Simplifying the manufacturing of n-type silicon solar cells with screen-printed aluminium-alloyed rear emitter

This work focuses on simplifying the fabrication process of our near-industrial n-type silicon solar cells with screen-printed aluminium-alloyed rear emitter. We investigate the structural and electrical properties of Al emitters alloyed on differently prepared Si surfaces. We demonstrate that the formation of a proper emitter neither requires a planar nor a non-diffused rear surface, thus allowing both-sided surface texturing and both-sided phosphorous doping during the n+ front surface field diffusion without the need of an additional protecting rear masking layer. On textured surfaces a careful choice of the printing and alloying conditions is essential to obtain Al-p+ emitters without shunts in form of locally non-alloyed regions. By adjusting the alloying conditions or by applying a simple rear surface conditioning step, shunts can be effectively prevented, thereby simultaneously increasing the internal reflectance and reducing the Al-p+ emitter saturation current density. Al alloying on P-diffused rear surfaces is shown to be uncritical. In summary, we demonstrate that Al alloying for p+ emitter formation can be easily realised on textured and P-diffused surfaces leading to a much more flexible fabrication of our n-type silicon solar cells.