Understanding Excitonic Behavior in Light Absorption and Recombination Process

Understanding excitonic behavior in light absorption and recombination process is urgently needed to regulate luminescent properties of two-dimensional (2D) perovskite; however, such information is still unexplored. Here, first, we demonstrate that pure phenethylamine lead bromine (PEA2PbBr4) nanosheets (NSs) possess strong exciton absorption and emission spectrum with high exciton binding energy (up to 310 meV) and prove that free excitons (FEs) play a decisive role in the optical transition process. Then, we design Cd-doped PEA2PbBr4 NSs to induce self-trapped excitons (STEs). Doping with isoelectric Cd naturally induces an impurity-driven lattice distortion and a strong exciton-phonon coupling, resulting in the STEs broadband extrinsic luminescence spectra. Further, the corresponding exciton fluorescent components of FEs and STEs can be effectively distinguished from the emission spectrum through spectral line-shape analysis, revealing the synergistic effect of exciton states in the recombination process. Unambiguously, this work will provide a deeper understanding of the exciton behavior and look forward to regulating exciton composition to obtain ideal luminescence properties.