Structural dynamics of CH(3)NH(3)(+) and PbBr(3)(−) in tetragonal and cubic phases of CH(3)NH(3)PbBr(3) hybrid perovskite by nuclear magnetic resonance

Understanding the structural dynamics of lead-halide perovskites is essential for their advanced use as photovoltaics. Here, the structural dynamics of the CH(3)NH(3) cation and PbBr(6) octahedra in the perovskite CH(3)NH(3)PbBr(3) were studied via nuclear magnetic resonance (NMR) to determine the mechanism of the transition from the tetragonal to cubic phase. The chemical shifts were obtained by (1)H, (13)C, and (207)Pb magic angle spinning NMR and (14)N static NMR. The chemical shifts of the (1)H nuclei in CH(3) and NH(3) remained constant with increasing temperature, whereas those of the (13)C and (207)Pb nuclei varied near the phase transition temperature (T(C) = 236 K), indicating that the structural environments of (13)C and (207)Pb change near T(C). The spin–lattice relaxation time T(1ρ) values for (1)H, (13)C, and (207)Pb nuclei increased with increasing temperature and did not exhibit an abrupt change near T(C). In addition, the two lines in the (14)N NMR spectra superposed into one line near T(C), indicating the occurrence of a phase transition to a cubic phase with higher symmetry than tetragonal. Consequently, the main factor causing the phase transition from the tetragonal to cubic phase near T(C) is a change in the surroundings of the (207)Pb nuclei in the PbBr(6) octahedra and of the C–N groups in the CH(3)NH(3) cations.