Abstract
N-type back-junction back-contact (BJ-BC) silicon solar cells have been successfully introduced in industry by Sunpower with efficiencies up to 23.4% and are being investigated by several research groups. For such n-type bulk Si solar cells, the formation of the p(+) emitter is still an issue. A traditional method is boron diffusion, which needs high temperature processes to form the emitter and to remove the silicate glass boron skin. In recent years, people have shown excellent results on n-type front contact rear junction cells with a screen-printed Al-alloyed emitter. In this work, we demonstrate the use of such emitters on n-type BJ-BC silicon solar cells. Different pitch sizes and emitter fractions have been studied. Clear trends of the short-circuit current densities have been observed. Light beam induced current technique is used to investigate this phenomenon. Different front surface field (FSF) profiles were applied to our cells. The shallower FSF with a lower surface doping concentration results in lower front surface recombination, which results in the best cell performance. Efficiencies of 19.1% under 1 Sun on BJ-BC solar cells with an aperture area of 2 cm x 2 cm have been achieved on n-type FZ and CZ silicon wafers. Good short-circuit current densities and fill factors have been obtained. Compared to the boron-diffused emitter BJ-BC solar cells, relatively low open-circuit voltages were obtained. Better quality emitter with more effective cleaning process steps and passivation layers have been developed, to result in a further increase in cell efficiency in the future work. Copyright (C) 2010 John Wiley & Sons, Ltd.