Origin of the anomalous Pb-Br bond dynamics in formamidinium lead bromide perovskites

Harishchandra Singh, Ruixiang Fei, Yevgeny Rakita, Michael Kulbak, David Cahen, Andrew M. Rappe, Anatoly I. Frenkel

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13 Scopus citations


Extended x-ray absorption fine structure spectroscopy of the light-harvesting formamidinium lead bromide (FAPbBr3) perovskite, a system with attractive optoelectronic performance, shows anomalously large variance in Pb-Br bond length, some 50% larger than in its inorganic CsPbBr3 counterpart. Using first-principles molecular dynamics simulations, we find a significant contribution to this variance coming from the FA cation, and show that the FA does not just tumble in its cuboctahedral Br12 cage, but instead stochastically sticks to, and detaches from one of the 12 nearest Br atoms after another, leading to the large variance in Pb-Br bond length. Our results demonstrate dynamic coupling between the FA-Br moiety and perovskite cage vibrations, and that tunability in dynamics can be achieved by changing the cation type and perovskite lattice parameter. Thus, our results provide information that needs to be considered in any of the intensely debated models of electron-phonon coupling in lead halide perovskites.

Original languageEnglish
Article number054302
JournalPhysical Review B
Issue number5
StatePublished - 1 Feb 2020
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2020 American Physical Society.


A.I.F. acknowledges support by National Science Foundation Grant No. DMR-1911592. R.F. and A.M.R. acknowledge support from the National Science Foundation, under Grant No. DMR-1719353. Computational support was provided by the National Energy Research Scientific Computing Center of the Department of Energy. X-ray absorption spectroscopy data were collected at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. A.I.F. and A.M.R. acknowledge support by Weston Visiting Professorships during their stays at the Weizmann Institute of Science. Y.R. and D.C. thank the US-Israel Binational Science Foundation, the Ullmann family foundation, and the Weizmann Institute's Sustainability and Energy Research Initiative for partial support.

FundersFunder number
DOE Office of Science
E.I. DuPont de Nemours & Co.
National Energy Research Scientific Computing Center
US Department of Energy
US-Israel Binational Science Foundation
Ullmann Family Foundation
Weizmann Institute's Sustainability and Energy Research Initiative
National Science Foundation1911592, 1719353
U.S. Department of Energy
American Committee for the Weizmann Institute of Science
Dow Chemical Company
Office of Science
Argonne National Laboratory
Northwestern University


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