Root cause analysis on corrosive potential-induced degradation effects at the rear side of bifacial silicon PERC solar cells

Abstract Potential induced degradation (PID) of solar cells can severely reduce a PV module's performance. In case of bifacial solar cells, the rear side is another source of PID as was found for industrially produced bifacial PERC solar cells from three different manufacturers. It is shown that a rear-side PID test can lead to more than 12% power degradation. The observed PID mechanisms are not completely recoverable implying long-term losses under field operation. This new, non-recoverable PID effects are characterized by a locally increased recombination at the rear side of the cells. From nano-scale analytics by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDXS) are performed and PID related defects are traced back to a local Si corrosion and delamination of the passivation layers. At the Si passivation interface an increased amount of SiOx, Na and further impurities are found that indicate an electrochemically driven corrosion process under cathodic conditions.