Metal chalcogenide complex ligands enhance the photoresponse in hybrid graphene/PbS quantum dot photodetectors†

Abstract

Short-wavelength infrared photodetectors with a wavelength range of 1–3 μm have attracted increasing attention in various fields, such as imaging and optical communications. As an alternative approach to high-performance infrared photodetectors, hybrid structures that combine graphene and lead sulfide quantum dots (PbS QDs) have been extensively investigated. However, conventional organic ligand-coated PbS QDs face challenges such as volatility and susceptibility to oxidation. Here, we report a methodology for switching the repulsive forces in various surface ligands. This methodology involved forming tight ionic pairs with cationic surfactants to change the colloidal stabilization process of metal chalcogenide complex (MCC)-capped PbS QDs from long-range electrostatic to short-range steric. The noncovalent surface modification remarkably improved the charge transfer efficiency at the graphene/PbS QDs interface upon using MCCs as a linker. The hybrid graphene/PbS QD photodetectors with MCC ligands exhibited superior detectivity up to 3 orders of magnitude higher than those with organic ligands due to the strong electron coupling between SLG and PbS QDs. Moreover, the carrier relaxation time of (NH₄)₃AsS₃-decorated QDs was dominated by efficient carrier transfer to the ligand states on timescales as fast as 1.03 ns. This work demonstrates that ligand engineering can significantly enhance the charge transfer process, which further boosts the responsivity and detectivity performances of the photoelectronic devices.