Abstract
Multilayer broadband antireflective (AR) coatings consisting of porous layers usually suffers poor functional durability. Based on a quarter-half-quarter multilayer structure, AR coatings with dense SiO2 film as the top layer are designed, and refractive index for each layer is optimized. After heat-treated at only 150 °C, refractive index of Nb2O5 film reaches to 2.072 (at 550 nm), which can meet design requirements of the middle layer. TiO2–SiO2 composites with controllable refractive indices are selected to be used as the bottom layer. The obtained triple-layer AR coating presents excellent performance, and the average transmittance at 400–800 nm attains 98.41%. Dense layers endow the multilayer structure good abrasion-resistance, and hexamethyldisilazane is further used to modify the surface of the AR coating, which can greatly improve the hydrophobicity of the coating. The proposed triple-layer broadband AR coating has potential value in practical applications of sol–gel deposition.
Highlights
Broadband antireflective (AR) coatings have attracted much attention in imaging devices, solar cells, display panels and laser systems by reducing reflective losses at interfaces over a broad range of wavelengths [1,2,3,4]
It is fortunate that refractive index dispersion is low for most oxide films in the visible and near-infrared regions
In the initial stage of coating system design, it is feasible to perform calculations while temporarily ignoring refractive index dispersion, and select the results best suited for a given application
Summary
Broadband antireflective (AR) coatings have attracted much attention in imaging devices, solar cells, display panels and laser systems by reducing reflective losses at interfaces over a broad range of wavelengths [1,2,3,4]. An effective 0% reflection can be achieved at a specific wavelength when a single-layer quarter-wave silica AR coating is applied onto flat substrates using the sol–gel method. The porosity between based-catalyzed silica colloid particles or acid-catalyzed silica linear oligomers lowers the refractive index of silica AR coating to the square root of the index of such optical substrates as fused quartz (1.46) and BK7 glass (1.52), i.e., approximately 1.22 [8,9,10,11]. The realization of broadband AR coatings needs to establish multilayer film structures, in which the refractive index and thickness of each layer must be carefully adjusted. Precedent studies have shown that, if a mesoporous film with ultralow refractive
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