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