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

The double-layer vanadium dioxide (VO₂) thin film patterned by SiO₂ spheres has been fabricated to enhance luminous transmittance (T_lum) without severely expense of solar modulation ability (ΔT_sol) for the thermochromic smart windows. The first layer of vanadium thin film was deposited on the substrate with self-assembly SiO₂ spheres and then the SiO₂ 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 VO₂ thin films. Compared with continuous VO₂ thin film(T_lum, 8.8%, ΔT_sol, 5.9%), the semi-perforated double VO₂ layer possesses orderly-patterned crater, which facilitate T_lum (42.6%) and only slightly attenuate the ΔT_sol (5.5%). The phase transition temperatures for continuous VO₂ thin film and the optimized semi-perforated VO₂ double layer thin film were 58 C and 52 C, respectively, far below 68 C of bulky VO₂. This structure should be very meaningful for the real application of VO₂-based smart window in the future. (orig.)