Enhancement of the Thermoelectric Performance of Cu 2 GeSe 3 via Isoelectronic (Ag, S)-co-substitution.

Recently, ternary Cu-based Cu-IV-Se (IV = Sb, Ge, and Sn) compounds have received extensive attention in the thermoelectric field. Compared with Cu-Sb-Se and Cu-Sn-Se, Cu-Ge-Se compounds have been less studied due to its poor Seebeck coefficient and high thermal conductivity. Here, the Cu 2 GeSe 3 material with high electrical conductivity was first prepared, and then, its effective mass was increased by doping with S, which led to the Seebeck coefficient of the doped sample being 1.93 times higher than that of pristine Cu 2 GeSe 3 at room temperature. Moreover, alloying Ag at the Cu site in the Cu 2 GeSe 2.96 S 0.04 sample could further cause a 5.16 times increase in the Seebeck coefficient at room temperature, and the lattice thermal conductivity was remarkably decreased because of the introduction of the dislocations in the Cu 2 GeSe 3 sample. Finally, benefitted from the high Seebeck coefficient and low thermal conductivity, a record high ZT = 0.9 at 723 K was obtained for the Cu 1.85 Ag 0.15 GeSe 2.96 S 0.04 sample, which increased 345% in comparison with the pristine Cu 2 GeSe 3 , and it is among the highest reported values for Cu 2 GeSe 3 -based thermoelectric.