Integration Processes for nPERT Si Solar Cells Using Single Side Emitter Epitaxy and front Side Laser Doping

This work focuses on the fabrication of nPERT(Passivated Emitter, Rear Totally Diffused) devices incorporating an epitaxially grown single side rear-emitter. Such epi-nPERT cells are fabricated in a simplified way using the selectivity of the epitaxial deposition, which is obtained by a PECVD-SiOxlayer, that not only mask the front but also passivates the cell. The cell performance is studied in terms of: i) various front surface fields (FSF) applied prior to emitter epitaxy and ii) usage of laser doping as an alternative to laser ablation for a front contacting scheme. The results show: i) a clear relationship between the depth of the homogeneous FSF and its impact on the open circuit voltage of the devices, with a shallow FSF having the highest VOC loss due to laser damage and ii) laser doping on devices with a relatively deep diffused FSF giving 8mV increase in VOC as compared to devices with ablated dielectrics and a VOC increase of almost 30mV in case a shallow selective FSF is applied. This results in a best efficiency obtained so far for the epi nPERT devices of 21.6% (226cm2).