Record Efficiency of PhosTop Solar Cells from n-type Cz UMG Silicon Wafers

Abstract

Highly purified n-type Upgraded Metallurgical Grade (UMG) silicon carries a large potential for high efficiency low cost solar cells. In this study, the industrially producible “PhosTop” solar cell concept is employed to manufacture large-area n-type rear junction solar cells from such a Si material with a screen-printed Al-alloyed full-area emitter featuring a selective phosphorous front surface field (FSF) and a SiO2/SiNx:H passivation on the front.Since resistivity at the seed end is about seven times as high as at the tail end of the UMG Si ingot and carrier lifetime decreases from seed to tail end, a clear dependence of the solar cells’ IV characteristics on the original position of the corresponding wafers in the UMG Si ingot is observable. Maximum conversion efficiency is reached (on a wafer which has been taken out at about one fifth of the ingot's length distant from the seed end) by η = 19.0% being, to the authors’ knowledge, the highest efficiency so far reported on industrial type solar cells manufactured from 100% UMG Si.