A Biaxially Polarized Molecular Interlayer for Efficient and Color‐Stable Perovskite LEDs

Abstract Ion migration, especially taking place at the interface of perovskite/charge transport layer, poses great threats to the stability of perovskite light–emitting diodes (PeLEDs). However, the existing strategies mitigating ion migration sacrifice efficient charge injection, thus limiting the PeLED performances. Herein, an interfacial layer of a biaxially charge‐polarized molecule, bi‐4‐(N‐carbazolyl)phenyl)phenylphosphine oxide (BCPO), is applied. The strong surface coordination of BCPO not only manifests a high‐quality metal halide perovskites (MHPs) emitter with improved defect passivation and crystallinity but also establishes a rigorous vertical dipole alignment, inducing band‐bending for favorable electron injection. Additionally, the in‐plane geometry of the electron‐withdrawing carbazolylphenyl units achieves intimate lateral electrostatic contact with the MHPs surface, realizing stronger chemical interaction that suppresses the escape of halide at the interface. Encouraged by these achievements, the optimized PeLEDs with BCPO demonstrate maximum external quantum efficiency of 25.8% and T 50‐EL lifetime of 13.4 h, representing one of the best green PeLEDs reported. This work newly opens a synergistic strategy, combined with molecular structure design and interfacial engineering, for simultaneously realizing efficient and color‐stable PeLEDs, which tackles the crucial challenges for their commercialization.