Theory-Guided Synthesis of an Eco-Friendly and Low-Cost Copper Based Sulfide Thermoelectric Material

Cu3SbS4 is a copper-based sulfide composed of earth-abundant elements. We present a combined theoretical and experimental study of the thermoelectric properties of Ge-doped Cu3SbS4. On the basis of density functional theory, we found that the pristine compound is a semiconductor with a large density-of-state effective mass of ∼2.2 me for holes. Ge was predicted to be an effective p-type dopant that only slightly shifts the band structure of Cu3SbS4. The power factor was predicted to reach a maximum value with 10–15 mol % Ge-doping on the Sb site (n = (6–9) × 1020 cm–3) at high temperature (up to 700 K). Theory was used to guide the synthesis of optimally doped Cu3SbS4 bulk samples. Experimentally, Cu3SbS4 bulk samples were prepared by mechanical alloying and spark plasma sintering. The samples had very fine microstructures, with a grain size of ∼100–300 nm, which contributed to a much lower lattice thermal conductivity than reported in the literature. A maximum power factor of ∼1.08 mW K–2 m–1 was achieved with an optimized carrier concentration of ∼4.79 × 1020 cm–3, which is in good agreement with theoretical prediction, and a zT of ∼0.63 was obtained at 623 K.