Polyfluoroalkyl-silica porous coatings with high antireflection properties and low surface free energy for glass in solar energy application

Polyfluoroalkyl-silica porous coating stacks with durable antireflection (AR) properties have been obtained for photovoltaic (PV) application. An acid-catalyzed sol-gel process combined with evaporation induced self-assembly and the presence of a non-hydrolyzable polyfluoroalkyl group linked to the central atom of the silicon alkoxide was conducted. The aim was to obtain a low surface energy coating, devised to mitigate soiling adherence, without losing the AR properties of a baseline coating. In particular, the influence of polyfluoroalkyl chain length on the thickness, the water contact angle and optical transmission properties was first analyzed. The optimized polyfluoroalkyl-silica porous coating presented low surface energy < 20 mJ/m(2), even with the desired low roughness values required for obtaining a negligible scattering of the incoming solar radiation. This coating was studied as an AR mono-layer and as an external coating in an AR bi-layer stack, with the presence of an inner dense-structured silica layer, that contributed to both the optical performance and durability, acting as an alkali diffusion preventing layer. The AR bi-layer stack deposited on two sides of glass provided a transmittance gain of 7.1%. Those optical properties were inalterable after accelerated aging tests, which sustains the reliability of the materials for solar energy applications.