Ternary Pb1−xCdxS quantum dot-based UV-vis-NIR photoelectrochemical photodetection with superior photoresponsivity and detectivity

Abstract

Aqueous lead monosulfide (PbS) quantum dots (QDs) fabricated by conventional approaches display poor photodetection performance and unsatisfactory chemical stability, so various strategies for well-defined PbS QD-based heterostructures have been developed, which are usually complicated and unsuitable for large-scale production. In this work, homogeneous ultrasmall, uniform ternary Pb_1−xCd_xS QDs are rationally designed and successfully fabricated by an in situ aqueous coprecipitation method. The Pb_1−xCd_xS QDs have an average size of around 4 nm with narrow distribution, and show excellent optical absorption in the UV-vis-NIR region. The as-synthesized Pb_1−xCd_xS QDs are directly employed as active materials for the construction of photoelectrochemical (PEC)-type photodetectors (PDs), displaying excellent PEC photodetection performance with the best photocurrent density (80.92 μA cm⁻²), photoresponsivity (27 580 μA W⁻¹), response/recovery time (0.16/0.08 s), detectivity (9.7 × 10¹⁰ Jones) and durable cycling stability at x = 0.5. Interestingly, density functional theory (DFT) calculations demonstrate that the bandgap changes from having indirect characteristics (x = 0.25) to direct (x = 0.50), and then to indirect characteristics again (x = 0.75), and a very small direct bandgap for the Pb_0.50Cd_0.50S is obtained, in good agreement with the PEC results. It is anticipated that this contribution can shed light on new designs of high-performance homogeneous multi-elemental nanostructures and widen their practical applications in PEC-type PDs.