Compositional design of spectrally stable blue mixed-halide perovskite LEDs

This study tackles the significant challenge of phase separation in mixed halide (Br<sup>–</sup>/Cl<sup>–</sup>) perovskite systems, which severely affects the spectral stability of blue perovskite light-emitting diodes (PeLEDs). A compositional engineering strategy is proposed, precisely controlling the Cs:Pb molar ratio (1∶1 to 1.1∶1) in precursor solutions to construct a CsPb(Br<sub>1–<i>x</i></sub>Cl<sub><i>x</i></sub>)<sub>3</sub>/Cs<sub>4</sub>Pb(Br<sub>1–<i>x</i></sub>Cl<sub><i>x</i></sub>)<sub>6</sub> composite phase structure. Transmission electron microscopy (TEM) mapping and X-ray diffraction (XRD) analysis confirm that Cs<sub>4</sub>Pb(Br<sub>1–<i>x</i></sub>Cl<sub><i>x</i></sub>)<sub>6</sub> nanocrystals (5–8 nm in diameter) grow in situ and uniformly encapsulate CsPb(Br<sub>1–<i>x</i></sub>Cl<sub><i>x</i></sub>)<sub>3</sub> microparticles (50–100 nm). This composite architecture has double functional advantages: 1) the Cs<sub>4</sub>PbX<sub>6</sub> shell acts as a physical barrier, reducing halide ion migration activation energy and suppressing phase segregation during continuous operation; 2) the wide-bandgap (3.9–4.3 eV) Cs<sub>4</sub>PbX<sub>6</sub> induces quantum confinement effects, confining carriers within CsPbX<sub>3</sub> while passivating defect states, thereby improving perovskite performance. The optimized PeLED achieves notable improvements in brightness, external quantum efficiency, and operational stability, maintaining stable emission at 478 nm under a 50 mA/cm² current density. This is achieved by inhibiting halide phase separation and enhancing the efficiency of carrier recombination achieved by the cesium-lead halide heterojunction system. This work provides fundamental insights into phase-stable perovskite design via composite crystallization kinetics, providing a viable pathway toward commercial-grade blue PeLEDs for full-color displays.