WO3 for preparing large area electrochromic device is in an amorphous state (a-WO3) at 300 °C and in a crystalline state (c-WO3) at 400 °C and 500 °C. Experts say that the amorphous tungsten trioxide film has higher coloring efficiency and shorter response time than the crystalline tungsten trioxide film. It means that a-WO3 film has better electrochromic performance than c-WO3 film.
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Experts also introduced that, in general, tungsten oxide produced at lower temperatures is amorphous. When it is heat treated at a certain temperature, it is converted into a crystalline state. Generally, the so-called crystalline state refers to the predominant form in which solid objects exist. The amorphous state refers to a state in which the arrangement of atoms of a solid substance has a short-range order and a long-range disorder. That is to say, the tungsten trioxide prepared at lower temperatures has better electrochromic performance than tungsten trioxide prepared at higher temperatures.
