Dynamic, polar distortions in perovskite halides: Origins and impacts
Douglas Fabini a, Geneva Laurita b, Ram Seshadri c, Leo Diehl a d, Bettina Lotsch a d
a Max Planck Institute for Solid State Research, Germany
b Bates College
c University of California, Santa Barbara, Santa Barbara, United States
d Ludwig- Maximilians-Universität München (LMU), Königinstraße 10, München, Germany
Proceedings of Atomic-level characterization of hybrid perovskites (HPATOM)
Online, Spain, 2021 January 26th - 28th
Organizers: Dominik Kubicki and Amita Ummadisingu
Invited Speaker, Douglas Fabini, presentation 013
Publication date: 14th January 2021

After roughly a decade of intensive research on lead and tin halide perovskites, a consensus on the underlying mechanisms behind the remarkable performance of these materials as photovoltaics and radiation detectors remains elusive. However, anharmonicity of the lattice dynamics is intimately connected with several of the leading hypotheses. We will show that the chemistry and bonding of Sn(II) and Pb(II) lone pairs give rise to dynamic, polar distortions which are evident in pair distribution function analysis of total scattering experiments. These distortions are symptomatic of anharmonicity, and their amplitudes are chemically tunable over a wide range, with tin and bromine enhancing the effect relative to lead and iodine. The implications for defect screening, polaronic transport, and relativistic spin polarization (Rashba effects) will be addressed, as well as the prospects for rational design of highly polarizable semiconductors and bulk Rashba materials.

If time allows, we will briefly show via spectroscopies (NMR, photoemission, Mossbauer) and microscopy that an oxidized passivation layer forms at the surfaces of photocatalyst candidate, SnTiO3, limiting its utility for several reactions of interest. Ab initio study reveals that the susceptibility to oxidation is driven by a combination of covalent and electrostatic influences. The chemical and structural features which result in this behavior are also present in Sn(II) halide perovskites, suggesting similar challenges may arise at interfaces in (opto)electronic devices comprising these materials.

D.H.F. gratefully acknowledges financial support from the Alexander von Humboldt Foundation.

© Fundació Scito
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