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.

Perovskite solar cells (PSCs) are emerging efficient photovoltaic devices, with record-high power conversion efficiencies (PCE) of more than 25.5%. However, PSCs exhibit some drawbacks, such as poor stability upon exposure to moisture or humidity, ultraviolet (UV) radiation and heat, which in turn limits the device lifetime and performance. In addition, the introduction of perovskite films comes with associated toxicity, which is a major environmental concern. Furthermore, the application of titanium dioxide (TiO₂) as an electron transport layer (ETL) and 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) as a hole transport layer (HTL), causes device instability. The wide-bandgap characteristic of TiO₂ introduces charge carrier recombination in the ETL, which, in turn, impairs device performance. This is, over and above, the high cost of spiro-OMeTAD, coupled with its multi-step synthetic preparation method. To address the aforementioned shortcomings, approaches, such as modifying the interfacial architecture, have been explored by introducing versatile materials between the charge-collecting electrode and the perovskite active layers. In this regard, perovskite oxides are more appealing due to their wide bandgap and high electron mobility. However, perovskite oxides have limitations due to their agglomeration, which causes short-circuits and leakage current, in addition to their poor charge separation efficiency, surface hydrophilicity and weak visible-light absorption. As a result, nanocomposites of perovskite oxides with carbon-based materials, particularly graphene and its derivatives, have attracted significant research attention due to their exceptional optoelectronic properties, superior stability, and non-toxicity of graphene-based materials. Therefore, this review discusses the recent trends in graphene-based materials, their composites with perovskite oxides, effective ETLs or HTLs of PSCs and the subsequent improvement of photovoltaic performance. In addition, a summary of synthetic routes for perovskite oxides/graphene nanocomposites is presented. This review will foster the advancement of the fabrication of PSCs with improved PCE and stability.