Crystalline tungsten trioxide film can be prepared by magnetron sputtering deposition method and then by heat treatment. By magnetron sputtering deposition, an amorphous tungsten trioxide film is obtained, which is heated in air at 200°C, 250°C, 300°C, 350°C and 400°C and held for 30min for heat treatment. As the heat treatment temperature increases, the electrochromic properties of the amorphous tungsten trioxide film decrease. When the heat treatment temperature is higher than 350°C, the amorphous state is converted into a crystalline state.
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The colored crystalline WO3 film has lower absorption modulation capacity in the visible spectrum range (380nm-780nm) and solar spectrum than the amorphous WO3 film. But, the crystalline WO3 film has stronger reflective modulation in the near infrared region. The tungsten trioxide film deposited by heating the substrate to above 220°C is in a crystalline state. The electrochromic properties of such crystalline film are superior to those of the crystalline WO3 film obtained by heat treatment in air. But the discoloration properties of the two films are not significantly dependent on the respective preparation temperatures. Under the same electrochemical test parameters, the crystalline WO3 film has a lower color response rate than the amorphous WO3 film.
