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

Abstract

Porous three-dimensional electrochromic films composed of orthorhombic WO 3 ·H 2 O, hexagonal WO 3 , and rutile TiO 2 array (h-WO 3 /o-WO 3 ·H 2 O/r-TiO 2 , WWT) were controllably synthesized by a facile two-step hydrothermal technique. Due to the hydrophilicity and array structure of TiO 2 , the generation of high-quality o-WO 3 ·H 2 O 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 WO 3 . The formation of porous 3-dimensional structure and WO 3 –TiO 2 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 cm 2 C −1 at 633 nm and 136.8 cm 2 C −1 at 1600 nm), and a satisfactory cycling stability at the same time. Dual-band electrochromic film and device with high optical modulation was obtained by hydrothermal synthesizing porous three-dimensional h-WO 3 /o-WO 3 ·H 2 O/r-TiO 2 composite film. • High performance dual-band electrochromic films and device are obtained. • The films composed of orthorhombic WO 3 ·H 2 O, hexagonal WO 3 , and rutile TiO 2 array. • TiO 2 promoted the formation of o-WO 3 ·H 2 O due to the hydrophilicity and array structure. • The layered structure of o-WO 3 ·H 2 O reduced ion diffusion barrier and increased ion flux. • The h-WO 3 /o-WO 3 ·H 2 O/r-TiO 2 film has high optical modulation of 68.4% at 633 nm and 59.8% at 1600 nm.