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 (ΔT_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 °C) than the pure VO₂(M) thin film (67.9 °C). Furthermore, the fabrication process is well-reproducible, which is highly attractive for the mass production.