Electroluminescence from Spontaneously Generated Single-Vesicle Aggregates Using Solution-Processed Small Organic Molecules

Self-assembled aggregates offer great potential for tuning the morphology of organic semiconductors, thereby controlling their size and shape. This is particularly interesting for applications in electroluminescent (EL) devices, but there has been, to date, no reports of a functional EL device in which the size and color of the emissive domains could be controlled using self-assembly. We now report a series of molecules that spontaneously self-organize into small EL domains of sub-micrometer dimensions. By tailoring the emissive chromophores in solution, spherical aggregates that have an average size of 300 nm in diameter and emit any one color, including CIE D65 white, are spontaneously formed in solution. We show that the individual aggregates can be used in EL devices built either using small patterned electrodes or using a sandwich architecture to produce devices emitting in the blue, green, red, and white. Furthermore, sequential deposition of the three primary colors yields an RGB device in which single aggregates of each color are present in close proximity.

Lanthanum Hexaboride As Novel Interlayer for Improving the Thermal Stability of P3HT:PCBM Organic Solar Cells

For efficient organic photovoltaic (OPV) solar cells, a low work function electrode is necessary to enhance the built-in voltage of the active layer, thereby improving the overall efficiency. Calcium is often used for this purpose in the laboratory; however, its development on a larger scale is impaired by its high reactivity with oxygen and water and the resulting low stability of solar cells under operation. The influence of a novel interlayer, lanthanum hexaboride (LaB6), on the electronic properties of OPV is studied in this work. Similarly to calcium, when LaB6 is used as an interlayer, it enhances the built-in voltage in the device, leading to a higher fill factor (FF) and optimal open circuit voltage (V(oc)). As a result, optimized LaB6-based devices present significantly improved power conversion efficiencies. More importantly, while calcium/aluminum (Ca/Al) and aluminum (Al) cathodes lose their capacity to enhance the internal electrical field during thermal aging, the LaB6/aluminum (LaB6/Al) electrode remains stable. This remarkable effect results in a highly stable V(oc) and flat-band potential during aging.

Solution-Processed Small-Molecule Bulk Heterojunctions: Leakage Currents and the Dewetting Issue for Inverted Solar Cells

In organic photovoltaic (PV) devices based on solution-processed small molecules, we report here that the physicochemical properties of the substrate are critical for achieving high-performances organic solar cells. Three different substrates were tested: ITO coated with

PEDOT

PSS, ZnO sol-gel, and ZnO nanoparticles. PV performances are found to be low when the ZnO nanoparticles layer is used. This performance loss is attributed to the formation of many dewetting points in the active layer, because of a relatively high roughness of the ZnO nanoparticles layer, compared to the other layers. We successfully circumvented this phenomenon by adding a small quantity of polystyrene (PS) in the active layer. The introduction of PS improves the quality of film forming and reduces the dark currents of solar cells. Using this method, high-efficiency devices were achieved, even in the case of substrates with higher roughness.

New synthetic routes towards soluble and dissymmetric triphenodioxazine dyes designed for dye-sensitized solar cells

New π-conjugated structures are constantly the subject of research in dyes and pigments industry and electronic organic field. In this context, the triphenodioxazine (TPDO) core has often been used as efficient photostable pigments and once integrated in air stable n-type organic field-effect transistor (OFET). However, little attention has been paid to the TPDO core as soluble materials for optoelectronic devices, possibly due to the harsh synthetic conditions and the insolubility of many compounds. To benefit from the photostability of TPDO in dye-sensitized solar cells (DSCs), an original synthetic pathway has been established to provide soluble and dissymmetric molecules applied to a suitable design for the sensitizers of DSC. The study has been pursued by the theoretical modeling of opto-electronic properties, the optical and electronic characterizations of dyes and elaboration of efficient devices. The discovery of new synthetic pathways opens the way to innovative designs of TPDO for materials used in organic electronics.

Control of carrier mobilities for performance enhancement of anthracene-based polymer solar cells

Charge carrier mobilities in anthracene-based polymer solar cells were controlled using organic field-effect transistors. The best solar cell device performance was achieved using classical PCBM.

Di(p-methoxyphenyl)amine end-capped tri(p-thiophenylphenyl)amine based molecular glasses as hole transporting materials for solid-state dye-sensitized solar cells

Star shaped hole conducting molecular glasses were synthetized and applied in solid state dye-sensitized solar cells.

A solvent additive to enhance the efficiency and the thermal stability of polymer:fullerene solar cells

A novel bisazide molecule to be used in polymer–fullerene bulk heterojunction (BHJ) solar cells with two distinct functionalities is reported here.

Metal Residues in Semiconducting Polymers: Impact on the Performance of Organic Electronic Devices

The effect of impurities on the optoelectronic and charge transport properties of semiconducting polymers was investigated through the performance of organic photovoltaics (OPVs) and organic field effect transistors (OFETs), respectively. A model representative semiconducting polymer, i.e., poly(3-hexylthiophene) (P3HT), was synthesized and purified using different methods such as precipitation, metals' complexation, and Soxhlet extraction. After the purification processes, each fraction was analyzed to determine its composition in metals (impurities) by various techniques. OFETs and OPVs fabricated from these purified polymer fractions were found to show different charge carrier properties and photovoltaic behaviors. The purest fraction which was obtained after Soxhlet extraction complemented by metals' complexation with the help of ethylenediamine and 15-crown-5 ether showed the best performance in both OPVs and OFETs.

Thermal stabilisation of polymer-fullerene bulk heterojunction morphology for efficient photovoltaic solar cells

A novel stable bisazide molecule that can freeze the bulk heterojunction morphology at its optimized layout by specifically bonding to fullerenes is reported. The concept is demonstrated with various polymers: fullerene derivatives systems enable highly thermally stable polymer solar cells.

Supramolecular control of electronic properties in aromatic materials

The use of supramolecular interactions for controlling the electronic and photophysical properties of organic π-conjugated materials is described. This leads to materials presenting unique properties, such as light-induced switching of polarization (photopolism), or the spontaneous formation of highly luminescent vesicles. In another approach, reversible covalent bonds are used to prepare densely packed fullerene monolayers whose conductivity could be probed using conducting AFM.

Oligocarbazole-based chromophores for efficient thin-film dye-sensitized solar cells

Carb your enthusiasm: Carbazole-based sensitizers with high extinction coefficients are synthesized for application in dye-sensitized solar cells (DSCs). The dyes perform efficiently with both iodine and cobalt electrolytes, showing power conversion efficiencies of up to 5.8% on TiO₂ films of 15 μm thickness, and retaining 90% of their efficiency in devices with thinner films.

MoO3 Thickness, Thermal Annealing and Solvent Annealing Effects on Inverted and Direct Polymer Photovoltaic Solar Cells

Several parameters of the fabrication process of inverted polymer bulk heterojunction solar cells based on titanium oxide as an electron selective layer and molybdenum oxide as a hole selective layer were tested in order to achieve efficient organic photovoltaic solar cells. Thermal annealing treatment is a common process to achieve optimum morphology, but it proved to be damageable for the performance of this kind of inverted solar cells. We demonstrate using Auger analysis combined with argon etching that diffusion of species occurs from the MoO₃/Ag top layers into the active layer upon thermal annealing. In order to achieve efficient devices, the morphology of the bulk heterojunction was then manipulated using the solvent annealing technique as an alternative to thermal annealing. The influence of the MoO₃ thickness was studied on inverted, as well as direct, structure. It appeared that only 1 nm-thick MoO₃ is enough to exhibit highly efficient devices (PCE = 3.8%) and that increasing the thickness up to 15 nm does not change the device performance.

P3HT:PCBM, best seller in polymer photovoltaic research

In the fi eld of polymer-based photovoltaic cells, poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C₆₁ (PCBM) are, to date, the most-studied active materials around the world for the bulk-heterojunction structure. Various power-conversion effi ciencies are reported up to approximately 5%. This Research News article is focused on a survey of the tremendous literature published between 2002 and 2010 that exhibits solar cells based on blends of P3HT and PCBM.

Low-temperature UV processing of nanoporous SnO₂ layers for dye-sensitized solar cells

Connection of SnO₂ particles by simple UV irradiation in air yielded cassiterite SnO₂ porous films at low temperature. XPS, FTIR, and TGA-MS data revealed that the UV treatment has actually removed most of the organics present in the precursor SnO₂ colloid and gave more hydroxylated materials than calcination at high temperature. As electrodes for dye-sensitized solar cells (DSCs), the N3-modified 1-5 μm thick SnO₂ films showed excellent photovoltaic responses with overall power conversion efficiency reaching 2.27% under AM1.5G illumination (100 mW cm⁻²). These performances outperformed those of similar layers calcined at 450 °C mostly due to higher V(oc) and FF. These findings were rationalized in terms of slower recombination rates for the UV-processed films on the basis of dark current analysis, photovoltage decay, and electrical impedance spectroscopy studies.

The Third Injection Technique Workshop in Athens (TITAN)

The first Injection Technique workshop brought together endocrinologists and injection experts from around the world in Strasbourg in 1997. From its work came groundbreaking recommendations which advanced best practices in areas such as the use of a skin fold when injecting. The second Injection Technique workshop, with an expanded format including nurses and diabetes educators, took place in Barcelona in 2000. The initial stimulus to use shorter injecting needles can be said to date from this meeting. The third Injection Technique workshop was held in Athens in September 2009 and involved 127 experts from across the globe. After a comprehensive review of all publications since 2000 as well as several unpublished studies, the attendees divided into smaller groups to debate and draft new injecting recommendations based on the new data and their collective experience. This paper summarizes all the formal presentations given at this practical consensus workshop.

New injection recommendations for patients with diabetes

AIM

Injections administered by patients are one of the mainstays of diabetes management. Proper injection technique is vital to avoiding intramuscular injections, ensuring appropriate delivery to the subcutaneous tissues and avoiding common complications such as lipohypertrophy. Yet few formal guidelines have been published summarizing all that is known about best practice. We propose new injection guidelines which are thoroughly evidence-based, written and vetted by a large group of international injection experts.

METHODS

A systematic literature study was conducted for all peer-reviewed studies and publications which bear on injections in diabetes. An international group of experts met regularly over a two-year period to review this literature and draft the recommendations. These were then presented for review and revision to 127 experts from 27 countries at the TITAN workshop in September, 2009.

RESULTS

Of 292 articles reviewed, 157 were found to meet the criteria of relevance to the recommendations. Each recommendation was graded by the weight it should have in daily practice and by its degree of support in the medical literature. The topics covered include The Role of the Professional, Psychological Challenges, Education, Site Care, Storage, Suspension and Priming, Injecting Process, Proper Use of Pens and Syringes, Insulin analogues, Human and Pre-mixed Insulins, GLP-1 analogs, Needle Length, Skin Folds, Lipohypertrophy, Rotation, Bleeding and Bruising, Pregnancy, Safety and Disposal.

CONCLUSION

These injecting recommendations provide practical guidance and fill an important gap in diabetes management. If followed, they should help ensure comfortable, effective and largely complication-free injections.