Efficient silicon solar cells with dopant-free asymmetric heterocontacts

Abstract

A salient characteristic of solar cells is their ability to subject photo-generated electrons and holes to pathways of asymmetrical conductivity—‘assisting’ them towards their respective contacts. All commercially available crystalline silicon (c-Si) solar cells achieve this by making use of doping in either near-surface regions or overlying silicon-based films. Despite being commonplace, this approach is hindered by several optoelectronic losses and technological limitations specific to doped silicon. A progressive approach to circumvent these issues involves the replacement of doped-silicon contacts with alternative materials which can also form ‘carrier-selective’ interfaces on c-Si. Here we successfully develop and implement dopant-free electron and hole carrier-selective heterocontacts using alkali metal fluorides and metal oxides, respectively, in combination with passivating intrinsic amorphous silicon interlayers, resulting in power conversion efficiencies approaching 20%. Furthermore, the simplified architectures inherent to this approach allow cell fabrication in only seven low-temperature (≤200 C), lithography-free steps. This is a marked improvement on conventional doped-silicon high-efficiency processes, and highlights potential improvements on both sides of the cost-to-performance ratio for c-Si photovoltaics.

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Figure 1: Conceptual structure of the DASH solar cell.
Figure 2: Optoelectronic properties of carrier-selective layers.
Figure 3: Contact-level analysis of electron-selective contacts.
Figure 4: DASH cell level results.

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Acknowledgements

We would like to thank P. Frischmann for his assistance with IV measurements and A. Fell for his suggestions regarding the simulations. Device design, fabrication and characterization were funded by the Bay Area Photovoltaics Consortium (BAPVC). Materials characterization was supported by the Electronic Materials Programs, funded by the Director, Office of Science, Office of Basic Energy Sciences, Material Sciences and Engineering Division of the US Department of Energy under Contract No. DE-AC02- 05CH11231. XPS characterization was performed at the Joint Center for Artificial Photosynthesis, supported through the Office of Science of the US Department of Energy under Award Number DE-SC0004993. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy (Contract No. DE-AC02-05CH11231). Work at EPFL was supported by the Office fedéral de l’ énergie (OFEN). Work at the ANU was supported by the Australian Renewable Energy Agency (ARENA). The authors would like to thank the CSEM PV-center for wafer preparation and device metallization.

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Contributions

J.B. and A.J. conceived the idea. J.B. and J.G. carried out the device fabrication, electrical characterization and analysis. A.J.O., T.A. and T.C. assisted with device fabrication. M.H. and C.M.S.-F., assisted with materials characterization. H.O. and E.W.S. assisted with mask fabrication. A.C., S.D.W. and C.B. discussed the results. J.B. wrote the paper and all other authors provided feedback.

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Correspondence to Ali Javey.

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The authors declare no competing financial interests.

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Supplementary Notes 1-4, Supplementary Tables 1-3, Supplementary Figures 1-4, Supplementary References. (PDF 911 kb)

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Bullock, J., Hettick, M., Geissbühler, J. et al. Efficient silicon solar cells with dopant-free asymmetric heterocontacts. Nat Energy 1, 15031 (2016). https://doi.org/10.1038/nenergy.2015.31

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