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 (Tlum) and solar modulation ability (ΔTsol) 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 ΔTsol of VO2(12 nm)/W-VO2(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.