With their exceptional optoelectronic features, metal halide perovskites (MHPs) are pushing the next wave of energy-related materials research. Heretofore, most solid-state nuclear magnetic resonance (NMR) investigations have focused on readily accessible nuclei. In contrast, the halogen environments have been avoided due to their challenging quadrupolar nature. Here, we report a rapid 35/37Cl NMR strategy for MHPs, halide double perovskites (HDPs), and perovskite-inspired (PI) materials embracing ultra-wideline acquisition approaches at moderate and ultrahigh magnetic fields. The observed quadrupolar NMR parameters (C Q and η), supported by GIPAW–DFT computations, provide an analytical fingerprint revealing distinct features for chemically unique Cl environments sensitive to ion mixing, dimensionality, cell volume, and Cl coordinating polyhedra. Moreover, we report resolution between two nearly identical and two distinct Cl environments of 3D and 2D Cs-based lead halide perovskites, respectively. These results reveal a strategy for a routine and robust spectroscopic approach to analyze local Cl chemical environments in metal halide perovskites that can be extended broadly to other halogen-containing semiconductors.

Dwindling fossil fuels force humanity to search for new energy production routes. Besides energy generation, its storage is a crucial aspect. One promising approach is to store energy from the sun chemically in strained organic molecules, so-called molecular solar thermal (MOST) systems, which can release the stored energy catalytically. A prototypical MOST system is norbornadiene/quadricyclane (NBD/QC) whose energy release and surface chemistry need to be understood. Besides important key parameters such as molecular weight, endergonic reaction profiles, and sufficient quantum yields, the position of the absorption onset of NBD is crucial to cover preferably a large range of sunlight’s spectrum. For this purpose, one typically derivatizes NBD with electron-donating and/or electron-accepting substituents. To keep the model system simple enough to be investigated with photoemission techniques, we introduced bromine atoms at the 2,3-position of both compounds. We study the adsorption behavior, energy release, and surface chemistry on Ni(111) using high-resolution X-ray photoelectron spectroscopy (HR-XPS), UV photoelectron spectroscopy, and density functional theory calculations. Both Br2-NBD and Br2-QC partially dissociate on the surface at ∼120 K, with Br2-QC being more stable. Several stable adsorption geometries for intact and dissociated species were calculated, and the most stable structures are determined for both molecules. By temperature-programmed HR-XPS, we were able to observe the conversion of Br2-QC to Br2-NBD in situ at 170 K. The decomposition of Br2-NBD starts at 190 K when C–Br bond cleavage occurs and benzene and methylidene are formed. For Br2-QC, the cleavage already occurs at 130 K when cycloreversion to Br2-NBD sets in.

Lead-free metal halide double perovskites are gaining increasing attention for optoelectronic applications. Specifically, doping metal halide double perovskites using transition metals enables broadband tailorability of the optical bandgap for these emerging semiconducting materials. One candidate material is Mn(II)-doped Cs 2 NaBiCl 6 , but the nature of Mn(II) insertion on chemical structure is poorly understood due to low Mn loading. It is critical to determine the atomic-level structure at the site of Mn(II) incorporation in doped perovskites to better understand the structure−property relationships in these materials and thus to advance their applicability to optoelectronic applications. Magnetic resonance spectroscopy is uniquely qualified to address this, and thus a comprehensive three-pronged strategy, involving solid-state nuclear magnetic resonance (NMR), high-field dynamic nuclear polarization (DNP), and electron paramagnetic resonance (EPR) spectroscopies, is used to identify the location of Mn(II) insertion in Cs 2 NaBiCl 6 . Multinuclear ( 23 Na, 35 Cl, 133 Cs, and 209 Bi) one-dimensional (1D) magnetic resonance spectra reveal a low level of Mn(II) incorporation, with select spins affected by paramagnetic relaxation enhancement (PRE) induced by Mn(II) neighbors. EPR measurements confirm the oxidation state, octahedral symmetry, and low doping levels of the Mn(II) centers. Complementary EPR and NMR measurements confirm that the cubic structure is maintained with Mn(II) incorporation at room temperature, but the structure deviates slightly from cubic symmetry at low temperatures (<30 K). HYperfine Sublevel CORrelation (HYSCORE) EPR spectroscopy explores the electron−nuclear correlations of Mn(II) with 23 Na, 133 Cs, and 35 Cl. The absence of 209 Bi correlations suggests that Bi centers are replaced by Mn(II). Endogenous DNP NMR measurements from Mn(II) → 133 Cs (<30 K) reveal that the solid effect is the dominant mechanism for DNP transfer and supports that Mn(II) is homogeneously distributed within the double-perovskite structure.

No abstract

Metal-halide perovskites have both interesting structural characteristics and strong potential for applications in devices such as solar cells and light-emitting diodes. While not true perovskites, A2SnX6 materials are relatives of traditional ABX3 perovskites that commonly adopt the K2PtCl6 structure type. Herein, we use solid-state nuclear magnetic resonance (NMR) spectroscopy to explore the influence of group 1 (alkali metal) and group 17 (halogen) substitutions on octahedral tilting and spin–orbit (SO) coupling in A2SnX6 (A = K+, Rb+; X = Cl–, Br–, or I–) materials. For the monoclinic K2SnBr6 and tetragonal Rb2SnI6 compounds, the impact of static octahedral tilting on A-site environments is evident in the form of chemical shift anisotropy (CSA) and sizeable quadrupole coupling constants (C Qs) for 39K and 87Rb. Ultrahigh-field NMR analysis combined with periodic density functional theory (DFT) calculations enables successful determination of the relative orientation between the electric field gradient (EFG) and CSA tensors for 39K in K2SnBr6. The B-site polyhedral environments are probed throughout the compositional range via 119Sn NMR spectroscopy, demonstrating that the 119Sn chemical shift follows a normal halogen dependence (NHD). Quantum chemical modeling using scalar relativistic and SO DFT on cluster models shows that the NHD is driven by the SO term of the magnetic shielding. Consistent with SO heavy atom effects on NMR chemical shifts, the NHD can be explained in terms of the frontier molecular orbitals and the involvement of Sn and X atomic orbitals in Sn–X bonds. The importance of proper relativistic treatment of heavy atoms is also highlighted by comparing calculations of 119Sn chemical shifts at different levels of theory.