Post-mortem analysis of a commercial Copper Indium Gallium Diselenide (CIGS) photovoltaic module after potential induced degradation

An extensive post-mortem analysis was conducted on a commercial copper-(indium-gallium)-diselenide (CIGS) photovoltaic module that degraded after exposure to the high voltage stress of a standardized potential induced degradation (PID) test. We employed a custom-developed coring technique to extract samples from the full-size field module, which showed degraded and nondegraded areas (regarded as reference) in electroluminescence after the PID test. The resulting solar cell samples were compared based on their electrical properties and sodium profiles using a wide range of laboratory-based analysis techniques including photoluminescence and lock-in thermography imaging, current–voltage measurements, and glow discharge optical emission spectroscopy. The samples that were extracted from the degraded areas of the module showed lower photoluminescence intensity and had significantly lower open-circuit voltage V(_oc) and fill factor (FF) values in comparison with reference samples. An increased content of sodium within the absorber layer was also observed for these samples, linking sodium migration to PID. These observations at the module level are consistent with earlier reports on PID-stressed CIGS cells and mini-modules. This is to our knowledge the first reported study of a microscopic investigation on a real-life full-scale CIGS module after PID.