The assignee for this patent, patent number 8629603, is
Reporters obtained the following quote from the background information supplied by the inventors: "An organic light-emitting device (OLED) is a luminescence emitter by means of which electromagnetic radiation is produced from electric energy. The OLED has at least one organic active layer in which the electromagnetic radiation is produced. The active layer is arranged between an anode and a cathode. When a forward potential is applied, the anode injects holes into the active layer while the cathode injects electrons. The injected holes and electrons each drift (under the influence of an externally applied electric field) to the oppositely charged electrode and produce an electroluminescent emission on being recombined in the active layer.
"A particular advantage of an OLED is that it can be used as a large-area and homogeneous light source. That allows totally novel applications as an illuminant. Commercially available OLEDs such as 'ORBEUS CDW-031', a product offered by the applicant, currently still have a relatively low light yield. The aim, though, is for substantially higher yields and luminance densities to be achieved in the future. However, a problem associated with size and higher luminance densities is that the OLED heats up inside. That gives rise to thermal effects such as, for example, ageing of the different functional layers. Temperature distribution not being homogeneous across a large-area component, the result can be different local ageing processes within the layers which, when the component is operated for longer periods, will give rise to increased inhomogeneities in luminance density. Inhomogeneities of such kind are, though, undesired."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "One object of the present invention is to provide an organic light-emitting device in the case of which inhomogeneous temperature distribution is as far as possible prevented.
"Different embodiment variants of the organic light-emitting device have an active layer for producing electroluminescent radiation and a thermally-conducting layer for dissipating heat that is generated during an electroluminescence process. The thermally-conducting layer has a thermal conductivity of more than 200 W/mK, in particular more than 500 W/mK.
"The basic idea common to all the various embodiment variants is that a thermally-conducting layer for dissipating or, as the case may be, distributing heat is incorporated in the organic light-emitting device. The thermally-conducting layer has particularly good thermal conductivity. It is greater than the thermal conductivity of metals used in the organic light-emitting device. The conductivity of, for instance, aluminum is 200 W/mK. Carbon-based materials are in particular used as a thermally-conducting material. They can be in the form of, for example, carbon nano tubes: CNT). As a material, CNTs are particularly good thermal conductors so that heat generated in the device can be effectively transported to the outside. The electrical properties of CNTs which enable them to be used as a semiconductor or electrical conductor moreover allow them to be used in a particularly versatile manner in the organic light-emitting device's various materials. Finally, CNTs' optical properties make them suitable for only slightly affecting the device's luminance characteristics. Other materials, for example a thin thermally-conducting foil containing graphite, can be used if optical properties are not especially significant. The thermally-conducting foil can also contain metals in order to achieve a high thermal conductivity.
"The thermally-conducting layer is in various embodiment variants in direct contact with the active layer. The thermally-conducting layer can in this connection be in direct mechanical or, as the case may be, physical contact with the active layer. For example it can have been applied to the active layer. Heat produced in the active layer can thereby be ducted particularly efficiently from the active layer into other regions of the organic light-emitting device. Heat distribution in the active layer will furthermore be homogenized particularly efficiently. For example ageing processes in the active layer will consequently be homogenous in nature so that the organic light-emitting device's luminance characteristics will remain substantially homogeneous even when the the active layer undergoes ageing.
"The thermally-conducting layer (206) is in various embodiment variants located in a radiation-decoupling path of the electroluminescent radiation. The thermally-conducting layer therein preferably exhibits a sufficiently high degree of transparency for the electroluminescent radiation. Thus thermal homogenizing will be achieved specifically in a region in which the organic light-emitting device's luminance characteristics are produced or, as the case may be, substantially influenced.
"In many embodiment variants the thermally-conducting layer extends to an outer side of the device in order to dissipate the heat particularly well. In other embodiment variants the thermally-conducting layer is coupled to a heat sink, for example a cooling body. The heat is in some embodiment variants only distributed evenly inside the device to achieve even, which is to say homogeneous temperature distribution.
"The thermally-conducting layer therein has in some embodiment variants a multiplicity of separate partial regions. Said partial regions can be at any suitable locations inside the organic light-emitting device. It will thus be possible to obtain desired temperature distribution while the device is under a thermal load.
"In some embodiment variants the organic light-emitting device has an anode layer and the thermally-conducting layer is provided as an intermediate layer in the anode layer. That is particularly advantageous because the anode side frequently has a transparent metal oxide as layer material. Transparent metal oxides often have low thermal conductivity which is improved by the intermediate layer.
"In some embodiments of said variants the thermally-conducting layer is therein provided as a multiplicity of intermediate layers in the anode layer.
"In some embodiment variants the organic light-emitting device has an organic functional layer having the active layer. The thermally-conducting layer is provided as an intermediate layer in the organic functional layer. Said embodiment variants are particularly advantageous because heat is thereby dissipated from the organic light-emitting device's regions in which heat is frequently generated. Electromagnetic radiation is generated in the active layer by electroluminscence. That takes place through the recombination of electron-hole pairs (excitons) and their relaxation. Relaxation can, though, take place also by way of processes other than the emission of electromagnetic radiation, for example through quenching, during which heat is produced. However, even though undesired, those effects can never be totally suppressed. As regards heat dissipation, what is furthermore achieved by the thermally-conducting layer in the organic functional layer is that specifically the sensitive organic materials can be cooled particularly well by the structure of the cited embodiment variants; what, though, is at least achieved by the thermally-conducting layer is even distribution of the thermal energy and hence even thermal loading of the organic functional layer.
"In some embodiments of said variants the thermally-conducting layer is provided as a multiplicity of intermediate layers in the organic functional layer.
"In some embodiment variants the organic light-emitting device has a cathode layer that is covered by the thermally-conducting layer. That structure makes particularly good and hence also effective thermal decoupling possible since frequently no radiation is decoupled via the cathode layer. That applies all the more when the cathode layer has a metal, a metal alloy, or metal layers and hence likewise relatively good thermal conductors.
"In some embodiment variants the thermally-conducting layer is located between the anode layer and organic functional layer. The thermally-conducting layer can hence be provided in the organic light-emitting device with no major modifications to existing production processes. That arrangement furthermore offers the advantage that heat dissipating will be improved specifically at a location where very poor temperature equalizing otherwise takes place. In some embodiments the thermally-conducting layer extends in the form of separate strips on a boundary area between the anode layer and organic functional layer so that optical decoupling via the anode side will be affected as little as possible. In some embodiments the thermally-conducting layer extends like a network on the boundary area between the anode layer and organic functional layer."
For more information, see this patent: Baisl, Richard. Organic Light-Emitting Device with Homogeneous Temperature Distribution. U.S. Patent Number 8629603, filed
Keywords for this news article include: Electronics, Electromagnet,
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