Preparation and characterization of CuInS 2 nanorods and nanotubes from an elemental solvothermal reaction
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Shuyuan Zhang Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui, People’s Republic of China 230026
Yitai Qiana) Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, People’s Republic of China 230026 and Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui, People’s Republic of China 230026 (Received 27 November 2000; accepted 15 July 2001)
A simple and convenient solvothermal reaction has been developed to produce CuInS2 nanorods and nanotubes from the elements in ethylenediamine at 280 °C. The products were characterized by x-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy. Analysis shows that the coordinating ability of ethylenediamine and the existence of liquid In may play important roles in the growth of one-dimension nanocrystallites and the electron-transfer reaction. In addition, spherical CuInS2 micrometer particles were obtained at 350 °C.
I. INTRODUCTION
I–III–VI2 ternary semiconductor compounds such as CuInSe2 and CuInS2 with the chalcopyrite structure have been shown to be useful for nonlinear optical and direct energy gap materials.1,2 The most extensively studied I–III–VI2 compound is CuInSe2, which polycrystalline form has resulted in solar cell devices with efficiency close to 17%.3,4 Due to the narrow energy band gap of CuInSe2 (0.95–1.0 eV), the efficiency reduction of these devices with a modest increase of temperature is obvious. To minimize the negative temperature effects and to increase the open circuit voltage of the device, the wider energy band gap semiconductor compounds such as CuInS2 and CuGaInSe2 are currently being investigated.3 The CuInS2 material has a near optimum energy band gap (near 1.5 eV), which is matched well to the solar spectrum.5,6 Various fabrication methods proposed for CuInS 2 include single, dual, and three source coevaporation,7–9 spray pyrolysis,10 RF sputtering,11,12 electrodeposition,13 sequential deposition of Cu2S and In2S3,14 and sulfurization.11,12,15 However, it is difficult with almost all of these methods to maintain satisfactory stoichiometry, which has been known to critically
influence the device properties of CuInS2-based solar cells. The other limitation of some traditional routes is the use of highly toxic H2S.7–9,11,12,15 Recently, studies on nanostructure semiconductors with size-dependent optical and electronic properties have attracted considerable scientific and technological attention due to their applications.16–18 It has been found that the nanoscale CuInSe2 material has stronger absorption compared to bulk semiconductor and holds much promise for producing high-efficiency thin-film photovoltaics.19 It is reasonable to expect that CuInS2 nanomaterials have properties similar to those of CuInSe2 nanomaterials. Using particle size and morphology as control parameters to tailor band gap provides a novel approach t
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