Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2001-07-26
2004-07-13
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S504000, C313S505000
Reexamination Certificate
active
06762552
ABSTRACT:
TECHNICAL FIELD
The invention relates to an organic electroluminescent device having a plurality of independently addressable electroluminescent elements and a method of manufacturing thereof.
BACKGROUND AND SUMMARY
Generally, an organic electroluminescent (EL) device comprises at least a hole-injecting (an anode), an electron-injecting electrode (a cathode) and, sandwiched therebetween, an EL layer comprising an organic EL material. If a suitable voltage is applied to the electrodes, holes and electrons are injected from the electrodes. Recombination of a hole and electron inside the organic EL layer leads to emission of a photon, i.e. light. Using different organic EL materials, the color of the light emitted can be varied.
An organic EL device can be used as a light source, in particular one having a large surface area. Organic EL devices comprising a plurality of independently addressable electroluminescent elements (hereinafter also referred to as pixels) are particularly suitable for display purposes such as a monochrome or multi-color display device, a back light, a still image display, a segmented display device, or a matrix display of the passive or active type.
In the International patent application WO 99/21936, an organic EL device is disclosed which comprises a polymeric EL layer disposed between a hole-injecting electrode and a Ca electron-injecting electrode. To facilitate hole injection and hole transport, the indiumtinoxide (ITO) hole injecting electrode is provided with a hole injecting/transport layer of poly-3,4-ethylenedioxythiophene (PEDOT) deposited by means of spin-coating. Alternatively, poly-aniline (PANI) may be used. In the context of the invention the terms “charge injecting layer”, “charge transport layer” and “charge injecting/transport layer”, where charge refers to a hole and/or electron, are used interchangeably.
Efforts to modify the known EL device so as to obtain an EL device comprising a plurality of independently addressable EL elements by providing patterned electrode layers gave unsatisfactory results. When being driven at constant current, the brightness of a particular EL pixel was found to depend on the image to be displayed by addressing a number of EL pixels. In particular it appeared that the brightness of the light emitted by a particular addressed pixel was inversely proportional to the number of neighboring EL which are also addressed.
It is an object of the invention to provide, inter alia, an electroluminescent device comprising a plurality of independently addressable electroluminescent elements which does not have the above-mentioned disadvantage. Specifically, the invention aims to provide an EL device in which each EL pixel can be individually addressed without its brightness of emission being dependent on whether or not its neighboring pixels are addressed. This is to be the case even and in particular if the EL device is manufactured using a method in which at least a charge transport layer is processed from solution using a wet coating method such as spin-coating. Moreover, the EL device is to have a structure such that it can be manufactured using a simple and cost-effective manufacturing method.
In accordance with the invention, these and other objects are achieved by an organic electroluminescent device comprising a plurality of independently addressable electroluminescent elements, said device comprising:
a patterned first electrode layer comprising a plurality of first electrodes;
a second electrode layer;
an organic, optionally patterned, electroluminescent layer sandwiched between said first and said second electrode layer;
an organic charge transport layer having mutually separate charge transport areas which are positioned between the electroluminescent layer and the first electrode layer; and
a relief pattern separating said charge transport areas along each first electrode and between neighboring first electrodes.
In the EL device in accordance with the invention each EL pixel can be individually addressed such that, when driven at constant current, the brightness at which the pixel emits is substantially independent of whether any of the pixels neighboring the addressed pixel are addressed as well. This is even and in particular the case if the organic charge transport layer is provided from solution using a wet coating method such as spin-coating. An essential aspect of the invention is the relief pattern. It allows the charge transport layer to be patterned using a (non-selective) wet coating method in a simple and cost-effective manner.
In one respect, the invention is based on the insight that in the known EL device modified to include patterned electrode layers the charge transport layer is provided as a continuous layer. The continuous layer, being positioned directly adjacent the first electrode layer, connects first electrodes of different pixels. If a particular pixel is addressed, a leakage current flows to any non-addressed pixel neighboring the addressed pixel via the continuous charge transport layer. In contrast, no such leakage current flows between neighboring addressed pixels as their first electrodes are at the same potential. In the case of a floating electrode arrangement, the leakage current causes non-addressed EL elements neighboring the addressed pixel to inadvertently emit light as well. In order to substantially suppress the leakage current, the charge transport areas which are positioned between the EL and the first electrode layer are mutually separated along neighboring first electrodes. Being mutually separate no current can flow between these areas.
In addition, the invention is based on the finding that, in order to be able to provide a charge transport comprising such transport area in a simple and cost-effective manner and thus an EL device comprising such a layer, the EL device is to be provided with a relief pattern which extends between and along neighboring first electrodes. Surprisingly, the relief pattern allows the said patterned charge transport layer to be obtained using a wet coating method such as spin-coating. In the case of a non-selective coating method, it is observed that, as a suitable height and width of the relief pattern, the wet film containing the charge transport layer material or precursor material thereof which initially floods the entire substrate surface breaks up in mutually separate fluid areas extending along and between the relief pattern such that no charge transport material is left on top of the relief pattern. The fluid areas are then converted into charge transport areas which are separated along neighboring first electrodes. Furthermore, being separated along neighboring first electrodes the charge transport area are laid out such that first electrodes sharing a common second electrode are covered by different charge transport areas which is important in a floating electrode arrangement.
In EP-A-0880303 an EL device is disclosed comprising a plurality of independently addressable elements having a charge transport layer and a relief pattern in the form of banks. The purpose of the banks is to prevent the spreading of solution containing luminescent layer material provided by means of ink-jet printing into unwanted areas. Its purpose is therefore quite different from the purpose of the relief pattern in the present invention which is to assist in providing charge transport areas separated along neighboring first electrodes. Furthermore, the charge transport layers of EP-A-0880303 are patterned, if at all, in a different manner. EP-A-0880303 does not disclose an organic charge transport layer having mutually separate charge transport areas which are positioned between the electroluminescent layer and the first electrode layer and are separated along neighboring first electrodes. Also, the present invention allows the charge transport layer to be made substantially thinner (thickness typically less than 10% of height of relief pattern) than the charge transport layers disclosed in EP-A-0880303 which not only saves charge transport material
De Koning Jochem Petrus Maria
Duineveld Paulus Cornelis
Lammers Jeroen Herman
Liedenbaum Coen Theodorus Hubertus
Roelandse Cornelis Dirk
Koninklijke Philips Electronics , N.V.
Patel Ashok
Zimmerman Glenn
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