Electrical, optical and electrochromic properties of Ti:WO3 thin films deposited by the pulsed chemical spray technique

• Titanium doping concentration allows to control of the color bleaching kinetics.
• Titanium doping improves the H+ ion coefficient and coloration times.
• The spray pyrolysis method is a cost efficient method that produces good quality electrochromic materials.
• Titanium doping allows the control of the crystallography and the morphology and distribution of grain sizes.
• Ti:WO3 with Ti doping in the 2.0–6.0 at.% range is suitable for electrochromic applications.

Ti:WO3 thin films were deposited by the pulsed spray pyrolysis technique on FTO/glass substrates using WCl6 and TiCl3 precursors in the sprayed solution. The effect of titanium concentration in the solutions on structural, electrical, optical properties and on the electrochromic behavior of Ti:WO3 films been studied using physical and electrochemical techniques. The films are polycrystalline and the crystallographic microstructure remains constant for all films studied in this work. Modifications in structural surface details, electrical conductivity and in band gap values are observed as the Ti concentration is increased. During electrochromic response it has been observed that the color-bleaching kinetics, coloration efficiency, and chemical stability of electrochromic Ti:WO3 films are closely related to titanium doping concentration. While a nominal 2.0 at.% titanium doping produces best electrochromic response in Ti:WO3 films, the electrochemical stability is highest when the nominal concentration of titanium is about 6.0 at.%. The improved electrochromic behavior of the Ti:WO3 films can be explained from the improved H+ ion diffusion coefficient in the films during coloration and bleaching processes.