Electroless Co-P diffusion barrier for n-PbTe thermoelectric material

This work describes an in-depth study on the electroless deposition of Co–P via the addition of a reductant to a solution on a roughened, sensitized, and activated n-PbTe thermoelectric substrate. The Co–P layer facilitates the bonding of the thermoelectric module with the solder paste and serves as a diffusion barrier that prevents severe interaction between n-PbTe and Cu or Ni electrodes. Without this layer, a eutectic reaction produces molten PbTe because of the fast diffusion of Cu; moreover, a large Cu₂Te phase is formed, resulting in the depletion of Cu from the Cu electrode. In addition, Pb and Te diffuse along the grain boundaries of the Ni electrode in the Ni/n-PbTe joint. Cross-sectional images and elemental analysis results show that the Co–P layer could efficiently inhibit interdiffusion in the Ni/n-PbTe and Cu/n-PbTe joints. These results provide new insights for developing PbTe thermoelectric devices using Ni or Cu electrodes with high reliability at working temperatures.