Hybrid organic–inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (50 cm−1) optical phonons involving motion in the lead iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.

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The experimental data and analysis material that support the findings of this study are available in the Scholarly Materials And Research @ Georgia Tech repository (SMARTech), https://smartech.gatech.edu.

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  • 14 February 2019

    In the version of this Article originally published, the units of the Fig. 3a x axis were incorrectly given as meV. They should have been eV. This has now been corrected in all versions of the Article.


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A.R.S.K. acknowledges funding from EU Horizon 2020 via a Marie Sklodowska Curie Fellowship (Global) (project no. 705874). F.T. acknowledges support from a doctoral postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada and Fond Québécois pour la Recherche: Nature et Technologies. This work is partially supported by the National Science Foundation (award 1838276). C.S. acknowledges support from the School of Chemistry and Biochemistry and the College of Science of Georgia Institute of Technology. The work at Mons was supported by the Interuniversity Attraction Pole programme of the Belgian Federal Science Policy Office (PAI 6/27) and FNRS-F.R.S. Computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under grant no. 2.5020.11. D.B. is an FNRS Research Director.

Author information


  1. School of Physics, Georgia Institute of Technology, Atlanta, GA, USA

    • Félix Thouin
    • , Carlos Silva
    •  & Ajay Ram Srimath Kandada
  2. School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, USA

    • David A. Valverde-Chávez
    • , Ilaria Bargigia
    • , Carlos Silva
    •  & Ajay Ram Srimath Kandada
  3. Laboratory for Chemistry of Novel Materials, Department of Chemistry, Université de Mons, Mons, Belgium

    • Claudio Quarti
    •  & David Beljonne
  4. Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia, Milano, Italy

    • Daniele Cortecchia
    • , Annamaria Petrozza
    •  & Ajay Ram Srimath Kandada


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F.T., D.A.V.-C., I.B. and A.R.S.K. carried out transient absorption measurements. F.T. and D.A.V.-C. performed the analysis of the experimental data. C.Q. performed ab initio calculations. D.C. synthesized the samples. A.P. supervised the sample preparation activity, D.B. supervised the ab initio calculations, and C.S. and A.R.S.K. supervised the ultrafast spectroscopy activity. A.R.S.K. and C.S. conceived the project. All authors contributed to the redaction of the manuscript. F.T. and D.A.V.-C. are to be considered first co-authors, and C.S. and A.R.S.K. corresponding co-authors.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Carlos Silva or Ajay Ram Srimath Kandada.

Supplementary information

  1. Supplementary Information

    Supplementary Sections 1–5, Supplementary Figures 1–17, Supplementary Tables 1–2, Supplementary References 1–3

  2. NBT Normal Mode N1

    Video of normal mode N1 for (NBT)2PbI4 reported in Table I

  3. NBT Normal Mode N2

    Video of normal mode N2 for (NBT)2PbI4 reported in Table I

  4. NBT Normal Mode N3

    Video of normal mode N3 for (NBT)2PbI4 reported in Table I

  5. NBT Normal Mode N4

    Video of normal mode N4 for (NBT)2PbI4 reported in Table I

  6. NBT Normal Mode N5

    Video of normal mode N5 for (NBT)2PbI4 reported in Table I

  7. PEA Normal Mode M1

    Video of normal mode M1 for (PEA)2PbI4 reported in Table I

  8. PEA Normal Mode M2

    Video of normal mode M2 for (PEA)2PbI4 reported in Table I

  9. PEA Normal Mode M3

    Video of normal mode M3 for (PEA)2PbI4 reported in Table I

  10. PEA Normal Mode M4

    Video of normal mode M4 for (PEA)2PbI4 reported in Table I

  11. PEA Normal Mode M5

    Video of normal mode M5 for (PEA)2PbI4 reported in Table I

  12. PEA Normal Mode M6

    Video of normal mode M6 for (PEA)2PbI4 reported in Table I

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