GB2516607A - Organic electronic device - Google Patents

Abstract

An organic electronic device which comprises a metal anode 4 and a hole injection layer 6, said device further comprising a self-assembled monolayer (SAM) 22 between the metal anode 4 and the hole injection layer 6, the SAM 22 comprising a compound which has a moiety which is capable of adsorbing onto the surface of the metal anode 4 and a hydrophilic moiety. Also disclosed is a method of forming said device. Further disclosed is a material which can form a SAM which can passivate a metal anode in an organic electronic device and prevent oxidation of said anode, where the SAM contains a compound which has a hydrophilic group which improves the wettability of the surface of the anode. Also disclosed is a compound which can form a SAM, where the SAM reduces the contact resistance between a metal anode and a hole injection layer and contains a hydrophilic moiety. The hydrophilic moiety can be a derivative of benzotriazole or indazole, which has a hydroxyl, carboxy, carbonyl or thio hydrophilic substituent. The hydrophilic moiety can also be a thio compound with a hydrophilic tail, preferably a thioalkane or thioalkene.

Description

Organic Electronic Device

Field of the Invention

The present invention relates to organic electronic devices comprising a metal anode and a hole injection layer, wherein said device further comprises a self-assembled monolayer (SAM) between said metal anode and said hole injection layer that acts as a wettable anti-corrosion agent and to a method of manufacturing said devices.

Background to the Invention

Organic electronic devices provide many potential advantages including inexpensive, low temperature, large scale fabrication on a variety of substrates including glass and plastic. Examples of organic electronic devices include organic light emitting diodes, organic thin film transistors, organic photovoltaic devices, organic photosensors and organic memory array devices.

Organic light emitting diodes displays provide additional advantages as compared with other display technologies -in particular they are bright, colourful, fast-switching and provide a wide viewing angle. OLED devices (which here includes organometallic devices and devices including one or more phosphors) may be fabricated using either polymers or small molecules in a range of colours and in multicoloured displays depending upon the materials used. For general background information reference may be made, for example, to W090/13148, W095/06400, WO99/48160 and US4,539,570, as well as to "Organic Light Emitting Materials and Devices" edited by Zhigang Li and Hong Meng, CRC Press (2007), ISBN 10: 1- 57444-574X, which describes a number of materials and devices, both small molecule and polymer.

In its most basic form an organic light emitting diode (OLED) comprises a light emitting layer which is positioned between an anode and a cathode. Frequently a hole injection layer is incorporated in between the anode and the light emitting layer.

It functions to decrease the energy difference between the work function of the anode [e.g. indium tin oxide (ITO) which is commonly used because it is transparent] and the highest occupied molecular orbital (HOMO) of the light emitting layer, thereby increasing the number of holes introduced into the light emitting layer. In operation holes are injected through the anode, and if present the hole injection layer, into the light emitting layer and electrons are injected into the light emitting layer through the cathode. The holes and electrons combine in the light emitting layer to form an exciton which then undergoes radiative decay to provide light.

Some devices also incorporate a thin polymer interlayer between the hole injection layer and the light emitting layer. This plays an important role in improving the device efficiency and the lifetime of ROB light emitting polymer (LEF) OLEDs. For example, with an interlayer, blue LEP OLEDs with an external quantum efficiency of greater than 5% can be achieved, which is 35% higher than without the interlayer. It is believed that this may be due to the prevention of exciton quenching at the hole injection layer/light emitting layer interface.

Further important organic electronic devices are organic thin film transistors. Various arrangements for organic thin film transistors are known. One such device is an insulated gate field-effect transistor which comprises source and drain electrodes with a semiconductive material disposed therebetween in a channel region, a gate electrode disposed adjacent the semiconductive material and a layer of insulating material disposed between the gate electrode and the semiconductive material in the channel region.

An example of such an organic thin film transistor is a top-gate thin film transistor which comprises source and drain electrodes which are spaced apart with a channel region located therebetween. An organic semiconductor is deposited in the channel region and may extend over at least a portion of the source and drain electrodes. An insulating layer of dielectric material is deposited over the organic semiconductor and may extend over at least a portion of the source and drain electrodes. Finally, a gate electrode is deposited over the insulating layer. The gate electrode is located over the channel region and may extend over at least a portion of the source and drain electrodes.

The structure described above is known as a top-gate organic thin film transistor as the gate is located on the top side of the device. Alternatively, it is also known to provide the gate on the bottom side of the device to form a so-called bottom-gate organic thin film transistor comprising a gate electrode deposited on a substrate with an insulating layer of dielectric material deposited thereover. Source and drain electrodes are deposited over the insulating layer of dielectric material. The source and drain electrodes are spaced apart with a channel region located therebetween over the gate electrode. An organic semiconductor is deposited in the channel region and may extend over at least a portion of the source and drain electrodes.

The conductivity of the channel can be altered by the application of a voltage at the gate. In this way the transistor can be switched on and off using an applied gate voltage. The drain current that is achievable for a given voltage is dependent on the mobility of the charge carriers in the organic semiconductor in the active region of the device (the channel between the source and drain electrodes). Thus, in order to achieve high drain currents with low operational voltages, organic thin film transistors must have an organic semiconductor which has highly mobile charge carriers in the channel.

As in OLEDs, a hole injection layer may be incorporated in between the source and drain electrodes and the organic semiconductor layer. This functions to decrease the energy difference between the work function of the electrodes and the highest occupied molecular orbital (HOMO) of the organic semiconductor layer thereby increasing the number of holes introduced into the organic semiconductor layer.

Another important application of this technology is in the development of white OLED materials and a low cost anode architecture to make OLED lighting viable. This is a very big potential market (estimated to reach $6.3 billion by 2018). OLED lighting is a direct and viable competitor to existing technologies, particularly fluorescent lighting (whose lifetime can be shorter than advertised, can contain toxic materials including mercury and have practical inefficiencies due to fixture losses) and inorganic LEDs (which are good point sources of light but are not a good match for uniform, diffuse large area emission applications). OLED lighting is well suited to applications requiring uniform, diffuse large area emission.

An important recent development is the development of OLED lighting tiles in which traditional anode materials such as ITO or gold, both of which are difficult to process and expensive, are replaced by photo-patternable pre-cursor metal deposition technology (see, for example, WO-A-2004!068389). This method of forming a conductive metal region on a substrate comprises depositing on the substrate a solution of a metal ion, and depositing on the substrate a solution of a reducing agent, such that the metal ion and the reducing agent react together in a reaction solution to form a conductive metal region on the substrate. Using this technique, it is possible to deposit fine meshes of a metal on a substrate in a simple, cheap solution-processable way.

For low cost metals such as aluminium and especially copper, the ability to deposit very fine meshes of the order of sub 10 micron tracks on a substrate opens the door to the possibility of producing very flexible devices (contrast to ITO, which is brittle and can crack during processing) in which the fineness of the mesh gives very high transparency to the anode. ITO also has a high resistivity, which creates problems for large area lighting panels, for example, due to the large voltage drops encountered towards the centre of the device, giving rise to a significant drop in light intensity. The line metal tracks deposited by the method of WO-A-2004/068389 produce a highly conductive surface without the voltage drops experienced with ITO devices.

The use of copper and other metals such as aluminium in the photo-patternable deposition technique of WO-A-2004/068389 reduces cost both as a result of the replacement of expensive materials such as ITO (and gold where transparency in not important) and because the electroless plating technique disclosed is simpler, cheaper and more efficient than the sputtering techniques typically used for ITO.

This is particularly important in the development of low cost architecture for OLED lighting and organic thin film transistor displays. In both, the metal tracking (e.g. copper) is deposited by the solution-processable electroless plating technique on a transparent substrate (glass) and then the remaining layers are deposited using further solution-processable techniques as previously known in the art.

Additionally, in lighting devices in order to maximise efficiency an outcoupling film is placed on the bottom surface of the glass substrate to improve emission into glass compared to traditional ITO devices as a result of a reduction in guided modes by glass-index matched hole injection layer. Furthermore, the use of the outcoupling film to get the light out of the glass allows the use of thicker hole injection layers, improving manufacturing efficiency.

Other suitable techniques for the deposition of copper and other metals such as aluminium include vacuum deposition, printing, and photolithography.

However, there are problems with the use of metal tracking that is deposited using techniques such as electroless plating techniques, vacuum deposition or photolithography, especially preferred metals such as copper (which is both cheap and has a good conductivity) and aluminium. First, they oxidise readily. If an oxide layer develops on the metal surface then this increases the contact resistance between the metal and the hole injection layer that is deposited on it. This results in a reduction in the hole supply through the metal/hole injection layer interface, and hence reduces device efficiency. Second, hole injection layers comprise compounds such as PEDT which are hydrophilic compounds which are deposited from aqueous solutions. As a consequence, it is not easy to deposit an aqueous solution of a hole injection compound on a metal surface. Ideally, what is needed is something to make the surface more hydrophilic to improve the binding of the hole injection layer.

There is a clear need in the art to address these problems.

A wide variety of corrosion inhibitors are known in the art. Taking copper as an example, copper oxide can be removed from the surface of copper by immersing it in aqueous acetic acid for a couple of minutes. However, the oxide will quickly start to reform in air. For copper, one widely used example of a copper corrosion inhibitor is cuprotec3, which comprises benzotriazole. The use of benzotriazoles in particular as well as indazoles for the inhibition of copper corrosion has also been well known in the art for some time, e.g. the use of benzotriazole and indazole is disclosed and studied in J.B.Cotton, l.R. Scholes, Br. Corros. J. 2(1967)1. Ngoc Huu Huynh (PhD thesis 2004, Queensland University of Technology) discloses the use of some a number of heterocyclic compounds as copper corrosion inhibitors in acidic, aqueous environments. In one example, the use of 4-carboxybenzotriazole and 5-carboxybenzotriazole for copper corrosion inhibition in corrosive environments is disclosed. The carboxy groups were chosen on the grounds that it was postulated that they would increase corrosion inhibition in the targeted aqueous corrosive environments. There is no disclosure or suggestion that they could be used to prevent copper corrosion caused by atmospheric corrosion or by an electromigration effect.

J.M. Park and J.P. Bell, Epoxy Adhesion to Copper; Adhesive Aspects of Polymer Coatings. Symposium on Adhesion Aspects of Polymeric Coatings (1981: Minneapolis, 1983, 205-224) discloses the improvement in water resistance of copper-epoxy bonds by the inclusion of benzotriazole derivatives, including 5-hydroxytriazole between the copper and epoxy layer. The focus of the disclosure is improved resistance of the joints formed by, for example, copper plates using epoxy resin to water, especially boiling water. The use of further benzotriazoles and other aromatic derivatives as copper corrosion inhibitors in various devices, including electronic devices, is disclosed in, for example, US-A-2004!0217006, Vishnevs'kii, ft Fizika i Khimiya Tverdogo Tila (2006), 7(4), 748-750 and US-A-2009/0239380. A lot of this and prior art concludes that increased copper corrosion can be achieved by making benzotriazole derivatives more hydrophobic. See, for example, X.R.Ye et al., Applied Surface Science 135 (1998)307, However, there is no disclosure or suggestion in the prior art of the use of compounds in organic electronic devices that can both passivate the metal surface to prevent oxidation of the metal anode and increase the water contact angle so as to increase the wetability, thus allowing hydrophilic compounds to be deposited from aqueous solutions thereon, e.g. hole injection layers.

Summary of the Invention

The present inventors have made a significant breakthrough in relation to organic electronic devices and methods for their preparation that makes it possible to address the dual problem of the use of metal tracking as an anode (i.e. first, many oxidise readily reducing efficiency due to increased contact resistance; and second, hole injection layers which are deposited on the anode comprise compounds such as PEDT which are hydrophilic compounds -it is not easy to deposit an aqueous solution of a hole injection compound on a metal surface or on conventional corrosion inhibitors). The present inventors have discovered that by the use of self-assembled monolayers of molecules having particular properties between the metal surface and the hole injection layer, it is possible to both prevent oxidation of the metal surface and provide the desired hydrophilic surface to ensure that an ideal environment is provided for coating with the aqueous solution of the molecules of the hole injection layer.

Thus, in a first embodiment of the invention there is provided an organic electronic device comprising a metal anode and a hole injection layer, wherein said device further comprises a self-assembled monolayer (SAM) between said metal anode and said hole injection layer, said SAM comprising a compound which has a moiety which is capable of adsorbing onto the surface of said metal anode and a hydrophilic moiety.

As we discuss further below, there are many examples of suitable compounds with different moieties that are capable of absorbing onto the surface of the metal anode or also many examples of suitable moieties that are hydrophilic. The key feature of the organic electronic devices of the present invention is the incorporation of a SAM having these two moieties that have essentially two separate functions.

The moiety of the SAM which is capable of adsorbing onto the surface of the metal anode is the passivating element preventing oxidation of the metal surface, thus minimising contact resistance in the devices of the invention that would otherwise arise due to the presence of a thin film of metal oxide on the surface (e.g. copper oxide) hindering hole supply through the metal anode/hole injection layer interface.

The hydrophilic moiety is the moiety responsible for improving the wetability of the surface, changing the contact angle with water compared to the corresponding compound without the hydrophilic group. This improvement in hydrophilicity/wetability provides a hydrophilic surface on the metal giving an ideal environment for coating of the metal with the aqueous solution of the molecules of the hole injection layer, giving an optimum hole injection layer.

In a second aspect of the present invention there is provided a process for the manufacture of an organic electronic device comprising the following steps: (i) depositing a metal anode on a substrate; (ii) depositing a compound which is able to form a SAM on the surface of said metal anode, wherein said compound has a moiety which is capable of adsorbing onto the surface of said metal anode and a hydrophilic moiety; and (iii) depositing a hole injection layer on the SAM.

In a third aspect of the present invention there is provided a compound which is able to form a SAM for use in the passivation of a metal anode in an organic electronic device to prevent oxidation of said metal anode, wherein said compound has a hydrophilic group to improve the wetability of the surface of said anode.

In a fourth aspect of the present invention there is provided a compound which is able to form a SAM for use in an organic electronic device comprising a metal anode and a hole injection layer wherein said SAM is between said metal anode and said hole injection layer, wherein inclusion of said SAM reduces the contact resistance between said metal anode and said hole injection layer compared to an otherwise identical device in which said SAM is not present, said compound which is able to form said SAM further comprising a hydrophilic moiety.

Detailed Description of the Invention

The incorporation of a SAM having the properties recited above according to the present invention into the organic electronic devices of the invention addresses two of the key problems that have restricted the efficiency of devices including metal anodes that oxidise readily, including metal fine mesh devices such as copper or aluminium tracking, i.e. oxidation of the metal surface results in increased contact resistance with the hole injection layer (hence hindering hole supply through the metal/hole injection layer interface) and the lack of a hydrophilic surface to ensure that an ideal environment is provided for coating with the aqueous solution of the molecules of the hole injection layer to give a good coating of the hydrophilic hole injection layer.

The devices and manufacturing process of the present invention enable potentially all steps in the production of organic electronic devices (or nearly all, depending upon what is used as the cathode material in OLED devices, for example) to be solution-processable and easily scalable to manufacturing levels (as solution-based deposition techniques do not require a vacuum). The resulting devices are relatively cheap and have improved efficiency, including lower contact resistance due to the excellent corrosion inhibition provided by the SAMs used in the devices of the invention. Furthermore, efficiency is also improved as a result of the presence of the hydrophilic moiety such as a hydroxy group or carboxy group on the moiety which is capable of adsorbing onto the surface of the metal anode. The deposition of the hole injection layer from aqueous solution onto the hydrophilic surface that is presented by these groups when the SAM is adsorbed onto the surface of the metal anode greatly improves the wetability of the metal surface and ensures that an excellent, uniform hole injection layer is deposited on the metal surface. This further improves the injection of holes from the hole injection layer by giving an optimum metal-hole injecting layer interface.

Although not wishing to be bound by theory, we believe that changing the position of the hydrophilic group on the moiety which is capable of adsorbing onto the surface of the metal anode results in a change in the contact angle with water which results in a change in the surface energy of binding. This results in a change in the wetability of the molecules of the SAM when they are adsorbed onto the surface of the metal. It is believed that the optimal change in surface energy and hence improvement in wetability of the surface of the metal anode is achieved when the point of attachment of the hydrophilic moiety on the moiety which is capable of adsorbing onto the surface of said metal anode in the compound of the SAM is such that the distance of the hydrophilic group from the surface of the metal anode is maximised when the moiety which is capable of adsorbing onto the surface of the metal anode is adsorbed onto the surface of said metal anode.

In one preferred embodiment of the invention, the SAM consists of an aromatic compound which has a hydrophilic substituent. Preferably, said aromatic compound which has a hydrophilic substituent is a benzotriazole derivative, an indazole derivative, a benzimidazole derivative, a benzothiazole derivative or a benzooxazole derivative, more preferably a benzotriazole derivative or an indazole derivative and most preferably a benzotriazole derivative. The aromatic moiety acts as the moiety which is capable of adsorbing onto the surface of the metal anode. In particular, it is believed that the nitrogen atoms in the aromatic ring are responsible for the adsorption.

In the compounds of the SAM present in the devices of the invention the hydrophilic substituent is preferably selected from the group consisting of hydroxy, carboxy, carbonyl and thio substituents, and it is preferably a hydroxyl or carboxy substituent.

Where the SAM is an aromatic compound such as a benzotriazole derivative, the hydrophilic substituent is preferably at the 4-or 5-position on the aromatic ring group, and more preferably the 5-position. The most preferred compounds for use as a SAM in the devices of the present invention are 4-carboxybenzotriazole, 5-carboxybenzotriazole, 5-hydroxybenzotriazole and 4-hydroxybenzotrizole, and most preferably 5-hydroxybenzotriazole or 5-carboxybenzotriazole.

In another preferred embodiment of the present invention, the SAM consists of a thio compound having a hydrophilic tail. Preferred examples include thioalkane and thioalkene derivatives having from 6 to 24 carbon atoms and thio aromatic derivatives having from 5 to 14 carbon atoms in one or more aromatic rings. In each case said derivatives are substituted by a hydrophilic group selected from the group consisting of hydroxyl, carboxy and carbonyl. Most preferably said thio compound having a hydrophilic tail is 11 -thio-1 -undecanol or 4-thiophenol.

The organic electronic devices of the present invention comprising the SAM discussed above comprise a metal anode. The metal anode in the devices of the present invention is typically a metal which oxidises at room temperature (typically 25 to 37°C) in air. This covers most metals to some extent with the exception of the inert metals gold, platinum and palladium. Gold has been regularly used in devices in the prior art for the production of anodes in devices where transparency is not important. However, it suffers from various issues. First, obviously, it is very expensive. Second, it is difficult to process as it can only be deposited by means of thermal deposition techniques. Thus, the devices of the present invention incorporating the SAM discussed above are preferably those in which the metal anodes are oxidisable at room temperature (typically 25 to 37°C) in air. More preferably, they are metals selected from the group consisting of copper, aluminium, nickel and silver, more preferably copper. Preferably, the anode is in the form of a patterned metal tracking. As discussed further below, this can be deposited by means of an electroless plating technique such as that disclosed in WO-A- 2004/068389. Alternatively, it can be deposited by means of vacuum deposition or photolithography. These techniques enable the deposition of the metal tracking and enable precise patterned tracking to be produced (e.g. very fine meshes) with tracks of the order of sub 10 microns.

The hole injection layer preferably comprises a conducting material. It assists hole injection from the anode into the light emitting layer. Preferred examples of materials that may be used to form the hole injection layer are ones which are high conductivity, in particular those which have high lateral conductivity in order to spread the current from the anode of the device (which is particularly important when the anode is in the form of patterned metal tracking such as patterned copper metal tracking). Representative examples of materials that may be used to form the hole injection layer include poly(3,4-ethylenedioxythiophene) (PEDT), and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDT:PSS) (as disclosed in EPO9O1 176 and EP09471 23, along with other doped PEDI5); polyaniline as disclosed in US 5723873 and US 5798170; polypyrole; polyacrylic acid; and a fluorinated sulfonic acid, for example Nafion; optionally substituted polythiophene or poly(thienothiophene) such as PH51 0, a PEDT:PSS commercially available from Heraeus with a PEDT:PSS ratio of 1:2.5. 5% DM30 (by weight) is added to PH51 0 to increase the conductivity to >3003cm-i. Preferably, the hole injection layer comprises poly(3,4-ethylenedioxythiophene) (PEDT), poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDT:PSS), polyaniline, or polypyrole, and most preferably PEDI, or PEDT:PSS.

The organic electronic devices according to the present invention are any which incorporate a metal anode and a hole injection layer in which the inclusion of a SAM in accordance with the present invention will increase corrosion resistance of the metal anode, reduce contact resistance, improve the deposition of the hole injection layer as a result of the improved wetability of the metal surface and as a result increase device efficiency. Typical examples include organic light emitting diodes (including OLED lighting devices), organic thin film transistors, organic photovoltaic devices, organic photosensors, and organic memory array devices.

Preferably the device, e.g. OLED, comprises: (i) a metal anode; (ii) a SAM comprising a compound which has a moiety which is capable of adsorbing onto the surface of said metal anode and a hydrophilic moiety; (iii) a hole injection layer; (iv) an organic light emitting layer; and (v) a cathode.

Still more preferably the device, e.g. OLED, comprises: (i) a substrate; (ii) a metal anode on said substrate; (iii) a SAM consisting of a compound which has a moiety which is capable of adsorbing onto the surface of said metal anode and a hydrophilic moiety; (iv) a hole injection layer on said metal anode; (v) an organic light emitting layer; and (vi) a cathode on said organic light emitting layer.

Particularly preferred devices, e.g. OLEDs, additionally comprise an interlayer and an electron injection later. Preferably the interlayer is inbetween the hole injection layer and the light emitting layer and/or in between the anode and the hole injection layer.

If present, the electron injection layer is between the cathode and the organic light emitting layer. Preferred OLEDS of the present invention comprise an interlayer in between the hole injection layer and the light emitting layer.

Preferred devices of the invention are also encapsulated to avoid ingress of moisture and oxygen. Conventional encapsulation techniques may be used.

The substrate may be any material conventionally used in the art such as glass or plastic. Preferably the substrate is transparent. Preferably the substrate also has good barrier properties to prevent ingress of moisture or oxygen into the device.

The metal anode may comprise any metal with a workfunction suitable for injection of holes into the light emitting layer. If the anode is not required to be transparent (e.g. if the cathode is transparent) then opaque conducting materials such as opaque metals may be used as the anode. Preferably, the metal is one that is suitable for deposition by electroless plating techniques to give low cost, fine mesh tracking, e.g. copper or aluminium.

Preferably the anode is deposited by means of an electroless plating technique such as that disclosed in WO-A-2004/068389. These techniques, which can enable the deposition of the metal tracking by means of spin coating or an inkjet printer enable precise patterned tracking to be produced (e.g. very fine meshes) with tracks of the order of 10 microns. Alternatively, the anode may be deposited by blanket ion sputtering (see, for example US-A-5,556,520).

After the anode has been deposited, it is treated to remove aD oxide and other material from the surface of the metal. First, it is cleaned with a UVozone treatment for approximately 2 minutes to remove any organic contamination, Then, the substrate is immersed immediately in an aqueous acetic acid solution (typicaily I to 5 M, preferaby 2M acetic acid at aternperature of 50-70t (preferably 60t) or glacial acetic acid at room temperature for 1 minute to remove oxide from the surface of the anode. It is immedately removed from the acetic acid solution and quickly dried with a nitrogen gun. The dried oxide-free anode deposited on the substrate is then immediately transferred to be coaled with the next layer of the process (we have found that there is a window of a maximum of 2 minutes to begin the passivation process).

Preferably the SAM (examples of which are given above) is deposited by a solution-based processing method. Any conventional solution-based processing method may be used. Representative examples of solution-based processing methods include spin coating, gravure printing, flexigraphic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing. In one preferred method, deposition is by spin coating. The SAM, i.e. the Self-Assembled Monolayer, forms on the metal from the solution that is in contact with the metal during the soak time. The use of the spin-coater allows the excess SAM solution to be removed and for an effective way of rinsing. The conditions (RPM etc) do not influence the thickness of the SAM.Thus, after transfer of the substrate to a spin coater it can be flooded for example by a solution of the SAM of interest in isopropyl alcohol. This is then typically left for from seconds to 5 minutes, preferably 1 minute to 3 minutes and most preferably 2 minutes. After excess SAM solution is rinsed off, the substrate is flooded with solvent and the spin step is started (typically from 500 to 2000 rpm, preferably 1000 rpm, typically at 200 to 400 rpm/s acceleration, preferably 300 rpm/s). Spinning is typically performed for a period of from 15 seconds to 1 minutes, preferably for 30 seconds. At the end of this period, the resulting substrate with the deposited SAM layer is subjected to a dehydration bake in a nitrogen glovebox (e.g. at 70°C for 15 minutes).

Preferably the hole injection layer (examples of which are given above) is deposited on the SAM layer by a solution-based processing method. Any conventional solution-based processing method may be used. Representative examples of solution-based processing methods include spin coating, gravure printing, flexigraphic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing. In one preferred method, deposition is by spin coating. The parameters used for spin coating the hole injection layer such as spin coating speed, acceleration and time are selected on the basis of the target thickness for the layer. After deposition, the hole injection layer is preferably annealed by heating, e.g. at 150 to °C for 5 to 30 minutes in air.

Any compounds or combination of compounds suitable for use as an hole injection layer may be used in the device of the present invention. For example, PH510 as described above may be used. Other representative examples of well known interlayer compounds are discussed above but any compound having properties that makes it suitable for use as an hole injection layer may be used.

The thickness of the hole injection layer is preferably 15 to 200 nm and more preferably 150 nm.

The interlayer optionally present in the devices of the present invention may comprise any interlayer conventionally used for this purpose. Typical examples of interlayer compounds include poly(2,7-(9,9-di-n-octylfluorene)-alt-( 1,4-phenylene-4-sec-butylphenyl)imino)-1,4-phenylene)) (TFB).

TFB -EP2 228 847 Another example is Co-polymer 1. This is a copolymer comprising 50% Monomer 1, 42.5% FDA and 7.5% of the cross-linker TFBBCB: n-C6H13 Monomer 1 (WOO1/96454) -n-C6H13 Br C8HJ

I FDA

Br%1J3( Br Preferably the interlayer is deposited by a solution-based processing method. Any conventional solution-based processing method may be used. Representative examples of solution-based processing methods include spin coating, gravure printing, flexigraphic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing, e.g. spin coating. The parameters used for spin coating the interlayer such as spin coating speed, acceleration and time are selected on the basis of the target thickness for the layer. After deposition, the interlayer is preferably crosslinked by heating, e.g. at 150 to 200°C for 30 to 120 minutes in a nitrogen glove box.

The thickness of the interlayer is preferably 5 to 50 nm, more preferably 10 to 40 nm, and most preferably 20 to 30 nm.

The organic light emitting layer present in the devices of the present invention may comprise any conventional organic light emitting compound and/or organic light emitting polymer. Preferably the organic light emitting layer comprises a light emitting polymer. One example of such an organic light emitting material is Blend 1 which is a blend of Copolymer 2 and Monomer 2. Monomer 2 is a phosphorescent green dopant -known as fac tris(2-phenylpyridine) iridium or lr(ppy)3. Similar phosphorescent homoleptic or heteroleptic iridium complexes could be used. The host material for the lr(ppy)3 could be a phenanthrene or propellane polymer or a non-polymeric host, or a polyfluorene. Suitable organic phosphorescent compounds are described in the book "Organic Light Emitting Materials and Devices" by Zhigang Li and Hong Meng CRC Press (2007) ISBN 1-57444-574-X pp 369 to 375.

The same book in Chapter 2 describes a variety of light emitting polymers, including polyfluorenes, PPV and polythiophenes that would be suitable for use. Copolymer 2 is acopolymer consisting of 25% Monomer 1/Monomer 3(1:1) and 75% Monomer 1/Monomer 4.

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] 1-.*Th A\ Monomer 2 Monomer 1 (WO01/96454 generically) -n-C6H13 Monomer 3 IY-ri C6H13N' "-"C6H13 Monomer 4 The organic light emitting layer is preferably prepared by depositing a solution of the organic light emitting polymer on the hole injection layer or interlayer. Any conventional solution-based processing method may be used. Representative examples of solution-based processing methods include spin coating, gravure printing, flexigraphic printing, dip coating, slot die coating, doctor blade coating and ink-jet printing. In one preferred method, depositing is by spin coating. The parameters used for spin coating the light emitting layer such as spin coating speed, acceleration and time are selected on the basis of the target thickness for the light emitting layer. After depositing, the organic light emitting layer is preferably dried, e.g. at 100-150°C in a nitrogen glove box.

The thickness of the light emitting layer is preferably 50 to 350 nm and more preferably 75 to 150 nm.

The electron injection layer optionally present is preferably prepared by depositing a solution on the light emitting layer. The method is similar to that for the interlayer.

The electron injection layer optionally present in the devices of the present invention may comprise any conventional electron injection layer, typical examples can include thin layers of metal halides such as LiE or NaF or, preferably, salts of organic compounds or organic compounds doped with metal ions, which can be deposited from organic solution, such as lithium phenolates and 4,7-diphenyl-1,10-phenanthroline.

The cathode is selected from materials that have a workfunction allowing injection of electrons into the light-emitting layer or layers. Other factors influence the selection of the cathode such as the possibility of adverse interactions between the cathode and the light-emitting materials. The cathode may consist of a single material such as a layer of aluminium. Alternatively, it may comprise a plurality of metals, for example a bilayer of a low workf unction material and a high workfunction material such as calcium and aluminium as disclosed in WO 98/10621. The cathode may contain a layer containing elemental barium, for example as disclosed in WO 98/57381, AppI. Phys. Lett. 2002, 81(4), 634 and WO 02/84759. The cathode may contain a thin (e.g. 1-5 nm thick) layer of metal compound between the light-emitting layer(s) of the OLED and one or more conductive layers of the cathode, such as one or more metal layers. Exemplary metal compounds include an oxide or fluoride of an alkali or alkali earth metal,to assist electron injection, for example lithium fluoride as disclosed in WO 00/48258; barium fluoride as disclosed in AppI. Phys. Lett. 2001, 79(5), 2001; and barium oxide. In order to provide efficient injection of electrons into the device, the cathode preferably has a workfunction of less than 3.5 eV, more preferably less than 3.2 eV, most preferably less than 3 eV. Work functions of metals can be found in, for example, Michaelson, J. AppI. Phys. 48(11), 4729, 1977.

The cathode may be opaque or transparent. Transparent cathodes are particularly advantageous for active matrix devices because emission through a transparent anode in such devices is at least partially blocked by drive circuitry located underneath the emissive pixels. A transparent cathode comprises a layer of an electron injecting material that is sufficiently thin to be transparent. Typically, the lateral conductivity of this layer will be low as a result of its thinness. In this case, the layer of electron injecting material is used in combination with a thicker layer of transparent conducting material such as indium tin oxide.

It will be appreciated that a transparent cathode device need not have a transparent anode (unless, of course, a fully transparent device is desired), and so the transparent anode used for bottom-emitting devices may be replaced or supplemented with a layer of reflective material such as a layer of aluminium.

Examples of transparent cathode devices are disclosed in, for example, GB 2348316.

Preferably, there is no electron injection layer present and the cathode is a standard sodium fluoride stack, eg NaF (2nm)/Al (lOOnm)/Ag (lOOnm).

Suitable encapsulants include a sheet of glass, films having suitable barrier properties such as silicon dioxide, silicon monoxide, silicon nitride or alternating stacks of polymer and dielectric as disclosed in, for example, WO 01/81649 or an airtight container as disclosed in, for example, WO 01/19142. In the case of a transparent cathode device, a transparent encapsulating layer such as silicon monoxide or silicon dioxide may be deposited to micron levels of thickness, although in one preferred embodiment the thickness of such a layer is in the range of 20-300 nm.

In the process according to the second aspect of the invention, the metal anode is preferably pre-treated with an agent to remove all metal oxide and organic material from the surface of said metal anode. First, it is cleaned with an LJVozone treatment for approximately 2 minutes to remove any organic contamination, Then, the substrate is immersed immediately in anhydrous acetic acid or an aqueous acetic acid solution (either a I to 5 M aqueous acetic acid solution, preferably 2M aqueous acetic acid solution at a temperature of 3090°C, preferably 60°C or glacial acetic acid at room temperature) for 1 minute to remove oxide from the surface of the anode. It is immediately removed from the acetic acid solution and quickly dried wit.h a nitrogen gun. The dried oxide-free anode aid on the substrate is then immediately translerred to be coated with the next layer of the process.

In one preferred embodiment of the second aspect of the present invention, the treatment with an agent to remove all metal oxide from the surface of the metal surface and the deposition of a compound which is able to form a SAM on the surface of the metal anode are combined in a single solution process step.

We believe that in the process of the second aspect of the invention, the hydrophilic moiety of the compound of the SAM improves the wetability of the SAM compared to the equivalent compound without said hydrophilic group. Furthermore, the inclusion of said SAM reduces the contact resistance between the metal anode and the hole injection layer compared to an otherwise identical device in which said SAM is not present.

In a preferred embodiment of the second aspect of the second invention, there is provided a process wherein the metal anode is in the form of patterned metal tracking which is deposited on the substrate by means of a process selected from the group consisting of vapour deposition, sputtering (e.g. Leybold® blanket sputtering as described in, for example US-A-5556,520) and electroless plating, preferably electroless plating. The electroless plating technique is particularly preferably an electroless plating technique such as that disclosed in WO-A-2004/068389. This comprises in its most basic form the deposition on the substrate of a solution of ions of said metal, and the deposition on said substrate of a solution of a reducing agent, such that the metal ion and the reducing agent react together in a reaction solution to form a conductive metal region on said substrate to form a conductive metal region on the substrate. The reaction between the metal ions and the reducing agent is typically activated by an activator such as a second conductive metal that is different from the first. If used, the activator is typically first deposited on the substrate to give a patterned structure. The first metal ions and reducing agent are then deposited on the substrate in turn, to give the desired anode as metal tracking having the desired pattern.

A preferred process according to the present invention includes the following steps: (i) depositing a patterned metal tracking, preferably of copper, on a glass substrate by means of electroless plating, preferably by depositing on the glass substrate a solution of ions of said metal, and depositing on said glass substrate a solution of a reducing agent, such that the metal ions and the reducing agent react together in a reaction solution to form conductive metal regions on said substrate to form said patterned metal tracking; (ii) treating the patterned metal tracking with a 1 to 5 M solution of acetic acid to remove all oxide from the surface of the metal before immediately drying; (iii) depositing from solution a compound which is able to form a SAM on the surface of said patterned metal tracking prepared in step (ii), wherein said compound which is able to form a SAM has a moiety which is capable of adsorbing onto the surface of said patterned metal tracking and further has a hydrophilic moiety, said deposition preferably being performed by means of a process selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; (iv) depositing from solution a hole injection layer on the SAM prepared in step (iU) by means of a process preferably selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; (v) optionally depositing from solution an interlayer on said hole injection layer prepared in step (iv) by means of a process selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; (vi) depositing from solution an organic light emitting layer on said hole injection layer prepared in step (Ui) or interlayer prepared in step (v) by means of a process selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; and (vii) depositing a cathode on said organic light emitting layer prepared in step (vi) by thermal evaporation of a metal, metal oxide or metal halide, preferably a NaF/Al/Ag cathode, onto said organic light emitting layer.

Brief Description of the Drawings

Figures la and lb are schematic diagrams of atypical OLED; Figure 2 is a schematic diagram of a typical bottom emitter OLED according to the present invention; Figure 3 are plots of square root yield v. energy (eV) for devices according to the present invention compared to control devices to show relative work functions; Figures 4a, 4b, 4c, 4d, 4e, 41 and 4g are plots of square root yield v. energy (eV) for devices according to the present invention compared to control devices measured at different times to show stability; Figures 5a and 5b are plots of current density (mA/cm2) v. voltage (V) and a close up of a section thereof for devices according to the present invention compared to control devices; Figures Ga and Gb are plots of efficiency (EQE) v. voltage (V) and a close up of a section thereof for devices according to the present invention compared to control devices; Figure 7 is a plot of current density (mA'cm2) v. voltage (V) for the best device; Figure 8 is a plot of Efficiency (EQE) v. voltage (V) for the best device; and Figure 9 is a plot of efficiency (Lm/W) v. luminance (Cd/m2).

A cross-section through a basic structure of a typical OLED 1 is shown in Figure 1 a.

A glass or plastic substrate 2 supports a transparent anode layer 4 comprising, for example, a metal (e.g. copper or aluminium) anode in the form of patterned metal tracking having the order of sub 10 micron mesh on which is deposited a hole injection layer 6, an interlayer 8, an organic light emitting layer 10 and a cathode 12.

The hole injection layer 6, which helps match the hole energy levels of the anode layer 4 and the light emitting layer 10, comprises a conductive transparent polymer.

Cathode 12 comprises, for example, a trilayer of sodium fluoride, aluminium and silver. Contact wires 14 and 16 to the anode and the cathode respectively provide a connection to a power source 18.

In so-called "bottom emitter" devices, the multi-layer sandwich is deposited on the front surface of a planar glass substrate, with the reflecting electrode layer, usually the cathode, furthest away from the substrate, whereby light generated internally in the light emitting layer is coupled out of the device through the substrate. An example of a bottom emitter la is shown in Figure la, where light 20 is emitted through transparent anode 4 and substrate 2 and the cathode 12 is reflective.

Conversely, in a so-called "top emitter", the multi-layer sandwich is disposed on the back surface of the substrate 2, and the light generated internally in the light emitting layer 10 is coupled externally through a transparent electrode layer 12 without passing through the substrate 2. An example of a top emitter lb is shown in Figure lb. Usually the transparent electrode layer 12 is the cathode, although devices which emit through the anode may also be constructed. The cathode layer 12 can be made substantially transparent by keeping the thickness of cathode layer less than around 50-100 nm, for example.

A cross-section through a bottom-emitter device according to the present invention is shown in Figure 2. A glass or plastic substrate 2 supports a transparent anode layer 4 comprising a metal (e.g. copper) anode in the form of patterned metal tracking of the order 100 nm thickness. This can be deposited by, for example, an electroless plating technique such as that disclosed in WO-A-2004/068389 or by blanket ion sputtering (e.g. Leybold® blanket sputtering). On the metal tracking 4 there is deposited a SAM 22 consisting of a compound which has a moiety which is capable of adsorbing onto the surface of said metal anode and a hydrophilic moiety, e.g. a hydrophilic benzotriazole derivative such a 5-hydroxybenzotriazole or 5-carboxybenzotriazole. A hole injection layer 6 is deposited on the SAM. An interlayer 8, an organic light emitting layer 10 and a cathode 12 are then deposited consecutively. The hole injection layer 6, which helps match the hole energy levels of the anode layer 4 and the light emitting layer 10, comprises a conductive transparent polymer. Cathode 12 comprises, for example, a trUlayer of silver, aluminium and sodium fluoride. Contact wires 14 and 16 to the anode and the cathode respectively provide a connection to a power source 18.

The present invention may be further understood by consideration of the following

examples.

Example 1 Preparation of Substrates Treated with Different SAMs and Measurement of Water Contact Angle of the Resulting Treated Substrate (a) 2 inch (5.08 cm) 100 nm copper substrates were prepared by Leybold® blanket sputtering. The resulting substrates having copper anodes deposited thereon were then prepared for the deposition of a selection of molecules from solution for use as a SAM. The process was as follows.

(b) A SAM ink preparation was prepared. To do this, a 1 OmI vial was cleaned out with tetrahydrofuran and blown dry with a nitrogen gun. The desired amount of the SAM material that was being tested was weighed out into the 1 OmI vial in a glove box with an inert nitrogen ambient. A suitable amount of the desired solvent (isopropyl alcohol in the present tests) was added to the same 1 OmI vial in this glove box under the same conditions. The mixture was then vortexed for 1 to 2 minutes before placing onto a heated block for 1 hour or until fully dissolved in solution.

(c) An acetic acid solution bath was also prepared. This involved the filtration of up to 200m1 of 2M acetic acid into a beaker using a 0.45pm PVDF (polyvinylidene fluoride) filter. The beaker was then heated to 60°C. The temperature of the solution was allowed to stabilise for at least 20-SOmins before use.

(d) 2 Inch Panel Pre-Treatment The 2 inch (5.08 cm) substrate prepared in step (a) above was cleaned for 120s using UV-treatment to remove any organic contamination. The substrate was then placed in the 60°C 2M acetic acid beaker prepared in step (c) above for 1 or 3 mm to remove all oxide from the metal surface. The substrate was then extracted and immediately dried with a nitrogen blow gun (no water rinse).

(e) SAM Treatment of 2 Inch Pre-Treated Panel The 2 inch (5.08 cm) pre-treated substrate was immediately transferred to a Karl-Suss spin coater for the SAM treatment. The pre-treated substrate was flooded with the SAM prepared in step (b) above [which had been filtered using a 0.45pm PTFE (poiytetrafIuoroef.hyene) filter] and then this was allowed to stand for 2 minutes. The substrate was then rinsed with 1 OmI of isopropyl alcohol (which had been filtered using a 0.45pm PTFE). For this, the substrate was initially flooded with 2 ml of isopropyl alcohol. The substrate was then spun at 1000 rpm/300rpms/60s, and a further 8m1 of solvent were dispensed during spinning. At the end of this time, the resulting substrate with SAM deposited thereon was subjected to dehydration baking in a nitrogen gun at 70°C for 15 minutes.

A series of experiments was conducted to measure the water contact angle for untreated copper (with or without ozone treatment) and this was compared with the water contact angle when the copper surface had been treated with various compounds as follows.

CBTA 0

HOBTA OH

N HOrYNN r

H

H Benzotriazole-5-carboxylic acid 4-Hydroxy-1 H-benzotriazole (a.k.a. 5-Carboxybenzotriazole) F4TCNQ s.J. #c

S

MBI [JF>__EH 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane 2-Mercaptobenzimidazole HBT --,SF-H MBT x-N H \HSH HO' 4-Mercaptophenol 2-Mercaptobenzothiazole (a.k.a. 4-Hydroxybenzenethiol)

HUT HOSH

11 -Mercapto-1 -undecanol (a.k.a. 11 -Hydroxy-1 -undecanethiol) The results are summarised in the Table 1.

Table 1

Material Water Contact Angle (degree) 120s UV Ozone 31.5 No UV Ozone 31 Benzotriazole (BTA) 65 4-Hydroxybenzotriazole 54 5-Carboxybenzotriazole 30 F4TCNQ 71 MBI 71 MBT 67 HBT 31 HUT 32 It can thus be seen that there is a change in water contact angle depending upon the nature of the compound used to treat the surface of the copper and specifically the hydrophilicity of the substituent on the aromatic group. Alteration of the water contact angle alters the surface energy of the metal. This results in improved binding of the moiety capable of adsorbing to the metal surface with improved hydrophilicity as well as increased wetability. CBTA (30°), HBT (31 °) and HUT (32°) provide acceptable water contact angles when compared with no UV ozone control (31 0). These SAMs have hydrophilic tails. The good wetability on non-SAM-treated copper (the controls here) is due to the fact that they have a copper oxide layer (which is detrimental for electronic performance), whereas non-oxidised copper offers only poor wetability.

Untreated copper wets well but has an oxide layer on it which gives poor device performance. Copper once the oxide has been removed does not show good wetting until the oxide has reformed, hence the need to protect the copper with a SAM that gives a good contact angle to water It is also believed that changing the position of the hydrophilic group will change the surface energy. This will cause a change in the wetability of the compound when attached to a copper patterned substrate, hence providing the possibility of maximising the wetability. Our calculations show that maximisation of the wetability may be achieved by attachment of the hydrophilic group on the SAM molecule so that it is at the maximum distance from the surface of the metal when the moiety of the SAM molecule that adsorbs to the surface is actually adsorbed to the surface of the metal. 5-hydroxybenzotriazole and 5-carboxytriazole are two examples. The idea can be applied to any kind of group that can provide hydrophilicity when attached to any position on the benzene ring if the compound is also capable of adsorbing to the surface of the metal anode to form a SAM.

In a second subsequent experiment, the contact angle with SCA1 26-2 (FEDT) was measured. The results are as shown in Table 2.

Table 2

Material SCA126-2 Contact Angle (degree) l2QsUVOzone 47 No UV Ozone 40 4-Hydroxybenzotriazole 58 5-Carboxybenzotriazole 38 F4TCNQ 29 MBI 78 MBT 67 HBT 35 HUT 32 Once again, CBTA (38°), HBT (35°) and HUT (32°) provide acceptable contact angles when compared with no UV ozone control (40°).

Example 2 Comparison of Work Functions and Stabilities for SAM Treated Substrates (a) The substrates prepared in Example 1 were examined to determine their photoelectron spectrum with an AC-2, i.e. a plot of square root of photoelectron yield (which is proportional to the number of photoelectrons counted) vs incident photon energy (eV). This gives a measure of the work function of the SAM-treated copper relative to that of the native copper. The measurements were taken 1 minute after completion of the SAM treatment. As can be seen from Figure 3, the AC-2 response from F4TCNQ, HOTBA, CBTA, HBT and HUT treated copper substrates indicate higher work functions compared to that of native copper. By contrast, the AC-2 response from MBI and MBT both indicate lower work functions compared to that of native copper.

(b) The same procedure was followed as in (a) above, but this time measurements were taken at a number of times after preparation of the SAM-treated copper to determine stability of the substrates. Specifically, measurements were taken after 1 minutes, 10 minutes and 3 hours. From Figures 4a, 4b, 4c, 4d, 4e, 4f and 4g it can be seen that HOTBA, CBTA, HBT and HUT treated copper substrates show excellent stability throughout the 3 hour period of the test, whereas F4TCNQ, MBI and MBT all show poor stability with their work function moving towards that of native copper over the 3 hour test period. Where the copper surface has been treated with CBTA, for example, there is a shift away from the plot of square root yield v. energy relative to native copper at higher energy (above approximately 5.2 eV). This confirms that there is a clear difference in the surface of the copper as a result of the binding of the CBTA, i.e. confirmation of the stable attachment of the CBTA.

Example 3 Preparation of an OLED Containing a CBTA SAM OLED devices were prepared comprising the following: The substrate is glass obtained from Corning.

The anode is a copper anode of 100 nm thickness deposited on the substrate by a blanket sputtering technique as described in Example 1. The copper was patterned into a metal grid by photopatterning technique.

The substrate prepared was cleaned for 120s using UV-treatment to remove any organic contamination. The substrate was then placed in the 60°C 2M acetic acid beaker prepared for 1 mm to remove all oxide from the metal surface. The substrate was then extracted and immediately dried with a nitrogen blow gun (no water rinse).

The SAM, if present is 5-carboxybenzotriazole (also known as benzotriazole-5-carboxylic acid) and is deposited by spin coating to give a SAM layer as described in Example 1 on the copper anode. In the short SAM' device, the substrate is subjected to a 1 minute SAM treatment, whereas in the long SAM' device, the substrate is subjected to a 3 minute SAM treatment. As a control, a further device was prepared (the IPA rinse' device) in which only ispopropyl alcohol is included in the spinner and no 5-carboxybenzotriazole. This control is included to determine whether any benefit that is seen is solely due to the SAM or whether any benefit is resulting from the solvent rinse (as in the IRA rinse' device the solvent rinse takes place but there are no SAM molecules present).

The hole injection material is PHS1O, a PEDT:PSS commercially available from Heraeus with a PEDT:PSS ratio of 1:2.5. 5% DMSO (by weight) is added to PH51O to increase the conductivity to >300Scm-1 The interlayer material is Copolymer 1 (a compolymer comprising 50% Monomer 1, 42.5% FDA monomer and 7.5% of cross-linker TFBBCB -see above). The electroluminescent layer is a blend, namely a blend of Copolymer 2 and Monomer 2 (see above). The cathode is NaF (2nm)/Al (1 OOnm)/Ag (1 OOnm).

The hole injection layer was deposited from solution by spin coating using a Karl-Suss spin coater (spin speed 1500rpm for 60s in air). This was then dried at 130°C for 15 minutes in air. The resulting hole injection layer was 150 nm thick.

The Copolymer 1 interlayer (see above) was then deposited from a xylene solution using a Karl-Suss spin coateron the hole injection layer that was deposited in the previous step on each test device (spin speed 150rpm for 6s in a glove box; then X-link at 180°C for 60 minutes in N2 glove box to dry the interlayer). The resulting Copolymer 1 interlayer was 22 nm thick.

After each interlayer had been deposited on each test device, the electroluminescent layer which is a blend consisting of Copolymer 2 and Monomer 2 (see above) was then deposited from a xylene solution using a Karl-Suss spin coater on the interlayer that was deposited in the previous step on each test device (spin speed in glove box, 1500rpm for 7 sec. This was then baked at 130°C for 10 minutes in a glove box).

The resulting Copolymer 2:Monomer 2 blend electroluminescent layer was 100 nm thick.

Finally, after the electroluminescent layer had been deposited on each interlayer in each test device, each test device was blanket-deposited by successive thermal evaporation in a vacuum of successive layers of sodium fluoride (2 nm), aluminium (100 nm) and silver (100 nm) to give a trilayer NaF/Al/Ag cathode.

The details of the test devices prepared in accordance with the procedure above are as follows in Table 3:

Table 3

No Split Details HIL SolID IL SolID EL SolID 1 Au Control l5Onm 22 nm SHO21 lOOnm Copolymer2: Monomer 2 blend 2 Cu Control lSOnm 22 nm SHO21 lOOnm Copolymer2: Monomer 2 blend 3 Short SAM lSOnm 22 nm SHO21 lOOnm Copolymer2: treatment Monomer 2 blend 4 Long SAM l5Onm 22 nm SHO21 lOOnm Copolymer2: treatment Monomer 2 blend IRA Rinse (no l5Onm 22 nm SHO21 lOOnm Copolymer2: SAM) Monomer 2 blend Figures 5a and Sb, showing a plot of current density (mA'cm2) v. voltage (V) and a close up of a section thereof for the devices prepared above, showed the following: * The isopropyl alcohol rinse gave identical current density to the control device -the isopropyl alcohol treatment did not impact device performance, thus showing that the isopropyl alcohol rinse is not responsible for the reduction in leakage currents.

* The inclusion of a SAM layer boosted current density for devices comprising a copper anode closer to the current density levels achieved for the gold anode.

* There appeared to be little difference between the short and long SAM treatments The measurements for the best devices (see Figures 7 to 9) demonstrate the following: * It is confirmed that the SAM splits boost current density for the copper anode closer to levels achieved for the control gold anode anode.

* Furthermore, it is confirmed that there appears to be little difference between the short and long SAM treatments.

* The isopropyl alcohol rinse split gives identical current density to the copper control split, thus confirming that the increase in current density seen for copper with the SAM treatments is indeed due to the SAM, not just to the additional processing of the substrate.

Device data for the devices prepared in these experiments at 1000 Cd/rn2 are as shown below in Table 4:

Table 4

Median at 1000 Cd/rn2 Efficiency Split Name Voltage Current Lm/W 1) Au control 5.60 1.8 30.95 2) Cu control 6.10 1.9 26.40 3) Short_SAM 5.62 1.8 31.29 4) Long_SAM 5.74 1.9 29.49 5) IPA_Rinse 6.16 2.0 25.42 The SAM splits boost efficiency for the copper anode closer to levels achieved for gold anode.

There appears to be little difference between the short and long SAM treatments.

The isopropyl alcohol rinse split gives similar efficiency to the copper control split -i.e. the increase in efficiency seen for copper with the SAM treatments is indeed due to the SAM -not just to the additional processing of the substrate.

It can thus be seen from the table above that the performance of the devices according to the present invention comprising 5-carboxytriazole (whether short or long treatment) are significantly better than the copper control device (and the isopropyl alcohol control device). Furthermore, it can be seen that the performance (especially for the short treatment) is quite close to that of the gold control device.

This provides strong evidence that the inclusion of the SAM layer does indeed have the desired dual effect of reduced contact resistance and increased wetability.

Claims (33)

1. Claims 1. An organic electronic device comprising a metal anode and a hole injection layer, wherein said device further comprises a self-assembled monolayer (SAM) between said metal anode and said hole injection layer, said SAM comprising a compound which has a moiety which is capable of adsorbing onto the surface of said metal anode and a hydrophilic moiety.
2. 2. An organic electronic device according to claim 1, wherein the point of attachment of said hydrophilic moiety on said moiety which is capable of adsorbing onto the surface of said metal anode in the compound of the SAM is such that the distance of said hydrophilic group from the surface of the metal anode is maximised when the moiety which is capable of adsorbing onto the surface of said metal anode is adsorbed onto the surface of said metal anode.
3. 3. An organic electronic device according to claim 1 or claim 2, wherein said hydrophilic moiety of the compound of the SAM improves the wetability of the SAM compared to the equivalent compound without said hydrophilic group.
4. 4. An organic electronic device according to any one of claims 1 to 3, wherein the inclusion of said SAM reduces the contact resistance between said metal and said hole injection layer compared to an otherwise identical device in which said SAM is not present.
5. 5. An organic electronic device according to any one of claims 1 to 5, wherein said SAM consists of an aromatic compound which has a hydrophilic substituent.
6. 6. An organic electronic device according to claim 5, wherein said aromatic compound which has a hydrophilic substituent is a benzotriazole derivative or an indazole derivative, preferably a benzotriazole derivative.
7. 7. An organic electronic device according to any one of claims 1 to 6, wherein said hydrophilic substituent is selected from the group consisting of hydroxy, carboxy, carbonyl and thio substituents, preferably hydroxyl or carboxy.
8. 8. An organic electronic device according to any one of claims 5 to 7, wherein said hydrophilic substituent is at the 4-or 5-position on the aromatic ring group, preferably the 5-position.
9. 9. An organic electronic device according to any one of claims 5 to 8, wherein said SAM consists of a benzotriazole derivative selected from the group consisting of 4-hydroxy-1 -benzotriazole, 5-hydroxy-1 -benzotriazole, 4-carboxy-1 -benzotriazole and 5-carboxy-1 -benzotriazole.
10. 10. An organic electronic device according to any one of claims 1 to 4, wherein said SAM consists of a thio compound having a hydrophilic tail, more preferably a thioalkane or thioalkene derivative having from 6 to 24 carbon atoms or a thio aromatic derivative having from 5 to 14 carbon atoms in one or more aromatic rings, wherein said thioalkane, thioalkene and thio aromatic derivatives are substituted by a hydrophilic group selected from the group consisting of hydroxyl, carboxy and carbonyl, and most preferably said thio compound having a hydrophilic tail is 11 -thio- 1 -undecanol or 4-thiophenol.
11. 11. An organic electronic device according to any one of claims 1 to 10, wherein the metal of said metal anode is copper,aluminium, nickel or silver, preferably copper.
12. 12. An organic electronic device according to any one of claims 1 to 11, wherein the metal anode is in the form of a patterned metal tracking.
13. 13. An organic electronic device according to any one of claims 1 to 12, wherein said hole injection layer comprises at least one compound selected from poly(3,4- ethylenedioxythiophene) (PEDT), poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDT:PSS), polyaniline, PEDT:PSS at a ratio of PEDT:PSS of 1:2.5 or polypyrole, preferably PEDT or PEDT:PSS.
14. 14. An organic electronic device according to any one of claims 1 to 13 selected from an organic light emitting diode, an organic light emitting diode lighting device, an organic thin film transistor, an organic photovoltaic device, an organic photosensor and an organic memory array device.
15. 15. A process for the manufacture of an organic electronic device comprising the following steps: (i) depositing a metal anode on a substrate; (ii) depositing a compound which is able to form a SAM on the surface of said metal anode, wherein said compound has a moiety which is capable of adsorbing onto the surface of said metal anode and a hydrophilic moiety; and (iii) depositing a hole injection layer on the SAM.
16. 16. A process according to claim 15, wherein said metal anode is pie-treated with an agent to remove all metal oxide from the surface of said metal anode.
17. 17. A process according to claim 16, wherein said metal anode is pie-treated with anhydrous acetic acid or an aqueous solution of an acid, preferably acetic acid, more preferably a 1 to 5 M aqueous solution of acetic acid and most preferably a 2M aqueous solution of acetic acid, or glacial acetic acid at room temperature.
18. 18. A process according to any one of claims 15 to 17, wherein said hydrophilic moiety of the compound of the SAM improves the wetability of the SAM compared to the equivalent compound without said hydrophilic group.
19. 19. A process according to any one of claims 15 to 18, wherein the inclusion of said SAM reduces the contact resistance between said metal anode and said hole injection layer compared to an otherwise identical device in which said SAM is not present.
20. 20. A process according to any one of claims 15 to 19, wherein said SAM consists of an aromatic compound which has a hydrophilic substituent.
21. 21. A process according to claim 20, wherein said aromatic compound which has a hydrophilic substituent is a benzotriazole derivative or an indazole derivative, preferably a benzotriazole derivative.
22. 22. A process according to any one of claims claim 13 to 20, wherein said hydrophilic substituent is selected from the group consisting of hydroxy, carboxy, carbonyl and thio substituents, preferably hydroxyl or carboxy.
23. 23. A process according to any one of claims 20 to 22, wherein said substituent is at the 4-or 5-position on the aromatic ring group, preferably the 5-position.
24. 24. A process according to any one of claims 15 to 19, wherein said SAM consists of a thio compound having a hydrophilic tail, more preferably a thioalkane or thioalkene derivative having from 6 to 24 carbon atoms or a thio aromatic derivative having from 5 to 14 carbon atoms in one or more aromatic rings, wherein said thioalkane, thioalkene and thio aromatic derivatives are substituted by a hydrophilic group selected from the group consisting of hydroxyl, carboxy and carbonyl, and most preferably said thio compound having a hydrophilic tail is 11-thio-1-undecanol or 4-thiophenol.
25. 25. A process according to any one of claims 15 to 24, wherein the metal of said metal anode is copper or aluminium, preferably copper.
26. 26. A process according to any one of claims 15 to 25, wherein the metal anode is in the form of a patterned metal tracking.
27. 27. A process according to any one of claims 15 to 26, wherein said hole injection layer comprises poly(3,4-ethylenedioxythiophene) (PEDT), poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDT:PSS), polyaniline, or polypyrole, preferably PEDT or PEDT:PSS.
28. 28. A process according to any one of claims 15 to 27 for the manufacture of an organic electronic device selected from an organic light emitting diode, an organic thin film transistor, an organic photovoltaic device, an organic light emitting diode lighting device, an organic photosensor and an organic memory array device, preferably an organic light emitting diode or an organic thin film transistor.
29. 29. A process according to any one of claims 15 to 28, wherein the metal anode is in the form of patterned metal tracking which is deposited on the substrate by means of a process selected from the group consisting of vapour deposition, sputtering, printing and electroless plating, preferably electroless plating.
30. 30. A process according to any one of claims 15 to 29 for the preparation of an organic light emitting diode comprising the following steps: (i) depositing a patterned metal tracking, preferably of copper, on a glass substrate by means of electroless plating, preferably by depositing on the glass substrate a solution of ions of said metal, and depositing on said glass substrate a solution of a reducing agent, such that the metal ions and the reducing agent react together in a reaction solution to form conductive metal regions on said substrate to form said patterned metal tracking; (ii) treating the patterned metal tracking with a 1 to 5 M solution of acetic acid to remove all oxide from the surface of the metal before immediately drying; (iii) depositing from solution a compound which is able to form a SAM on the surface of said patterned metal tracking prepared in step (ii), wherein said compound which is able to form a SAM has a moiety which is capable of adsorbing onto the surface of said patterned metal tracking and further has a hydrophilic moiety, said deposition being performed by means of a process selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; (iv) depositing from solution a hole injection layer on the SAM prepared in step (iii) by means of a process selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; (v) optionally depositing from solution an interlayer on said hole injection layer prepared in step (iv) by means of a process selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; (vi) depositing from solution an organic light emitting layer on said hole injection layer prepared in step (iii) or interlayer prepared in step (v) by means of a process selected from the group consisting of spin coating, dip coating, slot die coating, doctor blade coating and ink-jet printing; and (vii) depositing a cathode on said organic light emitting layer prepared in step (vi), preferably by thermal evaporation of a metal, metal oxide or metal halide, preferably a NaF/Al/Ag cathode, onto said organic light omitting layer.
31. 31. A compound which is able to form a SAM for use in the passivation of a metal anode in an organic electronic device to prevent oxidation of said metal anode, wherein said compound has a hydrophilic group to improve the wetability of the surface of said anode.
32. 32. A compound which is able to form a SAM for use in an organic electronic device comprising a metal anode and a hole injection layer wherein said SAM is between said metal anode and said hole injection layer, wherein inclusion of said SAM reduces the contact resistance between said metal anode and said hole injection layer compared to an otherwise identical device in which said SAM is not present, said compound which is able to form said SAM further comprising a hydrophilic moiety.32. An organic electronic device as described and/or illustrated herein.
33. 33. A process of manufacturing an electronic device as described and/or illustrated herein.