(397ag) Tin Selenide Nanocrystals for Near-Infrared Applications

Near-infrared (NIR) absorbing semiconductor nanocrystals have exciting applications in photothermal therapy, photovoltaics, and infrared absorbing glass coatings or interlayers.  However, the most common NIR materials contain heavy metals, such as Cd, Hg or Pb, that are not environmentally friendly.  Tin Selenide (SnSe) has emerged as a heavy-metal-free alternative NIR material.  The typical synthesis of SnSe colloidal nanocrystals or quantum dots (QDs) involves the use of toxic and pyrophoric organometallic precursors (e.g., Baumgardner et al., J. Am. Chem. Soc., 2010, 132 (28), pp 9519–9521). We developed a new synthesis method for SnSe QDs that employs an air-stable tin(II) chloride-oleylamine (OLA) complex and selenium powder dissolved in trioctylphosphine (TOP) as precursors. SnSe QDs with size tunable bandgap and average diameters between 1.7 and 2.5 nm were synthesized by injecting the precursors into a hot coordinating solvent consisting of OLA and TOP.  The growth rate and final morphology of the nanocrystals were studied by TEM as functions of the processing conditions. Operating conditions that enable precise control over the final particle size and prevent particle aggregation were identified. The ultimate objective of our work is the development of a commercially viable method for manufacturing SnSe nanocrystals for NIR applications using readily available, air-stable precursors.