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 Cu 2 Se synthesized by high-pressure and high-temperature technique. With the increased Bi contents, the carrier mobility of Bi x Cu 2 Se samples distinctly decreased, while the Seebeck coefficient and electrical resistivity increased. The Bi x Cu 2 Se 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 Cu 2 Se-based samples. The lattice thermal conductivity of Cu 2 Se-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 Bi 0.005 Cu 2 Se sample, which was 25% higher than that of pristine Cu 2 Se (zT ~ 1.25). This work indicates the potential of heavy-element doping in boosting performance for liquid-like thermoelectrics.