A First-Principles Investigation on a New Group of Diamond-Like Semiconductors Cu4-Ii-Ge2-Vi7 (ii = Zn, Cd and Vi = S, Se) As Photovoltaic Absorbers

Many diamond-like semiconductors with tetrahedral bonds, such as Si, CdTe and Cu(In,Ga)Se2, have been utilized as absorbers in photovoltaics (PV). In this work, a novel group of diamond-like compounds, namely Cu4-IIGe2-VI7 with II = Zn/Cd and VI = S/Se, have been explored by first-principles means. From the calculations of the electronic structures and related optical properties, we have demonstrated that all these quaternaries have direct-type band structures, while their band gap energies are not suitable for PV applications. By anionic alloying, however, the width of the band gaps can be tuned to the desired energy. For example, the Cu4ZnGe2S4Se3 alloy has a suitable band gap of 1.34 eV. Our work provides the support and perspective for further experimental research on this group of semiconductors and their alloys as potential candidates in PV technologies.