Observation of optical density modulation based on electrochromic tantalum oxide films

We successfully used the sol-gel method to synthesize crack-free electrochromic (EC) tantalum pentoxide coatings on indium tin oxide glass at room temperatures. Colouring and bleaching states can be reversibly obtained with an applied voltage as low as 3.2 V. The achieved optical density modulation between the two states is estimated to be larger than 15%, which is the highest value among the reported tantalum oxide based EC films to date. Anomalous coloration, which is independent of the polarity of the biased voltage, is observed and explained by the double injection mechanism.