High trap densities in regions of reduced lifetime in multicrystalline silicon blocks
Evaluation of bulk material quality through lifetime measurements on as-cut wafers is restricted to material of very poor quality, due to the very high surface recombination velocity of unpassivated wafers. However, we find that the density of non-recombinative traps as extracted from QssPC lifetime measurements on as-cut wafers using the Hornbeck-Haynes trapping model may provide indication on regions of poor material quality, and may as such be employed as a useful tool during wafer inspection. We find that wafers originating from regions in a block corresponding to lifetime dips in the block scan exhibit distinctly higher densities of non-recombinative traps, and that solar cells processed from neighboring wafers reveal a corresponding drop in cell efficiency.
