Tunable Synthesis and Thermoelectric Property of Bi₂S₃ Nanowires

Bismuth sulfide (Bi 2 S 3 ) is a specific thermoelectric material that thermoelectric properties are anisotropic. One dimensional Bi 2 S 3 structure would improve the conductivity and Seebeck coefficient because of the anisotropic electron transmission and phonon scattering. The Bi 2 S 3 nanostructures with different morphologies are prepared by a modified composite molten salt method. The Bi 2 S 3 nanowires with lengths up to 20 μm and high crystallization are obtained. The thermoelectric properties of the synthesized samples with different morphologies are comparatively investigated. We find that the power factor of the film made from the Bi 2 S 3 nanowires is much larger than that of the film made by the Bi 2 S 3 nanosheets or nanowires mixed with sheets due to its lower resistivity and larger Seebeck coefficient. The low resistivity of the Bi 2 S 3 nanowires film is a result of the high carrier concentration and high carrier mobility due to the high orientation degree and better crystallization. The Bi 2 S 3 nanowires orientated along the film plane gives fast electron transmission along the a – c or b – c planes (electron crystal), and efficient phonon scattering between the cleaved a – c planes or b – c planes and between grains of the nanowires (phonon glass). The introduction of many interfaces from smaller size of grains, which scatter phonons more effectively than electrons, or serve to filter out the low-energy electrons at the interfacial energy barriers, allows the enhancement of Seebeck coefficient.