Large thermoelectric power factor of high-mobility transition-metal dichalcogenides with 1T phase

A great number of studies about monolayer transition metal dichalcogenides in recent years have revealed that this kind of compound has many metastable phases with unique physical properties, not just a 1H phase. Here, we focus on the 1T '' phase, already existing in the experiments, and systematically investigate the electronic structures and transport properties of MX2 (M = Mo, W; X = S, Se, Te) using first-principles calculations with Boltzmann transport theory. It is found that only three molybdenum compounds have a small direct band gap at the K point, which derives from the distortion of octahedral coordination [MoX6]. Among these three cases, the hole carrier mobility of MoSe2 is estimated to be as high as 690 cm(2)/Vs at room temperature, far higher than that in the other two MoX2. For this reason, the combination of the modest carrier effective mass and weak electron-phonon coupling leads to the outstanding transport performance of MoSe2. The Seebeck coefficient of MoSe2 is also evaluated to be as high as similar to 300 mu V/K at room temperature. Due to the temperature-dependent mobility of T-1.9 and higher Seebeck coefficient at low temperature, the highest thermoelectric power factor of MoSe2 is 10.2 x 10(-3) W/mK(2) at 200 K. More importantly, MoSe2 has a large thermoelectric power factor with a value of similar to 6.0 x 10(-3) W/mK(2) in the temperature range from 100 to 500 K. The present results suggest that 1T '' MoSe2 has high-performance carrier transport and is an excellent candidate for thermoelectric material.