Breakdown of the Static Picture of Defect Energetics in Halide Perovskites: the Case of the Br Vacancy in CsPbBr3
Ayala Cohen a, David A. Egger b, Andrew M. Rappe c, Leeor Kronik a
a Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel.
b Institute of Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
c Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104–6323, USA
nanoGe Perovskite Conferences
Proceedings of nanoGe International Conference on Perovskite Solar Cells, Photonics and Optoelectronics (NIPHO19)
International Conference on Perovskite Photonics and Optoelectronics
Jerusalem, Israel, 2019 February 24th - 27th
Organizers: Lioz Etgar and Paul Meredith
Oral, Ayala Cohen, presentation 039
Publication date: 21st November 2018

In this work, we consider the Br vacancy (VBr) in cesium lead bromide (CsPbBr3) as a prototype for the impact of structural dynamics on defect energetics in halide perovskites (HaPs). Using first principles molecular dynamics based on density functional theory, we find that the static picture of defect energetics breaks down; the energy of the VBr level is found to be intrinsically dynamic, oscillating by as much as 1 eV on the ps time scale at room temperature. These significant energy fluctuations are found to be correlated with the distance between the neighboring Pb atoms across the vacancy and with the electrostatic potential at their atomic sites. The unusually strong coupling of structural dynamics and defect energetics bears important implications for both experimental and theoretical analysis of defect characteristics in HaPs. Furthermore, it may hold significant ramifications for carrier transport and defect tolerance in this important class of photovoltaic materials.

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