Degradations of Multijunction Solar Cell Revealed by Absolute Electroluminescence Imaging

Multijunction solar cells (MJSCs) experience material degradation and reduced efficiency during long-term storage. Current defect analysis methods for III-V compound MJSCs are limited by a lack of intuitive tools and in-depth understanding, hindering improvements in yield and efficiency. Absolute electroluminescence (EL) is a powerful technique for visualization and predicting solar cell performance. In this study, we applied absolute EL to quantify performance and degradation mechanisms in subcells after 26 months of storage. Absolute EL imaging identified both potential and inherent defect types within the subcells. The detailed analysis of localized defect points showed reduced photon emission near the defect points. Using the reciprocity theorem and carrier balance model, we found that degradation in the InGaP/GaAs/InGaAs solar cell resulted in a 0.8% reduction in efficiency, largely due to nonradiative recombination (NR) losses. Additionally, the efficiencies of top, middle, and bottom cells decreased by reduced by 0.3%, 0.2%, and 0.3%, respectively. This work demonstrates that the absolute EL imaging technique provides a comprehensive and detailed method for understanding defects and energy losses during long-term storage in MJSC.