Microstructural Analysis of Local Silicon Corrosion of Bifacial Solar Cells as Root Cause of Potential‐Induced Degradation at the Rear Side

Abstract

Bifacial passivated emitter and rear cells (PERC+) can suffer from potential‐induced degradation (PID) of the rear side. Rear‐side PID tests of industrial solar cells lead to more than 12% power degradation that is not recoverable under illumination or dark storage. A microstructural root‐cause analysis of the rear side reveals localized spots with increased carrier recombination as the origin of the power losses. Morphology and defect distribution depend on the temperature (60 and 85 °C) applied for PID acceleration. Individual defects are analyzed at the atomic level, revealing a corrosion of the silicon bulk at the Si/AlOx interface. A laterally extending Na accumulation at the interface and an increased concentration of further impurities are observed together with large stacking fault defects. The formation of the defects will be discussed within a simple model for a cathodic corrosion of Si and the impact of interfacial contaminations during solar cell processing.