Modifying Roles of CuSbSe₂ in Realizing High Thermoelectric Performance of GeTe

Abstract Thermoelectric materials are widely researched for their energy conversion capabilities in the fields of power generation and refrigeration. And a superior thermoelectric conversion efficiency requires an excellent power factor and low thermal conductivity. Herein, a remarkable thermoelectric figure of merit（ZT） ∼ 2.6 at 673 K is realized in GeTe with 20% addition of CuSbSe₂. Multiple synergistic effects of CuSbSe₂ alloying collectively contribute to the excellent thermoelectric performance in GeTe. CuSbSe₂ alloying effectively tunes ultrahigh carrier density of GeTe to the optimum. The introduction of Cu, Sb, and Se atoms create numerous point defects that scatter high‐frequency phonons. Additionally, surplus CuSbSe₂ facilitates the formation of copper‐selenium phases, which embed at grain boundaries and generate interfaces after sintering. Combining the planar defects evolved from Ge vacancies, multi‐dimension defects effectively scatter multiple frequency phonons. An extraordinarily low lattice thermal conductivity of 0.3 Wm⁻¹ K⁻¹ at 673 K is obtained, approaching the theoretical estimation predicted by Cahill model. Eventually, the peak conversion efficiency of 7.4% is obtained in segmented device with ΔT of 419 K. The commingled effects of CuSbSe₂ in GeTe further open up an elitist route to designing high‐performance materials.