Titanium doping effects in electrochromic pulsed spray pyrolysed WO3 thin films

The influence of titanium doping on the electrochromic properties of WO3 thin films is studied. The systematics of different properties such as the structural phase change, the color-bleach kinetics, coloration efficiency, reversibility, stability, ion insertion/extraction capacity and change of W+ 6 states to W+ 5 states are observed to depend on doping concentration. The X-ray diffraction results reveal an amorphous phase at lower Ti concentration (2 and 6 at.%) and mixed WO3–TiO2 (monoclinic epsilon WO3 and rutile TiO2) phases at higher Ti concentration (10 at.%). The fibrous-reticulated morphology wanes and surface roughness increases as doping concentration increases. At higher Ti concentration (10 at.%), the film becomes completely granular and rough without fibrous-bridge-like network. The cycle stability, charge storage capacity and reversibility of the films are improved upon doping; however, coloration efficiency is decreases as Ti concentration increases. These results are discussed in terms of the effects of doping induced compositional inhomogeneity and disorder structure on the film properties.