Bottom-Up Fabrication of BN-Doped Graphene Electrodes from Thiol-Terminated Borazine Molecules Working in Solar Cells

Graphene exhibits exceptional properties, including high tensile strength, mechanical stiffness, and electron mobility. Chemical functionalization of graphene with boron and nitrogen is a powerful strategy for tuning these properties for specific applications. Molecular self-assembly provides an efficient pathway for the tailored synthesis of doped graphene, depending on the molecular precursor used. This study presents a scalable approach to synthesizing large-area boron- and nitrogen-doped graphene using two borazine precursors bearing thiol functionalities. After self-assembly on electropolished polycrystalline copper foil, the precursors undergo photopolymerization under UV irradiation, and subsequent annealing in vacuum transforms the cross-linked BN-doped layer into a graphenoid structure. X-ray photoelectron spectroscopy confirms the integration of the borazine rings into the BNC architecture, while Raman spectroscopy reveals a red shift in the characteristic G bands along with intense and broad D bands, highlighting boron-nitrogen contributions. Transmission electron microscopy provides insight into the morphology and structural quality of the BNC films. The BNC films were successfully integrated as counter electrodes in dye-sensitized solar cells, achieving a power conversion efficiency of up to 6% under 1 sun illumination and 11.8% under low-intensity indoor ambient light. Hence, this work not only establishes a straightforward, controllable route for heteroatom doping but also introduces a novel concept of Pt-free counter electrodes for efficient indoor energy harvesting applications.