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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 increase light absorption by scattering the incident light into the absorber layer. This increased absorption significantly improves the quantum efficiency of the solar cell. The layer thicknesses as well as the sizes of the surface feature used for light scattering are in the order of the wavelength of relevant sunlight. The research group studies the optical processes that lead to efficient light scattering and light trapping. The focus is the identification of optimized structures to further improve the efficiency of the solar cell. Experimental as well as numerical methods are applied for this purpose:

Scanning near-field optical microscopy is a unique method 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. Novel concepts for light scattering/guidance are investigated and their applicability for thin-film solar cells evaluated. The work is supported by optical simulations which allow for a more detailed knowledge and analysis as well as a further optimization of the structure. 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.

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