title: The dynamics of methylammonium ions in hybrid organic-inorganic perovskite solar cells.
abstract: Methylammonium lead iodide perovskite can make high-efficiency solar cells, which also show an unexplained photocurrent hysteresis dependent on the device-poling history. Here we report quasielastic neutron scattering measurements showing that dipolar CH3NH3(+) ions reorientate between the faces, corners or edges of the pseudo-cubic lattice cages in CH3NH3PbI3 crystals with a room temperature residence time of ∼14 ps. Free rotation, π-flips and ionic diffusion are ruled out within a 1-200-ps time window. Monte Carlo simulations of interacting CH3NH3(+) dipoles realigning within a 3D lattice suggest that the scattering measurements may be explained by the stabilization of CH3NH3(+) in either antiferroelectric or ferroelectric domains. Collective realignment of CH3NH3(+) to screen a device's built-in potential could reduce photovoltaic performance. However, we estimate the timescale for a domain wall to traverse a typical device to be ∼0.1-1 ms, faster than most observed hysteresis.
authors.affiliation: Department of Physics, Imperial College London, London SW7 2AZ, UK.
authors.forename: Aurelien M A
authors.initials: AM
authors.lastname: Leguy
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
authors.forename: Jarvist Moore
authors.identifier: 0000000319384430
authors.initials: JM
authors.lastname: Frost
authors.affiliation: Department of Physics, Imperial College London, London SW7 2AZ, UK.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: McMahon
authors.affiliation: Rutherford Appleton Laboratory, Harwell, Didcot OX11 0QX, UK.
authors.forename: Victoria Garcia
authors.initials: VG
authors.lastname: Sakai
authors.affiliation: Rutherford Appleton Laboratory, Harwell, Didcot OX11 0QX, UK.
authors.forename: W
authors.initials: W
authors.lastname: Kochelmann
authors.affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ, UK.
authors.forename: ChunHung
authors.initials: C
authors.lastname: Law
authors.affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ, UK.
authors.forename: Xiaoe
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK.
authors.forename: Fabrizia
authors.initials: F
authors.lastname: Foglia
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
authors.forename: Aron
authors.identifier: 0000000154607033
authors.initials: A
authors.lastname: Walsh
authors.affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ, UK.
authors.forename: Brian C
authors.initials: BC
authors.lastname: O'Regan
authors.affiliation: Department of Physics, Imperial College London, London SW7 2AZ, UK.
authors.forename: Jenny
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK.
authors.forename: João T
authors.identifier: 000000022590225X
authors.initials: JT
authors.lastname: Cabral
authors.affiliation: Department of Physics, Imperial College London, London SW7 2AZ, UK.
authors.forename: Piers R F
authors.initials: PR
authors.lastname: Barnes