A Solid-state NMR Study On The Structure And Molecular Motion Of Perovskite Materials

The study of the microscopic crystal structure and molecular motion is helpful to deepen the understanding of the structural mechanism related to the macroscopic properties of perovskite materials.In this work,we will use solid-state NMR,differential scanning calorimetry and other analytical methods to investigate the motions of CH₃NH₃⁺in MAPb Cl₃ perovskite and the structure and material properties induced by ion doping in FAPb I₃ perovskite.1.The molecular motions of methylammonium cations（MA）in the different phase structures of MAPb Cl₃ perovskites,including orthorhombic,tetragonal and cubic phase,were studied by using solid-state ²H NMR.By combination of experimental ²H NMR and pattern simulation,the motion models in the different phase structures of MAPb Cl₃ were established.The NMR results disclose the characteristics of the motions of MA in the different phase structures.The NMR results also shown that the changes of the motions of MA in the different temperatures are not accompanied with the changes in the phase structures.This observations in this work will deepen our understanding of the molecular mechanism of the MAPb Cl₃phase transitions.2.A serials of DMA-containing mixed cation and mixed halide perovskite single crystals with different doping ration,（DMAPb Br₃）_y（FAPb I₃）_1-y,were synthesized by using the inversion crystallization method（ITC）to enable detailed investigation on the structures,properties and long-term stability.The solid-state ²H NMR results reveal the dimethylamine cation（DMA）with larger ion size can indeed be doped into the FAPb I₃ and reorientate rapidly at the A site of the lattice.Our champion compound,（DMAPb Br₃）_0.05（FAPb I₃）_0.95,has better water-oxygen stability and the band gap only change slightly.