Large-Area n-Type PERT Solar Cells Featuring Rear p⁺ Emitter Passivated by ALD Al₂O₃

We present large-area n-type PERT solar cells featuring a rear boron emitter passivated by a stack of ALD Al₂O₃ and PECVD SiO_x. After illustrating the technological and fundamental advantages of such a device architecture, we show that the Al₂O₃/SiO_x 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/SiO_x 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 V_oc 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.