Emission-Tunable Quasi-2D (PEA)₂FA_<i>n</i>–1Pb_<i>n</i>Br_3<i>n</i>+1 Perovskite Films via an A-Site Cation-Assisted Strategy for Light-Emitting Diodes

Organic–inorganic hybrid perovskite crystals have attracted significant attention in recent years due to their outstanding optoelectronic properties. However, the application of low-dimensional perovskite films still faces substantial challenges. In this study, emission-tunable quasi-2D (PEA)2FAn–1PbnBr3n+1 perovskite films were synthesized by using an A-site cation-assisted strategy. The high-quality films were achieved by precisely controlling the precursor solution concentration, antisolvent pinning time, and the ratio of PEA to FA. The resulting quasi-2D perovskites exhibited a continuous emission band from 407 to 560 nm, with a maximum photoluminescence (PL) quantum yield of 52%. The 2D to 3D phase transition of the perovskite crystals was characterized using X-ray diffraction (XRD). Additionally, the introduction of an intermediate PEABr layer significantly enhanced the thermal stability of the films and extended the exciton PL lifetimes, attributed to the formation and passivation of the 2D phase at the interface. Finally, variable-color perovskite light-emitting diodes (LEDs) were fabricated, achieving a current efficiency of 29 cd/A and a brightness of 6179 cd/m2. These results demonstrate that cation engineering is an effective method for optimizing the optical properties of quasi-2D perovskites, ultimately facilitating the acquisition of high-performance perovskite LEDs based on low-dimension structures.