Bio-inspired TiO nano-cone antireflection layer for the optical performance improvement of VO thermochromic smart windows.

Vanadium dioxide (VO) is a promising material for thermochromic glazing. However, VO thermochromic smart windows suffer from several problems that prevent commercialization: low luminous transmittance (T) and low solar modulation ability (ΔT). 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 VO thermochromic smart window coated with a TiO antireflection layer with a novel nano-cone structure, is presented in this study to achieve high T and ΔT. Optimization for the key structure parameters is summarized based on the FDTD numerical simulations. The optimized structure exhibits a T of 55.4% with ΔT of 11.3%, an improvement of about 39% and 72% respectively compared to the VO 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 VO smart windows.