Solar Cell Package Eva Film Uv Cross-linking Studies

Crosslinked ethylene vinyl-acetate copolymer (EVA) as photovoltaic (PV) module encapsulant was prepared by UV irradiation. Photoinitiated crosslinking of EVA in the presence of benzophenone (BP) as photoinitiator and triallyl isocyanurate (TAIC) as crosslinker and characterization of the related properties have been studied by gel content, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), transmittance and adhesive strength measurements. The photoinitiated crosslinking efficiency of the EVA-BP-TAIC system and various factors affecting the crosslinking process, such as photoinitiator and crosslinker and their concentrations, irradiation temperature, and irradiation atmosphere were studied in detail and optimized by comparison of gel contents. The result shows that the optimal temperature is 100℃and the optimal duration of UV irradiation is 2 min. In the optimized condition, the effects of irradiation atmosphere and sample thickness on gel content of the PV-EVA are not that evident. The study also shows that the optimal concentration of the formulation with 1.0 wt% TAIC and 1.5 wt% BP is readily crosslinked to a gel content of 86.3% with 2 min UV-irradiation under the optimum conditions.The data from DSC show that the crosslinking density of photocrosslinked EVA increases and their crystallinities decrease after 2 min UV-irradiation. At the same time, photocrosslinking of EVA leads to a lowering of the melt temperature and a decrease of heat of fusion. The data from TGA tests give evidence that the thermal stability of photocrosslinked EVA samples is much better than that of the uncrosslinked EVA. The crosslinked EVA sheets have good transparency and the light transmittance is 92.8% between 400 to 1100 nm. The volume resistivity of the crosslinked EVA sheet is measured to be 1.25×1014Ωcm and the peel strength between glass and EVA is 66.8 N/cm, between TPT and EVA is 40.6 N/cm.