Yellow tungsten oxide, or tungsten trioxide, is a cathode discoloration material. The color contrast of tungsten trioxide is still relatively low compared to a composite electrode complementary electrochromic device assembled using WO3 and nickel oxide. Wherein nickel oxide is the anode coloring material preferred by researchers, which includes nickel oxide of ideal ratio (light green) and nickel oxide of non-ideal ratio (gray black).

Tungsten oxide for producing composite electrode complementary electrochromic device is a typical cathode coloring material. However, in practical applications, the coloring contrast of tungsten oxide is still relatively low. How to solve this problem? In this regard, experts say that if an anode coloring material and a cathode coloring material are assembled into a complementary electrochromic device, the coloring contrast can be greatly improved.

Tungsten trioxide is a cathode coloring material that can be assembled with an anode coloring material such as nickel oxide into a composite electrode complementary electrochromic device. In contrast to WO3, nickel oxide is such a type of material that carry out oxidization firstly and then discoloration. Nickel oxide can be used as a counter electrode to form a device together with a cathode coloring material such as tungsten oxide, thereby achieving the effect of storing ions and increasing the range of light modulation.

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.