Tuning Electron Injection and Recombination in CdTe Quantum Dots by Ligand-Shell Engineering

Controlling the forward and backward electron-transfer dynamics of light-harvesting systems is an incessant research interest in photovoltaic applications. To this end, glutathione (GSH)- and thiolactic acid (TLA)-capped CdTe quantum dots have been synthesized, and their charge-transfer kinetics have been probed. Although both systems possess similar thermodynamic driving forces, they exhibit distinct interfacial charge-transfer kinetics. Steady-state and time-resolved fluorescence quenching measurements reveal that the short-chain TLA shell facilitates rapid electron injection. In contrast, transient absorption spectroscopy demonstrates that the bulky, polydentate GSH shell significantly reduces the charge recombination, which is attributed to multidentate surface coordination that suppresses trap-assisted pathways and stabilizes the charge-separated state. Furthermore, these ligand-controlled properties are translated to the solid state, where GSH-capped QDs retain prolonged emission lifetimes. Collectively, these findings establish surface ligand engineering as a route to asymmetrically modulating electron transfer and recombination in QD-based light-harvesting systems.