High thermoelectric performance induced by strong anharmonic effects in monolayer (PbX)₂ (X = S, Se, Te)

Enhanced thermoelectric performance is restricted greatly by the interaction of various transport parameters, and this bottleneck urgently requires a solution. In this paper, first-principles calculations and Boltzmann transport theory are used to study the thermoelectric performance of two-dimensional $(PbX)2$ $(X=S,Se,Te)$ monolayers, and it is found that the thermoelectric performance can be enhanced significantly by applying a biaxial tensile strain. The room-temperature ZT values of the p-type $(PbS)2, (PbSe)2$⁠, and $(PbTe)2$ in zigzag (armchair) directions are boosted as high as 1.97 (1.35), 2.26 (1.31), and 2.45 (1.59), respectively. The results show that it is mainly attributed to the significantly reduced phonon thermal conductivity. Moreover, the sharply reduced phonon thermal conductivity is mainly due to the enhancement of the phonon scattering rate caused by strong phonon anharmonicity. In addition, the excellent ZT value of the p-type $(PbX)2$ $(X=S, Se, Te)$ monolayer exhibits their potential application in the thermoelectric field, and the external strain has a good prospect in enhancing the thermoelectric performance.