Abstract

WO₃-based photochromic composite films were fabricated using transparent urethane resin and iso-polytungstic acid peroxide (W-IPA). We attempted to improve its photochromic properties by adding elements on the 5th period: Y(+3), Zr(+4), Nb(+5), and Mo(+6). When yttrium chloride was added to the raw material, W-IPA, yttrium could not be added to WO₃ because it reacted with W-IPA. The coloration rate of WO₃ photochromic composites increased with the addition of Zr, Nb, and Mo. The bleaching rate of the WO₃-based composite films increased significantly with Zr addition, approximately 2.3 times faster than that of the non-doped film. The photochromic properties of the Zr/WO₃ composite films were also evaluated under sun light irradiation. All the films exhibited reversible photochromic properties in a one-day cycle. The degree of coloration significantly changed with sun light irradiation in summer (during the summer solstice) and winter (during the winter solstice). In summer, the coloration properties were adequate after 25 min of sunlight irradiation, and the bleaching properties returned to near the initial transmittance after 6 h of storage in the dark. These results indicate that the Zr/WO₃ composite films could be effectively controlled under sunlight in both winter and summer. Therefore, these films can be applied as smart windows.

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