Showing papers on "Organic semiconductor published in 1996"

Chemistry and electronic properties of metal-organic semiconductor interfaces: Al, Ti, In, Sn, Ag, and Au on PTCDA.

Abstract: The chemistry and electronic properties of interfaces formed between thin films of the archetype molecular organic semiconductor 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) and reactive and nonreactive metals are investigated via synchrotron radiation photoemission spectroscopy. In, Al, Ti, and Sn react at room temperature with the anhydride group of the PTCDA molecule, producing heavily oxidized interface metal species and thick interfacial layers with a high density of states in the PTCDA band gap. The penetration of the reactive metal species in the PTCDA film is found to be inversely related to their first ionization energy. The noble metals Ag and Au form abrupt, unreacted interfaces. The chemical and structural results correlate well with the electrical properties of the interfaces that show Ohmic behavior with the reactive metal contacts and blocking characteristics with the noble metals. The Ohmic behavior of the reactive metal contacts is ascribed to carrier hopping and/or tunneling through the reaction-induced interface states. \textcopyright{} 1996 The American Physical Society.

Finite Size Effects on Electroluminescence of Nanoscale Semiconducting Polymer Heterojunctions.

Abstract: Among the novel finite size effects observed in a series of nanoscale (25−100 nm) semiconducting polymer heterojunctions, such as polyquinoline(PPQ)/poly(p-phenylene vinylene) (PPV), is the reversible switching of electroluminescence (EL) colors (orange/red ↔ green) by the applied voltage. The finite size effects are related to the charge carrier ranges in semiconducting polymers and are expected to be important in electronic and optoelectronic devices from organic semiconductors.

Chemistry, diffusion, and electronic properties of a metal/organic semiconductor contact: In/perylenetetracarboxylic dianhydride

Abstract: We present a photoemission investigation of the interface between In and 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA). The interfacial region is very wide due to an anomalously fast diffusion of In into the organic layer. In also reacts with the anhydride end groups of the molecules. The absence of metal clustering, which permits diffusion, is believed to be due to the ionization of In and ion–ion repulsion in the PTCDA matrix. Finally, the ohmicity of the In/PTCDA contact is attributed to reaction‐induced electronic gap states created throughout the wide interfacial region upon formation of the interface. This study provides the first direct correlation between chemistry and electronic properties of a metal contact on an organic molecular semiconductor.

Organic light emitting diodes

Abstract: Organic light emitting diodes with a complex multilayer structure have been successfully fabricated for bright light emission in the entire visible spectral region. The CIE coordinates of the blue, green, and red emitting electroluminescent devices are plotted in the chromaticity diagram. Double heterostructure organic LEDs with separate hole injection and transport layers allow to achieve low turn-on voltages of only about 4 V and a significantly increased quantum efficiency.

C70 thin film transistors

Abstract: Organic semiconductors are being tested as the active electronic elements of thin film field effect transistors (TFTs) and light-emitting diodes. The basis for understanding the criteria for materials selection in organic TFTs is currently quite primitive, and in order to provide information on this question, the present work reports a study of TFTs fabricated from C{sub 70}. The fullerenes C{sub 60} and C{sub 70} are found to exhibit markedly different performances as the active semiconductor in TFT devices. 15 refs., 3 figs.

High-mobility pentacene organic thin film transistors

Abstract: Organic thin film transistors (TFTs), are of interest for use in broad area electronic applications. In active matrix liquid crystal displays, AMLCDs, for example, organic TFTs would allow the use of inexpensive, light-weight, and mechanically rugged plastic substrates as an alternative to glass. To date, organic TFTs have exhibited field effect mobilities and current on/off ratios too low to be useful for display technology. For example, organic TFTs based on /spl alpha/-sexithienyl typically have a maximum mobility near 0.05 cm/sup 2//V-s and a maximum on/off ration of about 10/sup 6/. We have fabricated organic TFTs using pentacene, a fused-ring aromatic hydrocarbon, as the active material. These new devices have field-effect mobility greater than 0.6 cm/sup 2//V-s and on/off ratio greater than 10/sup 8/.

Field-effect transistor

Abstract: PURPOSE: To set a field-effect transistor equal to or higher than amorphous silicon in mobility by a method wherein a channel section is formed of organic semiconductor material, and a gate insulating layer is formed of insulating polymer having cyano groups CONSTITUTION: A gate electrode 22 and a gate insulating layer 23 which includes insulating polymer having cyano groups are successively formed on a substrate 21, and a source electrode 24 and a drain electrode 25 are formed thereon An organic semiconductor layer 26 is provided so as to bridge a gap between the source electrode 24 and the drain electrode coming into contact with the gate insulating layer 23 At this point, a metal electrode, an ITO electrode or a high-doped conductive polymer electrode is used as the gate electrode 22 Polyacrylonitrile or cyanoethyl purlan is mainly used as polymer having cyano groups The above organic semiconductor is formed of dimethyl- sexithyophene, quartathyophene, and lead phthalocyanine

Influence of FeCl3 dopant on the electrical conductivity of pyrolysed aromatic polymers

Abstract: FeCl3 is used as a dopant of organic semiconductors which have polyconjugated structures (e.g. polyacetylene, polyphenylene), as well as for the intercalation of graphite. Semiconducting polymers can be also synthesized by the pyrolytic conversion of organic polymers. The influence of FeCl3 as a dopant for pyrolysed aromatic polymers at different pyrolysis temperatures up to 1000°C on their electrical conductivity, σ, has been investigated. In the materials poly-p-phenylene, o, m, p-polyphenylenes, novolac resin cured with hexamethylenetetramine, biomass of olive stones, lignin Kraft isolated from this biomass, three regions can be distinguished. The electrical conductivity is low up to 500 °C, between 500 and 700 °C it increases greatly, and above 700 °C it increases at a lower rate. For o, m, p-polyphenylenes, these regions (especially the first and the second) cannot be distinguished. Similar curves are generally obtained after doping of the pyrolysed materials. The ratio of the electrical conductivity of doped, σ to undoped, σ0, pyrolysed materials increases mainly between 500 and 700 °C with the exception of o, m, p-polyphenylenes, where the electrical conductivity decreases at all of the pyrolysis temperatures. The electrical conductivity of the materials is more strongly influenced by heating than by doping. The results are interpreted based on the structure of the materials using X-ray diffractograms, weight losses during the pyrolysis, and taking into consideration the reactions occurring during pyrolysis. FeCl3 is an effective dopant for organic semiconductors affected by charge transfer, but a less effective dopant for pyrolysed polymers and which do not lead to intercalation because of the low order and extension of the carbon layer formed in comparison to graphite.

Performance limits of organic transistors

Abstract: Field effect transistors with organic active layers are a fascinating new frontier in device physics. Devices have been made by many groups on a variety of substrates, including plastic, with a view to eventually develop low-cost, large-area electronic systems based on such transistor technology. Until recently, very little was known about charge transport phenomena in organic transistor active materials. We describe the results of a series of experiments which elucidate the mechanisms of carrier transport in thin film transistors (TFTs) based on oligothiophenes such as /spl alpha/-sexithiophene (/spl alpha/-6T) and their derivatives such as /spl alpha/,/spl omega/ dihexyl sexithiophene (H6T).

Organic photoconductor and element

Abstract: PURPOSE: To obtain the title organic photoconductor element capable of efficiently producing carrier using visible light by a method wherein said element is composed of an organic silicon highmolecule represented by a specific chemical formula containing silicon and an aromatic ring in a repeated unit having at least exceeding one coupling part of a silicon and an aromatic ring. CONSTITUTION: The title organic photoconductor and element is composed of an organic silicon high molecule containing silicon and an aromatic ring in a repeated unit having at least exceeding one coupling part of silicon and aromatic ring. It is recommended that the organic silicon high molecule has a repeated unit represented by the right hand formula wherein Ar represents aromatic group, R and R are the same or different to be hydrogen atom or hydrocarbon group while m and n representing an integer exceeding 1. Furthermore, the title organic photoconductor is composed of an assembly together with at least exceeding one element out of a metal, metallic oxide, inorganic semiconductor and organic semiconductor.

Organic thin film material and its production

Abstract: PURPOSE:To obtain the subject material exhibiting high function properties because of its excellent (high grade) structure-controlling property, excellent in stability due to the polymer, and useful as a photoconductive material, an organic semiconductor, etc., by vacuum-depositing different kinds of specific aromatic compounds on a substrate and subsequently irradiating the deposited compounds with light for a photochemical reaction. CONSTITUTION:This material is obtained by vacuum-depositing (A) an aromatic compound having a radical-generating group in the molecule [e.g. a compound of formula I (phi1 is the residue of benzene, naphthalene, anthracene, phenathrene, tetralin, etc.), a compound of formula II] and (B) an aromatic compound having an unsaturated bond in the molecule [e.g. a compound of formula III (phi2 is phi1), a compound of formula IV] on a substrate under a vacuum of Torr and subsequently subjecting the deposited compounds to a photochemical reaction by the irradiation of light. The objective material can also be obtained by using e.g. a compound of the formula HS-phi3-CidenticalCH (phi3 is phi1) instead of the components A and B.

Semiconductor device provided with organic semiconductor material

Abstract: A semiconductor device is provided with an organic material which is formed by a solid-state mixture of organic donor and organic acceptor molecules. A semiconducting solid-state mixture is known with molar ratios between donor and acceptor molecules of 1.3:2 and 1.66:2. The known solid-state mixture has the disadvantage that its electrical conductivity is comparatively high, so that it is not possible to manufacture switchable devices from the mixture. Here the material includes an n- or p-type semiconductor material, the n-type semiconductor material having a molar ratio between the donor and acceptor molecules below 0.05, and the p-type semiconductor material having this ratio above 20. These solid-state mixtures may be used for manufacturing switchable semiconductor devices. The n- and p-type organic solid-state mixtures can be used for manufacturing transistors, diodes, and field effect transistors in a same manner as, for example, doped silicon or germanium.

Molecular Design of Optical and Structural Properties of Organic Semiconductor Films: Thiophene-Based Oligomers

Abstract: Vacuum-deposited thin films of thiophene-based oligomers were prepared on fused silica glasses in order to elucidate the correlation between molecular structures and optical properties of solid films. Thiophene-based oligomers have well-barrier-well structures in quasi-one-dimensional backbone chains. It is demonstrated that both optical and structural properties of thiophene-based oligomer crystalline films can be controlled by the modification of the conjugation length and the barrier structure. These results represent a significant step toward good quality organic thin film devices.

Deposition of copper-phthalocyanine thin films by laser ablation and its application for an organic electroluminescence device

Abstract: The authors have applied the copper-phthalocyanine organic thin film fabrication technique via laser ablation for constructing a Schottky diode, and a double-layer electroluminescence (EL) cell consisting of a CuPc layer and an aluminum tris-8-hydroxyquinline (Alq/sub 3/) layer as a hole-transport and a luminescent layer.

Mechanism of formation for thin films of dibenzotetraazaannulene on an amorphous substrate

Abstract: We show that an important factor in the mechanism of formation for thin films of organic semiconductors is the change in the temperature gradient in the film as its thickness increases. In this case, an important role information of oriented films is played by both diffusional processes within clusters and by re-evaporation of small crystallites.

Near-field scanning optical microscopy imaging of luminescent polymers

Abstract: Conjugated polymers such as poly(p-pyridyl vinylene)(PPyV) have interesting photoluminescence and electroluminescence properties. These polymers have a high quantum yield of luminescence and are of great practical importance as light-emitting diodes or organic semiconductors. We have performed studies on thin films (about 50nm) of these polymers using the high spatial optical resolution of NSOM.

From organic conductors to bio-conductors

Abstract: Two major categories of organic solids are known to offer the prospect of electrical conduction. One of them consists of charge-transfer complexes such as BEDT-TTF salts. A large number of studies on charge-transfer complexes have been carried out and their conductivity ranges from semiconductor to superconductor. The other group comprises single component materials. Typical examples are polycyclic aromatic compounds and also phthalocyanines; their conductivities are not as good as those of the donor-acceptor kinds.1) As one of those single component organic semiconductors, a group of cytochromes, electron carrier in biological system, was offered. Cytochrome c3 (molecular weight = 13,995, 107 amino acid residers), an electron carrier in the reactions of very negative potentials in cells of Desulfovibrio, has four homes in the molecule.

Organic Transistors — Present and Future

Abstract: Organic materials are almost everywhere in electronic devices. They are used for instance in lithography and encapsulation. They are everywhere, but at the very heart of the device, upon which silicon still imposes its dictatorship. Nevertheless, organic semiconductors do exist, and have indeed been largely studied since the early fifties [1]. It has been shown that metal-semiconductor (MS) and metal-insulator-semiconductor (MIS) structures can be realized with these organic materials. Practical applications were even thought to be within reach in 1978, when a photovoltaic cell made with merocyanine — an organic dye — was claimed to present a power efficiency close to 1% under AMI solar illumination [2]. Unfortunately, this yield, which is still one order of magnitude too small, has not been improved to date, but the domain is still active [3–5].