A Solid-state NMR Study of Dimethylamine Cation-doped MAPbBr3 Perovskite Materials

Abstract

In this paper, 2H nuclear magnetic resonance (NMR) was performed to study the motions of the embedded cations in the cation-doped lead bromide perovskite (MA0.6DMA0.4PbBr3). By selectively deuterating dimethylamine (DMA) and methylammonium (MA) cations, we achieved selective NMR observations of the different embedded cations in the materials. The results show that at low temperatures, both the DMA and MA cations in the material have molecular motions close to the double rotation model. As the temperature increases, the motion freedom of the DMA and MA cations increases, and the motions gradually transform into fast isotropic motions. It was observed that the DMA cations have higher mobility than the MA cations in the same materials at the same temperature, indicating that there is a significant inhomogeneity in the states of cations in the material. Based on the study of the cation motions, the molecular mechanism of the phase transition of the material was discussed.

Keywords

• solid-state 2h nmr
• molecular motion
• selectively probing
• cation-doped perovskite
• dimethylamine cation