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

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.