Study On Preparation Technology Of SiO₂Antireflective Coatings By Sol-Gel Process

The SiO₂antireflective coatings have attracted great interest, mainly dueto their low refractive index, low-cost and to their potential application onsolar equipments and optical devices. The acid and base catalyzed SiO₂coatings, acid/base two-step catalyzed SiO₂/TiO₂coatings and porousSiO₂/TiO₂coatings were prepared via a sol-gel dip-coating technique. Theprepared coatings were characterized by UV-VIS、SEM、AFM、XRD、ellipsometer and CA, the effect of preparation conditions on coatingscapability, such as antireflection, scratch-resistance and self-cleaning, hasbeen discussed. The main contents were concluded as follows:1. The base-catalyzed silica sol was prepared using ammonia as catalyst,the effects of aging time, concentration of sol, usage of ammonia ontransmittance in visible light region were studied. The results revealed that thecoating had the best transmittance when the molar ratio ofTEOS:H₂O:NH₃:EtOH in the sol was1:2:0.64:37, and the sol was aged for5⁷days, the peak transmission of base-catalyzed SiO₂coating was up to98.5%, the average transmission was higher than that of the uncoated glass byabout7%. The base-catalyzed SiO₂coating has a loose surface structure, highporosity and larger SiO₂particles, resulting in poor mechanical strength.2. The acid-catalyzed silica sol was prepared using hydrochloric acid ascatalyst, the effects of aging time, concentration of sol, usage of water onoptical transparency were systematically studied. The results showed that thecoating had the best transmittance when the molar ratio ofTEOS:H₂O:HCl:EtOH was1:4:0.01:20and the sol was aged for3days, Thetransmittance of acid-catalyzed coating is lower compared to thebase-catalyzed coating, the average transmission is as low as93.4%. However,the structure of acid-catalyzed coating is dense, its porosity is low, as a resultof its excellent mechanical strength.3. The SiO₂antireflective coatings with high transmittance and enhancedscratch-resistance were prepared by acid/base two-step catalyzed method, andthen deposited a self-cleaning TiO₂coating on the SiO₂antireflection layer inorder to enhance the durability of the coating. The results revealed that theaverage transmittance of uncoated glass coated in this way increased by morethan6%in visible light region, showing better broadband antireflection appearance, with the needed antireflective performance of actual process.Additionally, the SiO₂/TiO₂bilayer coating has a dense structure, a lowroughness, excellent mechanical strength and self-cleaning function, whichenhanced the durability of the coating effectively.4. The porous SiO₂/TiO₂coating was fabricated by using a removabletemplate within the acid-catalyzed silica sol process, the preparationtechnology not only was simplified, but the porous SiO₂/TiO₂coating also hasa high transmittance, the peak transmittance was up to97.3%. The porouscoating has a low roughness and smaller particle size due to the inneracid-catalyzed SiO₂coating, as a result of its excellent mechanical strength.The self-cleaning function of the porous SiO₂/TiO₂coating has been improvedbecause of the outer TiO₂coating, after illuminated by ultraviolet light for2h,the5mg/L methyl orange can be degraded by56.5%in2h, the lifetime of theantireflective coating applied in actual process was greatly increased.