## 3 Results and Discussion
It is observed that 0.5% and 1% rGO significantly improve the \(FF\) (fill factor). However, for 2% and 4% rGO, there is a decrease in \(FF\), \(J_{sc}\), and \(V_{oc}\), possibly due to the trapping of photo-excited electrons, which reduces the photocurrent in the DSSC. As [PERSON] et al. reported, this phenomenon has already been observed, and the decrease in \(J_{sc}\) for higher rGO concentrations can be explained by the disintegration of rGO layers into tiny fragments that hinder charge transport in the DSSC. Thus, charge carriers are trapped in the rGO during measurement [50]. This argument is further supported by the analysis of the degree of disorder in the rGO structures, as indicated by the \(\mathrm{I_{D}}/\mathrm{I_{G}}\) ratio, estimated through Raman spectroscopy (Figure 4), which shows higher values for samples with higher rGO concentrations. This suggests that the structure does not facilitate electron flow through the device but instead generates recombination centers, which reduce the photocurrent and, consequently, the DSSC efficiency. Furthermore, SEM-FEG images (Figure 3) reveal a deficiency in the ZnO/ZnS compound in samples with higher concentrations of rGO. This could directly affect the charge transport process within the DSSC, as part of the solar radiation does not reach the dye molecules adsorbed on the surface of ZnO/ZnS. Consequently, this reduces the electron excitation process, impacting the photovoltaic conversion efficiency (_PCE_) [51]. It is also noted that for the pure ZnO/ZnS compound, a reduction in R\({}_{shl}\) (shunt resistance) is observed based on the slope of the J-V curve at \(J_{sc}\)[52; 53; 54]. This reduction in slope can be seen when compared to the curves of the compounds doped with 0.5% rGO and 1% rGO, directly impacting the \(FF\) and, consequently, the \(PCE\) of the ZnO/ZnS cell, which shows reduced values. According to [PERSON] and [PERSON], this decrease in R\({}_{shl}\) for pure ZnO/ZnS can be attributed to bulk defects in the semiconductor and at the interface. The authors explain that including ZnS leads to an increase in the leakage current of the photovoltaic device [55]. However, adding rGO can induce changes in the surface and bulk states of the system, providing improved conductivity, stability, and solar cell performance. Figure 3:0 Dark current curves of the photovoltaic cells for the ZnO/ZnS and ZnO/ZnSrGO samples. Moreover, none of the photovoltaic cells exhibited higher \(J_{sc}\) values than the ZnO/ZnS sample. However, they demonstrated superior \(FF\) and \(P_{max}\), leading to a higher \(PCE\). In this context, small amounts of rGO improved the flow of excited electrons, reducing the recombination process between electron-hole pairs in the DSSC. These findings significantly contribute to our understanding of DSSC performance. Therefore, the DSSC with 1% rGO exhibited the highest efficiency (Table 1), achieving a short-circuit current density (\(J_{sc}\)) of 0.6 mA/cm\({}^{2}\), an open-circuit voltage (\(V_{oc}\)) of 0.70 V, a fill factor (\(FF\)) of 57%, a maximum power of 0.238 mW, and a \(PCE\) of 0.24%. Figure 10 shows a schematic diagram of the behavior of the electrons inside the DSSC. Since the energy level of rGO is intermediate about the ZnO/ZnS compound and the FTO film, the photogenerated electrons that are transmitted from the dye to the ZnO/ZnS are rapidly transmitted to rGO in order to reduce the effects of recombination inside the cell. However, the photocurrent value decreases for more significant amounts of rGO (2% and 4%) due to the presence of charge-trapping centers.