High-performance PbS quantum dots photodetector based on NiO_x/PbS-EDT heterojunction hole transport layer

The development of lead sulfide (PbS) colloidal quantum dots (CQDs) with excellent photosensitivity, bandgap tunability and solution processability promises to address the high cost and integration difficulties of commercial Ⅲ-Ⅴ semiconductor near-infrared (NIR) detectors. Solution-phase ligand-exchanged (SPLE) PbS-I thin films have received increasing attention due to their high quality and excellent air stability. In recent years, reported PbS-I photodiodes have relied on regular n-i-p structure and solid-state ligand-exchanged (SSLE) PbS-EDT thin films as hole transport layers (HTL). Although these devices exhibit excellent external quantum efficiency (EQE) and responsivity, the large dark current limits the further improvement in detectivity. Considering the advantages of inverted-structure devices in noise suppression, we investigate the effects of three HTLs (NiO_x, PbS-EDT and NiO_x/PbS-EDT heterojunction) on the performance of PbS-I photodiodes. The experimental results show that the device with NiO_x/PbS-EDT as the HTL has lower dark current (1.6 × 10⁻³ mA·cm⁻²) under −1 V bias compared to the device with single NiO_x or PbS-EDT HTL, which lead to high detectivity (6.70 × 10¹¹ Jones) and responsivity (0.487 A·W⁻¹).