  Electrochromic devices, which dynamically change color under the applied
potential, are widely studied because of its wide range of applications such as
energy-efficient smart windows, rear view mirrors and display devices etc. In
this study we are reporting four layer electrochromic device based on tungsten
oxide as a electrochromic layer and nafion membrane as a ionic conducting
layer. Nafion membranes are generally used in fuel cell applications because of
its high ionic conductivity and high optical transparency which is suitable for
electrochromic device to attain higher efficiencies. We have prepared an
electrochromic device by sandwiching ITO coated glass and WO3 coated ITO thin
film between nafion membrane. The overall structure of the device is
Glass/ITO/WO3/Nafion/ITO/Glass. We deposited tungsten oxide thin films with
different thickness on ITO coated glass substrate at room temperature by using
reactive DC Magnetron sputtering and we studied the performance of the
electrochromic device with the function of thickness. We have observed that
electrochromic efficiency is increasing with increase in the tungsten oxide
layer thickness. The efficiency of the device increased from 24.8 cm2/C to
184.3 cm2/C.
