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The ground exciton state of formamidinium lead bromide perovskite nanocrystals is a singlet dark state

Nature Materials volume 18, pages 717–724 (2019)Cite this article

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Abstract

Lead halide perovskites have emerged as promising new semiconductor materials for high-efficiency photovoltaics, light-emitting applications and quantum optical technologies. Their luminescence properties are governed by the formation and radiative recombination of bound electron–hole pairs known as excitons, whose bright or dark character of the ground state remains unknown and debated. While symmetry analysis predicts a singlet non-emissive ground exciton topped with a bright exciton triplet, it has been predicted that the Rashba effect may reverse the bright and dark level ordering. Here, we provide the direct spectroscopic signature of the dark exciton emission in the low-temperature photoluminescence of single formamidinium lead bromide perovskite nanocrystals under magnetic fields. The dark singlet is located several millielectronvolts below the bright triplet, in fair agreement with an estimation of the long-range electron–hole exchange interaction. Nevertheless, these perovskites display an intense luminescence because of an extremely reduced bright-to-dark phonon-assisted relaxation.

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Fig. 1: Basic structural and optical characteristics of FAPbBr3 perovskite NCs.
Fig. 2: Fine structure of the bright triplet and the dark singlet exciton for FAPbBr3 NCs.
Fig. 3: Signature of the dark–bright magnetic coupling in the PL decay of a single NC.
Fig. 4: Polarization analysis of the bright and dark exciton recombination lines.
Fig. 5: Temperature dependence of the PL spectrum and the PL decay a single NC.

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All relevant data that support our experimental findings are available from the corresponding author upon reasonable request.

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Acknowledgements

We acknowledge the financial support from the French National Agency for Research, Région Aquitaine, Idex Bordeaux (LAPHIA Program) and the French Ministry of Education and Research. J.E. and B.L. acknowledge the Institut universitaire de France.

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Authors and Affiliations

  1. Université de Bordeaux, LP2N, Talence, France

    Philippe Tamarat, Jean-Baptiste Trebbia & Brahim Lounis

  2. Institut d’Optique and CNRS, LP2N, Talence, France

    Philippe Tamarat, Jean-Baptiste Trebbia & Brahim Lounis

  3. Empa-Swiss Federal Laboratories for Materials Science and Technology, Dubendorf, Switzerland

    Maryna I. Bodnarchuk, Rolf Erni & Maksym V. Kovalenko

  4. Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, Zürich, Switzerland

    Maksym V. Kovalenko

  5. Univ Rennes, INSA Rennes, CNRS, Institut FOTON – UMR 6082, Rennes, France

    Jacky Even

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Contributions

M.I.B. and M.V.K. prepared the samples. M.I.B., M.V.K and R.E. performed the ensemble characterization. P.T. performed the optical experiments. P.T., J.-B.T. and B.L. interpreted the data, which were analysed by P.T. and J.-B.T. B.L. and P.T. modelled the evolutions of the spectra and decay rates with temperature and magnetic fields. J.E. developed the model of exchange interaction. P.T., J.E. and B.L. wrote the manuscript with input from all authors. B.L. supervised the project.

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Correspondence to Brahim Lounis.

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Tamarat, P., Bodnarchuk, M.I., Trebbia, JB. et al. The ground exciton state of formamidinium lead bromide perovskite nanocrystals is a singlet dark state. Nat. Mater. 18, 717–724 (2019). https://doi.org/10.1038/s41563-019-0364-x

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