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 hydrophobic 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°, 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.