Design and preparation of broadband antireflective coatings with excellent mechanical properties

Double antireflective coatings with broadband, high-transmittance and scratch-resistance properties were prepared in this research by sol-gel method. The bottom layer was the mixture of silica nanoparticles and linear silicate polymers (SiO2 NPs-LPs) obtained from base/acid two-step catalyzed tetraethyl orthosilicate (TEOS), while the top layer was the mixture of hollow silica nanoparticles and linear silicate polymers (HSiO2 NPs-LPs). By optimizing the refractive index and the thickness of the double coatings, the optical performance of the double coatings was generally consistent with the results of theoretical design. The average transmittance in the wavelength range of 400-1200 nm reached 99.1%. Besides, through applying hydroxyl modification on the surfaces of silica particles and hollow spheres, the antireflective coatings exhibited excellent mechanical properties, with its pencil hardness reaching 5 H and critical load for scratch being 28.9 N. All these good features have made this coating promising in harsh outdoor conditions.