WO2008154938A1

WO2008154938A1 - Organic electroluminescent device

Info

Publication number: WO2008154938A1
Application number: PCT/EP2007/005366
Authority: WO
Inventors: Marco Colombo; Antonio Zaopo; Claudia Riccardi; Stefano Zanini
Original assignee: Pirelli and C SpA; Telecom Italia SpA
Current assignee: Pirelli and C SpA; TIM SpA
Priority date: 2007-06-19
Filing date: 2007-06-19
Publication date: 2008-12-24
Anticipated expiration: 2009-12-19

Abstract

Organic EL device comprising an EL unit and, on at least one side of said EL unit, a flexible substrate having coated thereon: (i) at least one lower layer comprising at least one inorganic material; (ii) at least one layer comprising a composition including (a) at least one organic polymer and (b) at least one layered material; (iii) at least one upper layer comprising at least one inorganic material; said at least one layer (ii) being interposed between said at least one lower layer and said at least one upper layer. The organic EL device of the present invention is able to reduce the permeation to moisture and oxygen, thus improving the life-time of the EL device, still maintaining a good transparency.

Description

ORGANIC ELECTROLUMINESCENT DEVICE

Field of the invention

The present invention relates to an organic electroluminescent (EL) device that resists to external moisture and oxygen permeation and to a method for producing a composition comprising at least one organic polymer and at least one nanosized layered material to be inserted in said organic EL device.

Background of the invention Many different types of products in the electronic field are sensitive to gases and liquids, which can cause deterioration of the product over a period of time. In particular, they may be adversely affected by moisture that degrades insulation and initiates corrosion.

Devices utilizing organic light-emitting materials are potential candidates for a great variety of displays, such as, for example, digital watches, telephones, laptop computers, pagers, cellular telephones, calculators, and the like. Organic light- emitting devices are relatively inexpensive to fabricate and potentially can be manufactured on flexible polymer substrates, which are lightweight and impact resistant. Polymers, however, are susceptible to the permeation of oxygen and moisture in the environment and, thus, the use of organic light-emitting devices fabricated on polymer substrates is currently limited by their poor environmental stability. Stability problems typically arise in the organic layers and the low work function electrode layer. If an organic light-emitting device is to be formed on a polymer substrate, it is necessary to reduce or eliminate the diffusion of oxygen and moisture through the substrate in order to avoid the degradation of the organic light-emitting device and/or other components of the device subject to adverse reactions with oxygen or water.

Although a organic light-emitting device electrode (typically indium tin oxide) typically located adjacent to the polymer substrate serves as a partial environmental barrier, its resistance to gas and liquid permeation is insufficient to protect sensitive layers of the organic light-emitting device.

Accordingly, some forms of further protection should be applied to the polymer to achieve the required resistance to water and oxygen.

Barrier coatings have been traditionally applied to polymer substrates to reduce their gas and liquid permeability. Such coatings typically consist of a single thin layer of inorganic material, such as aluminum oxide or silicone oxide, deposited on polymer substrates. However, such coatings provide insufficient protection due to, for example, unavoidable defects in the oxide layer, and particularly due to local adhesion failures between the substrate and the oxide layer during temperature cycling caused by differences in thermal coefficients of expansion.

United States Patent US 6,146,225 discloses a method for preventing water or oxygen from a source thereof reaching a device, said method comprising the steps of: depositing a first polymer layer between said device and said source; depositing an inorganic layer on said first polymer layer of said device by enhanced chemical vapour deposition; and depositing a second polymer layer on said inorganic layer.

United States Patent US 6,268,695 discloses an environmental barrier for an organic light-emitting device, said environmental barrier having of a foundation and a cover. Both the foundation and the cover having a top of three vacuum- deposited layers of (a) a first polymer layer, (b) a ceramic layer, and (c) a second polymer layer.

International Patent Application No. WO 03/094256 discloses a multi-layer barrier coating on a flexible substrate exhibiting improved resistance to gas and liquid permeation. The multi-layer barrier coating generally comprises alternating polymer and inorganic layers, and the layer immediately adjacent to the flexible substrate and the topmost isolation layer may both be inorganic layers. The surface of each deposited inorganic layers may be plasma-treated prior to the deposition of the polymer layer thereon, while the surfaces of the polymer layers are generally not plasma-treated.

The Applicant has observed that, while the resistance to liquid and gas permeation of substrates having barrier coatings known in the art is considerable, the resulting environmentally sensitive devices are still sufficiently permeable to limit their lifetime, particularly in applications requiring prolonged periods of operation and/or exposure to hot and humid environments. Thus, there is still a need for an improved flexible lightweight environmental barrier coating.

Organic EL device employing organic luminescent material/clay nanocomposite are known in the art.

For example, United States Patent US 6,593,688 discloses an electroluminescent device comprising a transparent substrate, a semitransparent electrode deposited on the transparent substrate, a clay nanocomposite emissive layer spin-coated with an organic EL material/clay nanocomposite, positioned on the semitransparent electrode, and a metal electrode deposited on the clay nanocomposite emissive layer. Said organic EL material/clay nanocomposite is prepared by blending an organic EL material and a nanoclay. As the content of the nanoclay is increased, the gas penetration is said to be reduced, thus obtaining an improved luminescent efficiency. The abovementioned EL material/clay nanocomposite is said to have an improved luminescent efficiency and stability.

United States Patent Application US 2005/170210 discloses an organic EL device, comprising an organic EL unit sealed by an encapsulation layer comprising a layered inorganic substance/polymer/curing agent nanocomposite. Said organic EL device may have a flat glass substrate. The abovementioned EL device is said to resists to external moisture and oxygen permeation.

Summary of the invention

However, the Applicant has noticed that the abovementioned EL devices may show some drawbacks.

For example, the Applicant has noticed that the extremely high content of nanoclays usually used does not allow to obtain a sufficient transparent encapsulating layer as required in EL field, in particular in case the light-emitting material is used in displays. Furthermore, the rigid glass substrate used does not allow to obtain a flexible device. Moreover, the encapsulation layer above disclosed require a heat-curing step which can be harmful for the organic EL unit.

The Applicant has faced the problem of providing flexible organic EL devices having a low permeation to moisture and oxygen for preventing degradation, still maintaining a good transparency.

Moreover, the Applicant has faced the problem of providing a flexible display which may be advantageously useful in mobile communication devices, said display being large enough to provide data services, such as mobile TV and, in general, information (e.g., alphanumeric characters and icons) to the final users with an acceptable viewing experience, albeit without increasing the dimensions and the weight of said mobile communication devices. For instance, flexible materials could allow large displays to be "rolled" into small devices

The Applicant has now found that an organic EL device, having at least a sandwich-layered structure onto a flexible substrate layer, wherein said structure comprises at least one layer including a composition comprising at least one organic polymer and at least one nanosized layered material, said at least one layer being positioned between at least two layers of inorganic materials, is able to reduce the permeation to moisture and oxygen, thus improving the life-time of the EL device, still maintaining a good transparency.

The Applicant has also found that said EL device may be advantageously used in as flexible displays in mobile communication devices.

In a first aspect, the present invention relates to an organic EL device comprising an EL unit and, on at least one side of said EL unit, a flexible substrate having coated thereon: (i) at least one lower layer comprising at least one inorganic material;

(ii) at least one layer comprising a composition including (a) at least one organic polymer and (b) at least one nanosized layered material;

(iii) at least one upper layer comprising at least one inorganic material; said at least one layer (ii) being interposed between said at least one lower layer (i) and said at least one upper layer (iii). In a second aspect, the present invention relates to a mobile communication device including a flexible display comprising an organic EL device comprising an EL unit and, on at least one side of said EL unit, a flexible substrate having coated thereon: (i) at least one lower layer comprising at least one inorganic material;

(ii) at least one layer comprising a composition including (a) at least one organic polymer and (b) at least one nanosized layered material; (iii) at least one upper layer comprising at least one inorganic material; said at least one layer (ii) being interposed between said at least one lower layer^' (i) and said at least one upper layer (iii).

For the aim of the present invention and of the claims which follows, the term "mobile communication device" is referred to mobile terminals, pagers, integrated mobile phones, personal digital assistants. Preferably, said mobile communication device is a mobile terminal for mobile communication systems, such as GSM or UMTS.

The present invention, in at least one of the abovementioned aspects, may show one or more of the preferred characteristics hereinafter described.

Preferably, said EL unit comprises at least one layer including at least one organic EL material and at least one conducting layer; more preferably said EL unit comprises at least one layer including at least one organic EL material interposed between two conducting layers.

Said at least one layer including at least one organic EL material typically comprises at least one organic luminescent materials which may be selected, for example, from: emissive conjugated polymers, emissive non-conjugated polymers, copolymers of conjugated and nonconjugated segments, blends of the emissive polymer with emissive or non-emissive polymers, emissive small organic molecules such as monomers or oligomers, blends of the small organic molecules with emissive or non-emissive polymers, or blends of emissive small organic molecules and non-emissive small organic molecules, or mixtures thereof.

Suitable choices for the emissive conjugated polymers include, but not limited to: poly(p-phenylene vinylene) or its derivatives such as MEH-PPV (poly[2-methoxy- 5-(2'-ethylhexyloxy)-p-phenylene vinylene]), poly(pyridyl vinylene phenylene vinylene) (PPyVPV), poly[1 ,4-(2,5-bis(1 ,4,7, 10-tetraoxaundecyl))phenylene vinylene]; polythiophene or its derivatives such as poly[3-hexylthiophene-co-3- cyclohexylthiophene] or poly[3-(4-methoxypheyl)thiophene-2,5-diyl]; poly(p- phenylene) or its derivatives such as dimethoxy-poly(p-phenylene), ladder poly(dihydrophenanthrene), or ladder poly(1 ,4-phenylene-2,5-thiophene); polyfluorene or its derivatives such as poly(9,9-dioctylfluorene), poly(2,7-bis(p- styryl)-9,9'-di-n-hexylfluorene sebacate); poly(arylene vinylene), where the arylene may be such moieties as naphthalene, anthracene, furylene, thienylene, oxadizole, or one of said moieties with functionalized substituents at various positions; derivatives of poly(arylene vinylene), where the arylene may be as in above, substituted at various positions on the arylene moieties; polyarylene or their derivatives substituted at various positions on the arylene moiety; polypyrrole or its derivatives; polyquinoline or its derivatives; polyacetylene o its derivatives; polyaniline or its derivatives; or mixtures thereof.

The emissive non-conjugated polymers have non-conjugated main chains and side chains substituted with emissive functional groups such as anthracene.

Organic luminescent monomers or oligomers include metal chelate complexes of ligand structure such as luminescent alumina quinone (Alq3), and rubrene, anthracene, perylene, coumarin 6, Nile red, aromatic diamine, TPD (N₁N¹- diphenyl-n,n^l-bis-(3-methylphenyl)-1 ,1'-biphenyl-4,4'-diamine), TAZ (3-(4- biphenyl)-4-phenyl-(4-tert-butylphenyl)1 ,2,4-triazole), or DCM (dicyanomethylene)- 2-methyl-6-(p-dimethylaminostyryl)-4H-pyran), or mixtures thereof.

Non-emissive polymers, such as poly(m-methylacrylic acid), polystyrene, or poly(9-vinylcarbazole) may be used as a matrix for blends with emissive compounds; besides, blends of organic luminescent monomers or oligomers with the above emissive conjugated polymers or emissive non-conjugated polymers may be also employed.

Further details about the above reported organic luminescent materials may be found, for example, in United States Patent US. 6,593,688 above cited. Said at least one conducting layer comprises, for example, metal oxides such as lead oxide, ITO (indium tin oxide), doped conducting polymers such as doped polyaniline, doped polypyrrole, PEDOT (polyethylene dioxyhiophene), doped polythiophene, or mixtures thereof. Preferably, said at least one conducting layer comprises indium tin oxide.

The organic EL device of the present invention comprises a flexible substrate on at least one side of said EL unit; preferably, said organic EL device of the present invention comprises a flexible substrate on both sides of said EL unit. More preferably, in the latter case, (i) at least one lower layer comprising at least one inorganic material, (ii) at least one layer comprising a composition including (a) at least one organic polymer and (b) at least one nanosized layered material, and (iii) at least one upper layer comprising at least one inorganic material, are coated on both the flexible substrates on the two sides of the EL unit, said at least one layer (ii) being interposed between said at least one lower layer (i) and said at least one upper layer (iii).

Preferably, said flexible substrate comprises at least one organic polymer which may be selected, for example, from: polystyrenes (PS); polyacrylates, such as polymethylmethacrylate (PMMA); polyvinylchloride (PVC); polyimides (Pl); polyetherimides (PEI); epoxy resins (ER); polyesters such as, polyethyleneterephthalate (PET); polycarbonates (PC); or mixtures thereof. Polyethyleneterephthalate (PET) is particularly preferred.

The thickness of said flexible substrate is preferably in the range of from 10 μm to 500 μm, more preferably in the range of from 15 μm to 200 μm, even more preferably in the range of from 20 μm to 100 μm.

According to one preferred embodiment, said at least one organic polymer (a) may be selected from organic polymers which are transparent in the visible range

(i.e. wavelengths between 400 nm and 750 nm). Generally speaking, transparency may be defined in terms of transmittance T=l/I_o, wherein I₀ is the intensity of the incident light and I is the light coming out the sample. Measured by an UV-Vis spectrophotometer, T, referred to a thickness of 1 mm, should be equal to or higher than 80%, preferably equal to or higher than 95% in the visible range. According to a further preferred embodiment, said at least one organic polymer (a) may be selected from amorphous polymers such as, for example: polystyrenes (PS), polyacrylates, such as polymethylmethacrylate (PMMA); polyvinylchloride (PVC); polyimides (Pl); epoxy resins ER); polyesters, such as polyethyleneterephthalate (PET); polycarbonate (PC); or mixtures thereof. Polystyrene is particularly preferred.

According to one preferred embodiment, said at least one nanosized layered material (b) has an individual layer thickness of from 0.1 nm to 30 nm, preferably of from 0.2 nm to 15 nm, more preferably of from 0.5 nm to 2 nm.

According to a further preferred embodiment, said at least one nanosized layered material (b) may be selected, for example, from: phyllosilicates such as, for example, smectites, for example, montmorillonite, bentonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite; vermiculite; halloisite; sericite; aluminate oxides; hydrotalcite; or mixtures thereof. Montmorillonite is particularly preferred. Said nanosized layered material generally contains exchangeable ions such as sodium (Na⁺), calcium (Ca²⁺), potassium (K⁺), magnesium (Mg²⁺), hydroxide (HO^'), or carbonate (CO₃ ^2"), present at the interlayer surfaces.

In order to render said at least one nanosized layered material (b) more compatible with the elastomeric polymer(s), the nanosized layered material (b) may be treated with at least one compatibilizing agent. Said compatibilizing agent is capable of undergoing ion exchange reactions with the ions present at the interlayers surfaces of the nanosized layered material.

According to one preferred embodiment, said at least one compatibilizing agent may be selected, for example, from the quaternary ammonium or phosphonium salts having the following general formula:

wherein:

Y₁ represents N or P;

R₁, R₂, R₃ and R₄, which may be equal or different from each other, represent a linear or branched C₁-C_2O alkyl or hydroxyalkyl group; a linear or branched C₁-C₂₀ alkenyl or hydroxyalkenyl group; a group -R₅-SH or

-R₅-NH wherein R₅ represents a linear or branched C₁-C₂₀ alkylene group; a C₆-C₁₈ aryl group; a C₇-C₂₀ arylalkyl or alkylaryl group; a C₅-C₁₈ cycloalkyl group, said cycloalkyl group possibly containing hetero atom such as oxygen, nitrogen or sulfur; - X₁"^" represents an anion such as the chloride ion, the sulphate ion or the phosphate ion; n represents 1 , 2 or 3.

Said nanosized layered material may be treated with the compatibilizing agent before adding it to the organic polymer(s). Alternatively, said nanosized layered material and the compatibilizing agent may be separately added to the organic polymer(s).

The treatment of said nanosized layered material with the compatibilizing agent may be carried out according to known methods such as, for example, by an ion exchange reaction between the layered material and the compatibilizer: further details are described, for example, in United States Patents US 4,136,103, US 5,747,560, or US 5,952,093.

Examples of nanosized layered materials which may be used according to the present invention and are available commercially are the products known by the name of Dellite^® HPS, Dellite^® 67G, Dellite^® 72T, Dellite^® 43B, from Laviosa Chimica Mineraria S.p.A.; Cloisite^® 25A, Cloisite^® 10A, Cloisite^® 15A, Cloisite^® 2OA, from Southern Clays; Nanofil^® 5, Nanofil^® 8, Nanofil^® 9, from Sϋd Chemie; Bentonite^® AG/3 from DaI Cin S.p.A.

According to one preferred embodiment, said at least one nanosized layered material (b) is present in the composition in an amount of from 1 % by weight to

15% by weight, preferably of from 2% by weight to 10% by weight, with respect to the total weight of the composition [i.e. organic polymer (a) + nanosized layered material (b)]. By this way, the defined amount of nonosized layered material allows to reduce the permeation of moisture and oxygen and, at the same time, to obtain an organic EL device having good transparency properties. In fact, an amount of nanosized layered material (b) higher than 15% by weight based on the total weight of the composition would lead to a not-acceptable hazing of the EL device.

The thickness of said at least one layer (ii) comprising said organic polymer (a) and said nanosized layered material (b) is preferably in the range of from 0.1 μm to 1.0 μm, more preferably in the range of from 0.3 μm to 0.6 μm.

As disclosed above, the organic EL device of the present invention comprises at least one lower layer (i) and at least one upper layer (iii) comprising at least one inorganic material.

According to one preferred embodiment, said at least one inorganic material may be selected, for example, from: metal oxides such as silicon dioxide, aluminum oxide, titanium oxide, indium oxide, tin oxide, indium tin oxide, tantalum oxide, zirconium oxide, niobium oxide; metal nitrides, such as silicon nitride; metal carbides; metal oxynitrides, such as silicon oxynitride; metal oxyborides, or mixtures thereof combinations thereof. Preferably, the inorganic materials are metal oxides, more preferably, silicon dioxide (usually called simply "silicon oxide" in the semiconductor industry), silicon nitride or silicon oxynitride, or mixtures thereof. Silicon dioxide is particularly preferred.

Preferably, said at least one lower layer (i) and said at least one upper layer (iii) comprise the same inorganic material.

The thickness of said at least one inorganic material lower layer (i) and of said at least one inorganic material upper layer (iii) is preferably in the range of from 0.03 μm to 1.0 μm, more preferably in the range of from 0.1 μm to 0.6 μm.

In a first preferred embodiment, the organic EL device of the present invention comprises one inorganic material lower layer (i) and one inorganic material upper layer (iii), a layer (ii) including (a) at least one organic polymer and (b) at least one nanosized layered material, being interposed between said lower and upper layer. In a second preferred embodiment, the organic EL device of the present invention further comprises a layer (iia) including (a) at least one organic polymer and (b) at least one nanosized layered material interposed between said inorganic material upper layer (i) and a further inorganic material upper layer (ia). In this embodiment, the layered material (b) may be selected from the same group cited above for the layer (ii) interposed between said inorganic material upper layer (i) and said inorganic material lower layer (iii).

Preferably said further layer (iia) comprises from 1 % by weight to 15% by weight, more preferably from 2% by weight to 10% by weight, of at least one nanosized layered material (b), with respect to the total weight of the composition [i.e. organic polymer (a) + nanosized layered material (b)].

Preferably, the thickness of said further layer (iia) is in the range of from 0.1 μm to 1.0 μm, more preferably in the range of from 0.3 μm to 0.6 μm. Furthermore, the inorganic material contained in said second upper layer (ia) may be selected from the same group of inorganic materials cited above. The thickness of said second inorganic material upper layer (ia) is preferably in the range of from 0.03 μm to 1.0 μm, more preferably in the range of from 0.1 μm to 0.6 μm.

Said at least one lower layer (i) and said at least one upper layer (iii) comprising inorganic material may be deposited by techniques allowing industrial-scale deposition of high-quality barrier coatings, such as, for example, Chemical Vapour Deposition (CVD), such as Metal Organic Chemical Vapour Deposition (MOCVD), Atmospheric Pressure Chemical Vapour Deposition (APCVD), Low Pressure Chemical Vapour Deposition (LPCVD), Ultra High Vacuum Chemical Vapour Deposition (UHVCVD) or Plasma Enhanced Chemical Vapour Deposition (PECVD); Physical Vapour Deposition (PVD), such as evaporative deposition, electron beam physical vapour deposition, sputtering deposition, pulsed laser deposition, thermal evaporation deposition. Preferably, said at least one lower layer (i) and said at least one upper layer (iii) comprising inorganic material are deposited by APCVD, PECVD or PCVD techniques.

Silicon dioxide deposition utilizes common source gases, including for example, silane and oygen, esamethyldisiloxane (HMDSO) and oxygen, dichlorosilane and nitrous oxide, or tetrahydrosiiicate, or mixtures thereof.

Preferably, the silicon dioxide is deposited by a PECVD technique starting from HMDSO and oxygen mixtures. Preferably, the initial residual pressure in the vacuum deposition chamber is lower than or equal to 10^"4 mbar and the HMDSO/oxygen mixture pressure is in the range of from 0.02 mbar to 0.5 mbar. More preferably, the HMDSO/oxygen partial pressure ratio is in the range of from 1.1 to 1 :14. More preferably, the deposition time is in the range of from 1 min to 60 min.

For the purpose of the present description and of the claims which follow, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

In a second aspect, the present invention relates to a process for producing a composition including at least one organic polymer and at least one nanosized layered material, said process comprising the steps of: a) dispersing at least one nanosized layered material in at least one solvent obtaining a mixture; b) dissolving at least one organic polymer in at least one solvent obtaining a solution; c) adding the mixture obtained in step a) with the solution obtained in step b) so as to obtain said organic polymer/nanosized layered material composition; wherein said process further comprises at least one sonicating step d).

The process of the present invention is able to obtain a homogeneous distribution of the nanosized layered material in said composition, in the absence of aggregates.

Preferably, said composition comprises from 1% by weight to 15% by weight, more preferably from 2% by weight to 10% by weight, of at least one nanosized layered material (b), with respect to the total weight of the composition [i.e. organic polymer + nanosized layered material].

Said dissolving steps a) and b) can be carried out independently to each other, simultaneously or at different times.

Preferably, said sonicating step d) is performed during or at the end of the mixing step c). More preferably, a further sonicating step e) is also performed during or at the end of the dissolving step a).

Preferably, said sonicating step is carried out by ultrasound treating said solution or said organic polymer/nanosized layered material composition for a period in the range of from 20 min to 120 min, more preferably of from 30 to 90 minutes.

By this way, a more homogeneous and regular distribution of nanosized layered material in said composition is obtained.

Suitable solvents useful in said dispersing step a) and in said dissolving step b), may be individually selected, for example, from hydrocarbons such as chloroform, methyl chloroform, chlorobenzene, o-dichlorobenzene, chloroethane, 1 ,1- dichloroethane, 1 ,2-dichloroethane, 1 ,1 ,2,2-tetrachloroethane, epichlorohydrin, trichloroethylene, tetrachloroethylene, or mixture thereof. 1 ,2-dichloroethane, or mixtures thereof, being preferred.

Preferably, the solvents used in dispersing step a) and in said dissolving step b), are the same or they are easily mixing one each other in order to make easier the mixing step c).

The process of the present invention for producing a polymer organic polymer/nanosized layered material composition provides a very clear solution, adapted to be used in an organic EL device wherein a high transparency is required.

Brief description of the drawings

The present invention will now be illustrated in further detail by means of an illustrative embodiment with reference to the attached figures, wherein: - Figure 1 is a cross-sectional view of a portion of a first embodiment of the organic EL device according to the present invention, and

- Figure 2 is a cross-sectional view of a portion of a second embodiment of the organic EL device according to the present invention.

Detailed description of the preferred embodiments

In particular, Figure 1 shows an organic EL device (1) comprising an EL unit (2) consisting in an organic active EL material layer (3), interposed between a first conducting layer (4a) and a second conducting layer (4b). On each side of the EL unit (2) is present, in order, a PET flexible substrate (5), a first layer (6) comprising inorganic material, a layer (7) including a composition comprising at least one organic polymer (a) and at least one nanosized layered material (b) and a second layer (8) comprising inorganic material.

In particular, Figure 2 shows an organic EL device (1) comprising an EL unit (2) consisting in an organic active EL material layer (3), interposed between a first conducting layer (4a) and a second conducting layer (4b). On each side of the EL unit (2) is present, in order, a PET flexible substrate (5), a first layer (6) comprising inorganic material, a layer (7) including a composition comprising at least one organic polymer (a) and at least one nanosized layered material (b), a second layer (8) comprising inorganic material, a further layer (9) identical to layer (7) and a third layer (10) comprising inorganic material.

In order to allow said organic active EL material to emit light, an electrical potential difference has to be applied between said first conducting layer (4a) and said second conducting layer (4b).

The present invention will be further illustrated below by means of a number of preparation examples, which are given for purely indicative purposes and without any limitation of this invention.

EXAMPLE 1

Preparation of organic polvmer/nanosized layered material composition Organic polymer/nanosized layered material composition was prepared as follows. 50 mg of Dellite^® HPS (high purified montmorillonite from Laviosa Chimica Mineraria) was dispersed in 2 ml of 1 ,1 ,2,2-tetrachloroethane (Sigma-AIdrich) and sonicated for 45 minutes with a Liarre Starsonic ultrasonic bath. The obtained mixture was then added to a solution of 0,950 g of polystyrene (available from Sigma-AIdrich, weight average molecular weight (Mw) 230,000, number average molecular weight (Mn) 140000) in 7.88 ml of 1 ,1 ,2,2-tetrachloroethane to give a final concentration of 6% in weight. The ratio organic polymer/nanosized layered material was 95/5. The resulting composition was further sonicated for additional 45 minutes obtaining finally a clear solution (1). The solution was kept at room temperature (23°C) under magnetic stirring.

In order to check the uniform distribution of the nanosized layered material in the organic polymer/nanosized layered material composition, an EDX (Energy Dispersive X-rays) analysis was carried out using a Hitachi S2700 SEM (scanning electron microscope) with an Oxford Si(Li) detector. Spectra were collected for 200 seconds, at 10 KeV on film of the above reported organic polymer/nanosized layered material composition having the following dimensions: 25 mm x 35 mm x 1 μm deposited by spin-coating onto a glass substrate.

Peaks of the characteristic elements of montmorillonite (Al, Si, O) were monitored in different areas of the obtained film. The analysis was performed on different films. Peaks heights resulted always reproducible, confirming the regular and homogeneous dispersion of the nanosized layered material in the organic polymer and the substantial absence of aggregates.

EXAMPLE 2

Preparation of coated flexible substrates Sample 1 (comparison)

The coated flexible substrate was prepared as follows.

To this aim a plasma deposition apparatus consisting of a cylindrical stainless steel vacuum chamber having a diameter of 30 cm was set up in a parallel plate configuration, the electrodes (upper electrode and lower electrode) being positioned at a distance of 8 cm from each other. The upper electrode was externally connected, through a semi-automated matching network (Advanced Energy ATX-600)and, to a 13.56 MHz-RF power supplier (Advanced Energy RFX-600) having a maximun power input of 600 W.

A 12x12 cm² polyethyelene therephthalate (PET) flexible film (Mylar A 23 type from DuPont Teijin Films), having a thickness of 23 μm, was placed on the lower electrode.

The vacuum chamber was first evacuated until the residual pressure of 10^"4 mbar was obtained, by means of a rotary pump (Varian SD-300) combined with a turbo- molecular pump (Leybold RS232).

Subsequently, hexamethyldisiloxane (HMDSO), available from Fluka, at a partial pressure of 0.03 mbar, and oxygen (O₂), at a partial pressure of 0.09 mbar, were feed onto the vacuum chamber. The plasma deposition time was of 30 minutes. Then, the injection of HMDSO and of O₂ was stopped and the chamber returned to the atmospheric pressure with air.

At the end of the above plasma deposition, a PET substrate coated with a silicon dioxide layer 0.5 μm thick, was obtained. From said coated PET substrate, four test pieces of 6 cm² x 6 cm² dimensions were obtained. The thickness of the silicon dioxide layer was measured by means of a profilometer (Dektak 8 Stylus Profiler).

One of said four test pieces was subjected to water vapour transmission (WVTR) measurement operating as disclosed below. The remaining three pieces were further treated as disclosed below in order to obtain Sample 2 (comparison), Sample 3 (invention) and Sample 4 (comparison).

Sample 2 (comparison) Sample 2 was obtained by depositing onto one of the remaining three pieces a further silicon dioxide layer, using the same procedure of Sample 1 , so obtaining a PET substrate coated with two silicon dioxide layers, each layer being 0.5 μm thick.

Sample 2 was subjected to water vapour transmission (WVTR) measurement operating as disclosed below.

Sample 3 (invention)

Sample 3 was obtained by depositing onto one of the remaining two pieces a layer of organic polymer/nanosized layered material composition obtained as disclosed in the above Example 1.

To this aim, said organic polymer/nanosized layered material composition was filtered with a polytetrafluoroethylene (PTFE) filter, and subsequently deposited onto the silicon dioxide layer by spin-coating using a Karl-Suss RC8 device, at 5000 rpm, for 60 seconds,

After the deposition, the sample was dried under vacuum at 8O⁰C for 72 hours, to obtain a 0.5 μm thick layer. Finally, the deposition of a further layer of silicon dioxide was performed, following the same procedure described for the preparation of Sample 1 , obtaining a multilayer product having the following structure: a PET substrate coated with a silicon oxide layer 0.5 μm thick, an organic polymer/nanosized layered material composition layer 0.5 μm thick, a silicon oxide layer 0.5 μm thick.

Sample 3 was subjected to water vapour transmission (WVTR) measurement operating as disclosed below.

Sample 4 (comparison) Sample 4 was obtained by depositing onto the remaining test piece a layer of organic polymer.

To this aim, a solution of 0,950 g of polystyrene (available from Sigma-Aldrich, weight average molecular weight (Mw) 230,000, number average molecular weight (Mn) 140000) in 7.88 ml of 1 ,1 ,2,2-tetrachloroethane to give a final concentration of 6% in weight, was prepared and was deposited, by spin coating, as disclosed above.

Finally, the deposition of a further layer of silicon dioxide was performed, following the same procedure described for the preparation of Sample 1 , obtaining a multilayer product having the following structure: a PET substrate coated with a silicon oxide layer 0.5 μm thick, an organic polymer layer 0.5 μm thick, a silicon oxide layer 0.5 μm thick.

Sample 4 was subjected to water vapour transmission (WVTR) measurement operating as disclosed below.

As disclosed above, the obtained samples 1-4 were subjected to water vapour transmission (WVTR) measurement. Said measurement, was carried out at 38°C and 90% of relative humidity, according to ASTM F 1249-05 standard, by means of an automatic system Permatran-W 3/60. The obtained data were given in the following Table 1.

TABLE 1

Sample 3 according to the present invention, having at least a sandwich- layered structure onto a flexible substrate layer, wherein said structure comprises a organic polymer/nanosized layered material composition layer positioned between two layers of inorganic materials, showed to be able to reduce the permeation to moisture and oxygen.

The above-described embodiments must be intended as mere non-limiting illustrations of several possible embodiments of the EL device of the present invention, it being clearly understood that any element pertaining to the device itself can be changed by the man skilled in the art in order to satisfy specific and contingent needs, while remaining in the scope of that described and claimed.

Claims

1. Organic EL device comprising an EL unit and, on at least one side of said EL unit, a flexible substrate having coated thereon: (i) at least one lower layer comprising at least one inorganic material;

(ii) at least one layer comprising a composition including (a) at least one organic polymer and (b) at least one nanosized layered material; (iii) at least one upper layer comprising at least one inorganic material; said at least one layer (ii) being interposed between said at least one lower layer and said at least one upper layer.

2. Organic EL device according to claim 1 , wherein said at least one nanosized layered material (b) is present in the composition in an amount of from 1 % by weight to 15% by weight with respect to the total weight of the composition.

3. Organic EL device according to claim 2, wherein said at least one nanosized layered material (b) is present in the composition in an amount of from 2% by weight to 10% by weight with respect to the total weight of the composition.

4. Organic EL device according to any preceding claims, wherein said at least one nanosized layered material (b) is montmorillonite.

5. Organic EL device according to any preceding claims, wherein the thickness of said at least one layer (ii) is in the range of from 0.1 μm to 1.0 μm.

6. Organic EL device according to any preceding claims, wherein the inorganic material is metal oxide.

7. Organic EL device according to claim 6, wherein the inorganic material is silicon dioxide, silicon nitride or silicon oxynitride or mixtures thereof.

8. Organic EL device according to any preceding claims, wherein the thickness of said at least one inorganic material lower layer (i) and of said at least one inorganic material upper layer (iii) is in the range of from 0.03 μm to 1.0 μm.

9. Organic EL device according to any preceding claims, wherein the flexible substrate is made of polyethyleneterephthalate.

10. Organic EL device according to any preceding claims, wherein the organic EL device further comprises a second layer (iia) including (a) at least one organic polymer and (b) at least one nanosized layered material interposed between said inorganic material upper layer (i) and a further inorganic material upper layer (ia).

11. Process for producing a composition including at least one organic polymer and at least one nanosized layered material, said process comprising the steps of: a) dispersing at least one nanosized layered material in at least one solvent obtaining a mixture; b) dissolving at least one organic polymer in at least one solvent obtaining a solution; c) adding the mixture obtained in step a) with the solution obtained in step b) so as to obtain an organic polymer/nanosized layered material composition; wherein said process further comprises at least one sonicating step d).

12. Process according to claim 11 , wherein said composition comprises from 1% to 15% by weight of at least one nanosized layered material (b), with respect to the total weight of the composition.

13. Process according to claim 11 or 12, wherein the sonicating step d) is performed during or at the end of the mixing step c).

14. Process according to claim 13, wherein the sonicating step is performed for a period in the range between 20 and 120 minutes.

15. Mobile communication device including a flexible display comprising an organic EL device according to any one of claims 1 to 10.

16. Mobile communication device according to claim 15, said mobile communication device being selected from mobile terminals, pagers, integrated mobile phones, personal digital assistants.

17. Mobile communication device according to claim 16, wherein said mobile communication device is a mobile terminal for mobile communication systems, such as GSM or UMTS.