High‐Performance Perovskite Light‐Emitting Diodes Enabled by Passivating Defect and Constructing Dual Energy‐Transfer Pathway through Functional Perovskite Nanocrystals

Abstract Quasi‐2D perovskites have emerged as a promising luminescent material for perovskite light‐emitting diodes (Pe‐LEDs). However, efficiency and stability are still obstacles to practical application due to numerous defects and inefficient energy transfer of perovskite films. Herein, functional phenethylammonium bromine‐modified CsPbBr₃ nanocrystals (PEA‐CsPbBr₃ NCs) are first introduced as multifunctional additive to simultaneously improve abovementioned problems. PEA‐CsPbBr₃ NCs not only serve as heteronuclear seeds and trigger growth, thus greatly reducing leakage current, but also deliver Cs⁺ and Br⁻ to passivate the intrinsic defects inside film. More importantly, the PEA‐CsPbBr₃ construct a new carrier‐transfer pathway from the small‐n phase of the quasi‐2D perovskite to the PEA‐CsPbBr₃, which not only accelerates the energy‐transfer process but also promotes radiation recombination of carriers due to stronger quantum confinement effect. Afterward, the poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate/poly[9,9‐dioctylfluoreneco‐N‐[4‐(3‐methylpropyl)]diphenylamine]:black phosphorus quantum dot double hole‐transport layer is successfully constructed to enhance its carrier‐injection and charge‐transport abilities. Consequently, a champion external quantum efficiency of 25.32% and maximal brightness of 128 842 cd m⁻² are achieved, which is the record efficiency of the quasi‐2D Pe‐LED with pure green emission at 530 nm. Moreover, an impressive 174 min lifetime is obtained at T₅₀, which is about five times longer than the control device.