JP2006173050A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EL element formed by laminating an organic layer at least composed of a plurality of light-emitting layers having different emission colors between a pair of electrodes, capable of emitting light for a long time with prescribed brightness and prolonging a lifetime. <P>SOLUTION: The EL element is formed by laminating an organic layer 5 at least composed of a plurality of light emitting layers having different emission colors between an anode (first electrode) 3 and a cathode (second electrode ) 6. The light emitting layer is composed of a first light emitting layer 5b located at the anode 3 side formed by mixing a first host material having hole transporting property and a first light emitting material, and a second light emitting layer 5c located at the cathode 6 side so as to contact the first light emitting layer 5b formed by mixing the first host material, a second host material capable of transporting hole and electron, and a second light emitting material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic EL (electroluminescence) element in which an organic layer having at least a plurality of light emitting layers is laminated between a pair of electrodes.

  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 injecting electrons from the second electrode, and the holes and electrons recombine in the light emitting layer. Therefore, it is desired to extend the life of light for a long time with a predetermined luminance.

As a method for extending the lifetime of an organic EL device, Patent Document 2 has one or more light emitting layers including a blue light emitting layer, and the blue light emitting layer is a hole (hole) transport layer and / or An organic EL device containing a hole transporting compound and / or an electron transporting compound in an electron transporting layer as a host material is disclosed. Patent Document 2 discloses that when a light emitting layer other than blue is provided, a light emitting material is added to a similar host material to emit light of a color different from blue.
JP 59-194393 A JP 2001-52870 A

  However, in an organic EL device including a plurality of light emitting layers having different emission colors, when the transport material is mixed in each light emitting layer, the concentration of the transport material contained in each light emitting layer is particularly equal. In such a case, there is a problem that the light emission efficiency is lowered due to the poor carrier balance in each light emitting layer, and the light emitting lifetime is shorter than that of the organic EL element when the transporting material is not mixed. .

  In view of such a problem, an object of the present invention is to provide an organic EL element having at least a plurality of light emitting layers and capable of extending the lifetime of emitting light at a predetermined luminance for a long time.

  In order to solve the above problems, the organic EL element of the present invention is an organic EL element formed by laminating an organic layer having at least a plurality of light emitting layers between an anode and a cathode, and as the light emitting layer, A first light-emitting layer, which is located on the anode side and is a mixture of a first host material having a hole transporting property and a first light-emitting material, and is formed on the cathode side so as to be in contact with the first light-emitting layer And a second light-emitting layer obtained by mixing the first host material, a second host material capable of transporting holes and electrons, and a second light-emitting material. To do.

  In addition, the present invention is characterized in that the second host material is made of an organic material whose electron mobility is higher than that of the first host material.

  In the invention, it is preferable that the second light emitting layer is formed so that the content of the first host material is 10 mass percent or more and 70 mass percent or less with respect to the entire layer. .

  Further, the present invention is characterized in that the organic layer has a hole transport layer formed between the anode and the first light emitting layer and made of the same material as the first host material. To do.

  Further, according to the present invention, the second light-emitting layer has a high concentration of the first host material on the side close to the first light-emitting layer in the layer, and faces away from the first light-emitting layer. The first host material is formed to have a low concentration.

  Further, according to the present invention, the first light-emitting layer has a high concentration of the first light-emitting material on the side close to the second light-emitting layer, and on the side far from the second light-emitting layer. The first light-emitting material is formed so that the concentration thereof becomes lower.

  In the present invention, the first and second light-emitting layers exhibit different emission colors, and the second light-emitting layer exhibits an emission color having a shorter emission main wavelength than the first light-emitting layer. It is characterized by that.

  In the invention, it is preferable that the second light emitting layer exhibits blue light emission.

  The present invention relates to an organic EL element in which an organic layer having at least a plurality of light-emitting layers is laminated between a pair of electrodes, and makes it possible to extend the lifetime of light emission for a long time with a predetermined luminance.

  Hereinafter, an embodiment in which an organic EL element of the present invention is applied to a segment type organic EL panel will be described with reference to the accompanying drawings.

  In FIG. 1, the organic EL panel is formed by arranging an organic EL element 1 on a translucent support substrate 2. The organic EL element 1 mainly includes a translucent first electrode (anode) 3, an insulating layer 4, an organic layer 5, and a second electrode (cathode) 6. Further, a sealing member 7 is disposed on the support substrate 2 so as to cover the organic EL element 1 in an airtight manner. Such an organic EL panel takes out light emitted from the organic EL element 1 from the support substrate 2 side, and obtains a white display by mixing yellow light emitted from a first light emitting layer and blue light emitted from a second light emitting layer, which will be described later. is there.

  The support substrate 2 is a translucent glass substrate having a rectangular shape.

  The first electrode 3 serves as an anode for injecting holes into the organic layer 5, and a conductive material such as ITO is deposited on the support substrate 2 by means of a vapor deposition method, a sputtering method or the like in a layered form having a film thickness of 50 to 200 nm. Are formed by patterning according to, for example, a Japanese character display design by photolithography etching or the like, and a lead character display segment portion 3a and lead portions that are respectively drawn from individual segments. 3b and an electrode portion 3c provided at the end portion of the lead portion 3b. The electrode portion 3c is intensively arranged on one side of the support substrate 2 and is electrically connected to a constant current source (not shown).

  The insulating layer 4 is made of an insulating material such as polyimide or phenol, and is formed into a layer shape by means such as sputtering, and has a predetermined shape at a non-light emitting location on the support substrate 2 by means of etching such as photolithography. Is formed. The insulating layer 4 has a window portion 4a corresponding to the display segment 3a and a notch portion 4b corresponding to an electrode portion to be described later of the second electrode 6, and displays the outline of the light emitting region clearly. A window 4a is formed so as to slightly overlap the peripheral edge of the display segment 3a of the electrode 3, and is disposed so as to cover the lead 3b in order to ensure insulation between the first electrode 3 and the second electrode 6. Is done.

  The organic layer 5 is formed with a predetermined size on the first electrode 3 and the insulating layer 4 so as to correspond to the location of the window 4a in the insulating layer 4, and as shown in FIG. The hole transport layer 5a, the first light emitting layer 5b, the second light emitting layer 5c, the electron transport layer 5d, and the electron injection layer 5e are sequentially laminated by means such as vapor deposition.

  The hole transport layer 5a has a function of capturing holes from the first electrode 3 and transmitting the holes to the light emitting layer 5c. For example, a hole transport material such as α-NPD which is an arylamine derivative is deposited. It is formed in a layer shape having a film thickness of 10 to 60 nm by such means.

  The first light emitting layer 5b uses the hole transporting material constituting the hole transporting layer 5a capable of transporting holes as a first host material, and the first host material includes electrons and holes. A first light-emitting material made of, for example, a naphthacene derivative that has a function of emitting light in response to recombination with yellow and emits yellow light is mixed by means such as co-evaporation to form a layer having a thickness of about 20 nm, for example. . The first host material is preferably a material that does not transport electrons when a constant current for driving the organic EL element 1 to emit light is applied. Further, as the first light emitting material, the highest occupied orbital level (hereinafter referred to as HOMO level) is smaller than the HOMO level of the first host material, and the electron affinity is the first host material. It is preferable to use a material having a larger electron affinity. By using such a material, holes or electrons are easily captured in the trap of the first light emitting material in the first light emitting layer 5b, and the first light emitting material 5b2 can be efficiently emitted. . Further, the first light emitting layer 5b has a low concentration of the first light emitting material in the vicinity of the hole transport layer 5a and is directed to the vicinity of the second light emitting layer 5d on the side far from the hole transport layer 5a. It is formed to become gradually higher. The first light-emitting material has a HOMO level of 5.4 eV, a lowest unoccupied orbital level (hereinafter referred to as a LUMO level) of 3.2 eV, and an energy gap value of 2.2 eV. ing. The HOMO levels of the first host material, the first light emitting material, and the second light emitting material to be described later were measured by AC-2 manufactured by Riken Keiki Co., Ltd. The LUMO levels of the material and the second light emitting material are optically estimated.

  The second light emitting layer 5c is an organic material capable of transporting holes and electrons, for example, a second host material made of IDE120 manufactured by Idemitsu Kosan Co., Ltd., and the first light emitting layer 5b. For example, manufactured by Idemitsu Kosan Co., Ltd., which has a function of emitting light in response to recombination of the host material with electrons and holes and has a light emission dominant wavelength shorter than the yellow light emission of the first light emitting material The second light-emitting material made of BD102 is mixed by means such as co-evaporation, and is formed into a thicker layer than the first light-emitting layer 5b having a thickness of about 30 nm, for example. As the second host material, an organic material having an electron mobility higher than that of the first host material is desirable, and a material that includes at least the energy gap of the second light-emitting material in the energy gap is used. . In the second light emitting layer 5c, the content of the first host material with respect to the entire layer is 10 mass percent or more and 70 mass percent. More preferably, the content of the first host material is 50% by mass or less. The second light-emitting layer 5c has a high concentration of the first host material in the vicinity of the first light-emitting layer 5b where holes are transported, and is close to the electron transport layer 5d where electrons are transported. It is formed to become gradually lower. The second host material has a HOMO level of 5.7 eV, the second light-emitting material has a HOMO level of 5.5 eV, and the second host material, the second light-emitting material, The difference in the HOMO level of the sample is 0.2 eV. The difference in the HOMO level between the second light emitting material and the second host material is preferably less than 0.3 eV. The second light-emitting material has a LUMO level of 2.7 eV and an energy gap value of 2.8 eV, which is larger than that of the first light-emitting material.

  The electron transport layer 5d is formed by forming an electron transport material such as aluminum quinolinol (Alq3), which is a chelate-based compound having a function of transmitting electrons to the light emitting layer 5c, into a layer shape having a film thickness of 20 to 60 nm by means such as vapor deposition. It becomes.

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

  The second electrode 6 serves as a cathode for injecting electrons into the organic layer 5, and a conductive material such as aluminum (Al) or magnesium silver (Mg: Ag) is deposited to a thickness of 50 to 200 nm by means such as vapor deposition. And is electrically connected to a lead portion 6 a provided on one side of the support substrate 2. Note that an electrode portion (leading portion) 6b is provided at the end portion of the lead portion 6a, and the lead portion 6a and the electrode portion 6b are formed of the same material as the first electrode 3. The electrode portion 6b is electrically connected to the constant current source.

  The sealing member 7 is formed by forming a concave portion 7a in a flat plate member made of, for example, a glass material by an appropriate method such as sandblasting, cutting, and etching. The sealing member 7 is airtightly disposed on the support substrate 2 via an adhesive (not shown) made of, for example, an ultraviolet curable epoxy resin, with the support portion 7b formed so as to surround the recess 7a. The organic EL element 1 is sealed with the sealing member 7 and the support substrate 2. The sealing member 7 is configured to be slightly smaller than the support substrate 2 so that the electrode portion 3c of the first electrode 3 and the electrode portion 6b of the second electrode 6 are exposed to the outside.

  The organic EL element 1 according to the present embodiment is formed by laminating an organic layer 5 having at least a plurality of light emitting layers between a first electrode 3 and a second electrode 6, and the first electrode 3 is used as the light emitting layer. The first light emitting layer 5b formed by mixing the first host material having a hole transporting property and the first light emitting material located on the side, and in contact with the first light emitting layer 5b on the second electrode 6 side A second light-emitting layer 5c formed by mixing the first host material and the second host material capable of transporting holes and electrons and the second light-emitting material. It will be. The second light emitting layer 5c is formed so that the content of the first host material is 10 mass percent or more and 70 mass percent or less with respect to the entire layer. Further, the first light emitting layer 5b has a high concentration of the first light emitting material on the side close to the second light emitting layer 5c in the layer, and the first light emitting layer 5b is further away from the second light emitting layer 5c. The light emitting material is formed so as to have a low concentration. The first and second light-emitting layers 5b and 5c show different emission colors, and the second light-emitting layer 5c shows an emission color having a shorter emission main wavelength than the first light-emitting layer 5b. is there. Further, the second light emitting layer 5c exhibits blue light emission.

  The organic EL element 1 having such a configuration emits yellow light in the interface region with the second light emitting layer 5c in the first light emitting layer 5b, and emits blue light in the entire layer in the second light emitting layer 5c. As shown, light is emitted mainly in a region near the first light-emitting layer 5b where the concentration of the first host material is high. In the first light emitting layer 5b located on the first electrode 3 side for injecting holes into the organic layer 5, the first host material having hole transportability is used as a single host material. Electrons are not easily transported into the light emitting layer 5b. Therefore, electrons injected from the second electrode 6 are mainly accumulated in the interface region with the first light emitting layer 5b in the second light emitting layer 5c, and a part of the electrons is collected from the second light emitting layer 5c to the first. It moves to the trap of the first light emitting material contained in the light emitting layer 5b and recombines with the holes in the first light emitting layer 5b, whereby yellow light emission is shown in the first light emitting layer 5b. Accordingly, it is possible to suppress the transport of electrons that do not contribute to light emission into the first light emitting layer 5b and improve the light emission efficiency, and it is possible to reduce the amount of current required for light emission. In addition, in order to favorably transport electrons into the first light emitting layer 5b, it is desirable that the second host material has an electron mobility higher than that of the first host material. Further, in the second light-emitting layer 5c that emits blue light, the second host material and the hole-transporting first host material are mixed host materials, so that the first light-emitting layer 5b to the second light-emitting layer 5c The holes can be transported well to the light emitting layer 5c, the holes can be moved well in the second light emitting layer 5c, and the resistance required for the hole movement can be reduced. . In addition, the organic material that serves as a dopant for the blue light-emitting layer (second light-emitting material in the second light-emitting layer 5c of the present embodiment) generally has a wide energy gap, and holes or electrons in the blue light-emitting layer. When the concentration of the transporting material is increased, holes or electrons are not easily transported to the dopant, and good blue light emission may not be obtained. By using the hole-transporting first host material, the hole-transporting material has a higher mobility of carriers (holes in the hole-transporting material and electrons in the electron-transporting material) than the electron-transporting material. Therefore, the content of the transport material in the entire second light emitting layer 5c is 10% by weight to 70% by weight, and the above effect can be achieved with a relatively low content that does not prevent good blue light emission. It is possible to obtain. With the above operations and effects, the organic EL element 1 can suppress deterioration of each material constituting the first and second light emitting layers 5b and 5c due to the passage of the light emission time. In the light emitting layers 5b and 5c, a decrease in light emission luminance can be suppressed, and the life can be extended.

  The organic EL element 1 has a hole transport layer 5a formed between the first electrode 3 and the first light emitting layer 5b as the organic layer 5 and made of the same material as the first host material 5b1. is there. By making the first host material 5b1 the same material as the hole transport layer 5a, it becomes possible to move holes from the hole transport layer 5a to the first light emitting layer 5b more smoothly.

  In the organic EL element 1, the second light emitting layer 5c has a higher concentration of the first host material on the side close to the first light emitting layer 5b, and gradually toward the side far from the first light emitting layer 5b. It is possible to make holes move more smoothly from the first light emitting layer 5b to the second light emitting layer 5c, and to accumulate holes in the second light emitting layer 5c. It becomes.

  In this embodiment, the organic EL element 1 of the present invention is applied to a segment type organic EL panel. However, the organic EL element of the present invention can also be applied to a dot matrix type organic EL panel. Further, the organic EL panels according to the first and second embodiments are provided with a translucent first electrode 3 and take out light emitted from the organic EL element 1 from the support substrate 2 side to perform a predetermined display. However, the organic EL element of the present invention is a so-called top emission type in which the second electrode on the organic layer is formed of a translucent conductive material, and a predetermined display is performed by taking out light from the sealing member side. It can also be applied to an organic EL panel.

The figure which shows the organic electroluminescent panel which is embodiment to which the organic electroluminescent element of this invention was applied. The expanded sectional view which shows the organic layer same as the above.

Explanation of symbols

1 Organic EL device 2 Support substrate 3 First electrode (anode)
4 Insulating layer 5 Organic layer 5a Hole transport layer 5b First light emitting layer 5c Second light emitting layer 5d Electron transport layer 5e Electron injection layer 6 Second electrode (cathode)

Claims (8)

An organic EL element formed by laminating an organic layer having at least a plurality of light emitting layers between an anode and a cathode,
As the light emitting layer, a first light emitting layer formed by mixing a hole-transporting first host material and a first light emitting material located on the anode side, and the first light emitting layer on the cathode side A second light-emitting layer formed by mixing a first host material, a second host material capable of transporting holes and electrons, and a second light-emitting material. An organic EL element characterized by comprising: 2. The organic EL element according to claim 1, wherein the second host material is made of an organic material whose electron mobility is higher than that of the first host material. The said 2nd light emitting layer is formed so that content of said 1st host material may be 10 mass% or more and 70 mass% or less with respect to the whole layer. Organic EL element. The said organic layer has a positive hole transport layer which is formed between the said anode and said 1st light emitting layer, and consists of the same material as said 1st host material. Organic EL element. The second light emitting layer has a high concentration of the first host material on the side close to the first light emitting layer in the layer, and the first host toward the side far from the first light emitting layer. 2. The organic EL device according to claim 1, wherein the organic EL device is formed so as to have a low material concentration. The first light-emitting layer has a high concentration of the first light-emitting material on the side close to the second light-emitting layer in the layer, and the first light-emitting layer faces away from the second light-emitting layer. 2. The organic EL device according to claim 1, wherein the organic EL device is formed so as to have a low concentration of the light emitting material. The first and second light-emitting layers exhibit different emission colors, and the second light-emitting layer has an emission color having a shorter emission main wavelength than the first light-emitting layer. Item 10. The organic EL device according to Item 1. The organic EL element according to claim 7, wherein the second light emitting layer exhibits blue light emission.

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