Nanoceramic VO2 thermochromic smart glass: A review on progress in solution processing

Progress in the development of energy-efficient coatings on glass has led to the study of smart glass with special functional coatings that can regulate solar energy in response to an external stimulus. Thermochromic smart windows are considered attractive because they are visibly transparent and can intelligently control the amount of solar heat (mainly in the near-infrared region) in response to changes in ambient temperature. Discovered over 50 years ago, VO2 is the most promising thermochromic material; however, related materials have not been commercialized because of problems related to cost-efficient preparation, stability and performance. To date, gas-phase deposition methods, such as sputtering and chemical vapor deposition, are the most common methods for the fabrication of VO2 films, but these methods are still dependent on innovative technologies to meet the requirements of practical applications and are excluded from the topic of the current paper. This paper reviews the state-of-the-art solution processes used to prepare VO2 films, with a special emphasis on polymer-assisted deposition methods. The VO2 films prepared by these methods show controllable morphology and thickness and complex optical properties compared with those prepared by gas-phase methods. In fact, single-layered films exhibit the highest integrated visible transparency (43%) and solar-energy modulation ability (14%). These studies suggest that chemical preparation is inexpensive, easy to scale up, and best suited for the practical applications of the fabricated materials.