Multiple tunnel diode peaks in I-V curves of a multijunction laser power converter

How to characterize tunnel diodes (TDs) in multijunction photovoltaic cells is a challenge. Here, we investigate a locally illuminated six junction InGaAs laser power converter (LPC) by measuring the wide-voltage-range I-V curves. Multiple TD peaks are observed in the reverse breakdown area of the dark-state I-V curve, while with increased laser power, the peaks break into more subpeaks successively, and the subcell photocurrent steps are found to shrink due to the moving subpeaks at the right side of the steps. A model of a multijunction LPC under localized illumination is proposed, and the shrinkage of a step originates from the larger local overproduced subcell photocurrent than the local peak current of the very TD below this subcell. Therefore, the correspondences between TD peaks in the I-V curves and their physical locations in the structure of the LPC are determined. This work gives in-depth insight into the current limiting mechanism of TDs in multijunction photovoltaic devices under non-uniform illumination and expands the knowledge of multijunction photovoltaic devices.