Design and preparation of a VO 2 -based high-performance metamaterial for smart windows

Vanadium dioxide (VO 2 ) is an ideal material for smart windows, which can initiate an automatic reversible metal-to-insulator transition from tetragonal to monoclinic structure at the transition temperature (Tc) of 68 °C, resulting in a large difference in near-infrared transmittance, but its application is limited by the poor luminous transmittance ( T lum ) and low solar modulation ability (Δ T sol ). Besides, metamaterials have shown their superiority as one of the strong competitors and candidates according to previous researches. In this paper, a VO 2 -based metamaterial structure (VO 2 (ms), where “ms” is an abbreviation for metamaterial structure) uniformly distributed with round holes was introduced to form a VO 2 (ms)/TiO 2 /VO 2 multilayer structure, which is designed and produced by simulation and polystyrene microsphere-assisted preparation for enhanced performance. The simulation results obtained a considerable T lum up to 50.4% and an ultra-high Δ T sol of 22.8%; this is due to the introduction of VO 2 (ms) which causes the multilayer structure to form metal–insulator–metal cavities at high temperatures and produces a resonance absorption effect. Meanwhile, it is found that the spacing of the round holes ( D ) has a great influence on the performance of the structure; specifically, an increase in D results in a slight decrease in both Δ T sol and T lum . Moreover, the experimentally prepared sample demonstrated a Δ T sol of 20.4% and a T lum of 42.6%, slightly lower than simulation because it has a larger spacing D , which is consistent with the analysis. In summary, both simulation and experiment can get ultra-high Δ T sol while guaranteeing a high T lum . Such enhanced performance will benefit the application for VO 2 -based smart windows.