[dipl] Perustieteiden korkeakoulu / SCI

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Browsing [dipl] Perustieteiden korkeakoulu / SCI by Department "Department of Applied Physics"

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  • Dye-sensitized nanostructured and organic photovoltaic cells: technical review and preliminary tests
    (2002) Halme, Janne
     School of Science | Master's thesis
    The solar electricity is presently a rapidly growing but often relatively expensive renewable energyform. Recently however, new molecular photovoltaic (PV) materials have been developed, whichcould enable a production of low-cost solar cells in the future. The thesis begins with a discussion of the current status of the PV technology and a shortintroduction to the different PV technologies and to the basics of photovoltaics. The dye-sensitized solar cell (DSSC) is an electrochemical solar cell where light absorption occursby dye molecules attached to a nanostructured TiO2 electrode. An introduction to the DSSC is givenincluding a short description of the operating principle of the cell and a discussion of the physicaland chemical processes behind it. A systematic literature review is done on the materials and mostessential preparation methods of the standard DSSC. The performance of the DSSC is reviewed in terms of the energy conversion efficiency and the longtermstability. The important directions of development are the transition from glass substrates toplastic foils and from batch processing to continuous processing as well as the use of solid stateelectrolytes. The glass-based DSSC technology is on the verge of commercialization and themanufacturing cost estimates for the technology are close to the projected costs of other PVtechnologies. The purely organic solar cells are discussed individually beginning with the discussion of thefundamentals of organic photovoltaics and an introduction of different types of organic photovoltaicmaterials including semiconducting polymers, dyes, pigments and liquid crystalline materials. Areview is done on the performance results of organic solar cells categorizing the cells by their devicearchitecture. The development of the organic PV materials is still at an early stage and no clearlyoutperforming materials or cell structures have yet emerged. Experimental results are reported including a demonstration of the dye-sensitization with a naturaldye as well as a preparation and testing of a series of ruthenium-dye based DSSCs. An efficiency of0.6% at about 600 W/m2 solar illumination was obtained for the DSSCs in outdoor measurements.
  • Inverkan av kväve, vismut och temperatur på vakans- och defektdistributionen i GaSb
    (2013) Segercrantz, Natalie
     School of Science | Master's thesis
  • NMR Techniques at Liquid Helium Temperatures
    (2010) Heikkinen, Petri J.
     School of Science | Master's thesis
    In this master’s thesis I describe our recently upgraded measurement techniques and devices based on the nuclear magnetic resonance (NMR) techniques used to investigate superfluid helium. At present, our research concentrates on the superfluid phase 3He-B. The most important part in our NMR circuit is a two-stage cryogenic MESFET preamplifier operating at 4 K. It is capacitively coupled to a high-Q (Q approximately 40000 in test conditions) LC-resonance circuit. The 3He-B sample is placed inside the superconducting pick-up coil, which is a part of the resonance circuit. High sensitivity and low noise levels are the requirements for the measurement circuitry. Our measurements have shown the signal-to-noise level to be around 8000 which is enough to detect small changes in the signal from the superfluid 3He-B sample. I also present the theories on which our measurements are based and analyze the NMR responses measured from the normal fluid and from the superfluid. The effect of rotation and vortices on the signal response is explained. We have also measured spin-wave spectra at different temperatures and rotation speeds. The data we have gathered shows the NMR response to be congruent with the theories and earlier measurements. All 3He measurements have been performed in a rotating cryostat, with which we can achieve sample temperatures below 500 μK. Overall, the measurement accuracy is enough to investigate the properties of 3He-B on approaching the zero temperature limit.