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, costeffectiveness 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.