JP2009071189A - Organic electroluminescent device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent device that exhibits high light-emission efficiency and has a small variation in chrominance. <P>SOLUTION: The organic electroluminescent device 10 includes a hole transporting material and an electronic transporting material as a light-emitting material and a host material, respectively, in a light-emitting layer 16, at least either of which has a concentration gradient in the direction of thickness of the light-emitting layer. Furthermore, a plurality of hole transporting intermediate layers 15a, 15b and 15c are arranged adjacent to a hole transporting layer 14 and a light-emitting layer, so as to transport holes to the light-emitting layer from the hole transporting layer. When assuming that ionizing potentials of materials included in the hole transporting intermediate layers are Ip(Lh-a), Ip(Lh-b) and Ip(Lh-c), an ionizing potential of the hole transporting material included in the light-emitting layer is Ip (light-emitting layer), and an ionizing potential of a material included in the hole transporting layer is Ip(H), the hole transporting intermediate layers satisfy a relationship of Ip(H)<Ip(Lh-a)<Ip(Lh-b)<Ip(Lh-c)<Ip(Oh). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent device.

  In recent years, light emitting devices using organic electroluminescent elements (organic EL elements) have been developed. FIG. 7 schematically shows the configuration of the organic EL element 1. An anode 3, an organic EL layer 8 (a hole transport layer 4, a light emitting layer 5, and an electron transport layer 6), a cathode 7, and the like are laminated on a substrate 2 such as glass. In the drawing, a partition, an insulating film, a sealing member, and the like are omitted. Further, the configuration is not limited to the configuration shown in FIG. 7, and there are cases where, for example, the transport layers 4 and 6 are not provided, or a charge injection layer is provided between the electrodes 3 and 7 and the transport layers 4 and 6. Holes and electrons are recombined in the light emitting layer 5 in the region sandwiched between the electrodes 3 and 7 by connecting to external wiring via the lead wires (terminals) of the bipolar electrodes 3 and 7 and applying an electric field. Flashes.

  When manufacturing a display device capable of color display, for example, after an anode is formed in a stripe shape on a substrate, an organic EL layer corresponding to red (R), green (G), and blue (B) is formed on the anode. Patterning is performed with an organic dye material or the like so that appears repeatedly. Next, a cathode is formed on the organic EL layer, and external wirings such as control wirings and signal wirings are connected to terminals (external connection terminals) of the respective electrodes. Thereby, organic EL layer elements corresponding to RGB can be arranged to form a pixel, and color display can be performed.

The material constituting the light emitting layer is required to have conditions such as good luminous efficiency, good carrier transportability, and good film formability, and may be composed of only the light emitting material. In addition, a host material or the like having a charge transporting property without emitting light may be mixed.
In addition, a light-emitting element has been proposed in which a light emission layer is provided with a concentration gradient so that the light emission efficiency is improved and the lifetime is increased (see, for example, Patent Documents 1 to 4).

JP 2001-155862 A JP 2001-189193 A Japanese Patent Laid-Open No. 2004-6102 JP 2002-313583 A

  An object of the present invention is to provide an organic electroluminescent device having high luminous efficiency and small variation in chromaticity.

In order to achieve the above object, the present invention provides the following organic electroluminescence device.
<1> a pair of electrodes composed of an anode and a cathode;
A light emitting layer disposed between the pair of electrodes;
A hole transport layer disposed between the anode and the light emitting layer;
Including an electron transport layer disposed between the cathode and the light emitting layer;
The light emitting layer includes a hole transporting material and an electron transporting material as a light emitting material and a host material, and at least one of the hole transporting material and the electron transporting material is arranged in the thickness direction of the light emitting layer. Having a concentration gradient, and
Between the hole transport layer and the light emitting layer, a plurality of (n layers: n ≧ 2) hole transport intermediate layers that mediate the transport of holes from the hole transport layer to the light emitting layer are the layers closest to the anode. In order, the hole transport intermediate layer 1 is arranged as the hole transport intermediate layer n and / or mediates the transport of electrons from the electron transport layer to the light emitting layer between the electron transport layer and the light emitting layer. A plurality (m layers: m ≧ 2) of electron transport intermediate layers are arranged in order from the layer closest to the cathode, electron transport intermediate layer 1... Electron transport intermediate layer m, and the plurality of hole transport intermediate layers. Ip (hole transport intermediate layer 1)... Ip (hole transport intermediate layer n), and the ionization potential of the hole transport material contained in the light emitting layer is Ip (light emitting layer). , The ionization potential of the material contained in the hole transport layer is Ip (hole transport layer) , Ea (electron transport intermediate layer 1)... Ea (electron transport intermediate layer m) and electron affinity of the electron transport material contained in the light emitting layer, respectively. When the electron affinity of the material contained in Ea (light emitting layer) and the electron transport layer is Ea (electron transport layer), Ip (hole transport layer) <Ip (hole transport intermediate layer 1) <. Ip (hole transport intermediate layer n) <Ip (light emitting layer) and / or Ea (electron transport layer)> Ea (electron transport intermediate layer 1)>...> Ea (electron transport intermediate layer m)> Ea (light emission) layer)
An organic electroluminescent element, characterized in that

<2> The organic electroluminescent element according to <1>, wherein the light emitting material has a concentration gradient in a thickness direction of the light emitting layer.

<3> The light-emitting layer includes a hole-transporting host material that is the hole-transporting material and an electron-transporting light-emitting material that is the electron-transporting material, and the concentration of the electron-transporting light-emitting material is Gradually decreasing from the cathode side toward the anode side, and
The plurality of hole transport intermediate layers are arranged, and each of the plurality (n layers: n ≧ 2) of the hole transport intermediate layers has an ionization potential of a material contained in the hole transport intermediate layer as an anode. , Ip (Oh-1)... Ip (Oh-n), the ionization potential of the host material contained in the light emitting layer, Ip (Lh), and the hole transport layer. When the ionization potential of the material is Ip (H), the relationship of Ip (H) <Ip (Oh-1) <... <Ip (Oh-n) <Ip (Lh) is satisfied. The organic electroluminescent element as described in <1> or <2>.

<4> The light emitting layer includes a hole transporting host material that is the hole transporting material and an electron transporting light emitting material that is the electron transporting material, and the concentration of the electron transporting light emitting material is Gradually decreasing from the cathode side toward the anode side, and
The plurality of electron transport intermediate layers are arranged, and the plurality of (m layers: m ≧ 2) electron transport intermediate layers are all closest to the cathode in electron affinity of the material contained in the electron transport intermediate layer. In order from the layer, Ea (Oe-1)... Ea (Oe-m), the electron affinity of the light emitting material contained in the light emitting layer is Ea (Ll), and the electron affinity of the material contained in the electron transport layer. <E>(E)> Ea (E)> Ea (Oe-1)>...> Ea (Oe-m)> Ea (Ll) The organic electroluminescent element as described in any one of <3>.
<5> The concentration of the electron-transporting light-emitting material in the region near the anode-side interface of the light-emitting layer is 0% or more and 50% or less with respect to the concentration in the region near the cathode-side interface of the light-emitting layer. <3> or <4>, wherein the organic electroluminescence device is characterized.

<6> The light emitting layer includes an electron transporting host material that serves as the electron transporting material and a hole transporting light emitting material that serves as the hole transporting material, and the concentration of the hole transporting light emitting material. Is gradually reduced from the anode side toward the cathode side, and
The plurality of electron transport intermediate layers are arranged, and the plurality of (m layers: m ≧ 2) electron transport intermediate layers are all closest to the cathode in electron affinity of the material contained in the electron transport intermediate layer. In order from the layer, Ea (Oe-1)... Ea (Oe-m), the electron affinity of the host material contained in the light emitting layer is Ea (Lh), and the electron affinity of the material contained in the electron transport layer. <1> or satisfying the relationship of Ea (E)> Ea (Oe-1)>...> Ea (Oe-m)> Ea (Lh) The organic electroluminescent element as described in <2>.

<7> The light emitting layer includes an electron transporting host material that serves as the electron transporting material and a hole transporting light emitting material that serves as the hole transporting material, and a concentration of the hole transporting light emitting material. Is gradually reduced from the anode side toward the cathode side, and
The plurality of hole transport intermediate layers are arranged, and each of the plurality (n layers: n ≧ 2) of the hole transport intermediate layers has an ionization potential of a material contained in the hole transport intermediate layer as an anode. , Ip (Oh-1)... Ip (Oh-n), the ionization potential of the light emitting material contained in the light emitting layer, Ip (Ll), and the material contained in the hole transport layer. When the ionization potential is Ip (H), the relationship of Ip (H) <Ip (Oh-1) <... <Ip (Oh-n) <Ip (Ll) is satisfied <1 >, <2>, and the organic electroluminescent element in any one of <6>.

<8> The concentration of the hole-transporting light-emitting material in the region near the cathode-side interface of the light-emitting layer is 0% to 50% with respect to the concentration in the region near the anode-side interface of the light-emitting layer. <6> or <7>, The organic electroluminescent element characterized by the above-mentioned.

<9> The total number of the plurality of hole transport intermediate layers and / or the plurality of electron transport intermediate layers is 2 or more and 5 or less, respectively, <3> to <8>, Organic electroluminescent element.

<10> The thickness of each of the plurality of hole transporting intermediate layers or the thickness of each of the plurality of electron transporting intermediate layers is from 0.1 nm to 5 nm, wherein <1> to <1> The organic light emitting element in any one of <9>.

<11> The total thickness of the plurality of hole transport intermediate layers or the total thickness of the plurality of electron transport intermediate layers is 0.2 nm to 30 nm, respectively. <1> The organic light emitting element in any one of-<10>.

<12> The organic electroluminescent element according to any one of <1> to <11>, wherein the peak wavelength of the emission spectrum is between 430 nm and 480 nm.

  According to the present invention, there is provided an organic electroluminescence device having high luminous efficiency and small variation in chromaticity.

Hereinafter, an organic electroluminescent device according to the present invention will be described with reference to the accompanying drawings.
FIG. 8 is a diagram showing modeled energy levels of the hole transport layer, the light emitting layer, and the electron transport layer for the three types of organic EL elements.
When the energy barrier between the light emitting layer and the adjacent layer is large, the amount of charge injection varies greatly due to fluctuations in the driving voltage. That is, since the recombination position in the light emitting layer is moved by the driving voltage, there is a problem that the chromaticity is changed by the driving voltage, that is, the luminance. However, if there is no difference in the concentration of the light emitting material in the light emitting layer (FIG. 8A), the change in chromaticity is small, which is not a problem.

  On the other hand, according to the experiments by the present inventors, for example, the light emission distribution in the light emitting layer in the organic EL device having a peak wavelength of the light emission spectrum between 430 nm and 480 nm is a distribution close to the electron transport layer (ETL) side. It has been shown experimentally. This is because the carrier balance in the light emitting layer is in a state of excessive holes and insufficient electrons, and such local light emission is considered to cause a decrease in light emission efficiency and a deterioration in durability due to concentration of light emission load.

  For such ETL-side local light emission, for example, a host material that exhibits hole transportability and a light-emitting material that exhibits electron transportability are used, and it is considered that more electrons can be injected into the light-emitting layer by increasing the concentration of the light-emitting material. It is done. However, in a light emitting layer having a high concentration of a light emitting material exhibiting electron transporting properties, a light emission distribution close to both the hole transport layer (HTL) side and the electron transport layer (ETL) side is observed. That is, when the concentration of the electron-transporting light-emitting material in the light-emitting layer is increased, electrons are injected into the light-emitting layer, but the injected electrons move to the vicinity of the interface on the HTL side without contributing to recombination. As a result, it is considered that the problem of local light emission near the interface cannot be solved.

  Therefore, when the concentration of the electron transporting light emitting material is decreased from the ETL side to the HTL side in order to improve the light emission efficiency and durability (FIG. 8B), the light emission distribution approaches the whole light emission, and the efficiency And an improvement in durability was observed. It is considered that the movement of the electrons injected into the light emitting layer was suppressed as it proceeded to the HTL side, and recombination began at the center of the light emitting layer. Thereby, the light emission distribution close to the cathode side is greatly improved, and the light emission efficiency and durability can be improved.

  However, if the light emitting layer has a concentration gradient as described above, the driving voltage decreases, and if the difference in ionization potential between the light emitting layer and the hole transport layer is large, it becomes difficult to inject holes into the light emitting layer. The change in the amount of injected holes increases with the driving voltage, and the light emission position changes depending on the driving voltage. And since the density | concentration of a luminescent material changes with light emission positions, chromaticity will change a lot when the light emission position changes with a drive voltage, ie, brightness | luminance.

  Therefore, the present inventors have intensively studied an organic EL element that can suppress the change in chromaticity even when the constituent material of the light emitting layer has a concentration gradient in the thickness direction. As a result, in order to reduce the barrier difference between the light-emitting layer and the adjacent layer related to electrons or holes between the light-emitting layer and the adjacent layer (electron transport layer or hole transport layer), a plurality of electron transport intermediate layers and By providing a hole transport intermediate layer by reducing the barrier stepwise (FIG. 8C), the luminance (driving voltage) dependence of the light emitting position in the light emitting layer having a concentration gradient is reduced, and the luminance is increased. Regardless of this, it was found that the change in chromaticity can be reduced, and the present invention has been completed.

1 to 4 show typical examples of the organic electroluminescent device according to the present invention. An organic electroluminescence device according to the present invention includes a pair of electrodes composed of an anode and a cathode, a light emitting layer disposed between the pair of electrodes, and a hole transport layer disposed between the anode and the light emitting layer. And an electron transport layer disposed between the cathode and the light emitting layer, and the light emitting layer includes a hole transporting material and an electron transporting material as a light emitting material and a host material. At least one of the transport material and the electron transport material has a concentration gradient in the thickness direction of the light emitting layer. Further, a plurality of (n layers: n ≧ 2) hole transport intermediate layers that are adjacent to the hole transport layer and the light emitting layer and mediate the transport of holes from the hole transport layer to the light emitting layer are closest to the anode. In order from the layer, the hole transport intermediate layer 1 is arranged as the hole transport intermediate layer n and / or is adjacent to the electron transport layer and the light emitting layer, and transports electrons from the electron transport layer to the light emitting layer. A plurality (m layer: m ≧ 2) of electron transport intermediate layers that mediate are arranged in order from the layer closest to the cathode, the electron transport intermediate layer 1... The electron transport intermediate layer m. Ip (hole transport intermediate layer 1)... Ip (hole transport intermediate layer n) respectively, and the ionization potential of the hole transport material contained in the light emitting layer is Ip (light emitting layer). ), The ionization potential of the material contained in the hole transport layer is Ip ( Hole transport layer), Ea (electron transport intermediate layer 1)... Ea (electron transport intermediate layer m), and electron transport material contained in the light emitting layer. And Ea (electron transport layer) as the electron affinity of the material contained in the electron transport layer, Ip (hole transport layer) <Ip (hole transport intermediate layer 1) < ... <Ip (hole transport intermediate layer n) <Ip (light emitting layer) and / or Ea (electron transport layer)> Ea (electron transport intermediate layer 1)>...> Ea (electron transport intermediate layer m) > Ea (light emitting layer)
It is characterized by becoming.

FIG. 1 shows an example of the configuration of an organic electroluminescent element according to the present invention (first embodiment).
In this embodiment, the organic EL element 10 is formed on the support substrate 12, and a hole transporting host material that is a hole transporting material and an electron transporting property that is an electron transporting material in the light emitting layer 16. The concentration of the electron transporting luminescent material is gradually decreased from the cathode 19 side toward the anode 13 side. A plurality of hole transport intermediate layers 15 a, 15 b, and 15 c that mediate the transport of holes from the hole transport layer 14 to the light emitting layer 16 are disposed between the light emitting layer 16 and the hole transport layer 14. Further, each of the plurality of hole transport intermediate layers 15a, 15b, and 15c has the ionization potential of the material contained in each of the hole transport intermediate layers 15a, 15b, and 15c, respectively, Ip (Oh-a), Ip ( Oh-b), Ip (Oh-c), when the ionization potential of the host material contained in the light emitting layer 16 is Ip (Lh), and when the ionization potential of the material contained in the hole transport layer 14 is Ip (H) 1p (H) <Ip (Oh-a) <Ip (Oh-b) <Ip (Oh-c) <Ip (Lh) (FIG. 1C). .

  In FIG. 1B, three layers of the hole transport intermediate layers 15a, 15b, and 15c are formed. However, if the total thickness of the hole transport intermediate layers 15a, 15b, and 15c is too large, it may hinder the injection of holes into the light emitting layer 16 and may cause a decrease in productivity. It is preferable to have 5 layers or less.

  FIG. 2 shows another example (second embodiment) of the configuration of the organic electroluminescent element according to the present invention. As in the first embodiment, the light emitting layer 16 of the organic EL element 20 includes a hole transporting host material and an electron transporting light emitting material, and the concentration of the electron transporting light emitting material is from the cathode 19 side to the anode 13 side. It is gradually decreasing toward. On the other hand, a plurality of electron transport intermediate layers 17a, 17b, and 17c that mediate the transport of electrons from the electron transport layer 18 to the light-emitting layer 16 are disposed between the light-emitting layer 16 and the electron transport layer 18. The electron transport intermediate layers 17a, 17b, and 17c have electron affinities of materials included in the electron transport intermediate layers 17a, 17b, and 17c, respectively, Ea (Oe-a), Ea (Oe-b), and Ea (Oe-c). ), When the electron affinity of the electron-transporting light-emitting material contained in the light-emitting layer 16 is Ea (Ll), and the electron affinity of the material contained in the electron-transporting layer 18 is Ea (E), It is comprised so that the relationship of Ea (E)> Ea (Oe-a)> Ea (Oe-b)> Ea (Oe-c)> Ea (Ll) may be satisfied (FIG. 2C).

  In FIG. 2B, three electron transport intermediate layers 17a, 17b, and 17c are formed between the light emitting layer 16 and the electron transport layer 18. However, the present invention is not limited to this, and two or more layers may be used. However, if the total thickness of the electron transport intermediate layers 17a, 17b, and 17c is too large, injection of electrons into the light emitting layer 16 may be hindered or productivity may be reduced. It is preferable to do.

  FIG. 3 shows another example (third embodiment) of the configuration of the organic electroluminescent element according to the present invention. In this organic EL element 30, the light emitting layer 16 includes an electron transporting host material and a hole transporting light emitting material, and the concentration of the hole transporting light emitting material gradually decreases from the anode 13 side toward the cathode 19 side. is doing. A plurality of electron transport intermediate layers 17 a, 17 b, and 17 c that mediate transport of electrons from the electron transport layer 18 to the light emitting layer 16 are disposed between the light emitting layer 16 and the electron transport layer 18. Furthermore, the electron affinity of the material contained in each electron transport intermediate layer 17a, 17b, and 17c is set to Ea (Oe-a), Ea (Oe-b), Ea (Oe-c), and the host contained in the light emitting layer 16, respectively. When the electron affinity of the material is Ea (Lh) and the electron affinity of the material contained in the electron transport layer 18 is Ea (E), Ea (E)> Ea (Oe-a)> Ea (Oe) -b)> Ea (Oe-c)> Ea (Lh) (FIG. 3C).

  Also in this embodiment, for the same reason as in the second embodiment, the electron transport intermediate layers 17a, 17b, and 17c between the light-emitting layer 16 and the electron transport layer 18 may be 2 layers or more and 5 layers or less. preferable.

  FIG. 4 shows another example (fourth embodiment) of the configuration of the organic electroluminescent element according to the present invention. As in the third embodiment, the light emitting layer 16 of the organic EL element 40 includes an electron transporting host material and a hole transporting light emitting material. The concentration of the hole transporting light emitting material is from the anode 13 side to the cathode 19. It gradually decreases toward the side. On the other hand, a plurality of hole transport intermediate layers 15 a, 15 b, and 15 c that mediate the transport of holes from the hole transport layer 14 to the light emitting layer 16 are disposed between the light emitting layer 16 and the hole transport layer 14. The ionization potentials of the materials included in each of the hole transport intermediate layers 15a, 15b, and 15c are included in Ip (Oh-a), Ip (Oh-b), Ip (Oh-c), and the light emitting layer 16, respectively. When the ionization potential of the light emitting material is Ip (Ll) and the ionization potential of the material contained in the hole transport layer 14 is Ip (H), both of them are Ip (H) <Ip (Oh-a) < It is configured to satisfy the relationship of Ip (Oh-b) <Ip (Oh-c) <Ip (Ll) (FIG. 4C).

  Also in this embodiment, for the same reason as in the first embodiment, the hole transport intermediate layers 15a, 15b, and 15c between the light emitting layer 16 and the hole transport layer 14 are not less than 2 layers and not more than 5 layers. It is preferable.

  In the present invention, the electron-transporting light-emitting material is a material that has higher electron-transport property than the hole-transport property and emits light, and the hole-transporting host material is a hole-transporting material rather than the electron-transporting property. It is a material that has high transportability and does not emit light. A hole-transporting light-emitting material is a material that has a hole-transport property stronger than an electron-transport property and emits light. An electron-transport host material has a electron-transport property stronger than a hole-transport property. And a material that does not emit light.

  In the case of the organic EL elements 10, 20, 30, 40 having any one of the first to fourth embodiments as described above, the light emitting layer 16, the hole transport layer 14, and / or the electron transport layer 18 are used. Are provided with a plurality of hole transport intermediate layers 15a to 15c and / or electron transport intermediate layers 17a to 17c. Compared with the case where one such hole transport intermediate layer is provided, holes and / or Alternatively, the barrier for injection of electrons into the light emitting layer can be significantly reduced. Therefore, even if the light emitting layer 16 has a concentration gradient, the luminance (driving voltage) dependency of the light emitting position becomes small, and the change in chromaticity can be made extremely small regardless of the luminance.

  The light emitting layer 16 of the organic EL device according to the present invention includes a light emitting material, an electron transporting host material, and a hole transporting host material as shown in FIG. 5, for example, and the light emitting material has no concentration gradient. The electron transporting host material and the hole transporting host material may have a concentration gradient in a predetermined direction. As described above, even if the concentration of the light emitting layer 16 is uniform in the thickness direction, the light emission position may change depending on the driving voltage, and thereby the variation range of chromaticity may increase. Even in such a case, the plurality of hole transport intermediate layers 15a, 15b, 15c and / or the plurality of electron transport intermediate layers 17a, 17b, 17c are satisfied so as to satisfy the relationship between the ionization potential and / or the electron affinity. By providing this, the fluctuation range of chromaticity can be reduced.

However, as shown in FIGS. 1 to 4, when the light emitting material has a concentration gradient in the thickness direction of the light emitting layer 16, the light emission efficiency is improved, but the variation range of chromaticity tends to be large. Therefore, the present invention is preferable because the luminous efficiency is further improved and the variation range of chromaticity can be more effectively suppressed.
Hereinafter, the constituent elements of the organic EL element according to the present invention will be described more specifically.

<Support substrate>
The support substrate 12 is not particularly limited as long as it has strength, light transmittance, and the like that can support the organic EL elements 10, 20, 30, and 40, and a known substrate can be used. For example, zirconia stabilized yttrium (YSZ), inorganic materials such as glass, polyethylene terephthalate, polybutylene phthalate, polyethylene naphthalate and other polyesters, polystyrene, polycarbonate, polyethersulfone, polyarylate, polyimide, polycycloolefin, norbornene resin, Organic materials such as poly (chlorotrifluoroethylene) can be mentioned.

  When glass is used as the support substrate 12, it is preferable to use alkali-free glass in order to reduce ions eluted from the glass. When soda lime glass is used, it is preferable to use a glass with a barrier coat such as silica.

When the support substrate 12 made of an organic material is used, it is preferable that the substrate is excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, and workability. In particular, when a plastic support substrate 12 is used, it is preferable to provide a moisture permeation preventive layer or a gas barrier layer on one side or both sides of the support substrate 12 in order to suppress the permeation of moisture and oxygen. As a material for the moisture permeation preventing layer or the gas barrier layer, an inorganic material such as silicon nitride or silicon oxide can be suitably used. The moisture permeation preventing layer or the gas barrier layer can be formed by, for example, a high frequency sputtering method.
Moreover, when using a thermoplastic support substrate, you may provide a hard-coat layer, an undercoat layer, etc. further as needed.

  There is no restriction | limiting in particular about the shape of the support substrate 12, a structure, a magnitude | size, etc., It can select suitably according to the use, the objective, etc. of an organic EL display element. In general, the shape of the support substrate 12 is preferably a plate shape from the viewpoints of handleability, ease of forming an organic EL element, and the like. The structure of the support substrate 12 may be a single layer structure or a laminated structure. Moreover, the support substrate 12 may be comprised with the single member, and may be comprised with two or more members.

  Note that light emitting devices using organic EL elements generally include a bottom emission method in which light emitted from the light emitting layer is extracted from the support substrate 12 side and a top emission method in which light emitted from the opposite side of the support substrate 12 is provided. Either method can be adopted. When manufacturing a top emission type organic EL light emitting device, it is not necessary to extract light from the support substrate 12 side. For example, a metal substrate such as stainless steel, Fe, Al, Ni, Co, Cu, or an alloy thereof, A silicon substrate can be used. With such a support substrate made of metal or the like, even if it is thin, it has high strength and has a high gas barrier property against moisture and oxygen in the atmosphere. When a metal support substrate is used, an insulating film for ensuring electrical insulation may be provided between the support substrate 12 and the lower electrode 13.

<Organic EL device>
The organic EL elements 10, 20, 30, and 40 according to the present invention adopt the following layer structure, for example, except for the plurality of hole transport intermediate layers 15a to 15c and the plurality of electron transport intermediate layers 17a to 17c. can do. However, the layer structure is not limited to these, and may be determined as appropriate according to the purpose.

Anode / hole transport layer / light-emitting layer / electron transport layer / cathode Anode / hole transport layer / light-emitting layer / block layer / electron transport layer / cathode Anode / hole transport layer / light-emitting layer / block layer / electron Transport layer / electron injection layer / cathode ・ Anode / hole injection layer / hole transport layer / light emitting layer / block layer / electron transport layer / cathode ・ Anode / hole injection layer / hole transport layer / light emitting layer / block layer / Electron transport layer / electron injection layer / cathode ・ Anode / hole transport layer / block layer / light emitting layer / electron transport layer / cathode ・ Anode / hole transport layer / block layer / light emitting layer / electron transport layer / electron injection layer / Cathode ・ Anode / Hole injection layer / Block layer / Hole transport layer / Light emitting layer / Electron transport layer / Cathode ・ Anode / Hole injection layer / Block layer / Hole transport layer / Light emitting layer / Electron transport layer / Electron Injection layer / cathode

  Normally, the electrode (lower electrode) 13 on the support substrate 12 side is used as an anode, and the electrode (upper electrode) 19 on the sealing substrate (not shown) side is used as a cathode, but the lower electrode is used as a cathode and the upper electrode is used as an anode. You can also. In the following description, a structure in which the anode 13 is sequentially formed on the support substrate 12 will be described, but it is also possible to reversely form the support substrate 12 from the cathode.

-Anode-
As long as the anode 13 has a function as an electrode for supplying holes to the organic EL layer, its shape, structure, size, etc. are not particularly limited, and it depends on the use and purpose of the organic EL element. It can select suitably from a well-known electrode material.
Suitable materials for the anode 13 include, for example, metals, alloys, metal oxides, conductive compounds, or mixtures thereof. As specific examples, conductive metal oxides such as tin oxide (ATO, FTO) doped with antimony or fluorine, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), gold Metals such as silver, chromium and nickel, and mixtures or laminates of these metals and conductive metal oxides, inorganic conductive materials such as copper iodide and copper sulfide, and organic conductivity such as polyaniline, polythiophene and polypyrrole Examples thereof include materials and laminates of these and ITO. Among these, a conductive metal oxide is preferable, and ITO is particularly preferable from the viewpoints of productivity, high conductivity, transparency, and the like.

Examples of the method for forming the anode 13 include a wet method such as a printing method and a coating method, a physical method such as a vacuum deposition method, a sputtering method, and an ion plating method, and a chemical method such as a CVD method and a plasma CVD method. In view of suitability for the material constituting the anode 13 and the like, it may be selected as appropriate. For example, when ITO is used as the anode material, the anode 13 can be formed according to a direct current or high frequency sputtering method, a vacuum deposition method, an ion plating method, or the like.
The position where the anode 13 is formed can be appropriately selected according to the use and purpose of the organic EL element, and may be formed on the entire support substrate 12 or a part thereof.

  The patterning for forming the anode 13 may be performed by chemical etching such as photolithography, or may be performed by physical etching using a laser or the like. Further, the mask may be overlapped, and vacuum deposition, sputtering, or the like may be performed, or may be performed by a lift-off method or a printing method.

The thickness of the anode 13 may be appropriately selected according to the material constituting the anode 13, but is usually about 10 nm to 50 μm, and preferably 50 nm to 20 μm.
Further, the resistance value of the anode 13 is preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less in order to reliably supply holes to the organic EL layer.

  When light is extracted from the anode side, the light transmittance is preferably 60% or more, and more preferably 70% or more. The transparent anode is described in detail in Yutaka Sawada's “New Development of Transparent Electrode Film” published by CMC (1999), and the matters described here can be applied to the present invention. For example, when using a plastic support substrate with low heat resistance, a transparent anode formed using ITO or IZO at a low temperature of 150 ° C. or lower is preferable.

-Organic EL layer-
Each of the organic EL elements according to the present invention has a structure in which an organic EL layer is sandwiched between an anode 13 and a cathode 19. Each layer constituting the organic EL layer can be suitably formed by any of a dry film forming method such as a vapor deposition method and a sputtering method, a transfer method, and a printing method.

-Light emitting layer-
The light emitting layer 16 is a layer having a function of receiving holes from the anode side and electrons from the cathode side and providing a field for recombination of holes and electrons to emit light when an electric field is applied.
In the present invention, the light-emitting material and the host material include a hole transporting material and an electron transporting material, and at least one of the hole transporting material and the electron transporting material has a concentration in the thickness direction of the light emitting layer 16. The light emitting layer 16 has a gradient. For example, as shown in FIG. 1A, the organic EL device 10 according to the first embodiment includes a hole transporting host material and an electron transporting light emitting material in the light emitting layer 16, The concentration of the electron transporting luminescent material gradually decreases from the cathode 19 side toward the anode 13 side.

  In particular, the light emission distribution in the light emitting layer in an organic EL device having a peak wavelength of the light emission spectrum between 430 nm and 480 nm usually tends to be in a state where the carrier balance in the light emitting layer is excessive in holes and insufficient in electrons. However, the organic EL device according to the present invention has a concentration gradient as described above, so that the carrier balance of holes and electrons in the light emitting layer is almost equal, and electrons and holes in the entire light emitting layer. Can recombine and emit light. Therefore, the organic EL device according to the present invention can exert a remarkable effect particularly when applied to an organic EL device having a peak wavelength of an emission spectrum between 430 nm and 480 nm.

(A) Electron-transporting luminescent material As the electron-transporting luminescent material, a known electron-transporting luminescent material can be used, and it may be a fluorescent luminescent material or a phosphorescent luminescent material.
Preferably, the electron-transporting light-emitting material has an electron affinity (Ea) of 2.5 eV to 3.5 eV and an ionization potential (Ip) of 5.7 eV to 7.0 eV.

In general, examples of phosphorescent materials include complexes containing transition metal atoms or lanthanoid atoms.
The transition metal atom is preferably ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, and platinum, more preferably rhenium, iridium, and platinum, and more preferably iridium, platinum. .
Examples of the lanthanoid atom include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these lanthanoid atoms, neodymium, europium, and gadolinium are preferable.

Examples of the ligand of the complex include G.I. Wilkinson et al., Comprehensive Coordination Chemistry, Pergamon Press, 1987, H.C. Examples include ligands described in Yersin's "Photochemistry and Photophysics of Coordination Compounds" published by Springer-Verlag 1987, Akio Yamamoto "Organic Metal Chemistry-Fundamentals and Applications-" .
Specific ligands are preferably halogen ligands (preferably chlorine ligands), aromatic carbocyclic ligands (eg, cyclopentadienyl anion, benzene anion, or naphthyl anion), Nitrogen-containing heterocyclic ligands (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, or phenanthroline), carbene ligands, diketone ligands (eg, acetylacetone), carboxylic acid ligands (eg, acetic acid) Ligands, etc.), alcoholate ligands (eg phenolate ligands, etc.), carbon monoxide ligands, isonitrile ligands, cyano ligands, more preferably nitrogen-containing heterocyclic ligands It is.
The complex may have one transition metal atom in the compound, or may be a so-called binuclear complex having two or more. Different metal atoms may be contained at the same time.

Among these, specific examples of the light emitting material include, for example, US6303238B1, US6097147, WO00 / 57676, WO00 / 70655, WO01 / 08230, WO01 / 39234A2, WO01 / 41512A1, WO02 / 02714A2, WO02 / 15645A1, WO02 / 44189A1, Japanese Patent Application Laid-Open No. 2001-247859, Japanese Patent Application No. 2000-33561, Japanese Patent Application No. 2002-117978, Japanese Patent Application Laid-Open No. 2002-225352, Japanese Patent Application No. 2002-233501, Japanese Patent Application No. 2001-239281, Japanese Patent Application Laid-Open No. 2002-170684, Japanese Patent Application Laid-Open No. 2002-226495, JP2002-234894A, JP2001247478, JP2001298470, JP2002-173684, JP2002-2036 8, JP 2002-203679, JP 2004-357791, Japanese Patent Application No. 2005-75340, and the like phosphorescent compounds described in patent documents such as Japanese Patent Application No. 2005-75341.
Although the example of a specific platinum complex is illustrated below, this invention is not limited to these.

(B) Hole transporting host material The hole transporting host material used in the light emitting layer 16 according to the present invention has an ionization potential Ip of 5.1 eV or more from the viewpoint of improving durability and lowering driving voltage. It is preferably 4 eV or less, more preferably 5.4 eV or more and 6.2 eV or less, and further preferably 5.6 eV or more and 6.0 eV or less. Further, from the viewpoint of improving durability and lowering driving voltage, the electron affinity Ea is preferably 1.2 eV or more and 3.1 eV or less, more preferably 1.4 eV or more and 3.0 eV or less, and 1.8 eV or more. More preferably, it is 2.8 eV or less.

Specific examples of such a hole transporting host include the following materials.
Pyrrole, carbazole, pyrazole, imidazole, azacarbazole, indole, azaindole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone, styrylanthracene, fluorenone, hydrazone, stilbene, silazane, aromatic tertiary Amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, polysilane compounds, poly (N-vinylcarbazole), aniline copolymers, thiophene oligomer thiophene oligomers, conductive polymer oligomers such as polythiophene, organic Examples thereof include silane, carbon film, and derivatives thereof.
Among them, indole derivatives, carbazole derivatives, azaindole derivatives, azacarbazole derivatives, aromatic tertiary amine compounds, or thiophene derivatives are preferable, and indole skeleton, carbazole skeleton, azaindole derivative, azacarbazole derivative and / or in the molecule are particularly preferable. Those having a plurality of aromatic tertiary amine skeletons are preferred.
Specific examples of such a hole transporting host include, but are not limited to, the following compounds.

(C) Hole transporting light emitting material The hole transporting light emitting material may be a fluorescent light emitting material or a phosphorescent light emitting material. The electron affinity (Ea) is preferably 1.2 eV or more and 3.1 eV or less, more preferably 1.4 eV or more and 3.0 eV or less, and further preferably 1.8 eV or more and 2.8 eV or less. The ionization potential (Ip) is preferably 5.1 eV or more and 6.4 eV or less, more preferably 5.4 eV or more and 6.2 eV or less, and further preferably 5.6 eV or more and 6.0 eV or less.

Specific examples of such hole transporting light-emitting materials include the following materials.
In addition to pyrrole compounds, indole compounds, carbazole compounds, imidazole compounds, polyarylalkane compounds, arylamine compounds, styryl compounds, styrylamine compounds, thiophene compounds, aromatic polycyclic condensation compounds, etc. And metal complexes.
The metal ion in the metal complex is not particularly limited, but is preferably a transition metal ion or a rare earth metal ion, more preferably an iridium ion or platinum, from the viewpoints of improving luminous efficiency, durability, and driving voltage. Ion, gold ion, rhenium ion, tungsten ion, rhodium ion, ruthenium ion, osmium ion, palladium ion, silver ion, copper ion, cobalt ion, nickel ion, lead ion, rare earth metal ion (for example, europium ion, gadolinium ion, Terbium ions, etc.) are preferred, more preferably iridium ions, platinum ions, gold ions, rhenium ions, tungsten ions, europium ions, cadolinium ions, terbium ions, and particularly preferably iridium ions. Platinum ion, a rhenium ion, europium ion, gadolinium ion, terbium ion, most preferably iridium ion. Among metal complexes having iridium ions, particularly preferred are metal complexes having a carbon-Ir bond and a nitrogen-Ir bond (in this case, the bond may be a coordination bond, an ionic bond or a covalent bond). is there.
Specific examples of the iridium complex are shown below, but the present invention is not limited thereto.

(D) Electron transporting host material The electron transporting host material preferably has an electron affinity Ea of 2.5 eV or more and 3.5 eV or less from the viewpoint of improving durability and lowering driving voltage. It is more preferably 3.2 eV or less, and even more preferably 2.8 eV or more and 3.1 eV or less. Further, from the viewpoint of improving durability and reducing driving voltage, the ionization potential Ip is preferably 5.7 eV or more and 7.5 eV or less, more preferably 5.8 eV or more and 7.0 eV or less, and 5.9 eV or more. More preferably, it is 6.5 eV or less.

Specific examples of such an electron transporting host include the following materials.
Pyridine, pyrimidine, triazine, imidazole, pyrazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiopyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, Fluorine-substituted aromatic compounds, heterocyclic tetracarboxylic anhydrides such as naphthaleneperylene, phthalocyanines, and derivatives thereof (may form condensed rings with other rings), metal complexes and metals of 8-quinolinol derivatives Examples thereof include various metal complexes represented by metal complexes having phthalocyanine, benzoxazole or benzothiazol as a ligand.

Preferred examples of the electron transporting host include metal complexes, azole derivatives (benzimidazole derivatives, imidazopyridine derivatives, etc.), and azine derivatives (pyridine derivatives, pyrimidine derivatives, triazine derivatives, etc.). To metal complex compounds are preferred. The metal complex compound is more preferably a metal complex having a ligand having at least one nitrogen atom, oxygen atom or sulfur atom coordinated to the metal.
The metal ion in the metal complex is not particularly limited, but is preferably beryllium ion, magnesium ion, aluminum ion, gallium ion, zinc ion, indium ion, tin ion, platinum ion, or palladium ion, more preferably beryllium ion, Aluminum ion, gallium ion, zinc ion, platinum ion, or palladium ion, and more preferably aluminum ion, zinc ion, or palladium ion.

  There are various known ligands contained in the metal complex. For example, “Photochemistry and Photophysics of Coordination Compounds”, Springer-Verlag, H.C. Examples include the ligands described in Yersin, published in 1987, “Organometallic Chemistry: Fundamentals and Applications”, Sakai Hanafusa, Yamamoto Akio, published in 1982, and the like.

The ligand is preferably a nitrogen-containing heterocyclic ligand (preferably having 1 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably 3 to 15 carbon atoms, and a monodentate ligand. Alternatively, it may be a bidentate or higher ligand, preferably a bidentate or higher and a hexadentate or lower ligand, or a bidentate or higher and lower 6 or lower ligand and a monodentate mixed ligand. preferable.
Examples of the ligand include azine ligands (for example, pyridine ligand, bipyridyl ligand, and terpyridine ligand), hydroxyphenylazole ligands (for example, hydroxyphenylbenzimidazole ligand, hydroxy Phenylbenzoxazole ligand, hydroxyphenylimidazole ligand, hydroxyphenylimidazopyridine ligand, etc.), alkoxy ligand (preferably 1-30 carbon atoms, more preferably 1-20 carbon atoms, particularly preferably carbon 1 to 10, for example, methoxy, ethoxy, butoxy, 2-ethylhexyloxy, etc., aryloxy ligands (preferably having 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, and particularly preferably carbon atoms). For example, phenyloxy, 1-naphthyloxy, 2-na Yloxy, 2,4,6-trimethylphenyl oxy, and 4-biphenyl-oxy and the like) and the like.

  A heteroaryloxy ligand (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, and particularly preferably 1 to 12 carbon atoms, such as pyridyloxy, pyrazyloxy, pyrimidyloxy, and quinolyloxy); Alkylthio ligand (preferably having 1 to 30 carbon atoms, more preferably having 1 to 20 carbon atoms, particularly preferably having 1 to 12 carbon atoms, such as methylthio, ethylthio, etc.), arylthio ligand (preferably having 6 carbon atoms) To 30, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenylthio, heteroarylthio ligand (preferably 1 to 30 carbon atoms, more preferably 1 to carbon atoms). 20, particularly preferably 1 to 12 carbon atoms, such as pyridylthio, 2-benzimidazolylthio, 2- Nsoxazolylthio and 2-benzthiazolylthio), siloxy ligands (preferably having 1 to 30 carbon atoms, more preferably 3 to 25 carbon atoms, particularly preferably 6 to 20 carbon atoms, A triphenylsiloxy group, a triethoxysiloxy group, and a triisopropylsiloxy group), an aromatic hydrocarbon anion ligand (preferably having 6 to 30 carbon atoms, more preferably 6 to 25 carbon atoms, and particularly preferably 6 carbon atoms). -20, for example, phenyl anion, naphthyl anion, anthranyl anion, etc., aromatic heterocyclic anion ligand (preferably having 1 to 30 carbon atoms, more preferably 2 to 25 carbon atoms, particularly preferably 2 carbon atoms). For example, pyrrole anion, pyrazole anion, triazole anion, oxazole anion On, benzoxazole anion, thiazole anion, benzothiazole anion, thiophene anion, and benzothiophene anion), indolenine anion ligand, etc., preferably nitrogen-containing heterocyclic ligand, aryloxy ligand, Heteroaryloxy group, siloxy ligand, aromatic hydrocarbon anion ligand, or aromatic heterocyclic anion ligand, more preferably nitrogen-containing heterocyclic ligand, aryloxy ligand, siloxy ligand A ligand, an aromatic hydrocarbon anion ligand, or an aromatic heterocyclic anion ligand.

  Examples of the metal complex electron-transporting host include, for example, JP-A-2002-23576, JP-A-2004-214179, JP-A-2004-221106, JP-A-2004-221665, JP-A-2004-221068, JP-A-2004-327313, etc. Examples include compounds described in the publication.

  Specific examples of such an electron transporting host include, but are not limited to, the following materials.

  Regarding the concentration distribution of each material constituting the light emitting layer 16, for example, as shown in FIG. 1 and FIG. 2, the concentration of the electron transporting light emitting material gradually decreases from the cathode 19 side toward the anode 13 side. As shown in FIGS. 3 and 4, the concentration of the hole-transporting light-emitting material is gradually decreased from the anode 13 side toward the cathode 19 side. For example, the concentration of the electron-transporting material on the cathode 19 side of the light-emitting layer 16 is decreased. If it is too low, electrons are not sufficiently injected into the light emitting layer 16, and if the concentration of the electron transport material is too high at the anode 13 side interface of the light emitting layer 16, electrons may leak to the adjacent layer, leading to a decrease in light emission efficiency. .

When the concentration of the electron transporting luminescent material is gradually decreased from the cathode side toward the anode side, the concentration of the electron transporting luminescent material in the region near the anode side interface is the electron transporting property in the region near the cathode side interface. It is preferable that it is 0% or more and 50% or less with respect to the density | concentration of this luminescent material, More preferably, it is 0% or more and 20% or less.
When the concentration of the hole-transporting luminescent material gradually decreases from the anode side to the cathode side, the concentration of the hole-transporting luminescent material in the region near the cathode-side interface is positive in the region near the anode-side interface. The concentration is preferably 0% or more and 50% or less, more preferably 0% or more and 20% or less, with respect to the concentration of the hole-transporting light-emitting material.
In the specification of the present application, the “region near the cathode side interface of the light emitting layer” is defined as a region having a thickness of 10% of the thickness of the entire light emitting layer from the cathode side interface of the light emitting layer. The “region near the anode side interface” is defined as a region having a thickness of 10% of the thickness of the entire light emitting layer from the anode side interface of the light emitting layer. Further, the density in the region is defined as indicating the average density in the region. Furthermore, the concentration of each material in the “region near the cathode side (anode side) interface of the light-emitting layer” is the time of flight secondary ion mass spectrometry (TOF-SIMS), etching X-ray photoelectron spectroscopy (XPS / ESCA), etc. It can be measured by the method.

-Electrically inactive materials-
The organic EL device according to the present invention contains the light emitting material and the host material (electron transporting material and hole transporting material) as described above in the light emitting layer 16, but is electrically inactive in the light emitting layer 16. Materials can also be included. An electrically inactive material is a material that does not have charge transportability (electron transportability and hole transportability) and does not emit light, and is also called a binder. The electrically inactive material included in the light emitting layer is preferably an organic material having an energy difference Eg of 4.0 eV or more between the highest occupied orbital and the lowest unoccupied orbital, more preferably 4.1 eV or more (a ) 5.0 eV or less, more preferably 4.2 eV or more and 5.0 eV or less. If the Eg is 4.0 eV or more, holes and / or electrons can be prevented from entering the inert material, carrier mobility can be kept more appropriate, and luminous efficiency and durability can be further improved. . As an electrically inactive material that can be included in the light emitting layer 16, both an organic material and an inorganic material can be used.

By including such an electrically inactive material (binder) in the light emitting layer 16, for example, the effect of suppressing the movement of holes in the light emitting layer 16 is exhibited. In the case where such an effect by the binder is sufficiently obtained, the light emitting layer 16 is preferably contained in an amount of 10 to 60% by mass, and more preferably 20 to 60% by mass.
When the binder is included, for example, as shown in FIG. 6, the binder may not have a concentration gradient, and the hole transporting material and the electron transporting material may have a concentration gradient, and the binder may be a light emitting layer. You may include so that it may have a concentration gradient in 16 thickness directions.

  The method of gradually decreasing or increasing the concentration of the light emitting material in the light emitting layer 16 is not particularly limited. For example, the concentration may be continuously increased linearly or curvedly from the cathode 19 side toward the anode 13 side. May be gradually increased. Further, when the host material or the electrically inactive material in the light emitting layer has a concentration gradient, it may be continuously reduced or increased linearly or curvedly in the thickness direction of the light emitting layer. May be gradually reduced or gradually increased.

  The above light emitting material and host material (electron transporting material and hole transporting material) are used, and if necessary, a binder (electrically inactive material) is used, preferably the light emitting material is directed in a predetermined direction. The light emitting layer 16 is formed so as to gradually decrease. The method for forming the light emitting layer 16 is not particularly limited as long as the concentration of the light emitting material can be formed so as to have the concentration gradient as described above, and is a dry film forming method such as a vapor deposition method or a sputtering method, or a transfer method. Any method such as a printing method or a printing method may be used, but co-evaporation is preferable. In the case of co-evaporation, a desired concentration distribution can be provided in the thickness direction of the light emitting layer 16 by controlling the deposition rate of each material.

  The thickness of the light emitting layer 16 is not particularly limited, but is usually 1 nm to 500 nm from the viewpoint of preventing the occurrence of pinholes in the light emitting layer 16 and obtaining sufficient light emission intensity. Is preferable, 5 nm to 200 nm is more preferable, and 10 nm to 100 nm is still more preferable.

-Hole injection layer, hole transport layer-
The hole injection layer and the hole transport layer 14 are layers having a function of receiving holes from the anode 13 or the anode side and transporting them to the light emitting layer side (cathode side). Specifically, the hole injection layer and the hole transport layer 14 include a carbazole derivative, an azacarbazole derivative, an indole derivative, an azaindole derivative, an imidazole derivative, a polyarylalkane derivative, a pyrazoline derivative, a pyrazolone derivative, a phenylenediamine derivative, an aryl Amine derivatives, amino-substituted chalcone derivatives, styryl anthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, organosilane derivatives, A layer containing various metal complexes typified by an Ir complex having carbon, phenylazole or phenylazine as a ligand is preferable.

The hole injection layer and / or hole transport layer of the organic EL device of the present invention can preferably contain an electron-accepting dopant from the viewpoints of lowering voltage and driving durability.
As the electron-accepting dopant introduced into the hole-injecting layer or the hole-transporting layer, an inorganic compound or an organic compound can be used as long as it has an electron-accepting property and oxidizes an organic compound. As the compound, halides such as ferric chloride, aluminum chloride, gallium chloride, indium chloride, and antimony pentachloride, and metal oxides such as vanadium pentoxide and molybdenum trioxide can be preferably used.

In the case of an organic compound, a compound having a nitro group, halogen, cyano group, trifluoromethyl group or the like as a substituent, a quinone compound, an acid anhydride compound, fullerene, or the like can be preferably used.
Specifically, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil, p-bromanyl, p-benzoquinone, 2,6-dichlorobenzoquinone 2,5-dichlorobenzoquinone, tetramethylbenzoquinone, 1,2,4,5-tetracyanobenzene, o-dicyanobenzene, p-dicyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5 , 6-dicyanobenzoquinone, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, p-cyanonitrobenzene, m-cyanonitrobenzene, o-cyanonitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1 Nitronaphthalene, 2-nitronaphthalene, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene, 9-cyanoanthracene, 9-nitroanthracene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, Examples include 2,4,7-trinitro-9-fluorenone, 2,3,5,6-tetracyanopyridine, maleic anhydride, phthalic anhydride, fullerene C60, and fullerene C70. In addition, JP-A-6-212153, JP-A-11-111463, JP-A-11-251067, JP-A-2000-196140, JP-A-2000-286054, JP-A-2000-315580, 2001-102175, JP-A-2001-160493, JP-A-2002-252085. , 2002-56985, 2003-157981, 2003-217862, 2003-229278, 2004-342614, 2005-72012, 2005-166537, 2005-209543, etc. Can be used.

  Among these, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil, p-bromanyl, p-benzoquinone, 2,6-dichlorobenzoquinone, 2 , 5-dichlorobenzoquinone, 1,2,4,5-tetracyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, 2,4,7-trinitro-9- Preferred are luolenone, 2,3,5,6-tetracyanopyridine, or C60, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil. P-bromanyl, 2,6-dichlorobenzoquinone, 2,5-dichlorobenzoquinone, 2,3-dichloronaphthoquinone, 1,2,4,5-tetracyanobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone Or 2,3,5,6-tetracyanopyridine is more preferable, and tetrafluorotetracyanoquinodimethane is particularly preferable.

  These electron-accepting dopants may be used alone or in combination of two or more. Although the usage-amount of an electron-accepting dopant changes with kinds of material, it is preferable that it is 0.01 mass%-50 mass% with respect to hole transport layer material, and it is 0.05 mass%-20 mass%. It is further more preferable and it is especially preferable that it is 0.1 mass%-10 mass%. When the amount used is 0.01% by mass or more with respect to the hole transport material, the effect of the present invention can be sufficiently exerted, and when it is 50% by mass or less, the hole transport ability is not impaired. ,preferable.

The thickness of the hole injection layer and the hole transport layer 14 is preferably 500 nm or less from the viewpoint of lowering the driving voltage.
The thickness of the hole transport layer 14 is preferably 1 nm to 500 nm, more preferably 5 nm to 200 nm, and still more preferably 10 nm to 200 nm. The thickness of the hole injection layer is preferably 0.1 nm to 200 nm, more preferably 0.5 nm to 200 nm, and still more preferably 1 nm to 200 nm.

-Hole transport intermediate layer that mediates the transport of holes from the hole transport layer to the light emitting layer-
In the first and fourth embodiments, a plurality of hole transport intermediate layers 15a, 15b, and 15c are disposed.

Examples of the material constituting the hole transport intermediate layers 15a, 15b, and 15c include the same materials as those used for the hole transport host, the hole injection layer, and the hole transport layer.
In addition, for example, the material used for the hole transport layer is doped with an electron accepting dopant such as F4-TCNQ (2,3,5,6-tetrafluoro-7,7,8,8tetracyanoquinodimethane) to form each hole. The transport intermediate layers 15a, 15b, and 15c can also be formed.

  When the organic EL element 10 of the first embodiment is used, the ionization potentials of the materials contained in the hole transport intermediate layers 15a, 15b, and 15c are respectively expressed as Ip (Oh-a) and Ip (Oh-b). , Ip (Oh-c), when the ionization potential of the hole transporting host material contained in the light emitting layer 16 is Ip (Lh), and when the ionization potential of the material contained in the hole transporting layer 14 is Ip (H) In addition, any of the hole transport intermediate layers 15a, 15b, and 15c satisfies the relationship of Ip (H) <Ip (Oh-a) <Ip (Oh-b) <Ip (Oh-c) <Ip (Lh). As described above, the constituent materials of the hole transport layer 14, the hole transport intermediate layers 15a, 15b, and 15c, and the light emitting layer 16 may be selected and sequentially formed.

  On the other hand, in the case of the organic EL device 40 of the fourth embodiment, the ionization potentials of the materials contained in the hole transport intermediate layers 15a, 15b, and 15c are respectively represented by Ip (Oh-a) and Ip (Oh-b). , Ip (Oh-c), when the ionization potential of the hole-transporting light-emitting material contained in the light-emitting layer 16 is Ip (Ll), and when the ionization potential of the material contained in the hole-transport layer 14 is Ip (H) In addition, any of the hole transport intermediate layers 15a, 15b, and 15c satisfies the relationship of Ip (H) <Ip (Oh-a) <Ip (Oh-b) <Ip (Oh-c) <Ip (Ll). As described above, the constituent materials of the hole transport layer 14, the hole transport intermediate layers 15a, 15b, and 15c, and the light emitting layer 16 may be selected and sequentially formed.

  The thicknesses of the hole transport intermediate layers 15 a, 15 b and 15 c adjacent to the light emitting layer 16 and the hole transport layer 14 are preferably thinner than those of the adjacent hole transport layer 14 and light emitting layer 16. Specifically, each of the hole transport intermediate layers 15a, 15b, and 15c has a thickness of 0.1 nm to 5 nm, and the entire thickness of the hole transport intermediate layers 15a, 15b, and 15c is 0.2 nm. The thickness is preferably 30 nm or less. If the thickness is in such a range, the hole transport intermediate layers 15a, 15b, and 15c as a whole are extremely thin, and the injection property is effectively improved almost without being affected by the mobility and durability of the materials of the other layers. The barrier difference between the hole transport layer and the light emitting layer can be reduced more effectively. The total thickness of the hole transport intermediate layers 15a, 15b, and 15c is more preferably 1 nm to 30 nm, and particularly preferably 3 nm to 30 nm.

-Electron injection layer, electron transport layer-
The electron injection layer and the electron transport layer 18 are layers having a function of receiving electrons from the cathode 19 or the cathode side and transporting them to the light emitting layer side (anode side). Specifically, the electron injection layer and the electron transport layer 18 are triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, fluorenone derivatives, anthraquinodimethane derivatives, anthrone derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives. Carbodiimide derivatives, fluorenylidenemethane derivatives, distyrylpyrazine derivatives, aromatic tetracarboxylic anhydrides such as naphthalene and perylene, phthalocyanine derivatives, metal complexes of 8-quinolinol derivatives, metal phthalocyanines, benzoxazoles and benzothiazoles A layer containing various metal complexes typified by a metal complex as a child, an organic silane derivative, and the like is preferable.

The electron injection layer and / or the electron transport layer of the organic EL device of the present invention preferably contains an electron donating dopant from the viewpoint of lowering the voltage and improving driving durability.
The electron donating dopant introduced into the electron injecting layer or the electron transporting layer only needs to have an electron donating property and a property of reducing an organic compound, such as an alkali metal such as Li or an alkaline earth metal such as Mg. Transition metals including rare earth metals and reducing organic compounds are preferably used.
As the metal, a metal having a work function of 4.2 eV or less can be preferably used. Specifically, Li, Na, K, Be, Mg, Ca, Sr, Ba, Y, Cs, La, Sm, Gd , And Yb.
Examples of the reducing organic compound include nitrogen-containing compounds, sulfur-containing compounds, and phosphorus-containing compounds. In addition, materials described in JP-A-6-212153, JP-A-2000-196140, 2003-68468, 2003-229278, 2004-342614, and the like can be used.

These electron donating dopants may be used alone or in combination of two or more.
Although the usage-amount of an electron donating dopant changes with kinds of material, it is preferable that it is 0.1 mass%-99 mass% with respect to electron transport layer material, and it is 1.0 mass%-80 mass%. Is more preferable, and 2.0 mass% to 70 mass% is particularly preferable. If the amount used is 0.1% by mass or more based on the electron transport layer material, the effect of the present invention can be sufficiently exerted, and if it is 99% by mass or less, the electron transport ability is not impaired, which is preferable.

The thicknesses of the electron injection layer and the electron transport layer 18 are each preferably 500 nm or less from the viewpoint of lowering the driving voltage.
The thickness of the electron transport layer 18 is preferably 1 nm to 500 nm, more preferably 5 nm to 200 nm, and still more preferably 10 nm to 100 nm. In addition, the thickness of the electron injection layer is preferably 0.1 nm to 200 nm, more preferably 0.2 nm to 100 nm, and still more preferably 0.5 nm to 50 nm.

-An electron transport intermediate layer that mediates the transport of electrons from the electron transport layer to the light emitting layer-
In the second and third embodiments, a plurality of electron transport intermediate layers 17a, 17b, and 17c that are adjacent to the light-emitting layer 16 and the electron transport layer 18 and mediate the transport of electrons from the electron transport layer 18 to the light-emitting layer 16 are used. Is placed.

Examples of the material constituting the electron transport intermediate layers 17a, 17b, and 17c include the same materials as those used for the electron transport host, the electron injection layer, and the electron transport layer.
For example, the electron transport intermediate layers 17a, 17b, and 17c can be formed by doping an electron donating dopant such as Li into the material used for the electron transport layer.

  And when setting it as the organic EL element 20 of 2nd Embodiment, the electron affinity of the material contained in the said electron carrying intermediate | middle layer 17a, 17b, 17c is respectively Ea (Oe-a), Ea (Oe-b), Any electron transport when Ea (Oe-c), the electron affinity of the light emitting material contained in the light emitting layer 16 is Ea (Ll), and the electron affinity of the material contained in the electron transport layer 18 is Ea (E) The intermediate layers 17a, 17b, and 17c also satisfy the relationship of Ea (E)> Ea (Oe-a)> Ea (Oe-b)> Ea (Oe-c)> Ea (Ll), The constituent materials of the electron transport intermediate layers 17a, 17b, and 17c and the electron transport layer 18 may be selected and sequentially formed.

  On the other hand, when it is set as the organic EL element 30 of 3rd Embodiment, the electron affinity of the material contained in the said electron carrying intermediate | middle layer 17a, 17b, 17c is respectively Ea (Oe-a), Ea (Oe-b), Any electron transport when Ea (Oe-c), the electron affinity of the host material contained in the light emitting layer 16 is Ea (Lh), and the electron affinity of the material contained in the electron transport layer 18 is Ea (E) The intermediate layers 17a, 17b, and 17c also satisfy the relationship of Ea (E)> Ea (Oe-a)> Ea (Oe-b)> Ea (Oe-c)> Ea (Lh), The constituent materials of the electron transport intermediate layers 17a, 17b, and 17c and the electron transport layer 18 may be selected and sequentially formed.

  The thicknesses of the electron transport intermediate layers 17a, 17b, and 17c adjacent to the light emitting layer 16 and the electron transport layer 18 are preferably thinner than the adjacent electron transport layer 18 and the light emitting layer 16. Specifically, The thickness of each of the electron transport intermediate layers 17a, 17b, and 17c is not less than 0.1 nm and not more than 5 nm, and the total thickness of the electron transport intermediate layers 17a, 17b, and 17c is not less than 0.2 nm and not more than 30 nm. Is preferred. If the thickness is in such a range, the electron transport intermediate layers 17a, 17b, and 17c as a whole are extremely thin, and the injection property is effectively improved with little influence of the mobility and durability of the materials of the other layers. The barrier difference between the electron transport layer and the light emitting layer can be reduced more effectively. The total thickness of the electron transport intermediate layers 17a, 17b, and 17c is more preferably 1 nm to 30 nm, and particularly preferably 3 nm to 30 nm.

-Hole blocking layer-
The hole blocking layer is a layer having a function of preventing holes transported from the anode side to the light emitting layer 16 from passing through to the cathode side. For example, when a plurality of hole transport intermediate layers 15a, 15b, and 15c that mediate hole transport are provided between the hole transport layer 14 and the light emitting layer 16, holes adjacent to the light emitting layer 16 on the cathode side are provided. A block layer can be provided.
Examples of organic compounds constituting the hole blocking layer include aluminum complexes such as BAlq (Aluminum (III) bis (2-methyl-8-quinolinato) -4-phenylphenolate), triazole derivatives, BCP (2,9-dimethyl). -4,7-diphenyl-1,10-phenanthrolin) and the like.
The thickness of the hole blocking layer is preferably 1 nm to 500 nm, more preferably 5 nm to 200 nm, and still more preferably 10 nm to 100 nm.
The hole blocking layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

-Cathode-
The cathode 19 usually has a function as an electrode for injecting electrons into the organic EL layer, and the shape, structure, size and the like are not particularly limited, and are known according to the use, purpose, etc. of the organic EL element. It can select suitably from electrode materials. Examples of the material constituting the cathode 19 include metals, alloys, metal oxides, electrically conductive compounds, and mixtures thereof. Specific examples include alkali metals (eg, Li, Na, K, Cs, etc.), alkaline earth metals (eg, Mg, Ca, etc.), gold, silver, lead, aluminum, sodium-potassium alloy, lithium-aluminum alloy, magnesium- Examples thereof include silver alloys, rare earth metals such as indium and ytterbium. These may be used singly or in combination of two or more from the viewpoint of achieving both stability and electron injection.

  Among these, the material constituting the cathode 19 is preferably an alkali metal or an alkaline earth metal from the viewpoint of electron injection, and a material mainly composed of aluminum is preferable from the viewpoint of excellent storage stability. The material mainly composed of aluminum is aluminum alone, an alloy of aluminum and 0.01 to 10% by mass of alkali metal or alkaline earth metal, or a mixture thereof (for example, lithium-aluminum alloy, magnesium-aluminum alloy, etc.) Say. The material of the cathode 19 is described in detail, for example, in JP-A-2-15595 and JP-A-5-121172, and the materials described in these publications can also be applied to the present invention. .

  There is no restriction | limiting in particular about the formation method of the cathode 19, It can form according to a well-known method. For example, the cathode 19 is configured from a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, or a chemical method such as a CVD method or a plasma CVD method. It can be formed according to a method appropriately selected in consideration of suitability with the material. For example, when a metal or the like is selected as the material of the cathode 19, the cathode 19 can be formed according to a sputtering method or the like, one or more of them simultaneously or sequentially.

  What is necessary is just to select the thickness of the cathode 19 suitably according to the material which comprises the cathode 19, and the taking-out direction of light, and it is about 1 nm-5 micrometers normally.

The patterning for forming the cathode 19 may be performed by chemical etching by photolithography or the like, or may be performed by physical etching by a laser or the like. Further, it may be performed by vacuum deposition, sputtering or the like with overlapping masks, or by a lift-off method or a printing method.
There is no restriction | limiting in particular in the formation position of the cathode 19, It may be formed in the whole on an organic electroluminescent layer, and may be formed in the part.

  Between the cathode 19 and the organic EL layer, a dielectric layer made of an alkali metal or alkaline earth metal fluoride or oxide may be formed with a thickness of 0.1 to 5 nm. This dielectric layer can also be understood as a kind of electron injection layer. The dielectric layer can be formed by, for example, a vacuum deposition method, a sputtering method, an ion plating method, or the like.

  By sequentially forming the lower electrode 13, the organic EL layers 14 to 18, and the upper electrode 19 on the support substrate 12, the light emitting layer 16 is interposed between the pair of electrodes 13 and 19 as shown in FIGS. The organic EL elements 10, 20, 30, and 40 in which the organic EL layers 14 to 18 including the above are disposed can be manufactured. As a result, the light emitting layer 16 sandwiched between the electrodes 13 and 19 emits light. For example, when the light emitting layer 16 corresponding to each color is formed so that RGB are repeatedly arranged in parallel on the substrate 12, an organic EL element including the light emitting layer 16 sandwiched between both electrodes 13 and 19 constitutes a pixel.

-Sealing-
After forming the cathode 19, it is preferable to cover and seal with a sealing member (protective layer) in order to suppress deterioration of the organic EL element due to moisture or oxygen. As the sealing member, glass, metal, plastic, or the like can be used.
Furthermore, external wirings such as control wirings and signal wirings are connected to the electrodes 13 and 19, respectively. Thereby, the light-emitting device or display apparatus by an organic EL element can be manufactured.
The organic EL device manufactured by the method as described above has a light emission distribution in the light emitting layer 16 approaching the entire light emission, improving the light emission efficiency and durability, and having a small variation in chromaticity due to the drive voltage. Become.

Examples of the present invention and comparative examples will be described below, but the present invention is not limited to the following examples.
In the following examples and comparative examples, “x% → y%” means that the concentration (mass%) on the anode side is x%, the concentration (mass%) on the cathode side is y%, and from the anode side. It shows that the concentration is continuously changing toward the cathode side.

<Example 1>
anode:
An ITO film (thickness: 100 nm) was formed on a support substrate (material: glass).

Hole injection layer:
After forming the ITO film (anode), using a vacuum deposition apparatus (1 × 10 ⁻⁶ torr), 2-TNATA (4,4 ′, 4 ″ -tris (2-naphthylphenylamino) triphenylamine) F4-TCNQ was doped with 1.0% to form a thickness of 160 nm.
The structural formulas of 2-TNATA and F4-TCNQ are as follows.

Hole transport layer:
NPD (N, N′-dinaphthyl-N, N′-diphenyl- [1,1′-biphenyl] -4,4′-diamine) was formed to a thickness of 10 nm.
The structural formula of NPD is as follows.

Multiple hole transport interlayers:
After forming the hole transport layer, a 3 nm thick hole transport intermediate layer was formed using Compound B. Next, using Compound A, a 3 nm-thick hole transport intermediate layer was formed.
The structural formulas of Compound A and Compound B are as follows.

Light emitting layer:
The light emitting layer is a mixed layer (thickness) by co-evaporation using mCP (N, N′-dicarbazolyl-3,5-benzene) as a hole transporting host material and compound E as an electron transporting light emitting material. 90 nm). During the co-evaporation, the concentration of the electron transporting light emitting material was continuously increased from 0% by mass to 60% by mass from the anode side interface to the cathode side interface by changing the deposition rate of each constituent material. . The concentration of each material in the region near the anode side interface is 1.3% by mass for Compound E and 98.7% by mass for mCP, and in the region near the interface for the cathode side is 59.7% by mass for Compound E, mCP. Was 40.3% by mass. The structural formulas of mCP and Compound E are as follows.

Electron transport layer (hole blocking layer):
After forming the light emitting layer, BAlq was deposited to a thickness of 40 nm. The structural formula of BAlq is as follows.

Cathode etc .:
A LiF film was laminated with a thickness of 1 nm, and further Al (thickness 100 nm) was laminated.

An organic EL element was produced as described above. The layer structure of this element, the thickness of each layer, etc. are as follows.
ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / Compound B (3 nm) / Compound A (3 nm) / mCP + 0 → 60 mass% Compound E (90 nm) / BAlq (40 nm ) / LiF (1 nm) / Al (100 nm)
The ionization potential of each layer is as follows.
Ip (Oh-1): 5.7 (Compound B)
Ip (Oh-2): 5.8 (Compound A)
Ip (Lh): 6.0
Ip (H): 5.4

  The external quantum efficiency, drive voltage, and chromaticity variation width of the obtained organic EL element (light emitting element) were measured.

<Measurement of external quantum efficiency>
The produced light emitting element was made to emit light by applying a DC voltage to the light emitting element using a source measure unit 2400 type manufactured by KEITHLEY. The emission spectrum and the amount of light were measured using a luminance meter SR-3 manufactured by Topcon Corporation, and the external quantum efficiency was calculated from the emission spectrum, the amount of light, and the current at the time of measurement.

As a result of the above measurement, the external quantum efficiency at 360 cd / m ² was 9.4%.
The drive voltage was 11.7V.

<Measurement of chromaticity>
The chromaticity was displayed on the X and Y coordinates using the CIE color system.
The fluctuation range of 100 to 20000 cd / m ² : ΔX = 0.01 or less / ΔY = 0.01 or less. As a result of the evaluation, the fluctuation range of chromaticity was small.

<Comparative Example 1>
An organic EL device was produced with the same layer configuration and thickness as in Example 1 except that the hole transport intermediate layer in Example 1 was not formed at all. The layer structure of this element, the thickness of each layer, etc. are as follows.

  ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / mCP + 0 → 60 mass% Compound E (90 nm) / BAlq (40 nm) / LiF (1 nm) / Al (100 nm)

About the obtained organic EL element, external quantum efficiency, a drive voltage, and chromaticity were measured. As a result, the external quantum efficiency at 360 cd / m ² was 9.1%, and the drive voltage was 12.5V. The variation range of chromaticity is a variation range of 100 to 20000 cd / m ² : ΔX = 0.03 / ΔY = 0.04.
Compared with the result of Example 1, a large value was shown.

<Comparative example 2>
A layer structure similar to that of Example 1 except that instead of the two hole transport intermediate layers of Example 1, only one compound A was used to form one hole transport intermediate layer (thickness 3 nm), An organic EL element was produced with a thickness. The layer structure of this element, the thickness of each layer, etc. are as follows.
ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / Compound A (3 nm) / mCP + 0 → 60 mass% Compound E (90 nm) / BAlq (40 nm) / LiF (1 nm) / Al (100 nm)
The ionization potential of each layer is as follows. Here, the Ip value of the compound A layer is Ip (Oh).
Ip (Oh): 5.8 (Compound A)
Ip (Lh): 6.0
Ip (H): 5.4

The external quantum efficiency, drive voltage, and chromaticity variation width of the obtained organic EL element (light emitting element) were measured. As a result, the external quantum efficiency at 360 cd / m ² was 9.2%, and the drive voltage was 12.0V. Further, the variation range of chromaticity was about the middle between Example 1 and Comparative Example 2.

<Comparative Example 3>
An organic EL device having the same layer configuration and thickness as in Example 2 except that a mixed layer of NPD and mCP was formed instead of the two hole transport intermediate layers (Compound A and Compound B) in Example 1. Was made. The layer structure of this element, the thickness of each layer, etc. are as follows.
ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / NPD + 0 → 100 mass% mCP (10 nm) / mCP + 0 → 60 mass% Compound E (90 nm) / BAlq (40 nm) / LiF (1 nm) / Al (100 nm)
The ionization potential of each layer is as follows. Here, the Ip value of the NPD + 0 → 100 mass% mCP layer is defined as Ip (Gh).
Ip (Gh): 5.4 (NPD) /6.0 (mCP)
Ip (Lh): 6.0
Ip (H): 5.4

About the obtained organic EL element, external quantum efficiency, a drive voltage, and chromaticity were measured. As a result, the external quantum efficiency at 360 cd / m ² was 9.4%, and the drive voltage was 12.3V. The variation range of chromaticity is a variation range of 100 to 20000 cd / m ² : ΔX = 0.03 / ΔY = 0.03
In comparison with the results of Example 1, a large value was shown.

<Comparative example 4>
Instead of the two hole transport intermediate layers (compound A and compound B) adjacent to the hole transport layer and the light emitting layer in Example 1, one hole transport intermediate layer is formed by co-evaporation of compound A and compound B. An organic EL element was produced with the same layer configuration and thickness as in Example 2 except that (thickness 3 nm) was formed. The layer structure of this element, the thickness of each layer, etc. are as follows.
ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / 50 mass% Compound A + 50 mass% Compound B (3 nm) / mCP + 0 → 60 mass% Compound E (90 nm) / BAlq ( 40 nm) / LiF (1 nm) / Al (100 nm)
The ionization potential of each layer is as follows. Here, the Ip value of the 50 mass% compound A + 50 mass% compound B layer portion is defined as Ip (Mh).
Ip (Mh): 5.8 (Compound A) /5.7 (Compound B)
Ip (Lh): 6.0
Ip (H): 5.4

About the obtained organic EL element, external quantum efficiency, a drive voltage, and chromaticity were measured. As a result, the external quantum efficiency at 360 cd / m ² was 9.3%, and the drive voltage was 11.8V. Also, the variation range of chromaticity is
Fluctuation range of 100 to 20000 cd / m ² : ΔX = 0.01 / ΔY = 0.02
And about halfway between Example 1 and Comparative Example 3.

<Example 2>
Anode, hole injection layer, hole transport layer:
The anode, hole injection layer, and hole transport layer were laminated in the same manner as in Example 1.

Light emitting layer:
The light-emitting layer was formed by co-evaporation using Compound F as the electron-transporting host material and Ir (ppy) ₃ (tris (2-phenylpyridine) iridium (III)) as the hole-transporting light-emitting material. 90 nm). During co-evaporation, the concentration of Ir (ppy) ₃ was continuously decreased from 60% by mass to 0% by mass from the anode side interface toward the cathode side interface by changing the deposition rate of each constituent material. . The concentration of each material in the region near the anode side interface is 58.5% by mass for Ir (ppy) _{3 and} 41.5% by mass for compound F. In the region near the interface on the cathode side, Ir (ppy) ₃ is 1.5% by mass and Compound F was 98.5% by mass. The structural formula of Compound F is as follows.

An electron transport interlayer that mediates the transport of electrons from the electron transport layer to the light-emitting layer:
After forming the light emitting layer, an electron transport intermediate layer (thickness 3 nm) of compound D and a compound C electron transport intermediate layer (thickness 3 nm) represented by the following structural formula were sequentially formed.

Electron transport layer (hole blocking layer):
BAlq was deposited to a thickness of 30 nm.

Cathode etc .:
Similarly to Example 1, a LiF film was laminated with a thickness of 1 nm, and further Al (thickness: 100 nm) was laminated.

An organic EL element was produced with the above configuration. The layer structure of this element, the thickness of each layer, etc. are as follows.
ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / Compound F + 60 → 0 mass% Ir (ppy) ₃ (90 nm) / Compound D (3 nm) / Compound C (3 nm) / BAlq (30 nm) / LiF (1 nm) / Al (100 nm)
The electron affinity of each layer is as follows.
Ea (Lh): 2.5 (Compound F)
Ea (Oe-1): 2.8 (Compound C)
Ea (Oe-2): 2.7 (Compound D)
Ea (E): 2.9 (BAlq)

About the obtained organic EL element, external quantum efficiency, a drive voltage, and chromaticity were measured. As a result, the external quantum efficiency at 360 cd / m ² was 8.2%, and the drive voltage was 11.4V.
Further, the fluctuation range of 100 to 20000 cd / m ² : ΔX = 0.01 or less / ΔY = 0.01 or less, and the fluctuation range of chromaticity was small.

<Comparative Example 5>
An organic EL device having the following layer structure and the thickness of each layer was produced.
ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / NPD (10 nm) / Compound F + 60 → 0 mass% Ir (ppy) ₃ (90 nm) / BAlq + 100 → 0 mass% compound F (20 nm) / BAlq (20 nm) / LiF (1 nm) / Al (100 nm)
The electron affinity of each layer is as follows. Here, the Ea value of the BAlq + 100 → 0 mass% compound F layer is defined as Ea (Ge).
Ea (Lh): 2.5 (Compound F)
Ea (Ge): 2.9 (BAlq) /2.5 (Compound F)
Ea (E): 2.9 (BAlq)

About the obtained organic EL element, external quantum efficiency, a drive voltage, and chromaticity were measured. As a result, the external quantum efficiency at 360 cd / m ² was 8.0%, and the drive voltage was 12.7V.
The variation range of chromaticity is a variation range of 100 to 20000 cd / m ² : ΔX = 0.02 / ΔY = 0.03
In comparison with the result of Example 2, a large value was shown.

<Example 3>
Anode, hole injection layer, hole transport layer:
The anode, hole injection layer, and hole transport layer were laminated in the same manner as in Example 1.

Multiple hole transport interlayers:
In the same manner as in Example 1, after forming the hole transport layer, Compound B was used to form a 3 nm thick hole transport intermediate layer. Next, using Compound A, a 3 nm-thick hole transport intermediate layer was formed.

Light emitting layer:
The light-emitting layer comprises compound G as an electron-transporting host material and bis (3,5-difluoro-2- (2-pyridyl) phenyl- (2-carboxypyridyl)) iridium (III) as a hole-transporting light-emitting material. ) (Firpiq) was used to form a mixed layer (thickness 90 nm) by co-evaporation. During the co-evaporation, the concentration of Firpiq was continuously decreased from 60% by mass to 0% by mass from the anode side interface toward the cathode side interface by changing the deposition rate of each constituent material. The concentration of each material in the region near the anode side interface is 58.3% by mass of Firpiq and 41.7% by mass of Compound G, and in the region near the interface of the cathode side is 1.0% by mass of Firpiq and Compound G. Was 99.0% by mass. The structural formulas of Compound G and Firpiq are as follows.

Electron transport layer (hole blocking layer):
As in Example 1, after forming the light emitting layer, BAlq was deposited to a thickness of 40 nm.

Cathode etc .:
A LiF film was laminated with a thickness of 1 nm, and further Al (thickness 100 nm) was laminated.

An organic EL element was produced as described above. The layer structure of this element, the thickness of each layer, etc. are as follows.
ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / Compound B (3 nm) / Compound A (3 nm) / Compound G + 60 → 0 mass% Firpiq (90 nm) / BAlq (40 nm ) / LiF (1 nm) / Al (100 nm)
The ionization potential of each layer is as follows.
Ip (Oh-1): 5.7 (Compound B)
Ip (Oh-2): 5.8 (Compound A)
Ip (Ll): 5.9
Ip (H): 5.4

About the obtained organic EL element, external quantum efficiency, a drive voltage, and chromaticity were measured. As a result, the external quantum efficiency at 360 cd / m ² was 9.2%, and the drive voltage was 11.5V.
Also, the variation range of chromaticity is
Fluctuation range of 100 to 20000 cd / m ² : ΔX = 0.01 / ΔY = 0.02
And the variation range of chromaticity was small.

<Comparative Example 6>
An organic EL device was produced with the same layer configuration and thickness as in Example 3 except that the hole transporting intermediate layer was not formed. The layer structure of this element, the thickness of each layer, etc. are as follows.

  ITO (100 nm) /2-TNATA+1.0 mass% F4-TCNQ (160 nm) / NPD (10 nm) / Compound G + 60 → 0 mass% Firpiq (90 nm) / BAlq (40 nm) / LiF (1 nm) / Al (100 nm)

About the obtained organic EL element, external quantum efficiency, a drive voltage, and chromaticity were measured. As a result, the external quantum efficiency at 360 cd / m ² was 9.1%, and the drive voltage was 12.0V.
The variation range of chromaticity is a variation range of 100 to 20000 cd / m ² : ΔX = 0.02 / ΔY = 0.04.
Compared with the result of Example 3, a large value was shown.

As mentioned above, although this invention was demonstrated, this invention is not limited to the said embodiment and Example.
For example, when manufacturing a light emitting device or a display device including the organic EL element according to the present invention, the driving method is not limited, and either a passive matrix method or an active matrix method can be adopted. The emission color is not limited, and the present invention can be applied to any of single color display, area color display, and full color display.

It is the schematic which shows an example (1st Embodiment) of the organic EL element which concerns on this invention. (A) Concentration distribution in the light emitting layer (B) Layer structure (C) Ionization potential level It is the schematic which shows an example (2nd Embodiment) of the organic EL element which concerns on this invention. (A) Concentration distribution in the light emitting layer (B) Layer structure (C) Electron affinity level It is the schematic which shows an example (3rd Embodiment) of the organic EL element which concerns on this invention. (A) Concentration distribution in the light emitting layer (B) Layer structure (C) Electron affinity level It is the schematic which shows an example (1st Embodiment) of the organic EL element which concerns on this invention. (A) Concentration distribution in the light emitting layer (B) Layer structure (C) Ionization potential level It is a figure which shows the other example of the density distribution in the light emitting layer of the organic EL element which concerns on this invention. It is a figure which shows the further another example of density | concentration distribution in the light emitting layer of the organic EL element which concerns on this invention. It is the schematic which shows an example of a structure of an organic EL element. It is the figure which modeled and showed the energy level of the positive hole transport layer in the three types of organic EL element, a light emitting layer, and an electron carrying layer. (A) When there is no concentration gradient in the light emitting layer (B) When there is a concentration gradient in the light emitting layer (C) There are a plurality of concentration gradients in the light emitting layer and adjacent to the light emitting layer and the hole transport layer. When there is a hole transport intermediate layer

Explanation of symbols

10 ... Organic electroluminescent device (organic EL device)
DESCRIPTION OF SYMBOLS 12 ... Support substrate 13 ... Anode 14 ... Hole transport layer 15a, 15b, 15c ... Hole transport intermediate layer which mediates transport of holes from the hole transport layer to the light emitting layer 16. -Light emitting layer 17a, 17b, 17c ... Electron transport intermediate layer that mediates transport of electrons from the electron transport layer to the light emitting layer 18 ... Electron transport layer 19 ... Cathode 20, 30, 40 ... Organic electric field Light emitting element (organic EL element)

Claims (12)

A pair of electrodes consisting of an anode and a cathode;
A light emitting layer disposed between the pair of electrodes;
A hole transport layer disposed between the anode and the light emitting layer;
Including an electron transport layer disposed between the cathode and the light emitting layer;
The light emitting layer includes a hole transporting material and an electron transporting material as a light emitting material and a host material, and at least one of the hole transporting material and the electron transporting material is arranged in the thickness direction of the light emitting layer. Having a concentration gradient, and
Between the hole transport layer and the light emitting layer, a plurality of (n layers: n ≧ 2) hole transport intermediate layers that mediate the transport of holes from the hole transport layer to the light emitting layer are the layers closest to the anode. In order, the hole transport intermediate layer 1 is arranged as the hole transport intermediate layer n and / or mediates the transport of electrons from the electron transport layer to the light emitting layer between the electron transport layer and the light emitting layer. A plurality (m layers: m ≧ 2) of electron transport intermediate layers are arranged in order from the layer closest to the cathode, electron transport intermediate layer 1... Electron transport intermediate layer m, and the plurality of hole transport intermediate layers. Ip (hole transport intermediate layer 1)... Ip (hole transport intermediate layer n), and the ionization potential of the hole transport material contained in the light emitting layer is Ip (light emitting layer). , The ionization potential of the material contained in the hole transport layer is Ip (hole transport layer) , Ea (electron transport intermediate layer 1)... Ea (electron transport intermediate layer m) and electron affinity of the electron transport material contained in the light emitting layer, respectively. When the electron affinity of the material contained in Ea (light emitting layer) and the electron transport layer is Ea (electron transport layer), Ip (hole transport layer) <Ip (hole transport intermediate layer 1) <. Ip (hole transport intermediate layer n) <Ip (light emitting layer) and / or Ea (electron transport layer)> Ea (electron transport intermediate layer 1)>...> Ea (electron transport intermediate layer m)> Ea (light emission) layer)
An organic electroluminescent element, characterized in that   The organic electroluminescent element according to claim 1, wherein the light emitting material has a concentration gradient in a thickness direction of the light emitting layer. The light emitting layer includes a hole transporting host material to be the hole transporting material and an electron transporting light emitting material to be the electron transporting material, and the concentration of the electron transporting light emitting material is on the cathode side. Gradually decreasing toward the anode side, and
The plurality of hole transport intermediate layers are arranged, and each of the plurality (n layers: n ≧ 2) of the hole transport intermediate layers has an ionization potential of a material contained in the hole transport intermediate layer as an anode. , Ip (Oh-1)... Ip (Oh-n), the ionization potential of the host material contained in the light emitting layer, Ip (Lh), and the hole transport layer. When the ionization potential of the material is Ip (H), the relationship of Ip (H) <Ip (Oh-1) <... <Ip (Oh-n) <Ip (Lh) is satisfied. The organic electroluminescent element according to claim 1. The light emitting layer includes a hole transporting host material to be the hole transporting material and an electron transporting light emitting material to be the electron transporting material, and the concentration of the electron transporting light emitting material is on the cathode side. Gradually decreasing toward the anode side, and
The plurality of electron transport intermediate layers are arranged, and the plurality of (m layers: m ≧ 2) electron transport intermediate layers are all closest to the cathode in electron affinity of the material contained in the electron transport intermediate layer. In order from the layer, Ea (Oe-1)... Ea (Oe-m), the electron affinity of the light emitting material contained in the light emitting layer is Ea (Ll), and the electron affinity of the material contained in the electron transport layer. Wherein Ea (E)> Ea (Oe-1)>...> Ea (Oe-m)> Ea (Ll) is satisfied. 3. The organic electroluminescent element according to any one of 3.   The concentration of the electron-transporting light-emitting material in a region near the anode-side interface of the light-emitting layer is 0% or more and 50% or less with respect to the concentration in a region near the cathode-side interface of the light-emitting layer. The organic electroluminescent element according to claim 3 or 4. The light emitting layer includes an electron transporting host material to be the electron transporting material and a hole transporting light emitting material to be the hole transporting material, and the concentration of the hole transporting light emitting material is the anode. Gradually decreasing from the side toward the cathode side, and
The plurality of electron transport intermediate layers are arranged, and the plurality of (m layers: m ≧ 2) electron transport intermediate layers are all closest to the cathode in electron affinity of the material contained in the electron transport intermediate layer. In order from the layer, Ea (Oe-1)... Ea (Oe-m), the electron affinity of the host material contained in the light emitting layer is Ea (Lh), and the electron affinity of the material contained in the electron transport layer. Wherein Ea (E)> Ea (Oe-1)>...> Ea (Oe-m)> Ea (Lh) is satisfied. The organic electroluminescent element according to claim 2. The light emitting layer includes an electron transporting host material to be the electron transporting material and a hole transporting light emitting material to be the hole transporting material, and the concentration of the hole transporting light emitting material is the anode. Gradually decreasing from the side toward the cathode side, and
The plurality of hole transport intermediate layers are arranged, and each of the plurality (n layers: n ≧ 2) of the hole transport intermediate layers has an ionization potential of a material contained in the hole transport intermediate layer as an anode. In order from the layer closest to Ip (Oh-1)... Ip (Oh-n), the ionization potential of the light emitting material contained in the light emitting layer is included in Ip (Ll), and the hole transport layer. When the ionization potential of the material is Ip (H), the relationship of Ip (H) <Ip (Oh-1) <... <Ip (Oh-n) <Ip (Ll) is satisfied. The organic electroluminescent element according to claim 1, claim 2, or claim 6.   The concentration of the hole-transporting luminescent material in the region near the cathode side interface of the light emitting layer is 0% or more and 50% or less with respect to the concentration in the region near the anode side interface of the light emitting layer. The organic electroluminescent element according to claim 6 or 7.   9. The organic electric field according to claim 3, wherein the total number of the hole transporting intermediate layers and / or the electron transporting intermediate layers is 2 or more and 5 or less. Light emitting element.   The thickness of each of the plurality of hole transporting intermediate layers and / or the thickness of each of the plurality of electron transporting intermediate layers is from 0.1 nm to 5 nm. Item 10. The organic light-emitting device according to any one of Items 9.   The total thickness of the plurality of hole transport intermediate layers and / or the total thickness of the plurality of electron transport intermediate layers are 0.2 nm or more and 30 nm or less, respectively. The organic light emitting device according to claim 10.   The peak wavelength of an emission spectrum is between 430 nm and 480 nm, The organic electroluminescent element as described in any one of Claims 1-11 characterized by the above-mentioned.