Boosting the thermoelectric performance of n-type Bi2S3 by hierarchical structure manipulation and carrier density optimization

Boosting the thermoelectric performance of n-type Bi2S3 by hierarchical structure manipulation and carrier density optimization

Te-free Bi2S3-based thermoelectric materials show great potential for eco-friendly and industrial scale-up applications because of their high-abundance, low-cost, low-toxicity, and low-thermal-conductivity features. However, their low figure of merit, ZT limits their further applications. In this work, we report a high ZT of ~0.8 at ~760 K in n-type polycrystalline Bi2S3 by a combination of hierarchical structure manipulation and carrier density optimization. A step-by-step fabrication by using mechanical alloying, high-pressure and high-temperature treatment, spark plasma sintering, and annealing leads to unique micro/nanostructures in polycrystalline Bi2S3 including refined grains, high-density Bi-rich nanoprecipitates, significant lattice distortions, and nanopores that confirmed by comprehensive characterizations, which contribute to significantly suppressed lattice thermal conductivity of 0.41 W m-1 K-1 at ~760 K. A further 0.5 mol% CuCl2-doping triggers impurity band in the electronic structure of Bi2S3 and narrows the bandgap for optimizing the carrier concentration at ~1×1020 cm-3, confirmed by both experimental results and first-principles density functional theory calculations. The optimized carrier concentration and maintained low lattice thermal conductivity give rise to a high power factor of ~5.3 μW cm-1 K-2 and high ZT that ranks as a top value. This work provides a new route to achieve high thermoelectric performance in n-type polycrystalline Bi2S3.