Conjugated Oligoelectrolyte as a Conductive Ligand for Highly Emissive Metal Halide Perovskite Nanocrystal
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Lead halide perovskite nanocrystals (PNCs) have been studied as emissive material owing to their exceptionally narrow full-width half maximum (FWHM) with high photoluminescence quantum yield (PLQY). Despite their excellent optical properties, insulating properties of oleyl ligand (OA) used for PNC synthesis significantly hinder the charge injection and cause low external quantum efficiency in the device level. Therefore, ligand engineering is considered the most important strategy for demonstration of efficient PNC. Herein, we introduce a conjugated oligoelectrolyte (COE), with semiconducting properties as a ligand for efficient PNC light emitting material. PFM6Br, a fluorene-based COE with ammonium bromide terminal groups, was successfully synthesized and introduced to green CsPbBr3 PNC by ligand exchange. The size and shape of PNCs were maintained after treatment due to effective passivation. In particular, the colloidal PNC exhibited excellent optical properties due to the energy transfer effect between PFM6Br and showed a high PLQY of 98% at 365 nm excitation.