Showing papers on "Organic semiconductor published in 1991"

Visible light emission from semiconducting polymer diodes

Abstract: We report visible light emission from Shottky diodes made from semiconducting polymers, confirming the discovery by the Cambridge group [Nature 347, 539 (1990)]. Our results demonstrate that light‐emitting diodes can be fabricated by casting the polymer film from solution with no subsequent processing or heat treatment required. Electrical characterization reveals diode behavior with rectification ratios greater than 104. We propose that tunneling of electrons from the recitifying metal contact into the gap states of the positive polaron majority carriers dominates current flow and provides the mechanism for light emission.

Three‐layered organic solar cell with a photoactive interlayer of codeposited pigments

Abstract: Three‐layered organic solar cell with an interlayer of codeposited pigments of n‐type perylene tetracarboxylic derivative (Me‐PTC) and p‐type metal‐free phthalocyanine (H2Pc) in between the respective pigment layers, was fabricated. Two times larger photocurrent compared to the double‐layered cell without an interlayer was obtained due to the efficient carrier photogeneration in a codeposited layer. The power conversion efficiency reached 0.7% under the intense white light of 100 mW cm−2.

Evidence for exciton confinement in crystalline organic multiple quantum wells.

Abstract: Multiple-quantum-well structures based on two crystalline organic semiconductors, namely, 3,4,9,10 perylenetetracarboxylic dianhydride and 3,4,7,8 naphthalenetetracarboxylic dianhydride, have been grown by organic molecular-beam deposition. Both optical-absorption and time-resolved photoluminescence measurements reveal a significant effect on the binding energy and the radiative recombination probability of excitons due to localization of carriers. Variational calculations of the ground-state exciton energy in quantum wells have been done, and the results agree with the experimental data. This provides evidence for exciton confinement in organic quantum-well structures.

Properties of the Organic‐on‐Inorganic Semiconductor Barrier Contact Diodes In/PTCDI/p‐Si and Ag/CuPc/p‐Si

Abstract: The properties are discussed of organic-on-inorganic (OI) semiconductor contact barrier diodes, where the 3, 4, 9, 10 perylenetetracarboxylic diimide (PTCDI) and the copper phthalocyanine (CuPc) serve as the organic thin film. The results presented can be fully understood in terms of the thermionic emission-space-charge-limited (TE-SCL) current model introduced for OI structures with prototypical aromatic compound; 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) vapour-deposited onto n- and p-Si substrates. Also, under moderate and high reverse bias voltages the results obtained can be understood in terms of the organic-on-inorganic heterojunction (OI-HJ) model. Comparisons between diode performances and theory are made. The contact barrier diodes exhibit high breakdown voltages and reverse dark currents limited by generation and recombination of carriers in the Si bulk. From the forward current-voltage characteristics at several temperatures, apparent OI contact barriers of Φbp = (0.63 ± 0.01) V for PTCDI and Φbp = (0.59 ± 0.02) V for CuPc, are formed with p-Si substrates. Studies of the I–U characteristics suggest the presence of an exponential trap distribution in the band-gap of the organic semiconductors used. The resulting diodes are superior in many respect to conventional Schottky diodes due to enhanced contact barriers and reduced edge effects.

Giant anisotropies in the dielectric properties of quasi‐epitaxial crystalline organic semiconductor thin films

Abstract: We have measured the indices of refraction and dielectric constants along different directions in thin films of the crystalline organic semiconductor compound 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA). The films were deposited via organic molecular beam deposition, resulting in single‐crystalline, ‘‘quasi‐epitaxial’’ films. Due to inherent asymmetries in the molecular crystal structure, film ordering results in giant anisotropies in their dielectric properties. For example, the index of refraction measured at a wavelength of λ=1.064 μm in the direction perpendicular to the substrate plane is n⊥ = 1.36 ± 0.01, whereas parallel to the plane, n∥=2.017±0.005, resulting in an index difference of Δn=0.66. Furthermore, the low‐frequency dielectric constant of the films is e⊥ = 1.9 ± 0.1 and e∥ = 4.5 ± 0.2. To our knowledge, these are the largest anisotropies ever measured for thin films. We discuss a guided wave polarization‐selective device which takes advantage of the large dielectric anisotropie...

Manufacture of field effect transistor

Abstract: PURPOSE:To obtain a method of manufacturing a field effect transistor, where an organic semiconductor thin film which is able to protect an electrode against deterioration, excellent in productivity, lightweight, and excellent in flexibility can be used as an active layer. CONSTITUTION:An organic thin film 11 is subjected to an activation treatment to turn into an organic semiconductor thin film 1, a source electrode 2 and a drain electrode 3 are formed on the organic semiconductor thin film 1, and a gate electrode 7 is formed so as to control conductivity between the source electrode 2 and the drain electrode 3.

Plasma polymerization of 1‐benzothiophene

Abstract: Semiconductive thin organic polymer films have been prepared by the plasma polymerization of 1‐benzothiophene. Characteristics of the polymeric products such as their electrical conductivities, optical properties, and electron spin properties have been examined in detail. Doping of these films with iodine has resulted in an increase in electrical conductivity by eight to nine orders of magnitude. The molecular structure of the products has also been discussed.

Electronic properties of conjugated polymers

Abstract: Conjugated polymers such as polyacetylene and polyparaphenylene are semiconductors which can be chemically doped to give very high values of electrical conductivity (up to 1000 Ω cm-1). There has been a considerable theoretical and experimental effort directed towards understanding the way in which dopants add charges to the polymer chains, and the nature of the transport processes that can then occur. The addition of charges to a conjugated chain causes the formation of localised defect states; these may be soliton states for trans-polacetylene, or more generally polaron or bipolaron states. These defect states are considered to control the transport, magnetic and optical properties of these materials.

Charge and spin transfer and optical properties in conducting porphyrin compounds

Abstract: Anisotropic materials made from stacked macrocycles have potential applications as organic conductors and nonlinear optical materials. Using self‐consistent‐field local density theory, we have been exploring the ground and excited state electronic structures of metal substituted tetraazaporphyrins, phthalocyanines, and tetrabenzoporphyrins. The calculated and measured polarized optical absorption peaks are in satisfactory agreement. The theoretical dipole oscillator strengths provide absolute intensities for verification of transition assignments, which are helpful for identifying low‐lying states and excitation mechanisms.

Photoelectrochemical Investigations of Molecular Semiconductors: Characterization of the Conduction Type of Various Substituted Porphyrins

Abstract: The charge transfer from thin film electrodes (thickness ≈ 130 nm) of the zinc(II) complexes of phthalocyanine (1), 2,3,9,10,16,17,23,24-octacyanophthalocyanine (2), tetrapyrido[2,3-b; 2′,3′-g; 2″,3″-1; 2′″,3′″-q]-5,10,15,20-tetraazaporphyrin (3) and tetrapyrazino[b;g;l;q]-5,10,15,20.tetraazaporphyrin (4) to oxygen or EDTA dissolved in an aqueous electrolyte was investigated. Illumination with visible light results in photocurrents which are characteristic for each of the studied compounds. The observations are discussed in terms of the band model suitable for molecular organic semiconductors. From the observed predominant direction of the photocurrent a trend in the band positions and the conduction type of the materials 1, 2, 3 and 4 is established. The transformation of a p-type into a n-type porphyrin solid can be achieved by appropriate chemical substitution in the ligand system.

Optical waveguides in crystalline organic semiconductor thin films

Abstract: Optical waveguiding in a crystalline organic semiconductor, namely, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA), has been demonstrated in slab and rib waveguides using both end‐fire and grating coupling at λ 1.064 μm. The effective indices of the transverse electric (TE) modes measured by means of grating coupling are in good agreement with theoretical prediction. A very low propagation loss of 2.5 dB/cm in a PTCDA rib waveguide has been determined from measurements of the scattered light intensity from the top surface of the guide.

Polarization-selective integrated optoelectronic devices incorporating crystalline organic thin films

Abstract: Certain crystalline organic semiconductor compounds, such as 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), when deposited by an ultrahigh vacuum process of organic molecular beam deposition, form highly ordered "quasi-epitaxial" films (32). Due to asymmetries in the molecular crystal structure of such compounds, the ordering of the films results in giant asymmetries in their dielectric properties. Such large dielectric asymmetries permit the construction of a variety of devices, including optical isolators (38), optically isolated lasers (48), optical isolated optical amplifiers (64), polarization-selective photodiodes (76), and metal-organic-inorganic semiconductor-metal detectors, among others.

Scanning Tunneling Microscopy at High Gap Resistances and on Chemically Modified Silicon Surfaces

Abstract: Scanning tunneling microscopy (STM) studies of organic or biological molecules are difficult to reproduce because strong tip‐surface interactions can displace weakly bound material at the surface. We have studied conducting organic monolayers and nucleic acids with our STM instrument at high gap resistance values (100 GΩ to 1 TΩ). We have succeeded in imaging chemically modified silicon surfaces. It is our desire to use these chemically modified surfaces in conjunction with higher gap values in the future to reliably image DNA.

Organic-based field-effect transistors: Critical analysis of the semiconducting characteristics of organic materials

Abstract: Conjugated polymers, e.g., polyacetylene and polythiophenes, conjugated thiophene oligomers and metallophthalocyanines have been proposed in the literature as organic semiconductors for the fabrication of organic-based field-effect transistors, FET. The poor performances generally shown by these FET have been attributed to the very low carrier mobility in organic semiconductors, and the improvement of this parameter has been the objective of a large number of works. The analysis of the mode of operation of organic-based FET, which operate through the formation of an accumulation layer, shows that an ohmic contribution has to be taken into account in the total observed current output of the devices. The conductivity of the organic semiconductor plays thus a significant role in the FET characteristics, although this point has been up to now rarely considered. In this regard, most of the claims in the literature about high mobility achievements are shown to be of limited significance. Conjugated oligomers are actually the only class of organic semiconductors presenting high mobility together with low conductivity, which, furthermore, indicates that interchain transfer of charge may be a much more efficient process than generally believed.

Manufacture of diode element

Abstract: PURPOSE:To provide a method for manufacturing a highly functional diode element which has a non-symmetrical structure utilizing an organic semiconductor, achieves a stable operation, and has a high withstand voltage in opposite direction. CONSTITUTION:A triclinic-type crystal 5 is formed at the side of a lower electrode 2 by performing vacuum deposition of lead phthalocyanine material while heating an insulation substrate 1 to 100 initially, a monochlinic-type crystal 6 is formed at the side of an upper electrode 4 by performing vacuum deposition by reducing the substrate temperature to a room temperature, and then an organic semiconductor thin film 3 in non-symmetrical structure is formed on an insulation substrate 1 in thickness direction.

A comparison of thick- and thin-film gas-sensitive organic semiconductor compounds

Abstract: The use of metal-based phthalocyanines in the construction of an array of gas-sensitive elements has been explored. A five-element array has been developed in which each of the sensor sites has an individual platinum heating element for independent temperature control. In this way the array can consist of different phthalocyanines and/or operating temperatures, allowing pattern-recognition techniques to be used in the detection of specific gases. The sensor array has been realized as a 28 pin dual in-line package based on an alumina substrate with laser scribed slots to give thermal isolation of adjacent sites. Two methods of phthalocyanine deposition have been investigated; a thin-film method utilizing low-pressure vapour deposition to give a sensor thickness of typically 1 μm, and a thick-film method whereby the phthalocyanine is made into a screen-printable ink, producing a typical sensor thickness of between 15 and 20 μm. The sensors produced by the two methods exhibit distinct morphological differences which significantly affect their respective sensitivities. It has been found that the more porous thick-film sensors have sensitivities comparable to that of their thin-film counterparts. These results support the theory that the conduction mechanisms in organic semiconductor gas sensors are primarily diffusion limited. Of the two fabrication methods described, the thick-film screen-printing technique is far more conducive to volume manufacture. Hence the comparability of the sensitivities of the two types of sensor suggests that screen printing of organic semiconductors is likely to prove a more viable method for the commercial production of gas-sensor arrays.

Polyacetylene Metal-Semiconductor Field-Effect Transistors

Abstract: Planar and sandwich types of polyacetylene metal-semiconductor field-effect transistors (MESFETs) have been fabricated. The current-vs-voltage (I-V) characteristics show that both types of MESFETs are depletion-mode transistors with low transconductances of about 10-6-10-7 s. Channel modulation has been observed in both types of transistors; however, pinch-off cannot be found even at the drain voltage of up to about -30 V. The performances of both types of MESFETs have been compared and the effects on the performance of the transistor have been discussed.

Reticulant doped semiconductive epoxies and plastics for high voltage applications

Abstract: Various techniques of doping epoxies and plastics for use in solving high-voltage problems associated with particle accelerators and high-voltage power supplies have been investigated. These studies have centered on two categories of dopants: antistatic additives and the organic charge-transfer salts tetrathiofulvalene (TF) and tetracyanoquinodimethane (TCNQ). A small percentage ( >

Synthetic design of liquid crystals for directional electron transport

Abstract: The construction of a solid state photovoltaic device composed of a thin film of organic semiconductor sandwiched between indium tin oxide electrodes is described. Macroscopic order is achieved in the photoactive thin film by exploiting the inherent tendency of liquid crystals to self-organize: columnar discotic phases with some crystalline dislocations constitute a possible photoinitiated conduction pathway between the illuminated and dark electrodes. A scientific rationale for the unusual photovoltaic effect observed in this symmetrical cell is offered, with particular emphasis on the molecular features necessary for efficient current generation. The efficiency of cells constructed from the zinc and palladium octakis(β-octoxyethyl) porphyrins is compared, and the possibility of analogously employing hexakis(alkoxy)triphenylenes and tetrakis(alkoxymethyl)tetrathiafulvalenes is considered.

Nonlinear type two terminal element and manufacture thereof

Abstract: PURPOSE:To prevent a short circuit between terminals, and to stabilize electrical characteristics by laminating an organic insulator or a semiconductor and an organic conductor layer onto a substrate electrode CONSTITUTION:An ITO electrode 2 is formed onto a glass substrate 1 through sputtering, and used as an anode Voltage is applied in acetonitrile in which pyrrole and sodium borofluoride are dissolved respectively while employing a platinum electrode as a cathode Borofluoride ions are taken in as a dopant, thus shaping a polypyrrole conductor layer 3 Pyrrole is polymerized in acetonitrile into which copper phthalocyanine sodium tetrasulfate is dissolved, voltage is applied, copper phthalocyanine tetrasulfate ions are taked on the conductor layer 3, and the conductor layer 4 of polypyrrole is laminated When reverse bias voltage is applied, only borofluoride ions are de-doped, and the organic semiconductor layer 3 is formed An intermediate layer changed into a semiconductor or an insulator by the de-doping is stabilized electrically, and a short circuit is not also generated

Manufacture of solid state capacitor

Abstract: PURPOSE:To heighten an impregnation property of an organic semiconductor complex and to obtain an electrolytic capacitor having various good characteristics by putting an organic semiconductor complex into a metal case while holding the case between two electrodes for supplying a large current and performing melting impregnation by means of generation heat loss. CONSTITUTION:A fixed amount of an organic semiconductor complex 2 is measured into an aluminum case 1 and fixed while being held between the electrodes 3 consisting of a metal having properly low electric conductivity and good thermal conductivity. Whereafter, a large current of DC, AC or combination thereof is fed to a same circuit in order to rapidly melt the organic semiconductor complex 2 by means of Joule's heat. Further, a preheated capacitor element 5 is put in a molten organic semiconductor 4 and impregnated, while a hole 6 to let water or a liquid flow is made inside the electrode 3. Upon finish of impregnation, the aluminium case 1 having been held and water cooled is cooled in order to quickly cool and solidify the molten organic semiconductor 4.

Photo-electric transducer

Abstract: PURPOSE:To achieve a large photo current and a photo-electric transducer which is inexpensive and has a large area by enabling a photo-activation layer to contain at least an organic semiconductor and a polysilane resin. CONSTITUTION:A photo-activation layer including at least a photoconductive organic semiconductor and a polysilane resin consists of a configuration which is sandwiched by a front electrode 1 and a rear surface electrode 4. In this photo-activation layer 2, the polysilane acts as a substance with the mobility of a carrier which is generated by a binder agent of the photoconductive semiconductor and a photoconductive organic semiconductor. Since light enters from the side of the front electrode 1, the front electrode 1 enables light to be transmitted. The light-activation layer needs not be a single layer and a light-activation layer 3 may be a layer which generates electric charge by light as in the light-activation layer 2 or a layer which enables electric charge which is generated by the light-activation layer 2 to be traveled efficiently. It is desirable that the film thickness of the light-activation layer should be 0.05-3mum.

Nonlinear two-terminal element

Abstract: PURPOSE:To prevent element characteristics from becoming asymmetric and to make an electric characteristic stable by laminating an organic conductor layer, an organic insulator or semiconductor layer and an organic conductor layer on a substrate electrode. CONSTITUTION:An electrode 2 is formed on a glass substrate 1 and employed as an anode. A polypyrrole conductor layer 3 wherein copper phthalocyanine tetrasulfate ions are taken as a dopant is formed on the electrode, and a conductor layer 4 of polypyrolle wherein forofluoride ions are taken as the dopant is laminated thereon. Moreover, a polypyrrole conductor layer 5 wherein copper phthalocyanine tetrasulfate sodium ions are taken as the dopant is laminated thereon, a reverse bias voltage is impressed thereon to remove only the borofluoride ions, and thereby the layer 4 is turned to be an organic semiconductor layer 4. In this way, an element can be prevented from becoming asymmetric, no damage is given to an organic insulator or a semiconductor in an intermediate layer since any metal or metal oxide film is not used for an upper electrode, and thus a stable nonlinear two-terminal element being free from short-circuit can be constructed.

Organic semiconductor element

Abstract: PURPOSE: To reinforce an organic semiconductor thin film to extract electrical signal or electrical energy without shortcircuiting a lower electrode and an upper electrode by sequentially stacking an organic semiconductor thin film, a polymer hydrogel sheet having a particular electrical conductivity and a metal used to form electrodes CONSTITUTION: A transparent conductive base material 1 is obtained by coating the surface of a transparent member such as a glass with a conductive film 2 consisting of stannic oxide A thin film 3 of organic semiconductor, a polymer hydrogel sheet 4 having electrical conductivity of 10 -4 S/cm or higher and a metal 4 which is used for electrodes such as gold, silver, etc, are sequentially stacked on the surface of the conductive film 2 of the transparent conductive base material 1 and moreover terminals 6, 6 are respectively attached to the conductive film 2 and metal 5 A polymer hydrogel includes polyacrylic acid gel, polyacrylamide and polyetherpolyulethane, etc COPYRIGHT: (C)1992,JPO&Japio

Wide-bandgap hydrogenated amorphous silicon carbide prepared from an aromatic carbon source

Abstract: By utilizing the aromatic molecule xylene, hydrogenated amorphous silicon carbide films are prepared for the first time from an aromatic carbon source. Good-quality films are obtained, over a wide range of optical bandgaps from 2.2 to 3.5 eV and carbon content from 0.4 to 0.9 atomic fraction. Infrared measurements indicate that the films contain a large amount of aromatic and olefinic sp/sup 2/ carbon bonding, the extent of which depends strongly on the deposition conditions. This unsaturated carbon imparts an unusual property to the material in that it can be doped with an electron acceptor, which increases the electrical conductivity by several orders of magnitude, in a manner similar to organic semiconductors. >

High value tantalum capacitors using organic semiconducting cathodes - uses tantalum foil with powdered tantalum sintered to its surface

Abstract: The Ta-capacitors with semiconducting cathode feature a Ta-foil or sheet which has on one or both surfaces Ta powder attached by sintering and an organic semiconducting cathode. The Ta-powder layer is pref. 0.01-0.5mm thick, esp. 50-100 micron. The carrier is pref. etched Ta-foil or sheet. The organic semiconductors used as cathode are pref. a TCNQ-complex, polyethylene, polypyrrole, polyaniline or polythiophene. The foil or sheet can be folded or spiralled and the cathode material is applied after the final shape has been achieved. Contacts can be made by including an Al-foil in the windings. USE/ADVANTAGE - The use of the modified foil or sheet results in a large are Ta-electrode which has a reduced penetration depth compared with a current sintered powder electrode. This allows easier penetration by the cathode material. The resulting electrode area is much larger than can be achieved using etched foils.

Functional Molecular Materials Derived from Organic Conducting Polymers

Abstract: Organic conjugated polymers form a new class of materials in which each macromolecular chain presents a high electrical conductivity. This unique property allows to represent these materials as a tridimensional network of molecular wires, able to carry informations. These wires can be chemically functionalized by the covalent binding of various prosthetic groups, presenting specific interactions whether with the chemical environment or with external physical quantities. Molecular transducers can thus be developed, and examples already exist on the molecular recognition exerted by functionalized conducting polymers toward ions or toward optically active species in solution. These structures open the promising field of molecular electronics, although the development of this new research area first requires the demonstration that the charge transport properties of these materials are efficient enough for them to be used as active layers in electronic devices. This step has been recently achieved, by the development of a new class of organic conjugated materials, conjugated oligomers, which present shorter conjugation length but much lower content of structural defects. The semiconducting properties of these oligomers have been determined through the characterization of field-effect transistors fabricated from these organic materials. A new all-organic thin film architecture has been proposed for these transistors, which shows comparable characteristics to those of a-Si:H based devices. These results confirm that organic conjugated polymers and oligomers can be used as active materials for the construction of electronic devices, and that their further functionalization will allow the development of new types of molecular transducers.

Thin‐film calorimetry and molecular electronics

Abstract: Understanding the effect of the doping process on organic semiconductors is a crucial step in the design of, for example, organic-based gas sensors. A method is presented here which allows the thermal changes which accompany the various steps in the doping process to be accurately monitored. The technique combines the high sensitivity of interferometric detection with the low thermal mass of a single-mode optical fiber.