Two-step ligand exchange to promote charge transfer in PbSe quantum dots photodetector for pulse monitoring

Abstract

Quantum dots (QDs) have emerged as promising materials for next-generation infrared semiconductors due to their facile solution processing, low-cost, tunable bandgap and great optoelectronic properties. However, the organic long-chain ligands that modify the surface of QDs hinder charge transfer, thus impairing the performance of the QD infrared photodetectors. Here, we report a two-step ligand exchange strategy that decouples the native long-chain ligands from the QDs using specific molecules, and then attaches the short-chain ligands, resulting in high response for lead-rich lead selenide (PbSe) QDs photodetectors. During the layer-by-layer thin film deposition process, the 1-octanethiol is first used for primary ligand exchange to remove stable ligands, followed by the 3-mercaptopropionic acid for secondary exchange to ensure thorough passivation of surface defects. The two-step processing PbSe QDs photodetector has a responsivity of up to 1.28 A/W, a detectivity of 9.65 × 1012 Jones and a record high external quantum efficiency of 144.4% at a bias voltage of 0.5 V at 1100 nm. Benefitting from the high performance, the PbSe QDs photodetector can be integrated into a pulse monitoring platform, achieving a physiological sign monitoring by capturing real-time pulse signals of human superficial arteries.