Bio-inspired TiO₂ nano-cone antireflection layer for the optical performance improvement of VO₂ thermochromic smart windows

Abstract

Vanadium dioxide (VO2) is a promising material for thermochromic glazing. However, VO2 thermochromic smart windows suffer from several problems that prevent commercialization: low luminous transmittance (Tlum) and low solar modulation ability (ΔTsol). The solution to these problems can be sought from nature where the evolution of various species has enabled them to survive. Investigations into the morphology of moths eyes has shown that their unique nanostructures provide an excellent antireflection optical layer that helps moths sharply capture the light in each wavelength from a wide angle. Inspired by this mechanism, a VO2 thermochromic smart window coated with a TiO2 antireflection layer with a novel nano-cone structure, is presented in this study to achieve high Tlum and ΔTsol. Optimization for the key structure parameters is summarized based on the FDTD numerical simulations. The optimized structure exhibits a Tlum of 55.4% with ΔTsol of 11.3%, an improvement of about 39% and 72% respectively compared to the VO2 window without an antireflection layer. Furthermore, wide-angle antireflection and polarization independence are also demonstrated by this nano-cone coating. This work provides an alternative method to enhance the optical performance of VO2 smart windows.