Enhancing the thermoelectric properties of 2D Bi₂Se₃ by 1D texturing with graphene

Jen Kai Wu^1,2*, Mario Hoffman¹, Yuan-Huei Chang¹, Ya Ping Hsieh²

¹Physics, National Taiwan University, Taipei, Taiwan
²Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan

* Presenter:Jen Kai Wu, email:D01222011@ntu.edu.tw

Two-dimensional thermoelectric materials have high potential as wearable generators if their performance can be enhanced. Unfortunately, conventional nanostructuring approaches that increase the thermoelectric figure of merit in three-dimensional thermoelectric are of limited usefulness in two-dimensional structures, since phonon-scattering across 2D material boundaries becomes ineffective. We here present a novel texturing approach to overcome these issues that is based on the formation of one-dimensional (1D) heterojunctions in the 2D material. To demonstrate the concept, ultrathin Bi₂Se₃ was synthesized by physical vapor deposition (PVD) on graphene, resulting in films of high quality, and with stoichiometric composition. Uniaxial wrinkles in the graphene were found to impede the growth of Bi₂Se₃ yielding an anisotropic 2D film with interspersed 1D discontinuities. The TE properties of these textured samples exhibit a clear anisotropic characteristic in agreement with their morphology. Carrier transport perpendiculare to the graphene wrinkle direction maximizes the impact of the 1D heterojunctions and results in an enhanced room-temperature ZT of 1.03 which represents the highest reported value for Bi₂Se₃. Our results are applicable to other 2D thermoelectrics and open up new routes for the materials design towards TE applications.

Keywords: Thermoelectric, Anisotropy, Bi₂Se₃