Towards industrial n-type PERT silicon solar cells: Rear passivation and metallization scheme

Recently, we presented an industrially feasible passivation and contacting scheme for the front side boron emitter of n-type silicon solar cells based on firing processes. On these cells, efficiencies up to 20.8% have been achieved on small areas. These cells feature a fully-metalized BSF on the rear side, which limits the VOC to about 655 mV. When changing to a PERT cell design with a passivated BSF, both the VOC as well as the JSC can be improved due to a reduced recombination at the rear and an improved optical confinement. In this work we studied different POCl3 diffusions for their applicability to n-type PERT solar cells with respect to passivation and metallization. The achieved results have been used to fabricate a first batch of n-type PERT solar cells, on which VOC values up to 671 mV have been measured. The improved internal quantum efficiency above 900 nm confirms the improvement of the rear side of the cell. The boron emitter of this cell was passivated wit h a stack of 5 Å ALD Al2O3 (four ALD cycles) and 70 nm PECVD SiNx. Thus the VOC of 671 mV demonstrates furthermore, that the Al2O3 thickness of fired Al2O3/SiNx stacks for the passivation of boron emitters can be drastically reduced to four atomic layers of Al 2O3.