In-Operando Characterization and Investigation of Individual Defects in GaAs Solar Cells

The ultimate constraint for a solar cell to reach its theoretical efficiency limit is the quality of the absorber material. It is common knowledge that the existence of structural defects degrades device performance. However, in a real device, it is unclear (1) how individual defects affect performance via different cell parameters, (2) how the impact depends on the operation conditions, and (3) how the impact varies from one defect to another. This work answers these questions through investigating individual dislocation defects in GaAs solar cells under different illumination conditions. An array of correlative and spatially-resolved techniques, including electroluminescence, photoluminescence, Raman, and current-voltage (I-V) characteristics, is used to identify and characterize the defects. By comparing the I-V characteristics with the laser beam focused at the defect and defect-free site, the adverse impact of the defects is quantitatively measured through changes in the key device parameters, including short-circuit current, open-circuit voltage, fill factor, energy-conversion efficiency, and shunt resistance. This study provides insights for both a fundamental understanding of defect physics and practical knowledge of defects in the single defect level.