Ultrahigh Power Factor and Electron Mobility in n-Type Bi₂Te₃–x%Cu Stabilized under Excess Te Condition

The thermoelectric (TE) community has mainly focused on improving the figure of merit (ZT) of materials. However, the output power of TE devices directly depends on the power factor (PF) rather than ZT. Effective strategies of enhancing PF have been elusive for Bi 2 Te 3 -based compounds, which are efficient thermoelectrics operating near ambient temperature. Here, we report ultrahigh carrier mobility of ∼467 cm 2 V –1 s –1 and power factor of ∼45 μW cm –1 K –2 in a new n-type Bi 2 Te 3 system with nominal composition Cu x Bi 2 Te 3.17 ( x = 0.02, 0.04, and 0.06). It is obtained by reacting Bi 2 Te 3 with surplus Cu and Te and subsequently pressing powder products by spark plasma sintering (SPS). The SPS discharges excess Te but stabilizes the high extent of Cu in the structure, giving unique SPS Cu x Bi 2 Te 3.17 samples. The analyzed composition is close to “Cu x Bi 2 Te 3 ”. Their charge transport properties are highly unusual. Hall carrier concentration and mobility simultaneously increase with the higher mole fraction of Cu contrary to the typical carrier scattering mechanism. As a consequence, the electrical conductivity is considerably enhanced with Cu incorporation. The Seebeck coefficient is nearly unchanged by the increasing Cu content in contrast to the general understanding of inverse relationship between electrical conductivity and Seebeck coefficient. These effects synergistically lead to a record high power factor among all polycrystalline n-type Bi 2 Te 3 -based materials.