Pristine and holey graphene quantum dots: Optical properties using time independent and dependent density functional theory

Abstract

The zero bandgap of graphene limits its utilization in optoelectronics. Quantum confinement in finite-size graphene structures, such as graphene quantum dots (GQDs) and holey GQDs, may offer a path for generating a wide range of HOMO-LUMO gaps. Edge terminations and pore passivations in these structures provide further means to alter their optical properties. In this work, we study the structural stabilities and optical properties of GQDs and holey GQDs with different sizes, edge terminations, and pore passivations, using density functional theory (DFT) as well as time dependent DFT. We find that the optical spectra of GQDs depend primarily on their size. Edge termination has a small influence on the spectra; shifting the absorption peaks by ~ 0.2 eV, which gets smaller for larger GQDs. Creation of pores in GQDs lead to the emergence of new peaks in their absorption spectra. Pore passivation seems to have the biggest effect on the absorption spectra of holey GQDs, while their termination leads to slight shifts in their peaks. Our results can be used to develop promising materials for many applications, such as biological sensors, and optoelectronic devices. • DFT and TDDFT are applied to study the optical properties of GQDs and holey GQDs. • The pore passivations and pore size affect the optical properties of GQDs. • There is a blueshift in the spectrum of TDDFT calculations as compared to the corresponding DFT calculations. • The spectral range and the broadening of the absorption are larger for holey GQDs than for GQDs. • Our results can be used to develop promising materials for many applications biological sensors, and optoelectronic devices.