Ultrafast Carrier Transfer and Hot Carrier Dynamics in PbS-Au Hybrid Nanostructures

Semiconductor-metal hybrid nanostructures (HNs) are promising materials for photovoltaics and photocatalysis because of their efficient charge separation in the excited state. However, analysis of their carrier dynamics has been limited to only a handful of HNs, such as CdSe-Au and CdS-Au. Herein, we synthesized and characterized PbS-Au HNs and examined their carrier dynamics by femtosecond near-IR pump-probe spectroscopy. A decrease in band-edge (1S) bleach yields was clearly observed in PbS-Au HNs as compared to PbS quantum dots (QDs) under 1S excitation, suggesting the existence of ultrafast carrier transfer from the 1S states of PbS QDs to Au nanoparticles (NPs) that was faster than the instrumental response function. A rise time analysis of 1S bleach dynamics determined that no hot carrier transfer was present. In addition to ultrafast carrier transfer, picosecond-scale carrier transfer was observed, with the rate constants increasing with Au NPs diameter. This difference between ultrafast and picosecond-scale carrier transfer is likely due to a difference in rate constants between electron and hole transfer.