Improving the cyclic stability of room-temperature-sputtered WO3 electrochromic film via an in-situ electrical annealing initiated by the intrinsic ITO transparent electrode

In order to improve the electrochromic properties, especially, the long-term cyclic stability, for the sputtered WO 3 film, various film annealing treatments including the substrate heating during film deposition and also the post-treatment in muffle furnace or in rapid thermal annealing (RTA) facility are usually adopted. However, these traditional annealing techniques have the obvious limitations in high cost, poor operational convenience and low thermal utilization efficiency. Herein, an in-situ electrical annealing initiated by the intrinsically attached ITO transparent electrode is proposed to directly anneal the contacted room-temperature-sputtered Nb-doped WO 3 (WNO) electrochromic film. After a systematic exploration on the in-situ electrical annealing parameters, the perfect temperature and time are screened out as 250 °C and 10 min, respectively. The annealed film at this point owns an outstanding cyclic stability, i.e., after 3000 electrochemical cycles, the light modulation keeps almost unchanged from 60.5 % to 59.9 %. The much denser and more robust microstructure resulted from the in-situ electrical annealing is responsible for such a higher electrochemically cyclic stability. Moreover, the laminated electrochromic device made of the in-situ electrically annealed WNO film is found to operate well. This work firstly demonstrates that the in-situ electrical annealing is practically viable for the treatment of room-temperature-sputtered electrochromic film.