Thermochromic properties of ZnO/VO2/ZnO films on soda lime silicate glass deposited by RF magnetron sputtering

A smart window based on VO2 is a promising thermochromic (TC) glass that can regulate heat flow through windows by solar modulation near room temperature. TC glasses with high visible-light transmittance and large difference in infrared transmittance between high-and low-temperature VO2 phases are required to save large amounts of energy in buildings. VO2-based multilayer films with a buffer layer and/or an anti-reflective (AR) layer are used when the films are deposited by sputtering. In this study, VO2-based multilayer films were pre-pared on soda lime glass using ZnO as both the buffer and the AR layers. The structure of the multilayer film was simulated using the optical constants measured from the deposited films. The effect of buffer and AR layers on the TC properties of VO2-based multilayer films prepared by sputtering was investigated by simulation of the multilayer structure and deposition of the films with the simulated structure. The TC properties were measured and compared with the calculated properties. Improved TC properties (luminous transmittance (Tlum) of-50%/ 46% (30 degrees C/80 degrees C) and solar modulation ability (Delta Tsol) of-14%), compared to those without the buffer and AR layer, were obtained from the ZnO/VO2/ZnO film deposited on glass. The calculated transmittances agree better with the measured ones when the optical constants measured directly from the deposited films are used and the roughnesses of the surface/interface of the multilayer films are considered in the calculation of the optical constants.