UV‐Induced Degradation and Associated Metastability in TOPCon Photovoltaic Modules: Understanding Kinetics and Cell Variance

ABSTRACT Tunnel oxide passivated contact (TOPCon) silicon photovoltaic (PV) modules are dominating the PV market, but they may be susceptible to degradation under ultraviolet (UV)‐containing light. Quantifying the impacts of UV‐induced degradation (UVID) is complicated by an associated metastability causing further degradation under dark storage and rapid recovery under sunlight. Here, we study modules that have −2.3% to −3.2% nonrecoverable UVID loss after 60 kWh/m 2 dose of 340 nm light and additional recoverable loss under dark storage. We use in situ electroluminescence (EL) imaging to characterize the post‐UVID metastability at the module level. The cell‐by‐cell dark degradation and recovery kinetics span a wide range from +6% to −70% changes in EL intensity after 520 h of dark storage, which returns to ± 4% of the initial post‐UVID EL intensity after illumination. The kinetics follow double exponential rates with dark storage degradation time constants of 345 and 45 h, and UV light recovery time constants of 5 min and 36 s. We propose that this is consistent with prior reports of kinetics for light‐soaking metastability in Al 2 O 3 passivation. Finally, we further show that cells having high UVID also have injection‐dependent effective carrier lifetimes and significant intra‐cell variance, suggesting possible origins of processing inconsistency.