Exchange of\nThiol Ligands on CuInS<sub>2</sub> Quantum\nDots in High Boiling Solvents

As-prepared quantum dots are covered with long-chain\nligands to\nprevent aggregation. When quantum dots are used in optoelectronic\ndevices such as solar cells and QD-LED, ligand exchange is necessary\nto replace long-chain ligands with short-chain ones to increase the\nefficiency of charge transfer from the quantum dots to the electrode.\nIn this study, we successfully exchanged 1-dodecanethiol (DDT) ligands\non CuInS<sub>2</sub> quantum dots with mercaptopropionic acid (MPA)\nligands by using a two-phase system of high-boiling hydrophilic and\nhydrophobic solvents. The ligand exchange to MPA was achieved by using\ndiethylene glycol (DEG) or ethylene glycol (EG) as the hydrophilic\nphase and tetradecane as the hydrophobic phase. The ligand exchange\nrate increased with increasing ligand exchange temperature. When quantum\ndot sensitized solar cells (QDSSCs) were fabricated using the ligand-exchanged\nquantum dots, a positive correlation was observed between the progress\nof ligand exchange and short-circuit current density. This is because\ncharge transfer efficiency from the quantum dots to the TiO<sub>2</sub> electrode was improved by the ligand exchange. This work has shown\nthat QDs synthesized using DDT can be applied to optoelectronic devices.