What Are Thermoelectric Devices?

Thermoelectric devices are solid-state components that convert temperature differences directly into electrical voltage, or conversely use electrical current to create and maintain a temperature difference, without moving parts. They operate through the Seebeck effect, Peltier effect, and Thomson effect, three interrelated phenomena collectively described by the theory of thermoelectricity. Because thermoelectric devices have no mechanical components, they are silent, vibration-free, and highly reliable, attributes that make them attractive for applications ranging from satellite power systems to consumer electronics cooling.

A thermoelectric device consists of pairs of p-type and n-type semiconductor legs connected electrically in series and thermally in parallel between two ceramic substrates. The semiconductor material in each leg is chosen to maximize the dimensionless figure of merit ZT, defined as the square of the Seebeck coefficient multiplied by electrical conductivity, divided by thermal conductivity. A ZT value above 1 is generally considered the threshold for practical applications, and bismuth telluride alloys near room temperature routinely achieve ZT values in this range.

Seebeck and Peltier Effects

The Seebeck effect, described by Thomas Johann Seebeck in 1821, is the generation of an electromotive force across a conductor or semiconductor subjected to a temperature gradient. When one junction of a thermoelectric pair is held at a higher temperature than the other, charge carriers diffuse from the hot side to the cold side, creating a measurable voltage. The Peltier effect, described by Jean Charles Athanase Peltier in 1834, is the complementary phenomenon: passing an electrical current through a thermoelectric junction causes one side to absorb heat and the other to release it. The direction of current flow determines which side is cooled and which is heated. Research on the co-existence of Seebeck and Peltier effects in thermoelectric modules has refined how engineers characterize and model these effects in real devices.

Thermoelectric Generators

A thermoelectric generator (TEG) exploits the Seebeck effect to produce electrical power from a heat source. One face of the module is placed against a hot surface, while the other is held at a lower temperature through a heat sink or cooling circuit; the resulting temperature gradient drives current through an external load. TEGs are used to recover waste heat from industrial exhaust streams, automotive engines, and space radioisotope thermoelectric generators (RTGs) such as those aboard the Voyager and Cassini spacecraft. Their power output scales with both the temperature difference and the number of thermoelectric pairs. Research from ETH Zurich on thermoelectric energy harvesting shows conversion efficiencies achievable from small temperature differentials, illustrating the potential for powering low-energy sensors and Internet of Things nodes.

Thermoelectric Coolers

Thermoelectric coolers (TECs), also called Peltier modules, use the Peltier effect to pump heat from a cold side to a hot side when driven by direct current. Unlike vapor-compression refrigerators, TECs require no refrigerant, produce no noise, and can be miniaturized to cool individual components. Common applications include maintaining stable temperatures in optical detectors, laser diodes, and laboratory instruments where tight thermal control is essential. The efficiency of a thermoelectric cooler is characterized by its coefficient of performance, which improves with higher ZT materials. Advances in bismuth telluride alloys, reviewed in PMC studies of Bi2Te3 thermoelectric generation, continue to push the performance boundaries of compact cooling modules.

Applications

Thermoelectric devices have applications in a wide range of disciplines, including:

• Spacecraft power generation from radioisotope heat sources
• Automotive waste heat recovery to supplement electrical systems
• Precision temperature control in medical and laboratory equipment
• Cooling of microelectronic components and photonic detectors
• Off-grid power generation for remote sensors and IoT nodes