Short-range ion dynamics in methylammonium lead iodide by multinuclear solid state NMR and¹²⁷I NQR

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.

Doping and phase segregation in Mn2+- and Co2+-doped lead halide perovskites from133Cs and1H NMR relaxation enhancement

“…In the case of lead halide perovskites, this translates to extremely wide spectra which are impractical to acquire. 42,66,67 In addition, owing to the efficient quadrupolar relaxation, the corresponding longitudinal relaxation times are typically below 1 s, leaving little room for PREs to operate. [68][69][70] On the other hand, 19 F is a spin 1/2 with relatively long longitudinal relaxation times which makes it perfectly suited for the task of detecting PREs.…”

Lead-Halide Scalar Couplings in 207Pb NMR of APbX3 Perovskites (A = Cs, Methylammonium, Formamidinium; X = Cl, Br, I)

“…For MAPbX 3 , Wasylishen reported in 1985 on the dynamics of the organic cation and phase transitions using 2 H and 14 N NMR 26 . Most of the subsequent studies concentrated on 1 H, 2 H, 13 C, 14 N, 15 N nuclei to characterize and understand the dynamics and mobility of the organic cations (MA or FA) [22][23][24][25][26][27][43][44][45] . Only a few studies concerned 133 Cs NMR 29,31,[46][47][48][49][50][51] .…”

“…As to the halides, NMR spectroscopy had thus far been hampered by their large quadrupolar constants, leading to massively broadened signals and distorted line shapes 52,53 . For this reason, halides are more commonly assessed with nuclear quadrupole resonance (NQR) spectroscopy 25,44,[54][55][56][57][58] . Sharma et al 59 (1987) and the dissertation by Ullmann (1998) 60 are, to our knowledge, the first reports on 207 Pb NMR of lead-halide perovskites.…”

Determination of the Full 207Pb Chemical Shift Tensor of Anglesite, PbSO4, and Correlation of the Isotropic Shift to Lead–Oxygen Distance in Natural Minerals

“…As a 'heavy' nuclide, lead has a very large chemical shift range, extending over approximately 10,000 ppm, which makes 207 Pb a sensitive reporter of the local electronic state [22][23][24]. Recently, there has been intensified interest in 207 Pb-NMR to characterise organolead halide perovskites, which have been identified as promising materials in photovoltaics [25][26][27]. Frequently, 207 Pb NMR studies are augmented with quantum-mechanical calculations of chemical shifts [16,17,24,27].…”

“…Recently, there has been intensified interest in 207 Pb-NMR to characterise organolead halide perovskites, which have been identified as promising materials in photovoltaics [25][26][27]. Frequently, 207 Pb NMR studies are augmented with quantum-mechanical calculations of chemical shifts [16,17,24,27]. While, in general, such calculations have matured to the point where their results are very useful for comparison with experimental data [28], calculations for heavy nuclei are still problematic, even when relativistic effects for the electrons are included [29].…”