Effects of Graphene in Dye-Sensitized Solar Cells Based on Nitrogen-Doped TiO₂ Composite

Graphene (GR) exhibits impressive photoelectric properties, including a large specific surface area, high charge-carrier mobility, high conductance, and fast electron transfer. In this study, the effect of GR on the performance of dye-sensitized solar cells (DSSCs) was investigated by mixing GR into N-doped TiO₂ photoelectrodes. GR/N-doped TiO₂ (GNT) nanoparticles were prepared using the sol–gel method. After preparation, the presence of GR in the photoelectrodes was confirmed using transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy analyses. After the addition of GR, the photoelectrodes displayed enhanced dye adsorption properties with lower internal resistances and faster transport times. Accordingly, DSSCs with these photoelectrodes generated high current density with a low electron-recombination rate. The maximum power conversion efficiency of DSSCs with GR/N-doped photoelectrodes was 9.32% with optimized DSSC parameters; this represents an enhancement of approximately 22% over that of DSSCs with N-doped photoelectrodes. The addition of excess GR weakened the crystallization of particles on the surface of photoelectrodes, which resulted in low dye adsorption and decreased efficiency of the DSSCs. In summary, the addition of GR promoted increased dye loading and enhanced DSSC efficiency. The optimal amount of GR for high-efficiency DSSCs was successfully determined in this study