Two-Step Ligand-Exchange-Assisted Charge Transfer in Graphene/PbS Quantum Dots Hybrid Near-Infrared Photodetector

Near-infrared photoelectric detectors are widely used in the military and national economy, such as aerospace, optical communication, and near-infrared imaging. Graphene/quantum dots (QDs) hybrid photodetectors possessing high responsivity and broadband spectral range have been prodigiously studied due to the combination of high mobility of graphene, broad spectral response, and high light absorption of QDs. However, the long-chain ligands that modify the outer surface of the QDs stem the transfer of charge carriers, thus hindering the performance of the hybrid photodetectors. Here, we demonstrate colossal response in Graphene/QDs detectors via a two-step ligand exchange method to exchange the inceptive long chains with specifically selected molecules. Prior to the solid-state ligand exchange, QDs were pretreated with methylammonium iodide (MAI) in solution as the first ligand exchange and 1,2-ethanedithiol (EDT) was redeposited after the tetrabutylammonium iodide (TBAI) ligand exchange in the second step to ensure complete passivation of surface defects. After the two-step ligand exchange process, the device performances have been significantly improved. The responsivity and detectivity of the device are 6.7 × 103 A·W–1and 1.86 × 109 Jones, respectively, which are increased by 2 orders of magnitude, heralding the development of high-performance near-infrared photodetection and imaging systems in integrated photonics applications.