Kuan Liu

“Predictive Mechanics and Photochemical Degradation Kinetics Modeling for Polymeric Encapsulants”

Advised by Prof. Reinhold H. Dauskardt

Abstract: Degradation of module encapsulant mechanical characteristics that lead to embrittlement and delamination remains a leading cause of failure in solar modules [1]. Extending module lifetimes beyond 30 years requires advanced predictive modeling that includes the fundamental materials degradation pathways and their dependence on operating temperature, UV, and moisture. We present a time-dependent multiscale mechanics model based on detailed molecular degradation reaction kinetics that connects the encapsulant mechanical properties including elastic modulus, yield strength, and adhesion energy to the degrading molecular structure and interfacial bond density with adjacent solar cell and glass substrates [2]. We show how the model is being validated using experimental characterization of the encapsulants’ molecular structure and mechanical properties with accelerated aging using DSC, FTIR, Soxhlet extraction (measuring degree of polymer crosslinking), gel permeation chromatography, nanoindentation, and adhesion testing. The model shows a marked improvement from previous models when compared with available experimental data from field aged modules. We describe applications to ethylene co-vinyl acetate (EVA), polyolefin elastomer (POE), and EPE (EVA/POE/EVA layered composite) encapsulants along with the ability to model sequences of exposures most relevant for accelerated testing. This includes the stressors (UV, temperature, humidity), their level and duration, and the order of sequences (e.g., UV weathering before or after hygrometric aging) to prescribe improved accelerated test sequences.