Inorganic Ligand Exchange Facilitating Carrier Transfer in Graphene/Ag2Se Quantum-Dot Near-Infrared Photodetectors

With the emergence of new applications of infrared photodetection technology, it is increasingly urgent to develop nontoxic and environmentally friendly alternative materials for heavy metal semiconductors. Research over the past decade has shown that silver selenide (Ag₂Se) quantum dots (QDs) have become effective substitutes for lead- and mercury-based QDs, especially in the near-infrared (NIR) region. Owing to the large electron mobility and wide spectral response characteristic of graphene and the high light absorption efficiency of QDs, the graphene/Ag₂Se QDs composite-based photodetectors (PDs) exhibit advantages of high responsivity and wide spectral detection range. However, long-chain ligands on the QDs’ surface limit the transport efficiency of charge carriers, which, in turn, affects the performance of PDs. Herein, in order to overcome this limitation, we propose photoconductive PDs based on graphene/Ag₂Se QDs, and a liquid-phase inorganic ligand exchange technique is introduced to replace the original long-chain ligand of QDs with a specific inorganic short-chain molecule in this study. Consequently, the designed graphene/Ag₂Se QDs PDs achieve a maximum responsivity of 2.878 × 10⁴ A/W at a 100 mV bias and a photocurrent of 66.60 μA under an 808 nm laser excitation. The ligand exchange strategy significantly improves the performance of Ag₂Se QDs, making them a strong candidate for NIR absorption and contributing to the development of novel PDs with small size, lightweight, low power consumption, and economic cost.