CuFeS2 nanocrystals composite with Sn nanoparticles as heavy metal-free thermoelectrics
Résumé
Thanks to their robustness and simple design, thermoelectric generators are interesting candidates for microscale energy harvesting applications. However current room temperature thermoelectrics based on heavy elements such PbTe or Bi2Te3 would preferably be replaced by more abundant, eco-friendly and low cost materials for use in widespread applications such as internet of things. CuFeS2 is an interesting semi-conductor in this scope. It shows high Seebeck and easy doping affording good n-type conduction. The too high thermal conductivity in bulk can be reduced in nanostructured pellets from pressed nanopowders. Here we describe nanocomposites made of CuFeS2 colloidal nanocrystals. Grown in organic solvents, the nanocrystals present a surface/core gap in chemical composition that can be tuned by non-stoichiometric conditions in synthesis, or by post synthesis surface treatment of nanocrystals in solution. The nanocrystals are then mixed with Sn nanoparticles for additional surface doping and hot-pressed into pellets. The nanocomposite pellets show a 5 times decrease in thermal conductivity down to 0.8W/m/K compared to bulk chalcopyrite, while electrical conductivity is maintained above 50S/cm. Perspectives of improvements using anisotropic nanocrystals in the composites will be discussed.