A Proof-of-concept Study on Enhancing the Visible Photoresponse of RGO/ZnO Devices with PbS Quantum Dots

Hybrid structures of zinc oxide nanorods (ZnO NRs) and reduced graphene oxide (RGO) are a promising platform for photodetection applications, owing to their excellent charge transport pathways and high stability. However, their operational range is intrinsically limited to the ultraviolet (UV) spectrum due to the wide optical band gap of ZnO (~3.37 eV), restricting their applicability in broadband photodetection. To circumvent this issue, in this study, we introduce lead sulfide quantum dots (PbS QDs) decoration to the RGO/ZnO-based photodetector. The deposition of 2 mg mL-1 PbS QDs successfully broadened the light absorption capabilities, as evidenced by a decreased optical band gap from 3.19 to 3.13 eV. Consequently, the fabricated RGO/ZnO-PbS NRs heterostructure photodetector demonstrates a remarkable improvement in performance achieving a maximum photo-current of 292.06 µA, with a 19.5-fold increase in responsivity and photoconductive gain, and nearly three times higher in detectivity, when excited with 395 nm (800 µW) light source. Nonetheless, the device also maintains a repeatable signal pattern over several on/off cycles. Therefore, this work not only presents a highly effective path for engineering the spectral response of ZnO-based devices but also validates the pivotal role of PbS QDs in creating high-performance, broadband photodetectors for next-generation optoelectronic applications.