Defect-engineered single crystal Bi2Te3 via Sb and Se doping for enhanced thermoelectric performance

Abstract

The limitation of the single crystal melt growth method to tune the microstructure of the materials in a controlled way and the need for enhancing the thermoelectric properties of single crystal grown Bismuth telluride (Bi₂Te₃), through defect and microstructural engineering, has motivated this work. In this work, we address this limitation through a controlled doping strategy using antimony (Sb) and selenium (Se) to introduce targeted defects and microstructural modifications within single-crystalline Bi₂Te₃. Sb and Se substitutions create atomic scale strain, point defects, and micro-grain structures, enhancing phonon scattering without significantly disrupting the crystalline order. The resulting defect-engineered single crystals exhibit improved thermoelectric performance, with a notable reduction in lattice thermal conductivity and retention of excellent electrical properties. The co-doped compositions, Bi₂Te_2.7Se_0.3 and (Bi0.98Sb_0.02)₂Te_2.7Se_0.3, exhibited significantly enhanced thermoelectric performance, with Seebeck coefficients reaching ~ 253 μV/K and − 211 μV/K, respectively, over the 10–400 K range. The power factor improved remarkably, showing a ~ 30-fold increase for Bi₂Te_2.7Se_0.3 and ~ 20-fold for the Sb-doped variant, while the figure of merit (ZT) improved by ~ 28.5 and ~ 14 times, respectively. Further, a flexible thermoelectric device fabricated from these optimized materials generated output power of 2.7 nW and 3.35 nW at ambient temperature. The non-monotonic variation of the Seebeck coefficient with Sb content, showing an optimal enhancement at x = 0.04, highlights the delicate balance between carrier concentration and band structure modification, emphasizing moderate Sb substitution achieves the most favorable conditions for thermoelectric performance. Our results present a scalable strategy for bridging the performance gap between pristine single crystals and heavily nanostructured thermoelectrics, opening new avenues for high-efficiency energy harvesting devices.