Defect Passivation via Dual‐Ligand Surface Modification for Bright and Stable Blue Emission in CsPbBr₃ Nanoplatelets

Abstract Achieving efficient and stable blue light‐emitting perovskite nanocrystals is a significant challenge for next‐generation optoelectronic devices. Here, a dual‐ligand surface engineering strategy is reported for quasi‐2D CsPbBr₃ nanoplatelets (NPLs) synthesized via ligand‐assisted reprecipitation. By synergistically co‐introducing didodecyldimethylammonium bromide to passivate bromine vacancies and hexylphosphonic acid to bind undercoordinated lead ions, the NPLs achieved a remarkable photoluminescence quantum yield of 93.7% and a narrow full‐width at half‐maximum of 19.27 nm. The enhanced photoluminescence (PL) lifetime (6.35 ns), reduced crystal disorder, slower bleach recovery kinetics, and improved thermal stability suggest that the suppressed non‐radiative pathways and strong exciton confinement (Eb = 141.76 meV) result from effective surface defect passivation and enhanced radiative recombination. Additionally, surface and structural characterizations confirmed the successful dual‐ligand integration and improved crystal integrity. The treated NPLs retained ∼57% PL under 450 min of ultraviolet (UV) light and ∼55% PL under 70% relative humidity, demonstrating strong UV and moisture stability. A prototype white light‐emitting device fabricated by integrating dual‐ligand‐treated NPLs achieves a wide color gamut (121% National Television System Committee, 90.4% ITU‐R Recommendation BT.2020), demonstrating their potential for high‐performance optoelectronics. This approach promotes defect suppression in low‐dimensional perovskites, paving the way for stable and efficient blue emitters.