Organische Solarzellen: Synthese und Stabilisierung tensidfreier organischer Halbleiterdispersionen

Die vorliegende Dissertation behandelt die Herstellung tensidfreier Nanopartikeldispersionen organischer Halbleiter. Die Forschung an diesem Thema motiviert sich aus der Diskussion, ob die üblicherweise beim Druckprozess organischer Solarzellen verwendeten, giftigen und umweltschädlichen organischen Lösungsmittel durch umweltfreundlichere Alternativen ersetzt werden können. In der Vergangenheit wurde bereits gezeigt, dass tensidfreie Nanopartikeldispersionen aus einem Gemisch der organischen Halbleiter Poly(3-hexylthiophen-2,5-diyl) (P3HT) und Inden-C$_{60}$-bisaddukt (ICBA) in Ethanol mit einer einfachen Fällungsmethode zugänglich sind und eine attraktive Alternative zur Verwendung chlorierter Lösungsmittel darstellen. Die Übertragung dieses vielversprechenden Ansatzes auf effizientere organische Halbleiter scheiterte bislang an der geringen kolloidalen Stabilität der Dispersionen. Daran anknüpfend bestand die Zielsetzung dieser Arbeit darin, Kriterien für die Bildung stabiler Dispersionen zu erarbeiten und schließlich die Anwendbarkeit der Fällungsmethode auf beliebige organische Halbleiter zu beurteilen. Ausgehend von Fällungen von P3HT in Ethanol wurde der Mechanismus der Partikelbildung und -stabilisierung untersucht. Dabei wurde gezeigt, dass eine elektrostatische Stabilisierung die zentrale Voraussetzung für die Bildung stabiler Dispersionen darstellt und weiterhin einen großen Einfluss auf die resultierende Partikelgröße hat. Zur Erklärung wurde ein Modell entwickelt: Nach Fällung im Nichtlösungsmittel kollabieren die Polymerketten und agglomerieren zu annähernd sphärischen Partikeln. Mit zunehmender Oberflächenladung und Partikelgröße steigt die repulsive Wechselwirkung zwischen den Nanopartikeln an, sodass der Agglomerationsprozess je nach Stabilisierung bei kleineren oder größeren Partikeln zum Erliegen kommt. Optische Anregung, Oxidation oder Protonierung des Polymers wurden als Methoden identifiziert, um eine Partikelladung zu erzeugen und somit die elektrostatische Stabilisierung zu erhöhen. Ohne zugesetzte Oxidationsmittel muss der Ladungsaustausch mit dem Dispersionsmedium stattfinden. Als besonders geeignete Dispersionsmedien für P3HT stellten sich die meisten protischen Lösungsmittel heraus, was eine Ladungserzeugung durch Protonierung nahelegt. Eine umfangreiche Versuchsreihe mit weiteren halbleitenden Polymeren führte zu der Schlussfolgerung, dass eine ausreichende elektrostatische Stabilisierung vor allem mit leicht ionisierbaren Polymeren gelingt. Nur wenige kommerziell erhältliche organische Halbleiter erfüllen dieses Kriterium, was die zuvor nicht erfolgreiche Übertragbarkeit der Fällungsmethode erklärt. Schließlich wurde in der Arbeit die Co-Fällung von P3HT mit verschiedenen Akzeptoren untersucht, mit dem Ziel, durchmischte Nanopartikel zu erhalten, wie sie für die Herstellung organischer Solarzellen benötigt werden. Hierbei wurde eine generelle Tendenz zur Sedimentation des Akzeptors beobachtet, wobei das Ausmaß dieser Separation vom jeweiligen Halbleiter abhing. Dispersionen mit ausgeprägter Separation des Akzeptors eigneten sich nicht zur Herstellung organischer Solarzellen. Neben ICBA zeigte auch Phenyl-C$_{71}$-Buttersäuremethylester (PC$_{71}$BM) eine geringe Separation und eine gute Durchmischung mit P3HT. Aus den P3HT:PC$_{71}$BM-Dispersionen wurden organische Solarzellen mit gutem Wirkungsgrad hergestellt. In der Summe wurden zahlreiche Kriterien für die Bildung stabiler, tensidfreier Nanopartikeldispersionen aus organischen Halbleitern identifiziert. Diese Kriterien werden nur von wenigen der derzeit gebräuchlichen organischen Halbleitern erfüllt

Microfluidics: Continuous‐Flow Synthesis of Nanoparticle Dispersions for the Fabrication of Organic Solar Cells

State-of-the-art solvents for the fabrication of organic solar cells are mostly toxic or hazardous. First attempts to deposit light-harvesting layers from aqueous or alcoholic nanoparticle dispersions instead have been successful on laboratory scale, enabling future eco-friendly production of organic solar cells. In this work, a scalable high-throughput continuous-flow microfluidic system is employed to synthesize surfactant-free organic semiconductor dispersions by nanoprecipitation. By adjusting the differential speed of the syringe pumps, the concentration of the initial solute and the irradiation of the microfluidic chip, the synthesis can be controlled for tailored dispersion concentrations and nanoparticle sizes. The resulting dispersions are highly reproducible, and the semiconductor inks are stable for at least one year. The synthesis of the dispersions is exemplified on a polymer/fullerene combination with large-scale availability

Organic Solar Cells: Electrostatic Stabilization of Organic Semiconductor Nanoparticle Dispersions by Electrical Doping

Organic semiconductor nanoparticle dispersions are electrostatically stabilized with the p-doping agent 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F$_4$TCNQ), omitting the need for surfactants. Smallest amounts of F$_4$TCNQ stabilize poly(3-hexylthiophene) dispersions and reduce the size of the nanoparticles significantly. The concept is then readily transferred to synthesize dispersions from a choice of light-harvesting benzodithiophene-based copolymers. Dispersions from the corresponding polymer:fullerene blends are used to fabricate organic solar cells (OSCs). In contrast to the widely used stabilizing surfactants, small amounts of F$_4$TCNQ show no detrimental effect on the device performance. This concept paves the way for the eco-friendly fabrication of OSCs from nanoparticle dispersions of high-efficiency light-harvesting semiconductors by eliminating environmentally hazardous solvents from the deposition process

Iodine‐Stabilized Organic Nanoparticle Dispersions for the Fabrication of 10% Efficient Non‐Fullerene Solar Cells

High-performance organic solar cells are deposited from eco-friendly semiconductor dispersions by applying reversible electrostatic stabilization while omitting the need for stabilizing surfactants. The addition of iodine fosters the oxidation (p-doping) of the light-harvesting polymer, effectively promoting the electrostatic repulsion of the nanoparticles and hence the colloidal stability of the respective dispersions. The oxidation of polymers with iodine is reversible: after thin-film deposition and after thermal evaporation of the iodine, the corresponding polymer:non-fullerene solar cells yield power conversion efficiencies of up to 10.6%

Copeptin for risk stratification in non-traumatic headache in the emergency setting: a prospective multicenter observational cohort study

In the emergency setting, non-traumatic headache is a benign symptom in 80% of cases, but serious underlying conditions need to be ruled out. Copeptin improves risk stratification in several acute diseases. Herein, we investigated the value of copeptin to discriminate between serious secondary headache and benign headache forms in the emergency setting.; Patients presenting with acute non-traumatic headache were prospectively enrolled into an observational cohort study. Copeptin was measured upon presentation to the emergency department. Primary endpoint was serious secondary headache defined by a neurologic cause requiring immediate treatment of the underlying disease. Secondary endpoint was the combination of mortality and hospitalization within 3 months. Two board-certified neurologist blinded to copeptin levels verified the endpoints after a structured 3-month-telephone interview.; Of the 391 patients included, 75 (19%) had a serious secondary headache. Copeptin was associated with serious secondary headache (OR 2.03, 95%CI 1.52-2.70, p < 0.0001). Area under the curve (AUC) for copeptin to identify the primary endpoint was 0.70 (0.63-0.76). After adjusting for age > 50, focal-neurological abnormalities, and thunderclap onset of symptoms, copeptin remained an independent predictive factor for serious secondary headache (OR 1.74, 95%CI 1.26-2.39, p = 0.001). Moreover, copeptin improved the AUC of the multivariate logistic clinical model (p-LR-test < 0.001). Even though copeptin values were higher in patients reaching the secondary endpoint, this association was not significant in multivariate logistic regression.; Copeptin was independently associated with serious secondary headache as compared to benign headaches forms. Copeptin may be a promising novel blood biomarker that should be further validated to rule out serious secondary headache in the emergency department.; Study Registration on 08/02/2010 as NCT01174901 at clinicaltrials.gov

Pair-Wise Regulation of Convergence and Extension Cell Movements by Four Phosphatases via RhoA

Various signaling pathways regulate shaping of the main body axis during early vertebrate development. Here, we focused on the role of protein-tyrosine phosphatase signaling in convergence and extension cell movements. We identified Ptpn20 as a structural paralogue of PTP-BL and both phosphatases were required for normal gastrulation cell movements. Interestingly, knockdowns of PTP-BL and Ptpn20 evoked similar developmental defects as knockdown of RPTPα and PTPε. Co-knockdown of RPTPα and PTP-BL, but not Ptpn20, had synergistic effects and conversely, PTPε and Ptpn20, but not PTP-BL, cooperated, demonstrating the specificity of our approach. RPTPα and PTPε knockdowns were rescued by constitutively active RhoA, whereas PTP-BL and Ptpn20 knockdowns were rescued by dominant negative RhoA. Consistently, RPTPα and PTP-BL had opposite effects on RhoA activation, both in a PTP-dependent manner. Downstream of the PTPs, we identified NGEF and Arhgap29, regulating RhoA activation and inactivation, respectively, in convergence and extension cell movements. We propose a model in which two phosphatases activate RhoA and two phosphatases inhibit RhoA, resulting in proper cell polarization and normal convergence and extension cell movements

Perinatal and 2-year neurodevelopmental outcome in late preterm fetal compromise: the TRUFFLE 2 randomised trial protocol

Introduction: Following the detection of fetal growth restriction, there is no consensus about the criteria that should trigger delivery in the late preterm period. The consequences of inappropriate early or late delivery are potentially important yet practice varies widely around the world, with abnormal findings from fetal heart rate monitoring invariably leading to delivery. Indices derived from fetal cerebral Doppler examination may guide such decisions although there are few studies in this area. We propose a randomised, controlled trial to establish the optimum method of timing delivery between 32 weeks and 36 weeks 6 days of gestation. We hypothesise that delivery on evidence of cerebral blood flow redistribution reduces a composite of perinatal poor outcome, death and short-term hypoxia-related morbidity, with no worsening of neurodevelopmental outcome at 2 years. Methods and analysis: Women with non-anomalous singleton pregnancies 32+0 to 36+6 weeks of gestation in whom the estimated fetal weight or abdominal circumference is <10th percentile or has decreased by 50 percentiles since 18-32 weeks will be included for observational data collection. Participants will be randomised if cerebral blood flow redistribution is identified, based on umbilical to middle cerebral artery pulsatility index ratio values. Computerised cardiotocography (cCTG) must show normal fetal heart rate short term variation (≥4.5 msec) and absence of decelerations at randomisation. Randomisation will be 1:1 to immediate delivery or delayed delivery (based on cCTG abnormalities or other worsening fetal condition). The primary outcome is poor condition at birth and/or fetal or neonatal death and/or major neonatal morbidity, the secondary non-inferiority outcome is 2-year infant general health and neurodevelopmental outcome based on the Parent Report of Children's Abilities-Revised questionnaire. Ethics and dissemination: The Study Coordination Centre has obtained approval from London-Riverside Research Ethics Committee (REC) and Health Regulatory Authority (HRA). Publication will be in line with NIHR Open Access policy. Trial registration number: Main sponsor: Imperial College London, Reference: 19QC5491. Funders: NIHR HTA, Reference: 127 976. Study coordination centre: Imperial College Healthcare NHS Trust, Du Cane Road, London, W12 0HS with Centre for Trials Research, College of Biomedical & Life Sciences, Cardiff University. IRAS Project ID: 266 400. REC reference: 20/LO/0031. ISRCTN registry: 76 016 200

Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an

Risk portfolio on modern finance has become increasingly technical, requiring the use of sophisticated mathematical tools in both research and practice. Since companies cannot insure themselves completely against risk, as human incompetence in predicting the future precisely that written in Al-Quran surah Luqman verse 34, they have to manage it to yield an optimal portfolio. The objective here is to minimize the variance among all portfolios, or alternatively, to maximize expected return among all portfolios that has at least a certain expected return. Furthermore, this study focuses on optimizing risk portfolio so called Markowitz MVO (Mean-Variance Optimization). Some theoretical frameworks for analysis are arithmetic mean, geometric mean, variance, covariance, linear programming, and quadratic programming. Moreover, finding a minimum variance portfolio produces a convex quadratic programming, that is minimizing the objective function ðð¥with constraintsð ð 𥠥 ðandð´ð¥ = ð. The outcome of this research is the solution of optimal risk portofolio in some investments that could be finished smoothly using MATLAB R2007b software together with its graphic analysis