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Optical near-field investigations of photonic structures for application in silicon-based thin-film solar cells

By Markus Ermes


In this thesis, light scattering and propagation inside a silicon-based thin-filmsolar cell is investigated using optical simulations based on the finite-differencetime-domain method. The special focus in this thesis lies in the analysis ofthe influence of randomly textured surfaces on cell performance. Due to therandom nature of these structures and their varying sizes, simulation domainshave to be sufficiently large to have a statistically significant distribution of features.The investigations focus on three different areas: The first area is lightscattering at different interfaces in transmission as well as reflection. Thesesimulations are compared to results from an improved scalar scattering modelproposed by Domin´e et al. [J. Appl. Phys. 107, p. 044504, 2010]. The agreementof both methods is very good, with the limits of the scalar model lyingin multiple interfaces and layers with a thickness below the peak-to-peakroughness of the surface. Secondly, the absorptance inside different hydrogenatedamorphous and microcrystalline silicon layers is investigated for differentstructures; these include comparisons between conformal surfaces andsurfaces as obtained in real devices by silicon growth. Further investigations inthis area included simple stretching of the surfaces along different axes, as wellas more complex modifications based on the scalar scattering theory; additionally,an amorphous/microcrystalline silicon solar cell is simulated and comparedto experimental results to find limitations in the simulation approach.All of these simulations show a better performance for steeper features witha lateral size of about 500 nm. Additionally, the changes in topograhpy introducedby the silicon growth has a significant impact on cell performance.The last part of this thesis compares optical simulations to measurements of ascanning near-field optical microscope (SNOM). When comparing simulatedintensities directly above a rough surface to measurements, it is found thatthe offset of the tip due to its finite physical size is the strongest influence,while light scattering at the tip has very little impact on (relative) intensitymeasurements

Publisher: Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Year: 2015
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