In the present study, nanostructured nickel sulfide/graphene oxide -polypyrrole (NiS/GO-Ppy) hybrid was prepared through a two-step electrochemical deposition method on fluorine-doped tin oxide (FTO) as a suitable counter electrode (CE) for Pt-free dye-sensitized solar cell (DSSC). At first, GO- Ppy film was deposited from a mixture containing pyrrole/sodium dodecyl benzene sulfonate/GO nanosheets using a chronoamperometry method at a constant potential of 0.8 V during 600 s onto FTO. Then, NiS was deposited from a solution containing 50 mM NiCl2.6 H2O and 1 M thiourea onto the GO-Ppy/FTO through a periodic potential reversal method by applying a cathodic potential of -0.90 V for 6 s followed by an anodic potential of 0.1 V for 24 s during 10 consecutive cycles. Several techniques such as field emission-scanning electron microscopy (FE-SEM), X-ray diffraction and Raman spectroscopy were used for the characterization of nanostructured NiS/GO-Ppy. The electrochemical behavior of NiS/GO-Ppy/FTO CE for I3 /I redox couple was studied using electrochemical impedance spectroscopy (EIS) and Tafel polarization. The symmetric cell based on the NiS/GO-Ppy/FTO CEs presented the lowest resistance against the charge transfer and the highest exchange current density. The performance of DSSC assembled with NiS/GO-Ppy/FTO CE and TiO2 photoanode was investigated through J–V test. The DSSC displayed the power conversion efficiency (PCE) about 6.32 % under AM 1.5 (100 mW cm-2).
