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A passivating contact for silicon solar cells formed during a single firing thermal annealing

Nature Energy volume 3, pages 800–808 (2018)Cite this article

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Abstract

Passivating contacts are indispensable for achieving high conversion efficiency in crystalline-silicon solar cells. Their realization and integration into a convenient process flow have become crucial research objectives. Here, we report an alternative passivating contact that is formed in a single post-deposition annealing step called ‘firing’, an essential step for current solar cell manufacturing. As firing is a fast (<10 s) and high-temperature (>750 °C) anneal, the required microstructural and electrical properties of the passivating contact are stringent. We demonstrate that tuning the carbon content of boron-doped silicon-based thin films inhibits firing-induced layer delamination without preventing a partial crystallization. The latter promotes charge-carrier selectivity, even in the absence of a diffused doped region beyond the oxide, by inducing hole accumulation near the wafer surface. We fabricated proof-of-concept solar cells employing the developed technology, demonstrating an open circuit voltage of 698 mV and an efficiency of 21.9%, and show how it could be a drop-in replacement for today’s rear contacts based on locally opened dielectric passivation stacks.

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Fig. 1: Fabrication steps of the FPC concept.
Fig. 2: The valence band-edge alignment.
Fig. 3: Surface passivation and charge carrier transport of the FPC.
Fig. 4: The FPC concept applied to proof-of-concept p-type hybrid solar cells.
Fig. 5: SIMS analysis of the FPC layers.
Fig. 6: The microstructure of the FPC layers.
Fig. 7: Fourier transform infrared spectroscopy of the single FPC stack.
Fig. 8: Hydrogen evolution in the FPC layer.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors gratefully acknowledge support by the Swiss National Science Foundation (SNF) under grant nos 200021_14588/1, 200021L_172924, 200021L_172924, IZLIZ2_156641 and CRSII2_154474/2, the Swiss Federal Office for Energy (SFOE) under grant no. SI/501253-01 and the National Research Fund Luxembourg (FNR) through grant INTER/SNF/16/11536628. B. El Adib (LIST) is thanked for his skilful technical assistance in the SIMS analysis and P. J. Fiala, A. N. Fioretti and A. Hessler are thanked for proofreading of the manuscript.

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Authors and Affiliations

  1. École Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin Film Electronics Laboratory, Neuchâtel, Switzerland

    Andrea Ingenito, Gizem Nogay, Quentin Jeangros, Esteban Rucavado, Monica Morales-Masis, Franz-Josef Haug, Philipp Löper & Christophe Ballif

  2. CSEM PV-Center, CSEM, Neuchâtel, Switzerland

    Christophe Allebé, Jörg Horzel, Matthieu Despeisse & Christophe Ballif

  3. Advanced Instrumentation for Ion Nano-Analytics (AINA), Luxembourg Institute of Science and Technology, Materials Research and Technology Department, Belvaux, Luxembourg

    Santhana Eswara, Nathalie Valle & Tom Wirtz

  4. Research Center for Photovoltaic, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

    Takashi Koida

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Contributions

A.I., P.L. and C.B. conceived the idea. A.I. designed the experiments and carried out the device and layer fabrication and characterization including lifetime, TLM, J–V, FTIR, Raman and optical microscopy analyses. G.N., C.A. and J.H. contributed to the solar cell fabrication process. Q.J. carried out the TEM observations, S.E. performed the SIMS measurements and E.R. and T.K. executed the thermal desorption spectroscopy analysis. P.L. and C.B. contributed to the definition and presentation of the paper contents. P.L., F.-J.H., M.M.-M., T.W., N.V., M.D. and C.B. discussed the results. A.I., P.L., M.D. and C.B. organized the research. A.I. wrote the paper, and all other authors provided feedback.

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Correspondence to Andrea Ingenito.

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A patent application has been filed (application number pat2522992PC00) for the fired passivating contact approach reported in the manuscript.

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Supplementary Notes 1–3, Supplementary Figures 1–3, Supplementary References

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Ingenito, A., Nogay, G., Jeangros, Q. et al. A passivating contact for silicon solar cells formed during a single firing thermal annealing. Nat Energy 3, 800–808 (2018). https://doi.org/10.1038/s41560-018-0239-4

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