Alternative Nb2O5-TiO2 thin films for electrochromic devices

Thin films of mixed oxides of Nb2O5-TiO2 with molar ratio Nb/Ti=3, have been prepared by sol-gel sonocatalytic method. The precursor sols consist of a mixture of niobium salt NbCl5, titanium alkoxide Ti(OPri)4, isopropanol and acetic acid. After addition of all components the mixture was sonicated. The films were deposited by dip-coating technique on ITO-Asahi Glass and then submitted to a final heat treatment at 560°C during 3 h in atmosphere of oxygen. The electrochromic properties of the films were investigated using in situ spectroelectrochemical method. The films exhibit a blue-gray coloration under lithium ions insertion with a reversible variation of the transmittance in the visible and near infrared range between 90% and 20%. The xerogels of Nb2O5-TiO2 also were characterized by X-ray diffraction, thermal analysis (DTA/TGA) and IR measurements. The morphology of the films was observed by scanning electron microscopy (SEM) and the topography by atomic force microscopy (AFM). These films appear suitable for architectural applications, where a minimum performance in depth color is required.