$Zr{O}_2/V{O}_2/Zr{O}_2$ sandwich structure with improved optical properties and weatherability for smart window application

Vanadium dioxide (VO${}_2$) is considered as an ideal thermochromic material for smart window due to its reversible metal insulator transition around 340 K. However, its application is limited by the low luminous transmittance (T${}_{lum}$), insufficient solar modulation ability (△T${}_{sol}$) and unsatisfactory service performance. In this work, ZrO${}_2$/VO${}_2$ bi-layer and ZrO${}_2$/VO${}_2$/ZrO${}_2$ tri-layer films were prepared on glass substrates by pulse laser deposition. The bottom ZrO${}_2$ film acted as a buffer layer, which is conducive to the formation of VO${}_2$ film, while the top ZrO${}_2$ film played the role of antireflection layer (ARL), which can effectively improve the optical properties of VO${}_2$ film. As the ZrO${}_2$ buffer layer increased from 30 nm to 150 nm, the T${}_{lum}$ of ZrO${}_2$/VO${}_2$ films increased from 32.8% to 50.9% while maintaining a high △T${}_{sol}$ of ~ 8%. After introducing ZrO${}_2$ ARL, both the T${}_{lum}$ and △T${}_{sol}$ of the optimized ZrO${}_2$ (150 nm)/VO${}_2$ (60 nm)/ZrO${}_2$ (100 nm) structure were further enhanced synchronously to 55.8% and 10.2%, respectively. Besides, the hydrophobic properties of the obtained ZrO${}_2$/VO${}_2$/ZrO${}_2$ films were greatly enhanced. More importantly, even after 32 h of boiling water treatment, the △T${}_{sol}$ of the optimized ZrO${}_2$/VO${}_2$/ZrO${}_2$ tri-layer film was only decreased to ~ 6.1%, while the T${}_{lum}$ maintained at ~ 50%. Our results suggested that the proposed ZrO${}_2$/VO${}_2$/ZrO${}_2$ structure not only played a key role in balancing and improving T${}_{lum}$ and △T${}_{sol}$, but also greatly extended the service life of VO${}_2$ smart window.