UV-Induced Degradation in N-Type TOPCon Modules: Exploring Metastability and Recovery Pathways

Modern solar PV technologies like Tunnel Oxide Passivated Contact (TOPCon) have shown notable power degradation in specific bills of materials (BOMs) under accelerated ultraviolet light-induced degradation (UVID) testing. Initial testing revealed a wide range of power degradation (-0.8% to -16%) after UV dose of 120 kWh/m² (280-400 nm) using metal halide lamps. The power loss due to UVID is mainly attributed to Voc degradation (passivation loss or reduction in carrier lifetime). A few BOMs also exhibited higher Isc losses, whereas the contribution of FF is small. With more data collection, it became evident that the high degradation observed in some modules was not statistically significant. UVID is not proving to be as severe as initially anticipated. Notably, the characteristic UVID signatures in EL images are observed in field-deployed modules, supporting the correlation between laboratory results and real-world performance. Another critical challenge associated with UV-sensitive modules is their metastable behavior, with pronounced sensitivity to dark conditions as indicated by remarkable power decline within a single day of dark storage, underscoring the necessity of precise timing in module characterization post UVID or field exposure. Furthermore, we have explored potential stabilization techniques, such as indoor/outdoor light soaking, current injection, and UV-365 nm exposure) and plan to contribute these findings to the development of updated IEC standards.