Electronic, phonon transport and thermoelectric properties of Cs2InAgCl6 from first-principles study

Abstract

We have studied electronic, phonon transport and thermoelectric properties of Cs2InAgCl6 using first-principles calculations. The PBE functional severely underestimates the bandgap and calculated value for fully relaxed Cs2InAgCl6 is 1.01 eV. Our calculated direct bandgap using TB-mBJ potential of partially relaxed Cs2InAgCl6 is 3.3 eV which agree with the measured value 3.3 eV whereas it is 2.53 eV for fully relaxed Cs2InAgCl6 and underestimates the experimental value by 23.3%. The In-5s and Ag-4d mainly formulate the direct bandgap. We have found that the lattice thermal conductivity (κl) is quite low (0.2 Wm−1K−1) in Cs2InAgCl6. The quite low phonon group velocity in the large weighted phase space and high anharmonicity (large phonon scattering) are responsible for low κl value. This halide possesses high Seebeck coefficient (∼900 μV/K at 700 K) because of its large bandgap. The maximum ZT value obtained at 700 K is ∼0.94. Therefore, we predict that Cs2InAgCl6 is a promising material for thermoelectric device applications.