Abstract:
In a method for producing an organic light emitting illuminant, a base electrode layer is formed over a substrate, an organic light emitting layer is formed over at least one portion of the base electrode layer, and a top electrode layer is formed over at least one portion of the organic light emitting layer, the layers being formed in the shape of strips. The strip-shaped formation of the layers is carried out in a coating process in an in-line vacuum coating system having stationary shadowing masks on the advancing substrate such that at least one area of the base electrode layer remains uncoated once the layers have been formed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage filing under section 371 of International Application No. PCT/EP2011/072035 filed on Dec. 7, 2011, and published in German on Jun. 14, 2012 as WO 2012/076587 A1 and claims priority of German patent application No. 10 2010 053 605.9 filed on Dec. 7, 2010, and German patent application No. 10 2011 075 092.4 filed on May 2, 2011, the entire disclosure of these applications being hereby incorporated herein by reference. 
     BACKGROUND ART 
     The present invention relates to a method for the production of organic light emitting illuminants, in particular organic light emitting diodes. 
     Organic light emitting illuminants, in particular organic light emitting diodes (OLEDs), are currently already used in many areas of consumer electronics, for example in display applications, and are also regarded as a future technology in the lighting sector. An OLED structure contains one or more organic light emitting layers (EML) arranged between two electrodes, for example a cathode and an anode on a substrate. Since, for the OLED structure, the mobility and thus the current density differ for electrons and holes, since the mobility of the holes in organic semiconductors in comparison is two orders of magnitude greater than the mobility of the electrons, an OLED usually additionally has two layers, a hole transport layer (HTL) and an electron transport layer (ETL), the task of which is to transport holes and electrons into the emission zone. 
       FIG. 1  illustrates a schematic construction of an OLED known from the prior art. It consists of a substrate  100 , on which an optionally smoothing layer  101 , an anode layer  102 , a hole transport layer  103  (HTL), at least one emission layer  104  (EML), an electron transport layer  105  (ETL) and a cathode layer  106  have been deposited in sequence. In  FIG. 1 , the emission layer  104  consists of three separate emission layers, which each emit light individually in different colors (e.g. red, green, blue) and can generate white light. 
     The organic light emitting layers emit light if a voltage is applied between anode and cathode. The applied voltage at the electrodes results in charge carrier injection in the organic material. This leads to charge carrier transport into the emission zone, where a recombination of the charge carriers takes place and the light emission is subsequently brought about. 
     In order to enable an electrical contact-connection of cathode and anode and also a current flowing through the emissive layers, the individual layers are not constructed over the whole area, but rather are deposited in a patterned fashion. One possibility for patterned deposition is disclosed by the document U.S. Pat. No. 7,049,757, which discloses a coating by means of shadow masks concomitantly guided with the substrate. Furthermore, the prior art in the document US 2005/0236975 A1 describes a patterning method in which the deposited layer is ablated by means of a laser. A further possibility for patterned deposition is lithographic/wet-chemical patterning, in particular for patterning the first bottom electrode applied on the substrate. These known methods have the disadvantage of complex handling of the concomitantly moving shadow masks and are unsuitable for the coating of flexible continuous substrates in the roll-to-roll method. 
     BRIEF SUMMARY OF INVENTION 
     It is an object of the present invention to increase the efficiency of inline vacuum treatment installations during the production of organic light emitting illuminants and in this case to simplify the steps for producing an electrical contact-connection for the cathode and anode. In this case, production is intended to be possible in a cost-effective manner, in particular in a commercially applicable manner, and with a higher throughput than heretofore. 
     The method according to the invention for the production of an organic light emitting illuminant is distinguished by the fact that the layers are deposited in strip-type fashion, wherein the layers are formed in strip-type fashion by means of coating in an inline vacuum coating installation with stationary shadow masks on the substrate guided past, such that at least one region of the bottom electrode layer remains uncoated after the layers have been formed, that is to say that at least one region of the bottom electrode layer is free of the subsequent coating after the layers have been formed. The layers formed in strip-type fashion include at least one organic light emitting layer, a top electrode layer and a conductor track layer. The wording that at least one region of the bottom electrode layer remains uncoated after the layers have been formed means that in each case after a strip-type coating of these layers, at least one region of the bottom electrode remains free of the coating. That means that, after the last layer has been deposited, at least one region of the bottom electrode is free of the coating. 
     With regard to the present invention, an “inline process control” means a physical transport of the substrate from one coating station to the next, in order to apply different layers, wherein the substrate is also transported further during the coating process. The method can be implemented in continuous installations with a continuously transporting substrate belt, either a continuous substrate in roll-to-roll coating or a quasi-continuous succession of synchronously moved successive planar package-type substrates. 
     In one advantageous development of the method according to the invention, the method comprises the step of forming an optional insulating smoothing layer above the substrate before the step of forming the bottom electrode layer. An insulating smoothing layer should be understood to be, for example, a lacquer for smoothing the substrate surface in order to avoid short circuits in and between the components in the case of rough surfaces. Preferably, the smoothing layer is formed above the substrate in planar fashion. 
     In one advantageous development of the method according to the invention, the method comprises the step of patterning the bottom electrode layer by means of a laser before the step of forming at least one organic light emitting layer. In the regions of the bottom electrode layer which have been treated by means of a laser, the material of the bottom electrode layer is removed as far as the substrate, optionally as far as the smoothing layer, with the result that regions of the bottom electrode layer which are electrically insulated from one another are formed. Preferably, for a respective organic light emitting illuminant, bottom electrode layers are separated into two regions of the bottom electrode layer, which are electrically insulated from one another. In this case, at least one portion of the regions that are electrically insulated from one another will remain uncoated by the subsequent application of the layers, that is to say free of the subsequent coating. As a result, a method is provided which combines the patterning methods, namely the laser patterning, and coating by means of stationary strip masks with one another in order to produce contact-connectable OLED components in a simple manner. This combination of processes can be carried out on a continuously moved continuous substrate or a quasi-continuous succession of substrate wafers in an inline coating installation, without stopping the substrate in front of the coating sources or the patterning stations and without concomitantly moving shadow masks. 
     In a further advantageous development of the method according to the invention, the method comprises the step of patterning at least one organic light emitting layer by means of a laser before the step of forming the top electrode layer. In this case, at least one organic light emitting layer can subsequently be laser-patterned after its patterned deposition by means of the shadow mask. 
     In accordance with a further advantageous development of the method according to the invention, the method comprises, after the step of forming the top electrode layer and the subsequent conductor track layer, the step of patterning them by means of the laser. As a result, regions of the top electrode layer and of the conductor track layer that are electrically insulated from one another can be separated. 
     According to the invention, the coating of the respective layer is effected by coating sources which are arranged below the line guidance of the substrates, that is to say which point substantially vertically upward. In this case, the substrate is guided horizontally past the coating sources, such that the coating direction runs vertically. In this case, the terms “horizontally” and “vertically” are also intended to include deviations of up to 20% from the actual horizontal and vertical, respectively, that is to say to mean that the substrate in this case is guided substantially horizontally past the coating sources, such that the coating direction runs substantially vertically. In this way, it is possible to use coating installations in which the coating sources are aligned vertically with respect to their coating direction and in which horizontal substrate transport is effected. This simplifies the handling of the substrate during transport, since said substrate can now be guided by means of transport rollers, for example. 
     Alternatively, other spatial relations between substrate, sources and coating direction can also be employed, for example vertically oriented substrates with a horizontal coating direction. 
     According to the invention, at least one stationary shadow mask is arranged between a respective coating source and in each case the substrates guided past. In this case, each stationary shadow mask has at least one strip-type opening through which a dynamic coating of the layers on the substrates guided past or moved past with strip-shaped structures is effected. As a result, it is possible to avoid the complex handling of concomitantly moving shadow masks. 
     With the aid of the stationary shadow masks, layers are deposited, such as the organic light emitting layers, the top electrode layer and the conductor track layer. The bottom electrode layer can be applied in planar or strip-type fashion. In the case where the bottom electrode layer is formed in strip-type fashion, a stationary shadow mask is provided between the corresponding coating source and the substrate guided past. 
     According to the invention, coating methods used include sputtering or thermal evaporation. Preferably, the layers, such as the bottom electrode layer, the organic light emitting layers, the top electrode layer and the conductor track layer, are formed by vapor deposition. The bottom electrode layer can optionally be deposited by means of sputtering inline or in an external installation. 
     In accordance with at least one embodiment of the invention, at least one of the electrode layers comprises a transparent conductive layer or a metal, preferably silver (Ag), or consists thereof. On account of its electrical conductivity, silver has very good properties as an electrode. In a further configuration of the method according to the invention, the bottom electrode layer is embodied as a transparent conductive layer. If the electrode layer which comprises the metallic layer or consists thereof is intended to be embodied as transmissive to the light emitted by the organic layer stack, then the metallic layer has to be made sufficiently thin. Preferably, the thickness of a semitransparent metallic layer is approximately 100 nm. 
     In accordance with at least one embodiment of the illuminant, the conductor track layer has at least one electrically conductive track which preferably comprises a metal or consists thereof. The electrically conductive track constitutes an electrical connection to the top electrode layer and can serve as a first contact region. The second contact region is correspondingly conductively connected to the second electrode, that is to say to the bottom electrode layer of the illuminant—for example via second electrical leads. 
     In one advantageous configuration of the method according to the invention, the method comprises, in the step of forming at least one organic light emitting layer in strip-type fashion, advantageously a plurality of, preferably three separate, organic light emitting layers, for forming an organic light emitting layer stack. In this case, an organic layer is in each case suitable for generating light in a different color in each case, for example red, green or blue. 
     In a further advantageous configuration of the method according to the invention, the organic light emitting layer stack comprises further organic layers, preferably a hole transport layer and an electrode transport layer. In this case, the layers are also formed in strip-type fashion, such that at least one region of the bottom electrode layer is free of the coating. 
     It is conceivable for the organic layer stack to comprise, besides the organic light emitting layer, further organic layers, such as, for example, a hole injecting layer, a hole transport layer, an electron blocker layer, an electron injecting layer, an electron transport layer and a hole blocker layer. In this case, the hole injecting layer, the hole transport layer and electron blocker layer are preferably arranged on the side of the organic layer stack facing the anode, while the electron injecting layer, the electron transport layer and the hole blocker layer are preferably arranged on that side of the organic layer stack which faces the cathode. In this case, the organic light emitting layer is preferably arranged between the electron blocker layer and the hole blocker layer. With the use of a plurality of light emitting layers, further electrical functional layers can be arranged between them. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING FIGURES 
       The invention is explained in greater detail below on the basis of preferred exemplary embodiments with reference to drawings, in which: 
         FIG. 1  shows a schematic construction of an organic light emitting illuminant according to the prior art. 
         FIGS. 2   a - 2   d  show plan views of the layer structure for individual steps of the method for the production of the organic light emitting illuminant, and 
         FIG. 3  shows a cross-sectional view of an organic light emitting illuminant produced by the method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The method according to the invention involves an inline vacuum coating installation in which the substrates or a large-area substrate are or is moved through the coating or processing stations and a plurality of organic light emitting illuminants are produced on said substrates/substrate. Although  FIGS. 2   a  to  2   d  illustrate four OLED structures on the substrate, the arrangement and number of the structures are not limited to this example, but a different combination of the OLED structures is also conceivable. 
     The first step of the method according to the invention involves providing a substrate  200 . The substrate  200  comprises aluminum or consists thereof. Its thickness is in the range of between 0.2 and 0.5 mm. The substrate is moved in a longitudinally extended vacuum coating installation with a substrate transport system (not illustrated) through the vacuum coating installation in a transport direction through various processing stations. 
     In the next step, a smoothing layer  201  is optionally applied over the substrate  200 . A smoothing layer  201  should be understood to be, for example, a lacquer for smoothing the substrate surface in order to avoid short circuits in and between the components in the case of rough surfaces of the substrate. Preferably, the smoothing layer  201  is formed above the substrate in a planar fashion. In the next step of the method according to the invention, a bottom electrode layer  202  is formed over the smoothing layer  201  in a planar fashion. The coating of the bottom electrode layer  202  can be effected by means of sputtering inline in the vacuum coating installation or in an external installation. It is also possible for the bottom electrode layer  202  to be formed by means of thermal evaporation. The bottom electrode layer  202  comprises silver (Ag) or consists thereof. After the process for coating the bottom electrode layer  202  has ended, the bottom electrode layer  202 , also called base electrode layer, can optionally be patterned by means of a laser.  FIG. 2   a  illustrates four identical structures (marked in black), in each case two in an upper and two in a lower part of the substrate, which were patterned by means of a laser, the center line running parallel to the transport direction of the substrate. The structures are arranged symmetrically with respect to one another along the center line and transversely with respect to the transport direction of the substrate. The regions marked in black, as can be seen in  FIG. 3 , constitute the regions of the bottom electrode layer  202  which were removed by means of a laser as far as the smoothing layer  201  or optionally as far as the substrate  200 . As a result, regions of the bottom electrode layer  202  that are electrically insulated from one another have been separated for the respective organic light emitting structure (OLE structure). The inner region of each of the four structures in each case constitutes a first electrically insulated region  202 . 1 . The region arranged in each case around one of the four structures in the form of a rectangle, also called outer region hereinafter, in each case constitutes the second electrical region  202 . 2 , insulated from the first region. The size of the respective rectangle corresponds to a quadrant of the substrate area. 
     In  FIG. 2   b , in the next step, at least one organic light emitting layer (emission layer)  203  is deposited in strip-type fashion over the bottom electrode layer  202 . The OLE layer  203  is deposited inline by thermal evaporation. The layer thickness is approximately 200 nm. Further OLE layers  203 . 2 ,  203 . 3  can also be applied in strip-type fashion. The strip-type deposition in  FIG. 2   b  is effected in each case in the upper and also in the lower part of the substrate with respect to the center line of the substrate, said center line running parallel to the transport direction of the substrate. In this case, it is important that at least one region of the bottom electrode layer  202  for in each case one of the four structures remains free of the coating, wherein the region for the respective structure has at least one region of the inner region  202 . 1  and outer region  202 . 2  of the structure. These two regions  202 . 1  and  202 . 2  are electrically insulated from one another. Since the emission layer  203  is likewise deposited over one of the regions of the bottom electrode layer  202  (marked in black) by virtue of the fact that the material of the bottom electrode layer  202  was removed as far as the substrate  200 , optionally as far as the smoothing layer  201 , by means of laser patterning, a part of the emission layer  203  is thus deposited directly on the substrate  200 , or on the smoothing layer  201 . Optionally, the OLED layers  203  can also be patterned by means of a laser (not illustrated). 
     In the next step of the method according to the invention, which is illustrated in  FIG. 2   c , a top electrode layer  204  is coated in strip-type fashion over at least one region of the OLE layer  203 , such that at least another region of the one layer of the OLE layer  203  remains free of the coating and the OLE-layer-free region of the bottom electrode layer  202  is not covered either. The top electrode layer  204  comprises silver or consists thereof. The coating is effected by thermal evaporation in the inline vacuum coating installation through an opening in the stationary shadow mask. The strip-type deposition in  FIG. 2   c  is effected in each case in the upper and also in the lower part of the substrate with respect to the center line of the substrate, said center line running parallel to the transport direction. Optionally, the top electrode layer  202  can be patterned by means of a laser for the purpose of separating top electrode regions that are electrically insulated from one another (not illustrated). 
     The next step of the method according to the invention, as illustrated in  FIG. 2   d , comprises applying conductor tracks  205  in strip-type fashion, wherein at least that region of the bottom electrode layer  202  which is free of OLE layers remains free of the conductor track coating. Preferably, the conductor track coating  205  is formed on the OLE layer  203  such that the OLE layer  203  projects on both sides transversely with respect to the transport direction of the substrate  200  below the top electrode layer  204  and conductor track coating  205 , in order to avoid a short circuit between bottom electrode layer  202  and top electrode layer  204 . The conductor track layer  205  constitutes at least one electrically conductive track which preferably comprises metal or consists thereof. It generally has a good electrical conductivity, such that it is particularly well suited to impressing charge carriers into the organic layer stack. Furthermore, the metallic track in  FIG. 2   d  is preferably embodied such that, from the area of the electrode encompassing it, it takes up only a small part of the top electrode layer. It constitutes an electrical connection to the top electrode layer and can serve as a contact region. The second contact region is correspondingly conductively connected to the second electrode, that is to say to the bottom electrode layer of the illuminant—for example via second electrical leads. 
     Optionally, the conductor track layer can be patterned by means of a laser (not illustrated). The method makes it possible for a plurality of OLE illuminants to be produced identically in an inline vacuum coating installation. 
     An OLE illuminant produced by the method according to the invention comprises according to  FIG. 3  a substrate  200 , on which a layer system is constructed. The layer system comprises in succession a smoothing layer  201 , a bottom electrode layer  202 , patterned by means of a laser, an OLE layer  203 , a top electrode layer  204  and a conductor track layer  205 . On account of the laser patterning, the patterned bottom electrode layer  202  comprises two regions  202 . 1 ,  202 . 2 , which are electrically insulated from one another. On account of the laser patterning, the material of the bottom layer electrodes  202  was removed as far as the smoothing layer  201 , which resulted in a trench being produced in the bottom electrode layer  202 , said trench separating the two regions  202 . 1 ,  202 . 2  from one another. The OLE layer consists of three separate OLE layers  203 . 1 ,  203 . 2 ,  203 . 3 , wherein each layer emits the light in a different color. The layers  203 . 1 ,  203 . 2 ,  203 . 3 ,  204 ,  205 ,  206  were deposited such that at least one region of the bottom electrode layer is free of the coating. This region of the bottom electrode layer comprises a portion of the two regions  202 . 1 ,  202 . 2  of the bottom electrode layer that are electrically insulated from one another. Since the OLE layers are likewise deposited over one of the regions of the bottom electrode layer which was patterned by means of a laser, a part of the emission layer is deposited in the region of the trench produced on account of the laser patterning directly on the smoothing layer. The strip-type top electrode layer  204  is deposited such that at least the OLE-layer-free region of the bottom electrode layer and at least one region of the OLE layer are free of the coating thereof. The conductor track layer  205  is likewise formed in strip-type fashion. In this case, it is preferably formed such that it takes up only a small part of the area of the top electrode  204 .