Color neutral nanocomposite nickel-tantalum oxide for electrochromic windows

Electrochromic windows can darken on demand to limit the solar gains entering a building to reduce the risk of overheating, while preserving the view towards the exterior. Yet, the switching speed and contrast as well as the durability of commercial products still need to be improved. Novel materials are investigated to address these shortcomings. Since gel or polymer electrolytes limit the durability of electrochromic glazing, all-solid state, inorganic devices are considered. The optical properties of doped nickel oxides were studied in order to obtain a color neutral anodic electrochromic oxide. The addition of tantalum was shown to increase the light transmittance and to provide a coating with better color neutrality compared to nickel vanadium oxides. The study of the crystalline structure by X-ray diffraction suggests that a nickel oxide-tantalum pentoxide nanocomposite is formed. These results are encouraging to use nickel tantalum oxide as an anodic electrochromic oxide.