Efficient and color stable blue perovskite light-emitting diodes achieved <i>via</i> dual-additive phase modulation

Despite remarkable progress in sky-blue perovskite light-emitting diodes (PeLEDs), achieving efficient and color stable pure-blue electroluminescence remains challenging due to halide phase segregation, low-dimensional phase-induced non-radiative recombination, and defect-related losses in mixed Cl-Br quasi-two-dimensional (quasi-2D) perovskites. Here, we propose a dual-additive strategy to regulate phase distribution and manage Cl incorporation in quasi-2D perovskites for pure-blue PeLEDs. By introducing Ethylenediammonium-dichloride (EDACl₂) to suppress high-<i>n</i> phases and incorporate Cl for bandgap broadening, combined with NaBr to eliminate low-<i>n</i> non-radiative centers and promote small-sized nanocrystals, we optimize radiative recombination toward wide-bandgap phase distribution. This approach enables spectrally stable pure-blue electroluminescence at 474 nm without compromising photoluminescence quantum yield. Further hole-transport-layer engineering yields a peak external quantum efficiency of 4.6%, with spectral stability maintained under extreme bias up to 10.4 V. Our work provides critical insights into phase and halide management for high-performance blue PeLEDs, advancing their potential in full-color displays and lighting technologies.