Recent advances in tungsten oxide-based chromogenic materials: photochromism, electrochromism, and gasochromism

As n-type and wide-bandgap semiconductor materials which are widely found in nature, tungsten oxides (WO_x) have attracted extensive attention because of their rich phase structures and unique sub-stoichiometric properties. Tungsten oxides have a good chromogenic response to optical, electrical, and gaseous stimuli, in which their phase changes with the change of temperature and ionic embeddedness, accompanied by significant changes in their optical properties. In addition, due to the presence of oxygen defects, the conductivity and adsorption capacity of tungsten oxides for surface substances are enhanced. These properties endow tungsten oxides with promising application potential in the optical and electronic device areas. This paper reviews the structural and optoelectrical properties of tungsten oxide-based chromogenic materials. Then we focus on the working mechanisms, performance indexes, and preparation methods of tungsten oxides in the field of intelligent chromogenic technology, including photochromism, electrochromism, and gasochromism of tungsten oxide-based chromogenic materials. Finally, a conclusion and outlook are provided, which may help to further advance the application of tungsten oxides in the field of smart chromogenic changes.