Advancing Steady-State and Sequenced Accelerated Aging for Assessing the Adhesion Degradation of Contemporary Encapsulants

Degradation of photovoltaic encapsulants leading to mechanical embrittlement and delamination remains a cause of failure in solar installations, characterized by a decrease in the adhesion energy, Gc, at the encapsulant/cell and encapsulant/glass interfaces. Understanding the encapsulants' degradation mechanisms under different environmental stressors with the loss of adhesion is essential to prevent premature debonding. The IEC 61215-, 61730-, 62788-and 63209-series standards currently use the chamber aging methods of damp heat, thermal cycling, dry heat, and UV weathering to qualify component materials with a basic robustness. However, these tests do not address the potential for encapsulant delamination in the intermediate-and long-term. To advance module design, we subjected coupon specimens (cell/encapsulant/glass laminates) with different encapsulants (EVA, POE, EPE) to 10,000 hours of aging under the following conditions: hot-dry (90 degrees C, ~1% RH), hot-humid (90 degrees C, 60% RH), warm-humid (60 degrees C, 60% RH), and IEC 62788-7-2 A3 (65 degrees C, 20% RH, UV of 0.8 W m-2 nm-1 at 340 nm). We measured the samples' Gc and the encapsulant layers' thermal properties in 2500-hour time increments to quantify the kinetic rates of interfacial degradation, elucidate which environmental stressors are most damaging, and refine our previous multiscale reliability model. We measured steep decreases in Gc for specimens under all conditions except for POE coupons under hot-dry, which retained a high Gc (thermally stable). We also investigated how the order of sequenced tests (e.g. UV weathering before / after hygrometric aging) affects interfacial and encapsulant degradation. The results can be incorporated into the industry including the IEC standards.