Highly enhanced thermoelectric properties of nanostructured Bi2S3 bulk materials via carrier modification and multi-scale phonon scattering

Abstract

Bismuth sulfide (Bi₂S₃) with an earth-abundant elemental composition has attracted wide attention as a promising n-type thermoelectric material in recent years. However, the thermoelectric performance of Bi₂S₃ is limited by its low electrical conductivity. It is therefore vital to choose an effective dopant for enhancing the electrical transport properties of Bi₂S₃. In this work, by using the solid-state reaction and the spark plasma sintering technique, Bi₂S₃ bulk materials doped with x mol% LaCl₃ (x = 0, 1.0, 2.0, 3.0) were successfully fabricated. The conductivity of Bi₂S₃ samples doped with 2 mol% LaCl₃ (about 153 S cm⁻¹) was one order of magnitude higher than that of the pristine Bi₂S₃ sample, resulting in a high power factor of 483 μW m⁻¹ K⁻² at 625 K. The lattice thermal conductivity of the doped samples decreased due to more grain boundaries, point defects and nano-precipitates. Consequently, a peak thermoelectric figure-of-merit (ZT) of 0.50 at 625 K was obtained for the Bi₂S₃ sample with 2 mol% LaCl₃ doping, which was over four times higher compared to that of pristine Bi₂S₃ (about 0.11 at 625 K). The results suggest that the dopant LaCl₃ is effective for modifying carrier concentration and reducing lattice thermal conductivity.