Defect Chemistry Engineering Promotes the Dopability of Cu for an Extraordinary Thermoelectric Performance of Hole-Doped PbSe with Resonant States
Jinchang Sun, Chenghao Xie, Wenjun Cui, Fan Yan, Jun Li, Jiaxu Zhang, Xiahan Sang, Xinfeng Tang, Gangjian Tan
Abstract
Cu substitution for Pb (Cu Pb ) has been theoretically predicted to introduce resonant states near the valence band edge of PbSe. However, experimentally, it has not been verified yet due to the extremely low solubility (∼0.3 atom %) of Cu Pb . In this study, we demonstrate that the solubility limit of Cu Pb is extended to at least 1.5 atom % in PbSe by pairing with an identical amount of Cu interstitials (Cu i ), while excess Cu precipitates out as a Cu 2 Se phase at grain boundaries. As a result of the increased dopability of Cu Pb, a significant enhancement of the Seebeck coefficient is realized in hole-doped PbSe because of Cu Pb -induced resonant states. This is also testified by first-principles calculations. Moreover, the rich point defects (Cu Pb, Cu i ), line defects (dislocations), and Cu 2 Se precipitates remarkably frustrate the phonon propagation of PbSe, leading to ∼45% reduction of lattice thermal conductivity ( κ lat ) at room temperature. At elevated temperatures (>623 K), there is a dynamic migration of Cu atoms from Cu 2 Se precipitates to tetrahedral interstices of the PbSe matrix as evidenced by the temperature-variant Hall study and thermal expansion coefficient measurement. This diffusion-like process of Cu further drops the κ lat to ∼0.27 W m –1 K –1 at 823 K. Consequently, a peak ZT of ∼1.8 at 873 K is achieved in the (Cu i ) 0.01 Pb 0.97 (Cu Pb ) 0.01 Na 0.02 Se sample. This work highlights the potential of the defect structure design in innovating new functional materials, particularly high-performance thermoelectrics.