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Great efforts have been made to improve the composition and structure of perovskite light‐emitting diodes (PeLEDs) through methods such as dimensional reduction or halide engineering, thereby reducing non‐radiative recombination. However, deep‐blue PeLEDs still face a deep valence band issue. The mismatched energy level alignment between the perovskite and the hole transport layer (HTL) leads to charge accumulation, resulting in imbalanced carrier transport and injection. Herein, to address the issues of imbalanced carrier injection and defect states in PeLEDs, a deep‐blue perovskite emitter using [4‐(3,6‐Dimethyl‐9H‐carbazol‐9‐yl)butyl]phosphonic acid (Me‐4PACz) as the material to promote hole transport and passivate defects is presented. The stepwise energy level structure design can effectively reduce the hole injection barrier and improve the carrier injection efficiency. Additionally, the electron‐rich P═O bond can effectively passivate the unsaturated Pb2+ in perovskite, reducing non‐radiative recombination caused by defects. Ultimately, stable deep‐blue PeLEDs (≈458 nm) are successfully fabricated with an external quantum efficiency (EQE) of 4.33%. This study provides new insights into the application of self‐assembled monolayers (SAMs) in PeLEDs. [ABSTRACT FROM AUTHOR]

The device performance of deep‐blue perovskite light‐emitting diodes (PeLEDs) is primarily constrained by low external quantum efficiency (EQE) especially poor operational stability. Herein, we develop a facile strategy to improve deep‐blue emission through rational interface engineering. We innovatively reported the novel electron transport material, 4,6‐Tris(4‐(diphenylphosphoryl)phenyl)‐1,3,5‐triazine (P‐POT2T), and utilized a sequential wet‐dry deposition method to form the homogenic gradient interface between electron transport layer (ETL) and perovskite surface. Unlike previous reports that achieved carrier injection balance by inserting new interlayers, our strategy not only passivated uncoordinated Pb2+ in the perovskite via P=O functional groups but also reduced interfacial carrier recombination without introducing new interfaces. Additionally, this strategy enhanced the interface contact between the perovskite and ETL, significantly boosting device stability. Consequently, the fabricated deep‐blue PeLEDs delivered an EQE exceeding 5 % (@ 460 nm) with an exceptional halftime extended to 31.3 minutes. This straightforward approach offers a new strategy to realize highly efficient especially stable PeLEDs. [ABSTRACT FROM AUTHOR]

The device performance of deep‐blue perovskite light‐emitting diodes (PeLEDs) is primarily constrained by low external quantum efficiency (EQE) especially poor operational stability. Herein, we develop a facile strategy to improve deep‐blue emission through rational interface engineering. We innovatively reported the novel electron transport material, 4,6‐Tris(4‐(diphenylphosphoryl)phenyl)‐1,3,5‐triazine (P‐POT2T), and utilized a sequential wet‐dry deposition method to form the homogenic gradient interface between electron transport layer (ETL) and perovskite surface. Unlike previous reports that achieved carrier injection balance by inserting new interlayers, our strategy not only passivated uncoordinated Pb2+ in the perovskite via P=O functional groups but also reduced interfacial carrier recombination without introducing new interfaces. Additionally, this strategy enhanced the interface contact between the perovskite and ETL, significantly boosting device stability. Consequently, the fabricated deep‐blue PeLEDs delivered an EQE exceeding 5 % (@ 460 nm) with an exceptional halftime extended to 31.3 minutes. This straightforward approach offers a new strategy to realize highly efficient especially stable PeLEDs. [ABSTRACT FROM AUTHOR]