Defect Passivation and Growth Regulation with CdAc ₂ Additive Enable Improved Efficiency of Pure‐Blue Quasi‐2D Perovskite Light‐Emitting Diodes

Quasi‐two‐dimensional (quasi‐2D) perovskite LEDs exhibit remarkable luminescence performance due to their multiple quantum well architectures. However, achieving efficient pure‐blue light emission remains challenging for display applications. Cadmium acetate (CdAc 2 ) is introduced as an additive for defect passivation and growth regulation in quasi‐2D perovskite. Density functional theory calculations predict that CdAc 2 can passivate halide vacancies. This is confirmed by prolonged carrier lifetimes and reduced trap densities. Additionally, the addition of CdAc 2 regulates the perovskite growth, reducing the average grain size from 26.0 nm to 10.5 nm and the roughness from 6.124 nm to 2.584 nm. This dual mechanism significantly suppresses nonradiative recombination and improves the photoluminescence quantum yield from 17.4 to 37.1%. The maximum external quantum efficiency of pure‐blue perovskite LEDs improves from 1.80 to 2.57%, with brightness increasing from 278.8 cd m − 2 to 355.8 cd m − 2 . This work paves the way for efficient quasi‐2D perovskite pure‐blue LEDs.