2-Bromohexadecanoic Acid as a Novel Bidentate Ligand for Passivation of Cesium Lead Halide Perovskite Nanocrystals with Near-Unity Photoluminescence Quantum Yield and Superior Photostability

Halide vacancies on the surfaces of cesium lead halide perovskite (CsPbX₃, X = Cl, Br, or I) nanocrystals (NCs) play a crucial role in their photoluminescence quantum yield (PLQY) and photostability. However, effectively passivating these vacancies remains a challenge. Here, 2-bromohexadecanoic acid (BHA) is introduced as a bidentate auxiliary ligand for CsPbX₃ NCs. The CsPbBr₃ and CsPbBr_1.5I_1.5 NCs, comodified with BHA, oleic acid (OA), and oleylamine (OLA) with 20% of OA substituted by BHA, are synthesized using a hot-injection technique and are designated as BHA-CsPbBr₃ and BHA-CsPbBr_1.5I_1.5 NCs. The BHA-CsPbBr₃ NCs exhibit a PLQY of 97% and retain 42.19% of their original intensity after 48 h of continuous ultraviolet light exposure. The photoluminescence (PL) properties, stability, and PL recombination mechanism of the BHA-CsPbBr₃ NCs are investigated in detail. It is believed that the carboxyl oxygen and ortho-bromine atoms enhance the binding strength of BHA to the surface of CsPbX₃. Additionally, the Br^- ions produced from the biomolecular nucleophilic substitution reaction between BHA and OLA partially occupy the anionic vacancies on the surface of CsPbX₃. These interactions reduce the halide vacancies and enhance the PL performance of CsPbX₃.