Belt furnace gettering and passivation of n-web silicon for high-efficiency screen-printed front-surface-field solar cells

Six different resistivities (0.32, 0.57, 1.2, 2.2, 9.1 and 20 Omega cm) were investigated to understand the dopant-defect interaction in n-type, antimony-doped, dendritic web silicon ribbon, and to study its response to gettering and passivation during belt furnace processing (BFP). The as-grown lifetime was found to be a strong function of resistivity with higher resistivity displaying higher lifetime. Phosphorus gettering at 925 degreesC/6 min raised the as-grown lifetime of similar to 1 mus in 20 Q cm n-web to 5.4 mus. A combination of phosphorus gettering followed by simultaneous Al gettering and SiN hydrogenation raised the 20 Q cm n-web lifetime to 78 mus. Unlike the as-grown web, the processed lifetime was greater than 75 mus for all resistivities, with no clear doping dependence. This is attributed to the very effective gettering and passivation during the belt furnace processing. Front surface field (FSF) n(+)m-n-p(+) cells were fabricated by spin-on phosphorus diffusion on the front and screen-printed Al on the back. A lifetime value of over 100 mus was obtained in a 14.2% screen-printed FSF n-web solar cell fabricated on 100-mum-thick 20 Q cut substrate. The screen-printed FSF cell fabricated on (111) FZ gave an efficiency of 14.9% with a fill factor of 77-61%. These results are supported by model calculations, which revealed a maximum efficiency of similar to 15% for 100-mum-thick planar screen-printed FSF cells and their insensitivity to bulk lifetime above 60 ps. Copyright (C) 2001 John Wiley & Sons, Ltd.