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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 V OC loss due to laser damage and ii) laser doping on devices with a relatively deep diffused FSF giving 8 mV increase in V OC as compared to devices with ablated dielectrics and a V OC increase of almost 30 mV 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% (226 cm 2 ). [ABSTRACT FROM AUTHOR]

Abstract In this work we investigated the optical and electrical performance of p-type epitaxial layers as the rear emitter of bifacial n-type PERT solar cells. In the first part of this paper, the surface morphology of epitaxial layers grown on textured surfaces is studied. Because of the epitaxial growth, a pyramids-rounding effect is observed as a result of {311} and {911} facet propagation. The growth pattern was quantified and modelled. In the second part of this paper, the optical performance of semi-device test structures is evaluated. The trend of the optical results in bifacial solar cell structures indicates that a final pyramid angle at the rear side around 20° gives the maximum light absorption in the wafer substrate. In this work we demonstrate that the epitaxial growth of the emitter on the textured rear side of these devices can already give a pyramid angle of 25° without having to introduce any additional polishing steps to modify the morphology of the textured surface. In the last part of this paper, we present the electrical results for semi-device structures created to quantify the recombination losses in the passivated and metallized regions of those p-type epitaxial emitters. These results indicate that by introducing a rear epitaxial emitter in the bifacial n-type PERT cell structure, we can increase the implied V oc up to 17 mV compared to a diffused emitter with the same sheet resistance. Highlights • The pyramids-rounding effect is simultaneously implemented during the epitaxial emitter growth step. • The trend of the optical results in bifacial solar cell structures indicates that a final pyramid angle at the rear side around 20° gives the maximum light absorption in the wafer substrate. In this work we demonstrate that the epitaxial growth of the emitter on the textured rear side of these devices can already give a pyramid angle of 25 ° without having to introduce any additional polishing steps to modify the morphology of the textured surface. • Thick but lowly doped epitaxial emitters reduce recombination loss compared to diffused counterpart. [ABSTRACT FROM AUTHOR]