Excellent Thermoelectric Properties in monolayer WSe Nanoribbons due to Ultralow Phonon Thermal Conductivity.

By using first-principles calculations combined with the nonequilibrium Green's function method and phonon Boltzmann transport equation, we systematically investigate the influence of chirality, temperature and size on the thermoelectric properties of monolayer WSe nanoribbons. The results show that the armchair WSe nanoribbons have much higher ZT values than zigzag WSe nanoribbons. The ZT values of armchair WSe nanoribbons can reach 1.4 at room temperature, which is about seven times greater than that of zigzag WSe nanoribbons. We also find that the ZT values of WSe nanoribbons increase first and then decrease with the increase of temperature, and reach a maximum value of 2.14 at temperature of 500 K. It is because the total thermal conductance reaches the minimum value at 500 K. Moreover, the impact of width on the thermoelectric properties in WSe nanoribbons is not obvious, the overall trend of ZT value decreases lightly with the increasing temperature. This trend of ZT value originates from the almost constant power factor and growing phonon thermal conductance.