DOI: https://doi.org/10.29363/nanoge.hpatom.2022.004
Publication date: 30th October 2021
Hybrid metal halide perovskites are a novel class of semiconductor that require anharmonic structural and electronic calculations to explain the contradiction of a soft, defective lattice and remarkable optoelectronic performance of fabricated devices. [1,2] One consequence of the anharmonicity is octahedral tilting instabilities driving structural phase transitions. [3,4] These instabilities have led to predictions of dynamic domains of the tetragonal phase persisting within the high temperature cubic phase. [5] In this work, we utilize neutron and X-ray single crystal diffuse scattering to probe structural correlations hidden within the cubic phases of CH3NH3PbI3 and CH3NH3PbBr3. Energy discrimination afforded by the CORELLI spectrometer allows us to distinguish between inelastic scattering from phonons and static scattering from defects. We find rods of diffuse intensity extending along the Brillouin zone edge, intersecting at the R-points, which imply the cubic phase contains dynamic 2D regions of tilted PbX6 octahedra. We reproduce the diffuse scattering with MD calculations [6] and, in comparison with the neutron and X-ray diffuse scattering data, find that the orientation of organic cations is similarly correlated. Inelastic neutron scattering suggests these regions are long-lived, and we use the MD results to visualize these regions. Finally, we discuss the impact of this 2D network on optoelectronic properties.
This work was supported by CHOISE, an Energy Frontier Research Center funded by the U.S. Department of Energy Office of Basic Energy Sciences.
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