Te-free compound Bi2SeS2 as a promising mid-temperature thermoelectric material

Abstract This study has investigated the thermoelectric property of a new sulfide compound Bi2SeS2, which is as an analogy of the traditional compound Bi2Te3 but with earth-abundant elemental composition. By investigating the electrical and thermal transport properties of 3 mol% Ag, Cu, AgBr and CuBr doped Bi2SeS2, it is revealed that Bi2SeS2 has the potential as a good thermoelectric material used at mid-temperature, benefiting from the lower thermal conductivity below 0.6 W/mK and higher power factor over 500 μW/mK2 at 723 K. A high ZT value of 0.71 can be finally obtained for the sample Bi2SeS2–3%CuBr at 723 K, which is two times higher than that of the undoped sample and also larger than those of most reported Bi2S3 and Bi2Se3 at the same temperature. The present work also suggests that Cu and CuBr are much more effective to improve the thermoelectric properties of Bi2SeS2 among all the dopants due to the obviously enhanced electrical conductivity. But the lattice thermal conductivity can be reduced significantly for the Ag doped sample, which indicates higher ZT value can be further expected via dual-doping to synergetic tuning of the electrical and thermal transport properties.