On the mechanism to suppress dark current via blending with an all-inorganic perovskite precursor in colloidal quantum dot photodetectors

PbS colloidal quantum dots (CQDs) are commonly used for infrared photodetectors due to their broad absorption range in the infrared region, size-dependent behavior, facile solution-synthesis processing and excellent optoelectronic properties. However, the conventional hot-injection method used to synthesize PbS CQDs is still complicated, and the device performance of pure PbS CQD photodetectors is not always very high due to the large density of surface states and the low mobility of the PbS CQD layer. In this paper, a ‘one-step’ method was firstly used to synthesize PbS CQDs capped with the short-chain ligand I (i.e., PbS-I), and then these were blended with an all-inorganic perovskite CsPbBr₃ precursor as the active layer via a facile solution process, thus high-performance photodetectors of Si/PbS:CsPbBr₃/Ag on a silicon wafer substrate were obtained after optimizing the volume ratio of PbS to the CsPbBr₃ precursor, and the underlying physical mechanism is believed to involve the surface passivation and the heightened carrier injection barrier, which is raised by the blending with CsPbBr₃. As a result, a maximum responsivity of 12.97 A W⁻¹ with a specific detectivity of 2.33 × 10¹² Jones under 4.8 μW cm⁻² 980 nm illumination at −1 V was obtained, as well as a responsivity of 4.38 A W⁻¹ with a specific detectivity of 1.43 × 10¹³ Jones in the self-driven mode.