Niobium Tungsten Oxides for Electrochromic Devices with Long-Term Stability.

There is a keen interest in the use of electrochromic materials because they can regulate light and heat, thereby reducing the cooling and heating energy. However, the long response time, short cycle life, and high power consumption of an electrochromic film hinder its development. Here, we report an electrochromic material of complex niobium tungsten oxides. The Nb 18 W 16 O 93 thin films in the voltage range of 0 to -1.5 V show good redox kinetics with the coloration time of 4.7 s and bleaching time of 4.0 s, respectively. The electrochromic device based on the Nb 18 W 16 O 93 thin film has an optical modulation of 53.1% at a wavelength of 633 nm, with the coloration efficiency of ∼46.57 cm 2 C -1 . An excellent electrochemical stability of 78.1% retention after 8000 cycles is also achieved. These good performances are due to the fast and stable Li-ion intercalation/extraction in the open framework of Nb 18 W 16 O 93 with multiple ion positions. Our work provides a strategy for electrochromic materials with fast response time and good cycle stability.