Atomic-scale microstructure of halide perovskites
Mathias Uller Rothmann a b, Judy Kim b c d, Juliane Borchert a, Kilian Lohmann a, Colum O'Leary b, Alex Sheader b, Laura Clark b, Henry Snaith a, Michael Johnston a, Peter Nellist b, Laura Herz a
a Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, United Kingdom
b Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH
c ePSIC, Diamond Light Source
d Rosalind Franklin Institute
Proceedings of Atomic-level characterization of hybrid perovskites (HPATOM)
Online, Spain, 2021 January 26th - 28th
Organizers: Dominik Kubicki and Amita Ummadisingu
Oral, Mathias Uller Rothmann, presentation 008
Publication date: 14th January 2021

Studying the crystallographic properties of these photoactive hybrid perovskites by transmission electron microscopy (TEM) has proved particularly challenging due to the large electron energies typically employed in these studies.[1] In particular, the very close structural relationship between a number of crystallographic orientations of the pristine perovskite and lead iodide has resulted in severe ambiguity in the interpretation of EM-derived information, severely impeding the advance of atomic resolution understanding of the materials.

Here, we successfully image the archetypal CH(NH2)2PbI3 (FAPbI3) and CH3NH3PbI3 (MAPbI3­) hybrid perovskites in their thin-film form with atomic resolution using a carefully developed protocol of low-dose STEM.[2] Our images enable a wide range previously undescribed phenomena to be observed, including a remarkably highly ordered atomic arrangement of sharp grain boundaries and coherent perovskite/PbI2 interfaces, with a striking absence of long-range disorder in the crystal. These findings explain why inter-grain interfaces are not necessarily detrimental to perovskite solar cell performance, in contrast to what is commonly observed for other polycrystalline semiconductors. Additionally, we observe aligned point defects and dislocations that we identify to be climb-dissociated, and confirm the room-temperature phase of CH(NH2)2PbI3 to be cubic. We further demonstrate that degradation of the perovskite under electron irradiation leads to an initial loss of CH(NH2)2+ ions, leaving behind a partially unoccupied, but structurally intact, perovskite lattice, explaining the unusual regenerative properties of partly degraded perovskite films. Our findings thus provide a significant shift in our atomic-level understanding of this technologically important class of lead-halide perovskites.

 

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