Two-dimensional silicon-carbon hybrids with a honeycomb lattice: New family for two-dimensional photovoltaic materials

We predict a series of new two-dimensional (2D) inorganic materials made of silicon and carbon elements (2D Si_xC_1-x) based on density functional theory. Our calculations on optimized structure, phonon dispersion, and finite temperature molecular dynamics confirm the stability of 2D Si_xC_1-x sheets in a two-dimensional, graphene-like, honeycomb lattice. The electronic band gaps vary from zero to 2.5 eV as the ratio x changes in 2D Si_xC_1-x changes, suggesting a versatile electronic structure in these sheets. Interestingly, among these structures Si_0.25C_0.75 and Si_0.75C_0.25 with graphene-like superlattices are semimetals with zero band gap as their π and π* bands cross linearly at the Fermi level. Atomic structural searches based on particle-swarm optimization show that the ordered 2D Si_xC_1-x structures are energetically favorable. Optical absorption calculations demonstrate that the 2D silicon-carbon hybrid materials have strong photoabsorption in visible light region, which hold promising potential in photovoltaic applications. Such unique electronic and optical properties in 2D Si_xC_1-x have profound implications in nanoelectronic and photovoltaic device applications.