SiO₂/SnO₂, SiO₂/TiO₂ Based Anti-reflection Film Design And Sol-gel Method Preparation

The optical thin films can be classified as antireflection coatings,high-reflective coatings and filter.Among these optical thin films,antireflection coatings?ARCs?play an important role in promoting the development of optical technologies.Thin-film ARCs can greatly reduce the unwanted reflection of light from the surface of the lenses and other optical elements.As a result,the light transmittance of these elements is greatly increased.And ARCs have wide application in many fields such as display panels,solar cells and optical lenses.Because of the advantages of simple operation process,low production costs,low heat treatment temperature and control over thickness and index of refraction,sol-gel method have been widely used in the preparation of ARCs.In this paper,various interference-type ARCs with homogeneous multilayers have been designed and prepared by the sol-gel dip-coating method.In this paper,we tried to design and optimize the ARCs with the aid of thin film design software?Essential Macleod?.Before any design is performed,the optical constants?refractive index and extinction coefficient?as well as the film thickness of pure SiO₂,SnO₂,Sb-SnO₂,TiO₂and SiO₂-SnO₂ composite thin films are extracted from their transmittance spectra using the envelope method based on the Essential Macleod software.SnO₂,Sb-SnO₂,and TiO₂ were used as high refractive index materials.SiO₂ and SiO₂-SnO₂ composite thin films with tunable refractive index were used as low and middle refractive index materials,respectively.SiO₂-SnO₂composite thin films with refractive index varying from 1.49 to 1.98 have been obtained by mixing the SiO₂ and SnO₂ sols together in different proportions.The results show that the refractive index of the SiO₂-SnO₂ composite films is proportional to the molar ratio of silica in the composite sols.With increasing SiO₂ ratios,the refractive index of the composite thin films sees a linear decrease.In this paper,SiO₂/SnO₂ and SiO₂/TiO₂ based double-layer,tri-layer and four-layer ARCs were successfully prepared by sol-gel process,respectively.For the design of double-layer ARCs,two classical stacks of?/4-?/4 V-shape and?/4-?/2 W-shape were mainly employed.In the visible region of 400-800 nm,the peak transmittance of the optimized SiO₂/SnO₂,SiO₂/Sb-SnO₂and SiO₂/TiO₂ ARCs was 99.02%,95.60%and 98.90%.And the average transmittance of these ARCs was 95.32%,93.43%and 95.04%,respectively.For the design of tri-layer ARCs,two classical stacks of?/4-?/4-?/4 and?/4-?/2-?/4 were mainly employed.In the visible region of400-800nm,thepeaktransmittanceoftheoptimizedSiO₂/SnO₂/SiO₂-SnO₂,SiO₂/Sb-SnO₂/SiO₂-SnO₂ and SiO₂/TiO₂/SiO₂-SnO₂ ARCs was 98.60%,97.12%and 99.60%.And the average transmittance of these ARCs was 96.50%,94.52%and 97.54%,respectively.For the design of four-layer ARCs,two stacks of?/4-?/4-?/4-?/4 and?/4-?/2-?/4-?/4 were mainly employed.In the visible region of 400-800 nm,the peak transmittance of the optimized SiO₂/SnO₂/SiO₂-SnO₂/SiO₂,SiO₂/Sb-SnO₂/SiO₂-SnO₂/SiO₂ and SiO₂/TiO₂/SiO₂-SnO₂/SiO₂ARCs was 97.60%,97.65%and 99.61%.And the average transmittance of these ARCs was94.86%,95.36%and 96.89%,respectively.From the transmittance spectra,we can find that the experimental transmittance spectrum is in good agreement with our theoretical design.The transmittance difference in some regions is probably due to some thickness deviation from the design value and the dispersion of the refractive index in the wavelength region.The studies also show that the width of the high transmittance region increases with the increase of the layers.