Illumination-Induced Changes in Methylammonium Lead Bromine Perovskites. An In Situ²H NMR Study

Methylammonium lead bromine (MAPbBr₃) perovskites have shown great potential for a wide variety of optoelectronic applications. However, the structural and dynamic properties of MAPbBr₃ have been typically probed in the absence of illumination. The present study addresses this issue by applying in situ solid-state ²H nuclear magnetic resonance (NMR) spectroscopy to investigate the rotational dynamics and orientations of MA cations in the different phase structures of MAPbBr₃ in detail. The results indicate that the orientations of the MA cations in MAPbBr₃ are widely distributed and that illumination induces changes in the rotational dynamics of the MA cations, while the apparent distribution of their orientations remains nearly unchanged. These results are expected to provide a useful viewpoint for understanding the molecular factors affecting the optoelectronic properties of MAPbBr₃.