WO2007116369A1 - An organic diode and a method for producing the same - Google Patents

An organic diode and a method for producing the same Download PDF

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Publication number
WO2007116369A1
WO2007116369A1 PCT/IB2007/051267 IB2007051267W WO2007116369A1 WO 2007116369 A1 WO2007116369 A1 WO 2007116369A1 IB 2007051267 W IB2007051267 W IB 2007051267W WO 2007116369 A1 WO2007116369 A1 WO 2007116369A1
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layer
organic
substrate
diode device
electron
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PCT/IB2007/051267
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French (fr)
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Michael Buechel
Petrus C. P. Bouten
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Koninklijke Philips Electronics N.V.
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/80—Constructional details
    • H10K50/805—Electrodes
    • H10K50/82—Cathodes
    • H10K50/826—Multilayers, e.g. opaque multilayers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/80—Constructional details
    • H10K30/81—Electrodes

Definitions

  • the present invention relates to an organic diode device having a glass substrate and a stack of layers on the substrate, the stack comprising a first electrode layer on the substrate, an organic layer on the first electrode layer, and a top layer, comprising a second electrode layer, on the organic layer.
  • the invention further relates to a method for producing such a device.
  • Such a device is disclosed e.g. in US 6,819,036 B2.
  • Devices of this kind may be used for lighting purposes and can have a large active area.
  • devices of this kind are not always reliable, and sometimes failures occur.
  • An object of the present invention is therefore to provide an organic diode device of the initially mentioned kind which is more reliable.
  • an organic diode device then has a substrate of glass, such as soda-lime or borosilicate glass, and a stack of layers on the substrate, the stack comprising a first electrode layer on the substrate, an organic layer on the first electrode layer, and a top layer, comprising a second electrode layer, on the organic layer, wherein the second electrode layer comprises a material from the following group of metals: Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, Yttrium, Cerium, Lanthanum, Molybdenum, Niobium, Tantalum, Tungsten, Vanadium, and Zirconium.
  • a substrate of glass such as soda-lime or borosilicate glass
  • the thermal expansion of the substrate may be matched with the thermal expansion of the top layer which provides an improved reliability, since the risk of short circuits between the first and second electrode layers may be reduced.
  • the second electrode layer may comprise an electron- injection layer and thereon an evaporated layer of Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, or Yttrium.
  • An evaporated metal layer can be applied directly on the electron- injection layer without damaging the organic layer.
  • the cathode layer may comprise an electron-injection layer, a protective layer evaporated on the electron-injection layer, and a sputtered or e-beam deposited layer on the evaporated layer.
  • the second electrode layer may comprise a structure with three or more metal layers, and the top layer may further comprise a thin film packaging layer.
  • the use of a laminated structure provides the possibility to choose the thermal expansion coefficient of the top layer, such that it closely matches the corresponding coefficient of the substrate.
  • the organic diode device may be arranged to function as a lighting device or as a solar cell device.
  • the active surface of the device may be greater than 0.5 cm 2 .
  • the method comprises depositing a first electrode layer on the substrate, depositing an organic layer on the first electrode layer, and depositing a top layer, comprising a second electrode layer, on the organic layer, wherein the top layer comprises a material from the following group of metals: Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, Yttrium, Cerium, Lanthanum, Molybdenum, Niobium, Tantalum, Tungsten, Vanadium, and Zirconium.
  • the second electrode layer may be created by applying an electron- injecting layer and evaporating thereon an layer of Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, or Yttrium.
  • the second electrode layer may created by applying an electron- injecting layer, evaporating a protection layer on the electron-injecting layer, and sputter or e- beam depositing a layer on the evaporated layer.
  • a thin film packaging layer may further be applied on top of the second electrode layer.
  • Fig 1 illustrates schematically an organic diode device.
  • Fig 2a and 2b illustrate how short circuits may occur in an organic diode device.
  • Fig 3 illustrates an organic diode device with a three-layer cathode.
  • Fig 1 illustrates schematically an organic diode device according to known art.
  • the device comprises a substrate 1, that typically may be made of transparent soda-lime glass and may be e.g. 0.4- 1.1 mm thick.
  • a first electrode layer 2 typically an anode layer, is deposited which may preferably be made of ITO (Indium Tin Oxide) which is both conductive and transparent.
  • ITO Indium Tin Oxide
  • This layer may be deposited on top of the substrate by means e.g. of sputter deposition and may be e.g. 150 nm thick.
  • an organic layer 3 is applied e.g. by spin coating, vapor deposition or printing. This layer may be e.g.
  • a second electrode layer 4 typically a cathode layer, is deposited, which may consist of aluminum and may be e.g. 100 nm thick.
  • the cathode layer further comprises an electron-injecting layer (not shown) at the organic layer to provide a suitable work function as seen from the organic layer.
  • the electron- injecting layer may typically comprise Barium, Lithium- fluoride, an organic Lithium salt, a highly doped organic material or a similar compound.
  • the anode and the cathode layers have different work functions.
  • the diode device may, in addition to the above mentioned layers, comprise hole-injecting layers, electron- and hole transportation layers, as well as electron- and hole blocking layers. These layers are not shown individually in the schematic fig 1, but are summarized as the organic layer 3.
  • the diode device begins emitting light 5 in the organic layer 3 due to electron-hole recombination. This light is emitted through the transparent anode and substrate layers 2,1.
  • Fig 2a and 2b illustrates how short circuits may occur in an organic diode device according to known art.
  • the substrate 1 comprises soda-lime glass, which is a common and inexpensive material and has a linear thermal expansion coefficient ( ⁇ ) of 9.0 ppm/K.
  • the device may be used e.g. as a backlighting arrangement for an LCD (liquid crystal display) in a mobile phone.
  • fig 2a ambient temperature e.g. 2O 0 C
  • the diode device is heated to about 70 0 C, and the situation illustrated in fig 2b occurs.
  • This temperature may appear high, but is perfectly realistic, e.g. if a mobile phone is placed under the windscreen of a parked car on a sunny day. It should be noted that specifications in the automotive industry often demand operation in the range between -4O 0 C and +12O 0 C.
  • the increased temperature makes all layers in the stack expand.
  • the cathode 4 will also expand in relation to the substrate 1.
  • the effect of this fact may be that the cathode layer 4 becomes somewhat wrinkled, even if this effect may be exaggerated in fig 2b.
  • the intermediate organic layer 3 is very soft compared to the substrate 1 and the cathode 4, and does not stop the top layer comprising the cathode from becoming wrinkled.
  • the heating of the device will thus result in the cathode 4 locally moving closer to the anode 2 on top of the substrate 1.
  • the increased current may damage the organic layer 3, and this damaging effect may not disappear simply because the device is subsequently cooled down. Instead, the damage may be permanent.
  • the inventors have found that the risk for a short circuit can be substantially decreased if the thermal expansion of the top layer ⁇ top , comprising the cathode, and the thermal expansion coefficient ⁇ su bstrate substrate can be matched, i.e.
  • the difference (Xdiff between these two coefficients can be kept lower than in the above example. It has further been understood that the organic layer need not be matched with the substrate and top layer, since the organic layer has a comparatively low elastic modulus. Therefore a normal organic, electroluminescent layer can still be used, having a much higher linear thermal expansion coefficient, e.g. over 40 ppm/K.
  • a single layer cathode which is matched with the substrate is used.
  • This cathode still comprises a thin (a few nanometers) electron-injecting layer, but this layer can be disregarded in a mechanical aspect. Therefore the term single layer refers to the top layer over the electron- injecting layer.
  • the Odifr of this cathode- substrate combination should be as low as possible. For different substrates, different cathode materials are conceivable.
  • the cathode may then preferably be chosen e.g. from the following materials:
  • These materials may be applied by thermal evaporation directly on top of the electron- injecting layer, without damaging the organics beneath.
  • the cathode material may preferably be chosen from the same table, preferably from the materials with thermal expansion coefficients in the lower range.
  • the top layer may, in addition to the cathode layer (including the electron- injection layer, which is so thin that it can be neglected from a mechanical point of view), comprise additional layers.
  • a thin film packaging layer 10 as illustrated in fig 1 may be applied. This layer serves to protect the cathode layer 4 from oxidization.
  • This additional layer gives a contribution to the effective linear thermal expansion coefficient of the top layer. More generally, by providing a laminated top layer, the effective thermal expansion coefficient of the top layer can in fact be chosen.
  • a first layer in a sandwiched structure has a first coefficient (X 1 , a first thickness hi, and a first elastic modulus E 1
  • a second layer has a second coefficient ⁇ 2 , a second thickness h 2 , and a second elastic modulus E 2
  • the effective thermal expansion coefficient ⁇ e ff of the structure may be calculated as:
  • Typical thin film packaging materials that may be used in this context are:
  • a protective layer comprising Aluminum, Silver or a material from table 1 may be applied on top of the electron-injection layer in order to allow the use of a material in the cathode that cannot be applied by thermal evaporation, such as the materials in the table below, which may be applied by sputter or e-beam deposition. These materials have low thermal expansion coefficients and may be used to match the cathode with the substrate.
  • the protective layer should, if e.g. Aluminum is used, typically be at least 50nm, in order to protect the organics from hot electrons and Ultra Violet light. However, depending on the application, thinner layers may be allowed in some cases.
  • an aluminum layer may be applied by thermal evaporation, on top of the electron-injection layer in order to protect the organic layer.
  • the electron- injection layers are usually so thin that they cannot provide this effect themselves.
  • a metal chosen from the table above is applied by sputter or e- beam deposition, e.g. molybdenum.
  • the organic layer is protected by the Aluminum layer, and is not damaged by the sputter or e-beam deposition.
  • the Molybdenum layer serves to reduce the effective thermal expansion coefficient of the top layer to a desired level, and its thickness may be chosen accordingly, using the above formula.
  • a thin film packaging layer may then be applied on top of the Molybdenum layer, if desired.
  • a protection layer by evaporation also allows the materials in Table 1 to be sputtered or deposited by e-beam as a cathode sub-layer. Sputter and e-beam deposition is generally quicker than thermal evaporation.
  • Fig 3 illustrates an embodiment with three metal sub-layers. Here a first cathode layer 7 is deposited on top of the organic layer 3. On top of the first cathode layer, a second 8 and a third 9 cathode layer is deposited. The three layers together form the cathode. The electron- injection layer beneath the first cathode layer 7 is not shown.
  • an Aluminum-Titanium- Aluminum cathode structure is used.
  • the first and third cathode layers 7, 9 may then be relatively thin and comprise Aluminum, and the second thicker layer 8 may comprise Titanium.
  • the Titanium, or other material may be applied by sputtering, since the organic layer 3 is protected by the first Aluminum cathode layer 7, which is already applied.
  • the linear thermal expansion coefficient of this three layer structure may be calculated with the above formula where the thickness of layers 7 and 9 add up to the parameter hi .
  • a four layer metal cathode may be used, e.g. (in order from the organic layer) Aluminum-Mo lybdenium- Aluminum-Titanium. The above mentioned formula may then be expanded to:
  • the first electrode, closest to the substrate, is the anode
  • the second electrode, on top of the organic layer is the cathode.
  • an OLED device where the first electrode is the cathode and the second electrode is the anode would be possible. This depends on the work functions of the used electrode materials, where the interface with the organic layer is realized.
  • the OLED device may be used a lighting device, but also solar cell applications are possible.
  • the inventive idea is particularly useful in devices having a large active area, e.g. greater than 0.5 cm 2 .
  • the total difference in thermal expansion between the substrate and the top layer may cause the cathode to move closer to the anode to a smaller extent.
  • the invention relates to an OLED device with improved reliability.
  • the thermal expansion coefficients of the OLED substrate and top layer are closely matched, such that it can be avoided, to a great extent, that short circuit damages occur when the OLED undergoes a substantial temperature change.
  • the organic layer/layers between the substrate and the top layer may however have thermal expansion coefficients deviating substantially from those of the top layer and the substrate.

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Abstract

The present invention relates to an OLED device with improved reliability. The thermal expansion coefficients of the OLED substrate (1) and cathode (4) are closely matched, such that it can be avoided, to a great extent, that short circuit damages occur when the OLED undergoes a substantial temperature change. The organic layer/layers (3) between the substrate and the cathode may however have thermal expansion coefficients deviating substantially from those of the cathode and the substrate.

Description

An organic diode and a method for producing the same
FIELD OF THE INVENTION
The present invention relates to an organic diode device having a glass substrate and a stack of layers on the substrate, the stack comprising a first electrode layer on the substrate, an organic layer on the first electrode layer, and a top layer, comprising a second electrode layer, on the organic layer. The invention further relates to a method for producing such a device.
BACKGROUND OF THE INVENTION
Such a device is disclosed e.g. in US 6,819,036 B2. Devices of this kind may be used for lighting purposes and can have a large active area. However, devices of this kind are not always reliable, and sometimes failures occur.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide an organic diode device of the initially mentioned kind which is more reliable.
This object is achieved by means of an organic diode device as defined in claim 1 and a method as defined in claim 9.
More specifically, an organic diode device then has a substrate of glass, such as soda-lime or borosilicate glass, and a stack of layers on the substrate, the stack comprising a first electrode layer on the substrate, an organic layer on the first electrode layer, and a top layer, comprising a second electrode layer, on the organic layer, wherein the second electrode layer comprises a material from the following group of metals: Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, Yttrium, Cerium, Lanthanum, Molybdenum, Niobium, Tantalum, Tungsten, Vanadium, and Zirconium.
In such an organic diode device the thermal expansion of the substrate may be matched with the thermal expansion of the top layer which provides an improved reliability, since the risk of short circuits between the first and second electrode layers may be reduced. The second electrode layer may comprise an electron- injection layer and thereon an evaporated layer of Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, or Yttrium. An evaporated metal layer can be applied directly on the electron- injection layer without damaging the organic layer. Alternatively, the cathode layer may comprise an electron-injection layer, a protective layer evaporated on the electron-injection layer, and a sputtered or e-beam deposited layer on the evaporated layer.
The second electrode layer may comprise a structure with three or more metal layers, and the top layer may further comprise a thin film packaging layer. The use of a laminated structure provides the possibility to choose the thermal expansion coefficient of the top layer, such that it closely matches the corresponding coefficient of the substrate.
The organic diode device may be arranged to function as a lighting device or as a solar cell device. The active surface of the device may be greater than 0.5 cm2. In a corresponding method for producing an organic diode device, having a glass substrate, the method comprises depositing a first electrode layer on the substrate, depositing an organic layer on the first electrode layer, and depositing a top layer, comprising a second electrode layer, on the organic layer, wherein the top layer comprises a material from the following group of metals: Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, Yttrium, Cerium, Lanthanum, Molybdenum, Niobium, Tantalum, Tungsten, Vanadium, and Zirconium.
The second electrode layer may be created by applying an electron- injecting layer and evaporating thereon an layer of Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, or Yttrium. Alternatively, the second electrode layer may created by applying an electron- injecting layer, evaporating a protection layer on the electron-injecting layer, and sputter or e- beam depositing a layer on the evaporated layer.
A thin film packaging layer may further be applied on top of the second electrode layer. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 illustrates schematically an organic diode device. Fig 2a and 2b illustrate how short circuits may occur in an organic diode device.
Fig 3 illustrates an organic diode device with a three-layer cathode.
DESCRIPTION OF PREFERRED EMBODIMENTS
Fig 1 illustrates schematically an organic diode device according to known art. The device comprises a substrate 1, that typically may be made of transparent soda-lime glass and may be e.g. 0.4- 1.1 mm thick. On top of the substrate 1 a first electrode layer 2, typically an anode layer, is deposited which may preferably be made of ITO (Indium Tin Oxide) which is both conductive and transparent. This layer may be deposited on top of the substrate by means e.g. of sputter deposition and may be e.g. 150 nm thick. On top of the anode layer, an organic layer 3 is applied e.g. by spin coating, vapor deposition or printing. This layer may be e.g. 100 nm thick and may in itself comprise a stack of different materials. On top of the organic layer 3, a second electrode layer 4, typically a cathode layer, is deposited, which may consist of aluminum and may be e.g. 100 nm thick. Typically, the cathode layer further comprises an electron-injecting layer (not shown) at the organic layer to provide a suitable work function as seen from the organic layer. The electron- injecting layer may typically comprise Barium, Lithium- fluoride, an organic Lithium salt, a highly doped organic material or a similar compound. As is well known to the skilled person, the anode and the cathode layers have different work functions. Further, the diode device may, in addition to the above mentioned layers, comprise hole-injecting layers, electron- and hole transportation layers, as well as electron- and hole blocking layers. These layers are not shown individually in the schematic fig 1, but are summarized as the organic layer 3. When a positive voltage is applied between the anode and the cathode layers of the organic diode device, the diode device begins emitting light 5 in the organic layer 3 due to electron-hole recombination. This light is emitted through the transparent anode and substrate layers 2,1.
Fig 2a and 2b illustrates how short circuits may occur in an organic diode device according to known art. In this case the substrate 1 comprises soda-lime glass, which is a common and inexpensive material and has a linear thermal expansion coefficient (α) of 9.0 ppm/K. The cathode comprises aluminum (α=23.8 ppm/K), and the organic layer has a linear thermal expansion coefficient higher than 40 ppm/K. The device may be used e.g. as a backlighting arrangement for an LCD (liquid crystal display) in a mobile phone. Starting out from the initial conditions in fig 2a (ambient temperature e.g. 2O0C) the diode device is heated to about 70 0C, and the situation illustrated in fig 2b occurs. This temperature may appear high, but is perfectly realistic, e.g. if a mobile phone is placed under the windscreen of a parked car on a sunny day. It should be noted that specifications in the automotive industry often demand operation in the range between -4O0C and +12O0C.
The increased temperature makes all layers in the stack expand. However, since the linear thermal expansion coefficient of the cathode 4 is much higher than the one of the substrate 1 , the cathode 4 will also expand in relation to the substrate 1. As illustrated in fig 2b, the effect of this fact may be that the cathode layer 4 becomes somewhat wrinkled, even if this effect may be exaggerated in fig 2b. The intermediate organic layer 3 is very soft compared to the substrate 1 and the cathode 4, and does not stop the top layer comprising the cathode from becoming wrinkled.
At some locations, e.g. in area 6 as illustrated in fig 2b, the heating of the device will thus result in the cathode 4 locally moving closer to the anode 2 on top of the substrate 1. This results in an increased electric field strength at these locations, which may cause an increased leakage current up to a short-circuit. The increased current may damage the organic layer 3, and this damaging effect may not disappear simply because the device is subsequently cooled down. Instead, the damage may be permanent. The inventors have found that the risk for a short circuit can be substantially decreased if the thermal expansion of the top layer αtop, comprising the cathode, and the thermal expansion coefficient αsubstrate substrate can be matched, i.e. the difference (Xdiff between these two coefficients can be kept lower than in the above example. It has further been understood that the organic layer need not be matched with the substrate and top layer, since the organic layer has a comparatively low elastic modulus. Therefore a normal organic, electroluminescent layer can still be used, having a much higher linear thermal expansion coefficient, e.g. over 40 ppm/K.
A description now follows of different examples providing improved reliability in an OLED device in this way.
Matched substrate-cathode pair with single layer cathode
In a first embodiment, a single layer cathode which is matched with the substrate is used. This cathode still comprises a thin (a few nanometers) electron-injecting layer, but this layer can be disregarded in a mechanical aspect. Therefore the term single layer refers to the top layer over the electron- injecting layer. The Odifr of this cathode- substrate combination should be as low as possible. For different substrates, different cathode materials are conceivable.
If the substrate is made of soda-lime glass (α=9.0 ppm/K), which is an inexpensive and common material, the cathode may then preferably be chosen e.g. from the following materials:
Figure imgf000006_0001
These materials may be applied by thermal evaporation directly on top of the electron- injecting layer, without damaging the organics beneath.
For instance, the difference Odifr between the thermal expansion coefficients for soda-lime glass and Titanium is only αgiass-ατi= 9.0-8.6=0.4, which provides an excellent match. Titanium may be applied using Titanium-sublimation pumps.
Of course, combinations of the above materials could also be used. Borosilicate glass is another suitable substrate material (α=4.8 ppm/K). When this glass material is used, the cathode material may preferably be chosen from the same table, preferably from the materials with thermal expansion coefficients in the lower range.
Composite top layers The top layer may, in addition to the cathode layer (including the electron- injection layer, which is so thin that it can be neglected from a mechanical point of view), comprise additional layers. Thus a thin film packaging layer 10, as illustrated in fig 1 may be applied. This layer serves to protect the cathode layer 4 from oxidization.
This additional layer gives a contribution to the effective linear thermal expansion coefficient of the top layer. More generally, by providing a laminated top layer, the effective thermal expansion coefficient of the top layer can in fact be chosen.
If a first layer in a sandwiched structure has a first coefficient (X1 , a first thickness hi, and a first elastic modulus E1, and a second layer has a second coefficient α2, a second thickness h2, and a second elastic modulus E2, the effective thermal expansion coefficient αeff of the structure may be calculated as:
Figure imgf000007_0001
Typical thin film packaging materials that may be used in this context are:
Figure imgf000007_0002
Additionally, a protective layer, comprising Aluminum, Silver or a material from table 1 may be applied on top of the electron-injection layer in order to allow the use of a material in the cathode that cannot be applied by thermal evaporation, such as the materials in the table below, which may be applied by sputter or e-beam deposition. These materials have low thermal expansion coefficients and may be used to match the cathode with the substrate. The protective layer should, if e.g. Aluminum is used, typically be at least 50nm, in order to protect the organics from hot electrons and Ultra Violet light. However, depending on the application, thinner layers may be allowed in some cases.
Figure imgf000008_0001
Thus, in one embodiment, an aluminum layer may be applied by thermal evaporation, on top of the electron-injection layer in order to protect the organic layer. The electron- injection layers are usually so thin that they cannot provide this effect themselves. On top of the aluminum layer, a metal chosen from the table above is applied by sputter or e- beam deposition, e.g. molybdenum. The organic layer is protected by the Aluminum layer, and is not damaged by the sputter or e-beam deposition. The Molybdenum layer serves to reduce the effective thermal expansion coefficient of the top layer to a desired level, and its thickness may be chosen accordingly, using the above formula. A thin film packaging layer may then be applied on top of the Molybdenum layer, if desired.
The application of a protection layer by evaporation also allows the materials in Table 1 to be sputtered or deposited by e-beam as a cathode sub-layer. Sputter and e-beam deposition is generally quicker than thermal evaporation. Fig 3 illustrates an embodiment with three metal sub-layers. Here a first cathode layer 7 is deposited on top of the organic layer 3. On top of the first cathode layer, a second 8 and a third 9 cathode layer is deposited. The three layers together form the cathode. The electron- injection layer beneath the first cathode layer 7 is not shown.
In one three layer embodiment, an Aluminum-Titanium- Aluminum cathode structure is used. The first and third cathode layers 7, 9 may then be relatively thin and comprise Aluminum, and the second thicker layer 8 may comprise Titanium. In this embodiment, the Titanium, or other material, may be applied by sputtering, since the organic layer 3 is protected by the first Aluminum cathode layer 7, which is already applied. The linear thermal expansion coefficient of this three layer structure may be calculated with the above formula where the thickness of layers 7 and 9 add up to the parameter hi . In another embodiment, a four layer metal cathode may be used, e.g. (in order from the organic layer) Aluminum-Mo lybdenium- Aluminum-Titanium. The above mentioned formula may then be expanded to:
OL3Jl3E3
Figure imgf000009_0001
Needless to say, even more layers may be used.
In the embodiments described above, the first electrode, closest to the substrate, is the anode, and the second electrode, on top of the organic layer, is the cathode. Of course an OLED device where the first electrode is the cathode and the second electrode is the anode would be possible. This depends on the work functions of the used electrode materials, where the interface with the organic layer is realized.
The OLED device may be used a lighting device, but also solar cell applications are possible. As is realized from the discussion in connection with figs 2a and 2b, the inventive idea is particularly useful in devices having a large active area, e.g. greater than 0.5 cm2. For smaller devices the total difference in thermal expansion between the substrate and the top layer may cause the cathode to move closer to the anode to a smaller extent.
In summary, the invention relates to an OLED device with improved reliability. The thermal expansion coefficients of the OLED substrate and top layer are closely matched, such that it can be avoided, to a great extent, that short circuit damages occur when the OLED undergoes a substantial temperature change. The organic layer/layers between the substrate and the top layer may however have thermal expansion coefficients deviating substantially from those of the top layer and the substrate. The invention is not restricted to the described embodiments. It can be altered in different ways within the scope of the appended claims.

Claims

CLAIMS:
1. An organic diode device, having a glass substrate (1) and a stack of layers on the substrate, the stack comprising a first electrode layer (2) on the substrate, an organic layer (3) on the first electrode layer, and a top layer (4), comprising a second electrode layer, on the organic layer, wherein the top layer comprises a material from the following group of metals: Cobalt,
Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, Yttrium, Cerium, Lanthanum, Molybdenum, Niobium, Tantalum, Tungsten, Vanadium, and Zirconium.
2. An organic diode device according to claim 1, wherein the second electrode layer comprises an electron- injecting layer and thereon an evaporated layer of Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, or Yttrium.
3. An organic diode device according to claim 1, wherein the second electrode layer comprises an electron- injecting layer, a protection layer evaporated on the electron- injecting layer, and a sputtered or e-beam deposited layer on the evaporated layer.
4. An organic diode device according to claim 3, wherein the top layer comprises a structure with three or more metal layers.
5. An organic diode device according to any of the preceding claims, wherein the top layer further comprises a thin film packaging layer.
6. An organic diode device according to any of the preceding claims, which is arranged to function as a lighting device.
7. An organic diode device according to any of claim 1-5, which is arranged to function as a solar cell device.
8. An organic diode device according to any of the preceding claims, which has an active surface greater than 0.5 cm2.
9. A method for producing an organic diode device, having a glass substrate (1), the method comprising depositing a first electrode layer (2) on the substrate, depositing an organic layer (3) on the first electrode layer, and depositing a top layer (4), comprising a second electrode layer, on the organic layer, wherein the top layer comprises a material from the following group of metals: Cobalt, Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, Yttrium, Cerium, Lanthanum, Molybdenum, Niobium, Tantalum, Tungsten, Vanadium, and Zirconium.
10. A method according to claim 9, wherein the second electrode layer is created by applying an electron-injecting layer and evaporating thereon an layer of Cobalt,
Chromium, Dysprosium, Iron, Neodymium, Nickel, Praseodymium, Samarium, Titanium, or Yttrium.
11. A method according to claim 9, wherein the second electrode layer is created by applying an electron-injecting layer, evaporating a protection layer on the electron- injecting layer, and sputter or e-beam depositing a layer on the evaporated layer.
12. A method according to any of claims 9-11, wherein a thin film packaging layer is applied on top of the second electrode layer.
PCT/IB2007/051267 2006-04-11 2007-04-10 An organic diode and a method for producing the same WO2007116369A1 (en)

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