Current thermoelectric materials and an evaluation of thermoelectric materials contacting approaches

In this paper a brief selection of state-of-the-art thermoelectric materials is described which are used for thermoelectric power generation. A summary of current advances in the field of thermoelectric (TE) materials which are used for TE power generation is presented. Among them, the class of filled skutterudite is very promising and extensively investigated. Skutterudites offer good power conversion efficiencies, with the high temperature side of the generators reaching up to 600 °C. Higher temperatures result in technological challenges related to thermomechanically induced stress. Additional difficulties at high temperatures can arise with respect to the reliability of the electrical contacts between the TE materials and metal connectors. Some contacting metals (e.g. silver) tend to diffuse into the active thermoelectric legs and thus are unsuitable for various high-temperature TE materials. As a first step towards a cascaded TE heat engine two Bi
2
Te
3
based TE generators have been evaluated with respect to the influence of TE-leg contacting approaches by measuring their figure-of-merit. While the elements of one TE generator were attached by means of vapor phase bonding using a tin based solder, the elements of the second generator were attached with a silver filled epoxy adhesive.