Manipulation of phase structure and Se vacancy to enhance the average thermoelectric performance of AgBiSe₂

The high-temperature cubic phase of AgBiSe₂ has been revealed to enable promising thermoelectric performance because of the high symmetry. In this work, it is shown that the cubic phase could be stabilized at room temperature by alloying SnSe. Although the effective mass increased, the decreased carrier concentration and mobility as well as the aggravated bipolar effect deteriorated the thermoelectric properties of the pure cubic phase. In contrast, the room-temperature rhombohedral AgBiSe₂ obtained a peak zT value of ∼0.66 at 723 K, which is attributed to the decreased thermal conductivity and increased power factor. Furthermore, reducing Se content not only increased the carrier concentration, but also increased the mobility due to the reduced energy barrier, and hence substantially improved the power factor over the whole temperature range. As a result, the peak zT and average zT were further enhanced in Ag_0.94Bi_0.94Sn_0.06Se_1.92. This work provides a novel strategy to optimize the thermoelectric performance of AgBiSe₂ material.