Partial shading of monolithically interconnected Cu(In,Ga)Se₂ (CIGSe) modules can lead to the formation of reverse bias induced defects. These localized defects permanently reduce the output of the PV module. The formation and propagation mechanisms of these defects is studied. Understanding these mechanisms can help to prevent or mitigate damage due to partial shading of CIGSe PV modules. A propagation mechanism is proposed based on both compositional changes found at the edges of the reverse bias induced defects and differences in observed propagation patterns caused by the lateral voltage drop over the TCO layer.

Partial shading of Cu(In,Ga)Se₂ modules can lead to the formation of reverse bias induced wormlike defects. These wormlike defects act as local shunts and permanently decrease module output. A good understanding of the formation and propagation mechanisms of these defects is needed in order to mitigate the negative effects, or to prevent these defects from forming. In this article, wormlike defects were formed on small nonencapsulated cells by exposing them to reverse bias conditions. Scanning electron microscopy-energy-dispersive X-ray spectroscopy measurements showed a rearrangement of elements: Indium, gallium, and copper were replaced by cadmium, whereas selenium was replaced by sulfur in the area around the defect. Moreover, additional electronic-defect levels were found in that area with spectrally resolved photoluminescence spectroscopy. Based on the material changes in the area close to the wormlike defects, a propagation mechanism is proposed. The model assumes a chemical reaction as the driving force for propagation instead of melting because of ohmic heating.