Distinct role of Sn and Ge doping on thermoelectric properties in p-type (Bi, Sb)2Te3-alloys

Herein, the influence of Sn and Ge doping on the structure and thermoelectric properties of p-type Bi2Te3-based thermoelectric materials is systematically studied. Sn and Ge exhibit distinct doping characteristics in Bi2Te3 based thermoelectric materials. Doping with Sn in BiSbTe alloy not only increases the carrier concentration but also induces resonant electronic states, greatly improving the Seebeck coefficient and power factor. A maximum power factor of 3.8 mWm(-1)K(-2) at 320 K is attained for Sn-0.002(Bi0.46Sb1.54)(0.999)Te-3 sample. In contrast, doping with Ge augments the carrier concentration very rapidly, resulting in a large deviation from the optimum carrier concentration (2 x 10(19) -2.5 x 10(19) cm(-3)). Thus, the increase in the electrical conductivity is cancelled out by the reduced Seebeck coefficient, producing an almost unchanged power factor of 3.5 mWm(-1) K-2 at room temperature. The enhanced electrical conductivity via doping with Sn or Ge increases the total thermal conductivity slightly and suppresses the bipolar thermal conductivity. Because of the significantly improved power factor and lower thermal conductivity in Sn doping samples, the maximum ZT value of 1.02 at 345 K is obtained for the sample with Sn doping of 0.002, which is 12% higher than that of the pristine sample.