Standardized cross-linking determination methods applied to POE encapsulants in lamination recipe emphasizing

Abstract

International audienceEthylene vinyl acetate is the most common encapsulation material in photovoltaic panels. Due to gradual engineering, it ensures to meet performance requirement of standard cells, low-cost and well understood cross-linking behaviour, both physically and chemically. Nowadays polyolefin elastomers (POE) have been entering the PV industry requirements by advanced cells concepts and/or novel degradation phenomena noticed on bifacial modules. POE exhibit several advantages based on its intrinsic high volume resistivity, low permeation, processability and most importantly, the absence of harmful by-products (such as acetic acid) generated upon humidity exposure[1, 2]. However, this new family of materials may behave differently from EVA during crosslinking, thus it is necessary to verify and adapt standard measurement methods. Therefore, the main objective of this study is to investigate the cross-linking behaviour of POEs with the final goal of exploring the process window of the lamination. The characterization methods like differential scanning calorimetry (DSC) and Soxhlet extraction have been used to determine crosslinking rate and chemical structure of several encapsulants. Similar to EVAs, cross-linking rate of POEs measured by Soxhlet extraction increases with lamination duration until reaching a plateau. The indirect cross-linking rate measurement by DSC analysis is usually favoured through its simple, fast implementation, absence of toxic chemicals when compared to Soxhlet extraction. Remarkable correlations between the two techniques were obtained for a commercially available POE, allowing the extension of the IEC standard to new encapsulants. Nevertheless, in the case of highly engineered materials, clear deviations are recorded, highlighting validity limits of direct correlation between Soxhlet and DSC methods