Thin-film thermoelectric devices with high room-temperature figures of merit

Abstract

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then - despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of ~2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices - more specifically, phonon-blocking, electron-transmitting superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W per square-cm. The localized cooling or heating occurs some 23,000 times faster than in state-of-the-art bulk thermoelectric devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, self-assembly of DNA microarrays, proteomic chips, fiber-optic switches and microelectrothermal systems. They can also serve to meet the emerging thermal management needs in advanced microprocessors, power electronics, laser devices, IR-imaging devices.