Impacts of Metal Impurities on Recombination Properties at Small Angle Grain Boundaries in Multicrystalline Silicon for Solar Cells

Abstract

The correlation between recombination properties and detailed misorientation angles at small angle grain boundaries SA-GBs in multicrystalline silicon (mc-Si) after metal contamination were evaluated. After metal contamination, EBIC contrast enhancements at > 1.5o SA-GBs were on the order of Fe/1000 oC > Ni/1000 oC > Ni/600 oC, while at < 1.5o SA-GBs they were seldom different from any contamination. These results might be attributed to Fe and Ni atoms forming different energy levels in recombination centers and the getting abilities of SA-GBs depending on misorientation angles, i.e., dislocation density at SA-GBs. Many dark spots were observed after Ni/600 oC. After Secco etching, we confirmed that the dark spots corresponded to etch pits. Denuded zones at vicinity of SA-GBs were observed after only Fe/1000 oC. The gettering ability of SA-GBs depends on dislocation density and the difference in recombination properties after metal contamination was affected by the types of metal impurities.