Elucidating the Methylammonium (MA) Conformation in MAPbBr₃ Perovskite with Application in Solar Cells

Hybrid organic-inorganic perovskites, MAPbX₃ (X = halogen), containing methylammonium (MA: CH₃-NH₃⁺) in the large voids conformed by the PbX₆ octahedral network, are the active absorption materials in the new generation of solar cells. CH₃NH₃PbBr₃ is a promising member with a large band gap that gives rise to a high open circuit voltage. A deep knowledge of the crystal structure and, in particular, the MA conformation inside the perovskite cage across the phase transitions undergone below room temperature, seems essential to establish structure-property correlations that may drive to further improvements. The presence of protons requires the use of neutrons, combined with synchrotron XRD data that help to depict subtle symmetry changes undergone upon cooling. We present a consistent picture of the structural features of this fascinating material, in complement with photocurrent measurements from a photodetector device, demonstrating the potential of MAPbBr₃ in optoelectronics.