Thermochromic properties of BN/VO2/BN trilayer films with low phase transition temperature and high hysteresis width

A novel thermochromic BN/VO2/BN trilayer thin film was deliberately designed and deposited using pulsed laser deposition combined with rapid thermal annealing. The structure, surface morphology, surface roughness, and thermochromic properties of the as-prepared sandwich structure film were analyzed. A BN buffer layer did not significantly reduce the phase transition temperature T-t, but rather played a role in modifying the surface morphology of VO2 thin film. Covering the BN/VO2 bilayer film with a second BN layer greatly reduced T-t with large hysteresis width, and luminous transmittance (T-lum) was also enhanced, whereas solar modulation efficiency (Delta T-sol) was reduced. In particular, when the thickness of BN was 70 nm, the resulting BN/VO2/BN trilayer film reached a low T-t value of 36 degrees C with large hysteresis width (25 degrees C) and a high T-lum (similar to 40%), but with a very low Delta T-sol. The properties revealed by this first attempt to use BN thin film in the fabrication of VO2-based multilayer sandwich structures open up a new path for the design of advanced thermochromic heterostructures with tunable functionalities for smart windows and optical storage devices.