First-Principles Design of Covalent Diamond–Graphene Nanoribbon Type-II Heterojunctions for Potential Photovoltaics and Photocatalysis Applications

The design of efficient heterojunctions for solar energy applications remains a significant challenge, particularly in optimizing charge separation and material stability for long-term performance. Here, we explore covalent Type-II heterojunctions formed by integrating diamond with graphene nanoribbons (GNRs), where electron density is modulated within the π-bonds of graphene’s six-membered rings. By tuning the GNR width and edge termination, the electronic structures of the heterojunctions can be systematically tailored. The resulting diamond-supported GNR (DS-GNR) heterojunctions generate a built-in electric field at the interface, enabling efficient separation of photogenerated electrons and holes and promoting interfacial charge transfer. Optical property analysis reveals strong visible-light absorption (∼105 cm–1), a broad absorption edge, effective charge separation, and light carrier effective masses, all of which are advantageous for photovoltaic applications. Furthermore, band alignment calculations demonstrate that several DS-GNR configurations meet the energy-level criteria for photocatalytic water splitting, highlighting their potential for solar-driven hydrogen production. Particularly, three-layer sp2-carbon GNRs form the desired Type-II alignment, with hydrogen-, hydroxyl-, and dihydrogen-terminated edges exhibiting suitable band positions for photocatalytic hydrogen evolution. These findings establish DS-GNR heterojunctions as promising candidates for both photovoltaic and photocatalytic energy conversion, offering design strategies for next-generation carbon-based materials in renewable energy technologies.