Investigation of the effects of aluminum treatment on silicon solar cells

Controlled investigation of the beneficial effects of aluminum treatment on silicon solar cells was conducted. It was found that Al treatment, which involved ~1 μm Al evaporation followed by a high temperature drive-in, can getter process-induced as well as grown-in defects and impurities by providing a sink. Additionally, forming gas anneal after the Al treatment can generate atomic hydrogen to passivate defects. Al treatment on low resistivity FZ cells gave less than 1% increase in cell efficiency, exclusively due to Al back surface field effect and not because of gettering or passivation. Cast polysilicon cells showed about 1% improvement in absolute cell efficiency, primarily due to the improved diffusion length via Al gettering of defects and contaminants. Finally, the Al treatment resulted in a 5.2% increase in absolute efficiency of EFG cells with 1.7% increase resulting from the Al gettering alone, 2.6% from hydrogen passivation due to the forming gas treatment alone, and 1.2% due to the passivation from the interaction between forming gas and Al