The effects of Ag nanoinclusions on thermoelectric properties of Ag 2 S semiconducting nanostructures, synthesized by a novel one-pot facile polyol method, have been investigated. The resulting products are characterized by powder XRD, EDAX, XPS, and UV−vis techniques. FESEM images reveal the formation of disc-shaped Ag 2 S nanoparticles with an average thickness of 52 nm and diameters ranging from 50 nm to a few hundreds of nm. All samples show a systematic reduction in electrical resistivity with increasing Ag content in the composites. The Seebeck coefficient (α) values for the Ag nanoparticle-incorporated Ag 2 S nanocomposites are notably high near 300 K because of the low-energy charge-carrier filtering effect, which is due to preferential scattering of low-energy electrons at the barrier potentials set up at metal−semiconductor interfaces. The theoretical fitting of α data reveals a systematic shift of the Fermi level toward the conduction band edge with increasing Ag content in the composites. A significantly improved thermoelectric power factor at 325 K is observed for a wide range of Ag nanoinclusions with the highest ZT of 0.0029 at 325 K in the Ag 2 S−Ag nanocomposite with 20.1% Ag.

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This is the first report on the enhanced thermoelectric (TE) properties of novel reaction-temperature (T Re ) and duration-induced Bi 2 S 3 -Bi nanocomposites synthesized using a facile one-step polyol method. They are well characterized as nanorod composites of orthorhombic Bi 2 S 3 and rhombohedral Bi phases in which the latter coats the former forming Bi 2 S 3 -Bi core− shell-like structures along with independent Bi nanoparticles. A very significant observation is the systematic reduction in electrical resistivity ρ with a whopping 7 orders of magnitude (∼10 7 ) with just reaction temperature and duration increase, revealing a promising approach for the reduction of ρ of this highly resistive chalcogenide and hence resolving the earlier obstacles for its thermoelectric application potentials in the past few decades. Most astonishingly, a TE power factor at 300 K of the highest Bi content nanocomposite pellet, made at 27 °C using ∼900 MPa pressure, is 3 orders of magnitude greater than that of hot-pressed Bi 2 S 3 . Its highest ZT at 325 K of 0.006 is over twice of that of similarly prepared CuS or Ag 2 S-based nanocomposites. A significantly improved TE performance potential near 300 K is demonstrated for these toxic-free and rare-earth element-free TE nanocomposites, making the present synthesis method as a pioneering approach for developing enhanced thermoelectric properties of Bi 2 S 3 -based materials without extra sintering steps.

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