Bifunctional Ligand Passivation Enables Stable Blue Mixed-Halide CsPb(Br/Cl)₃ Perovskite Quantum Dots toward Light-Emitting Diodes

Mixed-halide CsPb(Br/Cl)₃ perovskite quantum dots (PeQDs) have attracted extensive attention in light-emitting diodes (LEDs), but their low photoluminescent efficiency and especially poor stability impede their practical applications. Here, we employ bifunctional didodecyldimethylammonium thiocyanide (DDASCN) with a pseudohalogen SCN^- and branched DDA⁺ to obtain blue-emitting CsPbBr₂Cl PeQDs. DDASCN significantly boosts the photoluminescence quantum yield to 92% by inhibiting nonradiative recombination. Importantly, DDASCN PeQDs show excellent stabilities against air, UV light, heat, and polar solvents. These improved performances were explained by density functional theory calculation, which shows that SCN^- fills the Cl^- vacancy by simultaneously binding with undercoordinated Pb²⁺ and Cs⁺, while DDA⁺ connects undercoordinated Br^- and lies parallel to the PeQD core, leading to efficient passivation and a strong binding capacity. Finally, we achieved high-performance white LEDs by integrating our PeQDs, resulting in a color-rendering index of 92.9, a color gamut of 119.61%, and chromaticity coordinates of (0.33, 0.33). This provides an effective method to obtain efficient and stable CsPb(Br/Cl)₃ PeQDs for practical applications.