Beneficial Effect of Na2CO3 Additions on the Thermoelectric Performance of Melt‐Route Cu2Se

Abstract High‐performance thermoelectric materials require simultaneous reduction of thermal conductivity and electrical resistivity, among other criteria. Here it is shown that the introduction of Na 2 CO 3 into the melt‐route fabrication process for the well‐known thermoelectric Cu 2 Se has a beneficial and surprisingly strong effect. There is a significant enhancement in electrical conductivity which density functional theory calculations suggest may be due to the effect of Na and O doping in the Cu 2 Se matrix. There is also a 34% reduction in thermal conductivity which is likely due to a high density of defects causing scattering of phonons. Overall, however, there is only relatively a small change in Seebeck coefficient. A higher power factor of 12.6 µW cm −1 K −2 is achieved versus 8.8 µW cm −1 K −2 for standard Cu 2 Se. A very high value of zT of 2.3 is obtained at 804 K versus 1.1 for standard Cu 2 Se.