Synthesis and characterization of novel multi-layer silica thin films with tailored mesostructure as anti-reflective coatings

Photovoltaic devices are highly in need of glass covers to protect solar cells against environmental damage, especially for outdoor performance. Antireflective coatings on these glass covers are essential upon which many studies on designing new coating are ongoing to exhibit both satisfactory optical properties and adequate me-chanical stability. This study compares different types of three-layer mesoporous silica coatings with graded porosity fabricated by the evaporation-induced self-assembly method. Surfactant concentration was manipulated as an important variable to tailor different mesostructure designs. The deposition of coatings was performed by sequential spin-coating method. The effects of layers arrangement on light transmittance and water absorption were investigated. The fabricated transparent multi-layer coatings showed to have a uniform pore size of about 3 nm and a thickness of about 450 nm. The average transmittance of the coatings was approximately 96% in the wavelength range of 400-800 nm. It was concluded that the optical properties and water absorption of multi -layer coatings depend on the porosity of each layer and the interconnections of the layers upon which the desired properties can be tailored. The maximum constant transmittance in a wavelength range from 400 to 800 nm of tri-layer coatings was obtained when layer of lower porosity was at the bottom next to the glass. Fabricated samples with high smoothness, high transmittance, and low water absorption indicate positive prospects for solar glass applications.