Dye-Sensitized Solar Cells Based on an N-Doped TiO2 and TiO2-Graphene Composite Electrode

Abstract

In this work, the effect of graphene and nitrogen doping on the performance of dye-sensitized solar cells of pure TiO2 was studied. Pure and N-doped TiO2 nanoparticles were synthesized using a hydrothermal method, while graphene was prepared through the reduction of graphene oxide. The materials were characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), Raman, Brunauer–Emmett–Teller surface area analysis (BET) and ultraviolet-visible (UV-Vis) diffusion reflectance spectroscopy. Nitrogen dopant concentration varied from 0 at.% to 1.57 at.%. The results confirmed that all N-doped samples exhibited pure anatase phase with an average diameter in the range of 7–12 nm. The pore volume and BET surface area increased with the amount of nitrogen in TiO2. XPS investigation displayed an N1s peak around 397 eV, which suggested N-Ti-O structure in the TiO2 matrix. Moreover, optical measurements showed that the optical absorption edge of N-doped TiO2 exhibited a significant shift from ultraviolet to visible light region in comparison with pure TiO2. Dye-sensitized solar cells (DSSCs) were fabricated using N719 dye and various TiO2 based photoanodes. The photoanode of N-doped TiO2 modified with graphene showed the highest energy-conversion efficiency of 6.3%, while the efficiencies of pure and N-doped TiO2 cells are 0.41% and 1.21%, respectively. The improvement in conversion efficiency of graphene-based DSSC was attributed to the formed electron bridges between TiO2 and fluorine-doped tin oxide (FTO), which led to a reduction in the recombination rate of electron-hole pairs and an increase in the rate of electron transport.