Tuning coherent phonon dynamics in two-dimensional phenylethylammonium lead bromide perovskites

Organic-inorganic layered perovskites are two-dimensional quantum well layers in which the layers of lead halide octahedra are stacked between the organic cation layers. The packing geometry of the soft organic molecules and the stiff ionic crystals induce structural deformation of the inorganic octahedra, generating complex lattice dynamics. Especially, the dielectric confinement and ionic sublattice lead to strong coupling between the photogenerated excitons and the phonons from the polar lattice which intensively affects the properties for device applications. The anharmonicity and dynamic disorder from the organic cations participate in the relaxation dynamics coupled with excitations. However, a detailed understanding of this underlying mechanism remains obscure. This work investigates the electron-optical phonon coupling dynamics by employing ultrafast pump-probe transient absorption spectroscopy. The activated different optical phonon modes are observed via systematic studies of (PEA)2PbBr4 perovskite films on the ultrafast lattice vibrational dynamics. The experimental results indicate that solvent engineering has a significant influence on lattice vibrational modes and coherent phonon dynamics. This work provides fresh insights into electron-optical phonon coupling for emergent optoelectronics development based on layered perovskites.