JP2007134210A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element enabled to improve its light-emitting life, especially at high-temperature, high-brightness driving. <P>SOLUTION: The organic EL element is formed by laminating an organic layer 5 having at least a hole injection layer (a hole injection transport layer) 5a and a light-emitting layer 5b between a positive electrode and a negative electrode. An ionization potential of the positive electrode is to be higher than that of the hole injection layer 5a, and a difference between the former and the latter is to be 0.2 eV or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic EL (electroluminescence) element formed by laminating an organic layer having at least a hole injection layer and a light emitting layer between an anode and a cathode.

  An organic EL element, which is a self-luminous element formed of an organic material, includes, for example, a first electrode made of ITO (Indium Tin Oxide) or the like serving as an anode, an organic layer having at least a light emitting layer, and aluminum (Al And a non-translucent second electrode made up of, for example, are formed to form the organic EL element (see, for example, Patent Document 1).

  Such an organic EL element emits light by injecting holes from the first electrode, and by injecting electrons from the second electrode to recombine the holes and electrons in the light emitting layer. There is a demand for extending the lifetime of emitting light at a predetermined luminance for a long time.

  The first electrode and the light emitting layer have a problem that a barrier is generated against the movement of holes due to the difference in ionization potential, and the driving voltage at the time of light emission driving increases, and in order to reduce the driving voltage, A method of forming a hole injection layer made of a hole transporting material having an ionization potential higher than that of the anode and lower than that of the light emission layer between the anode and the light emitting layer is known (for example, a patent) Reference 1).

In order to improve the hole injection efficiency, the surface of the first electrode is activated by performing a surface treatment such as plasma treatment when the first electrode is formed, and the ionization potential of the first electrode is increased. There are known ways to increase it. Generally, the surface treatment is performed so that the ionization potential of the first electrode is 5.0 eV or more, and a material having an ionization potential of about 5.2 to 5.3 eV is used for the hole injection layer.
JP 59-194393 A

  By the way, when surface-treating the first electrode, depending on the treatment method, the ionization potential of the anode may be higher than the ionization potential of the hole injection layer. Conventionally, in such a case, it has been considered that the movement of holes between the first electrode and the hole injection layer is not affected. However, as a result of research and development, the inventor of the present application said that even in such a case, the light emission lifetime particularly during high-temperature and high-luminance driving is greatly affected by the relationship between the ionization potential of the first electrode and the hole injection layer. I found a problem.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an organic EL element capable of improving the light emission lifetime particularly when driving at high temperature and high luminance.

  In order to solve the above problems, the organic EL panel of the present invention is an organic EL element formed by laminating an organic layer having at least a hole injection layer and a light emitting layer between an anode and a cathode. The ionization potential is higher than the ionization potential of the hole injection layer, and the difference between the ionization potential of the anode and the ionization potential of the hole injection layer is 0.2 eV or less. element.

  The anode has an ionization potential higher than 5.4 eV.

  The hole injection layer has an ionization potential of 5.4 eV or more.

  The anode is characterized in that the surface thereof is plasma-treated.

  The present invention relates to an organic EL device in which an organic layer having at least a hole injection layer and a light-emitting layer is laminated between an anode and a cathode, and can particularly improve the light emission lifetime during high-temperature and high-luminance driving. It is possible.

  Hereinafter, embodiments in which the present invention is applied to a dot matrix type organic EL panel will be described with reference to the accompanying drawings.

  In FIG. 1, an organic EL panel A includes a support substrate 1, a first electrode (anode) 2, an insulating layer 3, a partition wall 4, an organic layer 5, a second electrode (cathode) 6, and a sealing. It is mainly composed of the member 7.

  The support substrate 1 is a translucent glass substrate having a rectangular shape.

  The first electrode 2 is formed by layering a light-transmitting conductive material such as ITO on the support substrate 1 by a method such as sputtering or vapor deposition, and patterning it in a stripe shape by a photolithography method, for example. is there. As shown in FIG. 1A, the first electrode 2 has an anode wiring portion 2a and an anode portion 2b. The anode wiring portion 2a is an anode terminal portion for electrically connecting to an external power source at the terminal portion. 2c. Further, the surface of the first electrode 2 is subjected to a surface treatment such as a plasma treatment, and the ionization potential Ip1 is higher than at least 5.4 eV. Further, the ionization potential Ip2 of a hole injection transport layer described later is used. It is formed so as to be higher.

  The insulating layer 3 is made of an insulating material such as polyimide or phenol, and is formed in a predetermined shape on a non-light emitting portion on the support substrate 1 by means such as photolithography. The insulating layer 3 is formed between the anode portions 2b of the first electrode 2 and is formed so as to slightly overlap the first electrode 2, and insulates the first electrode 2 from a second electrode described later. It is.

  The partition wall portion 4 is made of, for example, a phenol-based insulating material, and has a cross section formed in a reverse taper shape by means such as a photolithography method. The partition wall portion 4 is formed on the first electrode 2 and the insulating layer 3 so as to cross the anode portion 2b at a substantially right angle, and in a portion corresponding to a cathode wiring portion described later on the support substrate 1, FIG. ), The support substrate 1 is formed to have an arc shape when viewed from the organic EL element formation surface side.

  The organic layer 5 is formed on the first electrode 2 and the insulating layer 3, and as shown in FIG. 2, a hole injection transport layer (hole injection layer) 5a, a light emitting layer 5b, and an electron transport layer 5c. In addition, the electron injection layer 5d is sequentially laminated by means such as vapor deposition to form a layer having a thickness of about 80 to 280 nm.

  The hole injecting and transporting layer 5a has a function of capturing holes from the first electrode 2 and transmitting the holes to the light emitting layer 5c. For example, a hole transporting material having a high hole mobility such as an amine compound is used for the vapor deposition method or the like. It is formed in a layered form with a film thickness of about 20 to 80 nm by means. In the hole injection transport layer 5a, a material having an ionization potential Ip2 of 5.4 eV or more is used as the hole transport material. Further, in the hole injection transport layer 5a, the difference between the ionization potential Ip1 of the first electrode 2 after the plasma treatment and the ionization potential Ip2 of the hole injection transport layer 5a is 0.2 or less (Ip1-Ip2 ≦ 0. The hole transport material is selected so as to be 2). Further, the hole injection transport layer 5a has a glass transition temperature of 85 ° C. or higher (more preferably 100 ° C. or higher).

  As shown in FIG. 2, the light emitting layer 5 b is formed by doping a host material 5 e with at least a fluorescent material 5 f as a guest material by means of vapor deposition or the like to form a layer having a thickness of about 20 to 60 nm. The host material 5e can transport holes and electrons, and has a function of emitting light when the holes and electrons are transported and recombined, and is made of, for example, a distyrylarylene derivative. The host material 5e has a glass transition temperature of 85 ° C. or higher (more preferably 100 ° C. or higher). The fluorescent material 5f has a function of emitting light in response to recombination of electrons and holes, and is made of BD102 manufactured by Idemitsu Kosan Co., Ltd. that exhibits a predetermined emission color, for example, blue-green emission. Note that it is desirable that the amount of doping of the fluorescent material 5f is set so as not to cause concentration quenching. In this embodiment, the fluorescent material 5f is added so that the concentration in the light emitting layer 5b is 2 to 8%. Has been.

  The electron transport layer 5d has a function of transmitting electrons to the light emitting layer 5b. For example, an electron transport material having high electron mobility such as aluminum quinolinol (Alq3) which is a chelate compound is deposited by means such as vapor deposition. It is formed in a layer shape of about 20 to 60 nm.

  The electron injection layer 5e has a function of injecting electrons from the second electrode 6. For example, lithium fluoride (LiF) is formed into a layer having a thickness of about 1 nm by means such as vapor deposition.

  The second electrode 6 is formed by forming a conductive material such as aluminum (Al) or magnesium silver (Mg: Ag) into a layer having a thickness of about 50 to 200 nm by means such as vapor deposition. As a result, the arc-shaped cathode wiring portion 6a and the cathode portion 6b intersecting the transparent electrode 2 at a substantially right angle are formed (see FIG. 1A). Further, the cathode wiring portion 6 a is electrically connected to the connection wiring portion 8. The connection wiring portion 8a is formed together with the first electrode 2, and is made of the same material ITO. Further, the connection wiring portion 8 is formed with a cathode terminal portion 8a for electrical connection with the external power source at the terminal portion.

  As described above, the first electrode 2, the insulating layer 3, the partition wall portion 4, the organic layer 5, and the second electrode 6 are sequentially laminated on the support substrate 1, and are formed from the opposing portions of the anode portion 2 b and the cathode portion 6 b. An organic EL element in which light emitting pixels are provided in a matrix is obtained.

  The sealing member 7 is formed by forming a molded glass or flat plate member made of, for example, a glass material into a concave shape by an appropriate method such as sandblasting, cutting, and etching. The sealing member 7 is hermetically disposed on the support substrate 1 via an adhesive 7 a made of, for example, an ultraviolet curable epoxy resin, so that the organic EL element is sealed between the sealing member 7 and the support substrate 1. Stop. The sealing member 7 is configured to be slightly smaller than the support substrate 1 so that the anode terminal portion 2c of the first electrode 2 and the cathode terminal portion 8a connected to the second electrode 6 are exposed to the outside. The sealing member may have a flat plate shape. In this case, the sealing member is disposed on the support substrate via a spacer.

  As described above, the dot matrix type organic EL panel A using the organic EL element in which the pixels formed of the opposed portions of the anode portion 2b and the cathode portion 6b are provided in a matrix form is obtained. In the organic EL panel A, holes from the first electrode 2 and electrons from the second electrode 6 are recombined in the light emitting layer 5b to obtain blue-green light emission. Further, the organic EL panel A selects either one of the plurality of anode portions 2b and the plurality of cathode portions 6b formed in a stripe shape and applies a constant current, and the selected anode portion 2b and the cathode portion 6b face each other. It is driven by so-called passive driving, in which a pixel consisting of locations emits light.

  FIG. 3 is a diagram showing a result of evaluation in a high-temperature operation test described later with respect to an example obtained by the above configuration and a comparative example for comparison with the example. The vertical axis indicates the ratio (L / L0) of the current light emission luminance L to the initial luminance L0, and the horizontal axis indicates the drive time.

  Characteristic S1 shows the test result of Example 1. In Example 1, as the organic EL panel A, the first electrode 2 is formed with a film thickness of 100 nm, a line width of 290 μm, a line spacing of 40 μm and a number of 128, and the cathode 8 is formed with a film thickness of 100 nm, a line width of 290 μm, and a line spacing of 40 μm. In addition, it is formed of 64 lines and can display a monochrome color of 64 × 128 blue-green. Further, in Example 1, the first electrode 2 is formed by plasma treatment so that the ionization potential Ip1 becomes 5.6 eV, and the hole injection transport layer 5a has a hole transport property in which the ionization potential Ip2 is 5.43 eV. It is made of a material. That is, the difference between the ionization potential Ip1 of the first electrode 2 and the ionization potential Ip2 of the hole injection transport layer 5a in Example 1 is set to 0.17 eV (Ip1−Ip2 = 0.17 eV). In addition, the value of each ionization potential in an Example and a comparative example is measured by Riken Keiki Co., Ltd. AC-2.

  The characteristic S2 shows the test result of Example 2. In Example 2, the hole injection transport layer 5a is formed of a hole transport material having an ionization potential Ip2 of 5.5 eV, and the ionization potential Ip1 of the first electrode 2 and the ionization potential of the hole injection transport layer 5a. The organic EL panel A was formed in the same manner as in Example 1 except that the difference from Ip2 was 0.1 eV (Ip1-Ip2 = 0.1 eV).

  Characteristic S3 shows the test result of Comparative Example 1. In Comparative Example 1, the hole injection transport layer 5a is formed of a hole transport material having an ionization potential Ip2 of 5.2 eV, and the ionization potential Ip1 of the first electrode 2 and the ionization potential of the hole injection transport layer 5a. The organic EL panel A was formed in the same manner as in Example 1 except that the difference from Ip2 was 0.4 eV (Ip1-Ip2 = 0.4 eV).

  Characteristic S4 indicates the test result of Comparative Example 2. In Comparative Example 2, the hole injecting and transporting layer 5a is formed of a hole transporting material having an ionization potential Ip2 of 5.2 eV (however, different from the hole transporting material in Comparative Example 1). The organic EL panel A was fabricated in the same manner as in Example 1 except that the difference between the ionization potential Ip1 of the electrode 2 and the ionization potential Ip2 of the hole injection transport layer 5a was 0.4 eV (Ip1−Ip2 = 0.4 eV). Formed.

  Characteristic S5 shows the test result of Comparative Example 3. In Comparative Example 3, the hole injection / transport layer 5a is formed of a hole transport material having an ionization potential Ip2 of 5.38 eV, and the ionization potential Ip1 of the first electrode 2 and the ionization potential of the hole injection / transport layer 5a. The organic EL panel A was formed in the same manner as in Example 1 except that the difference from Ip2 was 0.22 eV (Ip1-Ip2 = 0.22 eV).

  As the high-temperature operation test, each of the organic EL modules of Examples 1 and 2 and Comparative Examples 1 to 3 is installed in a constant temperature bath of 85 ° C., and is lit up with an initial luminance L0 of 1000 cd / m 2. The time from the initial luminance L0 to halving (L / L0 = 0.5) was measured.

  As is clear from FIG. 3, in Examples 1 and 2, the time until the emission luminance is reduced by half from the initial luminance is longer than in Comparative Examples 1 to 3. FIG. 4 shows the relationship between the ionization potential and the emission lifetime of the hole injection transport layer 5a obtained from the test results of Examples 1 and 2 and Comparative Examples 1 to 3. In FIG. 4, the vertical axis indicates the time until the current emission luminance L is halved from the initial luminance L0, and the horizontal axis indicates the ionization potential value of the hole injection transport layer 5a. As apparent from FIG. 4, as in the present invention, the difference between the ionization potential Ip1 of the first electrode 2 and the ionization potential Ip2 of the hole injection transport layer 5a is 0.2 eV or less (Ip1-Ip2 ≦ 0. 2 eV), it is possible to improve the light emission lifetime of the organic EL element in the high temperature and high luminance light emission driving in which the atmosphere is 85 ° C. and the initial luminance L0 is 1000 cd / m 2.

  Although the present embodiment is a dot matrix type organic EL panel A, the present invention can be applied to a segment type organic EL panel and can also be applied to active driving.

  Further, the organic EL panel A of the present embodiment has a configuration in which the hole injection transport layer 5a is formed between the first electrode 2 and the light emitting layer 5b. In the present invention, the anode, the light emitting layer, A hole injection layer and a hole transport layer may be sequentially stacked between the layers.

  Further, in the organic EL panel A of the present embodiment, the light emitting layer 5b is obtained by doping the host material 5e with the fluorescent material 5f that emits light in blue-green. May emit light in other emission colors.

The figure which shows the organic electroluminescent panel to which this invention was applied. The expanded sectional view which shows the organic layer same as the above. The figure which shows the result of the high-temperature operation test of the Example and comparative example of an organic electroluminescent panel same as the above. The figure explaining the relationship between the ionization potential and emission lifetime of the positive hole injection transport layer of the Example and comparative example of an organic electroluminescent panel same as the above.

Explanation of symbols

A Organic EL panel 1 Support substrate 2 First electrode (anode)
3 Insulating layer 5 Organic layer 5a Hole injection transport layer (hole injection layer)
5b Light emitting layer 5c Electron transport layer 5d Electron injection layer 5e Host material 5f Fluorescent material 6 Second electrode (cathode)

Claims (4)

An organic EL element formed by laminating an organic layer having at least a hole injection layer and a light emitting layer between an anode and a cathode,
The ionization potential of the anode is higher than the ionization potential of the hole injection layer, and the difference between the ionization potential of the anode and the ionization potential of the hole injection layer is 0.2 eV or less. Organic EL element. The organic EL device according to claim 1, wherein the anode has an ionization potential higher than 5.4 eV. 2. The organic EL device according to claim 1, wherein the hole injection layer has an ionization potential of 5.4 eV or more. 2. The organic EL device according to claim 1, wherein the surface of the anode is plasma-treated.

Images