Power factor improvement in hydrothermally synthesized Bi2−xSbxTe3 (x=1.5) - carbon sphere composites

► Fabrication of Bi0.5Sb1.5Te3−δ composites. ► Addition of 1 wt% carbon spheres in the hydrothermal synthesis. ► Investigation of sintering temperature using encapsulating-and-sintering techniques. ► 360 °C-sintered composite showing the largest power factor of 15.4 μW/cm K2 at 205 K. ► 10-60% improvement over the counterpart without adding carbon spheres.