Highly transparent ultrathin vanadium dioxide films with temperature-dependent infrared reflectance for smart windows

Abstract

Vanadium dioxide (VO2) is a suitable material for energy-efficient smart windows that can modulate infrared (IR) light. Previous studies on smart windows using thick VO2 films achieved high modulation ratios in the IR region, but the transmittance in the visible region was low. To address this problem, we fabricated and investigated the characteristics of ultrathin VO2 films with pronounced metal–insulator transition. We prepared highly transparent smart windows by depositing a 10 nm-thick VO2 film on F-doped tin oxide film-coated glass. The IR transmittance of the smart window dramatically decreased with increasing temperature without a decrease in visible light. The IR transmittance change at a wavelength of 2500 nm was 50.1%, and the average transmittance in the visible region of 450–750 nm was 76.7%. These results are superior than those reported in earlier works discussing the IR modulation of ultrathin VO2 and the visible-light transmittance of thick VO2 films. We examined the switching behavior of the smart window. This work demonstrates, for the first time, the high IR modulation and rapid switching behaviors of highly transparent smart windows with ultrathin VO2 films, which could be very useful for energy savings in buildings.