Short-range ion dynamics in methylammonium lead iodide by multinuclear solid state NMR and 127I NQR.

Alessandro Senocrate,Igor Moudrakovski,Joachim Maier

doi:10.1039/c8cp01535j

Abstract

We explore the short-range ion dynamics in methylammonium lead iodide (MAPbI3, the archetypal halide perovskite) by means of solid-state NMR (1H, 13C, 14N, 15N and 207Pb) and Nuclear Quadrupolar Resonance (127I NQR), in combination with molecular dynamics simulations. We focus on the rotational motion of the methylammonium (MA) cation, and on the interaction between MA and the inorganic lattice, since these processes are linked to electronic carrier lifetimes, optical and electronic properties and even structural stability of this promising solar cell material. We show that the motion of the MA cation can be described by a bi-axial rotation, with similar interactions of CH3 and NH3+ groups with the inorganic framework. This motion becomes nearly isotropic above the cubic phase transition, dominating the spin-lattice relaxation of 1H, 13C and 15N through spin-rotational interactions. In addition, we observe strong cross-relaxation between 207Pb and 127I, which fully controls spin-spin and spin-lattice relaxation in 207Pb.

Highlights

The outstanding photo-electrochemical properties of hybrid organic–inorganic halide perovskites have motivated in recent years a massive number of studies on these promising solar cell materials.[1,2,3]
The broadening of 1H NMR signals in a stationary MAPbI3 sample is primarily due to the homonuclear dipole– dipole (DD) interaction between protons in the MA cation
DD interactions in solids can be quantified by the so-called second moment M2 of the spectrum, which can be calculated for 1H in MA based on the geometry of the system (Section 3, Electronic supplementary information (ESI)†)

Summary

Introduction

The outstanding photo-electrochemical properties of hybrid organic–inorganic halide perovskites have motivated in recent years a massive number of studies on these promising solar cell materials.[1,2,3] Even though these compounds were described nearly 40 years ago,[4] the characterization of their properties and application in devices is much more recent.[1,5] Despite the momentous effort already spent in characterizing these materials, a significant portion of the physics and chemistry underlying their properties is still missing.

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Conclusion