Structural characterization and iron detection at ∑3 grain boundaries in multicrystalline silicon

Transition-metal impurities gettered by grain boundaries (GBs) act as recombination centers of carriers and are regarded to be harmful defects in multicrystalline silicon (mc-Si) used for solar cell production. In this study, gettering of iron by ∑3 GBs in mc-Si was investigated by using transmission electron microscopy and annular dark-field (ADF) imaging. In the clean specimen, both straight ∑3{111} GB and zig-zag ∑3{110}, {112} GBs are not electrically active, whereas the zig-zag ∑3{110}, {112} GBs become electrically active when contaminated with iron. ADF images have shown that iron is preferentially gettered at the irregular parts of zig-zag ∑3{112} GB and exists in the form of clusters. The iron gettering abilities of these ∑3 GBs have been discussed.