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, G<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf>, 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°C, ~1% RH), hot-humid (90°C, 60% RH), warm-humid (60°C, 60% RH), and IEC 62788-7-2 A3 (65°C, 20% RH, UV of 0.8 W m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> nm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> at 340 nm). We measured the samples’ G<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> 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 G<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> for specimens under all conditions except for POE coupons under hot-dry, which retained a high G<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (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.