WO2008049577A1

WO2008049577A1 - Organic opto-electronic devices

Info

Publication number: WO2008049577A1
Application number: PCT/EP2007/009181
Authority: WO
Inventors: Hendrik Jan Bolink
Original assignee: Dsm Ip Assets B.V.
Priority date: 2006-10-25
Filing date: 2007-10-23
Publication date: 2008-05-02
Also published as: TW200826333A

Abstract

The invention relates to an organic opto-electronic device comprising an organic layer between an anode and cathode, the organic layer comprising: a) 1-70 wt% of a dendritic compound, b) 0-50 wt% of a compound for hole transport, c) 0-50 wt% of a compound for electron transport and d) 0-40 wt% of a compound for light emission, wherein the sum of elements b), c) and d) is more than 20 wt% and the dendritic compound is inert. The invention also relates to organic opto-electronic single layer devices and a solution based process for making an organic opto-electronic device such as OLED's.

Description

ORGANIC OPTO-ELECTRONIC DEVICES

The present invention relates to organic light emitting devices, such as polymer light emitting diodes, organic color displays, and, in particular, to a new highly efficient organic light emitting material based on dendritic compounds.

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include for example organic thin film transistors, organic photovoltaic cells, organic photodetectors, and organic electroluminescent devices, such as organic light emitting devices (OLEDs). For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

As used herein, the term "organic" includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto- electronic devices. "Small molecule" refers to any organic material that is not a polymer, and "small molecules" may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the "small molecule" class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter, and a group capable of transporting charges. OLEDs make use of thin organic films that emit light when a voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety. OLED devices are generally (but not always) intended to emit light through at least one of the electrodes, and one or more transparent electrodes may be useful in an organic opto-electronic devices. For example, a transparent electrode material, such as indium tin oxide (ITO)₁ may be used as the bottom electrode. A transparent top electrode, such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, may also be used. For a device intended to emit light only through the bottom electrode, the top electrode does not need to be transparent, and may be comprised of a thick and reflective metal layer having a high electrical conductivity. Similarly, for a device intended to emit light only through the top electrode, the bottom electrode may be opaque and/or reflective. Where an electrode does not need to be transparent, using a thicker layer may provide better conductivity, and using a reflective electrode may increase the amount of light emitted through the other electrode, by reflecting light back towards the transparent electrode. Fully transparent devices may also be fabricated, where both electrodes are transparent. Side emitting OLEDs may also be fabricated, and one or both electrodes may be opaque or reflective in such devices.

Organic light emitting diodes (OLEDs) based on low molecular weight and polymeric materials are in an advanced stage of application in flat panel displays. After the first reports of Tang and VanSlyke in 1987 and Burroughes et al. in 1990 rapid progress was achieved in optimization of the device parameters such as efficiency and brightness. However, in spite of these successful developments, new OLEDs with improved reliability and performance are still in demand.

In OLEDs luminescence is generated by recombination of electrons and holes injected into an organic material as the active layer. Recombination of electrons and holes in the active layer yields singlet or triplet excited states at the recombination centers. Efficient injection process requires molecules with a high energy LUMO (lowest unoccupied molecular orbital) and a low energy HOMO (highest occupied molecular orbital).

The organic active layer can be produced from electroconductive polymer, e.g. poly-phenylene-vinylene (PPV) or can preferably consist of "small" molecules, which have different functionalities like for example hole transporting molecules, electron transporting compounds, wide band gap host molecules, hole and exciton blocking molecules, and efficient fluorescent or phosphorescent molecules. The polymer layer can be prepared by spin coating; "small" molecules can be deposited to form thin films by thermal vacuum deposition, or preferably by solution based processes like for example spin coating, use of doctor blades, or inkjet printing. For a correct functioning of OLEDs it is important that the organic layer is completely transparent, meaning that the film does not scatter incident light, which is difficult to achieve when more than one small molecule is deposited using solution processing techniques such as spin coating. Therefore, OLEDs making use of small molecules with specific functionalities are usually prepared using vapor deposition techniques.

The use of a hole blocking layer in multilayer OLEDs is done to prevent the loss of excess holes to the cathode. In most cases the hole blocking layer (HBL) also functions as a barrier for the migration of excitons and is thus also an exciton blocking layer. The key characteristics of this layer is that its molecules have a HOMO energy lower than that of the molecules used to transport holes (positive charges) and a LUMO energy equivalent to or above that of the molecules used to transport electons (negative charges). This is indicated in the picture (fig 1), where the schematic energy level diagram of a high efficiency electrophosphorescent OLED is shown. Hole transport along the HOMO energy levels, electrons along the LUMO levels. Excitons are indicated as starbust patterns in the emission layer.

US 2005/0017629 describes a multilayer OLED consisting of 'small' molecules which are stacked into separate layers. The OLED comprises a substrate (not shown), an anode (ITO material; (+)), a hole transport layer (HTL), an emission layer (EL), an electron transport layer (ETL), a metal (cathode; (-)) and a protective layer (not shown). Holes h⁺ are transported from the anode to the emission layer, and electrons e^~ are transported from the cathode to the emission layer. In US

2005/0017629 the emission layer comprises a dendrimer having a lanthanide ion and that the dendrimer is active in the light emission. The OLED device is prepared in a standard high vacuum chamber at pressures of 10^"6 torr as appropriate. These types of

OLEDs have a reasonable performance, but are very expensive to make, are prepared in low yield, and can be made only in small sizes.

US 7,053,547 describes an example of an OLED comprising a polymer, which OLED has a reduced number of layers compared to the multilayer OLEDs. The advantage of these types of OLEDs is that they are simple to make with spin coating or inkjet printing techniques, but that they have a lower performance then the multilayer small molecule based OLEDs.

It is an object of the present invention to provide an improved OLED.

The improvement may for example be improved performance, improved efficiency or ability to be produced in a cost-efficient way. Particularly, the improvement may be a combination of good performance, high efficiency and ability to be prepared in a cost efficient way.

It is also an object of the invention to provide an OLED that has a high transparency such that the layer does not substantially scatter the incident or generated light.

The present invention comprises an organic opto-electronic device comprising at least one organic layer between an anode and cathode, at least one of the organic layer(s) comprising a. 1-70 wt% of a dendritic compound b. 0-50 wt% of a compound for hole transport c. 0-50 wt% of a compound for electron transport and d. 0.2-40 wt% of a compound for light emission, wherein the sum of elements b, c and d is more than 20 wt% and the at least a part of the dendritic compound is inert.

The weight-% (wt%) described in the present application are weight-% of the organic layer of the final device, i.e. after preparation steps such as curing, drying etc.

By being inert is here meant that the compound is not a main contributor to the transport of electrons or holes and that the compound is not a main comtributor to the emission of light. Hence a dendritic compound in a transmission metal complex of having a transmission metal bonded to it covalently is typically not considered inert.

It should be observed that herein the term inert is not related to chemical reactivity, and hence according to the present invention, an inert dendritic compound may for example be reactive towards other species in the compound, such as being capable of participating in a later curing reaction to form a network system.

By at least a part of the dendritic compound being inert is meant that the invention encompasses the situation where both an active dendritic compound (i.e. participating in the hole or electron transport and/or the light emission) and inert dendritic compounds are present.

Each of components a, b, c and d may - if present - independently be composed of one or more compounds. In the main embodiment, the sum of the weight of elements b, c and d, i.e. the compound for hole transport, the compound for electron transport and the compound for light emission, is more than 20 wt% based on the total weight of the organic layer. Typically, the sum of the weight of elements b, c and d is less than 80%, preferably less than 70% such as less than 50%.

Other components than a, b, c and d may also be present in the organic layers, such as for example organic or inorganic fillers, solvents, cross linkers and various additives known in the art.

The device according to the first aspect of the invention typically comprises several layers, each taking care of one or more of hole transport, electron transport, light emission and blocking of holes. It is preferred that at least one of the layers comprises more than one of these functions, as this reduces the required number of layers. In another aspect, the present invention comprises an organic optoelectronic device comprising at least one organic layer between an anode and cathode, at least one of the organic layer(s) comprising a. 1 -40 wt% of a dendritic compound b. 10-50 wt% of a compound for hole transport c. 10-50 wt% of a compound for electron transport and d. 0.2-40 wt% of a compound for light emission.

An advantage of the device of the present invention, is that the device has a simple structure containing (easily accessible) small molecules that are providing electron transport, hole transport and light emission functions. The fabrication of the device may also be relatively easy, compared to other multi-layer systems.

OLEDS of the present invention have the advantage that the molecules for electron transport and the molecules for hole transport are present in one and the same layer, whereby a very simple structured OLED is being formed.

Preferably the OLED of the present invention comprises an organic layer between an anode and cathode, the organic layer comprising a. 5-40 wt% of a dendritic compound b. 20-40 wt% of a compound for hole transport c. 20-40 wt% of a compound for electron transport and d. 1-10 wt% of a compound for light emission A further embodiment of the present invention is an organic optoelectronic device comprising an organic layer between an anode and cathode, the organic layer comprising a. 5-40 wt% of a hyperbranched molecule b. 20-40 wt% of a compound for hole transport c. 20-40 wt% of a compound for electron transport and d. 1-10 wt% of a compound for light emission

Another embodiment of the present invention is an organic optoelectronic device comprising an organic layer between an anode and cathode, the organic layer comprising a. 5-40 wt% of a hyperbranched molecule b. 20-40 wt% of a compound for hole transport c. 20-40 wt% of a compound for electron transport and d. 1-10 wt% of a compound for light emission wherein the hyperbranched molecule has the structure according to the formula

O

wherein

, H, (C₆-C_{1 0}) aryl or (C₁-C₂₀) (cyclo)alkyl; B = (C2-C24), optionally substituted, aryl or (cyclo)alkyl aliphatic diradical;

R¹ , R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the same or different, H, (Cβ-Cio) aryl or

(Ci-C8)(cyclo)alkyl radical and each n is independently 1-4.

In general, the dendritic compounds utilized according to the invention may optionally be chemically modified. Particularly, the OH functional end groups may be modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof. By a mixture thereof is meant that modification of each modified OH group need not be the same and that for each individual OH group, a mixture of functional groups may be included, such as modification of the OH group into an amine functional alkyl moiety bonded to the dendritic molecule via an ester or ether bond. Other examples of modification includes reacting to an endcaping group, such as a organic acid moiety (such as benzoic acid or a fatty acid), connecting to an C1-C24 (cyclo)alkyl moiety, an C1-C24 (cyclo)aryl moiety, a polyethylene oxides or polyprolylene oxides moiety, a moiety containing other functional groups like amine containing groups, phosphorous groups, thio groups, silicon containing groups or a polymer (such as the itself or neighboring dendritic polymers or another polymer component of the device. Modification of the OH end group was found to be particularly advantageous for hyperbranched compounds and most advantageous for hyperbranched polyesteramides. Another embodiment of the present invention is organic opto-electronic device comprising an organic layer between an anode and cathode, the organic layer comprising a. 1 -40 wt% of a dendritic compound b. 10-50 wt% of a compound for hole transport c. 10-50 wt% of a compound for electron transport and d. 0.2-40 wt% of a compound for light emission, wherein the device contains hole blocking components between the cathode and the organic layer consisting of molecules that have a HOMO energy lower than that of the molecules used to transport the positive charges and a LUMO similar or above the LUMO of the molecules used to transport the negative charges.

These OLED's have a combination of low molecular weight molecules with specific functionalities such as hole transport, electron transport and fluorescence or phosphorescence by adding a suitable dendritic molecule which forms after evaporation of solvent a highly transparant film by preventing phase separation and or crystallization of the different molecules in the film.

Description of the drawings

FIG 1 Schematic energy level diagram of high efficiency electrophosphorescent OLED.

FIG 2 current density and light intensity versus applied voltage and efficacy versus applied voltage for the OLED device described in the example.

Dendritic compounds are three-dimensional synthetic molecules, which incorporates repetitive branching sequences to create unique architecture.

Examples of dendritic compounds are dendrimers and hyperbranched polymers and molecules.

Dendrimers are highly branched molecules or polymers have a perfect or nearly perfect structural symmetry, density gradient displaying an intra- molecular minimum value and well-defined molecular weight and number of terminal groups. Dendrimers are prepared in a shell or generation wise synthesis from a core molecule, which leads to costly products with restricted options of fine-tuning of material properties. Synthetic procedures, developed for dendrimers preparation, permit nearly complete control over the critical molecular design parameters, such as size, shape, surface/interior chemical structure, and topology. Synthesis techniques provide effective routs to the dendrimer structures, including the Starburst divergent strategy (Tomalia and co-workers), the convergent growth strategy (Frechet and co- workers), and the self-assembly strategy (Zimmerman and co-workers).

Hyperbranched polymers are specific examples of dendritic compounds which have a less perfectly branched structure than dendrimers.

Hyperbranched polymers may be prepared in a less structured way than dentrimers leading to a more cost efficient and highly flexible synthesis with highly improved ability to fine-tuning of material properties. Combination of these features creates an environment within the hyperbranched molecules facilitate development and manufacturing of reliable and economical functional nanoscale materials with unique properties that could form the basis for new nanoscale devices and novel technologies. Examples of suitable hyperbranched molecules and synthesis can be found in for example WO 99/16810, WO 00/58388 and WO 01/62865, which are incorporate herein by reference in their entirety. Preferred hyperbranched molecules are hyperbranched polyesteramides as hyperbranched polyesteramides provides molecules with highly polar segments, wherein non-polar or low-polar segments may be included to realize highly tailorable properties. Particularly, it was found that hyperbranched polyesteramide polymers provided a superb vehicle for dispersing the various elements of the solution and hence prevented premature phase inversion during manufacturing of the opto-electronic devices. Examples of suitable hyperbranched molecules and polymers are the polymer containing at least two groups according to formula (I)

, H, (Cβ-C-io) aryl or (C₁-C₂₀) (cyclo)alkyl, B = (C2-C24), optionally substituted, aryl or (cyclo)alkyl aliphatic diradical,

R¹ , R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the same or different, H, (Cβ-C-io) ary' °^r (C-|-C8)(cyclo)alkyl radical and each n is independently 1-4.

Optionally at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof as discussed elsewhere.

Another example of a suitable dendritic compound is the hyperbranched polymer containing at least two groups according to formula (II):

O O R¹ R^J

-B- -N- -C- -O- -H (H)

Y H

in which

R" R^b

Y= -OH , H, (C₁-C₂₀) (cyclo) alkyl,

R° H

or (C₆-C₁₀) aryl,

B = (C2-C24), optionally substituted, aryl or (cyclo)alkyl aliphatic diradical, and

R1 , R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the same or different, H, (Cβ-C-io) ary' ^or (Ci-C8)(cyclo)alkyl radical. Yet another example is a polymer containing hydroxyalkylamide groups according to formula (III):

O R¹

-N- -O- -X^η (ill)

-B-

R' H

in which:

R⁴

Y = -C C O X² , H₁ (C₁-C₂₀) (cyclo)alkyl or (C₆-C₁₀)aryl

R^s H

R¹ R°

A = -N- -X^ or OH,

R ^ H

B = (C2-C24), optionally substituted, aryl or (cyclo)alkyl aliphatic diradical,

O R¹ R³

X¹ = -B- -N- -O-

Y H

X² = H or X¹ and

R1 , R², R3_? R4 R5 _an(j R6 _may independently of one another, be the same or different, H, (Cg-C-) Q) aryl or (Ci-C8)(cyclo)alkyl radical or CH2-OX².

In formulas (II) and (III) R groups may together or with neighbouring carbon atoms form part of a cycloalkyl group.

Another example of a suitable dendrimer is a polymer containing D- hydroxyalkylamide groups according to formula (IV):

O O H R^J

-B- -N- -O- -X¹ (IV)

Y H H

in which:

H H

Y = ? 9 O X² , H, (C₁-C₂₀) (cyclo)alkyl or (C₆-C₁₀)aryl,

H R^b

H

A = -N- -O- -X or OH,

H H

B = (C2-C24), optionally substituted, aryl or (cyclo)alkyl aliphatic diradical,

O O H H

X¹ = -C B C N C C O X'

Y H R-

χ2 = H or X¹ ,

R³ = H or (CQ-C^ Q) aryl or (C-_|-C8)alkyl radical and

R⁶ = H or (C6-C10) aryl or (C-|-C8)alkyl radical.

The weight average molecular mass of the polymer according to the invention is generally between 800 and 50,000, and preferably between 1000 g/mol and 25,000 g/mol.

In one preferred embodiment of the present invention, the dendritic compound has a glass-transition temperature (Tg) of at least 120 ^°C, more preferably a Tg of at least 130 ^°C.

For the use of the dendritic compound is used as a dispersant, it is preferred that the dendritic compound comprises a hyperbranched polymer or molecule containing at least two groups according to formula (I),

, H, (C₆-C₁₀) aryl or (C₁-C₂₀) (cyclo)alkyl, B = (C2-C24), optionally substituted, aryl or (cyclo)alkyl aliphatic diradical,

R-I , R2, R3, R⁴, R5 and R^ may, independently of one another, be the same or different, H, (Cβ-C-io) aryl or (C-|-C8)(cyclo)alkyl radical and each n is independently 1-4. It is preferred that at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof as discussed elsewhere. The concentration of the dendritic compound may vary quite widely between 0.1 to about 70 wt% based on the total weight of the solution for preparation of the organic layer or based on the total weight of the final organic layer (i.e. after optional curing and/or evaporation of optional solvents. Typically, the concentration of the dendritic compound when used solely as a dispersant is between 1 to 40 wt%, such as 2 to 30 wt% and particularly 5 to 20 wt%. In a preferred embodiment of the present invention the dendritic compounds are cross-linked after application. By cross-linking a reduced mobility of the organic layer is obtained, resulting in an increased life time of the device. Furthermore, a cross-linked organic layer will not redissolve when a next organic layer out of a solvent is applied. That limits the intermingling of the two organic layers and hence leads to an improved performance, predictability and/or durability of the device. Cross-linking can be achieved by adding an appropriate cross-linker to the formulation. Suitable chemistry can be found in the paint or coating industry where cross-linkable systems are used with a sufficiently long pot-life combined with a sufficiently good reactivity. After application the organic layer is for example heated up so that the cross- linking reaction is speeded up. Possibly, a catalyst can be added to further enhance the reactivity. Examples are combinations of alcohols with isocyanates or blocked isocyanates, amines with cyclic carbonates, carboxylic acid with epoxides, acetoacetates with (meth)acrylates. In a preferred embodiment, 5-20 wt% of cross linker is added to the formulation and is present in a cured stage in the device according to the invention. In this preferred embodiment, the device or the solution from where the organic layer is prepared comprises a curable compound. In one embodiment, the curable compound is a separate resin system including a cross linker, which may or may not incorporate the dendritic compound into the network during curing. In another embodiment, at least a part of the dendritic compound is curable by incorporating suitable reactive group(s) and are incorporated into the network during curing. The dendritic compound therefore comprises at least one reactive group. The dendritic compound may also work as a cross linker, which is particularly advantageous, as this reduces the number of components of the total system by the dendritic compound having more than one function. Another way of cross-linking the dendritic compounds is by implementing reactive moieties onto the dendritic compounds than can be cured by radicals, anions or cations that are formed by UV irradiation of UV latent catalysts. Examples of such reactive groups are acrylates, methacrylates, itaconates, diallyl groups for radical curing systems. Epoxides or combinations of epoxides with alcohols are suitable examples for cationic curing systems. Examples of suitable anionic curing systems are combinations of isocyanates with alcohols, epoxides with carboxylic acid and acetoacetates with (meth)acrylates.

Examples of hole transporting materials can be found in for example US 5,554,450, US 5,061 ,569, US 5,853,905 which are incorporated herein by reference. Specific examples are triphenylamine, carbazole and diphenylhydrazone containing compounds, described in the book: Organic Photoreceptors for Imaging Systems", appendix 3 by Paul M. Borsenberger y David S. Weiss, Marcel Dekker, Inc, NY 1998.

Examples of electron transporting materials are azoles, diazoles, triazoles, oxadiazoles, benzoxazoles, benzazoles and phenanthrolines, each of which may optionally be substituted. Particularly preferred substituents are aryl groups, in particular phenyl, oxadiazoles, in particular aryl-substituted oxadiazoles. Specific examples of an electron transporting compounds are tris-hydroxy-quinoline aluminum (AIQ₃), 3phenyl-4-(1-naphthyl)-5-phenyl-1 ,2,4-triazole and 2,9dimethyl-4,7-diphenyl- phenanthroline.

Examples of wide band gap host molecules are 4,4'- bis (carbazol-9- yl)biphenyl), known as CBP, and (4, 4', 4"- tris (carbazol-9-yl)triphenylamine), known as TCTA, disclosed in lkai et al. (Appl. Phys. Lett. , 79 no. 2,2001 , 156) and triarylamines such as tris-4-(N-3-methylphenyl-N- phenyl) phenylamine, known as MTDATA Exampels of hole and exciton blocking molecules are BAIq (4- biphenyloxolato aluminum(lll)bis(2-methyl-8-quinolinato)4-phenylphenolate), BCP(bathocuproine) and TPBI (1 ,3,5-tris(2-N-phenylbenzimidazolyl) benzene) as for example described by Adamovich et al. (Organic Electronics 4 (2003) 77-87).

Exampels of efficient fluorescent or phosphorescent molecules are 4- (dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM), or tris(2- phenylpyridine) Iridium(lll). The emission layer may emit monochrome light (such as for example one of red, green or blue light), or the emission layer may emit multichrome light, such as white light or light composed of several distinct wavelengths. Such multichrome emission may be realized by one type of fluorescent or phosphorescent molecules may emit light with several wavelengths or by utilizing a mixture of fluorescent or phosphorescent molecules

These materials may exist in small molecule form or may be provided as repeat units of a polymer, in particular as repeat units located in the backbone of a polymer or as substituents pendant from a polymer backbone. It is possible that the OLED of the present invention contains polymeric materials, as long as the transparency of the OLED is not disturbed by the presence of one or more polymers.

Transporting materials may be bipolar, i. e. capable of transporting holes and electrons. Suitable bipolar materials preferably contain at least two carbazole units (Shirota, J. Mater. Chem. , 2000,10, 1-25). Alternatively, a bipolar host material may be a material comprising a hole transporting segment and an electron transporting segment. An example of such a material is a polymer comprising a hole transporting segment and an electron transporting segment as disclosed in WO 00/55927 wherein hole transport is provided by a triarylamine repeat unit located within the polymer backbone and electron transport is provided by a conjugated polyfluorene chain within the polymer backbone.

Alternatively, the properties of hole transport and electron transport may be provided by repeat units pendant from a conjugated or non-conjugated polymer backbone. Homopolymers and copolymers may be used, including optionally substituted polyarylenes such as polyfluorenes, polyspirofluorenes, polyindenofluorenes or polyphenylenes as described above with respect to the hole transporting layer.

OLEDs are typically fabricated on a transparent substrate coated preliminary with the hole-injecting electrode. Usually, indium-tin-oxide (ITO) is used as the hole-injecting electrode, which forms transparent and electro-conductive anode layer. One or more organic layers are coated then by either thermal evaporation (in case of small organic dye molecules), by spin coating in case of polymers, or preferably by inkjet printing techniques. In addition to the active layer of the luminescent material itself, other organic layers may be used to enhance injection and transport of electrons and/or holes. Hole blocking layer and metal cathode (such as magnesium-silver alloy, lithium-aluminum or calcium) can be deposited on the top of the multi-layer structure using the high-vacuum sputtering technique. These metals are chosen for their low work functions in order to provide efficient injection of electrons. Total thickness of organic layers is about 100 nm. Two electrodes (e.g. ITO anode and metal cathode) add about 200 nm to the total thickness of the device. Therefore the overall thickness (and weight) of the OLED structure is determined mostly by the substrate.

Properties oleds

The OLEDs of the present invention are transparent in the visible wavelength range. Examples

Fabrication of the OLED Devices

OLED devices are prepared by spin coating a solution containing, a hole transporting molecule, an electron transporting molecule, an emitter (fluorescent or phosphorescent molecule) and a hyperbranched compound as film forming additive on pre-patterned ITO glass plates which are extensively cleaned, using chemical and UV-Ozon methods, just before the deposition of the organic layers. In some cases prior to the deposition of the light emitting layer a hole injection layer is deposited, in general an aqueous solution of Baytron-P (purchased from HC-Starck). The thickness of the light emitting layer is generally around 80 nm, and the thickness of the PEDOT:PSS is around 100 nm. In some cases an additional hole and exciton blocking layer was added prior to the deposition of the metal electrode. This blocking layer was prepared by thermally evaporating suitable molecules under a high vacuum (< 1 x10⁶ mbarr) to a typical thickness of 20-40 nm. The metal counterelectrode is applied using thermal vacuum evaporation (base pressure < 1 x10⁶ mbarr) , in most cases consisting of a bi- layer of 5 nm barium and 80 nm silver. The preparation of the OLED devices is done in an inert atmosphere glovebox (< 0.1 ppm O₂ and H₂O) to minimize effects of air and moisture. Current density and luminance versus voltage were measured using a Keithley 2400 source meter and a photodiode coupled to a Keithley 6485 picoampmeter using a Minolta LS100 to calibrate the photocurrent. An Avantes luminance spectrometer was used to measure the EL spectrum. Devices were characterised in inert atmosphere.

In a typical experiment, 300 mg of a Hybrane PB2295 (obtained from DSM Hybrane BV) is mixed with 300 mg of the hole transport molecule, Λ/,Λ/-diphenyl- Λ/,Λ/'bis(3-methyl-phenyl)-[1 ,1 '-biphenyl]-4,4'-diamine (TPD), 350 mg of the electron transporting molecule, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1 ,3,4-oxadiazole (tBu- PBD) and 50 mg of the phosporescent molecule, iridium(lll) tris-tolylpyridine (lr(tpy)₃)_. This mixture was dissolved in 30 ml of toluene to yield a completely transparent solution. The solution is filtered over a 0.45 micron filter and spin coated at 2000 rpm on patterned ITO covered substrates containing a 100 nm thick Baytron-P layer (resulting in an emitting layer thickness of around 80 nm). The thus obtained bi-layer film is transferred to a high vacuum chamber and evacuated to a base pressure of < 1 x10⁶ mbarr where a hole blocking layer of 20 nm is prepared by evaporating the molecule TPBI (1 ,3,5-tris(2-N-phenylbenzimidazolyl) benzene). The device preparation is completed by evaporating sequentially 5 nm of barium and 80 nm of silver by thermal vacuum evaporation.

The performance of OLED devices is typically expressed as the current density and luminance (light intensity) obtained versus applied voltage from which the efficacy versus voltage is directly derived. The results obtained for the above described device is depicted in fig 2 with the current density (closed squares) and light intensity (open circles) versus applied voltage (left) and efficacy versus applied voltage (right) are presented for the OLED device described above.

The OLED of the invention reached a luminance value of 100 cd/m2 below 12 V and has a current efficiency higher than 1 cd/A.

Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiments, and that various changes and modifications may be effected therein by skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.

Claims

1. An organic opto-electronic device comprising at least one organic layer between an anode and cathode, at least one of the organic layer(s) comprising a. 1 -70 wt% of a dendritic compound b. 0-50 wt% of a compound for hole transport c. 0-50 wt% of a compound for electron transport and d. 0-40 wt% of a compound for light emission, wherein the sum of elements b, c and d is more than 20 wt% and the at least a part of the dendritic compound is inert, i.e. not forming part of element b, c or d.

2. Device according to claim 1 wherein the organic layer comprises a. 1 -40 wt% of the dendritic compound b. 10-50 wt% of the compound for hole transport c. 10-50 wt% of the compound for electron transport and d. 0.2-40 wt% of the compound for light emission; preferably the organic layer comprises a. 5-40 wt% of the dendritic compound b. 20-40 wt% of the compound for hole transport c. 20-40 wt% of the compound for electron transport and d. 1-10 wt% of the compound for light emission.

3. Device according to any one of the claims 1 or 2, wherein the dendritic compound is a hyperbranched polymer or molecule containing at least two groups according to formula (I),

R4 R6

Y = C — OH

R5 H

R1 , R2, R3, R4_ R5 _anc| R6 _may independently of one another, be the same or different, H, (C₆-C₁Q) aryl or (C-|-C8)(cyclo)alkyl radical and each n is independently 1-4, optionally at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof.

Device according to claim 3, wherein the dendritic compound is a hyperbranched polymer or molecule comprising at least two groups according to formula (II):

O R¹ R^J

-B- -N- -O- -H (H)

H

in which

R" R^fc

Y= -OH , H, (C₁-C₂₀) (cyclo) alkyl,

R^s H

or (C₆-C₁₀) aryl,

R1 , R2, R3, R4_I R5 _ancj R6 _may independently of one another, be the same or different, H, (C₆-C₁₀) aryl or (C₁-C8)(cyclo)alkyl radical, optionally at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof.

5. Device according to anyone of claims 1-4, wherein the dendritic compound has a Tg of at least 100^°C, preferably the dendritic compound has a Tg of at least 130^°C.

6. Device according to anyone of claims 1-5, wherein the device comprises a hole transport blocking layer between the cathode and the organic layer comprising the hyperbranched molecule. 7. Device according to any one of the claims 1 to 6, comprising a curable compound, preferably the curable compound is a separate resin system or at least a part of the dendritic compound is curable, more preferably the dendritic compound comprises at least one reactive group.

8. Device according to any one of the claims 1 to 7, wherein the device is an organic light emitting device.

9. An organic opto-electronic device comprising an organic layer between an anode and cathode, the organic layer comprising a. 1-40 wt% of a dendritic compound b. 10-50 wt% of a compound for hole transport c. 10-50 wt% of a compound for electron transport and d. 0.2-40 wt% of a compound for light emission, wherein the dendritic compound is a hyperbranched polymer or molecule containing at least two groups according to formula (I),

, H, (C₆-C₁₀) aryl or (C₁-C₂₀) (cyclo)alkyl, B = (C2-C24). optionally substituted, aryl or (cyclo)alkyl aliphatic diradical,

R¹ , R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the same or different, H, (CQ-C^ Q) aryl or (Ci-C8)(cyclo)alkyl radical and each n is independently 1-4, optionally at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof.

10. Device according to claim 9, wherein the dendritic compound is a hyperbranched polymer or molecule comprising at least two groups according to formula (II):

O O

-B- -N- -O- -H (H)

FT H

in which

R< R^b

Y= -OH

■ H, (C₁-C₂₀) (cyclo) alkyl,

R ₃5 H

or (C₆-C_{1 0}) aryl,

R¹ , R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the same or different, H, (Cβ-C-irj) aryl or (Ci-C8)(cyclo)alkyl radical, optionally at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof. 1 1. Device according to claim 9 or 10, wherein the organic layer comprises a. 5-40 wt% of a dendritic compound b. 20-40 wt% of a compound for hole transport c. 20-40 wt% of a compound for electron transport and d. 1-10 wt% of a compound for light emission.

12. Device according to anyone of claims 9-11-4, wherein the dendritic compound has a Tg of at least 100°C, preferably the dendritic compound has a Tg of at least 130^°C.

13. Device according to anyone of claims 9-12, wherein a compound is present comprising the properties of hole transport and electron transport in one molecule, which properties are provided by repeat units pendant from a conjugated or non-conjugated polymer backbone.

14. Device according to anyone of claims 9-13, wherein the device comprises a hole transport blocking layer between the cathode and the organic layer comprising the hyperbranched molecule.

15. Device according to any one of the claims 14 to 14, wherein the hole transport blocking layer comprises a compound selected from the group consisting of

BAIq (4-biphenyloxolato aluminum(lll)bis(2-methyl-8-quinolinato)4- phenylphenolate), BCP(bathocuproine) and TPBI (1,3,5-tris(2-N- phenylbenzimidazolyl) benzene.

16. The device according to any one of the claims 9 to 15, comprising a curable compound, preferably the curable compound is a separate resin system or at least a part of the dendritic compound is curable, more preferably the dendritic compound comprises at least one reactive group.

17. Device according to any one of the claims 9 to 16, wherein the device is an electroluminescent device, preferably the electroluminescent device is an organic light emitting device.

18. A process for making an opto-electronic device, using a solution based processes, preferably using spin coating of a substrate with the solution.

19. Process according to claim 18, wherein the solution comprises a curable compound, and the process comprises the steps providing the solution on at least part of a substrate, thereafter at least partially curing the curable compound and optionally repeating the sequence to providing a multilayer device, preferably the curable compound comprises a dendritic compound.

20. Process according to claim 19, wherein the curable compound comprises a hyperbranched polymer or molecule containing at least two groups according to formula (I),

R^ , R2, R3, R4 R5 _ancj R6 _may independently of one another, be the same or different, H, (Cg-C-] ₀) aryl or (C-|-C8)(cyclo)alkyl radical and each n is independently 1-4, 21. optionally at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof. Use of a dendritic compound as a dispersant in the process for making an opto-electronic device.

22. Use according to claim 21 , wherein the dendritic compound comprises a hyperbranched polymer or molecule containing at least two groups according to formula (I),

■ H, (C₆-C_{1 0}) aryl or (C₁-C₂₀) (cyclo)alkyl, B = (C2-C24). optionally substituted, aryl or (cyclo)alkyl aliphatic diradical,

R¹ , R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the same or different, H, (Cβ-C-i o) aryl or (C-|-C8)(cyclo)alkyl radical and each n is independently 1-4, optionally at least one of the OH groups is modified into an ester, ether, amide, amine, thiol, polyethelene oxide, polypropylene oxide group, or a mixture thereof. 23. A composition suitable for use in the process of making an OLED, comprising solvent and components of anyone of claims 1-17. 24. An instrument comprising an electroluminescent device according to anyone of claims 1 to 17, preferably the electroluminescent device is an OLED.