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This paper proposes a kerfless wafer structure with built-in p-n junctions in n-type silicon wafers grown using Crystal Solar's high throughput epitaxy technology. Compared with a conventional p-type emitter by boron diffusion, ion implantation, or epitaxy, the built-in p-type emitter has a reduced and uniform doping concentration and increased thickness. The epitaxially grown wafers and conventional Czochralski (CZ) n-type wafers were processed into solar cells. A best efficiency of 22.5% with epitaxially grown wafers was achieved, with a 6 mV gain in open-circuit voltage, suggesting a high wafer quality and superiority of the deep epitaxial emitter over a standard boron-diffused emitter. Substrate reuse associated with the kerfless epitaxy technology is studied as well, with respect to its impact on solar cell efficiency. The data suggest no degradation in cell efficiency due to substrate reuse.

We present large-area n-type PERT solar cells featuring a rear boron emitter passivated by a stack of ALD Al2O3 and PECVD SiOx. After illustrating the technological and fundamental advantages of such a device architecture, we show that the Al2O3/SiOx stack employed to passivate the boron emitter is unaffected by the rear metallization processes and can suppress the Shockley-Read-Hall surface recombination current to values below 2 fA/cm2, provided that the Al2O3 thickness is larger than 7 nm. Efficiencies of 21.5% on 156-mm commercial-grade Cz-Si substrates are demonstrated in this study, when the rear Al2O3 /SiOx passivation is applied in combination with a homogeneous front-surface field (FSF). The passivation stack developed herein can sustain cell efficiencies in excess of 22% and Voc above 685 mV when a selective FSF is implemented, despite the absence of passivated contacts. Finally, we demonstrate that such cells do not suffer from light-induced degradation.