Double-layer VO2 thin film patterned by SiO2 spheres with improved thermochromic properties for smart windows

The double-layer vanadium dioxide (VO 2 ) thin film patterned by SiO 2 spheres has been fabricated to enhance luminous transmittance ( T lum ) without severely expense of solar modulation ability (Δ T sol ) for the thermochromic smart windows. The first layer of vanadium thin film was deposited on the substrate with self-assembly SiO 2 spheres and then the SiO 2 spheres was removed by ultrasonic oscillation. The orderly perforated vanadium thin film with regular pores formed. Afterwards, the second layer of vanadium thin film was deposited on the perforated vanadium thin film. The semi-perforated double layer of vanadium thin film formed and was rapid thermal annealed forming the semi-perforated double VO 2 thin films. Compared with continuous VO 2 thin film( T lum , 8.8%, Δ T sol , 5.9%), the semi-perforated double VO 2 layer possesses orderly-patterned crater, which facilitate T lum (42.6%) and only slightly attenuate the Δ T sol (5.5%). The phase transition temperatures for continuous VO 2 thin film and the optimized semi-perforated VO 2 double layer thin film were 58 °C and 52 °C, respectively, far below 68 °C of bulky VO 2 . This structure should be very meaningful for the real application of VO 2 -based smart window in the future.