Unravelling the atomic-level chemical structure, slow phase conversion or degradation pathways and rapid halogen hopping of cesium tin(ii) halide perovskites using solid-state 119Sn and 133Cs NMR spectroscopy.

Predictions of high thermoelectric performance in RECuZnP2 were verified by elastic, electrical, and thermal measurements. Low thermal conductivities result from strong anharmonicity, with electron transport limited by polar optical phonons.

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.

Mixed Sn–Pb halide perovskites are more stable at ambient conditions and can be tuned to give narrower band gaps than the all-Pb-containing counterparts (APbX3) used as photovoltaic materials. In the series CsSn x Pb1–x Br3, the crystal structure evolves from orthorhombic (space group Pnma for x = 0–0.8) to cubic (space group Pm m for x = 1), and the band gap decreases for Sn-richer compositions. It previously was unclear how the physical properties are related to structural changes entailed by the Sn–Pb mixing because the short- versus long-range arrangements have not been well characterized. Solid-state NMR spectroscopy of several NMR-active nuclei (119Sn, 133Cs, and 207Pb) supports the occurrence of complete disorder, with PbBr6 and SnBr6 octahedra distributed in random arrangements throughout the entire structure with no evidence for phase segregation. Compounds prepared by solvent-assisted vs solvent-free routes are compared and show differences in their degree of crystallinity and optical absorption properties.