A novel method to improve phase transition of VO2 thermochromic films by Cs0.32WO3 nanoparticles

•The VO2/Cs0.32WO3 composite film were firstly prepared.•The Cs0.32WO3 shortened the phase transition response time of VO2 film.•The Cs0.32WO3 improves the solar-heat shielding ability of VO2 film.•The composite film can occur phase transition at 30 °C.•The composite film maintained good thermochromic properties. The VO2/Cs0.32WO3 composite thermochromic films were designed to promote the practical application of the VO2-based smart windows. The addition of 0.9 wt% Cs0.32WO3 can significantly shorten the phase transition response time and improve the solar heat shielding capacity of VO2, while maintaining high visible light transmittance (49.6%) and good solar modulation ability (10.4%). Furthermore, the phase transition of the composite film can occur at indoor temperature of 30 °C, and the indoor temperature can be greatly reduced by 7.7 °C under the simulated solar irradiation. These excellent properties make the VO2/Cs0.32WO3 films promising as smart energy-saving windows.