Resistivity dependence of minority carrier lifetime and cell performance in p-type dendritic web silicon ribbon

This study shows that the bulk lifetime in 95 mum thick p-type dendritic we b silicon solar cells is a strong function of bulk resistivity. The higher the resistivity, the greater the bulk lifetime. This behavior is explained on the basis of dopant-defect interaction, which increases the lifetime lim iting trap concentration with the addition of dopant atoms. Model calculati ons show that in the absence of doping dependence of bulk lifetime (tau), s imilar to2 Omega cm web should give the best cell efficiency for bulk lifet imes below 30 mus. However, strong doping dependence of bulk lifetime in p- web cells shifts the optimum resistivity front 2 to 15 Omega cm. Bulk lifet ime in the as-grown web material was found to be less than I lis for all th e resistivities. After the cell processing which involves phosphorus getter ing, aluminum gettering, and SiN induced hydrogen passivation of defects, t he bulk lifetime increased to 6.68, 11, 31 and 68.9 mus in 0.62, 1.37, 6.45 and 15 Omega cm p-type web material, respectively. Therefore, cell process induced recovery of lifetime in web is doping dependent, which favors high resistivity. Solar cells fabricated on 95 gm thick web silicon by a manufa cturable process involving screen-printing and belt-line processing gave 14 .5% efficient 4 cm(2) cells on 15 Omega cm resistivity. This represents a r ecord efficiency for such a thin manufacturable screen-printed cell on a lo w-cost PV grade Si ribbon that requires no wafering or etching. (C) 2001 El sevier Science Ltd. All rights reserved.