Scanning X-ray Imaging Techniques for Characterization of Energy Materials

Research output: ResearchPh.D. thesis – Annual report year: 2019

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The large and ever-growing energy needs call for an urgent shift for sustainable energy sources. Associated to the current production of energy is the emission of noxious gases that among other undesirable effects contribute for an increase of the greenhouse effect and consequently to global warming. From the currently available energy sources, solar energy is the one with the biggest potential to fulfil our current and fu-ture energetic needs. To date, the main factors impeding upscaling and mass produc-tion of solar cell devices are associated to their high production costs or low efficien-cies, for which fossil fuels are still economically competitive.

The performance of solar cells, especially those from second- and third-generation, is largely determined by their micro- and nano-scale. To improve their conversion effi-ciency, scientists must first be able to measure and characterize the nanostructure of the devices produced by current synthesis methods, so that these may be improved or tuned to fulfil a specific need.
Emerging X-ray imaging techniques, such as coherent diffractive imaging methods, have the potential to reach extremely high resolutions and are well suited for this task. Currently the available spatial resolution delivered by such methods is limited by the X-ray beam properties and by the performance of the numerical algorithms used for image reconstruction. Furthermore, the combination of different X-ray imaging meth-ods allows for complementary information about the sample from which the local elec-tronic and chemical compositions can be derived.

This thesis is devoted to the improvement of current X-ray scanning imaging methods. Our main contributions lie in the development of numerical algorithms for image data analysis of X-ray fluorescence and X-ray ptychography. More specifically the thesis includes the theoretical background of the main types of X-ray-matter interaction, a brief description of some X-ray scanning imaging techniques, the description of the developed algorithms and the report of recent experimental measurements for the characterization of third-generation kesterite solar cells.
Original languageEnglish
PublisherTechnical University of Denmark (DTU)
Number of pages107
StatePublished - 2019
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