Abstract

• Electrochemical properties of electrochromic (EC) tungsten trioxide (WO3) thin films on the fluorine doped tin oxide (FTO) coated glass substrates have been studied. Different molar concentrations of WO3 precursor solution were sprayed on FTO glass substrates to synthesize amorphous and crystalline phase tungsten trioxide thin films by conducting different annealing temperature. From the different WO3 precursor concentrations, 0.05 M enabled to increase current densities of WO3 film. The present study indicated that the optimum processing condition of annealing temperature 400 oC and WO3 precursor concentration 0.05 M would produce the WO3 film with higher electrochemical current densities which is attributed to a higher crystallinity and lower band gap energy. In examining the electrochromic performance of WO3 film, its color is blue upon coloring and colorless upon bleaching and the coloration efficiency is 1.89 cm2C -1 in KI and 2.01 cm2C -1 in KCl electrolytes. The color change would be associated with the intercalation (deintercalation) of K+ ions. The diffusion of ions in the insertion/ extraction process thus play a role. The diffusion coefficient of WO3 film is observed to be quite high and is in the range of 1.1 – 1.4× 10-12 cm2 s -1 in both KI and KCl electrolytes. The higher electrochemical activity renders it as promising material for smart windows and energy saving applications.