Thermochromic performance of Mg-doped VO2 thin films on functional substrates for glazing applications

Abstract

The reversible phase transition VO2 exhibits, makes it a great candidate for energy efficient building glazing. Thus, a great need arises to optimize its optical and thermochromic properties, to be better suited for real smart window applications. In this study, thin films of Mg-doped VO2 have been successfully fabricated using RF reactive magnetron sputtering on commercially available products (glass coated with SnO2 buffer layer) and, for the first time, on ZnO/glass substrates, as an alternative buffer layer. Doping concentration is found to strongly affect the thermochromic properties of the films, namely the transition temperature (Tc) and transmittance modulation ability. XRD and SEM studies have been performed to examine the structural and morphological features of the Mg-doped films. Optical transmittance measurements vs. temperature have been used to calculate Tc and hysteresis width of the transition, resulting in the lowest recorded Tc value of 35°C, with respect to the literature, for an Mg-doped film (6at%). Furthermore, visible transmittance (Tlum) and solar modulation ability (ΔΤsol) have been determined for different doping concentration, and were correlated with an optical bandgap widening induced by the Mg presence. Overall, the 3at% Mg-doped film over ZnO/glass substrate presented the higher modulation ability of 4.5% and the best IR switching at 2000nm with a value of 26%.