Multinuclear NMR as a tool for studying local order and dynamics in CH3NH3PbX3 (X = Cl, Br, I) hybrid perovskites

We report on Pb-207, Br-79, N-14, H-1, C-13 and H-2 NMR experiments for studying the local order and dynamics in hybrid perovskite lattices. Pb-207 NMR experiments conducted at room temperature on a series of MAPbX(3) compounds (MA = CH3NH3+; X = Cl, Br and I) showed that the isotropic Pb-207 NMR shift is strongly dependent on the nature of the halogen ions. Therefore Pb-207 NMR appears to be a very promising tool for the characterisation of local order in mixed halogen hybrid perovskites. Pb-207 NMR on MAPbBr(2)I served as a proof of concept. Proton, C-13 and N-14 NMR experiments confirmed the results previously reported in the literature. Low temperature deuterium NMR measurements, down to 25 K, were carried out to investigate the structural phase transitions of MAPbBr(3). Spectral lineshapes allow following the successive phase transitions of MAPbBr(3). Finally, quadrupolar NMR lineshapes recorded in the orthorhombic phase were compared with simulated spectra, using DFT calculated electric field gradients (EFG). Computed data do not take into account any temperature effect. Thus, the discrepancy between the calculated and experimental EFG evidences the fact that MA cations are still subject to significant dynamics, even at 25 K.