Understanding of the contact of nanostructured thermoelectric n-type Bi2Te2.7Se0.3 legs for power generation applications

Traditional processes of making contacts (metallization layer) onto bulk crystalline Bi2Te3-based materials do not work for nanostructured thermoelectric materials either because of weak bonding strength or an unstable contact interface at temperatures higher than 200 degrees C. Hot pressing of nickel contact onto nanostructured thermoelectric legs in a one-step process leads to strong bonding. However, such a process results in large contact resistance in n-type Ni/Bi2Te2.7Se0.3/Ni legs, although not in p-type Ni/Bi0.4Sb1.6Te3/Ni legs. A systematic study was carried out to investigate the detailed reaction and diffusion at the interface of the nickel layer and n-type Bi2Te3-based thermoelectric material layer. We found that a p-type region formed within the n-type Bi2Te2.7Se0.3 during hot pressing due to Te deficiency and Ni doping, leading to a large contact resistance.