Austrian researchers analyzed commercial ethylene vinyl acetate-polyolefin-ethylene vinyl acetate (EPE) solar encapsulants and found that products sold under the same label can have significantly different material structures and performance. Although EPE provides better moisture barriers and thermal resistance than EVA and is rapidly gaining market share, the study cautions that its reliability and long-term behavior vary widely and require more in-depth research.
A research team from Austria has systematically investigated the chemical, optical, thermal and thermomechanical properties of commercially available coextruded ethylene vinyl acetate-polyolefin-ethylene vinyl acetate (EPE) encapsulation films. EPE encapsulant is part of the industry’s transition to TOPCon, HJT and tandem solar cells as it is believed to have superior electrical insulation and a moisture barrier.
“The novelty of our work is that we have deliberately challenged the current narrative around EPE,” said corresponding author Nikolina Pervan. pv magazine. “Rather than focusing on efficiency or cost benefits, we examined EPE at the material level and treated it as a complex multi-layer system. Our results suggest that evaluating EPE purely as a drop-in replacement risks overlooking critical reliability questions.”
“EPE grew from a 5% share in 2019 to 38% in 2024, while ethylene vinyl acetate (EVA) held 42% of the market share, indicating that EPE is already challenging EVA in the market,” she continued. “Manufacturers are already using EPE extensively. While science is often slower to catch up with industry and material-level data remains relatively scarce, EPE is already an industrially accepted encapsulant, as evidenced by its market share. However, the long-term effects of this encapsulant remain to be seen.”
Pervan added that his team was surprised to discover during testing that four encapsulants marketed under the same EPE label had substantially different material behavior and levels of technological maturity. “This indicates that EPE is not a single solution for all PV module designs, but rather a broad classification that currently groups systems with fundamentally different material behavior and reliability potential,” she said.
“In this context, we may be repeating a situation similar to early polyolefin development, where different formulations under one label led to very different performance results,” she further noted.
For their study, the researchers purchased four commercially available EPE encapsulants and tested them in both their uncured and cured (laminated) states. Lamination was performed by placing the encapsulant between two glass sheets, using a non-adhesive Teflon mat between the glass and the encapsulant layer. Ethylene vinyl acetate (EVA) and polyolefin elastomer (POE) were tested as reference materials.
Image: Polymer Competence Center Leoben GmbH (PCCL), Solar Energy Materials and Solar Cells, CC BY 4.0
The first series of tests looked at material identification of the encapsulants and included infrared spectroscopy, ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopy and light microscopy on cross-sections of the films and mini PV modules. Once the materials were identified, the team proceeded to analyze the performance of the encapsulant, including its water vapor transmission rate (WVTR) and its thermal and thermomechanical properties.
According to the results, the outer EVA layers of all EPE encapsulants were similar, with only minor differences in the vinyl acetate (VA) content. However, there were notable differences in the inner polyolefin layer: while EPE-1 has an inner layer of ethylene acrylate copolymer, EPE-2, EPE-3 and EPE-4 consist of core layers of ethylene-α-olefin copolymer, with different side groups and/or varying comonomer contents.
Image: Montanuniversität Leoben, Solar energy materials and solar cells, CC BY 4.0
“Differences in the cross-linking behavior were evident from the differential scanning calorimetry (DSC) analysis. EPE-1 was the only sample with a non-cross-linking inner polyolefin layer, whose high crystallinity reduced visible light transmission but also improved the barrier against water vapor,” the research team said. “The presence of a polyolefin layer improved the thermal resistance of the encapsulant. The co-extrusion process appeared to improve the dimensional stability of EPE-2, EPE-3 and EPE-4 compared to pure EVA film, while the non-crosslinking polyolefin in EPE-1 led to higher shrinkage and expansion.”
The analysis also showed that the WVTR of all EPEs was significantly lower than that of single-layer EVA. The layer distribution and uniformity of the EPE films tested were comparable, and complete wetting of the interconnections was achieved with all four EPE encapsulants.
“Our follow-up research will focus on cross-linking kinetics and thermomechanical behavior, in particular the thermal expansion coefficient compared to EVA and polyolefins, because these parameters directly drive the voltage development in PV modules,” concludes Pervan. “At the same time, we will investigate aging and additive migration to assess how these multi-layer systems evolve over decades. If EPE is to become a true long-term solution, these fundamental questions must be addressed systematically.”
The research work was presented in “Is EPE the future of PV encapsulation? A comprehensive assessment at material level”, published in Solar energy materials and solar cells. Scientists from the Austrian Polymer Competence Center Leoben (PCCL), the University of Leoben and the Austrian Research Institute for Chemistry and Technology (OFI) participated in the study.
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