Compositional Homogenization and Dielectric Modulation of Pb/Sr Mixed Perovskites for Efficient and Bright Deep‐Blue Light‐Emitting Diodes

Metal halide perovskites have emerged as promising candidates for next‐generation displays and lighting due to their tunable bandgap, high color purity, and solution processability. However, the performance of deep‐blue perovskite light‐emitting diodes (PeLEDs) lags far behind their red and green counterparts. Conventional strategies using low‐dimensional or mixed‐halide perovskites suffer from severe Auger recombination, phase separation, and chlorine‐vacancy‐induced nonradiative losses. Although Pb/Sr mixed B‐site compositional engineering provides excellent spectral stability, the compositional segregation and heterogeneity occurring during crystallization lead to poor film quality, low luminescence efficiency, and limited device performance. Herein, we introduce barium trifluoromethanesulfonate (Ba(OTf) 2 ) as a bifunctional additive to regulate the crystallization of Pb/Sr mixed perovskites. It synchronizes the crystallization kinetics of Pb and Sr via the formation of a ternary complex, suppresses compositional segregation, and passivates bromine vacancies, yielding highly homogeneous films with low defect densities. Moreover, Ba doping enhances the exciton binding energy through local dielectric modulation. Consequently, we achieve deep‐blue PeLEDs with a peak external quantum efficiency of 13.1% and a maximum luminance of 4821 cd m −2 at 467 nm, along with tunable emission from 450 to 470 nm. This work offers a viable route toward high‐performance alloyed perovskites for optoelectronic devices.