WO2023012084A1

WO2023012084A1 - A printing method by combining inks

Info

Publication number: WO2023012084A1
Application number: PCT/EP2022/071494
Authority: WO
Inventors: Gaëlle BÉALLE; Christoph Leonhard; Hsin-Rong Tseng; Manuel HAMBURGER; Margarita Wucherer-Plietker; Sabine KNIPPEL
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2021-08-02
Filing date: 2022-08-01
Publication date: 2023-02-09
Anticipated expiration: 2024-02-02
Also published as: KR20240045247A; JP2024528219A; CN117730638A

Abstract

The present invention relates to a printing method comprising the following steps: (a) providing a substrate, having at least two different pixel types, a first pixel type A and a second pixel type B, (b) printing a first ink A, containing at least one organic functional material A and at least one organic solvent A, into pixel type A or into the at least two different pixel types, (c) printing a second ink B, containing at least one organic functional material B, which is different from the organic functional material A, and at least one organic solvent B, into the at least two different pixel types A and B, and (d) thereafter drying the different pixel types, as well as to a kit of inks.

Description

A printing method by combining inks

Field of the invention

The present invention relates to a printing method by combing inks. The present invention further relates to a method for producing functional layers of organic light emitting diodes (OLEDs) and to a method for producing OLEDs, in particular full colour OLEDs by conducting the printing method of the present invention.

Background of the invention

OLED - organic light emitting diode - displays are extremely thin, lightweight and energy-efficient. They deliver a perfect image from every viewing angle with extraordinary colour brilliance and very high contrast. Due to the low energy consumption, small OLED displays are well suited for use in portable devices, like smartphones, digital frames, and digital cameras. OLED displays are suitable for televisions, monitors, large-area video walls, and in automotive applications.

OLED displays consist of arrays of individually controlled light emitting elements or pixels. For full colour displays, each pixel will consist of red, green, and blue (RGB) emitting sub-pixels, that can be individually controlled in order to collectively produce the desired image. In this regard, there are two main approaches for RGB colour patterning in OLED displays: (a) side-by-side RGB OLEDs; and (b) white OLEDs plus colour filters. In the first approach, each pixel consists of RGB OLED subpixels and the total light output of each device contributes directly to the final image without modification. In the latter case, three white OLED subpixels are combined with three color filters. The basic OLED cell structure forming the RGB OLEDs generally consists of organic semiconductor molecules deposited between conducting electrodes on a substrate of glass or flexible polymer film. When current flows between the electrodes, electrons and holes are injected into the organic semiconductors, which upon pairwise recombination generate excitons, which shift the organic molecules in an electronically excited state. They return from an electronically excited state to the ground state by emitting light. The molecular structure of the semiconductors used determines the colour of the emitted light. Specifically, an OLED stack comprises a plurality of functional organic layers including a hole injection layer, a hole transport layer, an emitting layer, an electron transport layer, and an electron injection layer. All these layers are situated between an anode and a cathode.

Breakdown of an OLED structure:

• Substrate (can be plastic, glass, or metal foil) - Foundation of the OLED.

• Anode (may or may not be transparent depending on the type of OLED) - Positively charged to inject holes (absence of electrons) into the organic layers that make up the OLED device.

• Hole Injection Layer (HIL) - Deposited on top of the anode this layer receives holes from the anode and injects them deeper into the device.

• Hole Transport Layer (HTL) - This layer supports the transport of holes across it so that they can reach the emissive layer.

• Emissive Layer (EML) - The layer where light is generated. The emissive layer consists of a colour defining emitter doped into a host. This is the layer where the electrical energy is directly converted into light. • Electron Transport Layer (ETL) - Supports the transport of electrons across it so that they can reach the emissive layer.

• Electron Injection Layer (EIL) - This layer receives electrons from the cathode and injects them deeper into the device.

• Cathode (may or may not be transparent depending on the type of OLED) - Negatively charged to inject electrons into the organic layers that make up the OLED device.

Since the entire light output of each device is utilized in image creation, the side-by-side approach provides the best power consumption efficiency.

This approach however requires the fabrication of RGB OLEDs side-by- side on the same substrate. Since organic semiconductors are usually not amenable with photolithographic processes due to their easy damage by solvents, fabricating OLEDs using different materials on the same substrate can only be done by their thermal deposition of OLED materials using shadow masks, or in the case of polymers and solution-processable small molecule materials, via printing-based techniques, such as inkjet printing.

OLED inkjet printing is a cost-effective way to produce large OLED displays. OLED inks can be precisely deposited onto a surface with efficient use of materials. No shadow masks are needed, compared to the OLED vaporization process. OLED inkjet printing is a less complex process and can be done at room temperature and atmospheric pressure.

For improving the OLED inkjet printing technique US 2019/0123308 A1 discloses a preparation method characterized in that by adding a soluble fluorine-containing insulation layer on the substrate, the solution drops for inkjet printing can favourably form the RGB luminescent layer in the subpixel pits, thereby greatly improving the production yield for the printing OLED display. CN 109130494 A provides an OLED inkjet printing device comprising a nozzle with an inkjet channel, an ink supply unit with a channel and a flexible member connected with the nozzle and the ink supply unit, characterised in that the flexible member can move relative to the nozzle and/or the ink supply unit and be communicated with the inkjet channel and the ink supply channel or disconnected from at least one of the inkjet channel and the ink supply channel as the movement of the flexible member.

US Patent 6,066,357 describes a method of making a full-colour organic light-emitting display comprising ink-jet printing of fluorescent dopants selected to produce red, green, or blue light emission from designated subpixels of the display. The dopants are printed sequentially from ink-jet printing compositions which permit printing of dopant layers over a lightemitting layer containing a host material selected to provide host light emission in a blue spectral region. The dopants are diffused from the dopant layer into the light-emitting layer by exposing the light-emitting layer and the dopant layers to vapor of a fluid or fluid mixture. When an ink-jet printing composition is formulated with a printing fluid having fluid vapours which promote dopant diffusion, the steps of ink-jet printing and diffusing of dopants can be combined to form a selectively doped light-emitting layer.

For the preparation of a full-colour OLED display by inkjet printing, a multitude of inks is necessary to prepare all printed layers, including up to three different HILs, three HTLs and three EMLs, i.e. a maximum of 9 inks in total. However, the number of inks used for printing is limited by the print head, because the print head can only take up a low number of individual inks, which makes printing OLED structures more difficult. Furthermore, since there are a multitude of inks and some of them are immiscible or reactive with each other, mixing these inks before printing would lead to precipitation in the inks before application. In this regard US 2013/0038651 A1 discloses an ink-jet printing method including the steps of dividing multiple ink droplet discharging pulses into two or more groups in an ink droplet discharging order, providing the multiple ink droplet discharging pulses to a pressure generator per scan line time, and discharging ink droplets from an ink droplet discharge head in accordance with the multiple ink droplet discharging pulses. The method further includes the steps of combining ink droplets of a former group as a first combined ink droplet, combining ink droplets of a latter group as a second combination droplet, combining the second combined ink droplet of the latter group with that of the former group before the ink droplets reach a target, and maintaining a prescribed amount of ink droplets landing on the target by decreasing the number of ink droplet discharging pulses.

US 2017/0213965 A1 discloses a manufacturing method of an organic light emitting diode display panel for reducing the number of inkjet heads used in inkjet printing or alleviating the swath mura at printing interfaces. The method comprises manufacturing an anode layer, a light emitting layer and a cathode layer on a base substrate, and the method can further comprise manufacturing by an entire-surface coating process a function layer having a first preset thickness between the anode layer and the light emitting layer; and in a first preset region of the function layer that has been manufactured, manufacturing by an inkjet printing process a function layer having a second preset thickness.

However, in the prior art there is still an urgent need to provide a process for manufacturing full-colour OLED displays with a reduced number of inks for simplifying the preparation of OLED displays as well as to reduce the cost of equipment and fabrication process. of the invention The present invention relates to a printing method comprising or consisting of the following steps:

(a) providing a substrate, having at least two different pixel types, a first pixel type A and a second pixel type B,

(b) printing a first ink A, containing at least one organic functional material A and at least one organic solvent A, into pixel type A or into the at least two different pixel types A and B,

(c) printing a second ink B, containing at least one organic functional material B, which is different from the organic functional material A, and at least one organic solvent B, into the at least two different pixel types A and B, and

(d) thereafter drying the different pixel types.

The present invention also relates to a method for producing functional layers, preferably functional layers of an organic light emitting diode (OLED), wherein the functional layers are produced by conducting the printing method of the present application.

The present invention furthermore relates to a method for producing an OLED, comprising or consisting of the following steps: a) providing a pair of electrodes, b) providing at least a Hole Injection Layer (HIL), a Hole Transport Layer (HTL) and an Emissive Layer (EML) between the pair of electrodes, characterized in that the Hole Injection Layer (HIL), the Hole Transport Layer (HTL) and/or the Emissive Layer (EML) is produced by conducting the printing method of the present application.

According to a preferred embodiment of the present invention, the OLED is a full-colour OLED.

The present invention furthermore relates to a kit of inks, containing at least two different inks, an ink A and an ink B, - wherein ink A contains at least a first organic functional material A and at least a first organic solvent A,

- wherein ink B contains at least a second organic functional material B and at least a second organic solvent B, and

- wherein the first organic functional material A and the second organic functional material B are different, characterized in that when mixed, both inks result in one ink containing at least a first organic functional material A, a second organic functional B, at least a first organic solvent A and at least a second organic solvent B.

The present invention furthermore relates to a method for the preparation of an ink, containing at least a first organic functional material A, a second organic functional B, at least a first organic solvent A and at least a second organic solvent B, characterized in that an ink A, containing at least a first organic functional material A and at least a first organic solvent A, and an ink B, containing at least a second organic functional material B and at least a second organic solvent B, wherein the first organic functional material A and the second organic functional material B are different, are mixed.

Figure 1 shows a schematic diagram of the fabrication process of a red/green/blue panel using a conventional printing method.

Figure 2 shows the photoluminescence images of the green and red pixel of the emissive layer as produced in Example 1 of the present application. Figure 3 shows a schematic diagram of the fabrication process of a red/green/blue panel using the method of the present invention.

Figure 4 shows a schematic diagram of the fabrication process of a red/green/blue/white panel using the method of the present invention.

Detailed description of the invention

The present invention relates to a printing method comprising or consisting of the following steps:

(d) thereafter drying the different pixel types.

According to the present invention, the substrate has at least two different pixel types, a first pixel type A and a second pixel type B.

Preferably, the substrate has at least three different pixel types, a first pixel type A, a second pixel type B, and a third pixel type C. More preferably, the substrate has three different pixel types, a first pixel type A, a second pixel type B, and a third pixel type C.

It is also possible that the substrate has four different pixel types, a first pixel type A, a second pixel type B, a third pixel type C, and a fourth pixel type D. According to the present application, the printing method can be any printing method known to a person skilled in the art, for example, flood coating, dip coating, spray coating, spin coating, screen printing, relief printing, gravure printing, rotary printing, roller coating, flexographic printing, offset printing or nozzle printing. Nevertheless, the preferred printing method is ink-jet printing.

The printing method of the present application, preferably the ink-jet printing method of the present application is used to produce a functional layer of an electronic device, preferably a functional layer of an organic light emitting diode (OLED).

The functional layer is preferably a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), an Emissive Layer (EML), an Electron Transport Layer (ETL) or an Electron Injection Layer (EIL), preferably a Hole Injection Layer (HIL), a Hole Transport Layer (HTL) or an Emissive Layer (EML).

In a preferred 1^st embodiment of the present invention, the method is characterised in that: the first ink A is printed into the at least two different pixel types A and B, and the second ink B is printed into the at least two different pixel types A and B.

In a preferred 2^nd embodiment of the present invention, the method is characterised in that the substrate has at least three, preferably three, different pixel types, a first pixel type A, a second pixel type B and a third pixel type C.

In the preferred 2^nd embodiment of the present invention, the method is preferably characterised in that the first ink A is printed into the at least three different pixel types A, B and C, and the second ink B is printed into the at least three different pixel types A, B and C. In the preferred 2^nd embodiment of the present invention, the method is more preferably characterised in that, the first ink A is printed into the three different pixel types, and the second ink B is printed into the three different pixel types.

The preferred 1 ^st and 2^nd embodiment are preferably used to prepare a hole-injection layer (HIL) of an OLED.

In one embodiment of the preferred 1 ^st and 2^nd embodiment, the first ink A contains at least one hole-transporting material as organic functional material and at least one organic solvent A.

As hole-transport material, any suitable material commonly used especially for OLEDs can be used. Preferred materials are described in the present application.

The at least one hole-transporting material is preferably a polymeric material, which has preferably a molecular weight Mw of > 10,000 g/mol, more preferably of > 25,000 g/mol and most preferably of > 50,000 g/mol.

In another embodiment of the preferred 1^st and 2^nd embodiment, the second ink B contains at least one dopant as organic functional material and at least one solvent B.

As dopant, any suitable material, preferably any suitable salt, commonly used especially for OLEDs, in particular in combination with the above- mentioned hole-transporting material, can be used. The term dopant as employed herein is also used for the term salt. Preferred salts are described for example in WO 2016/107668 A1 . The at least one dopant is preferably a low molecular weight material, which has preferably a molecular weight of < 3.000 g/mol, more preferably of < 2,000 g/mol and most preferably of < 1 ,000 g/mol.

The amount of the first ink A, which is printed into the at least three different pixel types A, B, and C, can be identical in all pixels or can differ from pixel type to pixel type, preferably it differs from pixel type to pixel type.

Also the amount of the second ink B, which is printed into the at least three different pixel types A, B, and C, can be identical in all pixels or can differ from pixel type to pixel type, preferably it differs from pixel type to pixel type.

Furthermore, in that the ratio of the amount of both inks, i.e. ink A and ink B, can be varied over a very broad range, it is also possible to vary the ratio of the hole-transporting material and the dopant over a very broad range.

As organic solvent A and organic solvent B any suitable organic solvent commonly used can be used.

Organic solvent A as well as organic solvent B can either be a single solvent or a mixture of solvents.

If organic solvent A and organic solvent B are single solvents, they can be identical or different.

Also, if organic solvent A and organic solvent B are a mixture of solvents, they can be identical or different.

As organic solvent A and organic solvent B, any suitable solvent or solvent mixture commonly used can be used. Preferred solvents and solvent mixtures are described in the present application.

If all pixels, i.e. pixel A, B and C, are printed using the method of the 1^st and 2^nd preferred embodiment, it is possible to vary the ratio from pixel to pixel with only two inks in total.

For the preparation of such a hole-injection layer, using a conventional printing technic, at least three different inks would be required. This shows the advantage of the method of the present invention.

Next to the hole-injection layer, in general a hole-transport layer is deposited via a printing technic.

As hole-transport material for the hole-transport layer, any suitable material commonly used especially for OLEDs can be used. Preferred materials are described in the present application.

For the different pixels, the same or different hole-transport materials can be used. Preferably, the same hole-transport material is used for all three different pixel types.

In another preferred embodiment of the present application, as holetransport material the same hole-transport material is used as for the holeinjection layer. As a result of this preferred embodiment, it is possible using the method of the present invention to print the hole-injection layer and the hole-transport layer with only two different inks.

For the preparation of such a hole-injection and hole-transport layer, using a conventional printing technic, at least four different inks would be required. This again shows the advantage of the method of the present invention.

In a 3^rd preferred embodiment of the present invention, the method is characterised in that the first ink A is printed into pixel type A, and the second ink B is printed into pixel type A and B.

In a preferred embodiment of the 3^rd preferred embodiment, both inks, i.e. ink A as well as ink B, contain at least one light emitting material, which are different from each other. In a more preferred embodiment, ink A contains a red light emitting material and ink B contains a green light emitting material.

In a 4^th preferred embodiment of the present invention, the method is characterised in that the first ink A is printed into pixel type A, the second ink B is printed into pixel type A and B, and a third ink C, containing at least one organic functional material C, which is different from the organic functional materials A and B, and at least one organic solvent C is printed into pixel type C.

In a preferred embodiment of the 3^rd and 4^th preferred embodiment, the first ink A, the second ink B and the third ink C, each contains at least one lightemitting material as organic functional material and at least one solvent.

In a further preferred embodiment of the 3^rd and 4^th preferred embodiment, each of the at least one light emitting materials of the first ink A, the second ink B and the third ink C is selected from the group consisting of fluorescent light emitting materials and phosphorescent light emitting material.

Preferably, the light-emitting material A of the first ink A is a light-emitting material emitting red light, preferably a phosphorescent light-emitting material emitting red light. Emitting red light according to the present invention means emitting light in the range from 600 to 750 nm.

Preferably, the light-emitting material B of the second ink B is a lightemitting material emitting green light, preferably a phosphorescent lightemitting material emitting green light. Emitting green light according to the present invention means emitting light in the range from 500 to 570 nm.

Preferably, the light-emitting material C of the third ink C is a light-emitting material emitting blue light, preferably a fluorescent light-emitting material emitting blue light. Emitting blue light according to the present invention means emitting light in the range from 420 to 480 nm.

In a preferred embodiment, the light-emitting material of the first ink A, the light-emitting material of the second ink B and the light-emitting material of the third ink C are low molecular weight materials, which have preferably a molecular weight of < 3.000 g/mol, more preferably of < 2,000 g/mol and most preferably of < 1 ,000 g/mol.

In a 5^th preferred embodiment of the present invention, the method of the present invention is characterized in that a fourth ink D, containing at least one organic functional material D, which is different from the organic functional materials A, B and C, and at least one organic solvent D, is printed into pixel type A, B and/or C, preferably printed into pixel type A, B and C. Preferably, the at least one organic functional material D is a matrix material.

In a 6^th preferred embodiment of the present invention, the printing method comprises the following steps:

(a) providing a substrate, having at least four different pixel types, a first pixel type A, a second pixel type B, a third pixel type C and a fourth pixel type D,

(b) printing a first ink A, containing at least one organic functional material A and at least one organic solvent A, into the at least pixel type A, B, C and

D,

(c) printing a second ink B, containing at least one organic functional material B, which is different from the organic functional material A, and at least one organic solvent B, into the at least three different pixel types B, C and D,

(d) printing a third ink C, containing at least one organic functional material C, which is different from the organic functional materials A and B, and at least one organic solvent C, into the at least pixel types C and D, and

(d) thereafter drying the different pixel types.

Preferably, the light-emitting material A of the first ink A is a light-emitting material emitting blue light, preferably a fluorescent light-emitting material emitting blue light. Emitting blue light according to the present invention means emitting light in the range from 420 to 480 nm.

Preferably, the light-emitting material C of the third ink C is a light-emitting material emitting red light, preferably a phosphorescent light-emitting material emitting red light. Emitting red light according to the present invention means emitting light in the range from 600 to 750 nm.

Furthermore, the light emitting material C is printed in pixel type C in such an amount that a red emission is achieved and the light emitting material C is printed in pixel type D in such an amount that a white emission is achieved.

Using the method of the 6^th preferred embodiment, it is possible to produce an R/G/B/W OLED panel with only 3 different inks.

As light emitting material, any suitable material commonly used can be used. Preferred materials are described in the present application.

The at least one light-emitting material is preferably a low molecular weight material, which has preferably a molecular weight of < 3.000 g/mol, more preferably of < 2,000 g/mol and most preferably of < 1 ,000 g/mol.

As matrix material, any suitable material commonly used can be used. Preferred materials are described in the present application.

The at least one matrix material is preferably a low molecular weight material, which has preferably a molecular weight of < 3.000 g/mol, more preferably of < 2,000 g/mol and most preferably of < 1 ,000 g/mol.

If, according to the method of the present invention, two different inks are printed into the same pixel type, e.g. an ink A and ink B, the printing results in one ink containing at least a first organic functional material A, a second organic functional B, at least a first organic solvent A and at least a second organic solvent B. In all preferred embodiments, i.e. 1^st to 6^th embodiment, the content of the organic functional materials A, B, C and/or D in the corresponding inks are respectively in the range from 0.001 to 20 weight-%, preferably in the range from 0.01 to 10 weight-%, more preferably in the range from 0.1 to 5 weight-% and most preferably in the range from 0.3 to 5 weight-%, based on the total weight of the inks.

In all preferred embodiments, i.e. the 1^st to 6^th embodiment, the organic solvents A, B, C and/or D have a boiling point in the range from 100 to 400°C, preferably in the range from 200 to 350°C, more preferably in the range from 225 to 325°C and most preferably in the range from 250 to 300°C.

In all preferred embodiments, i.e. the 1^st to 6^th embodiment, the organic functional materials A, B, C and/or D have respectively a solubility (measured at room temperature) in the corresponding organic solvents which is > 5 g/l, preferably > 10 g/l.

In all preferred embodiments, i.e. the 1^st to 6^th embodiment, the first, second, optional third and optional fourth ink have respectively a viscosity in the range from 0.8 to 50 mPas, preferably in the range from 1 to 40 mPas, and more preferably in the range from 2 to 15 mPas.

The viscosity of the inks and solvents according to the present invention is measured with a 1 ° cone-plate rotational rheometer of the type Discovery AR3 (Thermo Scientific). The equipment allows a precise control of the temperature and sheer rate. The measurement of the viscosity is carried out at a temperature of 25.0°C (+/- 0.2°C) and a sheer rate of 500 s’¹. Each sample is measured three times and the obtained measured values are averaged. In all preferred embodiments, i.e. the 1^st to 6^th embodiment, the first, second, optional third and optional fourth ink have respectively a surface tension in the range from 15 to 70 mN/m, preferably in the range from 10 to 50 mN/m and more preferably in the range from 20 to 40 mN/m.

The surface tension can be measured using a FTA (First Ten Angstrom) 1000 contact angle goniometer at 20°C. Details of the method are available from First Ten Angstrom as published by Roger P. Woodward, Ph.D. “Surface Tension Measurements Using the Drop Shape Method”. Preferably, the pendant drop method can be used to determine the surface tension. This measurement technique dispenses a drop from a needle in a bulk liquid or gaseous phase. The shape of the drop results from the relationship between the surface-tension, gravity and density differences. Using the pendant drop method, the surface tension is calculated from the shadow image of a pendant drop using http://www.kruss.de/services/education-theory/glossary/drop-shape- analysis. A commonly used and commercially available high precision drop shape analysis tool, namely FTA1000 from First Ten Angstrom, was used to perform all surface tension measurements. The surface tension is determined by the software FTA1000. All measurements were performed at room temperature which is in the range between 20°C and 25°C. The standard operating procedure includes the determination of the surface tension of each formulation using a fresh disposable drop dispensing system (syringe and needle). Each drop is measured over the duration of one minute with sixty measurements which are later on averaged. For each formulation three drops are measured. The final value is averaged over said measurements. The tool is regularly cross-checked against various liquids having well known surface tensions.

The present invention furthermore relates to a method for producing an OLED, preferably a full-colour OLED, containing between a pair of electrodes at least a Hole Injection Layer (HIL), a Hole Transport Layer (HTL) and an Emissive Layer (EML), characterized in that the Hole Injection Layer (HIL), the Hole-transport layer (HTL) and/or the Emissive layer (EML), preferably the Hole Injection Layer (HIL), the Hole-transport layer (HTL) and the Emissive layer (EML) are produced according to the method of the present invention.

According to the method of the present invention, inks A and B and optionally inks C and D are used. Each of these inks contains at least one organic functional material, which can be employed for the production of functional layers of electronic devices. Functional materials are generally the organic materials which are introduced between the anode and the cathode of an electronic device, preferably an OLED.

The term organic functional material denotes, inter alia, organic conductors, organic semiconductors, organic fluorescent compounds, organic phosphorescent compounds, organic light-absorbent compounds, organic light-sensitive compounds, organic photosensitisation agents and other organic photoactive compounds. The term organic functional material furthermore encompasses organometallic complexes of transition metals, rare earths, lanthanides and actinides.

The organic functional material is preferably an organic semiconductor selected from the group consisting of from hole injection materials (HIM), hole transport materials (HTM), hole blocking materials (HBM), electron injection materials (EIM), electron transport materials (ETM), electron blocking materials (EBM), exciton blocking materials (ExBM), host materials, emitter materials, and metal complexes.

Preferred embodiments of organic functional materials are disclosed in detail in WO 2011 Z076314 A1 . In a more preferred embodiment, the organic semiconductor is an emitting material selected from the group consisting of fluorescent emitters and phosphorescent emitters.

According to the present application the term emitter denotes a material which, after excitation, which can take place by transfer of any type of energy, allows a radiative transition into a ground state with emission of light. In general, two classes of emitter are known, namely fluorescent and phosphorescent emitters. The term fluorescent emitter denotes materials or compounds in which a radiative transition from an excited singlet state into the ground state takes place. The term phosphorescent emitter preferably denotes luminescent materials or compounds which contain transition metals.

Emitters are frequently also called dopants if the dopants cause the properties described above in a system. A dopant in a system comprising a matrix material and a dopant is taken to mean the component whose proportion in the mixture is the smaller. Correspondingly, a matrix material in a system comprising a matrix material and a dopant is taken to mean the component whose proportion in the mixture is the greater. Accordingly, the term phosphorescent emitter can also be taken to mean, for example, phosphorescent dopant.

The organic functional material can be a compound having a low molecular weight, a polymer, an oligomer or a dendrimer, where the organic functional material may also be in the form of a mixture. Thus, the inks used according to the method of the present invention may comprise two or more different compounds having a low molecular weight, one compound having a low molecular weight and one polymer or two polymers (blend). If the organic functional material is a low molecular weight compound, it has preferably a molecular weight of < 3,000 g/mol, more preferably of < 2,000 g/mol and most preferably of < 1 ,000 g/mol.

If the organic functional material is a polymeric compound, it has preferably a molecular weight Mw of > 10,000 g/mol, more preferably of > 25,000 g/mol and most preferably of > 50,000 g/mol.

The molecular weight Mw of the polymers here is preferably in the range from 10,000 to 2,000,000 g/mol, more preferably in the range from 25,000 to 1 ,000,000 g/mol and most preferably in the range from 50,000 to 300,000 g/mol. The molecular weight Mw is determined by means of GPC (= gel permeation chromatography) against an internal polystyrene standard.

The emitter materials are preferably selected from the class of organic electroluminescent emitter materials as outlined elsewhere within the present application.

The organic functional materials according to the present application are often characterized by their molecular frontier orbitals, i.e. the highest occupied molecular orbital (HOMO) (sometimes also referred to as valence band) and the lowest unoccupied molecular orbital (LIIMO) (sometimes also referred to as conduction band). The HOMO and LIIMO levels are routinely measured (by e.g. XPS=X-ray photoelectron spectroscopy, UPS=ultra-violet photoelectron spectroscopy or CV=cyclovoltammetry) or calculated (by quantum chemical methods such as (time dependent) DFT= density functional theory) which are known to the person skilled in the art. One skilled in the art is also aware of the fact that absolute values of these energy levels significantly depend on the method used. The applicant established a consistent combination method to determine the energy levels of organic semiconductors. The HOMO/LUMO levels of a set of semiconductors (more than 20 different semiconductors) are measured by CV with a reliable evaluation method and also calculated by the DFT of Gaussian 03W with the same correction functional, for example B3PW91 and the same basis set, for example 6-31 G(d). The calculated values are then calibrated according to the measured values. Such calibration factor is used for further calculation. The agreement between calculated and measured values is very good. Therefore, the comparison of the energy levels of this application is set on a sound base. The energy gaps or band gaps are obtained by the difference between HOMO and LIIMO energy levels.

The inks according to the present invention may comprise one or more organic functional materials selected from hole injection materials (HIM). A HIM refers to a material or unit capable of facilitating holes (i.e. positive charges) injected from an anode into an organic layer or an anode. Typically, a HIM has a HOMO level comparable to or higher than the work function of the anode, i.e. - 5.3 eV or higher.

The inks according to the present invention may comprise one or more organic functional materials selected from hole transport materials (HTM). A HTM refers to a material or unit capable of transporting holes (i.e. positive charges) injected from a hole injecting material or an anode. A HTM has usually a high HOMO, typically higher than -5.4 eV. In many cases, HIM can functions also as HTM, depending on the adjacent layer.

The inks according to the present invention may comprise one or more organic functional materials selected from hole blocking materials (HBM). A HBM refers to a material which, if deposited adjacent to an emissive layer or a hole transporting layer in a multilayer structure, prevents the holes flowing through. Usually, it has a lower HOMO as compared to the HOMO level of the HTM in the adjacent layer. Hole-blocking layers are frequently inserted between the light-emitting layer and the electron-transport layer in OLEDs.

The inks according to the present invention may comprise one or more organic functional materials selected from electron injection materials (EIM). An EIM refers to a material capable of facilitating electrons (i.e. negative charges) injected from cathode into an organic layer. The EIM usually has a LIIMO level comparable to or lower than the working function of the cathode. Typically, the EIM has a LIIMO lower than -2.6 eV.

The inks according to the present invention may comprise one or more organic functional materials selected from electron transport materials (ETM). An ETM refers to a material capable of transporting electrons (i.e. negative charges) injected from an E IM or a cathode. The ETM has usually a low LIIMO, typically lower than -2.7 eV. In many cases, an EIM can serve as ETM as well, depending on the adjacent layer.

The inks according to the present invention may comprise one or more organic functional materials selected from electron blocking materials (EBM). An EBM refers to a material which, if deposited adjacent to an emissive or electron transporting layer in a multilayer structure, prevents the electron flowing through. Usually, it has a higher LUMO as compared to the LUMO of the ETM in the adjacent layer.

The inks according to the present invention may comprise one or more organic functional materials selected from exciton blocking materials (ExBM). An ExBM refers to a material which, if deposited adjacent to an emissive layer in a multilayer structure, prevents the excitons diffuse through. ExBM should have either a higher triplet level or singlet level as compared to the emissive layer or other adjacent layer. The inks according to the present invention may comprise one or more organic functional materials selected from emitters. The term emitter refers to a material which, upon receiving excitonic energy by any kind of energy transfers from other materials, or by forming an exciton either electrically or optically, undergoes radiative decay to emit light. There are two classes of emitters, fluorescent and phosphorescent emitters. The term fluorescent emitter relates to materials or compounds which undergo a radiative transition from an excited singlet state to its ground. The term phosphorescent emitter, as used herein, relates to luminescent materials or compounds which comprise transition metals. This typically includes materials emitting light caused by spin forbidden transition(s), e.g., transitions from excited triplet states.

The inks according to the present invention may comprise one or more organic functional materials selected from metal complexes. According to quantum mechanics the transition from excited states with high spin multiplicity, e.g. from excited triplet states, to ground state is forbidden.

However, the presence of a heavy atom, for example indium, osmium, platinum and europium, results in a strong spin-orbit coupling, i.e. the excited singlet and triplet are mixed so that triplet gains some singlet character; and if singlet-triplet mixing yields a radiative decay rate faster than the non-radiative event, then the luminance can be efficient. This kind of emission can be achieved using metal complex, as firstly reported by Baldo et al.; Nature 395, 151-154 (1998). Further metal complexes can also function as efficient and broad-band light absorbing materials or dyes, as for example Ru complex reported by B. O'Regan & M. Graetzel, Nature 353, 737 (1991 ).

The term dopant as employed herein is also used for the term emitter or emitter material. The inks according to the present invention may comprise one or more organic functional materials selected from host materials. Host materials are usually used in combination with emitter and have, in general, larger energy gaps between the HOMO and the LIIMO as compared to emitter materials. In addition, host materials behave either as electron or hole transport material. Host materials can also have both electron and hole transport properties. In case singlet transitions are predominantly responsible for photoluminescence in OLEDs, a maximal overlap between the absorption spectrum of the emitter with the photoluminescence spectrum of the host material is highly desirable. This ensures the energy transfer from the host material to the emitter.

Host material is also called matrix or matrix material, preferably if a host is meant which is used in combination with a phosphorescent emitter in an OLEDs. And for copolymer, comprising emitter unit, the polymer backbone has the same meaning as host.

Further to HIMs mentioned elsewhere herein, suitable HIMs are phenylenediamine derivatives (US 3615404), arylamine derivatives (US 3567450), amino-substituted chaicone derivatives (US 3526501 ), styrylanthracene derivatives (JP Showa 54 (1979) 110837), hydrazone derivatives (US 3717462), acylhydrazones, stilbene derivatives (JP Showa 61 (1986) 210363), silazane derivatives (US 4950950), polysilane compounds (JP Heisei 2 (1990) 204996), PVK and other electrically conductive macromolecules, aniline-based copolymers (JP Heisei 2 (1990) 282263), electrically conductive, macromolecular thiophene oligomers (JP Heisei 1 (1989) 211399), PEDOT:PSS (spin-coated polymer), plasma- deposited fluorocarbon polymers (US 6127004, US 6208075, US 6208077), porphyrin compounds (JP Showa 63 (1988) 2956965, US 4720432), aromatic tertiary amines and styrylamines (US 4127412), triphenylamines of the benzidine type, triphenylamines of the styrylamine type, and triphenylamines of the diamine type. Arylamine dendrimers can also be used (JP Heisei 8 (1996) 193191 ), phthalocyanine derivatives, naphthalocyanine derivatives, or butadiene derivatives, are also suitable.

Preferably, the HIM is selected from monomeric organic compounds comprising amine, triarylamine, thiophene, carbazole, phthalocyanine, porphyrine and their derivatives.

Particular preference is given to the tertiary aromatic amines

(US 2008/0102311 A1 ), for example N,N’-diphenyl-N,N’-di(3-tolyl)benzidine (= 4,4’-bis[N-3-methylphenyl]-N-phenylamino)biphenyl (NPD) (US 5061569), N,N’-bis(N,N’-diphenyl-4-aminophenyl)-N,N-diphenyl-4,4’- diamino-1 ,1’-biphenyl (TPD 232) and 4,4’,4”-tris[3-methylphenyl)phenyl- amino]-triphenylamine (MTDATA) (JP Heisei 4 (1992) 308688) or phthalocyanine derivatives (for example H2Pc, CuPc, CoPc, NiPc, ZnPc, PdPc, FePc, MnPc, CIAIPc, CIGaPc, CllnPc, CISnPc, CI2SiPc, (HO)AIPc, (HO)GaPc, VOPc, TiOPc, MoOPc, GaPc-O-GaPc).

Particular preference is given to the following triarylamine compounds of the Formulae 1 (TPD 232), 2, 3, and 4, which may also be substituted, and further compounds as disclosed in US 7399537 B2, US 2006/0061265 A1 , EP 1661888 B1 , and JP 08292586 A.

Formula 1 Formula 2

Formula 3 Formula 4

Further compounds suitable as hole injection material are disclosed in EP 0891121 A1 and EP 1029909 A1. Hole injection layers in general are described in US 2004/0174116.

In principle any HTM known to one skilled in the art can be employed in formulations according to the present invention. Further to HTM mentioned elsewhere herein, HTM is preferably selected from amines, triarylamines, thiophenes, carbazoles, phthalocyanines, porphyrines, isomers and derivatives thereof. HTM is particularly preferably selected from amines, triarylamines, thiophenes, carbazoles, phthalocyanines, and porphyrines. Suitable materials for hole-transporting layers are phenylenediamine derivatives (US 3615404), arylamine derivatives (US 3567450), aminosubstituted chaicone derivatives (US 3526501 ), styrylanthracene derivatives (JP A 56-46234), polycyclic aromatic compounds (EP 1009041 ), polyarylalkane derivatives (US 3615402), fluorenone derivatives (JP A 54- 110837), hydrazone derivatives (US 3717462), stilbene derivatives (JP A 61-210363), silazane derivatives (US 4950950), polysilanes (JP A 2- 204996), aniline copolymers (JP A 2-282263), thiophene oligomers, polythiophenes, PVK, polypyrroles, polyanilines and further copolymers, porphyrin compounds (JP A 63-2956965), aromatic dimethylidene-type compounds, carbazole compounds, such as, for example, CDBP, CBP, mCP, aromatic tertiary amine and styrylamine compounds (US 4127412), and monomeric triarylamines (US 3180730). Even more triarylamino groups may also be present in the molecule. Preference is given to aromatic tertiary amines containing at least two tertiary amine units (US 4720432 and US 5061569), such as, for example, 4,4’-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD) (US 5061569) or MTDATA (JP A 4-308688), N,N,N’,N’-tetra(4-biphenyl)diaminobiphenylene (TBDB), 1 ,1-bis(4-di-p-tolylaminophenyl)cyclohexane (TAPC), 1 , 1 -bis(4-di- p-tolylaminophenyl)-3-phenylpropane (TAPPP), 1 ,4-bis[2-[4-[N,N-di(p- tolyl)amino]phenyl]vinyl]benzene (BDTAPVB), N,N,N’,N’-tetra-p-tolyl-4,4’- diaminobiphenyl (TTB), TPD, N,N,N’,N’-tetraphenyl-4,4’”-diamino- 1 ,1’:4’,1”:4”,T”-quaterphenyl, likewise tertiary amines containing carbazole units, such as, for example, 4 (9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9- yl)phenyl]benzeneamine (TCTA). Preference is likewise given to hexa- azatriphenylene compounds in accordance with US 2007/0092755 A1 .

Particular preference is given to the following triarylamine compounds of the Formulae 5 to 10, which may also be substituted, and as disclosed in EP 1162193 B1 , EP 650955 B1 , Synth. Metals 1997, 91 (1 -3), 209, DE 19646119 A1 , WO 2006/122630 A1 , EP 1860097 A1 , EP 1834945 A1 , JP 08053397 A, US 6251531 B1 , and WO 2009/041635 A1 .

In principle any HBM known to one skilled in the art can be employed in formulations according to the present invention. Further to HBM mentioned elsewhere herein, suitable hole-blocking materials are metal complexes (US 2003/0068528), such as, for example, bis(2-methyl-8-quinolinolato)(4- phenylphenolato)-aluminium(lll) (BAIQ). Fac-tris(1 -phenylpyrazolato- N, C2)iridium(l 11) (Ir(ppz)s) is likewise used for this purpose

(US 2003/0175553 A1 ). Phenanthroline derivatives, such as, for example, BCP, or phthalimides, such as, for example, TMPP, are likewise employed.

Further, suitable hole-blocking materials are described in WO 00/70655 A2, WO 01/41512 and WO 01/93642 A1 .

In principle any EIM known to one skilled in the art can be employed in formulations according to the present invention. Further to EIM mentioned elsewhere herein, suitable EIM elsewhere herein, EIMs, which comprises at least one organic compound selected from metal complexes of 8- hydroxyquinohne, heterocyclic organic compounds, fluorenones, fluorenylidene methane, perylenetetracarboxylic acid, anthraquinone dimethanes, diphenoquinones, anthrones, anthraquinonediethylenediamines, isomers and derivates thereof can be used according to the invention.

Metal complexes of 8 hydroxyquinoline, such as, for example, Alqs and Gaqs, can be used as EIM for electron-injection layers. A reducing doping with alkali metals or alkaline-earth metals, such as, for example, Li, Cs, Ca or Mg, at the interface to the cathode is advantageous. Preference is given to combinations which include Cs, for example Cs and Na, Cs and K, Cs and Rb or Cs, Na and K.

Heterocyclic organic compounds, such as, for example, 1 ,10- phenanthroline derivatives, benzimidazoles, thiopyran dioxides, oxazoles, triazoles, imidazoles or oxadiazoles, are likewise suitable. Examples of suitable five-membered rings containing nitrogen are oxazoles, thiazoles, oxadiazoles, thiadiazoles, triazoles, and compounds which are disclosed in US 2008/0102311 A1.

Preferred EIMs are selected from compounds of the Formulae 11 to 13, which may be substituted or unsubstituted.

Organic compounds, such as fluorenones, fluorenylidene methane, perylenetetracarboxylic acid, anthraquinone dimethanes, diphenoquinones, anthrones and anthraquinonediethylenediamines, can also be employed, for example

Formula 15

Formula 14

In principle any ETM known to one skilled in the art can be employed in formulations according to the present invention. Further to ETM mentioned elsewhere herein, suitable ETM is selected from the group consisting of imidazoles, pyridines, pyrimidines, pyridazines, pyrazines, oxadiazoles, chinolines, chinoxalines, anthracenes, benzanthracenes, pyrenes, pery- lenes, benzimidazoles, triazines, ketones, phosphinoxides, phenazines, phenanthrolines, triarylboranes, isomers and derivatives thereof.

Suitable ETMs for electron-transporting layers are metal chelates of 8 hydroxyquinoline (for example Liq, Alqs, Gaqs, Mgq2, Znq2, Inqs, Zrq4), Balq, 4 azaphenanthrene-5-ol/Be complexes (US 5529853 A; e.g. Formula 16), butadiene derivatives (US 4356429), heterocyclic optical brighteners (US 4539507), benzazoles, such as, for example, 1 ,3,5-tris(2-N-phenyl- benzimidazolyl)benzene (TPBI) (US 5766779, Formula 17), 1 ,3,5-triazines, pyrenes, anthracenes, tetracenes, fluorenes, spirobifluorenes, dendrimers, tetracenes, for example rubrene derivatives, 1 ,10-phenanthroline derivatives (JP 2003/115387, JP 2004/311184, JP 2001/267080, WO 2002/043449), silacyl-cyclopentadiene derivatives (EP 1480280, EP 1478032, EP 1469533), pyridine derivatives (JP 2004/200162 Kodak), phenanthrolines, for example BCP and Bphen, also a number of phenanthrolines bonded via biphenyl or other aromatic groups (US 2007/0252517 A1 ) or phenanthrolines bonded to anthracene (US 2007/0122656 A1 , e.g. Formulae W and 19), 1 ,3,4-oxadiazoles, for example Formula 20, triazoles, for example Formula 21 , triarylboranes, for example also with Si (e.g. Formula 48), benzimidazole derivatives and other N heterocyclic compounds (cf. US 2007/0273272 A1 ), silacyclopentadiene derivatives, borane derivatives, Ga oxinoid complexes.

Formula 20 Formula 21

Preference is given to 2,9,10-substituted anthracenes (with 1 - or 2-naphthyl and 4- or 3-biphenyl) or molecules which contain two anthracene units (US 2008/0193796 A1 ). Preference is likewise given to anthracene-benzimidazole derivatives, such as, for example, the compounds of Formulae 22 to 24, and as disclosed in, e.g., US 6878469 B2, US 2006/147747 A, and EP 1551206 A1.

Formula 22 Formula 23 Formula 24

In principle any EBM known to one skilled in the art can be employed in formulations according to the present invention. Further to EBM mentioned elsewhere herein, transition-metal complexes, such as, for example, lr(ppz)3 (US 2003/0175553) can be employed as materials for an electronblocking layer.

Preferably, the EBM is further selected from amines, triarylamines and their derivatives.

It is known to a person skilled in the art that the selection of ExBMs suitable for formulations according to the present invention depends on the energy gap of the adjacent layer. Suitable ExBMs are supposed to have a bigger energy gap, either singlet or triplet than the functional material in the adjacent layer which is preferably an emissive layer. Further to ExBMs mentioned elsewhere herein, substituted triarylamines, such as, for example, MTDATA or 4,4’,4”-tris(N,N-diphenylamino)triphenylamine (TDATA), can be used as ExBM for electron-blocking layers. Substituted triarylamines are described, for example, in US 2007/0134514 A1 .

N-substituted carbazole compounds, such as, for example, TCTA, or heterocycles, such as, for example, BCP, are also suitable.

Metal complexes, such as, for example, lr(ppz)s or Alqs, can likewise be used for this purpose.

In principle any host material known to one skilled in the art can be employed in formulations according to the present invention. Depending on the kind of emitter employed host materials can be separated into two categories, hosts for fluorescent emitter and hosts for phosphorescent emitter, whereby the latter is often referred to as matrix or matrix material.

Formulations according to the present invention may also comprise more than one host material, preferably it comprises 3 host materials, more preferably it comprises 2 host materials, and most preferably it comprises one host material. If a formulation according to the present invention comprises at least two host materials, the host materials are also referred to as co-host or co-host materials.

Preferred host materials suitable for fluorescent emitter are selected from anthracenes, benzanthracenes, indenofluorenes, fluorenes, spirobifluorenes, phenanthrenes, dihydrophenanthrenes, thiophenes, triazines, imidazole and derivatives thereof.

Particularly preferred host materials for fluorescent emitter are selected from the classes of the oligoarylenes (for example 2,2‘,7,7‘-tetraphenyl- spirobifluorene in accordance with EP 676461 or dinaphthylanthracene), in particular the oligoarylenes containing condensed aromatic groups, such as, for example, phenanthrene, tetracene, coronene, chrysene, fluorene, spirofluorene, perylene, phthaloperylene, naphthaloperylene, decacyclene, rubrene, the oligoarylenevinylenes (for example 4,4’-bis(2,2- diphenylethenyl)-1 ,1’-biphenyl (DPVBi) or 4,4-bis-2,2-diphenylvinyl-1 ,1- spirobiphenyl (spiro-DPVBi) in accordance with EP 676461 ), the polypodal metal complexes (for example in accordance with WO 2004/081017), in particular metal complexes of 8 hydroxyquinoline, for example aluminium(lll) tris(8-hydroxyquinoline) (aluminium quinolate, Alqs) or bis(2- methyl-8-quinolinolato)-4-(phenylphenolinolato)aluminium, also with imidazole chelate (US 2007/0092753 A1 ) and quinoline-metal complexes, aminoquinoline-metal complexes, benzoquinoline-metal complexes, the hole-conducting compounds (for example in accordance with WO 2004/058911 ), the electron-conducting compounds, in particular ketones, phosphine oxides, sulfoxides, etc. (for example in accordance with WO 2005/084081 and WO 2005/084082), the atropisomers (for example in accordance with WO 2006/048268), the boronic acid derivatives (for example in accordance with WO 2006/117052) or the benzanthracenes (e.g. DE 102007024850). Particularly preferred host materials are selected from the classes of the oligoarylenes, containing naphthalene, anthracene, benzanthracene and/or pyrene, or atropisomers of these compounds, the ketones, the phosphine oxides and the sulfoxides. Very particularly preferred host materials are selected from the classes of the oligoarylenes, containing anthracene, benzanthracene and/or pyrene, or atropisomers of these compounds. For the purposes of the present application, an oligoarylene is intended to be taken to mean a compound in which at least three aryl or arylene groups are bonded to one another.

Further preferred host materials for fluorescent emitter are selected, in particular, from compounds of the Formula 25

Ar⁴-(Ar⁵)_p-Ar⁶ Formula 25 wherein Ar⁴, Ar⁵, Ar⁶ are on each occurrence, identically or differently, an aryl or heteroaryl group having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals and p is 1 , 2, or 3, the sum of the TT-electrons in Ar⁴, Ar⁵ and Ar⁶ is at least 30 if p = 1 and is at least 36 if p = 2 and is at least 42 if p = 3.

It is particularly preferred in the host materials of the Formula 25 for the group Ar⁵ to stand for anthracene, which may be substituted by one or more radicals R¹, and for the groups Ar⁴ and Ar⁶ to be bonded in the 9 and 10-positions. Very particularly preferably, at least one of the groups Ar⁴ and/or Ar⁶ is a condensed aryl group selected from 1 - or 2-naphthyl, 2-, 3- or 9-phenanthrenyl or 2-, 3-, 4-, 5-, 6- or 7-benzanthracenyl, each of which may be substituted by one or more radicals R¹. Anthracene-based compounds are described in US 2007/0092753 A1 and US 2007/0252517 A1 , for example 2-(4-methylphenyl)-9,10-di-(2-naphthyl)anthracene, 9-(2- naphthyl)-10-(1 ,1 ’-biphenyl)anthracene and 9,10-bis[4-(2,2- diphenylethenyl)phenyl]anthracene, 9, 10-diphenylanthracene, 9, 10- bis(phenylethynyl)anthracene and 1 ,4-bis(9’-ethynylanthracenyl)benzene. Preference is also given to host materials containing two anthracene units (US 2008/0193796 A1 ), for example 10,10’-bis[1 ,1’,4’,1”]terphenyl-2-yl-9,9’- bisanthracenyl.

Further preferred host materials are derivatives of arylamine, styrylamine, fluorescein, perynone, phthaloperynone, naphthaloperynone, diphenylbutadiene, tetraphenylbutadiene, cyclopentadienes, tetraphenylcyclopentadiene, pentaphenylcyclopentadiene, coumarine, oxadiazole, bisbenzoxazoline, oxazone, pyridine, pyrazine, imine, benzothiazole, benzoxazole, benzimidazole (US 2007/0092753 A1 ), for example 2,2 ,2 -(1 ,3,5-phenylene)tns[1 -phenyl-1 H-benzimidazole], aldazines, stilbene, styrylarylene derivatives, for example 9, 10-bis[4-(2,2- diphenylethenyl)phenyl]anthracene, and distyrylarylene derivatives (US 5121029), diphenylethylene, vinylanthracene, diaminocarbazole, pyran, thiopyran, diketopyrrolopyrrole, polymethine, mellocyanine, acridone, quinacridone, cinnamic acid esters and fluorescent dyes.

Particular preference is given to derivatives of arylamine and styrylamine, for example 4,4’-bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB).

Preferred compounds with oligoarylene as hosts for fluorescent emitter are compounds as disclosed in, e.g., US 2003/0027016 A1 , US 7326371 B2, US 2006/043858 A, US 7326371 B2, US 2003/0027016 A1 ,

WO 2007/114358, WO 2008/145239, JP 3148176 B2, EP 1009044,

US 2004/018383, WO 2005/061656 A1 , EP 0681019B1 , WO 2004/013073A1 , US 5077142, WO 2007/065678, and US 2007/0205412 A1. Particularly preferred oligoarylene-based compounds are compounds of the Formulae 26 to 32.

Formula 26 Formula 27 Formula 28

Formula 32

Further host materials for fluorescent emitter can be selected from spirobifluorene and derivates thereof, for example Spiro-DPVBi as disclosed in EP 0676461 and indenofluorene as disclosed in US 6562485.

The preferred host materials for phosphorescent emitter, i.e. matrix materials, are selected from ketones, carbazoles, triarylamines, indenofluorenes, fluorenes, spirobifluorenes, phenanthrenes, dihydrophenanthrenes, thiophenes, triazines, imidazoles and their derivatives. Some preferred derivatives are described below in more detail.

If a phosphorescent emitter is employed, e.g. as electroluminescent component in organic light emitting diodes (OLEDs), the host material must fulfil rather characteristics as compared to host materials used for fluorescent emitter. The host materials used for phosphorescent emitter are required to have a triplet level which is higher in energy as compared to the triplet level of the emitter. The host material can either transport electrons or holes or both of them. In addition, the emitter is supposed to have large spin-orbital coupling constants in order to facilitate singlet-triplet mixing sufficiently. This can be enabled by using metal complexes.

Preferred matrix materials are N,N-biscarbazolylbiphenyl (CBP), carbazole derivatives (for example in accordance with WO 2005/039246,

US 2005/0069729, JP 2004/288381 , EP 1205527 or DE 102007002714), azacarbazoles (for example in accordance with EP 1617710, EP 1617711 , EP 1731584, JP 2005/347160), ketones (for example in accordance with WO 2004/093207), phosphine oxides, sulfoxides and sulfones (for example in accordance with WO 2005/003253), oligophenylenes, aromatic amines (for example in accordance with US 2005/0069729), bipolar matrix materials (for example in accordance with WO 2007/137725), silanes (for example in accordance with WO 2005/111172), 9,9-diarylfluorene derivatives (e.g. in accordance with DE 102008017591 ), azaboroles or boronic esters (for example in accordance with WO 2006/117052), triazole derivatives, oxazoles and oxazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, distyrylpyrazine derivatives, thiopyran dioxide derivatives, phenylenediamine derivatives, tertiary aromatic amines, styrylamines, indoles, anthrone derivatives, fluorenone derivatives, fluorenylidenemethane derivatives, hydrazone derivatives, silazane derivatives, aromatic dimethylidene compounds, porphyrin compounds, carbodiimide derivatives, diphenylquinone derivatives, phthalocyanine derivatives, metal complexes of 8 hydroxyquinoline derivatives, such as, for example, Alqs, the 8 hydroxyquinoline complexes may also contain triarylaminophenol ligands (US 2007/0134514 A1 ), various metal complex-polysilane compounds with metal phthalocyanine, benzoxazole or benzothiazole as ligand, holeconducting polymers, such as, for example, poly(N-vinylcarbazole) (PVK), aniline copolymers, thiophene oligomers, polythiophenes, polythiophene derivatives, polyphenylene derivatives, polyfluorene derivatives.

Further particularly preferred matrix materials are selected from compounds comprising indolocarbazoles and their derivatives (e.g. Formulae 33 to 39), as disclosed for examples in DE 102009023155.2, EP 0906947B1 , EP 0908787B1 , EP 906948B1 , WO 2008/056746A1 , WO 2007/063754A1 , WO 2008/146839A1 , and WO 2008/149691 A1 .

Examples of preferred carbazole derivatives are, 1 ,3-N,N- dicarbazolebenzene (= 9,9’-(1 ,3-phenylene)bis-9H-carbazole) (mCP), 9,9’- (2,2’-dimethyl[1 , 1 ’-biphenyl]-4,4’-diyl)bis-9H-carbazole (CDBP), 1 ,3- bis(N,N’-dicarbazole)benzene (= 1 ,3-bis(carbazol-9-yl)benzene), PVK (polyvinylcarbazole), 3,5-di(9H-carbazol-9-yl)biphenyl and compounds of the Formulae 40 to 44.

Preferred Si tetraaryl compounds are, for example, (US 2004/0209115, US 2004/0209116, US 2007/0087219 A1 , US 2007/0087219 A1 ) the compounds of the Formulae 45 to 50.

A particularly preferred matrix for phosphorescent dopants is the compound of Formula 51 (EP 652273 B1 )

Formula 51

Further particularly preferred matrix materials for phosphorescent dopants are selected from compounds of the general Formula 52 (EP 1923448 B1 ).

[M(L)₂]_n Formula 52 wherein M, L, and n are defined as in the reference. Preferably M is Zn, and L is quinolinate q, and n is 2, 3 or 4. Very particularly preferred are [Znq2]2, [Znq2]3, and [Znq2]4.

Preference is given to co-hosts selected from metal oxinoid complexes whereby lithium quinolate (Liq) or Alqs are particularly preferred.

The emitter compound is required to have a smaller band gap as compared to the host compound. In general, smaller band gaps can be achieved by extending the TT-electron system of conjugated molecular systems. Emitter compounds tend, therefore, to have more extended conjugated TT-electron systems than host molecules. Many examples have been published, e.g. styrylamine derivatives as disclosed in JP 2913116B and WO 2001/021729 A1 , and indenofluorene derivatives as disclosed in WO 2008/006449 and WO 2007/140847.

Blue fluorescent emitters are preferably polyaromatic compounds, such as, for example, 9,10-di(2-naphthylanthracene) and other anthracene derivatives, derivatives of tetracene, xanthene, perylene, such as, for example, 2,5,8, 11 -tetra-t-butylperylene, phenylene, for example 4, 4’-(bis(9- ethyl-3-carbazovinylene)-1 ,1’-biphenyl, fluorene, arylpyrenes (US 2006/0222886), arylenevinylenes (US 5121029, US 5130603), derivatives of rubrene, coumarine, rhodamine, quinacridone, such as, for example, N,N’-dimethylquinacridone (DMQA), dicyanomethylenepyrane, such as, for example, 4 (dicyanoethylene)-6-(4-dimethylaminostyryl-2- methyl)-4H-pyrane (DCM), thiopyrans, polymethine, pyrylium and thiapyryhum salts, penflanthene, indenoperylene, bis(azinyl)imme-boron compounds (US 2007/0092753 A1 ), bis(azinyl)methene compounds and carbostyryl compounds.

Further preferred blue fluorescent emitters are described in C.H. Chen et al.: "Recent developments in organic electroluminescent materials" Macromol. Symp. 125, (1997), 1-48 and “Recent progress of molecular organic electroluminescent materials and devices” Mat. Sci. and Eng. R, 39 (2002), 143-222.

Preferred fluorescent dopants according to the present invention are selected from the class of the monostyrylamines, the distyrylamines, the tristyrylamines, the tetrastyrylamines, the styrylphosphines, the styryl ethers and the arylamines.

A monostyrylamine is taken to mean a compound which contains one substituted or unsubstituted styryl group and at least one, preferably aromatic, amine. A distyrylamine is taken to mean a compound which contains two substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. A tristyrylamine is taken to mean a compound which contains three substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. A tetrastyrylamine is taken to mean a compound which contains four substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. The styryl groups are particularly preferably stilbenes, which may also be further substituted. The corresponding phosphines and ethers are defined analogously to the amines. For the purposes of this invention, an arylamine or an aromatic amine is taken to mean a compound which contains three substituted or unsubstituted aromatic or heteroaromatic ring systems bonded directly to the nitrogen. At least one of these aromatic or heteroaromatic ring systems is preferably a condensed ring system, preferably having at least 14 aromatic ring atoms. Preferred examples thereof are aromatic anthracene- amines, aromatic anthracene-diammes, aromatic pyrene-ammes, aromatic pyrene-diamines, aromatic chrysene-amines and aromatic chrysenediamines. An aromatic anthracene-amine is taken to mean a compound in which one diarylamino group is bonded directly to an anthracene group, preferably in the 9 position. An aromatic anthracene-diamine is taken to mean a compound in which two diarylamino groups are bonded directly to an anthracene group, preferably in the 9,10-position. Aromatic pyreneamines, pyrene-diamines, chrysene-amines and chrysene-diamines are defined analogously thereto, where the diarylamino groups on the pyrene are preferably bonded in the 1 position or in the 1 ,6-position.

Further preferred fluorescent dopants are selected from indenofluorene- amines and indenofluorene-diamines, for example in accordance with WO 2006/122630, benzoindenofluorene-amines and benzoindeno-fluorene- diamines, for example in accordance with WO 2008/006449, and dibenzoindenofluorene-amines and dibenzoindenofluorene-diamines, for example in accordance with WO 2007/140847.

Examples of dopants from the class of the styrylamines are substituted or unsubstituted tristilbene-amines or the dopants described in

WO 2006/000388, WO 2006/058737, WO 2006/000389, WO 2007/065549 and WO 2007/115610. Distyrylbenzene and distyrylbiphenyl derivatives are described in US 5121029. Further styrylamines are found in US 2007/0122656 A1.

Particularly preferred styrylamine dopants and triarylamine dopants are compounds of the Formulae 53 to 58 and as disclosed in US 7250532 B2, DE 102005058557 A1 , CN 1583691 A, JP 08053397 A, US 6251531 B1 , and US 2006/210830 A.

Formula 57 Formula 58 Further preferred fluorescent dopants are selected from the group of triarylamines as disclosed in EP 1957606 A1 and US 2008/0113101 A1 .

Further preferred fluorescent dopants are selected from derivatives of naphthalene, anthracene, tetracene, fluorene, periflanthene, indenoperylene, phenanthrene, perylene (US 2007/0252517 A1 ), pyrene, chrysene, decacyclene, coronene, tetraphenylcyclopentadiene, pentaphenylcyclopentadiene, fluorene, spirofluorene, rubrene, coumarine (US 4769292, US 6020078, US 2007/0252517 A1 ), pyran, oxazone, benzoxazole, benzothiazole, benzimidazole, pyrazine, cinnamic acid esters, diketopyrrolopyrrole, acridone and quinacridone (US 2007/0252517 A1 ).

Of the anthracene compounds, particular preference is given to 9,10- substituted anthracenes, such as, for example, 9,10-diphenylanthracene and 9,10-bis(phenylethynyl)anthracene. 1 ,4-Bis(9’-ethynylanthracenyl)- benzene is also a preferred dopant.

Examples of phosphorescent emitters are revealed by the applications WO 00/70655, WO 01/41512, WO 02/02714, WO 02/15645, EP 1191613, EP 1191612, EP 1191614 and WO 2005/033244. In general, all phosphorescent complexes as used in accordance with the prior art for phosphorescent OLEDs and as are known to the person skilled in the art in the area of organic electroluminescence are suitable, and the person skilled in the art will be able to use further phosphorescent complexes without inventive step.

The phosphorescent emitter may be a metal complex, preferably with the formula M(L)_Z, wherein M is a metal atom, L is in each occurrence independently of one another an organic ligand that is bonded to or coordinated with M via one, two or more positions, and z is an integer > 1 , preferably 1 , 2, 3, 4, 5 or 6, and wherein, optionally, these groups are linked to a polymer via one or more, preferably one, two or three positions, preferably via the ligands L.

M is in particular a metal atom selected from transition metals, preferably selected from transition metals of group VIII, or lanthanoides, or actinides, particularly preferably selected from Rh, Os, Ir, Pt, Pd, Au, Sm, Eu, Gd, Tb, Dy, Re, Cu, Zn, W, Mo, Pd, Ag, or Ru, and very particularly preferably selected from Os, Ir, Ru, Rh, Re, Pd, or Pt. M may also be Zn.

Preferred ligands are 2 phenylpyridine derivatives, 7,8-benzoquinoline derivatives, 2 (2-thienyl)pyridine derivatives, 2 (l -naphthyl)pyridine derivatives or 2 phenylquinoline derivatives. All these compounds may be substituted, for example by fluoro- or trifluoromethyl substituents for blue. Auxiliary ligands are preferably acetylacetonate or picric acid.

In particular, complexes of Pt or Pd with tetradentate ligands of the Formula 59 as disclosed in US 2007/0087219 A1 , wherein R¹ to R¹⁴ and Z¹ to Z⁵ are as defined in the reference, Pt porphyrin complexes having an enlarged ring system (US 2009/0061681 A1 ) and Ir complexes are suitable, for example 2, 3, 7, 8, 12, 13, 17, 18-octaethyl-21 H, 23H-porphyrin-Pt(ll), tetraphenyl-Pt(ll)-tetrabenzoporphyrin (US 2009/0061681 A1 ), cis-bis(2- phenylpyridinato-N,C2’)Pt(ll), cis-bis(2-(2’-thienyl)pyridinato-N, C3’)Pt(ll), cis-bis(2-(2’-thienyl)quinolinato-N, C5’)Pt(l I), (2-(4,6-difluorophenyl)- pyridinato-N, C2’)Pt(l I) acetylacetonate, or tris(2-phenylpyridinato- N, C2’)lr(l 11) (Ir(ppy)s, green), bis(2-phenylpyridinato-N, C2)lr(l 11) acetylacetonate (lr(ppy)2 acetylacetonate, green, US 2001/0053462 A1 , Baldo, Thompson et al. Nature 403, (2000), 750-753), bis(1 - phenylisoquinolinato-N,C2’)(2-phenylpyridinato-N,C2’)iridium(lll), bis(2- phenylpyridinato-N,C2’)(1 -phenylisoquinolinato-N,C2’)iridium(lll), bis(2-(2’- benzothienyl)pyridinato-N,C3’)iridium(lll) acetylacetonate, bis(2-(4’,6’- difluorophenyl)pyridinato-N,C2’)iridium(l 11) piccolinate (Firpic, blue), bis(2- (4’,6’-difluorophenyl)pyridinato-N,C2’)lr(l 11) tetrakis(1 -pyrazolyl)borate, tns(2-(biphenyl-3-yl)-4-tert-butylpyndine)-mdium(lll), (ppz)2lr(5phdpym) (US 2009/0061681 A1 ), (45ooppz)₂lr(5phdpym) (US 2009/0061681 A1 ), derivatives of 2 phenylpyridine-lr complexes, such as, for example, iridium(lll) bis(2-phenylquinolyl-N,C2’)acetylacetonate (PQIr), tris(2- phenylisoquinolinato-N, C)lr(l 11) (red), bis(2-(2’-benzo[4,5- a]thienyl)pyridinato-N,C3)lr acetylacetonate ([Btp2lr(acac)], red, Adachi et al. Appl. Phys. Lett. 78 (2001 ), 1622-1624).

Formula 59

Also suitable are complexes of trivalent lanthanides, such as, for example, Tb³⁺ and Eu³⁺ (J. Kido et al. Appl. Phys. Lett. 65 (1994), 2124, Kido et al. Chem. Lett. 657, 1990, US 2007/0252517 A1 ), or phosphorescent complexes of Pt(ll), lr(l), Rh(l) with maleonitrile dithiolate (Johnson et al., JACS 105, 1983, 1795), Re(l) tricarbonyl diimine complexes (Wrighton, JACS 96, 1974, 998 inter alia), Os(ll) complexes with cyano ligands and bipyridyl or phenanthroline ligands (Ma et al., Synth. Metals 94, 1998, 245) or Alqs without a host.

Further phosphorescent emitters with tridentate ligands are described in US 6824895 and US 7029766. Red-emitting phosphorescent complexes are mentioned in US 6835469 and US 6830828. A particularly preferred phosphorescent dopant is a compound of Formula

60 and further compounds as disclosed, e.g., in US 2001/0053462 A1 .

A particularly preferred phosphorescent dopant is a compound of Formula

61 and further compounds as disclosed, e.g., in WO 2007/095118 A1

Further derivatives are described in US 7378162 B2, US 6835469 B2, and J P 2003/253145 A.

Further to metal complex mentioned elsewhere herein, a suitable metal complex according to the present invention can be selected from transition metals, rare earth elements, lanthanides and actinides is also subject of this invention. Preferably the metal is selected from Ir, Ru, Os, Eu, Au, Pt, Cu, Zn, Mo, W, Rh, Pd, or Ag.

The inks according to the present invention may also comprise organic functional material which is selected from polymers, oligomers, dendrimers, and blends. The functional polymer is characterized in that different functions may be incorporated into one large molecule or a blend of large molecules. The functions are, inter alia, the ones of a hole injection material, hole transport material, electron blocking material, emissive material, hole blocking material, electron injection material, electron transport material, and dye. The functions which are incorporated into a polymer can be categorized into different groups. By choosing the desired functional groups and the ratio between them, the polymer can be tuned to have the desired function(s).

The difference between polymers, oligomers and dendrimers is due to the size, size distribution, and branching of the molecular entities as defined above.

Different structures are, inter alia, those as disclosed and extensively listed in WO 2002/077060 A1 and in DE 10337346 A1 . The structural units may originate, for example, from the following groups:

Group 1 : units which increase the hole-injection and/or transport properties of the polymers; it corresponds to the HIMs or HTMs as described above.

Group 2: units which increase the electron-injection and/or transport properties of the polymers; it corresponds to the EIMs or ETMs as described above.

Group 3: units which have combinations of individual units from group 1 and group 2.

Group 4: units which modify the emission characteristics to such an extent that electrophosphorescence may be obtained instead of electrofluorescence; typically, it corresponds to the phosphorescent emitter, or more preferably emissive metal complexes as described above.

Group 5: units which improve the transition from the so-called singlet state to higher spin states, e.g. to a triplet state.

Group 6: units which influence the morphology and/or emission colour of the resultant polymers. Group 7: units which are typically used as backbone and which may have electron transport function, hole transport function or both.

Group 8: units which have strong absorption in at least one wavelength from UV to infrared. It corresponds to the dye materials as described above.

Preferably, the said organic functional material is a hole transport or injection polymer comprising units of group 1 , which are preferably selected from units comprising the low molecular weight HTMs or HIMs as described above.

Further preferred units of group 1 are, for example, triarylamine, benzidine, tetraaryl-para-phenylenediamine, carbazole, azulene, thiophene, pyrrole and furan derivatives and further O, S or N containing heterocycles with a high HOMO. These arylamines and heterocycles preferably result in an HOMO in the polymer of greater than 5.8 eV (against vacuum level), particularly preferably greater than 5.5 eV.

A preferred polymeric HTM or HIM is a polymer comprising at least one repeating unit of the following Formula 62.

Formula 62 wherein

Ar¹ which may be the same or different, denote, independently if in different repeat units, a single bond or an optionally substituted mononuclear or polynuclear aryl group, Ar² which may be the same or different, denote, independently if in different repeat units, an optionally substituted mononuclear or polynuclear aryl group,

Ar³ which may be the same or different, denote, independently if in different repeat units, an optionally substituted mononuclear or polynuclear aryl group, and m is 1 , 2 or 3.

Examples of polymeric HTMs are as disclosed in WO 2007/131582 A1 and WO 2008/009343 A1 .

Preferably, the said organic functional material is an electron transport or injection polymer comprising units of group 2, which are preferably selected from groups comprising the low molecular weight ETMs or EIMs as described above.

Further preferred units of group 2, which have electron-injection or electrontransport properties, are, for example, pyridine, pyrimidine, pyridazine, pyrazine, oxadiazole, quinoline, quinoxaline and phenazine derivatives, but also triarylboranes and further O, S or N containing heterocycles having a low LIIMO. These units in the polymer preferably result in an LIIMO of less than 2.7 eV (against vacuum level), particularly preferably less than 2.8 eV.

Preferably, the said organic functional material is a polymer comprising units of group 3, in which structures which increase the hole mobility and the electron mobility (i.e. units of group 1 and 2) are bonded directly to one another. Some of these units may serve as emitters and shift the emission colour into the green, yellow or red. Their use is thus suitable, for example, for the production of other emission colours or a broad-band emission from originally blue-emitting polymers.

Preferably, the said organic functional material is a polymer comprising units of group 4, which is preferably selected from the groups comprising phosphorescent emitter, particularly emissive metal complexes as described above. Particular preference is given here to corresponding structural units which contain elements from groups 8 to 10 (Ru, Os, Rh, Ir, Pd, Pt).

Preferably, the said organic functional material is a polymeric triple matrix comprising units of group 5, which can improve the transition from the singlet state to the triplet state and which, employed in support of the structural elements of group 4, improve the phosphorescence properties of these structural elements. Suitable for this purpose are, in particular, carbazole and bridged carbazole dimer units, as described in DE 10304819 A1 and DE 10328627 A1 . Also suitable for this purpose are ketones, phosphine oxides, sulfoxides, sulfones, silane derivatives and similar compounds, as described in DE 10349033 A1. Further preferred structure units can be selected from groups comprising the low molecular weight phosphorescent matrices as described above.

Preferably, the said organic functional material is a polymer comprising units of group 6, which influence the morphology and/or emission colour of the polymers, are, besides those mentioned above, those which have at least one further aromatic or another conjugated structure which do not fall under the above-mentioned groups, i.e. which have only little effect on the charge-carrier mobilities, which are not organometallic complexes or which have no influence on the singlet-triplet transition. Structural elements of this type may influence the morphology and/or emission colour of the resultant polymers. Depending on the unit, they can therefore also be employed as emitters. Preference is given here, in the case of fluorescent OLEDs, to aromatic structures having 6 to 40 C atoms or also tolan, stilbene or bisstyrylarylene derivatives, each of which may be substituted by one or more radicals R¹. Particular preference is given here to the incorporation of 1 ,4-phenylene, 1 ,4-naphthylene, 1 ,4- or 9,10-anthrylene, 1 ,6-, 2,7- or 4,9- pyrenylene, 3,9- or 3,10-perylenylene, 4,4'-biphenylylene, 4,4"- terphenylylene, 4,4' bi 1 ,1 '-naphthylylene, 4,4‘-tolanylene, 4,4'-stilbenylene or 4,4"-bisstyrylarylene derivatives.

Preferably, the said organic functional material is a polymer comprising units of group 7 which contain aromatic structures having 6 to 40 C atoms which are typically used as polymer backbone. These are, for example, 4,5- dihydropyrene derivatives, 4,5,9, 10-tetrahydropyrene derivatives, fluorene derivatives as disclosed for example in US 5962631 , WO 2006/052457 A2 and WO 2006/118345A1 , 9,9‘-spirobifluorene derivatives as disclosed for example in WO 2003/020790 A1 , 9,10-phenanthrene derivatives as disclosed, for example, in WO 2005/104264 A1 , 9,10-dihydrophenanthrene derivatives as disclosed for example in WO 2005/014689 A2, 5,7- dihydrodibenzooxepine derivatives and cis- and trans-indenofluorene derivatives as disclosed for example in WO 2004041901 A1 , WO 2004113412 A2 and, binaphthylene derivatives as disclosed for example in WO 2006/063852 A1 , and further units as disclosed for example in WO 2005/056633 A1 , EP 1344788 A1 and WO 2007/043495 A1 , WO 2005/033174 A1 , WO 2003/099901 A1 and DE 102006003710.

Further preferred structural elements of group 7 are selected from fluorene derivatives, as disclosed for example in US 5,962,631 , WO 2006/052457 A2 and WO 2006/118345 A1 , spiro-bifluorene derivatives as disclosed for example in WO 2003/020790 A1 , benzofluorene, dibenzofluorene, benzothiophene, dibenzofluorene and their derivatives as disclosed for example in WO 2005/056633 A1 , EP 1344788 A1 and WO 2007/043495 A1 . Preferably, the said organic functional material is a polymer comprising units of group 8, which can be selected from the groups comprising the dye materials as described above. The conjugated polymers suitable for organic solar cells, as summarized for example by F.C. Krebs, in Solar Energy Materials and Solar Cells, Vol91 , 953 (2007), can also be used as the said further organic functional material in the present invention.

Preference is given to polymers suitable for use in the present invention which simultaneously comprise one or more units selected from groups 1 to 8. It may likewise be preferred for more than one structural unit from a group to be present simultaneously.

Preference is given to polymers suitable for use in the present invention which, besides structural units of an emitter, also comprise at least one structural unit of the above-mentioned groups. At least two structural units are particularly preferably from different classes of those mentioned above.

The proportion of the different classes of groups, if present in the polymer, is preferably in each case at least 5 mol%, particularly preferably in each case at least 10 mol%. In particular, one of these structural units is selected from the group of hole-conducting units and the other group is an emitting unit, where these two functions (hole conduction and emission) may also be taken on by the same unit.

However, a smaller proportion of the emitting units, in particular green- and red-emitting units, may also be preferred, for example for the synthesis of white-emitting copolymers. The way in which white-emitting copolymers can be synthesised is described in detail in DE 10343606 A1 .

In order to ensure adequate solubility, it is preferred for on average at least

2 non-aromatic C atoms to be present in the substituents per repeating unit. Preference is given here to at least 4 and particularly preferably at least 8 C atoms. In addition, individual C atoms of these may be replaced by 0 or S. However, it is entirely possible for this to mean that a certain proportion of repeating units does not carry any further non-aromatic substituents.

In order to avoid impairing the morphology of the film, it is preferred to have no long-chain substituents having more than 12 C atoms in a linear chain, particularly preferably none having more than 8 C atoms and in particular none having more than 6 C atoms.

The polymer used as organic functional material in the present invention may be a statistical or random copolymer, an alternating or regioregular copolymer, a block copolymers or a combination thereof.

In another preferred embodiment, the said polymer is a side-chain nonconjugated polymer, which is especially important for phosphorescent OLEDs based on polymer. In general, such a phosphorescent polymer is obtained by means of radical copolymerization of vinyl compounds, and comprises at least one phosphorescent emitter and at least one charge transport unit on side chain, as disclosed in US 7250226 B2. Further examples for such phosphorescent polymers are disclosed for example in JP 2007/211243 A2, JP 2007/197574 A2, US 7250226 B2, and JP 2007/059939 A.

In a further preferred embodiment, the said polymer is a main-chain nonconjugated polymer, where the backbone units are connected by spacer on main-chain. Like side-chain non-conjugated polymer, main-chain nonconjugated polymers give also a high triplet level. An example for triplet OLEDs based on main-chain non-conjugated polymers is disclosed in DE 102009023154.

In a further embodiment, the said polymer can also be a non-conjugated polymer for fluorescent OLEDs. Preferred singlet non-conjugated polymers are, for example, side-chain polymers with anthracenes, benzanthracenes and their derivatives in the side-chain, as disclosed in JP 2005/108556, JP 2005/285661 , and JP 2003/338375.

The said polymers can also act as ETM or HTM, preferably the polymer is a non-conjugated polymer.

Devices according to the present invention may also comprise additional layer which were not deposited by using an ink according to the present invention. The additional layer may be deposited by a technique from solution or by vapour deposition. Hereby the specific method employed depends on the characteristics of the material used and a person skilled in the art has no problem to select the appropriate technique. The material which is deposited can be any material used in the field of electronic and opto-electronic multilayer structures. In particular the material may be any material described herein. Furthermore, the materials may be selected from organic and inorganic functional materials as outlined below.

Inorganic compounds, such as p type Si and p type SiC, and inorganic oxides, e.g., vanadium oxide (VOx), molybdenum oxide (MoOx) or nickel oxide (NiOx) can also be used as HIM.

Electron injection layers (EILs) are often constructed from an insulator and semiconductor.

Preferred alkali metal chalcogenides for EILs are Li2O, LiO, Na2S, Na2Se, NaO, K2O, and CS2O.

Preferred alkaline-earth metal chalcogenides for EILs are CaO, BaO, SrO, BeO, BaS, and CaSe. Preferred halides of alkali metals for EILs are LiF, NaF, KF, CsF, LiCI, KCI, and NaCI.

Preferred halides of alkaline-earth metals for EILs are CaF2, BaF2, SrF2, MgF2, and BeF2.

It is likewise possible to employ alkali metal complexes, alkaline-earth metal complexes, rare-earth metals (Sc, Y, Ce, Th, Yb), rare-earth metal complexes, rare-earth metal compounds (preferably YbFs, ScFs, TbFs) or the like.

The structure of EILs is described, for example, in US 5608287, US 5776622, US 5776623, US 6137223, US 6140763, US 6914269.

An electron-transport layer may consist of an intrinsic material or comprise a dopant. Alqs (EP 278757 B1 ) and Liq (EP 0569827 A2) are examples of intrinsic layers. 4,7-diphenyl-1 ,10-phenanthroline (Bphen): Li 1 :1

(US 2003/02309890) and rubrene/LiF are examples of doped layers.

According to the method of the present invention, inks A and B are used, and inks C and D are optionally used. Each of these inks contains at least one of the organic solvents A, B, C and D.

The solvents A, B, C and D, as used in the different inks, can be identical or different.

Furthermore, the solvents A, B, C and D, as used in the different inks, can be single solvents or mixtures of two or more different solvents.

As solvent material, any suitable solvent commonly used especially for printing of OLEDs can be used. Preferred solvents are described in the present application. The organic solvents A, B, C and/or D have a boiling point in the range from 100 to 400°C, preferably in the range from 200 to 350°C, more preferably in the range from 225 to 325°C and most preferably in the range from 250 to 300°C.

Preferred solvents of the inks A, B, C and D are independent from each other and preferably organic solvents which include inter alia, ketones, ethers, esters, amides such as di-Ci-2-alkylformamides, sulfur compounds, nitro compounds, hydrocarbons, halogenated hydrocarbons (e.g. chlorinated hydrocarbons), aromatic or heteroaromatic hydrocarbons (e.g. naphthalene derivatives) and halogenated aromatic or heteroaromatic hydrocarbons.

More preferred solvents can be chosen from one of the following groups: substituted and non-substituted aromatic or linear ethers such as 3- phenoxytoluene or anisole; substituted and non-substituted arene derivatives such as cyclohexylbenzene; substituted and non-substituted aromatic or linear esters such as butyl benzoate or ethyl p-toluate; substituted or non-substituted indanes such as hexamethylindane; substituted and non-substituted aromatic or linear ketones such as dicyclohexylmethanone; substituted and non-substituted heterocycles such as pyrrolidinones, pyridines, pyrazines; other fluorinated or chlorinated aromatic hydrocarbons, substituted or non-substituted naphthalenes such as alkyl substituted naphthalenes, such as 1 -ethyl naphthalene.

Particularly preferred solvents are, for example, 1 -ethyl-naphthalene, 2- ethylnaphthalene, 2-propylnaphthalene, 2-(1 -methylethyl)-naphthalene, 1 - (1 -methylethyl)-naphthalene, 2-butylnaphthalene, 1 ,6-dimethylnaphthalene, 2,2'-dimethylbiphenyl, 3,3'-dimethylbiphenyl, 1 -acetylnaphthalene, 1 ,2,3,4- tetramethylbenzene, 1 ,2,3,5-tetramethyl-benzene, 1 ,2,4,5-tetramethyl- benzene, 1 ,2,4-trichlorobenzene, 1 ,2-dihydronaphthalene, 1 ,2-dimethy- Inaphthalene, 1 ,3-benzodioxole, 1 ,3-diisopropylbenzene, 1 ,3-dimethyl- naphthalene, 1 ,4-benzodioxane, 1 ,4-diisopropylbenzene, 1 ,4-dimethyl- naphthalene, 1 ,5-dimethyltetralin, 1 -benzothiophene, thianaphthalene, 1 -bromonaphthalene, 1 -chloromethylnaphthalene, 1 -methoxynaphthalene,

1 -methylnaphthalene, 2-bromo-3-bromomethylnaphthalene, 2-bromo- methyl-naphthalene, 2-bromonaphthalene, 2-ethoxynaphthalene,

2-isopropyl-anisole, 3,5-dimethyl-anisole, 5-methoxyindane, 5-methoxy- indole, 5-tert-butyl-m-xylene, 6-methylquinoline, 8-methylquinoline, acetophenone, benzothiazole, benzylacetate, butylphenylether, butyl benzoate, ethyl p-toluate, cyclohexylbenzene, decahydronaphthol, dimethoxytoluene, 3-phenoxy-toluene, diphenylether, propiophenone, hexylbenzene, hexamethylindane, isochromane, phenylacetate, propiophenone, veratrol, pyrrolidinone, N, N-dibutylaniline, cyclohexyl hexanoate, menthyl isovalerate, dicyclohexyl methanone, ethyl laurate, ethyl decanoate.

Besides the above-mentioned components, especially the organic functional materials and the solvents, the inks of the invention may comprise further additives and processing assistants. These include, inter alia, surface-active substances (surfactants), lubricants and greases, additives which modify the viscosity, additives which increase the conductivity, dispersants, hydrophobising agents, adhesion promoters, flow improvers, antifoams, deaerating agents, diluents, which may be reactive or unreactive, fillers, assistants, processing assistants, dyes, pigments, stabilisers, sensitisers, nanoparticles and inhibitors.

In addition to the materials mentioned above, an organic electroluminescent device according to the present invention may comprise at least one anode, at least one cathode and one or more substrates. The electrodes (cathode, anode) are selected for the purposes of the present invention in such a way that their band energies correspond as closely as possible to those of the adjacent, organic layers in order to ensure highly efficient electron or hole injection.

Preferred materials for the anode are metal oxides selected from, but not limited to, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO), ZnO, InO, aluminium-zinc-oxide (AlZnO), and other metal oxides such as Al- and In-zinc oxide doped with zinc oxide, magnesium-indium-oxide, and nickel-tungsten-oxide. Metal nitrides such as galliumnitrides and metal selenides such as zinc-selenide and metal-sulfides such as zinc-sulfide can also be used. Further materials that can be used for anodes are electrically conducting polymers, e.g. polythiophenes and polypyrroles.

The anode can be transparent, opaque, or reflective. The anode can also adopt an intermediate state, e.g. both being partially reflective and partially transparent.

If the anode is not or only partially transparent further conducting materials can be used. Preferred materials for non-transparent or partially transparent anodes are selected from, but not limited to, Au, Ir, Mo, Pd, Pt, Cu, Ag, Sn, C, Al, V, Fe, Co, Ni, W, and mixtures thereof. The conducting materials can also be mixed with further conducting materials as described above, e.g. In- Cu.

The anode is preferably transparent and a particularly preferred material for the anode is ITO. In the case of a bottom-emitting device glass or plastic is preferably coated with ITO. In the case of a top-emitting device the anode comprises preferably a reflecting material. Further materials can be used for anodes, which are known to the person skilled in the art.

A flexible and transparent combination of substrate and anode is described in US 5844363 B2 and US 6602540 B2, for instance. The cathode can be transparent, opaque, or reflective. The cathode is selected from a metal or an alloy with a low work function. Preferably metals, alloys, or conducting compounds or materials with a work function of less than 4.0 eV are used. Particularly preferred cathodes are selected from, but not limited to, Ba, Ca, Sr, Yb, Ga, Cd, Si, Ta, Sb, Zn, Mg, Al, In, Li, Na, Cs, Ag, mixtures of two or more elements such as alloys comprising Mg/AI or Al/Li or Al/Sc/Li or Mg/Ag or metal oxides such as ITO or IZO.

Further preferred materials for cathodes, used to form a thin dielectric layer, are selected from a metal which is mixed with LiF, Li2O, BaF2, MgO, or NaF. A typical combination is LiF/AI.

A Mg/AI cathode with ITO layer on top is described in US 5703436, US 5707745, US 6548956 B2, US 6576134 B2. A Mg/Ag alloy is described in US 4885221.

The substrate may be rigid or flexible. It may be transparent, translucent, opaque or reflective. The materials used can be glass, plastic, ceramic or metal foils, where plastic and metal foils are preferably used for flexible substrates. However, semiconductor materials, such as, for example, silicone wafers or printed circuit board (PCB) materials, can also be employed in order to simplify the generation of conductor tracks. Other substrates can also be employed.

The glass used can be, for example, soda-lime glass, Ba- or Sr-containing glass, lead glass, aluminium silicate glass, borosilicate glass, Ba borosilicate glass or quartz.

Plastic plates can consist, for example, of polycarbonate resin, acrylic resin, vinyl chloride resin, polyethylene terephthalate resin, polyimide resin, polyester resin, epoxy resin, phenolic resin, silicone resin, fluorine resin, polyether sulfide resin or polysulfone resin. For transparent films, use is made, for example, of polyethylene, ethylenevinyl acetate copolymers, ethylene-vinyl alcohol copolymers, polypropylene, polystyrene, polymethyl methacrylate, PVC, polyvinyl alcohol, polyvinylbutyral, nylon, polyether ether ketone, polysulfone, polyether sulfone, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, polyvinyl fluoride, tetrafluoroethylene-ethylene copolymers, tetrafluoroethylene- hexafluoropropylene copolymers, polychlorotrifluoroethylene, polyvinylidene fluoride, polyester, polycarbonate, polyurethanes, polyimide or polyether imide.

The substrate is provided with a hydrophobic layer. The substrates are preferably transparent.

Other materials than those mentioned here can also be used. Suitable materials are known to the person skilled in the art.

After the application of an ink of the present invention to a substrate or a functional layer already applied, a drying step is carried out in order to remove the solvent(s). The drying can preferably be carried out at relatively low temperature and over a relatively long period in order to avoid bubble formation and to obtain a uniform coating. The drying here can preferably be carried out at a pressure in the range from 10’⁶ mbar to 1 mbar, more preferably in the range from 10’⁶ mbar to 10’² mbar and most preferably in the range from 10’⁶ mbar to 10’⁴ mbar. During the drying process, the temperature of the substrates can be varied from -5°C to 40°C.

It may furthermore be provided that the process is repeated a number of times, with formation of different or identical functional layers. Crosslinking of the functional layer formed can take place here in order to prevent dissolution thereof, as is disclosed, for example, in EP 0637899 A1 . The present invention furthermore relates to a kit of inks, containing at least two different inks, an ink A and an ink B,

- wherein ink A contains at least a first organic functional material A and at least a first organic solvent A,

In a preferred embodiment, the first organic solvent A and the second organic solvent B are different.

The present invention also relates to an electronic device, preferably an organic light emitting diode (OLED), characterized in that at least one layer is prepared using the method of the present invention. An electronic device is taken to mean a device which comprises anode, cathode and at least one functional layer in between, where this functional layer comprises at least one organic functional material.

The organic electronic device is preferably an organic light emitting diode (OLED), an organic integrated circuit (O-IC), an organic field-effect transistor (O-FET), an organic thin-film transistor (O-TFT), an organic lightemitting transistor (O-LET), an organic solar cell (O-SC), an organic photovoltaic (OPV) cell, an organic optical detector, an organic photoreceptor, an organic field-quench device (O-FQD), an organic electrical sensor, a light-emitting electrochemical cell (LEC) or an organic laser diode (O-laser), more preferably an organic light emitting diode (OLED).

Surprisingly, it has been found that, with the application of the method of the present application, the components of the different inks are combined only for a short period of time before they are dried. Consequently, a possible reaction between the components, especially the reactive components, can be avoided to a great extent.

Furthermore, when one component of an ink is insoluble in one solvent which is however suitable for printing or would form polymorph in this solvent, this component could be stored and processed in another solvent and combined with the printing-suitable solvent only shortly before drying. As a consequence, the precipitation of the composition in an ink during storage can be prevented.

In addition, as shown above and in the working examples, with the use of the printing method of the present invention, it is possible to manufacture, for example a full-colour OLED display with a reduced number of inks compared with a conventional printing method. As a result, the preparation of OLED displays can be simplified, and it is possible to reduce the costs of the equipment and the fabrication process.

These above-mentioned advantages are not accompanied by an impairment of the other electronic properties.

The invention is explained in greater detail below with reference to working examples, but without being restricted thereby.

Working Examples

In the working examples, the following materials are used.

HTM-1 is a polymer (i.e. polymer P2) and DP-1 is a salt (i.e. salt D1 ) as described in WO 2016/107668 A1.

The remaining materials as used in the working examples are shown in the following Table 1 .

Table 1

Comparative Example 1

Preparation of a red/green/blue panel using a conventional printing method

A substrate comprising three different pixel types A, B and C was provided. The hole injection layer (HIL) was prepared in that three inks, i.e. Ink A, Ink B, and Ink C, are used, each containing the materials HTM-1 and DP-1 , but in different ratios. The hole transport layer (HTL) was prepared in that one ink, i.e. Ink D, is used for all three pixel types. The emitting layer (EML) was prepared in that three different inks, i.e. Ink E, Ink F, and Ink G, are used. As can be seen from the following Table 2, in total, 7 different types of inks are required to fabricate such a conventional R/G/B panel. The device fabrication process is shown in Figure 1 .

Table 2

Example 1

Preparation of a red/green emissive layer

An Ink H, containing the materials H1 :H2:G-DP1 in a ratio 1 :3:1 , was prepared in 3-Phenoxytoluene (3-PT) in a concentration of 20 g/L. An Ink I, containing the material R-DP1 , was prepared in 3-PT in a concentration of 10 g/L. The volume of each ink, as used for the two pixels is shown in the following Table 3. The photoluminescence image of both pixels, i.e. Pixel A and Pixel B, is shown in Figure 2. As can be seen, Pixel B was prepared in that two inks, i.e. Ink H (G-EML) and Ink I (red dopant) are printed into the same pixel separately, and the resulting Pixel B emits red light.

Table 3

Example 2

Preparation of a red/green/blue panel according to the method of the present invention

(1) Preparation of the hole injection layer (HIL)

A substrate comprising pixel types A, B and C was provided. An Ink J, containing the hole transport material HTM-1 in 3-PT in a concentration of 10 g/L, was prepared. An Ink K, containing the p-dopant material DP-1 in 3- PT in a concentration of 1 g/L, was prepared. The volume of each ink as used in each pixel is shown in the following Table 4.

The different dopant ratios can be achieved in that different drop volumes of Ink J and Ink K in different pixels are printed to achieve the different hole- injection and hole transport properties.

The different thicknesses can be achieved in that different volumes of both inks are printed.

Table 4

After the HIL layer was printed in the different pixels, the solvent was removed in a vacuum chamber at a pressure of 10’⁵ mbar and then annealed at a temperature of 225°C for 30 minutes.

(2) Preparation of the hole transport layer (HTL)

On top of the hole injection layer, the hole transport layer (HTL) layer was printed, using Ink J, containing the hole transport material HTM-1 in 3-PT in a concentration of 8 g/L. The volume (pL) of the ink as used for each pixel is shown in the following Table 5.

Table 5

(3) Preparation of the emitting layer (EML)

An Ink H (G-EML ink), containing the materials H1 :H2:G-DP1 in a ratio 1 :3:1 , was prepared in 3-PT in a concentration of 20 g/L. An Ink I, containing the red dopant material R-DP1 , was prepared in 3-PT in a concentration of 10 g/L. An Ink M (B-EML), containing the materials H3:B- DP1 in a ratio 99:1 , was prepared in 3-PT in a concentration of 12 g/L. The volume (pL) of each ink as used in the different pixels is shown in the following Table 6. The different thicknesses and colour emissions can be achieved by different drop volumes.

Table 6

The fabrication process is shown in Figure 3. In total, only 5 different types of inks are needed to fabricate the R/G/B panel, which shows great benefit of equipment cost reduction.

Example 3

Preparation of an R/G/B/W emissive layer

(1) Preparation of hole injection layer (HIL)

A substrate comprising pixel types A, B, C, and D was provided. An Ink J, containing the hole transport material HTM-1 , was prepared in 3-PT in a concentration of 10 g/L. An Ink K, containing the p-dopant material DP-1 , was prepared in 3-PT in a concentration of 1 g/L. The volume of each ink as used in the different pixels is shown in the following Table 7. The different dopant ratios can be achieved in that different drop volumes of Ink J and Ink K in different pixels are printed to achieve different hole-injection and hole transport properties.

Table 7

(2) Preparation of the hole transport layer (HTL)

On top of the hole injection layer, the hole transport layer (HTL) layer was printed, using Ink J, containing the hole transport material HTM-1 in 3-PT in a concentration of 8 g/L. The volume (pL) of the ink as used for each pixel is shown in the following Table 8.

Table 8

(3) Preparation of the emitting layer (EML)

An Ink M (B-EML), containing the materials H1 :H2:B-DP1 in a ratio 33:66:1 , was prepared in 3-PT in a concentration of 12 g/L. An Ink N (G-DP1 ), containing the green dopant material (G-DP1 ), was prepared in 3-PT in a concentration of 10 g/L. An Ink 0, containing the red dopant material R- DP1 , was prepared in 3-PT in a concentration of 2 g/L. The volume (pL) of each ink as used in different pixels is shown in the following Table 9. The different thicknesses and colour emissions can be achieved by different drop volumes.

Table 9

The fabrication process is shown in Figure 4. In total, only 5 different types of inks are needed to fabricate the R/G/B/W panel. In comparison, the conventional fabrication process to fabricate such an R/G/B/W panel, would require 8 inks. This clearly demonstrates that the process of the present invention has a great benefit concerning the reduction of the equipment costs as well as better flexibility concerning the panel pixel design.

Claims

- 75 -

Claims A printing method comprising the following steps:

(d) thereafter drying the different pixel types. The method according to claim 1 , characterised in that:

- the first ink A is printed into the at least two different pixel types A and B, and

- the second ink B is printed into the at least two different pixel types A and B. The method according to claim 1 , characterised in that the substrate has at least three, preferably three, different pixel types, a first pixel type A, a second pixel type B and a third pixel type C. The method according to claim 3, characterised in that:

- the first ink A is printed into the at least three different pixel types A, B and C, and

- the second ink B is printed into the at least three different pixel types A, B and C. The method according to claim 4, characterised in that, - 76 -

- the first ink A is printed into the three different pixel types A, B and C, and

- the second ink B is printed into the three different pixel types A, B and C. The method according to claim 4 or 5, characterized in that the first ink A contains at least one hole-transporting material as organic functional material and at least one organic solvent A. The method according to claim 6, characterized in that the at least one hole-transporting material is a polymeric material. The method according to one or more of claims 4 to 7, characterized in that the second ink B contains at least one dopant as organic functional material and at least one solvent B. The method according to claim 8, characterized in that the at least one dopant is a low molecular weight material, having a molecular weight of < 3.000 g/mol. The method according to one or more of claims 4 to 9, characterized in that the amount of the first ink A, which is printed into the at least three different pixel types A, B and C, differs from pixel type to pixel type. The method according to one or more of claims 4 or 10, characterized in that the amount of the second ink B, which is printed into the at least three different pixel types A, B and C, differs from pixel type to pixel type. The method according to claim 1 , characterised in that:

- the first ink A is printed into pixel type A, and - 77 -

- the second ink B is printed into pixel type A and B.

13. The method according to claim 3, characterised in that:

- the first ink A is printed into pixel type A,

- the second ink B is printed into pixel type A and B, and

- a third ink C, containing at least one organic functional material C, which is different from the organic functional materials A and B, and at least one organic solvent C is printed into pixel type C.

14. The method according to claim 13, characterized in that the first ink A, the second ink B and the third ink C, each contains at least one lightemitting material as organic functional material and at least one solvent.

15. The method according to claim 14, characterized in that each of the at least one light emitting materials of the first ink A, the second ink B and the third ink C is selected from the group consisting of fluorescent light emitting materials and phosphorescent light emitting material.

16. The method according to claim 14 or 15, characterized in that lightemitting material A of the first ink A is a light-emitting material emitting red light, preferably a phosphorescent light-emitting material emitting red light.

17. The method according to one or more of claims 14 to 16, characterized in that light-emitting material B of the second ink B is a light-emitting material emitting green light, preferably a phosphorescent light-emitting material emitting green light.

18. The method according to one or more of claims 14 to 17, characterized in that light-emitting material C of the third ink C is a light-emitting material emitting blue light, preferably a fluorescent lightemitting material emitting blue light. - 78 - The method according to one or more of claims 14 to 18, characterized in that the light-emitting material of the first ink A, the second ink B and the third ink C are low molecular weight materials, having a molecular weight of < 3.000 g/mol. The method according to one or more of claims 13 to 19, characterized in that a fourth ink D, containing at least one organic functional material D, which is different from the organic functional materials A, B and C, and at least one organic solvent D, is printed into pixel type A, B and/or C, preferably printed into pixel type A, B and C. The method according to claim 20, characterized in that the at least one organic functional material D is a matrix material. The method according to one or more of claims 1 to 19 comprising the following steps:

(b) printing a first ink A, containing at least one organic functional material A and at least one organic solvent A, into the at least pixel type A, B, C and D,

(e) thereafter drying the different pixel types. - 79 - The method according to one or more of claims 1 to 22, characterized in that printing of ink A and ink B into the same pixel type, results in one ink containing at least a first organic functional material A, a second organic functional B, at least a first organic solvent A and at least a second organic solvent B. The method according to one or more of claims 1 to 23, characterized in that the content of the organic functional materials A, B, C and/or D in the corresponding inks are respectively in the range from 0.001 to 20 weight-%, preferably in the range from 0.01 to 10 weight-%, more preferably in the range from 0.1 to 5 weight-% and most preferably in the range from 0.3 to 5 weight-%, based on the total weight of the inks. The method according to one or more of claims 1 to 24, characterized in that the organic solvents A, B, C and/or D have a boiling point in the range from 100 to 400°C, preferably in the range from 200 to 350°C, more preferably in the range from 225 to 325°C and most preferably in the range from 250 to 300°C. The method according to one or more of claims 1 to 25, characterized in that the organic functional materials A, B, C and/or D have respectively a solubility in the corresponding organic solvents which is > 5 g/l, preferably > 10 g/l. The method according to one or more of claims 1 to 26 characterized in that the first, second, optional third and optional fourth ink have respectively a viscosity in the range from 0.8 to 50 mPa s, preferably in the range from 1 to 40 mPa s, and more preferably in the range from 2 to 15 mPa s. - 80 -

28. The method according to one or more of claims 1 to 27, characterized in that the first, second, optional third and optional fourth ink have respectively a surface tension in the range from 15 to 70 mN/m, preferably in the range from 10 to 50 mN/m and more preferably in the range from 20 to 40 mN/m.

29. The method according to one or more of claims 1 to 28, characterized in that the printing method is an ink-jet printing method.

30. The method according to claim 29, characterized in that the ink-jet printing method is used to produce a functional layer of an electronic device, preferably a functional layer of an organic light emitting diode (OLED).

31 . The method according to claim 30, characterized in that the functional layer is a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), an Emissive Layer (EML), an Electron Transport Layer (ETL) or an Electron Injection Layer (EIL), preferably a Hole Injection Layer (HIL), a Hole Transport Layer (HTL) or an Emissive Layer (EML).

32. A method for producing an OLED, containing between a pair of electrodes at least a Hole Injection Layer (HIL), a Hole Transport Layer (HTL) and an Emissive Layer (EML), characterized in that the Hole Injection Layer (HIL) is produced according to the method as claimed in one or more of claims 4 to 11 .

33. The method according to claim 32, characterized in that the Hole Transport Layer (HTL) is produced by using a first ink A according to claim 1.

34. The method according to claim 32 and 33, characterized in that the Emissive Layer (EML) is produced according to the method as claimed in one or more of claims 12 to 21 . - 81 - The method according to one or more of claims 32 to 34, characterised in that the OLED is a full-colour OLED. A kit of inks, containing at least two different inks, an ink A and an ink B,

- wherein the first organic functional material A and the second organic functional material B are different, characterized in that when mixed, both inks result in one ink containing at least a first organic functional material A, a second organic functional B, at least a first organic solvent A and at least a second organic solvent B. A kit according to claim 36, characterized in that the first organic solvent A and the second organic solvent B are different. A method for the preparation of an ink, containing at least a first organic functional material A, a second organic functional B, at least a first organic solvent A and at least a second organic solvent B, characterized in that an ink A, containing at least a first organic functional material A and at least a first organic solvent A, and an ink B, containing at least a second organic functional material B and at least a second organic solvent B, wherein the first organic functional material A and the second organic functional material B are different, are mixed.