(734e) Synthesis and Characterization of Tin Selenide Nanocrystals Using Air-Stable Precursors

Near-infrared (NIR) absorbing semiconductor nanocrystals, also known as quantum dots (QDs), have unique properties, such as size tunable bandgap, and potential applications in photothermal therapy, photovoltaics, and infrared absorbing glass coatings or interlayers. SnSe QDs are attractive as NIR materials, because they do not contain a heavy metal, such as Cd, Hg or Pb.  The synthesis of SnSe colloidal QDs from organometallic precursors that are highly toxic and pyrophoric has been reported in the literature (e.g., Franzman et al., J. Am. Chem. Soc., 2010, 132 (12), pp 4060–4061; Baumgardner et al., J. Am. Chem. Soc., 2010, 132 (28), pp 9519–9521). Our study focuses on the development of 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 average diameter between 1.7 and 2.5 nm were synthesized by injecting the precursors in a hot coordinating solvent consisting of OLA and TOP.  The effects of reaction conditions on the growth kinetics and final morphology of the QDs were investigated. A high OLA concentration in the growth solvent was found to be necessary for activating the reaction forming SnSe nuclei. On the other hand, TOP was found to hinder SnSe nucleation and, at increased concentrations, to yield larger particles. The relative amounts of precursors, OLA and TOP in the growth mixture control the growth kinetics and the aggregation of the QDs. The evolution of QD size and morphology as function of reaction time for different relative amounts of precursors, OLA and TOP has been studied using TEM. The formation of aggregates has been studied as function of reaction conditions and methods of controlling their size and shape have been identified.  Growth conditions that provide precise control over the final particle size and prevent particle aggregation have been identified. The ultimate objective of this study is the development of a practical method for manufacturing SnSe QDs using readily available, air-stable precursors.