Transparent nanostructured titania coatings with selfcleaning and antireflective properties for photovoltaic glass surfaces

Transparent titania (TiO2) coatings having self-cleaning and antireflection (AR) properties, for application as surface functional layer in cover glasses of photovoltaic (PV) devices, were prepared, characterized and tested. The coating preparation is made by forming first a nanosol through controlled hydrolysis of a tetraisopropyl orthotitanate (TIPT) precursor. The nanosol is then deposited on the glass substrates by dipcoating with a subsequent step of calcination. This work reports the effect of the preparation parameters on both optical and morphological properties of the obtained coatings. The nanostructure and texture of the samples were characterized by X-ray diffraction, UV-vis spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM), while transmittance measurements were carried out to assess the AR properties. Self-cleaning properties were investigated by water contact angle measurements and photocatalytic activity tests. Films with good optical characteristics and high transmittance (T losses < 1 % compared to bare glass) have been obtained at low dip-coating speed (6 mm/s) and high nitric acid concentration (HNO3 0.5 N). The best transmittance values were obtained by calcination of the sample at 500 °C, but a higher amount of acid catalyst in the nanosol synthesis allows to reduce the calcination temperature to 400 °C, while maintaining good optical properties and crystallinity of the thin film.