High thermoelectric performance in n-type bismuth sulfide by carrier concentration tuning and dense nanodomains

Bi2S3 is regarded as one of the most promising thermoelectric materials because of its abundance, cost-effectiveness and environmentally friendly characteristics. This work delves into the impact of interstitial Cu on the composition, microstructure, and thermoelectric properties of the Cl-doped Bi2S3 bulks. The introduction of interstitial Cu as donors generates free electrons without compromising electron mobility. The excessive Cu induces the precipitation of Cu/Bi-rich phase and the Cu ions dynamically diffuse from these precipitates into the Bi2S3 lattice with increasing temperature. This effect significantly enhances electrical conductivity and power factor across a broad temperature range. Intriguingly, dense nanodomains are successfully constructed in the Bi2S3 sample. This unique defect, coupled with interstitial Cu, nanodomains, precipitates, and dislocations, establishes the hierarchical structures, leading to a low lattice thermal conductivity of 0.34 W m−1 K−1. Notably, the sample incorporating 4 at.% Cu achieves an exceptional peak ZT value of 0.67 at 673 K.