Photoinduced Charge Transfer Characteristics of PbS Quantum Dot–Graphene Heterostructure

The composite of quantum dots (QDs) with graphene (GR) has significantly enhanced its potential for optoelectronic applications. Although existing research has experimentally confirmed the excellent optoelectronic properties of quantum dots-graphene (QD-GR) heterostructures, the underlying charge transfer mechanisms have not been fully elucidated. This study uses the Marcus theory to investigate the photoinduced charge transfer characteristics of QD-GR heterostructures under external electric field (<i><b>F</b>_ext</i>) modulation. We first constructed a lead sulfide quantum dots-graphene (PbS QD-GR) heterojunction model using a minimal-sized lead sulfide quantum dots (PbS QDs) cluster and a single-layer flake graphene. Next, we systematically analyzed the electronic state distribution at the interface and elucidated the essential mechanism underlying the heterojunction's structural stability. The excited state properties of the PbS QD-GR heterojunction under <i><b>F</b>_ext</i> modulation were systematically investigated. Finally, based on Marcus theory, the reorganization energy (λ), Gibbs free energy (Δ<i>G</i>) and electron coupling matrix element (<i>V_da</i>) were quantitatively calculated to reasonably predict the charge transfer rate (<i>K</i>). The study revealed that the charge separation rate significantly exceeds the charge recombination rate (<i>KCS</i> ≫ <i>KCR</i>), demonstrating the heterostructure's exceptional exciton dissociation capability. Our findings elucidate the trend of charge transfer parameters in specific PbS QD-graphene heterojunctions under external electric fields, thereby providing theoretical support for a deeper understanding of optoelectronic device performance.