Effect of bias voltage on the electrochromic properties of WO₃ films

Electrochromism is the phenomena of reversible colour change in electrochromic (EC) materials due to a small applied voltage. Tungsten oxide (WO₃) is one of the most studied cathodic electrochromic materials for its applications in smart windows, displays and rear-view ymirrors. In this work, WO₃ films were fabricated on indium tin oxide (ITO) coated glass via the sol-gel spin-coating method. The influence of bias voltage on the EC properties of the fabricated WO₃ films was studied. The optical properties were characterised by using ultraviolet-visible (UV-Vis) spectrophotometer and the EC properties were characterised by the chronoamperometry (CA) method. The fabricated WO₃ films exhibited an optical transmittance of 80 % in the visible range. CA measurements revealed an increase in colouring and bleaching time and intercalated charge density as bias voltage was increased. Moreover, the colouring and bleaching transmittance of the WO₃ films were found to decrease as bias voltage was increased. Within our measurement range, bias voltage of 1.0 V was found to be the optimum bias voltage where it corresponds to 34 % optical modulation and higher colouration efficiency of 22.6 cm²/C. (paper)