An approach for obtaining thermochromic smart windows with excellent performance and low phase transition temperature based on VO₂/ tungsten-doped VO₂/VO₂ composite structure

Tungsten-doped vanadium dioxide (W-VO2) has a low phase transition temperature (Tc), but the poor thermochromic properties hinders its application in the field of smart windows. In this work, we proposed and fabricated VO2(x nm)/W-VO2(x nm)/VO2(x nm) composite films with different thickness (x = 10, 12, 15 and 20) on quartz glass substrate by pulsed laser deposition. The bottom VO2 layer was served as buffer layer to improve the crystallinity of W-VO2 layer, while the top VO2 layer was to strengthen the thermochromic properties of the composite films. With the increase of x from 10 to 20, XRD and SEM results suggested that the crystallinity and grain morphology of the obtained composite films can be largely regulated. In particular, when x = 12, the luminous transmittance (T-lum) and solar modulation ability (dT(sol)) are as high as 61.1 % and 8.0 %, respectively, while maintaining a low Tc of 45.9 C. Through in -situ annealing treatment, the Tlum and dTsol of VO2(12 nm)/WVO2(12 nm)/VO2(12 nm) further significantly enhanced to 79.3 % and 9.1 %, and Tc also reduced slightly to 41.4 C. SEM characterization suggested that the improved optical properties can be attributed to the Localized Surface Plasmon Resonance (LSPR) effect of the spherically structured W-VO2 nanoparticles. The results in this study confirmed that the thermochromic properties of W-VO2 could be optimized by controlling its grain morphology, which provided a new strategy for the application of W-VO2 films in the field of smart windows.