The cost-effective production of flexible electronic components will profit considerably from the development of solution-processable, organic semiconductor materials. Particular attention is focused on soluble semiconductors for organic field-effect transistors (OFETs). The hitherto differentiation between "small molecules" and polymeric materials no longer plays a role, rather more the ability to process materials from solution to homogeneous semiconducting films with optimal electronic properties (high charge-carrier mobility, low threshold voltage, high on/off ratio) is pivotal. Key classes of materials for this purpose are soluble oligoacenes, soluble oligo- and polythiophenes and their respective copolymers, and oligo- and polytriarylamines. In this context, micro- or nanocrystalline materials have the general advantage of somewhat higher charge-carrier mobilities, which, however, could be offset in the case of amorphous, glassy materials by simpler and more reproducible processing.

Printed electronics is an emerging technology with huge potential. Market studies predict a multi‐billion dollar market size within less than 5 years. Due to its compatibility with flexible substrates and low‐cost fabrication, printed electronics is able to bring electronic functionality to markets unfit for rigid and expensive silicon electronics. Key to its success are innovative printing technologies and high‐quality material systems, engineered for specific device applications. Printed electronics is a complex multidisciplinary research area, with still a number of fundamental problems to be solved before the technology can grow to its full potential. Evonik Industries is involved in the development of printed electronics through its unique science‐to‐business concept. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thick film ͑Ն5 m thick͒ semiconducting polymer diodes incorporating poly͑triarylamine͒ ͑PTAA͒ have been produced and applied as direct x-ray detectors. Experiments determined that a rectifying diode behavior persists when increasing the thickness of the active layer above typical thin film thicknesses ͑Ͻ1 m͒, and the electrical conduction mechanism of the diodes has been identified. Direct current and photoconductivity measurements on indium tin oxide/ poly͑3,4-ethylenedioxythiophene͒/poly͑styrenesulfonate͒/PTAA/metal diodes confirm that carrier conduction occurs via a Poole-Frenkel mechanism. The energy band structure of diodes ͑having gold or aluminum top electrodes͒ has been elucidated and used to explain the resulting electrical characteristics. Theoretical calculations show that, upon irradiation with x-rays, the diode quantum efficiency increases with increasing polymer film thickness. The diodes produced here display characteristics similar to their thin film analogs, meaning that they may be operated in a similar way and therefore may be useful for radiation dosimetry applications. Upon irradiation, the diodes produce an x-ray photocurrent that is proportional to the dose, thus demonstrating their suitability for direct x-ray detectors. The x-ray photocurrent remains the same in a device after a cumulative exposure of 600 Gy and after aging for 6 months.

The growth kinetics of ZnO nanorods in methanol is studied by a combination of scanning and high-resolution transmission electron microscopy and X-ray diffraction analysis. In the early stage of growth oriented attachment of 2−3 spheroidal crystallites to rod-like structures occurs. Later, rods of up to 90 nm in length with a hexagonal cross-section up to 18 nm in diameter form by ripening. Our main finding is that the growth follows a power law as a function of the ripening time with exponents of 0.32 to 0.39 for the length and 0.17 to 0.21 for the diameter. In contrast to previous studies on the growth of ZnO rods in alcohols our results indicate that the growth is dominated by anisotropic Ostwald ripening that is limited by volume diffusion.

Die kostengünstige Fertigung flexibler elektronischer Bauelemente dürfte in Zukunft stark von der Entwicklung aus Lösung prozessierbarer, organischer Halbleitermaterialien profitieren. Besondere Aufmerksamkeit gilt dabei zurzeit löslichen Halbleitern für organische Feldeffekttransistoren (OFETs). Die bis vor einiger Zeit vorgenommene Trennung zwischen “kleinen Molekülen” und polymeren Materialien spielt mittlerweile keine Rolle mehr – entscheidend ist vielmehr die Verarbeitbarkeit der Materialien aus Lösung zu homogenen Halbleiterschichten mit optimalen elektronischen Eigenschaften (hohe Ladungsträgermobilität, geringe Schwellspannung, hohes An/Aus‐Verhältnis). Die Materialien der Wahl sind hier lösliche Oligoacene, lösliche Oligo‐ und Polythiophene oder entsprechende Copolymere sowie Oligo‐ und Polytriarylamine. Mikro‐ oder nanokristalline Materialien bieten dabei allgemein den Vorteil etwas höherer Ladungsträgermobilitäten; amorphe, glasartige Materialien könnten dies jedoch durch eine einfachere und besser reproduzierbare Verarbeitung wettmachen.

Summary: The synthesis of new fluorene containing photocrosslinkable reactive mesogens is described. Both monodisperse trimers or pentamers and oligomeric mixtures containing two photocrosslinkable acrylate end groups were obtained by Suzuki‐cross‐coupling reactions. The pentamer 12a shows an ideal phase behavior for orientation experiments with a broad nematic phase between the glass transition at −10 °C and 123 °C. In the oligomeric mixtures 14a–g the transition temperature from the nematic to the isotropic phase can be tailored from 100 to 310 °C by adjusting the molecular weight of the oligomers by end‐capping. This process can be easily characterized by MALDI‐TOF spectroscopy. The pentamer 12a and the oligomeric mixture 14c were oriented on rubbed polyimide layers and orientation ratios of 15:1 in photoluminescence were obtained. Experiments with different film thicknesses show that the orientation is not homogeneous throughout the film but decreases with increasing distance from the orientation layer. magnified image

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