Normal and inverted hysteresis in perovskite solar cells

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO$_2$/CH$_3$NH$_3$PbI$_{3-x}$Cl$_x$/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, the behavior strictly depending on the pre-poling bias. NH typically appears at pre-poling biases larger than the open circuit bias, while pronounced IH occurs for negative bias pre-poling. The transition from NH to IH is marked by a intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model (DEM). Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the non-linear polarization. Introducing a three step measurement protocol, which includes stabilization, pre-poling and measurement, we put forward the difficulties and possible solutions for a correct PCE evaluation.Comment: 11 pages, 10 figure

An Electroactive Oligo-EDOT Platform for Neural Tissue Engineering

The unique electrochemical properties of the conductive polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) make it an attractive material for use in neural tissue engineering applications. However, inadequate mechanical properties, and difficulties in processing and lack of biodegradability have hindered progress in this field. Here, the functionality of PEDOT:PSS for neural tissue engineering is improved by incorporating 3,4-ethylenedioxythiophene (EDOT) oligomers, synthesized using a novel end-capping strategy, into block co-polymers. By exploiting end-functionalized oligoEDOT constructs as macroinitiators for the polymerization of poly(caprolactone), a block co-polymer is produced that is electroactive, processable, and bio-compatible. By combining these properties, electroactive fibrous mats are produced for neuronal culture via solution electrospinning and melt electrospinning writing. Importantly, it is also shown that neurite length and branching of neural stem cells can be enhanced on the materials under electrical stimulation, demonstrating the promise of these scaffolds for neural tissue engineering

High‐Volume Processed, ITO‐Free Superstrates and Substrates for Roll‐to‐Roll Development of Organic Electronics

The fabrication of substrates and superstrates prepared by scalable roll‐to‐roll methods is reviewed. The substrates and superstrates that act as the flexible carrier for the processing of functional organic electronic devices are an essential component, and proposals are made about how the general availability of various forms of these materials is needed to accelerate the development of the field of organic electronics. The initial development of the replacement of indium‐tin‐oxide (ITO) for the flexible carrier materials is described and a description of how roll‐to‐roll processing development led to simplification from an initially complex make‐up to higher performing materials through a more simple process is also presented. This process intensification through process simplification is viewed as a central strategy for upscaling, increasing throughput, performance, and cost reduction

International integration under the conditions of contested statehood : Kosovo's prospects under the Status Quo

Welcher Weg erwartet entstehende Staaten, die nicht allgemein anerkannt sind, in ihren Bestrebungen nach internationaler Integration inmitten internationaler Umstrittenheit und ohne einvernehmliche Vereinbarung mit ihren Vorgängerstaat? Diese Masterarbeit untersucht den Fall des Kosovo als unabhängigen und weithin anerkannten, doch für einen Teil der internationalen Gemeinschaft umstrittenen Staat, insbesondere für Serbien als ehemalige Hoheitsgewalt. Das Ziel der Arbeit ist es, die Integrationsaussichten des Kosovo im internationalen System und insbesondere im UN-System unter den Bedingungen der umstrittenen Staatlichkeit einzuschätzen. Das Konzept der Staatlichkeit wird zuerst angesichts des Völkerrechts und der Staatenpraxis analysiert, um zu klären, ob umstrittenen Staaten eine erhebliche internationale Beteiligung vorenthalten wird, weil sie den Anforderungen der Staatlichkeit nicht gerecht werden oder aus anderen Gründen. Anschließend wird die internationale Integration des Kosovo erfasst und anhand der Vergleichsmethode in Bezug gebracht mit anderen umstrittenen Staaten, insbesondere mit Palästina und Taiwan, sowie mit unumstrittenen Staaten, insbesondere mit Albanien und Serbien. Die Herausforderungen und Hindernisse, denen dieser Integrationsprozess gegenübersieht, sowie die angewandten Praktiken und Strategien, um sie zu überwinden, werden anhand der Fallstudienmethode analysiert. Die Analyse des UN-Systems zeigt, dass Kosovo unter dem Status Quo ohne wesentliche Hindernisse eine Mitgliedschaft in vier weitere UN-Sonderorganisationen (WHO, WIPO, UNIDO, IFAD) erlangen kann, während in anderen schwieriger. Zudem wird der Status des Beobachterstaats in der UNO als eine erreichbare und durchaus plausible Alternative zur UNO-Mitgliedschaft erachtet, da er Staatsanerkennung implizieren, die internationale Subjektivität und Beteiligung stärken, und den Beitritt zu zahlreichen UN-Verträgen und Justizmechanismen (wie IStGH und IGH) ermöglichen würde.What path awaits emerging states that lack universal recognition of their statehood in their quest for international integration amidst international contestation and the lack of a consensual settlement with their predecessor state? This thesis investigates the case of Kosovo as an independent and widely recognised state but yet contested by a segment of the international community and particularly by Serbia as its former sovereign. It aims to assess its prospects of integration in the international system under the conditions of contested statehood, focusing in particular on the UN system. The concept of statehood is initially analysed against the background of international law and state practice to understand whether contested states are denied meaningful international participation due to the failure to meet the requirements of statehood or on grounds unrelated to that. Kosovos international integration is subsequently assessed and put into perspective by drawing on the comparative method to make comparisons with other contested states, particularly with Palestine and Taiwan, as well as with confirmed states in its context, most notably Albania and Serbia. The challenges and obstacles faced in this process and the practices and strategies employed to overcome them, are examined by drawing on the case study method. The analysis of the UN system reveals that Kosovo may be able to expand its membership to four more UN specialised agencies (WHO, WIPO, UNIDO, IFAD) without substantive difficulties, while others are less likely attainable under the status quo. Moreover, the thesis argues that ‘non-member observer state status in the UN may be an attainable and viable alternative to UN membership, as such a status would imply statehood recognition, strengthen Kosovos international subjectivity, increase its international participation, and facilitate accession to numerous UN treaties and international mechanisms of justice, most notably the ICC and ICJ.Leonat PulaZusammenfassungen in Deutsch und EnglischKarl-Franzens-Universität Graz, Masterarbeit, 2019(VLID)443164

Electrochemical and In Vitro Biological Evaluation of Bio-Active Coatings Deposited by Magnetron Sputtering onto Biocompatible Mg-0.8Ca Alloy

The use of resorbable magnesium alloys in the design of implants represents a new direction in the healthcare domain. Two main research avenues are currently explored for developing or improving metallic biomaterials: (i) increase of their corrosion resistance by designed compositional and structural modifications, and (ii) functionalization of their surfaces by coating with ceramic or polymeric layers. The main objective of this work was to comparatively assess bio-functional coatings (i.e., highly-crystallized hydroxyapatite and silica-rich glass) deposited by radio-frequency magnetron sputtering (RF-MS) on a biodegradable Mg-0.8Ca alloy (0.8 wt.% of Ca). After probing their morphology (by scanning electron microscopy) and structure (by Fourier transform infrared spectroscopy and grazing incidence X-ray diffraction), the corrosion resistance of the RF-MS coated Mg-0.8Ca substrates was electrochemically tested (in synthetic biological media with different degrees of biomimicry), and their cytocompatibility was assessed in osteoblast and fibroblast cell cultures. By collective assessment, the most promising performances, in terms of mass loss (~7% after 12 days), hydrogen release rate (~6 mL/cm2 after 12 days), electrochemical corrosion parameters and cytocompatibility, were obtained for the crystalline HA coating

Partial replacement of Pb2+ in MAPbI2.6Cl0.4 perovskite films and their photovoltaic performance

Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI2.6Cl0.4 hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1-xZnxI2.6Cl0.4 based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion efficiency) range, compared to pristine MAPbI2.6Cl0.4 based devices