Ultrafast Charge Transfer Enhancement in CdS-MoS₂ via a Linker Molecule

Hybrid systems, which take advantage of the low material dimensionality, have great potential for designing nanoscale devices. Quantum dots can be combined with two-dimensional (2D) monolayers to achieve success in photovoltaics and water splitting. In such colloidal systems, ligand molecules play an important role in stabilizing the nanostructures, but their role in heterostructure device performance is still poorly understood. In this study, time-dependent density functional theory is employed to explore how the cysteine ligand affects the charge transfer across the CdS-MoS2 heterostructure, at the ultrafast time scale. We show that the cysteine ligand enhances charge transfer, not only by coupling the CdS and MoS2 electronic states across the junction but also through enhanced electron-phonon coupling, where the carrier energy is quickly dissipated to high-frequency local vibrational modes arising from the lighter ligand atoms. This enhanced electron-phonon mechanism associated with the ligand is expected to be broadly applicable to most solution-based nanodevices.