Characterization of nanoparticulated WO₃ electrochromic thin films prepared via precipitation reaction of peroxotungstic acid solution

Amorphous WO₃ thin films with a nanoparticulated morphology were fabricated using a combination of electrodeposition and electrophoretic deposition via the precipitation reaction of a peroxotungstic acid (PTA) solution. Due to the presence of the precipitated WO₃ nanoparticles in the aged PTA solution, the electrophoretic deposition and electrodeposition occur simultaneously, which results in a grainy surface morphology in which nano-sized WO₃ particles are embedded on a smooth WO₃ thin film. The WAT-5 sample prepared with a PTA solution aged for 5 days exhibited faster ion intercalation/de-intercalation kinetics (coloration time of 3 s and bleaching time of 1 s), a greater transmittance modulation (68.36%), and a higher coloration efficiency (41.29 cm²/C) with better cyclic stability (91% retention during 300 cycles) than a WO₃ thin film fabricated using the PTA solution without the aging process. The nanoparticulated morphology enhanced the active reaction area by expanding the interface between the electrolyte and the electrochromic material. Such results indicate that the electrochromic characteristics of WO₃ thin films can be improved simply by adjusting the aging period of the PTA solution.