WO2008135891A1

WO2008135891A1 - Organic light emitting diode device

Info

Publication number: WO2008135891A1
Application number: PCT/IB2008/051620
Authority: WO
Inventors: Stefan P. Grabowski; Hans-Helmut Bechtel
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2007-05-02
Filing date: 2008-04-28
Publication date: 2008-11-13
Also published as: TW200913339A

Abstract

The invention relates to an organic light emitting diode (OLED) device (1) with a substrate material (10) as a carrier, which is coated or superimposed by several sequent layers, comprising: a first electrode layer (11), a plurality of organic layers (12) for light emission and charge transport, a second electrode layer (13), at least one light scattering layer (14) and a protective layer (15), whereas the emitted light of the organic layers (12) leaves the OLED by passing the substrate material (10).

Description

ORGANIC LIGHT EMITTING DIODE DEVICE

FIELD OF THE INVENTION

The present invention relates to an organic light emitting diode device with a substrate material as a carrier, which is coated or superimposed by several sequent layers, comprising a first electrode layer, a plurality of organic layers for light emission and charge transport and a second electrode. Additionally a light scattering layer is applied to the organic light emitting diode device. BACKGROUND OF THE INVENTION

Organic light emitting diodes (OLED) are of great interest as superior flat-panel systems in recent years. These systems utilise current passing through a thin- film of organic material to generate light. The colour of the emitted light and the efficiency of the energy conversion from current to light are determined by the composition of the organic thin- film material and in particular of the surrounding layer system. In general, OLEDs comprise a substrate material, which is used as a carrier plate, whereas the different layers are deposited on each other by subsequent depositing methods.

These layers consist of very thin deposited materials with thicknesses between 5 and 200 nm of organic substances on glass or plastic substrates, covered with electrically conducting and optically transparent oxide layers. The first electrode layer, located next to the substrate material, and the light emitting organic layers, the anode layer is deposited, which comprises an Indium tin oxide (ITO) material, whereas the second electrode layer may be performed as the cathode layer featuring an aluminium or silver material.

Above this electrode-organic layers-electrode - sandwich are arranged several functional layers. The plurality of organic layers may concern fluorescent or phosphorescent emitter layers, hole injection, transportation and blocking layers, electron transportation, injection and blocking layers, whereas these layers feature a thickness of approximately 5 nm to lOOnm.

The US patent application US 2006/0250084 Al discloses an organic light emitting diode (OLED) device, which is performed as a top emitting OLED. The top emitting OLEDs describe an emission of the generated light within the organic layers by placing the aluminium cathode at the opposite of the substrate material. This OLED comprises a light scattering layer, whereas scattering layers are known to improve light output from an OLED device. The scattering layer is applied next to the organic layers, and is deposited adjacent to the substrate material. Light emitted from the OLED device at higher angles than the critical angle of total reflection that would have otherwise been trapped can penetrate into the scattering layer and be scattered out of the device. The use of light scattering techniques is well known and is suitable to increase the light-output efficiency of said OLED devices, whereas different arrangements of the light scattering layers are also well known. But usually the arrangement of said scattering layers are deposited adjacent to the substrate material, and represent the first layer, onto which the subsequent layers, comprising the organic layers for light emitting, are being deposited.

Indeed, many different layer systems are known, but unfortunately by applying the scattering layer as the layer, which is arranged between the substrate material and the light emitting layers leads to the effect, that the scattering layer features a surface roughness after depositing, which is much higher than the roughness of the other layers and in particular higher than the roughness of the substrate material surface. But the method of manufacturing these OLEDs requires layers, being deposited one onto the other in a subsequent way on the light scattering layer. Unfortunately the surface roughness, based on the surface of said scattering layer, carries forward to each following layer. This effect leads to a lowered electrical efficiency, lower durability, and features an inhomogeneous flaw distribution. Moreover the organic layers for light emission may feature irregularities within said layers, which lead to black spots and a lowered brightness of the emitted light in inhomogeneous local fields.

Next to the limited durability and the reduced electrical light efficiency the appearance of OLEDs in a non-powered state is affected negatively by applying a light scattering layer next to the light-out-coupling surface. The reflectivity is reduced due to the absorbing, coloured or luminescence scattering centres, embodied as small particles within the light scattering layer. Moreover, the surface of the non-powered OLED features a coloured appearance, if luminescent scattering layers like phosphor layers are used within the scattering layer. This leads to a limited applicability of the OLED, because a neutral colour mirror- like surface in the non-powered state of the OLED mostly is desirable.

SUMMARY OF THE INVENTION Thus, an object of the invention is to eliminate the above mentioned disadvantages. In particular it is an objective of the present invention to provide an organic light emitting diode, featuring a high electric- optic efficiency, high stability and lifetime and a valuable appearance in a non-powered state.

This objective is achieved by an organic light emitting diode device as taught by claim 1 of the present invention. Preferred embodiments of the invention are defined by the subclaims.

The invention discloses, that the at least one light scattering layer is arranged onto the second electrode layer on the opposite of the substrate material, whereas the emitted light of the organic layers leaves the OLED by passing the substrate material.

The layer system according to the invention takes advantage of an improved depositing behaviour of the electrode layers and the plurality of organic layers for light emission, because these layers may directly be deposited onto the substrate material, even though a light scattering layer is applied close to the organic layers. After depositing the electrode layers and the plurality of organic layers onto the substrate material, the scattering layer may be arranged on the system of different layers, and the organic layers are not negatively affected by a negative surface roughness due to the deposition of the scattering layer. This leads to an improved durability of the OLED, whereas a local damaging of the organic layers can be avoided and dark regions and reduced electric-optic efficiency in local areas within the emitting field of the OLED may not appear.

Moreover, the OLED with a layer system according to the invention features an improved appearance in a non-powered state. Due to the arrangement of the light scattering layer behind the electrode layers and the plurality of organic layers with respect to the light out coupling surface, the negative effect of appearance due to the scattering material, and in particular the scattering centres can be avoided.

The present invention also is embodied in improvements to the outer front and rear surfaces of the OLED, because a protective layer is arranged onto backside of the layer system, arranged on the opposite site of the substrate material. Advantageously, the substrate material or the protective layer comprise a glass material, with hard and scratch resistant properties. By applying a protective layer next to the light scattering layer, a damaging of the layer system may be avoided and leads to a robust OLED device.

The present invention even embodies a first electrode layer and a second electrode layer, which comprise transparent materials with respect to the visual range, whereas the transparency of the second electrode layer features a value of at least 50%. The material of the second electrode layer may be performed as an aluminium material and preferred an argent material. The transparent materials of the electrode layers permit a light passing and thus an interaction of the light, emitted by the plurality of organic layers, with the light scattering layer behind the second electrode.

The part of the light, which is emitted by the organic layers and which is directed towards said light scattering layer, may interact with said scattering layer as long as the light may leave the OLED device by passing the substrate material without a trap-effect of total reflection at the boundary surfaces between the layers or substrate material. Advantageously, the protective layer features a reflective coating, arranged towards the light scattering layer, whereas the protective layer comprises a thickness of at least 0.7mm. The reflective coating preferably comprises an aluminium layer with a thickness of 0.05μm to 1.5μm and preferred 0.2μm. The material of the reflective coating likewise can be selected of the group of metal coating, comprising an argent layer.

In the manufacturing of the protective layer including the reflective coating on the surface towards the light scattering layer, it is intended to deposit the reflective coating onto the surface of the protective layer before the protective layer will be combined with the substrate material including the different layers. Furthermore, it is an advantage to deposit the light scattering layer onto the reflective coating of the protective layer, before these two systems, including the substrate material with different layers and the protective layer with the coating and the scattering layer are combined to each other. By applying this succession of manufacturing- and assembling steps it is possible to obtain an even surface both of the reflective coating and the light scattering layer, which leads to an increased electrical-optical efficiency and an improved performance of the entire OLED.

According to another embodiment of the present invention the organic light emitting diode is provided with an edge sealing arrangement, which is arranged between the substrate material and the protective layer. Both, the substrate material and the protective layer may consist of a glass material, thus, both glass substrates may be sealed by laser welding, by gluing or any other joining technique. If the substrate material and the protective layer are joined to each other, the joining results in a sealing effect, in order to protect said different layers and in particular the electrode layers and the light emitting organic layers against external environmental influence. The edge sealing arrangement forms a closed outline across the whole OLED. In particular a glass laser welding process may be preferably applied, because a bridging of the gap between the both glass substrates is possible.

In order to improve the interaction of the light, emitted by the organic layers, with the light scattering layer, a transparent optical coupling layer is arranged between the second electrode layer and the light scattering layer. The transparent optical coupling layer is arranged adjacent to the light scattering layer or is provided by the scattering layer itself.

It is an advantage, if the optical coupling layer features a refractive index n > 1.25, preferred n > 1.4, more preferred n > 1.5 and most preferred n > 1.7. The better the refractive index of the optical coupling layer, the better is the interaction of the emitted light with the scattering layer. The scattering layer can be provided with a thickness between 5...200μm, whereas the number of different layers within the scattering layer can be higher than one single layer. The final layer of the scattering layers may then be provided as the optical transparent coupling layer.

In its preferred embodiment, the light scattering layer comprises a dielectric, optical not scattering matrix material with a refractive index nl, which contains particles with a refractive index n2, whereas the absolute value of the difference n2 - nl amounts at least iWf = 0.05. The particles within the matrix material provide a high number of scattering centres. The scattering effect is based on the difference between the first and the second refractive index nl and n2, whereas higher differences between both refractive indices lead to a higher scattering effect. The name particle is used here for the scattering centre, which means that also gas inclusions in the matrix material such as air bubbles are considered as scattering particles with n2 = 1. The material composition between the matrix material and the material of the particles can be of any known combination, applied for scattering layers. In the following, preferred material compositions are named.

According to a first embodiment of the material composition of the scattering layer, the optical matrix material is performed as an oil, comprising a perfluoric-polyether oil or a silicone oil, whereas the particles are performed as zirconium oxide particles (ZrC^) with a concentration of approximately 5% within the oil. Advantageously, the average diameter of the particles amounts approximately d(50%) = 800nm. Whereas in general the average diameters of the particles may amount between 100 nm and 30 μm. By applying this material composition with 5vol-% of zirconium oxide the OLED emits light within the white wavelength spectrum. The oil, in particular the perfluoric-polyether oil, is named as FOMBLIN®, which is used preferably as a scattering fluid for carrying the particles, forming the scattering centres.

According to a second embodiment of the material composition of the scattering layer, the optical matrix material contains fluorescent dyes as perylene, e.g. perylene tetracarbonic acid named as Lumogen® F capable of at least partly converting light passing through this layer by absorbing light of a wavelength λl at the fluorescent components and reemitting this light at a wavelength λ2. Scattering centres within the matrix material may comprise transparent particles or phosphor particles, such as an europium or cerium containing phosphor particle, such as CaS:Eu and YAG:Ce, respectively. The emitted light of the OLED features a wavelength within the blue range. This material-composition leads to a conversion effect within the scattering layer, whereas the colour of the emitted light may be determined by the relation between the YAG- and the CaS-material with respect to the grain size of the crystals and the concentration of composition of the perylene dyes. According to a third embodiment of the material composition of the scattering layer, which also leads to an emission of light within the blue wavelength range, the optical matrix material is based on a fluorescent layer with phosphor or scattering particles, combined with a reflective layer between the substrate material and the first electrode. This arrangement leads to an effect of limiting the blue light emission, and the light features lower colour temperatures. Thus, the first electrode layer is performed as an Indium-Tin-Oxide (ITO) layer, whereas a reflective layer is deposited in between this layer and the substrate material, which comprises a λ/4-layer for limiting direct blue light emission. The influence on the OLED-emission is based on micro- cavity-effects. Micro-cavity-effects lead to spectral narrowing of the emission band, combined with an enhancement of the peak intensity and improved output.

According to a fourth embodiment of the material composition of the scattering layer, combined with an advanced layering of the OLED, the reflective layer is deposited at the substrate material, comprising an interface layer for controlling the relation of emitted light and converted light within the scattering layer. This embodiment relates to a combination of a phosphor scattering layer and a reflective layer within the blue wavelength range at the substrate material, to provide a glass-air-interface. This arrangement allows an influencing of the obtained emission spectrum of the OLED- emission, in order to provide convenient colour properties of the emitted light.

According to a fifth embodiment of the material composition of the scattering layer, this layer comprises a red phosphor material, whereas the organic layers emit light with blue and green wavelength by applying a reflective layer for reflecting blue wavelength at the light out coupling surface. The light emitting organic layers emit light within a blue and a green spectral range, whereas these colours are converted by the scattering layer into a red wavelength. By additional partially reflecting layers in the light out coupling area different relations between red, green and blue light emission may be adjusted. By this way, different colour temperatures of said OLED-light source may be provided with convenient characteristics of the colouring of the OLED and with convenient characteristics of the appearance of the OLED in a non powered state. Additional details, characteristics and advantages of the objective of the invention are disclosed in the depending claims and the following description of the respective figures - which are only shown in an exemplary fashion - show preferred embodiments of the invention, which will be described in conjunction with the accompanying figures, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an organic light emitting diode device with a layer system according to the present invention; Figure 2 shows an organic light emitting diode device with a layer system, including an optical coupling layer between the light scattering layer and the reflective coating on the surface of the protective layer; and

Figure 3 shows an organic light emitting diode device with an edge sealing arrangement. DETAILED DESCRIPTION OF EMBODIMENTS

The organic light emitting diode device 1, shown in Figure 1, comprises a substrate material 10, which is used as a carrier plate. By a depositing procedure, which is not specified within the present invention, several layers are deposited in a subsequent arrangement. Onto the substrate material 10 a first electrode layer 11 is deposited, whereas the first electrode layer 11 may be performed as an Indium-Tin-Oxide (ITO). This ITO-layer features a light transparent characteristic, in order to provide an OLED device 1, which is performed as a bottom emitting OLED. Onto the ITO-layer 11 are deposited several organic layers 12 for light emission and charge transportation. These light emitting layers 12 form the active light emitting part of the entire device 1. These layers may concern fluorescent and phosphorescent emitter layers, a hole blocking layer, an electron transport layer or additionally an electron injection layer, whereas these layers feature a thickness of approximately 5 nm to 100 nm.

Next to the plurality of organic layers 12 a second electrode layer 13 is deposited, in order to perform a sandwich arrangement of two electrode layers 11 and 13 for a current supply to the organic layers 12. The second electrode layer 13 is performed as a transparent electrode layer, which features a transparency of at least 50 %. In the case of phosphor light scattering layers 14, which are deposited next to the second electrode layer 13, the relation between the transmission of the first electrode layer 11 and the second electrode layer 13 may lead to different color rates of the emitted light and different compositions of the emitted light of the device 1. The light scattering layer 14 comprises a dielectric, optical non scattering matrix material, which contains particles in order to provide scattering centers.

Next to the light scattering layer 14 a protective layer 15 is arranged as a last, and thus as an outside layer, whereas the protective layer 15 also can be seen as a substrate material, suitable for material depositing processes. Between the protective layer 15 and the light scattering layer 14 a reflective coating 16 is deposited, in order to provide a mirror effect of the protective layer 15. This reflective coating 16 may comprise a 0.3μm aluminum coating, in order to avoid a top emission of the OLED device 1. In order to point up the interaction of the light scattering layer 14, three different optical paths are exemplary shown and described in the following.

The first optical path of emitted light within the organic layers 12 is shown with an arrow 19. The light, emitted within the organic layers 12, leaves these layers by passing the transparent first electrode layer 11 and the substrate material 10. Due to the angle of no reflection within the boundary surfaces of the different layers and the substrate material 10 the first optical path 19 shows a direct out coupling of light of the OLED device 1. Regarding the second optical path 20 the light shows a total reflection effect at the boundary layer between the organic layers 12 and the first electrode layer 11 due to the angle of reflection and a trap-effect occurs. Therefore, the light reflects at the first electrode layer 11 and is then directed towards the light scattering layer 14 and enters the light scattering layer 14. Within the light scattering layer 14, the direction of the second optical path 20 will be deflected in different directions by the scattering effect, thus the light features different angles.

Hence, the trap effect lasts as long as the angle between the second optical path 20 and the border layers show a total reflection effect. Not until an angle is reached, under which the second optical path 20 may pass the boundary layers, it may leave the optical device 1.

A third exemplary optical path 21 is shown with a reflecting behavior, already described by the second optical path 20, and which shows a total reflection effect at the boundary of the glass-air- surface of the substrate material 10. This reflection leads to deflection of the third optical path into the light scattering layer 14, which leads to an angle between the optical path 21 and the plurality of boundary layers, by which the optical path 21 may be coupled out of the device 1.

In Figure 2 is shown the organic light emitting diode 1 with respect to the present invention. The layer system, comprising the first electrode layer 11 , the organic layers 12 and the second electrode layer 13 is already shown in Figure 1. Between the light scattering layer 14 and the second electrode layer 13 an optical coupling layer 18 is deposited, in order to improve the efficiency of light into the light scattering layer 14. The manufacturing method of the organic light emitting diode device 1 can be based on two parts being manufactured: At first the substrate material 10 is provided with at least the two electrode layers 11 and 13 and the organic layers 12 in between the electrode layers. The second part is embodied in the protective layer 15, which is coated with a reflective coating and the light scattering layer 14. As a final layer the optical coupling layer 18 is deposited onto the light scattering layer 14. As a last manufacturing step part 1 and part 2 will be connected to each other. By this way of manufacturing, a roughness in the surface of the light scattering layer 14 does not lead to a negative effect on the different layers.

In Figure 3 is shown the organic light emitting diode device 1 with the substrate material 10 and the protective layer 15. In between the substrate material 10 and the protective layer 15 are arranged said different layers according to the present invention. At the site bends of the OLED an edge sealing arrangement 17 is shown. This sealing arrangement may be provided as a glue arrangement or a welding arrangement. The edge sealing arrangement 17 is only shown in an exemplary fashion, whereas a sealing effect may also be provided by any different known joining methods of the substrate material 10 and the protective layer 15. The present invention is not limited by the embodiment described above, which is represented as an example only and can be modified in various ways within the scope of protection defined by the appending patent claims. Thus, the invention is also applicable to different embodiments, in particular of the design of the OLED-device.

LIST OF NUMERALS

1 organic light emitting diode device 10 substrate material 11 first electrode layer

12 organic layers

13 second electrode layer

14 light scattering layer

15 protective layer 16 reflective coating

17 edge sealing arrangement

18 optical coupling layer

19 first optical path

20 second optical path 21 third optical path

Claims

CLAIMS:

1. An organic light emitting diode (OLED) device (1) with a substrate material (10) as a carrier, which is coated or superimposed by several sequent layers, comprising: a first electrode layer (11), a plurality of organic layers (12) for light emission and charge transport, a second electrode layer (13), at least one light scattering layer (14) and a protective layer (15), whereas the emitted light of the organic layers (12) leaves the OLED by passing the substrate material (10).

2. A device (1) according to claim 1, characterised in that the substrate material (10) and the protective layer (15) comprise a glass material.

3. A device (1) according to claim 2, characterised in that the substrate material (10) comprises a transparent glass material, in order to perform the organic light emitting diode device (1) for emitting light by passing the light through the substrate material (10).

4. A device (1) according to claim 1 to 3, characterised in that the first electrode layer (11) and the second electrode layer (13) comprise transparent materials with respect to the visual range, whereas the transparency of the second electrode layer (13) features a value of at least 50%.

5. A device (1) according to any of the previous claims, characterised in that the protective layer (15) features a reflective coating (16), arranged towards the light scattering layer (14), whereas the protective layer (15) comprises a thickness of at least 0.1mm and the reflective coating comprises an aluminium layer with a thickness of 0.05μm to 1 μm and preferred 0.2μm.

6. A device (1) according to any of the previous claims, characterised in that an edge sealing arrangement (17) is arranged between the substrate material (10) and the protective layer (15).

7. A device (1) according to any of the previous claims, characterised in that in between the second electrode layer (13) and the light scattering layer (14) is arranged a transparent optical coupling layer (18).

8. A device (1) according to claim 7, characterised in that the optical coupling layer (18) features a refractive index of n > 1.25, preferred n > 1.4, more preferred n > 1.5 and most preferred n > 1.7.

9. A device (1) according to any of the previous claims, characterised in that the light scattering layer (14) comprises a dielectric, optical matrix material with a refractive index nl, which contains particles with a refractive index n2, whereas the absolute value of the difference n2 - nl amounts at least iWf = 0.05.

10. A device (1) according to claim 9, characterised in that the average diameter of the particles within the optical transparent material amounts from

IOnm to lOOμm, preferred from 50nm to 50μm and most preferred from lOOnm to 30μm.

11. A device (1) according to claim 9 or 10, characterised in that the optical matrix material is performed as an oil, comprising a perfluoric-polyether-oil or a silicon oil and the particles are performed as ZrC>2 particles with a concentration of approx. 5% within the oil, featuring an average diameter of approx. 800nm.

12. A device (1) according to claim 9 to 10, characterised in that the optical

> matrix material within the scattering layer (14) contains fluorescent dyes as perylene capable of at least partly converting light passing through this layer by absorbing light of a wavelength λl at the fluorescent components and reemitting this light of a wavelength λ2.