Tungsten oxide can be used to prepare an all-solid-state electrochromic device. It indicates that the raw material tungsten oxide powder with good electrochromic properties has met the following two basic requirements:
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1.0 It must have a color center or have some absorption mechanism for visible light.
2.0 It requires mixed conductance, i.e., electrical conductance and ion conductance, which is required to maintain electrical neutrality.
In this regard, experts say that the vacancies of the material are governed by thermodynamic laws. At room temperature, the concentration of the coloring center in the solid is about 10^17-10^19cm-1, which makes the maximum optical density that can be obtained very limited. At the same time, the room temperature ion mobility of most materials is very low. Therefore, for most materials, electrochromism cannot be observed, and even for alkali halide crystals, it must be heated to a high temperature to achieve a higher vacancy concentration and sufficiently large ion mobility.
