Color Tunable Vanadium Dioxide/Fluorescent Organic Small Molecule Two-Layer Composite Films With Thermochromic Property

Vanadium dioxide (VO2), a typical thermochromic material, can be used for smart windows, which can effectively reduce the building energy consumption. However, the unpopular color of the VO2-based smart windows has become one of the issues restricting its wide applications. Herein we report on VO2-based fluorescent two layer composite films, which contain the thermochromic VO2 layer and the photoluminescent organic small molecule layer. Under sunlight, the fluorescent organic small molecule layers of 4,4'-bis[2-(2-methoxyphenyl)ethenyl]biphenyl (CBS-127) and 4,4'-bis[2-(2-sodiumsulfophenyl)-ethenyl]biphenyl (CBS-X) absorb ultraviolet irradiation and emit blue light, thus the strong absorption effect of the pure VO2 film in the blue region (hence the yellow brown color) can be effectively compensated, improving the color of the films. Compared with the VO2 film, the two-layer composite films not only maintain high luminous transmittance (T-lum,T-average > 70%) and solar regulation efficiency (Delta T-sol > 8%), but also undergo reversible color change from yellow brown to blue under sunlight, and the UV blocking property is significantly improved as well. These properties are beneficial to the promotion and application of the VO2-based smart windows.