Coloured TiO2 based glazing obtained by spray pyrolysis for solar thermal applications

Titanium dioxide thin films with coloured reflections were deposited on glass substrate by robotic spray pyrolysis deposition using titanium (IV) isopropoxide as a precursor and air as a carrier gas. The filmsʹ optical properties were analyzed by UV–vis–NIR spectrometry using a 150 mm integrating sphere and spectroscopic ellipsometry (SE). The surface properties were evaluated by atomic force microscopy (roughness and morphology) and contact angle measurement (wettability). The colour variation of the films was determined in the CIE (Commission Internationale dʹEclairage) L⁎a⁎b⁎ colour system by using the total reflectance spectra measured in the visible range. Thin films with low roughness (<4.5 nm), high transparency (>70%) in the UV–vis–NIR region and hydrophilic properties were obtained. The optical properties, particularly transmittance are not influenced by humidity exposure. The colour of the films depends on the number of deposition sequences due to thickness and surface topology modification. By varying the deposition sequences brownish, purple, light-violet or purple–brown coloured reflections can be obtained. These coloured TiO2 thin films will be used in solar collectorsʹ glazing, supporting increased architectural acceptance.