Nano silver sintering metallurgy to realize thermoelectric interconnect for bismuth tellurides

In thermoelectric generator devices, it is essential to have the internal interconnect with low electrical resistance and enough thermomechanical strength at the joints. Herein, silver nanoparticles are synthesized aqueously by chemical reduction of silver nitrate with ferrous sulfate, and they are formulated into nano silver paste for the sintering interconnect. The jointing performance of silver paste is first understood by sintering experiments in nitrogen between copper substrates or bars at 250–350 °C and structural evolution of nano silver. Then the silver paste is employed to bond the metallized bismuth tellurides and copper bars at 300 °C, where the p- and n-type Bi 2 Te 3 bars are plated either with Ni or Ni/Cu films. The interface resistivity and shear strength are less than 1 μΩcm 2 and 24–27 MPa for Cu−Cu bar connection, respectively, and those for Cu−Ni/Bi 2 Te 3 bars are about 10 μΩcm 2 and 6–8 MPa, which is raised to 8–10 MPa with Ni/Cu double metallization. The microstructures are investigated for the interfaces and fractures. Nickel and copper could diffuse into each other, which improves the fracture mode of the metallurgical junctions. Thermoelectric devices are manufactured with silver interconnect at 260 °C in air for demonstration, and the interface resistivity for Cu/Ni/Au−Ni/Bi 2 Te 3 legs can be reduced to less than 10 μΩcm 2 . • Nano Ag are synthesized abundantly and formulated to paste in eco-friendly solvents. • Ag paste sintering is used to bond p- and n-Bi2Te3 with Cu for thermoelectric device. • The middle Cu film strengthens the joint between sintered Ag and plated Ni on Bi2Te3. • Ni/Bi2Te3 diffusion layer is responsible for the interface resistivity and strength. • High temperature favors to sinter Ag, but may degrade semiconductor Ohmic contact.