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

: Müller, R.; Reichel, C.; Schrof, J.; Padilla, M.; Selinger, M.; Geisemeyer, I.; Benick, J.; Hermle, M.


Solar energy materials and solar cells 142 (2015), S.54-59
ISSN: 0927-0248
International Conference on Crystalline Silicon Photovoltaics (SiliconPV) <5, 2015, Constance>
Zeitschriftenaufsatz, Konferenzbeitrag
Fraunhofer ISE ()
Solarzellen - Entwicklung und Charakterisierung; Silicium-Photovoltaik; Herstellung und Analyse von hocheffizienten Solarzellen

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.