The investigation of wrinkled ZnO as antireflective, protective, hydrophobic layer on the thermochromic VO2 films for smart windows

Abstract

Vanadium dioxide (VO₂) is commonly employed in smart windows for its excellent thermochromic properties. However, its limited luminous transmittance (T_lum) and insufficient solar modulation capability (ΔT_sol) have severely limited its commercial application. In this study, the VO₂ films are prepared through rapid thermal annealing of the sputtered vanadium film on the quartz glass substrate. Then the wrinkled ZnO films are prepared as the antireflection layer on top of the VO₂ films using the sol-gel method. The light propagation path on the films surface is altered by the wrinkled topology, trapping most light within the ridges and valleys, while reducing reflection and increasing light transmittance. Compared with single-layer VO₂ films, the wrinkled ZnO/VO₂ bilayer structure can significantly increase T_lum from 33.3 to 47.7%, ΔT_sol from 5.6 to 7.9%, and decreases phase transition temperature (T_t) from 57.35 °C to 50.34 °C, the thermal hysteresis width (ΔT) from 14.8 °C to 12.78 °C. Furthermore, this structure exhibits an excellent water contact angle of 97.36 °, with its hydrophobic properties allowing ZnO films to function as a protective layer. Even after being exposed to air at room temperature for 60 days, the bilayer structure can still maintain its initial thermochromic performance. The results of this study provide new possibilities for improving the performance of smart windows.