Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-01-28
2004-12-28
Garrett, Dawn (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S502000, C313S506000, C313S509000, C313S512000, C427S066000
Reexamination Certificate
active
06835470
ABSTRACT:
The present invention relates to an electroluminescent device comprising two electrodes, between which there is arranged at least one electroluminescent organic semiconductor layer, and a substrate supporting the said device, as well as an electric current source connected to the electrodes in an electrically conductive manner. The invention also concerns a method of manufacturing such a device.
Within the meaning of the invention, the expression “at least one electroluminescent organic semiconductor layer” means an electrically conductive, possibly multilayer, organic material in which an electroluminescence phenomenon may arise when on the one hand electrons and on the other hand positive holes are injected therein. The recombination of these charges with opposite signs causes the emission of light. This is therefore, in the sense of the invention, an electroluminescence said to be by injection.
The phenomenon of electroluminescence using organic semiconductors was revealed for the first time in the 1960s and the development of these electroluminescent systems based on organic thin films dates from the second half of the 1980s. In this regard reference can be made to the following publications: A. L. Kraft, A. C. Grimsdale, A. B. Holmes, Electroluminescent conjugated polymers—Seeing polymers in a new light, Angew. Chem. Int. Ed. (1998) 37, 402-428, and R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, R. N. Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos, J. L. Bredas, M. Lögdlund, W. R. Salaneck, Electroluminescence in conjugated polymers, Nature/1999/397, 121-128.
In the majority of the cases of the systems used, it is the glass which is taken as a substrate. Successive thin layers constituting the electroluminescent system are deposited on this. More recently, PET (polyethylene terephthalate) has been envisaged for replacing glass. Glass and PET being transparent, indium-tin oxide (ITO) is deposited directly on this substrate, constituting the positive electrode intended, in DC current, to inject positive holes into the organic semiconductor, which is in its turn deposited in one or more layers, possibly consisting of different molecules, on the layer of ITO. Finally, a thin layer of aluminium, magnesium or calcium is deposited on the whole, constituting in DC current the negative electrode intended to inject electrons into the organic semiconductor. It is the hole-electron recombination which generates the light emitted by the system through the glass or PET substrate. In the systems which use alternating current (SCALE: Symmetrically Configured Alternating current Light Emitting devices), the same electrodes are found (ITO on glass or on PET and aluminium, copper or gold) but electrodes no longer necessarily need to have a working function different from each other.
These devices have the drawback that the substrate is a thermally insulating material. During use at high power density this substrate does not allow an appropriate release of heat, which can result in disturbance in the device. In addition, in the case of glass, the substrate is fragile whilst in the case of PET it is flexible. Neither of these two substrates therefore resists the static and dynamic mechanical stresses borne during the use of electroluminescent devices.
Systems are also known which make use of “phosphoruses” as a source of electroluminescence. These phosphoruses are inorganic compounds which are separated from a conductive rigid substrate by a dielectric layer, possibly with variable resistance. The phosphoruses are generally encapsulated, for example in a polymerisable resin. They are placed in an alternating electric field which moves the electrons created within them by thermal agitation and the corresponding positive holes created in the valency band. These electrons produce excitations by collision, with the subsequent production of light. This is therefore in this case what is called intrinsic electroluminescence (see for example WO-97/46053 and U.S. Pat. No. 3,626,240).
To excite the “phosphoruses” it is necessary to create an alternating field of sufficient intensity, and hence the necessity for the presence of a dielectric and/or resistive layer. The result is high electrical voltages of 60 to 500 V in oscillating alternating current at 50 Hz-2.5 kHz and high thicknesses of approximately 100 &mgr;m.
The purpose of the present invention is to develop an electroluminescent device with an organic semiconductor which makes it possible to avoid these problems in a simple fashion.
An electroluminescent device as described at the start has been provided according to the invention, in which the substrate consists of a metal or metallic alloy. Such a substrate has sufficient thermal conductivity to allow discharge of the heat released by the electroluminescent system, especially when the latter is used at high power density.
Advantageously the metallic alloy is a steel, for example soft steel or stainless steel. Steel offers the property of being both rigid and easy to shape, which is advantageous for many applications of electroluminescent devices, such as illuminating panels and external or internal luminaires, decorative systems and fixed or programmable display systems.
According to one advantageous embodiment of the invention, a first electrode is disposed on a first side of the said at least one layer of electroluminescent organic semiconductor, on a first surface thereof which faces the substrate, and a second electrode is disposed on a second side of the said at least one layer of electroluminescent organic semiconductor, on a second surface thereof which is opposite the substrate, this second electrode allowing an at least partial passage of light.
As already mentioned, the device can comprise one or more successive layers of electroluminescent organic semiconductor. First surface and second surface mean, in the case of a single layer of semiconductor, the two faces thereof. In the case of several successive layers, they are the two external faces of this set of layers.
Using a substrate made of metal, metallic alloy or steel advantageously has the effect of allowing a reversal in the arrangement of the layers in the electroluminescent system compared with that of the systems according to the state of the art. This is because the light emitted by the device no longer passes through the substrate but only through one of the electrodes, the one opposite to the substrate, and through any external encapsulation thereof in transparent material, preferably impervious to water and air.
Advantageously, to manufacture this electrode situated opposite the substrate the most transparent possible material is used. It is possible to envisage for example inorganic electrode materials as used in the known electroluminescent or photovoltaic devices for electrodes supported directly by a glass or PET substrate. It is possible to cite, as non-exhaustive examples, indium-tin oxide (ITO), indium-zinc oxide (IZO) or systems based on indium-(zinc, gallium) oxides or ZnO, SnO2, ZnS, CdS, ZnSe, ZnxCd1-xO, ZnTe. It is also possible to use organic transparent electrically conductive materials, such as for example p-doped conjugated polymers, polypyrrole, polythiophene, polyaniline, polyacetylene (CHx) as well as derivatives of mixtures of these substances. It is also possible to make use of several of these superimposed conductive layers, for example a layer of ITO coated with a conjugated polymer.
As a transparent encapsulation material, it is possible to provide by way of example a thin layer of silica deposited for example by the so-called PECVD (Physical Enhanced Chemical Vapour Deposition) technique (SiOx).
According to one advantageous embodiment of the invention, the substrate is connected to the current source. The steel is a good electronic conductor and it can therefore serve as a current feed for one of the electrodes with which it is contact. The substrate can itself serve as an electrode.
It is obviously possible also to provide a device according to the invention in which the s
Magain Pascal
Winand Rene
Browdy and Neimark , P.L.L.C.
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