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

ZrW 2 O 8 with excellent negative thermal expansion coefficient and anti-reflective property, was successfully introduced onto VO 2 thermochromic films. With an increase in temperature, thermal expansion mismatch appears at the interface between VO 2 and ZrW 2 O 8 layers, and the concave-shaped structures are formed to collect more light. Additionally, ZrW 2 O 8 serves as an anti-reflective coating, which results in a significant enhancement in luminous transmittance . The luminous transmittance of VO 2 /ZrW 2 O 8 and ZrW 2 O 8 /VO 2 /ZrW 2 O 8 films is 71.9% and 75.7%, respectively, which have shown significant improvement compared to 39.8% for intrinsic VO 2 film. In addition, the solar modulation value of VO 2 /ZrW 2 O 8 and ZrW 2 O 8 /VO 2 /ZrW 2 O 8 films have also been improved compared to VO 2 film, and the obtained value for bi-layer film is higher than that of tri-layer film. The results obtained for VO 2 /ZrW 2 O 8 and ZrW 2 O 8 /VO 2 /ZrW 2 O 8 films have shown a remarkable improvement over other bi-layer or tri-layer structures. The described VO 2 /ZrW 2 O 8 and ZrW 2 O 8 /VO 2 /ZrW 2 O 8 films with enhanced luminous transmittance and solar modulation make them promising materials for the application in smart windows .