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The double-layer vanadium dioxide (VO2) thin film patterned by SiO2 spheres has been fabricated to enhance luminous transmittance (Tlum) without severely expense of solar modulation ability (ΔTsol) 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(Tlum, 8.8%, ΔTsol, 5.9%), the semi-perforated double VO2 layer possesses orderly-patterned crater, which facilitate Tlum (42.6%) and only slightly attenuate the ΔTsol (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.

In this study, the VO2/Au/VO2 sandwiched structure was fabricated by rapid thermal annealing of sputtered V/Au/V sandwiched structure to modify the intrinsic unpleasant brown–yellow color of VO2 films based on the localized surface plasmon resonance (LSPR) for smart windows. The morphology, crystalline structures, and optical transmittance spectra of the sandwich structure were characterized by scanning electron microscopy, X-ray diffraction and UV-VIS-NIR spectrophotometry, respectively. The obtained results indicate that the VO2/Au/VO2 sandwich structure with different Au nanoparticles sizes shows different color from brown–yellow to blue–green due to the appearance and redshift of LSPR peak. Moreover, the phase-transition temperature for the optimized VO2/Au/VO2 sandwich structure was only 42.5 °C, far below 68 °C for bulky VO2. The optimized VO2/Au/VO2 thin films could simultaneously meet the requirements of comfortable color and a reduced phase-transition temperature, and these excellent features would benefit the practical application of VO2 thin film-based smart windows.