Optimized Module Packaging for Silicon Heterojunction Solar Cells and Increased PID Resistance

Recent studies showed that silicon heterojunction (SHJ) solar cells can be prone to potential induced degradation (PID) when encapsulated with a low volume resistivity ethylene vinyl acetate (EVA). We perform PID test in humid conditions (85°C/85% RH) on glass/glass one-cell modules with and without an edge sealant, to ensure an uniformly applied potential all over the module surface. We also analyze the effect of moisture ingress by using these module structures. We demonstrate that with the proper module packaging (i.e. a glass/glass structure with edge sealant), EVA can be used as an encapsulant material for SHJ solar cells. PID can be completely prevented even when subjected to extended tests (e.g. eight times the 96 h of test duration foreseen in the IEC Technical Specification for c-Si modules). On the other hand, SHJ modules packaged in a glass/glass structure using EVA (and no edge seal) start exhibiting a degradation in performance after 192 h of PID test (i.e. twice the test duration foreseen by IEC TS 62804-1). The degradation becomes considerable after 800 h of test, driven by a reduction in shortcircuit current (JSC), fill factor (FF) and open-circuit voltage (VOC).