Abstract
The search for new optical materials capable of absorbing light in the frequency range from visible to near infrared is of great importance for applications in optoelectronic devices. In this paper, we report a theoretical study of the electronic and optical properties of hybrid structures composed of fullerenes adsorbed on graphene and on graphene nanoribbons. The calculations are performed in the framework of the density functional theory including the van der Waals dispersive interactions. We found that the adsorption of the C fullerenes on a graphene layer does not modify its low energy states, but it has strong consequences for its optical spectrum, introducing new absorption peaks in the visible energy region. The optical absorption of fullerenes and graphene nanoribbon composites shows a strong dependence on photon polarization and geometrical characteristics of the hybrid systems, covering a broad range of energies. We show that an external electric field across the nanoribbon edges can be used to tune different optical transitions coming from nanoribbon–fullerene hybridized states, which yields a very rich electro-absorption spectrum for longitudinally polarized photons. We have carried out a qualitative analysis on the potential of these hybrids as possible donor-acceptor systems in photovoltaic cells.
Highlights
Nanostructures based on carbon allotropes have been intensively studied in the last two decades due to the possibility of modulating and controlling their optical and transport properties for novel optoelectronic applications [1] and development of photovoltaic devices [2,3]
In the framework of the density functional theory (DFT), we have calculated the electronic band structure, the density of states (DOS) and the optical spectrum of two different types of hybridized configurations: C60 fullerenes physisorbed on a graphene monolayer and graphene nanoribbons functionalized with different fullerene molecules
We found that the adsorption of the C60 fullerenes on the single layer graphene (SLG) does not modify the low energy states of the pristine graphene maintaining its metallic character, but it has strong consequences on its optical spectrum, introducing two new absorption peaks in the visible energy range
Summary
Nanostructures based on carbon allotropes have been intensively studied in the last two decades due to the possibility of modulating and controlling their optical and transport properties for novel optoelectronic applications [1] and development of photovoltaic devices [2,3]. Several hybrid nanostructures with particular geometric configurations are formed with different carbon allotropes through covalent or non-covalent interactions, with complexes such as graphene–nanotubes, graphene–fullerenes, nanoribbon–fullerenes, nanotube–fullerenes and nanobuds [6]. These have been proposed and synthesized for many applications in optoelectronics, photonics, energy storage and solar cells. The most studied system has been the C60 –graphene composite, in particular for applications in lithium batteries, electrodes for photovoltaics applications, supercapacitors, [7] and it has been studied in other fields such as organic thermoelectric materials [8].
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