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- Lindblad, Rebecka, 1984-
(författare)
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Electronic Structures and Energy Level Alignment in Mesoscopic Solar Cells : A Hard and Soft X-ray Photoelectron Spectroscopy Study
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Photoelectron spectroscopy is an experimental method to study the electronic structure in matter. In this thesis, a combination of soft and hard X-ray based photoelectron spectroscopy has been used to obtain atomic level understanding of electronic structures and energy level alignments in mesoscopic solar cells. The thesis describes how the method can be varied between being surface and bulk sensitive and how to follow the structure linked to particular elements. The results were discussed with respect to the material function in mesoscopic solar cell configurations.The heart of a solar cell is the charge separation of photoexcited electrons and holes, and in a mesoscopic solar cell, this occurs at interfaces between different materials. Understanding the energy level alignment between the materials is important for developing the function of the device. In this work, it is shown that photoelectron spectroscopy can be used to experimentally follow the energy level alignment at interfaces such as TiO2/metal sulfide/polymer, as well as TiO2/perovskite.The electronic structures of two perovskite materials, CH3NH3PbI3 and CH3NH3PbBr3 were characterized by photoelectron spectroscopy and the results were discussed with support from quantum chemical calculations. The outermost levels consisted mainly of lead and halide orbitals and due to a relatively higher cross section for heavier elements, hard X-ray excitation was shown useful to study the position as well as the orbital character of the valence band edge.Modifications of the energy level positions can be followed by core level shifts. Such studies showed that a commonly used additive in mesoscopic solar cells, Li-TFSI, affected molecular hole conductors in the same way as a p-dopant. A more controlled doping can also be achieved by redox active dopants such as Co(+III) complexes and can be studied quantitatively with photoelectron spectroscopy methods.Hard X-rays allow studies of hidden interfaces, which were used to follow the oxidation of Ti in stacks of thin films for conducting glass. By the use of soft X-rays, the interface structure and bonding of dye molecules to mesoporous TiO2 or ZnO could be studied in detail. A combination of the two methods can be used to obtain a depth profiling of the sample.
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| 3. |
- Johansson, Erik, 1967-
(författare)
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Assessment of Enterprise Information Security : How to make it Credible and Efficient
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Information is an important business asset in today’s enterprises. Hence enterprise information security is an important system quality that must be carefully managed. Although enterprise information security is acknowledged as one of the most central areas for enterprise IT management, the topic still lacks adequate support for decision making on top-management level. This composite thesis consists of four articles which presents the Enterprise Information Security Assessment Method (EISAM), a comprehensive method for assessing the current state of the enterprise information security. The method is useful in helping guide top-management’s decision-making because of the following reasons: 1) it is easy to understand, 2) it is prescriptive, 3) it is credible, and 4) it is efficient. The assessment result is easy to understand because it presents a quantitative estimate. The result can be presented as an aggregated single value, abstracting the details of the assessment. The result is easy to grasp and enables comparisons both within the organization and in terms of industry in general. The method is prescriptive since it delivers concrete and traceable measurements. This helps guide top-level management in their decisions regarding enterprise-wide information security by highlighting the areas where improvements efforts are essential. It is credible for two reasons. Firstly, the method presents an explicit and transparent definition of enterprise information security. Secondly, the method in itself includes an indication of assessment uncertainty, expressed in terms of confidence levels. The method is efficient because it focuses on important enterprise information security aspects, and because it takes into account how difficult it is to find security related evidence. Being resource sparse it enables assessments to take place regularly, which gives valuable knowledge for long-term decision-making. The usefulness of the presented method, along with its development, has been verified through empirical studies at a leading electric power company in Europe and through statistical surveys carried out among information security experts in Sweden. The success from this research should encourage further researcher in using these analysis techniques to guide decisions on other enterprise architecture attributes.
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