JP2011009498A - Organic electroluminescent element - Google Patents

Abstract

An object of the present invention is to provide an organic EL device that does not have a layer that prevents penetration of holes and electrons into a counter electrode, and that has a high efficiency and a long lifetime.
The present invention provides an anode, three or more hole injecting and transporting layers formed on the anode, a light emitting layer formed on the hole injecting and transporting layer, and a light emitting layer formed on the light emitting layer. In the organic EL device having the above-described cathode, the three or more hole injecting and transporting layers are arranged in order from the anode side in the order of the first, second,..., Nth (n ≧ 3) integers. a hole injection transport layer, the electron affinity of the constituent material of the light emitting layer Ea _0, the electron affinity of the constituent material of the hole injection transport layer of the first x (x = 1 to n an integer) when the Ea _x , Ea ₀ ≦ Ean, x = 2 to _n , Ea _x ≦ Ea _x−1 , and the ionization potential of the constituent material of the light emitting layer is Ip ₀ , and the x th hole injection transport layer When the ionization potential of the constituent material is Ip _x , Ip ₀ ≧ Ip _n , and x = 2 to _n , Ip _x > Ip _x−1. An organic EL element is provided.
[Selection] Figure 2

Description

  The present invention relates to an organic electroluminescence device having a structure in which three or more charge injection transport layers and a light emitting layer are sequentially laminated between an anode and a cathode.

  An organic electroluminescence (hereinafter, electroluminescence may be abbreviated as EL) element is made of a material having a hole or electron injection function, a transport function, and a blocking function in order to achieve long life and high efficiency. It is common to take a multilayer structure in which a plurality of layers are laminated. Further, in an organic EL device having a multilayer structure, in order to efficiently confine holes and electrons in the light emitting layer, a blocking layer that prevents penetration of holes or electrons to the counter electrode side is provided between the electrode and the light emitting layer. It is common to provide it.

  However, in an organic EL element having a multilayer structure, there is a concern that deterioration occurs at the interface of each layer during driving, resulting in a decrease in light emission efficiency or a decrease in luminance due to deterioration of the element. In particular, in an organic EL element provided with a blocking layer, electric charges are likely to accumulate at the interface, and therefore, deterioration is likely to occur at the interface, and there is a concern about luminance deterioration.

In order to suppress the occurrence of deterioration at the interface of each layer during driving, a method of devising materials used for the hole injection transport layer and the electron injection transport layer has been proposed.
For example, Patent Document 1 discloses that an organic semiconductor layer (a hole injection transport layer or an electron injection transport layer) is formed of an organic compound and an oxide in order to improve the hole injection property from the anode and the electron injection property from the cathode. It is disclosed that it is composed of a conductive dopant, or an organic compound and a reducing dopant, or an organic compound and conductive fine particles.
However, since the organic EL element described in Patent Document 1 includes an inorganic charge barrier layer (blocking layer) between the organic semiconductor layer (hole injection transport layer or electron injection transport layer) and the organic light emitting layer, As described above, there are concerns about a decrease in light emission efficiency and deterioration of the element.

  In addition, for example, in Patent Document 2, an electron-accepting dopant is doped in an organic compound layer in contact with the anode for the purpose of lowering an energy barrier in hole injection from the anode to the organic compound layer (hole injection transport layer). A method is disclosed. Further, for example, in Patent Document 3 and Patent Document 4, an electron-donating dopant is added to the organic compound layer in contact with the cathode for the purpose of lowering an energy barrier in electron injection from the cathode to the organic compound layer (electron injection transport layer). A method of doping is disclosed.

JP 2000-315581 A Japanese Patent Laid-Open No. 11-251067 JP-A-10-270171 JP-A-10-270172

However, it is not sufficient to lower the energy barrier in hole injection from the anode or the energy barrier in electron injection from the cathode in order to effectively suppress the decrease in luminous efficiency and device degradation. It is considered effective to have an element configuration that does not have a layer that prevents the penetration of holes and electrons.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a highly efficient and long-life organic EL element that does not have a layer that prevents penetration of holes and electrons into the counter electrode. And

  As a result of intensive studies in view of the above circumstances, the present inventors have determined that at least one of the electron affinity of the constituent material of the hole injection transport layer and the ionization potential of the constituent material of the electron injection transport layer is the same as that of the constituent material of the light emitting layer. The ionization potential and electron affinity are set so as not to prevent charge penetration to the counter electrode, and materials used for the hole injecting and transporting layer, the electron injecting and transporting layer, and the light emitting layer are appropriately selected. It has been found that by optimizing the element structure, an organic EL element having a higher efficiency and a longer life can be obtained as compared with a conventional organic EL element.

The present invention includes an anode, three or more hole injecting and transporting layers formed on the anode, a light emitting layer formed on the hole injecting and transporting layer, and a cathode formed on the light emitting layer. In which the three or more hole injection / transport layers are arranged in order from the anode side in the order of the first, second,..., Nth (n ≧ 3) hole injection / transport. When the electron affinity of the constituent material of the light emitting layer is Ea ₀ , and the electron affinity of the constituent material of the x-th (x = 1 to n) hole injecting and transporting layer is Ea _x , Ea ₀ ≦ Ea _x ≦ Ea _x−1 for all of E a _n and x = 2 to _n , and the ionization potential of the constituent material of the light emitting layer is Ip ₀ , and the ionization of the constituent material of the x th hole injection transport layer An organically characterized by Ip _x ≧ Ip _x−1 for all of Ip ₀ ≧ Ip _n and x = 2 to _n , _where Ip _x is potential An EL element is provided.

According to the present invention, since the electron affinity of the constituent material of each hole injecting and transporting layer and the light emitting layer is Ea ₀ ≦ Ea _n and x = 2 to _n , Ea _x ≦ Ea _x−1 . There is no charge accumulation at the interface between each hole injecting and transporting layer and the light emitting layer, deterioration can be suppressed, and an organic EL element with high efficiency and long life can be obtained.
In addition, since the ionization potentials of the constituent materials of each hole injection transport layer and the light emitting layer are Ip ₀ ≧ Ip _n and x = 2 to _n , Ip _x > Ip _x−1. As a result, there is a slight energy barrier in the hole transport from each hole injection transport layer to the light emitting layer, thereby controlling the injection of holes into the light emitting layer and improving the light emission efficiency. Is possible.

In the above invention, when the first electron injecting and transporting layer is formed between the light emitting layer and the cathode, and the ionization potential of the constituent material of the first electron injecting and transporting layer is Ip ₁ ′, Ip ₀ It is preferable that Ea ₀ ≦ Ea ₁ ′ when ≧ Ip ₁ ′ and the electron affinity of the constituent material of the first electron injecting and transporting layer is Ea ₁ ′. By having the electron injecting and transporting layer where Ip ₀ ≧ Ip ₁ ′, there is no charge accumulation at the interface between the first electron injecting and transporting layer and the light emitting layer during driving, and deterioration can be suppressed, and high efficiency. Thus, a long-life organic EL element can be obtained. Further, since Ea ₀ ≦ Ea ₁ ′, the electron transport from the cathode to the light emitting layer becomes smooth.

In the above invention, a second electron injection / transport layer is formed between the light emitting layer and the first electron injection / transport layer, and the ionization potential of the constituent material of the second electron injection / transport layer is set to Ip ₂ ′. When Ip ₀ ≧ Ip ₂ '≧ Ip ₁ ′ and when the electron affinity of the constituent material of the second electron injecting and transporting layer is Ea ₂ ′, Ea ₀ <Ea ₂ ′ <Ea ₁ 'Is preferred. By setting Ip ₀ ≧ Ip ₂ '≧ Ip ₁ ′, it is possible to suppress deterioration at the interfaces of the first electron injection transport layer, the second electron injection transport layer, and the light emitting layer during driving. This is because by setting Ea ₀ <Ea ₂ ′ <Ea ₁ ′, electron transport from the cathode to the light emitting layer becomes smooth.

In the above invention, three or more electron injecting and transporting layers are formed between the light emitting layer and the cathode, and the three or more electron injecting and transporting layers are first, first, When the ionization potential of the constituent material of the y-th (y = 1 to m) electron injecting and transporting layer is Ip _y ′ , Ip ₀ ≧ Ip _m ′, y = 2 to _m , Ip _y ′ ≧ Ip _y−1 ′, and when the electron affinity of the constituent material of the y-th electron injecting and transporting layer is Ea _y ′, It is preferable that Ea _y ′ <Ea _y−1 ′ for all of Ea ₀ ′ ≦ Ea _m ′ and y = 2 to _m . By having such an electron injecting and transporting layer, it is possible to smoothly transport electrons to the light emitting layer. In addition, there is no charge accumulation at the interface between each electron injecting and transporting layer and the light emitting layer during driving, so that deterioration can be suppressed and a highly efficient and long-life organic EL element can be obtained. .

The present invention includes an anode, a light emitting layer formed on the anode, three or more electron injection / transport layers formed on the light emitting layer, and a cathode formed on the electron injection / transport layer. In the organic EL element, the three or more electron injecting and transporting layers are first, second,..., M (an integer of m ≧ 3) electron injecting and transporting layers in order from the cathode side, When the ionization potential of the constituent material of the light emitting layer is Ip ₀ and the ionization potential of the constituent material of the y-th (y = _{1 to m} ) electron injection and transport layer is Ip _y ′, Ip ₀ ≧ Ip _m ′, For all y = 2 to m, Ipy _y ≧ Ipy _-1 ′, the electron affinity of the constituent material of the light emitting layer is Ea ₀ , and the electronic affinity of the constituent material of the yth electron injecting and transporting layer is When Ea _y ′, Ea ₀ ≦ Ea _m ′, and y = 2 to _m , Ea _y ′ <Ea _y−1 ′ An organic EL element is provided.

According to the present invention, since the ionization potentials of the constituent materials of the electron injecting and transporting layer and the light emitting layer are Ip ₀ ≧ Ip _m ′ and y = 2 to _m , Ip _y ′ ≧ Ip _y−1 ′. There is no charge accumulation at the interface between the electron injecting and transporting layer and the light emitting layer, deterioration can be suppressed, and an organic EL element with high efficiency and long life can be obtained.
In addition, since the electron affinity of the constituent materials of each electron injecting and transporting layer and the light emitting layer is Ea ₀ ≦ Ea _m ′ and y = 2 to _m , Ea _y ′ <Ea _y−1 ′, As a result, there is a slight energy barrier in electron transport from each electron injection transport layer to the light emitting layer, so that the injection of electrons into the light emitting layer can be controlled and the light emission efficiency can be increased. is there.

In the above invention, the first hole injection transport layer between the light-emitting layer and the anode is formed, when the electron affinity of the constituent material of the first hole injection transport layer was Ea _1, Ea It is preferable that Ip ₀ ≧ Ip ₁ when ₀ ≦ Ea ₁ and the ionization potential of the constituent material of the first hole injection transport layer is Ip ₁ . By satisfying Ea ₀ ≦ Ea ₁ , there is no charge accumulation at the interface between the first hole injecting and transporting layer and the light emitting layer, deterioration can be suppressed, and a highly efficient and long-life organic EL element can be obtained. It is possible. Further, when Ip ₀ ≧ Ip ₁ , hole transport from the anode to the light emitting layer becomes smooth.

Moreover, in the said invention, the 2nd positive hole injection transport layer is formed between the said light emitting layer and the said 1st positive hole injection transport layer, The electron of the constituent material of the said 2nd positive hole injection transport layer When the affinity is Ea ₂ , Ea ₀ ≦ Ea ₂ ≦ Ea ₁ and when the ionization potential of the constituent material of the second hole injection transport layer is Ip ₂ , Ip ₀ > Ip ₂ > Ip ₁ is preferable. This is because by setting Ea ₀ ≦ Ea ₂ ≦ Ea ₁ , it is possible to suppress deterioration at the interface between the hole injecting and transporting layer, the second hole injecting and transporting layer, and the light emitting layer during driving. In addition, since Ip ₀ > Ip ₂ > Ip ₁ , hole transport from the anode to the light emitting layer becomes smooth.

  Furthermore, in the present invention, it is preferable that the hole injecting and transporting layer and the electron injecting and transporting layer contain a bipolar material capable of transporting holes and electrons. By using a bipolar material for the hole injecting and transporting layer and the electron injecting and transporting layer, deterioration at the interface of the hole injecting and transporting layer, the light emitting layer, and the electron injecting and transporting layer during driving can be effectively suppressed. It is.

  In the above case, the bipolar material contained in the hole injecting and transporting layer is preferably the same as the bipolar material contained in the electron injecting and transporting layer. This is because, if these bipolar materials are the same, even if holes penetrate into the electron injecting and transporting layer or electrons penetrate into the hole injecting and transporting layer, these layers are not easily deteriorated.

  In the above case, the light emitting layer may contain a bipolar material that can transport holes and electrons. In this case, it is preferable that the bipolar material contained in the hole injection transport layer, the bipolar material contained in the electron injection transport layer, and the bipolar material contained in the light emitting layer are the same. As described above, if these bipolar materials are the same, even if holes penetrate into the electron injecting and transporting layer or electrons penetrate into the hole injecting and transporting layer, these layers are unlikely to deteriorate. is there.

  Furthermore, in the present invention, the light emitting layer preferably contains a host material and a light emitting dopant, and the concentration of the light emitting dopant in the light emitting layer is preferably distributed. This is because the distribution of the luminescent dopant concentration can balance the holes and electrons injected into the luminescent layer.

  In the present invention, the light emitting layer may contain a host material and two or more kinds of light emitting dopants. For example, by including a light-emitting dopant that easily transports holes rather than electrons and a light-emitting dopant that easily transports electrons rather than holes, it is possible to balance the holes and electrons injected into the light-emitting layer. Because. In addition, for example, energy transfer can be caused smoothly by further containing a light emitting dopant having an excitation energy between the excitation energy of the host material and the light emitting dopant.

  According to the present invention, at least one of the ionization potential and the electron affinity of the constituent material of the hole injection transport layer and the light emitting layer and the ionization potential and the electron affinity of the constituent material of the electron injection transport layer and the light emitting layer are determined in advance. By using this relationship, it is possible to suppress deterioration at the interface between the hole injecting and transporting layer and the light emitting layer and the interface between the electron injecting and transporting layer and the light emitting layer during driving, and to smoothly transport charges from the electrode to the light emitting layer. It is possible to improve the efficiency and to obtain a stable life characteristic.

It is a schematic sectional drawing which shows an example of the organic EL element of this invention. It is a schematic diagram which shows an example of the band diagram of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is explanatory drawing which shows the operation mechanism of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is a schematic diagram which shows the other example of the band diagram of the organic EL element of this invention.

Hereinafter, the organic EL device of the present invention will be described in detail.
The organic EL device of the present invention can be divided into two embodiments depending on the layer structure. In the following, each embodiment will be described separately.

I. First Embodiment A first embodiment of the organic EL device of the present invention is an anode, three or more hole injection / transport layers formed on the anode, and light emission formed on the hole injection / transport layer. An organic EL device having a layer and a cathode formed on the light-emitting layer, wherein the three or more hole injection / transport layers are arranged in order from the anode side in the first, second,. a positive hole injection transport layer of the n (integer n ≧ 3), the electron affinity of the constituent material of the light emitting layer Ea _0, when the electron affinity of the constituent material of the hole injection transport layer of the first x and the Ea _x , Ea ₀ ≦ Ean, x = 2 to _n , Ea _x ≦ Ea _x−1 , and the ionization potential of the constituent material of the light emitting layer is Ip ₀ , and the x th hole injection transport layer when the ionization potential of the constituent material was _{Ip x, Ip 0 ≧ Ip n} , for all _{x = 2~n Ip x> Ip x} -1 der It is characterized in.

FIG. 1 is a schematic cross-sectional view showing an example of an organic EL element of the present embodiment, and FIGS. 2 and 3 are schematic views showing examples of band diagrams of the organic EL element shown in FIG. In FIG. 1, the case where n = 3 is considered as an example.
As illustrated in FIG. 1, the organic EL element 1 of this embodiment includes a transparent substrate 2, an anode 3, a first hole injection transport layer 4, and a second hole injection transport layer on the transparent substrate 2. 5, a third hole injecting and transporting layer 6, a light emitting layer 7, a first electron injecting and transporting layer 8, and a cathode 9 are sequentially laminated.
In this organic EL element, the ionization potential of the constituent material of the first hole injection transport layer 4 is Ip ₁ , the ionization potential of the constituent material of the second hole injection transport layer 5 is Ip ₂ , and the third Assuming that the ionization potential of the constituent material of the hole injection / transport layer 6 is Ip ₃ and the ionization potential of the constituent material of the light emitting layer 7 is Ip ₀ , as shown in FIG. 2, Ip ₁ <Ip ₂ <Ip ₃ <Ip _It may be ₀ , or Ip ₁ <Ip ₂ <Ip ₃ = Ip ₀ as illustrated in FIG.
Also, the electron affinity of the constituent material of the first hole injection transport layer 4 is Ea ₁ , the electron affinity of the constituent material of the second hole injection transport layer 5 is Ea ₂ , and the third hole injection transport. If the electron affinity of the constituent material of the layer 6 is Ea ₃ and the electron affinity of the constituent material of the light emitting layer 7 is Ea ₀ , Ea ₀ <Ea ₃ <Ea ₂ <Ea ₁ as illustrated in FIG. Alternatively, as exemplified in FIG. 3, Ea ₀ = Ea ₃ = Ea ₂ = Ea ₁ may be satisfied.

According to the present invention, three or more hole injecting and transporting layers are formed between the anode and the light emitting layer so that Ip _x > Ip _x-1 for all of Ip ₀ ≧ Ip _n and x = 2 to _n . As a result, holes can be smoothly transported from the anode to the light emitting layer through each hole injecting and transporting layer. Therefore, for example, even when the band gap energy of the constituent material of the light emitting layer is relatively large and the difference between the work function of the anode and the ionization potential Ip ₀ of the constituent material of the light emitting layer is relatively large, the light emission Transport of holes to the layer can be facilitated.
Further, three or more hole injecting and transporting layers are formed between the anode and the light emitting layer so that Ea _x ≦ Ea _x−1 for all of Ea ₀ ≦ Ean and x = 2 to _n . Thus, deterioration at the interface between the hole injecting and transporting layer and the light emitting layer can be suppressed.

  In the organic EL device of this embodiment, it is preferable that one or more electron injecting and transporting layers are formed between the light emitting layer and the cathode.

For example, as shown in FIG. 1, it is preferable that a first electron injecting and transporting layer 8 is formed between the light emitting layer 7 and the cathode 9.
In this case, when the ionization potential of the first electron injection transport layer 8 is Ip ₁ ′, Ip ₁ ′ <Ip ₀ as illustrated in FIG. 2, or Ip ₁ ′ = as illustrated in FIG. Ip ₀ is preferred. When the electron affinity of the first electron injecting and transporting layer 8 is Ea ₁ ′, Ea ₀ <Ea ₁ ′ as illustrated in FIG. 2 or Ea ₀ = Ea ₁ as illustrated in FIG. 'Is preferred.

Normally, in such an organic EL element, Ea _x ≦ Ea _x−1 for all of Ip ₁ ′ ≦ Ip ₀ , Ea ₀ ≦ Ea _n , and x = 2 to _n , the charge recycle can be efficiently performed in the light emitting layer. It is difficult to generate a bond and generate an excited state and to deactivate radiation, resulting in a decrease in light emission efficiency, hole and electron penetration into the counter electrode, and injection of electrons into the hole injection and transport layer. It is assumed that the lifetime characteristics deteriorate due to the injection of holes into the injection transport layer. However, the ionization potential of the constituent materials of the first electron injecting and transporting layer and the light emitting layer is Ip ₁ ′ ≦ Ip ₀ , and the electron affinity of the constituent materials of each hole injecting and transporting layer and the light emitting layer is Ea ₀ ≦ Ea _Since Ea _x ≦ Ea _x−1 for all of _n and x = 2 to _n , although holes and electrons penetrate through the counter electrode, holes and electrons are smoothly transported between the anode and the cathode. In addition, it is possible to suppress deterioration at the interfaces of the hole injection / transport layers, the light emitting layer, and the first electron injection / transport layer during driving. In addition, since holes and electrons are transported smoothly, holes and electrons are recombined throughout the light emitting layer, so that the recombination efficiency of holes and electrons is not significantly reduced. Accordingly, the ionization potential Ip ₁ '≦ Ip ₀ next to the material of the first electron injection transport layer and the luminescent layer and an electron affinity of the constituent material of the hole injection transport layer and the luminescent layer is Ea ₀ ≦ Ea _n , By appropriately selecting materials used for each of the hole injecting and transporting layer, the first electron injecting and transporting layer, and the light emitting layer so that Ea _x ≦ Ea _x−1 for all of x = 2 to n, It is possible to increase the efficiency and obtain a significantly stable life characteristic.

  Moreover, it becomes easier to inject electrons into the light emitting layer by forming the first electron injecting and transporting layer on the cathode side of the light emitting layer so that the electron affinity of the light emitting layer and the first electron injecting and transporting layer has the above relationship. Therefore, the recombination efficiency between holes and electrons in the light emitting layer is increased.

FIG. 4 is a schematic cross-sectional view showing another example of the organic EL element of the present embodiment, and FIGS. 5 and 6 are schematic views showing examples of band diagrams of the organic EL element shown in FIG. 4, respectively.
In the present embodiment, as illustrated in FIG. 4, it is preferable that a second electron injection / transport layer 10 is formed between the light emitting layer 7 and the first electron injection / transport layer 8.
In this case, the ionization potential of the constituent material of the light emitting layer 7 is Ip ₀ , the ionization potential of the constituent material of the first electron injection transport layer 8 is Ip ₁ ′, and the ionization potential of the constituent material of the second electron injection transport layer 10 is When Ip ₂ ′ is set, it is preferable that Ip ₀ ≧ Ip ₂ ′ ≧ Ip ₁ ′ as illustrated in FIGS. 5 and 6. Further, the electron affinity of the constituent material of the light emitting layer 7 is Ea ₀ , the electron affinity of the constituent material of the first electron injection / transport layer 8 is Ea ₁ ′, and the electron affinity of the constituent material of the second electron injection / transport layer 10 is Ea. _{When 2} ′, it is preferable that Ea ₀ <Ea ₂ ′ <Ea ₁ ′ as illustrated in FIG.

FIG. 7 is a schematic cross-sectional view showing another example of the organic EL element of the present embodiment, and FIGS. 8 and 9 are schematic views showing examples of band diagrams of the organic EL element shown in FIG. 7, respectively. .
In this embodiment, it is preferable that three or more electron injection / transport layers are formed between the light emitting layer 7 and the cathode 9 as illustrated in FIG. In FIG. 7, a case where three electron injecting and transporting layers are formed will be described.
The formed three electron injecting and transporting layers are sequentially designated as the first electron injecting and transporting layer 8, the second electron injecting and transporting layer 10, and the mth (m = 3) electron injecting and transporting layer 11 from the cathode 9 side. The ionization potential of the constituent material of the light emitting layer 7 is Ip ₀ , the ionization potential of the constituent material of the first electron injection transport layer 8 is Ip ₁ ′, and the ionization potential of the constituent material of the second electron injection transport layer 10 is Ip _2. ′, When the ionization potential of the constituent material of the third electron injecting and transporting layer 11 is Ip ₃ ′, as illustrated in FIGS. 8 and 9, Ip ₀ ≧ Ip ₃ ′> Ip ₂ ′> Ip ₁ ′ Preferably there is. Further, the electron affinity of the constituent material of the light emitting layer 7 is Ea ₀ , the electron affinity of the constituent material of the first electron injection / transport layer 8 is Ea ₁ ′, and the electron affinity of the constituent material of the second electron injection / transport layer 10 is Ea. ₂ ′, when the electron affinity of the constituent material of the third electron injecting and transporting layer 11 is Ea ₃ ′, Ea ₀ <Ea ₃ ′ <Ea ₂ ′ <Ea ₁ ′, as illustrated in FIG. Is preferred.

  4 to 9, the relationship between the configuration not described above and the ionization potential of each constituent material of the hole injection transport layer and the light emitting layer and the electron affinity are the same as those described in FIGS. Since it is the same, description is abbreviate | omitted.

In this embodiment, the first, second,..., M-th (m ≧ 3 integer) electron injecting and transporting layers are formed in order from the cathode side, and the y-th (y = 1 to m) integer electrons. When the ionization potential of the constituent material of the injection transport layer is Ip _y ′, the electron injection transport layer is formed so that Ip _y ≧ Ip _y−1 ′ for all of Ip ₀ ≧ Ip _m ′ and y = 2 to _m By doing so, there is no charge accumulation at the interface between each electron injecting and transporting layer and light emitting layer during driving, and deterioration can be suppressed. When the electron affinity of the constituent material of the y-th electron injecting and transporting layer is Ea _y ′, Ea ₀ ≦ Ea _m ′ and y = 2 to _m satisfy Ea _y ′ <Ea _y−1 ′. By forming such an electron injecting and transporting layer, electrons can be smoothly transported to the light emitting layer through a plurality of electron injecting and transporting layers. Therefore, a highly efficient and long-life organic EL element can be obtained.

In the present invention, since the conventional blocking layer is not provided, it is considered that it is difficult to efficiently recombine holes and electrons in the light emitting layer as described above. Therefore, it is effective to optimize the element configuration in order to improve the light emission efficiency. For example, (1) the thickness of the light emitting layer is made relatively thick, (2) Ip _n <Ip ₀ , (3) Ea ₀ <Ea _m ′, (4) the light emitting layer is a host material and a light emitting dopant. When the light emitting layer contains the host material and the light emitting dopant, the light emitting dopant in the light emitting layer is made to be included in the band gap of the host material. The luminous efficiency can be improved by providing a distribution in the concentration of (6) forming a plurality of hole injecting and transporting layers, (7) forming a plurality of electron injecting and transporting layers, and the like.

  Hereinafter, each structure in the organic EL element of this embodiment is demonstrated.

1. Ionization potential and electron affinity In this embodiment, the electron affinity of the constituent material of the light-emitting layer is Ea ₀ , and the constituent material of the x-th (x = 1 to n, integer of n ≧ 3) hole injecting and transporting layer When the electron affinity is Ea _x , Ea _x ≦ Ea _x−1 for all of Ea ₀ ≦ Ean and x = 2 to _n , and the ionization potential of the constituent material of the light emitting layer is Ip ₀ , xth when the ionization potential of the constituent material of the hole injection transport layer was Ip _x, when the _{Ip x, Ip 0 ≧ Ip n} , for all x = 2- through n is Ip _x> Ip _x-1.

  In addition, the ionization potential of the constituent material of each layer including the electron injection transport layer described later refers to the ionization potential of the material when each layer is made of a single material, and each layer is a host material. When it is composed of a dopant, it means the ionization potential of the host material. Similarly, the electron affinity of the constituent material of each layer means the electron affinity of the material when each layer is made of a single material, and each layer is made of a host material and a dopant. In some cases, it refers to the electron affinity of the host material.

Regarding the relationship between the ionization potentials of the constituent materials of the hole injection transport layer and the light emitting layer, the ionization potential of the constituent material of the light emitting layer is Ip ₀ , and the configuration of the xth (x = 1 to n) integer hole injection transport layer. Assuming that the ionization potential of the material is Ip _x , Ip ₀ ≧ Ip _n , and x = 2 to _n may _satisfy Ip _x > Ip _x−1 . Among them, Ip ₀ > Ip _n is preferable. . This is because the presence of some energy barrier in the hole transport from the first hole injection transport layer to the light emitting layer can control the injection of holes and increase the light emission efficiency.

Ip _0> difference Ip ₀ and Ip _n in the case of Ip _n, and, Ip as a difference between _x and ip _x-1, but is different depending on the material of the hole injection transport layer and the luminescent layer Specifically, each is preferably set to 0.1 eV or more, more preferably in the range of 0.2 eV to 0.5 eV.

The electron affinity of the constituent material of the hole injecting and transporting layer and the light emitting layer is as follows: the electron affinity of the constituent material of the light emitting layer is Ea ₀ , and the xth (x = 1 to n) integer hole injecting and transporting layer. the electron affinity of the constituent material when the Ea _{x of,} Ea ₀ ≦ Ea _n, may but if Ea _x ≦ Ea _x-1 for all x = 2- through n, among _{others, Ea 0 <Ea n, x} = It is preferable that Ea _x <Ea _x−1 for all of 2 to n. If Ea ₀ <Ea _n , x = 2 to _n , Ea _x <Ea _x−1 , and Ip ₀ > Ip _n , x = 2 to _n , Ip _x > Ip _x−1 Since the band gap energy of the constituent material of the layer can be made relatively large, for example, when the light emitting layer contains a host material and a light emitting dopant, the ionization potential of the host material and the light emitting dopant is improved in order to improve the light emission efficiency. This is because it becomes easy to select the host material and the light-emitting dopant so that the electron affinity satisfies a predetermined relationship.

Ea ₀ <Ea _n, if for all x = 2- through n of Ea _x <Ea _x-1, the difference between Ea ₀ and Ea _n, and, as the difference between Ea _x and Ea _x-1, the hole injection Although it differs depending on the constituent materials of the transport layer and the light emitting layer, specifically, it is preferably 0.1 eV or more, and more preferably in the range of 0.2 eV to 0.5 eV.

When the first electron injecting and transporting layer is formed between the light emitting layer and the cathode, the relationship between the ionization potentials of the constituent materials of the light emitting layer and the first electron injecting and transporting layer is as follows. the ionization potential of the constituent material Ip _0, 'when a, Ip ₀ ≧ Ip _1' an ionization potential of the constituent material of the first electron injection transport layer Ip ₁ is preferably, among others, Ip _0> Ip ₁ ' It is preferable that If Ip ₀ > Ip ₁ ′ and Ea ₀ <Ea ₁ ′, the band gap energy of the constituent material of the light emitting layer can be made relatively large. For example, when the light emitting layer contains a host material and a light emitting dopant In addition, it is easy to select the host material and the light emitting dopant so that the ionization potential and the electron affinity of the host material and the light emitting dopant satisfy a predetermined relationship in order to improve the light emission efficiency.

In the case of Ip ₀ > Ip ₁ ′, the difference between Ip ₀ and Ip ₁ ′ differs depending on the constituent materials of the light emitting layer and the electron injecting and transporting layer, but specifically 0.1 eV or more. Is preferable, and more preferably in the range of 0.2 eV to 0.5 eV.

The electron affinity of the constituent material of the light emitting layer and the first electron injecting and transporting layer is as follows: the electron affinity of the constituent material of the light emitting layer is Ea ₀ , and the electron affinity of the constituent material of the electron injecting and transporting layer is Ea ₁ ′. In general, Ea ₀ ≦ Ea ₁ ′. Among these, it is preferable that Ea ₀ <Ea ₁ ′. This is because the presence of a certain energy barrier in the electron transport from the first electron injecting and transporting layer to the light emitting layer makes it possible to control the electron injection and increase the light emission efficiency.

In the case of Ea ₀ <Ea ₁ ′, the difference between Ea ₀ and Ea ₁ ′ differs depending on the constituent materials of the light emitting layer and the electron injecting and transporting layer, but specifically 0.1 eV or more Is preferable, and more preferably in the range of 0.2 eV to 0.5 eV.
Even when the difference between Ea ₀ and Ea ₁ ′ is relatively large, electrons can be transported from the electron injecting and transporting layer to the light emitting layer if the driving voltage is relatively high.

When a second electron injecting and transporting layer is formed between the first electron injecting and transporting layer and the light emitting layer, the ionization of the first electron injecting and transporting layer, the second electron injecting and transporting layer, and the light emitting layer Regarding the potential relationship, the ionization potential of the constituent material of the light emitting layer is Ip ₀ , the ionization potential of the constituent material of the second electron injection transport layer is Ip ₂ ′, and the ionization potential of the constituent material of the first electron injection transport layer is 'when _{the, ip 0 ≧ ip 2' ip} 1 is preferably ≧ ip ₁ '. This is because deterioration at the interfaces of the first electron injection transport layer, the second electron injection transport layer, and the light emitting layer during driving can be suppressed.

When the second electron injection / transport layer is formed between the first electron injection / transport layer and the light emitting layer, the first electron injection / transport layer, the second electron injection / transport layer, The electron affinity of the light emitting layer is composed of Ea ₀ as the constituent material of the light emitting layer, Ea ₂ ′ as the constituent material of the second electron injecting and transporting layer, and the structure of the first electron injecting and transporting layer. 'when the normally Ea ₀ ≦ Ea _2' electron affinity of the material Ea ₁ are ≦ Ea ₁ '. Among these, it is preferable that Ea ₀ <Ea ₂ ′ <Ea ₁ ′. When the difference between Ea ₀ and Ea ₁ ′ is relatively large, it becomes difficult for electrons to be transported from the first electron injecting and transporting layer to the light emitting layer, but the first so that Ea ₀ <Ea ₂ ′ <Ea ₁ ′. Since the second electron injecting and transporting layer is formed between the electron injecting and transporting layer 1 and the light emitting layer, electrons are transferred from the first electron injecting and transporting layer to the light emitting layer through the second electron injecting and transporting layer. This is because it can be transported smoothly. In addition, since there are some energy barriers in the electron transport from the first electron injection transport layer to the second electron injection transport layer and the electron transport from the second electron injection transport layer to the light emitting layer, This is because the injection efficiency can be controlled and the luminous efficiency can be increased.

In the case of Ea ₀ <Ea ₂ ′ <Ea ₁ ′, the difference between Ea ₀ and Ea ₂ ′ and the difference between Ea ₂ ′ and Ea ₁ ′ include the first electron injection transport layer and the second electron injection transport Although it differs depending on the constituent material of the layer and the light emitting layer, specifically, it is preferably set to 0.1 eV or more, more preferably in the range of 0.2 eV to 0.5 eV.

When three or more electron injecting and transporting layers are formed between the light emitting layer and the cathode, the first, second,..., Mth (m ≧ 3 integer) electron injecting and transporting layers from the cathode side, respectively. As for the relationship between the ionization potentials of the electron injection transport layers and the light emitting layer, when the ionization potential of the constituent material of the yth (y = 1 to m) electron injection transport layer is Ip _y ′ , Ip ₀ ≧ Ip _m ′ and y = 2 to _m are preferably Ip _y ′ ≧ Ip _y−1 ′. This is because deterioration at the interface between each electron injection / transport layer and the light emitting layer during driving can be suppressed.

When three or more electron injecting and transporting layers are formed between the light emitting layer and the cathode, the relationship between the electron affinity of each electron injecting and transporting layer and the light emitting layer is y (y = 1 to m). 'when the normally Ea ₀ ≦ Ea _m' the electron affinity of the constituent material for the electron injecting and transporting layer of an integer) Ea _y is, for all y = 2 to m and _{Ea y '<Ea y-1} ' . Among them, Ea _y <Ea _y−1 ′ is preferable for all of Ea ₀ <Ea _m ′ and y = 2 to _m . When the difference between the work function of the cathode and the electron affinity of the constituent material of the light emitting layer is relatively large, it becomes difficult to transport electrons from the cathode to the light emitting layer, but all of Ea ₀ <Ea _m ′, y = 2 to _m By forming a plurality of electron injecting and transporting layers between the cathode and the light emitting layer so that Ea _y '<Ea _y−1 ' This is because electrons can be transported smoothly. In addition, since there is a slight energy barrier in electron transport from the first electron injection transport layer to the light emitting layer, electron injection can be controlled and light emission efficiency can be increased.

  The ionization potential of the constituent material of each layer is formed by depositing the constituent material by a vacuum vapor deposition method, and the ionization potential of the vapor deposition film is measured by UPS (ultraviolet photoelectron spectroscopy) (for example, measuring instrument name “AC-2” or “ AC-3 "and Riken Keiki). As a method for measuring electron affinity, first, HOMO energy is obtained by UPS (ultraviolet photoelectron spectroscopy) (for example, “AC-2” manufactured by Riken Keiki Co., Ltd.), and then an energy gap measurement value by light absorption and the above HOMO energy. The method of calculating from is adopted.

2. Hole injection / transport layer The three or more hole injection / transport layers used in the present invention are the first, second,..., Nth (n ≧ 3 integer) hole injection / transport layers in order from the anode side. It is formed between the anode and the light emitting layer, and has a function of stably injecting or transporting holes from the anode to the light emitting layer.

  Usually, the first hole injecting and transporting layer functions as a hole injecting layer, and the second to nth (n ≧ 3 integer) hole injecting and transporting layers function as a hole transporting layer.

  The constituent material of each hole injecting and transporting layer is not particularly limited as long as it is a material that can stably transport holes injected from the anode into the light emitting layer. In addition to the compounds exemplified above, arylamines, starburst amines, phthalocyanines, vanadium oxide, molybdenum oxide, ruthenium oxide, aluminum oxide and other oxides, amorphous carbon, polyaniline, polythiophene, polyphenylene vinylene and other highly conductive materials Molecules and their derivatives can be used. Conductive polymers such as polyaniline, polythiophene, polyphenylene vinylene, and derivatives thereof may be doped with an acid. Specifically, N, N′-bis (naphthalen-1-yl) -N, N′-bis (phenyl) -benzidine (α-NPD), 4,4,4-tris (3-methylphenylphenylamino) ) Triphenylamine (MTDATA), poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid (PEDOT / PSS), polyvinylcarbazole (PVCz), and the like.

In particular, the constituent material of each hole injecting and transporting layer is preferably a bipolar material that can transport holes and electrons.
Note that a bipolar material is a material that can stably transport both holes and electrons, and when a unipolar device for electrons is produced using a material doped with a reducing dopant, electrons are It refers to a material that can be stably transported and can transport holes stably when a unipolar device of holes is produced using a material doped with an oxidizing dopant. When producing a unipolar device, specifically, an electron unipolar device is produced using a material doped with Cs or 8-hydroxyquinolinolatolithium (Liq) as a reducing dopant, and is oxidized. A hole unipolar device can be fabricated using a material doped with V ₂ O ₅ or MoO ₃ as a dopant.
By using such a bipolar material for each hole injecting and transporting layer, deterioration at the interface between the light emitting layer and each hole injecting and transporting layer during driving can be effectively suppressed.

  Examples of the bipolar material include a distyrylarene derivative, a polyaromatic compound, an aromatic condensed ring compound, a carbazole derivative, and a heterocyclic compound. Specifically, 4,4′-bis (2,2-diphenyl-ethen-1-yl) diphenyl (DPVBi), 4,4′-bis (carbazol-9-yl) biphenyl (CBP) represented by the following formula: ), 2,2 ', 7,7'-tetrakis (carbazol-9-yl) -9,9'-spiro-bifluorene (spiro-CBP), 4,4' '-di (N-carbazolyl) -2' , 3 ', 5', 6'-tetraphenyl-p-terphenyl (CzTT), 1,3-bis (carbazol-9-yl) -benzene (m-CP), or 3-tert-butyl-9, Examples include 10-di (naphth-2-yl) anthracene (TBADN), and derivatives thereof.

  Any material that is confirmed to be capable of transporting both hole and electron carriers by the above method can be used as the bipolar material in the present invention.

  In the case where all of the first, second,..., N-th (n ≧ 3 integer) hole injecting and transporting layers contain bipolar materials, the bipolar materials contained in these layers may be the same. May be different. Furthermore, even when all of the first, second,..., Nth (n ≧ 3 integer) hole injecting and transporting layers and the light emitting layer contain bipolar materials, the bipolar materials contained in these layers are: , May be the same or different.

In addition, when each hole injecting and transporting layer and an electron injecting and transporting layer described later contain a bipolar material, the bipolar material contained in each hole injecting and transporting layer and the electron injecting and transporting layer may be the same. May be different. Especially, it is preferable that the bipolar material contained in each positive hole injection transport layer and an electron injection transport layer is the same. This is because, if these bipolar materials are the same, even if holes penetrate into the electron injecting and transporting layer and electrons penetrate into each hole injecting and transporting layer, these layers are not easily deteriorated. Further, when these layers are formed by a vacuum vapor deposition method or the like, a common vapor deposition source can be used, which is advantageous in the manufacturing process.
Furthermore, when each of the hole injection transport layer, the electron injection transport layer, and the light emitting layer contains a bipolar material, the bipolar material contained in each hole injection transport layer, the electron injection transport layer, and the light emitting layer is the same. It may or may not be. Especially, it is preferable that the bipolar material contained in each hole injection transport layer, an electron injection transport layer, and a light emitting layer is the same. If these bipolar materials are the same, as described above, even if holes penetrate into the electron injecting and transporting layer or electrons penetrate into each hole injecting and transporting layer, these layers are unlikely to deteriorate. It is. Further, when these layers are formed by a vacuum vapor deposition method or the like, a common vapor deposition source can be used, which is advantageous in the manufacturing process.

When the constituent material of the hole injecting and transporting layer adjacent to the anode is an organic material (organic compound for hole injecting and transporting layer), the hole injecting and transporting layer is at least at the interface with the anode. You may have the area | region where the oxidizing dopant was mixed with the organic compound for use. A hole injection barrier from the anode to the hole injection transport layer by having a region in which the organic dopant for the hole injection transport layer is mixed with an oxidizing dopant at least at the interface with the anode. This is because the driving voltage can be reduced.
In the organic EL device, the hole injection process from the anode to the organic layer, which is basically an insulator, is oxidation of the organic compound on the anode surface, that is, formation of a radical cation state (Phys. Rev. Lett., 14 , 229 (1965)). By previously doping the hole injection transport layer in contact with the anode with an oxidizing dopant that oxidizes the organic compound, the energy barrier for hole injection from the anode can be lowered. In the hole injecting and transporting layer doped with the oxidizing dopant, an organic compound in a state oxidized by the oxidizing dopant (that is, a state in which electrons are donated) exists, so that the hole injection energy barrier is small, The driving voltage can be lowered compared to the organic EL element.
Further, when the constituent material of the hole injection / transport layer not adjacent to the anode is an organic compound for hole injection / transport layer, the hole injection / transport layer is at least on the anode side, the organic compound for hole injection / transport layer It may have a region in which an oxidizing dopant is mixed.

  The oxidizing dopant is not particularly limited as long as it has a property of oxidizing the organic compound for hole injection transport layer, but an electron accepting compound is usually used.

As the electron-accepting compound, both inorganic and organic materials can be used. When the electron accepting compound is an inorganic substance, for example, Lewis such as ferric chloride, aluminum chloride, gallium chloride, indium chloride, antimony pentachloride, molybdenum trioxide (MoO ₃ ), vanadium pentoxide (V ₂ O ₅ ), etc. Examples include acids. Moreover, when an electron-accepting compound is organic substance, a trinitrofluorenone etc. are mentioned, for example.

Among them, as the electron-accepting compound, a metal oxide is _preferable, MoO _3, V 2 _{O 5} is preferably used.

When the hole injecting and transporting layer adjacent to the anode has a region where an oxidizing dopant is mixed with the organic compound for the hole injecting and transporting layer, the hole injecting and transporting layer has at least the above region at the interface with the anode. For example, the hole injecting and transporting layer may be uniformly doped with an oxidizing dopant, and the content of the oxidizing dopant is continuously increased from the light emitting layer side to the anode side. Thus, the oxidizing dopant may be doped, or the oxidizing dopant may be locally doped only in the interface with the anode of the hole injection transport layer.
The same applies to the case where a hole injecting and transporting layer not adjacent to the anode side has the above region.

  The oxidizing dopant concentration in the hole injecting and transporting layer is not particularly limited, but the molar ratio of the organic compound for hole injecting and transporting layer and the oxidizing dopant is the organic compound for hole injecting and transporting layer: oxidation. It is preferable that it is in the range of 1:10 to 1:10. This is because if the ratio of the oxidizing dopant is less than the above range, the concentration of the organic compound for the hole injecting and transporting layer oxidized by the oxidizing dopant may be too low to obtain a sufficient doping effect. If the ratio of the oxidizing dopant exceeds the above range, the oxidizing dopant concentration in the hole injecting and transporting layer far exceeds the organic compound concentration for the hole injecting and transporting layer, and the holes oxidized by the oxidizing dopant. This is because the concentration of the organic compound for the injecting and transporting layer is extremely lowered, so that the doping effect may not be sufficiently obtained.

  The number of hole injection / transport layers in the present embodiment is not particularly limited as long as it is 3 or more and can smoothly transport holes between the anode and the light emitting layer. In this embodiment, three layers are preferable.

  As a method for forming each hole injection transport layer, for example, a dry method such as a vacuum deposition method or a sputtering method, or a printing method, an ink jet method, a spin coating method, a casting method, a dipping method, a bar coating method, a blade coating method, or the like. Examples thereof include wet methods such as a method, a roll coating method, a gravure coating method, a flexographic printing method, and a spray coating method.

  Among these, as a method for forming a hole injection transport layer doped with an oxidizing dopant, a method of co-evaporating an organic compound for a hole injection transport layer and an oxidizing dopant is preferably used. In this co-evaporation technique, an oxidizing dopant having a relatively low saturation vapor pressure, such as ferric chloride and indium chloride, can be deposited in a crucible by a general resistance heating method. On the other hand, when the vapor pressure is high even at room temperature and the pressure inside the vacuum device cannot be kept below the predetermined vacuum level, the vapor pressure can be controlled by controlling the orifice (opening diameter) like a needle valve or mass flow controller, Alternatively, the vapor pressure may be controlled by cooling the sample holding portion so that the temperature can be controlled independently.

  In addition, as a method of mixing the oxidizing dopant with the organic compound for the hole injection transport layer so that the content of the oxidizing dopant continuously increases from the light emitting layer side to the anode side, for example, A method of continuously changing the deposition rate of the organic compound for the hole injection transport layer and the oxidizing dopant can be used.

  The thickness of each hole injecting and transporting layer is not particularly limited as long as it is a thickness that sufficiently injects holes from the anode and transports holes to the light emitting layer. Can be set in the range of about 0.5 nm to 1000 nm, and is preferably in the range of 5 nm to 500 nm.

  The thickness of the hole injecting and transporting layer doped with the oxidizing dopant is not particularly limited, but is preferably 0.5 nm or more. The hole injecting and transporting layer doped with the oxidizing dopant is not particularly limited because the organic compound for the hole injecting and transporting layer exists in the state of radical cation even in the absence of an electric field, and acts as an internal charge. is there. Also, even if the hole injection / transport layer doped with the oxidizing dopant is made thick, the device voltage does not increase, so the distance between the anode and the cathode is set longer than in the case of a normal organic EL device. By doing so, the risk of a short circuit can be greatly reduced.

3. Electron Injecting and Transporting Layer In this embodiment, it is preferable that one or more electron injecting and transporting layers are formed between the light emitting layer and the cathode.

  In one or more electron injecting and transporting layers used in this embodiment, it is preferable that the ionization potential and the electron affinity of the constituent materials of the electron injecting and transporting layer and the light emitting layer satisfy the relationship described above.

When only one electron injecting and transporting layer, that is, only the first electron injecting and transporting layer is formed, the first electron injecting and transporting layer has an electron injecting layer having an electron injecting function, and an electron transporting function. Any one of the electron transport layers may be used, or a single layer having both an electron injection function and an electron transport function may be used.
In addition, when a plurality of electron injecting and transporting layers are formed, when the first, second,..., M-th (m ≧ 3 integer) electron injecting and transporting layers are formed from the cathode side, One electron injection / transport layer functions as an electron injection layer, and the second,..., M-th electron injection / transport layers function as electron transport layers.

  The constituent material of the electron injection layer is not particularly limited as long as the material can stabilize the injection of electrons into the light emitting layer. In addition to the compounds exemplified in the light emitting material of the light emitting layer described below, Ba, Ca, Li, Cs, Mg, Sr and other alkali metals or alkaline earth metals alone, magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride, lithium fluoride, cesium fluoride and other alkali metals Or alkaline earth metal fluorides, alkali metal alloys such as aluminum lithium alloys, metal oxides such as magnesium oxide, strontium oxide and aluminum oxide, and organic complexes of alkali metals such as sodium polymethyl methacrylate polystyrene sulfonate be able to.

  The constituent material of the electron transport layer is not particularly limited as long as it is a material capable of transporting electrons injected from the cathode into the light emitting layer. For example, bathocuproin (BCP), bathophenanthroline ( And phenanthroline derivatives such as Bpehn), triazole derivatives, oxadiazole derivatives, and aluminum quinolinol complexes such as tris (8-hydroxyquinolinolato) aluminum (Alq3).

Especially, it is preferable that the constituent material of each electron injection transport layer is a bipolar material which can transport a hole and an electron. By using a bipolar material for each electron injecting and transporting layer, deterioration at the interface between the light emitting layer and each electron injecting and transporting layer during driving can be effectively suppressed.
Since the bipolar material is described in the section of the hole injecting and transporting layer, description thereof is omitted here.

  When all of the first, second,..., M-th (m ≧ 3 integer) electron injecting and transporting layers contain bipolar materials, the bipolar materials contained in these layers may be the same or different. It may be. Further, the first, second,..., Nth (n ≧ 3 integer) hole injecting and transporting layer, the first, second,..., The mth electron injecting and transporting layer, and the light emitting layer are all bipolar materials. Also, the bipolar material contained in these layers may be the same or different.

When the constituent material of the electron injecting and transporting layer adjacent to the cathode is an organic compound (organic compound for electron injecting and transporting layer), the electron injecting and transporting layer is formed at least on the interface with the cathode and on the organic compound for electron injecting and transporting layer. You may have the area | region where the reducing dopant was mixed. The electron injection transport layer has a region where a reducing dopant is mixed with the organic compound for the electron injection transport layer at least at the interface with the cathode, thereby reducing the electron injection barrier from the cathode to the electron injection transport layer, This is because the driving voltage can be reduced.
In the organic EL device, the electron injection process from the cathode to the organic layer, which is basically an insulator, is reduction of the organic compound on the cathode surface, that is, formation of a radical anion state (Phys. Rev. Lett., 14, 229 (1965)). By previously doping a reducing dopant that reduces the organic compound into the electron injection transport layer in contact with the cathode, the energy barrier for electron injection from the cathode can be lowered. In the electron injecting and transporting layer, an organic compound in a state reduced by a reducing dopant (that is, a state in which electrons are received and electrons are injected) exists, so that an electron injection energy barrier is small, and a conventional organic EL device As a result, the drive voltage can be reduced. Furthermore, a stable metal such as Al that is generally used as a wiring material can be used for the cathode.
Further, when the constituent material of the electron injection / transport layer not adjacent to the cathode is an organic compound for an electron injection / transport layer, the electron injection / transport layer is at least on the cathode side, and the reducing compound is added to the organic compound for the electron injection / transport layer. May have a mixed region.

  The reducing dopant is not particularly limited as long as it has a property of reducing the organic compound for the electron injecting and transporting layer, but an electron donating compound is usually used.

As the electron donating compound, a metal (metal simple substance), a metal compound, or an organometallic complex is preferably used. Examples of the metal (metal simple substance), the metal compound, or the organometallic complex include those containing at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and transition metals including rare earth metals. it can. Among them, it is preferable that the material contains at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and transition metals including rare earth metals having a work function of 4.2 eV or less. Examples of such a metal (metal simple substance) include Li, Na, K, Cs, Be, Mg, Ca, Sr, Ba, Y, La, Mg, Sm, Gd, Yb, and W. Examples of the metal compound include metal oxides such as Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O, MgO, and CaO, LiF, NaF, KF, RbF, CsF, and MgF _2. , CaF ₂ , SrF ₂ , BaF ₂ , LiCl, NaCl, KCl, RbCl, CsCl, MgCl ₂ , CaCl ₂ , SrCl ₂ , BaCl _{2 and} other metal salts. Examples of the organometallic complex include organometallic compounds containing W, 8-hydroxyquinolinolatolithium (Liq), and the like. Of these, Cs, Li, and Liq are preferably used. This is because good electron injection characteristics can be obtained by doping these into the organic compound for the electron injection transport layer.

When the electron injecting and transporting layer has a region in which the reducing dopant is mixed with the organic compound for the electron injecting and transporting layer, the electron injecting and transporting layer only needs to have the above region at least at the interface with the cathode. The electron injecting and transporting layer may be uniformly doped with a reducing dopant, and the reducing dopant is doped so that the content of the reducing dopant continuously increases from the light emitting layer side to the cathode side. Alternatively, the reducing dopant may be locally doped only in the interface of the electron injecting and transporting layer with the cathode.
The same applies when the electron injecting and transporting layer not adjacent to the cathode has the above-described region.

  The reducing dopant concentration in the electron injecting and transporting layer is not particularly limited, but is preferably about 0.1 to 99% by weight. This is because if the reducing dopant concentration is less than the above range, the concentration of the organic compound for the electron injecting and transporting layer reduced by the reducing dopant may be too low to obtain a sufficient doping effect. Further, when the reducing dopant concentration exceeds the above range, the reducing dopant concentration in the electron injecting and transporting layer far exceeds the organic compound concentration for the electron injecting and transporting layer, and the organic for the electron injecting and transporting layer reduced by the reducing dopant. This is because, since the concentration of the compound is extremely lowered, a sufficient doping effect may not be obtained in the same manner.

  The number of electron injecting and transporting layers in this embodiment is one or more, and is not particularly limited as long as electrons can be smoothly transported between the cathode and the light emitting layer, but is three or more. It is particularly preferable that there are three layers.

  As a method for forming the electron injecting and transporting layer, for example, a dry method such as a vacuum deposition method or a sputtering method, or a printing method, an ink jet method, a spin coating method, a casting method, a dip coating method, a bar coating method, or a blade coating method. And wet methods such as a roll coating method, a gravure coating method, a flexographic printing method, and a spray coating method.

Among them, as a method for forming an electron injecting and transporting layer doped with a reducing dopant, a method of co-evaporating the organic compound for electron injecting and transporting layer and a reducing dopant is preferably used.
When a thin film can be formed by application from a solution, a spin coating method, a dip coating method, or the like can be used as a method for forming an electron injecting and transporting layer doped with a reducing dopant. In this case, the organic compound for electron injecting and transporting layer and the reducing dopant may be dispersed in an inert polymer.

  In addition, as a method of mixing the reducing dopant with the organic compound for the electron injection transport layer so that the content of the reducing dopant continuously increases from the light emitting layer side to the cathode side, for example, the above electron injection A method of continuously changing the deposition rate of the organic compound for the transport layer and the reducing dopant can be used.

  The thickness of the electron injection / transport layer is not particularly limited as long as the electron injection function is sufficiently exerted. In addition, the thickness of the electron injecting and transporting layer is not particularly limited as long as the electron injecting function is sufficiently exerted.

  The thickness of the electron injecting and transporting layer doped with the reducing dopant is not particularly limited, but is preferably in the range of 0.1 nm to 300 nm, more preferably in the range of 0.5 nm to 200 nm. Is within. If the thickness is less than the above range, the effect of doping may not be sufficiently obtained due to the small amount of the organic compound for the electron injecting and transporting layer reduced by the reducing dopant existing in the vicinity of the cathode interface. is there. Further, if the thickness exceeds the above range, the film thickness of the entire electron injecting and transporting layer is too thick, which may increase the driving voltage.

4). Light emitting layer The light emitting layer used in the present invention has a function of emitting light by providing a recombination field between electrons and holes. Examples of the constituent material of the light emitting layer include a dye material, a metal complex material, and a polymer material.

  Examples of dye-based materials include cyclopentadiene derivatives, tetraphenylbutadiene derivatives, triphenylamine derivatives, oxadiazole derivatives, pyrazoloquinoline derivatives, distyrylbenzene derivatives, distyrylarylene derivatives, silole derivatives, thiophene ring compounds, pyridine Examples thereof include a ring compound, a perinone derivative, a perylene derivative, an oligothiophene derivative, a trifumanylamine derivative, a coumarin derivative, an oxadiazole dimer, and a pyrazoline dimer.

  Examples of metal complex materials include aluminum quinolinol complex, benzoquinolinol beryllium complex, benzoxazole zinc complex, benzothiazole zinc complex, azomethylzinc complex, porphyrin zinc complex, europium complex, iridium metal complex, platinum metal complex, etc. Al, Zn, Be, Ir, Pt, etc., or rare earth metals such as Tb, Eu, Dy, etc., and the ligand has an oxadiazole, thiadiazole, phenylpyridine, phenylbenzimidazole, quinoline structure, etc. A metal complex etc. can be mentioned. Specifically, tris (8-hydroxyquinolinolato) aluminum (Alq3) can be used.

  Examples of the polymer material include polyparaphenylene vinylene derivatives, polythiophene derivatives, polyparaphenylene derivatives, polysilane derivatives, polyacetylene derivatives, polyvinylcarbazole, polyfluorenone derivatives, polyfluorene derivatives, polyquinoxaline derivatives, polydialkylfluorene derivatives, and Examples thereof include copolymers thereof. Moreover, what polymerized said pigment-type material and metal complex-type material is also mentioned.

  Further, the constituent material of the light emitting layer may be a bipolar material. This is because by using the bipolar material for the light emitting layer, it is possible to effectively suppress deterioration at the interfaces of the hole injecting and transporting layer, the light emitting layer, and the electron injecting and transporting layer during driving.

The bipolar material used for the light emitting layer may itself be a light emitting material that emits fluorescence or phosphorescence, or may be a host material doped with a light emitting dopant described later.
Since the bipolar material is described in the section of the hole injecting and transporting layer, description thereof is omitted here.

  In addition, a light emitting dopant that emits fluorescence or phosphorescence may be added to the light emitting layer for the purpose of improving the light emission efficiency and changing the light emission wavelength. That is, the light-emitting layer may contain a host material such as the above-described dye-based material, metal complex-based material, polymer-based material, or bipolar material, and a light-emitting dopant.

  Examples of the luminescent dopant include perylene derivatives, coumarin derivatives, rubrene derivatives, quinacridone derivatives, squalium derivatives, porphyrin derivatives, styryl dyes, tetracene derivatives, pyrazoline derivatives, decacyclene, phenoxazone, quinoxaline derivatives, carbazole derivatives, fluorene derivatives, iridium (Ir ) Compounds, platinum compounds, gold compounds, osmium compounds, ruthenium (Ru) compounds, rhenium (Re) compounds, and the like. More specifically, 2,5,8,11-tetra-tert-butylperylene (2,5,8,11-Tetra-tert-butylperylene) (perylene derivative), 2,3,6,7-tetrahydro- 1,1,7,7, -Tetramethyl-1H, 5H, 11H-10- (2-benzothiazolyl) quinolidino- [9,9a, 1gh] coumarin (C545t) (2,3,6,7-Tetrahydro-1 , 1,7,7, -tetramethyl-1H, 5H, 11H-10- (2-benzothiazolyl) quinolizino- [9,9a, 1gh] coumarin (C545t)) (coumarin derivative), (5,6,11,12 ) -Tetraphenylnaphthacene ((5,6,11,12) -Tetraphenylnaphthacene) (rubrene derivative) and Tris (2-phenylpyridine) iridium (III) (Ir) (ppy) 3), Tris (1-phenylisoquinoline) iridium (III); Ir (piq) 3), bis (3,5-difluoro-2- (2-pyridyl) ) Phenyl- (2-carboxypyridyl) iridium (III) (Bis (3,5-difluoro-2- (2-pyridyl) phenyl- (2-carboxypyridyl) iridium (III); FIrpic)) Compound).

When the light emitting layer contains a light-emitting dopant and a host material, when the electron affinity of the host material Ea _h, the electron affinity of the light emitting dopant was Ea _d, an Ea h _{<Ea d,} and the ionization potential of the host material the Ip _h, when the ionization potential of the light-emitting dopant was Ip _d, it is preferable that Ip h> Ip _d. This is because, when the electron affinity and ionization potential of the host material and the luminescent dopant satisfy the above relationship, holes and electrons are trapped by the luminescent dopant, so that the luminous efficiency can be improved.

  Here, the ionization potential and the electron affinity in a single molecule of the host material and the light emitting dopant constituting the light emitting layer are obtained as follows. The ionization potential is obtained by UPS (ultraviolet photoelectron spectroscopy) (for example, measuring instrument name “AC-2” manufactured by Riken Keiki Co., Ltd.). On the other hand, as a method for measuring electron affinity, first, HOMO energy is obtained by UPS (ultraviolet photoelectron spectroscopy) (for example, “AC-2” manufactured by Riken Keiki Co., Ltd.), and then an energy gap measurement value by light absorption and the above HOMO energy. The method of calculating from is adopted.

Moreover, when a light emitting layer contains a host material and a light emitting dopant, it is preferable that there exists distribution in the density | concentration of the light emitting dopant in a light emitting layer. This is because traps by hole or electron light-emitting dopants can be controlled, and a highly efficient device can be obtained.
In the present invention, since a blocking layer for preventing holes and electrons injected into the light emitting layer from penetrating to the counter electrode is not provided, the organic EL element having a conventional blocking layer is formed in the same manner as the organic light emitting device. It is difficult to balance injected holes and electrons.
Therefore, as a result of various studies by the present inventors, it has been found that the luminous efficiency is improved by giving a distribution to the concentration of the luminescent dopant in the luminescent layer. For example, when the luminescent dopant is more likely to transport holes than electrons, the hole injection tends to be excessive, so the concentration of the luminescent dopant in the light emitting layer is directed from the cathode side to the anode side. The light emission efficiency is improved by providing the concentration gradient so as to increase. This is because by increasing the concentration of the luminescent dopant on the anode side, more holes injected from the anode into the hole injecting and transporting layer and transported to the luminescent layer are trapped by the luminescent dopant in the luminescent layer. It is thought that this is because it is trapped by more light-emitting dopant on the side to prevent penetration into the cathode. Also, for example, when the luminescent dopant is more likely to transport electrons than holes, the electron injection tends to be excessive, so the concentration of the luminescent dopant in the light emitting layer is directed from the anode side to the cathode side. The light emission efficiency is improved by providing the concentration gradient so as to increase. This is because by increasing the concentration of the luminescent dopant on the cathode side, more electrons injected from the cathode into the electropositive injection transport layer and transported to the luminescent layer are trapped by the luminescent dopant in the luminescent layer. It is thought that this is because it is trapped by more light-emitting dopant and penetrates to the anode.

  As the concentration distribution of the light emitting dopant in the light emitting layer, it is only necessary to have a distribution in the light emitting dopant concentration, for example, the light emitting dopant concentration may have a concentration gradient that continuously changes in the thickness direction of the light emitting layer, A region having a relatively high light emitting dopant concentration and a region having a relatively low concentration may be mixed.

  When the luminescent dopant concentration has a concentration gradient that continuously changes in the thickness direction of the luminescent layer, the luminescent dopant concentration may be high on the hole injection transport layer side, or high on the electron injection transport layer side, It is appropriately selected so that the injection balance of holes and electrons can be maintained. For example, when the injection of holes is excessive, the luminescent dopant concentration is preferably high on the hole injection transport layer side so that the injected holes can be trapped on the anode side. For example, when the injection of electrons is excessive, it is preferable that the concentration of the luminescent dopant is high on the electron injection transport layer side so that the injected electrons can be trapped on the cathode side.

  Further, when a region having a relatively high emission dopant concentration and a region having a relatively low emission are mixed, for example, a region having a relatively high emission dopant concentration is provided on the hole injection transport layer side, and electron injection transport is performed. A region having a relatively low emission dopant concentration may be provided on the layer side, a region having a relatively low emission dopant concentration on the hole injection transport layer side, and a emission dopant concentration on the electron injection transport layer side. A relatively high region may be provided, the luminescent dopant concentration may be periodically changed in the thickness direction of the luminescent layer, and is selected as appropriate so that the injection balance of holes and electrons can be maintained. For example, when hole injection is excessive, a region with a relatively high emission dopant concentration is provided on the hole injection transport layer side so that the injected holes can be trapped on the anode side, and electron injection It is preferable that a region having a relatively low emission dopant concentration is provided on the transport layer side. In addition, for example, when the injection of electrons is excessive, a region having a relatively low emission dopant concentration is provided on the hole injection transport layer side so that the injected electrons can be trapped on the cathode side. It is preferable that a region having a relatively high emission dopant concentration is provided on the layer side.

  Furthermore, the light emitting layer may contain a host material and two or more kinds of light emitting dopants. For example, when the difference in excitation energy between the host material and the light-emitting dopant is relatively large, energy transfer is caused smoothly by further including a light-emitting dopant having an excitation energy between the excitation energy of the host material and the light-emitting dopant. And the luminous efficiency can be improved. In addition, for example, by containing a light emitting dopant that easily transports holes rather than electrons and a light emitting dopant that easily transports electrons rather than holes, it is possible to balance the holes and electrons injected into the light emitting layer. And luminous efficiency can be improved.

  In addition, when a light emitting layer contains a 2 or more types of light emission dopant, each light emission dopant may light-emit each, and only 1 type may light-emit. For example, when the light emitting layer contains a first light emitting dopant and a second light emitting dopant having an excitation energy smaller than the excitation energy of the host material and larger than the excitation energy of the first light emitting dopant, In any case, including a third light-emitting dopant that easily transports holes rather than electrons and a fourth light-emitting dopant that easily transports electrons than holes, the magnitude and distribution of excitation energy of the light-emitting dopant Depending on the state and concentration, light emission of one kind or each light emitting dopant can be obtained.

  In the case where the light emitting layer contains two or more kinds of light emitting dopants, from the viewpoint of improving the light emission efficiency, the light emitting layer includes a first light emitting dopant that is smaller than the excitation energy of the host material and is lower than the excitation energy of the first light emitting dopant. A second light-emitting dopant having a large excitation energy, or a third light-emitting dopant that easily transports holes rather than electrons, and a fourth light-emitting dopant that easily transports electrons rather than holes. can do.

  When the light-emitting layer contains a first light-emitting dopant and a second light-emitting dopant having an excitation energy smaller than the excitation energy of the host material and larger than the excitation energy of the first light-emitting dopant, As a luminescent dopant, it can select from the above-mentioned luminescent dopant suitably, and can use it. For example, when Alq3 that emits green light is used as the host material and DCM that emits red light is used as the first light emitting dopant, rubrene that emits yellow light is used as the second light emitting dopant, whereby Alq3 (host material) → rubrene (second light emitting). Energy transfer can be caused smoothly in the order of (dopant) → DCM (first emission dopant).

  Moreover, when a light emitting layer contains the 3rd light emission dopant which is easy to transport a hole rather than an electron, and the 4th light emission dopant which is easy to transport an electron rather than a hole, as a 3rd light emission dopant and a 4th light emission dopant Can be appropriately selected from the above-mentioned light emitting dopants according to the combination of the constituent materials of the hole injecting and transporting layer and the electron injecting and transporting layer and the host material of the light emitting layer. For example, when TBADN is used for the hole injecting and transporting layer and the electron injecting and transporting layer, CBP is used as the host material of the light emitting layer, and rubrene is used as the light emitting dopant, rubrene becomes a light emitting dopant that facilitates transporting holes rather than electrons. For example, when TBADN is used for the hole injecting and transporting layer and the electron injecting and transporting layer, CBP is used as the host material of the light emitting layer, and anthracenediamine is used as the light emitting dopant, the anthracene diamine is easier to transport electrons than holes. It becomes.

  Whether the light-emitting layer comprising the host material and the light-emitting dopant can transport holes more easily than electrons or whether it can transport electrons more easily than holes depends on whether the host material and the single light-emitting dopant are used. This can be confirmed by evaluating the angle dependence of the radiation pattern of the emission spectrum of an organic EL device having a light emitting layer containing. That is, it can be confirmed from the wavelength of the emission spectrum, the refractive index of the material, the optical path length until light is extracted from the light emitting layer by the organic EL element, and the angle dependency of the radiation pattern.

  When the light-emitting layer contains a third light-emitting dopant that easily transports holes rather than electrons and a fourth light-emitting dopant that easily transports electrons rather than holes, the third light-emitting dopant and the fourth light emission in the light-emitting layer The dopant concentration preferably has a concentration gradient that continuously changes in the thickness direction of the light emitting layer. Moreover, it is also preferable that the light emitting layer has a relatively high region and a relatively low region, respectively, of the third light emitting dopant and the fourth light emitting dopant. This is because the holes and electrons injected into the light emitting layer can be balanced.

  When the concentration of the third light emitting dopant and the fourth light emitting dopant in the light emitting layer has a concentration gradient, the concentration of the third light emitting dopant is high on the hole injecting and transporting layer side, and the concentration of the fourth light emitting dopant is on the electron injecting and transporting layer side. The concentration of the third light emitting dopant may be high on the electron injecting and transporting layer side, and the concentration of the fourth light emitting dopant may be high on the hole injecting and transporting layer side. The dopant concentration may be high on the hole injection / transport layer side, and the third light emission dopant concentration and the fourth light emission dopant concentration may be high on the electron injection / transport layer side.

  Among these, the concentration of the third light-emitting dopant that easily transports holes rather than electrons is higher on the hole injection / transport layer side, and the concentration of the fourth light-emitting dopant that easily transports electrons than holes is higher on the electron injection / transport layer side. And high. In addition, the concentration of the third light-emitting dopant that easily transports holes rather than electrons is higher on the electron injection / transport layer side, and the concentration of the fourth light-emitting dopant that easily transports electrons than holes is higher on the hole injection / transport layer side. It is also preferable. This is because it is possible to effectively balance the injection of holes and electrons.

  In addition, when the light emitting layer includes a region having a relatively high concentration and a region having a relatively low concentration of the third light emitting dopant and the fourth light emitting dopant, a region having a relatively high third light emitting dopant concentration is present. A region having a relatively low third emission dopant concentration may be provided on the electron injection / transport layer side, and a region having a relatively low third emission dopant concentration may be provided on the hole injection / transport layer side. A region provided on the transport layer side and having a relatively high third light emitting dopant concentration may be provided on the electron injection transport layer side. A region having a relatively high fourth light emitting dopant concentration may be provided on the hole injecting and transporting layer side, and a region having a relatively low fourth light emitting dopant concentration may be provided on the electron injecting and transporting layer side. A region having a relatively low 4-emission dopant concentration may be provided on the hole injection / transport layer side, and a region having a relatively high 4th emission dopant concentration may be provided on the electron injection / transport layer side.

  Among the above, a region having a relatively low third light emission dopant concentration that facilitates transport of holes rather than electrons is provided on the hole injection transport layer side, and a region having a relatively high third light emission dopant concentration is electron injection transport. A region having a relatively high fourth light-emitting dopant concentration that is provided on the layer side and that is easier to transport electrons than holes is provided on the hole injecting and transporting layer side, and has a relatively high fourth light-emitting dopant concentration. It is preferable that the low region is provided on the electron injecting and transporting layer side. In addition, a region having a relatively high third emission dopant concentration that facilitates transport of holes rather than electrons is provided on the hole injection transport layer side, and a region having a relatively low third emission dopant concentration is provided on the electron injection transport layer side. A region having a relatively low fourth light emitting dopant concentration that is provided on the hole injecting and transporting layer side, and that has a relatively high fourth light emitting dopant concentration. Is preferably provided on the electron injecting and transporting layer side. This is because it is possible to effectively balance the injection of holes and electrons.

  The thickness of the light emitting layer is not particularly limited as long as it provides a function of emitting light by providing a recombination field between electrons and holes, and is set to, for example, about 1 nm to 200 nm. be able to. Among them, in order to increase the luminous efficiency by increasing the injection balance of holes and electrons by increasing the thickness of the light emitting layer, the thickness of the light emitting layer is preferably in the range of 10 nm to 100 nm, more preferably. Is in the range of 30 nm to 80 nm.

  As a method for forming the light emitting layer, for example, a dry method such as a vacuum deposition method or a sputtering method, or a printing method, an ink jet method, a spin coating method, a casting method, a dipping method, a bar coating method, a blade coating method, or a roll coating method. And wet methods such as a gravure coating method, a flexographic printing method, and a spray coating method.

  Further, when the light emitting layer is patterned, it may be applied separately by a masking method for pixels having different light emission colors, or a partition may be formed between the light emitting layers. As a constituent material of the partition wall, a photocurable resin such as a photosensitive polyimide resin or an acrylic resin, a thermosetting resin, an inorganic material, or the like can be used. Furthermore, you may perform the process which changes the surface energy (wetting property) of a partition.

Furthermore, as a method for forming a light emitting layer containing a host material and a light emitting dopant, a method of co-evaporating the host material and the light emitting dopant is preferably used.
Note that when a thin film can be formed by application from a solution, a spin coating method, a dip coating method, or the like can be used as a method for forming a light-emitting layer containing a host material and a light-emitting dopant. In this case, the host material and the light emitting dopant may be dispersed in an inert polymer.

  In addition, in order to distribute the light emitting dopant concentration in the light emitting layer, for example, a method of changing the deposition rate of the host material and the light emitting dopant continuously or periodically can be used.

5. Anode The anode used in the present invention may be transparent or opaque, but it needs to be a transparent electrode when light is extracted from the anode side.

  For the anode, a conductive material having a large work function is preferably used so that holes can be easily injected. The anode preferably has as low resistance as possible. Generally, a metal material is used, but an organic substance or an inorganic compound may be used. Specific examples include tin oxide, indium tin oxide (ITO), and indium zinc oxide (IZO).

The anode can be formed using a general electrode forming method, and examples thereof include a sputtering method, a vacuum deposition method, and an ion plating method.
The thickness of the anode is appropriately selected depending on the target resistance value, visible light transmittance, and type of conductive material.

6). Cathode The cathode used in the present invention may be transparent or opaque, but needs to be a transparent electrode when light is extracted from the cathode side.

For the cathode, it is preferable to use a conductive material having a small work function so that electrons can be easily injected. Moreover, it is preferable that the cathode has as low resistance as possible. Generally, a metal material is used, but an organic substance or an inorganic compound may be used. Specifically, Al, Cs, Er, etc. as a simple substance, MgAg, AlLi, AlLi, AlMg, CsTe, etc. as an alloy, Ca / Al, Mg / Al, Li / Al, Cs / Al, Cs ₂ O / Al, LiF / Al, include _ErF 3 / Al or the like.

The cathode can be formed using a general electrode forming method, and examples thereof include a sputtering method, a vacuum deposition method, and an ion plating method.
Further, the thickness of the cathode is appropriately selected depending on the target resistance value, visible light transmittance, and type of conductive material.

7). Substrate The substrate in the present invention supports the above anode, hole injection / transport layer, light emitting layer, electron injection / transport layer, cathode, and the like. When the anode or the cathode has a predetermined strength, the anode or the cathode may also serve as the substrate, but usually the anode or the cathode is formed on the substrate having the predetermined strength. In general, when an organic EL device is produced, since the organic EL device can be stably produced by laminating from the anode side, the anode, hole injection transport is usually provided on the substrate. A layer, a light emitting layer, an electron injecting and transporting layer, and a cathode are laminated in this order.

  The substrate may be transparent or opaque, but needs to be a transparent substrate when light is extracted from the substrate side. Examples of the transparent substrate that can be used include glass substrates such as soda lime glass, alkali glass, lead alkali glass, borosilicate glass, aluminosilicate glass, and silica glass, and resin substrates that can be formed into a film.

II. Second Embodiment A second embodiment of the organic EL device of the present invention includes an anode, a light emitting layer formed on the anode, three or more electron injecting and transporting layers formed on the light emitting layer, and An organic EL device having a cathode formed on an electron injection / transport layer, wherein the three or more electron injection / transport layers are arranged in order from the cathode side in the order of the first, second,. ≧ 3), the ionization potential of the constituent material of the light emitting layer is Ip ₀ , and the ionization potential of the constituent material of the y-th (y = 1 to m) electron injection / transport layer is Ip _{When y} ′, Ip ₀ ≧ Ip _m ′, y = 2 to _m in all cases, Ip _y ′ ≧ Ip _y−1 ′, and the electron affinity of the constituent material of the light emitting layer is Ea ₀ , When the electron affinity of the constituent material of the electron injection / transport layer of _y is Ea _y ′, all of Ea ₀ ≦ Ea _m ′ and y = 2 to _m Ea _y ′ <Ea _y−1 ′.

FIG. 10 is a schematic cross-sectional view showing an example of the organic EL element of the present embodiment, and FIGS. 11 and 12 are schematic views showing examples of band diagrams of the organic EL element shown in FIG. In FIG. 10, the case where m = 3 is considered as an example.
In this embodiment, as illustrated in FIG. 10, the organic EL element 1 includes an anode 3, a first hole injection transport layer 4, a light emitting layer 7, and a third electron injection on a substrate 2. A transport layer 11, a second electron injection / transport layer 10, a first electron injection / transport layer 8, and a cathode 9 are sequentially stacked.
The ionization potential of the constituent material of the light-emitting layer 7 is Ip ₀ , the ionization potential of the constituent material of the first electron injection / transport layer 8 is Ip ₁ ′, and the ionization potential of the constituent material of the second electron injection / transport layer 10 is Ip ₂ ′. When the ionization potential of the constituent material of the n-th electron injecting and transporting layer 11 is Ip ₃ ′, as shown in FIG. 11, Ip ₀ > Ip ₃ ′> Ip ₂ ′> Ip ₁ ′ Alternatively, as illustrated in FIG. 12, Ip ₀ = Ip ₃ ′ = Ip ₂ ′ = Ip ₁ ′ may be satisfied.
Further, the electron affinity of the constituent material of the light emitting layer 7 is Ea ₀ , the electron affinity of the constituent material of the first electron injection / transport layer 8 is Ea ₁ ′, and the electron affinity of the constituent material of the second electron injection / transport layer 10 is Ea. ₂ ′, when the electron affinity of the constituent material of the n-th electron injecting and transporting layer 11 is Ea ₃ ′, Ea ₀ <Ea ₃ ′ <Ea ₂ ′ <Ea ₁ ′, as illustrated in FIG. Alternatively, as exemplified in FIG. 12, Ea ₀ = Ea ₃ ′ <Ea ₂ ′ <Ea ₁ ′ may be satisfied.

According to the present invention, three or more electron injecting and transporting layers are provided between the cathode and the light emitting layer so that Ea _y ′ <Ea _y−1 ′ for all of Ea ₀ ≦ Ea _m ′ and y = 2 to _m. Thus, electrons can be smoothly transported from the cathode to the light emitting layer through each electron injecting and transporting layer. Therefore, for example, even when the band gap energy of the constituent material of the light emitting layer is relatively large and the difference between the work function of the cathode and the electron affinity of the constituent material of the light emitting layer is relatively large, The transport of electrons can be facilitated.
_{Also, Ip 0 ≧ Ip m ',} y = for all _{2~m Ip y' ≧ Ip y-} 1 3 -layer or more electron injecting and transporting layer between the cathode and the light-emitting layer so as to 'is formed Therefore, deterioration at the interface between the electron injecting and transporting layer and the light emitting layer can be suppressed.

  In the organic EL device of this embodiment, it is preferable that one or more hole injection / transport layers are formed between the light emitting layer and the anode.

For example, as shown in FIG. 10, it is preferable that a first hole injection transport layer 4 is formed between the anode 2 and the light emitting layer 7.
In this case, when the electron affinity of the _first hole injecting and transporting layer 4 is Ea ₁ , it is preferable that Ea ₀ ≦ Ea ₁ as illustrated in FIG. 11 and FIG. Further, when the ionization potential of the first hole injection transport layer 4 and Ip _1, as illustrated in FIGS. 11 and 12, it is preferable that Ip ₀ ≧ Ip _1.

Usually, in such an organic EL element, Ea ₀ ≦ Ea ₁ and Ip ₀ ≧ Ip _m ′, y = 2 to _m , Ip _y ′ ≧ Ip _y−1 ′. It is difficult to efficiently generate charge recombination to generate an excited state and to deactivate radiation, resulting in a decrease in light emission efficiency, hole and electron penetration to the counter electrode, and electrons to the hole injection transport layer. It is assumed that the lifetime characteristics deteriorate due to injection or injection of holes into the electron injection transport layer. However, in the present invention, the electron affinity of the constituent material of the first hole injection transport layer and the light emitting layer is Ea ₀ ≦ Ea ₁ and the ionization potential of the constituent material of each electron injection transport layer and the light emitting layer is , Ip ₀ ≧ Ip _m ′ and y = 2 to _m , Ip _y ′ ≧ Ip _y−1 ′, so that holes and electrons penetrate through to the counter electrode, but there are holes between the anode and the cathode and Since electrons are transported smoothly, it is possible to suppress deterioration at the interfaces of the electron injection / transport layers, the light emitting layer, and the first hole injection / transport layer during driving. In addition, since holes and electrons are transported smoothly, holes and electrons are recombined throughout the light emitting layer, so that the recombination efficiency of holes and electrons is not significantly reduced. Therefore, the electron affinity of the constituent material of the first hole injection transport layer and the light emitting layer is Ea ₀ ≦ Ea ₁ and the ionization potential of the constituent material of each electron injection transport layer and the light emitting layer is Ip ₀ ≧ Ip _m ′. , Y = 2 to m, and appropriately select materials used for each of the electron injecting and transporting layer, the first hole injecting and transporting layer, and the light emitting layer so that Ip _y '≧ Ip _y−1 '. As a result, it is possible to increase the efficiency and obtain a significantly stable life characteristic.

  In addition, by forming the first hole injecting and transporting layer on the anode side of the light emitting layer so that the ionization potentials of the light emitting layer and the first hole injecting and transporting layer have the above-described relationship, Since it becomes easy to inject | pour, the recombination efficiency of the hole and electron in a light emitting layer becomes high.

FIG. 13 is a schematic cross-sectional view showing another example of the organic EL element of the present embodiment, and FIGS. 14 and 15 are schematic views showing examples of band diagrams of the organic EL element shown in FIG.
In this embodiment, as illustrated in FIG. 13, it is preferable that a second hole injection / transport layer 5 is formed between the light emitting layer 7 and the first hole injection / transport layer 4.
In this case, the electron affinity of the constituent material of the light emitting layer 7 is Ea ₀ , the electron affinity of the constituent material of the first hole injection transport layer 4 is Ea ₁ , and the electron affinity of the constituent material of the second hole injection transport layer 5. the when the Ea _2, as illustrated in FIGS. 14 and 15, is preferably _{Ea 0 ≦ Ea 2 ≦ Ea 1} . The ionization potential of the constituent material of the light emitting layer 7 is Ip ₀ , the ionization potential of the constituent material of the first hole injection transport layer 4 is Ip ₁ , and the ionization potential of the constituent material of the second hole injection transport layer 5 is When Ip ₂ is satisfied, it is preferable that Ip ₀ > Ip ₂ > Ip ₁ as illustrated in FIG.

  Note that the configuration not described above and the relationship between the ionization potential of each constituent material of the hole injecting and transporting layer and the light emitting layer, and the electron affinity are the same as those described with reference to FIGS. Omitted.

In this embodiment, the hole injecting and transporting layer is formed so that the electron affinity of the constituent materials of the first hole injecting and transporting layer, the second hole injecting and transporting layer, and the light emitting layer is Ea ₀ ≦ Ea ₂ ≦ Ea _1. By forming, there is no charge accumulation at the interface between each hole injecting and transporting layer and the light emitting layer during driving, and deterioration can be suppressed. In addition, the hole injection transport layer is formed so that the ionization potentials of the constituent materials of the first hole injection transport layer, the second hole injection transport layer, and the light emitting layer are Ip ₀ > Ip ₂ > Ip _1. Thus, holes can be smoothly transported to the light emitting layer through the plurality of hole injecting and transporting layers. Therefore, a highly efficient and long-life organic EL element can be obtained.

  In addition, about each structure in the organic EL element of this embodiment, since it is the same as that of what was demonstrated by "I. 1st embodiment", description here is abbreviate | omitted.

III. Third Embodiment A third embodiment of the organic EL device of the present invention has a plurality of light emitting units in which three or more hole injection transport layers and a light emitting layer are sequentially laminated between an opposing anode and cathode. An organic EL element in which a charge generation layer is formed between the adjacent light emitting units, and the first, second,..., Nth (n ≧ 3 integer) hole injection in order from the anode side. When the electron affinity of the constituent material of the light emitting layer is Ea ₀ and the electron affinity of the constituent material of the x-th (x = 1 to n) hole injecting and transporting layer is Ea _x , Ea ₀ Ea _x ≦ Ea _x−1 for all of ≦ Ean and x = 2 to _n , and the ionization potential of the constituent material of the light emitting layer is Ip ₀ , and the constituent material of the xth hole injection transport layer is when the ionization potential was Ip _x, is _{Ip x> Ip x-1 Ip} 0 ≧ Ip n, for all x = 2- through n And it is characterized in and.

FIG. 16 is a schematic cross-sectional view showing an example of the organic EL element of this embodiment, and FIG. 17 is a schematic view showing an operation mechanism of the organic EL element shown in FIG.
As illustrated in FIG. 16, the organic EL element 1 includes an anode 3, a light emitting unit 12 a, a charge generating layer 13 a, a light emitting unit 12 b, a charge generating layer 13 b, a light emitting unit 12 c, and a cathode 9 sequentially stacked on the substrate 2. It has been done. That is, light emitting units and charge generation layers are alternately and repeatedly formed between the anode and the cathode. In general, in an organic EL element, holes (h) are injected from the anode side and electrons (e) are injected from the cathode side, and the holes and electrons are recombined in the light emitting unit to generate an excited state and emit light. In the organic EL element, three light emitting units 12a, 12b, and 12c are stacked via the charge generation layers 13a and 13b. As illustrated in FIG. 17, holes (h), Electrons (e) are injected from the cathode 9 side, holes (h) are injected in the direction of the cathode 9 and electrons (e) are injected in the direction of the anode 3 by the charge generation layers 13a and 13b, and the light emitting units 12a, 12b, Recombination of holes and electrons occurs in 12c, and a plurality of light emission occurs between the anode 3 and the cathode 9.

  Further, each of the light emitting units 12a, 12b, and 12c has three or more hole injecting and transporting layers (in FIG. 16, the first hole injecting and transporting layer 4 and the second hole injecting and transporting layer from the anode 3 side). 5, a third hole injecting and transporting layer 6), a light emitting layer 7 and a first electron injecting and transporting layer 8 are sequentially laminated.

  Hole injection means the generation of radical cations by extracting electrons from the valence band of the layer. The electrons extracted from the valence band of the hole injection / transport layer in contact with the cathode side of the charge generation layer are injected into the conduction band of the electron injection / transport layer in contact with the anode side of the charge generation layer. Reused to produce. In the charge generation layer, the radical anion state (electrons) and the radical cation state (holes) move in the anode direction and the cathode direction, respectively, when a voltage is applied, thereby transferring electrons to the light emitting unit in contact with the anode side of the charge generation layer. Then, holes are injected into the light emitting unit in contact with the cathode side of the charge generation layer. That is, when a voltage is applied between the anode and the cathode, holes are injected from the anode side and electrons are injected from the cathode side. At the same time, electrons and holes are generated in the charge generation layer and separated from the charge generation layer. Electrons generated in the charge generation layer are directed toward the anode and injected into the adjacent light emitting unit, and holes generated in the charge generation layer are directed toward the cathode and injected into the adjacent light emitting unit. Subsequently, these electrons and holes recombine in the light emitting unit to generate light.

  Therefore, according to this embodiment, when a voltage is applied between the anode and the cathode, the light emitting units are connected in series and emit light simultaneously, and high current efficiency can be realized.

  In an organic EL element having a structure in which a single light emitting unit is sandwiched between an anode and a cathode (hereinafter referred to as an organic EL element of a single light emitting unit in this section), “electrons (number) measured in an external circuit” The upper limit of the quantum efficiency, which is the ratio of photons (number) / second to / second, was theoretically 1 (= 100%). On the other hand, there is no theoretical limit in the organic EL element of this embodiment. As described above, the hole (h) injection illustrated in FIG. 17 means the extraction of electrons from the valence bands of the light emitting units 12b and 12c, and the cathode 9 of the charge generation layers 13a and 13b. The electrons extracted from the valence bands of the light emitting units 12b and 12c that are in contact with the side are injected into the conductive bands of the light emitting units 12a and 12b that are in contact with the anode 3 side of the charge generation layers 13a and 13b, respectively. Because it is reused to produce Therefore, the quantum efficiency of each light emitting unit stacked via the charge generation layer (in this case, the number of electrons (number) / second that (apparently) passes through each light emitting unit, and the number of photons emitted from each light emitting unit (number ) / Second ratio)) is the quantum efficiency of the organic EL device of the present embodiment, and there is no upper limit.

  Further, the luminance of the organic EL element of the single light emitting unit is substantially proportional to the current density, and a high current density is inevitably necessary to obtain high luminance. On the other hand, since the element lifetime is inversely proportional to the current density, not the driving voltage, high luminance light emission shortens the element lifetime. On the other hand, the organic EL device of this embodiment has a current density of n light emitting units having the same configuration between the anode and the cathode, for example, when it is desired to obtain n times the luminance at a desired current density. N-fold luminance can be realized without increasing the density. N times the luminance can be realized without sacrificing the lifetime.

  Further, in the organic EL element of a single light emitting unit, the power conversion efficiency (W / W) has been lowered due to the increase in driving voltage. On the other hand, in the case of the organic EL device of this embodiment, when n light emitting units are present between the anode and the cathode, the light emission start voltage (turn on voltage) and the like are approximately n times, so that a desired luminance is obtained. However, since the quantum efficiency (current efficiency) is also approximately n times, the power conversion efficiency (W / W) does not change in principle.

  Moreover, according to this embodiment, since there are multiple layers of light emitting units, there is an advantage that the risk of element short-circuiting can be reduced. Since the organic EL element of a single light emitting unit has only one light emitting unit, if an (electrical) short circuit occurs between the anode and the cathode due to the influence of a pinhole or the like existing in the light emitting unit, there is no immediate effect. There is a possibility of becoming a light emitting element. On the other hand, in the case of the organic EL element of this embodiment, since a plurality of light emitting units are laminated between the anode and the cathode, it is a thick film, and the risk of short circuit can be reduced. Furthermore, even if a specific light emitting unit is short-circuited, the other light emitting units can emit light, and the situation of no light emission can be avoided. In particular, in the case of constant current driving, the driving voltage is only reduced by a short-circuited light emitting unit, and a light emitting unit that is not short-circuited can emit light normally.

  Furthermore, for example, when an organic EL element is applied to a display device having a simple matrix structure, the voltage drop due to the wiring resistance and the temperature rise of the substrate are greatly increased as compared with the case of the organic EL element of a single light emitting unit due to the decrease in current density. Can be reduced. Also in this point, the organic EL element of this embodiment is advantageous.

Further, for example, when the organic EL element is applied to a use that uniformly shines a large area, particularly for illumination, the above-described feature works sufficiently advantageously. In the organic EL element of a single light emitting unit, the specific resistance ( ^{−10 −4} Ω · cm) of a transparent electrode material typified by an electrode material, particularly ITO, etc. is the specific resistance of a metal ( ^{−10 −6} Ω · cm). ), The voltage (V) (or electric field E (V / cm)) applied to the light-emitting unit decreases as the distance from the power feeding portion increases. May cause uneven brightness (brightness difference). On the other hand, when obtaining a desired luminance as in the organic EL element of the present embodiment, if the current value can be greatly reduced as compared with the organic EL element of a single light emitting unit, the potential drop can be reduced, resulting in a substantially uniform result. Large area light emission can be obtained.

18A and 18B are schematic views showing examples of band diagrams of light emitting units in the organic EL element shown in FIG.
In this light emitting unit, the ionization potential of the constituent material of the first hole injection transport layer 4 is Ip ₁ , the ionization potential of the constituent material of the second hole injection transport layer 5 is Ip ₂ , and the third Assuming that the ionization potential of the constituent material of the hole injection transport layer 6 is Ip ₃ and the ionization potential of the constituent material of the light emitting layer 7 is Ip ₀ , as illustrated in FIG. 18A, Ip ₁ <Ip ₂ <Ip ₃ <Ip ₀ may be satisfied, and as illustrated in FIG. 18B, Ip ₁ <Ip ₂ <Ip ₃ = Ip ₀ may be satisfied.
Also, the electron affinity of the constituent material of the first hole injection transport layer 4 is Ea ₁ , the electron affinity of the constituent material of the second hole injection transport layer 5 is Ea ₂ , and the third hole injection transport. Assuming that the electron affinity of the constituent material of the layer 6 is Ea ₃ and the electron affinity of the constituent material of the light emitting layer 7 is Ea ₀ , as illustrated in FIG. 18A, Ea ₀ <Ea ₃ <Ea ₂ <Ea ₁ As illustrated in FIG. 18B, Ea ₀ = Ea ₃ = Ea ₂ = Ea ₁ may be satisfied.

According to the present invention, three or more hole injecting and transporting layers are formed between the anode and the light emitting layer so that Ip _x > Ip _x-1 for all of Ip ₀ ≧ Ip _n and x = 2 to _n . As a result, holes can be smoothly transported from the anode to the light emitting layer through each hole injecting and transporting layer. Therefore, for example, even when the band gap energy of the constituent material of the light emitting layer is relatively large and the difference between the work function of the anode and the ionization potential Ip ₀ of the constituent material of the light emitting layer is relatively large, the light emission Transport of holes to the layer can be facilitated.
Further, three or more hole injecting and transporting layers are formed between the anode and the light emitting layer so that Ea _x ≦ Ea _x−1 for all of Ea ₀ ≦ Ean and x = 2 to _n . Thus, deterioration at the interface between the hole injecting and transporting layer and the light emitting layer can be suppressed.

As the organic EL device of this embodiment, the light emitting unit preferably has one or more electron injecting and transporting layers between the light emitting layer and the cathode or the charge generation layer.
Hereinafter, as an example of the organic EL element of the present embodiment, one having an electron injecting and transporting layer will be described with reference to the drawings.

For example, as shown in FIG. 16, the first electron injection / transport layer 8 is preferably formed between the light emitting layer 7 and the cathode 9 or the charge generation layers 13a and 13b.
In this case, when the ionization potential of the first electron injecting and transporting layer 8 is Ip ₁ ′, it is preferable that Ip ₁ ′ ≦ Ip ₀ as illustrated in FIG. Further, 'when a, Ea ₀ ≦ Ea ₁ as illustrated in FIG. 18' the electron affinity of the first electron injection transport layer 8 Ea ₁ is preferably.

In the above case, the ionization potential of the constituent material for the electron injecting and transporting layer and light emitting layer is Ip ₀ ≧ Ip ₁ ', and an electron affinity of the constituent material of the hole injection transport layer and the luminescent layer is Ea ₀ ≦ Ea _n , X = 2 to n, Ea _x ≦ Ea _x−1 . Therefore, as in the case of the first embodiment, each of the hole injecting and transporting layer, the light emitting layer, and the electron injecting and transporting layer during driving It is possible to suppress deterioration at the interface. Therefore, it is possible to obtain a highly efficient and long-life organic EL element.

  The relationship between the ionization potential and the electron affinity of the hole injecting and transporting layer, the light emitting layer, and the electron injecting and transporting layer is the same as that described in the section of “I. First embodiment”, and the description is omitted here. .

  In the present embodiment, there are a plurality of light emitting positions that are separately separated. Conventionally, in an organic EL element (multi-photon emission) in which a plurality of light emitting units are stacked via a charge generation layer, the interference effect becomes more prominent as the element thickness increases, and the color tone (that is, the emission spectrum shape) increases. There was a problem that it changed greatly. Specifically, the shape of the emission spectrum changes, the emission at the original emission peak position is offset by a significant interference effect, resulting in a significant reduction in emission efficiency and the angular dependence of the emission pattern of emission. Will occur. In general, by controlling the optical film thickness from the light emitting position to the reflective electrode, it is possible to deal with a problem due to the interference effect.

However, even if the front luminance can be improved by controlling the optical film thickness, the oblique luminance tends to decrease due to the interference effect because the optical path length changes.
In contrast, in the present embodiment, holes and electrons are not recombined predominantly at the interface between the light emitting layer and the blocking layer as in the prior art, but holes and electrons are recombined throughout the light emitting layer. Therefore, the viewing angle dependence of the emission color can be improved as compared with the conventional multi-photon emission.

  Hereinafter, each structure in the organic EL element of this embodiment is demonstrated. Note that the anode, the cathode, and the substrate are the same as those described in the first embodiment, and a description thereof is omitted here.

1. Charge generation layer In this embodiment, the charge generation layer is an electrically insulating layer having a predetermined specific resistance. When voltage is applied, holes are injected toward the cathode of the device, and electrons are injected toward the anode. A layer that plays the role of

The charge generation layer preferably has a specific resistance of 1.0 × 10 ² Ω · cm or more, and more preferably 1.0 × 10 ⁵ Ω · cm or more.

  The charge generation layer preferably has a visible light transmittance of 50% or more. When the visible light transmittance is less than the above range, the generated light is absorbed when passing through the charge generation layer, and a desired quantum efficiency (current efficiency) can be obtained even if it has a plurality of light emitting units. This is because it may disappear.

  The material used for the charge generation layer is not particularly limited as long as it has the above specific resistance, and any of inorganic materials and organic materials can be used.

  In particular, the charge generation layer preferably contains two different types of substances that can form a charge transfer complex composed of a radical cation and a radical anion by an oxidation-reduction reaction. A charge transfer complex consisting of a radical cation and a radical anion is formed by oxidation-reduction reaction between these two substances, and the radical cation state (hole) and the radical anion state (electron) in the charge transfer complex are applied with voltage. Sometimes moving in the cathode direction or the anode direction respectively allows holes to be injected into the light emitting unit in contact with the cathode side of the charge generation layer and electrons to be injected into the light emitting unit in contact with the anode side of the charge generation layer.

  The charge generation layer may be formed by laminating layers composed of two different kinds of substances, or may be a single layer containing two different kinds of substances.

  The two types of substances to be used in the charge generation layer include (a) an organic compound having a hole transporting property, that is, an electron donating property, and (b) an oxidation-reduction reaction with the organic compound (a). It is preferably an inorganic substance or an organic substance capable of forming a charge transfer complex. In addition, it is preferable that a charge transfer complex is formed by a redox reaction between the component (a) and the component (b).

  Whether or not the two kinds of substances constituting the charge generation layer can form a charge transfer complex by an oxidation-reduction reaction can be confirmed by spectroscopic analysis means. Specifically, each of the two types of substances does not exhibit an absorption spectrum peak in the near-infrared region with a wavelength of 800 nm to 2000 nm, but a mixed film of two types of substances has a near-infrared wavelength of 800 nm to 2000 nm. If a peak in the absorption spectrum is shown in the region, formation of a charge transfer complex by oxidation-reduction reaction between the two types of substances as evidence (or evidence) clearly suggesting electron transfer between the two types of substances. Can be confirmed.

  As an organic compound of (a) component, an arylamine compound can be mentioned, for example. The arylamine compound preferably has a structure represented by the following formula (1).

Here, in the above formula, Ar ₁ , Ar ₂ , and Ar ₃ each independently represents an aromatic hydrocarbon group that may have a substituent.

  As such an arylamine compound, for example, an arylamine compound described in JP-A No. 2003-272860 can be used.

In addition, examples of the component (b) substance include V ₂ O ₅ , Re ₂ O ₇ , 4F-TCNQ, and the like. Furthermore, the material used as the component (b) may be a material used for the hole injecting and transporting layer.

  The charge generation layer is described in detail in JP-A No. 2003-272860.

2. Light-Emitting Unit A plurality of light-emitting units in the present embodiment are formed between an anode and a cathode facing each other, and three or more hole injection transport layers and a light-emitting layer are sequentially laminated. Further, in the hole injection transport layer and the light emitting layer constituting the light emitting unit, the ionization potential and the electron affinity of the constituent material of each layer satisfy a predetermined relationship.

  In the light emitting unit used in this embodiment, one or more electron injecting and transporting layers may be formed on the anode side from the light emitting layer.

  Since the light emitting layer, the hole injecting and transporting layer, and the electron injecting and transporting layer are the same as those described in the first embodiment, description thereof is omitted here.

  In this embodiment, a plurality of light emitting units are stacked via the charge generation layer. The number of stacked light emitting units is not particularly limited as long as it is a plurality, that is, two or more layers, and may be, for example, three layers, four layers, or more. It is preferable that the number of stacked light emitting units is a number with which high luminance can be obtained.

Moreover, the structure of each light emitting unit may be the same or different.
For example, a three-layer light emitting unit that emits red light, green light, and blue light can be stacked. In this case, white light can be generated. When such an organic EL element that generates white light is used for illumination, for example, high luminance generated from a large area can be obtained.

  In the case of an organic EL element that generates white light, the intensity and hue of light emitted from each light emitting unit are selected so that they combine to produce white light or light close to white light. There are many combinations of light emitting units that can be used to generate light that appears white, in addition to the combinations of red light, green light, and blue light described above. For example, a combination of blue light and yellow light, red light and cyan light, or green light and magenta light can be cited. Thus, white light is emitted using a two-layer light emitting unit that emits two colors of light. Light can be generated. Moreover, an organic EL element can also be obtained by using a plurality of these combinations.

  In addition, it can be applied to a color display device by a color conversion method using an organic EL element that generates blue light. Conventionally, a light emitting material that generates blue light has a problem that its lifetime is short. However, the organic EL element of this embodiment has a high efficiency and a long lifetime, and thus is advantageous for such a color display device.

IV. Fourth Embodiment A fourth embodiment of the organic EL device of the present invention has a plurality of light emitting units in which a light emitting layer and three or more electron injecting and transporting layers are sequentially laminated between opposing anodes and cathodes. , An organic EL element in which a charge generation layer is formed between the adjacent light emitting units, and the first, second,..., M-th (m ≧ 3 integer) electron injecting and transporting layers in order from the cathode side. And the ionization potential of the constituent material of the light emitting layer is Ip ₀ , and the ionization potential of the constituent material of the y-th (y = 1 to m) electron injection and transport layer is Ip _y ′, Ip ₀ ≧ Ip For all _m ′, y = 2 to _m , Ip _y ′ ≧ Ip _y−1 ′, and the electron affinity of the constituent material of the light emitting layer is Ea ₀ , and the constituent material of the y th electron injecting and transporting layer is 'when a, Ea ₀ ≦ Ea _m' electron affinity Ea _y, Ea _y for all _{y = 2~m '<Ea y-} 1 It is characterized by being '.

FIG. 19 is a schematic cross-sectional view showing an example of the organic EL element of this embodiment.
As illustrated in FIG. 19, the light emitting units 12 a, 12 b, and 12 c of the present embodiment are respectively formed from the anode 3 side from the first hole injecting and transporting layer 4, the light emitting layer 7, and three or more electron injecting and transporting layers ( In FIG. 19, a third electron injection / transport layer 11, a second electron injection / transport layer 10, and a first electron injection / transport layer 8) are sequentially stacked.

20A and 20B are schematic views showing examples of band diagrams of light emitting units in the organic EL element shown in FIG.
The ionization potential of the constituent material of the light-emitting layer 7 is Ip ₀ , the ionization potential of the constituent material of the first electron injection / transport layer 8 is Ip ₁ ′, and the ionization potential of the constituent material of the second electron injection / transport layer 10 is Ip ₂ ′. When the ionization potential of the constituent material of the third electron injecting and transporting layer 11 is Ip ₃ ′, as illustrated in FIG. 20A, Ip ₀ > Ip ₃ ′> Ip ₂ ′> Ip ₁ ′. Alternatively, as illustrated in FIG. 20B, Ip ₀ = Ip ₃ ′ = Ip ₂ ′ = Ip ₁ ′ may be satisfied.
Further, the electron affinity of the constituent material of the light emitting layer 7 is Ea ₀ , the electron affinity of the constituent material of the first electron injection / transport layer 8 is Ea ₁ ′, and the electron affinity of the constituent material of the second electron injection / transport layer 10 is Ea. ₂ ′, when the electron affinity of the constituent material of the third electron injecting and transporting layer 11 is Ea ₃ ′, as illustrated in FIG. 20A, Ea ₀ <Ea ₃ ′ <Ea ₂ ′ <Ea ₁ ′ Alternatively, as illustrated in FIG. 20B, Ea ₀ = Ea ₃ ′ <Ea ₂ ′ <Ea ₁ ′.

According to the present invention, three or more electron injecting and transporting layers are provided between the cathode and the light emitting layer so that Ea _y ′ <Ea _y−1 ′ for all of Ea ₀ ≦ Ea _m ′ and y = 2 to _m. Thus, electrons can be smoothly transported from the cathode to the light emitting layer through each electron injecting and transporting layer. Therefore, for example, even when the band gap energy of the constituent material of the light emitting layer is relatively large and the difference between the work function of the cathode and the electron affinity of the constituent material of the light emitting layer is relatively large, The transport of electrons can be facilitated.
_{Also, Ip 0 ≧ Ip m ',} y = for all _{2~m Ip y' ≧ Ip y-} 1 3 -layer or more electron injecting and transporting layer between the cathode and the light-emitting layer so as to 'is formed Therefore, deterioration at the interface between the electron injecting and transporting layer and the light emitting layer can be suppressed.

  Note that the configuration other than the light emitting unit and the operation mechanism are the same as those described in the section “III. Third Embodiment”, and therefore description thereof is omitted here.

  As the organic EL element of this embodiment, it is preferable that the light emitting unit has one or more hole injection / transport layers between the light emitting layer and the anode or the charge generation layer.

For example, as shown in FIG. 19, it is preferable that the first hole injection transport layer 4 is formed between the light emitting layer 7 and the cathode 3 or the charge generation layers 13a and 13b.
In this case, when the electron affinity of the _first hole injecting and transporting layer 4 is Ea ₁ , it is preferable that Ea ₀ ≦ Ea ₁ as illustrated in FIG. Further, the ionization potential of the first hole injection transport layer 4 when the Ip _1, as illustrated in FIG. 20, it is preferable that Ip ₀ ≧ Ip _1.

In the above case, the electron affinity of the constituent material of the first hole injecting and transporting layer and the light emitting layer is Ea ₀ ≦ Ea ₁ , and the ionization potential of the constituent material of each electron injecting and transporting layer and the light emitting layer is Ip ₀ ≧ Since Ip _y ′ ≧ Ip _y−1 ′ for all of Ip _m ′ and y = 2 to _m , as in the case of the second embodiment, the hole injecting and transporting layer, the light emitting layer, and the electrons during driving Deterioration at the interface of each layer of the injection transport layer can be suppressed. Therefore, it is possible to obtain a highly efficient and long-life organic EL element.

  The relationship between the ionization potential and the electron affinity of the hole injecting and transporting layer, the light emitting layer, and the electron injecting and transporting layer is the same as that described in the section of “I. First embodiment”, and the description is omitted here. .

  Regarding each configuration of the organic EL element of the present embodiment, regarding each layer constituting the light emitting unit, the section of “II. Second Embodiment” and the other sections in the section of “III. Third Embodiment” Since they are the same as those described, description thereof is omitted here.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Hereinafter, the present invention will be specifically described using examples and comparative examples.
First, the structural formula, ionization potential, and electron affinity of the materials used in the examples are shown in Table 1 below.

[Example 1]
(Production of organic EL element)
First, an ITO substrate in which ITO was patterned into a 2 mm wide line as an anode on a glass substrate was prepared. On the ITO substrate, TBADN and MoO ₃ were deposited in a weight ratio of 67:33 under a vacuum degree of 10 ^-5 Pa so that the total film thickness was 50 nm at a deposition rate of 1.5 mm / sec. A first hole injecting and transporting layer was formed. Subsequently, TBADN was deposited by vapor deposition so as to have a film thickness of 10 nm at a deposition rate of 1.0 Å / sec, thereby forming a second hole injecting and transporting layer. Further, TCTA was deposited by vapor deposition under a vacuum degree of 10 ⁻⁵ Pa so as to have a total film thickness of 10 nm at a vapor deposition rate of 1 kg / sec, thereby forming a third hole injection / transport layer.

Next, using 4,4'-bis (carbazol-9-yl) biphenyl (CBP) as the host material and Ir (piq) ₃ as the luminescent dopant serving as the luminescent center, the third hole injection transport described above CBP and Ir (piq) ₃ are vacuum-deposited on the layer to a thickness of 30 nm at a deposition rate of 1 Å / sec under a vacuum degree of 10 ^-5 Pa so that the Ir (piq) ₃ concentration is 5 wt%. To form a light emitting layer.

Next, on the light emitting layer, TBADN is deposited by vacuum deposition to a thickness of 10 nm at a deposition rate of 1 cm / sec under a vacuum degree of 10 ^-5 Pa to form a second electron injecting and transporting layer. did. Next, on the second electron injecting and transporting layer, TBADN and Liq are formed to a thickness of 10 nm at a deposition rate of 1 mm / sec by co-evaporation under the condition of a weight ratio of 1: 1 and a degree of vacuum of 10 ^-5 Pa. A first electron injecting and transporting layer was formed.

  Finally, Al was deposited on the first electron injecting and transporting layer as a cathode to a thickness of 100 nm at a deposition rate of 5 mm / sec.

[Example 2]
(Production of organic EL element)
Until the formation of the light emitting layer, the same method as in Example 1 was used. On the ITO substrate, the first hole injecting and transporting layer 40 nm, the second hole injecting and transporting layer 10 nm, the third hole injecting and transporting layer 10 nm, and the light emission A layer 30 nm was formed.

After the formation of the light emitting layer, TBADN was deposited by vacuum deposition to a thickness of 10 nm at a deposition rate of 1 Å / sec under a vacuum degree of 10 ⁻⁵ Pa to form a third electron injecting and transporting layer. Next, on the third electron injecting and transporting layer, Alq3 was deposited by vacuum deposition to a thickness of 10 nm at a deposition rate of 1 Å / sec under the condition of a vacuum degree of 10 ⁻⁵ Pa. An injection transport layer was formed. Subsequently, Alq3 and Liq are deposited at a weight ratio of 1: 1 at a vacuum degree of 10 ^-5 Pa by co-evaporation to a film thickness of 10 nm at a deposition rate of 1 mm / sec to form a first electron injecting and transporting layer. did.

  Finally, Al was deposited on the first electron injecting and transporting layer as a cathode to a thickness of 100 nm at a deposition rate of 5 mm / sec.

[Example 3]
(Production of organic EL element)
First, an ITO substrate in which ITO was patterned into a 2 mm wide line as an anode on a glass substrate was prepared. On the ITO substrate, TBADN and MoO ₃ were deposited in a weight ratio of 67:33 under a vacuum degree of 10 ^-5 Pa so that the total film thickness was 50 nm at a deposition rate of 1.5 mm / sec. A first hole injecting and transporting layer was formed. Subsequently, TBADN was deposited by vapor deposition at a deposition rate of 1.0 10 / sec so as to have a film thickness of 10 nm, thereby forming a second hole injecting and transporting layer.

Next, CBP and Ir (piq) ₃ are added to Ir (piq) ₃ on the second hole injecting and transporting layer using CBP as a host material and Ir (piq) ₃ as a light emitting dopant serving as an emission center. ₃ ) A light emitting layer was formed by vacuum deposition to a thickness of 30 nm at a deposition rate of 1 Å / sec under a vacuum degree of 10 ⁻⁵ Pa so that the ₃ concentration was 5 wt%.

On the light-emitting layer, TBADN was deposited by vacuum deposition at a deposition rate of 1 10 / sec and a thickness of 10 nm under the condition of a vacuum degree of 10 ⁻⁵ Pa to form a third electron injecting and transporting layer. Next, on the third electron injecting and transporting layer, Alq3 was deposited by vacuum deposition to a thickness of 10 nm at a deposition rate of 1 Å / sec under the condition of a vacuum degree of 10 ⁻⁵ Pa. An injection transport layer was formed. Subsequently, Alq3 and Liq are deposited at a weight ratio of 1: 1 at a vacuum degree of 10 ^-5 Pa by co-evaporation to a film thickness of 10 nm at a deposition rate of 1 mm / sec to form a first electron injecting and transporting layer. did.

  Finally, Al was deposited on the first electron injecting and transporting layer as a cathode to a thickness of 100 nm at a deposition rate of 5 mm / sec.

[Example 4]
(Production of organic EL element)
First, an ITO substrate in which ITO was patterned into a 2 mm wide line as an anode on a glass substrate was prepared. On the ITO substrate, copper phthalocyanine (CuPc) was deposited to a thickness of 10 nm at a deposition rate of 1 mm / sec under the condition of a vacuum degree of 10 ^-5 Pa to form a first hole injecting and transporting layer. did. Next, TBADN and MoO ₃ are mixed on the first hole injecting and transporting layer at a weight ratio of 67:33 under a vacuum degree of 10 ⁻⁵ Pa and a total film thickness of 40 nm at a deposition rate of 1.5 Å / sec. Then, TBADN was deposited by vapor deposition at a deposition rate of 1.0 Å / sec to a film thickness of 10 nm to form a second hole injecting and transporting layer. Further, TCTA was deposited by vapor deposition under a vacuum degree of 10 ⁻⁵ Pa at a deposition rate of 1 Å / sec to a total film thickness of 10 nm, thereby forming a third hole injecting and transporting layer.

Next, using CBP as the host material and Ir (ppy) ₃ as the light emitting dopant serving as the light emission center, CBP and Ir (ppy) ₃ are added to Ir (ppy) ₃ on the third hole injecting and transporting layer. ₃ ) A light emitting layer was formed by vapor deposition under a condition of a vacuum of 10 ⁻⁵ Pa and a film thickness of 30 nm at a deposition rate of 1 Å / sec so that the ₃ concentration was 5 wt%.

Next, on the light emitting layer, TBADN is deposited by vacuum deposition to a thickness of 10 nm at a deposition rate of 1 cm / sec under a vacuum degree of 10 ^-5 Pa to form a second electron injecting and transporting layer. did. Next, on the second electron injecting and transporting layer, TBADN and Liq are formed to a thickness of 10 nm at a deposition rate of 1 mm / sec by co-evaporation under the condition of a weight ratio of 1: 1 and a degree of vacuum of 10 ^-5 Pa. A first electron injecting and transporting layer was formed.

  Finally, Al was deposited on the first electron injecting and transporting layer as a cathode to a thickness of 100 nm at a deposition rate of 5 mm / sec.

[Comparative Example 1]
(Production of organic EL element)
Similar to the method used in Example 1, on the ITO substrate, the first hole injecting and transporting layer 70 nm, the light emitting layer 30 nm, the second electron injecting and transporting layer 10 nm, the first electron injecting and transporting layer 10 nm, and the cathode To form an organic EL element.

[Comparative Example 2]
(Production of organic EL element)
Similar to the method used in Example 1, the first hole injection transport layer 50 nm, the second hole injection transport layer 10 nm, the light emitting layer 30 nm, the first electron injection transport layer 30 nm on the ITO substrate, and A cathode was formed to produce an organic EL device.

[Evaluation]
Table 2 shows the light emission characteristics of the organic EL elements of Examples 1-4 and Comparative Examples 1-2.

When the organic EL elements of Examples 1 to 4 and Comparative Examples 1 and 2 were compared, the organic EL element of Example 1 had a luminous efficiency of front luminance of 10 cd / A. Moreover, in the organic EL element of Example 2, the luminous efficiency of front luminance was 12 cd / A. Moreover, in the organic EL element of Example 3, the luminous efficiency of front luminance was 14 cd / A. Furthermore, in the organic EL element of Example 4, the luminous efficiency of front luminance was 28 cd / A. On the other hand, in the organic EL device of Comparative Example 1, the luminous efficiency of front luminance was 8 cd / A. Further, in the organic EL element of Comparative Example 2, the luminous efficiency of the front luminance was 6 cd / A.
Regarding the lifetime characteristics, the luminance half-life from the initial luminance of 1000 cd / m ² was observed under a constant current density. As a result, the organic EL device of Example 1 achieved 240 hours of luminance reduction. In the organic EL device of Example 2, the time for the luminance to be halved was 250 hours. In the organic EL device of Example 3, the time for the luminance to be reduced to half was 300 hours. Furthermore, in the organic EL element of Example 4, the time for the luminance to be halved achieved 370 hours.

DESCRIPTION OF SYMBOLS 1 ... Organic EL element 2 ... Substrate 3 ... Anode 4 ... 1st positive hole injection transport layer 5 ... 2nd positive hole injection transport layer 6 ... 3rd positive hole injection transport layer 7 ... Light emitting layer 9 ... Cathode 8 ... 1st electron injection transport layer 10 ... 2nd electron injection transport layer 11 ... 3rd electron injection transport layer 12a, 12b, 12c ... Light-emitting unit 13a, 13b ... Charge generation layer

Claims (13)

An organic electroluminescence device comprising: an anode; three or more hole injection / transport layers formed on the anode; a light-emitting layer formed on the hole injection / transport layer; and a cathode formed on the light-emitting layer. A luminescence element,
The three or more hole injecting and transporting layers are first, second,..., Nth (n ≧ 3 integer) hole injecting and transporting layers in order from the anode side, and the constituent material of the light emitting layer the electron affinity Ea _0, when the electron affinity of the constituent material of the hole injection transport layer of the first x (x = 1 to n an integer) as the _{Ea x, Ea 0 ≦ Ea n} , of x = 2- through n When Ea _x ≦ Ea _x−1 for all, and when the ionization potential of the constituent material of the light emitting layer is Ip ₀ and the ionization potential of the constituent material of the x-th hole injection transport layer is Ip _x , An organic electroluminescence device characterized in that Ip _x > Ip _x−1 for all of ₀ ≧ Ip _n and x = 2 to _n . A first electron injection / transport layer is formed between the light emitting layer and the cathode, and when the ionization potential of the constituent material of the first electron injection / transport layer is Ip ₁ ′, Ip ₀ ≧ Ip ₁ ′ There, and 'when the, Ea ₀ ≦ Ea _1' electron affinity of the constituent material of the first electron injection transport layer Ea ₁ organic electroluminescent device according to claim 1, characterized in that a. When a second electron injecting and transporting layer is formed between the light emitting layer and the first electron injecting and transporting layer, and the ionization potential of the constituent material of the second electron injecting and transporting layer is Ip ₂ ′, Ip _{When 0} ≧ Ip ₂ '≧ Ip ₁ ′ and the electron affinity of the constituent material of the second electron injecting and transporting layer is Ea ₂ ′, Ea ₀ <Ea ₂ ′ <Ea ₁ ′ The organic electroluminescent element according to claim 2, wherein Three or more electron injecting and transporting layers are formed between the light emitting layer and the cathode, and the three or more electron injecting and transporting layers are first, second,. Ip ₀ ≧ Ip _{m where} the ionization potential of the constituent material of the electron injection / transport layer of y (y = 1 to m) is Ip _y ′. When Ip _y ′ ≧ Ip _y−1 ′ for all of y, y = 2 to m, and Ea _y ′ as the electron affinity of the constituent material of the y-th electron injecting and transporting layer, Ea ₀ ≦ Ea _2. The organic electroluminescence device according to claim 1, wherein Ea _y ′ <Ea _y−1 ′ for all of _m ′ and y = 2 to _m . An organic electroluminescence device having an anode, a light emitting layer formed on the anode, three or more electron injection transport layers formed on the light emission layer, and a cathode formed on the electron injection transport layer Because
The three or more electron injecting and transporting layers are first, second,..., M-th (m ≧ 3 integer) electron injecting and transporting layers in order from the cathode side, and ionization of the constituent material of the light emitting layer. When the potential is Ip ₀ and the ionization potential of the constituent material of the y-th (y = 1 to _m ) electron injection and transport layer is Ip _y ′, all of Ip ₀ ≧ Ip _m ′ and y = 2 to _m Ip _y '≧ Ip _y−1 ′, and the electron affinity of the constituent material of the light emitting layer is Ea ₀ , and the electron affinity of the constituent material of the y-th electron injecting and transporting layer is Ea _y ′, An organic electroluminescence device characterized in that Ea _y ′ <Ea _y−1 ′ for all of Ea ₀ ≦ Ea _m ′ and y = 2 to _m . When a first hole injection / transport layer is formed between the light emitting layer and the anode, and Ea ₁ is an electron affinity of a constituent material of the first hole injection / transport layer, Ea ₀ ≦ Ea ₁ 6. The organic electroluminescent device according to claim 5, wherein Ip ₀ ≧ Ip ₁ when the ionization potential of the constituent material of the first hole injection transport layer is Ip ₁ . When a second hole injecting and transporting layer is formed between the light emitting layer and the first hole injecting and transporting layer, and the electron affinity of the constituent material of the second hole injecting and transporting layer is Ea ₂ Ea ₀ ≦ Ea ₂ ≦ Ea ₁ , and when the ionization potential of the constituent material of the second hole injection transport layer is Ip ₂ , Ip ₀ > Ip ₂ > Ip ₁ The organic electroluminescent element according to claim 6.   The said hole injecting and transporting layer and the said electron injecting and transporting layer contain the bipolar material which can transport a hole and an electron, The claim 2, the claim 3, the claim 6, the claim 6 Item 8. The organic electroluminescence device according to Item 7.   9. The organic electroluminescence device according to claim 8, wherein the bipolar material contained in the hole injection / transport layer and the bipolar material contained in the electron injection / transport layer are the same.   The organic light-emitting device according to claim 8, wherein the light emitting layer contains a bipolar material capable of transporting holes and electrons.   The bipolar material contained in the hole injecting and transporting layer, the bipolar material contained in the electron injecting and transporting layer, and the bipolar material contained in the light emitting layer are the same. The organic electroluminescent element of description.   The organic material according to any one of claims 1 to 11, wherein the light emitting layer contains a host material and a light emitting dopant, and the concentration of the light emitting dopant in the light emitting layer is distributed. Electroluminescence element.   The organic light-emitting device according to any one of claims 1 to 12, wherein the light-emitting layer contains a host material and two or more kinds of light-emitting dopants.

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