Theoretical study of thermoelectric properties of few-layer MoS2 and WSe2

Abstract

Molybdenum disulfide (MoS₂) and tungsten diselenide (WSe₂) are prototypical layered two-dimensional transition metal dichalcogenide materials, with each layer consisting of three atomic planes. We refer to each layer as a trilayer (TL). We study the thermoelectric properties of 1–4TL MoS₂ and WSe₂ using a ballistic transport approach based on the electronic band structures and phonon dispersions obtained from first-principles calculations. Our results show that the thickness dependence of the thermoelectric properties is different under n-type and p-type doping conditions. Defining ZT_1st peak as the first peak in the thermoelectric figure of merit ZT as doping levels increase from zero at 300 K, we found that ZT_1st peak decreases as the number of layers increases for MoS₂, with the exception of 2TL in n-type doping, which has a slightly higher value than 1TL. However, for WSe₂, 2TL has the largest ZT_1st peak in both n-type and p-type doping, with a ZT_1st peak value larger than 1 for n-type WSe₂. At high temperatures (T > 300 K), ZT_1st peak dramatically increases when the temperature increases, especially for n-type doping. The ZT_1st peak of n-type 1TL-MoS₂ and 2TL-WSe₂ can reach 1.6 and 2.1, respectively.