Superhydrophilic self-cleaning surfaces based on TiO2 and TiO2/SiO2 composite films for photovoltaic module cover glass

摘要

Self-cleaning surfaces have excelled in recent years in energy and environmental fields. In particular, in solar energy area, these surfaces are used to avoid soiling accumulation on photovoltaic (PV) modules. So far TiO₂ has been widely used due to its photocatalytic activity and photo-induced superhydrophilicity. However, this oxide has some limitations since it reduces the glass transmittance and it rapidly reestablish the water contact angle in dark environments. In order to circumvent these limitations, composites TiO₂/SiO₂ have been proposed. For photovoltaic application, besides a good transparency in the wavelength region 300–1800?nm and self-cleaning properties, the coating should also present long durability and adequate adhesion to endure the outdoor conditions. Aiming at developing a coating with these properties, in this work, TiO₂/SiO₂ composites containing different titanium content have been synthesized and compared with pure TiO₂ films in relation to adhesion, transparency and hydrophilicity. Both films have been deposited over low iron float glass substrates by sol–gel dip-coating technique and different calcination temperatures (400, 500, 600°C) and Si/Ti molar rates (Si₈₆Ti₁₄, Si₄₀Ti₆₀) have been considered. TiO₂/SiO₂ films showed higher transmittance in visible range compared with pure TiO₂. TiO₂/SiO₂ films showed superhydrophilic character before and after ultraviolet irradiation, with water contact angles near to 0°. Furthermore, as predicted, TiO₂/SiO₂ films could keep the superhydrophilic character in dark environments, in contrast with pure TiO₂ films. Both TiO₂ and TiO₂/SiO₂ films exhibited good adherence and it is shown that higher calcination temperatures and higher titanium content enhance such property. All films presented abrasion resistant property in contact with sponge and detergent. It has been demonstrated that high transmittance, self-cleaning and adherent composite has been obtained by a simple sol–gel route presenting good potential to be applied on photovoltaics systems