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.
Highlights
Vanadium dioxide (VO2) is a promising material for thermochromic glazing
There are two important indices to quantify the optical performance of the VO2 thermochromic smart windows, which are luminous transmittance (Tlum) and solar modulation ability (∆Tsol)
It should be noted that the main purpose of this study is to investigate the improvement of optical performance by adding nano-cones, so only one planar TiO2 antireflection layer is adopted even though multiple layers may lead to better Tlum and ΔTsol
Summary
VO2 thermochromic smart windows suffer from several problems that prevent commercialization: low luminous transmittance (Tlum) and low solar modulation ability (ΔTsol). 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. To fulfill the demand of human vision and energy efficiency, improving luminous transmittance (Tlum) and solar modulation ability (i.e. the difference of solar transmittance (Tsol) between cold and hot states of materials or ΔTsol) simultaneously are key for the practical applications of VO2 smart windows in buildings[5].
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