Electronic and vibrational properties of quaternary chalcogenides and their structural diversity

Quaternary chalcogenides derived from simpler II-VI zinc-blende systems are of great interest to many applications, including photovoltaics, solar cells, and thermoelectricity. Such materials allow for a diverse distribution of their cation atoms, which enables fine electronic properties tuning while maintaining a low thermal conductivity. Here we report electronic structure simulations of CuZn₂InSe₄, taken as a representative from a larger class of chalcogenides. It is found that the structural diversity due to cation and polyhedral arrangements has direct consequences in the electronic structure, especially for the conduction and valence band shifts. The simulations further indicate that hybrid functionals are needed to account for the s-p and p-d orbital hybridization around the Fermi level. We also find that the low thermal conductivity of all phases is mainly attributed to the direct metal-chalcogen bonds making up the lattice. The phonon dispersion further show that the main scattering channel comes from a low frequency optical band hybridized with acoustic phonons.