Band Modulation and Strain Fluctuation for Realizing High Average zT in GeTe

Abstract Recently, GeTe has emerged as a very promising thermoelectric material. However, the pristine GeTe exhibits intrinsically low Seebeck coefficient and high thermal conductivity. Therefore, resolving these issues is critical for further promoting its thermoelectric performance. Herein, PbTe and AgSbTe₂ are chosen to form a solid solution with GeTe. Benefitting from the converged electronic bands and reduced thermal conductivity after AgSbTe₂ alloying, the thermoelectric performance of GeTe‐based materials is effectively improved. In addition, PbTe alloying can optimize the carrier concentration and further improve the effective mass, and thus a remarkable enhancement in the Seebeck coefficient is realized. Moreover, intense phonon scattering occurs due to the introduced point defects at the Ge site, and the lattice thermal conductivity is effectively reduced to be as low as ≈0.47 W m⁻¹ K⁻¹. As a result, a high zT of ≈0.7 at 323 K and ≈2.4 at 723 K can be achieved in (Pb_0.15Ge_0.85Te)_0.8(AgSbTe₂)_0.2, leading to a record‐high average zT of ≈1.8 and a high conversion efficiency of ≈14.8% under the temperature difference of 500 K.