New rapid method for optical non-destructive determination of the degree of crosslinking of PV module encapsulants

The degree of crosslinking in encapsulants is a critical parameter in photovoltaic (PV) module production, significantly influencing module performance and reliability. Despite its importance, the industry-standard Soxhlet extraction method for assessing crosslinking is offline, time-intensive, and unsuitable to implement for real-time process monitoring. This study explores the application of near-infrared (NIR) spectroscopy as a faster, non-destructive alternative for determining encapsulant crosslinking. Test laminates using an ethylene vinyl acetate (EVA) encapsulant with varying crosslinking times were analyzed using both Soxhlet extraction and NIR spectroscopy. NIR spectra were processed using multivariate data analysis methods for qualitative classification and quantitative prediction. The classification model demonstrated clear separation between encapsulants with high and low degrees of crosslinking. The prediction model achieved high accuracy prediction of the degree of crosslinking. These findings highlight the potential of NIR spectroscopy for rapid, inline classification and quantification of encapsulant crosslinking. Future work will focus on expanding the models to include alternative encapsulant materials, such as polyolefin-based films, and optimizing measurement setups to accommodate double-glass module designs.