Electronic and thermoelectric properties of chalcopyrite compounds Cu₂(XY)S₄ (X= Zn, Cd and Y= Sn, Pb): first-principles study

In this work, we have presented a correlation between the bond length and electronic properties of Cu₂XYS₄ (X= Zn, Cd and Y= Sn, Pb) from the first-principles calculation. Lattice parameters, bond length, electronic structure and partial density of state are determined by using density functional theory based on generalized gradient approximation. Further, we have calculated the thermoelectric properties in relation to electronic band energy from the Boltzmann transport theory. The room temperature (300 K) optimum value of electrical conductivity is found to be 5×105 S m for Cu₂CdPbS₄, Seebeck coefficient is 320 µV/K for Cu₂ZnSnS₄, thermal conductivity is 0.12 W/m K for Cu₂ZnSnS₄, and the optimal figure of merit is 0.68 for Cu₂ZnSnS₄. This study shows that the stronger interaction between (Zn, Sn) and S atoms leads to the combination of heavy and light bands in the valence region which improves the thermoelectric performance. It is concluded that the Cu₂ZnSnS₄ and Cu₂CdSnS₄ compounds can be considered as potential materials for thermoelectric applications due to their strong bonding interactions. (author)