Analysis of n-type IBC solar cells with diffused boron emitter locally blocked by implanted phosphorus

•Novel simplified process sequence for the fabrication of IBC solar cells.•Synergistic combination of ion implantation and furnace diffusion.•Investigation of reverse breakdown for IBC solar cells without gap.

Interdigitated back-contact (IBC) solar cells were fabricated with a process sequence combining local ion implantation of phosphorus and full area BBr3 furnace diffusion resulting in conversion efficiencies of up to 22.4%. The highly doped emitter and BSF are in direct contact to each other (p+n+ junction) leading to a controlled junction breakdown at low reverse-bias voltages of around 5 V. The breakdown was located at the p+n+ junction and found to be homogeneously distributed over the whole cell area. This is not critical for module integration as the absolute temperature rise of a reverse-biased cell was determined to be less than 35 K. After reverse breakdown, the conversion efficiency degraded by 1–2% absolute due to additional recombination at the p+n+ junction. The cell performance could be fully recovered by a short annealing at 300 °C indicating that the Al2O3 passivation was altered by the reverse breakdown. This might be a fundamental issue for Al2O3 passivated IBC solar cells without gap between emitter and BSF, independent from the doping method.