TOPCON PV Modules UV Exposure: Uncovering Hidden Instabilities

The rapid expansion of GW-scale photovoltaic installations in desert environments is shifting the spotlight to the stability of new-generation PV module technologies under harsh conditions. High UV irradiance, a characteristic challenge of desert regions, has raised concerns about the long-term performance of emerging technologies, particularly the TOPCon PV modules, which technology is currently gaining rapidly increasing market share in the PV industry. In a collaborative study with leading solar institutes, TOPCON modules from different manufacturers were subjected to accelerated UV exposure at elevated temperatures to detect potentially hidden degradation pathways. The results from our preliminary studies demonstrated a notable power degradation in 3 out of 5 TOPCon modules tested compared to PERC modules. In terms of the specific batches of PV modules considered, the three TOPCon modules that showed abnormal degradation exhibited power losses of around 8% after a UV dose exposure of 90 kWh/m². PERC modules exhibited lower values around 2% degradation (based on the UV aging study conducted at DEWA R&D). When UV exposure was combined with dark storage, the power degradation in the affected TOPCon modules increased significantly, reaching 13% to 16.5% (as observed in the UV aging study at F-CSP). Significant changes in the electrical parameters of the modules were observed after the UV exposure. However, light soaking was found to stabilize the performance of TOPCon modules after periods of dark storage. The combined impact of UV aging, dark storage, and light soaking revealed significant changes in the stability of TOPCon PV modules. Electroluminescence (EL) imaging detected the formation of a distinct checkered pattern in some of the TOPCon modules, accompanied by intense UV fluorescence (UVF) at cell edges and along multi-busbar soldering points. Interestingly, these specific structural changes were not observed in the PERC modules, underscoring their stability after high-dose UV exposure. These findings highlight critical challenges and uncover the hidden instability of TOPCon, emphasizing the need for further interlaboratory testing and reliability studies to mitigate possible unknown degradation risks in high-UV environments.