Contrasting roles of trivalent dopants M (M = In, Sb, Bi) in enhancing the thermoelectric performance of Ge_0.94M_0.06Te

Thermoelectric materials can achieve the interconversion of electricity and heat, providing potential for power generation. It is a challenge to elevate conversion efficiency due to the coupled thermoelectric parameters. Herein, the high thermoelectric performance is successfully achieved in GeTe-based thermoelectric materials by single doping trivalent dopant M (M=In, Sb, Bi). The high conversion efficiency of ∼10.3% and power density of ∼ 0.6 W cm⁻² under a temperature difference of 419 K are realized in a segmented single-leg device. And the remarkable hardness of ∼ 2.92 GPa in M-doped GeTe provides a prospect for device application. The advanced performance in M-doped GeTe is mainly ascribed to its high ZT value through manipulating deformation potential. The three trivalent dopants facilitate band convergence due to the enhanced symmetry, which increases effective mass without scarifying carrier mobility. Compared with In and Sb, Bi element can be the most effective dopant to decrease deformation potential from 25.3 eV to 17.2 eV. The low deformation potential by doping with Bi leads to high weighted mobility, further optimizing the power factor. The In-doped GeTe exhibits low lattice thermal conductivity at ambient temperature because of the softened phonons, while the lattice thermal conductivity of Bi-doped GeTe is significantly decreased at high temperature due to the larger atomic mass and size of Bi than that of the other two series. Consequently, the highest ZT of ∼1.9 at 723 K is attained in Ge_0.94Bi_0.06Te which outperforms other single-doped GeTe-based thermoelectric materials.