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

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 4 300 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.