Vinyl-Functionalized Polyolefins for Fast Photovoltaic Cell Encapsulation

Polyolefins (POs) are considered a promising candidate for photovoltaic cell encapsulation due to their high volume resistivity, low water-vapor permeability, and outstanding outdoor stability. However, POs without functionalization have a low rate of cross-linking, which significantly slows the solar cell encapsulation process. Herein, we describe the use of a polymer product-engineering approach in which reactive pendent vinyl groups are controllably incorporated in PO polymer chains to accelerate their cross-linking reactions. The POs having limited vinyl functionalities of 0.02–0.37 mol % were synthesized via the copolymerization of ethylene, 1-octene, and vinylnorbornene or 1,9-decadiene at different monomer concentrations. The vinyl groups in the POs readily react with curing agents, increasing cross-linking rates by 14-fold up to 179.7 Pa·s–1, as measured by the enhancement of the storage modulus (G′). The maximum G′ value representing the melt strength was also increased from 11.3 to 69.0 kPa due to the high curing degree in the POs. The use of a curing agent could be reduced by 50%, and no curing coagent was required in the PO curing process. The vinyl-functionalized POs had a light transmittance of 91%, a good volume resistivity of 7.05 × 1016 Ω·m, a low water-vapor permeability of 2.31 × 10–12 g·m·m–2·s–1·Pa–1, and an improved mechanical strength after curing. The damp-heat and UV aging had little effect on their light transmittance. Our approach of synthesizing functional POs with pendent vinyl groups thus promises the development of new high-performance polymer materials for photovoltaic cell encapsulation.