Environmental-Friendly Solution-Processable Route to Size-Controlled SnTe Nanocrystals

Colloidal semiconductor nanocrystals (NCs) have attracted attention as promising materials for various applications.¹ The ability to precisely control their size and shape through solution-processable synthesis allows for fine-tuning their electrical and optical characteristics. Pb- and Hg-based chalcogenides (PbX and HgX, X = S, Se, and Te) have been extensively explored for electronic, optical, and optoelectronic applications.² In comparison, less toxic alternatives such as tin(II) telluride (SnTe) have been studied much less and should be further researched to conserve the environment. With its narrow bandgap, SnTe NC is prospective for short-wave to mid-infrared spectrum photodetection. Also, they are expected to become a lead-free alternative for thermoelectric materials.³ Significant challenges in synthesizing SnTe NCs stemming from their instability and oxidation-prone precursors hamper their further research. <br/> Herein, we present a novel, cost-effective, and solution-processable method for synthesizing monodisperse SnTe NCs via the simple reaction of trioctylphosphine telluride (TOPTe) with tin (II) bromide (SnBr₂) in conjunction with solely capping ligand oleylamine (OLA). The resulting NCs exhibited a cubic rock-salt crystal structure identical to their bulk of SnTe (space group, ). The NC diameters can be tuned from 8.9 to 44 nm by adjusting the reaction temperature and time. Our modified post-treatment process effectively isolated smaller NCs with narrow size distributions by exploiting the distinct solubility properties of the components and employing gradient density ultracentrifugation.<br/> Furthermore, the synthesized SnTe NCs were air-stable and could demonstrate electrical conductivity without introducing short ligands² and halide treatments³, which are typically vital to obtaining conductive pathways in the other NCs. Our observation might suggest the extended reach of the electron Bohr radius of the SnTe NC, signifying its quantum confinement.<br/> The synthetic procedure developed here offers an alternative path for the size-controlled synthesis of other monodisperse chalcogenide NCs using low-cost and environmentally friendly precursors, representing an advancement in colloidally synthesized semiconductors.<br/> <br/>Ref.: [1] M. Liu, N. Yazdani et al. Nat. Electron<i>.</i> 4, 548-558 (2021); [2] K.M. Tsoi, Q. Dai et al. Acc. Chem. Res. 46, 3, 662–671 (2013); [3] M.V. Kovalenko, et al. JACS. 129, 11354-11355 (2007); [4] R. Miranti et al. Appl. Phys. Lett. 117, 173101 (2020).