## 3 Results and Discussion
(**a**) I–V curves of the bare Bi\({}_{2}\)O\({}_{2}\)Se under different light intensities. (**b**) A typical device response at 550–1000 nm. (**c**) Responsivity and detectivity of the bare Bi\({}_{2}\)O\({}_{2}\)Se detector at 405–1000 nm. (**d**) The dynamic response speed of the device under 550 nm at P = 2.33 mW/cm\({}^{2}\). of the quantum dots. After two repeated spin-coating cycles, the optimal thickness of the PbS quantum dot layer was achieved, ensuring a dense distribution of the PbS quantum dots on the detector. Next, we will investigate the performance of the PbS QDs/Bi\({}_{2}\)O\({}_{2}\)Se photodetector in detecting signals in the visible light and infrared spectrum. The schematic representation of this device is shown in Figure 4a. As shown in Figure 4b, introducing PbS QDs into Bi\({}_{2}\)O\({}_{2}\)Se was observed to increase the channel current by approximately 10 times under dark conditions, a phenomenon attributed to the electron transfer from PbS QDs to Bi\({}_{2}\)O\({}_{2}\)Se. Under excitation at 550 nm, the photocurrent (3648 nA) in the hybrid photodetector was nearly 13 times that of bare Bi\({}_{2}\)O\({}_{2}\)Se (280 nA). This significant enhancement in photocurrent is attributed to the charge transfer between PbS and Bi\({}_{2}\)O\({}_{2}\)Se, along with a higher electron mobility in Bi\({}_{2}\)O\({}_{2}\)Se compared to PbS QDs. This enhancement is due to the increased number of carriers within Bi\({}_{2}\)O\({}_{2}\)Se, leading to a reduction in the transit time within the transport channel and thereby enhancing the photodetection performance of the hybrid photodetector [44]. Figure 4c illustrates the variation of photocurrent at 550 nm under different light intensities. Figure 3: Preparation and characterization of PbS QDs/Bi\({}_{2}\)O\({}_{2}\)Se. (**a**) TEM images of PbS QDs. (**b**) The absorption spectrum of the PbS quantum dot solution used shows the first excitation peak at around 1100 nm. (**c**) Schematic diagram of the preparation process for the PbS QDs/Bi\({}_{2}\)O\({}_{2}\)Se hybrid heterojunction. Responsivity and detectivity are important metrics for assessing the performance of photodetectors, and they can be obtained based on the following equations [45; 46; 47]:  
\[R=\frac{I_{ph}}{PA}\]  
\[D^{*}=\frac{\sqrt{A}R}{\sqrt{2 eI_{d}}}\]  
where \(P\) is the light power intensity, \(R\) is the responsivity, e is the electron charge, \(I_{d}\) is dark current, and \(A\) is the effective device area. As the light intensity increases, the photocurrent of the hybrid photodetector also increases continuously, and the hybrid heterojunction photodetector also exhibits a fast response speed. However, we observed a gradual decrease in the responsivity and detectivity of the hybrid photodetector with  
Figure 4: Photodetection performance and band alignment of the PbS/Bi\({}_{2}\)O\({}_{2}\)Se hybrid photodetector. (**a**) The tetragonal crystal structure of Bi\({}_{2}\)O\({}_{2}\)Se. (**b**) I–V curves of bare Bi\({}_{2}\)O\({}_{2}\)Se and PbS/Bi\({}_{2}\)O\({}_{2}\)Se hybrid photodetectors under dark conditions and illumination at a wavelength of 550 nm (2.33 mW/cm\({}^{2}\)). (**c**) A typical device response at 550 nm under varied light intensities from 2.33 mW/cm\({}^{2}\) to 0.2 mW/cm\({}^{2}\). (**d**) Responsivity and detectivity of the Bi\({}_{2}\)O\({}_{2}\)Se/PbS hybrid photodetector under illumination by a 550 nm laser at various power levels with a bias of 1 V. (**e**) The dynamic response speed of the device under 550 nm at P = 2.33 mW/cm\({}^{2}\). (**f**) Response spectra of Bi\({}_{2}\)O\({}_{2}\)Se and Bi\({}_{2}\)O\({}_{2}\)Se/PbS hybrid photodetectors. (**g**) UPS test graphs of bare PbS and Bi\({}_{2}\)O\({}_{2}\)Se. (**h**) Drawing on the estimated valence band positions and work function values from UPS, a band diagram is depicted illustrating the carrier transfer situation between PbS and Bi\({}_{2}\)O\({}_{2}\)Se upon contact. increasing light intensity (Figure 4d).