Boosting "phonon drag" thermoelectric power at thin film interface

What is it about?

Thermoelectric materials can generate electric power from waste heat energy. Conversely, they can also generate a temperature gradient when electric current is applied to them. These materials are expected for application to power generators and coolers or heaters for temperature control. To develop these applications, a thermoelectric material showing high thermoelectric power even on applying low thermal energy is required. However, conventional thermoelectric materials exhibit high conversion efficiency at high temperatures, whereas there are only a few candidates that show high conversion performance at below room temperature. On the other hand, FeSb2 is known as a potential low-temperature thermoelectric material with the record-high thermoelectric power originating from the huge “phonon-drag effect” due to the strong interaction of electrons and phonons. If the phonon-drag effect is strong, the flowing phonons can drive the electrons to produce extra thermoelectric voltage when a temperature difference is applied. However, this phenomenon is observed only at extremely low temperature < 40 K. Thus, new approaches to enhance phonon drag effect at higher temperature are necessary for their effective use in thermoelectric cooling and energy conversion.

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Photo by Onur Binay on Unsplash

Photo by Onur Binay on Unsplash

Why is it important?

In this paper, we found that the phonon drag effect persists at much higher temperature up to 240 K and enhances thermoelectric power in FeSb2 thin films deposited on SrTiO3 single-crystals. The FeSb2 films showed phonon drag thermopower (Sg) peak at temperature ~ 60 K, and the Sg peak value was largely enhanced by varying film thicknesses from 10 to 100 nm. In addition, the onset temperature where Sg starts to appear can be largely increased due to the enhanced electron–phonon interaction by phonon leakage from the SrTiO3 substrate to the thin FeSb2 layer. The heterostructuring with an oxide would be effective approach to enhance phonon drag effect to increase thermoelectric power in higher temperature region.

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