High Carrier Mobility and High Figure of Merit in the CuBiSe2 Alloyed GeTe

According to the Mott's relation, the figure‐of‐merit of a thermoelectric material depends on the charge carrier concentration and carrier mobility. This explains the observation that low thermoelectric properties of GeTe‐based materials suffer from the degraded carrier mobility, on account of the fluctuation of electronegativity and ionicity of various elements. Here, high‐performance CuBiSe2 alloyed GeTe with high carrier mobility due to the small electronegativity difference between Cu and Ge atoms and the weak ionicity of CuTe and BiTe bonds, is developed. Density functional theory calculations indicate that CuBiSe2 alloying increases the formation energy of Ge vacancies and correspondingly reduces the amount of Ge vacancies, leading to an optimized carrier concentration and a high power factor of ≈37.4 µW cm−1 K−2 at 723 K. Moreover, CuBiSe2 alloying induces dense point defects and triggers ubiquitous lattice distortions, leading to a reduced lattice thermal conductivity of 0.39 W m−1 K−1 at 723 K. These synergistic effects result in an optimization of the carrier mobility, the carrier concentration, and the lattice thermal conductivity, which favors an enhanced peak figure‐of‐merit of ≈2.2 at 723 K in (GeTe)0.94(CuBiSe2)0.06. This study provides guidance for the screening of GeTe‐based thermoelectric materials with high carrier mobility. The thermoelectric properties of GeTe‐based materials usually suffer from reduced carrier mobility. In this study, alloying CuBiSe2 into GeTe allows high intrinsic carrier mobility and a high zT of ≈2.2 at 723 K and an average zT of 1.4 from 300 to 723 K in (GeTe)0.94(CuBiSe2)0.06.