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Superb Material for Solar Cells

Microcrystalline Silicon Carbide

Photovoltaic is an inexhaustible, clean source of energy. However, production costs for solar cells are still relatively high. The shiny power generators could become more economical if they could be constructed from the thinnest layers possible. Thin-film solar cells based on a silicon material, in which the atomic components are not arranged in crystal lattices, are already being produced. Crystalline material is better suited for the side of the window facing the sun. A team of Jülich scientists is developing a particularly promising material for this. At the Institute of Energy and Climate Research (IEK), they are producing microcrystalline silicon carbide, a material made of many tiny crystals that consist of 50% silcon atoms and 50% carbon atoms.

Hot wireInside this chamber, a hot wire glows while gaseous monomethylsilane is decomposing. This produces films of silicon carbide that are particularly advantageous for solar cells.
Copyright: Forschungszentrum Jülich

Microcrystalline silicon carbide offers numerous advantages: charge carriers are very mobile in the substance, it is extremely stable and it is transparent. This makes it ideal for use as a window layer in thin-film solar cells. The window layer is the side from which the sunlight hits a solar cell. In so doing, silicon carbide also reduces light reflection. This "antireflection" and the high transparency cause the light to be especially well used. At Jülich, the so-called hot-wire technique is employed to fabricate the material. This enables high-quality microcrystalline layers to be produced that are between 10 and 60 nanometres (millionths of a millimetre) thick. Solar cells with this type of window layer are already achieving an efficiency level of 9.6%.

For the especially effective tandem solar cells, like those developed in Jülich, a special type of silicon carbide is required. The researchers can produce this by incorporating aluminium atoms into the material. This "doping" generates positive charges in the silicon carbide, which are known as "holes". For this process, trimethylaluminium is used, like that also used in LED production.

For the refinement of the production processes, IEK works together with the Fraunhofer Institute for Surface Engineering and Thin Films in Braunschweig, Germany. Using numerous methods available at Forschungszentrum Jülich, the researchers are repeatedly analysing the way that silicon carbide changes in response to various interventions – so that the material will soon be ready for real-life applications.