Hydrophobic anti-reflective silica hybrid film with tunable refractive index

As one of the important optical films, the anti-reflection film can effectively reduce light reflection at the optical interface, and has wide application potentials in the fields of solar power generation, high-power laser systems, optical devices. However, besides high transmittance, strong environmental resistance and mechanical properties are also needed for anti-reflection coatings in practical applications. In this paper, a series of single-layer hy-drophobic anti-reflection silica coatings with adjustable refractive index between 1.13 and 1.44 is obtained via the hybridization of hydrophobic-modified alkali-catalyzed silica hollow nanospheres with hydrophobic acid-catalyzed silica in different proportions, and then used for the construction of double-layer membranes where the top layer has a refractive index of 1.19 and the bottom layer has a refractive index of 1.25. The single-layer film can exhibit nearly perfect transmittance up to 99.2 %, and meanwhile, the double-layer film exhibits excellent broadband anti-reflection with an average transmittance of 98.7 % in the wavelength range from 300 to 900 nm. The hydrophobicity of these films is excellent, and the maximum water contact angle reaches 142 degrees, so the dust pollution hardly leads to the decline of its optical performance. Moreover, the addition of acid-catalyzed sol improves the mechanical properties of the hybrid film while maintaining good transmittance even after the rubbing test.