High performance wide-spectrum mixed PbS CQDs photodetector

PbS quantum dots have attracted significant attention in the near-infrared (NIR) region due to their excellent optoelectronic properties. However, the preparation of large-sized PbS quantum dots and devices that can detect across the entire NIR to short-wave infrared (SWIR) spectrum remains a significant challenge. In this study, we propose a method that involves multiple injections of sulfur precursors during the synthesis process via thermal injection, which broadens the absorption wavelength of PbS quantum dots to 2123 nm. Furthermore, we mix single-injection PbS (PbS_I) and triple-injection PbS (PbS_III) quantum dots to form bulk homojunctions, due to the 0.05 eV Fermi level offset between them. The internal built-in electric fields between the junctions effectively facilitate exciton dissociation. Broadband photodetectors are then fabricated using the mixed quantum dots as the photoactive layer. Benefiting from efficient carrier separation, the dark current of the infrared photodetector based on mixed quantum dots reaches 3.3 × 10⁻⁶ A, which is lower than that of photodetectors based on either single-sized quantum dots. Moreover, the hybrid device exhibits a responsivity of 4.3 mA/W at a long wavelength of 1940 nm. This represents a 7.4 fold improvement compared to the PbS_I quantum dot photodetector and a 3 fold enhancement compared to the PbS_III counterpart, indicating a significant improvement in the responsivity of the photodetector.