Persistent Exciton Dressed by Weak Polaronic Effect in Rigid and Harmonic Lattice Dion-Jacobson 2D Perovskites

The emerging two-dimensional (2D) Dion-Jacobson (DJ) perovskites with bidentate ligands have attracted significant attention due to enhanced structural stability compared with conventional Ruddlesden-Popper (RP) perovskites with monodentate ligands linked by van der Waals interactions. However, how the pure chemical bond lattice interacts with excited state excitons and its impact on the exciton nature and dynamics in 2D DJ-perovskites, particularly in comparison to RP-perovskites, remains unexplored. Herein, by a combined spectroscopy study on excitonic and structural dynamics, we reveal a persistent exciton dressed by a weak polaronic effect in DJ-perovskite due to their rigid and harmonic lattice, in striking contrast to significantly screened exciton polaron observed in RP-perovskites. Despite the similar exciton binding energy (∼0.3 eV) in both n = 1 DJ- and RP-perovskites with near-identical crystal structure, photoexcitation results in a slightly screened exciton with minimal structural relaxation and a retained binding energy of ∼0.29 eV in DJ-perovskites but strongly screened exciton polaron with a binding energy of ∼0.13 eV in RP-perovskites. Structural dynamics further highlight the rigid and harmonic lattice motion in DJ-perovskites, as opposed to the thermally activated anharmonic lattice in RP-perovskites, arising from their distinct bonding modes. Our study offers insights into modulating excited state properties in 2D perovskites, simulating the rational design of hybrid semiconductors with tailored properties and functionalities.