Study On Preparation And Properties Of Graded-refractive-index Silicon Dioxide Antireflection Coating

Recently,with the social development,the energy crisis and environmental pollution have been extremely critical.As a clean and renewable energy,the solar energy has attracted more and more attentions.The studies on how to improve the utilization of solar energy have become great upsurges.It was confirmed that the anti-reflection films deposited on the photovoltaic/photo-thermal surface could effectively increase the conversion efficiencies.Among the researches,the practical application of the anti-reflection films was limited because of the narrow anti-reflection band although they had high transmittance.In this paper,the broadband anti-reflection films which showed high transmittance in the broad wavelength range of 400～1000 nm were prepared.The main contents include:（1）the soluble PEG used as pore former was added into the acidic silica sol,then the sol was washed several times by deionized water and the pore structures were formed during the eduction of PEG.In this way,the gradual refractive index SiO₂single anti-reflection films（water-washed single anti-reflection films）were prepared in which the porosities increased and the refractive indexes decreased from inside to outside,respectively.Effects of the formula weights of PEG,dosage of PEG,temperatures and times of the water-washing on the efficiencies of the anti-reflection films were studied.It was found that the highest transmittance of 98.4%was obtained when the formula weight and dosage of PEG were 400and 0.4 m L,respectively.Too high formula weight of PEG or excessive PEG would increase the pore diameters,leading to the severe scattering.Besides,the anti-reflection film prepared at 60°C for 60 minutes during the water-washing process showed the best performance.Too high temperatures or too long time of the water-washing process would result in the exfoliation of the films and low temperatures or short time of the water-washing process would be hard to the obtain the gradual refractive index anti-reflection films.The water-washed single anti-reflection film with hardness of 5H showed good mechanical performance but poor hydrophobicity.（2）appropriate amount of DDS used as pore former was added into the acidic silica sol and the DDS-modified acidic silica sol was obtained.Then the glass substrates with deposition of the sol by pulling method were heated-treated at high temperature.With the thermal decomposition of the abundant methyl-groups in DDS,numerous pore structures were generated and the DDS-modified SiO₂anti-reflection films were obtained.Effects of the dosages of DDS/HCl catalyst and the pulling rates on the performance of the DDS-modified SiO₂anti-reflection films were studied.The film prepared with the dosage of DDS of 4 m L,the heat-treatment temperature of 450°C and the soaking time of 30 minutes showed the highest transmittance of 97.6%.Less DDS would lead to the lack of pores and high refraction while excessive DDS would result in the cracks of the films.It was found that the DDS-modified SiO₂anti-reflection films had much better hydrophobicity than the water-washed single anti-reflection film.Appropriate amount of PEG used as pore former was added into the acidic silica sol and the PEG-modified acidic silica sol was obtained.Effects of the formula weights of PEG,dosage of PEG,heating rate on the efficiencies of the PEG-modified SiO₂anti-reflection films were studied.It was found that the highest transmittance of 98.0%was obtained when the formula weight and dosage of PEG were 600and 4.5 m L,the heating rate of 30°C/min,respectively.The hydrophobicity-treated PEG-modified SiO₂anti-reflection films has good hydrophobicity.（3）although the regular SiO₂anti-reflection film had strong binding force with the glass substrate,but it also showed high refraction and low transmittance,too.In this paper,the gradual refractive index SiO₂multi-anti-reflection film with strong binding force and high transmittance was constructed by using the regular SiO₂anti-reflection film as base film,DDS-modified SiO₂anti-reflection film as central film and DDS-modified SiO₂alkaline anti-reflection film as top film,respectively.Effects of the dosages of HCl catalyst/TEOS precursor on the transmittance of the regular SiO₂anti-reflection film,effects of the dosage of DDS and H₂O on the transmittance of the DDS-modified SiO₂alkaline anti-reflection film were both studied.The three best single anti--reflection films prepared at the optimal process conditions were constructed in order so that the gradual refractive index SiO₂double/triple anti-reflection films with higher transmittance were obtained.This was attributed to the extremely high transmittance of the DDS-modified SiO₂alkaline anti-reflection film.Meanwhile,the strong banding force between the multi-anti-reflection film and glass substrate also inhibited the exfoliation of the alkaline anti-reflection film.