Thiol-Amine Complexes for the Synthesis and Surface Engineering of SnTe Nanomaterials toward High Thermoelectric Performance.

Abstract

SnTe has attracted significant research interest as a lead-free alternative to PbTe; however, its intrinsically high hole concentration results in an undesirably low Seebeck coefficient and elevated electronic thermal conductivity, thus significantly limiting its thermoelectric (TE) performance. Herein, we present a cost-effective, binary thiol-amine-mediated colloidal synthesis method to synthesize Bi-doped SnTe nanoparticles, eliminating the use of tri-n-octylphosphine-based precursors. The introduction of an electron-rich Bi dopant reduces the hole concentration and increases the Seebeck coefficient. Furthermore, post-synthetic surface treatment with chalcogenidocadmate complexes promotes atomic interdiffusion during annealing and consolidation, leading to compositional redistribution and modulation of the electronic band structure. Density functional theory (DFT) calculations reveal that co-modification <i>via</i> Bi doping and CdSe-derived chalcogen incorporation reduces the energy offset at the valence band maxima from 0.30 eV to 0.10 eV, thereby enhancing valence band degeneracy. The synergistic structural and electronic band structure modulations produce an SnTe-based material with a record high power factor of 2.1 mW m^-1 K^-2 at 900 K, a maximum TE figure of merit (<i>zT</i>) of 1.2, and a promising theoretical conversion efficiency of 8.3%. This study reports a versatile and scalable colloidal synthesis strategy that integrates hierarchical structural modulation with electronic band engineering, offering a synergistic route to significantly enhance the TE performance.