Title of Invention

LIGHT EMITTING COMPONENT AND METHOD FOR IT'S MANUFACTURING

Abstract

The invention relating to a light emitting component with organic layers with several layers between a base contact and a top contact and the suitable manufacturing process, is the basis for the task of increasing the possibility of modification of layers with an improved ability of structuring. This is resolved on the arrangement side in a manner that at least one polymer layer and two molecule layers are arranged, wherein, if the top contact is a cathode, then the layer next to the top contact is built up as an electron transporting molecule layer and is doped through an organic or inorganic donor, wherein the electron transport layer covers an organic main substance and a donor type doping substance and the molecular mass of the dopant is greater than 200g/mol. If the top contact is an anode, then the layer next to the top contact is built up as a p-doped holes transporting molecular layer and is doped with an organic or inorganic acceptor, wherein the holes transport layer covers an organic main substance and an acceptor type doping substance and the molecular mass of the dopant is greater than 200g/mol. On the process side the solution is in the fact that at least one of the layers is evaporated as molecular layer, wherein the molecular layer is doped in such a manner that in a vacuum from two separately regulated sources a mix evaporation takes place.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION (See Section 10, rule 13) LIGHT EMITTING COMPONENT AND METHOD FOR IT"S MANUFACTURING; NOVALED GMBH of TATZBERG 49, 013 07 DRESDEN, GERMANY, GERMAN COMPANY The following specification particularly describes the nature of the invention and the manner in which it is to be performed : - The invention relates to a light emitting component with organic layers, especially an organic LED consisting of several layers between a base contact on a substrate and a top contact, with a polymer layer (consisting of polymer) built up as layers, and with layers built up as molecule layer consisting of small molecules brought in the vacuum. The invention relates also to the procedure for manufacturing of a light emitting component, in which, on a substrate a basic contact is brought on, thereafter, several layers and finally a top contact. Since the demonstration of low operating voltages by Tang et al. 1987 [C. W. Tang et at., Appl. Phys. Lett. 51 (12), 913 (1987)], organic LEDs are prospective candidates for the implementation of large area displays and other applications, like e.g. illumination elements. These consist of a series of thin (typically Inm to 1 µm) layers of organic materials, which are preferably vacuum evaporated in form of small molecules, whereby so-called OLED are produced, or can be spun-on, printed or can be applied in another suitable form (polymers), whereby so-called PLED can be produced. Through injecting charge carriers (electrons from one side and holes from the other side) from the contacts in the organic layers located in-between as a result of an externally fed voltage, followed by formation of excitons (electron - hole pairs) in an active zone and the radiating recombination of these excitons, light is produced and it is emitted by the LEDs. Normally organic light emitting diodes in the form of PLED are based on the following layer structure: 1. Substrate (transparent, e.g. glass) 2. Anode (transparent, mostly indium tin oxide (ITO)) 3. Hole transport or hole injection layer (mostly PEDOT:PSS or 4. PANI - poly-aniline with addition of PSS; PEDOT = polyethylene dioxythlophene, PSS = polystyrene sulfonate) Active polymer (emits light) 5. Cathode (mostly a metal with low work function like barium, calcium) The polymer layers, i.e. the hole transport layer or hole injection layer and the active polymer are produced from a liquid solution (in water or in solvent). The contacts (anode, cathode) typically through vacuum processes. The advantages of this structure for user, e.g. displays is the multiplicity of processes for the production of polymer layers, among these such processes, which allow a simple lateral structuring of PLED, namely the inkjet printing. In this process different polymers of three colors are printed on previously prepared spots, whereby neighboring areas emerge with different emission color. The disadvantage - among other things - is in the fact that no more than two different polymer layers can be applied in a meaningful manner, since the solvents of polymers must be so selected, that these do not influence mutually, which means these do not attack the base material. It means that the emitting polymer must be good enough simultaneously for the transport of electrons and for injection of electrons from the cathode, it is a requirement, which represents the strong restriction for the material selection and the structure optimization. Further, one can with great difficulty change the sequence of structure for a given material system, that means like in the above case one must make a start with anode. This is especially disadvantageous for the integration of PLED on active matrix display substrates with n- channel transistors as switching element. The use of transparent top contacts (also as cathode) is equally difficult, since these are mostly produced through a sputter process (e.g. ITO). This, however, destroys organic materials. Since the upper most layer in a PLED is a emitting layer, the efficiency of the light production of organic LED is thereby is reduced. An improvement of stability against sputter damages can be achieved through bringing-in a vacuum evaporated layer made of small molecules. However, in this case, electron injection from the cathode also poses a problem, A further disadvantage of the above structure is that one can achieve an efficient electron injection only with highly instable contact materials like barium or calcium. These materials get attacked by oxygen and water. Organic LEDs in the form of OLEDs are built-up from vacuum evaporated small molecules. If the molecules, which are supposed to build the layers of OLED, are small enough, then these can be brought-on without deterioration by a thermal process. For this purpose, the molecules are evaporated in the vacuum (due to greater open path length). In order to improve the injection from the contacts in the organic layer and to increase the conductivity of transport layers, the transport layers can be doped through mix evaporation with organic or inorganic dopants, which are acceptors (for hole doping) or donors (for electron doping). For this purpose, the dopants at the beginning of the evaporation process should not exist in their final form, as long as the alternatively used precursor material (which can also be modified one, e.g. by using electron radiation) builds dopant. The production of mixed layers takes place typically through mix (co) evaporation. In addition to the doped transport layers more intrinsic (that means not doped) intermediate layers must be brought-in with certain energy related properties (patent DE 100 58 578, M. Pfeiffer et al. "light emitting component with organic layers", submitted on the 20..11.2000; X. Zhou et al., Appl. Phys. Lett, 78,410 (2001)). The structure of the OLED is then a pin-hetero structure: 1. Carrier, substrate, 2. Electrode, hole injecting (anode = plus pole), preferably transparent, 3. p-doped holes injecting and transporting layer, 4. Thinner hole side block layer made of a material whose band positions match with the band positions of the surrounding layers, 5. Light emitting layer, 6. Electron side block layer (typically thinner than the layer mentioned below) made of a material, whose band positions match with the band positions of the surrounding layers, 7. n-doped electron injecting and transporting layer, 8. Electrode, mostly a metal with low work function, electron injecting (cathode = minus pole) Advantages of this structure are the individual optimizing ability of features of individual layers, the adjustable large gap of emitting layer to the contacts, the very good injection of charge carrier in the organic layers and the low thickness of layers not having good conductivity (4; 5; 6). Thus very low operating voltages () having simultaneously high efficiency of light generation can be achieved, like it is described in J. Huang, M. Pfeiffer, A. Werner, J. Blochwitz, Sh. Liu, K. Leo, Appl. Phys. Lett., 80,139-141 (2002); low voltage organic electroluminescent devices using pin structures. As represented in the DE 101 35 513.0 and in X.Q Zhou et al., Appl. Phys. Lett. 81, 922 (2002), besides, this structure can be easily inverted and top emitting or fully transparent OLEDs can be implemented, as described in the DE 10215 210.1. The disadvantage of this structure is in the fact that a lateral structuring of OLED structure for the buildup of multi-color pixel in a display can follow only through shadow masks. This process has limitation with respect to smallest achievable pixel sizes ( In the US 2003/020073AI the use of evaporated block layers and electron transport layers on a polymer hole transport layer has been described. In this arrangement there is a possibility, to laterally structure the polymer layer, to produce a full color display. However, in this arrangement the injection of charge carriers (here electrons from the cathode in the molecular electron transport layer) is problematic, which increases the operating voltage of the hybrid polymer small molecules OLED. Thus it is the task of the invention to increase the flexibility of structuring a light emitting component and the injection of charge carriers in the organic layers while maintaining good structure ability. This task is resolved on the arrangement side in such a way that at least one polymer layer and two molecule layers are arranged, wherein, if the top contact is a cathode, then the layer next to the top contact is built-up as ail electron transporting molecule layer and is doped with organic or inorganic donor, wherein the n-type dopant covers an organic main substance and a donor type doping substance and the molecular mass of the dopant is greater than 200g/mol, or, if the top contact is an anode, then the layer next to the top contact is built-up as p-doped hole transporting molecule layer and is doped with an organic or inorganic acceptor, wherein the dopant covers an organic main substance and an acceptor type doping substance and the molecular mass of the dopant is greater than 200g/mol, Through the inclusion of molecule layers a considerably higher flexibility in the layer bond can be achieved, whereas the simultaneous existence of polymer layers serves the purpose of easier structure ability without the significant use of shadow masks. The dopant should consist of organic, inorganic or metal organic molecule, which has a molar mass of greater 200g/mol preferred as greater 400g/mol. Here it is important that in the layer active dopant has this molar mass. For example, CS2CO3 (caesium carbonate, molar mass approx. 324g/mol) is not suitable as donor for the n-doping of electron transport layer in the sense of the invention. CS2CO3 as such a comparatively stable compound, which is no more in position to transfer one or more electrons on another molecule (the matrix material). However, in a vaporization process above 615°C (decomposition temperature), molecular CS would be freed, which would be in a position as dopant to transfer an electron on the matrix material. The molar mass of Cs is, however, 132g/mol. Caesium has as a dopant the disadvantage to be built in the matrix layer as relatively small molecule or atom not stable against diffusion, with negative influences on the working life of the organic light emitting component. Logically it valid in case of p-doping of hole transport layer with a strong acceptor (for inverted POLED structure). Both the molecular evaporated layers are the non-doped intermediate layer (reference serial number 5 in the design example described below) and the doped transport layer. Since the energy related barrier of the charge carrier injection from the doped transport layer in the polymer emitter layer for usual emitter polymers like poly-phenylene vinylene, PPV, (in case of traditionally known layer structure with polymer hole transport layer on a substrate the barrier for injection of electrons) is too large, a non-doped intermediate layer must be added, which is considerably thinner than the doped transport layer and whose LUMO energy level (LUMO: highest occupied molecular orbital) must be between the doped transport layer and the emission polymer layer. One consequence is that on one hand charge carriers can be injected better in the emitter polymer layer, on the other hand also non-radiative recombination processes occur on the marginal area from the emitter polymer layer to the doped transport layer, wherein normally these almost compulsorily occur in case of high energetic barriers. Light emitting component wherein a polymer layer is arranged, which simultaneously builds up an emitter layer and a transport layer. Light emitting component wherein more than two polymer layers are arranged. Light emitting component wherein only one molecule layer is arranged, which is doped. Light emitting component wherein the matrix material of the doped layer equal to the matrix material of the intermediated layer. Light emitting component wherein one polymer layer is arranged, on its side facing the base contact as well as on its side facing the top contact borders on to one molecule layer each. Light emitting component wherein contacts have been built-up transparent. Light emitting component wherein it consists of multiple-arrangement of identical light emitting components, which are electrically bonded with each other through a bonding layer. Light emitting component wherein the bonding layer has a contact and can be controlled through this. Light emitting component wherein the bonding layer and/or the contact has been designed as transparent. Light emitting component wherein the donor dopant in the electron transport layer is wolfram paddle wheel [ W2 (hpp)4] with hpp =1,3,4,6, 7,8 hexahydro-2H-pyrimido-[l, 2-a]-pyrimidine. On the process side the task is resolved in the a manner that at least one of the layers is applied as polymer layer and at least one of the layers is evaporated as molecule layer, wherein the molecule layer is doped. In the beneficial manner the doping of molecule layer follows in a vacuum from two separately regulated sources as a mix evaporation. The application of polymer layers can be done very precisely with simple means. This structuring then serves simultaneously for the structuring of future light emitting component, without requiring expensive structuring steps or means. As against this, the application molecule layers prevents that as a result of the presence of normally only two disjunctioned solvents the modification of polymer layers is highly restricted and increases the possibility of structuring most varied layer combinations. Method, wherein the dopants are produced only in the vacuum from a precursor, wherein a base material acting as precursor is evaporated, which forms the dopant during the evaporation process. Method wherein at least one of the polymer layers is produced and doped through bringing in a mix layer of a solution or through a consecutive application of materials followed by diffusion of dopants in the polymer layer The invention should be explained in detail on the basis of a design example, The related drawings show Fig.l a first layer structuring of an invention specific organic LED. Fig,2 a second, layer structuring of an invention specific organic LED electrically inverse to Fig.l As shown in Fig.l, on a substrate 1 a transparent basic contact 2 is applied as anode. On this base contact 2 a first polymer layer is deposited as polymer hole transport layer 3 and a second polymer layer as polymer emitter layer 4, this layer bond made up of first and second polymer layer consists of PEDOT:PSS (Baytron-P) by H.C.Starck, Germany, On this a first molecule layer is evaporated as intermediate layer 5, which consists of a layer of 10nm Bphen (Batophenanthroline). On this there is a second molecule layer in the form of an electron transport and injection layer 6 made of BPhen:Cs (molar doping concentration approx. 10:1 to 1:1). At the end the organic LED as per Fig.l is provided with a top contact 7 made of aluminum. Molecular Cs is to be considered in this context as a non-suitable, electron releasing dopant, since Cs has a too small molar mass, for being able to achieve a diffusion-stable doped layer. Therefore, doping materials having molar mass greater than 200g/mol are planned, preferably greater than 400g/mol., and have a redox potential in the field of Cs. Cs has a standard redox potential of -2.922 V and an ionization energy of 3,88 eV. The ionization energy of the dopant is less than 4.1 eV. A example for one of these dopants is Wolfram paddle wheel [W2 (hpp)4]: Wolfram-paddle wheel has an ionization potential of approx. 3.75 eV. The structure of the single negative hpp-anion is as follows: From comparing with the gas ionization potential of molecular Cs of 3.9 eV and the electron affinity of BPhen as layer of approx, 2.4 eV it can be estimated that it is essential that the donor dopant for OLED transport materials shows an ionization potential of less than 4.1 eV. The doped layer (in the above example BPhen:Cs) must have a conductivity in the range of 1E-7 S/cm to lE-3S/cm, preferably in a range from lE-6S/cm to 5E-5S/cm, The conductivity of the non-doped intermediate layer (in the above example BPhen) must be in the range of approx, 1E-10S/cm to 5E-8S/cm. The conductivity of non-doped layer is , thus, is worse by 50% than that of the doped layer. The preferred thickness ranges of doped layer are between 40 nm and 500 ran, preferred range 50 nm to 300 ran, the range for the non-doped intermediate layer is between 2 nm and 30 nm, preferred range 5 nm to 15 nm. The un-doped layer must be considerably thinner - due to its low conductivity - than the doped layer. The considerations with respect to layer thickness and conductivity are logically applicable also for the p-doping of hole transport layer according to the design example 2 given further below. This design form can be modified in that a single layer can occur as polymer hole transport layer 3 and as polymer emitter layer 4, which takes over both the functions, which means only one polymer layer can be present. Further, the base contact 2 can also be built-up as non-transparent (e.g. gold, aluminum) and then the top contact 7 as cathode transparent, e.g. through an ITO layer produced in a sputter process. Due to doping of the layer 6 an electron injection of ITO in layer 6 is still possible. Further, the dopant concentration in case of organic dopants can be between 1:1000 and 1:20 and in case inorganic dopants between 1:1000 and 3:1. As it is apparent, the invention specific organic LED consists of polymer as well as molecule layers and can be termed as POLED or hybride OLED. An alternative design form is shown in Fig.2. It shows a structure electrically inverse to Fig.l. On a substrate 1 a base contact 2 is provided as cathode. The base contact 2 is designed as non- transparent cathode (calcium, barium or aluminum), however, it can also be transparent (ITO). On this base contact 2 a first polymer layer is deposited as polymer electron transport layer 8 and a second polymer layer as polymer emitter layer 4. On this a first molecule layer is evaporated as intermediate layer 9, which can consist of 10nm TPD (tri-phenyl Diamine). On this there is a second molecule layer in the form of a hole transport and injection layer 10 of e.g. m-MTDATA doped with F4-TCNQ (tris (3-methyl phenyl phenyl amino) - Triphenylamine doped with terrafluoro-tetracycanoquino dimethane) in molar ratio approx, 50:1. At the end the organic LED as per Fig.2 is provided with an anode as top contact 7 of e.g. transparent ITO. Other design forms not represented in detail are contained in exchanging the sequence of polymer and molecule layers, that means, first to bring on the substrate 1 for base contact 2 a doped molecule layer 10 or 6, and thereafter, the lateral structure able polymer layers 4 and 8 or 3. further alternative to this a design is possible, in which an active polymer emitter layer 4 is surrounded by organic molecule layers. If on the base contact 2 an anode is brought on, then the immediate sequence is molecular doped hole injection and transport layer 10, intermediate layer 9, polymer layer 4, intermediate layer 5 and molecular doped electron transport layer 10 and top contact 7 as cathode. If the cathode is brought on as base contact 2 on the substrate 1, then the sequence is inverted. Claim: 1. Light emitting component with organic layers consisting of several layers between a base contact on a substrate and a top contact, with layers as polymer layers, which consist of polymer and with layers built-up as molecule layer, which consist of small molecules brought on in the vacuum, characterized by the fact that at least one polymer layer (3, 4) and two molecule evaporated layers (5, 6) are arranged, said molecular evaporated layers are the non doped intermediate layer (5) and the doped transport layer (6), wherein, if the top contact (7) is a cathode, the layer next to the top contact (7) is built-up as an electron transporting molecule layer and if it is doped by an organic or inorganic donor, wherein the n-type dopant covers an organic main substance and a donor type doping substance and if the molecular mass of the dopant is greater than 200g/mol, or if the top contact (7) is an anode, the layer next to the top contact (7) is built-up as a p-doped hole transporting molecule layer and if it is doped by an organic or inorganic accepter, wherein the dopant covers an organic main substance and a accepter type doping substance and if the molecular mass of the dopant is greater than 200g/mol. 2. Light emitting component as claimed in claim 1 wherein a polymer layer is arranged, which simultaneously builds up an emitter layer and a transport layer. 3. Light emitting component as claimed in claim 1 or 2, wherein more than two polymer layers (3,4) are arranged. 4. Light emitting component as claimed in one of the claims 1 to 3 wherein only one molecule layer is arranged, which is doped. 5. Light emitting component as claimed in one of the claims 1 to 3 wherein the matrix material of the doped layer (9) is equal to the matrix material of the intermediated layer (5). 6. Light emitting component as claimed in one of the claims 1 or 2 wherein one polymer layer is arranged, on its side facing the base contact (2) as well as on its side facing the top contact (7) borders on to one molecule layer each. 7. Light emitting component as claimed in one of the claims 1 to 6 wherein contacts (2, 7) have been built-up transparent. 8. Light emitting component as claimed in one of the claims 1 to 7 wherein it consists of multiple-arrangement of identical light emitting components, which are electrically bonded with each other through a bonding layer. 9. Light emitting component as claimed in claim 8 wherein the bonding layer has a contact and can be controlled through this. 10. Light emitting component as claimed in claim 8 or 9 wherein the bonding layer and/or the contact has been designed as transparent. 11. Light emitting component as claimed in one of the claims 1 to 10 wherein the donor dopant in the electron transport layer is wolfram paddle wheel [ W2 (hpp)4] with hpp =1,3,4,6, 7, 8 hexahydro-2H-pyrimido-[l, 2-a]-pyrimidine. 12. Light emitting component as claimed in one of the claims 1 to 11 wherein the doped layer has a conductivity in a range from lE-7s/cm to lE-3S/cm. 13. Light emitting component as claimed in one of the claims 1 to 12 wherein the doped layer has a conductivity in a range from lE-6S/cm to 5E-5S/cm. 14. Light emitting component as claimed in one of the claims 1 to 13 wherein the conductivity of non-doped intermediate layer is at least less than half of the conductivity of the doped layer. 15. Light emitting component as claimed in one of the claims 1 to 14 wherein the doped layer has a thickness in a range from 40 nm to 500 ran. 16. Light emitting component as claimed in one of the claims 1 to 15 wherein the doped layer has a thickness in a range from 50 nm to 300 nm. 17. Light emitting component as claimed in one of the claims 1 to 16 wherein the non-doped intermediate layer has a thickness in a range form 2 nm to 30 nm. 18. Light emitting component as claimed in one of the claims 1 to 17 wherein the non-doped intermediate layer has a thickness in a range from 5nm to 15 nm. 19. Light emitting component as claimed in one of the claims 1 to 18 wherein the non-doped layer is built-up thinner than the doped layer. 20. Light emitting component as claimed in one of the claims 1 to 19 wherein the donor dopant has an ionization potential of less than 4.1eV. 21. Light emitting component as claimed in one of the claims 1 to 20 wherein the dopant concentration in case of organic dopants is between 1:1000 and 1:20 and in case of inorganic dopants between 1:1000 and 3:1. 22. A method for manufacturing a light emitting component as per one of the claims 1 to 21, in which on a substrate a base contact, thereafter, several layers and at the end a top contact are brought on, characterized by the fact, that at least one of the layers is applied as polymer layer and at least one of the layers is evaporated as molecule layer, wherein the molecule layer is doped and the doping of the molecule layer takes place in a vacuum from two separately controlled sources as a mix evaporation. 23. Method as claimed in claim 22, wherein the dopants are produced only in the vacuum from a precursor, wherein a base material acting as precursor is evaporated, which forms the dopant during the evaporation process, 24. Method as claimed in one of the claims 22 & 23, wherein the dopant concentration in case of organic dopant is between 1:1000 and 1:20 and in inorganic between 1:1000 and 3:1. 25. Method as claimed in one of the claims 22 to 24 wherein at least one of the polymer layers is produced and doped through bringing in a mix layer of a solution or through a consecutive application of materials followed by diffusion of dopants in the polymer layer. 26. Method as claimed in one of the claims 22 to 25 wherein in the electron transport layer a donor dopant Wolfram paddlewheel [W2 (hpp)4] with hpp = 1, 3, 4, 6, 7, 8-Hexahydro-2H-pyrimido-[l, 2-a]-pyrimidin is used. Dated this 9th day of August, 2004. (DARSHANA H. JOSHI) ASEAN SAARC PATENT & TRADE MARK SERVICES AGENT FOR NOVALED GMBH

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