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Anharmonicity and octahedral tilting in hybrid vacancy-ordered double perovskites

DOI: 10.1021/acs.chemmater.7b04516 DOI Help

Authors: Annalise E. Maughan (Colorado State University) , Alex M. Ganose (Colorado State University) , Andrew M. Candia (Colorado State University) , Juliette T. Granger (Colorado State University) , David O. Scanlon (University College London; Diamond Light Source) , James R. Neilson (Colorado State University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: November 2017

Abstract: The advantageous performance of hybrid organic-inorganic perovskite halide semiconductors in optoelectronic applications motivates studies of their fundamental crystal-chemistry. In particular, recent studies have sought to understand how dipolar, dynamic, and organic cations, such as methylammonium (CH3NH3+) and formamidinium (CH(NH2)2+) affect physical properties such as light absorption and charge transport. To probe the influence of organic-inorganic coupling on charge transport, we have prepared the series of vacancy-ordered double perovskite derivatives, A2SnI6, where A = Cs+, CH3NH3+, and CH(NH2)2+. Despite nearly identical cubic structures by powder X-ray diffraction, replacement of Cs+ with CH3NH3+ or CH(NH2)2+ reduces conductivity through a reduction in both carrier concentration and carrier mobility. We attribute the trends in electronic behavior to anharmonic lattice dynamics from the formation of hydrogen bonds that yield coupled organic-inorganic dynamics. This anharmonicity manifests as asymmetry of the inter-octahedral I−I pair correlations in the X-ray pair distribution function of the hybrid compounds, which can be modeled by large atomistic ensembles with random rotations of rigid [SnI6] octahedral units. The presence of soft, anharmonic lattice dynamics holds implications for electron-phonon interactions, as supported by calculation of electron-phonon coupling strength that indicates the formation of more tightly-bound polarons and reduced electron mobilities with increasing cation size. By exploiting the relatively decoupled nature of the octahedral units in these defect-ordered perovskite variants, we can interrogate the impact of organic-inorganic coupling and lattice anharmonicity on the charge transport behavior of hybrid perovskite halide semiconductors.

Diamond Keywords: Semiconductors

Subject Areas: Chemistry, Materials, Physics

Facility: 11-ID-B at Advanced Photon Source

Added On: 04/12/2017 09:37

Discipline Tags:

Physical Chemistry Materials Science Energy Materials Metallurgy Perovskites Physics Electronics Chemistry

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