Preparation of VO2@SiO2@TiO2/PU composite film. The as-prepared particles were ultrasonically dispersed in deionised water and an appropriate amount of the saline coupler KH-570 was added under stirring. To this solution, the organic matrix material, polyurethane (PU, DISPERCOLLU 54, Bayer), was added with stirring for 10 min. Finally, the mixture was uniformly cast onto a PC substrate using an auto- matic coating machine and then dried to prepare the VO2 solar cell.