Morphology control of copper indium disulfide nanocrystals

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Morphology control of copper indium disulfide nanocrystals Marta Kruszynska, Holger Borchert, Jürgen Parisi and Joanna Kolny-Olesiak University of Oldenburg, Department of Physics, Energy and Semiconductor Research Laboratory, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany ABSTRACT In this report, we present a hot-injection strategy for the synthesis of CuInS2 (CIS) nanocrystals with hexagonal, pyramidal and nanorod shapes. For that purpose copper (I) and indium (III) acetates were dissolved in oleylamine as a high-boiling solvent. Tert-dodecanethiol (t-DDT) was used as a sulfur source. It was mixed with 1-dodecanothiol (1-DDT) and injected at a high temperature. The presence of the second dodecanethiol was necessary to control the growth of the synthesized nanocrystals. We observed a strong influence of the t-DDT amount on the morphology of the CIS nanocrystals. By the variation of the injected solution uniform CIS nanorods with different aspect ratio and size were obtained. INTRODUCTION A number of studies have been already reported on the synthesis of monodispersed binary chalcogenide semiconductor nanocrystals, while much less attention is focused on the ternary I-III-VI2 family, e.g. CuInS2 (CIS) nanocrystals [1-4]. This material is of great interests for photovoltaic applications due to the high absorption coefficient (~105 cm-1) in the visible region and radiation stability, a band gap of ~1.5 eV, and a relatively low toxicity [5-8]. CIS nanocrystals can be a promising candidate for organic-inorganic hybrid solar cells, since recently a successful charge transfer was observed in CIS/polymer blends [9]. Apart from photovoltaic applications, CIS nanoparticles can, e.g., be used as a fluorescence marker for in vivo biological imaging [10]. Various routes for the synthesis of CIS nanoparticles were presented in the literature. CIS nanocrystals have been prepared by a solvothermal method as well as a single source decomposition and hot-injections technique [12-13]. Depending on the reaction conditions CuInS2 nanoparticles can have different crystallographic structures: chalcopyrite, wurtzite or zincblende [14-17]. Although, CIS nanocrystals with different morphology, e.g. nanotubes, hexagonal platelets and quasi-spherical particles, could be synthesized, it is still a challenge to obtain nanocrystals with a narrow size and shape distribution. There are only few reports about a successful synthesis of monodisperse CIS nanocrystals [6, 18]. In some cases, the synthesis leads to the formation of Cu2S-In2S3 heterostructured nanocrystals [19]. In this report, we present a synthetic strategy to obtain CuInS2 nanocrystals with controllable shape and size. We use a method based on our previous work [18] and study the influence of the composition of the injection solution, containing a mixture of 1-dodecanothiol and tert-dodecanothiol, on the shape of the resulting nanocrystals. The structure, morphology and composition of the final materials were characterized by powder x-ray diffraction (XRD), transmission and sc

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