Annealing effect on the electrochromic properties of amorphous WO3 films in Mg2+ based electrolytes

Abstract Electrochromic （EC） devices have many important commercial applications ranging from car rear-view mirrors, e-paper, sunglasses, to architectural smart windows. The corrosiveness of acid and the unsafety of Li+ based electrolyte are the significant issues that restrict the performance and large-scale application of EC devices. The bivalent cation Mg2+ has been proved to be efficient EC insertion ion to solve these issues. In this study, the WO3 films are deposited on ITO glass substrates by electron beam evaporation and the influence of annealing on the structure, morphology and optical properties are studied. The diffusion coefficient of Mg2+ in WO3 films is 10−11–10−10 cm2/s, and decreases with increase of annealing temperature. The WO3 films annealed at 200 °C shows the lager ΔT and long-term cyclic stability. Meanwhile, the ΔT of EC device with the structure of Glass/ITO/WO3/MgCl2 liquid Electrolyte/ITO/Glass is approximately 34.6%. These findings provides huge support for the application of Mg2+ based electrolyte in the new generation of EC devices.