Enhanced thermoelectricity at the ultra-thin film limit

TL;DR

This paper demonstrates that thermal co-evaporation can produce ultra-thin Sb$_2$Te$_3$ and Bi$_2$Te$_3$ films with significantly enhanced thermoelectric properties, approaching practical levels for room-temperature cooling.

Contribution

It shows a cost-effective method to achieve high thermoelectric performance in ultra-thin films, previously only possible with expensive techniques.

Findings

Seebeck coefficient increases to ~500 μV/K in films thinner than 50 nm

Total Seebeck coefficient reaches ~1 mV/K in ultra-thin films

Estimated ZT value of ~2 indicates high thermoelectric efficiency

Abstract

At the ultra-thin film limit, quantum confinement strongly improves thermoelectric figure of merit in materials such as Sb$_2$Te$_3$ and Bi$_2$Te$_3$. These high quality films have only been realized using well controlled techniques such as molecular beam epitaxy. We report a two fold increase in the Seebeck coefficient for both p-type Sb$_2$Te$_3$ and n-type Bi$_2$Te$_3$ using thermal co-evaporation, an affordable approach. At the thick film limit greater than 100 nm, their Seebeck coefficients are around 100 $\mu V/K$, similar to results obtained in other work. When the films are thinner than 50 nm, the Seebeck coefficient increases to about 500 $\mu V/K$. With a total Seebeck coefficient $\sim$ 1 mV/K and an estimate ZT $\sim$ 2, this pair of materials is the first step to a practical micro-cooler at room temperature.