Abstract
Blue-emitting perovskites can be easily attained by precisely tuning the halide ratio of mixed halide (Br/Cl) perovskites (MHPs). However, the adjustable halide ratio hinders the passivation of Cl vacancies, the main source of trap states leading to inferior performance of blue MHP light-emitting diodes (LEDs). Here, we report a strategy for passivating Cl vacancies in MHP quantum dots (QDs) using nonpolar solvent-soluble organic pseudohalide [n-dodecylammonium thiocyanate (DAT)], enabling blue MHP LEDs with greatly enhanced efficiency. Density functional theory calculations reveal that the thiocyanate (SCN-) groups fill in the Cl vacancies and remove electron traps within the bandgap. DAT-treated CsPb(BrxCl1-x)(3) QDs exhibit near unity (similar to 100%) photoluminescence quantum yields, and their blue (similar to 470 nm) LEDs are spectrally stable with an external quantum efficiency of 6.3%, a record for perovskite LEDs emitting in the range of 460-480 nm relevant to Rec. 2020 display standards, and a half-lifetime of similar to 99 s.