Computational modelling of doped graphene quantum dots for energy applications Nasiru Aminu Rano, Xue Yong and Natalia Martsinovich Department of Chemistry, University of Sheffield, UK Graphene quantum dots (GQDs) have gained tremendous attention in academia and industry for their diverse applications in energy, sensing, bioimaging, optoelectrical, photocatalysis etc. Their non-toxicity and intrinsic inert carbon properties make them one of the thriving areas of research interest. Their optical absorption and emission properties are particularly useful for applications such as light harvesting and LEDs. However, understanding the factors that control the electronic structure and the optical properties of these promising materials is challenging and needs to be explored. In this research, the effect of different configurations of heteroatom dopants (N, S, O) on the structure and electronic properties of GQDs was investigated using DFT and TD-DFT calculations. Computational modelling of doped GQDs was done using B3LYP/cc-pVTZ method to study their structural stabilities, electronic properties, and optical properties. The configurations of the heteroatom dopants had a significant effect on optical properties and electronic structures. Doping resulted in a narrowing of the electronic band gap and caused a red shift in absorption for both nitrogen and sulphur dopants, and for co-doped N and S. Graphitic nitrogen had the strongest effect in reducing the HUMO-LUMO gap of GQDs from 2.82 eV (un-doped) to 1.17 eV (doped). Stabilities of the doped structures were evaluated by calculating formation energies. The structures with edge positions of the dopants were found to be the most favourable for both nitrogen and sulphur, e.g. amino nitrogen and thiophene sulfur. However, there was no correlation between their stabilities and optical properties of these doped GQDs. These results will help in understanding the relationship between the structure, and electronic and optical properties of GQDs leading to new applications in energy-related technologies.
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