Design and preparation of a VO2-based high-performance metamaterial for smart windows

Vanadium dioxide (VO2) 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 (Tlum) and low solar modulation ability (ΔTsol). Besides, metamaterials have shown their superiority as one of the strong competitors and candidates according to previous researches. In this paper, a VO2-based metamaterial structure (VO2(ms), where “ms” is an abbreviation for metamaterial structure) uniformly distributed with round holes was introduced to form a VO2(ms)/TiO2/VO2 multilayer structure, which is designed and produced by simulation and polystyrene microsphere-assisted preparation for enhanced performance. The simulation results obtained a considerable Tlum up to 50.4% and an ultra-high ΔTsol of 22.8%; this is due to the introduction of VO2(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 ΔTsol and Tlum. Moreover, the experimentally prepared sample demonstrated a ΔTsol of 20.4% and a Tlum 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 ΔTsol while guaranteeing a high Tlum. Such enhanced performance will benefit the application for VO2-based smart windows.