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Title: Anharmonicity and Octahedral Tilting in Hybrid Vacancy-Ordered Double Perovskites

The advantageous performance of hybrid organic-inorganic perovskite halide semiconduc- tors 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 (CH 3 NH 3 + ) and formamidinium (CH(NH 2 ) 2 + ) affect physical properties such as light absorption and charge transport. Here, to probe the influence of organic- inorganic coupling on charge transport, we have prepared the series of vacancy-ordered double perovskite derivatives, A 2SnI 6, where A = Cs +, CH 3NH 3 +, and CH(NH 2) 2 +. Despite nearly identical cubic structures by powder X-ray diffraction, replacement of Cs + with CH 3NH 3 + or CH(NH 2) 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 [SnI 6] octahedral units. The presence of soft, anharmonic latticemore » 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. Finally, 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.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [2] ;  [1]
  1. Colorado State Univ., Fort Collins, CO (United States). Dept. of Chemistry
  2. Univ. College London, London (United Kingdom). Dept. of Chemistry; Univ. College London, London (United Kingdom). Thomas Young Centre; Science and Technology Facilities Council (STFC), Harwell Campus, Oxford (United Kingdom). Diamond Light Source, Ltd.
Publication Date:
Grant/Contract Number:
SC0016083; AC02-06CH11357
Type:
Published Article
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Name: Chemistry of Materials; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Research Org:
Colorado State Univ., Fort Collins, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Contributing Orgs:
Advanced Photon Source; ARCHER UK National Supercomputing Service; EPSRC Centre for Doctoral Training in Molecular Modeling and Materials Science
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1414778
Alternate Identifier(s):
OSTI ID: 1410796