Diagnosis and analysis on inverted metamorphic five-junction solar cells via integrating-sphere absolute
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This study presents a comprehensive diagnostic analysis of two inverted metamorphic Al0.09Ga0.42InP/Al0.2GaAs/GaAs/In0.17GaAs/In0.46GaAs five-junction solar cells (IMM-5JSCs) with AM1.5G efficiencies of 35.5% and 33.4%, utilizing an integrating-sphere-based absolute electroluminescence (EL) measurement technique. A systematic theoretical framework is developed to extract the dark and illuminated current density-voltage (J-V) characteristics of individual subcells from absolute EL spectra, with full consideration of luminescence coupling (LC) effects. Through external radiative efficiency (ERE) analysis, we achieve a cross-institutional comparison of crystal quality with subcells of the NREL-reported IMM-6JSC and uncover the root causes of performance discrepancies between the devices. The AlGaInP and GaAs subcells in our IMM-5JSCs exhibit comparable or superior lattice quality, while the AlGaAs and In0.17GaAs in IMM-5JSCs show slightly inferior quality, and the In0.46GaAs subcell demonstrates the poorest material quality. The EL-derived subcell light J-V characteristics yield overall open-circuit voltage and short-circuit current density predictions that closely match experimental values, with deviations within 36 mV and 0.04 mA/cm2, respectively, but fill factor (FF) and conversion efficiency were overestimated by approximately 3% and 1%. Based on these diagnostic findings, we propose and compare targeted optimization strategies. This work provides a reliable, non-contact diagnostic tool for evaluating subcell performance in complex multijunction architectures, identifies optimization directions through comparative device analysis, and offers actionable guidance for advancing IMM-5JSC performance.
