WO2012127400A1

WO2012127400A1 - Oled with a shunting layer

Info

Publication number: WO2012127400A1
Application number: PCT/IB2012/051295
Authority: WO
Inventors: Florent Monestier
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2011-03-21
Filing date: 2012-03-19
Publication date: 2012-09-27

Abstract

The invention relates to the field of organic electroluminescent light-emitting devices (OLEDs) providing a large organic electroluminescent bottom emitting device with a homogeneous luminance over the entire emitting area, where the OLED device has a good lifetime behavior and can be produced with a high yield. The OLED device according to the present invention comprises a transparent substrate (2) coated with a transparent conductive layer as a bottom electrode (3), one or more electroluminescent layer stacks (4) deposited on top of the bottom electrode (3), each comprising an organic layer stack (41) with at least one organic light emitting layer, a reflective top electrode (42) on top of the organic layer stack (41) and an insulating layer (43) fully covering at least the top electrode (42), where the organic layer stack (41) is suitably shaped to prevent the top electrode (42) from contacting the bottom electrode (3) directly, wherein the bottom electrode (3) comprises first areas (31) covered by the one or more electroluminescent layer stacks (4) and at least one second area (32) not covered by the electroluminescent layer stack (4), wherein an electrically conductive shunting layer (5) is deposited on top of the second areas (32) of the bottom electrode (3) and at least partly on top of the insulating layer (43) to distribute a driving current across the bottom electrode (3) by providing a second conductive path (SCP) at least between the second areas (32). The invention further relates to a method for manufacturing such an OLED device (1).

Description

OLED WITH A SHUNTING LAYER

FIELD OF THE INVENTION

The invention relates to the field of organic electroluminescent light-emitting devices (OLEDs) with homogeneous brightness and a method to manufacture such OLEDs. BACKGROUND OF THE INVENTION

Standard organic light-emitting devices (OLEDs) nowadays comprise an organic layer stack arranged between two electrodes deposited on top of a substrate, typically a glass substrate. Two different types of OLEDs can be distinguished with respect to the direction of light emission. In so-called top emitters the light leaves the OLED device through a transparent top electrode and a transparent cover lid while a bottom electrode and/or the substrate is reflective. The cover lid is mandatory in order to prevent the environment, especially moisture and oxygen, from reaching the organic layer stack. In the so-called bottom emitters, the light leaves the OLED device through a transparent bottom electrode (usually the anode) and a transparent substrate (e.g. glass) while the second electrode (typically the cathode) is reflective. From the production point of view, bottom emitting OLED devices are preferred.

The bottom emitting OLED devices use common transparent thin- film bottom electrodes that exhibit a high sheet resistance of equal to or more than 0.1 Ω/square, where the term "square" denotes the electrode area. The resistance especially of the bottom electrode imposes limits on the maximum size of a light-emitting area if a homogeneous luminance is to be obtained over the entire emitting area. For current material systems, this maximum area with homogeneous brightness is of the order of 4 times 4 centimeters. The electrical sheet resistance of the transparent electrode, usually made of indium-tin-oxide (ITO), is much larger than the sheet resistance of the reflective electrode typically made of aluminum. Furthermore the optimization of the ITO anode is compromised by optical and electrical requirements. Moreover, thin film technology is not sufficient for large-area production of sufficiently thick ITO-layers to improve the electrical properties of such thick layer, which would be expensive and time consuming. In bottom emitters with transparent ITO electrodes deposited on top of glass substrates, grid lines made of a highly conductive material might be deposited on top of the transparent anode to improve the current distribution across the ITO layer. However, the local grid lines introduce morphology into the subsequent layer stack, which might result in flashovers between both electrodes due to sharp edges of the grid lines. The grid lines have to be coated with an insulating material to obtain an OLED device with a sufficient lifetime behavior. However, the coated grid lines on one hand result in a non-active area for generating light, which is visible to the outside as black lines and on the other hand result in a reduced overall brightness of such OLED device due to the decreased active light-emitting layer.

The international patent application WO 2008/135902 Al discloses an OLED device as a top emitter with a reflective electrode deposited on top of a substrate and with a transparent conductive electrode on top of the layer stack. The transparent electrode might be made of ITO. On top of the transparent conductive electrode a non-uniformly arranged grid is deposited in order to avoid high voltage problems as present in OLED devices with grids on the bottom electrode as described previously. The grid is designed non-uniformly to minimize inhomogeneity of the current distribution in the emissive layer underneath. However, the grid lines are still within the light-emitting area resulting in visible black lines, which is not desired. This solution is not applicable to bottom emitting OLEDs since the transparent electrode having a high sheet resistance is arranged between substrate and organic layers in a bottom emitting OLED.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a large organic electroluminescent bottom emitting device with a homogeneous luminance over the entire emitting area, where the OLED device has a good lifetime behavior and can be produced with a high yield.

This object is achieved by an organic electroluminescent light-emitting device comprising a transparent substrate coated with a transparent conductive layer as a bottom electrode, one or more electroluminescent layer stacks deposited on top of the bottom electrode, each comprising an organic layer stack with at least one organic light emitting layer, a reflective top electrode on top of the organic layer stack and an insulating layer on top of the top electrode suitably shaped to prevent a direct electrical contact between the top electrode and the bottom electrode, wherein the bottom electrode comprises first areas covered by the one or more electroluminescent layer stacks and at least one second area not covered by the electroluminescent layer stack, wherein an electrically conductive shunting layer is deposited on top of the second areas of the bottom electrode and at least partly on top of the insulating layer to distribute a driving current across the bottom electrode by providing a second conductive path at least between and/or along the second areas and the insulating layer is further shaped to prevent a direct electrical contact between the top electrode and the shunting layer. The OLED device according to the present invention provides a bottom emitting device with a homogeneous luminance over the entire emitting area, where the OLED device has a good lifetime behavior and can be produced with a high yield. Common indium-tin-oxide (ITO) covered glass substrates can still be used to manufacture the OLED device without any required modification. The shunting lines present at the backside (non light-emitting side) of the OLED device maintains the flat topology of the electroluminescent layer stack preventing any field enhancement effects due to sharp edges as a result of a non- flat topology leading to a high production yield. The present OLED device is therefore a cheap and reliable solution, where the required manufacturing steps can be executed easily.

The organic electroluminescent device may utilize organic small molecules or polymers to produce light, when a driving voltage of a few volts is applied to the

electroluminescent layer stack via the top and bottom electrodes. Accordingly, OLEDs may be referred to as small molecule organic light emitting devices (SMOLEDs) or polymer light emitting devices (PLEDs). However, SMOLEDS are preferred because of their better light emission performance. OLEDs emitting the light through the substrate are denoted as bottom-emitter. The substrate of bottom emitters is made of a transparent material, e.g. glass or plastic, having two essentially parallel surfaces. The term "transparent" denotes layers or materials, which major part (area) is transparent. The electroluminescent layer stack comprises at least two electrodes with the bottom electrode typically as the anode and the top electrode typically as the cathode and with an organic layer stack in between. In some embodiments, there might be a plurality of organic layers arranged between the electrodes, such as hole transport layer, electron transport layer, hole blocking layers, electron blocking layers, one or more light emitting layers, e.g. comprising a host material with embedded light emitting molecules. A large number of different electroluminescent layer stacks comprising a different number/type of layers is known to skilled people, which are able to choose a suitable electroluminescent layer stack in dependence on the desired application.

Alternatively organic layer stacks may comprise only one organic layer able to emit light. In bottom-emitters, the bottom electrode deposited on top of the substrate is typically made of a transparent conductive oxide material, commonly indium-tin-oxide (ITO). Alternative suitable transparent conductive oxides are doped zinc oxide or poly(3,4- ethylenedioxythiophene)poly(styrenesulfonate), usually referred to as Pedo PPS. The top electrode as a reflective layer is a metal layer typically made of aluminum with thicknesses of 20 - 150nm. The organic layer stack and/or the top electrode are suitably shaped to prevent the top electrode from contacting the bottom electrode directly.

The electroluminescent layer stack might be covered by a cover lid in order to prevent moisture or oxygen penetrating into the organic light-emitting layer stack to provide OLEDs with a sufficient life-time. The cover lid is made of any suitable rigid material providing a sufficient barrier against diffusion of moisture and/or oxygen into the

encapsulated volume between cover lid and substrate. The cover lid is sealed on top of the substrate by applying a suitable sealing material being sufficiently gas tight, at least against moisture and oxygen, e.g. glass frit (non conductive material) or conductive sealing material (e.g. epoxy glue with conductive filler). The term "sealed on top of the substrate" denotes a tight connection between cover lid and substrate. In case of substrates with additional layers (e.g. contact pads for first and/or second electrodes) on top, the cover lid is sealed to the substrate across theses layers. The cover lid has an inner and outer side, where the inner side denotes the side of the cover lid facing towards the electroluminescent layer stacks. The outer side is correspondingly the other side of the cover lid. The shape of the cover lid is adapted to provide a gap between the inner side of the cover lid and the shunting layer. The gap shall prevent any mechanical impact to the cover lid from the outside of the OLED device reaching the electroluminescent layers. A getter material might be arranged inside the gap, typically attached to the inner side of the cover lid. The gap between cover lid and

electroluminescent layer stack could have dimensions up to a few millimeters. Typically the gap is filled with gas, e.g. dry nitrogen. Alternatively the gap might be filled with dry ambient air.

The insulating layer can be made of any material with a resistance sufficiently high to prevent a current flow between the top and bottom electrodes and a current flow between the shunting layer and the top electrode via the insulating material, which is capable to degrade the performance of the OLED device. The suitably shaped insulating layer denotes a layer deposited at least partly on top of the top electrode enclosing at least the edges of top electrode and organic layer stack in order to prevent a direct electrical contact between the top electrode and the bottom electrode. Additionally the insulation layer has to cover at least the area of the top electrode covered by the shunting layer to prevent a direct electrical contact between the top electrode and the shunting layer. Preferably the insulation layer also covers areas of the organic layer stack covered by the shunting layer to improve the measures against shorts between top electrode and bottom electrode or shunting layer. To be able to provide electrical contacts to the top electrode in order to connect the top electrode to a power source, the intended contact areas (contact pad) of the top electrode should be not covered by the insulation layer. In case of preparing an insulation layer fully covering the top electrode, the contact areas for contacting the top electrode to the power source have to be cleaned after deposition of the insulation layer. As an example this cleaning step could be done be laser ablation of small areas of the insulation layer not required for short prevention purposes, e.g. at areas of the top electrode outside the electroluminescent layer stack such as the contact pad. Furthermore the organic layer stack has to be suitably shaped to prevent the top electrode from contacting the bottom electrode. Here the organic layer stack preferably covers an area of the bottom electrode larger than the area, which is covered by the top electrode. The shape of the organic layer stack subsequently forms a rim around the entire area covered by the top electrode. The area of the bottom electrode covered by the organic layer stack is at least a major part of the first area. The areas covered by the organic layer stack are the light emitting areas of the OLED device. In some embodiments, where the insulating layer fully covers the top electrode, but the rim of the organic layer stack is large enough to let the insulating layer extending only into the rim without covering the edge of the organic layer stack, the first area of the electroluminescent layer stack is equal to the area of the bottom electrode covered by the organic layer stack. In other embodiments, the insulating layer may extend to the area of the bottom electrode around the organic layer stack, than the first area covering the bottom electrode is defined by the area covered by the insulating layer. Subsequently the second areas are the areas of the bottom electrode not covered by the organic layer stack and not covered by the insulating layer stack, respectively. The OLED device according to the present invention may comprise one second area, which may extend in small connected lines via the bottom electrode or may comprise multiple separate second areas, which are connected together via the shunting layer. In an embodiment the insulating layer covers the edges of the organic layer stack and/or the top electrode with an overlap of at least 0.1 mm. The term overlap denotes the horizontal extension of the insulating layer beyond the edge of the other layers.

The shunting layer shall distribute the current across the bottom electrode by bypassing the bottom electrode between and/or along the second areas (providing a second conductive path). In case of small second areas arranged in an array of second areas, the second conductive path is preferably established at least between the second areas. In case of second areas shaped as long stripes, the second conductive path is mainly established along each of the second areas. In this case another conductive path connecting different stripe-like second areas is not mandatory but can be established additionally. Therefore the shunting layer is in an electrical contact to the bottom electrode via the second areas. The shunting layer should be made of a material with low resistance, e.g. metal, not to cause additional current losses within the shunting layer. Metal layers can be deposited easily and fast, e.g. with thermal evaporation or sputtering techniques. Preferred shunting layers are made of copper or aluminum having a very good electrical conductivity and correspondingly a very low resistance and a good adhesion with the bottom electrode. The shunting layer may also be made of a material with not such a high electrical conductivity but prepared as a thicker layer. The shunting layer might be prepared as a contiguous layer covering the second areas and major parts of the first areas or might be structured to obtain a certain shape. The shunting layer as a contiguous layer is preferred to achieve the best current distribution.

As an example, suitable materials for the insulating layer are photoresist materials such as AZ 1518, e.g. from Clariant, or HPR 504, e.g. from Fujifilm. Both photoresist materials enables deposition of photoresist layer of thicknesses up to 2 - 2.5 μιη with good adhesion properties. Other insulating layers could be utilized as a thin film encapsulation to encapsulate the OLED device. Such insulating layers comprise a layer stack of organic/inorganic layers, e.g. a layer stack of SiN-OCP-Si . These layer stacks could be deposited by mask patterning or patterned afterward by laser ablation. Also thick inorganic compounds like Lithium Fluoride (LiF) could be used for insulating layers. As an example a LiF layer can be easily deposited by thermal evaporation with a shadow mask. LiF layers with a thickness at least up to 100 nm are not conductive. Molybdenum dioxide (Mo02) or Tungstene oxyde (W0₃) are other alternative materials for isulating layers. People skilled in the art may apply other suitable photoresist materials for depositing the photoresist layer within the scope of the present invention.

In the present invention, the term "conductive" always denotes an electrically conductive material or component, even if the term "electrically" is not used. The term "insulating" denotes materials or layers having a high resistance or high sheet resistance resulting in preventing any current flow through this material, which is not negligible for the operation of the OLED device.

In an embodiment the bottom electrode comprises an outer rim with third areas not covered by the electroluminescent layer stack, where the shunting layer is in an electrical contact also to the third areas. The outer rim denotes the area of the bottom electrode which is not intended to be covered with an electroluminescent layer stack. The rim may be present on one, two, three or four sides of the bottom electrode. However, the non- covered third areas are only parts of such rim, e.g. one side of the rim, where the bottom electrode provides a contact pad for being connected to a power source. The third areas might be separated from the second areas or may be connected to the second areas.

In another embodiment a distance between adjacent second areas is less than 8 cm, preferably less than 6 cm, more preferably less than 5 cm, even more preferably less than 4 cm. The allowable distance between adjacent second areas to still obtain an essentially homogeneous brightness of the light emitting areas mainly depends on the sheet resistance of the transparent bottom electrode, but also on the conductivity of the organic layer stack allowing a current flow between the top and bottom electrodes corresponding to the efficiency of the organic layer stack. If the organic stack is more effiicient in terms of Cd/A, the current flowing between the top and bottom electrodes will be lower for a fixed luminance which will induce a lower drop voltage between shunting lines or second areas on the bottom electrode where the current is injected. Therefore, in case of more efficient organic stacks, the distances between second areas could be higher.

In another embodiment the size of the second area in one direction is below the threshold of visibility for human eyes. For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD (1.2 arc minute per line pair, or a 0.35 mm line pair, at 1 m). As an example, circular second areas are not visible for human eyes, if these areas have a diameter equal or below 0.35 mm. The same holds for rectangular second areas, where the width of the second areas is equal or below 0.35 mm. In case of OLED devices comprising one or more light emitting surfaces with a light scattering behavior, the size of non- visible second areas can even be larger.

In another embodiment the electroluminescent layer stacks are arranged suitable to provide a distance between adjacent top electrode layers of equal or less than 0.7 mm, preferably equal or less than 0.6 mm, more preferably equal or less than 0.5 mm. To minimize the risk of having any direct electrical contact between both electrodes of one electroluminescent layer stack or between the top electrode and the shunting layer, the distance between adjacent top electrodes should be larger than the size of the second areas between the adjacent top electrodes. The distances given above allow the deposition of an insulating layer with sufficient insulation properties between top electrodes and shunting layer.

In another embodiment the shunting layer is prepared as a contiguous layer covering all second areas and at least all areas between the second areas. The shunting layer according to this embodiment connects all second areas and provides a homogenous current distribution over the part of the bottom electrode area defined by the second areas and the areas of the bottom electrode between the second areas. In a preferred embodiment the shunting layer comprises a minimum thickness of 20 nm, preferably more than 50 nm, more preferably more than 100 nm, in order to distribute the current for the bottom electrode with negligible losses across the entire area of the shunting layer.

The invention further related to a method for manufacturing an organic electroluminescent light-emitting device as claimed in the present invention, characterized in, that method comprises the following steps:

- Providing a substrate covered with a transparent conductive layer as a bottom electrode, one or more electroluminescent layer stacks on top of the bottom electrode, each comprising an organic layer stack with at least one organic light emitting layer, a reflective top electrode on top of the organic layer stack and an insulating layer on top of the top electrode suitably shaped to prevent a direct electrical contact between the top electrode and the bottom electrode, wherein the bottom electrode comprises first areas covered by the one or more electroluminescent layer stacks and at least one second area not covered by the electroluminescent layer stack; and

Depositing an electrically conductive shunting layer on top of the second areas of the bottom electrode and at least partly on top of the insulating layer to distribute a driving current across the bottom electrode by providing a second conductive path at least between and/or along the second areas and the insulating layer is further shaped to prevent a direct electrical contact between the top electrode and the shunting layer.

The substrate covered by the layers underneath the shunting layer may be deposited by techniques known by skilled people such as thermal evaporation, sputtering etc. The structuring of the electroluminescent layer stacks, especially the creation of first, second, and third areas, might be executed by common structuring techniques applied from OLED devices such as lithography etc. The technique chosen to deposit the shunting layer should be any technique enabling a fast deposition of a layer with thicknesses of several tens of nanometers. In an embodiment the shunting layer is deposited by thermally evaporating copper as the material of the shunting layer.

In an embodiment of the method, the organic layer stack and the top electrode are prepared as contiguous layers, where the second areas are obtained by removing the organic layer stack and the top electrode above the second areas by laser ablation. This deposition technique enables the preparation of different kind of structures starting with the same deposition process for organic layer stack and the top electrode. The flexible structuring opportunity enables the production of differently structured OLED devices on demand. Laser ablation processes applied to OLED devices and the corresponding process parameters are known to skilled people.

In an embodiment the second areas are obtained by structured deposition of the one or more electroluminescent layer stacks, where the structured deposition prevents any material deposition on top of the second areas. Such OLED devices can be produced in a subsequent deposition process, where an OLED device fully protected against environmental conditions leaves the deposition chamber. The following deposition of the shunting layer does not affect any layer within the organic layer stack and the top electrode and insulating layers on top. In an embodiment the structured deposition is mask deposition shielding the second areas in order to prevent material deposition on top of the second areas. Mask deposition is a well known structuring technique already applied in OLED device

manufacturing. In a preferred embodiment the structured deposition is adapted to provide electroluminescent layer stacks shaped as parallel stripes with lines as second areas in between. In such devices the second areas extend along the entire side of a stripe-like organic layer stack enabling a good current distribution into the electroluminescent layer stack.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1 : OLED device with shunting lines according to prior art in a side view.

Fig. 2: OLED device according to the present invention with shunting layer in a side view.

Fig. 3: An embodiment of an OLED device according to the present

invention in a top view with an array of circular second areas shown (a) without the shunting layer, and (b) with a shunting layer on top of the electroluminescent layer stacks.

Fig. 4: another embodiment of an OLED device according to the present invention with electroluminescent layer stacks and second areas arranged as stripes (a) in a side view, and (b) in a top view. DETAILED DESCRIPTION OF EMBODIMENTS

Fig.1 shows an OLED device with shunting lines SL according to prior art in a side view as a bottom emitter. The shunting line SL is arranged on top of the bottom electrode 3, which is deposited on top of a substrate 2. The light-emission 10 takes place through the transparent bottom electrode 3 and the transparent substrate 2. The shunting line SL suitable to distribute the driving current across the bottom electrode 3 in order to achieve an OLED device with homogeneous brightness has a typical width of a few millimeters and a thickness of typically 0.6 μιη. The thick and commonly rectangular shaped shunting lines SL introduce a topology into the OLED layer stack resulting in edges within the layer stacks comprising an organic layer stack 41 and a top electrode 42, which may lead to field enhancement and resulting shorts occurring in the neighborhood of such edges. To reduce the risk of shorts, the shunting lines SL are covered by a thick non-conductive protective cover layer PC. However, the mandatory minimum width of the shunting lines of at least a few millimeters in order to be able to distribute the driving current without significant losses and the additional required protective cover leads to non light-emitting areas NE-PA within the OLED device, which are visible due to its large width. Visible non light-emitting areas disturb the impression of the light-emitting OLED and should be avoided.

Fig. 2 shows an OLED device according to the present invention with a shunting layer 5 in a side view. The OLED device 1 is arranged as a bottom emitter with light emission 10 through the transparent bottom electrode 3 and the transparent substrate 2, e.g. made of glass or plastic. The organic electroluminescent light-emitting device 1 comprises a transparent substrate 2, which is coated with a transparent conductive layer as a bottom electrode 3. On top of the bottom electrode 3 one or more electroluminescent layer stacks 4 are deposited, each comprising an organic layer stack 41 with at least one organic light emitting layer and a reflective top electrode 42 on top of the organic layer stack 41. In order to be able to deposit a shunting layer 5 on top of the present layers, an insulating layer 43 fully covers the top electrode 42 and the organic layer stack 41. The insulating layer 43 preferably covers the edges of the organic layer stack 41 and the top electrode 42 with an overlap OV of at least 0.1 mm. In other embodiment, a full coverage of only the top electrode 42 could also be sufficient. The organic layer stack 41 is suitably shaped to prevent the top electrode 42 from contacting the bottom electrode 3 directly within the covered

electroluminescent layer stack 4. The bottom electrode 3 comprises first areas 31 covered by the electroluminescent layer stacks 4 as indicated by the dashed arrows. Between the first areas, a second area 32 not covered by the electroluminescent layer stacks 4 is shown. The electrically conductive shunting layer 5 is deposited on top of the second areas 32 of the bottom electrode 3 in order to electrically contact the bottom electrode 3 to provide a second conductive path SCP (indicated as horizontal arrow) on top of the electroluminescent layer stack in addition to the first conductive path FCP (indicated as horizontal arrow within the bottom electrode 3) directly through the bottom electrode 3. To be able to distribute the major part of the driving current across the bottom electrode 3 via the second areas 32, the shunting layer 5 also extends to the first areas 31 by covering the insulating layer 43 above the first areas 31 partly or fully. The shunting layer 5 on top of the electroluminescent layer stack 4 can be applied with a large width or even as a contiguous layer without introducing any additional topology into the electroluminescent layer stacks 4 avoiding any risk due to filed enhancement at sharp edges and therefore providing OLED devices 1 with a good lifetime performance, while the required current distribution properties of the shunting layer 5 is also maintained due to the large width of the shunting layer 5 for the major part of the shunting layer (areas outside the second areas 32) and the possibility to adjust the thickness of the shunting layer 5 to any thickness fulfilling the requirements for a sufficient conductivity of the shunting layer 5. As an example, the shunting layer 5 made of copper comprises a minimum thickness of 20 nm, preferably more than 50 nm, more preferably more than lOOnm. It is even more preferably to provide a shunting layer with a thicknesses of at least 200 nm in order to be sure that the metal layer is thicker than organic stack in order to reach the flat part on top of the insulating layer in case of shading effects during shunting layer deposition.

Furthermore, the non light-emitting area NE with a width DT corresponding to the distance between adjacent top electrode layers 42 is significantly smaller compared to OLED devices with prior art shunting lines SL. Here the width DT is not limited to minimum widths required to provide a good electrical conductivity in a horizontal direction. With common deposition and structuring techniques (e.g. mask evaporation and/or laser ablation) the size S of the second area 32 in one direction can be adjusted below the threshold of visibility for human eyes. As an example, circular second areas 32 are not visible for human eyes, if these areas have a diameter equal or below 0.35 mm. The same holds for rectangular second areas 32, where the width of the second areas is equal or below 0.35 mm. The width of the second area 32 as shown in figure 2 is about 0.2 mm. The width of the non light- emitting area depends on the structure of the top electrodes 42 on top of the organic layer stack 41. A distance DT between adjacent top electrode layers 42 of 0.7 mm defines a non light emitting area with a width of 0.7 mm. With current deposition and structuring techniques, it is possible to prepare a layer stack with a distance DT of less than 0.6 mm, e.g. 0.5 mm, 0.4 mm or 0.3 mm. If additionally scattering effects are applied within the light path, non light- emitting areas NE with a width (or diameter) below 0.35 mm can be achieved easily.

Fig.3 shows an embodiment of an OLED device according to the present invention in a top view with an array of circular second areas 32 shown (a) without the shunting layer 5, and (b) with a shunting layer 5 on top of the electroluminescent layer stacks 4. The array of second areas 32 has a maximum distance D between adjacent second areas 32 in order to provide an OLED device with homogeneous brightness of the emitted light. The maximum distance depends on the electrical sheet resistance of the bottom electrode 3, typically ITO, and the electrical properties of the electroluminescent layer stack, where the bottom electrode 3 gives the major influence to the maximum distance. A homogeneous brightness could be achieved with ITO bottom electrodes 3, if the distance D is less than 8 cm, preferably less than 6 cm, more preferably less than 5 cm, even more preferably less than 4 cm. The second areas 32 are shaped as circular areas of a diameter of 0.2mm and are arranged as a 3 x 3 array in this example. The light-emitting surface is a 16 x 16 cm area. The shown dimensions are not true to scale for ease of understanding. The bottom electrode has a rectangular shape with a U-shaped rim of a third area 33 not covered by the insulating layer 43. The second areas 32 are not covered by the insulating layer 43 as displayed as white circular areas. The top electrode 42 extends to an area (contact pad) not covered by the bottom electrode 3 in order to be able to be contacted with a connection 6t to the power supply. For insulation purposes, the insulating layer 43 extends to the contact pad to prevent any electrical contact to the shunting layer (not resent in figure 3 a) leaving a suitable contact area of the contact pad uncovered. In figure 3b, the shunting layer 5 is deposited as a rectangular layer on top of the major part of the insulating layer 43. The shunting layer 5 covers all second areas 32 (as indicated by the dashed white circles) and the areas between the second areas 32. Furthermore, the shunting layer 5 extends to the U-shaped rim as third area 33 of the bottom electrode 3 to improve the current distribution properties of the shunting layer 5 in comparison to a shunting layer 5, which has not electrical contact to the third areas 33. On top of the shunting layer 5 being in an electrical contact to the bottom electrode 3 via the second and third areas 32, 33, a connection 6b is applied to the power supply in order to be able to apply a driving voltage to the bottom electrode 3 of the OLED device. Fig.4 shows another example of an OLED device according to the present invention with electroluminescent layer stacks 4 and second areas 32 arranged as stripes (a) in a side view, and (b) in a top view. As shown in figure 4a, the insulating layer 43 only covers the top electrodes 42 fully, but not the organic layer stack 41. This is also sufficient to prevent a non-desired electrical contact between top electrode 42 and bottom electrode 3 and shunting layer 5. Here the distance D between adjacent second areas 32 could be the same distance as shown in figure 3, also the distance DT between adjacent top electrodes 42. The distance DT should be sufficient to enable a full coverage of the top electrode 42 by the insulting layer 43. The connection 6b between power supply and bottom electrode 3 can be established via the shunting layer 5 being in contact to the bottom electrode 3. However, it is preferred to cover both the top electrode 42 and the organic layer stack 41 with the insulating layer 43.

As shown in figure 4b, the electroluminescent layer stacks 4 are arranged as parallel stripes divided by the second areas 32 as non-covered lines between the stripes. To be able to contact the top electrodes 42 with connections 6t to the power supply (not shown here), the top electrodes 42 are not covered by the insulating layer 43 at both sides of the stripes. In principal, a non-covered area at one side of the stripes would be sufficient to contact the top electrode. The shunting layer 5 is deposited on top of the area of stripes and lines as only indicated by the dashed rectangular area for ease of understanding. The connection 6b between power source (not shown here) and bottom electrode is established via the shunting layer 5. However, the connection 6b to the bottom electrode 3 might be established directly to the bottom electrode 3 in other embodiments. The distances and thicknesses given for the embodiment shown in figure 3 are also applicable to the

embodiment shown in figure 4. However people skilled in the art may choose a different shape or pattern of second areas and electroluminescent layer stacks 4 in between within the scope of this invention.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

LIST OF NUMERALS

1 OLED device according to the present invention

2 transparent substrate

3 bottom electrode

31 first area of the bottom electrode

32 second area of the bottom electrode

33 third area of the bottom electrode

4 electroluminescent layer stack

41 organic layer stack

42 top electrode

43 insulating layer

5 shunting layer

6b connection between bottom electrode and power supply

6t connection between top electrode and power supply

10 emitted light

D distance between second areas

DT distance between adjacent top electrode layers

FCP first conductive path

NE non light-emitting area

NE-PA non light-emitting area in a prior art OLED device

OV overlap, area of the insulating layer exceeding the edges of the organic layer stack and/or the top electrode

S size of the second area in at least one direction

SCP second conductive path

SL shunting line according to prior art

PC protection cover for a shunting line according to prior art

Claims

CLAIMS:

1. An organic electroluminescent light-emitting device (1) comprising a transparent substrate (2) coated with a transparent conductive layer as a bottom electrode (3), one or more electroluminescent layer stacks (4) deposited on top of the bottom electrode (3), each comprising an organic layer stack (41) with at least one organic light emitting layer, a reflective top electrode (42) on top of the organic layer stack (41) and an insulating layer (43) on top of the top electrode (42) suitably shaped to prevent a direct electrical contactbetween the top electrode (42) and the bottom electrode (3), wherein the bottom electrode (3) comprises first areas (31) covered by the one or more electroluminescent layer stacks (4) and at least one second area (32) not covered by the electroluminescent layer stack (4), wherein an electrically conductive shunting layer (5) is deposited on top of the second areas (32) of the bottom electrode (3) and at least partly on top of the insulating layer (43) to distribute a driving current across the bottom electrode (3) by providing a second conductive path (SCP) at least between and/or along the second areas (32) and the insulating layer is further shaped to prevent a direct electrical contact between the top electrode (42) and the shunting layer (5).

2. The organic electroluminescent light-emitting device (1) as claimed in claim 1, characterized in, that the bottom electrode (3) comprises an outer rim with third areas (33) not covered by the electroluminescent layer stack (4), where the shunting layer (5) is in an electrical contact also to the third areas (33).

3. The organic electroluminescent light-emitting device (1) as claimed in claim 1 or 2, characterized in, that a distance (D) between adjacent second areas (32) is less than 8 cm, preferably less than 6 cm, more preferably less than 5 cm, even more preferably less than 4 cm.

4. The organic electroluminescent light-emitting device (1) as claimed in any preceding claim, characterized in, that the size (S) of the second area (32) in one direction is below the threshold of visibility for human eyes.

5. The organic electroluminescent light-emitting device (1) as claimed in any preceding claim, characterized in, that the electroluminescent layer stacks (4) are arranged suitable to provide a distance (DT) between adjacent top electrode layers (42) of equal or less than 0.7 mm, preferably equal or less than 0.6 mm, more preferably equal or less than 0.5 mm.

6. The organic electroluminescent light-emitting device (1) as claimed in any preceding claim, characterized in, that the shunting layer (5) is prepared as a contiguous layer covering all second areas (32) and at least all areas (31) between the second areas (32).

7. The organic electroluminescent light-emitting device (1) as claimed in claim 6, characterized in, that shunting layer (5) comprises a minimum thickness of 20 nm, preferably more than 50 nm, more preferably more than lOOnm.

8. The organic electroluminescent light-emitting device (1) as claimed in any preceding claim, characterized in, that the shunting layer (5) is made of copper.

9. The organic electroluminescent light-emitting device (1) as claimed in any preceding claim, characterized in, that the insulating layer (43) covers the edges of the organic layer stack (41) and/or the top electrode (42) with an overlap (OV) of at least 0.1 mm.

10. A method for manufacturing an organic electroluminescent light-emitting device (1) as claimed in claim 1, characterized in, that method comprises the following steps:

Providing a substrate (2) covered with a transparent conductive layer as a bottom electrode (3), one or more electroluminescent layer stacks (4) on top of the bottom electrode (3), each comprising an organic layer stack (41) with at least one organic light emitting layer, a reflective top electrode (42) on top of the organic layer stack (41) and an insulating layer (43) on top of the top electrode (42) suitably shaped to prevent a direct electrical contact between the top electrode (42) and the bottom electrode (3), wherein the bottom electrode (3) comprises first areas (31) covered by the one or more electroluminescent layer stacks (4) and at least one second area (32) not covered by the electroluminescent layer stack (4); and

Depositing an electrically conductive shunting layer (5) on top of the second areas (32) of the bottom electrode (3) and at least partly on top of the insulating layer (43) to distribute a driving current across the bottom electrode (3) by providing a second conductive path (SCP) at least between and/or along the second areas (32) and the insulating layer is further shaped to prevent a direct electrical contact between the top electrode (42) and the shunting layer (5).

11. The method as claimed in claim 10, characterized in, that the shunting layer (5) is deposited by thermally evaporating copper as the material of the shunting layer (5).

12. The method as claimed in claim 10 or 11, characterized in, that the organic layer stack (41) and the top electrode (42) are prepared as contiguous layers, where the second areas (32) are obtained by removing the organic layer stack (41) and the top electrode (42) above the second areas (32) by laser ablation.

13. The method as claimed in claim 10 or 11, characterized in, that the second areas (32) are obtained by structured deposition of the one or more electroluminescent layer stacks (4), where the structured deposition prevents any material deposition on top of the second areas (32).

14. The method as claimed in claim 13, characterized in that the structured deposition is adapted to provide electroluminescent layer stacks (4) shaped as parallel stripes with lines as second areas (32) in between.

15. The method as claimed in any of claims 12 to 14, characterized in that the structured deposition is mask deposition shielding the second areas (32) in order to prevent material deposition on top of the second areas (32).