Accelerated Testing of UV‐Induced Degradation in TOPCon and Heterojunction Solar Cells: Critical Parameters, Mechanistic Insights, and Implications

Long‐term reliability of high‐efficiency tunnel oxide passivated contact (TOPCon) and silicon‐heterojunction (HJT) modules seem threatened by ultraviolet light‐induced degradation (UVID), yet the kinetics and triggers of the defect mechanisms remain poorly understood. We systematically investigate UVID in unencapsulated industrial solar cells under variations of UV spectrum, intensity, temperature, and concurrent visible illumination (VIS) and correlate resulting losses with hydrogen redistribution measured by ToF‐SIMS. Short‐wavelength UV photons strongly enhance UVID and drive near‐surface defect formation, whereas elevated cell temperatures during exposure substantially suppress degradation. For a fixed exposure time, the defect generation scales linearly with cumulative UV photon dose, but the net UVID amplitude depends critically on the accumulated thermal budget. Under combined UV + VIS illumination near‐outdoor conditions, although at open contacts, UVID is almost completely suppressed, indicating that continuous carrier injection promotes repassivation and prevents stable defect buildup. Post‐UV dark storage induces additional metastable degradation in the TOPCon group, which, like the initial UVID, is reversible by visible light soaking at elevated temperature. Our results substantiate hydrogen‐mediated interface changes as the most likely key driver of UVID and highlight that accelerated UV tests must account for spectral shape, temperature history, and concurrent VIS illumination to reproducibly determine UVID in field performance.