Effects of NbCl5-doping on the thermoelectric properties of polycrystalline Bi2S3

Abstract

Bi2S3 is considered a potential thermoelectric material owing to its non-toxic and earth-abundant components and intrinsically low thermal conductivity. However, owing to its low electrical conductivity and the coupling relationship between the electric transport properties and thermal transport properties, achieving a high ZT value for polycrystalline Bi2S3 is a major challenge. In this work, a high-valence halogen compound, NbCl5, was employed to enhance the thermoelectric properties of polycrystalline Bi2S3 fabricated by the melting method combined with the spark plasma sintering technique. The enhanced electrical conductivity of polycrystalline Bi2S3 is derived from the increased carrier concentration, which is caused by the substitution of Nb and Cl ions into Bi and S sites, respectively. A peak power factor of 363 μWm−1K‒2 was obtained for Bi2S3 with 1.0 ​wt% NbCl5 doping at 623 ​K. Finally, a maximum ZT of ~0.28, which is approximately four times higher than that of the pristine Bi2S3 sample, was obtained. This work proves that NbCl5 is an effective n-type dopant for the Bi2S3 system, and indicates that high thermoelectric performance can be realized for Bi2S3 with environmentally friendly and low-cost elements.