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Abstract 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)butylphosphonic 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 Pb 2+ 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.
Li et al. (Fri,) studied this question.