VO2-based sol-gel multilayer thin films: a green approach for energy-efficient smart windows

Vanadium dioxide (VO2) has aroused great attention due to its temperature-driven dramatic change in optical properties. Specifically, it shows a reversible metal-to-insulator transition (MIT) around a critical temperature of 68°C (341 K). Despite the great interest in this material thanks to the potential thermochromic smart windows application, there is still a long way to go. The aim of this work is the optimization of the optical performance of a solution-based synthesized TiO2/VO2 multilayer, modulating the thickness of every layer. Two key parameters mainly characterize the optical performance of a vanadia-based thin film: its luminous transmittance (Tlum, 380 nm-780 nm) and the solar-energy modulation ability ΔTsol. TiO2 has been selected thanks to its good adhesion both to a glass substrate and VO2 thin film, in addition to this, it should act as a buffer layer for the crystalline VO2 film deposition and its suitable refractive index can improve the luminous transmittance of the whole film. A further optimization of performance could be the deposition of an inorganic protective thin film to increase thermochromic VO2 layer durability. Anti-reflective, hydrophobic and photocatalytic properties to degrade pollutants are desirable.