Is EPE the future of PV encapsulation? A comprehensive material-level assessment

Coextruded ethylene vinyl acetate - polyolefin - ethylene vinyl acetate (EPE) encapsulant films were developed in response to industrial demand and to support the technological transition in photovoltaic modules (PV) towards higher-efficiency solar cells that are more sensitive to moisture than previous generations. EPE was designed to combine cost-effectiveness and processability of ethylene vinyl acetate (EVA) with the superior electrical insulation and moisture barrier properties of polyolefin. This study systematically investigates the chemical, optical, thermal, and thermo-mechanical properties of commercially available EPE encapsulants. The outer EVA layers of all EPE encapsulants were comparable, showing only slight differences in vinyl acetate content. The main difference between the four EPE encapsulants was found in the inner polyolefin layer. EPE-1 has an ethylene acrylate copolymer, whereas EPE-2; −3; −4 have ethylene α-olefin copolymer core layers, but with different side groups and/or varying comonomer contents. The water vapor transmission rate (WVTR) of all EPE films is significantly lower than that of EVA. Differences in the crosslinking behaviour were evident from thermal analysis. EPE-1 was the only sample with a non-crosslinking inner polyolefin layer, whose high crystallinity reduced visible-light transmission but also enhanced barrier to water vapor. The co-extrusion process appeared to improve the dimensional stability of EPE-2; −3; −4, compared to standard EVA. Overall, EPE encapsulants fulfil their intended purpose of reducing WVTR. However, the long-term impact of the EVA layer at the cell interface under environmental exposure remains to be evaluated. • Co-extruded multilayer EPE significantly reduce WVTR compared to standard EVA. • Core layer chemistry varies significantly across commercial brands, impacting crystallinity and visible-light transmission. • Non-crosslinking polyolefin core enhances moisture barriers but lead to higher thermal shrinkage.