VO₂-based colorful smart windows with self-cleaning function

Smart windows hold promise for mitigating energy demand for indoor heating or cooling. However, VO₂-based thermochromic smart windows face challenges such as high phase transition temperature, limited window color options, and a lack of functional diversity. Herein, we investigated the colorful smart windows utilizing the tungsten-doped VO₂ thin films with the phase transition temperature of approximately 23.5 °C. The surface color of these smart windows can be dynamically adjusted from brown to purple, cyan, yellow, and red by tuning the thickness of the wave-impedance matching layer of HfO₂ film, resulted from the interference effect of the HfO₂ layer and the underlying W_xV_1-xO₂ layer. Moreover, the HfO₂-coated W_xV_1-xO₂ thin film with the HfO₂ thickness of 132 nm demonstrates superior optical performance with a solar modulation ability of 9.35 %, the low-temperature luminous transmission of 36.81 %, and the high-temperature luminous transmission of 38.03 %. In addition, the incorporation of SiO₂ nanoparticles into the HfO₂-coated W_xV_1-xO₂ thin films results in the superhydrophobic property with a water contact angle of 162.1^° due to the formed rough surface, which is favor to the self-cleaning of the windows surface.