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 (CsPbX, 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 CsPbX NCs. The CsPbBr and CsPbBrI 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-CsPbBr and BHA-CsPbBrI NCs. The BHA-CsPbBr 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-CsPbBr 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 CsPbX. Additionally, the Br ions produced from the biomolecular nucleophilic substitution reaction between BHA and OLA partially occupy the anionic vacancies on the surface of CsPbX. These interactions reduce the halide vacancies and enhance the PL performance of CsPbX.