Study Of Antireflection Coating Based On Cationic-nonionic Polymer-SiO₂ Core-shell Particle Dispersion

Solar photovoltaic（PV）power generation is the focus of the world’s research on clean energy nowadays.Antireflection coating can be applied to the surface of photovoltaic glass to increase the transmittance of sunlight and enhance the photoelectric conversion efficiency of PV modules.Nowadays,many technologies used to prepare antireflection coatings are not suitable for outdoor large-area substrates,but the single-layer porous antireflection coating prepared by sol-gel method is relatively simple and low cost,and is suitable for large area applications.However,it is still difficult to prepare high transmittance antifeflection coating with more commonly used materials,which can achieve high hardness,homogeneous internal pores and full closed surface at the same time.Antireflection coatings coated on the photovoltaic glasses usually face the problem of maintaining the balance between high transmittance and high hardness.Moreover,the surface of the prepared antireflection coating is prone to generate outer pores,and the existence of these outer pores will make the coatings face the problems of cleaning difficulty and low transmittance,thus reducing the service life of antireflection coatings.To solve these problems,cationic/nonionic polyurethane dispersions（PUD）and cationic/nonionic epoxy dispersions were first prepared by cationic and nonionic hydrophilic monomers.These two cationic/nonionic polymer dispersions can provide two types of polymer particle templates.By using the two types of polymer particles as template respectively while using tetraethylorthosilicats（TMOS）as precursor,an acid catalyzed sol-gel preparation method was applied to prepare cationic/nonionic polymer-SiO₂ core-shell particle dispersion;Core-shell particle dispersion was utilized to prepare antireflection formulation in conjunction with acidic SiO₂ sol binder,coating the substrate by dip-coating process,SiO₂ antireflection coating was formed on the surface of substrate after calcination at high temperature.Two systems were finally obtained:antireflection coatings based on cationic/nonionic PUD particles and antireflection coatings based on cationic/nonionic Epoxy dispersion particles.FTIR spectra was used to characterize the cationic/nonionic polymer-SiO₂ dispersions,and the results showed that SiO₂ was successfully introduced into cationic/nonionic polymer dispersions.The morphology of the polymer-SiO₂ particles was analyzed by transmission electron microscopy（TEM）,and the core-shell structure of the particles was confirmed.The average particle size（Dav）and polydispersity index（PDI）test results showed that,during the acid-catalyzed sol-gel process,TMOS were first loosely diffused to the surface of cationic-nonionic template particles,then hydrolysis-condensation reaction happened to form dense SiO₂ shell on the surface of particles,and obtaining core-shell particles;the shell thickness of core-shell particles increased with the increase of reaction time（t）,reaction pH and the amount of used TMOS.Morphological structures of the surface and cross-section of prepared antireflection coatings were invesgated by scanning electron microscopy（SEM）,and the analysis results showed that the coating surface had no obvious pores,prone to be a fully closed surface,and uniform pores generated by sacrificing polymer particles could be observed in the cross-section of antireflection coating.The optical properties of antireflection coatings were analyzed by UV-visible spectrophotometer（UV-Vis）,and the results show that antireflection coating based on PUD particles had the highest transmittance of 98.6%at 548nm,and antireflection coating based on Epoxy particles had the highest transmission of 98.8%at 550nm.All the antireflection coating based on cationic/nonionic polymer dispersion particles can reach the hardness of 3H.