Showing papers on "Organic semiconductor published in 1993"
TL;DR: In order to analyze the correlation between charge transport and structural properties in conjugated oligomers, sexithiophene, 6T, was substituted by hexyl groups, both on the terminal α positions and as pendant groups in the β position as mentioned in this paper.
Abstract: In order to analyze the correlation between charge transport and structural properties in conjugated oligomers, sexithiophene, 6T, was substituted by hexyl groups, both on the terminal α positions (α,ωDH6T) and as pendant groups in the β position (β,β'DH6T). Structural characterizations by X-ray diffraction show that vacuum-evaporated thin films of 6T and α,ωDH6T consist of layered structures in a monoclinic arrangement, with all-trans planar molecules standing on the substrate. When compared to 6T, α,ωDH6T is mainly characterized by a very large increase of molecular organization at the mesoscopic level, evidenced by a much longer range ordering
743 citations
Patent•
30 Jul 1993TL;DR: A field effect transistor has a channel between a source electrode and a drain electrode made from an organic semiconductor as discussed by the authors, where the channel is a mixture of at least two different organic compounds.
Abstract: A field effect transistor has a channel between a source electrode and a drain electrode made from an organic semiconductor. In one form of the invention, the channel is a mixture of at least two different organic compounds. In another form of the invention, the channel is a lamination of at least two films of different organic compounds. The channel can also be a π-conjugated block copolymer of at least two different types of monomers.
112 citations
TL;DR: In this article, a hierarchy of placement of dyes in p-n heterojunction de-vices was proposed to optimize the short-circuit current density, and computer modeling of Schottky barrier cells, with parameters fit to experimental results and incorporating field-dependent carrier generation, were used to optimize power efficiency.
Abstract: In our work with the phthalocyanines and perylenes, we have formulated a hierarchy of placement of dyes in p-n heterojunction de- vices to optimize the short-circuit current density. Computer modeling of Schottky barrier cells, with parameters fit to experimental results and incorporating field-dependent carrier generation, were used to optimize the power efficiency. The model predicts an optimum carrier concentra- tion density and suggests different hierarchies for utilization of Forster radiationless energy transfer. Synthesis and purification of materials is also discussed. In terms of purity, most materials used in the literature are shown to have been quite below solar grade. A newly devised pu- rification technique is introduced. A hydration mechanism is shown to exist for chloroaluminum phthalocyanine, previously thought immune to hydration. The latter mechanism had been mistaken before for a simple phase transformation and can be induced by various different treatments with organic nonsolvents for chloroaluminum phthalocyanine. Testing of p-n and Schottky barrier cells is also discussed. The different capaci- tance versus voltage (C-V) spectroscopies are compared, and the case for the small-signal method is argued over the triangular voltage sweep. Several cautions on the interpretation of the C-V curves are noted.
105 citations
27 Aug 1993
TL;DR: A survey of dye materials for the emission layer in the multilayer organic electroluminescent (EL) device is discussed in this article in terms of emission color and fluorescent efficiency.
Abstract: Survey of dye materials for the emission layer in the multilayer organic electroluminescent (EL) device is discussed in terms of emission color and fluorescent efficiency. Organic semiconductors for the electron or the hole transport layer in the EL device are proposed for preparing stable homogeneous thin layer. Requirement of accomplishing the confinement of the singlet excitons generated by the recombinations of injected electrons and holes is discussed by using three layer EL devices with extremely thin bimolecular emission layer. Then the emphasis is laid on the size effects in three layer EL device with double heterojunctions on the spontaneous emission. Variations of the intensity and pattern of outer emission through semitransparent ITO glass substrate with the spacing between the emission layer and the metallic electrode are discussed theoretically and experimentally. And variation of the fluorescent lifetime or the radiative decay rate with the spacing is also discussed theoretically and experimentally.
43 citations
TL;DR: In this article, it was shown that each of four alternating layers of two organic molecules grows in a crystalline form without sufficient strain to induce amorphous growth, regardless of significant lattice mismatch which might exist between the alternating films.
Abstract: We directly observe by reflection high‐energy electron diffraction, the quasiepitaxial growth of crystalline organic quantum‐well structures grown by the ultrahigh vacuum process of organic molecular beam deposition. We show that each of four alternating layers of two organic molecules grows in a crystalline form without sufficient strain to induce amorphous growth, regardless of significant lattice mismatch which might exist between the alternating films. Our results clearly demonstrate the ability to engineer a completely new class of van der Waals‐bonded thin film materials and structures based on crystalline organic semiconductors, with applications to optoelectronics.
34 citations
TL;DR: In this paper, a new method for doping organic semiconductors was presented, where the organic materials were evaporated by the Knudsen method under UHV conditions and were subsequently investigated spectroscopically.
32 citations
TL;DR: In this article, the static curr entvoltage (J-U) characteristics have been studied using sandwich cells of the type Cu-organic compound-Al/Cu, and the experiments showed that for lower values of intensity of electric field E (E = 6 × 10 2 -2 × 10 4 V/cm) J-U characteristics are ohmic.
27 citations
TL;DR: In this article, the authors measured the carrier mobility of a series of unsubstituted, α alkyl-substitution, and β-alkyl -substitized thiophene oligomers nT on field effect transistors.
27 citations
TL;DR: In this article, the authors obtained the highest dc electrical conductivity of 1.0×10−1 S/cm at room temperature in the PTCDA-polymerized sample film with a rf power of 10 W.
Abstract: Homogeneous semiconductive organic thin films were obtained by the radio‐frequency (rf) plasma polymerization of 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) and related compounds such as 3,4,9,10‐perylenetetracarboxylic diimide (PTCDI) and perylene. The highest dc electrical conductivity of 1.0×10−1 S/cm at room temperature was obtained in the PTCDA‐polymerized sample film prepared with a rf power of 10 W. The conductivity of the films prepared with a rf power of 60 W was lower by three orders of magnitude than those with a rf power of 10 W. Furthermore, the conductivities of the PTCDA‐ and the PTCDI‐polymerized films decreased by exposure to air. In order to clarify these phenomena, the structure and optical properties of the sample films were examined based on the infrared, the electron spectroscopy for chemical analysis, and the ultraviolet‐visible measurements.
23 citations
TL;DR: In this article, drift mobility measurements were performed on the hole-transport organic semiconductor chloro-aluminum phthalocyanine using a time-of-flight technique, and the dependence of drift mobility on field was examined in order to elucidate the charge transport mechanism.
17 citations
TL;DR: In this paper, the first observation of free-carrier-induced index modulation in crystalline organic waveguides was made, where two light beams with wavelengths of 1.06 and 0.514 μm from a first source (12) and a second source (34) were used as the guided and the pump light sources, respectively.
Abstract: All-optical modulation occurs in crystalline organic semiconductor waveguides (10a) grown by the ultrahigh vacuum process of organic molecular-beam deposition onto substrates (10b). Two light beams with wavelengths of 1.06 and 0.514 μm from a first source (12) and a second source (34), respectively, may be used as the guided and the pump light sources, respectively. A resonant non-linear coefficient at room temperature of 5.4×10 -5 cm 2 /W at 1.06 μoccurs at a pump intensity of 1.0 W/cm 2 . This large non-linear effect is attributed to free electron-hole pairs produced by the dissociation of excitons generated by the short wavelength beam. A carrier lifetime of (17±1) us, which determines the modulator switching time, is in good agreement with theoretical predictions. This appears to be the first observation of free-carrier-induced index modulation in crystalline organic waveguides.
01 Mar 1993
TL;DR: In this article, the electronic structure of polypyrrole films and (2,5-DMe-Dicyanoquinonediimine)2Ag, Rb single crystals using a combination of electrochemical preparation and electron-spectroscopical techniques (XPS, UPS, HREELS).
Abstract: We characterize the electronic structure of polypyrrole films and (2,5-DMe-Dicyanoquinonediimine)2Ag, Rb single crystals using a combination of electrochemical preparation and electron-spectroscopical techniques (XPS, UPS, HREELS). These studies allow to characterize the electronic structure, to conclude on the particular conductivity mechanisms for controlled order and structures, and to determine the strength of both, the electron-phonon and the electron-electron interactions.
TL;DR: In this article, the dependence of the dark and photovoltaic characteristics of metal-insulator-semiconductor (MIS) devices of the structure Al/Al-oxide/TPP/Au (TPP=tetraphenylporphyrin) on the thickness of the interfacial-oxide layer is described.
Abstract: The dependence of the dark and photovoltaic characteristics of metal-insulator-semiconductor (MIS) devices of the structure Al/Al-oxide/TPP/Au (TPP=tetraphenylporphyrin) on the thickness of the interfacial-oxide layer is described. Iodine-doped MgTPP devices show a variation of open-circuit photovoltage, short-circuit photocurrent, fill factor, power conversion efficiency, and capacitance with Al-oxide thickness, in a manner similar to inorganic MIS structures. An optimum oxide thickness of around 2 mu m is observed for highest photovoltaic efficiency. The properties of oxygen/water vapor-doped ZnTPP and H/sub 2/TPP cells appear dependent upon the extent of oxide growth on the aluminum electrode during the doping process. >
01 Jan 1993
TL;DR: In this article, the carrier mobility of a series of unsubstituted, α, β and β alkyl susbtituted thiophene oligomers nT has been measured on field effect transistors based on these organic semiconductors.
Abstract: The carrier mobility μFET of a series of unsubstituted, α alkyl susbtituted and β alkyl susbtituted thiophene oligomers nT has been measured on field-effect transistors based on these organic semiconductors. A steep rise of μFET with conjugation length n has been observed up to the hexamer 6T. For a given length n, alkyl substitution in a position leads to a further important increase of mobility, which reaches values close o 1 cm2V−1s−1 in the case of α,ω dihexyl sexithiophene. These important values, which express high efficiency in intermolecular charge transfer, are attributed to polycrystallinity and long range structural ordering, which appear in thin films of these molecules, as shown by X-ray data. This structural organization is highly dependent on the nature of alkyl substitution of the oligomers, thus allowing a molecular engineering of their semiconducting properties. FET characterizations on micro-scaled devices open various applications in the fields of flat panel display with interactive matrices, and also of digital devices.
TL;DR: In this paper, the authors showed that the electrical resistivities of pentacene thin films doped with iodine in the direction parallel to the substrate plane fit the T−1/3 dependence well.
Abstract: The logarithmic electrical resistivities of pentacene (PEN) thin films doped with iodine in the direction parallel to the substrate plane fit the T−1/3 dependence well. This indicates that the lateral transport of the film was governed by two‐dimensional variable range hopping. In contrast, the logarithmic resistivities of the films perpendicular to the substrate were observed to be almost independent of temperature and to be weakly T−1/2 dependent. This shows that the tunneling mechanism is predominant in perpendicular transport. Two‐dimensional conduction of the film was confirmed by these transport properties, which was expected from the intercalated structure of PEN film doped with iodine.
01 Mar 1993
TL;DR: In this paper, the most common dopant for the widely used α-sexithiophene (α6T), FeCl3, was co-sublimed with the oligothiophene under UHV-conditions.
Abstract: A new method for doping organic semiconductors is presented. The most common dopant for the widely used α-sexithiophene (α6T), FeCl3, was co-sublimed with the oligothiophene under UHV-conditions. The solid-state doping effects were studied for systematically varied dopant concentrations in-situ with XPS. UPS, and HREELS. Up to a doping level of one effective charge per α6T the results can be interpreted as polaron formation. At higher dopant concentrations polaron bands are most probably formed.
TL;DR: In this paper, the synthesis of new derivatives of the asparagic acid is described and the temperature dependence of the electrical conductivity and Seebeck coefficient for respective compounds are studied using the thin films deposited from the solution.
TL;DR: In this paper, the influence of different substrates and their temperature T s during deposition is observed to modify the dominant stacking orientation of LiPc. The anisotropy of the films influences the angle-dependent magnetic properties as the linewidth ΔB 1 2 and the g factor of ESR experiments.
Journal Article•
Patent•
26 Feb 1993
TL;DR: In this paper, a spacer is provided between an anode foil and a cathode foil, which are composed of valve action metal, the electrode foils are wound and a capacitor element is formed and a case is stored in a case whose top is opened, the material is melted by heating to be organic semiconductor melted liquid.
Abstract: PURPOSE:To provide a method of producing an electrolytic capacitor, which contributes to the improvement of the characteristics of the electrolytic capacitor by improving the cooling solidifying process of an organic semiconductor CONSTITUTION:A spacer 3 is provided between an anode foil 1 and a cathode foil 2 which are composed of valve action metal, the electrode foils are provided with an anode terminal 4 and a cathode terminal 5 to be wound and a capacitor element 6 is formed Organic semiconductor material is stored in a case 7 whose top is opened, the material is melted by heating to be organic semiconductor melted liquid 8 After impregnating the capacitor element 6 with the organic semiconductor melted liquid 8, the organic semiconductor is cooled step by step using cooling media of a plurality of temperature levels At least after cooling the organic semiconductor using the first cooling medium 9 which is 60 degC-150 degC, the organic semiconductor is cooled by using the second cooling medium 11 which is 0 degC-60 degC so as to manufacture a solidified organic semiconductor 13 The opening of the case 7 is sealed by a seal 14
01 Jan 1993
TL;DR: In this article, the experimental characterization of two well established aromatic compounds, 3,4,9,10-perylenetetetricarboxylic dianhydride (PTCDA) and 1, 4,5,8-naphthalenet-etric-carboxyric dianohydride (NTCDA), and optoelectronic device fabrication are presented.
Abstract: Today’s electronic and photonic devices are mainly based on inorganic materials. In the field of optoelectronic devices III–V compound semiconductors are predominant because of the direct band structure of these alloys. However, organic compounds may emerge to a remarkable enrichment. In the near future they will support or partly replace inorganic materials. Especially polymers and cristalline organic semiconductors are promising candidates for application in photonic devices. The experimental characterization of two well established aromatic compounds, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), and optoelectronic device fabrication are subjects of this contribution. We first discuss the deposition of crystalline organic layers by UHV sublimation. Optimized growth conditions even facilitate the growth of homogeneous quantum well structures. In view of applications in optoelectronic devices ohmic and Schottky contacts and organic-inorganic heterostructures are investigated. A planar photodetector is presented as a first example.