Exciton Transfer Dynamics and Annihilation in Rubidium–Cesium-Alloyed, Quasi-Two-Dimensional Perovskite

Light-emitting diodes (LEDs) based on perovskite materials are a new group of devices that are currently undergoing rapid development. A significant fraction of these devices is based on quasi-2D perovskites fabricated with large organic cations. In this work, we describe the ultrafast scale dynamics in a quasi-2D PEA2(Rb0.6Cs0.4)2Pb3Br10 perovskite material with an excess of RbBr, which was previously used to fabricate blue-emitting perovskite LEDs. The results obtained using transient absorption spectroscopy are consistent with the assumption that the carrier dynamics in this material are dominated by excitons, most of which decay by exciton–exciton annihilation when high-intensity excitation is used. Furthermore, a slow energy transfer between different quasi-2D domains taking place within 50 ps was observed. The content of the RbBr did not show any strong influence on the observed dynamics. Our results show that the exciton–exciton annihilation proceeds much faster in thin (n = 2) quasi-2D domains than in thick (n ≥ 4) domains. This finding implies that perovskites with high-n, quasi-2D domains are preferable for efficient perovskite lasers and bright perovskite LEDs.