How to achieve 23% efficient large-area Cu plated n-PERT cells?

This paper presents the different strategies which have been studied at imec in order to reduce the front surface recombination of our monofacial high-efficiency rear-junction (RJ) n-PERT diffused cells. These devices feature: a laser doped selective FSF on a lightly POCl
₃
diffused front side; front contacts by Ni/Cu plating followed by immersion Ag plating; a diffused rear boron emitter passivated with an Al
₂
O
₃
/PECVD SiO
_x
stack and sputtered rear AlSi contacts. Each of the three main parameters contributing to the front recombination has been tackled, starting from the reduction of the metal front recombination (by improving the laser doping process), then the reduction of the contact fraction with the implementation of busbar free cells and finally, a further reduction in the recombination of the passivated areas, by improving the thermal treatment of the dielectrics. This study shows that an average 23% efficiency is within reach for large-area double-side contacted RJ PERT cells, with voltages over 700 mV and an average FF of 80.7%.