Cumulative Anomalous Behavior of TOPCon Solar Cells Under Ultraviolet Irradiation
Tunnel oxide passivated contact (TOPCon) solar cells, despite achieving commercial efficiencies up to 25.6% and a theoretical limit of 28.7%, exhibit ultraviolet-induced degradation (UVID) that threatens long-term reliability. This study investigates the metastable behavior of industrial-scale TOPCon cells under dark storage and cumulative ultraviolet (UVA-365 nm) irradiation at 200 W/m². Dark storage over 60 days revealed a decay in minority carrier lifetime (τ) by 13%, with implicit open-circuit voltage (i-Voc) and implicit fill factor (i-FF) decreasing by 0.17% and 0.30%, respectively. Critically, short-term UV exposure (approximately 1 s) produced an anomalous efficiency enhancement: average power conversion efficiency (PCE) increased by 0.07%, open-circuit voltage (Voc) by 0.89 mV, and fill factor (FF) by 0.15% across a batch of 4677 cells. Prolonged UV irradiation, however, reversed these gains, causing passivation degradation and net PCE loss. This dual behavior—initial improvement followed by deterioration—is attributed to the interplay between hydrogen-mediated defect metastability and UV-induced interface damage. The findings establish a previously unreported UV-induced recovery mechanism and provide a quantitative basis for optimizing UV pre-treatment in TOPCon manufacturing, potentially enabling efficiency gains without additional capital expenditure.