N-PERT Back Junction Solar Cells: an Option for the Next Industrial Technology Generation?

Abstract

In this work, we present back-junction (BJ) n-PERT (Passivated Emitter, Rear Totally Diffused) solar cells with a processing sequence based on an industrial-type p-PERC (Passivated Emitter and Rear Cell) process, with the addition of a boron diffusion. Through this, we achieve efficiencies up to 20.5% on n-PERT BJ solar cells, which do not degrade under subsequent illumination. For comparison, reference p-PERC solar cells fabricated on 1 and 3  cm boron-doped Cz-Si achieve efficiencies up to 20.6% before light-induced degradation (LID) and 20.1% (3  cm) and 19.7% (1  cm), respectively, after LID. We find that the width of the laser contact opening (LCO) on the rear strongly influences the n-PERT BJ solar cell performance. Wider LCOs significantly increase the short- circuit current, open-circuit voltage, and pseudo fill factor, resulting in efficiency increase of up to 1.2% absolute. We attribute this to an increased thickness and homogeneity of the Al-p + regions beneath the contacts, which effectively reduces recombination at the contacts. By varying the metallization fraction on the rear side, we determine the specific contact resistance of the Al contact to be c = (8 ± 2) m cm 2 and the saturation current density to be J0.met of (320 ± 50) fA/cm 2 .