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.