Dual‐Strategy Engineering: Mg ²⁺ Doping and In Situ Liquid Ligand Passivation for High‐Performance Pure Red Perovskite LEDs

Abstract Mixed‐halide perovskite nanocrystals (PeNCs), such as CsPbBr _x I _3‐x , offer tunable emission and high photoluminescence quantum yield (PLQY) for pure red perovskite light‐emitting diodes (PeLEDs). However, surface defects and phase instability, worsened by long‐chain ligands, reduce stability and efficiency. A dual‐strategy approach is developed by combining Mg ² ⁺ doping with in situ 1,8‐octanedithiol passivation to fabricate stable, efficient CsPbBr _x I _3‐x PeNCs films. Mg ² ⁺ doping induces lattice contraction, suppresses iodine vacancies, and enhances phase stability. In situ 1,8‐octanedithiol treatment, using ethyl acetate as a nonpolar antisolvent, replaces insulating ligands with short‐chain HS ⁻ ‐terminated ligands, passivating defects. These PeNC films enable pure red PeLEDs with a 635 nm emission peak, an external quantum efficiency (EQE) of 24.2%, a luminance of 14406 cd m ^{− 2} , and a half‐life of 69 min at 1000 cd m ^{− 2} , outperforming pristine PeNCs‐based devices (EQE of 3.15%, T ₅₀ of 12 min). This in situ strategy minimizes deposition‐induced defects, offering a scalable route for high‐performance PeLEDs in display technologies.