WO2004017441A1

WO2004017441A1 - Organic optoelectronic device encapsulation package

Info

Publication number: WO2004017441A1
Application number: PCT/GB2003/003615
Authority: WO
Inventors: Peter Lodge; Paul Routley; Martin Richardson
Original assignee: Cambridge Display Technology Limited
Priority date: 2002-08-17
Filing date: 2003-08-15
Publication date: 2004-02-26
Also published as: GB2407436B; GB2407436A; AU2003255805A1; GB0219223D0; GB0503033D0

Abstract

The present invention relates to an encapsulated organic optoelectronic device which comprises a substrate, an organic optoelectronic device situated on the substrate, a sealing cap comprising a perimeter seal flange having an upper and a lower surface, the lower surface of the perimeter seal flange being bonded to the substrate and forming a hermetic seal around the optoelectronic device. The lower surface of the perimeter seal flange has a textured surface enabling stronger adhesion between the substrate and the sealing cap and providing greater resistance to the permeation of atmospheric moisture and oxygen.

Description

ORGANIC OPTOELECTRONIC DEVICE ENCAPSU LATION PACKAGE

Background of the invention

Field of the invention

The present invention relates to an encapsulated organic optoelectronic device and a method of preparing an encaps ulated organic optoelectronic device.

Brief description of the prior art

The past decade has seen an increasing amount of research into the use of organic materials in optoelectronic devices, examples of such devices include organic electroluminescent devices, as disclosed in WO90/131-48 and organic photovoltaic devices, as disclosed in US5670791. Both organic electroluminescent devices and organic photovoltaic devices are organic diodes comprising a layer of organic material between two electrodes. Organic electroluminescent devices emit light on the passage of a current between the two electrodes. Organic electroluminescent devices have a wide range of applications in the display industry. Organic photovoltaic devices generate a current between the two electrodes when light is incident upon the device. Organic photovoltaic devices are viewed as a replacement for inorganic silicon solar cells. Advantages associated with the use of organic optoelectronic devices include a greater flexibility in the design of materials and the tailoring of device properties and improved processability.

A significant disadvantage associated with organic optoelectronic devices is that ^"the organic optoelectronic materials used in the devices are sensitive to oxygen and moisture thus exposure to the atmosphere can significantly reduce the operational lifetime of organic optoelectronic evices, for example ca using the formation of black spots on organic electroluminescent displays. In particular, in organic diodes both the organic optoelectronic material used in the device and the low work function mate rial used to form the cathode of the device are sensitive to ambient oxygen and moisture.

A number of approaches have been used to protect the materials of organic optoelectronic devices from the environment. In particular a method involving sealf ng the devices using a metal cap or can which is bonded to the device substrate is widely used. In general a material which acts to absorb any oxygen or moisture in the encapsulated package is also sealed in with the device, an example of this method of encapsulation is disclosed in US5882761 . A number of refinements to this encapsulation technique have been made including the use of different adhesives, disclosed in USG210815, and different absorbers, also known as getters, disclosed in WO01/19142. Although this encapsulation technique has allowed the production of organic optoelectronic devices with operational lifetimes sufficient for commercial applications the method has a number of disadvantages. The adhesive seal between the metal sealing cap and the substrate is often permeable and allows the ingress of oxygen and water vapour into the device . The mechanical strength of the adhesive seal between the sealing cap and the substrate is often not sufficiently strong resulting in the sealing caps becoming detached from the substrate, exposing the organic optoelectronic device to the atmosphere. In some cases the sealing cap becomes completely separated from the substrate.

An alternative method of encapsulating organic optoelectronic devices comprises depositing a layer of passivating materia I over the upper surface of the device, this layer acts to seal the device from the environment, an example of this encapsulation technique is disclosed in WO00/36665. Although this technique does not have the disadvantages associated with the adhesive seal used in the ab ove described process, the materials used to form the barrier layer over the organic optoelectronic device are often not sufficiently impermeable to oxygen and moisture to provide a device with a long operational lifetime. Moreover the barrier materials are generally deposited using expensive vacuum equipment such as by physi cal vapour deposition.

The problem remains to provide an encapsulated organic optoelectronic device which is hermetically sealed from the environment, has sufficient mechanical strength and a long operating lifetime.

Summary of the invention

The present inventors have developed a technique for encapsulating organic optoelectronic devices which overcomes the problems of the prior art and provides an encapsulated organic optoelectronic device and a method fo r encapsulating organic optoelectronic devices. In a first em odiment the present invention provides an encapsulated organic optoelectronic device comprising a substrate, an organic optoelectronic device situated on said substrate, a sealing cap comprising a perimeter seal flange having an upper and a lower surface, said lower surface of said perimeter seal flange bonded to said substrate and forming a hermetic seal around said optoelectronic device, characterised in that said lower surface of said perimeter seal flange has a textured surface.

The present inventors have found that by providing a textured surface at the bonding interface between the sealing cap or can and the substrate the mechanical strength of the bond can be greatly increased thus preventing the cap becoming loose. This method of sealing the device also limits the ingress of atmospheric oxygen and water vapour into the device.

In the present invention the lower surface of the perimeter seal flange is textured. The term textured means that the surface comprises discontin uities or nonplanar interruptions in an ordinarily smooth or planar surface. Such discontinuities or nonplanar interruptions include projections from the plane of the smooth surface and depressions in the plane of the smooth surface.

Preferably the region of the substrate at the bonding interface with the lower surface of the perimeter seal flange is substantially smooth. The term substantially smooth means that the surface is substantially free from discontinuities or nonplanar interruptions in the ordinarily planar surface. However the region of the substrate at the bonding interface with the lower surface of the perimeter seal flange may comprise surface imperfections such as are usually associated with such substrate materials as glass or plastic. More preferably the region of the substrate at the bonding interface with the lower surface of the perimeter seal flange does not comprise discontinuities or nonplanar interruptions of greater trian 5 microns above or below the mean surface of the substrate. The present inventors have found that the use of a substrate which is substantially smooth at the bonding interface with the lower surface of the perimeter seal flange avoids the necessity of providing a patterned substrate surface which is complementary to, and so interlocks with, the textured surface of the perimeter seal flange. This is advantageous in that it avoids both the need for further a step of patterning the lower surface and the need for a step of aligning surface features of the lower surface of the perimeter seal flange with any surface features of the substrate. In the present invention the perimeter seal flange is bonded to the substrate. This bond may be formed by any suitable means such as an adhesive, for example an organic adhesive, a low melting glass frit or a low meltin g metal alloy. Where a suitable substrate and perimeter seal flange are available the bond may be formed directly between the two components, alternatively the bond may be formed by a separate bonding agent such as an adhesive.

The textured surface preferably comprises a plurality of raised features, a plurality of recessed features or both a plurality of raised features and a plurality of recessed features. The raised or recessed features preferably comprise a feature having a regular geometrical shape such as a square, rectangular, triangular, hexagonal, circular or ellipsoid cross-section. Preferably the raised or recessed features have a dimension in the plane of the lower surface of the perim eter seal flange of between 5 and 30 micrometers, more preferably between 10 and 2.5 micrometers. The height of the raised features or the depth of the recessed features is preferably between 5 and 25 micrometers and more preferably between 10 and 20 micrometers above or b»elow the plane of the lower surface of the perimeter seal flange as appropriate. Preferably the raised or recessed features do not comprise a dimension in the plane of the lower surface of the perimeter seal flange of greater than 50 microns.

The textured surface of the perimeter seal flange of the present invention comprises features such as indentations or protrusions below and above the mean plane of the surface of the perimeter seal flange, as opposed to holes passing through the perimeter seal flange. Where the sealing caps of the present invention comprise recessed features these features are not of sufficient depth such that they pass from one side of the sealing cap to the other. The recessed features in embodiments of the present invention comprise indentations in the lower surface of the perimeter seal flange as distinct from holes passing through the lower surface to the upper surface of the perimeter seal flange.

The raised or recessed features of the present invention may have a variety of arrangements on the lower surface of the perimeter seal flange. It is preferred that the raised features or the recessed features are arranged in a series of rows parallel to the edge of the perimeter seal flange. It is considered that a greater number of surface features gives rise to a stronger bond between the lower surface of the perimeter seal flange and the substrate, therefore it is preferred that the lower surface of the perimeter seal flange comprises greater than 50 raised or recessed features, more preferably greater than 75 and most preferably greater ^"than 100.

The lower surface of the perimeter seal flange is preferably bonded to fhe substrate using an adhesive, preferably an organic adhesive, most preferably a UV curing epoxy adhesive.

The organic optoelectronic device of the present invention is a device comprising an organic optoelectronic material. Organic optoelectronic materials are o rganic materials with optical and/or electronic properties, such properties include electroluminescence, photoluminescence, fluorescence, photoconductivity and conductivity. In a preferred embodiment the organic optoelectronic device is an organic diode comprising a high work function electrode, at least one layer of organic optoelectronic material and a low work function electrode. The high work function electrode is preferably selected from the group comprising indium-tin oxide (ITO), tin oxide, aluminum or indium doped zinc oxide, magnesium-indium oxid , cadmium tin- oxide, gold, silver, nickel, palladium and platinum, most preferably the high work function electrode is ITO. The low work function electrode is preferably selected from the group comprising Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Yb, Sm and Al , alloys of such metals, alloys of such metals in combination with other metals, for example the alloys MgAg and LiAI. The low work function electrode preferably comprises multiple layers, for example Ca/AI, Ba/AI or LiAI/AI. The organic diode may further comprise a layer of dielectric material between the low work fun ction and the layer of organic optoelectronic material, in particular it is preferred to use an alkali or al kaline earth metal fluoride as a dielectric layer between the low work function electrode and the layer of organic optoelectronic material. The organic optoelectronic device is preferably an organic diode and most preferably an organic light emitting diode or an organic photovoltaic diode. An organic light e itting diode comprises a t least a layer of organic light emitting material. An organic photovoltaic diode comprises at least a layer of organic photoconductive material. The organic optoelectronic device may be an organic transistor.

In a further embodiment the present invention provides a method for preparing encapsulated optoelectronic devices, the method comprises; providing a sealing cap comprising a perimeter seal flange having an upper and a lower surface, said lower surface being textured, providing a substrate and an optoelectronic device situated on said substrate, providing an adhesive on at least one of said substrate or said lower surface of said perimeter seal flange, contacting said substrate with said lower surface of said perimeter seal flange such that said adhesive for s a hermetic seal between said substrate and said lower surface of said perimeter seal flange.

In a further embodiment the present invention provides a method of preparing an encapsulated organic optoelectronic device comprising; providing a sealing cap comprising a perimeter seal flange having an upper and a lower surface, processing said perimeter seal flange to cause said lower surface to be textu red, providing a substrate and an optoelectronic device situated on said substrate . providing an adhesive on at least one of said substrate or said lower surface of said perimeter seal flange, contacting said substrate with said lower surface of said perimeter seal flange such that said adhesive forms a hermetic seal between sai d substrate and said lower surface of said perimeter seal flange. Preferably said perimeter seal flange is processed using laser surface texturing.

In the above methods preferably the adhesive is situated on said lower surface of the perimeter seal flange. Preferably the method comprises the further step of UV curing said adhesive. Preferably the method is carried out in an inert atmosphere.

Detailed description of the invention

Brief description of the drawings

Figure 1 illustrates an encapsulated organic optoelectronic devic .

Figure 2 shows the lower surface of a cap or can suitable for sealing an organic optoelectronic device.

Figure 3 shows a magnified view of a sealing cap having a perimeter seal flange having a textured lower surface.

Description of preferred embodiments

An encapsulated organic optoelectronic device according to the present invention is shown in Figure 1. The encapsulated device 100 is situated on a substrate 101 , the optoelectronic device 102 lies on the surface of the substrate and is hermetically sealed by the sealing cap 103. The sealing cap comprises a cover 107 which lies over the organic optoelectronic device and a perimeter seal flange 104 which provides an interface between the sealing cap and the substrate 101. An adhesive 105 is provided at the interface between the substrate and the lower surface of the perimeter seal flange, the adhesive acts to bond the sealing cap to the substrate ensuring that the organic optoelectronic is hermetically sealed. The present inventors have found that providing the lower surface of the perimeter seal flange with a textured surface provides a seal of increased mechanical strength and impermeability.

Organic optoelectronic devices which may be encapsulated using the method of the present invention include electroluminescent, photoluminescent, fluorescent and photoconductive organic devices and organic transistors. In particular the encapsulation method of the present invention is useful for the encapsulation of organic diodes such as organic light emitting diodes and organic photovoltaic diodes.

Organic light emitting diodes comprise a layered structure comprising a lower electrode situated on a substrate, a layer, or several layers, of organic light emitting material and an upper electrode. When a voltage is supplied across the electrode c*f the device opposite charge carriers, namely electrons and holes, are injected into the organic light emitting material. The electrons and holes recombine in the layer of organic light emitting material resulting in the emission of light. One of the electrodes, the anode, comprises a high work function material suitable for injecting holes into the layer of organic light emitting material, this material typically has a work function of greater than 4.3 eV and may be selected from the group comprising indium-tin oxide (ITO), tin oxide, aluminum or indium doped zinc oxide, magnesium-indium oxide, cadmium tin-oxide, gold, silver, nickel, palladium and platinum. The anode material is deposited by sputtering or vapour deposition as appropriate.

The other electrode, the cathode, comprises a low work function material suitable for injecting electrons into the layer of organic light emitting material. The low work function material typically has a work function of less than 3.5 eV and may be selected from the group including Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Yb, Sm and Al . The cathode may comprise an alloy of such metals or an alloy of such metals in combination with other metals, for example the alloys MgAg and LiAI. The cathode preferably comprises multiple layers, for example Ca/AI, Ba/AI or LiAI/AI. The device may further comprise a layer of dielectric material between the cathode and the emitting layer, such as is disclosed in WO 97/42665. In particular it is preferred to use an alkali or alkaline earth metal fluoride as a dielectric layer between the cathode and the emitting material. A particularly preferred cathode comprises LiF/Ca/AI, with a layer of LiF of thickness from 1 to 10nm, a layer of Ca of thickness of 1 to 25nm and a layer of Al of thickness 10 to 500nm. Alternatively a cathode comprising BaF₂/Ca/AI may be used. The cathode materials are deposited by vacuum d eposition methods. The low work function material of the cathode is very sensitive to oxygen and water with the highly reactive metals being rapidly oxidised. Oxidation of these metals may cause the light emitting device to cease functioning and often causes the appearance of black spots on the light emitting device. In order to provide light emitting devices with long operational lifetimes it is essential to hermetically seal the device to prevent the sensitive metal cathode being eixposed to oxygen and /vater.

For light emission to occur from the device it is preferred that either the cathode, the anode or both be transparent or semi-transparent. Su itable materials for transparent anodes include ITO and thin layers of metals such as platinum. Suitable materials for transparent cathodes include a thin layer of electron injecting material in proximity to the layer of organic light emitting material and a thicker layer of transparent conductive material overlying the layer of electron injecting material e.g. a cathode structure comprising Ca/Au. Where neither the cathode nor the anode is transparent or semi-transparent light emission occurs through the edge of the device.

Organic light emitting materials include polymeric light emitting materials, su ch as disclosed in Bernius et al Advanced Materials, 2000, 12, 1737, low molecular weight light emitting materials such aluminum trisquinoline, as disclosed in US5294S69, light emitting dendrimers as disclosed in W099/21935 and phosphorescent mate rials as disclosed in WO00/70655. The light emitting material may comprise a blend of a light emitting material and a fluorescent dye or may comprise a layered structure of a light emitting material and a fluorescent dye. Due to their processability soluble light emitting materials are preferred, in particular soluble I ight-emitting polymers. Light emitting polymers include polyfluorene, polybenzothiazole, polytriarylamine, poly phenylenevinylene) and polythiophene. Preferred light emitting polymers include homopolymers and copolyrners of 9,9-di-n-octylfluorene (F8), N,N-bis(phenv1)-4-sec- butylphenylamine (TFB) and benzothiadiazole (BT).

The organic light emitting device may include further organic layers between the anode and cathode to improve charge injection and evice efficiency. In particular a layer of hole-transporting material may be situated over the anode. The hole- transport material serves to increase charge conduction through the device. The preferred hole-transport material used in the art is a conductive organic polymer such as polystyrene sulfonic acid doped polyethylene dioxythiophene (PEDOT:PSS) as disclosed in W098/O5187, although other hole transporting materials such as doped polyaniline or TPD (N,N'-diphenyl-N,N'-bis(3-rnethylphenyl)[1 ,1'-biphenyl]-4,4'- diamine) may also be used. A layer of electron transporting or hole bl ocking material may be positioned between the layer of light emitting material and the cathode if required to improve device efficiency.

Organic photovoltaic diodes have a similar structure to organic light emitting diodes comprising a layer of organic photoconductive material between an anode and a cathode. Organic heterojunction photovoltaic devices are a particular class of organic photovoltaic devices and operate in the manner described as follows. The electrodes of different work function set up an internal electric field across the device. The organic layer comprises a mixture of a material having a higher electron affinity and a material having a lower electron affinity. Absorption of light by the materials of the organic layer generates bound electron-hole pairs, termed excitons. E≡xcitons generated on the material of lower electron affinity dissociate by transfer of an electron to the material of higher electron affinity, the material of lowe r electron affinity is sometimes referred to as the electron donor or simply donor. Excitons generated on the material of higher electron affinity dissociate by transfer of a hole to the material of lower electron affinity, the material of higher electron affinity is sometimes referred to as the electron acceptor or simply acceptor. The electrons and holes generated by dissociation of the excitons then move through the device, with electrons moving to the lower work function cathode and holes movin g to the higher work function anode. In this way light incident on the device generates a current which may be used in an external circuit.

Suitable anode and cathode materials for an organic photovoltaic device are those described above. O rganic heterojunction photovoltaic diodes are currently one of the most efficient types of organic photovoltaic devices. Organic heteroju notion photovoltaic devices comprising an organic electron donor and an organic electron acceptor are disclosed in US5331183. A variety of structures of the o rganic photovoltaic devices are possible. The electron donor and electron acceptor may comprise polymers or low molecular weight compounds. The electron donor and acceptor may be present as two separate layers, as disclosed in W099/49525, or as a blend or so called bulk heterojunction, as disclosed in US5670791. The electron donor and acceptor may be selected from perylene derivatives such as N, N'- diphenylglyoxaline-3, 4, 9, 10-perylene tetracarboxylic acid diacidamide, fullerenes (C₆₀), fullerene derivatives and fullerene containing polymers and semiconducting organic polymers such as polyfluorenes, polybenzothiaztoles, polytriarylamines, poly(phenylenevinylenes), polyp henylenes, polythiophenes, polypyrroles, polyacetylenes, polyisonaphthalenes and polyquinolines . Preferred polymers incl ude MEH-PPV (poly(2-methoxy, 5-(2.'-ethyl)hexyloxy-p-phen-ylenevinylene)), MEH-CM- PPV (poly (2,5-bis (nitrilemethyl)-l- methoxy-4- (2'-ethyl-hexyloxy) benzene-co-2,5- dialdehyde-l-methoxy4- (2'-ethyI hexyloxy) benzene)) and CN-PPV cyano substituted PPV, polyalkylthiophenes, such as poly(3-hexylthiophene), POPT poly(3 (4- octylphenyI)thiophene) and poly(3-dodecylthiophene), polyfluorenes, such as poly(2,7-(9,9-di-n-octylfluorene), poly(2,7-(9,9-di-n-octylfluorene)-benzothiadiazole) and poly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)). Typical device structures include a blend of N, IM'-diphenylglyoxaline-3, 4, 9, 10-perylene tetracarboxylic acid diacidamide and poly(3-dodecylthiophene), a layered structure comprising a layer of MEH-PPV and a layer of C₆₀, a blend of MEH-PPV and C₆o₃ a layered structure comprising a layer of MEH-CN-PPV and a layer of POPT, a ble d comprising MEH-PPV and CN-PPV and a blend comprising poly(3-hexylthiophene) and poly(2,7-(9,9-di-n-octylfluorene)-(4,7-di-2-thienyl-(benzothiazole)). Organic photovoltaic devices may comprise auxiliary organic layers between the electrodes for improving charge collection and transport.

In the operation of both organic light emitting devices and organic photovoltaic devices excited states are generated in the organic optoelectronic materials. These excited states are generated on charge recombination rior to emission of light in light emitting devices and on the absorbtion of a photon of incident light in photovoltaic devices. These excited states are highly reactive and will react with any oxygen or water present in the device, this reaction is irreversible so that continued operation of these devices in the presence of oxygen and water leads to degradation of the devices. For this reason it is necessary to hermetically seal the organic optoelectronic device against th e ingress of oxygen and water.

The substrate of the organic optoelectronic device shou Id provide mechanical stability to the device and act as a barrier to seal the dev ice from the environment. Where it is desired that light enter or leave the device t rough the substrate, the substrate should be transparent or semi-transparent. Gl ass is widely used as a substrate due to its excellent barrier properties and transparency. Other suitable substrates include ceramics, as disclosed in WO02/23579 and plastics such as acrylic resins, polycarbonate resins, polyester resins, polyethylene terephthalate resins and cyclic olefin resins. Plastic substrates may require a barrier coating to ensure that they remain impermeable. The substrate may comprise a composite material such as the glass and plastic composite disclosed in EP0949850.

Organic optoelectronic devices may be prepared by any suitable method known to those skilled in the art. Typically the substrate will comprise a glass sheet, a layer of anode material, such as ITO, may be deposited by sputtering. The ITO or other anode material may, if required, be patterned using either additive methods during deposition, such as printing, or using subtractive methods following deposition, such as photolithography. The organic layers of the device may be deposited by vapour deposition, this is a particularly suitable method for the deposition of low molecular weight organic optoelectronic materials. Where the organic optoelectronic materials are soluble they may be advantageously deposited by solution processing techniques. Solution processing techniques include selective methods of deposition such as screen printing and ink-jet printing and non-selective methods such as spin coating and doctor blade coating. Organic semiconductive polymers are particularly suited to deposition using ink-jet printing, as disclosed for example in EP0880303.

To provide effective encapsulation of the device it is preferred that a seal is formed directly between the material of the sealing cap and the material of the substrate. Where the organic optoelectronic materials are deposited by selective deposition techniques the materials are generally not deposited over the substrate in the area which will eventually form the seal to the sealing cap. Where materials are deposited on the substrate by non-selective deposition techniques it is preferred to remove the deposited materials from the area of the substrate which will eventually form the seal to the sealing cap. The deposited organic material may be removed mechanically, for example by scraping but it is preferred to remove deposited organi c material by laser ablation.

The cathode and any additional dielectric layers may be deposited using vapour deposition. Auxiliary layers and features may be included in the organic optoelectronic devi ce as appropriate to i prove charge injection or to facilitate patterning of the device. In order to provide an electrical input to the organic optoelectron ic device, or an electrical output from the organic optoelectronic device electrical connectors are provided which electrically contact the device and which may be contacted to an external circuit. In the case of organic optoelectronic diodes contacts are made to both anode and cathode. One of the contacts may be formed by patterning the lower electrode which is situated on the substrate such that a lead out is formed which passes under the eventual sealing region of the device. The contact to the upper electrode may be formed by depositing a lead out from the upper electrode to the outside of the device either during the deposition of the upper el ectrode or in a separate deposition step.

Following the above described preparation of the organic optoelectronic diode 102 the device will typically comprise an anode 102a, a moisture and air sensitive organic layer 102b and a moisture and air sensitive cathode 102c. To protect the sensitive layers of the device from the atmosphere the device is hermetically sealed using a sealing cap 103 which is bonded to the surface of the substrate using an adhesive 105. The sealing cap typically comprises a cover part 107 which lies over the organic optoelectronic device and a perimeter seal flange 104. Figure 2 shows a view from above of a sealing cap 200, the cover part 202 is of sufficient size to lie over the organic optoelectronic device, the perimeter seal flange 201 lies around the edge of the cover part and is of a sufficient width to provide a surface area for forming a seal between the sealing cap and the substrate. The sealing cap may be formed of glass, ceramic, plastic, metal or metal alloy. Metal is preferred due to its impermeability and the ease of manufacture and processing of shaped metal sealing caps. Suitable metals include aluminum, steel, brass and stainless steel. The sealing cap is attached to the substrate using an adhesive, the adhesive may be selected from radiation curable resins such as acrylics, acrylic urethanes, epoxies, thermal curing resins such as epoxy resins may also be used. A low melting glass frit or metal alloy may be used to seal the device as an alternative to organic adhesives. Ultraviolet curable epoxy resins are preferred. The encapsulated device will generally also include a material for absorbing oxygen and moisture, this material, known as a getter, may be bonded to the underside of the sealing cap.

As previously discussed the prior art devices encapsulated in this manner suffer from the significant disadvantage that the seal provided by the adhesive bond is inadequate and allows the ingress of oxiygen and moisture into the device. Additionally the seal provided by the ad esive is often mechanically weak, allowing the sealing cap to become detached from the substrate.

The inventors of the present invention have found that by providi rig the sealing cap with a textured surface on the lower surface of the perimeter se l flange encapsulated organic optoelectronic devices with significantly greater resistance to the ingress of oxygen and moisture and with greater mechanical strength can be prepared.

The sealing cap of the present invention typically comprises a sheet of aluminum or stainless steel which has be formed into a structure having a recessed portion 202 of sufficient size to accommodate the organic optoelectronic device and any getter material but which does not contact the organic optoelectronic device. The structure has a flange 201 running around the perimeter of the recessed portion. Such sealing caps may be stamped from metal sheets. The perimeter seal flange will typically have a width of between 1 and 25mm, preferably between 2 and 5mm. The material used to form the sealing cap may have a thickness of between 0> .1 and 1mm, preferably approximately 0.2mm. The height of the recessed portion of the sealing cap above the perimeter seal flange should be sufficient to allow adequate space for the organic optoelectronic device and if necessary the getter material and may be of between 0.5 to 2mm, preferably of between 1 and 1.5mm.

The sealing caps of the present invention have a textured surface on the lower surface of the perimeter seal flange. In a preferred method the textured surface may be formed while the sealing cap is itself being formed, for example where the sealing cap is formed by mechanical stamping the die used to press the cap may be patterned with raised portions. Alternatively the sealing cap may be provided with a textured surface after it has been formed. In this case the textured surface may be provided manually, for example by abrading the lower surface of the perimeter seal flange with an abrasive material, but it is preferred that the textured surface is formed using a technique such as laser texturing or e-beam texturing. Laser texturing involves using a pulsed laser, such as an Nd-YAG UV laser, to drill holes into the sealing cap.

The texturing on the lower surface of the perimeter seal flange may comprise raised portions, which extend above the plane of the lower surface of the perimeter seal flange, recessed portions, which are recessed below the plane of the lower surface of the perimeter seal flange or a combination of both raised and recessed features. The features which form the texture may have a range of cross-sections in the plane of the lower surface of the perimeter seal flange such as such square, rectangular, triangular, hexagonal, circular or ellipsoid cross-sections. Recessed features are preferred as these are considered to give improved keying resulting in better adhesion.

Figure 3 shows a portion of the lower surface of a s ealing cap 300 having a perimeter seal flange textured with a series of recessed features 301, the recessed features have a square cross-section in the plane of the lower surface of the perimeter seal flange. The recessed features may have dimensions in the plane of the lower surface of the perimeter seal flange of 1 to 500 microns, preferably 100 to 250 microns. Where the features are formed by a mechanical stamping process they preferably have dimensions in the plane of the lower surface of the perimeter seal flange of 1 to 5O0 microns, preferably 100 to 250 microns. Where the recessed features are formed by laser texturing they preferably have a smaller size having a dimension in the plane of the lower surface of the perimeter seal flange of 1 to 25 microns, preferably 5 to 10 m icrons. The depth of the recessed features may toe of between 5 and 25 m icrons and preferably is of between 10 and 20 microns. In figure 3 the recessed features are arranged in a series of parallel rows following the edge of the perimeter seal flange with the recessed features being evenly distributed across the area of the lower surface of the perimeter seal flange. Other arrangements of the features wh ich form the texture are possible, for example where the features are offset to each rather than forming parallel rows or where the features are offset and form a hexagonal pattern.

Following the forming and if necessary the separate patterning of the sealin g caps they are cleaned. The sealing caps are washed in an organic solvent such as trichloroethylene or tetrahydrofuran, vacuum baked for several tens of hours and exposed to an ultraviolet light source. The sealing caps are then transferred to a glove box having an inert atmosphere such as an N₂ atmosphere. It is necessary to carry out the encapsulation of the organic optoele ctronic diodes in an inert atmosphere as the sensitive cathode of the organ ic optoelectronic diode is deposited by vapour deposition in a vacuum chamber and d evices with a freshly deposited air sensitive cathode are generally placed in a glove box to avoid any exposure to the atmosphere. In the glove box a suitable getter may be bonded on the inside surface of the sealing cap. The getter may comprise a desiccant in the form of a powder in a porous package, a pressed pellet or a powder within a polymer film. Suitable materials for the getter include materials which absorb moisture whilst retaining a solid state, for example phosphorus pentoxide, zeolites, silica, alkali and alkaline earth metal sulfates and perchlorates. The getter is bonded to the inside surface of the sealing cap using a suitable adhesive such as a radiation curable epoxy resin.

After attachment of the getter, adhesive is applied to the perimeter seal flange of the sealing cap. Adhesive may be applied to the substrate in addition to or in preference to the adhesive applied to the sealing cap . The adhesive may be dispensed manually, using a dispensing robot or by a printing technique such as screen printing. The adhesive is preferably a UV curable epoxy resin such as DELO 4673 available from Supratec, although other adhesives discussed above may also be used. The adhesive is generally deposited on all fou r sides of the perimeter seal flange of the sealing cap in the form of a continuous bead having a width of, for example, 1 to 5mm. Following the coating of the adhesive onto the perimeter seal flange the sealing cap is first aligned with and then contacted with the substrate. The alignment of the sealing cap and the substrate may be carried out using an automated system comprising a robotic arm and a camera or, where appropriate, the sealing cap and substrate may be manually aligned. Pressure may be applied to the sealing cap, substrate or both during the curing of the adhesive. Where the adhesive is a UV curable resin pressure may be applied simultaneously with exposure of the device to UV light. It may be necessary to protect the organic optoelectronic material of the device from exposure to UV light during the curing process, this may be achieved, by providing a cover over the organic optoelectronic material, in some cases the organic optoelectronic material may be shielded by further features of the optoelectronic device itself.

To cure the UV adhesive the devices are exposed to a UV source for between 30 and 120 seconds, preferably for between 60 and 90 seconds. The UV source may have a power of between 30 and 100 mW/cm², preferably between 40 and 60 mW/cm². Following UV exposure the devices are allowed to cure for a further 24 hours. The encapsulated devices may then be cleaned, connected to appropriate driving electronics and packaged. Examples

A stainless steel sealing cap having a length of 40nnm, a width of 30mm and s perimeter seal flange of width 5mm is prepared by mechanical stamping. The stamp is patterned to provide the perimeter seal flange of the sealing cap with a text-ured surface comprising five rows of indentations having a square cross-section in the plane of the perimeter seal flange and having a length of 200 microns and a depth of 10 microns (Figure 3 shows a similarly patterned sealing cap). The sealing caps are washed in trichloroethylene, vacuum baked at 250° C for 100 hours, passed u nder an ultraviolet light and placed inside a glove box having a nitrogen atmosphere.

A glass substrate having a length of 45mm and a width of 35mm with a layer of unpatterned ITO (available from Applied Films) is cleaned by ultrasonification in deionised water/detergent, dried and exposed to ultraviolet light. A layer of PEDOT:PSS comprising a 0.5% aqueous solution ^available from Bayer as B*aytron) is t en spin-coated onto the substrate forming a layer of thickness 50mm over the ITO . A layer of a yellow light-emitting polyphenylene vinylene (available from Covion) is then spin-coated onto the PEDOTPSS layer from a 1.5% solution in xylene solvent, forming a layer of light emitting material of thickness 100nm over the layer of PEDOTPSS. The layers of PEDOTPSS and light emitting polymer are then removed from an area having a width of 10mm around the edge of the glass substrate using laser ablation (suitable apparatus is available from Excitech)_ The device is then transferred to a vacuum chamber where a cathode comprising a lower layer of 5nm Ba and an upper layer of 1000nm Al is vapour deposited over the active area of the device (suitable vacuum deposition equipment is available from Tokki Corporation). The device is then transferred to the above mentioned glove box avoiding exposure to the atmosphere.

A g etter (available from SAvES Getters) is attached to the inside of the sealing cap and a robot is used to apply a 5mm bead of UV curing epoxy resin (DELO 4Θ73 available from Supratec) over the perimeter seal flange of the sealing cap. A robot and camera system is used to align the sealing cap to the substrate, the sea ling cap and substrate are brought into contact and the device is exposed to UV light of power 45rnW/cm² for 90 seconds . Following exposure to UV the adhesive is allowe d to cure for a further 24 hours. Comparisons to control devices in which the perimeter seal flange of the sealing cap does not comprise a textured surface were carried out. Shear strength tests indicate that the sealing cap of the devices of the present invention is more firmly bound to the substrate. Accelerated lifetime tests indicate that the sealing caps of the present invention have a lower propensity be become detached from the substrate at elevated temperature and humidity than sealings caps in which the perimeter seal flange does not have a textured surface. Accelerated lifetime tests were carried out at 85°C and 80% humidity with the easured lifetime being the time taken for the luminance of the device to fall to half of its initial value at a constant current.

A sealing cap having a perimeter seal flange with a textured surface was also prepared using a laser texturing technique. A stainless steel sealing cap having a length of 40mm, a width of 30mm and a perimeter seal flange of width 5mm was prepared by mechanical stamping. The perimeter seal flange was patterned by exposure to a Nd-YAG tripled UV pulsed laser, the pattern comprised circular holes of 10 microns diameter and 10 microns depth, three rows of holes of 300 micron spacing were produced parallel to the edge of the perimeter seal flange. An organic light emitting device was prepared according to the protocol above and encapsulated using the laser textured sealing cap and a UV curing epoxy ad hesive as described above. Shear strength tests showed the laser textured sealing cap to provide a stronger seal than the untextured prior art sealing cap. Accelerated lifetime tests showed that the laser textured sealing caps had less propensity to become detached from the substrate than prior art untextured sealing caps.

Claims

1. An encapsulated organic optoelectronic device comprising:

a substrate,

an organic optoelectronic device situated on said substrate,

a sealing cap comprising a perimeter seal flange having an upper and a lower surface,

said lower surface of said perimeter seal flange bonded to said substrate and forming a hermetic seal around said optoelectronic device,

characterised in that said lower surface of said perimeter seal flange h as a textured surface.

2. An encapsulated organic optoelectronic device according to claim 1 wherein said textured surface comprises a plurality of raised features.

3. An encapsulated organic optoelectronic device according to claim 1 wherein said textured surface comprises a plurality of recessed features.

4. An encapsulated organic optoelectronic device according to claim 1 wherein said textured surface comprises a plurality of raised features and a plurality of recessed features.

5. An encapsulated organic optoelectronic device according to any of claims 2 to 4 wherein said raised features or said recessed features have a dimension in the plane of said lower surface of said perimeter seal flange of between 5 and 30 microns, preferably between 10 and 25 microns.

6. An encapsulated organic optoelectronic device according to claim 2 or claim 4 wherein said raised features have a height above the plane of said lower surface of said perimeter seal flange of between 5 and 25 microns, preferably between 10 and 20 microns.

7. An encapsulated organic optoelectronic device according to claim 3 or claim 4 wherein said recessed features have a depth below the plane of said lower surfa ce of said perimeter seal flange of between 5 and 25 microns preferably between 10 a nd 20 microns.

8. An encapsulated organic optoelectronic device according to any of claims 2 to 4 wherei n said raised features or said recessed features are arranged in a series of rows parallel to the edge of said perimeter seal flange.

9. An encapsulated organic optoelectronic device according to claim 1 further comprising an adhesive bonding said lower surface of said perimeter seal flange to said substrate.

10. An encapsulated organic optoelectronic device according to claim 9 wherein said adhesive comprises a UV curing epoxy adhesive.

11. A method of preparing an encapsulated organic optoelectronic device comprising;

providing a sealing cap comprising a perimeter seal flange having an upper and a lower surface, said lower surface being textured,

providing a substrate and an optoelectronic device situated on said substrate,

providing an adhesive on at least one of said substrate or said lower surface of said perimeter seal flange,

contacting said substrate with said lower surface of said perimeter seal flange such that said adhesive forms a her etic seal between said substrate and said lower surface of said perimeter seal flange.

12. A method of preparing an encapsulated organic optoelectronic device comprising;

providing a sealing cap comprising a perimeter seal fla nge having an upper and a lower surface, processing said perimeter seal flange to cause said lower surface to be textured,

providing a substrate and an optoelectron ϊc device situated on said substrate,

contacting said substrate with said lower surface of said perimeter seal flange such that said adhesive forms a hermetic seal between said substrate and said lower surface of said perimeter seal flange.

13. A method according to claim 12 wherein said perimeter seal flange is processed using laser surface texturing.

14. A method according to claim 11 orcla im 12 wherein said adh esive is provided on said lower surface of said perimeter seal lange.

15. A method according to claim 1 1 or 12 further comprising the step of UV curing said adhesive.

16. A method according to claim 11 or cla im 12 wherein said method is carried out in an inert atmosphere.