## 3 Results and Discussion
However, under illuminated conditions, the device shows a current variation between 10\({}^{-8}\) and 10\({}^{-4}\) A (0 to 1.5 V), inducing a change in the current of as much as approximately one order of magnitude. From the curve obtained under light conditions, the asymmetry in the  
Figure 7: I–V graphs in light and dark conditions for (**a**) PEDOT:PSS-CuBi\({}_{2}\)O\({}_{4}\) NP and (**b**) PEDOT:PSS devices. (**c**) \(\sigma\)–V graphs in light conditions for PEDOT:PSS-CuBi\({}_{2}\)O\({}_{4}\) NP devices. current magnitude is more evident depending on the polarity of the external voltage and indicative of a pure ideal diode behavior. Meanwhile, obtaining such low current values for darkness conditions, as mentioned previously, is indicative of high resistance inside the device. This could be associated with the NPs that compose the bulk heterojunction and some of the interphases present in the architecture of the device. When comparing these results with those obtained for a device made mainly of a pristine PEDOT:PSS film (Figure 7b), it is observed that the latter device exhibits an ambipolar and ohmic behavior. However, higher current values are observed for the same applied voltage range, indicating apparently higher conductivities. Additionally, unlike the glass/ITO/PEDOT:PSS-CuBi\({}_{2}\)O\({}_{4}\) NP/Ag device, no significant influence of the light or dark conditions is observed on charge transport. The difference in the behavior between the two devices is due to the presence of the CuBi\({}_{2}\)O\({}_{4}\) NPs. Despite that, the CuBi\({}_{2}\)O\({}_{4}\) NPs generate the n-p junction with the PEDOT:PSS, where these nanoparticles have a semiconductor behavior, which allows them to be used in optoelectronic devices, preferably under light conditions. The difference between the curves measured in light and dark conditions (Figure 7a) also indicates the possible use of these NPs in light-emitting diodes. To understand the conduction mechanisms of the device, the voltage-dependent conductivity (\(\sigma\)) in the heterojunction device was assessed at room temperature and is shown in Figure 7c. The graph has been divided into three different regions corresponding to the three different regimes of charge transport [57] previously mentioned. In the first regime, the behavior follows [PERSON]'s law, and it depends on the residual charges present inside the device [58]. During the second regime, the conductivity is dominated by the diffusion of the charges along the device and its interfaces [59]. Meanwhile, in the third regime, the conductivity is dominated by carrier drift or the saturation region [60]. The change in charge transport regimes is associated with the accumulation of charges inside the device, mainly by traps; however, the observed continuous increase in the conductivity (Figure 7c) indicates the feasibility of using the films with CuBi\({}_{2}\)O\({}_{4}\) NPs as components for diode-type devices. Each of the mentioned regions results in a different slope which is a consequence of the conduction mechanisms involved in the device conductivity at different voltages. On the other hand, conductivity values at room temperature for PEDOT:PSS/CuBi\({}_{2}\)O\({}_{4}\) NPs (Figure 7c) are in the range for semiconductor materials (10\({}^{-6}\) to 10\({}^{2}\) S cm\({}^{-1}\)) [61]. The inclusion of CuBi\({}_{2}\)O\({}_{4}\) NPs in PEDOT:PSS increases the conductivity, where the conductivity of pure PEDOT:PSS was about 39 S cm\({}^{-1}\)[62], and the obtained conductivity values for the device were as high as 4 S cm\({}^{-1}\) at 1.5 V, which is higher than the value of the pristine PEDOT:PSS (2 S cm\({}^{-1}\), Figure 7b). Additionally, these results indicate a higher conductivity compared to other 2D/PEDOT:PSS composite materials [4]. According to [PERSON] et al.