Efficient Deep‐Red Perovskite Light‐Emitting Diodes Based on a Vertical 3D/2D Perovskite Heterojunction

Abstract Metal halide perovskites hold a great promise for the development of electroluminescent and down‐conversion light‐emitting diodes (LEDs) owing to their easily tunable optical bandgaps, high photoluminescence quantum yields (PLQYs) and excellent color purity. 3D structural perovskites, valued for their high charge carrier transport capacity, have garnered much attention for high‐performance electroluminescent LEDs with low operating voltages. However, solution‐processed 3D perovskite films always suffer from the generation of defect‐induced trap states on the surfaces and at the grain boundaries, resulting in nonradiative recombination that detracts from the electroluminescence performance. Herein, a 3D/2D heterostructure is constructed to reduce the surface defects of CsPbI x Br 3‐x based 3D perovskites by reconfiguring the surface of the 3D perovskite film with fluorine para‐substituted phenethylammonium iodine (p‐FPEAI). The analysis of charge carrier dynamics indicates a decrease in trap‐assisted nonradiative recombination and a notable increase in radiative recombination in the red 3D/2D perovskite films. Consequently, the cutting‐edge deep‐red LEDs with the resultant 3D/2D heterostructure perovskite as the emissive layer demonstrate a high external quantum efficiency of 22.2% and a very stable electroluminescence peak at 674 nm. The proposed p‐FPEAI‐assisted surface engineering is considered a resultful approach for advancing the development of high‐performance LEDs with perovskite heterojunction.