Thermoelectric Performance of Cu₈SiS₆ with High Electronic Band Degeneracy

Thermoelectric (TE) generators are a kind of clean energy technology that can harvest electrical energy from waste heat. However, scant attention has been paid to the potential influence of the bonding orbitals on TE properties, which has severely hindered the exploitation of TE materials. Herein, a simple but effective strategy based on crystal field theory was proposed here to sift out potential TE materials based on the orbital degeneracy engineering that comprises the electronic bands. A typical p-type material Cu 8 SiS 6 composed of CuS 4 tetrahedra–units was selected and investigated. When the ligands–sulfur atoms get close to the center copper ion in a unit CuS 4, the degeneracy of the d orbital would split due to the static electric field, leading to a high density of state at the top of the valence band, thus enhancing the Seebeck coefficient. It was found that Cu 7.92 SiS 6 shows a zT of 0.24 at 850 K. The orbital degeneracy engineering approach is promising to extend to other class of TE materials, thereby substantially accelerating the screening and design of novel TE materials.