO3/o-WO3·H2O/r-TiO2, WWT) were controllably synthesized by a facile two-step hydrothermal technique. Due to the hydrophilicity and array structure of TiO2, the generation of high-quality o-WO3·H2O was significantly promoted, which can reduce the energy barrier to ion diffusion and increase the ion flux by introducing structural water in the interlayer region of WO3. The formation of porous 3-dimensional structure and WO3–TiO2 heterojunction increases the effective contact area, alters the distribution of energy bands, and promotes charge transport, resulting in significantly improved electrochromic properties. An impressive dual-band electrochromic performance with high optical modulation of 68.4% at 633 nm and 59.8% at 1600 nm was achieved in WWT film, respectively, with a fast switching speed (11s/3.3 s at 633 nm and 3 s/9.4 s at 1600 nm for coloring/bleaching), high coloration efficiency (46 cm2 C−1 at 633 nm and 136.8 cm2 C−1 at 1600 nm), and a satisfactory cycling stability at the same time.