Stabilizing CsPbBr3 quantum dots with conjugated aromatic ligands and their regulated optical behaviors

Abstract

Surface modifications of lead halide perovskite quantum dots (QDs) are promising for perusing improved stability and regulated optical properties. We have successfully introduced 1-alkyl-3-methyl-imidazolium cations, a kind of ionic liquids with conjugated aromatic head groups, as proper surface ligands via ligands exchange (LE) method. After surface modification, it is found that there is approximately 10 cm−1 chemical shift of the infrared (IR) absorption peak for the ligand compared to its derived raw imidazolium salts, suggesting that there is interaction between the imidazolium cations and the QDs. The theoretical simulations on structure optimization and frontier molecular orbitals (FMOs) prove that the interaction is enabled by a preferred N-Pb bonding on the surface and a close matching in energy levels of the ligands and CsPbBr3. X-ray photoelectron spectroscopy (XPS) results show a significant decrease in ligand density as well as a better passivation of surface Pb2+ defects. The modified QDs show better stabilities for their solution can survive after 72 h duration of intensive light illumination whilst obvious aggregation and degradation is found after only 24 h for the parent QDs solution. Accordingly, the modified QDs present better performance as phosphor in the white light-emitting diodes (WLEDs) device. The research gives an insight into the surface engineering of QDs with conjugated head groups, and suggests the potential application of the modified QDs as inks in flexible devices and phosphors in WLEDs.