Enhancing power factor and ZT in non-toxic Bi2S3 bulk materials via band engineering and electronic structure modulation

Bismuth sulfide-based thermoelectric materials have attracted considerable interest owing to their abundance of raw materials and non-toxicity. However, their poor electrical properties, particularly their conductivity, have limited their practical applications. In this work, a melting method and spark plasma sintering were employed to synthesize bulk Bi 2 S 3 materials. The dopant MoCl 5 was used to regulate the electrical properties of Bi 2 S 3 . The results showed that Mo can significantly enhance the conductivity of Bi 2 S 3 compared to other transition metals. The doped sample exhibited an almost two-orders-of-magnitude rise in conductivity relative to the Bi 2 S 3 sample in its pure form. Due to its superior conductivity, the Bi 2 S 3 +1 wt% MoCl5 sample achieved an excellent power factor of 550 μW m −1 K −1 which is the maximum ever reported in the Bi 2 S 3 system. Simultaneously, the ZT value of this sample approached 0.70 at 773 K, which is a six-fold improvement compared to the pristine sample. Density functional theory was applied to understand the electronic structure changes of the Mo-doped sample, which revealed that trace amounts of MoCl 5 doping could significantly boost the density of states in the vicinity of the conduction band and shift the Fermi level to the valence band, leading to a reduction in the bandgap and an increase in free electrons. This work offers new insights into the role of Mo elements in thermoelectric materials and provides a good strategy for augmenting the thermoelectric figures of merit of other n-type thermoelectric materials with inadequate electrical conductivity in the future.