JP2007149605A - Organic electroluminescent element, and organic electroluminescent display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an organic electroluminescent element, having high light emission efficiency capable of adjusting the cavity, lowering operation voltage, and enhancing reliability. <P>SOLUTION: The organic electroluminescent element is equipped with an intermediate unit arranged between a cathode and an anode, a first light-emitting unit arranged between the cathode and the intermediate unit, a second light-emitting unit arranged between the anode and the intermediate unit, and a cavity-adjusting unit arranged contiguous to the intermediate unit between the intermediate unit and the second light emitting unit. The intermediate unit has a first electron extraction layer for extracting the electrons from the cavity-adjusting unit, and an electron injection layer adjacent to the anode side of the first electron extraction layer. The cavity-adjusting unit has a first cavity-adjusting layer, formed contiguous to the cathode side of the first electron extraction layer, from which electrons are extracted by the first electron extraction layer, and a second electron extraction layer for extracting the electrons from an electron supply layer that is adjacent to the cathode side. <P>COPYRIGHT: (C)2007,JPO&INPIT

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.

  In an organic EL element, a charge transport layer, a charge injection layer, or the like for transferring holes or electrons is generally provided between an electrode and a light emitting layer.

  In Patent Document 1, in the structure in which a hole injection layer, a hole transport layer, an electron capture layer, a light emitting layer, and an electron transport layer are stacked from the anode side to the cathode side, the lowest conduction band level of the base material of the electron capture layer is It has been proposed to lower the conduction band minimum level of the base material of the hole transport layer and the lowest conduction band level of the base material of the light emitting layer. This prevents deterioration of the base material of the hole transport layer on the anode side.

  In Patent Document 2, it has been proposed that a mixed layer formed by mixing constituent materials of adjacent hole transport layers is interposed at the interface between two adjacent hole transport layers. It is described that the adhesion between the charge transport layers can be improved and the light emission efficiency and the luminance life can be improved.

  In Patent Document 3, it is proposed to control the electron transport efficiency by alternately laminating the cathode buffer layer and the electron transport layer at least twice between the cathode and the light emitting layer.

Conventionally, a tertiary arylamine material such as NPB (N, N′-di (naphthacene-1-yl) -N, N′-diphenylbenzidine) is used as the hole transport layer. If the hole transport layer made of NPB or the like is made thicker for adjustment, the carrier mobility of the hole transport material such as NPB is low, which causes a problem that the drive voltage becomes high. Therefore, there has been a demand for an element structure of an organic EL element that can reduce the driving voltage even when the film thickness of NPB or the like is increased.
JP 2003-151776 A JP 2004-207000 A JP 2003-229269 A 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 that can adjust a cavity, have high luminous efficiency, reduce driving voltage, and increase reliability.

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. A second light emitting unit disposed on the intermediate unit, and a cavity adjusting unit disposed between the intermediate unit and the second light emitting unit and provided adjacent to the intermediate unit,
The intermediate unit has a first electron extraction layer for extracting electrons from the cavity adjustment unit, and an electron injection layer adjacent to the anode side of the first electron extraction layer,
The cavity adjustment unit is provided adjacent to the cathode side of the first electron extraction layer, the first cavity adjustment layer from which electrons are extracted to the first electron extraction layer, and the electron from the electron supply layer adjacent to the cathode side. A second electron extraction layer for extracting
Absolute value of the lowest unoccupied molecular orbital (LUMO) energy level of the first electron extraction layer | LUMO (B) | and absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the first cavity adjustment layer HOMO (A) | is in a relationship of | HOMO (A) | --LUMO (B) | ≦ 1.5 eV, 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 work function | WF (C) | is smaller than | LUMO (B) |
Absolute value | LUMO (D) | of the lowest unoccupied molecular orbital (LUMO) energy level of the second electron extraction layer and absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the electron supply layer | HOMO (E ) | Is in a relationship of | HOMO (E) | --LUMO (D) | ≦ 1.5 eV, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first cavity adjustment layer | LUMO (A ) | And | LUMO (D) | are in a relationship of | LUMO (A) | <| LUMO (D) |.

  In the present invention, an intermediate unit is provided between the first light emitting unit and the second light emitting unit, and the cavity adjustment unit is disposed between the intermediate unit and the first light emitting unit so as to be adjacent to the intermediate unit. Is provided. Therefore, the cavity can be adjusted by adjusting the film thickness of the cavity adjusting unit. The light emitted from the second light-emitting unit passes through the intermediate unit, the cavity adjusting unit, and the first light-emitting unit, and is generally reflected by the cathode formed from a metal thin film, and again the first light-emitting unit and cavity adjusting unit. , Through the intermediate unit, the first light emitting unit, and the anode, and emitted to the outside. Therefore, the cavity of the light emitted by the second light emitting unit can be effectively adjusted by adjusting the film thickness of the cavity adjusting unit.

  The intermediate unit is provided with a first electron extraction layer for extracting electrons from the cavity adjustment unit, and an electron injection layer adjacent to the anode side of the first electron extraction layer.

  The cavity adjustment unit is provided adjacent to the cathode side of the first electron extraction layer, and includes a first cavity adjustment layer from which electrons are extracted by the first electron extraction layer, and an electron supply layer located on the cathode side. A second electron extraction layer for extracting electrons is provided.

In the intermediate unit, | LUMO (B) | of the first electron extraction layer and | HOMO (A) | of the first cavity adjustment layer are:
│HOMO (A) │-│LUMO (B) │ ≦ 1.5eV ………… (1)
Are in a relationship.

  Therefore, the first electron extraction layer can easily extract electrons from the adjacent first cavity adjustment layer.

Also, | LUMO (C) | or | WF (C) | of the electron injection layer adjacent to the anode side of the first electron extraction layer and | LUMO (B) | of the first electron extraction layer are
│LUMO (C) │ or │WF (C) │ <│LUMO (B) │ ……… (2)
Are in a relationship. Therefore, the electrons extracted by the first electron extraction layer are supplied to the electron injection layer, and are supplied from the electron injection layer to the second light emitting unit.

The | LUMO (D) | of the second electron extraction layer in the cavity adjustment unit and the electron supply layer | HOMO (E) | adjacent to the cathode side of the second electron extraction layer are:
│HOMO (E) │-│LUMO (D) │ ≦ 1.5eV ………… (3)
Are in a relationship. Therefore, the second electron extraction layer can easily extract electrons from the electron supply layer.

Also, │LUMO (A) │ of the first cavity adjustment layer and │LUMO (D) │ of the second electron extraction layer are
│LUMO (A) │ <│LUMO (D) │ ……… (4)
Are in a relationship. Therefore, the electrons extracted by the second electron extraction layer are blocked by the first cavity adjustment layer, and electrons accumulate in the second electron extraction layer. For this reason, a high electric field is locally applied, the energy band is changed by this high electric field, and it is considered that the drive voltage can be suppressed from increasing even if the thickness of the first cavity adjustment layer is increased. It is done.

  In the intermediate unit of the present invention, the first electron extraction layer extracts electrons from the first cavity adjustment layer of the cavity adjustment unit, and the extracted electrons are passed through the electron injection layer to the second light emitting unit on the anode side. Supply. In the second light emitting unit, the holes supplied from the anode and the electrons are combined to emit light. On the other hand, holes are generated in the first cavity adjustment layer from which electrons have been extracted.

  In the cavity adjustment unit, the second electron extraction layer extracts electrons from the adjacent electron supply layer, and the extracted electrons are accumulated in the second electron extraction layer as described above, and thereby locally high. An electric field is generated. The electrons accumulated in the second electron extraction layer are combined with holes generated in the first cavity adjustment layer. In the electron supply layer from which electrons have been extracted, holes are generated, and the holes are supplied to the first light emitting unit on the cathode side, and are combined with the electrons supplied from the cathode, so that the first light emitting unit emits light.

  As described above, in the present invention, electrons are supplied from the intermediate unit and the cavity adjustment unit to the second light-emitting unit on the anode side, and holes are supplied to the first light-emitting unit on the cathode side. The unit can emit light efficiently. Further, as described above, electrons accumulate in the second electron extraction layer, and thus a high electric field is locally applied. For this reason, even if the film thickness of the 1st cavity adjustment layer in a cavity adjustment unit is made thick, since the raise of a drive voltage can be suppressed, high luminous efficiency is obtained.

  Furthermore, in the present invention, as described above, electrons are blocked by the first cavity adjustment layer of the cavity adjustment unit. Therefore, excessive supply of electrons to the anode side can be prevented, so that the device life can be extended and the device reliability can be improved.

  In the present invention, the electron supply layer is preferably formed from a hole transporting material. If the light-emitting layer provided in the first light-emitting unit uses a hole transporting material as a host material, this light-emitting layer can be used as an electron supply layer. Therefore, in the present invention, the electron supply layer may be provided in the first light emitting unit.

  In the present invention, the electron supply layer may be a second cavity adjustment layer provided in the cavity adjustment unit. In this case, in addition to the first cavity adjustment layer, the film thickness of the second cavity adjustment layer can also be increased and can be used for cavity adjustment.

  In the present invention, the first and second cavity adjusting layers are preferably formed from a hole transporting material. Examples of such hole transporting materials include tertiary arylamine materials.

  Moreover, in this invention, the cavity adjustment unit may combine the 1st cavity adjustment layer and the 2nd electron extraction layer, and may have these layers in a some repeating unit. That is, in the cavity adjustment unit, a laminated structure of the first cavity adjustment layer / second electron extraction layer / first cavity adjustment layer / second electron extraction layer, or first cavity adjustment layer / second It may have a laminated structure of an electron extraction layer / first cavity adjustment layer / second electron extraction layer / first cavity adjustment layer / second electron extraction layer. The preferred film thickness of the cavity adjusting layer is generally in the range of 10 to 700 nm. If the thickness of the cavity adjustment layer is too large, the drive voltage becomes too high, causing a problem that the light emission efficiency is lowered. For this reason, when the thickness of the cavity adjustment layer is desired to be larger than this range, the second electron extraction layer is appropriately inserted, and a plurality of repeating units of the first cavity adjustment layer and the second electron extraction layer are provided. Is preferred.

  In the present invention, an electron transport layer may be provided between the electron injection layer in the intermediate unit and the second light emitting unit. The absolute value | LUMO (F) | of the energy level of the lowest unoccupied molecular orbital (LUMO) of such an electron transport layer is set to be smaller than | LUMO (C) | or | WF (C) |.

In the present invention, │HOMO (A) │ of the first cavity adjustment layer and │HOMO (D) │ of the second electron extraction layer are
│HOMO (A) │ <│HOMO (D) │ ……… (5)
It is preferable that the relationship is

  By finding the equation of (5) above, holes are accumulated at the interface between the first cavity adjustment layer and the second electron extraction layer, whereby a higher electric field can be applied locally, and the drive voltage can be further increased. It is thought that it can be reduced.

  In the present invention, examples of the material for forming the first and / or second electron extraction layer include pyrazine derivatives represented by the following structural formulas.

(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.)
Further, the material forming the first and / or second electron extraction layer of the present invention is more preferably 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.)
In the present invention, the first and / or second electron extraction layer may be doped with an electron extraction promoting material for promoting electron extraction. The absolute value of the lowest unoccupied molecular orbital (LUMO) energy level | LUMO (G) |
│HOMO (A) │ or │HOMO (E) │> │LUMO (G) │> │LUMO (B) or │LUMO (D) │ ……… (6)
It is preferable that the relationship is

  The difference between | HOMO (A) | and | LUMO (G) | and the difference between | HOMO (E) | and | LUMO (G) | are preferably 1.5 eV or less. By making such a difference, the difference between │HOMO (A) │ and │LUMO (B) │ and the difference between │HOMO (E) │ and │LUMO (D) │ become larger than 1.5 eV. However, even when the voltage becomes 2.0 eV, for example, electrons can be easily extracted by the electron extraction layer.

  Each of the first light emitting unit and the second light emitting unit in the present invention may be a single light emitting layer, or may have a laminated structure in which a plurality of light emitting layers are laminated. For example, a white light emitting unit in which an orange light emitting layer and a blue light emitting layer are stacked may be used.

  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. And an active matrix driving substrate provided with an active element of the above, an organic electroluminescent element is arranged on the active matrix driving substrate, and the electrode provided on the substrate side of the cathode and the anode is a transparent electrode. Type organic electroluminescent display device, wherein an organic electroluminescent device is disposed between a cathode, an anode, an intermediate unit disposed between the cathode and the anode, and between the cathode and the intermediate unit The first light emitting unit and the second light emitting unit disposed between the anode and the intermediate unit. And a cavity adjustment unit disposed between the intermediate unit and the second light emitting unit and provided adjacent to the intermediate unit, the intermediate unit having a first electron extraction layer for extracting electrons from the cavity adjustment unit And an electron injection layer adjacent to the anode side of the first electron extraction layer, and the cavity adjustment unit is provided adjacent to the cathode side of the first electron extraction layer. A first cavity adjustment layer from which electrons are extracted, and a second electron extraction layer for extracting electrons from an electron supply layer adjacent to the cathode side, and the lowest unoccupied molecular orbital (LUMO) of the first electron extraction layer ) Absolute value of energy level | LUMO (B) | and absolute value of energy level of highest occupied molecular orbital (HOMO) of first cavity adjustment layer | HOM (A) | is in a relationship of | HOMO (A) | --LUMO (B) | ≦ 1.5 eV, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the electron injection layer | LUMO (C) | Or absolute value of work function | WF (C) | is smaller than | LUMO (B) | and is the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the second electron extraction layer | LUMO (D) | And the absolute value | HOMO (E) | of the highest occupied molecular orbital (HOMO) of the electron supply layer is in a relationship of | HOMO (E) | --LUMO (D) | ≦ 1.5 eV, The absolute value of the lowest unoccupied molecular orbital (LUMO) energy level of the first cavity adjustment layer | LUMO (A) | and | LUMO (D) | are | LUMO (A) | It is characterized by being in a relationship .

  In the organic electroluminescent display device of the present invention, when the organic EL element is a white light emitting element, a color filter can be arranged between the organic EL element and the substrate to obtain a color display device.

  An organic electroluminescent display device according to another aspect of the present invention includes an organic electroluminescent element having an element structure sandwiched between an anode and a cathode, and a display signal corresponding to each display pixel. An active matrix driving substrate provided with active elements for supplying to the active matrix, and a transparent sealing substrate provided opposite to the active matrix driving substrate, and sealing the organic electroluminescent element with the active matrix driving substrate. A top emission type organic electroluminescent display device which is arranged between a stop substrate and uses a transparent electrode as an electrode provided on the sealing substrate side of a cathode and an anode, wherein the organic electroluminescent element is a cathode An anode, an intermediate unit disposed between the cathode and the anode, and the cathode and the intermediate The first light emitting unit disposed between the knit, the second light emitting unit disposed between the anode and the intermediate unit, and disposed between the intermediate unit and the second light emitting unit and adjacent to the intermediate unit. The intermediate unit has a first electron extraction layer for extracting electrons from the cavity adjustment unit, and an electron injection layer adjacent to the anode side of the first electron extraction layer. The cavity adjustment unit is provided adjacent to the cathode side of the first electron extraction layer, and includes a first cavity adjustment layer from which electrons are extracted to the first electron extraction layer, and an electron supply layer adjacent to the cathode side. An absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first electron extraction layer | LUMO B) | and the absolute value | HOMO (A) | of the energy level of the highest occupied molecular orbital (HOMO) of the first cavity adjustment layer is | HOMO (A) |-| LUMO (B) | ≦ 1. 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 from | LUMO (B) | The absolute value of the lowest unoccupied molecular orbital (LUMO) energy level of the second electron extraction layer | LUMO (D) | and the absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the electron supply layer | HOMO (E) | is in a relationship of | HOMO (E) | --LUMO (D) | ≦ 1.5 eV, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first cavity adjustment layer | LUMO (A) │ and │LUMO (D) │ are characterized by a relationship of │LUMO (A) │ <│LUMO (D) │.

  In the organic electroluminescent display device, when the organic EL element is a white light emitting element, a color filter can be disposed between the organic EL element and the sealing substrate to obtain a color display device.

  Since the organic EL display device of the present invention includes the organic EL element of the present invention, the cavity can be adjusted for each emission color, and the driving voltage can be reduced to reduce power consumption. Can do. Further, an organic EL display device having high reliability can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, it is set as the organic electroluminescent element which can adjust a cavity, has high luminous efficiency, can reduce a drive voltage, and can improve reliability, and an organic electroluminescent display apparatus using the same. Can do.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to a following example.

  FIG. 1 is a diagram schematically showing HOMO and LUMO energy levels of each layer constituting the intermediate unit and the cavity adjusting unit in the organic EL device of the embodiment according to the present invention. In this embodiment, the intermediate unit 1 includes a first electron extraction layer 3, an electron injection layer 4, and an electron transport layer 8. The cavity adjustment unit 2 includes a first cavity adjustment layer 5 and a second electron extraction layer 6. An electron supply layer 7 is provided on the cathode side of the second electron extraction layer 6.

In FIG. 1, the LUMO of the first electron extraction layer 3 is shown as L _B and the HOMO is shown as H _B. Also shows LUMO of the electron injection layer 4 as _{L C,} shows the LUMO of the electron transport layer 8 as _{L F,} show the LUMO of the first cavity layer 5 _L A, the HOMO as _{H A.} Further, the LUMO of the second electron-withdrawing layer 6 shows _L D, the HOMO as _{H D,} shows the HOMO of the electron supply layer 7 as _{H E.}

Referring to FIG. 1, in the organic EL device according to the present invention, and L _B of the first electron-withdrawing layer, each of the difference in the absolute value of H _A of the first cavity adjustment layer 5 in the following 1.5eV is there. Therefore, the first electron extraction layer 3 can easily extract electrons from the first cavity adjustment layer 5. The absolute value of L _C of the electron injection layer 4 is smaller than the absolute value of L _B of the first electron-withdrawing layer 3, the absolute value of L _F of the electron transport layer 8 is smaller than the absolute value of L _C . Therefore, the electrons extracted by the first electron extraction layer 3 are supplied to the anode side through the electron injection layer 4 and the electron transport layer 8.

In the present invention, the absolute value of L _D of the second electron-withdrawing layer 6, the difference between the absolute value of H _E of the electron supply layer 7 is less than 1.5 eV. Therefore, the second electron extraction layer 6 can easily extract electrons from the electron supply layer 7. The absolute value of L _A of the first cavity adjustment layer, since smaller than the absolute value of L _D of the second electron-withdrawing layer 6, electrons withdrawn by the second electron-withdrawing layer 6 is first Blocked by the cavity adjustment layer 5 and accumulated in the second electron extraction layer 6. Accordingly, a high electric field is locally applied and the energy level is distorted, so that the driving current can be reduced.

  Holes are generated in the electron supply layer 7 from which electrons have been extracted, and the holes are supplied to the cathode side.

  In the present invention, electrons can be supplied from the intermediate unit 1 and the cavity adjustment unit 2 to the anode side and holes can be supplied to the cathode side as described above. Therefore, the light emitting unit located on the anode side and the light emitting unit located on the cathode side can each emit light efficiently. Further, as described above, since a high electric field is locally applied, the driving voltage can be reduced, and even if the thickness of the first cavity adjustment layer 5 is increased, an increase in the driving voltage can be suppressed. it can.

  Moreover, since it is possible to suppress excessive supply of electrons to the anode side by the first cavity adjustment layer 5, it is possible to improve the lifetime characteristics of the element and to improve the reliability.

(Examples 1-9 and Comparative Examples 1-6)
Examples 1 to 9 and Comparative Examples 1 to 6 having a hole injection layer, a hole transport layer, a second light emitting unit, an intermediate unit, a cavity adjustment unit, a first light emitting unit, an electron transport layer, and a cathode shown in Table 1. An organic EL element was prepared. In the following tables, the numbers in () indicate the thickness (nm) of each layer.

  As the substrate, a glass substrate in which an ITO (indium tin oxide) film as an anode was formed on a glass substrate was used. A hole injection layer was formed by forming a fluorocarbon (CFx) layer on the ITO film. (15s) in Table 1 means the film formation time (seconds).

  On the hole injection layer formed as described above, each layer shown in Table 1 was sequentially laminated by a vapor deposition method.

  The hole transport layer was formed by laminating a HAT-CN6 layer on the NPB layer.

  The first light emitting unit and the second light emitting unit are white light emitting units in which a blue light emitting layer is stacked on an orange light emitting layer. The orange light emitting layer is disposed on the anode side, and the blue light emitting layer is disposed on the cathode side. In the table, “%” means “% by weight” unless otherwise specified.

  On the hole transport layer formed as described above, an orange light emitting layer and a blue light emitting layer were deposited.

  The orange light emitting layer uses NPB as a hole transporting host material, TBADN as an electron transporting host material, and DBzR as a dopant material. The blue light emitting layer uses TBADN as an electron transporting host material, NPB as a hole transporting host material, and TBP as a dopant material.

  In Example 6, Example 7, and Comparative Example 5, the first light emitting unit and the second light emitting unit are formed from a single white light emitting layer. Accordingly, DBzR, which is an orange light emitting dopant, and TBP, which is a blue light emitting dopant, are contained in one layer. Note that an NPB layer is formed on the anode side in the first light emitting unit and the second light emitting unit.

  As the electron transport layer of the intermediate unit, an electron transport material can be used. In the examples and comparative examples shown in Table 1, BCP is used. The LUMO of BCP is -2.7 eV. The film thickness of the electron transport layer of the intermediate unit is preferably in the range of 1 to 100 nm.

As the electron injection layer of the intermediate unit, alkali metals, alkaline earth metals and oxides thereof can be used. In the examples and comparative examples shown in Table 1, Li ₂ O, Li, or Mg is used. The work function of Li is 2.9 eV, and the work function of Mg is 3.9 eV. In the case of a metal oxide such as Li ₂ O, the work function of a metal such as Li may be within the scope of the present invention. The thickness of the electron injection layer is preferably in the range of 0.1 to 10 nm.

  HAT-CN6 is used as the first electron extraction layer of the intermediate unit. HAT-CN6 has a LUMO of −4.4 eV and a HOMO of −7.0 eV. The film thickness of the first electron extraction layer is preferably in the range of 1 to 150 nm.

In Comparative Example 4, a V ₂ O ₅ layer is used instead of the first electron extraction layer.

  NPB is used as the first cavity adjustment layer of the cavity adjustment unit. The LUMO of NPB is -2.6 eV and the HOMO is -5.4 eV.

  HAT-CN6 is used as the second electron extraction layer of the cavity adjustment unit. The film thickness of the second electron extraction layer is preferably in the range of 1 to 150 nm.

  As the electron transport layer formed on the first light emitting unit, an electron transport layer having a stacked structure of an Alq layer and a BCP layer is formed. In Examples 6 and 7 and Comparative Example 5, the electron transport layer is formed only from the BCP layer.

On the electron transport layer, a cathode having a laminated structure of a Li ₂ O layer and an Al layer is formed.

  NPB is N, N′-di (1-naphthyl) -N, N′-diphenylbenzidine and has the following structure.

  HAT-CN6 is hexaazatriphenylenehexacarboxylic nitrile and has the following structure.

  TBADN is 2-tertiary-butyl-9,10-di (2-naphthyl) anthracene and has the following structure.

  DBzR is 5,12-bis {4- (6-methylbenzothiazol-2-yl) phenyl} -6,11-diphenylnaphthacene and has the following structure.

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

  BCP is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline and has the following structure.

  Alq is tris- (8-quinolinato) aluminum (III) and has the following structure.

[Evaluation of organic EL elements]
About each organic EL element produced as mentioned above, drive voltage, luminous efficiency, and luminance half life were measured. The measurement results are shown in Table 2. The measurement result is a value at a drive current of 40 mA / cm ² .

  As is apparent from the results shown in Table 2, in Examples 1 to 9 according to the present invention, the driving voltage is low, the light emission efficiency is good, and the luminance half-life is also long.

  Comparing Example 1 provided with the cavity adjusting unit and Comparative Example 1 not provided with the cavity adjusting unit, Example 1 is driven at the same driving voltage, although the luminous efficiency is slightly inferior to Comparative Example 1. The luminance half-life is longer than that of Comparative Example 1. Therefore, the cavity can be adjusted by providing the cavity adjusting unit without increasing the drive voltage and without deteriorating the life characteristics.

  In Comparative Example 2 in which NPB in the cavity adjustment unit is replaced with Alq, the driving voltage is remarkably increased and the luminance half-life is remarkably shortened.

Further, in Comparative Example 4 in which HAT-CN6 in the cavity adjustment unit is replaced with V ₂ O ₅ , the light emission efficiency is lowered and the luminance half life is remarkably shortened.

  Further, as is clear from the comparison between Examples 6 and 7 and Comparative Example 5 and the comparison between Examples 8 and 9 and Comparative Example 6, when the total film thickness of the NPB layer is greatly increased, the first It can be seen that the drive voltage can be reduced by inserting a plurality of HAT-CN6 layers, each of which is an electron extraction layer, at appropriate intervals.

[Organic EL display device]
FIG. 2 is a cross-sectional view showing a bottom emission type organic EL display device 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 display device, 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 17 as indicated by arrows.

Referring to FIG. 2, a first insulating layer 18 is provided on a substrate 17 made of a transparent substrate such as glass. The first insulating layer 18 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 18. 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 a second insulating layer 19. Yes. A third insulating layer 14 is provided on the gate electrode 22. The second insulating layer 19 is made of, for example, SiN _x and SiO ₂ , and the third insulating layer 14 is made of SiO ₂ and SiN _x .

A fourth insulating layer 15 is formed on the third insulating layer 14. The fourth insulating layer 15 is made of, for example, SiN _x . A color filter layer 9 is provided in a portion of the pixel region on the fourth insulating layer 15. As the color filter layer 9, color filters such as R (red), G (green), and B (blue) are provided. A first planarization film 16 is provided on the color filter layer 9. A through hole portion is formed in the first planarization film 16 above the drain electrode 21, and a hole injection electrode 18 made of ITO (indium oxide) formed on the first planarization film 16 is through. It is introduced in the hall. A hole injection / transport unit 10 is formed on the hole injection electrode (anode) 18 in the pixel region. A second planarizing film 19 is formed in a portion other than the pixel region.

  On the hole injecting / transporting unit 10, a laminated light emitting unit 11 is provided. The laminated light emitting unit 11 has a structure in which an intermediate unit and a cavity adjusting unit are provided between the first light emitting unit and the second light emitting unit according to the present invention.

  An electron transport layer 12 is provided on the multilayer light emitting unit 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 / transport unit 10, the stacked light emitting unit 11, the electron transport layer 12, An electron injection electrode (cathode) 13 is laminated to constitute an organic EL element.

  In the laminated light emitting unit 11 of the present embodiment, a light emitting unit in which an orange light emitting layer and a blue light emitting layer are laminated is used. Therefore, the laminated light emitting unit 11 emits white light. This white light emission is emitted to the outside through the substrate 17, but since the color filter layer 9 is provided on the light emission side, R, G, or B color is emitted according to the color of the color filter layer 9. The In the case of an element that emits light in a single color, the color filter layer 9 may be omitted.

  FIG. 3 is a cross-sectional view showing a top emission type organic EL display device of an embodiment according to the present invention. The organic EL display device of the present embodiment is a top emission type organic EL display device that emits light above the substrate 17 for display as shown by arrows.

  The portion from the substrate 17 to the anode 18 is fabricated in substantially the same manner as in the embodiment shown in FIG. However, the color filter layer 9 is not provided on the fourth insulating layer 15 and is disposed above the organic EL element. Specifically, a color filter layer 9 is attached on a transparent sealing substrate 16 made of glass or the like, an overcoat layer 15 is coated thereon, and this is applied on the anode 18 through the transparent adhesive layer 14. It is attached by sticking to. Further, 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 18, 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 9 may be a pigment type or a dye type. Its thickness is about 1 μm.

  The white light emitted from the multilayer light emitting unit 11 is emitted to the outside through the sealing substrate 16. However, since the color filter layer 9 is provided on the light emission 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 9 is provided in a wider range than the embodiment shown in FIG. ing. According to the present embodiment, a wider area can be used as the pixel area, and the aperture ratio can be increased. In addition, since the light emitting 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.

The schematic diagram which shows the energy level of LUMO and HOMO of each layer which comprises the intermediate | middle unit and cavity adjustment unit in one Example according to this invention. Sectional drawing which shows the bottom emission type organic electroluminescence display of the Example according to this invention. Sectional drawing which shows the top emission type organic electroluminescence display of the Example according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Intermediate unit 2 ... Cavity adjustment layer 3 ... 1st electron extraction layer 4 ... Electron injection layer 5 ... 1st cavity adjustment layer 6 ... 2nd electron extraction layer 7 ... Electron supply layer 8 ... Electron transport layer

Claims (13)

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, and a cavity adjusting unit disposed between the intermediate unit and the second light emitting unit and provided adjacent to the intermediate unit,
The intermediate unit includes a first electron extraction layer for extracting electrons from the cavity adjustment unit, and an electron injection layer adjacent to the anode side of the first electron extraction layer,
The cavity adjustment unit is provided adjacent to the cathode side of the first electron extraction layer, the first cavity adjustment layer from which electrons are extracted to the first electron extraction layer, and the electron supply adjacent to the cathode side A second electron extraction layer for extracting electrons from the layer,
Absolute value | LUMO (B) | of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first electron extraction layer and absolute energy level of the highest occupied molecular orbital (HOMO) of the first cavity adjustment layer The value | HOMO (A) | is in the relationship of | HOMO (A) | --LUMO (B) | ≦ 1.5 eV, 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 work function | WF (C) | is smaller than | LUMO (B) |
Absolute value | LUMO (D) | of the lowest unoccupied molecular orbital (LUMO) energy level of the second electron extraction layer and absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the electron supply layer | HOMO (E) | is in a relationship of | HOMO (E) | --LUMO (D) | ≦ 1.5 eV, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first cavity adjustment layer | An organic electroluminescent element characterized in that LUMO (A) | and | LUMO (D) | have a relationship of | LUMO (A) | <| LUMO (D) |.   The organic electroluminescent element according to claim 1, wherein the electron supply layer is provided in the first light emitting unit.   The organic electroluminescent element according to claim 1, wherein the electron supply layer is a second cavity adjustment layer provided in the cavity adjustment unit.   The organic electroluminescent device according to any one of claims 1 to 3, wherein the first and second cavity adjusting layers are formed of a hole transporting material.   The organic electroluminescent device according to claim 4, wherein the hole transporting material is a tertiary arylamine material.   6. The organic material according to claim 1, wherein the cavity adjustment unit has a plurality of repeating units in combination of the first cavity adjustment layer and the second electron extraction layer. Electroluminescent element. An electron transport layer is provided between the electron injection layer in the intermediate unit and the second light emitting unit;
The absolute value | LUMO (F) | of the energy level of the lowest unoccupied molecular orbital (LUMO) of the electron transport layer is smaller than | LUMO (C) | or | WF (C) | 6. The organic electroluminescent device according to any one of 6 above. The organic electro according to any one of claims 1 to 7, wherein the first and / or second electron extraction layer is formed of a pyrazine derivative represented by the structural formula shown below. Luminescent element.

(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 said 1st and / or 2nd electron extraction layer is formed from the hexaazatriphenylene derivative represented by the following structural formula, The any one of Claims 1-7 characterized by the above-mentioned. Organic electroluminescent device.

(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 drive 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 A bottom emission type organic electroluminescence device in which the organic electroluminescent element is disposed on the active matrix driving substrate, and an electrode provided on the substrate side of the cathode and the anode is a transparent electrode. A cent display device,
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, and a cavity adjusting unit disposed between the intermediate unit and the second light emitting unit and provided adjacent to the intermediate unit. Prepared,
The intermediate unit includes a first electron extraction layer for extracting electrons from the cavity adjustment unit, and an electron injection layer adjacent to the anode side of the first electron extraction layer,
The cavity adjustment unit is provided adjacent to the cathode side of the first electron extraction layer, and a first cavity adjustment layer from which electrons are extracted to the first electron extraction layer, and an electron supply adjacent to the cathode side A second electron extraction layer for extracting electrons from the layer,
Absolute value | LUMO (B) | of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first electron extraction layer and absolute energy level of the highest occupied molecular orbital (HOMO) of the first cavity adjustment layer The value | HOMO (A) | is in the relationship of | HOMO (A) | --LUMO (B) | ≦ 1.5 eV, 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 work function | WF (C) | is smaller than | LUMO (B) |
Absolute value | LUMO (D) | of the lowest unoccupied molecular orbital (LUMO) energy level of the second electron extraction layer and absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the electron supply layer | HOMO (E) | is in a relationship of | HOMO (E) | --LUMO (D) | ≦ 1.5 eV, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first cavity adjustment layer | An organic electroluminescent display device characterized in that LUMO (A) | and | LUMO (D) | have a relationship of | LUMO (A) | <| LUMO (D) |.   The organic electroluminescent device according to claim 10, wherein the organic electroluminescent device is a white light emitting device, and a color filter is disposed between the organic electroluminescent device and the substrate. NETCENT display device. An active matrix drive 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, and a cavity adjusting unit disposed between the intermediate unit and the second light emitting unit and provided adjacent to the intermediate unit. Prepared,
The intermediate unit includes a first electron extraction layer for extracting electrons from the cavity adjustment unit, and an electron injection layer adjacent to the anode side of the first electron extraction layer,
The cavity adjustment unit is provided adjacent to the cathode side of the first electron extraction layer, and a first cavity adjustment layer from which electrons are extracted to the first electron extraction layer, and an electron supply adjacent to the cathode side A second electron extraction layer for extracting electrons from the layer,
Absolute value | LUMO (B) | of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first electron extraction layer and absolute energy level of the highest occupied molecular orbital (HOMO) of the first cavity adjustment layer The value | HOMO (A) | is in the relationship of | HOMO (A) | --LUMO (B) | ≦ 1.5 eV, 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 work function | WF (C) | is smaller than | LUMO (B) |
Absolute value | LUMO (D) | of the lowest unoccupied molecular orbital (LUMO) energy level of the second electron extraction layer and absolute value of the energy level of the highest occupied molecular orbital (HOMO) of the electron supply layer | HOMO (E) | is in a relationship of | HOMO (E) | --LUMO (D) | ≦ 1.5 eV, and the absolute value of the energy level of the lowest unoccupied molecular orbital (LUMO) of the first cavity adjustment layer | An organic electroluminescent display device characterized in that LUMO (A) | and | LUMO (D) | have a relationship of | LUMO (A) | <| LUMO (D) |.   The organic electroluminescent device according to claim 12, 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.

Images