Investigations on the Formation of Stacking Fault-like PID-shunts

AbstractPotential-induced degradation of the shunting type (PID-s) of silicon solar cells is attributed to planar defects at the cell front surface. Stacking fault crystal defects with a length of few micrometers penetrating the p-n junction cause shunts when they are decorated with Na atoms. The target of this work is to improve knowledge on the formation of these stacking fault defects.Two approaches are utilized to find out if stacking faults develop during the cell process or if they evolve from defect nuclei during PID-stress. One approach is chemical defect etching and subsequent microscopy of stacking fault related signatures. Statistical evaluation of etched defects on cell areas with and without PID-s indicates that stacking faults are not present before PID stress is applied to the solar cell. The second approach utilizes iterative SEM/EBIC imaging of PID-shunts in the course of proceeding degradation. EBIC investigations after each PID test reveal that a fraction of investigated stacking faults grow as a function of the PID stress duration.It is concluded that stacking faults grow under the influence of Na penetration. It is assumed that nuclei for the formation of stacking faults are microscopic defects such as dislocations or precipitates associated with surface defects on the silicon surface