Abstract

Anti-reflective coatings are used in photovoltaic systems to minimize reflectance thus optimizing efficiency. Besides excellent optical properties, these coatings need to provide good mechanical properties due to hostile environmental conditions. Therefore, this study aims at designing anti-reflective coatings based upon multi layers of TiO2 and SiO2 by magnetron sputtering on glass and silicon substrates at room temperature. Afterwards, these coatings were thermally annealed at 400, 500 and 600 degrees C to study the influence of such treatment on their optical and mechanical properties. Samples prepared at room temperature and annealed at 400 degrees C showed an optimized reflectance of about 2%. Advanced materials characterization techniques were used to elucidate the microstructural evolution of the multi-layers. The multi-layers annealed at 400 degrees C demonstrated a dense and smoothly packed microstructure with homogenous grains (50 nm in size), with a phase transformation from amorphous to anatase. In addition, exposure and damage of the glass substrate were detected for elevated temperatures (500 and 600 degrees C), thus increasing the reflectance. Nanoindentation revealed an improved hardness, elasticity, and resistance against plastic deformation for the sample annealed at 400 degrees C. Consequently, anti reflective coatings with post-annealing treatment at 400 degrees C, unify two complementary aspects such as improved mechanical properties (extended durability) and enhanced collection abilities over a broader wavelength range (increased efficiency).