The synthesis and performance of Zr-doped and W–Zr-codoped VO2 nanoparticles and derived flexible foils

Abstract

Vanadium dioxide (VO₂) is a key material for thermochromic smart window applications because of its Mott phase transition properties. However, the applications of VO₂ have been restricted because of its drawbacks in performance, including high phase transition temperature (T_c), low luminous transmittance (T_lum), limited solar energy modulation ability (ΔT_sol) and unpleasant color. Various studies have been undertaken to resolve these problems but the improvement in any one aspect is always accompanied by a deterioration of the others. This paper reports that Zr doping can simultaneously decrease T_c, increase T_lum, improve ΔT_sol and modify the color of VO₂ foils. The T_c value decreased from 68.6 °C to 64.3 °C at 9.8% Zr-doping; meanwhile, the composite foils prepared from Zr-doped VO₂ nanoparticles exhibited excellent luminous transmittance (up to 60.4%) and solar energy modulation ability (up to 14.1%). The experimental optical band gap was 1.59 eV for the undoped VO₂, which increased to 1.89 eV at 9.8% doping. As a result, the color of the Zr-doped foils was modified to increase their luminous transmittance and lighten the yellowish color of the VO₂ foil. The first-principles calculation was in good agreement with the experiment results. The W–Zr-codoped VO₂ nanoparticles were prepared to further decrease the transition temperature (28.6 °C), while simultaneously maintaining the luminous transmittance (48.6%) and solar energy modulation ability (4.9%) of the derived foils.