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  • Disputas: 2019-11-29 13:15 21A 342 Eva Erikssonsalen
    Blazinic, Vanja
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Probing the effects of photodegradation of acceptor materials in polymer solar cells: bulk, surface, and molecular level2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Polymer solar cells (PSC) have reached record power conversion efficiencies of over 15%. The operational lifetime of PSCs, however, has to increase for their use in large area outdoor applications. In this work, a set of spectroscopic techniques (UV-vis, FTIR, NEXAFS, XPS) was used to study the impact of exposure to light and air (photo-oxidation) on the photoactive layer and its components. We focused on the electron acceptor components: the fullerene derivatives, PC60BM and PC70BM, and the polymer N2200. A comparative study of photo-oxidized PC60BM and PC70BM thin films by UV-vis and FTIR spectroscopy has shown that both materials undergo similar photochemical transformation, with the process being faster in PC60BM, due to the greater curvature of the C60 cage. Comparing experimental FTIR, XPS and NEXAFS spectra of the photo-oxidized PC60BM thin films with the calculated spectra for a large variety of photo-oxidation products, it was found that dicarbonyl and anhydride groups attach to the C60 cage during photo-oxidation. The study of photo-oxidized TQ1:PC70BM blend films by spectroscopic and J-V measurements shows that deterioration of the charge transport in PC70BM is the major contributor to the device performance degradation. Kelvin Probe measurements demonstrated that the charge transport deterioration was due to upward band bending and gap states being formed on the surface of photo-oxidized PC70BM. The TQ1:PC70BM blends films were further studied by AFM-IR in order to determine the lateral distribution of pristine components, as well as the photo-oxidation products. It was found that anhydride oxidation products of PC70BM are equally distributed over the blend film surface. The PC70BM is replaced with the polymer N2200 in the blend with TQ1. The photostability in air of the blend and its neat components was studied by UV-vis and FTIR spectroscopy. The spectra show that thermal annealing improves the photostability in air of both components.

  • Disputas: 2019-12-05 09:00 9C 203, Karlstad
    Frodeson, Stefan
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörs- och kemivetenskaper (from 2013). Environmental and Energy Systems.
    Towards Understanding the Pelletizing Process of Biomass: Perspectives on Energy Efficiency and Pelletability of Pure Substances2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The use of fossil resources has to decrease and the use of renewable resources has to increase significantly to mitigate the climate change. In this change towards more renewable resources, biomasses will play an important role, both for energy use and for products. Thus, the utilization of biomasses must be optimized, both linked to which biomass species that are used, as well as the actual production processes. This thesis relates to the production of lignocellulosic biomass pellets, with the purpose to increase the understanding of how a pellet process can be improved. 

    There are many benefits to pelletize the biomass, such as increased density, more economical transports solutions and increased doseability. However, there is a lack of knowledge on how different biomass species affect the actual pelletizing. This causes pellet producers to strive for a feedstock with a chemical composition that is as uniform as possible, which reduces the possibility of increasing intake of, for example, seasonal or residual products of other kinds.

    If pellet producers can handle, predict and combine different biomaterials over time without stopping the production, new ways of acquiring raw materials for production would be possible. This will be important for future pellet producers, as the general use of biomasses will increase, so will the competition of the raw material. It will also be of importance in developing countries, which have a greater variation in wood species than today's large pellets producing countries. 

    This work has been focused on understanding biomasses pelletability, and the method has been to start with components such as, cellulose, hemicellulose, lignin etc. Results shows that there is a significant difference between the hemicelluloses, xylan and glucomannan, in terms of pelletability. During pelletizing, xylan changes its form, generates hard pellets and, correlated to pelletability, xylan are affected by actual moisture content or added water to the process. Glucomannan, however, shows the opposite, a low impact on pelletability and a minimal impact from water during the pelletizing process. A difference that can explain the difference in pelletability, between hardwood and softwood. 

    Solutions to improve the pelletizing process have also been studied. One result is that adding oxidized starch additive, reduces the energy consumption in the pelletizer and increasing the durability of the pellets, more than native starches. Another result is that a two-stage drying technique, reduces the heat power consumption per tonne of dried materialand at the same time increases the drying capacity. Also, the possibilities for a pellet producer to handle, predict and combine different biomaterials has been studied. Presented results show howbiomasses from Zambia can be used as an single resource or in different resources combinations in a pellet production. 

    Finally, a recommendation to pellet researchers to include the cellulose material, Avicel, in single pellet studies. By using the same reference material, the methods can be normalized and the pelletability of biomaterials can be validated in a new way. This step would develop the research in the field, and the possibility of increased use of biomass towards the use of more renewable resources in pellet production.