DFT Study on the Electronic Structure and Optical Properties of Graphene Quantum Dots Doped with Sulfur, Aluminum, and Copper

Abstract This study employs density functional theory (DFT) to investigate the effects of different concentrations of sulfur (S), aluminum (Al), and copper (Cu) doping on the properties of graphene quantum dots (GQDs). The results show that doping generally reduces the bandgap. Meanwhile, the density of states (DOS) analysis reveals that doping introduces new electronic states, significantly altering the energy level distribution. Structurally, electron localization function (ELF) analysis illustrates the bonding characteristics between the dopant atoms and the GQDs: Al forms polar covalent bonds with carbon, resulting in relatively minor planar distortion, whereas Cu and S doping cause evident local structural deformation. Charge transfer analysis indicates that all doped systems exhibit n-type characteristics. Although Al and Cu doping enhance charge transfer efficiency, they also accelerate electron–hole recombination, leading to decreased intensity in the ultraviolet absorption spectra. Furthermore, electron–hole analysis was conducted to explore the nature of electronic excitations in the absorption spectra, revealing the underlying mechanism of the doping-induced redshift and intensity reduction. Overall, at the concentration of two sulfur dopants, the electronic structure and optical response of GQDs can be effectively modulated, providing theoretical support for their application in solar cells and other optoelectronic devices