Ultrafast charge transfer dynamics in lead sulfide quantum dots probed with resonant Auger spectroscopy at the lead M-edge.

PbS quantum dots (QDs) hold significant potential for next-generation photovoltaic and photodetector applications due to their size-dependent electronic properties and strong absorption in the near-infrared region. In this study, we investigate charge transfer dynamics in PbS quantum dots of varying sizes, bulk PbS, and PbI reference samples using Resonant Auger- (RAS) and Core-Hole Clock Spectroscopy (CHCS). Mapping the Pb M-edge, we capture attosecond-scale electron transfer, using the Pb 3d core-hole lifetime as an internal clock. Our results reveal that PbS bulk samples and larger quantum dots exhibit faster charge transfer rates compared with smaller quantum dots and PbI, which display slower rates. Additionally, by comparing charge transfer times in the Pb MNN and S KLL Auger regions, we demonstrate consistent behavior across different resonant excitation edges, reinforcing our understanding of how quantum dot size and ligand environment influence charge transport. These insights highlight the importance of optimizing QD size and surface chemistry to improve charge transfer efficiency, a critical factor for high-performance energy materials.