Quantitative analysis of subgrain boundaries in Si multicrystals and their impact on electrical properties and solar cell performance

We implement spatially resolved x-ray rocking curve for quantitative analysis of subgrain boundary (sub-GB) density in Si multicrystals with controlled microstructures by "dendritic casting method." The oriented crystal grains made it possible to analyze a large area over different crystal grains by using the same optical configuration. Sub-GBs were found to be spatially localized in a particular region and spread in the growth direction of the ingot. By combining sub-GB density with a separate measurement of minority carrier diffusion length, carrier recombination velocity at sub-GBs was revealed to be at the same order as random GBs. Furthermore, by analyzing electroluminescence images of a solar cell with different detection wavelengths, sub-GBs were shown to behave as shunts with stronger activity than random GBs.