Preparation And Properties Of PVB Encapsulant Used In Solar Cell Modules

Building-integrated photovoltaic （BIPV） is the important development field ofphotovoltaic industry. As a encapsulation material for a solar cell module, polyvinyl butyral（PVB） encapsulant used in BIPV will have a great market prospect. Its excellent agingresistance and thermally conductive and electroinsulating performance are greatly importantto manufacture the solar cell module possessing satisfying encapsulating quality andlong-term service performance.In this work, the PVB encapsulants were prepared by melt extrusion and mould pressingmethod using PVB containing18¹9wt%polyvinyl alcohol （PVOH） as the matrix,triethylene glycol di-2-ethylhexoate （3G8）, dibutyl sebacate （DBS） and dioctyl phthalate（DOP） as the plasticizer, respectively. The basic process conditions were explored anddetermined. According to the performance requirements for PVB encapsulant used in a solarcell module, the compatibility between PVB and plasticizer, and the effects of the type andcontent of a plasticizer were studied on the processing flowability of PVB resin, the tensilestrength, elongation at break and adhesive performance of PVB encapsulants. Theexperimental results indicate that the PVB encapsulant containing35phr3G8, PE-3, canpossess good processing property whose melt flow rate （MFR） is2.3g/10min, and good basicmechanical properties whose tensile strength, elongation at break and adhesive strength are23.2MPa,267%,35.2N/cm, respectively. PE-3can meet the performance requirements forPVB encapsulant used in a solar cell module. Therefore, the basic composition of PVBencapsulant can be determined to be PVB/3G8（100/35）.Based on it, the anti-aging system of PVB encapsulant was designed. The effects ofdifferent anti-aging systems on visible light transmittance （T） and yellowness index （YI） ofPVB encapsulants were investigated by thermal oxidation accelerated aging test at120.The structure changes of PVB in the process of thermal oxidation were charactered by meansof thermogravimetric analysis （TG） and infrared spectrum （FTIR）, and aging mechanism ofPVB was discussed and analyzed. The results show that PVB encapsulant SE-8can exhibitexcellent aging resistance, in which the anti-aging system is composed of antioxidantsSongnox1135LQ （AO-3）, Songnox2246（AO-6） and Irgafos168（P-1） and photostabilizerTinuvin770（UVS-2）. After being aged in hot air at120for316hours, SE-8can stillmaintain94.3%of transmission, which is slightly lower than that of the unaged SE-8,96.5%,and its yellow index increment （YI） is only0.04. The PVB/Al₂O₃composites were prepared by melt blending using alumina （Al₂O₃） asthermally conductive filler, and the thermally conductive and electroinsulating performancewere systematically studied, in order to establish the experimental basis for preparing PVBencapsulant used in solar cell with excellent thermal insulation property. The experimentalresults show that among the examined three kinds of surface treatment agents,γ-glycidoxypropyltrimethoxysilane （KH-560）, titanium tetrabutoxide （TC） and stearic acid（SA）, and in their dosage range, and three kinds of filler particle size,1to3μm,10μm and30nm, treating Al₂O₃with the particle size of1to3μm with1.0wt%of KH-560is moreconducive to improving the thermal conductivity of PVB/Al₂O₃composites; and the thermalconductivity of PVB/Al₂O₃composites increase with an increase in the Al₂O₃content.Contrasting and analyzing the thermal conductivity of the measured values of PVB/Al₂O₃composites and predicted values of Maxwell-Eucken model and Agari model indicate thatwith a further increasing Al₂O₃content, when it is higher than25phr or6.3vol%, the Al₂O₃particles in the PVB/Al₂O₃composites can form the partly continuous heat-conduction chains.And when the Al₂O₃content is70phr or15.9vol%, the prepared PVB/Al₂O₃composite canexhibit good comprehensive performance, whose thermal conductivity, volume resistivity,tensile strength and elongation at break are0.375W/m·K,1.65×10¹²Ω·m,21.4MPa and265%, respectively.