From soft harmonic phonons to fast relaxational dynamics in CH₃NH₃PbBr₃

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DOIResolve DOI: https://doi.org/10.1103/PhysRevB.92.100303
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  1. National Research Council Canada. Security and Disruptive Technologies
FormatText
TypeArticle
Journal titlePhysical Review B
ISSN1098-0121
1550-235X
Volume92
Issue10
Pages100303-1–100303-5
Abstract
The lead-halide perovskites, including CH₃NH₃PbBr₃, are components in cost effective, highly efficient photovoltaics, where the interactions of the molecular cations with the inorganic framework are suggested to influence the electronic and ferroelectric properties. CH₃NH₃PbBr₃ undergoes a series of structural transitions associated with orientational order of the CH₃NH₃ (methylammonium) molecular cation and tilting of the PbBr₃ host framework. We apply high-resolution neutron scattering to study the soft harmonic phonons associated with these transitions, and find a strong coupling between the PbBr₃ framework and the quasistatic CH₃NH₃ dynamics at low energy transfers. At higher energy transfers, we observe a PbBr₆ octahedra soft mode driving a transition at 150 K from bound molecular excitations at low temperatures to relatively fast relaxational excitations that extend up to ∼50–100 meV. We suggest that these temporally overdamped dynamics enables possible indirect band gap processes in these materials that are related to the enhanced photovoltaic properties.
Publication date
PublisherAPS (American Physical Society)
LanguageEnglish
Peer reviewedYes
NPARC number23001091
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Record created2016-12-12
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