JP4434872B2 - Organic electroluminescent device and organic electroluminescent display device - Google Patents

Description

  The present invention relates to an organic electroluminescent element and an organic electroluminescent display device.

  Organic electroluminescent elements (organic EL elements) are being actively developed from the viewpoint of application to displays and lighting. The driving principle of the organic EL element is as follows. That is, holes and electrons are injected from the anode and the cathode, respectively, and these are transported through the organic thin film, recombined in the light emitting layer to generate an excited state, and light emission can be obtained from this excited state. In order to increase the luminous efficiency, it is necessary to inject holes and electrons efficiently and transport the organic thin film. However, since the movement of carriers in the organic EL element is limited by the energy barrier between the electrode and the organic thin film and the low carrier mobility in the organic thin film, there is a limit to improving the light emission efficiency.

  On the other hand, as another method for improving the light emission efficiency, there is a method of laminating a plurality of light emitting layers. For example, it may be possible to obtain higher luminous efficiency than a single layer by laminating an orange light-emitting layer and a blue light-emitting layer that are in a complementary color relationship so as to be in direct contact with each other. For example, when the light emission efficiency of the blue light emitting layer is 10 cd / A and the light emission efficiency of the orange light emitting layer is 8 cd / A, when these are stacked to form a white light emitting element, the light emission efficiency of 15 cd / A Is obtained.

  However, when three or more light emitting layers are laminated so as to be in direct contact with each other, improvement in light emission efficiency cannot be obtained. This is because there is a limit to the expansion of the recombination region of electrons and holes, and the recombination region does not extend over three layers.

In Non-Patent Document 1, two light emitting units are stacked via inorganic semiconductor layers such as V ₂ O ₅ and ITO, carriers are generated inside the inorganic semiconductor layer, and the carriers are supplied to the two light emitting layers. A method has been reported. This method uses carriers contained in the inorganic semiconductor layer, and a high voltage must be applied in order to generate carriers. For this reason, a drive voltage becomes high and cannot be applied to low voltage drive of a portable device or the like.

Patent Documents 1 to 4 also propose an organic EL element in which a plurality of light emitting units are stacked via a charge generation layer or the like, but it is necessary to drive at a high voltage, and high luminous efficiency can be obtained. It wasn't.
JP 2003-272860 A JP 2003-264085 A Japanese Patent Laid-Open No. 11-329748 JP 2004-39617 A 2004 Spring 51st Applied Physics Related Conference Lecture Proceedings No. 3 Page 1464 Lecture number 28p-ZQ-14 “Carrier recombination organic EL device with double insulation layer” SYNTHESIS, April, 1994, 378-380 “Improved Synthesis of 1,4,5,8,9,12-Hexaazatriphenylenehexacarboxylic Acid”

  An object of the present invention is to provide an organic EL element and an organic EL display device which can be driven at a low voltage and have high light emission efficiency in an organic EL element including at least two light emitting units.

  The organic EL device of the present invention includes a cathode, an anode, an intermediate unit disposed between the cathode and the anode, a first light emitting unit disposed between the cathode and the intermediate unit, and the anode and the intermediate unit. And a second light-emitting unit that emits a color disposed in the intermediate unit, the intermediate unit is provided with an electron extraction layer for extracting electrons from an adjacent layer adjacent to the cathode side, and the lowest empty molecule of the electron extraction layer The absolute value of the energy level of the orbital (LUMO) | LUMO (A) | and the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the adjacent layer | HOMO (B) | | LUMO (A) | ≦ 1.5 eV, the light emitting layer located on the intermediate unit side of the first light emitting unit contains an arylamine hole transport material, and the light emitting layer is adjacent The intermediate unit is provided adjacent to the electron extraction layer so as to function as a hole, and the intermediate unit supplies holes generated by the extraction of electrons from the light emitting layer by the electron extraction layer to the first light emitting unit, and extracts the extracted electrons. It is characterized in that it is supplied to the second light emitting unit.

  According to the present invention, the intermediate unit is provided between the first light emitting unit and the second light emitting unit, and the electronic extraction layer is provided in the intermediate unit. In addition, the light emitting layer located on the intermediate unit side of the first light emitting unit contains an arylamine-based hole transporting material, and the light emitting layer is provided adjacent to the electron extraction layer. Therefore, in the present invention, the light emitting layer functions as an adjacent layer. According to the present invention, by causing the light emitting layer located on the intermediate unit side of the first light emitting unit to function as an adjacent layer, the driving voltage can be lowered and the luminous efficiency can be reduced as compared with the case where the adjacent layer is provided in the intermediate unit. Can be increased.

  In the present invention, the first light emitting unit and the second light emitting unit emit light by a mechanism described below.

  The absolute value of the HOMO energy level of the adjacent layer | HOMO (B) | and the absolute value of the LUMO energy level of the electron extraction layer | LUMO (A) | are | HOMO (B) | | ≦ 1.5 eV. That is, the LUMO energy level of the electron extraction layer is close to the HOMO energy level of the adjacent layer. For this reason, the electron extraction layer can extract electrons from the adjacent layer. Due to the extraction of electrons from the adjacent layer, holes are generated in the adjacent layer. In the present invention, since the light emitting layer located on the intermediate unit side of the first light emitting unit is used as the adjacent layer, holes are generated in the light emitting layer in the first light emitting unit. The holes generated in the first light emitting unit are recombined with electrons from the cathode, whereby the first light emitting unit emits light.

  On the other hand, the electrons extracted by the electron extraction layer are supplied to the second light emitting unit and recombined with the holes supplied from the anode, whereby the second light emitting unit emits light.

  Therefore, according to the present invention, a recombination region can be formed in each of the first light-emitting unit and the second light-emitting unit, whereby each of the first light-emitting unit and the second light-emitting unit emits light separately. Can be made.

  In the present invention, in order for the electron extraction layer to extract electrons from the adjacent layer, the LUMO energy level of the electron extraction layer is preferably closer to the HOMO energy level of the adjacent layer than the LUMO energy level of the adjacent layer. . That is, it is preferable that the absolute value | LUMO (B) | of the LUMO energy level of the adjacent layer satisfies the following relationship.

│HOMO (B) │-│LUMO (A) │ <│LUMO (A) │-│LUMO (B) │
In addition, since the absolute value of the LUMO energy level of the material used as the electron extraction layer is generally smaller than the absolute value of the energy level of the adjacent layer, the absolute value of each energy level is as follows: It is shown by the relational expression.

0eV <│HOMO (B) │-│LUMO (A) │ ≦ 1.5eV
In the present invention, an electron injection layer is preferably provided on the anode side of the electron extraction layer. The absolute value of the LUMO energy level of the electron injection layer | LUMO (C) | or the absolute value of the work function | WF (C) | is the absolute value of the LUMO energy level of the electron extraction layer | LUMO (A) | Preferably it is smaller. The electrons extracted from the electron extraction layer move to the electron injection layer and are supplied from the electron injection layer to the second light emitting unit.

  In the present invention, an electron transport layer is preferably provided between the electron injection layer in the intermediate unit and the second light emitting unit. The absolute value of LUMO energy level | LUMO (D) | of the electron transport layer is smaller than the absolute value of LUMO energy level of the electron injection layer | LUMO (C) | or the absolute value of work function | WF (C) | It is preferable. When the electron transport layer is provided, the electrons that have moved to the electron injection layer are supplied to the second light emitting unit through the electron transport layer. Therefore, the intermediate unit supplies the electrons extracted by the electron extraction layer to the second light emitting unit via the electron injection layer and the electron transport layer.

  Each of the first light emitting unit and the second light emitting unit in the present invention may be formed of a single light emitting layer, or may be configured by laminating a plurality of light emitting layers so as to be in direct contact with each other. However, the present invention is particularly useful when at least one of the first light-emitting layer and the second light-emitting layer has a structure in which two light-emitting layers are stacked in direct contact with each other. That is, in such a case, when the first light emitting unit and the second light emitting unit are directly stacked, a structure in which three or four light emitting layers are directly stacked is formed, and as described above, recombination of electrons and holes is performed. Due to the limited extent of the region, the recombination region does not span three or four light emitting layers. For this reason, recombination occurs at one location in the thickness direction of the three or four light emitting layers, and high luminous efficiency cannot be obtained. In addition, since the first light emitting unit and the second light emitting unit recombine in a region different from the recombination region in the case where each of the first light emitting unit and the second light emitting unit emits light separately, the light emission color of the combination of the first light emitting unit and the second light emitting unit May emit different colors.

  According to the present invention, by providing an intermediate unit between the first light emitting unit and the second light emitting unit, recombination can be performed in each of the first light emitting unit and the second light emitting unit. That is, a recombination region can be formed in each of the first light emitting unit and the second light emitting unit, and each of the first light emitting unit and the second light emitting unit can independently emit light. For this reason, while being able to obtain high luminous efficiency, it is possible to emit the same color as the emission color of the combination of the first light emitting unit and the second light emitting unit.

  In the present invention, the electron extraction layer can be used without particular limitation as long as the absolute value of the LUMO energy level is 1.5 eV smaller than the absolute value of the HOMO energy level of the adjacent layer. As a specific example, for example, it can be formed from a pyrazine derivative represented by the structural formula shown below.

（ここで、Ａｒはアリール基を示し、Ｒは水素、炭素数１〜１０のアルキル基、アルキルオキシ基、ジアルキルアミン基、またはＦ、Ｃｌ、Ｂｒ、ＩもしくはＣＮを示す。）
本発明において、さらに好ましくは、以下に示す構造式で表わされるヘキサアザトリフェニレン誘導体から電子引き抜き層を形成することができる。

(Here, Ar represents an aryl group, and R represents hydrogen, an alkyl group having 1 to 10 carbon atoms, an alkyloxy group, a dialkylamine group, or F, Cl, Br, I, or CN.)
In the present invention, more preferably, an electron extraction layer can be formed from a hexaazatriphenylene derivative represented by the structural formula shown below.

（ここで、Ｒは水素、炭素数１〜１０のアルキル基、アルキルオキシ基、ジアルキルアミン基、またはＦ、Ｃｌ、Ｂｒ、ＩもしくはＣＮを示す。）
本発明における第１の発光ユニット及び第２の発光ユニットを構成する発光層は、ホスト材料とドーパント材料から形成されていることが好ましい。必要に応じてキャリア輸送性の第２のドーパント材料が含有されていてもよい。ドーパント材料としては、１重項発光材料であってもよいし、３重項発光材料（燐光発光材料）であってもよい。

(Here, R represents hydrogen, an alkyl group having 1 to 10 carbon atoms, an alkyloxy group, a dialkylamine group, or F, Cl, Br, I, or CN.)
The light emitting layer constituting the first light emitting unit and the second light emitting unit in the present invention is preferably formed of a host material and a dopant material. If necessary, a carrier-transporting second dopant material may be contained. The dopant material may be a singlet light-emitting material or a triplet light-emitting material (phosphorescent material).

  In the present invention, an arylamine hole transporting material is contained in the light emitting layer located on the intermediate unit side of the first light emitting unit. The arylamine hole transporting material is preferably contained in the light emitting layer in an amount of 50% by weight or more, and more preferably 70% by weight or more. The arylamine-based hole transporting material is preferably contained in the light emitting layer as a host material.

In the present invention, the electron injection layer in the intermediate unit may be formed from, for example, alkali metals such as Li and Cs, alkali metal oxides such as Li ₂ O, alkaline earth metals, alkaline earth metal oxides, and the like. preferable.

  In the present invention, the electron transport layer in the intermediate unit can be formed of a material generally used as an electron transport material in the organic EL element.

  The organic electroluminescent display device of the present invention supplies an organic electroluminescent element having an element structure sandwiched between an anode and a cathode and a display signal corresponding to each display pixel to the organic electroluminescent element. An active matrix driving substrate provided with the active element and a transparent sealing substrate provided opposite to the active matrix driving substrate, and an organic electroluminescent element is formed between the active matrix driving substrate and the sealing substrate. A top emission type organic electroluminescent display device having a transparent electrode as an electrode provided on the sealing substrate side of a cathode and an anode, wherein the organic electroluminescent element comprises a cathode and an anode An intermediate unit disposed between the cathode and the anode, and the cathode and the intermediate unit. A first light emitting unit disposed between the anode and the second light emitting unit disposed between the intermediate unit and the intermediate unit for extracting electrons from an adjacent layer adjacent to the cathode side. The electron extraction layer is provided, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the electron extraction layer | LUMO (A) | and the absolute energy level of the highest occupied molecular orbital (HOMO) of the adjacent layer The value | HOMO (B) | is in a relationship of | HOMO (B) |-| LUMO (A) | ≦ 1.5 eV, and the light emitting layer located on the intermediate unit side of the first light emitting unit is an arylamine-based A hole transport material is provided, and is provided adjacent to the electron extraction layer so that the light emitting layer functions as the adjacent layer; Supplies the generated holes in the first light-emitting unit by drawing in, is characterized by supplying electrons and withdrawing the second light-emitting unit.

  When the organic electroluminescent element is a white light emitting element, it is preferable to dispose a color filter between the sealing substrate and the organic electroluminescent element.

  Since the organic electroluminescent display device of the present invention is a top emission type display device, the light emitted by the organic electroluminescent element is emitted from the sealing substrate on the side opposite to the side where the active matrix is provided. Emitted. In general, an active matrix circuit is formed by laminating a large number of layers. In the case of a bottom emission type, emitted light is attenuated by the presence of such an active matrix circuit, but the organic electroluminescent display device of the present invention. Can emit light without being affected by such an active matrix circuit. In particular, since the organic electroluminescent device of the present invention has a plurality of light emitting units, the number of films through which emitted light passes is smaller in the case of the top emission type than in the case of the bottom emission type, so that the light interference. The degree of freedom of design for controlling the attenuation of the emitted light or the attenuation of the viewing angle of the emitted light can be increased.

  The organic EL element and the organic EL display device of the present invention are an organic EL element including at least two light emitting units, and are an organic EL element and an organic EL display device that can be driven at a low voltage and have high luminous efficiency.

  FIG. 1 is a schematic cross-sectional view showing an organic EL element according to the present invention. As shown in FIG. 1, a first light emitting unit 41 and a second light emitting unit 42 are provided between the cathode 51 and the anode 52. An intermediate unit 30 is provided between the first light emitting unit 41 and the second light emitting unit 42. The first light emitting unit 41 is provided on the cathode 51 side with respect to the intermediate unit 30, and the second light emitting unit 42 is provided on the anode 52 side with respect to the intermediate unit 30. An electronic extraction layer is provided in the intermediate unit 30. An adjacent layer is provided on the cathode 51 side of the electron extraction layer. In the present invention, since the adjacent layer is a light emitting layer in the first light emitting unit 41, it is provided in the first light emitting unit.

  FIG. 2 is a diagram showing an energy diagram around the intermediate unit. The intermediate unit 30 includes an electron extraction layer 31, an electron injection layer 32, and an electron transport layer 33. On the cathode side of the electron extraction layer 31, an adjacent layer 40 that is a light emitting layer on the intermediate unit 30 side of the first light emitting unit 41 is provided. A second light emitting unit 42 is provided on the anode side of the intermediate unit 30. In FIG. 2, only the light emitting layer on the intermediate unit 30 side of the second light emitting unit 42 is shown.

  As shown in FIG. 2, it is preferable to provide an electron injection layer 32 between the electron extraction layer 31 and the second light emitting unit 42. Furthermore, an electron transport layer 33 is preferably provided between the electron injection layer 32 and the second light emitting unit 42.

  In the embodiment shown in FIG. 2, the electron extraction layer 31 is formed of hexaazatriphenylene hexacarbonitrile (hereinafter referred to as “HAT-CN6”) represented by the following structural formula. HAT-CN6 can be manufactured by the method described in the nonpatent literature 2, for example.

また、電子注入層３２は、Ｌｉ（金属リチウム）から形成されている。

The electron injection layer 32 is formed of Li (metallic lithium).

  The electron transport layer 33 is made of BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) having the following structure.

本発明において、電子引き抜き層３１の厚みは、１〜１５０ｎｍの範囲内であることが好ましく、さらに好ましくは５〜１００ｎｍの範囲内である。電子注入層３２の厚みは、０．１〜１０ｎｍの範囲であることが好ましく、さらに好ましくは０．１〜１ｎｍの範囲内である。電子輸送層３３の厚みは、１〜１００ｎｍの範囲内であることが好ましく、さらに好ましくは５〜５０ｎｍの範囲内である。

In the present invention, the thickness of the electron extraction layer 31 is preferably in the range of 1 to 150 nm, more preferably in the range of 5 to 100 nm. The thickness of the electron injection layer 32 is preferably in the range of 0.1 to 10 nm, more preferably in the range of 0.1 to 1 nm. The thickness of the electron transport layer 33 is preferably in the range of 1 to 100 nm, and more preferably in the range of 5 to 50 nm.

  In the embodiment shown in FIG. 2, the adjacent layer (light-emitting layer) 40 uses NPB (N, N′-di (naphthacene-1-yl) -N, N′-diphenylbenzidine) having the following structure as a host material. Contains.

図２に示す実施例において、第２の発光ユニット４２として示している発光層は、以下の構造を有するＴＢＡＤＮ（２−ターシャリー−ブチル−９，１０−ジ（２−ナフチル）アントラセン）をホスト材料として含有している。

In the embodiment shown in FIG. 2, the light-emitting layer shown as the second light-emitting unit 42 hosts TBADN (2-tertiary-butyl-9,10-di (2-naphthyl) anthracene) having the following structure. Contains as a material.

図２に示すように、電子引き抜き層３１のＬＵＭＯエネルギーレベルの絶対値（４．４ｅＶ）と、隣接層４０のＨＯＭＯエネルギーレベルの絶対値（５．４ｅＶ）との差は、１．５ｅＶ以内である。また、電子注入層３２のＬＵＭＯエネルギーレベル（仕事関数）の絶対値は、電子引き抜き層３１のＬＵＭＯエネルギーレベルの絶対値よりも小さく、電子輸送層３３のＬＵＭＯエネルギーレベルの絶対値は、電子注入層３２のＬＵＭＯエネルギーレベルの絶対値よりも小さい。

As shown in FIG. 2, the difference between the absolute value (4.4 eV) of the LUMO energy level of the electron extraction layer 31 and the absolute value (5.4 eV) of the HOMO energy level of the adjacent layer 40 is within 1.5 eV. is there. The absolute value of the LUMO energy level (work function) of the electron injection layer 32 is smaller than the absolute value of the LUMO energy level of the electron extraction layer 31, and the absolute value of the LUMO energy level of the electron transport layer 33 is the electron injection layer. Less than the absolute value of 32 LUMO energy levels.

  Therefore, the electron extraction layer 31 can extract electrons from the adjacent layer 40 when a voltage is applied to the anode and the cathode. The extracted electrons pass through the electron injection layer 32 and the electron transport layer 33 and are supplied to the second light emitting unit 42.

  In the adjacent layer 40, holes are generated because electrons are extracted. The holes recombine with electrons supplied from the cathode in the first light emitting unit. As a result, light is emitted in the first light emitting unit.

  The electrons supplied to the second light emitting unit recombine with the holes supplied from the anode in the second light emitting unit 42. As a result, light is emitted in the second light emitting unit 42.

  As described above, according to the present invention, recombination regions can be formed in the first light emitting unit and the second light emitting unit, respectively, and light can be emitted. As a result, the light emission efficiency can be increased, and light can be emitted with the light emission colors of the first light emission unit and the second light emission unit.

  According to the invention, the light emitting layer on the intermediate unit side of the first light emitting unit functions as an adjacent layer. Accordingly, the first light emitting unit is provided so as to be in direct contact with the electron extracting layer, and the driving voltage can be lowered as compared with the case where an adjacent layer is provided between the electron extracting layer and the first light emitting unit. , Luminous efficiency can be improved.

<Experiment 1>
(Examples 1 to 3 and Comparative Example 1)
Organic EL elements of Examples 1 to 3 and Comparative Example 1 having an anode, a hole transport layer, a second light emitting unit, an intermediate unit, a first light emitting unit, an electron transport layer, and a cathode shown in Table 1 were produced. As shown in Table 1, in Examples 1 to 3, the “HAT-CN6” layer, which is the electron extraction layer of the intermediate unit, is provided adjacent to the first light emitting unit so as to be in direct contact. In Comparative Example 1, an NPB layer is provided as an adjacent layer between the “HAT-CN6” layer, which is an electron extraction layer, and the first light emitting unit. In the following table, the numbers in () indicate the thickness (nm) of each layer.

The anode was prepared by forming a fluorocarbon (CF _x ) layer on a glass substrate on which an ITO (indium tin oxide) film was formed. The fluorocarbon layer was formed by plasma polymerization of CHF ₃ gas. The thickness of the fluorocarbon layer was 1 nm.

  On the anode prepared as described above, a hole transport layer, a second light emitting unit, an intermediate unit, a first light emitting unit, an electron transport layer, and a cathode were sequentially deposited by an evaporation method.

  The hole transport layer was formed from NPB.

  The first light emitting unit and the second light emitting unit are formed by stacking an orange light emitting layer (NPB + 3.0% DBzR) and a blue light emitting layer (TBADN + 2.5% TBP). In any light emitting unit, the orange light emitting layer is located on the anode side and the blue light emitting layer is located on the cathode side. % Is% by weight unless otherwise specified.

  In the orange light emitting layer, NPB is used as a host material and DBzR is used as a dopant material. DBzR is 5,12-bis {4- (6-methylbenzothiazol-2-yl) phenyl} -6,11-diphenylnaphthacene and has the following structure.

青色発光層は、ＴＢＡＤＮをホスト材料として用いており、ＴＢＰをドーパント材料として用いている。

The blue light emitting layer uses TBADN as a host material and TBP as a dopant material.

  TBP is 2,5,8,11-tetra-tertiary-butylperylene and has the following structure.

作製した各有機ＥＬ素子について、色度（ＣＩＥ（ｘ，ｙ））、及び発光効率を測定し、測定結果を駆動電圧とともに表２に示した。なお、発光効率は、１０ｍＡ／ｃｍ²における値である。

About each produced organic EL element, chromaticity (CIE (x, y)) and luminous efficiency were measured, and the measurement result was shown in Table 2 with the drive voltage. The luminous efficiency is a value at 10 mA / cm ² .

表２に示す結果から明らかなように、第１の発光ユニットのオレンジ色発光層を隣接層として用いた実施例１〜３においては、中間ユニット内のＮＰＢ層を隣接層として用いた比較例１に比べ、駆動電圧が低くなっていることがわかる。また、発光効率も向上していることがわかる。これは、第１の発光ユニットのオレンジ色発光層を電子引き抜き層に隣接して設けることにより、電子引き抜き層からの電子引き抜きにより発生したホールが効率良く第１の発光ユニットに供給されるためであると思われる。

As is apparent from the results shown in Table 2, in Examples 1 to 3 using the orange light emitting layer of the first light emitting unit as the adjacent layer, Comparative Example 1 using the NPB layer in the intermediate unit as the adjacent layer It can be seen that the drive voltage is lower than It can also be seen that the luminous efficiency is improved. This is because by providing the orange light emitting layer of the first light emitting unit adjacent to the electron extracting layer, holes generated by electron extraction from the electron extracting layer are efficiently supplied to the first light emitting unit. It appears to be.

  The reason why the organic EL element in which the intermediate unit is provided between the first light emitting unit and the second light emitting unit according to the present invention exhibits high luminous efficiency is as follows. That is, in the organic EL element according to the present invention, since the second light emitting unit is located on the anode side, it has a relatively large number of holes. Therefore, when there is no intermediate unit, there is a shortage of electrons. On the other hand, since the first light emitting unit is located on the cathode side, it has a relatively large number of electrons, and if there is no intermediate unit, the hole is insufficient.

  As described above, when there is no intermediate unit, the four light emitting layers are in continuous and direct contact with each other, so that carriers recombine in one region of the four light emitting layers. According to the present invention, by providing an intermediate unit in the middle of the four light emitting layers, the shortage of electrons in the second light emitting unit on the anode side can be compensated, and the shortage of holes in the first light emitting unit on the anode side can be compensated. . As described with reference to FIG. 2, when a voltage is applied to the anode and the cathode, electrons are extracted from the adjacent layer in the first light emitting unit to the electron extraction layer, and the LUMO of the electron extraction layer is detected. The extracted electron enters into. Further, as a result of electrons being extracted, holes are generated in the HOMO of the adjacent layer. The electrons of the LUMO of the electron extraction layer enter the LUMO of the electron transport layer through the electron injection layer in the intermediate unit, and then enter the second light emitting unit and recombine with the holes injected from the anode. At this time, in addition to the electrons from the intermediate unit, electrons injected from the cathode and not consumed by the first light emitting unit are considered to contribute to recombination at the same time. Thereby, the orange light emitting layer and the blue light emitting layer in the second light emitting unit emit light at the same time, and complementary color white light emission occurs.

  On the other hand, holes generated in the HOMO of the adjacent layer of the first light emitting unit and holes from the anode that are not consumed in the second light emitting unit move to the first light emitting unit in a high electric field, In the light emitting unit, it recombines with electrons injected from the cathode. Thereby, the orange light emitting layer and the blue light emitting layer of the first light emitting unit emit light at the same time, and complementary color white light emission is generated.

As described above, since white light emission occurs at two locations of the first light emitting unit and the second light emitting unit, the light emission efficiency is doubled. In the case of a conventional organic EL element in which a plurality of light emitting units are combined with an inorganic semiconductor layer such as V ₂ O ₅ interposed, a carrier originally present in the inorganic semiconductor layer is used. On the other hand, in the present invention, carriers are separated from a neutral organic layer in which no carrier exists, that is, an adjacent layer, and light is emitted using this carrier. Therefore, the organic EL device of the present invention can be driven at a lower drive voltage than conventional devices. That is, light can be emitted with an energy for extracting electrons (difference between LUMO of the electron extraction layer and HOMO of the adjacent layer) and an energy difference for injecting the generated electrons into the light emitting layer on the anode side.

In the present invention, the luminous efficiency can be doubled, so that the reliability of the element can be improved. For example, when continuous light emission is performed at an initial luminance of 5000 cd / m ² , a normal organic EL element must emit light as it is at a luminance of 5000 cd / m ² . In contrast, in the organic EL device of the present invention, the emission efficiency is doubled, one light-emitting unit in the device if caused to emit light at a luminance of 2500 cd / m ^2, which is half of 5000 cd / m ² Good. Therefore, the amount of current flowing through the element may be half, and the load on the element is reduced. Since the lifetime of the element in continuous light emission is affected by the value of the flowing current, the lifetime of the element can be improved according to the present invention.

  As described above, according to the present invention, it can be seen that by providing the electron extraction layer in the intermediate unit, an organic EL element that can be driven at a low voltage, has high emission efficiency, and exhibits a desired emission color can be obtained. .

<Experiment 2>
Table 3 shows an anode, a hole injection layer, a second light emitting unit, an intermediate unit, a first light emitting unit, an electron transport layer, and a cathode, and the thickness x of the Li ₂ O layer in the intermediate unit is set to 0. Organic EL devices with different thicknesses of 1 nm, 0.2 nm, 0.3 nm, 0.5 nm, 1 nm, and 3 nm were produced.

第１の発光ユニット及び第２の発光ユニットにおけるオレンジ色発光層は、実施例１〜３におけるオレンジ色発光層と同様である。また、青色発光層は、８０重量％のＴＢＡＤＮをホスト材料として用い、２．５重量％のＴＢＰを第１のドーパント材料として用い、２０重量％のＮＰＢを第２のドーパント材料として用いている。

The orange light emitting layer in the first light emitting unit and the second light emitting unit is the same as the orange light emitting layer in Examples 1 to 3. The blue light-emitting layer uses 80% by weight TBADN as a host material, 2.5% by weight TBP as a first dopant material, and 20% by weight NPB as a second dopant material.

With respect to each organic EL element in which the thickness of the Li ₂ O layer was changed, the light emission efficiency at 10 mA / cm ² was measured, and the result is shown in FIG.

As is clear from the results shown in FIG. 3, it can be seen that light emission is possible when the Li ₂ O film thickness is in the range of 0.1 nm to 10 nm. It can also be seen that the luminous efficiency is particularly high when the Li ₂ O film thickness is in the range of 0.1 nm to 3 nm. Therefore, also in the present invention, the thickness of the electron injection layer (Li ₂ O layer or the like) in the intermediate unit is preferably in the range of 0.1 nm to 10 nm, more preferably in the range of 0.1 nm to 3 nm. It turns out that it is in.

  FIG. 4 is a cross-sectional view showing an organic EL display device including an organic EL element according to an embodiment of the present invention. In this organic EL display device, light emission in each pixel is driven using a TFT as an active element. A diode or the like can be used as the active element. In this organic EL element, a color filter is provided. This organic EL display device is a bottom emission type display device that emits and displays light below the substrate 1 as indicated by arrows.

Referring to FIG. 4, a first insulating layer 2 is provided on a substrate 1 made of a transparent substrate such as glass. The first insulating layer 2 is made of, for example, SiO ₂ and SiN _x . A channel region 20 made of a polysilicon layer is formed on the first insulating layer 2. A drain electrode 21 and a source electrode 23 are formed on the channel region 20, and a gate electrode 22 is provided between the drain electrode 21 and the source electrode 23 via the second insulating layer 3. Yes. A fourth insulating layer 4 is provided on the gate electrode 22. The second insulating layer 3 is made of, for example, SiN _x and SiO ₂ , and the third insulating layer 4 is made of SiO ₂ and SiN _x .

A fourth insulating layer 5 is formed on the third insulating layer 4. The fourth insulating layer 5 is made of, for example, SiN _x . A color filter layer 7 is provided in the pixel region on the fourth insulating layer 5. As the color filter layer 7, color filters such as R (red), G (green), and B (blue) are provided. A first planarizing film 6 is provided on the color filter layer 7. A through hole portion is formed in the first planarization film 6 above the drain electrode 21, and a hole injection electrode 8 made of ITO (indium oxide) formed on the first planarization film 6 is through. It is introduced in the hall. A hole injection layer 10 is formed on the hole injection electrode (anode) 8 in the pixel region. A second planarizing film 9 is formed in a portion other than the pixel region.

  On the hole injection layer 10, a white light emitting element layer 11 laminated according to the present invention is provided. The light emitting element layer 11 has a structure according to the present invention in which the first light emitting unit is laminated on the second light emitting unit via an intermediate unit. An electron transport layer 12 is provided on the light emitting element layer 11, and an electron injection electrode (cathode) 13 is provided on the electron transport layer 12.

  As described above, in the organic EL element of this example, the hole injection electrode (anode) 8, the hole injection layer 10, the light emitting element layer 11 having the structure according to the present invention, and the electron transport are formed on the pixel region. The layer 12 and the electron injection electrode (cathode) 13 are laminated to constitute an organic EL element.

  The light emitting element layer 11 emits white light. This white light emission is emitted to the outside through the substrate 1, but since the color filter layer 7 is provided on the light emission side, R, G, or B color is emitted according to the color of the color filter layer 7. The

  FIG. 5 is a sectional view showing an organic EL display device of an embodiment according to the present invention. The organic EL display device of this embodiment is a top emission type organic EL display device that emits light and displays it above the substrate 1 as shown by arrows.

  The portion from the substrate 1 to the anode 8 is fabricated in substantially the same manner as the embodiment shown in FIG. However, the color filter layer 7 is not provided on the fourth insulating layer 5 and is disposed above the organic EL element. Specifically, the color filter layer 7 is attached on a transparent sealing substrate 10 made of glass or the like, and an overcoat layer 15 is coated thereon, and this is applied to the anode 8 via the transparent adhesive layer 14. It is attached by sticking to. In this embodiment, the positions of the anode and the cathode are reversed from those in the embodiment shown in FIG.

  A transparent electrode is formed as the anode 8, and is formed, for example, by laminating ITO having a thickness of about 100 nm and silver having a thickness of about 20 nm. As the cathode 13, a reflective electrode is formed. For example, an aluminum, chromium, or silver thin film having a thickness of about 100 nm is formed. The overcoat layer 15 is formed with an acrylic resin or the like to a thickness of about 1 μm. The color filter layer 7 may be a pigment type or a dye type. Its thickness is about 1 μm.

  White light emitted from the light emitting element layer 11 is emitted to the outside through the sealing substrate 16, but since the color filter layer 7 is provided on the light emitting side, R, G or B color is emitted. Since the organic EL display device of this embodiment is a top emission type, the region where the thin film transistor is provided can also be used as the pixel region, and the color filter layer 7 is provided in a wider range than the embodiment shown in FIG. ing. The light emitting element layer 11 is formed of an organic EL element according to the present invention and is a light emitting element layer having high light emission efficiency. However, according to this embodiment, a wider area can be used as a pixel area, and thus the light emission efficiency of the light emitting element layer 11 is improved. The advantages of a high light emitting element layer can be fully utilized. Further, since the light emitting element layer having a plurality of light emitting units can be formed without considering the influence of the active matrix, the degree of freedom in design can be increased.

In the above embodiment, a glass plate is used as the sealing substrate. However, the sealing substrate is not limited to the glass plate in the present invention. For example, an oxide film such as SiO ₂ or a nitride film such as SiN _{x is used.} A film-like material can also be used as a sealing substrate. In this case, since a film-like sealing substrate can be directly formed on the element, there is no need to provide a transparent adhesive layer.

  In each of the above embodiments, an organic EL element in which two light emitting units (a first light emitting unit and a second light emitting unit) are arranged between an anode and a cathode is illustrated, but the number of light emitting units in the present invention is not limited. Is not limited to two, and three or more light emitting units may be provided, and an intermediate unit may be provided between the respective light emitting units.

The typical sectional view showing the organic EL element of one example according to the present invention. The figure which shows the energy diagram of an intermediate unit periphery. Shows the relationship between the thickness of li ₂ O layer and the light emitting efficiency. Sectional drawing which shows the bottom emission type organic electroluminescence display using the organic electroluminescent element of the Example according to this invention. Sectional drawing which shows the organic electroluminescence display of the Example according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... 1st insulating layer 3 ... 2nd insulating layer 4 ... 3rd insulating layer 5 ... 4th insulating layer 6 ... 1st planarization film 7 ... Color filter layer 8 ... Hole injection electrode 9 DESCRIPTION OF SYMBOLS ... 2nd planarizing film 10 ... Hole injection layer 11 ... Light emitting element layer 12 ... Electron transport layer 13 ... Electron injection electrode 14 ... Transparent adhesive layer 15 ... Overcoat layer 16 ... Sealing substrate 20 ... Channel region 21 ... Drain Electrode 22 ... Gate electrode 23 ... Source electrode 30 ... Intermediate unit 31 ... Electronic extraction layer 32 ... Electron injection layer 33 ... Electron transport layer 40 ... Adjacent layer 41 ... First light emitting unit 42 ... Second light emitting unit 51 ... Cathode 52 …anode

Claims (9)

A cathode, an anode, an intermediate unit disposed between the cathode and the anode, a first light emitting unit disposed between the cathode and the intermediate unit, and disposed between the anode and the intermediate unit A second light emitting unit to be
The intermediate unit is provided with an electron extraction layer for extracting electrons from an adjacent layer adjacent to the cathode side, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the electron extraction layer | LUMO (A) │ and the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the adjacent layer │HOMO (B) │ is in a relationship of │HOMO (B) │-│LUMO (A) │≤1.5eV ,
The light emitting layer located on the intermediate unit side of the first light emitting unit contains an arylamine-based hole transporting material, and is adjacent to the electron extraction layer so that the light emitting layer functions as the adjacent layer. Provided,
The intermediate unit supplies holes generated by extracting electrons from the light emitting layer by the electron extracting layer to the first light emitting unit and supplies the extracted electrons to the second light emitting unit. An organic electroluminescent element.   The organic electroluminescent device according to claim 1, wherein the arylamine hole transporting material is contained in the light emitting layer as a host material. An electron injection layer is provided adjacent to the anode side of the electron extraction layer, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the electron injection layer | LUMO (C) | or the absolute value of the work function | WF (C) | is smaller than | LUMO (A) |
3. The organic electroluminescent device according to claim 1, wherein the intermediate unit supplies the electrons extracted by the electron extraction layer to the second light emitting unit through the electron injection layer. An electron transport layer is provided in the intermediate unit between the electron injection layer and the second light emitting unit, and the absolute value of the energy level of the lowest unoccupied molecular orbital of the electron transport layer | LUMO (D) | Is smaller than | LUMO (C) | or | WF (C) |
The organic electroluminescence according to claim 3, wherein the intermediate unit supplies electrons extracted by the electron extraction layer to the second light emitting unit through the electron injection layer and the electron transport layer. Cent element.   5. The structure according to claim 1, wherein at least one of the first light-emitting unit and the second light-emitting unit has a structure in which two light-emitting layers are stacked in direct contact with each other. The organic electroluminescent element as described. The organic electroluminescent device according to claim 1, wherein the electron extraction layer is formed of a pyrazine derivative represented by the structural formula shown below.

(Here, Ar represents an aryl group, and R represents hydrogen, an alkyl group having 1 to 10 carbon atoms, an alkyloxy group, a dialkylamine group, or F, Cl, Br, I, or CN.) The organic electroluminescent device according to claim 1, wherein the electron extraction layer is formed of a hexaazatriphenylene derivative represented by the structural formula shown below.

(Here, R represents hydrogen, an alkyl group having 1 to 10 carbon atoms, an alkyloxy group, a dialkylamine group, or F, Cl, Br, I, or CN.) An active matrix driving substrate provided with an organic electroluminescent element having an element structure sandwiched between an anode and a cathode, and an active element for supplying a display signal corresponding to each display pixel to the organic electroluminescent element And a transparent sealing substrate provided opposite to the active matrix driving substrate, the organic electroluminescent element is disposed between the active matrix driving substrate and the sealing substrate, the cathode and the A top emission type organic electroluminescent display device in which an electrode provided on the sealing substrate side of the anode is a transparent electrode,
The organic electroluminescent device includes the cathode, the anode, an intermediate unit disposed between the cathode and the anode, and a first light emitting unit disposed between the cathode and the intermediate unit. A second light emitting unit disposed between the anode and the intermediate unit,
The intermediate unit is provided with an electron extraction layer for extracting electrons from an adjacent layer adjacent to the cathode side, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the electron extraction layer | LUMO (A) │ and the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the adjacent layer │HOMO (B) │ is in a relationship of │HOMO (B) │-│LUMO (A) │≤1.5eV ,
The light emitting layer located on the intermediate unit side of the first light emitting unit contains an arylamine-based hole transporting material, and is adjacent to the electron extraction layer so that the light emitting layer functions as the adjacent layer. Provided,
The intermediate unit supplies holes generated by extracting electrons from the light emitting layer by the electron extracting layer to the first light emitting unit and supplies the extracted electrons to the second light emitting unit. An organic electroluminescent display device. The organic electroluminescent device according to claim 8, wherein the organic electroluminescent device is a white light emitting device, and a color filter is disposed between the organic electroluminescent device and the sealing substrate. Electroluminescent display device.

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