Oxide Semiconductors For Organic Opto-electronic Devices

Development of transparent oxide semiconductors (TOS) from Earth-abundant materials is of great interest for cost-effective thin film device applications, such as solar cells, light emitting diodes (LEDs), touch-sensitive displays, electronic paper, and transparent thin film transistors. The need of inexpensive or high performance electrode might be even greater for organic photovoltaic (OPV), with the goal to harvest renewable energy with inexpensive, lightweight, and cost competitive materials. The natural abundance of zinc and the wide bandgap ($sim$3.3 eV) of its oxide make it an ideal candidate. In this dissertation, I have introduced various concepts on the modulations of various surface, interface and bulk opto-electronic properties of ZnO based semiconductor for charge transport, charge selectivity and optimal device performance. I have categorized transparent semiconductors into two sub groups depending upon their role in a device. Electrodes, usually 200 to 500 nm thick, optimized for good transparency and transporting the charges to the external circuit. Here, the electrical conductivity in parallel direction to thin film, i.e bulk conductivity is important. And contacts, usually 5 to 50 nm thick, are optimized in case of solar cells for providing charge selectivity and asymmetry to manipulate the built in field inside the device for charge separation and collection. Whereas in Organic LEDs (OLEDs), contacts provide optimum energy level alignment at organic oxide interface for improved charge injections. For an optimal solar cell performance, transparent electrodes are designed with maximum transparency in the region of interest to maximize the light to pass through to the absorber layer for photo-generation, plus they are designed for minimum sheet resistance for efficient charge collection and transport. As such there is need for material with high conductivity and transparency. Doping ZnO with some common elements such as B, Al, Ga, In, Ge, Si, and F result in n-type doping with increase in carriers resulting in high conductivity electrode, with better or comparable opto-electronic properties compared to current industry-standard indium tin oxide (ITO). Furthermore, improvement in mobility due to improvement on crystallographic structure also provide alternative path for high conductivity ZnO TCOs. Implementing these two aspects, various studies were done on gallium doped zinc oxide (GZO) transparent electrode, a very promising indium free electrode. The dynamics of the superimposed RF and DC power sputtering was utilized to improve the microstructure during the thin films growth, resulting in GZO electrode with conductivity greater than 4000 S/cm and transparency greater than 90 %. Similarly, various studies on research and development of Indium Zinc Tin Oxide and Indium Zinc Oxide thin films which can be applied to flexible substrates for next generation solar cells application is presented. In these new TCO systems, understanding the role of crystallographic structure ranging from poly-crystalline to amorphous phase and the influence on the charge transport and optical transparency as well as important surface passivation and surface charge transport properties. Implementation of these electrode based on ZnO on opto-electronics devices such as OLED and OPV is complicated due to chemical interaction over time with the organic layer or with ambient. The problem of inefficient charge collection/injection due to poor understanding of interface and/or bulk property of oxide electrode exists at several oxide-organic interfaces. The surface conductivity, the work function, the formation of dipoles and the band-bending at the interfacial sites can positively or negatively impact the device performance. Detailed characterization of the surface composition both before and after various chemicals treatment of various oxide electrode can therefore provide insight into optimization of device performance. Some of the work related to controlling the interfacial chemistry associated with charge transport of transparent electrodes are discussed. Thus, the role of various pre-treatment on poly-crystalline GZO electrode and amorphous indium zinc oxide (IZO) electrode is compared and contrasted. From the study, we have found that removal of defects and self passivating defects caused by accumulation of hydroxides in the surface of both poly-crystalline GZO and amorphous IZO, are critical for improving the surface conductivity and charge transport. Further insight on how these insulating and self-passivating defects cause charge accumulation and recombination in an device is discussed. With recent rapid development of bulk-heterojunction organic photovoltaics active materials, devices employing ZnO and ZnO based electrode provide air stable and cost-competitive alternatives to traditional inorganic photovoltaics. The organic light emitting diodes (OLEDs) have already been commercialized, thus to follow in the footsteps of this technology, OPV devices need further improvement in power conversion efficiency and stable materials resulting in long device lifetimes. Use of low work function metals such as Ca/Al in standard geometry do provide good electrode for electron collection, but serious problems using low work-function metal electrodes originates from the formation of non-conductive metal oxide due to oxidation resulting in rapid device failure. Hence, using low work-function, air stable, conductive metal oxides such as ZnO as electrons collecting electrode and high work-function, air stable metals such as silver for harvesting holes, has been on the rise. Devices with degenerately doped ZnO functioning as transparent conductive electrode, or as charge selective layer in a polymer/fullerene based heterojunction, present useful device structures for investigating the functional mechanisms within OPV devices and a possible pathway towards improved air-stable high efficiency devices. Furthermore, analysis of the physical properties of the ZnO layers with varying thickness, crystallographic structure, surface chemistry and grain size deposited via various techniques such as atomic layer deposition, sputtering and solution-processed ZnO with their respective OPV device performance is discussed. We find similarity and differences in electrode property for good charge injection in OLEDs and good charge collection in OPV devices very insightful in understanding physics behind device failures and successes. In general, self-passivating surface of amorphous TCOs IZO, ZTO and IZTO forms insulating layer that hinders the charge collection. Similarly, we find modulation of the carrier concentration and the mobility in electron transport layer, namely zinc oxide thin films, very important for optimizing device performance.

A Divine Round Trip: the Literary and Christological Function of the Descent/Ascent Leitmotif in the Gospel of John

The thesis of this dissertation is that the Descent/Ascent Leitmotif, which includes the language of not only descending and ascending, but also going, coming, and being sent, performs a significant literary and christological function in the Gospel of John. The Evangelist's Descent/Ascent Leitmotif becomes the Gospel's organizing principal, drawing together a constellation of verbs and a number of themes, including Jesus-Son's origin, identity, relationship to God, authority, signs and works, life, and glory. In the introductory chapter, after providing a layout of the dissertation, the discussion turns to the spacial dimensions and christological importance of the vertical and horizontal depictions of the descending, ascending, coming, going, and being sent verbs. The focus of chapter two is to explain and illustrate, using a version of the Cinderella story, a method that serves to identify the Leitmotif and the verbs, motifs, and themes the Leitmotif draws within its constellation. This approach, titled a thematic structural method, integrates works from thematic scholars Horst Daemmrich and Eugene Falk with works from literary structural scholars A. J Greimas and Roland Barthes, and is a tool to analyze the influence of the Leitmotif as the Gospel's organizing principal on the relationships between the Leitmotif and numerous themes from which John's Christology emerges. The task of chapter three is to explain the rationale for the selection of the Leitmotif's verbs of descending, ascending, coming, going, and being sent. Chapters four and five investigate how the Evangelist, with the repetition of the Leitmotif, constructs his narrative to tell the story of the historical Jesus and shape the Evangelist's Christology. Additionally, the focus is to analyze the transforming influences of the Descent/Ascent Leitmotif on the themes of Jesus-Son's origin, identity, relationship to the Father, and authority, through his signs and works, life, and glory. The Descent/Ascent Leitmotif depicts a divine round trip, and the emphasis of chapter six is to examine the role of the Leitmotif in Jesus-Son's departure from the world and return to God. The Evangelist's use of the Leitmotif in Jesus' prayer to the Father (John 17) and the promise of the Paraclete are included in this chapter. Due to the Descent/Ascent Leitmotif's inherent spatial overtones, elements related to Jesus' return, including heaven, world, the hour, and his form after his resurrection, are explored from a cosmological and ontological perspective.

A role for Dynamin-dependent endocytosis during Drosophila gastrulation

Gastrulation, a process conserved among many higher organisms, is the directed migration of cells into layers that will establish various tissues targeted to become anatomical structures. This process is accomplished through another conserved morphogenetic event, known as cell intercalation. Early in development, this movement of cells within an organized tissue leads to unique cellular arrangements where neighboring cells contract their shared interfaces in order to meet at a shared vertex. In this thesis, I present work that demonstrates a requirement for Dynamin-dependent endocytosis during these contraction events. Using quantitative analysis, I have identified varied cell behaviors during experiments which knockdown the function of dynamin. In addition, I demonstrate the existence of an antagonistic relationship between Dynamin and the Myosin II motor protein. Lastly, localization and functional studies I performed for this work suggest a role for Sorting Nexin proteins during plasma membrane reorganization required for Dynamin-dependent endocytosis.

Schleiermacher's Doctrine of Biblical Authority: An Alternative to Content-Based/Supernaturalist and Function-Based Rationalist Models

Author: Kerry W. Holton Title: SCHLEIERMACHER’S DOCTRINE OF BIBLICAL AUTHORITY: AN ALTERNATIVE TO CONTENT-BASED/SUPERNATURALIST AND FUNCTION- BASED/RATIONALIST MODELS Advisor: Theodore M. Vial, Jr. Degree Date: August 2015 This dissertation examines Friedrich Schleiermacher’s understanding of biblical authority and argues that, as an alternative to strictly supernaturalistic and rationalistic models, his understanding allows the New Testament to speak authoritatively in Christian religion in an age of critical, historical awareness. After classifying Schleiermacher’s position in a typology of the doctrine of biblical authority, this dissertation explores his conception of divine revelation and inspiration vis-à-vis scripture. It demonstrates that although he did not believe there is warrant for the claim of a direct connection between divine revelation and scripture, or that scripture is the foundation of faith, he nonetheless asserted that the New Testament is authoritative. He asserted the normative authority of the New Testament on the basis that it is the first presentation of Christian faith. This dissertation examines Schleiermacher’s “canon within the canon,” as well as his denial that the Old Testament shares the same normative worth and inspiration of the New. Although this dissertation finds difficulty with some of Schleiermacher’s views regarding the Old Testament, it names two significant strengths of what is identified as his evangelical, content-based, and rationalist approach to biblical authority. First, it recognizes and values the co-presence and co-activity of the supernatural and the natural !ii in the production of the New Testament canon. This allows both scripture and the church to share religious authority. Second, it allows Christian faith and the historical-method to coexist, as it does not require people to contradict what they know to be the case about science, history, and philosophy. Thus, this dissertation asserts that Schleiermacher’s understanding of biblical authority is a robust one, since, for him, the authority of scripture does not lie in some property of the texts themselves that historians or unbelievers can take away.