BiSe with intrinsic low thermal conductivity has considered as a promising thermoelectric (TE) material at nearly room temperature. To improve its low thermoelectric figure of merit (zT), in this work, Sb and Te isovalent co-alloying was performed and significantly optimized its TE property with weakly anisotropic characteristic. After substituting Sb on Bi sites, the carrier concentration is suppressed by introduction of Sb- Se site defects, which contributes to the increased absolute value of Seebeck coefficient (|S|). Further co-alloying Te on Se of the optimized composition Bi_0.7Sb_0.3Se, the carrier concentration increased without affecting the |S| due to the enhanced effective mass, which leads to a highest power factor of 12.8 μW/(cm·K²) at 423 K. As a result, a maximum zT of ~0.54 is achieved for Bi_0.7Sb_0.3Se_0.7Te_0.3 along the pressing direction and the average zT (zT_ave) (from 300 K to 623 K) are drastically improved from 0.24 for pristine BiSe sample to 0.45. Moreover, an energy conversion efficiency ~4.0% is achieved for a single leg TE device of Bi_0.7Sb_0.3Se_0.7Te_0.3when applied the temperature difference of 339 K, indicating the potential TE application.

Bi₂Te₃-based materials were prepared by direct ink writing (DIW) 3D printing and their microstructure and thermoelectric properties were investigated with an emphasis on the effect of the content of DMF and Te/Se addition. As the mass ratio of DMF in the composition increased from 6.5% to 8.0% (in mass), the electrical conductivity deteriorated because of the corresponding increased porosity and organic remains in the samples. However, the volatilization of DMF would reduce the fluidity of the slurry. Thus, thermoelectric slurry with 7.0% DMF is the most suitable mass ratio for 3D printing. Additionally, adding Te in the p-type Bi_0.4Sb_1.6Te₃ and adding Se in the n-type Bi₂Te_2.6Se_0.4 have significantly improved their electrical conductivity due to the increased carrier concentration and mobility. Combining with the moderate Seebeck coefficient (~200 μV/K), high power factors with ~802 μW·m⁻¹·K⁻² and 1266 μW·m⁻¹·K⁻² were obtained for the n-type Bi₂Te_2.6Se_0.4+10%Se and p-type Bi_0.4Sb_1.6Te₃+7%Te, respectively, which result in the final relatively high zT values of 0.68 at 573 K and 0.56 at 330 K for n-type and p-type 3D-printed samples.