Effect of Cu/In doping on the thermoelectric transport properties of Bi-Sb-Te alloys

Herein we report the effect of Cu/In doping on the electronic and thermal transport properties of Bi-Sb-Te thermoelectric alloys. To closely examine the role of each doping element when incorporated in a Bi_0.4Sb_1.6Te₃ alloy, different groups of samples were prepared and characterized, including undoped Bi_0.4Sb_1.6Te₃, In single-doped samples and In and Cu doped ones. It was observed that Cu and In had different impacts on the thermoelectric properties of the Bi_0.4Sb_1.6Te₃. For example, the Hall carrier concentration of Bi_0.4Sb_1.6Te₃ was increased by Cu doping and decreased by In doping while maintaining Hall mobility, which suggests that the physical parameters related to the thermoelectric transport can be carefully controlled by doping with Cu and In. In addition, we found that the electronic structure of Bi_0.4Sb_1.6Te₃ can be modified by Cu/In doping. The density of states effective mass (m^∗) value of the Cu-doped sample (1.07 m₀) was increased. However the m^∗ of the In-doped sample (0.85 m₀) was decreased compared to the pristine sample (0.97 m₀). Cu single-doped Bi_0.4Sb_1.6Te₃ exhibited the maximum thermoelectric figure-of-merit because of the complexity of substitutional doping on Bi/Sb sites. Our results indicate that to enhance the performance of thermoelectric materials by doping with more than one element a well-designed doping strategy is required.