VO2/TiO2 bilayer films for energy efficient windows with multifunctional properties

Abstract

Vanadium dioxide/titanium dioxide bilayer films have been investigated as a thermochromic coating for application as intelligent window glazings for buildings. The nanostructured VO₂ and TiO₂ films were deposited on fluorine doped tin oxide coated glass substrates using electric field assisted aerosol assisted chemical vapour deposition (ElFi-AACVD) and sol–gel spin coating, respectively. Their thermochromic properties were investigated using scanning electron microscopy, X-ray diffraction, variable temperature UV/Vis/NIR and X-ray photoelectron spectroscopies. Compared to bare VO₂ films, the VO₂/TiO₂ bilayer films exhibit an increase in visible light transmittance of up to 30%, an increase in integrated luminous transmittance, with values up to 66%, and a higher transmittance modulation in the near infrared of up to 20% at the thermochromic transition temperature. The TiO₂ top layer not only enhances visible light transmittance, but also serves to protect the VO₂ bottom layer from oxidation. The bilayer films are shown to exhibit photo-induced super-hydrophilicity. These properties are affected by the morphology of the VO₂ under-layer.