Sodium decoration of PID-s crystal defects after corona induced degradation of bare silicon solar cells

It is proven that potential-induced degradation leading to shunting of crystalline silicon solar cells (PID-s) is caused by stacking fault-like planar crystal defects penetrating the p-n junction that become decorated with sodium due to high electric fields across the dielectric antireflective coating (ARC). Often it is assumed that sodium found in PID-s affected cells originates from the cover glass used for photovoltaic modules. In this contribution, we show that PID-s also occurs at bare silicon solar cells without polymer foil or glass encapsulation. Using corona discharge induced degradation, it is shown that sodium decorated, shunting crystal defects are generated. This sodium likely originates from contaminations present on the solar cell surface. Therefore, it is concluded that PID-s of solar modules also mainly arises from sodium contaminations of the solar cell surface and not from the glass. Whether PID-s occurs or not depends on the electric field across the ARC, influenced by the electrical resistance of polymer foil and glass. So called sodium-free glass results in a low electric field due to the high resistance of the glass.