High-entropy mixtures of pristine fullerenes for solution-processed transistors and solar cells

The solubility of pristine fullerenes can be enhanced by mixing C-60 and C-70 due to the associated increase in configurational entropy. This "entropic dissolution" allows the preparation of field-effect transistors with an electron mobility of 1 cm(2) V-1 s(-1) and polymer solar cells with a highly reproducible power-conversion efficiency of 6%, as well as a thermally stable active layer.Funding Agencies|Swedish Research Council, Formas; Chalmers Area of Advance Energy; Knut and Alice Wallenberg Foundation through two Wallenberg Academy Fellowships; European Research Council (ERC) [637624]</p

Decrease in shunt volume in patients with cryptogenic stroke and patent foramen ovale

<p>Abstract</p> <p>Background</p> <p>In patients with patent foramen ovale (PFO) there is evidence supporting the hypothesis of a change in right-to-left shunt (RLS) over time. Proven, this could have implications for the care of patients with PFO and a history of stroke. The following study addressed this hypothesis in a cohort of patients with stroke and PFO.</p> <p>Methods</p> <p>The RLS volume assessed during hospitalisation for stroke (index event/T0) was compared with the RLS volume on follow-up (T1) (median time between T0 and T1 was 10 months). In 102 patients with a history of stroke and PFO the RLS volume was re-assessed on follow-up using contrast-enhanced transcranial Doppler/duplex (ce-TCD) ultrasound. A change in RLS volume was defined as a difference of ≥20 microembolic signals (MES) or no evidence of RLS during ce-TCD ultrasound on follow-up.</p> <p>Results</p> <p>There was evidence of a marked reduction in RLS volume in 31/102 patients; in 14/31 patients a PFO was no longer detectable. An index event classified as cryptogenic stroke (P < 0.001; OD = 39.2, 95% confidence interval 6.0 to 258.2) and the time interval to the follow-up visit (P = 0.03) were independently associated with a change in RLS volume over time.</p> <p>Conclusions</p> <p>RLS volume across a PFO decreases over time, especially in patients with cryptogenic stroke. These may determine the development of new strategies for the management in the secondary stroke prevention.</p

On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC17_{17}BM Solar Cells

The photophysical properties and solar cell performance of the classical donor–acceptor copolymer PCDTBT (poly($\textit{N}$-9′-heptadecanyl-2,7-carbazole-$\textit{alt}$ -5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole))) in relation to unintentionally formed main chain defects are investigated. Carbazole–carbazole homocouplings (Cbz hc) are found to significant extent in PCDTBT made with a variety of Suzuki polycondensation conditions. Cbz hc vary between 0 and 8 mol% depending on the synthetic protocol used, and are quantified by detailed nuclear magnetic resonance spectroscopy including model compounds, which allows to establish a calibration curve from optical spectroscopy. The results are corroborated by extended time-dependent density functional theory investigations on the structural, electronic, and optical properties of regularly alternating and homocoupled chains. The photovoltaic properties of PCDTBT:fullerene blend solar cells significantly depend on the Cbz hc content for constant molecular weight, whereby an increasing amount of Cbz hc leads to strongly decreased short circuit currents J$_{sc}$. With increasing Cbz hc content, J$_{sc}$decreases more strongly than the intensity of the low energy absorption band, suggesting that small losses in absorption cannot explain the decrease in J$_{sc}$ alone, rather than combined effects of a more localized LUMO level on the TBT unit and lower hole mobilities found in highly defective samples. Homocoupling-free PCDTBT with optimized molecular weight yields the highest efficiency up to 7.2% without extensive optimization.F.L., M.S., and R.F. gratefully acknowledge the EPSRC for funding. M.S. thanks the University of Freiburg (Innovationsfond Forschung) and the DFG for funding (SPP 1355). D.F. acknowledges the Alexander von Humboldt foundation for a postdoctoral research fellowship. A.D.Z.M. and C.M. thank the Swedish Research Council for funding

From fullerene acceptors to non-fullerene acceptors: prospects and challenges in the stability of organic solar cells

The recent emergence of non-fullerene small molecule acceptors has reinvigorated the field of organic solar cells, already resulting in significant breakthroughs in their power conversion efficiency and discovery of remarkable new science. The stability and degradation of this class of materials and devices, on the other hand, has to date received relatively less attention. Herein, we present a critical review into the fundamentally different degradation mechanisms of non-fullerene acceptors compared to fullerene acceptors, as well as the very different roles they play upon the charge carrier generation and recombination kinetics and the resulting solar cell stability. We highlight in particular the prospect of the emergence of non-fullerene acceptors in addressing several major degradation mechanisms related to the use of fullerene acceptors, in conjunction with a number of unique degradation mechanisms that only exist in non-fullerene acceptors, which would provide an important guideline for further developments toward achieving long-term stability of organic solar cells

Glass-forming ternary blends: towards stable Polymer Solar Cells

The globally increasing use of electricity goes hand in hand with climate change and the gradual depletion of fossil sources of fuel. To address these challenges renewable sources of energy are in high demand. Solution-processable organic solar cells receive particular attention because they promise to combine a set of highly attractive features including low manufacturing cost through large-area and continuous printing, as well as low weight, flexibility and semitransparency. The stability of the light-harvesting organic photovoltaic materials, which typically consist of a finely mixed blend of an electron donor and acceptor, plays a key role in the development of efficient and durable organic solar cells. One essential condition for both high-yield production and a long lifetime is excellent thermal stability. The organic photovoltaic material must be able to withstand high fabrication and operation temperatures.The aim of this thesis is to explore the use of ternary blends as a tool to improve the often insufficient thermal stability of organic photovoltaic materials. Ternary blends are a relatively new concept within the field of organic photovoltaics. This thesis focuses on blends of a donor polymer and a mixture of the two most common neat fullerenes, C60 and C70. Processing of the neat fullerene alloy is facilitated through a highly advantageous increase in solubility, which is found to correlate with the increase in entropy upon mixing. As a result, solar cells with a power conversion efficiency of 6 % are realized, a record for devices based on neat fullerenes. A high tendency for glass formation of polymer:C60:C70 ternary blends is found to induce a high degree of thermal stability due to a glass transition temperature in excess of 200\ub0C. Vitrification of ternary blends is discussed in terms of the entropy of mixing, which reduces the rate of both crystal nucleation and growth. Finally, this thesis provides an overview of the current state-of-the-art, discussing both fullerene as well as fullerene-free ternary blends

Faustino Zerio "Biurko"

Bargotako (Nafarroa) euskararen suspertzaile, euskaldun berria, apaiza, idazle, irakasle, euskara-irakasle, zenbait aldizkaritako kolaboratzaile: zeruko argia, goiz argi, arantzazu, euskera, principe de viana, euzkadi egunkaria. Euskaraz idatzitakoen artean: olerkiak eta narrazioa

Euskal kanta zahar batzuk eskolarako. 'Algunas antiguas canciones escolares en euskera'

Resumen tomado de la web del Departamento de EducaciónOfrece una selección de canciones de Navarra hecha por el padre Donostia. Organiza las partituras por temas y hace un análisis musicológico de cada una de ellas.NavarraBiblioteca General de Navarra; Calle Plaza San Francisco, s. n.; 31001 Pamplona;ES

Glass Forming Acceptor Alloys for Highly Efficient and Thermally Stable Ternary Organic Solar Cells

The stability of donor:acceptor (D:A) semiconductor blends plays a key role in the development of solution-processed organic solar cells. One essential condition for both high-yield production and a long lifetime is excellent thermal stability. Recently, A1:A2 acceptor mixtures have received considerable attention and alloys of two miscible acceptors are singled out as a powerful tool for the design of efficient and durable organic solar cells. This progress report introduces a thermodynamic rationale for the superior thermal stability and reproducibility that is observed for some ternary blends. The increase in entropy upon mixing of several acceptors reduces the tendency for phase separation as well as crystallization, which facilitates the controlled formation of a fine blend nanostructure. Further, when combined with a high glass transition temperature many ternary blends can be readily quenched into a glassy state. Recent progress with regard to the thermal stability and efficiency of D:A1:A2 ternary blends is summarized in the light of the thermodynamic and kinetic arguments discussed in this article. Both, fullerene and fullerene-free acceptor alloys now yield solar cell efficiencies in excess of 10%, which indicates that ternary blends are a promising avenue that is poised to considerably enhance the prospect of organic photovoltaics

Plasmonic Nanospectroscopy for Thermal Analysis of Organic Semiconductor Thin Films

Organic semiconductors are key materials for the next generation of thin film electronic devices like field-effect transistors, light-emitting diodes and solar cells. Accurate thermal analysis is essential for the fundamental understanding of these materials, for device design, stability studies and quality control because desired nanostructures are often far from thermodynamic equilibrium and therefore tend to evolve with time and temperature. However, classical experimental techniques are insufficient because the active layer of most organoelectronic device architectures is typically only on the order of hundred nanometers or less. Scrutinizing the thermal properties in this size range is, however, critical because strong deviations of the thermal properties from bulk values due to confinement effects, and due to pronounced influence of the substrate become significant. Here, we introduce plasmonic nanospectroscopy as an experimental approach to scrutinize the thickness dependence of the thermal stability of semi-crystalline, liquid-crystalline and glassy organic semiconductor thin films down to the sub-100 nm film thickness regime. As the main result we find a pronounced thickness dependence of the glass transition temperature of ternary polymer:fullerene blend thin films, and their constituents, which can be resolved with exceptional precision by the plasmonic nanospectroscopy method, that relies on remarkably simple instrumentation