FIELD OF THE INVENTION

The invention relates to an optoelectronic device and a method for the production of such a device, said device comprising two electrode layers with a functional layer in between. The optoelectronic device may particularly be an Organic Light Emitting Diode (OLED).

BACKGROUND OF THE INVENTION

The WO 2010/05301 Al discloses an optoelectronic device, particularly an OLED, in which electronic components are arranged in consecutive layers. To provide electrical access to the inner layers, conductor bridges running perpendicularly through the layers are used. These are produced either by drilling holes into the layers and filling them with electrically conductive material, or by building up structured layers that comprise holes at the later positions of the bridges (Fig. 4B). SUMMARY OF THE INVENTION

Based on this background it was an object of the present invention to provide an optoelectronic device with a high robustness that can cost-effectively be produced.

This object is achieved by a method according to claim 1 and an optoelectronic device according to claim 4. Preferred embodiments are disclosed in the dependent claims.

According to its first aspect, the invention relates to a method for the production of an optoelectronic device, for example of an OLED or a photo voltaic cell, said method comprising the following steps:

a) The provision of a first electrode layer. As the term "layer" indicates, this component shall substantially be flat (particularly planar), i.e. it has a low thickness in comparison to its width- and/or depth-extensions in directions orthogonal to the thickness. Furthermore, this layer shall be electrically conductive such that it can later on function as an electrode. In many cases the first electrode layer will further be transparent for the light that shall be generated or processed by the optoelectronic device.

b) Depositing one or more islands (directly or indirectly) on the first electrode layer. In the following, the expression "island(s)" will be used to refer to this/these island or islands. The island(s) shall have a substantially smaller width and/or depth than the first electrode layer, rising perpendicularly to the first electrode layer. In the following description, the convention will be adopted that the direction from the electrode layer to the island(s) corresponds to a direction from "bottom" to "top" (or "lower" to "upper").

c) Depositing first a functional layer and then a second electrode layer on the first electrode layer and the island(s) such that this functional layer and second electrode layer cover the island(s). The composition of the "functional layer" depends on the particular embodiment of the optoelectronic device, and it may comprise a plurality of sub-layers. In case of a photo voltaic cell, the functional layer will for example comprise photosensitive material. The second electrode layer may typically consist of metal, and it may optionally be transparent. After the deposition of the functional layer and the second electrode layer, these resulting surface will typically be uneven with the (covered) island(s) rising above the surrounding plane.

d) Disposing a cover above the second electrode layer, wherein said cover comprises at least one conductor and wherein the disposition is done such that this conductor is (at least partially) located above the island(s). If there are several conductors and islands, it suffices if one conductor is located above each island. The cover is a component that usually provides the interface of the optoelectronic device to the environment.

Accordingly, the cover is typically designed with a certain mechanical stability. Moreover, it is usually electrically isolating besides in dedicated regions where the conductor is located. It should be noted that the location of the conductor "above the island(s)" comprises both the case that there is an (electrical) contact between the conductor and the island(s) or not.

The described method has the advantage that an optoelectronic device with a layered design can be produced that comprises vertically running components - the islands - without a need to structure the layers (electrode layers, functional layer) already during deposition or to post-process them e.g. by drilling. The production of the optoelectronic device can hence be facilitated and made more cost effective.

The island or at least one of a plurality of islands of the manufactured optoelectronic device may be electrically conductive, for example by comprising or consisting of an electrically conductive material. In this case the second electrode layer and optionally also the functional layer is removed at the location of said conductive island before the cover is disposed in step d) of the above method. Preferably, this removal takes place above said island and additionally also in a certain surrounding of it. After the removal, an electrically conductive bridge is available that provides the conductor of the cover with access to the first electrode layer deeper down in the stack of layers.

In other embodiments of the invention, which may be realized separately or in combination with the aforementioned one, the island or at least one of a plurality of islands is electrically isolating, and the conductor of the cover contacts the second electrode layer above said isolating island. As the connection between the second electrode layer and some conductor (here of the cover) is usually accompanied with some mechanical stress, failures like cracks in the materials may occur at such locations. Arranging the connection between the second electrode layer and a conductor above an electrically isolating island has the advantage that such cracks cannot disrupt the function of the whole device by a short-circuit because the respective layers are separated by the isolating island.

In line with the aforementioned embodiment, the invention further relates to an optoelectronic device comprising the following components:

A first electrode layer.

At least one electrically isolating island disposed on the first electrode layer.

- A functional layer that is disposed on the first electrode layer and that embeds (and optionally also covers) the island.

A second electrode layer that covers the functional layer and the island.

A cover with at least one conductor that electrically contacts the second electrode layer at the island(s).

The optoelectronic device can be produced by a method of the kind described above. Reference is therefore made to the above description for more information on the details, advantages and modifications of this device. Additionally to the electrically isolating islands, the optoelectronic device may preferably also comprise electrically conductive islands that are contacted by at least one conductor of the cover and that provide access to the first electrode layer.

In the following, various preferred embodiments of the invention will be described that relate both to the method in general and to the optoelectronic device with the electrically isolating island(s). According to a first preferred embodiment, there is a plurality of islands that are arranged in a pattern on the first electrode layer. If there are both electrically conductive and isolating islands, each of these types may be present in a separate pattern. These patterns may then be related to each other, for example be interlaced. The pattern of islands requires that the conductor(s) of the cover is/are arranged such that it/they can contact the associated islands.

The cover may in general be realized in a variety of shapes and designs. In a preferred embodiment, the cover comprises an electrically isolating substrate, for example a plate of plastic or glass, which carries at least one conductor line on the side that faces the second electrode layer in the assembled optoelectronic device. The conductor line can for example be applied to the surface of the isolating substrate by printing.

In a further development of the aforementioned embodiment, the cover comprises at least one feedthrough that connects the conductor line with the opposite side of the cover. In this case the optoelectronic device can favorably be contacted at the upper surface of the cover.

The cover is preferably attached to the second electrode layer and/or to electrically conductive islands with the help of a conductive glue. Typically, this conductive glue is arranged between the at least one conductor of the cover and the second electrode layer and/or the electrically conductive island(s), providing both mechanical attachment and electrical connection between the respective components. To minimize the effect of mechanical stress that may occur due to shrinking effects, the conductive glue is preferably applied in small isolated spots (instead of continuous lines or areas).

In a further development of the invention, a ring of glue connects the cover to the layers below (i.e. to the second electrode layer, the functional layer, the first electrode layer and/or a substrate). Most preferably, this ring is closed. It provides a sealing of the optoelectronic device, and it typically runs along the periphery of the cover.

In another embodiment, the second electrode layer and optionally also the functional layer and further optionally also the first electrode layer is/are removed along a closed contour line. The layered structure that constitutes the optoelectronic device is therefore interrupted along this contour line, i.e. it is restricted to the area inside said line. In this way optoelectronic devices with various shapes can readily be produced.

In a further development of the aforementioned embodiment, the at least one conductor of the cover does not extend beyond the area that is encircled by the contour line. This guarantees that the functional optoelectronic device is restricted to the encircled area. The island(s) on the first electrode layer usually induce(s) an uneven, three-dimensional surface at the level of the second electrode layer. When a planar cover is placed onto this uneven surface, there will therefore usually remain some cavities. In a preferred embodiment, such cavities between the cover and the lower layers are filled with a thermally isolating (and preferably also electrically isolating) filling material, for example with resins, inert oils or liquid getter materials.

In general, the first electrode layer might be self-supporting and constitute the outermost layer at the bottom of the optoelectronic device. In many cases, the first electrode layer will however be disposed on some substrate that provides mechanical stability and support. Moreover, such a substrate will typically be electrically isolating. It may further be transparent to allow the passage of light that is generated or processed by the device.

In a preferred realization, the functional layer comprises an electroluminescent organic material. In this case the whole optoelectronic device can constitute an Organic Light Emitting Diode (OLED).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. These embodiments will be described by way of example with the help of the accompanying drawings in which:

Figures 1 and 2 illustrate two steps of the manufacturing of an OLED using masks for the structuring of layers;

Figures 3-7 illustrate consecutive manufacturing steps of an OLED

according to the present invention;

Figure 8 shows a view onto the bottom side of the cover that is used in the aforementioned manufacturing procedure;

Figures 9-11 illustrate consecutive manufacturing steps of an alternative

OLED comprising electrically isolating islands;

Figure 12 shows a top view onto a substrate with top layers in which various contour lines of these layers have been removed.

Like reference numbers or numbers differing by integer multiples of 100 refer in the Figures to identical or similar components. DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will in the following be described with respect to an Organic Light Emitting Diode (OLED), though its principles can be applied in many other situations as well.

Figures 1 and 2 illustrate a conventional manufacturing of OLEDs (e.g. for Displays and Lighting) which consists of a series of processing steps that are design specific.

The first of these steps is the manufacturing of a substrate 1 , which may for example be made from glass or plastics. On the substrate, a structured layer of a transparent conductor 2 (e.g. a transparent conductor oxide (TCO), ZnO, ITO, PEDOT:PSS, etc.) is created. Optionally, metal lines 3 (e.g. MAM, CrAlCr, Cu, etc.) are additionally applied onto said conductor. The main function of this patterning step is to create electrically separated areas where later on the cathode and the anode will be electrically connected. This patterning can either be done by subtractive methods like photo lithography or laser ablation, where a full area coating is removed in certain areas. Alternatively a patterned deposition of the layers can be applied. Examples are printing of silver pastes, printing of PEDOT:PSS, sputtering through shadow masks, etc.

In the next steps the OLED functional layers 4 are applied. This stage is shown in Figure 1. Small molecule OLEDs are for example deposited by thermal evaporation in vacuum. The deposition of the organic material must be restricted in such a way that at least the cathode contacts are not coated. Usually also the anode contacts are protected from the coating in order to achieve good electrical contacting later on. This structured deposition is achieved by means of shadow masks Ml . These masks are specific for each OLED design and are placed on top of the substrate during organic deposition. This can either be done in physical contact or with a small gap between the substrate and the mask. During the deposition process the shadow mask Ml will be coated with the organic material.

Figure 2 shows the next step, which is the deposition of the cathode 5. This may also happen in a vacuum thermal evaporation process. Also in this case the layer must be structured, i.e. the anode contact point is left out during deposition, because otherwise there is a short circuit between the cathode and the anode. Moreover, the cathode 5 must have electrical contact with the cathode contact point on the substrate 1. Also in this cathode deposition a shadow mask M2 is used to protect areas in the device from deposition. Again the mask will be coated with material, in this case the cathode material (typically metals like copper, silver, aluminum, gold, etc). As the coated areas for organics and cathode are different, a different set of masks must be used in both processes. Various modifications of the described process are possible, for example: Besides a TCO and metal often an insulating layer is used as well to coat the edges of the patterned TTO and metal layers as they often show sharp edges. In TCO-only designs, only a TCO layer is present and no metallization on the substrate. In case of top emitting OLEDs, the substrate can be non-transparent, but the cathode must be transparent. In case of inverted OLEDs, the position of anode and cathode is exchanged.

The main disadvantages of the described process are:

As the masks are design specific, a design change requires a new set of masks. This limits the throughput time for a design change and increases costs.

- The masks are coated during deposition. This requires regular cleaning and incurs costs, and loose particles from the masks can lead to short circuits and reduce the yield.

Masks are only available for small substrate sizes as thermal expansion of the mask during processing leads to patterning inaccuracy.

- The mask handling in vacuum is very expensive.

In view of the above considerations, an alternative OLED design and an alternative manufacturing process are proposed here in which particularly the masking steps are avoided (the used materials can be the same as cited above).

Figure 3 shows the first step of the aforementioned manufacturing process. A substrate 101 (e.g. glass) with a first electrode layer 102 on top is provided. In the following it will be assumed that said electrode layer is a transparent conductive oxide (TCO) like zinc oxide doped with aluminum. On the TCO layer 102 metal droplets are deposited in a regular pattern, yielding a plurality of (conductive) islands 103. The droplets can for instance easily be deposited using ink jet printing of silver inks. A typical droplet height h is about 0.5 μιη to 2 μιη. In general terms, the islands 103 shall be higher than the thickness of the (organic and electrode) layers 104, 105 that are deposited next (cf. Fig. 4). After deposition of the islands 103 a curing step is applied in order to increase the conductivity of the metal pastes. This can for example be done in a thermal treatment process, typically 30 min at 150°C for nano-inks.

Figure 4 shows the next manufacturing step, in which the previously achieved intermediate product 100a is coated full area with the functional OLED layers 104, i.e. with the organic electroluminescent materials, and with a second electrode layer 105, i.e. the cathode metal. No shadow mask is required for this process. After the aforementioned deposition of layers a structuring process is required, which is shown in Figure 5. Using a laser system, for example a picosecond green laser beam LI, the cathode metal 105 is removed on top of the metal islands 103 as well as in the vicinity of these islands. Typical feature sizes of the removed areas are 300 μιη in diameter.

Figure 6 shows a second step, in which the organic layer 104 is removed. This can either be done using the same laser system or by using a UV laser beam L2 in the presence of oxygen. In this case debris is largely avoided as the organic material is oxidized and can be extracted. The ablated area must be smaller or equal to the area which was cleared from the cathode metal.

In order to electrically contact the obtained OLED structure lOOd as well as to hermetically seal the OLED a special cover lid 110 is used. The manufacturing of this cover 110 is described in the following with respect to Figure 7 and 8.

In a first step a plane glass plate 111 is coated with conductive tracks 112a, 112b. This can easily done using screen printing of metal pastes followed by a thermal annealing or by laser mass transfer of metal. The applied pattern may consist of two conductors with comb like structures that merge into each other without having electrical contact. The distance between the individual lines of a single conductor structure is equal to the spacing of the islands 103 on the substrate (in x-direction). Both conductors 112a, 112b are electrically contacted to metal feedthroughs 114 in the glass lid, which realize an electrical connection through the glass.

On top of the conductors 112a, 112b electrically conductive glue 113a, 113b is applied. For one conductor 112b the spacing of the droplets 113b is equal to the spacing of the islands 103 on the substrate (in y-direction). For the other conductor 112a the deposition of glue 113a is not restricted in position. Breaking of the lines is however recommended in order to avoid long conductive glue traces which can cause mechanical stress on the cathode.

In a last preparation step the cover 110 is coated with a thin glue rim 115 along its periphery. This rim 115 will later on seal the OLED device.

In the next step of the OLED manufacturing shown in Figure 7, the prepared cover lid 110 is placed on top of the preprocessed substrate lOOd. The glue droplets 112b are aligned with the islands 103 on the substrate. By mechanical force the electrical contact between the glue and the islands is realized for the anode contacts and between the cathode 105 and the glue lines 113a for the cathode contacts. In the same process the rim glue 115 is brought into contact with the substrate. This process ideally works with a hermetic sealing as this would not require a water absorbing getter (descidant). For example a laser frit sealing process can be used. In this case the process is very reliable as the laser sealing line is on the TCO only and not on TCO and metal as in classical OLEDs. In addition the line width of the OLED seal would be minimum which is ideal for seamless tiling. Another possible hermetic sealing can be realized by using metal pastes.

The finished OLED devices 100 realized in this fashion can be contacted via the glass lid 110.

The conductive glue by its nature causes a certain amount of mechanical stress as it shrinks during the drying process. In order to avoid mechanical damage to the OLED cathode, the above process can be modified as will be described in the following with respect to Figures 9 to 11.

Figure 9 shows the starting step of this alternative manufacturing procedure. In contrast to the process illustrated in Figure 3, now two interlaced patterns of islands 203, 206 are deposited on the first electrode layer 202 above the substrate 201. The new pattern consists of islands 206 of an insulating material. These insulating droplets 206 are placed between the electrically conductive (metal) islands 203. The distance between the islands is mainly determined by the maximum current to be drawn per surface area and by the requirement on homogeneity of the OLED light emission. The voltage drop and therefore the drop in light output is limited to the distance between two neighboring metal islands 203. Typical distances (in x- and/or y-direction) are between about 5 mm and about 2 cm.

As in the previous case, the obtained intermediate product 200a is then coated full area with an organic layer 204 and a second electrode layer 205 (cathode). This is shown in Figure 10.

Similar to the previous process flow, the cathode 205 on top of the metal islands 203 and in its vicinity is removed using a laser system. The same holds for the organic material 204 in this area. The OLED layers 204, 205 on top of the insulator islands 206 can remain in place.

Figure 11 shows the resulting substrate with its layers on top when a cover lid 210 is placed on top of this from above. In this case the strips of conductive glue (113 in Figure 8) are replaced by glue droplets 213a in the same y-spacing as the spacing of the insulator islands 206. If the glue causes mechanical damage to the cathode 205 locally, this will not lead to a short circuit as the contact area is on top of an insulating area. In order to optimize the thermal management of the OLED, the space between the conductor lines 112a, 112b or 212a, 212b and between the conductive glue spots can be filled with an insulating, thermally conductive material. In this case the heat generated will be conducted towards the cover lid. In addition as there is no cavity any more, the OLED is not sensitive any more for changes in outside pressure.

The described processes can be varied in several ways, for example:

Instead of transparent conductive oxides, an organic conductor like PEDOT:PSS can be used.

The glass cover lid can be replaced by other insulating materials. - The glass cover lid can be replaced by a metal lid if the anode and/or the cathode current distribution grid is printed onto an insulating layer.

smOLED can be replaced by Polymer OLED material.

Instead of laser removal of the layer(s) also other patterning processes can be used, for example mechanical patterning or plasma etching.

The described processes can also be used to create random shaped OLEDs by a post deposition process. This is illustrated in Figure 12 in a top view onto the cathode 305 of a substrate (the organic layer and the substrate are beneath the cathode). In this case after the removal of the cathode and the organic layer on top of the conductive islands 303, another laser process is applied. In this process a laser is used to remove the cathode layer and the organic layer along the contour 320 of an OLED 300 that shall be created. The removed cathode layer has to be preferably larger or equal to the removed organic layer. On the cover lid (not shown) an adequate pattern of glue rim and electrical contacts have to be printed accordingly. After the sealing process the OLED is separated via standard scribe and break processes.

Finally it is pointed out that in the present application the term "comprising" does not exclude other elements or steps, that "a" or "an" does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Moreover, reference signs in the claims shall not be construed as limiting their scope.