Highly Efficient Red Perovskite Light‐Emitting Diodes with Reduced Efficiency Roll‐Off Enabled by Manipulating Crystallization of Quasi‐2D Perovskites

Abstract CsPbI₃ is attractive for efficient and cost‐effective red perovskite light‐emitting diodes (PeLEDs), but its black phases still suffer from the metastable structure. The incorporation of large‐size organic cations has been widely used to construct quasi‐2D perovskites to stabilize the black phases. However, the multiple‐phase quasi‐2D perovskites usually show abundant interface defects and enhanced Auger recombination, leading to the low luminance and serious efficiency roll‐off in PeLEDs. Herein, highly efficient red PeLEDs are demonstrated with high luminance and low efficiency roll‐off realized by manipulating the crystallization kinetics of phenethylamine bromide (PEABr) incorporated CsPbI₃. PEABr‐CsPbI₃ nanocrystal films with much larger and more oriented β‐CsPbI_xBr_3‐x grains are successfully obtained through appropriately increasing PbI₂ content and coordinating with anti‐solvent treatment. The carrier recombination dynamics investigations reveal that the trap‐assisted recombination and Auger recombination are greatly reduced in the passivation‐free PEABr‐CsPbI₃ films by rational crystallization regulation. A peak external quantum efficiency (EQE) up to 19.6% is achieved in the red PeLEDs with a stable emission peak at 672 nm, which is maintained as high as 17.2% at a high luminance of over 1000 cd m⁻². This study could shed light on modulating the crystallization kinetics of pervoskites to optimize carrier recombination dynamics toward high performance PeLEDs.