Enhanced Thermoelectric Transport Properties in Cu-added Bi₂Se₃ Polycrystalline Alloys

The addition of Cu to layered Bi₂Te₃-based thermoelectric alloys has been studied as an effective way to enhance thermoelectric transport properties. In this study, the influence of adding Cu to Bi₂Se₃ alloys, which have the same rhombohedral crystal structure as Bi₂Te₃, was investigated by synthesizing a series of Cu_xBi₂Se₃ (x = 0, 0.004, 0.008, 0.012, and 0.016) alloys. The power factors of all the Cu-added samples were enhanced compared with that of the pristine Bi₂Se₃ sample, primarily because of the increase in electrical conductivity. The power factor for the Cu_0.016Bi₂Se₃ sample (x = 0.016) was 0.80 mW/mK², a 35% increase compared to 0.59 mW/mK² for the pristine sample at 520 K. A decrease in the total and lattice thermal conductivity was observed for the Cu-added samples, caused by additional point defect scattering after doping. The lattice thermal conductivity of the Cu_0.016Bi₂Se₃ sample (x = 0.016) was 0.56 W/mK, a 42% reduction. Consequently, the zT values of all the Cu-added samples were enhanced, and the maximum zT value was 0.38 for the Cu_0.016Bi₂Se₃ sample (x = 0.016) at 520 K, a 48% increase compared to that of pristine Bi₂Se₃.