Point defect-dominated ring defect formation limiting TOPCon solar cell performance in low-oxygen Cz Silicon

High-efficiency tunnel oxide passivating contact (TOPCon) solar cells have matured as an industrial technology, yet their performance is compromised by edge ring-like defects whose formation mechanism remains incompletely understood. In this work, we demonstrate that in current low-oxygen Czochralski silicon, these ring defects arise primarily from radial non-uniformity in interstitial oxygen ([Oi]) and intrinsic point defects. Localized oxygen enrichment or point defect concentrations falling within a relatively low yet critical threshold range—typically near the wafer edge—sufficiently accelerate oxygen precipitate (OP) formation kinetics. This acceleration leads to regions of high OP density, manifesting as the critical multiple rings observed in photoluminescence images. This work provides the first direct experimental evidence—combining Fourier-transform infrared spectroscopy, positron annihilation lifetime spectroscopy, preferential etching, and controlled annealing experiments—for the critical role of point defects in driving ring defect formation under low-oxygen conditions. These findings offer valuable theoretical insights and practical guidance for optimizing crystal growth processes to suppress such defects in industrial TOPCon production. Edge ring-like defects limit the performance of high-efficiency tunnel oxide passivating contact solar cells. Here, the authors show that ring defects in low-oxygen Czochralski silicon arise from oxygen and point-defect nonuniformities that accelerate oxygen precipitation near wafer edges, providing direct evidence for the role of point defects in defect formation.