Towards 20% efficient large‐area screen‐printed rear‐passivated silicon solar cells

Abstract

ABSTRACTWe have implemented a baseline solar cell process based on today's standard industrially manufactured silicon solar cells. Using this process, we achieve conversion efficiencies up to 18.5% applying 125 × 125 mm² pseudo‐square p‐type 2–3 Ω cm boron‐doped Czochralski silicon wafers featuring screen‐printed front and rear contacts and a homogenously doped 70 Ω/□ n+‐emitter. Optimizing a print‐on‐print process for the silver front side metallization, we reduce the finger width from 110 to 70 µm, which increases the conversion efficiency up to 18.9% due to the reduced shadowing loss. In order to further increase the efficiency, we implement two different dielectric rear surface passivation stacks: (i) a silicon dioxide/silicon nitride stack and (ii) an aluminium oxide/silicon nitride stack. The rear contacts to the silicon base are formed by local laser ablation of the passivation stack and aluminium screen printing. The dielectric layer stacks at the rear decrease the surface recombination velocity from Seff,rear = 350 cm/s for a full‐area Al back surface field down to Seff,rear = 70 cm/s and increase the internal reflectance from 61% up to 91%. The improved solar cell rear increases the conversion efficiency η up to an independently confirmed value of 19.4%, the short‐circuit current density Jsc up to 38.9 mA/cm² and the open‐circuit voltage Voc up to 662 mV. The detailed solar cell analysis reveals potential to further increase the conversion efficiency towards 20% in the near future. Copyright © 2011 John Wiley & Sons, Ltd.