Sequential Crystallization Decouples Cs ₄ PbBr ₆ and CsPbBr ₃ Phases Enabling Efficient Perovskit

ABSTRACT

Cesium lead bromide has emerged as a leading candidate for high‐performance perovskite light‐emitting diodes (PeLEDs) in next‐generation optoelectronics. However, the formation of the 0D Cs ₄ PbBr ₆ phase often accompanies CsPbBr ₃ crystallization and is difficult to regulate, hampering the efficiency of LED devices in scalable production. In particular, 0D and 3D perovskite phases often crystallize as disordered structures, leading to poor crystalline quality and a high density of defects in the perovskite films. To address this challenge, we employed an additive‐mediated sequential crystallization (AMSC) strategy using 3‐carboxyphenylphosphonic acid (3‐CPPA) to modulate the crystallization kinetics of the 0D and 3D phases. Through strong interactions between the additive and perovskite precursors, the initial CsPbBr ₃ formation is effectively slowed, allowing for temporally separated crystallization of Cs ₄ PbBr ₆ and CsPbBr ₃ phases. This separated crystallization process significantly enhances the film quality of CsPbBr ₃ phase. Remarkably, the AMSC strategy drives the Cs ₄ PbBr ₆ phase toward the film surface, thereby forming a favorable surface morphology and effectively improving the light outcoupling efficiency of PeLEDs. By leveraging this synergic strategy, we achieve an ultrahigh photoluminescence quantum yield (PLQY) reaching nearly 100% and realize an efficient external quantum efficiency (EQE) of 35.3% in green PeLEDs, underscoring the critical role of phase crystallization engineering in optimizing perovskite emitters.