## 4 Conclusions  
In summary, our research has revealed the potential of rGO when used in small amounts with the ZnO/ZnS compound to enhance its photovoltaic capacity. The results indicate that while rGO introduced during the heterostructure synthesis process via MAH treatment does not significantly increase the \(J_{sc}\) of the solar cells, it can enhance power balance and shunt resistance when applied in small quantities. This improvement contributes to an increase in the _PCE_ of the solar cells. Specifically, the solar cells with lower concentrations of rGO (0.5% and 1%) demonstrated higher efficiencies, achieving a 14.2% increase compared to the pure ZnO/ZnS photoelectrode. Furthermore, samples with small amounts of rGO demonstrate longer electron lifetimes, indicating a reduced electron-hole recombination rate.  
It is important to note that when the concentration of rGO exceeds 1%, the material starts to exhibit electron trapping centers. This behavior is attributed to the number of structural defects observed during the characterization process caused by the turbulent method used.  
The ZnO/ZnS:1% rGO system showed potential due to its response, with a prominent _FF_ and _PCE_, indicating a better performance balance among the solar cells. This balance of performance provides reassurance about the thoroughness of our research. Although the DSSC response improved, further investigations are necessary regarding the incorporation of rGO into the ZnO/ZnS structure and its applications in other photonic processes.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15010291/s1](https://www.mdpi.com/article/10.3390/app15010291/s1)]([https://www.mdpi.com/article/10.3390/app15010291/s1](https://www.mdpi.com/article/10.3390/app15010291/s1)), Figure S1: XRD pattern of graphene oxide. Figure S2: Photoelectrodes of the samples: (a) ZnO/ZnS; (b) ZnO/ZnS:0.5% rGO; (c) ZnO/ZnS:1% rGO; (d) ZnO/ZnS2% rGO; (e) ZnO/ZnS4% rGO.  
Conceptualization, M.L.M., C.D.F. and T.K.P.; methodology, T.K.P., R.D.C., C.D.F., C.F.d.M.J. and L.T.G.; validation, T.K.P., R.D.C. and C.D.F.; formal analysis, T.K.P., C.D.F. and M.L.M.; investigation, T.K.P., C.D.F., R.D.C., E.C.M. and E.L.; resources, C.F.d.M.J., M.M.F., C.W.R., S.d.S.C., P.L.G.J., E.L. and M.L.M.; data curation, T.K.P. and C.F.d.M.J.; writing--original draft preparation, T.K.P. and C.F.d.M.J.; writing--review and editing, R.D.C., L.T.G., C.F.d.M.J. and M.L.M.; supervision, M.L.M.; funding acquisition, M.L.M., C.D.F., M.M.F., E.C.M. and P.L.G.J. All authors have read and agreed to the published version of the manuscript.  
This study was partly financed by the Brazilian agencies CAPES - Finance Code 001, CNPq (432242/2018-0), (MCT/CNPq 458452/2014-9), (INCT-NAMITEC/CNPq 406193/2022-3) and CNPq (406311/2023-4), FAPERGS (22/2551-0000604-3) and (24/2551-0001289-3).  
Not applicable.  
The data supporting the findings of this study are available from the corresponding author upon reasonable request.  
The authors acknowledge the LIEC Laboratory of the Federal University of Sao Carlos, SP, Brazil by the field-scanning electron microscopy (SEM-FEG) and X-ray diffraction (XRD) measurements.  
There are no conflicts to declare.