Defect-induced current coupling in multi-junction solar cells revealed by absolute electroluminescence imaging

An electroluminescence (EL) anomaly singular spot was observed in an industry-standard InGaP/GaAs multi-junction solar cell (MJSC). Affected by this singular spot, the spatially resolved subcell current distributions were found to exhibit unique opposite characteristics, which we call “defect-induced current coupling.” Herein, we conducted systematic investigations to reveal the defect-induced current coupling phenomenon, for the first time, through the absolute EL imaging technique. Specifically, a modified carrier-balance model was first proposed to describe the subcell optoelectronic distribution around the singular spot. Then, optical and electrical properties including subcell non-radiative recombination distributions, J–V characteristics, essential photovoltaic parameters, and energy losses were quantitatively extracted for characterizing the performance inhomogeneity caused by the defect-induced coupling. Moreover, a three-dimensional distributed circuit model was established to numerically simulate the absolute EL emissions and extract local electrical parameters around the singular spot. Simulation results revealed that the defect-induced current coupling phenomenon is attributed to the deterioration of weak-diode and shunt parameters at the GaAs bottom cell, and the efficiency of the MJSC was estimated to be reduced by 0.408% compared with the defect-free MJSC model.