Metal Halide Perovskite and Perovskite-like Materials through the Lens of Ultra-wideline ^35/37Cl NMR Spectroscopy

Abstract

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.

Triangulating Dopant-Level Mn(II) Insertion in a Cs2NaBiCl6Double Perovskite Using Magnetic Resonance Spectroscopy

“…For C Q ( 209 Bi) = 40.0 MHz, a relatively sharp peak is predicted to appear at a higher frequency, ∼(9 MHz, 9 MHz), as shown in Figure S15c. Although a broader peak is seen near this region, that signal appears to arise from interactions with 35 Cl, based on the fits shown in Figure 6e. If signals from 35 Cl and 209 Bi overlap, a much more intense signal would be expected in the region between (9 MHz, 9 MHz) and (10 MHz, 10 MHz).…”

“…For example, solid-state nuclear magnetic resonance (NMR) − and electron paramagnetic resonance (EPR) ,− spectroscopies are powerful methods that can discern short-(<5 Å) to medium-(<10 Å (NMR), <50 Å (EPR)) range structures, and thus are complementary characterization methods for materials analyses (Figure d). , The chemical and magnetic environments about the A, B′, B″, and X sites in the double perovskite considered here can be assessed through its NMR-active quadrupolar nuclei (Table S1). In practice, the 133 Cs nucleus behaves like pseudo I = 1/2 nuclear spin because of its small quadrupole moment, , and thus the local chemical structures about the A-site for halide perovskites have been extensively characterized using 133 Cs NMR spectroscopy. ,− Similarly, 23 Na NMR spectroscopy has been routinely applied to decode the chemical structures of various crystalline and amorphous solids, and the sensitivity of 35 Cl to local structure , has prompted some 35 Cl NMR investigations of perovskites, , but there is limited literature on 209 Bi NMR spectroscopy due to its large quadrupole moment and sizable quadrupolar interactions. ,, Due to the inherent insensitivity of NMR spectroscopy, some investigators have turned to high-field dynamic nuclear polarization (DNP) NMR spectroscopy − to enhance the observed NMR signals through the transfer of polarization from unpaired electrons, allowing the acquisition of NMR spectra for challenging NMR nuclei. ,, For the materials considered here, the paramagnetic Mn 2+ ion provides an endogenous source of unpaired electrons to achieve direct polarization transfer to nearby nuclei in the perovskite structure and may inform on how this transition metal engages the bulk material. This novel application of endogenous DNP NMR spectroscopy allows the assessment of the influence of paramagnetic nuclei on the neighboring chemical environments, working in tandem with EPR as a direct probe on nearby nuclear spins.…”

“…HYSCORE spectrum of the 0.23% Mn(II)-doped Cs 2 NaBiCl 6 sample, acquired at 1189.6 mT at 30 K (a). The full simulated spectrum (b) with signals arising from interactions with133 Cs in blue,23 Na in red, and the two35 Cl sites in green and purple. The individual simulated sites for 133 Cs,23 Na, and the two35 Cl sites (c−f), respectively.…”

“…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.…”

Chlorination of Hydrogenated Silicon Nanosheets Revealed by Solid-State Nuclear Magnetic Resonance Spectroscopy

“…35 Cl has a nuclear spin of 3/2, a natural isotopic abundance of 75%, and a gyromagnetic ratio close to that of 15 N, making it appealing for solid-state NMR experiments. However, acquisition of 35 Cl solid-state NMR spectra is often challenging because quadrupolar signal broadening results in central-transition (CT) NMR spectra that are typically megahertz broad, especially for terminal, covalently bonded Cl atoms. − 35 Cl solid-state NMR spectra are generally obtained under static conditions with Car–Purcell–Meiboom–Gill (CPMG) and frequency-stepped acquisition techniques. − Unfortunately, static 35 Cl solid-state NMR experiments often suffer from poor sensitivity and resolution. Here, we show that 1 H­{ 35 Cl} and 29 Si­{ 35 Cl} Resonance-Echo Saturation-Pulse DOuble-Resonance (RESPDOR) NMR experiments can be used to directly confirm the presence of chlorinated Si atoms in Si-NS.…”