Hybrid crystalline sp2-sp3 carbon as a high-efficiency solar cell absorber

Carbon is a versatile element that has allotropes with both sp(2) (graphene) and sp(3) (diamond) bonding. However, none of the allotropes can be used as light-absorber materials in solar cells due to either too large or too small band gap. Here, we propose a novel concept that enables a tunable band gap of carbon phases with sp(2) carbon atoms within a sp(3) carbon structure. The tunability is due to the quantum confinement effect. By embedding the sp(2) atoms within the sp(3) structure, we can design new carbon allotropes with ideal optical properties for optoelectronic applications. Five carbon allotropes incorporated this structural feature were identified by combining this new concept with our freshly developed multi-objective inverse band structure design approach. They all have proper band gaps for optical absorption, and the simulated photovoltaic efficiency of C-10-C is even higher than conventional absorber materials such as GaAs, which indicates that C-10-C with mixed sp(2)-sp(3) hybridization may have potential application as light-absorber material in electronic and optoelectronic devices. (C) 2016 Elsevier Ltd. All rights reserved.