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.