Microscopic (Dis)order and Dynamics of Cations in Mixed FA/MA Lead Halide Perovskites

Author(s)
Helen Grüninger, Menno Bokdam, Nico Leupold, Paul Tinnemans, Ralf Moos, Gilles A. De Wijs, Fabian Panzer, Arno P. M. Kentgens
Abstract

Recent developments in the field of high efficiency perovskite solar cells are based on stabilization of the perovskite crystal structure of FAPbI(3) while preserving its excellent optoelectronic properties. Compositional engineering of, for example, MA or Br mixed into FAPbI(3) results in the desired effects, but detailed knowledge of local structural features, such as local (dis)order or cation interactions of formamidinium (FA) and methylammonium (MA), is still limited. This knowledge is, however, crucial for their further development. Here, we shed light on the microscopic distribution of MA and FA in mixed perovskites MA(1-x)FA(x)PbI(3) and MA(0.15)FA(0.85)PbI(2.55)Br(0.45 )by combining high-resolution double-quantum H-1 solid-state nuclear magnetic resonance (NMR) spectroscopy with state-of-the-art near-first-principles accuracy molecular dynamics (MD) simulations using machine-learning force-fields (MLFFs). We show that on a small local scale, partial MA and FA clustering takes place over the whole MA/FA compositional range. A reasonable driving force for the clustering might be an increase of the dynamical freedom of FA cations in FA-rich regions. While MA(0.15)FA(0.85)PbI(2.55)Br(0.45 )displays similar MA and FA ordering as the MA(1-x)FA(x)PbI(3) systems, the average cation-cation interaction strength increased significantly in this double mixed material, indicating a restriction of the space accessible to the cations or their partial immobilization upon Br- incorporation. Our results shed light on the heterogeneities in cation composition of mixed halide perovskites, helping to exploit their full optoelectronic potential.

Organisation(s)
Computational Materials Physics
External organisation(s)
Radboud University, University of Twente, Universität Bayreuth
Journal
Journal of Physical Chemistry C
Volume
125
Pages
1742-1753
No. of pages
12
ISSN
1932-7447
DOI
https://doi.org/10.1021/acs.jpcc.0c10042
Publication date
01-2021
Peer reviewed
Yes
Austrian Fields of Science 2012
103018 Materials physics, 104026 Spectroscopy
Portal url
https://ucris.univie.ac.at/portal/en/publications/microscopic-disorder-and-dynamics-of-cations-in-mixed-fama-lead-halide-perovskites(3986efc3-e71b-4e88-aee1-92b02a8ec9bb).html