Development of 2-sided polysilicon passivating contacts for co-plated bifacial n-PERT cells

The current work is aimed at the development of the building blocks for the integration of polysilicon-based passivating contacts in co-plated n-PERT front junction solar cells. We show that both n-type poly and p-type poly layers (called n-poly and p-poly hereafter) can be obtained simultaneously by the sintering of undoped (i-poly) layers during the POCI3 diffusion that induces the auto-doping from an existing B-doped emitter. State of the art J0 values with very high uniformity were measured for n-poly, auto doped p-poly, and boron emitter. The total area weighted J0 of a passivated cell before metallization is calculated to be around 32 fA/cm2• We also show the viability of a laser oxidation process to pattern the front p-poly Si layer without measurable damage. Finally, we demonstrate laser ablation and plating processes that induce only very limited damage, leading to a high iVoc of around 700 mV for asymmetric samples with p and n-poly passivated surfaces.