ZrO2/VO2/ZrO2 sandwich structure with improved optical properties and weatherability for smart window application

Vanadium dioxide (VO2) 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 (Tlum), insufficient solar modulation ability (△Tsol) and unsatisfactory service performance. In this work, ZrO2/VO2 bi-layer and ZrO2/VO2/ZrO2 tri-layer films were prepared on glass substrates by pulse laser deposition. The bottom ZrO2 film acted as a buffer layer, which is conducive to the formation of VO2 film, while the top ZrO2 film played the role of antireflection layer (ARL), which can effectively improve the optical properties of VO2 film. As the ZrO2 buffer layer increased from 30 nm to 150 nm, the Tlum of ZrO2/VO2 films increased from 32.8% to 50.9% while maintaining a high △Tsol of ~ 8%. After introducing ZrO2 ARL, both the Tlum and △Tsol of the optimized ZrO2 (150 nm)/VO2 (60 nm)/ZrO2 (100 nm) structure were further enhanced synchronously to 55.8% and 10.2%, respectively. Besides, the hydrophobic properties of the obtained ZrO2/VO2/ZrO2 films were greatly enhanced. More importantly, even after 32 h of boiling water treatment, the △Tsol of the optimized ZrO2/VO2/ZrO2 tri-layer film was only decreased to ~ 6.1%, while the Tlum maintained at ~ 50%. Our results suggested that the proposed ZrO2/VO2/ZrO2 structure not only played a key role in balancing and improving Tlum and △Tsol, but also greatly extended the service life of VO2 smart window.