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.