Facile Fabrication of Composite Vanadium Oxide Thin Films with Enhanced Thermochromic Properties

In general, high-purity monoclinic VO2 (VO2(M)) was considered as a prerequisite for obtaining VO2-based thermochromic coatings with high performance. The coexistence of other vanadium oxides (such as V3O7 and V2O5) in VO2 coatings was regarded as an unfavorable issue. Here, we investigate the microstructures and thermochromic properties of the composite vanadium oxide (CVO) thin films. The results demonstrate that the proper coexistence of high valent vanadium oxides (V3O7 and V2O5) in VO2-based films can remarkably enhance the thermochromic performance of films. The CVO thin films were prepared by a room-temperature sputtering process followed by a modified rapid annealing routine in air. The structural analyses (X-ray diffraction, Raman spectroscopy, and transmission electron microscopy) reveal the coexistence of VO2(M), V3O7(M), and V2O5(O) in CVO thin films. The luminous transmittance (T-lum) and solar modulation ability (Delta T-sol) of the CVO thin film obtained by an optimal preparation process are 1.93 and 1.34 times those of the pure polycrystalline VO2 thin film, respectively. Moreover, the CVO thin film exhibits lower semiconductor-to-metal transition temperature (60.8 degrees C) than the pure VO2(M) thin film (67.9 degrees C). Furthermore, the fabrication process is well-reproducible, which is highly attractive for the mass production.