Thermoelectricity: from principles to applications

We know that electrical energy can be generated directly from mechanical energy (dynamos) or, indirectly, from thermal energy as in power plants, via the obligatory passage through mechanical energy (turbines). Thermoelectricity, on the other hand, involves the direct conversion of heat into electricity, through the use of appropriate materials. It also has the added benefit of enabling the design of refrigerators. The late 1990s saw renewed interest in energy conversion using thermoelectric effects. There are three thermoelectric effects resulting from the coupling of electrical and thermal conduction phenomena: the Seebeck, Peltier and Thomson effects. They were discovered in the first part of the 19th century, but it wasn't until the 1950s that these effects were exploited to produce cold or generate electricity, thanks to the development of semiconductors and the work of the Leningrad school led by Ioffe . Energy converters based on thermoelectric technology offer a number of advantages, such as the absence of moving parts and fluids, simplicity of implementation, high reliability and the advantage of being "clean" for the environment. Thermoelectric refrigerators and generators are used in applications where their advantages compensate for their high cost and relatively low performance. For example, Peltier effect refrigeration is used in portable refrigerators for domestic or medical use, in air conditioning (automobiles, etc.) and in the cooling of optoelectronic components (infrared detectors, etc.). Thermoelectric generators have been successfully developed since 1962 to power NASA space probes (Voyager I and II, Galileo, Cassini...) over long periods (over 22 years for some missions). Given the current need for new sources of energy, thermoelectric generators could play an increasingly important role in the production of electricity from waste heat sources (e.g., thermal effluent from car exhausts).

This article reviews the thermoelectric theme. The first part is devoted to a review of electrical and thermal conduction phenomena in solids. Thermoelectric effects will then be presented, starting with their experimental manifestation. An interpretation of these effects will then be proposed, based on the macroscopic approach of irreversible thermodynamics, and the microscopic approach of intuitive arguments. The fundamentals of solid-state energy conversion by thermoelectric effects will be discussed in the third part, where we will introduce the dimensionless figure of merit that allows us to gauge the quality of materials for energy conversion. Finally, the...