Interplay between flexoelectric and thermoelectric effects in bismuth telluride thin films*

Flexoelectricity is a phenomena for which a strain gradient induces an internal polarization in semiconductor and dielectric materials. This effect can be used to enhance thermoelectric properties, and to enable the collection of photo-generated carriers without the need of a p-n junction. In this context, flexoelectricity was claimed to be the reason behind the variation of Seebeck coefficient in bismuth telluride (Bi₂Te₃) thin films deposited on different substrates, and was shown in many materials under illumination. However, a clear explanation of the relation between the applied strain and the detected signal is still missing, along with a comprehensive theoretical and experimental analysis.
We will present the experimental demonstration of flexoelectric effect in Bi₂Te₃ thin films deposited on flexible substrates, by magnetron sputtering. We will show and discuss how the open circuit voltage in our samples can be varied as a function of applied strain, temperature, and illumination level. Our results help to shed light on the relation between applied strain, material polarization, and the thermo/photoelectric performance, revealing new possible applications of the flexoelectric effect in low-gap materials.