The combination of VO₂ nanoparticle and flat films with enhanced thermochromic properties for smart windows

The double-sided VO₂ nanoparticle and flat films were grown by magnetron sputtering and rapid thermal annealing on the sapphire substrate. For the VO₂ flat film, the luminous transmittance (T_lum) increased while the solar modulation (ΔT_sol) decreased as the film thickness decreased. However, the rutile VO₂ nanoparticles possessing the localized surface plasmon resonance (LSPR) excited at ~1250 nm is helpful to improve the ΔT_sol. Therefore, the combination of VO₂ nanoparticles and flat film on one substrate was designed to achieve the optimum between T_lum and ΔT_sol. The single-sided VO₂ nanoparticles film showed a high T_lum of 72% with a ΔT_sol of 3.1%, and the single-sided VO₂ flat film exhibited an increased ΔT_sol of 4.9%, while the T_lum decreased to 49%. The double-sided VO₂ nanoparticle and flat films presented an excellent ΔT_sol of 9.3% and a slightly attenuated T_lum of 45%. This work provides a feasible structure to significantly enhance the ΔT_sol accompanied by little sacrificing the T_lum, which may be beneficial in the application of VO₂-based smart windows.