Expand band gap and suppress bipolar excitation to optimize thermoelectric performance of Bi0.35Sb1.65Te3 sintered materials

Abstract Bismuth-telluride-based alloys have been the state-of-art thermoelectric candidates near room temperature. However, sintered samples with higher ZT values in a wide temperature range are still urgently needed for further applications. Especially owing to the small band gap, the minority carriers are boosted at higher temperature and the thermoelectric properties are severely deteriorated. Here, we prepared p-type Bi0.35Sb1.65Te3-xSex samples by hot pressing to enlarge the band gap and suppress the bipolar excitation. Although the carrier concentrations are slightly increased by the tiny Se alloying, the Seebeck coefficients above 400 K are significantly improved, and the bipolar and lattice contributions to thermal transport are obviously reduced. The x = 0.04 sample thus achieves an average value of 1.1 between 300 and 500 K, and the constructed thermoelectric device produces an output power density of 0.36 W cm−2 and conversion efficiency of 5.24% at a temperature difference of 200 K. These results suggest that Se-doped Bi0.35Sb1.65Te3 is a robust candidate for low-grade heat harvest near room temperature.