General rules of the sub-band gaps in group-IV (Si, Ge, and Sn)-doped I-III-VI2-type chalcopyrite compounds for intermediate band solar cell: A first-principles study

Highlights: • The absolute energy positions of IBs from the same dopant do not show big changes. • Sn-doped CuAlSe₂ has been selected out as a potential candidate for IBSC. • Alloying with isovalent cation to adjust the sub-band gaps has been demonstrated. - Abstract: In this work, we have investigated Si, Ge and Sn doped at III-site(Ga or Al) in CuGaSe₂, CuAlSe₂, AgGaSe₂, and AgAlSe₂ as the candidates for intermediate band solar cell (IBSC), and demonstrated that the absolute energy levels of the intermediate band from a given group IV dopant in various Se-based chalcopyrite hosts do not show remarkable changes. This is resulted from the fact that the intermediate band originates from the same antibonding state of IV-s and Se-p states. The intermediate bands sequence of Ge^* < Sn^*< Si from the different dopants in the same chalcopyrite host is explained by a simple model based on the atomic orbital energy and bond interaction. Furthermore, Sn-doped CuAlSe₂ with the suitable main-gap and sub-gaps has been selected out as a potential candidate for IBSC, and alloying with isovalent cations to adjust to proper sub-band gaps has been demonstrated in Ge-doped (Ag,Cu)AlSe₂ and Ag(Ga,Al)Se₂.