Copper-doping defect-lowered perovskite nanosheets for deep-blue light-emitting diodes

Mixed-halide blue perovskites CsPb(Br/Cl)₃ are considered promising candidates for developing efficient deep-blue perovskite light-emitting diodes (PeLEDs), but their low photoluminescence quantum yield (PLQY), environmental instability, and poor device performance gravely inhibit their future development. Here, we employ a heteroatomic Cu²⁺ doping strategy combined with post-treatment Br^- anion exchange to prepare high-performance deep-blue perovskites CsPb(Br/Cl)₃. The Cu²⁺ doping strategy significantly decreases the intrinsic chlorine defects, ensuring that the inferior CsPbCl₃ quantum dots are transformed into two-dimensional nanosheets with enhanced violet photoluminescence and increased exciton binding energy. Further, with the post-treatment Br^- anion exchange, the as-prepared CsPb(Br/Cl)₃ nanosheets with more radiation recombination and less ion migration present an enhanced PLQY of 94% and better humidity stability of 30 days. Based on the optimized CsPb(Br/Cl)₃, we fabricated deep-blue PeLEDs with luminescence emission at 462 nm, a maximum luminance of 761 cd m^-2, and a current density of 205 mA cm^-2. This work puts forward a feasible synthesis strategy to prepare efficient and stable mixed-halide blue perovskite CsPb(Br/Cl)₃ and related blue PeLEDs, which may promote the further application of mixed-halide perovskites in the blue light range.