Enhancement of the thermoelectric performance via defect formation and device fabrication for Cu26Ti2(Sb,Ge)6S32 colusite

Abstract

A copper-based multicomponent sulphide, Cu₂₆Ti₂(Sb,Ge)₆S₃₂ colusite, is a promising thermoelectric material. We investigated the effects of sulphur deficiency on the crystal structure, electronic structure, and thermoelectric properties in the series Cu₂₆Ti₂Sb₄Ge₂S_32−x. By combining experiments and ab initio calculations, we found that sulphur deficiency induced the formation of interstitial Cu atoms in the sphalerite-like framework of Cu₂₆Ti₂Sb₄Ge₂S₃₂. This resulted in a decrease in the hole carrier concentration and a susbtantial enhancement of ZT up to unity at 673 K. We also fabricated a power generation device composed of the sulphur-deficient colusite, Ni–Sb-based compounds (interface material), and Ni. The maximum conversion efficiency of the device reached 3.2% with a temperature difference of 266 K.