Gradient Variation Oxygen-Content Vanadium–Oxygen Composite Films with Enhanced Crystallinity and Excellent Durability for Smart Windows

Vanadium dioxide (VO2)-based smart windows show excellent promise for energy-saving and have been extensively researched. However, for the glass industry-compatible magnetron sputtering process, VO2 films are difficult to obtain and have homogeneous crystalline state, leaving them lacking the ideal solar modulation (ΔTsol) and sensitivity (narrow hysteresis loop). More importantly, the instability of VO2 hinders its commercialization. Multilayer structures have been repeatedly investigated to solve these problems. Unfortunately, the mediocre thermochromic properties as well as the complex and expensive manufacturing steps still hinder its commercialization. In this work, we prepared gradient variation oxygen-content vanadium–oxygen composite films (V2O3/VO2/V2O5, VOgv) with enhanced crystallinity and excellent durability by one-step continuous sputtering. According to optical measurements, the ΔTsol of the VOgv films was significantly increased by 145% (from 6.85 to 16.80%) compared to VO2 films, and the width of the hysteresis loop was reduced by 67% (from 19.34 to 6.36 °C), while the VOgv films exhibited a wider preparation window. The accelerated tests have shown that the film has an equivalent service life of approximately 20 years. We exploited the intrinsic similarity in properties of homologous compounds of vanadium oxide and simplified the preparation process, which is supposed to break the existing application bottlenecks and increase the commercializing possibility of VO2-based thermochromic smart windows.