Structural dynamics of CH₃NH₃⁺ and PbBr₃^- in tetragonal and cubic phases of CH₃NH₃PbBr₃ hybrid perovskite by nuclear magnetic resonance.

ABSTRACT: Understanding the structural dynamics of lead-halide perovskites is essential for their advanced use as photovoltaics. Here, the structural dynamics of the CH₃NH₃ cation and PbBr₆ octahedra in the perovskite CH₃NH₃PbBr₃ 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 ¹H, ¹³C, and ²⁰⁷Pb magic angle spinning NMR and ¹⁴N static NMR. The chemical shifts of the ¹H nuclei in CH₃ and NH₃ remained constant with increasing temperature, whereas those of the ¹³C and ²⁰⁷Pb nuclei varied near the phase transition temperature (T_C?=?236 K), indicating that the structural environments of ¹³C and ²⁰⁷Pb change near T_C. The spin-lattice relaxation time T_1? values for ¹H, ¹³C, and ²⁰⁷Pb nuclei increased with increasing temperature and did not exhibit an abrupt change near T_C. In addition, the two lines in the ¹⁴N 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 ²⁰⁷Pb nuclei in the PbBr₆ octahedra and of the C-N groups in the CH₃NH₃ cations.

SUBMITTER: Lim AR 

PROVIDER: S-EPMC7403148 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature