Adsorption of vinazene molecule on graphene layer by computational approach

Abstract

Graphene is a 2D nanomaterial sheet with considerably high charge carrier mobility and stable sp 2 hybrid structure but shows metallic behavior in pure form which limits its scope of advanced applications in semiconductor electronics industry. Adsorption is the process in which atoms, ions or molecules from a substance adhere to the surface of the adsorbent and is considered to be a potential approach to band gap opening. In this study, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods are used to investigate the adsorption of 2-vinyl- 4,5-dicyanoimidazole (vinazene) molecule to a graphene layer to show its potential for the organic photovoltaic applications. The objectives of this project are to determine the energy bandgap, the adsorption energy and the optical properties of the optimized structure of the vinazene-graphene system. The structural and electronic properties of vinazene molecule were first calculated using the Gaussian 09 program, a DFT-based software. For the combined system, the electronic and optical properties were calculated at several vinazene-graphene separation distances (1.0-12.0 Å) using the Dmol3 program, a software that incorporates both the DFT and TD-DFT methods at the level of generalized gradient approximation (GGA). The results showed that the adsorption of the vinazene molecule to graphene layer has opened up the energy bandgap with calculated values in the range of 0.12-0.19 eV. As for the adsorption energy the results showed that there are stronger intermolecular forces at shorter separation distance which significantly increase the adsorption values. The absorption spectra of the vinazene-graphene system which were calculated using TD-DFT method however showed only slight differences when compared to those from the previous studies. Thus, these results concerning the energy band gap, adsorption energy, and the optical properties highlight the potential of the vinazene-graphene system for the organic photovoltaic applications and point to new avenues for further research on graphene.