Large thermoelectric power factor of high-mobility transition-metal dichalcogenides with 1T^{″} phase

Abstract

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 MX_{2}(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 [MoX_{6}]. Among these three cases, the hole carrier mobility of MoSe_{2} is estimated to be as high as 690cm^{2}/Vs at room temperature, far higher than that in the other two MoX_{2}. For this reason, the combination of the modest carrier effective mass and weak electron-phonon coupling leads to the outstanding transport performance of MoSe_{2}. The Seebeck coefficient of MoSe_{2} is also evaluated to be as high as ∼300μV/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 MoSe_{2} is 10.2×10^{−3}W/mK^{2} at 200 K. More importantly, MoSe_{2} has a large thermoelectric power factor with a value of ∼6.0×10^{−3}W/mK^{2} in the temperature range from 100 to 500 K. The present results suggest that 1T^{″}MoSe_{2} has high-performance carrier transport and is an excellent candidate for thermoelectric material.