A bioinspired solution for spectrally selective thermochromic VO₂coated intelligent glazing

We present a novel approach towards achieving high visible transmittance for vanadium dioxide (VO2) coated surfaces whilst maintaining the solar energy transmittance modulation required for smart-window applications. Our method deviates from conventional approaches and utilizes subwavelength surface structures, based upon those present on the eyeballs of moths, that are engineered to exhibit broadband, polarization insensitive and wide-angle antireflection properties. The moth-eye functionalised surface is expected to benefit from simultaneous super-hydrophobic properties that enable the window to self-clean. We develop a set of design rules for the moth-eye surface nanostructures and, following this, numerically optimize their dimensions using parameter search algorithms implemented through a series of Finite Difference Time Domain (FDTD) simulations. We select six high-performing cases for presentation, all of which have a periodicity of 130 nm and aspect ratios between 1:9 and 8:8. Based upon our calculations the selected cases modulate the solar energy transmittance by as much as 23:1% whilst maintaining high visible transmittance of up to 70.3%. The performance metrics of the windows presented in this paper are the highest calculated for VO2 based smart-windows.