Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
2000-02-15
2003-04-29
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S102000, C257S103000, C313S498000, C313S499000, C313S500000, C313S506000, C313S507000, C313S509000, C313S511000
Reexamination Certificate
active
06555840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to charge-transport structures and to a method of manufacturing such structures. This invention is especially concerned with organic electro-luminescent structures but also has application in other organic optoelectronic structures such an organic photo-voltaic devices, and in organic transistors and other electronic structures where charge flows through the structure in operation.
2. Description of the Related Art
An organic electro-luminescent structure is disclosed by C. W. Tang et al in Appl. Phys. Lett. 51(12), Sep. 21, 1987, pages 913 to 915, in which an aromatic diamine layer is vacuum deposited onto an indium tin oxide-coated glass substrate. An 8-hydroxyquinoline aluminium (Alq) layer is vacuum deposited on top of the diamine layer and an Mg:Ag electrode is deposited on top of the Alq layer. The diamine layer is a hole-transport layer whilst the Alq layer is an electron transport layer. In use, holes are injected via the indium tin oxide layer into the diamine layer whilst electrons are injected via the Mg:Ag electrode into the Alq layer. Recombination of holes and electrons takes place in the Alq layer adjacent to its interface with the diamine layer so as to produce light emission in the 500-600 nm region.
J. H. Burroughes et al in Nature, vol. 347, Oct. 11, 1990, pages 539 to 541, disclose organic electro-luminescent structures based on a layer of poly(p-phenylene vinylene) [PPV] sandwiched between top and bottom electrodes. The PPV layer is formed by spin-coating a thin film of PPV precursor followed by thermal conversion to form the PPV layer. In use, such structure emits in the green-yellow part of the spectrum.
C. W. Tang et al in J. Appl. Phys. 65(9), May 1, 1989, pages 3610 to 3616, disclose organic electro-luminescent structures similar to those disclosed by C. W. Tang et al (supra) but where a layer of doped Alq is provided at the interface between a diamine layer and an undoped Alq layer, or is provided within the undoped Alq layer adjacent to the interface. The doped Alq layer is produced by evaporation of Alq and dopant at different deposition rates. The concentration of dopant affects the emission wavelength of the structure.
M. Matsuura et al in Asia Display '95, pages 269 to 272, disclose multi-colour organic electro-luminescent structures based on a blue emitting layer which is modified in certain regions with colour changing media (CCMs) which change the emission colour from blue to green or red to enable an RGB colour display to be obtained. The blue emitting structure is obtained using ITO as an anode, an unspecified hole-transport layer, an electron-transporting layer consisting of 1,4-bis(2,2-diphenylvinyl)biphenyl [DPVBi], with an Mg:Ag cathode. The CCMs are deposited by a patterned printing technique on a glass plate. The patterned CCMs are then covered by a protecting layer followed by formation of the ITO anode, the organic hole-transport and electron-transport layers. Thus, in this structure, the CCMs are disposed on the opposite side of the anode to the organic charge-transport layers and are encapsulated in a protecting layer.
J. Bharathan et al in Applied Physics Letters, volume 72, No. 21, pages 2660 to 2662, disclose organic electro-luminescent devices wherein red-, green- and blue-emitting polymers are printed in the desired pattern on a substrate by ink-jet printing. In this structure, a layer consisting of the desired pattern, for example red-green-blue dots for a multicoloured display, is printed on to a substrate and then a polymer is spin-coated over the top of the pattern to form a uniform buffer layer which seals pin-holes in the ink-jet printed layer. In a particular example, an aqueous solution of polyethylenedioxy thiophene is ink-jet printed onto an ITO electrode formed on a substrate to produce the desired pattern. Then, the pattern to covered with a spin-cast film of poly[2-methoxy-5-2′-ethylhexyloxy-1,4-phenylene vinylene]. However, the provision of the dots adjacent to the ITO electrode can lead to undesirable quenching of emission in use.
Chang et al, Appl. Phys. Lett., Vol 73. No. 18, Nov. 2, 1998, pages 2561 to 2563, disclose the production of patterned dual-colour polymer light-emitting pixels using hybrid ink-jet printing technology where a hole-injection layer of spin-cast polyaniline is formed on an ITO anode supported by a glass substrate. Subsequently, a polymer buffer layer of a wide band gap, water-soluble blue emitting polymer, poly[2,5-bis[2-(N,N,N-triethylammonium)ethoxy]-1,4-phenylene-alt-1,4-phenylene] dibromide [PPP-NET
3
+
], is spin cast onto the polyaniline layer. Such a structure emits blue light in use. An ink-jet printer is used to print dots of a red-orange emitting, water-soluble polymer, poly(5-methoxy-(2-propanoxysulfonide)-1,4-phenylene vinylene) (MPS-PPV). The MPS-PPV is dissolved in an aqueous solution and diffuses into the spin-cast buffer layer of PPP-NET
3
+
. Then, cathodes are deposited on top of the buffer layer to complete the structure. However, the techniques described by Chang et al do not ensure that the surface of the buffer layer on which the cathodes are deposited is completely smooth. Thus, there is still a risk that the cathodes will be non-uniform leading to so-called “edge effects” and to a poor service life. Also, the provision of the dots adjacent to the cathodes can lead to undesirable quenching of emission in use.
Hebner et al in Appl. Phys. Lett., vol. 72, No. 5, Feb. 2, 1998, pages 519 to 521, disclose an organic light emitting structure in which ink-jet printing is used to apply a patterned layer of polyvinylcarbazole doped with various types of coloured dye onto an ITO anode supported on a polyester substrate. The ink-jet printer is operated in a mode to create a continuous sheet of polymer rather than discrete dots so as to facilitate subsequent formation of metal cathodes over the top of the ink-jet printed layer. However, it it difficult, when ink-jet printing, to avoid the formation of pin holes even when operating the ink-jet printer in a mode to create a continuous sheet of polymer. This produces non-uniform electrodes leading to so-called “edge effects” and to a poor service life. Also, the provision of the dots adjacent to the cathodes can lead to undesirable quenching of emission in use.
In an attempt to overcome the problem of undesirable thickness non-uniformities, it has been proposed by T. Hebner et al in a presentation of Materials Research Society —Fall Meeting, Boston, USA, Nov. 30-Dec. 4, 1998, see the Abstract on page 366, and T. R. Hebner et al in Appl. Phys. Lett, vol. 72, No. 13, Sep. 28, 1998, pages 1775 to 1777, to achieve local tuning of the ultra-violet fluorescence and electro-luminescence by local application of wet dye-containing droplets after a uniform organic film is created by spin-coating. In the Abstract, there is described a method of diffusing dopants into a PVK host polymer layer, wherein the dopants are C47, C6 and nile red dopants for blue, green and red devices. In such method, an ink-jet printer is used and the solvent is said to be compatible with ink-jet printers. However, solvents such as acetone are employed, which is reported to create a hole in the polymer film. The use of acetone leads to significant lateral transport of the dyes through the film leading to build-up at the edges. The films are very thin and the dye diffuses all the way through the film. As a result, the PVK host layer is basically uniformly doped throughout the thickness of the film.
EP-A-0643549 describes an internal junction organic electroluminescent device in which an organic electroluminescent medium disposed between an anode and a cathode has a hole injecting and transporting layer contiguous with the anode and an electron injecting and transporting layer contiguous with the cathode. The electron injecting and transporting layer includes an electron injecting layer in contact with the cath
Anderson Sally
Hudson Andrew James
Tombling Craig
Weaver Michael Stuart
Flynn Nathan J.
Renner , Otto, Boisselle & Sklar, LLP
Sefer Ahmed N.
Sharp Kabushiki Kaisha
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