| Iron disulfide in pyrite modification is one of the most promising materials in solar cell application, since 1983 Tributsch and co-workers showed the first optical response. As pyrite exhibits an absorption coefficient on the order of 1 mio/cm and possesses a band gap of 0.8 to 1.2 eV, it is under intensive investigation. While basic wet chemical approaches towards these nanocrystals are developed, more often the control of shape and surface capping are under-researched. Here, we report on the synthesis and shape control of iron pyrite nanostructures. On the basis of a recently published hot injection synthesis for spherical nanocrystals, particle stabilization as well as shape and size dispersion are improved and controlled by the use of various stabilizers. The resulting spherical particles are characterized by optical and electrochemical methods with regard to their band gap and solar cell application. Post synthetic particle annealing in the presence of respective stabilizing molecules keeps the shape nearly unaffected, whereas size dispersion as well as colloidal stability are strongly influenced. On the other hand, the addition of extra ligands in situ to the reaction mixture influences particle stability as well as shape. However, utilizing both methods various shapes are accessible, such as spheres (8-10 nm diameter) as well as round (20-30 nm diameter) or angular sheets (50-100 nm edge length), respectively. The resulting spherical particles are characterized by optical spectroscopy as well as electrochemical methods. As bulk pyrite exhibits an indirect band gap featureless absorbance spectra are obtained. Nevertheless, using the energy dependent absorption coefficient, an indirect band gap of 1.1 eV is determined. However, the edges of valence and conduction band are electrochemically addressable for particles deposited onto gold substrates. Following these results, a band gap of approximately 1.6 eV is found. |
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