Aqueous synthesis of tin- and indium-doped WO(3) films via evaporation-driven deposition and their electrochromic properties

M-doped WO(3) (M = Sn or In) films were prepared from aqueous coating solutions via evaporation-driven deposition during low-speed dip coating. Sn- and In-doping were easily achieved by controlling the chemical composition of simple coating solutions containing only metal salts and water. The crystallinity of the WO(3), Sn-doped WO(3), and In-doped WO(3) films varied with heating temperature, where amorphous and crystalline films were obtained by heating at 200 and 500 °C, respectively. All the amorphous and crystalline films showed an electrochromic response, but good photoelectrochemical stability was observed only for the crystalline samples heated at 500 °C. The crystalline In–WO(3) films exhibited a faster electrochromic color change than the WO(3) or Sn–WO(3) films, and good cycle stability for the electrochromic response in the visible wavelength region.