Enhancing the thermoelectric performance of Bi2S3: A promising earth-abundant thermoelectric material

Recently, bismuth sulfide (Bi 2 S 3 ) has attracted much attention in the thermoelectric community owing to its abundance, low cost, and advanced properties. However, its poor electrical transport properties have prevented Bi 2 S 3 devices from realizing high thermoelectric performance. In this work, our motivation is to decrease the large electrical resistivity, which is recognized as the origin of the low ZT value in undoped Bi 2 S 3 . We combined melting and spark plasma sintering (SPS) in a continuous fabrication process to produce Bi 2 S 3- x Se x ( x = 0, 0.09, 0.15, 0.21) and Bi 2 S 2.85- y Se 0.15 Cl y ( y = 0.0015, 0.0045, 0.0075, 0.015, 0.03) samples. Our results show that Se alloying at S sites can narrow the band gap and activate intrinsic electron conduction, leading to a high power factor of ~ 2.0 μW·cm -1 ·K -2 cat room temperature in Bi 2 S 2.85 S 0.15 , about 100 times higher than that of undoped Bi 2 S 3 . Moreover, our further introduction of Cl atoms into the S sites resulted in a second-stage optimization of carrier concentration and simultaneously reduced the lattice thermal conductivity, which contributed to a high ZT value of ~ 0.6 at 723 K for Bi 2 S 2.835 Se 0.15 Cl 0.015 . Our results indicate that high thermoelectric performance could be realized in Bi 2 S 3 with earth-abundant and low-cost elements.