Published October 25, 2021 | Version v1
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Quantifying photoinduced polaronic distortions in inorganic lead halide perovskites nanocrystals

  • 1. École Polytechnique Fédérale de Lausanne, Laboratory of Ultrafast Spectroscopy (LSU) and Lausanne Centre for Ultrafast Science (LACUS), CH-1015 Lausanne, Switzerland.
  • 2. Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland.
  • 3. National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
  • 4. LabCri, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
  • 5. Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 S. Cass Ave., Lemont, IL 60439, USA
  • 6. Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Ave, Lemont, IL, 60439, USA.
  • 7. Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
  • 8. Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1, CH-8093 Zürich, Switzerland.
  • 9. Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
  • 10. Department of Physics, University of Pavia, I-27100 Pavia, Italy

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Description

The development of next generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb-Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, associated with the activation of a longitudinal optical phonon mode at 18 meV by electron-phonon coupling, and we quantify the associated structural changes with atomic-level precision. Key to this achievement is the combination of time-resolved and temperature-dependent studies at Br K-edge and Pb L3-edge X-ray absorption with refined ab-initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temperature-dependent XAS results rules out thermal effects as the primary source of distortion of the Pb-Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr3 perovskites photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.

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References

Preprint
O. Cannelli et. al, arXiv:2103.02575 (2021)

Journal reference (Paper in which the data and results are desribed)
O. Cannelli, et al., Journal of the American Chemical Society, 143, 9048−9059 (2021), doi: 10.1021/jacs.1c02403