Highly stable electrochromic cells based on amorphous tungsten oxides prepared using a solution‐annealing process

In this work, a facile sol–gel and annealing technique was employed to prepare amorphous electrochromic tungsten oxide thin films at a relatively low temperature. Specifically, ammonium metatungstate hydrate was blended in dimethylformamide and was used as the precursor for obtaining highly uniform and transparent amorphous WOx by simple spin-coating and calcining in ambient air at 250°C for 2 hours. The film exhibits an unprecedented stability over 4000 operational cycles with a high coloration efficiency of 125 cm2 C−1 and fast switching times of 5 seconds for the colored state and 2.5 seconds for the bleaching state. Therefore, the prepared amorphous tungsten oxide film is a prominent material for the next generation of electrochromic devices that can be used in smart windows and electronic display devices.