Performance Optimization of ZnO QDs/F8BT Heterojunction-Based UV–Visible Photodetectors Using MoO x Hole Transport Layer

This article investigates the effect of the MoO x hole transport layer (HTL) on the performance of a poly(9,9-dioctylfluorene-alcohol-benzothiadiazol) (F8BT) and ZnO colloidal quantum dots (CQDs) heterojunction-based ultraviolet-visible (UV-vis.) photodetector fabricated on indium-tin oxide (ITO) substrates. The performance of the conventional ITO/ZnO CQDs/F8BT/Ag (Device-1) structure is compared with that of the proposed ITO/ZnO CQDs/F8BT/MoO x /Ag (Device-2) structure. The MoO x HTL in the proposed device is used to enhance the hole transport and reduce the dark current by preventing electron injection from anode under reverse bias. On the other hand, the trapping of photogenerated electrons at the intrinsic defects of ZnO CQDs has been explored for enhancing the external quantum efficiency (EQE) beyond 100% by trap-assisted photomultiplication phenomenon. The maximum responsivity ([Formula Omitted], specific detectivity ([Formula Omitted], EQE, rise time ([Formula Omitted], and fall time ([Formula Omitted] of Device-2 (Device-1) were obtained as 44 A/W (24 A/W), [Formula Omitted] Jones ([Formula Omitted] Jones), [Formula Omitted]14171% (7729%), 0.016 s (0.026 s), and 0.018 s (0.030 s), respectively, under −1 V bias voltage and 25-[Formula Omitted]/cm2 light intensity of 385-nm wavelength. Furthermore, the MoO x HTL in Device-2 introduced the self-biased feature of the photodetector with the maximum values of [Formula Omitted], [Formula Omitted], EQE, [Formula Omitted], and [Formula Omitted] as [Formula Omitted]59 mA/W, [Formula Omitted] Jones, 18.98%, 0.012 s, and 0.017 s, respectively, under zero-bias operation and 25-[Formula Omitted]/cm2 intensity of 385 nm.