Graphene quantum dots with a Stone-Wales defect as a topologically tunable platform for visible-light harvesting

In this work, we report for the first time the crucial role of topological anomalies like Stone-Wales (SW)–type bond rotations in tuning the optical properties of graphene quantum dots (GQDs). By means of first-principles calculations, we first show that the structural stability of GQDs strongly depends on the position of SW defects. Optical absorption spectra are then computed using electron-correlated methodology to demonstrate that SW-type reconstruction is responsible for the appearance of new defect-induced peaks below the optical gap and dramatically modifies the optical absorption profile. In addition, our investigations signify that electron correlation effects become more dominant for SW-defected GQDs. We finally establish that the introduction of SW defects at specific locations strongly enhances light absorption in the visible range, which is of prime importance for designing light harvesting, photocatalytic, and optoelectronic devices.

Figure 1

Schematic diagram of hydrogen passivated (a) GQD-64, (b) SW1-GQD-64, and (c) SW2-GQD-64.

Figure 2

Charge density plots of $\mathrm{H}-1$ and H orbitals of GQD-64 obtained from the TB model [(a)–(b)] and PPP-HF model [(c)–(d)], $\mathrm{H}-1$, H, L, and $\mathrm{L}+1$ orbitals of SW1-GQD-64 and SW2-GQD-64 obtained from the TB model [(e)–(h) and (m)–(p)] and PPP-HF model [(i)–(l) and (q)–(t)]. Gray, blue, red, and black spheres correspond to $\le$10%, $>10\%–40\%$, >40%–70%, and >70% of the maximum charge density distribution, respectively.

Figure 3

Linear optical absorption spectra of GQD-64, SW1-GQD-64, and SW2-GQD-64 computed using the tight-binding (TB) model and the PPP model at the HF level. The spectrum has been broadened with a uniform line width of 0.1 eV.

Figure 4

Linear optical absorption spectra of (a) GQD-64, (b) SW1-GQD-64, and (c) SW2-GQD-64 computed employing PPP-CI methodology. The spectrum has been broadened with a uniform line width of 0.1 eV. Blue, violet, and green lines denote the locations of the most intense absorption peaks of these systems.