Effect of TiO2 doping and post-annealing on the electrochromic properties of WO3 thin films prepared by thermal evaporation

The research investigated how TiO 2 doping levels between 0% and 6% during thermal evaporation affected WO 3 thin film properties through structural and optical, and electrochromic measurements. The X-ray diffraction (XRD) and Raman spectroscopy results showed that the deposited films existed mainly as amorphous material until they underwent 400 ˚C annealing, which caused them to transform into monoclinic WO 3 in the pure sample. The films became less crystalline and their lattice structure became more distorted when TiO 2 content increased, but no TiO 2 phase appeared independently. The scanning electron microscopy (SEM) results demonstrated that TiO 2 doping and annealing treatment created a porous structure that supported supports ion movement. The electrochemical tests showed that all films demonstrated reversible proton insertion and extraction properties, but Annealing significantly improved the electrochromic response of the films. While the undoped annealed WO 3 film exhibited the fastest coloration and bleaching response, the nominal annealed 6 wt% TiO 2 -WO 3 film achieved the highest coloration efficiency of 41.76 cm²/C together with an optical modulation of 41%, demonstrating a trade-off between switching speed and optical performance. These results demonstrate the potential of thermally evaporated TiO 2 -WO 3 thin films for electrochromic applications. However, further long-term cycling studies are required before assessing their suitability for practical smart-window devices.