High‐Performance Green Light‐Emitting‐Diode Enabled by Simultaneous Phase Engineering and Crystallization Regulation

Quasi‐2D metal halide perovskites light‐emitting diodes (PeLEDs) are promising candidates for next‐generation light‐emitting diodes due to their excellent photoelectric properties and convenient solution preparation. However, challenges remain in suppressing the formation of low‐ n phases while enhancing the quantum confinement effect. Here, a co‐modification strategy is adopted that combines organic amine cations with different molecular structures to improve quasi‐2D perovskite performance. Specifically, the addition of Amantadine hydrobromide (AMAN), which features a large steric hindrance, effectively disrupted phenethylammonium bromide (PEABr) aggregation. This steric hindrance isolated PEABr molecules, thereby preventing the formation of low‐ n phases (e.g., n ≤3) and promoting a concentrated phase distribution. The crystallization kinetics of the quasi‐2D perovskite films are further investigated using in situ photoluminescence. Results showed that AMAN delayed the nucleation and crystallization processes by adsorbing onto the perovskite surface and impeding epitaxial crystal growth. This inhibition reduced crystal size, strengthened the quantum confinement effect, and improved the photoluminescence quantum yield (PLQY). As a result, the champion device achieved an external quantum efficiency of 30.84%. This co‐modification strategy, which effectively suppresses low‐ n phases while enhancing exciton binding energy and PLQY, provides valuable insights into designing molecular structures for optimizing the performance of quasi‐2D perovskite light‐emitting diodes.