A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Electron and ambipolar transport in organic field-effect transistors.

Acenes have long been the subject of intense study because of the unique electronic properties associated with their pi-bond topology. Recent reports of impressive semiconductor properties of larger homologues have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purification, as well as for fabricating organic electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in solution. These new functionalization strategies have recently allowed the synthesis of acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as investigation of their associated structure/property relationships.

The larger acenes: versatile organic semiconductors.

Field-effect transistors based on solution-processible organic semiconductors have experienced impressive improvements in both performance and reliability in recent years, and printing-based manufacturing processes for integrated transistor circuits are being developed to realize low-cost, large-area electronic products on flexible substrates. This article reviews the materials, charge-transport, and device physics of solution-processed organic field-effect transistors, focusing in particular on the physics of the active semiconductor/dielectric interface. Issues such as the relationship between microstructure and charge transport, the critical role of the gate dielectric, the influence of polaronic relaxation and disorder effects on charge transport, charge-injection mechanisms, and the current understanding of mechanisms for charge trapping are reviewed. Many interesting questions on how the molecular and electronic structures and the presence of defects at organic/organic heterointerfaces influence the device performance and stability remain to be explored.

Device Physics of Solution‐Processed Organic Field‐Effect Transistors

Organic semiconductor lasers.

We report the first organic light-emitting field-effect transistor. The device structure comprises interdigitated gold source and drain electrodes on a $\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}{\mathrm{O}}_{\mathrm{2}}$ substrate. A polycrystalline tetracene thin film is vacuum sublimated on the substrate forming the active layer of the device. Both holes and electrons are injected from the gold contacts into this layer leading to electroluminescence from the tetracene. The output characteristics, transfer characteristics, and the optical emission properties of the device are reported. A possible mechanism for electron injection is suggested.

Light-emitting field-effect transistor based on a tetracene thin film.

The knowledge about properties of electronic traps in organic semiconductors is one of the major keys for the understanding and optimization of charge transport in organic devices. In the present article the density of occupied states of the most prominent pristine small molecule systems and selected polymers are reported determined, by fractional thermally stimulated current and luminescence techniques. In order to distinguish between impurity and structurally based traps, model systems of doped as well as differently deposited layers were studied. In addition, the influence of detected traps on steady state I–V and dynamic time-of-flight characteristics are reported. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic traps in organic transport layers

Photostimulable x-ray storage phosphors in form of image plates are a promising alternative to conventional two-dimensional x-ray detectors. By absorption of ionizing radiation, electrons and holes are generated and captured locally to form a dose proportional latent image. The stored information is read out by scanning with a focussed HeNe laser. This leads to a local excitation of the trapped electrons which subsequently recombine with the trapped holes causing the emission of light. The information is then recorded by means of a photomultiplier, digitized by an A/D converter and displayed with the aid of a computer. The present state of the field of storage phosphors is reviewed in the following areas: the image principle, today's understanding of the nature of the storage centers, their physical generation, and the optically stimulated charge transfer paths. In addition, improvements and applications of these phosphors will be discussed for existing and future commercial devices.

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Photostimulable x-ray storage phosphors: a review of present understanding

An ambipolar pentacene transistor with top-gold and top-calcium contacts has been realized by utilizing a parallactic shadow mask effect during vapor deposition. The pentacene deposited on top of a silicon dioxide gate insulator is doped by Ca at the pentacene/SiO2 interface in order to compensate electron traps. An equivalent circuit model based on a resistor-capacitor network has been developed to describe the basic electrical properties of the transistor. Shockley-like analytical expressions for the output and transfer characteristic, as well as an analytical expression for the potential and charge-carrier distribution in the channel, are derived under the assumption of a high electron-hole recombination probability. The model has been fitted to our experimental results and yields comparable mobilities for both holes and electrons in the order of 0.1cm2∕Vs. The increasing threshold voltages, with an increase in gate voltage, are discussed as an indication for trapped charge carriers within the insulato...

A pentacene ambipolar transistor: Experiment and theory

We report on light emission from a polymeric transistor that utilizes interdigitated source and drain electrodes with channel length of 5 μm in a bottom gate configuration based on a Si/SiO2 substrate. The polymer investigated is poly[9,9-di(ethylhexyl)fluorene] deposited by spin coating from chloroform solution to achieve an active layer thickness of 40 nm. Light emission occurs above drain source voltages of −60 V and the light intensity can be controlled by the gate voltage. Emission occurs close to the drain electrode as determined by optical microscopy. The transistor operates in hole accumulation mode without saturation of the output characteristics.

Heinz von Seggern

Papers

Light-emitting field-effect transistor based on a tetracene thin film.

Electronic traps in organic transport layers

Photostimulable x-ray storage phosphors: a review of present understanding

A pentacene ambipolar transistor: Experiment and theory

Light emission from a polymer transistor