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KAgX (X = S, Se): High-Performance Layered Thermoelectric Materials for Medium-Temperature Applications

Xue-Liang Zhu, Hengyu Yang, Wu-Xing Zhou, Baotian Wang, Ning Xu, Guofeng Xie
ACS applied materials & interfaces 2020 v.12 no.32 pp. 36102-36109
density functional theory, equations, heat transfer, selenium, sulfur, thermal conductivity
Monolayer KAgX are a class of novel two-dimensional (2D) layered materials with efficient optical absorption and superior carrier mobility, signifying their potential application prospect in photovoltaic (PV) and thermoelectric (TE) fields. Motivated by the recent theoretical studies on the KAgX monolayer, we carried out systematic investigations on the TE performance of KAgS and KAgSe monolayers, employing density functional theory (DFT) and semiclassical Boltzmann transport equation (BTE). For both KAgSe and KAgS monolayers, large Grüneisen parameters, low group velocities, and short phonon scattering time greatly hinder their heat transport and result in an ultralow thermal conductivity, 0.26 and 0.33 W m–¹ K–¹ at 300 K, respectively. A twofold degeneracy appearing at the Γ point and the abrupt slope of the density of states (DOS) near the Fermi level give rise to high Seebeck coefficients of KAgX monolayers. Due to the ultralow thermal conductivity and excellent electronic transport performance, the ZT values as high as 4.65 (3.11) and 4.05 (2.63) at 500 (300) K in the n-type doping for KAgSe and KAgS monolayers are obtained. The exceptional performance of KAgX monolayers sheds light on their immense potential applications in the medium-temperature (around 300–500 K) thermoelectric devices and greatly stimulates further experimental synthesis and validation.