Proceedings of nanoGe September Meeting 2015 (NFM15)
Publication date: 8th June 2015
The study of nanometer sized crystallites is an interesting and ongoing field of research. Binary compounds, e.g. CdS(e), CdTe, PbS(e), have often served as technical relevant model systems to understand property changes due to quantum confinement. More recently, the interest of the scientific community was focused on the replacement of cadmium-based materials by less toxic quantum dots (QDs) with high potential for optoelectronic applications. CuInS2 is a non-toxic semiconductor material from the chalcopyrite family that has attracted much attention.
Synthesis of CuInS2 often results in products with broad absorbance spectra consisting of several features. This absorbance behavior could be the result of various factors, namely a wide size distribution, electron density leakage from the core of the crystals into the ligand layer and/or intra-bandgap states. However, a final conclusion on the habit of CuInS2 nanocrystals is still missing. To obtain desired properties and therefore optimum device performance, an accurate adjustment of the mean particle size and particle size distribution (PSD) are key factors.Accurate characterization is seen as a key-requirement for any successful post-processing which further narrows the size distribution.
In the present contribution, a detailed study of the size distribution of CuInS2 QDs and its influence on the optical characteristics is presented. Size-selective precipitation (SSP) was chosen to classify the nanocrystals into several fractions. By means of analytical ultracentrifugation and deconvolution of absorbance spectra, information on the size distribution of the feed and the individual fractions was gained. Furthermore, detailed characterization of the crystal structure and the composition is carried out to distinguish between properties inherent to the dispersity of the material CuInS2 at the nanometer size regime and those associated with unwanted variations in sample quality. Our results provide deep insight into the correlation between particle size and various optical characteristics such as bandgap energy, absorption and emission features and the broadness of the emission signal. Additionally, the photoluminescence quantum yield could be improved by performing SSP. These structure-property relationships are only gained due to the unique combination of different highly advanced analytical techniques.
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