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  • Public defence: 2017-02-03 13:15 21A342, Karlstad
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Materials and Device Engineering for Efficient and Stable Polymer Solar Cells2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polymer solar cells form a promising technology for converting sunlight into electricity, and have reached record efficiencies over 10% and lifetimes of several years. The performance of polymer solar cells depends strongly on the distribution of electron donor and acceptor materials in the active layer. To achieve longer lifetimes, degradation processes in the materials have to be understood. In this thesis, a set of complementary spectroscopy and microscopy techniques, among which soft X-ray techniques have been used to determine the morphology of polymer:fullerene based active layers. We have found that the morphology of TQ1:PC70BM films is strongly influenced by the processing solvent and the use of solvent additives. We have also found, by using soft X-ray techniques, that not only the light-absorbing polymer TQ1, but also the fullerene is susceptible to photo-degradation in air. Moreover, the fullerene degradation is accelerated in the presence of the polymer. Additionally, this thesis addresses the role of the interfacial layers for device performance and stability. The commonly used hole transport material PEDOT:PSS has the advantage of being solution processable at room temperature, but this layer is also known to contribute to the device degradation. We have found that low-temperature processed NiOx is a promising alternative to PEDOT:PSS, leading to improved device performance. Even for encapsulated polymer solar cells, some photo-induced degradation of the electrical performance is observed and is found to depend on the nature of the hole transport material. We found a better initial stability for solar cells with MoO3 hole transport layers than with PEDOT:PSS. In the pursuit of understanding the initial decrease in electrical performance of PEDOT:PSS-based devices, simulations were performed, from which a number of degradation sources could be excluded.

  • Public defence: 2017-02-10 09:00 9C203, Karlstad
    Křepela, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science.
    Křepela, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science.
    The Weighted Space Odyssey2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The common topic of this thesis is boundedness of integral and supremal operators between weighted function spaces.

    The first type of results are characterizations of boundedness of a convolution-type operator between general weighted Lorentz spaces. Weighted Young-type convolution inequalities are obtained and an optimality property of involved domain spaces is proved. Additional provided information includes an overview of basic properties of some new function spaces appearing in the proven inequalities.

    In the next part, product-based bilinear and multilinear Hardy-type operators are investigated. It is characterized when a bilinear Hardy operator inequality holds either for all nonnegative or all nonnegative and nonincreasing functions on the real semiaxis. The proof technique is based on a reduction of the bilinear problems to linear ones to which known weighted inequalities are applicable.

    Further objects of study are iterated supremal and integral Hardy operators, a basic Hardy operator with a kernel and applications of these to more complicated weighted problems and embeddings of generalized Lorentz spaces. Several open problems related to missing cases of parameters are solved, thus completing the theory of the involved fundamental Hardy-type operators.