Electron/exciton–phonon coupling in FAPbBr3 single crystals

Electron-phonon interactions have significant influences on the photoluminescent (PL) emissions and carrier dynamics of the hybrid perovskite CH(NH 2 ) 2 PbBr 3 (FAPbBr 3 ). Here, we investigate these interactions in a FAPbBr 3 single crystal using femtosecond laser excitation. Temperature-dependent PL spectra (80-310 K) are analyzed to separate the contributions of acoustic and longitudinal optical (LO) phonons to the PL linewidth. We find that LO phonons dominate the PL linewidth broadening above 80 K. Free and defect-bound exciton binding energies are examined via Arrhenius analysis, revealing that defected-bound excitons have lower binding energy than free excitons. Additionally, temperature-dependent X-ray diffraction and PL measurements reveal a tetragonal-to-orthorhombic phase transition near 180 K and a freezing behavior of the FA + cations around 150 K. In contrast to the octahedral tilting transition, the freezing of FA + rotations induces a remarkable shift in PL peak energy and alters exciton-phonon coupling. These findings clarify the intrinsic electron/exciton-phonon interactions in FAPbBr 3 single crystals and provide insight for optimizing their optoelectronic performance.