Theoretical investigation of the electronic structure and thermoelectric performance of 2D GeSb2Te4 and GeBi2Te4

Thermoelectric technology is attractive for waste heat recovery and clean energy; it is highly desired as a potential power supply. In this paper, we investigated the stability, elastic, electronic structures and thermoelectric properties of unexplored 2D materials, GeSb2Te4 and GeBi2Te4, which deliver high stability, acceptable cleavage energies (0.32–0.33 J/m2), and narrow band gaps of 0.80 and 0.69 eV. We also revealed that the septuple layers possess anisotropic electron and hole mobilities of about 1593.71/791.50 and 522.04/240.52 cm2/Vs, which result in high conductivities of 107–108 S/m, as well as desirable thermoelectric power factors of 28.08–70.382 mW/Km2. Besides, owing to the low group velocities and strong dissipative scattering for low-lying phonons, the materials inherit the low lattice thermal conductivities of 1.51 and 0.41 W/mK. As a result, their thermoelectric figure of merit reaches 1.60 and 1.70 at 300 K, and rises further to 3.80 and 4.16 at 700 K. Together, 2D GeSb2Te4 and GeBi2Te4 are suitable candidates for low-medium temperature thermoelectric application.