Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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Description
White organic light emitting diodes (WOLEDs) are currently being developed as the next generation of solid state lighting sources. Although, there has been considerable improvements in device efficiency from the early days up until now, there are still major drawbacks for the implementation of WOLEDs to commercial markets. These drawbacks include short lifetimes associated with highly efficient and easier to fabricate device structures. Platinum (II) complexes are been explored as emitters for single emissive layer WOLEDs, due to their higher efficiencies and stability in device configurations. These properties have been attributed to their square planar nature. Tetradentate platinum (II) complexes in particular have been shown to be more rigid and thus more stable than their other multidentate counterparts. This thesis aims to explore the different pathways via molecular design of tetradentate platinum II complexes and in particular the percipient engineering of a highly efficient and stable device structure. Previous works have been able to obtain either highly efficient devices or stable devices in different device configurations. In this work, we demonstrate a device structure employing Pt2O2 as the emitter using mCBP as a host with EQE of above 20% and lifetime values (LT80) exceeding 6000hours at practical luminance of 100cd/m2. These results open up the pathway towards the commercialization of white organic light emitting diodes as a solid state lighting source.
ContributorsOloye, Temidayo Abiola (Author) / Li, Jian (Thesis advisor) / Alford, Terry (Committee member) / Adams, James (Committee member) / Arizona State University (Publisher)
Created2016
Description
The structure-function relation in Biology suggests that every biological molecule has evolved its structure to carry out a specific function. However, for many of these processes (such as those with catalytic activity) the structure of the biomolecule changes during the course of a reaction. Understanding the structure-function relation thus becomes a question of understanding biomolecular dynamics that span a variety of timescales (from electronic rearrangements in the femtoseconds to side-chain alteration in the microseconds and more). This dissertation deals with the study of biomolecular dynamics in the ultrafast timescales (fs-ns) using electron and X-ray probes in both time and frequency domains.
It starts with establishing the limitations of traditional electron diffraction coupled with molecular replacement to study biomolecular structure and proceeds to suggest a pulsed electron source Hollow-Cone Transmission Electron Microscope as an alternative scheme to pursue ultrafast biomolecular imaging. In frequency domain, the use of Electron Energy Loss Spectroscopy as a tool to access ultrafast nuclear dynamics in the steady state, is detailed with the new monochromated NiON UltraSTEM and examples demonstrating this instrument’s capability are provided.
Ultrafast X-ray spectroscopy as a tool to elucidate biomolecular dynamics is presented in studying X-ray as a probe, with the study of the photolysis of Methylcobalamin using time-resolved laser pump – X-ray probe absorption spectroscopy. The analysis in comparison to prior literature as well as DFT based XAS simulations offer good agreement and understanding to the steady state spectra but are so far inadequate in explaining the time-resolved data. However, the trends in the absorption simulations for the transient intermediates show a strong anisotropic dependence on the axial ligation, which would define the direction for future studies on this material to achieve a solution.
It starts with establishing the limitations of traditional electron diffraction coupled with molecular replacement to study biomolecular structure and proceeds to suggest a pulsed electron source Hollow-Cone Transmission Electron Microscope as an alternative scheme to pursue ultrafast biomolecular imaging. In frequency domain, the use of Electron Energy Loss Spectroscopy as a tool to access ultrafast nuclear dynamics in the steady state, is detailed with the new monochromated NiON UltraSTEM and examples demonstrating this instrument’s capability are provided.
Ultrafast X-ray spectroscopy as a tool to elucidate biomolecular dynamics is presented in studying X-ray as a probe, with the study of the photolysis of Methylcobalamin using time-resolved laser pump – X-ray probe absorption spectroscopy. The analysis in comparison to prior literature as well as DFT based XAS simulations offer good agreement and understanding to the steady state spectra but are so far inadequate in explaining the time-resolved data. However, the trends in the absorption simulations for the transient intermediates show a strong anisotropic dependence on the axial ligation, which would define the direction for future studies on this material to achieve a solution.
ContributorsSubramanian, Ganesh (Author) / Spence, John (Thesis advisor) / Rez, Peter (Committee member) / Alford, Terry (Committee member) / Weierstall, Uwe (Committee member) / Kirian, Richard (Committee member) / Arizona State University (Publisher)
Created2016
Description
Interconnection methods for IBC photovoltaic (PV) module integration have widely been explored yet a concrete and cost-effective solution has yet to be found. Traditional methods of tabbing and stringing which are still being used today impart increased stress on the cells, not to mention the high temperatures induced during the soldering process as well. In this work and effective and economical interconnection method is demonstrated, by laser welding an embossed aluminum (Al) electrode layer to screen-printed silver (Ag) on the solar cell. Contact resistivity below 1mΩ.cm2 is measured with the proposed design. Cross-sectional analysis of interfaces is conducted via Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDXS) methods. Typical laser weld phenomenon observed involves Al ejection at the entrance of the weld, followed by Al and Ag fusing together mid-way through the weld spot, as revealed by cross-sectional depth analysis. The effects of voltage and lamp intensity are also tested on the welding process. With the range of voltages tested, 240V seems to show the least process variability and the most uniform contact between Al and Ag layers, upon using an Ethylene-Vinyl Acetate (EVA) encapsulant. Two lamp intensities were also explored with a Polyolefin (POE) encapsulant with Al and Ag layers seen welded together as well. Smaller effect sizes at lamp 2 intensity showed better contact. A process variability analysis was conducted to understand the effects of the two different lamps on welds being formed. Lamp 2 showed a bi-modal size distribution with a higher peak intensity, with more pulses coupling into the sample, as compared to lamp 1.
ContributorsSukumar Mony, Sujyot (Author) / Holman, Zachary (Thesis advisor) / Alford, Terry (Committee member) / Yu, Zhengshan (Committee member) / Arizona State University (Publisher)
Created2019