Enhancing thermoelectric efficiency of highly conductive CuSbTe₂ alloy by reducing electrical thermal conductivity via heavy Se doping

Recently, CuSbTe₂, one of the I-V-VI-based compounds, has received attention as a promising thermoelectric (TE) material that exhibits a narrow bandgap with high electrical conductivity. In this study, the evolution of electrical and thermal transport properties of CuSbTe₂ by heavy Se doping was investigated by synthesizing a series of CuSb(Te_1−xSe_x)₂ (x = 0, 0.1, 0.2, 0.3, and 0.4) compositions. The high electrical conductivity of CuSbTe₂ (5400 S/cm) is gradually decreased to 1800 S/cm by Se doping with x = 0.4 at 300 K with decreased carrier concentration and mobility. Due to this large reduction in electrical conductivity, the power factor of pristine CuSbTe₂ significantly decreased to 0.98 mW/mK² for x = 0.4 by 25%, along with reduced density-of-states effective mass at 550 K. Nevertheless, the lattice thermal conductivity was reduced by 5%, and the electrical thermal conductivity was significantly reduced by 67% for x = 0.4 at 550 K. Consequently, the total thermal conductivity of pristine CuSbTe₂ (2.76 W/mK) is significantly reduced to 1.65 W/mK for x = 0.4 by 40%, mainly owing to the significant reduction of electrical thermal conductivity, which originates from the reduced electrical conductivity. Therefore, an enhanced TE figure of merit (zT) of 0.33 at 550 K is observed for CuSb(Te_0.6Se_0.4)₂ (x = 0.4), which was 26% higher than that of CuSbTe₂. In addition, the expected zT for various carrier concentrations is calculated by using a single parabolic band model. It was found that the zT could be further enhanced by reducing the carrier concentration, which can be achieved by further doping of electrons.