Enhanced chemical stability of VO2nanoparticles by the formation of SiO2/VO2 core/shell structures and the application to transparent and flexible VO2-based composite foils with excellent thermochromic properties for solar heat control

Abstract

Vanadium dioxide is a key material for thermochromic smart windows that can respond to environmental temperature and modulate near infrared irradiation by changing from a transparent state at low temperature to a more reflective state at high temperature, while maintaining visible transmittance. VO₂ thermochromism is commonly used in films on glass that function as smart windows. Flexible VO₂ nanocomposite foils are able to combine the intrinsic properties of VO₂ nanoparticles with the added functionalities contributed by nanoscale and interface effects, such as increased visible transparency and infrared modulation ability. These foils are promising for applications in construction and automotive glasses to increase energy efficiency. However, VO₂ nanoparticles may be unstable, and they are difficult to prepare in stable dispersive suspensions. In this paper, we report a novel all-solution process that can be used to prepare transparent, stable and flexible VO₂-based composite films. These films exhibit UV-shielding properties and an excellent temperature-responsive thermochromism in the near infrared region. A typical film has a solar modulation efficiency of 13.6%, which is the highest value for VO₂ thermochromic films with comparable visible transmittance. Coating the VO₂ nanoparticles with a thin SiO₂ shell significantly improved their anti-oxidation and anti-acid abilities. This result represents an important breakthrough in VO₂ thermochromism, and it may have applications for near infrared modulation of glass used in construction or cars.