Multiple Synergistic Effects Induced by Ge Doping Enhance the Thermoelectric Performance of n-Type PbTe

Abstract

The strong coupling between electrical and thermal transport in thermoelectric (TE) materials remains a formidable challenge for achieving high performance. In this work, we propose a Cu/Ge co-doping strategy to synergistically optimize the thermoelectric properties of n-type PbTe. Ge, with its smaller ionic radius, expands the tetrahedral interstitial spaces of the PbTe lattice, thereby promoting the interstitial solid solution of Cu and increasing the room-temperature Hall carrier concentration by approximately 60%. This, together with the Ge-induced band flattening effect, optimizes the electrical transport properties. Moreover, the lattice softening effect induced by Ge doping significantly reduces the lattice thermal conductivity. As a result, the Cu_0.002Pb_0.99Ge_0.01Te sample achieves a peak zT of ~1.4 at 673 K, with an average power factor PF_avg of ~30 μW cm^-1 K^-2 and an average zT_avg of ~1.0 in the temperature range of 300-723 K. This work provides valuable insights for further optimization of PbTe-based thermoelectric materials.