WO2018229488A1

WO2018229488A1 - Organic light-emitting diode device with pixel definition layer

Info

Publication number: WO2018229488A1
Application number: PCT/GB2018/051627
Authority: WO
Inventors: Alexander Doust; Sean Whelan; Martina Pintani
Original assignee: Cambridge Display Technology Limited; Sumitomo Chemical Company Limited
Priority date: 2017-06-16
Filing date: 2018-06-14
Publication date: 2018-12-20
Also published as: GB2563448A; GB201709644D0

Abstract

Organic light-emitting diode device. An organic light-emitting diode device includes a layer structure. The layer structure includes a transparent or translucent substrate (11). The layer structure also includes a transparent or translucent anode layer (12) disposed on the transparent or translucent substrate (11) and including one or more first electrodes. The layer structure also includes a hole-injection layer (13) disposed over the anode layer (12). The layer structure also includes a light-emitting layer (15) disposed over the hole-injection layer (13). The layer structure also includes a cathode layer (18) disposed over the light-emitting layer (15) and comprising one or more second electrodes. The layer structure also includes a pixel definition layer (17) disposed within the layer structure between the hole-injection layer (13) and the cathode layer (18), the pixel definition layer (17) formed of a printed organic insulator and comprising one or more apertures defining one or more corresponding pixel areas.

Description

ORGANIC LIGHT-EMITTING DIODE DEVICE WITH PIXEL DEFINITION LAYER

Field of the invention

The present invention relates to organic light-emitting diode devices and methods of fabricating organic light-emitting diode devices.

Background

Figure i, shows an OLED device ι which is useful for understanding the present invention. The OLED device i includes a transparent or translucent substrate 2 through which emitted light is transmitted to an exterior. A transparent or translucent anode layer 3 is disposed over the substrate 2. The anode layer 3 may include multiple, separate, electrodes. The anode layer 3 is typically formed of indium tin oxide (ΓΓΟ), indium zinc oxide (IZO) or other suitable transparent or translucent conductive material. Once or more bank structures 4 are deposited over the substrate 2 and anode layer 3 prior to deposition of the active OLED layers.

Active OLED layers are deposited within the active pixel areas defined by the bank structures 4. A polymer hole transport layer 5 is deposited over the areas of the anode layer 3 exposed by the bank structures 4. A light-emitting layer 6 is deposited over the hole-transport layer 5. Depending on the choice of materials for the hole-transport layer 5 and light-emitting layer 6, an intermediate layer 7 (sometimes also called an "interlayer") may be deposited between the hole-transport layer 5 and the light- emitting layer 6. For some material combinations, the intermediate layer 7 may not be required, in which case the Hght-emitting layer 6 may be deposited directly onto the hole transport layer 5. A cathode layer 8 is deposited in electrical contact with the light-emitting layer 6. Often, the cathode layer 8 is electrically coupled to the light- emitting layer 6 by an intervening polymeric or non-polymeric electron-injection layer 9. The cathode layer 3 may include multiple, separate, electrodes. The OLED device 1 is manufactured using lithographic methods to define the bank structure 4 and to pattern the cathode layer 8. However, lithographic methods are expensive, in part due to the common requirements for tight control of environmental conditions. Although the OLED layers 5, 6, 7, 9 can be readily deposited using spin- coating or printing methods, the complexity and costs of defining the active pixel areas may be a barrier to new applications of OLED devices. It has been suggested to produce OLED devices using alternative structures. For example, US 2014/0353512 Ai describes an OLED device in which a continuous organic light-emitting layer is formed by printing over a set of electrodes deposited on a substrate. The active pixel areas are defined by a thin insulating metal fluoride layer disposed on top of the organic light-emitting layer. The metal fluoride layer is applied by deposition through a mask. However, deposition by sputtering or evaporation through a mask requires controlled environmental conditions which may limit throughput and/or increase investment and processing costs.

KR 10-0919352 Bi describes structures for passive or active matrix red-green-blue displays, in which first banks are deposited over a continuous hole-transport layer or intermediate layer in order to define pixels. Red, green and blue organic electroluminescent layers are disposed over the intermediate layer, within the areas defined by the first banks. The first banks prevent mixing of the different inks which are used to define the red, green and blue pixels. The first banks are made of material which is water repellent, such as a fluorine resin, or material which has been treated to make it water repellent by treatment with fluorine gas plasma. This provides a high contact angle of 60° or more to water, which aids segregation of the red, green and blue organic electro-luminescent materials.

Summary

According to a first aspect of the invention there is provided an organic light-emitting diode device including a layer structure. The layer structure includes a transparent or translucent substrate. The layer structure also includes a transparent or translucent anode layer disposed on the transparent or translucent substrate and including one or more first electrodes. The layer structure also includes a hole-injection layer disposed over the anode layer. The layer structure also includes a light-emitting layer disposed over the hole-injection layer. The layer structure also includes a cathode layer disposed over the light emitting layer and comprising one or more second electrodes. The layer structure also includes a pixel definition layer disposed within the layer structure between the hole-injection layer and the cathode layer, the pixel definition layer formed of a printed organic insulator and comprising one or more apertures defining one or more corresponding pixel areas.

Thus, organic light-emitting diode devices maybe provided using a structure which is less complex and simpler to manufacture.

The pixel definition layer being formed of a printed organic insulator maybe alternatively expressed as the pixel definition layer being formed of an organic insulator which is available in a printable formulation.

Each aperture may have a minimum dimension of greater than or equal to 0.5 mm.

Each aperture may have a minimum dimension of greater than or equal to 1 mm, greater than or equal to 2 mm, greater than or equal to 5 mm or 10 greater than or equal to mm. Each aperture may have an area of greater than or equal to 0.25 mm², greater than or equal to 1 mm², greater than or equal to 10 mm², or greater than or equal to 100 mm².

The pixel definition layer may include at least two apertures defining at least two corresponding pixel areas. At least a continuous portion of each of the hole-injection layer and light-emitting layer may span the at least two apertures. At least part of the cathode layer maybe separated from the electron-injection layer by the pixel definition layer. The transparent or translucent substrate may include two or more layers. The layer structure of the organic light-emitting diode device may also include an intermediate layer disposed between the hole-injection layer and the light-emitting layer. At least a continuous portion of the intermediate layer may span the at least two apertures.

The layer structure of the organic light-emitting diode device may also include an electron-injection layer disposed between the light-emitting layer and the cathode layer. At least a continuous portion of the electron-injection layer may span the at least two apertures.

The electron injection layer may be formed from a polymeric conductive material. The electron injection layer maybe formed from a metal halide material. The metal halide layer may be formed of sodium fluoride.

The layer structure of the organic light-emitting diode device may also include an electron-transporting layer disposed between the electron-injection layer and the light- emitting layer.

The electron-injection layer may also be an electron-transporting layer.

The pixel definition layer may be disposed on the hole-injection layer such that the hole-injection layer is between the pixel definition layer and the anode layer.

The pixel definition layer may be disposed on the Ught-emitting layer such that the light-emitting layer is between the pixel definition layer and the anode layer.

The pixel definition layer maybe disposed on the intermediate layer such that the intermediate layer is between the pixel definition layer and the anode layer.

The pixel definition layer may be disposed on the electron-injection layer such that the electron-injection layer is between the pixel definition layer and the anode layer.

The pixel definition layer may be disposed on the electron-transporting layer such that the electron-transporting layer is between the pixel definition layer and the anode layer. The anode layer may include a single, continuous first electrode. The anode layer may be continuous or substantially continuous across the organic light-emitting diode device. The cathode layer may include a single, continuous second electrode. The cathode layer may be continuous or substantially continuous across the organic light-emitting diode device.

The anode layer may include a plurality of first electrodes extending in a first direction and spaced apart in a second direction, the second direction being different to the first direction. The cathode layer may include a plurality of second electrodes extending in the second direction and spaced apart in the first direction. The pixel definition layer may include apertures defining pixel areas corresponding to each intersection of the first and second electrodes.

Each aperture may define a single pixel area. Each aperture may define at least one boundary of one or more pixel areas.

The substrate may be a flexible substrate. A flexible substrate may be made of a material which may be bent to a radius of curvature of 100 mm or less without undergoing permanent deformation or damage. A flexible substrate may be capable of bending to radii of 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, 10 mm or less, or 5 mm or less without experiencing permanent deformation or damage. A flexible substrate maybe capable of withstanding bending to a bend radius of 10 mm for at least one thousand cycles of bending and unbending without experiencing permanent deformation or damage.

The cathode layer may be formed of conductive ink. The cathode layer may be formed of conductive ink containing metallic particles. The metallic particles may be silver. The cathode layer may be formed of conductive ink containing carbon black. The cathode layer does not contain poly(3,4-ethylenedioxythiophene) (PEDOT).

The cathode layer may be a thin metallic layer deposited by sputtering or evaporation. The cathode layer may be formed of aluminium. When the electron-injection layer is formed of a metal halide material, the electron-injection layer and the cathode layer may be deposited using sequential sputtering steps or sequential evaporation steps. The pixel definition layer may be sufficiently thick to function as a cathode separator layer. The pixel definition layer thickness may be greater than or equal to 100 nm. The pixel definition layer may be greater than or equal to 1 μm, greater than or equal to 10 μm or greater than or equal to 100 μm thick. The pixel definition layer may be no more than 500 μm thick.

The area of each aperture may decrease through the thickness of the pixel definition layer in a direction away from the anode layer.

The transparent or translucent substrate may be polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or polyimide. The transparent or translucent anode layer may be formed from indium tin oxide (ITO) or indium zinc oxide. The light-emitting layer may be a light-emitting polymer layer.

According to a second aspect of the invention there is provided a layer structure which includes a transparent or translucent substrate, a transparent or translucent anode layer disposed on the transparent or translucent substrate and comprising one or more first electrodes, a hole-injection layer disposed over the anode layer, and a light- emitting layer disposed over the hole-injection layer. Each of the hole-injection layer, and the light-emitting layer is a continuous layer.

The layer structure of the second aspect may not include a cathode layer. The layer structure of the second aspect may also include a continuous intermediate layer disposed between the hole-injection layer and the light-emitting layer.

The layer structure of the second aspect may also include a continuous electron injection layer disposed over the light-emitting layer.

The layer structure of the second aspect may also include a continuous electron- transporting layer disposed between the electron-injection layer and the light-emitting layer. The light-emitting layer may be a light-emitting polymer layer. The transparent or translucent substrate may be polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or polyimide. The transparent or translucent anode layer may be formed from indium tin oxide (ITO) or indium zinc oxide.

A continuous layer maybe continuous or substantially continuous across the layer structure.

According to a third aspect of the invention there is provided a method including receiving a transparent or translucent substrate, depositing a transparent or translucent anode layer over the transparent or translucent substrate, the transparent or translucent anode layer including one or more first electrodes, depositing a hole- injection layer over the anode layer, depositing a light-emitting layer over the hole- injection layer, and printing a pixel definition layer such that hole-injection layer is between the pixel definition layer and the anode layer. The pixel definition layer is formed of an organic insulator and includes one or more apertures defining one or more corresponding pixel areas.

Each aperture may have a minimum dimension of greater than or equal to 0.5 mm, greater than or equal to 1 mm, greater than or equal to 2 mm, greater than or equal to 5 mm or 10 greater than or equal to mm. Each aperture may have an area of greater than or equal to 0.25 mm², greater than or equal to 1 mm², greater than or equal to 10 mm², or greater than or equal to 100 mm².

The pixel definition layer may include at least two apertures defining at least two corresponding pixel areas. At least a continuous portion of each of the hole-injection layer and the light-emitting layer may span the at least two apertures.

One or more of the hole-injection layer and the light-emitting layer may be deposited by printing. One or more of the hole-injection layer and the light-emitting layer may be deposited by spin-coating. When the electron-injection layer takes the form of a metal halide material, the metal halide material may be deposited by evaporation or sputtering. The metal halide material may be sodium fluoride.

The method may also include depositing an intermediate layer between the hole- injection layer and the light-emitting layer. The method may also include depositing an electron-injection layer over the light- emitting layer

The electron-injection layer may be formed of a polymeric conductive material or a metal halide material.

The method may also include depositing an electron-transporting layer between the electron-injection layer and the light-emitting layer. The intermediate layer may be deposited by printing or by spin-coating. The electron- injection layer may be deposited by printing or by spin-coating. The electron- transporting layer may be deposited by printing or by spin-coating.

The pixel definition layer maybe printed onto the hole-injection layer such that the hole-injection layer is between the pixel definition layer and the anode layer.

The pixel definition layer may be printed onto the light-emitting layer such that the light-emitting layer is between the pixel definition layer and the anode layer. The pixel definition layer may be printed onto the intermediate layer such that the intermediate layer is between the pixel definition layer and the anode layer.

The pixel definition layer may be printed onto the electron-injection layer such that the electron-injection layer is between the pixel definition layer and the anode layer.

The pixel definition layer may be printed onto the electron-transporting layer such that the electron-transporting layer is between the pixel definition layer and the anode layer.

According to a fourth aspect of the invention there is provided a method including receiving a layer structure. The layer structure includes a transparent or translucent substrate and a transparent or translucent anode layer disposed on the transparent or translucent substrate. The transparent or translucent anode layer includes one or more first electrodes. The method also includes depositing a hole-injection layer over the anode layer, depositing a light-emitting layer over the hole-injection layer, and printing a pixel definition layer such that hole-injection layer is between the pixel definition layer and the anode layer. The pixel definition layer is formed of an organic insulator and includes one or more apertures defining one or more corresponding pixel areas.

Each aperture may have a minimum dimension of greater than or equal to 0.5 mm, greater than or equal to 1 mm, greater than or equal to 2 mm, greater than or equal to 5 mm or 10 greater than or equal to mm. Each aperture may have an area of greater than or equal to 0.25 mm², greater than or equal to 1 mm², greater than or equal to 10 mm², or greater than or equal to 100 mm². The pixel definition layer may include at least two apertures defining at least two corresponding pixel areas. At least a continuous portion of each of the hole-injection layer and the light-emitting layer may span the at least two apertures.

The method may also include depositing an intermediate layer between the hole- injection layer and the light-emitting layer.

The method may also include depositing an electron-injection layer over the light- emitting layer. According to a fifth aspect of the invention there is provided a method including receiving a layer structure. The layer structure includes a transparent or translucent substrate, a transparent or translucent anode layer disposed on the transparent or translucent substrate and including one or more first electrodes, a hole-injection layer disposed over the anode layer and a light-emitting layer disposed over the hole- injection layer. Each of the hole-injection layer and the light-emitting layer is a continuous layer. The method also includes printing a pixel definition layer onto the electron-injection layer. The pixel definition layer is formed of an organic insulator and includes one or more apertures defining one or more corresponding pixel areas. Each aperture may have a minimum dimension of greater than or equal to 0.5 mm, greater than or equal to 1 mm, greater than or equal to 2 mm, greater than or equal to 5 mm or 10 greater than or equal to mm. Each aperture may have an area of greater than or equal to 0.25 mm⁸, greater than or equal to 1 mm² greater than or equal to 10 mm^a, or greater than or equal to 100 mm³. The pixel definition layer may include at least two apertures defining at least two corresponding pixel areas. At least a continuous portion of each of the hole-injection layer and the light-emitting layer may span the at least two apertures. The layer structure may also include an intermediate layer disposed between the hole- injection layer and the light-emitting layer.

The layer structure may also include an electron-injection layer disposed over the light- emitting layer.

The layer structure may also include an electron transporting layer disposed between the electron-injection layer and the light-emitting layer.

A continuous layer may be continuous or substantially continuous across the layer structure.

According to a sixth aspect of the invention there is provided a method including receiving the layer structure of the second aspect, and printing a pixel definition layer onto the electron-injection layer. The pixel definition layer is formed of an organic insulator and includes one or more apertures defining one or more corresponding pixel areas.

The methods of the third to sixth aspects may also include depositing a cathode layer over the light-emitting layer. The cathode layer may be deposited by printing. The cathode layer may be formed of conductive ink containing metallic particles. The metallic particles maybe silver. The cathode layer maybe formed of conductive ink containing carbon black. The cathode layer does not contain poly(3,4-ethylenedioxythiophene) (PEDOT).

The cathode layer maybe deposited by evaporation or sputtering.

The cathode layer may be deposited as a continuous layer and patterned using laser ablation.

Printed layers may be deposited by screen printing. Printed layers may be deposited by ink-jet printing. Printed layers may be deposited by gravure printing. Printed layers may be deposited by flexographic printing.

Pixel areas maybe co-extensive with apertures. The light-emitting layer may be a light-emitting polymer layer.

Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example, with reference to Figures 2 to 13 of the accompanying drawings in which:

Figure 1 is a cross-sectional view of an OLED device which is useful for understanding the invention;

Figure 2 is a cross-sectional view of a first OLED device;

Figure 3 is a cross-sectional view of a second OLED device;

Figure 4 is a cross-sectional view of a third OLED device;

Figure 5 is a cross-sectional view of a fourth OLED device;

Figure 6 is a plan view of a first pixel area configuration;

Figure 7 is a plan view of a second pixel area configuration;

Figure 8 is a plan view of a third pixel area configuration

Figure 9 shows a comparison of light emissions from several OLED devices;

Figure 10 compares current density-voltage characteristics of several OLED devices; Figure 11 is a process flow diagram of a first method of manufacturing an OLED device;

Figure 12 is a process flow diagram of a second method of manufacturing an OLED device; and

Figure 13 is a cross-sectional view of a fifth OLED device. Detailed Description of Certain Embodiments

In the following, like parts are denoted by like reference numbers.

Rfiferring to Figure 2, a first organic light-emitting diode (OLED) device 10 is shown. The first OLED device 10 includes a transparent or translucent substrate 11, a transparent or translucent anode layer 12, a hole-injection layer 13, an intermediate layer 14, a light-emitting layer 15, an electron-injection layer 16, a printed pixel definition layer 17, and a cathode layer 18. Light emitted from the first OLED device 10 is transmitted to the exterior through the transparent or translucent substrate 11. The transparent or translucent substrate 11 may be formed of polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or polyimide or similar polymeric materials which can be transparent or translucent. The transparent or translucent substrate 11 may typically have a thickness of around 125 μιη. The transparent or translucent substrate 11 may be rigid, but is preferably flexible. A flexible substrate 11 is made of a material which may be bent to a radius of curvature of 100 mm or less without undergoing permanent deformation or damage. Substrates 11 with greater flexibility may be used such as, for example, substrates 11 capable of bending to radii of 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, 10 mm or less, or 5 mm or less without experiencing permanent deformation or damage. For example, a flexible material maybe capable of withstanding bending to a bend radius of 10 mm for at least one thousand cycles of bending and unbending without experiencing permanent deformation or damage. The substrate 11 need not be a single piece of material, and the substrate 11 may be made up or two or more separate substrates joined, bonded or laminated to one another.

The transparent or translucent anode layer 12 is supported on the substrate 11 between the substrate 11 and the hole-injection layer 13. The anode layer 12 may include one or more first electrodes 23, 31 (Figures 6 and 8). In some examples, the anode layer 12 may take the form of a single, continuous first electrode. In other examples, the anode layer 12 may be patterned into a number of separate first electrodes in order to permit individual pixels or groups of pixels to be separately addressable. The anode layer 12 may be formed from indium tin oxide (ITO), indium zinc oxide (IZO) or other transparent or translucent conductive materials having compatible work functions.

The anode layer may typically have a thickness of around 65 nm. Fine metal wires may provide the first electrodes of the anode layer, provided that such wires are sufficiently thin. The anode layer 12 is deposited onto the substrate 11 using any suitable method such as photo-lithographic or printing methods.

Transparency of the substrate 11 and the anode layer 12 is relative to the emission wavelength of the OLED device 10. A material may be considered transparent if it transmits 70% or more of light at the emission wavelength of the OLED device 10. In other examples, a material may be considered transparent if it transmits 50% or more of light at the emission wavelength. In practice, the OLED device 10 may emit light across a range of wavelengths, and transparency may be considered with respect to a peak emission wavelength of the OLED device 10, or with respect to a reference wavelength. The hole-injection layer 13 is supported over the anode layer 12, between the anode layer 12 and the intermediate layer 14. The hole-injection layer 13 takes the form of a layer of a conducting organic material. The hole-injection layer 13 has a thickness which is typically around 50 nm. Preferred conducting organic materials are polyethylenedioxythiophene (PEDOT) doped with a polyacid, for example polystyrene sulfonic acid (PSS); and polythiophenes, for example Plexcore ® available from Plextronics, Inc.

The intermediate layer 14 (sometimes also referred to as a "hole transporting layer") is supported on the hole injection layer 13, between the hole injection layer 13 and the light-emitting layer 15. The intermediate layer 14 takes the form of a layer comprising or consisting of a polymeric or non-polymeric hole-transporting material. The hole- transporting material of the intermediate layer 14 is preferably an aromatic amine or a polymer comprising arylamine repeat units. Exemplary hole-transporting polymers are as described in WO 99/54385, WO 2005/049546 and WO 2013/108022, the contents of which are incorporated herein by reference. The intermediate layer 14 may typically have a thickness of around 22 nm. In some examples, the intermediate layer 14 may not be required and the hole-injection layer 13 may directly contact the light-emitting layer 15.

The light-emitting layer 15 comprises one or more light-emitting materials and is arranged between the hole injection layer 13 and the cathode layer 18. The light- emitting layer 15 is uniform and continuous, such that when two or more light-emitting material is present, the two or more materials are mixed or blended throughout the light-emitting layer 15. In the example shown in Figure 2, the light-emitting layer 15 is supported on the intermediate layer 14. Light-emitting materials may be fluorescent materials, phosphorescent materials or a mixture of fluorescent and phosphorescent materials. Preferred light-emitting materialsnare conjugated polymers, more preferably polyfluorenes, examples of which are described in Bernius, M. T.,

Inbasekaran, M., O'Brien, J. and Wu, W., Progress with Light-Emitting Polymers. Adv. Mater., 121737-1750, 2000, the contents of which are incorporated herein by reference. In this way, the light-emitting layer 15 may be a light-emitting polymer layer. The light-emitting layer 15 may comprise a host material and a fluorescent or phosphorescent light-emitting dopant. Preferred phosphorescent dopants are row two or row three transition metal complexes, preferably complexes of ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum or gold, most preferably complexes of iridium. The particular material selected for the light-emitting layer 15 depends on the desired range of emission wavelengths of the OLED device 10.

The electron-injection layer 16 is supported on the light-emitting layer 15, between the light-emitting layer 15 and the cathode layer 18. The purpose of the electron-injection layer is to mediate any energy difference between the work function of the cathode layer 18 electrodes (also sometimes referred to as the highest occupied molecular orbital, or HOMO) and the conduction band (also sometimes referred to as the lowest unoccupied molecular orbital, or LUMO) of the light-emitting layer 15. The electron-injection layer 16 typically has a thickness of around 10 nm. The electron-injection layer 16 comprises or consists of an n-doped, non-polymeric or polymeric conductive material. The electron injection layer 16 is preferably a conductive polymer comprising one or more arylene repeat units, optionally one or more repeat units selected from fluorene, phenylene and anthracene. Suitable n-dopants are 2,3~dihydro-iH-benzoimidazoIes, optionally 1,3-Dimethyl-2-phenyl-2,3-dihydro-iH-benzoimidazole (DMBI) and 4-(2,3- Dmydro-i,3-dimethyl-iH-bena

Alternatively, the electron-injection layer 16 may be formed of a metal compound. Preferably, the metal compound is a metal fluoride, more preferably an alkali or alkali earth fluoride, most preferably LiF, NaF or KF.

For some combinations of cathode material and light-emitting material, the electron injection layer 16 may be omitted. Optionally, an additional electron transporting layer (not shown), sometimes also referred to as a "hole-blocking" layer, may be provided between the electron injection layer 16 and the light-emitting layer 15. An electron transporting layer conducts electrons but does not conduct holes. In some examples, the electron-injection layer 16 may provide the functions of an electron transporting layer in addition to those of the electron-injection layer 16.

The cathode layer 18 is disposed over the electron-injection layer 16 and the pixel definition layer 17. The cathode layer 18 includes one or more second electrodes 24, 27, 32 (Figures 6 to 8). In some examples, the cathode layer 18 may take the form of a single, continuous first electrode. In other examples, the cathode layer 18 may be patterned into a number of separate second electrodes in order to permit individual pixels or groups of pixels to be separately addressable. The cathode layer is formed of conductive material, often metallic. The cathode layer 18 may take the form of a metallic layer, preferably aluminium. Alternatively, the cathode layer 18 may be printed using conductive ink containing conductive particles such as, for example, silver particles or carbon black. The cathode layer 18 does not contain poIy(3,4- ethylenedioxythiophene) GPEDOT).

Preferably, the second electrode of the cathode layer 18 consist of a metal, more preferably a metal having a work function of more than 3.5 eV, preferably at least 4.0 eV, most preferably aluminium. The cathode layer 18 may take the form of a thin metallic layer deposited by sputtering or evaporation.

A further layer comprising or consisting of a metal having a work function of more than 3.5 eV, preferably at least 4.0 eVmay be disposed adjacent to the cathode layer 18.

Work functions of elemental metals are as given in the CRC Handbook of Chemistry and Physics, 87^th Edition, 12-114. For any given element, the first listed work function value applies if more than one work function value is listed.

In the example shown in Figure 2, the pixel definition layer 17 is supported on the electron-injection layer 16. The pixel definition layer 17 is formed by printing an organic insulator such as, for example, a dielectric ink, a photo-resist polymer or other similar insulating, printable inks. The ink selection depends upon the insulating properties and also upon the printability in terms of parameters such as wettability and the extent of ink bleeding away from the location of deposition. Ink selection also dependent upon compatibility with the OLED layer upon which the pixel definition layer is printed. For example, a first ink may be used to print the pixel definition layer 17 over the hole-injection layer. However, when the pixel definition layer 17 is printed over the light emitting layer 15, a second ink maybe preferred instead. Preferably, the ink selected will set/cure to provide a pixel definition layer 17 which may withstand voltages up to 5 V across a thickness of 1 μm.

The pixel definition layer 17 includes one or more apertures defining one or more corresponding pixel areas. At least part of the cathode layer 18 may be separated from the electron-injection layer 16 by the pixel definition layer 17. The pixel definition layer 17 may be sufficiently thick to function as a cathode separator layer. When the pixel definition layer 17 is sufficiently thick to function as a cathode separator layer, the cathode layer 18 may be deposited as a thin layer by evaporation or sputtering without the need for a mask.

The OLED devices of the present specification are intended for applications in which each individual pixel area is relatively large and uniformly emissive. The OLED devices of the present specification are not intended for providing high pixel density displays, such as those used by, for example, televisions, monitors, mobile telephones, tablet computers and so forth. Each aperture has a minimum dimension of greater than or equal to 0.5 mm, determined as the minimum dimension of an aperture within the plane of the pixel definition layer 17. In some examples, each aperture may have a minimum dimension of greater than or equal to 1 mm, greater than or equal to 2 mm, greater than or equal to 5 mm or greater than or equal to 10 mm. In other examples, each aperture may have an area of greater than or equal to 0.25 mm^a, greater than or equal to 1 mm², greater than or equal to 10 mm², or greater than or equal to 100 mm².

When the pixel definition layer 17 includes two or more apertures to define two or more corresponding pixel areas, each of the hole-injection layer 13, the intermediate layer 14, the light-emitting layer 15 and the electron-injection layer 16 spans the two or more apertures continuously. In this way, the complexity of the OLED device 10 is reduced. In particular, the active pixel areas of the OLED device 10 need not be defined until the printing of the pixel definition layer 17. This allows for a layer structure comprising the substrate 11, anode layer 11, hole-injection layer 13, optional intermediate layer 14, Ught-emitting, layer 15 and electron-injection layer 16 to be quickly customised for a specific configuration of active pixel areas in a simple one step process of printing the pixel definition layer 17.

Referring also to Figure 3, a second OLED device 19 is shown.

The second OLED device 19 is the same as the first OLED device 10, except that the pixel definition layer 17 has been printed on the light-emitting layer 15.

Referring also to Figure 4, a third OLED device 20 is shown.

The third OLED device 20 is the same as the first and second OLED devices 10, 19, except that the pixel definition layer 17 has been printed on the intermediate layer 14. Referring also to Figure 5, a fourth OLED device 21 is shown.

The fourth OLED device 21 is the same as the first, second and third OLED devices 10, 19, 20, except that the pixel definition layer 17 has been printed on the hole-injection layer 13.

The precise position of the pixel definition layer 17 within the OLED layer structure is not critical. OLED devices may include more or fewer layers than the first to fourth OLED devices 10, 19, 20, 21, and the pixel definition layer 17 may be printed directly on any layer of an OLED device stack, provided that the pixel definition layer is separated from the anode layer 12 by at least the hole-injection layer 13. In this way, the pixel definition layer 17 may be printed to define the active pixel areas after or during deposition of the active OLED layers. This may help to facilitate high throughput processing, for example, in a roll-to-roll printing process in the case when the substrate 11 is flexible.

Anode and cathode laver geometries

An OLED device 10, 19, 20, 21 may employ a variety of different layouts for the first electrodes of the anode layer 12, the second electrodes of the cathode layer 18 and the two or more apertures of the pixel definition layer 17.

Referring also to Figure 6, a first pixel area configuration 22 is shown. The first pixel area configuration 22 is produced by a first anode layer 12a, a first cathode layer 18a and a first pixel definition layer 17a. The remaining layers 11, 13, 14, 15, 16 of the OLED device lo, 19, 20, 21 are continuous and substantially uniform, and are not shown in Figure 6 for reasons of brevity. The first anode layer 12a takes the form of a single continuous first electrode 23 and the first cathode layer 18a takes the form of a single continuous second electrode 24. The first pixel definition layer 17a includes a number of apertures 25a, 25g forming corresponding active pixel areas. For example, the apertures 25a, 25g may be shaped and arranged to form an image, design or logo. When current is driven between the anode and cathode layers 12a, 18a, the regions of the light-emitting layer 15 which coincide with the apertures 25a, 25g will emit light and the image, design or logo will be illuminated. Overlying colour filters, for example disposed on the opposite side of the substrate n to anode layer 12a, may allow different apertures 25a, 25g to be viewed as different colours. Referring also to Figure 7, a second pixel area configuration 26 is shown.

The second pixel area configuration 26 is produced by a second anode layer 12b, a second cathode layer 18b and a second pixel definition layer 17b. The remaining layers 11, 13, 14, 15, 16 of the OLED device io, 19, 20, 21 are continuous and substantially uniform, and are not shown in Figure 7 for reasons of brevity.

In the same way as the first pixel area configuration 22, the second anode layer 12b of the second pixel area configuration 26 takes the form of a single continuous first electrode 23. Unlike the first pixel area configuration 22, the second cathode layer 18b takes the form of a plurality of individual pixel electrodes 27. The second pixel definition layer 17a includes a number of individual pixel apertures 28 forming corresponding active pixel areas. In the example shown in Figure 7, each individual pixel aperture takes the form of a square aperture, and the individual pixel apertures are arranged in a regular grid. An individual pixel electrode 27 is provided

corresponding to and overlying each of the individual pixel apertures 28. In this particular example, the individual pixel electrodes 27 are square, with a side length slightly longer than that of the individual pixel apertures 28. Each individual pixel electrode 27 is connected to a corresponding conductive trace 29. In this way, each pixel electrode 27 maybe individually addressed to cause light emission from the active pixel area defined by the corresponding individual pixel aperture 28. Overlying colour filters, for example disposed on the opposite side of the substrate 11 to anode layer 12a, may allow different individual pixel apertures 28 to be viewed as different colours.

Referring also to Figure 8, a third pixel area configuration 30 is shown.

The third pixel area configuration 30 is produced by a third anode layer 12c, a third cathode layer 18c and a third pixel definition layer 17c. The remaining layers 11, 13, 14, 15, 16 of the OLED device 10, 19, 20, 21 are continuous and substantially uniform, and are not shown in Figure 8 for reasons of brevity. The third anode layer 12c includes a number of rectangular, elongate first electrodes 31, each elongate first electrode 31 extending in a first direction oriented parallel to the y- axis shown in Figure 8. The elongate first electrodes 31 are spaced apart in a second direction, the second direction being different to the first direction y. In the example shown in Figure 8, the second direction is aligned parallel to the x-axis. The third cathode layer includes a number of rectangular, elongate second electrodes 32, each elongate second electrode 32 extending in the second direction x. The elongate second electrodes 32 are spaced apart in the first direction y. The third pixel definition layer 17c includes a number of apertures 33 defining or partly defining pixel areas corresponding to each intersection of the first and second elongate electrodes 31, 32. In the example shown in Figure 8, the apertures 33 take the form of rectangular, elongate apertures extending in the first direction y and spaced apart in the second direction x. Alternatively, the apertures 33 may take the form of rectangular, elongate apertures extending in the second direction x and spaced apart in the first direction y. In either case, each aperture 33 defines two edges of active pixel areas corresponding to intersections of the first and second electrodes 31, 32. Alternatively, the apertures 33 defining pixel areas corresponding to each intersection of the first and second elongate electrodes 31, 32 may take the form of individual pixel apertures 28, as for the second pixel area configuration 26.

Each of the first and second elongate electrodes 31, 32 is configured to be individually addressable. In this way, each active pixel area defined by the intersection of the first and second elongate electrodes 31, 32 and by the apertures 33 may be illuminated by addressing an appropriate combination of first and second elongate electrodes 31, 32. Overlying colour filters, for example disposed on the opposite side of the substrate 11 to anode layer 12a may allow different active pixel areas to be viewed as different colours.

Experimental results

Referring also to Figure 9, light emission is shown from each of an OLED device 1 useful for understanding the invention, and also from examples of the second, third and fourth OLED devices 19, 20, 21.

It may be observed that light emission is achieved for the example of the second OLED device 19, in which the pixel definition layer 17 has been printed directly onto the Iight- emitting layer 15. Similarly, light emission may be observed from the example of the third OLED device 20 in which the pixel definition layer 17 has been printed directly onto the intermediate layer 14, and from the example of the fourth OLED device 21 in which the pixel definition layer 17 has been printed directly onto the hole-injection layer 14. The active pixel areas of the example second, third and fourth OLED devices 19, 20, 21 are observed to be slightly reduced with respect to the example of the OLED device 1. The reduction in active pixel area is believed to be the result of ink flow into the active pixel area during printing of the pixel definition layers 17. It may be expected that process optimisation will permit such reductions in the active pixel area to be reduced or avoided entirely. For example, slight modifications of the print mask area or ink viscosity maybe made so as to optimise the process and reduce or avoid unwanted ink flows during printing of the pixel definition layer 17.

Referring also to Figure 10, current-voltage (IV) curves are shown corresponding to the OLED devices shown in Figure 9.

The solid line, labelled SUB, corresponds to the example of the OLED device 1 having pixels defined by bank structures 4 deposited on the substrate 2. The dotted line, labelled LEP, corresponds to the example of the second OLED device 19, having the pixel definition layer 17 printed directly onto the light-emitting layer 15. The dashed line, labelled IL, corresponds to the example of the third OLED device 20 having the pixel definition layer 17 printed directly onto the intermediate layer 14. The chained line, labelled R, corresponds to the example of the fourth OLED device 21 having the pixel definition layer 17 printed directly onto the hole-injection layer 13. The data have been normalised according to the active areas determined based on Figure 9.

It may be observed that even accounting for differences in observed emissive areas, as visible in Figure 9, the examples of the second, third and fourth OLED devices 19, 20, 21 show reduced currents in response to a given voltage. However, it may also be observed that the reduction in current observed for proof-of-concept devices may be reduced or eliminated as the process is further optimised.

In the examples shown in Figures 9 and 10, all OLED devices 1, 19, 20, 21 included an electron injection layer 16 in the form of a sodium fluoride, NaF, layer overlaid with an aluminium cathode layer 18 in the form of an aluminium layer. The NaF and aluminium layers were both deposited using vacuum techniques for the purposes of the example OLED devices. In the examples shown in Figures 9 and 10, all of the OLED devices l, 19, 20, 21 included an intermediate layer 14.

First method of manufacturing an OLED device

Referring also to Figure 11, a process-flow diagram of a method of manufacturing the first OLED device 10 is shown.

The transparent or translucent anode layer 12 is deposited on the transparent or translucent substrate 11 (step Si). The first electrodes forming the transparent or translucent anode layer are preferably formed of ITO, and may be deposited using standard lithographic techniques. Alternatively, the transparent or translucent anode layer 12 may be formed using a printing process. Preferred printing processes include screen printing and ink-jet printing. Other suitable printing processes include gravure or flexographic printing. The transparent or translucent substrate 11 may be rigid, but is preferably flexible.

It is possible to use a transparent or translucent substrate 11 having a transparent or translucent anode layer 12 pre-deposited thereon. In such an example, the deposition of the transparent or translucent anode layer 12 (step Si) may be omitted.

The hole-injection layer 13 is deposited over the transparent or translucent anode layer 12 and the transparent or translucent substrate 11 to form a continuous layer (step S2). Optionally, if an intermediate layer 14 is to be used, the intermediate layer 14 is deposited on the hole-injection 13 layer to form a continuous layer (step S3). The light- emitting layer 15 is deposited over the hole-injection layer 13 or, if included, the intermediate layer 14, in either case to form a continuous layer (step S4).

Each of the hole-injection layer 13, intermediate layer 14 and light-emitting layer 15 may be deposited by spin coating, or by printing. Preferred printing processes include screen printing and ink-jet printing. Other suitable printing processes include gravure or flexographic printing. Alternatively, any method of solution processing polymers may be employed, provided that the resulting hole-injection layer 13, intermediate layer 14 and/or light-emitting layer 15 are continuous on the underlying layer or layers. The hole-injection layer 13, intermediate layer 14 and light-emitting layer 15 are preferably deposited having a relatively uniform thicknesses. The electron-injection layer 16 is deposited over the light-emitting layer 15 to form a continuous layer (step S5). The electron-injection layer 16 maybe non-polymeric, for example a metal-fluoride such as NaF. Preferably, the electron-injection layer 16 takes the form of a layer of conductive polymeric material. The electron-injection layer 16 is preferably deposited having a relatively uniform thickness.

When the electron-injection layer 16 is a metal-fluoride such as NaF, the electron- injection layer 16 may be deposited by evaporation or sputtering methods. When the electron-injection layer 16 is a layer of conductive polymeric material, the electroninjection layer 16 may be formed by spin-coating or printing. Preferred printing processes include screen printing and ink-jet printing. Other suitable printing processes include gravure or flexographic printing. Alternatively, any method of solution processing polymers may be employed, provided that the resulting electron- injection layer 16 is continuous on the underlying layer or layers.

The pixel definition layer 17 is printed onto the electron-injection layer 16 (step S6). Preferred printing processes include screen printing and ink-jet printing. Other suitable printing processes include gravure or flexographic printing. The pixel definition layer 17 is formed from an insulating polymeric material such as, for example, a printable photo-resist material.

Printing of the pixel definition layer 17 is useful for the OLED devices according to the present specification because these OLED devices are intended to provide relatively large area, uniformly emissive pixel areas. By contrast, pixel definition layers 17 printed using a preferred method of screen printing may be poorly suited to producing high pixel density displays such as, for example, televisions, monitors or screens for mobile phones, tablet computers and so forth.

The cathode layer 18 is deposited over the pixel definition layer 17 and the portions of the electron-injection layer which are exposed by the apertures of the pixel definition layer 17 (step S7). The cathode layer is formed of conductive material, often metallic. The cathode layer 18 may take the form of a sputtered or evaporated metallic layer, preferably formed of aluminium. Alternatively, the cathode layer 18 maybe printed using conductive ink containing conductive particles such as, for example, silver particles or carbon black. The cathode layer 18 does not contain poly(3,4- ethylenedioxythiophene) (PEDOT). In another alternative, the cathode layer may be deposited as a continuous layer and subsequently patterned using laser ablation. A laser ablation process may damage underlying active OLED layers such as the electronic-injection layer 16, light emitting layer 15, intermediate layer 14 and hole-injection layer 13. However, since the ablated regions are not intended to emit light, any such damage from laser ablation may be acceptable, provided that the heat affected zone (HAZ) of the laser used in the ablation process is not excessively large. The OLED device 10 is then sealed/encapsulated to protect the active OLED layers from environmental conditions such as moisture and so forth (step S8). One example of suitable sealing takes the form of an aluminium foil (not shown) having a thickness of 20 μm laminated to an outer layer (not shown) of polyethylene terephthalate (PET) having a thickness of 25 μm. The outer layer (not shown) may be chemically or thermally bonded to the foil (not shown), or alternatively the foil (not shown) may be deposited onto or chemically/thermally bonded to the outer layer (not shown) before the sealing is applied to the OLED device 10 using a layer of pressure sensitive adhesive. The sealing is not limited to this example, and any other sealing which sufficiently reduces the ingress of moisture into the OLED device 10 may be used instead.

The first method of manufacturing an OLED device 10 maybe carried out substantially using high volume roll-to-roll processing techniques, for example when the cathode layer 18 is also printed. When the cathode layer 18 is deposited by evaporation or sputtering, the preceding steps (steps Si to S6) may be performed using roll-to-roll processing techniques. In addition to the hereinbefore described advantage of reduced device complexity, the possibility of manufacturing OLED devices 10 using high volume methods may increase throughout and/or reduce costs. The method can be adapted to produce the second, third or fourth OLED devices 19, 20, 21 by re-ordering the printing of the pixel definition layer 17.

For example, in a method of manufacturing the second OLED device 19, the printing of the pixel definition layer 17 (step S6) is carried out after the deposition of the light- emitting layer 15 (step S4) and before the deposition of the electron-injection layer 16 (step S5). In a method of manufacturing the third OLED device 20, the printing of the pixel definition layer 17 (step S6) is carried out after the deposition of the intermediate layer 14 (step S3) and before the deposition of the light-emitting layer 15 (step S4).

In a method of manufacturing the fourth OLED device 21, the printing of the pixel definition layer 17 (step S6) is carried out after the deposition of the hole-injection layer 13 (step S2) and before the deposition of the intermediate layer 14 (step S3). Second method of manufacturing an OLED device

Refening also to Figure 12, a second method of manufacturing a first OLED device 10 is shown.

A section of pre-deposited OLED sheet (not shown) is received (step S9). The pre- deposited OLED sheet takes the form of a layer structure including the transparent or translucent substrate 11 having the transparent or translucent anode layer 12 disposed on the transparent or translucent substrate 11. The transparent or translucent anode layer 12 may be a single continuous first electrode 23 or the transparent or translucent anode layer 12 may be patterned with two or more first electrodes, for example elongate first electrodes 31. The hole-injection layer 13 is disposed on the anode layer 17 as part of the layer structure. The light-emitting layer 15 is disposed on the hole-injection layer 13 as part of the layer structure. Optionally, the intermediate layer 14 maybe disposed between the hole-injection layer 13 and the light-emitting layer 15. The electron injection layer 16 is disposed on the light-emitting layer 15 as part of the layer structure. The electron-injection layer 16 of the pre-deposited OLED sheet (not shown) is in the form of a layer of conductive polymeric material. In the layer structure of the pre- deposited OLED sheet (not shown), each of the hole-injection layer, the light-emitting layer and the electron injection layer is a continuous layer. The pre-deposited OLED sheet (not shown) does not include a cathode layer 18.

The transparent or translucent substrate 11 is preferably flexible so that the pre- deposited OLED sheet (not shown) is also flexible. This permits the pre-deposited OLED sheet (not shown) to be supplied in large quantities from a roll. The pixel definition layer 17 is printed onto the pre-deposited OLED sheet (not shown), directly onto the electron-injection layer 16 (step S10) in the same way as for the first method (see step S6). The cathode layer 18 is deposited (step S11) in the same way as for the first method (see step S7). The OLED device 10 is sealed to prevent

environmental degradation of the OLED materials (step S12) in the same way as for the first method (step S8).

In this way, the pre-deposited OLED sheet (not shown) may be adapted to define an end-user's required active pixel areas in a single printed step. This may be particularly useful for low-volume production runs, for example prototype or bespoke products. Even for high-volume production, the second method may have lower initial set-up costs and does not require expertise in solution processing methods for making OLEDs, since the final manufacturer need only define the active pixel regions by printing the pixel definition layer 17 before subsequently depositing the cathode layer 18.

There are some restrictions which arise from pre-deposition of the anode layer 12. However, the second method provides a great degree of flexibility and control for defining the active pixel areas by printing the pixel definition layer 17.

Modifications

It will be appreciated that many modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of OLED devices, and which maybe used instead of or in addition to features already described herein.

Features of one embodiment may be replaced or supplemented by features of another embodiment.

In some examples of the first OLED device 10, the pixel definition layer may be printed to a thickness sufficient to act as a cathode separator. This may enable use of a uniform deposition process for the cathode layer 18, with the pixel definition layer 17 thickness causing the cathode layer 18 to be discontinuous at the edges of the apertures so as to define isolated second electrodes. For example, the pixel definition layer 17 may have a thickness of greater than or equal to 100 nm. The pixel definition layer may have a thickness of greater than or equal to 1 μm, greater than or equal to 10 μm or greater than or equal to 100 μπι. The pixel definition layer may have a thickness of no more than 500 μm. The use of a uniform deposition process for the cathode layer 18 may be more reliable if the pixel definition layer 17 is printed to include an "overhang" so as to increase the discontinuity of the cathode layer 18.

For example, referring also to Figure 13, a fifth OLED device 34 is shown.

The fifth OLED device 34 is the same as the first OLED device 10, except that the pixel definition layer 17 is replaced by a second pixel definition layer 35. The second pixel definition layer 35 is approximately the same thickness as the pixel definition layer 17 when intended for use as a cathode separator. The main difference to the pixel definition layer 17 is that the apertures 36 of the second pixel definition layer 35 have an area which generally decreases through the thickness of the second pixel definition layer 35 in a direction away from the anode layer 12. In this way, an upper surface 37 of the second pixel definition layer 35 which contacts the cathode layer 18 overhangs a lower surface 38 of the second pixel definition layer 35 which contacts the electron- injection layer 16. The projection of the aperture 36 in the upper surface 37 onto the electron-injection layer 16 defines a shadow region 39, within which no, or negligible, quantities of cathode material will be deposited during a uniform deposition of the cathode layer 18.

Compared to using a thick pixel definition layer 17 as a cathode separator, the second pixel definition layer 35 is expected to provide more reliable isolation of separate electrodes of the cathode layer 18. This will improve the yield of functional OLED devices 34 by reducing the incidence of cathode layer 18 short circuits.

Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

1. An organic light-emitting diode device comprising a layer structure which comprises:

a transparent or translucent substrate;

a transparent or translucent anode layer disposed on the transparent or translucent substrate and comprising one or more first electrodes; .

a hole-injection layer disposed over the anode layer;

a light-emitting layer disposed over the hole-injection layer;

a cathode layer disposed over the light-emitting layer and comprising one or more second electrodes; and

a pixel definition layer disposed within the layer structure between the hole- injection layer and the cathode layer, the pixel definition layer formed of a printed organic insulator and comprising one or more apertures defining one or more corresponding pixel areas.

2. An organic light-emitting diode device according to claim i, wherein each aperture has a minimum dimension of greater than or equal to substantially 0.5 mm.

3. An organic light-emitting diode device according to claim 1 or claim 2, wherein the pixel definition layer comprises at least two apertures defining at least two corresponding pixel areas, and wherein at least a continuous portion of each of the hole-injection layer and light-emitting layer spans the at least two apertures.

4. An organic light-emitting diode device according to any preceding claim, wherein the layer structure further comprises an intermediate layer disposed between the hole-injection layer and the light-emitting layer.

5. An organic light-emitting diode device according to any preceding claim, wherein the layer structure further comprises an electron-injection layer disposed between the light-emitting layer and the cathode layer.

6. An organic light-emitting diode device according to claim 5, wherein the electron injection layer comprises a polymeric conductive material or the electron injection layer comprises a metal halide material.

7. An organic light-emitting diode device according to claim 5 or claim 6, wherein the layer structure further comprises an electron-transporting layer disposed between the electron-injection layer and the light-emitting layer.

8. An organic light-emitting diode device according to claim 5 of claim 6, wherein the electron-injection layer is also an electron-transporting layer.

9. An organic light-emitting diode device according to any preceding claim, wherein the pixel definition layer is disposed on the hole-injection layer such that the hole-injection layer is between the pixel definition layer and the anode layer.

10. An organic light-emitting diode device according to any one of claims 1 to 8, wherein the pixel definition layer is disposed on the light-emitting layer such that the light-emitting layer is between the pixel definition layer and the anode layer.

11. An organic light-emitting diode device according to claim 4, wherein the pixel definition layer is disposed on the intermediate layer such that the intermediate layer is between the pixel definition layer and the anode layer.

12. An organic light-emitting diode device according to any one of claims 5 to 8, wherein the pixel definition layer is disposed on the electron-injection layer such that the electron-injection layer is between the pixel definition layer and the anode layer.

13. An organic hght-emitting diode device according to claim 7, wherein the pixel definition layer is disposed on the electron-transporting layer such that the electron- transporting layer is between the pixel definition layer and the anode layer.

14. An organic light-emitting diode device according to any preceding claim, wherein the anode layer comprises a single, continuous first electrode.

15. An organic light-emitting diode device according to any preceding claim, wherein the cathode layer comprises a single, continuous second electrode.

16. An organic light-emitting diode device according to any one of claims 1 to 13, wherein: the anode layer comprises a plurality of first electrodes extending in a first direction and spaced apart in a second direction, the second direction being different to the first direction;

the cathode layer comprises a plurality of second electrodes extending in the second direction and spaced apart in the first direction;

the pixel definition layer includes apertures defining pixel areas corresponding to each intersection of the first and second electrodes.

17. An organic light-emitting diode device according to any preceding claim, wherein the substrate is a flexible substrate.

18. An organic light-emitting diode device according to any preceding claim, wherein the cathode layer comprises conductive ink.

19. An organic light-emitting diode device according to any one of claims 1 to 17, wherein the cathode layer comprises a thin metallic layer deposited by sputtering or evaporation.

20. An organic light-emitting diode device according to claim 19, wherein the pixel definition layer is sufficiently thick to function as a cathode separator layer.

21. An organic light-emitting diode device according to claim 19 or claim 20, wherein the area of each aperture decreases through the thickness of the pixel definition layer in a direction away from the anode layer.

22. An organic light-emitting diode device according to any preceding claim, wherein the light-emitting layer is a light-emitting polymer layer.

23. A layer structure comprising:

a transparent or translucent substrate;

a transparent or translucent anode layer disposed on the transparent or translucent substrate and comprising one or more first electrodes;

a hole-injection layer disposed over the anode layer;

a light-emitting layer disposed over the hole-injection layer;

wherein each of the hole-injection layer and the light-emitting layer is a continuous layer.

24. A layer structure according to claim 23, further comprising a continuous intermediate layer disposed between the hole-injection layer and the light-emitting layer.

25. A layer structure according to claim 23 or claim 24, further comprising a continuous electron injection layer disposed over the light-emitting layer.

26. A layer structure according to claim 25, further comprising a continuous electron-transporting layer disposed between the electron-injection layer and the light- emitting layer.

27. A layer structure according to any one of claims 23 to 26, wherein the light- emitting layer is a light-emitting polymer layer.

28. A method comprising:

receiving a transparent or translucent substrate;

depositing a transparent or translucent anode layer over the transparent or translucent substrate, the transparent or translucent anode layer comprising one or more first electrodes;

depositing a hole-injection layer over the anode layer;

depositing a light-emitting layer over the hole-injection layer;

printing a pixel definition layer such that hole-injection layer is between the pixel definition layer and the anode layer, the pixel definition layer being formed of an organic insulator and comprising one or more apertures defining one or more corresponding pixel areas

29. A method according to claim 28, further comprising depositing an intermediate layer between the hole-injection layer and the light-emitting layer.

30. A method according to claim 28 or claim 29, further comprising depositing an electron-injection layer over the light-emitting layer;

31. A method according to claim 30, wherein the electron-injection layer is formed of a polymeric conductive material or a metal halide material.

32. A method according to claim 30 or claim 31, further comprising depositing an electron-transporting layer between the electron-injection layer and the light-emitting layer.

33. A method according to any one of claims 28 to 32, wherein the pixel definition layer is printed onto the hole-injection layer such that the hole-injection layer is between the pixel definition layer and the anode layer.

34. A method according to any one of claims 28 to 32, wherein the pixel definition layer is printed onto the light-emitting layer such that the light-emitting layer is between the pixel definition layer and the anode layer.

35. A method according to claim 29, wherein the pixel definition layer is printed onto the intermediate layer such that the intermediate layer is between the pixel definition layer and the anode layer.

36. A method according to any one of claims 30 to 32, wherein the pixel definition layer is printed onto the electron-injection layer such that the electron-injection layer is between the pixel definition layer and the anode layer.

37. A method according to claim 32, wherein the pixel definition layer is printed onto the electron-transporting layer such that the electron-transporting layer is between the pixel definition layer and the anode layer.

38. A method comprising:

receiving a layer structure, the layer structure comprising:

a transparent or translucent substrate;

depositing a hole-injection layer over the anode layer;

depositing a light-emitting layer over the hole-injection layer

printing a pixel definition layer such that hole-injection layer is between the pixel definition layer and the anode layer, the pixel definition layer being formed of an organic insulator and comprising one or more apertures defining one or more corresponding pixel areas.

39. A method according to claim 38, further comprising depositing an intermediate layer between the hole-injection layer and the light-emitting layer.

40. A method according to claim 38 or claim 39, further comprising depositing an electron-injection layer over the light-emitting layer.

41. A method comprising:

receiving a layer structure, the layer structure comprising:

a transparent or translucent substrate;

a hole-injection layer disposed over the anode layer;

a light-emitting layer disposed over the hole-injection layer;

wherein each of the hole-mjection layer and light-emitting layer is a continuous layer;

printing a pixel definition layer onto the electron-injection layer, the pixel definition layer being formed of an organic insulator and comprising one or more apertures defining one or more corresponding pixel areas.

42. A method according to claim 41, wherein the layer structure further comprises an intermediate layer disposed between the hole-injection layer and the light-emitting layer.

43. A method according to claim 41 or claim 42, wherein the layer structure further comprises an electron-injection layer disposed over the light-emitting layer.

44. A method according to claim 43, wherein the layer structure further comprises an electron transporting layer disposed between the electron-injection layer and the hght-emitting layer.

45. A method comprising:

receiving a layer structure according to any one of claims 23 to 27;

printing a pixel definition layer over the light-emitting layer, the pixel definition layer being formed of an organic insulator and comprising one or more apertures defining one or more corresponding pixel areas.

46. A method according to any one of claims 28 to 45, wherein each aperture has a minimum dimension of greater than or equal to 0.5 mm.

47. A method according to any one of claims 38 to 45, wherein the pixel definition layer comprises at least two apertures defining at least two corresponding pixel areas, and wherein at least a continuous portion of each of the hole-injection layer and light- emitting layer spans the at least two apertures.

48. A method of making an organic light-emitting diode device comprising:

the method according to any one of claims 28 to 47;

depositing a cathode layer over the light-emitting layer.

49. A method according to claim 48, wherein the cathode layer is deposited by printing.

50. A method according to claim 48, wherein the cathode layer is deposited by evaporation or sputtering.

51. A method according to any one of claims 28 to 50, wherein the light-emitting layer is a light-emitting polymer layer.