Use of CsPbCl3 Quantum Dots as a Chlorine Source Enables Formation of Thick Quasi‐2D Perovskite Films for High‐Performance Blue Light Emitting Diodes

Abstract Achieving efficient and stable blue‐emitting quasi‐two‐dimensional (quasi‐2D) perovskite light‐emitting diodes (LEDs) remains a challenge due to the poor solubility of conventional chloride precursors and the difficulty to form thick, uniform films with a well‐controlled phase distribution. A new strategy is proposed to address this challenge using CsPbCl 3 quantum dots (QDs) capped with oleylamine (OLA) ligands as an alternative chlorine source. It is demonstrated how the use of these QDs enables formation of quasi‐2D perovskite films with vertically aligned crystalline structure, thickness over 100 nm, and improved stability. OLA ligands regulate the crystal phase distribution and grain boundaries, suppressing the appearance of small‐ n 2D phases and reducing the number of crystal defects, while inorganic CsPbCl 3 QD cores induce vertical crystallization of quasi‐2D perovskite films, endowing them with enhanced structural stability. The use of this non‐conventional chlorine source is proven instrumental in improving external quantum efficiency of quasi‐2D perovskite sky‐blue LEDs, reaching 26.2% at 485 nm, with significantly enhanced electroluminescence stability both in terms of peak position and brightness. This study demonstrates a novel methodology using CsPbCl 3 QDs capped with conventional organic ligands to achieve thick quasi‐2D perovskite layers for blue LEDs, addressing existing limitations in perovskite optoelectronics.