2D RUDDLESDEN-POPPER PEROVSKITES BA2MAn-1PbnI3n+1 AS STUDIED BY SOLID-STATE NMR

Lead Halide Perovskites are semiconductors used in different optoelectronic devices (e.g. sensitizers for solar cells, photodetectors, LEDs). 2D Ruddlesden-Popper (RP) perovskites (L2An-1BnX3n+1) are layered materials made by perovskite layers separated by large monoammonium cations L+, whose ammonium head is oriented towards the perovskite layers. The perovskite sheets have the usual perovskite structure of corner-sharing BX6 octahedra and A+ cations in the cavities. The number of planes of BX6 octahedra in each perovskite sheet is specified by n. Solid-State NMR stands out as characterization technique of Lead Halide Perovskites thanks to its ability to study ion dynamics, compositional variations and ion incorporation, chemical interactions and degradation mechanisms [1]. In the present study, we investigated the series of 2D RP perovskites BA2MAn-1PbnI3n+1 for n=1, 2 and 3 and their 3D analogous MAPbI3 (Figure 1) by Solid-State NMR. 207Pb, 1H, and 13C spectra recorded under Magic Angle Spinning and/or static conditions allowed the structural characterization of these systems; the obtained results have been discussed also by comparison with very recent literature [2]. In addition, the spin-lattice relaxation times T1 of 207Pb were measured to evaluate if different Pb sites show distinct relaxation behaviors. Finally, the spatial proximity between the organic cations BA and MA was probed by 2D PMLG Spin Diffusion experiments. Fig. 1. Schematic structure of 2D RP perovskites BA2MAn-1PbnI3n+1 for n=1, 2, 3, 4, and of the corresponding 3D perovskites MAPbI3. Here BA is butylammonium and MA is methylammonium. References [1] W. M. J. Franssen, A. P. M. Kentgens, Solid State Nucl. Magn. Reson. 2019, 100, 36-44. [2] J. Lee, W. Lee, K. Kang, T. Lee, S. K. Lee, Chem. Mater. 2021, 33, 370-377.