Persistent\nExciton Dressed by Weak Polaronic Effect\nin Rigid and Harmonic Lattice Dion–Jacobson 2D Perovskites

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