Abstract:

Vanadium dioxide (VO2) nanoparticles with reversible semiconductor-metal phase transition holds the tremendous potential as a thermochromic material for the energy-saving smart glazing. However, the trade-off between improving the luminous transmittance (T-lum) while sacrificing the solar modulation ability (Delta T-sol) hampers its bench-to-market translation. Previous studies of anti-reflection coatings (ARCs) focused primarily on increasing Tlum while neglecting DTsol, which is a key energy-saving determinant. The intrinsically low Delta T-sol (< 16%) is due to the fact that VO2 has a higher refractive index (RI) from 500 nm to 2200 nm wavelength (lambda) below its critical transition temperature (tau(c)), which causes excessive reflection at a lower temperature. This study aims to investigate ARCs with tunable RI (1.47-1.92 at lambda = 550 nm) to improve the antireflection effect at a lower temperature, thereby maximizing Delta T-sol for various VO2 nanosubstrates, e.g. continuous thin films, nanocomposites, and periodic micro-patterning films. We showed that the best performing coatings could maximize Delta T-sol (from 15.7% to 18.9%) and increase T-lum(avg) (from 39% to 44%) simultaneously, which surpasses the current benchmark specifications ever reported for ARC-coated VO2 smart glazing. In addition, the cytotoxicity analyses evidence that ARCs are feasible to improve the cyto-compatibility of VO2 nanoparticles-based nanocomposites. The presented RI-tunable ARC, which circumvents the complex materials selection and optical design, not only paves the way for practical applications of VO2-based smart windows but also has extensive applications in the field of solar cells, optical lenses, smart display, etc. (C) 2017 Elsevier B.V. All rights reserved.