The field of polymer solar cells is a field with an exponential growth in the number of published papers. It is a field defined by a set of challenges including; efficiency, stability and processability. Before all of these challenges have been addressed; polymer solar cells will not be a commercial success. This dissertation is devoted primarily to the study of the stability of polymer solar cells, and more specifically to designing and verifying experimental techniques, procedures, and automated solutions to stability tests and characterization. The goal of the project was to expand the knowledge of the degradation mechanisms involved in roll-to-roll coated polymer solar cells. While only a part of the experiments have directly involved roll-to-roll coated devices, most of the work is applicable to coated devices. The first part of the dissertation is devoted to the study of in-depth morphology of polymer solar cells using ellipsometry. It was demonstrated that ellipsometry can be used as a non destructive depth profiling technique to obtain compositional morphology of the active layer of roll-to-roll coated samples. The second and third part is devoted to the study of photo-chemical degradation of the active layer materials. The second part details the building of an automated setup for stability tests and presents results on thickness and absorbance dependence of the photo-chemical stability, acceptor stability, and the influence of intrinsic polymer parameters on stability. In the third part two light concentrating setups, built during the PhD, are detailed and results based on high intensity photodegradation studies presented. In the last part of the dissertation the use of TOF-SIMS for polymer solar cell characterization is detailed and the results on intrinsic barrier effects and degradation patterns are summarized.
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Krebs, Frederik C, Norrman, Kion
Department of Energy Conversion and Storage, Technical University of Denmark, 2013