Remarkably enhanced thermoelectric properties of Bi2S3 nanocomposites via modulation doping and grain boundary engineering

BiS with its low toxicity, earth-abundant composition, and intrinsically low thermal conductivity, has been considered to be a promising thermoelectric (TE) materials. However, its low electrical conductivity restricts the enhancement of its TE properties. In this work, nanostructured BiS bulk materials with high electrical transport properties were fabricated by combining modulation doping and grain boundary engineering via mechanical alloying, a hydrothermal procedure, and spark plasma sintering. For an 80 wt% (BiS + 0.6 mol% CuCl)@Bi + 20 wt% BiS@Bi (BS-3) bulk sample, the metallic bismuth existing in grain boundaries not only provides an effective electronic path but also inhibits the diffusion of doping elements, leading to a high electrical conductivity value of 35 Scm at 323 K, which is three orders of magnitude higher than that of a pristine BiS sample. Furthermore, because of the significantly enhanced electrical conductivity and the relatively low thermal conductivity, the highest ZT of 0.54 is reached for the BS-3 sample at 673 K, which is approximately 5 times higher than that of pristine BiS. The results reveal that this novel strategy of combining modulation doping and grain boundary engineering is expected to significantly enhance the electrical conductivity and TE properties for the instinct low electrical conductivity materials.