High-sensitivity broadband colloidal quantum dot heterojunction photodetector for night-sky radiation

Being with excellent photosensibility, bandgap tunability and solution processibility, lead sulfide (PbS) colloidal quantum dot (CQD) gets one of the most attracting nanomaterials for photodetectors and light-harvesting devices. Usually short ligands are used to passivate the surface of CQDs to enhance the carrier mobility in QD films, and different types of ligands show distinct influence on the physical/electrical properties on the passivated CQD films. In this paper, a high-sensitivity broadband photodetector based on PbS-EDT/PbS-TBAl heterojunction by band-alignment engineering was presented. After optimizing the thickness of PbS CQD films, we found that the maximum specific detectivity of the photodiode ITO/ZnO(40 nm)/PbS-TBAl(160 nm)/PbS-EDT(40 nm)/Au reached to 3.93 × 10¹³ Jones and 5.52 × 10¹³ Jones under 2.0 μW/cm² 910 nm and 1.9 μW/cm² 500 nm illuminations, respectively, showing excellent stability in air and high sensitivity to weak signal (i.e. night-sky radiation). Further, the device performance of photodiode ITO/ZnO/PbS-TBAl/PbS-EDT/Au is compared with that of the control device ITO/ZnO/PbS-TBAI/Au, and the underneath mechanism for the enhanced performance is discussed.