TOF-SIMS investigation of degradation pathways occurring in a variety of organic photovoltaic devices - the ISOS-3 inter-laboratory collaboration

The present work is the fourth (and final) contribution to an inter-laboratory collaboration that was planned at the 3rd International Summit on Organic Photovoltaic Stability (ISOS-3). The collaboration involved six laboratories capable of producing seven distinct sets of OPV devices that were degraded under well-defined conditions in accordance with the ISOS-3 protocols. The degradation experiments lasted up to 1830 hours and involved more than 300 cells on more than 100 devices. The devices were analyzed and characterized at different points of their lifetimes by a large number of non-destructive and destructive techniques in order to identify specific degradation mechanisms responsible for the deterioration of the photovoltaic response. Work presented herein involves time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to study chemical degradation in-plane as well as in-depth in the organic solar cells. Various degradation mechanisms were investigated and correlated with cell performance. For example, photo-oxidation of the active material was quantitatively studied as a function of cell performance. The large variety of cell architectures used (some with and some without encapsulation) enabled valuable comparisons and important conclusions to be drawn on degradation behaviour. This comprehensive investigation of OPV stability has significantly advanced the understanding of degradation behaviour in OPV devices, which is an important step towards large scale application of organic solar cells.     

New method and treatment technique applied to interband transition in GaAs<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>P<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> ternary alloys

In this paper we presented a new method (Eigen-Coordinates (ECs)) that can be used for calculations of the critical points (CPs) energy of the interband-transition edges of the heterostructures. This new method is more accurate and complete in comparison with conventional ones and has a wide range of application for the calculation of the fitting parameters related to nontrivial functions that initially have nonlinear fitting parameters that are difficult to evaluate. The new method was applied to determine the CPs energies from the dielectric functions of the MBE grown GaAs_1−xP _x ternary alloys obtained using spectroscopic ellipsometry (SE) measurements at room temperature in the 0.5-5 eV photon energy region. The obtained results are in good agreement with the results of the other methods.     

Light scattering by some nematic liquid crystals due to phase transitions

New computer modelling of light scattering and its propagation through liquid crystal has been presented using T-matrix method in the structural phase transition regions. Numerical aspects of light scattering process, which are based on numerically solving Maxwell's equations, were calculated for some nematic liquid crystals. Firstly, we described in detail T-matrix method for computing light scattering from nematic liquid crystals and presented results of benchmark computations for the considered model. We reported results of extensive calculations for polydisperse, randomly oriented rod-like multilayered systems (nematic liquid crystals). Our results are associated with light scattering by ferroelectric and ferroelastic materials.     

The invertibility of adapted perturbations of identity on the Wiener space

Let $(W,H,\mu )$ be the classical Wiener space. Assume that $U=I_W+u$ is an adapted perturbation of identity, i.e., $u:W\to H$ is adapted to the canonical filtration of W. We give some sufficient analytic conditions on u which imply the invertibility of the map U. To cite this article: A.S. Üstünel, M. Zakai, C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Spirobifluorene Metallaaromatics

Spirobifluorene derivatives find use in many end-user applications. Therefore, further expansion of their scope is the focus of many research studies. However, although the optical properties of spirobifluorenes can be greatly tuned through incorporation of metal complexes, to date, spirobifluorene metallaaromatics remain unknown. Taking advantage of the versatility of our methodology for the synthesis of metallaaromatic systems, this work reports the first metallaaromatic spirobifluorene compound. The presence of an Ir atom was found to redshift the absorption maximum by ca. 1.1 eV compared to bare spirobifluorene. Additionally, X-ray analysis as well as anisotropy of the current-induced density calculations revealed this compound to be of aromatic nature. The high stability in solution, solid state, under air, and at high temperature, as well as distinct optical properties of this new class of compounds are expected to open new frontiers for chiroptical and optoelectronic applications.     

Distinct Helical Molecular Orbitals through Conformational Lock**

Several theoretical studies have proposed strategies to generate helical molecular orbitals (Hel-MOs) in [n]cumulenes and oligoynes. While chiral even-[n] cumulenes feature Hel-MOs, odd-[n] cumulenes may also present them if the terminal groups lie in different planes. However, the proposed systems have been either experimentally unfeasible or resulted in opposite pseudo-degenerated Hel-MOs. We hereby demonstrate the introduction of a remarkable energy difference between helical orbitals of opposite twist by fixing the torsion angle between the terminal groups in butadiyne fragments. To experimentally lock the conformation of the terminal groups, we designed and synthesized cyclic architectures by combining acetylenes with chiral spirobifluorenes. The high stability of these systems with distinct helical orbitals allowed their isolation and full characterization. In our view, these results constitute a step further in the development of real systems presenting helical molecular orbitals.     

Photosynthetic hydrogen production

Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis has a great potential as can use clean and cheap sources—water and solar energy. In oxygenic photosynthetic microorganisms electrons and protons produced from water and redirected by the photosynthetic electron-transport chain via ferredoxin to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e^? and H⁺ recombine and form molecular hydrogen. Hydrogenase activity can be very high but is extremely sensitive to the photosynthetically evolved O₂ that leads to reduced and unstable H₂ production. However, presently, several approaches are developed to improve the energetic efficiency to generate H₂. This review examines the main available pathways to improve the photosynthetic H₂ production.     

Application of colloidal palladium modifier for the determination of As, Sb and Pb in a spiked sea water sample by electrothermal atomic absorption spectrometry

Colloidal palladium was used as a chemical modifier for analysis of complex samples by electrothermal atomic absorption spectrometry. In order to demonstrate high potential of the modifier, optimization of the time–temperature program of the atomizer was limited with only pyrolysis and atomization temperatures. Fixed palladium modifier masses were applied (6 μg for pure analyte solutions and 15 μg for matrix-containing solutions). It was shown that in the presence of colloidal palladium, interference-free determinations of As, Sb and Pb are possible up to at least 450 μg of chloride ion, or 40 μg of sulfate ion (as their sodium salts) in the atomizer. Colloidal palladium was used for the direct determination of As, Sb and Pb in a spiked sea water sample (from Bosphorus channel near Istanbul) by means of the calibration graphs prepared with pure analyte solutions. The detection limits for As, Sb and Pb in a sea water matrix calculated according to 2σ criteria are 5.4, 3.6 and 1.1 ng ml⁻¹, respectively (for sample volume 10 μl). In unspiked sea water, the contents of As, Sb and Pb were found to be below the detection limits. Recoveries of spiked analytes (25 and 50 ng ml⁻¹) were in the region of 98–112% depending on the nature of analyte and the concentration of spike.     

Synthesis,characterization, and crystal structure of 6,7a-dichloro-3a-hydroxyoctahydro-1<Emphasis Type="Italic">H</Emphasis>-indene-2,5-diyl diacetates

The first syntheses and characterizations of 6,7a-dichloro-3a-hydroxyoctahydro-1H-indene-2,5-diyl diacetates were successfully obtained starting from indan-2-ol. Epoxidation of 2 was carried out using mCPBA in methylene chloride followed by acetylation using acetyl chloride to furnish the diacetates. The structures of all synthesized compounds were characterized by spectroscopic methods.