Enhanced Electrical Properties of Bi_2−xSb_xTe₃ Nanoflake Thin Films Through Interface Engineering

Abstract

The structure–property relationship at interfaces is difficult to probe for thermoelectric materials with a complex interfacial microstructure. Designing thermoelectric materials with a simple, structurally‐uniform interface provides a facile way to understand how these interfaces influence the transport properties. Here, we synthesized Bi2−xSbxTe3 (x = 0, 0.1, 0.2, 0.4) nanoflakes using a hydrothermal method, and prepared Bi2−xSbxTe3 thin films with predominantly (0001) interfaces by stacking the nanoflakes through spin coating. The influence of the annealing temperature and Sb content on the (0001) interface structure was systematically investigated at atomic scale using aberration‐corrected scanning transmission electron microscopy. Annealing and Sb doping facilitate atom diffusion and migration between adjacent nanoflakes along the (0001) interface. As such it enhances interfacial connectivity and improves the electrical transport properties. Interfac reactions create new interfaces that increase the scattering and the Seebeck coefficient. Due to the simultaneous optimization of electrical conductivity and Seebeck coefficient, the maximum power factor of the Bi1.8Sb0.2Te3 nanoflake films reaches 1.72 mW m−1 K−2, which is 43% higher than that of a pure Bi2Te3 thin film.

Atomic-Resolution Interfacial Reaction Mechanism between Bi2Te3-Based Alloys and Ni Electrodes

“…Among all the crystalline surfaces, the (0001) surfaces are the most stable and the most commonly found surfaces in exfoliated BT bulk samples, strongly textured BT thin films, and BT nanoflakes. 30 Therefore, atomicresolution investigations on the interfacial reaction between Ni and BT(0001) surfaces provide essential structural information on how to optimize the BT(0001)/Ni interface for TE devices.…”

“…Bi 2 Te 3 (BT)-based alloys are the most widely used TE materials with great potential for commercial applications. − The most commonly used n-type and p-type Bi 2 Te 3 -based alloys are Bi 2 Te 2.7 Se 0.3 (BTS) and Bi 0.5 Sb 1.5 Te 3 (BST), respectively, both of which are designed by controlling the carrier type and concentration through doping. ,− Due to good matching with BT-based alloys, low resistance, and good service stability, Ni metal and alloys serve as ideal electrode materials for both BST and BTS TE materials. ,,, Ni can interact with BST and BTS to form intermetallics, and the reaction is mainly controlled by Ni diffusion into the TE material matrix. , However, the interfacial reaction mechanism is still obscure as both BST and BTS have complicated chemical compositions, resulting in preferential reaction and phase separation at the atomic scale. Moreover, BT-based alloys with an anisotropic van der Waals (vdW) layered structure have demonstrated strong anisotropic electron and phonon transport properties. − BT/Ni interface structural evolution and diffusion behavior also critically depend on the interface orientation.…”

“…Moreover, BT-based alloys with an anisotropic van der Waals (vdW) layered structure have demonstrated strong anisotropic electron and phonon transport properties. − BT/Ni interface structural evolution and diffusion behavior also critically depend on the interface orientation. Among all the crystalline surfaces, the (0001) surfaces are the most stable and the most commonly found surfaces in exfoliated BT bulk samples, strongly textured BT thin films, and BT nanoflakes . Therefore, atomic-resolution investigations on the interfacial reaction between Ni and BT(0001) surfaces provide essential structural information on how to optimize the BT(0001)/Ni interface for TE devices.…”