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Hydrothermal synthesis of materials for intermediate band solar cells
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Chemistry.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

Solar energy is an abundant energy source that may provide an environmentally friendly alternative to fossil fuels. The utilization of the solar energy have so far been limited by various energy losses in the photovoltaic devices. Intermediate band solar cells use a three photon absorption process to take advantage of a larger range of photon energies compared to conventional solar cells, increasing the maximum eciency of the solar cell. Iron substituted copper gallium disulphide (CGFS) has been proposed as one of the most promising systems, based on eciency calculations. Recently a CGFS with promising absorption properties has been synthesized, suggesting that an intermediate band may indeed be introduced to the CuGaS2 band gap. In this thesis, hydrothermal synthesis is used to make a parameter study of the unsubstituted CuGaS2 to optimize the phase purity. Iron substitution into the lattice has been attempted and a preliminary study of the reaction mechanisms has been made. Phase identication of the products has been made using x-ray diraction (XRD) and the diractograms have been analysed using Rietveld and Pawley renements to determine phase composition, lattice parameters and crystallite sizes. The microstructure of the products has been characterized using scanning electron microscopy (SEM), and energy dispersive spectroscopy analysis (EDS) has been used to determine the composition of the dierent microstructures. Reflectance spectroscopy has been attempted to find the absorption properties of the material. The major findings are that a parameter combination of 200-250 degrees reaction temperature, 30 hour reaction time and a copper and gallium precursor concentration of 0.15M or higher gives the most phase pure product of ca. 95 atomic percent CuGaS2. Degree of filling of the autoclave was not found to have a large effect on the product, though extreme fill factors were not tested. It is suggested that the CuGaS2 crystallites grow by a continuous reaction between the precipitated secondary phases and the unreacted precursors in the solution. A reaction temperature above 160 degrees or a reaction time over 1 hour is needed for nucleation of CuGaS2. Indications of iron substitution into the CuGaS2 lattice by hydrothermal synthesis were found, which has not been previously reported. The obtained products were not phase pure enough to make accurate reffinements on lattice positions.

Place, publisher, year, edition, pages
Institutt for kjemi , 2013. , 134 p.
URN: urn:nbn:no:ntnu:diva-21158Local ID: ntnudaim:6919OAI: diva2:631295
Available from: 2013-06-20 Created: 2013-06-20 Last updated: 2013-06-20Bibliographically approved

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