Thermochromic properties and low emissivity of ZnO:Al/VO2 double-layered films with a lowered phase transition temperature

We studied the optical and semiconductor–metal (S–M) transition properties of ZnO:Al/VO2/substrate double-layered films that consisted of a ZnO:Al top layer and a VO2 bottom layer. ZnO:Al and VO2 films were grown on fused silica substrates by radio frequency magnetron sputtering and polymer-assisted deposition, respectively. The ZnO:Al/VO2/substrate films displayed low emissivity (0.31–0.32) with integrated luminous transmittance (Tlum>46%) and thermochromic properties (ΔTsol>4.1%). The low emissivity and thermochromic properties were independently introduced by the transparent conductive ZnO:Al layer and the VO2 layer. In addition, the S–M transition temperatures for VO2 shifted to lower temperatures after the ZnO:Al deposition process, which was due to the formation of surface nonstoichiometry—oxygen deficiency that was induced by the ZnO:Al deposition process.