Forging the impossible: the route to efficiency in thermoelectricity

Thermoelectricity is a physical phenomenon discovered at the end of the 18th century. In principle it provides a very convenient way to convert heat into electricity with no needs for moving parts. However, its use for electric generation has only begun over the last few decades. The reason for this delay is that the efficiency of thermoelectric generators is ruled by an awkward combination of transport coefficients that may be hardly optimized. As a matter of fact, the perfect thermoelectric material should have the thermal conductivity of a glass, the electrical conductivity of a metal, and the Seebeck coefficient of a dielectric. Search for such an “impossible material” has not discouraged scientists, however. In this lecture I will summarize the most important steps that thermoelectric material science has taken over the last fifty years, showing how the need for effective thermoelectrics has triggered a major enhancement of our understanding of the interplay between transport processes and the structural characteristics of materials. The targets of this line of work for the next decade will be discussed. Paradoxically enough, the achievements in increasing thermoelectric efficiency are now setting additional chemical and mechanical constraints to material scientists and technologists. Thus, current research on thermoelectrics is addressing not only efficient but also geo-abundant, flexible, and ecofriendly materials that may fit the requirements of near-future macro and microharvesting. Its implications in modern thermoelectric research will be also presented.