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Institute of Energy and Climate Research

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Optics

In silicon-based thin-film solar cells, textured contact layers are used to scatter the incident light into the absorber layer. This light scattering significantly improves the quantum efficiency of the solar cell. The layer thicknesses as well as the surface feature sizes are in the order of the wavelength of relevant sunlight or below. The research group studies the optical processes that lead to efficient light scattering and light trapping with focus on the identification of optimized structures to further improve the efficiency of the solar cell. Scanning near-field optical microscopy is used to measure local scattering properties and the spatial distribution of guided optical modes. This technique provides insight for the optimization of the light trapping in the solar cell. The global light scattering into the far-field is measured by an angular resolved scattering setup.

Textured transparent conductive oxides are studied that were developed in the research group „light scattering contacts“ or provided by project partners. Furthermore, layer stacks successively deposited on top of these textured surfaces are investigated to obtain information about light trapping inside the solar cell. In collaboration with the research group „device simulation“, the experimental results are supported by optical simulations where Maxwell’s equations are solved rigorously for the real structure. These simulations provide additional insights to the light trapping process in solar cells that is hardly or not accessible by experiment. Additionally, artificial surface modifications can be applied to find structures with optimized light trapping properties. These simulations require the knowledge about the optical properties of the materials, namely the refractive index and the extinction coefficient. These properties are obtained from spectroscopic ellipsometry and complemented by photothermal deflection spectroscopy.

Layerstack

Team leader:

Dr. Karsten Bittkau


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