Current leakage and fill factor in multi-junction solar cells linked via absolute electroluminescence characterization

Direct link between current-leakage features and fill factors was demonstrated in GaInP/GaAs 2-junction solar cells via combining measurements of absolute electroluminescence (EL) intensity and EL imaging. The drops of subcell external radiative efficiency under low injection level have shown large differences among the solar cells fabricated in the same batch, which lead to the difference in the fill factor (FF) and performance of the cells under illumination. The absolute EL images clearly revealed that a current leakage, instead of higher non-radiative recombination rates, in the GaAs-subcell caused the significant degradation in its ηext at low injection current and in the lower FF. The absolute EL provides a powerful way to diagnose FF in addition to open-circuit voltage of individual subcells in MJ solar cells.