Insights into the Fluorescence Quenching of CdSeS Quantum Dots by Thiophenol Ligands
Due to the high surface-to-volume ratio of quantum dots (QDs), their surface ligands play a crucial role, especially in mediating energy and charge transfer processes. Short-chain ligands such as thiophenols with aromatic units have been commonly used as capping layers in quantum dot light-emitting diodes to enhance charge transport and charge injection. However, the impact of thiophenols on charge recombination in photophysical processes is not entirely clear. In this study, we systematically explored the effects of thiophenol derivatives with different substituents on the excited electron–hole recombination process in alloyed CdSeS QDs of high brightness (photoluminescence quantum yield ∼85%). Noteworthy, we observed that thiophenols quenched the photoluminescence (PL) of QDs (rich in Cd sites on the surface) and introduced a short lifetime decay channel caused by hole capturing. Meanwhile, the PL decay lifetime (τavg) of QDs was increased. Upon the addition of oleylamine (OAm), the PL intensity of the QDs was enhanced and τavg was decreased. These results indicated that the exposed Cd dangling bonds on the surface of QDs were passivated by OAm. Therefore, thiophenols unequivocally acted as hole acceptors while simultaneously causing more surface defect sites exposed on the surface of QDs, thereby limiting the radiative recombination of electrons and holes. These discoveries will have significant implications for the ligand engineering of QDs.
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