High Thermopower and Optical Properties of A2MoS4 (A = K, Rb, Cs) and Cs2MoSe4

The current work analyzes the electronic, structural, mechanical, thermoelectric (TE), and optical properties of alkali-based transition metal chalcogenides A2MoS4 (A = K, Rb, Cs) and Cs2MoSe4 using methods based on first principles. The electronic, structural, and mechanical properties are analyzed using projected augmented wave (PAW) potentials. The electronic structure calculations show them to be direct bandgap semiconductors. From the TE properties, it is found that all the compounds possess huge thermopower especially for the holes, and this along with low lattice thermal conductivity enables us to predict A2MoS4 (A = K, Rb, Cs) and Cs2MoSe4 to be a good class of material for TE applications. Also, the optical properties are found to be nearly isotropic in the low energy region, which also might fetch potential applications in the visible range. The nearly isotropic optical properties along with giant thermopower are the highlights of the current study, which sets a platform for exploring future device applications.