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Coming dissertations at Uppsala university

  • Alternative back contacts for CZTS thin film solar cells Author: Sven Englund Link: Publication date: 2020-02-26 13:50

    In this thesis, alternative back contacts for Cu2ZnSnS4 (CZTS) thin film solar cells were investigated. Back contacts for two different configurations were studied, namely traditional single-junction cells with opaque back contacts and transparent back contacts for possible use in either tandem or bifacial solar cell configuration.

    CZTS is processed under chemically challenging conditions, such as high temperature and high chalcogen partial pressure. This places great demands on the back contact. Mo is the standard choice as back contact, but reacts with chalcogens to form MoS(e)2 while the CZTS decomposes, mainly into detrimental secondary phases. Thin MoS(e)2 is assumed to be beneficial for the electrical contact, but excessive thickness is detrimental to solar cell performance. The back contact acts as diffusion medium for Na during annealing when soda-lime glass is used as substrate. Na influences both defect passivation and doping in CZTS and increases the efficiency of the solar cells. The ability of the back contact to facilitate Na diffusion is an important property that must be monitored.

    Titanium nitride (TiN) as an interlayer between the opaque molybdenum (Mo) and CZTS as well as complete replacement of Mo with TiN back contacts were investigated. TiN was found to be chemically stable in typical anneal conditions. Formation of MoS(e)2 was observed only in areas where the TiN interlayers did not fully cover the Mo, following from the surface roughness of Mo and insufficient step-coverage of the sputter-deposition of TiN. Thick TiN interlayers (200 nm) were found to increase the diffusion of Na to the absorber layer from the glass substrate. For precursors annealed in sulfur atmosphere, improved device efficiency was observed for increased TiN thickness.

    Transparent back contacts can be used in either tandem configurations where two or more absorber materials are used to more efficiently use different parts of the solar spectra, or in bifacial solar cells to allow light to reach the absorber layer from two sides and thus increase the photocurrent. Thus far only a few studies have investigated transparent back contact materials in CZTS solar cell devices. Antimony-doped tin oxide (ATO) was studied as a transparent back contact for CZTS. Annealing of bare ATO resulted in complete reaction with S to form Sn–S compounds. When annealed below the CZTS, ATO was found to be stable at low temperature (<550 °C), and in some aspects even improved its properties. ATO back contacts resulted in significantly increased formation of Sn–S secondary phases on the CZTS absorber surface compared to the Mo reference. Sn–S secondary compounds on the absorber surface made it challenging to obtain good device performance. Adhesion and device behavior could be improved by pre-addition of NaF on the precursor prior to annealing.

  • Development and evaluation of analytical techniques for antibodies and antibody-drug conjugates : From verification of conjugation to stability testing Author: Malin Källsten Link: Publication date: 2020-02-26 12:57

    Antibody-drug conjugates (ADCs) are becoming increasingly important in oncology. ADCs are inherently heterogeneous analytes. For a successful drug candidate to go through to the clinic, extensive characterization and evaluation of the constructs are necessary. The drug-to-antibody ratio (DAR) directly determines the toxicity and efficacy of the product and has to be closely monitored during the entire process.

    In this thesis, several analytical techniques suitable for DAR determination in early-stage development have been evaluated against two more readily available options. The main focus in all studies has been on cysteine-linked ADCs, due to their prevalence in successful designs and their higher demand on the analytical set-up.

    The comparisons showed that mass spectrometry (MS) derived DAR values did conform well with hydrophobic interaction chromatography derived values, irrespective of which MS instrument was used. For MS instruments, overall the desolvation was found to have a bigger impact on the apparent DAR values than the resolution of the instrument and low-resolution instruments, such as triple quadrupoles, can be viable options for DAR determination in early-stage development. Furthermore, it also could be concluded that MS-derived DAR values are susceptible to alterations in the sample preparation workflow.

    Stability testing is vital to ensure a safe product. In this thesis, different compositions of mobile phases in size exclusion chromatographic (SEC) were tested for their ability to elute ADC aggregates. It was concluded that sufficient ionic strength to elute ADC aggregates from a SEC column purely by adding ammonium acetate cannot be achieved without exceeding salt concentrations compatlible with MS sources.

    Finally, two new analytical workflows have been designed by applying a proteomic desalting protocol and supercharging reagents to mAb and ADC samples. Both techniques showed promise; the magnetic beads as a more flexible desalting alternative for mAbs and ADCs and the addition of selective supercharging reagents for improved sensitivity and peak shapes in MS spectra (without significant alterations of the derived DAR values).

    Taken together, this thesis provides guidance on many aspects of ADC analysis from DAR determination to aggregate detection. The gathered knowledge can help setting up faster or more reliable quality checks for new candidates.

  • Avtalets räckvidd I : Om avtals tredjemansverkningar, särskilt vid tredjemansavtal och direktkrav Author: Oskar Mossberg Link: Publication date: 2020-02-24 12:39

    The idea that a contract should affect other people than the parties has seemingly always been a provocative notion. A contract binds the contracting parties – and only them – together in a legal relationship, and yet according to contemporary law a contract can have various legal effects for third parties, i.e. non-parties. The parties can conclude a contract for the benefit of a third party, and third parties can be affected by the contracts of others pursuant to both statutory law and uncodified general principles of law.

    The legal theme of contractual third party effects involves both theoretical and practical challenges. This doctoral dissertation addresses a number of these challenges, by examining (mainly) Swedish and Nordic private law sources. The study explores third party contracts and direct claims, as well as the relationship between these two legal figures, by placing them in a historical and theoretical context and by performing a series of contextualizing readings of sources revealing developments in both case law and legal scholarship.

    The research is based on a legal scientific methodology, enriched by theoretical and methodological imports pillaged from the classical teachings and contemporary scholarship on rhetoric. The result can be characterized as a form of rhetorically infused, topically oriented, hermeneutic study of contemporary legal discourse on third party effects of contract.