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Coming dissertations at Uppsala university

  • In the confines of Cu(In,Ga)Se2 thin film solar cells with rear surface passivating oxide layers Author: Dorothea Ledinek Link: Publication date: 2019-09-09 11:11

    The material supply to build renewable energy conversion systems needs to be considered from both a cost and an energy security perspective. For Cu(In,Ga)Se2 (CIGS) thin film solar cells the use of indium in the absorber layer is most problematic. The material input per service unit can be reduced, if the absorber layers are thinned down without a loss in power conversion efficiency.

    Thinning down absorber layers can increase the conversion efficiency. However, for real CIGS solar cells absorption losses and recombination rates at the rear surface between the CIGS absorber and the Mo rear contact as well as shunt-like behavior increase. Thus, both rear surface passivation and optical management are essential for maintaining high power conversion efficiencies.

    In this work, thin oxide layers, so-called passivation layers, are introduced between the CIGS absorber layer and the Mo contact. They can passivate the CIGS surface, if the CIGS-oxide interface has a lower defect density than the CIGS-Mo interface and/or if they contain a negative fixed oxide charge, which increases the hole concentration and reduces the electron concentration in the CIGS in the vicinity of the oxide.

    As these oxides are insulators, electrical conduction through the passivation layer has to be ensured. In this work, nanopoint contacts were etched into ALD-Al2O3 passivation layers in CIGS solar cells. These solar cells had 0.5 -1.5 µm thin absorber layers with a low In content and a high band gap. Ga grading was not used. Although absorber layers with a high Ga content have a short minority carrier diffusion length, a passivation effect could be discerned with the help of external quantum efficiency measurements and current-voltage measurements under varying temperatures in combination with optical and electrical modeling with a two-diode model. Moreover, the possibility of leaving out the additional fabrication step has been explored for ALD-Al2O3 and HfO2 as passivation layers. The results suggest that the passivation layer does not necessarily need to be opened for electrical conduction in an additional fabrication step, if sodium fluoride (NaF) is deposited onto Al2O3 layers prior to CIGS evaporation. In this case solar cells with 215 nm absorber layers and 6 nm thin passivation layers have a power conversion efficiency of 8.6 %, which is 3 % (absolute) higher than the conversion efficiency on a reference. Shunt-like behavior is additionally reduced. For the HfO2 layers photoluminescence data indicate a good passivation effect, but the layers need to be opened up to ensure conduction.

  • Trees of Knowledge : Science and the Shape of Genealogy Author: Petter Hellström Link: Publication date: 2019-09-06 13:37

    This study investigates early employments of family trees in the modern sciences, in order to historicise their iconic status and now established uses, notably in evolutionary biology and linguistics. Moving beyond disciplinary accounts to consider the wider cultural background, it examines how early uses within the sciences transformed family trees as a format of visual representation, as well as the meanings invested in them.

    Historical writing about trees in the modern sciences is heavily tilted towards evolutionary biology, especially the iconic diagrams associated with Darwinism. Trees of Knowledge shifts the focus to France in the wake of the Revolution, when family trees were first put to use in a number of disparate academic fields. Through three case studies drawn from across the disciplines, it investigates the simultaneous appearance of trees in natural history, language studies, and music theory. Augustin Augier’s tree of plant families, Félix Gallet’s family tree of dead and living languages, and Henri Montan Berton’s family tree of chords served diverse ends, yet all exploited the familiar shape of genealogy.

    While outlining how genealogical trees once constituted a more general resource in scholarly knowledge production—employed primarily as pedagogical tools—this study argues that family trees entered the modern sciences independently of the evolutionary theories they were later made to illustrate. The trees from post-revolutionary France occasionally charted development over time, yet more often they served to visualise organic hierarchy and perfect order. In bringing this neglected history to light, Trees of Knowledge provides not only a rich account of the rise of tree thinking in the modern sciences, but also a pragmatic methodology for approaching the dynamic interplay of metaphor, visual representation, and knowledge production in the history of science.

  • Challenges of transnational parenthood : Exploring different perspectives of surrogacy in Sweden and India Author: Anna Arvidsson Link: Publication date: 2019-09-06 13:16

    Transnational surrogacy challenges traditional norms of parenthood, especially motherhood; additionally, it is viewed as the exploitation of poor women. The overall aim of this thesis was to shed light on the consequences of an unregulated situation on surrogacy in the Swedish and Indian contexts, and to give different perspectives on surrogacy and the surrogate. The experiences of using transnational surrogacy and the consequences of using this reproductive method in a context of a largely unregulated situation had rarely been explored at the start of the study. Between 2012 and 2015, qualitative interviews were conducted with commissioning parents in Sweden who used transnational surrogacy mainly in India, as well as with social workers in Sweden, who have handled cases regarding the legal recognition of parenthood. To capture a non-western perspective on surrogacy, the views of women and men in different social strata in Assam, India were explored through individual interviews and focus group discussions. At the start of the project, India was the most common country to turn to for surrogacy. The results reveal that both commissioning parents and social workers needed to navigate inadequate parental legislation, with the result that commissioning parents felt questioned as parents. Social workers tried to balance the protection of the surrogate’s rights with the child’s best interest. The ethical aspects made the users of surrogacy ambivalent, and, for social workers, it resulted in further reluctance to handle legal parenthood cases. However, from an Assamese point of view, no ethical considerations were expressed; instead, the surrogate would either be stigmatized for her act and seen as though she was “selling her child,” or seen as a woman doing a noble act, helping a childless couple. All the informants demonstrated a pragmatic view of legal parenthood, but the current legal situation in Sweden limits the scope to act as parents in relation to society, because of the length of time it takes to be recognized as legal parents. This comes with a risk for children. From the perspective of reproductive justice, a clearer regulation on surrogacy, and kinship rules that are more adjusted to the current family practice, are needed. Additionally, to limit the risks for all parties involved in the surrogacy process, a more transparent surrogacy process is needed.