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.
