Abstract:
A light-emission device with a two-dimensional OLED element and an encapsulation element for protecting the OLED element. The light-emission device furthermore has a support, on which the OLED element is arranged in such a way that the encapsulation element points toward the support, and an electrical conductor element for an electrical connection between the support and the OLED element. wherein the electrical conductor element is elastic in a normal direction to the OLED element. By way of example, the conductor element can be helical. As a result of the elastic property thereof, the conductor element can absorb mechanical tension while ensuring reliable electrical contacting. Hence, this can reduce or even avoid the risk of the electrical connection between the support and the OLED element being disadvantageously influenced or impaired by forces which can occur when handling the light-emission device or which can be generated by temperature variations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of PCT Application No. PCT/EP2013/056897 filed on Apr. 2, 2013, which claims priority to German Patent Application No. 10 2012 205 625.4 filed on Apr. 5, 2012, the disclosures of which are incorporated in their entirety by reference herein. 
     TECHNICAL FIELD 
     The invention relates to a light-emission device with a two-dimensional OLED element (OLED: organic light-emitting diode) and an encapsulation element for protecting the OLED element. 
     BACKGROUND 
     On the basis of the OLED, novel light-emission devices or luminous elements can be realized. As two-dimensional luminous bodies that have a moderate luminance in comparison with inorganic LEDs (LED: light-emitting diode), OLEDs are particularly suitable for the production of two-dimensional diffuse light sources, such as for example luminous panels. Large-area, diffusely radiating light sources are desired in particular for general lighting applications, with OLEDs offering promising future potential for these application areas. As a consequence of the thin-film technology used in the production of OLEDs, it can also become possible to realize flexible luminous bodies that open up previously unknown possibilities for lighting rooms. 
     SUMMARY 
     An OLED element has two two-dimensionally formed electrodes, between which an “active” or organic layer of organic material is embedded. When a suitable voltage is applied to it or it is impressed with a suitable current, the active organic layer emits light. At least one of the two electrodes is in this case transparent, in order to make it possible for the light generated to be given off through this electrode to the outside. 
     For practical applications, in particular general lighting applications, the most uniformly possible light-emitting OLEDs, i.e. OLEDs that give off light as uniformly as possible by way of their radiating surface, are desired or required. By analogy with inorganic LEDs, OLEDs are current-operated components. This means that the luminance of an OLED is correlated with the current flowing through the light-emitting, active layer of the OLED. To realize uniformly light-emitting OLEDs, a luminance that is homogeneous over the two-dimensional extent of the OLED within the light-emitting layer is therefore required. However, this is problematic in the production of correspondingly large-area OLED elements. 
     For example, the transparent electrode may be realized by means of a transparent conductive oxide (TCO: transparent conductive oxide) or by means of transparent metal layers. The electrical conductivity of these transparent electrode materials is comparatively low, and consequently the voltage drop within the electrode is not negligible. On account of the current/voltage characteristic of an OLED, small differences in voltage within an electrode surface area have the effect of undesired perceptible differences in brightness. 
     In a specific example, in the case of an OLED element, indium-tin oxide (ITO: indium tin oxide) with a layer thickness of about 100 nm may be used as the transparent electrode, the ITO layer being applied to a substrate, in particular a glass substrate, and possibly serving as an anode. This is followed by the organic or active layer, which may comprise multiple sub-layers, with a layer thickness of altogether about 100 to 200 nm. Subsequently, a metallic cathode, which may for example comprise aluminum, is applied with a layer thickness of about 100 to 500 nm in thickness. In the case of correspondingly large-area OLED elements, the highly ohmic resistance of the ITO layer may achieve values of 10 or 20 ohms/square. It must be borne in mind that, with respect to its overall two-dimensional form, electrical contacting of the ITO layer is only possible from the peripheral region. 
     For the protection of an OLED element constructed in this way, it is also known to provide an encapsulation element, which is arranged covering the two electrodes and the organic intermediate layer and which extends at the lateral peripheries up to the glass substrate. 
     Apart from a low effective sheet resistance of the transparent electrode, a feed-in of current that is as uniform as possible is therefore also particularly necessary for a uniformly radiating OLED. Thus, in order to improve the homogeneity of the luminance distribution of the radiated light over the two-dimensional extent of the OLED, often multiple feeding-in points for the operating current are provided in a distributed manner over the lateral peripheral region of the OLED element, i.e. there are peripherally on one or both electrodes multiple electrical contacting regions by way of which the electrodes are electrically contacted. 
     Typically, contacting of the OLED element that is as symmetrical as possible is aimed for here. In particular, the anode generally has multiple contacting regions, since it generally has a lower conductivity than the cathode. However, it may also be provided that the cathode or both electrodes, the anode and the cathode, have multiple contacting regions by way of which the operating current flows in and away. 
     The invention is based on the object of providing a corresponding improved light-emission device. In particular, the light-emission device is intended to have improved mechanical and electrical properties. 
     This object is achieved with the subject matter mentioned in the independent claim. Particular embodiments of the invention are specified in the dependent claims. 
     According to the invention, a light-emission device that has a two-dimensional OLED element and an encapsulation element for protecting the OLED element is provided. Furthermore, the light-emission device has a support, on which the OLED element is arranged in such a way that the encapsulation element faces the support, and an electrical conductor element for an electrical connection between the support and the OLED element, the electrical conductor element being elastic in a direction perpendicular to the OLED element. 
     Use of the support has the particularly suitable effect of allowing current to be supplied to the OLED element at multiple lateral peripheral areas of the OLED element. As a result, a particularly homogeneous supply of current to the OLED element is made possible. In this case, the conductor element can, on account of its elastic property, absorb mechanical stresses while ensuring reliable electrical contacting. This makes it possible to reduce or even avoid the risk of the electrical connection between the support and the OLED element being disadvantageously influenced or impaired by forces that can occur when handling the light-emission device or can be produced by temperature fluctuations. In this way, the electrical and mechanical properties of the light-emission device are improved. 
     The OLED element advantageously has an electrical contact region for a first electrode of the OLED element that is elongate—when considered perpendicularly to the OLED element—, the electrical conductor element being connected to the contact region in an electrically conducting manner. In this way it can be achieved that the voltage drop at the contact region is particularly small and the current input is particularly homogeneous. In this way, a particularly homogeneous light emission of the OLED element is consequently made possible. In this case, the electrical contact region is also preferably arranged alongside the encapsulation element—when considered perpendicularly to the OLED element. In this way, the OLED element can be suitably designed such that it has a particularly large light-emitting surface area. 
     Furthermore, at least in first approximation, the encapsulation element is preferably rectangular—when considered perpendicularly to the OLED element—, so that it accordingly has four sides, the electrical contact region being formed in such a way that, along one of the four sides, it extends over at least one quarter, preferably over at least one third, of the length of this one side. In this way, a particularly homogeneous current input into the OLED element is furthermore made possible. 
     Also advantageously with respect to a particularly homogeneous current input, the light-emission device also has at least one further contact region for the first electrode that is designed and arranged in a way analogous to the first-mentioned contact region for the first electrode. 
     Correspondingly advantageously, the light-emission device also has a second electrical contact region for a second electrode of the OLED element, the second contact region being designed and arranged in a way analogous to the contact region for the first electrode. 
     A particularly good electrical connection between the support and the OLED element can be achieved if the electrical conductor element consists of metal or is metallized. The electrical conductor element preferably consists of a metal foil or a metal wire or a flexible printed circuit board. In particular, the electrical conductor element may consist of copper or aluminum or an alloy from or with copper and/or aluminum. 
     The electrical conductor element is advantageously electrically connected to the contact region for a first electrode and/or to a support contact region formed on the support by way of at least one joining location, preferably by way of multiple joining locations. Furthermore, the at least one joining location is in this case formed by soldering or adhesive bonding, in particular with an anisotropic adhesive or a conductive adhesive. In this way, particularly reliable electrical contacting is made possible. 
     Particularly suitable elasticity of the electrical conductor element can be achieved if the conductor element is elongate and has a 180° bend in a portion along its length. In particular, the electrical conductor element may be spiral or undulating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail below on the basis of exemplary embodiments and with reference to the drawings, in which: 
         FIG. 1  shows a diagram of a cross section through a light-emission device according to the invention as provided by a first exemplary embodiment, 
         FIG. 2  shows a diagram of a view of a rear side of the OLED element of the light-emission device, 
         FIG. 3  shows a diagram, corresponding to  FIG. 1 , in relation to a second exemplary embodiment and 
         FIG. 4  shows a corresponding diagram in relation to a third exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , a diagram of a cross section through a light-emission device according to the invention is shown. The light-emission device comprises an OLED element, an encapsulation element  15  and a support  20 . 
     In  FIG. 2 , a view of the OLED element and the encapsulation element  15 —without the support  20 —is shown. In addition,  FIG. 2  is used as a basis for discussing the OLED element and the encapsulation element  15 . 
     The OLED element is formed in such a way that it is two-dimensional overall. It therefore has a significantly greater extent in a first direction x and in a second direction y, oriented at right angles to the first direction, than in a third direction z, which is oriented at right angles to the first direction x and at right angles to the second direction y. For example, it may be provided that the extent of the OLED element in the direction z is less than one tenth of its extent in the direction x and/or its extent in the direction y. 
     The two-dimensional form of the OLED element accordingly allows the definition of a plane in which the OLED element has a maximum projecting surface area—in the example shown therefore a plane that is defined by the directions x and y. In  FIG. 1  there is shown in this sense a view of the OLED element perpendicularly to this plane or in (or counter to) the direction z. This direction is also referred to here as “perpendicular to the OLED element” or “perpendicular” for short. 
     As is the case in the example shown, the extent of the OLED element in the direction x may be equal to its extent in the direction y, so that, when considered “perpendicularly”, it has a square form. It may, however, also be designed such that, when correspondingly considered, it has generally a rectangular form or some other form, for example a hexagonal form. 
     The OLED element may be of such a size that—when considered perpendicularly—it has a surface area of at least 1 cm2, preferably of at least 10 cm2, for example at least 20 cm2. 
     The OLED element may be constructed in the way described at the beginning. In particular, it may accordingly have four layers, to be precise—from the “rear” to the “front” with reference to the diagram of FIG.  1 —a substrate  10 , for example a glass substrate, a first electrode arranged thereupon, an organic layer arranged on the first electrode and a second electrode arranged on the organic layer. 
     The encapsulation element  15  may be designed in particular in such a way that it extends over that electrode that lies opposite the substrate  10  with reference to the organic layer. The encapsulation element  15  may for example be formed from glass. It may be formed by a sheet. 
     As shown by way of example in  FIG. 2 , the encapsulation element  15  preferably has—when considered perpendicularly—a smaller surface area than the substrate  10 , it being located completely within the perpendicular projection of the substrate  10 . In this way, it can extend at all its lateral peripheries up to the substrate  10 , and thus protect the electrodes and the organic layer particularly well from environmental influences. 
     Accordingly, in the view outlined in  FIG. 1 , the two electrodes and the organic layer are covered by the encapsulation element  15 . 
     The OLED element also has an electrical contact region  11  for a first electrode, for example for the anode. When considered perpendicularly, the contact region  11  is preferably elongate. In this way it can be achieved that the current input into the OLED element for operating the OLED element is particularly uniform and, as a consequence, the light emission of the OLED element is particularly homogeneous. Furthermore, the elongate design allows contacting of the first electrode to be achieved with a particularly low transfer resistance. 
     As is the case in the example shown, the contact region  11  may be arranged alongside the encapsulation element  15 —when seen perpendicularly to the OLED element. In particular, —when considered perpendicularly—the contact region  11  is arranged within the perpendicular projection of the substrate  10  but outside the perpendicular projection of the encapsulation element  15 . When considered in this way, the contact region  11  preferably directly borders the encapsulation element  15  with one of its two longitudinal sides. Given a robust design of the OLED element, this design allows a particularly large light-emitting surface area of the OLED element to be achieved. 
     When considered perpendicularly, the encapsulation element  15  preferably has the same form as the substrate  10 , but with a slightly smaller surface area. Thus, in particular with correspondingly concentric alignment of these two parts, a peripheral region on which the contact region  11  is arranged can be formed on the substrate  10 . 
     As is the case in the example shown, the encapsulation element  15  may accordingly be rectangular, at least in first approximation, so that it accordingly has four sides S 1 , S 2 , S 3 , S 4 . A particularly good current input can be achieved if the contact region  11  is formed in such a way that, along one of the four sides, here the side S 1 , it extends over almost half the length  1  of this side S 1 . For example, the design may be such that the contact region  11  extends over at least one quarter, preferably over at least one third, of the length  1 . 
     The OLED element advantageously also has at least one further contact region  11 ′ for the first electrode, which is designed and arranged in a way analogous to the first-mentioned contact region  11  for the first electrode, in particular is arranged analogously on at least one further side of the four sides S 2 , S 3 , S 4 . In particular, a correspondingly designed further contact region  11 ′ for the first electrode may be respectively arranged on each of the three further sides S 2 , S 3 , S 4 . 
     For the second electrode or the cathode, the design is preferably analogous with respect to at least one contact region  12  or corresponding further contact regions  12 ′. In this case, the contact regions  11 ,  11 ′ for the first electrode are preferably arranged such that they alternate with the contact regions  12 ,  12 ′ for the second electrode, in particular running around the periphery of the encapsulation element  15 . 
     As shown, a contact region  11 ,  11 ′ for the first electrode and a contact region  12 ,  12 ′ for the second electrode are advantageously formed respectively on each of the four sides S 1 , S 2 , S 3 , S 4 . If in this case—as shown by way of example in FIG.  2 —the design is also such that a contact region  11 ,  11 ′ of the first electrode and a contact region  12 ,  12 ′ of the second electrode respectively lie precisely opposite in each case on two opposing sides of the four sides S 1 , S 2 , S 3 , S 4 , a particularly homogeneous current input into the OLED element can be realized. 
     A corresponding design with respect to the contact regions for the two electrodes may for example also be provided in the case of a corresponding hexagonal form of the encapsulation element  15  or of the OLED element. 
     As indicated in  FIG. 2  by I-I, the section shown in  FIG. 1  extends perpendicularly to the direction x and thereby runs through the contact region  11 . The substrate  10  of the OLED element can be seen in  FIG. 2 , but the further individual layers of the OLED element are not represented for reasons of overall clarity. Furthermore, the contact region  11  and the encapsulation element  15  can be seen. 
     The OLED element is therefore arranged on the support  20  such that the encapsulation element  15  faces the support  20 . The support  20  may likewise be of a two-dimensional design and in that case be arranged such that it is aligned parallel to the OLED element. The support  20  may in this case be for example a support plate. 
     The support  20  is preferably designed in such a way that, when the OLED element is viewed perpendicularly, it has a surface area that is at least as large as the surface area of the encapsulation element  15 , preferably at least as large as the surface area of the OLED element, the relative arrangement between the support  20  and the OLED element being such that the perpendicular projection of the encapsulation element  15 , preferably of the OLED element, lies completely within the perpendicular projection of the support  20 , or at most is congruent with the latter. This makes it possible that, starting from the support  20 , the feed-in of current is brought up to the OLED elements from all lateral peripheral regions thereof, so that the feed-in of current is particularly uniform. 
     The support  20  may be transparent or not transparent. For example, the support  20  may consist of glass, PMMA (polymethylmethacrylate), PET (polyethylene terephthalate), metal or plastic. For example, the support  20  may be formed by a PET film. 
     The support  20  may have a surface  25 , which faces the OLED element and on which conductor tracks are applied for supplying current to the OLED element, or be correspondingly formed as a PCB (printed circuit board). In particular, on the support  20 , preferably on the surface  25 , there may be formed a support contact region  21 , which is designed or intended for electrically conducting connection to the OLED element and which is accordingly electrically connected for example to one of the conductor tracks. The support contact region  21  is preferably also elongate, preferably in a way analogous to the contact region  11  for the first electrode. 
     In particular when a film or flexible PCB is used, the OLED element may be flexibly designed, so that the light-emission device as a whole can be flexibly designed. 
     Furthermore, the light-emission device has an electrical conductor element  31  for an electrical connection between the support  20  and the OLED element  10 . The electrical conductor element  31  may be accordingly electrically connected on the side of the support  20  in particular to the support contact region  21  and on the side of the OLED element to the contact region  11 . 
     The electrical conductor element  31  is designed in such a way that it is elastic in a direction perpendicular to the OLED element  10 —here in the direction z. In this way it is achieved that the electrical contact between the conductor element  31  and the OLED element on the one hand and the support  20  on the other hand is reliably retained even in the event of mechanical loading of the light-emission device or stress caused by temperature fluctuations. 
     In the first exemplary embodiment shown here, the electrical conductor element  31  is spirally designed to achieve the elastic property, in particular—as shown —, such that the conductor element  31  extends along a cylindrical, preferably circular-cylindrical spiral. The orientation of the conductor element  31  is in this case preferably such that the axis A—indicated in  FIG. 1  by dotted lines—of the spiral or of the conductor element  31  is oriented parallel to the longitudinal axis of the contact region  11  or to the side S 1  of the encapsulation element  15 . The diameter of the conductor element  31  perpendicularly to the axis A thereof corresponds in this case at least substantially to the distance between the contact region  11  and the support  20 , so that a contact location on the contact region  11  and a contact location on the support  20  are respectively formed within a turn of the spiral. 
     The conductor element  31  preferably has multiple turns, for example at least three turns, so that at least three contact locations are respectively formed on the contact region  11  on the one hand and the support  20  on the other hand. In the example shown, the conductor element  31  has six turns, so that six contact locations K 1  . . . K 6  are formed on the contact region  11  and six contact locations T 1  . . . T 6  are formed on the support  20  or on the support contact region  21 . 
     To achieve a particularly homogeneous supply of current, the conductor element  31  in this case preferably extends over at least 80% of the length of the contact region  11 . 
     The conductor element  31  is preferably metallic. The contact locations K 1  . . . K 6  are preferably formed by a joining technique or are joining locations. The joining locations between the conductor element  31  and the contact region  11  are formed for example by adhesive bonding, in particular with a conductive adhesive or an anisotropic adhesive. The joining locations between the conductor element  31  and the support  20  or the support contact region  21  are formed for example by adhesive bonding, in particular with a conductive adhesive or an anisotropic adhesive, or by soldering. 
     The combination of the solid connection by means of a joining technique with the intrinsically flexible conductor element  31  makes it possible particularly suitably for absorbing mechanical stresses, such as may occur when there are changes in temperature or under mechanical loading of the light-emission device. The current transmission is in this case reliably ensured. The risk of damage to the solid connecting contacts is prevented or at least significantly reduced. 
     The light-emission device preferably has a correspondingly designed further conductor element for each further contact region  11 ′ for the first electrode. 
     The electrical connection of the second electrode or cathode is preferably provided in an analogous way. 
     In particular, the design of the light-emission device is preferably analogous on all four sides S 1 , S 2 , S 3 , S 4 . 
     In this way, a multi-sided feed-in of the currents into the OLED element  10  is realized. In the case of such a multi-sided feed-in of the currents into the OLED element  10 , the “individual connections” for the anode and cathode respectively are preferably brought together by way of the support  20 . In this case, an additional series resistor or additional conductor track length may be used if need be to set the current conduction such that the organic layer of the OLED element is supplied with current in such a way that particularly homogeneous illumination of the surface area or emission of light can be achieved. 
     A possibly existing different current profile on the support  20  can be compensated by a correspondingly chosen, suitable dimensioning of the supply lines to the individual connection areas or contacting regions of the support  20 , and a particularly good homogeneity of the light of the OLED element can thus be achieved. 
     The metallic conductor element  31  also makes it possible for the current be directed very well in the transverse direction or in the direction y; this would not be ensured by contact pads alone, on account of the limited transverse conductivity. 
     In  FIG. 3 , a diagram corresponding to  FIG. 1  in relation to a second exemplary embodiment is shown. Unless otherwise mentioned, the statements made with respect to the first exemplary embodiment also apply analogously to the second exemplary embodiment. The designations are used analogously. 
     In the case of the second exemplary embodiment, the electrical conductor element, here denoted by  32 , consists of a thin, highly conductive metal foil or a metal wire or a flexible printed circuit board, for example of copper, aluminum or an alloy from or with these materials. The feed-in of current on the OLED element  10  takes place in this way two-dimensionally, in particular by a contact between the conductor element  32  and the contacting region  11  that is formed longitudinally along the contacting region  11 . The contact is preferably in turn formed by a joining technique, for example by means of conductive adhesive or anisotropic adhesive, so that an elongate joining location is formed. The joining location is in this case advantageously made to be of such a size that it extends over at least 80% of the length of the contact region  11 . 
     The contacting region  11  may be formed for example by thin-film or thick-film technology. The comparatively low conductivity of the contacting region  11  can be increased by a corresponding joining technique. 
     On the side of the support  20 , the connection may in turn be realized likewise by means of a corresponding joining technique (for example a soldering technique, conductive adhesive, anisotropic adhesive). 
     The electrical connection of the cathode may in turn be formed in an analogous way. 
     The conductor element  32  may for example be metallic or metallized. 
     The conductor element  32  according to the second exemplary embodiment also makes possible particularly good compensation of thermally induced or mechanical stresses that would lead to a failure of the contact connection in the case of a corresponding rigid connection. 
     In  FIG. 4 , a diagram corresponding to  FIG. 1  in relation to a third exemplary embodiment is shown. Unless otherwise mentioned, the above statements also apply analogously to the third exemplary embodiment. The designations are in turn used analogously. 
     The electrical conductor element, here denoted by  33 , is designed according to the third exemplary embodiment in an undulating form, so that—as in the case of the first exemplary embodiment—multiple contact locations, here for example three contact locations K 1  . . . K 3  are formed on the contact region  11  and multiple contact locations, here by way of example four contact locations T 1  . . . T 4 , are formed on the support  20  or on the support contact region  21 . 
     “Distributed contacting”, which can compensate very well for thermal loadings or mechanical stresses and makes possible a connection that is stable in the long term, is in turn made possible in this way. 
     It can be stated more generally with respect to all of the exemplary embodiments that the conductor element  31 ,  32 ,  33  is preferably elongate to achieve its elastic property and thereby has a 180° bend in a portion along its length. In particular, the alignment of the conductor element  31 ,  32 ,  33  is in this case such that the 180° bend is formed in a plane oriented at right angles to the two-dimensional OLED element. In the case of the first exemplary embodiment, the 180° bend is formed in a plane defined by the direction x and the direction z, in the case of the second exemplary embodiment in a plane defined by the direction y and the direction z. 
     The multiple contact locations or joining locations in the case of the first and third exemplary embodiments or a correspondingly elongate joining location in the case of the second exemplary embodiment allows the current input into the OLED element to be realized with particularly little loss. 
     The OLED element and/or the support  20  and/or contact areas may be made transparent or opaque. 
     It may also be provided that multiple OLED elements are arranged correspondingly on the support  20 . 
     The light-emission device according to the invention is distinguished in particular by the following properties: 
     robust connection of the OLED element to the support 
     particularly homogeneous current distribution within the OLED element to achieve a particularly homogeneous emission of light 
     low transfer resistances between the electrical conductor element and the OLED element 
     high efficiency of the light-emission device