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 CsPbBr1.5I1.5 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-CsPbBr1.5I1.5 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.