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

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 Bi_2−xSb_xTe₃ (x = 0, 0.1, 0.2, 0.4) nanoflakes using a hydrothermal method, and prepared Bi_2−xSb_xTe₃ 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 Bi_1.8Sb_0.2Te₃ nanoflake films reaches 1.72 mW m⁻¹ K⁻², which is 43% higher than that of a pure Bi₂Te₃ thin film.