KR101200860B1 - Tandem oled having stable intermediate connectors - Google Patents

Abstract

Tandem OLEDs are anodes; Cathode; A plurality of organic electroluminescent unit devices disposed between the anode and the cathode; And an intermediate connection disposed between each adjacent organic electroluminescent unit, wherein each organic electroluminescent unit comprises at least one light emitting layer, wherein the intermediate connection is a high work function having a work function of at least 4.0 eV. At least a metal layer, wherein the intermediate connection has a sheet resistance higher than 100 kΩ per square, and the high work function metal layer improves the operational stability of the OLED.

Description

Tandem OLED HAVING STABLE INTERMEDIATE CONNECTORS

The present invention relates to the manufacture of tandem (or cascaded or stacked) organic electroluminescent devices by providing a plurality of organic electroluminescent (EL) units.

An organic electroluminescent (EL) device or organic light emitting diode (OLED) is an electronic device that emits light in response to an applied potential. The structure of an OLED in turn comprises an anode, an organic EL medium and a cathode. The organic EL medium disposed between the anode and the cathode usually consists of an organic hole transport layer (HTL) and an organic electron transport layer (ETL). Holes and electrons recombine to emit light in the ETL near the interface of the HTL / ETL. Tang et al., "Organic electroluminescent diodes", Applied Physics Letters , 51, 913 (1987) and commonly assigned US Pat. No. 4,769,292 teach very effective OLEDs using this layer structure. Thereafter, a number of OLEDs with different layer structures have been disclosed. See, for example, Adachi et al., "Electroluminescence in Organic Films with Three-Layer Structure", Japanese Journal of Applied Physics , 27, L269 (1988) and Tang et al. "Electroluminescence of doped organic thin". films ", Journal of Applied There is a three layer OLED containing an organic light emitting layer (LEL) between HTL and ETL, as disclosed in Physics , 65, 3610 (1989). LEL typically comprises a host material doped with a guest material, where the layer structure is represented as HTL / LEL / ETL. There are also other multilayer OLEDs that contain a hole injection layer (HIL) and / or an electron injection layer (EIL) and / or a hole blocking layer and / or an electron blocking layer in the device. These structures further improved the device performance.

In addition, US Pat. No. 6,107,734 to Tanaka et al., Incorporated herein by reference, to further improve the performance of OLEDs; US Pat. No. 6,337,492 to Jones et al .; Japanese Patent Publication No. 2003045676A and US Patent Publication No. 2003/0189401 A1 to Kido et al .; US Patent No. 6,717,358 to Liao et al., US Patent Publication No. 2003/0170491 A1 and commonly assigned US Patent Application No. 10 / 437,195, filed May 13, 2003, entitled “Cascaded Organic Electroluminescent Device Having Connecting Units with n-Type and p-Type Organic Layers "), in-line OLEDs (or stacked OLEDs or cascades), manufactured by vertically stacking several individual OLEDs and driven by a single power source A new class of OLED structures called OLEDs). For example, US Pat. No. 6,107,734 to Tanaka et al. Teaches a 3-EL-unit unit tandem OLED using In-Zn-O (IZO) films or Mg: Ag / IZO films as intermediate connections, pure tris The luminous efficiency of 10.1 cd / A was achieved from the (8-hydroxy-quinoline) aluminum emitting layer. Kido et al., "High Efficiency Organic EL Devices Having Charge Generation Layers", SID 03 Digest , 964 (2003), use In-Sn-O (ITO) films or V ₂ O ₅ films as intermediate connections. A 3-EL-unit tandem OLED was fabricated and achieved luminous efficiency up to 48 cd / A from the fluorescent dye doped emitting layer. Liao et al., "High-efficiency tandem organic light-emitting diodes", Applied Physics Letters , 84, 167 (2004), taught a 3-EL-unit tandem OLED using an organic "pn" junction layer doped as intermediate junction, emitting 136 cd / A from phosphorescent dye doped emitting layer. Efficiency was achieved.

Using organic "p-n" bonding layers as intermediate connections is effective for optical out-coupling and easy manufacture of devices. However, it is also necessary to use inorganic intermediate connections in tandem OLEDs as another method. Therefore, there is still a need for research on stable inorganic intermediate connections.

The use of IZO or ITO films as intermediate connections results in high lateral conductivity resulting in pixel crosstalk problems. In addition, the production of IZO and ITO films requires sputtering, which can cause damage to the underlying organic layer. Although pixel crosstalk can be limited by using a V ₂ O ₅ film as an intermediate junction, V ₂ O ₅ is classified as a highly toxic component (see, for example, the Aldrich catalogue) and is difficult to thermally evaporate.

Summary of the Invention

It is an object of the present invention to produce tandem OLEDs using non-toxic materials.

Another object of the present invention is to manufacture tandem OLEDs with improved operational stability.

It is another object of the present invention to manufacture tandem OLEDs with improved drive voltages.

It is a further object of the present invention to produce tandem OLEDs with improved power efficiency.

Another object of the present invention is to produce tandem OLEDs with improved optical transparency.

These objects include: a) an anode; b) a cathode; c) a plurality of organic electroluminescent unit devices disposed between the anode and the cathode; And d) an intermediate connection disposed between each adjacent organic electroluminescent unit, wherein each organic electroluminescent unit comprises at least one light emitting layer, the intermediate connection having a high work function having a work function of at least 4.0 eV. At least a metal layer, and a metal compound layer, wherein the intermediate connection has a sheet resistance higher than 100 kΩ per square, and a high work function metal layer is achieved by the tandem OLED which improves the operational stability of the OLED. do.

Advantageous Effects of the Invention

An advantage of the present invention is that the materials used to make tandem OLEDs can be nontoxic. This is important for a wide range of applications of OLEDs.

Another advantage of the present invention is that by using a high work function thin layer (thin as small as 0.2 nm) in the intermediate connection, the operational stability of the tandem OLED can be improved.

Another advantage of the present invention is that by using an intermediate connection having a thin layer of high work function metal, the driving voltage of the tandem OLED can be reduced. As a result, the power efficiency of the tandem OLED can be improved.

A further advantage of the present invention is that the intermediate interconnect can be as thin as about 2 nm, thereby achieving effective light transmission in tandem OLEDs.

Another advantage of the present invention is that all the layers used in the production of tandem OLEDs can be produced in the same vacuum chamber by thermal evaporation methods, thus enabling low manufacturing costs and high production yields.

1 is a schematic cross-sectional view of a tandem OLED according to the present invention having a plurality of organic EL unit devices and having an intermediate connection between each organic EL unit device.

2 is a schematic cross-sectional view of one of the organic EL unit apparatuses having the layer structure of "HTL / LEL / ETL" of the tandem OLED according to the present invention.

Figure 3 is a schematic cross-sectional view of an intermediate connection of the tandem OLED according to the invention with a layer structure of "low work function metal layer / high work function metal layer / metal compound layer".

4 is a schematic cross-sectional view of another intermediate connection of the tandem OLED according to the invention with a layer structure of "n-type semiconductor layer / high work function metal layer / metal compound layer".

Figure 5 is a schematic cross-sectional view of another intermediate connection with a layer structure of "high work function metal layer / metal compound layer" of the tandem OLED according to the invention.

6 is a graph of normalized luminance versus operating time of a tandem OLED and reference device according to the invention at room temperature under a constant drive current density of 80 mA / cm ² .

7 is a graph of the drive voltage versus operating time of a tandem OLED and reference device according to the invention at room temperature under a constant drive current density of 80 mA / cm ² .

It should be noted that FIGS. 1-5 are not to scale because the individual layers are too thin and the thickness differences of the various layers are so large that they cannot be shown to scale.

* Explanation of symbols for the main parts of the drawings

100: tandem OLED

110: anode

120: EL unit

120.1: First EL Module

120.2: Second EL Module

120. (N-1): (N-1) th EL unit device

120.N: Nth EL unit device

130: intermediate connection

130.1: First intermediate connection (or first connection)

130.2: second intermediate connection (or second connection)

130. (N-1): (N-1) th intermediate connection (or (N-1) th connection)

140: cathode

150: voltage / current source

160: electrical conductor

220: EL unit

221: hole transport layer

222: light emitting layer

223: electron transport layer

330: intermediate connection

331: low work function metal layer

332: metal layer of high work function

333: metal compound layer

430: intermediate connection

431: n-type semiconductor layer

530: intermediate connection

Commonly assigned U.S. Patent No. 6,717,358 to Liao et al., U.S. Patent Publication No. 2003/0170491 A1 and commonly assigned U.S. Patent Application No. 10 / 437,195, filed May 13, 2003 In the invention (named “Cascaded Organic Electroluminescent Device Having Connecting Units with n-Type and p-Type Organic Layers”), the layer structure of a tandem OLED (or cascaded OLED or stacked OLED) is disclosed. The device structure includes an anode, a cathode, a plurality of organic EL unit devices, and a plurality of connection unit devices (or later referred to as intermediate connections), wherein each intermediate connection is disposed between the two organic EL unit devices. In this tandem structure, only one external power source is needed to connect the anode and cathode (positive potential is applied to the anode and negative potential is applied to the cathode). Having effective light transmission and charge injection, tandem OLEDs exhibit high electroluminescence efficiency.

The present invention improves the performance of OLEDs by making tandem OLEDs and creating intermediate connections in the device that include at least a high work function metal layer and a metal compound layer.

1 shows a tandem OLED 100 according to the present invention. This tandem OLED has an anode 110 and a cathode 140, at least one of which is transparent. N organic EL unit devices 120 (where N is an integer greater than 1) are disposed between the anode and the cathode. These organic EL unit devices, which are sequentially stacked on each other, on the anode and also on the cathode, are referred to as 120.1 to 120.N, where 120.1 is the first EL unit (adjacent to the anode) and 120.N is the Nth Unit device (adjacent to the cathode). The term EL unit device 120 denotes any unit device of the EL unit devices named 120.1 to 120.N in the present invention. An intermediate connecting portion (or connecting portion) 130 is disposed between any two adjacent organic EL unit devices. N organic EL unit devices are accompanied by a total of N-1 intermediate connections, which are referred to as 130.1 to 130. (N-1). The intermediate connecting portion 130.1 is disposed between the organic EL unit devices 120.1 and 120.2. The intermediate connector 130.2 is disposed between the organic EL unit device 120.2 and the next EL unit device, and the intermediate connector 130. (N-1) is an organic EL unit device 120. (N-1) and 120. N) is placed between. The term intermediate connector 130 refers to any of the connections named 130.1 to 130. (N-1) herein. The tandem OLED 100 is externally connected to a voltage / current source 150 via an electrical lead 160.

The potential generated by the voltage / current source 150 between the pair of contact electrodes, anode 110 and the cathode 140, is such that the anode 110 is more positive than the cathode 140. The application of the tandem OLED 100 is activated. The externally applied potential is distributed between these unit devices in proportion to the electrical resistance of each of the N organic EL unit devices. The potential across the tandem OLED injects holes (positively charged carriers) from the anode 110 into the first organic EL unit 120.1 and electrons (negatively charged carriers) from the cathode 140 to N. The second organic EL unit device 120.N. At the same time, electrons and holes are generated at each intermediate connection 130.1 to 130. (N-1) and separated from each intermediate connection. For example, the electrons thus generated at the intermediate connecting portion 130. (N-1) are injected into the organic EL unit 120. (N-1) adjacent to the anode. Similarly, holes generated in the intermediate connecting portion 130. (N-1) are injected into the organic EL unit 120.N adjacent to the cathode. These electrons and holes then recombine in the corresponding organic EL unit to produce light, which is observed through the transparent electrode or electrodes of the OLED. In other words, electrons injected from the cathode strongly flow from the Nth organic EL unit to the first organic EL unit, and emit light in each organic EL unit.

Each organic EL unit 120 of the tandem OLED 100 can support hole and electron transport, and electron hole recombination to generate light. Each organic EL unit device 120 may include a plurality of layers. There are a number of EL multilayer structures known in the art that can be used as the organic EL unit of the present invention. These are HTL / ETL, HTL / LEL / ETL, HIL / HTL / LEL / ETL, HIL / HTL / LEL / ETL / EIL, HIL / HTL / electron blocking layer or hole blocking layer / LEL / ETL / EIL, HIL / HTL / LEL / hole-blocking layer / ETL / EIL. Each organic EL unit of the tandem OLED may have the same or different layer structure as other organic EL unit. The layer structure of the first organic EL unit unit adjacent to the anode is preferably HIL / HTL / LEL / ETL, and the layer structure of the Nth organic EL unit unit adjacent to the cathode is preferably HTL / LEL / ETL / EIL, The layer structure of another organic EL unit device is preferably HTL / LEL / ETL. 2 (EL unit 220) shows that the EL unit 220 has an HTL 221, an LEL 222, and an ETL 223. The EL unit of the tandem OLED 100 according to the present invention ( An embodiment of 120 is shown.

Organic layers of organic EL units can be prepared from small molecular OLED materials or polymeric LED materials, or mixtures thereof, known in the art. The corresponding organic layer of each organic EL unit of the tandem OLED may be the same or different from the other corresponding organic layers. Some organic EL units may be polymers and other units may be small molecules.

Each organic EL unit can be selected to improve performance or to obtain desired properties such as light transmittance through the OLED multilayer structure, driving voltage, luminous efficiency, luminescent color, manufacturability, device stability, and the like.

In order to reduce the driving voltage of the tandem OLED, it is desirable to make each organic EL unit device as thin as possible without sacrificing electroluminescence efficiency. It is preferable that the thickness of each organic EL unit device is less than 500 nm, more preferably 2 to 200 nm. Further, the thickness of each layer in the organic EL unit device is preferably less than 200 nm, more preferably 0.1 to 100 nm.

The number of organic EL unit devices of the tandem OLED is two or more in principle. Preferably, the number of organic EL units of the tandem OLED is such that the luminous efficiency of the cd / A unit is improved or maximized. For lamp applications, the number of organic EL units can be determined according to the maximum power supply voltage.

As is well known, conventional OLEDs include anodes, organic media and cathodes. In the present invention, the tandem OLED includes an anode, a plurality of organic EL unit devices, a plurality of intermediate connectors and a cathode, wherein the intermediate connector is a new feature of the tandem OLED.

For tandem OLEDs to function efficiently, the intermediate connections need to provide effective carrier injection into adjacent organic EL unit devices. Because of lower resistivity than organic materials, metals, metal compounds or other inorganic compounds can be effective for carrier injection. However, low resistivity can result in low sheet resistance, resulting in pixel crosstalk. If the lateral currents that pass through adjacent pixels and cause pixel crosstalk are limited to less than 10% of the current used to drive the pixels, the lateral resistance r _ic of the intermediate connection is eight times the resistance of the tandem OLED. Should be at least Typically, the idle resistance between two electrodes of a conventional OLED is about several kΩ, and the tandem OLED should have a resistance of about 10 to several tens of kΩ between the two electrodes. Therefore, R _ic must be greater than 100 kΩ. Considering that the spacing between each pixel is smaller than 1 square, the sheet resistance of the intermediate connection should be greater than 100 kΩ per square (lateral resistance is equal to the product of the sheet resistance and the square number). Since the sheet resistance is determined by the resistivity and thickness of the film (sheet resistance is equal to the film resistivity divided by the film thickness), if the layer constituting the intermediate connection is selected from metals, metal compounds or other inorganic compounds with low resistivity, If the layer is thin enough, the sheet resistance of the intermediate connections greater than 100 kΩ per square can still be achieved.

Another condition for the tandem OLED to function efficiently is that the light transmittance of the layers constituting the organic EL unit and the intermediate connection must be as high as possible so that the lines generated in the organic EL unit can escape from the unit. . By simple calculation, if the light transmittance of each intermediate connection is 70% of the emitted light, the tandem OLED will never be twice as efficient as the conventional device, regardless of how many EL units there are in the device. There is no big profit because there is no. The layers constituting the organic EL unit are generally light transparent to the lines produced by the EL unit, and therefore their transparency is generally not a concern in the manufacture of tandem OLEDs. As is known, metals, metal compounds or other inorganic compounds may have low transparency. However, when the layer constituting the intermediate connection is selected from metals, metal compounds or other inorganic compounds, light transmission higher than 70% can still be achieved if the layer is sufficiently thin. Preferably, the intermediate connection has a light transmission of at least 75% in the visible region of the spectrum.

Therefore, intermediate connections provided between adjacent organic EL unit devices are important because they are necessary to provide effective electron and hole injection into adjacent organic EL unit devices without causing pixel crosstalk and without sacrificing light transparency. 3 shows one embodiment of the intermediate connection of the present invention. The intermediate connection 330 includes a low work function metal layer 331, a high work function metal layer 332, and a metal compound layer 333. Here, a low work function metal is defined as a metal having a work function of less than 4.0 eV. Similarly, a high work function metal is defined as a metal having a work function of at least 4.0 eV. The low work function metal layer 331 is disposed adjacent to the ETL of the organic EL unit toward the anode, and the metal compound layer 333 is disposed adjacent to the HTL of the other organic EL unit toward the cathode. . The low work function metal layer 331 is selected to provide effective electron injection to adjacent electron transport layers. The metal compound layer 333 is selected to provide effective hole injection to adjacent hole transport layers. Preferably, the metal compound layer includes, but is not limited to, a p-type semiconductor. The high work function metal layer 332 is selected to improve the operational stability of the OLED by preventing possible interactions or interdiffusion between the low work function layer 331 and the metal compound layer 333.

4 shows another embodiment of the intermediate connection of the invention. The intermediate connector 430 includes an n-type semiconductor layer 431, a high work function metal layer 332, and a metal compound layer 333. The n-type semiconductor layer 431 is disposed adjacent to the ETL of the organic EL unit apparatus toward the anode side, and the metal compound layer 333 is disposed adjacent to the HTL of the other organic EL unit apparatus toward the cathode side. By n-type semiconductor layer is meant herein an electrically conductive layer having electrons as the main charge carrier. Likewise, a p-type semiconductor layer means an electrically conductive layer having holes as the main charge carriers. Similar to the low work function metal layer 331 in FIG. 3, the n-type semiconductor layer 431 is selected to provide efficient electron injection into adjacent electron transport layers. As in FIG. 3, the metal compound layer 333 is selected to provide efficient hole injection into adjacent hole transport layers, and the high work function metal layer 332 is formed of the n-type semiconductor layer 431 and the metal compound layer ( 333) is selected to improve the operational stability of the OLED by preventing possible interactions or interdiffusion.

When the ETL of the EL unit is an n-type doped organic layer, the layer structure of the intermediate connector is a high one where the intermediate connector 530 is disposed adjacent to the n-type doped ETL of the organic EL unit toward the anode side. It can be simplified as shown in FIG. 5, which in turn comprises a metal compound layer 333 disposed adjacent to the HTL of the other organic EL unit toward the hydrous metal layer 332 and the cathode side. The metal compound layer 333 is selected to provide efficient hole injection into the adjacent hole transport layer, and the high work function metal layer 332 is a possible interaction between the n-type doped ETL and the metal compound layer 333 or It is chosen to improve the operational stability of the OLED by preventing interdiffusion. As used herein, an n-type doped organic layer means that the layer is electrically conductive and the charge carriers are primarily electrons. Conductivity is provided by the creation of a charge-transfer complex as a result of electron transfer from the dopant to the host material. Depending on the concentration and efficiency of the dopant in donating electrons to the host material, the electrical conductivity of the layer can change over several times. Having an n-type doped organic layer as the ETL of the EL unit, electrons can be efficiently injected into the ETL from adjacent intermediate connections.

In order for the intermediate connection to have an effective light transmission (light transmission of 75% or more in the visible region of the spectrum), an effective carrier injection capacity and an effective operational stability, the thickness of the layer of the intermediate connection must be carefully considered. The low work function metal layer 331 of the intermediate connection has a thickness of 0.1 to 5.0 nm, preferably 0.2 to 2.0 nm. The thickness of the high work function metal layer 332 in the intermediate connection is 0.1 to 5.0 nm, preferably 0.2 to 2.0 nm. The thickness of the metal compound layer 333 in the intermediate connection is 0.5 to 20 nm, preferably 1.0 to 5.0 nm. The thickness of the n-type semiconductor layer 431 in the intermediate connection is 0.5 to 20 nm, preferably 1.0 to 5.0 nm.

The material used for the manufacture of the intermediate connection is basically selected from non-toxic materials. The low work function metal layer 331 includes Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Nd, Sm, Eu, Tb, Dy or Yb. Preferably, the low work function metal layer 331 comprises Li, Na, Cs, Ca, Ba or Yb.

The high work function metal layer 332 is formed of Ti, Zr, Ti, Nb, Ta, Cr, Mo, W, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Al, In or Sn. Preferably, the high work function metal layer 332 comprises Ag, Al, Cu, Au, Zn, In or Sn. More preferably, the high work function metal layer 332 comprises Ag or Al.

The metal compound layer 333 is a stoichiometric oxide or non-titanium oxide of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, zinc, silicon or germanium. -Stoichiometric oxides, or mixtures thereof. The metal compound layer 333 is a stoichiometric sulfide or non-stoichiometric amount of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, silicon or germanium. It may be selected from theoretical sulfides, or mixtures thereof. The metal compound layer 333 is a stoichiometric selenide of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, silicon or germanium. Or non-stoichiometric selenides, or mixtures thereof. The metal compound layer 333 is a stoichiometric telluride of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, silicon or germanium. Or non-stoichiometric tellurides, or mixtures thereof. The metal compound layer 333 is a stoichiometric nitride of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, zinc, gallium, silicon, or germanium Or non-stoichiometric nitrides, or mixtures thereof. The metal compound layer 333 is also a stoichiometric of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, zinc, aluminum, silicon or germanium. Carbides or non-stoichiometric carbides, or mixtures thereof.

The metal compound layer 333 may be selected from MoO ₃ , NiMoO ₄ , CuMoO ₄ , WO ₃ , ZnTe, Al ₄ C ₃ , AlF ₃ , B ₂ S ₃ , CuS, GaP, InP or SnTe. Preferably, the metal compound layer 333 may be selected from MoO ₃ , NiMoO ₄ , CuMoO ₄ or WO ₃ .

The n-type semiconductor layer 431 includes, but is not limited to, ZnSe, ZnS, ZnSSe, SnSe, SnS, SnSSe, LaCuO ₃ or La ₄ Ru ₆ O ₁₉ . Preferably, n-type semiconductor layer 431 comprises ZnSe or ZnS.

Intermediate connections can be created by thermal evaporation, electron beam evaporation or ion sputtering techniques. Preferably, a thermal evaporation method is used to deposit all materials in the production of tandem OLEDs comprising intermediate connections.

In-line OLEDs of the present invention are typically provided on a supporting substrate, where the cathode or anode can be in contact with the substrate. The electrode in contact with the substrate is called a bottom electrode for convenience. Conveniently, the bottom electrode is an anode, but the invention is not limited to such a configuration. The substrate may be light transmissive or opaque, depending on the intended light emitting direction. Light transmission is required to observe the EL emission through the substrate. Clear glass or plastic is often used in this case. In applications where EL emission is observed through the top electrode, the transmittance of the bottom support is not critical and can therefore be light transmissive, light absorptive or light reflective. Substrates used in this case include, but are not limited to, glass, plastics, semiconductor materials, silicon, ceramics, and circuit board materials. Of course, there is a need in these device configurations to provide a light-transparent top electrode.

If EL emission is observed through anode 110, the anode should be transparent or substantially transparent to the emission of interest. Typical transparent anode materials used in the present invention include indium tin oxide (ITO), zinc indium oxide (IZO) and tin oxide, but include aluminum- or indium-doped zinc oxide, indium magnesium oxide and tungsten nickel oxide. Other metal oxides may also work well. In addition to these oxides, metal nitrides such as gallium nitride, and metal selenides such as zinc selenide, and metal sulfides such as zinc sulfide may also be used as anodes. For applications where EL emission is observed only through the cathode electrode, the transmission characteristics of the anode are not critical and any conductive material may be used, whether it is transparent, opaque or reflective. Examples of conductors for this use include, but are not limited to, gold, iridium, molybdenum, palladium and platinum. Typical anode materials, which may or may not be permeable, have a work function of at least 4.0 eV. The desired anode material is typically deposited by any suitable manner such as evaporation, sputtering, chemical vapor deposition or electrochemical means. The anode can be patterned using well known photolithographic processes. Optionally, the anode can be polished prior to depositing another layer to reduce surface roughness to reduce electrical shorts or improve resistivity.

Although not always necessary, it is often useful to provide HIL in an organic EL unit. HIL may serve to reduce the drive voltage of the tandem OLED by improving the film forming properties of subsequent organic layers and facilitating hole injection into the HTL. Suitable materials for use in HIL include the polypyrroline compounds described in US Pat. No. 4,720,432, the plasma-deposited fluorocarbon polymers described in US Pat. No. 6,208,075, and some aromatic amines such as m-MTDATA (4,4). ', 4 "-tris [(3-ethylphenyl) phenylamino] triphenylamine). Other hole injection materials reported to be useful in organic EL devices are described in EP 0 891 121 A1. And EP 1 029 909 A1. P-type doped organic layers are also useful for HILs described in US Pat. No. 6,423,429. P-type doped organic layers are electrically conductive and chargeable. The carrier is predominantly a hole, as the electron-transfer complex is created as a result of the hole transfer from the dopant to the host material, thereby providing conductivity.

The HTL of the organic EL unit contains one or more hole transport compounds, such as aromatic tertiary amines, wherein the aromatic tertiary amine is bound to only carbon atoms (one or more of which are members of the aromatic ring) It is understood that the compound contains an atom. One form of aromatic tertiary amines may be arylamines such as monoarylamines, diarylamines, triarylamines or polymeric arylamines. Examples of monomeric triarylamines are described in US Pat. No. 3,180,730 to Klupfel et al. Other suitable triarylamines substituted with one or more vinyl radicals and / or having one or more active hydrogen-containing groups are disclosed in US Pat. Nos. 3,567,450 and 3,658,520 to Brantley et al.

A more preferred class of aromatic tertiary amines is to include at least two aromatic tertiary amine residues described in US Pat. Nos. 4,720,432 and 5,061,569. HTLs can be prepared from monoaromatic tertiary amine compounds or mixtures thereof. Examples of useful aromatic tertiary amines are the following compounds:

1,1-bis (4-di-p-tolylaminophenyl) cyclohexane;

1,1-bis (4-di-p-tolylaminophenyl) -4-phenylcyclohexane;

N, N, N ', N'-tetraphenyl-4,4 "'-diamino-1,1 ': 4', 1": 4 ", 1" '-quaterphenyl;

Bis (4-dimethylamino-2-methylphenyl) phenylmethane;

1,4-bis [2- [4- [N, N-di (p-tolyl) amino] phenyl] vinyl] benzene (BDTAPVB);

N, N, N ', N'-tetra-p-tolyl-4,4'-diaminobiphenyl;

N, N, N ', N'-tetraphenyl-4,4'-diaminobiphenyl;

N, N, N ', N'-tetra-1-naphthyl-4,4'-diaminobiphenyl;

N, N, N ', N'-tetra-2-naphthyl-4,4'-diaminobiphenyl;

N-phenylcarbazole;

4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPB);

4,4'-bis [N- (1-naphthyl) -N- (2-naphthyl) amino] biphenyl (TNB);

4,4'-bis [N- (1-naphthyl) -N-phenylamino] p-terphenyl;

4,4'-bis [N- (2-naphthyl) -N-phenylamino] biphenyl;

4,4'-bis [N- (3-acenaphthenyl) -N-phenylamino] biphenyl;

1,5-bis [N- (1-naphthyl) -N-phenylamino] naphthalene;

4,4'-bis [N- (9-anthryl) -N-phenylamino] biphenyl;

4,4'-bis [N- (1-antryl) -N-phenylamino] -p-terphenyl;

4,4'-bis [N- (2-phenanthryl) -N-phenylamino] biphenyl;

4,4'-bis [N- (8-fluoranthenyl) -N-phenylamino] biphenyl;

4,4'-bis [N- (2-pyrenyl) -N-phenylamino] biphenyl;

4,4'-bis [N- (2-naphthasenyl) -N-phenylamino] biphenyl;

4,4'-bis [N- (2-peryleneyl) -N-phenylamino] biphenyl;

4,4'-bis [N- (1-coronylyl) -N-phenylamino] biphenyl;

2,6-bis (di-p-tolylamino) naphthalene;

2,6-bis [di- (1-naphthyl) amino] naphthalene;

2,6-bis [N- (1-naphthyl) -N- (2-naphthyl) amino] naphthalene;

N, N, N ', N'-tetra (2-naphthyl) -4,4 "-diamino-p-terphenyl;

4,4'-bis {N-phenyl-N- [4- (1-naphthyl) -phenyl] amino} biphenyl;

2,6-bis [N, N-di (2-naphthyl) amino] fluorene;

4,4 ', 4 "-tris [(3-methylphenyl) phenylamino] triphenylamine (MTDATA); and

4,4'-bis [N- (3-methylphenyl) -N-phenylamino] biphenyl (TPD).

Another class of useful hole transport materials includes the polycyclic aromatic compounds described in EP 1 009 041. Tertiary aromatic amines having more than two amine groups can be used, including oligomeric materials. Air, such as poly (3,4-ethylenedioxythiophene) / poly (4-styrenesulfonate), also called poly (N-vinylcarbazole) (PVK), polythiophene, polypyrrole, polyaniline and PEDOT / PSS Polymer hole transport materials such as coalescing may be used.

As described in more detail in US Pat. Nos. 4,769,292 and 5,935,721, the LEL of the organic EL unit includes a luminescent or fluorescent material in which electroluminescence occurs as a result of electron-hole pair recombination in this region. The LEL may comprise a single material, but more typically includes a guest material or a host material doped with compounds, wherein the luminescence is primarily derived from the dopant and may be of any color. The host material of the LEL may be an electron transport material, a hole transport material, or another material or mixture of materials that supports hole-electron recombination. Dopants are typically selected from highly fluorescent dyes, but phosphorescent compounds such as the transition metal complexes described in WO 98/55561, WO 00/18851, WO 00/57676 and WO 00/70655 are also useful. . Dopants are typically coated at 0.01 to 10 weight percent on the host material. Polymeric materials such as polyfluorene and polyvinylarylene (eg poly (p-phenylenevinylene), PPV) can also be used as host materials. In this case, the small molecular dopant may be dispersed in molecular form in the polymer host, or may be added by copolymerizing the dopant into the host polymer as a trace component.

An important relationship for selecting a dye as a dopant is the comparison of the electron energy band gap. For efficient energy transfer from the host to the dopant molecule, a necessary condition is that the band gap of the dopant must be smaller than the band gap of the host material. For phosphorescent emitters, it is also important that the triplet energy level of the host be high enough to allow energy to be transferred from the host to the dopant.

Host and release molecules known for this use are described in US Pat. No. 4,768,292; No. 5,141,671; 5,150,006; 5,150,006; 5,151,629; 5,405,709; 5,405,709; No. 5,484,922; 5,593,788; 5,593,788; 5,645,948; 5,645,948; 5,683,823; 5,683,823; 5,755,999; 5,755,999; 5,928,802; 5,928,802; No. 5,935,720; 5,935,721; And 6,020,078, but is not limited to such.

Metal complexes of 8-hydroxyquinoline (oxine) and similar derivatives constitute a class of useful host materials that can support electroluminescence. Examples of useful chelated oxynoid compounds are the following compounds:

CO-1: aluminum trisoxine (aka tris (8-quinolinolato) aluminum (III));

CO-2: magnesium bisoxine [aka bis (8-quinolinolate) magnesium (II)];

CO-3: bis [benzo {f} -8-quinolinolato] zinc (II);

CO-4: bis (2-methyl-8-quinolinolato) aluminum (III) -μ-oxo-bis (2-methyl-8-quinolinolato) aluminum (III);

CO-5: indium trisoxine [aka tris (8-quinolinolato) indium];

CO-6: aluminum tris (5-methyloxine) [aka tris (5-methyl-8-quinolinolato) aluminum (III)];

CO-7: lithium auxin [aka, (8-quinolinolato) lithium (I)];

CO-8: gallium auxin [aka tris (8-quinolinolato) gallium (III)]; And

CO-9: zirconium auxin [aka tetra (8-quinolinolato) zirconium (IV)].

Other classes of useful host materials include derivatives of anthracenes, such as 9,10-di- (2-naphthyl) anthracene and derivatives thereof described in US Pat. No. 5,935,721; Distyrylarylene derivatives described in US Pat. No. 5,121,029; And benzazole derivatives such as, but not limited to, 2,2 ', 2 "-(1,3,5-phenylene) tris [1-phenyl-1H-benzimidazole].

Useful fluorescent dopants include derivatives of anthracene, tetracene, xanthene, perylene, rubrene, coumarin, rhodamine, quinacridone, dicyanomethylenepyrane compound, thiopyrane compound, polymethine compound, pyryllium and thiaryryllium compound , Fluorene compounds, periplanthene derivatives, indenoferylene derivatives, bis (azinyl) amine boron compounds, bis (azinyl) methane compounds, and carbostyryl compounds.

Preferred thin film-forming materials for use in preparing the ETL of the organic EL unit of the present invention are metal chelated oxynoid compounds, including chelates of auxin itself, also commonly referred to as 8-quinolinol or 8-hydroxyquinoline. These compounds aid in the injection and transport of electrons, exhibit high performance levels, and are easily deposited to form thin films. Exemplary oxynoid compounds have been listed above.

Other electron transport materials include various butadiene derivatives disclosed in US Pat. No. 4,356,429, and various heterocyclic optical brighteners described in US Pat. No. 4,539,507. Benzazole and triazine are also useful electron transport materials.

N-type doped organic layers are also useful for ETL, as described, for example, in US Pat. No. 6,013,384. The n-type doped organic layer includes a host organic material and one or more n-type dopants. The host material of the n-type doped organic layer includes small molecular materials or polymeric materials, or mixtures thereof. It is preferable that this host material is selected from said electron transport material.

Materials used as n-type dopants of n-type doped ETLs include metals or metal compounds having a work function of less than 4.0 eV. Particularly useful dopants include alkali metal, alkali metal compounds, alkaline earth metals and alkaline earth metal compounds. The term "metal compound" includes organometallic complexes, metal-organic salts and inorganic salts, oxides and halides. Among the classes of metal-containing n-type dopants, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Nd, Sm, Eu, Tb, Dy or Yb, and their inorganics Or organic compounds are particularly useful. The material used as the n-type dopant of the n-type doped organic layer of the intermediate linkage also includes an organic reducing agent having strong electron donating properties. "Strong electron donating property" means that the organic dopant must be able to donate at least some of the charge to the host to create a charge-transfer complex with the host. Non-limiting examples of organic molecules include bis (ethylenedithio) -tetrathiafulvalene (BEDT-TTF), tetrathiafulvalene (TTF) and derivatives thereof. In the case of a polymeric host, the dopant may be any of the above, or may be a material dispersed in the host in molecular form or copolymerized with the host as a trace component. When doped with a suitable n-type dopant, the doped organic layer exhibits primarily electron transport properties. The concentration of n-type doped is preferably 0.01 to 20% by volume.

Although not always necessary, it is often useful to provide an EIL to the EL unit. EIL can serve to lower the drive voltage of tandem OLEDs by facilitating electron injection into the ETL and increasing electrical conductivity. Suitable materials for use in the EIL are those ETLs doped with strong reducing agents or low work function metals (<4.0 eV). Other inorganic electron injection materials may also be useful in organic EL unit devices, which are described in the following paragraphs.

If luminescence is observed only through the anode, the cathode 140 used in the present invention may be made of almost any conductive material. Preferred materials have effective film-forming properties to ensure effective contact with the underlying organic layer, promote electron injection at low voltages and have effective stability. Useful cathode materials often contain low work function metals (<4.0 eV) or metal alloys. One preferred cathode material consists of an Mg: Ag alloy having a percentage of 1 to 20% silver as described in US Pat. No. 4,885,221. Another suitable class of cathode materials includes two layers comprising a thin inorganic EIL in contact with an organic layer (eg, ETL), wherein the organic layer is capped with a thicker conductive metal layer. In this case, the inorganic EIL preferably comprises a low work function metal or metal salt, in which case no thicker capping layer is needed to have a low work function. One such cathode consists of a thin LiF layer and a thicker Al layer as described in US Pat. No. 5,677,572. Other useful cathode material sets include, but are not limited to, those disclosed in US Pat. Nos. 5,059,861, 5,059,862, and 6,140,763.

If luminescence is observed through the cathode, the cathode should be transparent or nearly transparent. In such applications, the metal must be thin, or use transparent conductive oxides or include these materials. The light transparency cathodes are U.S. Patent Nos. 4,885,211, 5,247,190, 5,703,436, 5,608,287, 5,837,391, 5,677,572, 5,776,622, 5,776,623, 5,714,838, 5,969,474, 5,739,545 5,981,306, 6,137,223, 6,140,763, 6,172,459, 6,278,236, 6,284,393, JP 3,234,963 and EP 1 076 368. Cathode materials are typically deposited by thermal evaporation, electron beam evaporation, ion sputtering or chemical vapor deposition. Where necessary, including but not limited to through-mask deposition, integral shadow masking (such as described in US Pat. Nos. 5,276,380 and EP 0 732 868), laser ablation, and selective chemical deposition Patterning can be accomplished by a number of well known methods.

In some cases, the LEL and ETL of the organic EL unit can optionally be made of a single layer that functions to support luminescence and electron transport. It is also known in the art that release dopants can be added to HTL, which can serve as a host. Multiple dopants may be added to one or more layers, for example, to produce white-emitting OLEDs by mixing blue- and yellow-emitting materials, cyan- and red-emitting materials, or red-, green- and blue-emitting materials. Can be. White-emitting devices are described, for example, in US Patent Publication No. 2002/0025419 A1; U.S. Patent 5,683,823; 5,503,910; 5,503,910; 5,405,709; 5,405,709; No. 5,283,182; EP 1 187 235; And EP 1 182 244.

Additional layers such as electron or hole blocking layers taught in the art can be used in the devices of the present invention. As in US Patent Publication No. 2002/0015859 A1, hole blocking layers are commonly used to improve the efficacy of phosphorescent emitter devices.

The above-mentioned organic materials are suitably deposited through vapor-phase methods such as thermal evaporation, but can be deposited from a solvent with an optional binder to improve fluid, eg film formation. If the material is a polymer, solvent deposition is useful, but other methods such as sputtering or heat transfer from the donor sheet can be used. The material to be deposited by thermal evaporation can often be vaporized from an evaporation "boat" made of tantalum material, as described, for example, in US Pat. No. 6,237,529, or first coated onto a donor sheet and then closer to the substrate. Can be sublimated. Layers with a mixture of materials may use separate evaporation boats or may premix the materials and coat from a single boat or donor sheet. In the case of a full color display, pixelation of the LEL may be required. Shadow masks, integral shadow masks (US Pat. No. 5,294,870), space-limited thermal dye transfer from donor sheets (US Pat. Nos. 5,688,551, 5,851,709 and 6,066,357) and inkjet methods (US Pat. No. 6,066,357). Can be used to achieve this pixelated deposition of LEL. For organic EL units or other organic layers of intermediate interconnections, pixelated deposition is not necessarily required.

Most OLEDs are sensitive to moisture or oxygen, or both, so they are typically alumina, bauxite, calcium sulfate, clay, silica gel, zeolites, alkali metal oxides, alkaline earth metal oxides, sulfates, or drying agents such as metal halides and perchlorates. With an inert atmosphere such as nitrogen or argon. Encapsulation and drying methods include, but are not limited to, those described in US Pat. No. 6,226,890. In addition, barrier layers such as SiO _x , Teflon and alternating inorganic / polymer layers are known in the art for encapsulation.

The following examples are provided to further understand the present invention. For simplicity, the materials and layers prepared from them are shortened as follows:

ITO: indium tin oxide; Used to create a transparent anode on a glass substrate;

CF _x : polymerized fluorocarbon layer; Used to create a hole injection layer over ITO;

NPB: N, N'-di (naphthalen-1-yl) -N, N'-diphenyl-benzidine; Used to create hole transport layers in organic EL units;

Alq: tris (8-hydroxyquinoline) aluminum (III); Used as a host in producing the light emitting layer, and used as a host in producing the n-type doped electron transport layer of the organic EL unit;

C545T: 10- (2-benzothiazolyl) -1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H, 5H, 11H (1) benzopyrano (6,7, 8-ij) quinolizin-11-one; Used as a green dopant of the light emitting layer of the EL unit device;

Li: lithium; Used as an n-type dopant in producing an n-type doped electron transport layer of an organic EL unit;

Mg: Ag: Magnesium: silver with a volume ratio of 10: 0.5; Used to create a cathode.

In the examples below, an adjusted thickness monitor (INFICON IC / 5 Deposition Controller) was used to control and measure the thickness and doping concentration of the organic layer in place. The EL characteristics of all the devices manufactured using a constant current source (KEITHLEY 2400 SourceMeter) and photometer (PHOTO RESEARCH SpectraScan PR 650) at room temperature were evaluated. Report colors using International Lighting Commission (CIE) coordinates.

Conventional OLED manufacturing methods are as follows: Glass substrates up to 1.1 mm thick coated with a transparent ITO conductive layer were cleaned and dried using a commercially available glass scrubber tool. The thickness of the ITO is about 42 nm, and the sheet resistance of the ITO is about 68 Ω / square. The surface of the ITO was then treated with an oxidizing plasma to control the surface as an anode. By decomposing the CHF ₃ gas in an RF plasma treated camber, a 1 nm thick CF _x layer was deposited as HIL on a clean ITO surface. The substrate was then transferred to a vacuum deposition chamber (TROVATO MFG. INC) to deposit all other layers on the substrate. 10 ^- was deposited according to evaporate from the heated boat under a vacuum of ⁶ Torr to the layer sequence:

1. EL module

a) HTL, about 90 nm thick, including NPB;

b) LEL, 30 nm thick, 1.0 vol% Alq doped with C545T; And

c) The first ETL, 30 nm thick, containing Alq doped with 1.2 vol% Li.

2. Cathode: Approx. 210 nm thick with MgAg.

After depositing these layers, the device was transferred from the deposition chamber to a dry box (VAC Vacuum Atmosphere Company) to encapsulate the device. The EL performance of the device at 20 mA / cm ² and room temperature was measured.

This conventional OLED requires a drive voltage of about 6.1V to pass 20mA / cm ² . Under this test condition, the device has a luminance of 2110 cd / m ² , a luminous efficiency of about 10.6 cd / A, and a power efficiency of about 5.45 lm / W. Its CIEx and CIEy are 0.279 and 0.651, respectively, and have an emission peak at 520 nm.

Example 2 (comparative)

In-line OLEDs were fabricated in the manner described in Example 1, and the deposited layer structure was as follows:

1. First EL unit

a) HTL, thickness about 100 nm, including NPB;

b) LEL, 20 nm thick, with Alq doped with 1.0 vol% C545T; And

c) First ETL, 40 nm thick, with Alq doped with 1.2 vol% Li.

2. First intermediate connection:

a) metal layer of high work function, thickness 10nm, Ag included.

3. Second EL unit

a) HTL, about 70 nm thick, including NPB;

b) LEL, 20 nm thick, with Alq doped with 1.0 vol% C545T; And

c) First ETL, 40 nm thick, with Alq doped with 1.2 vol% Li.

4. Cathode: Thickness 210nm, including MgAg.

This tandem OLED requires about 22.9V of drive voltage to pass 20mA / cm ² . Under this test condition, the device has a luminance of 937 cd / m ² , a luminous efficiency of about 4.68 cd / A, and a power efficiency of about 0.64 lm / W. Its CIEx and CIEy are 0.179 and 0.689, respectively, and have an emission peak at 516 nm. The drive voltage is almost four times that of Example 1 at 20 mA / cm ² , and the luminous efficiency is less than half of Example 1. This clearly indicates that a single layer of high work function metal cannot produce effective intermediate connections in tandem OLEDs. The very high driving voltage is due to the high injection barrier formed between the high work function layer and the EL unit device. Low luminous efficiency is due to poor carrier injection between the intermediate connection and the EL unit and light absorption of the thick metal layer.

Example 3 (comparative)

Tandem OLEDs were fabricated in the manner described in Example 2 and the deposited layer structure was as follows:

1. First EL unit

a) HTL, about 90 nm thick, including NPB;

b) LEL, 30 nm thick, with Alq doped with 1.0 vol% C545T; And

c) The first ETL, 30 nm thick, containing Alq doped with 1.2 vol% Li.

2. First intermediate connection:

a) metal compound layer, 2 nm thick, with MoO ₃ .

3. Second EL unit

a) HTL, thickness about 88 nm, including NPB;

b) LEL, 30 nm thick, with Alq doped with 1.0 vol% C545T; And

c) The first ETL, 30 nm thick, containing Alq doped with 1.2 vol% Li.

4. Cathode: Thickness 210nm, including MgAg.

This tandem OLED requires a drive voltage of about 14.3V to pass 20mA / cm ² . Under this test condition, the device has a brightness of 4781 cd / m ² , a luminous efficiency of about 23.9 cd / A, and a power efficiency of about 5.24 lm / W. Its CIEx and CIEy are 0.267 and 0.660, respectively, and have an emission peak at 520 nm. The driving voltage is about 2.3 times that of Example 1 at 20 mA / cm ² , and the luminous efficiency is about 2.3 times that of Example 1. This indicates that 2 nm thick MoO ₃ as a metal compound layer can produce effective intermediate connections in tandem OLEDs. The operational stability of the device at 80 mA / cm ² and room temperature was tested. FIG. 6 shows the decrease in normalized luminance over operating time, and FIG. 7 shows the increase in driving voltage over operating time. At 80 mA / cm ² , the initial luminance of the device is about 21,220 cd / m ² . If this current density is kept unchanged, its lifetime at this brightness (defined as operating time when 50% of its initial brightness falls) is about 145 hours. If the device was tested at an initial luminance of 100 cd / m ² , its operating life would be longer than 145 × 212.2 = 30,769 hours. However, when testing the voltage increase during operation, the voltage increase between the initial value and the value after it was driven until the device reached its service life increased from about 18 V (18.53 V to 22.13 V at 80 mA / cm ²⁾ . )to be. If the device is driven at a constant voltage, its initial brightness will fall much faster than when driven at a constant current, and thus its life will be much shorter. Therefore, although MoO ₃ is a non-toxic material, it is not sufficiently stable when used alone as an intermediate linkage.

Example  4

The first intermediate connection is 1) a high work function metal layer, 0.5 nm thick, including Ag; And 2) a tandem OLED having the same layer structure as in Example 3, except that the metal compound layer, 2 nm thick, and MoO _{3 were} included.

This tandem OLED requires about 13.4V of drive voltage to pass 20mA / cm ² . Under this test condition, the device has a brightness of 4627 cd / m ² , a luminous efficiency of about 23.1 cd / A, and a power efficiency of about 5.43 lm / W. Its CIEx and CIEy are 0.270 and 0.660, respectively, and have an emission peak at 520 nm. The driving voltage is about 2.2 times that of Example 1 at 20 mA / cm ² , and the luminous efficiency is about 2.2 times that of Example 1. This indicates that Ag / MoO ₃ bilayers can create effective intermediate connections in tandem OLEDs. The operational stability of the device at 80 mA / cm ² and room temperature was tested. FIG. 6 shows the decrease in normalized luminance over operating time, and FIG. 7 shows the increase in driving voltage over operating time. At 80 mA / cm ² , the initial luminance of the device is about 20,130 cd / m ² . If this current density is kept unchanged, its operating life at this luminance is about 164 hours. When the device is tested at an initial luminance of 100 cd / m ² , its operating life will be longer than 164 × 201.3 = 33,013 hours.

When comparing the performance of Example 4 with that of Example 3, the initial drive voltage of Example 4 at 20 mA / cm ² is about 1V lower, resulting in higher power efficiency and longer lifetime. In addition, when investigating the voltage increase during operation, the voltage increase between the initial value and the value after it was driven until the device reached its lifetime increased to about 0.7 V (from 17.8 V to 18.5 V at 80 mA / cm ²⁾ . ). This voltage increase is much smaller than in Example 3. If both Examples 3 and 4 are driven at a constant voltage, then Example 4 will have a much longer life than Example 3. Therefore, by incorporating a high work function metal layer and a metal compound layer, a stable intermediate connection can be produced. This stable intermediate connection not only reduces the initial drive voltage, but also improves the lifetime of the tandem OLED.

Claims (31)

delete a) an anode; b) a cathode; c) a plurality of organic electroluminescent unit devices disposed between the anode and the cathode; And d) an intermediate connection disposed between each adjacent organic electroluminescent unit, Each organic electroluminescent unit comprises at least a hole transport layer, a light emitting layer and an electron transport layer, Each intermediate connection is a low work function metal layer having a work function of less than 4.0 eV, a high work function metal layer having a work function of at least 4.0 eV, disposed adjacent to the electron transport layer of the organic electroluminescent unit, And a metal compound layer, The intermediate connection has a sheet resistance higher than 100 kΩ per square, Tandem OLED in which a high work function metal layer improves the operational stability of the OLED. a) an anode; b) a cathode; c) a plurality of organic electroluminescent unit devices disposed between the anode and the cathode; And d) an intermediate connection disposed between each adjacent organic electroluminescent unit, Each organic electroluminescent unit comprises at least a hole transport layer, a light emitting layer and an electron transport layer, Each intermediate connection comprises an n-type semiconductor layer disposed adjacent to an electron transport layer of the organic electroluminescent unit, a high work function metal layer having a work function of 4.0 eV or greater, and a metal compound layer, The intermediate connection has a sheet resistance higher than 100 kΩ per square, Tandem OLED in which a high work function metal layer improves the operational stability of the OLED. a) an anode; b) a cathode; c) a plurality of organic electroluminescent unit devices disposed between the anode and the cathode; And d) an intermediate connection disposed between each adjacent organic electroluminescent unit, Each organic electroluminescent unit comprises at least a hole transport layer, a light emitting layer and an electron transport layer, The electron transport layer is an n-type doped organic layer, Each intermediate connection comprises a high work function metal layer having a work function of at least 4.0 eV, and a metal compound layer, disposed adjacent to the electron transport layer of the organic electroluminescent unit, The intermediate connection has a sheet resistance higher than 100 kΩ per square, Tandem OLED in which a high work function metal layer improves the operational stability of the OLED. 5. The method according to any one of claims 2 to 4, A tandem OLED wherein the thickness of the high work function metal layer of the intermediate connection is 0.1 to 5.0 nm. 5. The method according to any one of claims 2 to 4, Tandem OLED wherein the high work function metal layer of the intermediate connection is between 0.2 and 2.0 nm. 5. The method according to any one of claims 2 to 4, In-line OLED, wherein the thickness of the metal compound layer of the intermediate connection is 0.5 to 20 nm. 5. The method according to any one of claims 2 to 4, In-line OLED, wherein the thickness of the metal compound layer of the intermediate connection is 1.0 to 5 nm. The method of claim 2, A tandem OLED wherein the low work function metal layer of the intermediate connection is between 0.1 and 10 nm thick. The method of claim 2, A tandem OLED wherein the low work function metal layer of the intermediate connection is between 0.2 and 2.0 nm thick. The method of claim 3, wherein In-line OLED, wherein the thickness of the n-type semiconductor layer of the intermediate connection is 0.5 to 20 nm. The method of claim 3, wherein In-line OLED, wherein the thickness of the n-type semiconductor layer of the intermediate connection is 1.0 to 5.0 nm. 5. The method according to any one of claims 2 to 4, Tandem OLED, wherein the intermediate connections have a light transmission of at least 75% in the visible region of the spectrum. 5. The method according to any one of claims 2 to 4, High work function metal layers are Ti, Zr, Ti, Nb, Ta, Cr, Mo, W, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn In-line OLED comprising Al, In or Sn. 5. The method according to any one of claims 2 to 4, In-line OLED, wherein the high work function metal layer comprises Ag, Al, Cu, Au, Zn, In or Sn. 5. The method according to any one of claims 2 to 4, In-line OLED, wherein the high work function metal layer comprises Ag or Al. 5. The method according to any one of claims 2 to 4, The metal compound layer is a stoichiometric oxide or non-stoichiometric of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, zinc, silicon or germanium Tandem OLED selected from oxides, or mixtures thereof. 5. The method according to any one of claims 2 to 4, The metal compound layer comprises a stoichiometric or non-stoichiometric sulfide of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, silicon or germanium, Or an in-line OLED selected from mixtures thereof. 5. The method according to any one of claims 2 to 4, The metal compound layer is a stoichiometric selenide or non-stoichiometric selenium of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, silicon or germanium Tandem OLED selected from cargoes, or mixtures thereof. 5. The method according to any one of claims 2 to 4, The metal compound layer is a stoichiometric telluride or non-stoichiometric tellurium of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, silicon or germanium Tandem OLED selected from cargoes, or mixtures thereof. 5. The method according to any one of claims 2 to 4, The metal compound layer is a stoichiometric nitride or non- of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, zinc, gallium, silicon or germanium Tandem OLEDs selected from stoichiometric nitrides, or mixtures thereof. 5. The method according to any one of claims 2 to 4, The metal compound layer is a stoichiometric carbide or non- of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, manganese, iron, ruthenium, rhodium, iridium, nickel, palladium, platinum, copper, zinc, aluminum, silicon or germanium Tandem OLED selected from stoichiometric carbides, or mixtures thereof. 5. The method according to any one of claims 2 to 4, Tandem OLED wherein the metal compound layer is selected from MoO ₃ , NiMoO ₄ , CuMoO ₄ , WO ₃ , ZnTe, Al ₄ C ₃ , AlF ₃ , B ₂ S ₃ , CuS, GaP, InP or SnTe. 5. The method according to any one of claims 2 to 4, Tandem OLED wherein the metal compound layer is selected from MoO ₃ , NiMoO ₄ , CuMoO ₄ or WO ₃ . The method of claim 2, Tandem OLED wherein the low work function metal layer comprises Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Nd, Sm, Eu, Tb, Dy or Yb. The method of claim 2, In-line OLED, wherein the low work function metal layer comprises Li, Na, Cs, Ca, Ba or Yb. The method of claim 3, wherein In-line OLED, wherein the n-type semiconductor layer comprises ZnSe, ZnS, ZnSSe, SnSe, SnS, SnSSe, LaCuO ₃ or La ₄ Ru ₆ O ₁₉ . The method of claim 3, wherein In-line OLED, wherein the n-type semiconductor layer comprises ZnSe or ZnS. 5. The method according to any one of claims 2 to 4, Tandem OLED in which the intermediate connection is produced by thermal evaporation. 5. The method according to any one of claims 2 to 4, Tandem OLED in which the intermediate connection is created by electron beam evaporation. 5. The method according to any one of claims 2 to 4, Tandem OLED in which the intermediate connection is created by ion sputtering technique.

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