Combined negative thermal expansion and anti-reflective effects of ZrW2O8 layer on the VO2 films with an enhanced luminous transmittance

Abstract

ZrW2O8 with excellent negative thermal expansion coefficient and anti-reflective property, was successfully introduced onto VO2 thermochromic films. With an increase in temperature, thermal expansion mismatch appears at the interface between VO2 and ZrW2O8 layers, and the concave-shaped structures are formed to collect more light. Additionally, ZrW2O8 serves as an anti-reflective coating, which results in a significant enhancement in luminous transmittance. The luminous transmittance of VO2/ZrW2O8 and ZrW2O8/VO2/ZrW2O8 films is 71.9% and 75.7%, respectively, which have shown significant improvement compared to 39.8% for intrinsic VO2 film. In addition, the solar modulation value of VO2/ZrW2O8 and ZrW2O8/VO2/ZrW2O8 films have also been improved compared to VO2 film, and the obtained value for bi-layer film is higher than that of tri-layer film. The results obtained for VO2/ZrW2O8 and ZrW2O8/VO2/ZrW2O8 films have shown a remarkable improvement over other bi-layer or tri-layer structures. The described VO2/ZrW2O8 and ZrW2O8/VO2/ZrW2O8 films with enhanced luminous transmittance and solar modulation make them promising materials for the application in smart windows.