Thermoelectric performance of Ag 2 GeX 3 (X = S, Se, Te) with intrinsically low lattice thermal conductivity: A first principles study

Low lattice thermal conductivity is one of the key factor for excellent thermoelectric performance of materials. In this work, we have systematically studied the thermoelectric properties of Ag 2 GeX 3 (X = S, Se, Te) by first -principles calculations in combination with Boltzmann transport theory. In terms of phonon transmission performance, due to the low frequency of acoustic phonons, strong coupling between low -frequency optical phonons and acoustic phonons, and relatively strong anharmonicity, Ag 2 GeX 3 (X = S, Se, Te) exhibits extremely low lattice thermal conductivity of 0.30 Wm -1 K -1 , 0.28 Wm -1 K -1 and 0.65 Wm -1 K -1 at room temperature, respectively. At the same time, Ag 2 GeX 3 (X = S, Se, Te) also exhibits good electrical transport performance. The appropriate band gap and high slope of electronic density of states (DOS) near the Fermi level result in a large Seebeck coefficient of the materials. As a result, the optimal ZT values of p(n)-type Ag 2 GeX 3 (X = S, Se, Te) are 1.4(1.2), 2.2(0.7), and 0.9(0.7) at 800 K, respectively. These results demonstrate outstanding thermoelectric performance of Ag 2 GeSe 3 for energy conversion applications.