Realization of higher thermoelectric performance by dynamic doping of copper in n-type PbTe

It is a great challenge to optimize a material's thermoelectric performance due to the strong correlation between its thermoelectric-transport properties, especially the electrical-transport properties. Optimizing the peak zT using a constant carrier concentration is commonly adopted because of the difficulty in realizing the optimum temperature-dependent carrier concentration, but this is not meaningful for real applications, in which the average zT value over the working temperature range is much more important. Here we propose an effective strategy involving the dynamic doping effect of interstitial Cu atoms to fully optimize the electrical-transport properties of n-type PbTe over a wide temperature range. By using Cu intercalation, the temperature-dependent carrier concentration of PbTe is found to well match the theoretically optimal profile. Furthermore, high carrier mobility is largely maintained because the dynamic behavior of the interstitial Cu does not alter the band structure and therefore change the effective mass. Consequently, a peak zT of similar to 1.3 and a calculated leg efficiency of 12% were achieved for the sample with 0.2 at% Cu. Based on our findings, we further proposed a concept of 'interstitial engineering' to reinforce the dynamic doping effect, which is of fundamental importance for optimizing the thermoelectric properties.