In-situ spectroscopic studies of electrochromic tungsten oxide films

Tungsten oxide thin films were prepared using an ethanolic solution of tungsten hexachloride (WCl6) by sol-gel spin coating. The films were spin coated on indium. tin oxide (ITO) coated glass substrate at temperatures in the range of 100-450degreesC. The films were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) UV- visible spectroscopy and cyclic voltammetry (CV). XRD showed that they had a polycrystalline WO3 structure for heat treatment temperatures at above 350degreesC. The SEM examinations showed that the surface texture was very uniform and homogeneous. In-situ electrochemical reduction Of WO3/ITO (2M HCl) produced a blue color in less than a second. Coloration efficiency (CE) was found to be 21 cm(2)/mC. In situ spectroscopic investigations showed that these films could be used as a working electrode in electrochromic devices.