Achieving high-performance n-type PbTe via synergistically optimizing effective mass and carrier concentration and suppressing lattice thermal conductivity

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Introducing resonant levels is a potent strategy to improve the thermoelectric properties of the thermoelectric systems. However, the beneficial effect of resonant levels tends to be weakened with rising temperature for the PbTe system. This motivates us to introduce dynamic doping of Cu into Cr-doped n-type PbTe to achieve the fully optimized carrier transport over a wide temperature range. As a consequence, an extraordinary figure of merit, ZT of ∼ 0.55 at room temperature, a peak ZT of ∼ 1.31 at 773 K and an average ZT of ∼ 1.02 in the range of 323 to 823 K are obtained in the Pb0.975Cr0.025Te-0.2%Cu. Additionally, how co-doped of Cr and Cu contributes to suppressing thermal transports is still ambiguous. Herein, we employ comprehensive electron microscopy investigations to reveal that the synergistic incorporation of Cr and Cu into the PbTe matrix results in a series of phonon scattering sources, including massive point defects, high-density of nanoscale precipitates, microscale secondary phases, and dense grain boundaries, which can significantly reduce the lattice thermal conductivity by enhancing phonon scattering. This work clarifies the fundamental Cr-doping mechanism in PbTe and demonstrates that dynamic Cu-doping engineering is an effective approach to boosting thermoelectric performance, which should be applied in other thermoelectric materials.