Induced effects by the substitution of Zn in Cu ₂ZnSnX₄ (X = S and Se)

Based on the density functional theory with hybrid functional approach, we have studied the structural and thermodynamic stabilities of Cu₂MSnX₄ (M = Zn, Mg, and Ca; X = S and Se) alloy, and have further investigated the electronic and optical properties of stable Cu₂MgSnS₄ and Cu₂MgSnSe₄ phases. Thermal stability analysis indicates that Cu₂MgSnS₄ and Cu₂MgSnSe₄ are thermodynamically stable, while Cu₂CaSnS₄ and Cu₂CaSnSe₄ are unstable. The ground state configuration of the compound changes from kesterite into stannite structure when Zn atoms are substitued by larger Mg or Ca atoms. An energy separation between stannite and kesterite phase similar to that of CZTS is observed. Calculated electronic structures and optical properties suggest that Cu₂MgSnS₄ and Cu₂MgSnSe₄ can be efficient photovoltaic materials. - Highlights: • The substitution for Zn atom induced the different ground state structures. • The substitution of Mg is thermodynamically stable, while the Ca case is unstable. • Mg-substituted compounds can be efficient photovoltaic materials.