Proceedings of nanoGe Fall Meeting 2021 (NFM21)
Publication date: 23rd September 2021
Cesium lead halide perovskite quantum dots (QDs) have gained significant attention as next-generation optoelectronic materials; however, their properties are highly dependent on their surface chemistry. The surfaces of cuboidal CsPbBr3 QDs have been intensively studied by both theoretical and experimental techniques, but fundamental questions still remain about the atomic termination of the QDs. The binding sites and modes of ligands at the surface remain unproven. Herein, we demonstrate that solid-state NMR spectroscopy allows the unambiguous assignment of organic surface ligands via 1H, 13C, and 31P NMR. Surface-selective 133Cs solid-state NMR spectra show the presence of an additional 133Cs NMR signal with a unique chemical shift that is attributed to Cs atoms terminating the surface of the particle and which are likely coordinated by carboxylate ligands. Dipolar dephasing curves that report on the distance between the surface ammonium ligands and Cs and Pb were recorded using double resonance 1H{133Cs} RESPDOR and 1H{207Pb} S-REDOR experiments. Model QD surface slabs with different possible surface terminations were generated from the CsPbBr3 crystal structure, and theoretical dipolar dephasing curves considering all possible 1H−133Cs/207Pb spin pairs were then calculated. Comparison of the calculated and experimental dephasing curves indicates the particles are CsBr terminated (not PbBr2 terminated) with alkylammonium ligands substituting into some surface Cs sites, consistent with the surfaceselective 133Cs NMR experiments. These results highlight the utility of high-resolution solid-state NMR spectroscopy for studying ligand binding and the surface structure of nanomaterials.
Solid-state NMR experiments and data analysis (Y.C., F.P., and A.J.R.) were supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. A.H.F. is grateful to the U.S. Department of Energy Office of Science Undergraduate Laboratory Internship (SULI) program for the assistantship and opportunity to participate in the SULI program. The Ames Laboratory is operated for the U.S. DOE by Iowa State University under Contract DE-AC02-07CH11358. The quantum dot synthesis and surface chemistry were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award DE-FG02-11ER46826 to R.L.B. S.R.S. acknowledges support from the Graduate Research Fellowship Program of the National Science Foundation. We are grateful to Prof. Javier Vela (ISU and Ames Laboratory) for providing access to the glovebox used to pack rotors and store samples.
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