Two impurity energy level regulation leads to enhanced thermoelectric performance of Ag1−xCdxIn5Se8

The tetrahedrally bonded diamond-like compound AgIn5Se8 is proved to be a promising thermoelectric material due to its intrinsically low thermal conductivity. For the pristine AgIn5Se8 compound, however, the inferior electrical properties generally result in a limited zT value, owing to its wide band gap, up to 1.1 eV. Here, we report on the synthesis of AgIn5Se8 compound through a quick and convenient solid-state reaction route. Furthermore, the two impurity energy levels are regulated in those doped samples by incorporating Cd2+ ions at Ag+ lattice sites; the electron concentration dramatically increases, resulting in greatly enhanced electrical conductivity and thus a thermoelectric power factor over the entire temperature range. Combined with the intrinsically low lattice thermal conductivity, Cd-doped Ag1−xCdxIn5Se8 with x = 0.05 reaches the highest zT value of 0.63 at 883 K, favorably improved by 40% compared with that of the pristine AgIn5Se8.