Optimization of Ni2+/Ni3+ ratio in reduced graphene oxide/nickel oxide nanohybrids for platinum free dye sensitized solar cells

Abstract A strategy has been explored to design a novel network of reduced graphene oxide (rGO)/nickel oxide (NiO) nanohybrids with optimized Ni 2+ /Ni 3+ ratio for the fabrication of compact, flexible, and large area Pt-free dye sensitized solar cells (DSSCs). The rGO/NiO nanohybrids were synthesized by a hydrothermal method and characterized by field emission scanning electron microscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. These studies demonstrate that the rGO/NiO nanohybrids with Ni 2+ rich species show high catalytic activity toward the I¯/I 3 ¯ redox reaction. This led to the fabrication of improved DSSCs with power conversion efficiency as high as 3.69% with these nanohybrids as counter electrodes in comparison with DSSC devices containing counter electrodes based on rGO (1.71%) and NiO (0.75%).