Band structure and microstructure modulations enable high quality factor to elevate thermoelectric performance in Ge_0.9Sb_0.1Te-x%FeTe₂

GeTe is an excellent mid-temperature thermoelectric material with various freedom degrees to tune the thermoelectric performance, which has drawn intensive attentions. Herein, superior thermoelectric performance of GeTe-based materials is achieved through significantly elevating quality factor B with FeTe₂ introduction. First-principles calculations show that introducing FeTe₂ into GeTe can increase the density of states due to the contribution of the 3d orbital of Fe, leading to an enhancement of effective mass from ∼2.21m₀ in Fe-free sample to ∼3.01 m₀ in Ge_0.9Sb_0.1Te–2%FeTe₂, which could maintain high electrical transport properties. Meanwhile, the lattice thermal conductivity is drastically suppressed by Van der Waals gaps, Fe-rich nanoprecipitates and strain field fluctuations with minimal disruption on carrier transport, leading to a minimum lattice thermal conductivity of ∼0.54 Wm^-1 K⁻¹. Ultimately, a superior ZT ∼2.1 at 723 K and a ZT_ave of ∼1.25 at 300–773 K are attained in Ge_0.9Sb_0.1Te–1%FeTe₂.