Manipulating Phase and Defect Distribution of Quasi-2D Perovskites via a Synergistic Strategy for Enhancing the Performance of Blue Light-Emitting Diodes.

Quasi-two-dimensional (quasi-2D) mixed-halide perovskites are a requisite for their applications in highly efficient blue perovskite light-emitting diodes (PeLEDs) owing to their strong quantum confinement effect and high exciton binding energy. The pace of quasi-2D blue PeLEDs is hindered primarily by two factors: challenges in precisely managing the phase distribution and defect-mediated nonradiative recombination losses. Herein, we utilize 2,2-diphenylethylamine (DPEA) with bulky steric hindrance to disturb the assembly process of a slender spacer host cation, 4-fluorophenylethylammonium (-F-PEA), enhancing phase distribution management in quasi-2D PeLEDs. The DPEA not only inhibits the small- phase but also strengthens carrier transport and alleviates exciton quenching. In addition, dual additives─formamidine acetate (FAoAc) and guanidine thiocyanate (GASCN)─were incorporated to assist phase tailoring and passivation of remaining defects in the perovskite films. The C═O and SCN groups can coordinate with Pb to suppress the charge trap density and nonradiative recombination. As a result of employing a synergetic strategy for comprehensive phase distribution regulation and defect passivation, the optimized device achieves blue emission at 479 nm with a 5× improvement in external quantum efficiency (EQE) and a 13× increase in device operating stability. This synergetic strategy paves a simple route for phase management and defect passivation toward high-performance blue-emission PeLEDs.