WO2006008942A1 - Organic el element - Google Patents

Abstract

An organic EL element having a structure wherein a solid layer comprising an organic luminescent layer is sandwiched by a cathode and an anode, characterized in that the above cathode contains magnesium in a proportion of less than 50 percent. The above organic EL element reduces the voltage necessary for driving an organic EL element and enhances the effect of reducing the damage which the solid layer suffers from the lamination of an electrode formed thereon.

Description

 Specification

 Organic EL device

 Technical field

 [0001] The present application relates to an organic EL (Electro Luminescence) element.

 Background art

 Organic EL elements are self-luminous and have high visibility and are completely solid elements, so that they are excellent in impact resistance and easy to handle. For this reason, research and development and practical application as pixels for graphic displays, pixels for television image display devices, or surface light sources are being promoted. Such an organic EL element is often formed by sequentially laminating an anode, an organic solid layer, and a cathode on a substrate. As a cathode laminated on an organic solid layer, a magnesium alloy or magnesium silver is used. Alloys are used, and alloys containing more than 50 percent magnesium are used based on all metal atoms present in the alloy (Patent Document 1).

 Patent Document 1: Japanese Patent Laid-Open No. 2-15595

 Disclosure of the invention

 Problems to be solved by the invention

However, when a conventional cathode is used, when the cathode is stacked on the organic solid layer, the organic solid layer is damaged.

[0004] In addition, an organic EL element can be obtained by reducing the thickness of an organic solid layer, particularly a light emitting layer, for example.

4. The power that has the advantages of being able to drive at a low voltage of 5V and having a quick response. Today, it is desired to develop an organic EL device that can be driven at a lower voltage.

[0005] The present application has been made under such circumstances, and can reduce the voltage at the time of driving the organic EL element, and the organic solid layer is affected by the lamination of electrodes formed thereon. An example of the problem is to provide an organic EL device having a cathode that improves the effect of reducing damage.

 Means for solving the problem

[0006] In order to solve the above problems, the invention according to claim 1 includes at least an organic light emitting layer. An organic EL device having a structure in which a solid layer sandwiched between a cathode and an anode is characterized in that the cathode contains magnesium in a proportion of less than 50 percent.

 [0007] In order to solve the above problems, the invention according to claim 2 is an organic EL element having a structure in which a solid layer including at least an organic light emitting layer is sandwiched between a cathode and an anode, wherein the cathode comprises magnesium. It is formed by a magnesium-containing alloy containing less than 50 percent!

 [0008] In order to solve the above problem, the invention according to claim 3 is an organic EL device having a structure in which a solid layer including at least an organic light emitting layer is sandwiched between a cathode and an anode, wherein the cathode is composed of a plurality of layers. And at least one of them is formed of a magnesium-containing alloy containing magnesium in a proportion of less than 50 percent.

 Brief Description of Drawings

FIG. 1 is a schematic cross-sectional view showing a first embodiment of an organic EL element of the present application.

 FIG. 2 is a schematic cross-sectional view showing a second embodiment of the organic EL element of the present application.

 FIG. 3 is a schematic cross-sectional view showing a third embodiment of the organic EL element of the present application.

 FIG. 4 is a schematic cross-sectional view showing a fourth embodiment of the organic EL element of the present application.

 FIG. 5 is a schematic cross-sectional view showing a fifth embodiment of the organic EL element of the present application.

 FIG. 6 is a schematic cross-sectional view showing a sixth embodiment of the organic EL element of the present application.

 FIG. 7 is a schematic cross-sectional view showing a seventh embodiment of the organic EL element of the present application.

 FIG. 8 is a schematic sectional view showing an eighth embodiment of the organic EL element of the present application.

 FIG. 9 is a schematic cross-sectional view showing a ninth embodiment of the organic EL element of the present application.

 FIG. 10 is a schematic sectional view showing a tenth embodiment of the organic EL element of the present application.

 FIG. 11 is a schematic sectional view showing an eleventh embodiment of an organic EL element of the present application.

 FIG. 12 is a schematic cross-sectional view showing a twelfth embodiment of the organic EL element of the present application.

 FIG. 13 is a schematic sectional view showing a thirteenth embodiment of the organic EL element of the present application.

 FIG. 14 is a schematic sectional view showing a fourteenth embodiment of an organic EL element of the present application.

 FIG. 15 is a schematic cross-sectional view showing a fifteenth embodiment of an organic EL element of the present application.

FIG. 16 is a schematic sectional view showing a sixteenth embodiment of an organic EL element of the present application. FIG. 17 is a graph showing voltage-current characteristics of an organic EL device according to the present application.

 FIG. 18 is a graph showing voltage-current characteristics of an organic EL device according to the present application.

[0010] The meanings of the main symbols in the figure are as follows.

 1 · · · · cathode, a · · 'magnesium-containing alloy, b, c, d-·' conductive layer, 2 · · · solid layer, 3 · · · cathode, 4 · · · substrate, 11 · · · cathode , 12 ... Electron injection layer, 13 ... Light emitting layer, 14 ... Hole transport layer, 15 ... Hole injection layer, 16 ... Transparent anode, 17 ... Transparent substrate, 21 ... Cathode, 26 ... ··· Anode, 27 ·· 'Substrate, 31 ··· Cathode, Β ··· Light extraction direction, Or' · · Solid layer.

 BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the organic EL element of the present application will be described with reference to FIG.

FIG. 1 is a schematic cross-sectional view showing a first embodiment of the organic EL element of the present application.

[0013] The organic EL element has a structure in which a solid layer including at least an organic light emitting layer is sandwiched between a cathode and an anode. Specifically, as shown in FIG. 3. Solid layer 2 and negative electrode 1 are stacked in this order (solid layer 2 is sandwiched between cathode 1 and anode 3). In such an organic EL element, the organic EL element of the present application is characterized in that the cathode 1 constituting the organic EL element contains magnesium in a proportion of less than 50%.

 Here, “the cathode 1 contains less than 50 percent of magnesium” means, for example, that the cathode 1 is formed of a magnesium-containing alloy containing less than 50 percent of magnesium. Say things. This will be specifically described below.

 [0015] The organic EL element of the present application is characterized in that the cathode 1 constituting the element is formed of a magnesium-containing alloy a containing magnesium at a ratio of less than 50 percent.

 Here, “magnesium (Mg) is included in a proportion of less than 50 percent” means that the number of magnesium atoms is less than 50 percent of the total number of metal atoms present in the magnesium-containing alloy layer. Is to do.

[0017] Thus, the cathode 1 is formed of the magnesium-containing alloy a containing magnesium in a proportion of less than 50%, whereby the voltage at the time of driving the organic EL element can be reduced. (This will be discussed later). [0018] The magnesium-containing alloy a constituting the cathode 1 is made of a magnesium-containing alloy that contains magnesium in a proportion of less than 50 percent. However, metals other than magnesium for forming the alloy are particularly limited. For example, it may be a simple substance such as silver (Ag) or an alloy such as ITO (Indium Tin Oxide). Further, it is not necessary to use one kind of metal other than magnesium for forming the alloy. Both Ag and ITO may be used.

 [0019] The magnesium content is not particularly limited as long as it is less than 50 percent. By lowering the magnesium content in the magnesium-containing alloy, the voltage at the time of driving the organic EL element can be reduced. However, if there is too little magnesium, a useful effect cannot be obtained. The minimum content is preferably 0.73% or more. Specifically, the proportion of magnesium in the magnesium-containing alloy is preferably 1.45% or more and 40% or less, and particularly preferably 45% or more and 20% or less.

 FIG. 2 is a schematic cross-sectional view showing a second embodiment of the organic EL element of the present application.

 FIG. 1 shows the force when the cathode 1 has a single-layer structure. The present application is not limited to this, and the cathode 1 has a multi-layer structure as shown in FIG. Also good. The configuration other than the cathode 1 in FIG. 2 (the configuration of the substrate 4, the anode 3, and the solid layer 2) is the same as that in FIG.

 [0022] As shown in Fig. 2, when the cathode 1 has a multi-layer structure, magnesium containing at least one layer of magnesium constituting the cathode 1 in a proportion of less than 50%. What is necessary is just to be formed with the alloy a. That is, as shown in FIG. 2, the cathode 1 is formed of a plurality of layers, at least one of which is formed of the magnesium-containing alloy a, and the other layers are the conductive layers b, c, d. What is necessary is just to be comprised by.

[0023] Thus, the cathode 1 is composed of a plurality of layers, and at least one of them is formed of the magnesium-containing alloy a containing magnesium at a ratio of less than 50 percent, whereby the organic EL The voltage at the time of driving the element can be lowered, and when the conductive layer b or d is formed on the layer containing the magnesium-containing alloy a !, the solid layer 2 is damaged. (This will be described later). Note that the conductive layers b, c, and d constituting the cathode 1 are not particularly limited as long as materials used as conventional electrodes are appropriately selected and used. For example, ITO, IZO, SnO (tin oxide) transparent conductive film (such as those doped with fluorine or antimony), Z

 2

 An ηθ (zinc oxide) transparent conductive film (such as one doped with aluminum or gallium) can be suitably used.

[0025] The thickness of the cathode 1 can be appropriately selected depending on the application, for example, 5ηπ! It should be about ~ 500nm.

 [0026] As shown in FIGS. 1 and 2, when the cathode 1 made of a magnesium-containing alloy a having a magnesium content of less than 50% is used, first, the voltage during driving of the organic EL element is lowered. The special effect of being able to be made can be acquired. Second, when the electrode is composed of a plurality of layers, that is, a layer formed of the magnesium-containing alloy a is laminated on the solid layer 2, and further, the ITO layers b, c are formed thereon by sputtering or the like. When d is laminated, the solid layer 2 is prevented from being damaged by the plasma, and the effect of reducing the damage to the solid layer 2 due to the lamination of the cathode can be obtained. In view of the effect, when the cathode 1 has a laminated structure, the layer formed of the magnesium-containing alloy a functions as a cathode and protects the solid layer 2 from damage during cathode formation. It is thought that it functions as a so-called buffer layer.

 Here, as shown in FIG. 2, the layer formed of the magnesium-containing alloy a of the cathode 1 is not limited to the structure sandwiched between the conductive layers b, c, d. As shown in FIG. 4, the layer formed of the magnesium-containing alloy a may be disposed at any position on the cathode 1. Specifically, as shown in FIG. 3, the layer formed of the magnesium-containing alloy a may be laminated on the outermost layer of the cathode 1, and as shown in FIG. 4, magnesium is less than 50 percent. The layer formed of the magnesium-containing alloy a contained in the ratio may be formed at least at a position in contact with the solid layer (see symbol a in FIG. 3), that is, the innermost layer of the cathode 1.

[0028] In view of the second effect (the effect of reducing the damage that the solid layer 2 suffers from the lamination of the cathode) while exerting force, a conductive material is formed on the magnesium-containing alloy as shown in FIG. 2 and FIG. When layers are stacked, the voltage at the time of driving the organic EL element can be lowered, Since it can also have an effect of reducing damage to the solid layer, it is desirable that the layer formed by the magnesium-containing alloy be placed inside the outermost layer.

[0029] Here, in FIGS. 2 to 4, force indicating a structure in which one layer formed of the magnesium-containing alloy a and three conductive layers are stacked is not limited to this structure. Absent. Specifically, when the cathode has a multi-layer structure, at least one layer should be formed of a magnesium-containing alloy containing magnesium in a proportion of less than 50 percent, and thus is formed of a magnesium-containing alloy. In addition to a plurality of layers, the conductive layer may be two layers, or three or more layers.

[0030] The solid layer 2 (see Figs. 1 to 4) constituting the organic EL element of the present application may also be of a single-layer structure in which only the light-emitting layer can be used, as will be described later. The electron injection layer, the light emitting layer, the hole transport layer, and the hole injection layer may be stacked to form a multilayer structure. A specific configuration of the solid layer 2 will be described later.

[0031] Also, the anode 3 (see FIGS. 1 to 4) constituting the organic EL element of the present application has a function of injecting holes into the solid layer. Therefore, there is no particular limitation as long as a conventional force is used as long as a layer having an energy level at which holes are easily injected is used. Specifically, ITO or the like can be preferably used.

[0032] Also, the substrate 4 (see FIGS. 1 to 4) is not particularly limited, and as will be described later, the organic EL element is used like a top emission structure or a bottom emission structure. Any selection may be made according to the situation and required performance. When transparency is required, for example, a plastic substrate or a glass substrate can be used.

Hereinafter, embodiments of the organic EL element of the present application will be described with reference to the drawings.

[0034] The fifth to tenth embodiments have a structure in which a cathode is provided on a solid layer.

[0035] First, the fifth embodiment and the sixth embodiment have a structure in which a cathode formed only of a magnesium-containing alloy is provided on a solid layer. By having a magnesium-containing alloy power containing magnesium in a proportion of less than 50 percent, the voltage at the time of driving the organic EL element can be reduced, and the effect can be obtained.

[0036] The organic EL element that works on the fifth embodiment shown in FIG. 5 includes a transparent anode 16 on a transparent substrate 17, A solid layer Or (a hole injection layer 15, a hole transport layer 14, a light emitting layer 13, an electron injection layer 12) and a negative electrode 11 are stacked in this order. Here, the electron injection layer 12 is not limited to be made of an organic material, and may be made of an inorganic material.

 [0037] Here, the hole injection layer 15 constituting the solid layer Or is a layer provided between the anode 16 and the light-emitting layer 13 for accelerating the injection of holes from the anode. It has the effects of lowering the drive voltage of EL elements, stabilizing hole injection and extending the life of the elements, and covering anode protrusions to reduce element defects. The material of the hole injection layer 15 may be selected as appropriate so that its ion energy is between the work function of the anode and the ion energy of the light emitting layer.

 [0038] The hole transport layer 14 is a layer provided between the hole injection layer 15 and the light emitting layer 13 for promoting the transport of holes, and the hole transport layer 14 is a positive layer. It functions to transport the holes to the light emitting layer 13. The material of the hole transport layer 14 may be appropriately selected so that the ion energy is between the hole injection layer 15 and the light emitting layer 13!

 [0039] The light emitting layer 13 is a layer that transports electrons and holes and further provides a field for recombination of electrons and holes. Since the light emitting layer 13 is functionally injected with both electrons and holes, resistance to simultaneous injection is used to extend the lifetime of the device. Therefore, the material of the light emitting layer 13 may be selected as appropriate so as to satisfy the above properties!

 Furthermore, the electron injection layer 12 is provided between the cathode 11 and the light emitting layer 13 and has a function of promoting the injection of electrons from the cathode 11. Effects such as lowering the driving voltage of organic EL elements, stabilizing electron injection and extending the life of the elements, strengthening the adhesion of the cathode 11, improving the uniformity of the light emitting surface, and reducing element defects Demonstrate. The electron affinity of the electron injection layer 12 may be appropriately selected so as to be between the work function of the cathode and the electron affinity of the light emitting layer.

In the organic EL device according to the fifth embodiment, the anode injects holes into the hole injection layer 15, while the cathode injects electrons into the electron injection layer 12. The injected holes and electrons each move toward the oppositely charged electrode. As a result, when a voltage is applied between both electrodes, light is emitted by recombination of holes injected from the anode and electrons injected from the cathode into the light emitting layer. The fifth embodiment is a so-called “bottom emission structure” organic EL element that extracts light only from the substrate side. Therefore, the substrate 17 and the anode 16 formed on the substrate 17 A transparent (or translucent) material is used.

 In the organic EL element of the present application, as shown in FIG. 6, the electron injection layer may not be laminated (sixth embodiment).

 In addition to such a “bottom emission structure”, a “transparent structure” shown in the seventh embodiment and the like, and a “top emission structure” shown in the ninth embodiment and the like can be used.

 Specifically, the seventh embodiment shown in FIG. 7 is a so-called “transparent structure” organic EL element that extracts light from both the substrate side and the opposite side of the substrate.

 [0046] The cathode 21 of the organic EL element that works well with the seventh embodiment shown in FIG. 7 has a structure formed of any one of a magnesium-containing alloy alone, a magnesium-containing alloy, and a laminated type of a transparent conductive layer. be able to. Here, when the cathode is made by stacking a transparent conductive layer on a magnesium-containing alloy, the magnesium-containing alloy is in contact with the electron injection layer 12.

 [0047] In order to extract light from both the substrate side and the opposite side of the substrate, both the substrate 17 and the anode 16 produced on the substrate 17 are transparent. The cathode 21 which is a feature of the present application is provided on the side opposite to the substrate, but light can be extracted with any structure by forming the cathode thin.

 Furthermore, in the organic EL element of the present application, as shown in FIG. 8, the electron injection layer may not be stacked (eighth embodiment).

 [0049] The organic EL element that works on the ninth embodiment shown in FIG. 9 is a so-called "top emission structure" organic EL element that extracts light only from the side opposite to the substrate.

 [0050] Even in this case, the cathode may be thinly formed as in the seventh embodiment. On the other hand, in the organic EL element of the “top emission structure”, it is not necessary to extract light from the substrate. Therefore, the combination of the anode 26 and the substrate 27 is an opaque anode Z substrate, transparent anode Z opaque substrate, transparent It may be composed of a misalignment of the substrate with the anode Z opaque layer.

[0051] Note that even in the "top emission structure", as shown in FIG. 10, the electron injection layer may not be stacked (tenth embodiment). [0052] Unlike the organic EL elements described above, the eleventh to sixteenth embodiments described below have a structure in which a cathode is provided on a substrate. As described above, the organic EL element of the present application can also have a structure in which the cathode is provided on the substrate (reverse stacking structure), and even in this case, the voltage at the time of driving the organic EL element is lowered. The effect can be achieved.

 FIGS. 11 to 16 show the eleventh to sixteenth embodiments of the organic EL element of the present application.

 [0054] These organic EL devices have a cathode 31 or a cathode 21, a solid layer Or (electron injection layer 12, light emitting layer 13, hole transport layer 14, and hole injection layer 15) on a substrate 27, transparent It is formed by laminating anode 16 or opaque anode 26 in this order.

The eleventh embodiment and the twelfth embodiment are “top emission structure” organic EL elements, and the twelfth embodiment is obtained by removing the electron injection layer from the eleventh embodiment.

In addition, the thirteenth embodiment and the fourteenth embodiment are “transparent structure” organic EL elements, and the fourteenth embodiment is the same as the thirteenth embodiment except for the electron injection layer.

Further, in the fifteenth embodiment and the sixteenth embodiment, the “bottom emission structure” organic E

In the sixteenth embodiment, the electron injection layer is removed from the fifteenth embodiment.

 Example

 [0058] Next, the voltage drop when driving the element of "one cathode formed of a magnesium-containing alloy containing magnesium in a proportion of less than 50%", which is a feature of the present application, is as follows. Examples will be described.

 [Example 1]

 A magnesium-containing alloy composed of magnesium (Mg) and silver (Ag) was prepared.

[0060] Specifically, the ratio of Mg and Ag in the magnesium-containing alloy was changed so that the ratio of Mg and Ag was as follows: Sample l; Mg: Ag = 73.6: 10, Sample 2; Mg: Ag Samples 1 to 3 were prepared so that = 7.4: 10, Sample 3; Mg: Ag = 0.7: 10. Here, Sample 1 is not a cathode formed of a magnesium-containing alloy having the characteristics of the present application, but the experimental results of Sample 2 and Sample 3 using the magnesium-containing alloy having the characteristics of the present application are compared. Used for It is a thing.

 [0061] Fig. 17 shows the results of examining voltage-current characteristics using these magnesium-containing alloys.

 As is clear from FIG. 17, when the voltage-current characteristics of each sample are compared, the voltage at the time of element driving decreases as the magnesium content decreases. From this result, the magnesium-containing alloy It can be seen that the voltage at the time of element driving can be further lowered by lowering the content of magnesium in the element.

 [0063] (Example 2)

 A magnesium-containing alloy such as Mg and Ag was prepared, and an ITO layer was laminated thereon.

 [0064] Specifically, the ratio of Mg and Ag in the magnesium-containing alloy was changed so that the ratio of Mg to Ag was as follows: Sample 4; Mg: Ag = 73.6: 10, Sample 5; Mg: Ag = 7.4: 10, Sample 6; Samples 4 to 6 were prepared so that Mg: Ag = 0.7: 10, and an ITO layer was laminated thereon. Here, Sample 4 is not a cathode formed of a magnesium-containing alloy having the characteristics of the present application, but in order to compare the experimental results of Sample 5 and Sample 6 using the magnesium-containing alloy having the characteristics of the present application. It is what was used.

 [0065] Fig. 18 shows the results of investigating the voltage-current characteristics using these magnesium-containing alloys.

 As is clear from FIG. 18, when the voltage-current characteristics of each sample are compared, the voltage at the time of element driving decreases as the magnesium content decreases, as in Example 1. The results also show that the voltage at the time of element driving can be further reduced by lowering the magnesium content in the magnesium-containing alloy.

 [0067] Further, when Example 1 and Example 2 were compared, in both cases, it was possible to further reduce the voltage at the time of element driving by lowering the magnesium content in the magnesium-containing alloy. .

[0068] Further, for example, the drive voltage values at the current density of 50 mA Zcm ^{2 in} the graphs of Sample 3, Sample 2, and Sample 1 shown in FIG. 17 are 7.3, 7.5, and 7.7 V, respectively. However, the values of the drive voltage at the current density of 50 mAZcm ^{2 in} the graphs of Sample 6, Sample 5, and Sample 4 shown in FIG. 18 are 7.8, 8.2, and 8.5 V, respectively. [0069] From this, the difference in the driving voltage of Sample 6, Sample 5, and Sample 4 shown in FIG. 18 is larger than the difference in the driving voltage of Sample 3, Sample 2, and Sample 1 shown in FIG. I understand.

[0070] Therefore, in the case of using a cathode in which an ITO layer is laminated on a magnesium-containing alloy, as the Mg ratio decreases, the ratio of preventing damage to the solid layer 2 during the ITO lamination increases. I understand.

[0071] Therefore, based on these results, a magnesium-containing alloy having Mg and Ag force is produced, and the effect of preventing damage when the cathode having the ITO layer laminated thereon is laminated on the solid layer 2 is further increased. I was able to reduce the voltage.

[0072] Note that the range in which the element driving voltage is used varies depending on the application and may be arbitrarily used depending on the design matter as long as sufficient luminance can be obtained.

[0073] As described above, the organic material using the magnesium-containing alloy in the ratio shown in the present application as a cathode.

In the EL element, the voltage at the time of driving the element can be lowered, and further, the effect of reducing the damage that the solid layer receives due to the lamination of the electrodes formed thereon can be improved.

[0074] Further, as shown in the embodiment, "bottom emission type organic EL display" that extracts only the side force of the substrate, "top emission type organic EL display" that extracts only the side force opposite to the substrate, substrate It can be applied to a “transparent organic EL display” that extracts light from both the side and the opposite side of the substrate.

Note that the organic EL element of the present application is not limited to the above embodiment. Any device that has substantially the same configuration as the technical idea described in the scope of the patent request and that exhibits the same function and effect is included in the technical scope of the organic EL device of the present application. It is.

Claims

The scope of the claims  [1] In an organic EL device having a structure in which a solid layer including at least an organic light emitting layer is sandwiched between a cathode and an anode,  The organic EL device, wherein the cathode contains magnesium in a proportion of less than 50 percent.  [2] In an organic EL device having a structure in which a solid layer including at least an organic light emitting layer is sandwiched between a cathode and an anode,  The organic EL device, wherein the cathode is formed of a magnesium-containing alloy containing magnesium in a proportion of less than 50 percent. [3] In an organic EL device having a structure in which a solid layer including at least an organic light emitting layer is sandwiched between a cathode and an anode,  The organic EL device, wherein the cathode is composed of a plurality of layers, at least one of which is formed of a magnesium-containing alloy containing magnesium in a proportion of less than 50 percent. [4] The layer according to claim 3, wherein the layer formed by the magnesium-containing alloy containing less than 50% of the magnesium is formed at a position in contact with the solid layer. Organic EL element. [5] A magnesium-containing alloy containing less than 50 percent of the magnesium 5. The organic EL device according to claim 1, which is an alloy composed of a mixture of magnesium and silver.