Solid-State NMR and NQR Spectroscopy of Lead-Halide Perovskite Materials

Abstract

Two-and three-dimensional lead-halide perovskite (LHP) materials are novel semiconductors that have generated broad interest owing to their outstanding optical and electronic properties. Characterization and understanding of their atomic structure and structure−property relationships are often nontrivial as a result of the vast structural and compositional tunability of LHPs as well as the enhanced structure dynamics as compared with oxide perovskites or more conventional semiconductors. Nuclear magnetic resonance (NMR) spectroscopy contributes to this thrust through its unique capability of sampling chemical bonding element-specifically ( 1/2 H, 13 C, 14/15 N, 35/37 Cl, 39 K, 79/81 Br, 87 Rb, 127 I, 133 Cs, and 207 Pb nuclei) and locally and shedding light onto the connectivity, geometry, topology, and dynamics of bonding. NMR can therefore readily observe phase transitions, evaluate phase purity and compositional and structural disorder, and probe molecular dynamics and ionic motion in diverse forms of LHPs, in which they can be used practically, ranging from bulk single crystals (e.g., in gamma and X-ray detectors) to polycrystalline films (e.g., in photovoltaics, photodetectors, and light-emitting diodes) and colloidal nanocrystals (e.g., in liquid crystal displays and future quantum light sources). Herein we also outline the immense practical potential of nuclear quadrupolar resonance (NQR) spectroscopy for characterizing LHPs, owing to the strong quadrupole moments, good sensitivity, and high natural abundance of several halide nuclei ( 79/81 Br and 127 I) combined with the enhanced electric field gradients around these nuclei existing in LHPs as well as the instrumental simplicity. Strong quadrupole interactions, on one side, make 79/81 Br and 127 I NMR rather impractical but turn NQR into a high-resolution probe of the local structure around halide ions.

Mixed Conductivity of Hybrid Halide Perovskites: Emerging Opportunities and Challenges

“…For this purpose, further development of analytical methods is needed, in particular those that can directly relate the structural and optoelectronic properties, while monitoring the changes during operation. Methods based on solid-state NMR spectroscopy (Piveteau et al, 2020) and photoluminescence mapping (Doherty et al, 2020) that can be related to the structure at the nanoscale are particularly promising. These studies should be complemented with temperature-dependent analysis as well as establishing appropriate models for the analysis of optoelectronic properties to further deepen the fundamental understanding of the coupling between electronic and ionic processes.…”

DFT Simulations as Valuable Tool to Support NMR Characterization of Halide Perovskites: the Case of Pure and Mixed Halide Perovskites

“…Nuclear Magnetic Resonance (NMR) is rapidly becoming a standard tool for the structural characterization of halide perovskite materials. Indeed, either stand alone or in combination with other characterization tools, this spectroscopic technique has recently demonstrated its strength by unveiling the detailed material structure of various halide perovskite systems, as in the case of 3D mixed halide compounds, [12,29] 3D mixed A‐cation systems, [30–34] 2D layered perovskites [37,38] and quantum dots [39,43] . Interpretation of NMR measurements is however inherently complicated by the complexity of the measured NMR features, often arising from the convolution of many structured signals.…”

“…Recent studies include the characterization of A‐mixed halide perovskites, [30–34] demonstration of halide (iodine) diffusion in working devices, [35] characterization of thermal and water‐induced structural decomposition, [36] and characterization of dimensionally confined perovskite systems, as layered 2D systems, [37,38] nanoparticles, [39,40] and deficient‐halide perovskites [19,41] . A remarkable overview of results related to NMR characterization of metal halide perovskites can be found in Refs [42,43] …”

Guidelines for the characterization of metal halide nanocrystals

“…We mention only a few examples here. NMR spectroscopy, with all of its ancillary techniques, will play an increasing role in elucidating not only the ligand shell but also the structure and composition of the inorganic core [95]. Solidstate NMR has been already used to identify the position of dopants in NCs [96] and to elucidate the surface termination of halide perovskite NCs [97].…”