Phase Control via Solubilities of Metal Halide Additives in Blue Quasi-2D Perovskite Light-Emitting Diodes

Precise modulation of crystallization kinetics is pivotal for overcoming phase segregation in efficient blue quasi-two-dimensional (Q-2D) perovskite light-emitting diodes (PeLEDs). Here, we introduce a solubility-driven co-additive strategy employing YCl3 and ZnCl2 to overcome the inherent nonuniformity of phases and abundant defect states in conventional solution-processed films. Exploiting their differential solubility, YCl3 accelerates nucleation while ZnCl2 retards crystal growth via precursor interaction, enabling tailored phase evolution. This kinetic regulation effectively suppresses parasitic low- and high-n phases, establishing a flattened energy landscape with high spatial homogeneity. Furthermore, effective defect passivation boosted the photoluminescence quantum yield (PLQY) from 18.75% to 41.88%. Consequently, the resulting PeLEDs exhibited a peak external quantum efficiency (EQE) of 8.87% and a maximum operational duration (T50) of 22.68 min. This work elucidates a solubility-driven approach to kinetic control, offering a scalable pathway for precise phase engineering in perovskite-based optoelectronics.