Enhanced power factor of n-type Bi2Te2.8Se0.2 alloys through an efficient one-step sintering strategy for low-grade heat harvesting

Abstract

Hot deformation (HD) has been reported as an effective approach to recover the degraded power factor of n-type Bi₂Te₃-based alloys prepared by hot pressing (HP). In this work, we report an alternative one-step sintering strategy with a high peak temperature up to 560 °C and a short heating period of hundreds of seconds for preparing high-performance n-type Bi₂Te_2.8Se_0.2 alloys. A peak thermoelectric figure of merit (ZT) of 1.1 was achieved at 440 K for our optimized sample, and it was comparable to the ZTs of textured HD materials but higher than those of the untreated ZM ingot and HP materials reported in the literature. The enhanced ZT mainly comes from the remarkably improved power factor, especially at high temperatures, by optimizing the milling conditions and the peak sintering temperature. Our work demonstrates that, instead of repressing HP materials at a higher temperature, tuning the peak temperature of a short powder sintering process could effectively enhance the power factor through manipulating the donor-like effect, which thereby affects both the carrier concentration and mobility. Moreover, the short heating period prevents severe grain growth and thus helps to maintain relatively low thermal conductivity. A compact thermoelectric generator (TEG) with a surface area of 10 mm by 10 mm was further developed based on n-type Bi₂Te_2.8Se_0.2 alloys prepared in this work and p-type Bi_0.5Sb_1.5Te₃ alloys from our previous study. An open-circuit voltage of 398.6 mV and a maximum output power of 15.5 mW were achieved for the fabricated TEG under a temperature difference of 128 °C, demonstrating the great potential of the developed materials for thermal energy harvesting.