Comparison of gettering effects during phosphorus diffusion for one- and double-sided emitters

A key issue for future solar cell processes is a diffusion sequence which enables fast and clean production, for example by spin-on and spray-on dopants. These diffusion processes have in common that the emitter diffusion is applied on one wafer side, whereas the POCl₃ emitter process leads to double-sided doping. For higher throughput the POCl₃ process could be adapted by using one slot for two wafers. This so called back-to-back process leads to one-sided emitters and increases industrial throughput but could result in lower cell efficiency due to reduced gettering during phosphorus diffusion. In this study we investigate the difference in solar cell performance for cells processed in a back-to-back and standard POCl₃ process. Furthermore, X-ray fluorescence and SIMS measurements were performed on Cz material to study the effect of emitter over-compensation by aluminium. These experiments should clarify if the phosphorus of double-sided emitter cells is partly overcompensated or diffuses into the Al layer of the rear contact.