Sculptured thin film vanadium dioxide thermochromic coatings grown by oblique angle deposition: investigation of transmittance response and modulation enhancement by experiment and theoretical modeling

Abstract

The fabrication of highly functional VO₂ thermochromic coatings involves costly chemical precursors and complex fabrication procedures, one of the main constraints in the commercialization of VO₂-based smart windows. Here, we have shown a simple fabrication method (low-processing temperature and environmentally friendly methodology) for VO₂ sculptured thin films (STF) through industrially scalable magnetron sputtering followed by annealing in ambient air. The angular and polarization-dependent anisotropic thermochromic performance is noticed in STF VO₂ with a columnar tilt of β = 20° attained at a maximum oblique angle of 85°. The optimal thermochromic performance with high luminous transmittance of T_lum(avg) = 43%, near-infrared (NIR), and solar modulation abilities of ΔT_nir = 7.7% and ΔT_sol = 11% respectively, is obtained when the light transmits along the inclined columns of STF VO₂. The theoretical modeling of the STF VO₂-based nanostructure composed of prolate spheroid VO₂ nanocolumns shows a promising structural design for the optimal modulation reached by finding a balance between STF VO₂ thickness and porosity. Simulation using the structural design of STF VO₂ with 11% porosity, employing experimental thickness and β as simulation parameters, gives the best fitting to the experimental results, which confirms the validity of the model. The angular-dependent thermochromic response attained in this work is beneficial to maintain indoor thermal and visual comfort during the sun's varying angled rays throughout the day, different seasons, and geographic locations.