Understanding how atoms move inside materials is crucial for improving their performance. This project focused on the local structure and movement of organic cations in metal halide perovskites (MHPs), a class of materials with strong potential for solar cells and light‑emitting devices.
Neutron scattering techniques, quasielastic and inelastic neutron scattering (QENS and INS), played a key role in this work. These methods can directly track the position and motion of light elements such as hydrogen, providing unique insight into molecular dynamics that are difficult to capture with other techniques.
By examining both low‑dimensional and three‑dimensional systems, including MBAMnCl₃·2H₂O, layered APbBr₄ compounds, (1,3‑XDA)₂PbBr₆, and lead‑free perovskites such as FASnX₃ and FA₂SnI₆, the study showed how molecular motion depends strongly on structure, composition, and temperature. Across these materials, the dynamics were found to evolve from simple local rotations to more complex, collective motion involving entire cations.
Importantly, the results connect these microscopic motions to material performance. Slower molecular dynamics were linked to reduced stability of photoluminescence. In addition, light‑induced experiments on MAPbBr₃ demonstrated that illumination directly changes both the structure and the molecular motion, showing that cation dynamics play an active role in converting light into energy.
Overall, this work provides a clearer and more integrated picture of how structure and dynamics shape the behaviour of perovskite materials, helping guide the design of more efficient and stable optoelectronic technologies.