VO2-ZnO composite films with enhanced thermochromic properties for smart windows

Abstract

VO2 film is a promising thermochromic material in smart windows due to its reversible metal to insulator transition (MIT) accompanied with an abrupt change of transmittance in near-infrared region at around 68 °C (T>68 °C, translucent; T < 68 °C, transparent), but which has not been widely applied because its low luminous transmittance (<60%) and solar modulation efficiency (<10%) are difficult to be improved simultaneously. In order to solve this problem, the ZnO-VO2 composite film was prepared by a facile method, in which commercial ZnO nanoparticles (NPs) and VO2 micro-particles were mixed by ball milling method to form the composites. By introducing ZnO NPs into the composite film, the luminous transmittance (Tlum) of the composite film was increased by 16.9% (from 54.9% to 63.9%) and the solar modulation efficiency (ΔTsol) was increased by 14.1% (from 9.9% to 11.3%) compared to the pure VO2 composite film. This was because ZnO NPs not only played the role of antireflection, but also prevented VO2 particles from agglomeration by dispersing around VO2 particles. Furthermore, the two-layered film based on ZnO-VO2 composites exhibited an astonishing ΔTsol of 18.8%, while maintaining excellent Tlum of 54.3%. This work could provide a simple and novel idea for us to improve the thermochromic properties of VO2 films and simultaneously to promote their practical application.