In order to understand the effect of Pb-CuI co-doping on the thermoelectric performance of Bi2Te3, n-type Bi2Te3 co-doped with x at% CuI and 1/2x at% Pb (x = 0, 0.01, 0.03, 0.05, 0.07, and 0.10) were prepared via high temperature solid state reaction and consolidated using spark plasma sintering. Electron and thermal transport properties, i.e., electrical conductivity, carrier concentration, Hall mobility, Seebeck coefficient, and thermal conductivity, of CuI-Pb co-doped Bi2Te3 were measured in the temperature range from 300 K to 523 K and compared to corresponding x% of CuI-doped Bi2Te3 and undoped Bi2Te3. The addition of a small amount of Pb significantly decreased the carrier concentration, which could be attributed to the holes from Pb atoms, thus the CuI-Pb co-doped samples show a lower electrical conductivity and a higher Seebeck coefficient compared to CuI-doped samples with similar x values. The incorporation of Pb into CuI-doped Bi2Te3 rarely changed the power factor because of the trade-off relationship between the electrical conductivity and the Seebeck coefficient. The total thermal conductivity(κtot) of co-doped samples (κtot ~1.4 W/m∙K at 300 K) is slightly lower than that of 1% CuI-doped Bi2Te3 (κtot~1.5 W/m∙K at 300 K) and undoped Bi2Te3 (κtot ~1.6 W/m∙K at 300 K) due to the alloy scattering. The 1% CuI-Pb co-doped Bi2Te3 sample shows the highest ZT value of 0.96 at 370 K. All data on electrical and thermal transport properties suggest that the thermoelectric properties of Bi2Te3 and its operating temperature can be controlled by co-doping.
Generalized Scharfetter–Gummel schemes for electro-thermal transport in degenerate semiconductors using the Kelvin formula for the Seebeck coefficient
