Materials with thermoelectric effects

Thermoelectric effects (TE) enable the transformation of caloric (or thermal) energy into electrical energy, or vice versa, and its applications therefore include both (micro)-cooling and electricity generation from waste heat sources.

The search for new, non-polluting sources of energy has become a major challenge for modern society, particularly since the signing of the Kyoto Protocol. This is why the generation of electricity from waste heat using thermoelectric modules (see: Seebeck effect) has emerged as a reservoir of "green" energy. In addition to electricity generation, thermoelectric materials, which are capable of cooling (see: Peltier effect), provide a means of removing heat from microelectronics components. For the former, the low efficiency of thermoelectric systems has long limited their appeal. In the case of the latter, conventional methods (air/water) no longer meet requirements, due to miniaturization and the power densities to be dissipated. In both cases, new concepts have led to remarkable progress since 1995, justifying the very recent appearance of this theme in numerous conferences and national programs in various countries.

Understanding the physical phenomena involved in thermoelectricity and developing materials with TE properties have been the focus of two periods of intense activity.

Between 1821 and 1851, the three thermoelectric effects (Seebeck, Peltier and Thomson) were discovered and understood from a macroscopic point of view. Their potential applications in temperature measurement, refrigeration and electricity generation were also recognized. Then, from the late 1930s to the early 1960s, there was a period of significant progress, during which an understanding of microscopic phenomena developed, and most of the semiconductor materials in use today were discovered and optimized. However, the efficiency of these materials was woefully inadequate to compete with compression-expansion cycle refrigeration or for economically viable power generation applications, and the end of this period of research is well summed up by: "Thermoelectricity, the breakthrough that never came true".

More recently, since the early 1990s, there has been renewed interest in thermoelectricity, due in particular to the emergence of environmental concerns about the gases used in refrigeration and greenhouse gas emissions, and the desire to develop alternative energy sources.

The two main areas of research concern the development of new materials with complex and/or open structures, and the development of known materials in new low-dimensional forms (quantum wells, nanowires, nanograins, thin films, nanocomposites, etc.). Several of these new materials have interesting thermoelectric...