Degradation of Bifacial PERC and Al-BSF Cell Minimodules with White and Clear Encapsulant Combinations in Modified Damp Heat

Minimodules with half-cell variants of multi-Si Al-BSF, mono-Si bifacial PERC, and multi-Si bifacial PERC, with backside encapsulant variations of UV cutoff and white EVA and POE are exposed, stepwise, to modified damp heat (80°C/85%RH) conditions. The modified damp heat is run at 80C/85 % relative humidity to maintain a temperature below the glass transition temperature of PET, maintaining conditions that are more similar to outdoor operation. I-V and EL results show corrosion is the predominant form of degradation, being most severe in the white EVA modules. Al-BSF cells in particular show large degree of power loss compared to the PERC cell counterparts when used in combination with white EVA encapsulant. There were no statistically significant differences in loss between multi- and mono-Si bifacial PERC cells. Correlating EL and I-V features suggests corrosion is not initiated at the busbars, instead reaching the busbars after significant corrosion has already occurred. Post exposure analysis confirm resistive losses through corrosion are the predominant loss mechanism from the exposure.