A combined single crystal neutron/X-ray diffraction and solid-state nuclear magnetic resonance study of the hybrid perovskites CH₃NH₃PbX₃ (X = I, Br and Cl)

The ¹H and ¹³C NMR spectra in methylammonium lead halide perovskites, CH₃NH₃PbX₃ (X = I, Br and Cl) show that the CH₃NH₃⁺ units undergo dynamic reorientation, as the organic component tumbles in the perovskite cage. In addition, the differences in the anomalously long relaxation times of the protons associated with the CH₃ and not the NH₃ groups indicate that only the amine end of the CH₃NH₃⁺ group is interacting with the inorganic network. Using this information, we have refined some single crystal X-ray and neutron diffraction data to probe their unusual structures in more detail. Furthermore, impedance spectroscopy has been used to monitor the high-temperature phase transition of CH₃NH₃PbI₃, which confirms a significant increase in conductivity, when it is in its high temperature and higher symmetry structural regime. The optical band-gaps of each halide perovskite were determined using UV-visible spectroscopy and are consistent with previous reports.