Hierarchical NiO@NiS@graphene nanocomposite as a sustainable counter electrode for Pt free dye-sensitized solar cell

Recent studies in DSSC has been concentrated on developing counter electrode (CE) with low cost materials which has high power conversion efficiency, as well as high catalytic property. NiO has been studied as CE for high short circuit current in DSSC because of its wide bandgap. In this work nickel oxide@nickel sulfide@ graphene (NiO@NiS@G) nanocomposite was synthesized by hydrothermal method. Structural composition of NiO@NiS@G nanocomposite was revealed by X-ray diffraction (XRD) and confirmed the formation of NiO@ NiS@G nanocomposites. Raman spectroscopy is the most effective tool for the analysis of carbon-based materials. The D band and G band of Raman spectrum confirmed the conversion of graphene (G) from graphene oxide (GO). X-ray photoelectron spectroscopy (XPS) shows the presence of Ni, O, C and S atoms in the composition. The morphology analysis revealed the formation of NiO@NiS nanoplates anchored on the surface of the graphene sheets. The as-synthesized materials were coated on FTO (fluorine-doped fin oxide) substrate by spray coat technique and their catalytic properties were studied. The electrochemical activity (peak separation Epp) of NiO@NiS@G nanocomposite (391 mV) was high compared to NiO@NiS (496 mV) and exhibited excellent stability compared with NiO@NiS. Further, the charge transfer resistance of commercial N, NiO@NiS@G, and NiO@NiS was measured by Electrochemical Impedance Spectroscopy (EIS), with the resistance values of 15.7, 23.2, and 36.8 Omega, respectively. The efficiency of a solar cell with NiO@NiS@G is 2.10% which is high compared with NiO@NiS (1.68%).