Cto-graphene: A Two-Dimensional Graphene Allotrope with High Hole Mobility

Graphene allotropes with nonhexagonal carbon rings have huge potential in the application of field-effect transistors. However, two-dimensional nonhexagonal graphene allotropes with an appropriate band gap and a high hole mobility are still rare. Here, a novel two-dimensional graphene allotrope, cto-graphene, consisting of triangular and octagonal carbon rings was designed by using first-principles calculations. Cto-graphene is a metallic and anisotropic two-dimensional ultraplanar graphene allotrope with a band gap of 0.99 eV. The energy per atom of cto-graphene (−8.57 eV/atom) is much lower than that of penta-graphene and slightly larger than that of planar T-graphene, indicating that it is a metastable graphene allotrope. The calculated hole mobilities are 7.3 × 10 4 and 1.3 × 10 4 cm 2 V –1 s –1 along the armchair and zigzag directions, respectively. The carrier mobility depends on the structural orientation. The hole mobility of cto-graphene is better than those of some previously reported graphene allotropes, such as C 568 and pentagraphyne. It is also an optical material, which corresponds to the absorption spectrum diffusing in the visible region and a portion of the ultraviolet region. The exceptional carrier mobility and superior optical performance make cto-graphene a potential candidate for future field-effect transistors, optical solar cells, and optoelectronic devices.