Controllable synthesis of hexagonal WO3 nanorod-cluster films with high electrochromic performance in NIR range

Abstract Hexagonal WO3 (h-WO3) nanorod-cluster films were controllably synthesized by a facile template-free hydrothermal technique. The pH value and the amount of urea in the precursor have critical influences on the crystal form and morphology of the WO3 film. The obtained uniform WO3 films feature a porous structure of clusters composed of h-WO3 nanorods with diameter of 6–10 nm and length of up to several hundred nanometers. Due to the novel microstructure and crystalline phase, the high electrochromic performance in NIR range with a high optical modulation of 46% in 1600 nm, fast switching speed (2.4 s for coloration and 3.6 s for bleaching), high coloration efficiency (106.1 cm2 C−1 in 1600 nm), and an excellent cycling stability (more than 96% charge capacity retained after 1000 cycles) was achieved.