Chemical Composition Engineering Leading to the Significant Improvement in the Thermoelectric Performance of AgBiSe₂-Based n-Type Solid Solutions

In this work, we have improved the thermoelectric performance of n-type AgBiSe2 by engineering its chemical compositions. This engineering is realized by doping Ag2Se at first and then In and S in succession. Finally, the lattice thermal conductivity (κL) reduces from 0.39 W K–1 m–1 to 0.15 W K–1 m–1, and the power factor (PF) enhances from 2.80 μW/(cm K2) to 4.84 μW/(cm K2) at ∼770 K. The reduction in κL is ascribed to the mass/size mismatch and/or structure anharmonicity, while the enhancement in PF is caused by the improved electrical conductivity via the creation of In and S impurity levels within the gap. As a result, the highest ZT value reaches 0.94 (using measured Cp). This value stands among the highest in the n-type AgBiSe2 system, which proves that the composition engineering is a practical route to improve the TE performance in this system.