Tailoring the optoelectronic properties of graphyne and graphdiyne: nitrogen/sulfur dual doping versus oxygen containing functional groups

Modification of nanostructures is essential in designing materials for application in electronics and optoelectronics. In this article, the electronic structure tuning and optical properties engineering of modified graphyne (GY) and graphdiyne (GDY) are investigated by first principles density functional theory (DFT) calculations. The model GY/GDY nanoflakes are subjected to i) edge functionalization by carbonyl and carboxyl groups and ii) doping with N atom and codoping with N,S atoms. The change in the electronic and optical properties of GY/GDY due to systematic functionalization and doping is reported. It is observed that the concentration of impurity is important to tune the energy gap. The energy gap for GY/GDY flakes can be tuned over a range similar to 1.20 eV by varying the concentration of CO functional group. In contrast, the energy gap is insensitive to the number of COOH groups. Alternatively, the energy gap can be controlled from 0.11 to 0.68 eV by varying the N/S doping level. Upon codoping, S atom plays a role of hole doping and N acts as an electron doping. The optical response of considered systems was also monitored from the infrared to the UV region. Red shift of absorption peaks has been observed for the doped and functionalized GY/GDY flakes as compared to the original pristine systems. Increasing the dopant content results in intensive peaks which are highly shifted to the lower energies. This tunable optical response indicates that modified GY/GDY nanoflakes are prominent candidates for application in UV-light protection devices.