VO2-based composite films with exemplary thermochromic and photochromic performance

Abstract

Vanadium dioxide (VO2) is one of the best candidates for thermochromic smart windows, which undergoes a metal–insulator transition at a critical temperature (Tc) 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 (Tlum) and low solar modulation efficiency (ΔTsol). 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 (ΔTsol = 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.