Thermochromism of vanadium dioxide films controlled by the thickness of ZnO buffer layer under low substrate temperature

Highlights: • Solar energy modulation ability of 13.11% is obtained via ZnO buffer layer. • Phase transition temperature can reach 45 °C without doping. • ΔT_sol and T_lum can be enhanced simultaneously by employing the ZnO buffer layer. High-quality vanadium dioxide (VO₂) thermochromic thin films were fabricated on ZnO/soda-lime glass via direct current magnetron sputtering at a low temperature of 320 °C. The ZnO polycrystalline film was used as a buffer layer between glass substrate and VO₂ film to improve the thermochromic property of VO₂ film. The results of XRD, Raman spectrum, SEM and visible-infrared spectrum indicated that the thickness of the ZnO buffer layer has a significant effect on the physical and thermochromic performances of VO₂ films. The surface morphologies of all VO₂ films can be divided into three groups by employing ZnO buffers with different thicknesses. The film with thin buffer (56 nm) exhibited a weak crystallinity, low phase temperature and low solar energy modulability compared with the pristine sample. However, the crystallinity and solar switching efficiency of VO₂ films noticeably increased as the thickness of the buffer layer increased further (thicker than 56 nm). The calculated modulability of solar energy of the VO₂ film with a 235-nm thick ZnO buffer layer is about 13.11%, which may be beneficial in the application of VO₂ films for smart energy-efficient windows.