Cation Dynamics and Structural Stabilization in Formamidinium Lead Iodide Perovskites

26 February 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The vibrational dynamics of pure and methylammonium-doped formamidinium lead iodide perovskites
(FAPbI3) has been investigated by high-resolution neutron spectroscopy. For the ?first time, we provide an exhaustive and accurate analysis of the cation vibrations and underlying local structure around the organic moiety in these materials using ?first-principles electronic-structure
calculations validated by the neutron data. Inelastic Neutron Scattering experiments on FAPbI3
provide direct evidence of the formation of a low-temperature orientational glass, unveiling the
physico-chemical origin of phase metastability in the tetragonal structure. Further analysis of these
data provides a suitable starting point to understand and explore the stabilization of the perovskite
framework via doping with small amounts of organic cations. In particular, we ?find that hydrogen
bonds in FAPbI3 are strengthened in a synergistic manner as a result of cage deformation induced
by the dynamics of the neighbouring methylammonium cations.


Organometal Halide Perovskites
Inelastic Neutron Scattering Spectroscopy
Terahertz Spectroscopy Exploring Dynamics
Formamidinium Lead Iodide Perovskites
Methylammonium Lead Iodide
Ab Initio Modelling
Solid-State DFT
VdW Interactions
Dispersion Corrections
Harmonic Lattice Dynamics
Lattice Dynamics
Phonon Calculations
Hydrogen Dynamics
Phase Transitions
Glass Formation
Photovoltaic Materials
Perovskite Solar Cells
Ab Initio Molecular Dynamics


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