Tungsten doped M-phase VO2 mesoporous nanocrystals with enhanced comprehensive thermochromic properties for smart windows

Abstract

The phase transition temperature (~68 °C) of M-VO2 film can be lowered significantly by tungsten (W) doping into the crystal lattice of VO2 due to the reduction of the strength of V-V pair interaction. However, W doping was always coupled with a serious weakening of luminous transmittance and solar modulation efficiency because W dopants can increase the electron concentration of VO2 film. Herein, the simultaneous introduction of W dopants and mesopores into M-VO2 nanocrystals was employed to prepare VO2 film. Interestingly, the obtained 0.4 at% W-doped mesoporous VO2 nanocrystals based composite films exhibited enhanced comprehensive thermochromic performance with excellent solar modulation efficiency (ΔTsol = 11.4%), suitable luminous transmittance (Tlum = 61.6%) and low phase transition temperature around 43 °C, much lower than 65.3 °C of undoped VO2. It was demonstrated that the lower phase transition temperature of VO2 can be primarily attributed to abundant lattice distortion after W doping, whereas the mesoporous structure can facilitate the uniform distribution of W dopants in VO2 nanocrystals, enhance the luminous transmittance and guarantee enough VO2 nanocrystals in the composite film to keep relatively high solar modulation efficiency. Therefore, this work can provide a new way to balance the three important parameters for the thermochromic performance of VO2 film (ΔTsol, Tlum and Tc) and probably promote the application of VO2 nanocrystals in the energy efficient windows.