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

Abstract

Te-free Bi 2 S 3 -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 Bi 2 S 3 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 Bi 2 S 3 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% CuCl 2 -doping triggers impurity band in the electronic structure of Bi 2 S 3 and narrows the bandgap for optimizing the carrier concentration at ~1 × 10 20 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 Bi 2 S 3 . • A record-high ZT of ~0.8 at 760 K is achieved in n-type polycrystalline Bi 2 S 3 . • CuCl 2 -doping triggers impurity band of Bi 2 S 3 and narrows its bandgap. • An optimized n e of ~1 × 10 20 cm −3 leads to a high S 2 σ of ~5.3 μW cm −1 K −2 at 760 K. • Unique micro/nanostructures significantly suppress κ l to 0.41 W m −1 K −1 at 760 K.