Comparison of Recombination Activity of Grain Boundaries in Various Multicrystalline Silicon Materials

We compare the recombination properties of grain boundaries in conventionally-solidified p-type, ntype and high performance p-type multicrystalline silicon wafers in terms of their surface recombination velocities, and evaluate their response to phosphorus gettering and hydrogenation. Overall, grain boundaries in the conventional p-type samples were found to be more recombination active than those in the high performance p-type and conventional n-type samples. As-grown grain boundaries in high performance multicrystalline silicon were not recombination active and only became active after thermal processes. In contrast, grain boundaries in the n-type samples were already recombination active in the as-grown state, but show a dramatic reduction in their recombination strength after gettering and hydrogenation. Distinct sub-bandgap photoluminescence spectra were detected from grain boundaries that are already active before gettering, and also those activated by gettering, suggesting different origins for their recombination activities. Moreover, the detrimental influence of grain boundaries on solar cell devices is discussed with the aid of numerical simulations.