The greatest challenge in graphene-based material synthesis is achieving large surface area of high conductivity. Thus, tuning physico-electrochemical properties of these materials is of paramount importance. An even greater problem is to obtain a desired dopant configuration which allows control over device sensitivity and enhanced reproducibility. In this work, substitutional doping of graphene oxide (GO) with nitrogen atoms to induce lattice–structural modification of GO resulted in nitrogen-doped reduced graphene oxide (N-rGO). The effect of doping temperatures and various nitrogen precursors on the physicochemical, optical, and conductivity properties of N-rGO is hereby reported. This was achieved by thermal treating GO with different nitrogen precursors at various doping temperatures. The lowest doping temperature (600 °C) resulted in less thermally stable N-rGO, yet with higher porosity, while the highest doping temperature (800 °C) produced the opposite results. The choice of nitrogen precursors had a significant impact on the atomic percentage of nitrogen in N-rGO. Nitrogen-rich precursor, 4-nitro-ο-phenylenediamine, provided N-rGO with favorable physicochemical properties (larger surface area of 154.02 m² g⁻¹) with an enhanced electrical conductivity (0.133 S cm⁻¹) property, making it more useful in energy storage devices. Thus, by adjusting the doping temperatures and nitrogen precursors, one can tailor various properties of N-rGO.

The design and fabrication of electronic devices based on graphene nanomaterials are dependent on the tuning of Fermi levels. This can be achieved by doping graphene oxide (GO) with an electron-withdrawing (p-type) or electron-donating (n-type) species that causes changes in the electron density and enhances the electrochemical properties. In this research, the effect of boron content on the optical, electrochemical, and conductivity properties of GO was investigated. Boron-doped reduced graphene oxide (B-rGO) was synthesized via a chemical vapor deposition method by using GO and varying amounts of boric anhydride, as a boron precursor, at a doping temperature of 600 °C. The B-rGO samples were characterized by standard spectroscopic techniques. B-rGO had a sheet structure with various graphene islands and disordered regions. The highest boron content incorporated into the reduced GO framework was 7.12%. B-rGO samples manifested strong absorption in the ultraviolet region. An electronic band structure with a low charge resistance of 20.23 Ω and enhanced electrical conductivity properties of 5.920 S cm⁻¹ was observed and noted to be dependent on the concentration of boron incorporated. All the B-rGO samples demonstrated a p-type conductivity behaviour which is attributed to an increase in the density of states near the Fermi level. This work opens a new avenue for the fabrication of solar cells based on p-type B-rGO.

Semiconductor materials have been recently employed in photovoltaic devices, particularly dye-sensitized solar cells (DSSCs), to solve numerous global issues, especially the current energy crisis emanating from the depletion and hazardous nature of conventional energy sources, such as fossil fuels and nuclear energy. However, progress for the past years has been mainly limited by poor electron injection and charge carrier recombination experienced by DSSCs at the photoanode. Thus, novel semiconductor materials such as bismuth oxide (Bi₂O₃) have been investigated as an alternative photoanode material. In this study, Bi₂O₃ was integrated with nitrogen- or boron-doped reduced graphene oxide (N-rGO or B-rGO, respectively) via a hydrothermal approach at a temperature of 200 °C. Various instrumental techniques were used to investigate the morphology, phase structure, thermal stability, and surface area of the resulting nanocomposites. The incorporation of N-rGO or B-rGO into Bi₂O₃ influenced the morphology and structure of the nanocomposite, thereby affecting the conductivity and electrochemical properties of the nanocomposite. B-rGO/Bi₂O₃ exhibited a relatively large surface area (65.5 m² g⁻¹), lower charge transfer resistance (108.4 Ω), higher charge carrier mobility (0.368 cm² V⁻¹ s⁻¹), and higher electrical conductivity (6.31 S cm⁻¹) than N-rGO/Bi₂O₃. This led to the fabrication of B-rGO/Bi₂O₃ photoanode-based DSSCs with superior photovoltaic performance, as revealed by their relatively high power conversion efficiency (PCE) of 2.97%, which outperformed the devices based on N-rGO/Bi₂O₃, rGO/Bi₂O_3, and Bi₂O₃ photoanodes. Therefore, these results demonstrate the promising potential of heteroatom-doped rGO/Bi₂O₃-based nanocomposites as photoanode materials of choice for future DSSCs.