Synergistic shallow impurity levels and multiscale defect engineering in GeTe-based thermoelectrics

By the coordinated implementation of shallow impurity level and multiscale defect engineering, this study achieves the simultaneous optimization of electrical transport and thermal conduction in GeTe-based thermoelectric (TE) materials. This synergistic mechanism originates from the unique electronic configuration of Ni, whose d–sp orbital hybridization introduces shallow impurity levels that promote valence band convergence, thereby enhancing the effective mass of carriers and the Seebeck coefficient. Concurrently, in situ reactions between Ni and Ge form NiGe nanophases (10–30 nm), constructing multiscale defect structures that enable full-spectrum phonon scattering and suppress the lattice thermal conductivity of the Ge_0.885Sb_0.1Ni_0.015Te sample to ~0.8 W∙m⁻¹∙K⁻¹ at 323 K. Leveraging this cooperative optimization, Ge_0.885Sb_0.1Ni_0.015Te attains a peak dimensionless figure of merit (ZT) value of 2.15 at 773 K and an average ZT_avg of ~1.45 (323–773 K). A fabricated single-leg device achieves a conversion efficiency of ~10% under ∆T = 420 K, ranking among the top performances in the field. This work establishes a solid foundation for enhancing the performance and expanding the applications of GeTe-based TE materials.