Electrical Performance of the Side Region in a Multi-crystalline Silicon Ingot

This paper investigates the impact of low minority carrier lifetime areas (red-zones) in multi-crystalline silicon ingots on cell efficiency. Wafers, sliced parallel to the sidewall, were analyzed using µ-PCD and PL to determine minority lifetimes and identify crystal defects. These wafers were then processed into solar cells, and their performance was assessed through cell conversion efficiency and electroluminescence (EL) measurements. The findings reveal a decrease in minority lifetime moving from the wall inward, followed by an increase beyond approximately 14 mm. This pattern is mirrored in cell efficiency. Notably, in regions where the minority lifetime is less than 1µs, cell efficiency drastically drops, and shunting areas are visible in EL images. Conversely, in areas with lifetimes exceeding 1µs, cell efficiency returns to normal levels. These results provide guidelines for optimally cropping the sides of the ingot.