Effects of Ag off-stoichiometry on mechanical and thermoelectric properties of ductile AgCuSe0.6S0.4

Recently, AgCuSe-based ductile inorganic thermoelectric (TE) materials have attracted great interests because they can simultaneously achieve excellent TE performance and good deformability at room temperature. The composition-performance relationship of p-type AgCuSe-based ductile inorganic TE materials have been systematically investigated, but the related investigation on n-type AgCuSe-based ductile inorganic TE materials is still absent. In this work, a series of n-type ductile Ag1+xCuSe0.6S0.4 (x = −0.02, −0.01, 0, 0.01, and 0.02) samples are prepared. The effects of Ag off-stoichiometry on the phase composition, mechanical, and TE properties are systematically investigated. The crystal structure of AgCuSe0.6S0.4 can accommodate a small amount of Ag-excess to maintain the phase purity, but very little Ag-deficiency can induce the formation of secondary phases. The Ag off-stoichiometry has little influence on the mechanical performance. Introducing Ag-excess can increase the carrier concentration to optimize the electrical conductivity and power factor, leading to enhanced TE figure-of-merit (zT). The zT of Ag1.02CuSe0.6S0.4 is 0.17 at 300 K. The six-couple in-plane flexible TE device fabricated based on Ag1.02CuSe0.6S0.4 demonstrates high output performance that is superior to the organic flexible TE devices. This work deepens the understanding on the novel AgCuSe-based ductile inorganic TE materials.