Copper nanoparticle-induced plasmon-enhanced photoconductive gain in MoO₃ hole-transporting layer for high-performance near-infrared quantum dot photodetectors

Photomultiplication-type photodetectors offer an effective strategy to achieve high gain without complex device architectures. However, most existing systems rely on relatively high operating voltages and exhibit relatively low device performance. In this paper, a high-performance PbS quantum dot near-infrared photodetector ITO/ZnO/PbS/[MoO₃/Cu-NPs/MoO₃]/Ag, in which a Cu nanoparticles (Cu-NPs) layer is embedded in the MoO₃ hole-transporting layer to achieve plasmon-assisted photoconductive gain, is presented. As the result, an ultrahigh external quantum efficiency of 63,250 % with a specific detectivity (D *) of 1.3 × 10¹⁴ Jones are obtained from photodetector ITO/ZnO(60 nm)/PbS(240 nm)/[MoO₃(20 nm)/Cu-NPs(2 nm)/MoO₃ (40 nm)]/Ag under 0.2 μW/cm² 980 nm illumination at −1 V. Further, the underlain mechanism for the enhanced performance is discussed in detail with the help of finite-difference time-domain (FDTD) simulations, our results reveal that the incident light absorption into the device strongly depends on the thickness of the MoO₃ layer, as well as the size of the Cu-NPs and the embedding depth of Cu-NPs layer in the MoO₃ layer. Also, the optimal thickness of 60 nm for the MoO₃ layer, the diameter of 2 nm for Cu-NPs and a distance of 20 nm for Cu-NPs layer to the PbS/MoO₃ interface are determined and these parameters are in agreement with our experimental results. Therefore, it provides a facile method to obtain plasma-assisted photoconductive gain for near-IR optoelectronics.