Effects of Bi doping on thermoelectric properties of Cu2Se materials by high-pressure synthesis

Motivated by prototypes that the heavy-element doping can effectively tune carrier and phonon transport behavior, we studied the influence of Bi doping on the thermoelectric properties of Cu2Se synthesized by high-pressure and high-temperature technique. With the increased Bi contents, the carrier mobility of BixCu2Se samples distinctly decreased, while the Seebeck coefficient and electrical resistivity increased. The BixCu2Se samples exhibited multiple microstructures including abundant grain boundaries, micropores and lattice defects. Various phonon scattering mechanisms generated relatively low lattice thermal conductivity below 0.55 Wm(-1) K-1 for all Cu2Se-based samples. The lattice thermal conductivity of Cu2Se-based samples increased after Bi doping due to reduced degree of disorder of Cu+ ions, which weakened phonon scattering. Due to the significantly reduced thermal conductivity, a peak zT value of 1.57 at 873 K was obtained for Bi0.005Cu2Se sample, which was 25% higher than that of pristine Cu2Se (zT similar to 1.25). This work indicates the potential of heavy-element doping in boosting performance for liquid-like thermoelectrics.