Enhancing photovoltaic modules encapsulation: Optimizing lamination processes for Polyolefin Elastomers (POE) through crosslinking behavior analysis

Polyolefin elastomers (POEs) have recently been introduced in the photovoltaic (PV) industry, addressing the requirements of advanced cell concepts and mitigating novel degradation phenomena in bifacial modules. Notable for their high volume resistivity, low permeation, and processability, POEs offer advantages such as the absence of harmful by-products like acetic acid upon humidity exposure. However, adapting standard measurement methods becomes imperative, as the crosslinking behavior of POEs may differ significantly from ethylene-vinyl acetate copolymer (EVA). This study aims to examine the crosslinking behavior of POEs, with the ultimate goal of exploring the lamination process window. Differential scanning calorimetry (DSC) and Soxhlet extraction have been employed to characterize the crosslinking rate and chemical structure of various POE encapsulants. Notably, we obtained remarkable correlations between these two techniques for two commercially available POEs, allowing the extension of the IEC standard to new encapsulants. We further devise a recommendation to adapt the IEC62788-1-6 standard on crosslinking rate measurement. The prolongation of the standardized Soxhlet extraction duration to min. 24 h is demonstrated as an optimum given that most POEs have a lower target gel content value in comparison to EVA. The presented methodology demonstrates that fast feedback DSC analysis, when calibrated to material-specific curves, can provide quantitative and accurate results. One of the many possible practical implications of this insight is to encourage encapsulant suppliers to establish correlation graph for their material, and hence assisting improved accuracy in lamination development and quality control.