Puthran, S.Hegde, G.S.Prabhu, A.N.Wang, Y.-L.Kuo, Y.K.Joshi, S.Udayashankar, N.K.Nayak, R.2026-02-032025Journal of Materials Science, 2025, 60, 42, pp. 20529-20557222461https://doi.org/10.1007/s10853-025-11567-1https://idr.nitk.ac.in/handle/123456789/20006The 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 (Bi<inf>2</inf>Te<inf>3</inf>), 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 Bi<inf>2</inf>Te<inf>3</inf>. 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, Bi<inf>2</inf>Te<inf>2.7</inf>Se<inf>0.3</inf> and (Bi0.98Sb<inf>0.02</inf>)<inf>2</inf>Te<inf>2.7</inf>Se<inf>0.3</inf>, exhibited significantly enhanced thermoelectric performance, with Seebeck coefficients reaching ~ 253 ?V/K and ? 211 ?V/K, respectively, over the 10–400 K range. The power factor improved remarkably, showing a ~ 30-fold increase for Bi<inf>2</inf>Te<inf>2.7</inf>Se<inf>0.3</inf> 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. © The Author(s) 2025.AntimonyAntimony compoundsBismuth compoundsCrystal atomic structureCrystal microstructureCrystalline materialsDoping (additives)Point defectsSeebeck coefficientSeleniumSelenium compoundsSingle crystalsTellurium compoundsThermal conductivityThermoelectric equipmentBismuth tellurideCrystal meltDefect engineeringDoping strategiesGrowth methodMelt growthMicrostructural engineeringSeebeckThermoelectric performanceThermoelectric propertiesCarrier concentration