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 electronhole pairs and an increase in the rate of electron transport.