Synergistically enhanced thermoelectric properties of Bi2S3 bulk materials via Cu interstitial doping and BiCl3 alloying

Bi2S3 is composed of inexpensive and environmental friendliness elements, which has received extensive interests and been investigated as a promising mid-temperature thermoelectric material for years. Even pure Bi2S3 possesses a high Seebeck coefficient and low thermal conductivity, its low electrical conductivity leads to a low figure of merit (ZT) value. In this work, Bi2S3 fabricated by solid-state melting combined with spark plasma sintering can significantly enhance the thermoelectric performance via introducing small amounts of Cu and BiCl3. Cu interstitial doping and Cl substitution on S site result in a large increase in electrical conductivity. Additionally, the enhanced phonon scattering is derived from the point defects caused by element doping, the grain boundaries, and the small amount of secondary phase, which leads to the low thermal conductivity. Finally, a high ZT value of 0.7 is obtained at 773 K and reaches a large average ZT of 0.36 in the temperature range from room temperature (RT) to 773 K for the Cu-interstitial-doped and BiCl3-alloyed (Cu0.01Bi2S3 + 0.175 mol% BiCl3) sample. Furthermore, the mechanical properties of the Cu0.01Bi2S3 + 0.175 mol% BiCl3 sample are lower than those of other Bi2S3 samples, which stem from the weak chemical bonding strength.