Thermoelectrics

Quantum Dots - Reawakening the Thermoelectric Industry

Thermoelectric devices are solid state semiconductor components that create a temperature gradient when driven with an electric current or create an electrical current when placed in a temperature gradient. Essentially they use charge carriers to "drag" heat from one side of the device or vice versa. Thermoelectric technology is over a century old. The applications for long lived, compact generators and heating and cooling elements are robust. However, to date thermoelectric devices have not become widespread and are only used in niche applications for cooling sensitive photodetectors or integrated circuits, in power systems for deep space probes, and small portable coolers.

Thermoelectric devices are not more ubiquitous because, simply stated, they are not efficient. These devices rely on a curious mix of attributes, namely large charge carrier mobility and high phonon (lattice vibrations) scattering that do not readily occur in bulk materials. The best materials in nature's arsenal are small bandgap semiconductors and semimetals, but they still do not enable the efficiencies required for a widespread technology adoption.

Many researchers are working diligently on nanocomposite materials that artificially induce phonon scattering, thereby inhibiting heat transfer due to lattice vibrations while facilitating electron and hole conduction. One of the artificial nanomaterials approaches being explored involves the creation of semiconductor nanocrystals inclusions of one semiconductor within another semiconductor host. They are produced by codepositing several types of semiconductor nanocrystals that as a thin or thick film followed by a thermal or chemically induces fusion process. Results to date have been promising, with improvements by up to 100% of the Zt coefficient (the basic thermoelectric figure of merit) being reported.