Recent progress in VO2 smart coatings: Strategies to improve the thermochromic properties

Vanadium dioxide (VO2) has attracted a great interest for smart coating applications because of its promising thermochromic properties. Thermochromic performance of VO2 is closely related to the phase composition and the microstructure, which are largely dependent on the synthesis method and growth control. This review summarizes the recent progress in fabrication of VO2 by gas deposition. Representative deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), sol–gel and chemical solution methods and their relative merits are discussed. To be practically applicable, high-performance thermochromic VO2 films are desired, often featured with a suitable phase transition temperature (Tc), high luminous transmittance (Tlum) and good modulation capability of solar energy (ΔTsol). Focused on the strategies used to improve thermochromic properties, this review also covers topics such as multilayer construction, elemental doping, substrate selection, and structure modification. Some theoretical progresses in understanding thermochromic coatings, including phase transition mechanism and energy modeling are also provided. Although significant progress has been made in improving the thermochromic performance of VO2 films, challenges are still present, particularly in commercial applications. Discussions on future trend and perspectives, as well as some important issues, of VO2 films used as smart coatings will be given finally.