Beneficial Influence of Co-Doping on Thermoelectric Efficiency with Respect to Electronic and Thermal Transport Properties

Substitutional doping is known to be effective in reducing lattice thermal conductivity in order to enhance the thermoelectric efficiency. However, the effect of co-doping of two different substituents has not been investigated exclusively. Here, the effect of Ag and Ga co-doping in p-type Bi _0.42 Sb _1.58 Te ₃ alloys is examined with respect to the electronic and thermal transport properties, and the results are compared to cases of Ag-doping and Ga-doping separately. When the Ag and Ga are individually doped, the Ag-doping increases the hole concentration, and the Ga-doping reduces it. When both Ag and Ga are co-doped, their opposite effects on the carrier concentration cancelled each other while maintaining the optimal concentration of the pristine Bi _0.42 Sb _1.58 Te ₃ . An analysis of the lattice thermal conductivity reduction by the Ag and Ga co-doping confirms that the co-doping is as effective as the cumulative effect of each single doping. As a result, the co-doped Bi _0.42 Sb _1.58 Te ₃ alloys have power factors comparable to that of the pristine Bi _0.42 Sb _1.58 Te ₃ , and a drastically reduced lattice thermal conductivity owing to cumulative influences from the two independent dopants. Consequently, the co-doping provides a beneficial effect in enhancing the thermoelectric efficiency by effectively suppressing the lattice thermal conductivity while maintaining high power factors.