Thermoelectric performance optimization of n-type PbTe by In and Cu2Te co-doping and anomalous temperature-dependent transport

Abstract

The thermoelectric performance of p-type PbTe was found to be superior to that of n-type PbTe, mainly owing to the successful band engineering of the p-type materials. Here, we report a novel band engineering effect, namely temperature-dependent impurity level, in n-type PbTe achieved by In and Cu₂Te co-doping. Above 700 K, the co-doped material exhibited an uncommon increase in the Seebeck coefficient, which is very different from the behavior of the single Cu₂Te- and In-doped compounds. We show that the thermoelectric transport of the co-doped compound can be explained by the temperature-dependent impurity level as In produces the impurity level state and Cu₂Te ensures proper carrier concentration. Owing to the optimization of the power factor by the impurity level, the co-doped compound exhibited a peak zT of 1.5 at 773 K and an average zT_avg of 0.94. The thermoelectric performance was further examined by fabricating a thermoelectric module containing seven pairs of legs.