Short-Range Methylammonium Dynamics in Methylammonium Lead Iodide
Alessandro Senocrate a b, Igor Moudrakovski a, Joachim Maier a
a Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569, Stuttgart
b École Polytechnique Fédérale de Lausanne EPFL, CH
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Alessandro Senocrate, 192
Publication date: 11th February 2019

The short-range dynamics involving the organic cation in hybrid halide perovskites has been related to the extended carrier lifetimes of these systems.[1,2] Furthermore, the interaction between the organic cations and the inorganic framework through hydrogen bonding has been suggested to contribute to structural stability, while also influencing optical and electronic properties.[3-5] In this contribution,[6] we apply extensive 1H, 13C, 14N, 15N solid state NMR analysis to clarify the rotational mode of motion of the organic MA cation in the tetragonal and in the cubic phase of methylammonium lead iodide (MAPbI3). The measurements show that the motion of the MA cation in MAPbI3 can be described by a bi-axial reorientation, which develops into a nearly isotropic rotation above the cubic phase transition (T > 327 K). As such, it becomes a dominant contribution to the spin-lattice relaxation of 1H, 13C and 15N through spin-rotational interactions. Interestingly, we observe no evidence of preferential interactions between the CH3 or NH3+ groups composing the methylammonium cation and the inorganic framework. We complement these studies by including 207Pb NMR and 127I NQR spectroscopic and relaxation data, where we observe strong cross-relaxation between 207Pb and 127I, which fully dominates spin-spin and spin-lattice relaxation in 207Pb.

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