Hicham Brine

Phosphorescent hybrid organic-inorganic light-emitting diodes.

Owing to extensive research carried out in recent decades, organic light-emitting diodes (OLEDs) represent one of the most developed technologies in the field of organic electronics. The demonstration of color tunability and high efficiency, together with the possibility of producing flexible devices, has already brought OLEDs into the displays market. Moreover, a report of white OLEDs with a power conversion efficiency comparable or superior to fluorescent lamps places OLEDs among the candidates for the next generation light source. However, the lack of reliable low-cost fabrication techniques for large areas remains one of the major issues preventing the mass production of OLEDs. State-of-the-art devices are multilayer structures prepared by sequential layer deposition using high-vacuum techniques, which complicates large area mass production. In addition, OLEDs employ low work function cathodes and need to be encapsulated to avoid fast degradation resulting from the exposure to atmospheric oxygen andmoisture. Therefore, the use of solution processing methods and air-stable materials is very appealing, since it would significantly lower the fabrication costs. In this context, hybrid light-emitting devices (HyLEDs) have recently attracted attention because they fulfill both requirements. HyLEDs generally consist of a polymer electroluminescent layer sandwiched in between two metal oxide thin films, functioning as the electron injection layer (EIL: TiO2, ZnO, ZrO2) and the hole injection layer (HIL: MoO3). [3–6] Since they rely on air-stable metal oxides as charge injectionmaterials, these devices are, in principle, less air sensitive and require less stringent encapsulation. At the same time, the use of light-emitting polymers (LEPs) allows the electroluminescent organic layer to be processed by simple solution methods. The initial limited efficiencies of HyLEDs have been considerably improved by introducing an additional layer of Cs2CO3 between the metal oxide cathode and the LEP, and efficiencies up to 8 cdA 1 have been achieved. HyLEDs using fluorescent emitters such as polyfluorenes and poly(phenylenevinylene) derivatives are intrinsically limited owing to their inability to harvest triplet excitons. As a result of simple spin statistics, three out of four electrically generated excitons are triplets and hence the

Hybrid organic-inorganic light emitting diodes: effect of the metal oxide

Hybrid organic-inorganic light emitting diodes (HyLEDs), employing metal oxides as the electron injecting contacts, are interesting as an alternative to OLEDs. Until recently, the metal oxide of choice was either titanium dioxide or zinc oxide. In this work two wide bandgap metal oxides, HfO2 and MgO, are employed as electron injecting layer in HyLEDs. It is demonstrated that both the current density and the luminance values obtained are directly related to the barriers for electron injection (from the ITO to the metal oxide) and for hole transfer to the same metal oxide, outlining a new design rule for the optimization of HyLEDs. Record device efficacies (3.3 cd/A, >10000 cd/m2) using the commonly used emitting polymer (F8BT) are obtained.

SiPMs coated with TPB: coating protocol and characterization for NEXT

Silicon photomultipliers (SiPM) are the photon detectors chosen for the tracking readout in NEXT, a neutrinoless \bb decay experiment which uses a high pressure gaseous xenon time projection chamber (TPC). The reconstruction of event track and topology in this gaseous detector is a key handle for background rejection. Among the commercially available sensors that can be used for tracking, SiPMs offer important advantages, mainly high gain, ruggedness, cost-effectiveness and radio-purity. Their main drawback, however, is their non sensitivity in the emission spectrum of the xenon scintillation (peak at 175 nm). This is overcome by coating these sensors with the organic wavelength shifter tetraphenyl butadiene (TPB). In this paper we describe the protocol developed for coating the SiPMs with TPB and the measurements performed for characterizing the coatings as well as the performance of the coated sensors in the UV-VUV range.

Zinc oxide nanocrystals as electron injecting building blocks for plastic light sources

Hybrid inorganic–organic light emitting devices (HyLEDs) employing ZnO nanocrystals as one of their metal oxide contacts lead to very bright devices on plastic substrates with performances superior to those obtained from the rigid counterparts employing planar films of bulk ZnO. The superior performance is related to the increase in the bandgap of the ZnO nanocrystals caused by quantum confinement effects. We demonstrate that this effect diminishes with increasing annealing temperature of the ZnO nanocrystal layer due to a gradual decrease of the bandgap towards the bulk ZnO value. Therefore, best performances were obtained with room temperature processing of the ZnO nanocrystals.

Nucleant layer effect on nanocolumnar ZnO films grown by electrodeposition.

Different ZnO nanostructured films were electrochemically grown, using an aqueous solution based on ZnCl2, on three types of transparent conductive oxides grow on commercial ITO (In2O3:Sn)-covered glass substrates: (1) ZnO prepared by spin coating, (2) ZnO prepared by direct current magnetron sputtering, and (3) commercial ITO-covered glass substrates. Although thin, these primary oxide layers play an important role on the properties of the nanostructured films grown on top of them. Additionally, these primary oxide layers prevent direct hole combination when used in optoelectronic devices. Structural and optical characterizations were carried out by scanning electron microscopy, atomic force microscopy, and optical transmission spectroscopy. We show that the properties of the ZnO nanostructured films depend strongly on the type of primary oxide-covered substrate used. Previous studies on different electrodeposition methods for nucleation and growth are considered in the final discussion.

Meniscus coated high open-circuit voltage bi-layer solar cells

Neat bi-layer solar cells of a fullerene acceptor and a cyanine dye donor were prepared using meniscus coating. Meniscus coating is very material efficient and leads to high quality pinhole-free films. The cells exhibit high open circuit voltages of 1 volt, only 0.8 eV below the band gap of the cyanine dye. This is one of the smallest differences reported for organic solar cells and illustrates an almost optimal donor-acceptor energy level alignment.