Enhanced the thermoelectric properties of n-type Bi₂S₃ polycrystalline by iodine doping

Bi₂S₃ is one of eco-friendly alternative compounds for thermoelectric devices. However, the low electrical conductivity of pristine Bi₂S₃ is the main restriction for a high ZT value. In this work, a series of iodine doped Bi₂S₃ polycrystalline samples are successfully prepared by melting combined with plasma activated sintering (PAS), and the relationships among composition, microstructure and thermoelectric properties are investigated. The X-ray diffraction (XRD) results shows that the content of the secondary phase BiS₂ is closely related to the doped concentration of iodine. The doped concentration of iodine can directly affect the electrical conductivity and the Seebeck coefficient, resulting in the relatively high power factor of 3.1 μWcm⁻¹K⁻² at 773 K while doping 1.0 mol% BiI₃. Moreover, the thermal conductivity is also reduced moderately. As a result, a maximum ZT value of 0.58 is obtained, which is 4 times higher than that of pristine Bi₂S₃.