Understanding of the contact of nanostructured thermoelectric n-type Bi[subscript 2]Te[subscript 2.7]Se[subscript 0.3] legs for power generation applications

Abstract

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 °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/Bi[subscript 2]Te[subscript 2.7]Se[subscript 0.3]/Ni legs, although not in p-type Ni/Bi[subscript 0.4]Sb[subscript 1.6]Te[subscript 3]/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 Bi[subscript 2]Te[subscript 3]-based thermoelectric material layer. We found that a p-type region formed within the n-type Bi[subscript 2]Te[subscript 2.7]Se[subscript 0.3] during hot pressing due to Te deficiency and Ni doping, leading to a large contact resistance.