WO3 has excellent electrochromic properties, such as high coloring efficiency, reversibility, long memory time. It plays an important role in the research of electrochromic materials and devices. However, WO3 dissolves in proton type electrolyte, which limit its application in proton type electrolyte of electrochromic device. Research shows that nano-composite oxide electrochromic material can improve the stability of the device, shorten response time, extending the life time. Ta2O5 has excellent ion and proton conductivity, also it has excellent transparency in a wide wavelength range, good thermal stability, mechanical and chemical stability which is commonly used in solid-state electrochromic devices. Therefore, complex Ta2O5 and WO3 phase together would combine the advantages of two materials and then achieve a higher mechanical and chemical compatibility, thereby improve the stability and longevity of the device.
Shim reported that W-Ta oxide nano composite thin film is more stable in chemical and proton conducting property than pure WO3 thin film. Ta-doped thin film can improve electrochromic property, cycle stability and acid corrosion capacity of tungsten oxide thin film, but doping amount must be controlled within a certain range. When the doping amount is 5%-10%, the W1－xTaxO3 composite thin film would have better coloring efficiency. When doping amount is 15%, electrochromic property of W1－xTaxO3 equals to pure WO3 thin film. Keep adding doping amount of Ta would result in exceed and cause negative impact to thin film.