π–π Interactions Mediated Pyrene Based Ligand Enhanced Photoresponse in Hybrid Graphene/PbS Quantum Dots Photodetectors

Hybrid graphene and quantum dots (QDs) photodetectors merge the excellent conductivity and ambipolar electric field sensitivity of graphene, with the unique properties of QDs. A critical aspect for the photoresponsivity of these devices is charge transfer at the graphene/QDs interface. Here we use 1-pyrene butyric acid (PBA)-coated PbS QDs with single layer graphene (SLG) to investigate the effect of pyrene as a π-π mediator to enhance charge transfer at the SLG/QDs junction under illumination. The surface chemistry at the QD-QD and SLG/QD interface is studied before and after treatment with the conventional tetrabutylammonium iodide (TBAI) QD linker. The hybrid SLG/QD photodetectors prepared using PBA as a SLG-QD linker demonstrate a photoresponse up to 30% higher than that recorded for devices where only TBAI is used, due to the strong electron coupling between SLG and QDs. Transconductance measurements show that PBA provokes electron depletion in SLG ascribed to the tendency to delocalize the QDs holes, favouring their transfer to SLG. This surface ligand is found to improve the interaction between the QDs light absorbers and the SLG charge collector, leading to an increased photodetection response. Ligand engineering demonstrates able to enhance charge dynamics and thus boost the performance of the hybrid device.