Antireflective (AR) SiO2 coatings were developed in this work to increase the transmittance of glass in the visible light range of 400-800 nm, due to their potential applications in solar energy systems. Additionally, double-layer AR coatings were prepared by covering the AR SiO2 layer with a dense TiO2 layer to protect the AR layer from environmental effects. SiO2 coatings were obtained using sol-gel and dip coating methods, with acid- and base-catalyzed silica sols as precursors. Only a 1% transmittance increase was gained with acid-catalyzed SiO2 coating due to its dense structure. On the contrary, SiO2 coatings formed by base-catalyzed sol exhibited transmittance values >99% in the 460-660 nm range and 99.8% at 550 nm, corresponding to the wavelength of maximum intensity in the solar spectrum. These high values were attributed to the porous structure of the film, revealed by SEM and AFM analysis, and the optimized thickness of the coating achieved at 90-120 mm/min withdrawal speeds. The transmittance of base-catalyzed SiO2 coatings decreased to an average value of 96.2% after being coated with the high refractive index TiO2 layer. However, a 5-6% improvement in glass transmittance in the 400-800 nm range was still achieved by optimizing the thickness of each layer using different withdrawal speeds and varying the concentration and types of precursor sols. Characterization of the coatings was performed with SEM, AFM, EDS, and FTIR analysis.
