VO₂-based composite films with exemplary thermochromic and photochromic performance

Vanadium dioxide (VO₂) is one of the best candidates for thermochromic smart windows, which undergoes a metal–insulator transition at a critical temperature (T_c) of ∼68 °C, accompanied with a huge transmittance contrast in the near-infrared range. However, the application of VO₂-based smart windows is limited by the poor luminous transmittance (T_lum) and low solar modulation efficiency (ΔT_sol). Besides, the intrinsic yellow–brown color of the VO₂ film does not change before and after the phase transition, which is not satisfactory. In order to solve the above-mentioned issues, a photochromic material [6-nitro-1′,3′,3′-trimethylspiro-[2H-1-benzopyran-2,2′-indoline] (spiropyran)] has been employed to combine with VO₂ nanoparticles to form a hybrid composite film. This newly designed nanostructure demonstrates exemplary solar modulation efficiency (ΔT_sol = 23.58%) along with color change from yellow to pink as the light sources change. Moreover, this hybrid composite could block ultraviolet radiation, a crucial index to evaluate the performance of the VO₂-based smart windows, which will be promising for industrial applications.