Methodology for local ageing and damage development characterization of solar glass/encapsulant interfaces under superimposed fatigue stresses and environmental influences

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In this paper, a novel fracture mechanics test-setup was developed, implemented and applied for assessment of the fatigue delamination behavior of glass/encapsulant laminates under superimposed mechanical stresses and environmental influences. Double cantilever beam (DCB) specimens with glass substrates were prepared using ethylene vinyl-acetate copolymer (EVA) or polyolefin elastomer (POE) encapsulants. Displacement-controlled fatigue tests were conducted at 80 °C under dry (5% rh) and humid (80% rh) conditions. The damage zone ahead of the delamination crack tip was monitored with a topside mounted camera system. A superior delamination resistance of POE based double glass laminates was ascertained. Under less service-relevant, hot-dry conditions, the glass laminates exhibited a mm-sized damage process zone ahead of the crack tip, in which void nucleation and fibril formation took place. While the POE laminate failed also in a cohesive manner within the encapsulant at 80 °C and 80% rh (i.e., hot-humid), the crack was propagating in the glass/EVA laminate close to the interface in a brittle manner. Local ageing mechanisms were confirmed for the fractured EVA laminates by XPS. The superposition of mechanical and thermal stresses along with humidity resulted in sodium ion migration presumably promoting deacetylation of EVA. Interestingly, the analyzed degradation products were in good agreement with data obtained for damp heat aged glass/foil PV modules characterized subsequently by monotonic delamination testing. The main advantage of the novel environmental fracture mechanics methodology is the high acceleration factor (50 to 100x faster) compared to conventional ageing and delamination testing of PV modules. • Novel concept for highly accelerated delamination testing of PV module interfaces. • Superimposed mechanical fatigue stresses and environmental influences. • Service-relevance confirmed for glass/EVA interface under hot-moist conditions. • Potential acceleration factor of 50–100 due to local ageing effects. • High-throughput screening of novel material formulations & interfaces.