Degradation Mechanisms and the Role of Sequenced Accelerated Testing To Ensure Long-Term Solar Module Encapsulation

DuraMAT has developed a multi-scale mechanics model based on photovoltaic (PV)-specific degradation reaction kinetics that connects the encapsulant mechanical properties to the degrading polymer molecular structure and interfacial bond density with the adjacent solar cell and glass substrates.

We are validating the model with experimental characterization of encapsulants and representative coupons (cell/encapsulant/glass laminates) after selecting accelerated aging conditions and sequenced exposures. Coupon adhesion testing showed significant decreases in the adhesion energy, G_c, of ethylene-vinyl acetate (EVA)/cell and EVA/ polyolefin elastomer (POE)/EVA (EPE)/cell interfaces after 5,000 hours of hot-dry (90°C, ~1% RH [relative humidity]), hot-humid (90°C, 60% RH), and warm-humid (60°C, 60% RH) aging (panel (c) in the figure). The POE/cell interface retained a high G_c after hot-dry aging but degraded under hot-humid and warm-humid aging, demonstrating the role of moisture in accelerating hydrolytic depolymerization reactions at the encapsulants’ interfaces. Note that despite interfacial degradation, the G_c values are still significantly above the spontaneous critical field delamination threshold of ~160 J/m².

Adhesion testing on EVA coupons after hot-humid (90°C, 60% RH) aging verifies faster hydrolytic depolymerization at the encapsulant interface compared to hot-dry (90°C, ~1% RH) aging, but both conditions degrade the adhesion energy significantly. POE coupons exhibited the best stability after exposure with all accelerated aging conditions.

Degradation of the mechanical characteristics of encapsulants, leading to embrittlement and delamination, remains a leading cause of premature failure in PV modules. Ensuring module lifetimes beyond 30 years require advanced predictive modeling, which must include the fundamental materials degradation pathways and their dependence on operating temperature, UV, and moisture.