Bifunctional\nLigand Passivation Enables Stable Blue\nMixed-Halide CsPb(Br/Cl)<sub>3</sub> Perovskite Quantum Dots toward\nLight-Emitting Diodes

Mixed-halide CsPb(Br/Cl)<sub>3</sub> perovskite quantum\ndots (PeQDs)\nhave attracted extensive attention in light-emitting diodes (LEDs),\nbut their low photoluminescent efficiency and especially poor stability\nimpede their practical applications. Here, we employ bifunctional\ndidodecyldimethylammonium thiocyanide (DDASCN) with a pseudohalogen\nSCN<sup>–</sup> and branched DDA<sup>+</sup> to obtain blue-emitting\nCsPbBr<sub>2</sub>Cl PeQDs. DDASCN significantly boosts the photoluminescence\nquantum yield to 92% by inhibiting nonradiative recombination. Importantly,\nDDASCN PeQDs show excellent stabilities against air, UV light, heat,\nand polar solvents. These improved performances were explained by\ndensity functional theory calculation, which shows that SCN<sup>–</sup> fills the Cl<sup>–</sup> vacancy by simultaneously binding\nwith undercoordinated Pb<sup>2+</sup> and Cs<sup>+</sup>, while DDA<sup>+</sup> connects undercoordinated Br<sup>–</sup> and lies\nparallel to the PeQD core, leading to efficient passivation and a\nstrong binding capacity. Finally, we achieved high-performance white\nLEDs by integrating our PeQDs, resulting in a color-rendering index\nof 92.9, a color gamut of 119.61%, and chromaticity coordinates of\n(0.33, 0.33). This provides an effective method to obtain efficient\nand stable CsPb(Br/Cl)<sub>3</sub> PeQDs for practical applications.