JPWO2012169151A1 - Organic electroluminescent device - Google Patents

Abstract

As a structure that does not use strong electron donating substances such as alkali metals and can move the electron charge in the direction of the anode as viewed from the charge generation (carrier generation) site and inject it into the light emitting layer, Provided is a new structure of an organic EL element having a structure in which an insulating organic material layer is provided at a portion serving as a barrier, and further capable of reducing a driving voltage. An anode, a cathode, a plurality of light emitting units including a light emitting layer located between the anode and the cathode, and an intermediate layer located between the plurality of light emitting units, wherein the intermediate layer is And an insulating organic material layer provided in a portion that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit, and an organic layer adjacent to the insulating organic material layer, An organic electroluminescent device, wherein a region adjacent to the intermediate layer and a region of the organic layer adjacent to the insulating organic material layer are doped with the same type of carrier.

Description

  The present invention relates to an organic electroluminescent element (hereinafter sometimes abbreviated as “organic EL element”) used for a planar light source and a display element.

In recent years, an organic EL element having a light emitting layer made of an organic compound between an anode and a cathode, which are opposed to each other, has attracted attention as a means for realizing a large-area display element driven at a low voltage. Tang et al. Of Eastman Kodak Company has adopted a structure in which organic compounds having different carrier transport properties are stacked, and holes and electrons are injected in a balanced manner from the anode and the cathode, respectively, in order to increase the efficiency of the device. By making the thickness of the organic layer sandwiched between the anodes 200 nm or less, we succeeded in obtaining high luminance and high efficiency sufficient for practical application of 1000 cd / m ² and an external quantum efficiency of 1% at an applied voltage of 10 V or less. did.

For example, according to Patent Documents 1 to 6, it is said that a device capable of emitting light with a lower applied voltage can be provided by setting the film thickness of the entire organic layer sandwiched between the cathode and the anode to 1 μm or less. If the film thickness is in the range of 100 to 500 nm, it is said that an electric field (E = Vcm ⁻¹ ) useful for obtaining light emission with an applied voltage of 25 V or less can be obtained.

  The structure of the organic EL element has been developed on the basis of the structure shown by Tang et al. As described above. Recently, for example, as shown in Patent Document 7 and Patent Document 8, a structure sandwiched between electrodes. An organic EL element having a structure in which a plurality of light emitting units are stacked so that can be connected in series has been developed. This technology has been attracting attention as a technology that enables the organic EL device to dramatically extend its life, achieve high brightness required for light sources and illumination, and emit light uniformly over a large area. This is because the structure of the organic EL element of Tang et al. Which requires a large current despite the low voltage cannot satisfy these requirements.

  Next, as described in Patent Document 8, the inventor of the present application devised and realized an organic EL element having a series type (tandem type) structure, and ITO (Indium Tin Oxide) or IZO (IZO ( Instead of a transparent electrode material such as Indium Zinc Oxide, a plurality of light emitting units can be connected in series by using a low-conductivity electrification layer. In this organic EL element, only the region where the cathode and the anode intersect with each other emits light as in the conventional organic EL element, and the sputtering process that is essential for the formation of the transparent electrode becomes unnecessary. It is recognized as the most useful among the structures of organic EL elements, and has been widely known as a multiphoton organic EL element. The reason for being referred to as multiphoton is that if the number of light emitting units is set to a predetermined number or more, the number of photons exceeding the number of electrons passing through the organic EL element can be generated.

  However, this multi-photon organic EL element has a problem that it requires a manufacturing process several times that of a conventional organic EL element. There is also a problem that it is difficult to control the manufacturing process because the chemical doping method described in Document 14 must be used.

The series organic EL element is suitable for emitting light over a large area with uniform intensity. When compared with the conventional organic EL element, the series organic EL element can increase the voltage V required to obtain the same luminance by multiplying by the number of units, and the current I is almost equal to the number of units. You can make it smaller by the amount you removed As a result, the element resistance (ratio of voltage to current: VI ⁻¹ ) increases by approximately the square of the number of units, the voltage drop due to the surface resistance of the external electrode can be reduced, and a substantially uniform potential in the surface can be realized. Because.

Needless to say, the uniformity of the potential, in other words, the uniformity of the luminance, increases as the number of units increases. However, according to the present inventor's previous knowledge, when a luminance of 3000 cdm ⁻² or more necessary for illumination is required, a light emitting area of about 5 inches diagonal is approximately uniform in a laminate of several units. Although light emission can be realized, for example, when the light emission area is 15 inches or more diagonally, uniform light emission with such high brightness is impossible with a laminate of several units, and at least about 15 units are considered necessary. It is almost impossible to produce such a large number of unit laminates efficiently and at low cost.

  The reason why it is impossible to produce such a multi-unit laminate efficiently and at low cost is that the manufacturing method is complicated. That is, as proposed by the present inventors in Patent Document 8, the production of a charge generation layer provided for generating hole charges and electron charges is very complicated.

  For example, in claim 1 or 2 of Patent Document 8, the charge transfer complex formed at the contact interface formed by mixing or stacking a metal oxide having a strong electron-donating property and an amine-based organic compound having a high electron-accepting property is as if the charge is charged. It is described that an electron charge and a hole charge necessary for excitation of the luminescent substance are supplied from the generation layer to the light emitting unit. However, in actuality, in the configuration described in Patent Document 8, although electrons are generated in the metal oxide by the applied electric field at the interface, holes are generated in the amine organic compound. Thus, both the hole and electron charges are not automatically supplied to the light-emitting substance, and as shown in the specific examples, strong charges such as alkali metals are always present at the site in contact with the anode side of the charge generation layer. A technique is required for causing an electron donating substance to act on an electron transporting organic substance and promoting electron injection into the organic substance.

  This is because there is a large energy difference between the electron transporting organic material and the metal oxide, and a strong electron donation such as an alkali metal is required to inject electrons generated in the metal oxide into the electron transporting organic material. This is because it is necessary to perform carrier doping with a conductive material and to effectively reduce the injection barrier with the electron transporting organic substance by the space charge of the ionized dopant.

  When the injection efficiency is low, holes move predominantly in the light-emitting layer containing the light-emitting substance in the light-emitting unit located on the anode side of the charge generation layer, and the excess holes exist in excess in the charge generation layer. It undergoes a process in which current flows due to non-radiative recombination with electrons. The light emitting layer portion exists only as a hole current resistor, and the light emitting material does not emit light. That is, even if a multiphoton organic EL device is produced by forming a “charge generation layer made of a charge transfer complex” in Patent Document 8, no effect is actually obtained.

  Examples of a method for supplying alkali metal into the film include a method in which alkali metal is directly evaporated by resistance heating (resistance heating vapor deposition method), a method using a film containing a compound containing alkali metal ions, and the like. Is proposed in Patent Document 8.

Furthermore, if an oxide, carbonate, composite oxide, composite carbonate, or the like containing an alkali metal ion is further deposited by electron beam evaporation, the electron beam evaporation method itself converts the metal in the compound from the ionic state to the metal. Since it is one of the means for reducing to an atomic state, as a result, an alkali metal can be allowed to act on an electron transporting organic substance. Furthermore, in exceptional cases, cesium carbonate (CsCO ₃ ) may be capable of producing metal cesium by reduction simply by resistance heating in vacuum without using an electron beam evaporation method.

  For alkali metal compounds such as oxides, carbonates, composite oxides, composite carbonates and the like, for example, in Patent Document 9 or Patent Document 10, an electron injection layer or an intermediate cathode layer containing lithium carbonate or lithium oxide ( It is described that a layer called an interface layer is formed so as to be in contact with the anode side of the charge generation layer, and these documents do not clearly describe the vapor deposition method. If the film is formed by the usual resistance heating vapor deposition method regardless of the electron beam vapor deposition method, the alkali metal ions in the compound are not reduced to the metal, so that it becomes impossible to transport the electronic charge to the luminescent material as described above. This is easily verified by experiment.

  When this alkali metal makes contact with the luminescent organic substance of the organic EL element, the luminescent organic substance loses its luminescent property due to its strong reducibility (this phenomenon is sometimes called luminescence quenching). In this manufacturing process, it is necessary to install it in a place separated from a manufacturing chamber for forming a layer made of an organic substance such as a light emitting layer. Therefore, when it is necessary to repeatedly manufacture substantially the same process many times, such as a multi-photon organic EL element having a plurality of light emitting units, a plurality of vapor deposition chambers are installed and what is between them. The process of forming the charge generation layer and the layer in contact therewith becomes complicated, and there is a problem that the product price is increased in combination with the complexity of the control of each process.

  In contrast to the prior art as described above, the present inventors have conducted intensive studies, and the present inventors have proposed reducing substances such as alkali metals (strong electron donation) that have been indispensable for the structure of multi-photon organic EL devices that have been proposed and developed previously. An organic EL element that exhibits substantially the same performance as the conventional one has been proposed (Patent Document 11) while avoiding the use of an organic substance (thus greatly simplifying the manufacturing process). More specifically, as a result of intensive investigations, the present inventors have determined that an electron charge (radical anion state electron) in the direction of the anode as viewed from the charge generation site without using a strong electron donating substance such as an alkali metal. As a structure that can move (accepting semiconductor molecules) into the light-emitting layer, we have found a structure in which an insulating organic material layer is provided at a site that acts as a barrier against charge transfer to the light-emitting layer. Completed organic EL device with

JP 59-194393 A Japanese Unexamined Patent Publication No. 63-264692 Japanese Patent Laid-Open No. 2-15595 US Pat. No. 4,539,507 U.S. Pat. No. 4,769,292 US Pat. No. 4,885,211 Japanese Patent Laid-Open No. 11-329748 Japanese Patent No. 3933591 JP 2006-135145 A JP 2007-123611 A International Publication No. WO2010 / 113493

  However, the stack type organic EL element proposed in Patent Document 11 requires a driving voltage as high as that of the conventional organic EL element, and the present inventors have yet improved from the viewpoint of energy saving and the like. As a result, it was further studied that the structure of the organic EL element was repeated. And in the organic EL element in the above-mentioned patent document 11, if the charge injection into the light emitting layer can be made more efficient with respect to the element in which the insulating organic material layer is provided in the direction of the anode as viewed from the charge generation site, the driving voltage is set. The present inventors have found that a reduced stack type organic EL device structure can be obtained, and have completed the present invention. That is, the object of the present invention is a structure that does not use a strong electron donating substance such as an alkali metal and can be injected into the light emitting layer by moving the electron charge in the direction of the anode as viewed from the charge generation (carrier generation) site. An object of the present invention is to provide a new structure of an organic EL element that has a structure in which an insulating organic material layer is provided at a site that becomes a barrier against the movement of electric charges to a light emitting layer, and can further reduce the driving voltage.

In order to solve the above problems, the present invention provides a first aspect as follows:
The anode,
A cathode,
A plurality of light emitting units including a light emitting layer located between the anode and the cathode;
An intermediate layer located between the plurality of light emitting units,
The intermediate layer is composed of an insulating organic material layer provided at a site that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit, and an organic layer adjacent to the insulating organic material layer,
The region adjacent to the intermediate layer of the light emitting unit and the region adjacent to the insulating organic material layer of the organic layer are doped with the same type of carrier (dopant),
An organic electroluminescent element (hereinafter referred to as “organic EL element”) is provided. According to the present invention having such a configuration, the efficiency of charge injection from the intermediate layer to the light emitting unit can be increased, the voltage loss in the intermediate layer can be greatly reduced, and the stack type organic that operates at a lower driving voltage. An EL element can be realized.

  In the organic EL device of the present invention, the difference between the electron affinity of the organic substance constituting the organic layer and the ionization potential of the layer adjacent to the side of the organic layer opposite to the insulating organic layer side is 1 It is preferably 4 eV or less. According to the present invention having such a configuration, the efficiency of charge injection from the intermediate layer to the light emitting unit can be increased more reliably, the voltage loss in the intermediate layer can be greatly reduced, and the operation is performed at a lower driving voltage. A stack type organic EL element can be realized.

  In the organic EL device of the present invention, it is preferable that the organic material constituting the organic layer contains a hexaazatriphenylene derivative. Since the hexaazatriphenylene derivative has a deep electron affinity, if it is used, it can generate a sufficient carrier density, more reliably increase the efficiency of charge injection from the intermediate layer to the light emitting unit, and in the intermediate layer Voltage loss can be greatly reduced, and an increase in drive voltage can be suppressed.

  In the organic EL device of the present invention, the carrier is preferably an n-type carrier (dopant) such as a metallocene derivative. If this is used, sufficient carrier density can be generated more reliably, the efficiency of charge injection from the intermediate layer to the light emitting unit can be more reliably increased, and the voltage loss in the intermediate layer can be greatly reduced, An increase in drive voltage can be suppressed.

In the organic EL device of the present invention, the carrier is, for example, the following formula:

It is preferable that it is n type carriers (dopants), such as an alkylamine derivative shown by these. If this is used, sufficient carrier density can be generated more reliably, the efficiency of charge injection from the intermediate layer to the light emitting unit can be more reliably increased, and the voltage loss in the intermediate layer can be greatly reduced, An increase in drive voltage can be suppressed.

  Moreover, in the organic EL element of the said invention, it is preferable that the said insulating organic substance layer contains the organometallic complex which has (beta) -diketone type ligand. If this is used, the dielectric constant of the insulating organic layer can be further reduced, the efficiency of charge injection from the intermediate layer to the light emitting unit can be more reliably increased, and the voltage loss in the intermediate layer can be greatly reduced. And an increase in driving voltage can be suppressed.

In order to solve the above-described problems, the present invention provides a second aspect,
There is provided an organic electroluminescent device characterized by having a layer containing a heterocyclic compound and a metallocene derivative.

  The metallocene derivative preferably includes Co or Ni, and the heterocyclic compound is preferably a pyridine derivative, a triazine derivative, a phenanthroline derivative, or a hexaazaphenylene derivative.

In order to solve the above problems, the present invention provides a third aspect,
A metallocene derivative and the following formula:

(Wherein, Ar ₁ , Ar ₂ and Ar ₃ are each independently an aryl group which may have a substituent), and a layer containing
An organic electroluminescent device is provided.

  According to these second and third aspects of the present invention, in the laminated structure of the organic EL element, the efficiency of charge injection into the light emitting unit can be increased, and the voltage loss in each layer can be greatly reduced. A stack type organic EL element that operates at a low driving voltage can be realized.

  Here, the characteristic feature of the present invention is “an intermediate layer positioned between a plurality of light emitting units”, that is, “an insulating organic material layer provided at a site that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit; An “intermediate layer composed of an organic layer adjacent to the insulating organic layer” will be described. The role of this intermediate layer is to inject the same amount of electrons into the light emitting unit adjacent to the unit on the anode side of the intermediate layer and holes into the unit on the cathode side. By maintaining this balance of injection, each light emitting unit is equivalently connected in series, and the operation expected as a stacked element can be obtained.

  The intermediate layer in the organic EL device of the present invention acts as a so-called “charge generation layer” in the layer or at one interface (more precisely, acts as a carrier generation layer or a carrier generation interface), and is generated at the other interface. It has a function of injecting the thus-prepared carrier into the light emitting unit in contact with the interface. Specifically, a layer including a material having a deep electron affinity or a layer composed of the material is converted into a hole transport layer having a shallow ionization potential (for example, a layer composed of NPB or other triphenylamine derivatives). Next, by applying an electric field, holes can be generated on the hole transport layer side, and at the same time, electrons can be generated on the intermediate layer side.

  Conventionally, in various literatures, a layer having such a function is referred to as a “charge generation layer”, and it has been described that a special configuration or an effect is generated, but this phenomenon itself is an organic EL. There is nothing special in the technical field of the element, and it is well known to those skilled in the art. For example, it is a well-known fact that ITO that has been used for the anode of an organic EL element can inject holes into an amine-based hole transport layer. In addition, ITO is an n-type semiconductor, and the fact that its “work function” is the energy level of the conduction band, that is, the electron affinity, if there is an interface having such an energy level relationship, on the amine side. It is immediately understood that holes can be injected. Therefore, conventionally, in various literatures, there are many misunderstandings regarding the so-called “charge generation layer” that a combination of an electron-accepting compound and an electron-donating compound or the generation of a charge transfer complex is necessary. There are many descriptions of whether this has been achieved by construction, but this property is determined purely by the energy relationship.

  Next, as described above, the deep electron affinity of the organic material constituting the organic layer and a layer adjacent to the side of the organic layer opposite to the insulating organic material layer side (for example, a hole transport layer in a light emitting unit) ) Is not more than 1.4 eV, preferably not more than 0.8 eV, and it is preferable because carriers can be generated more reliably. In the case of ITO and an amine-based hole transport material, it is known that the work function of ITO, that is, the electron affinity, varies depending on the surface treatment with oxygen and the like, and is generally in the range of 4.7 eV to 5.3 eV. . Further, for example, D.I. J. et al. Millonon, I.D. G. Hill, C.I. Shen, A.D. Kahn, J .; Schwartz, J.A. Appl. Phys. Vol. 87 (2000), 572, a voltage of about 4.1 eV to 4.5 eV is obtained, and it is shown that hole injection is possible even when the difference from the ionization potential of the hole transport layer is 1.34 eV. Has been.

  The electron affinity of the amine hole transport material is 5.4 eV for 4,4′-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl (NPB), and 5 for triphenylenediamine (TPD). .5 eV, starburst amine derivatives are known to be about 5.0 eV to 5.2 eV. Therefore, if the difference between the electron affinity of the layer having a deep electron affinity and the ionization potential of the hole transport layer is 1.4 eV or less, carrier generation is sufficiently possible.

The value of 1.4 eV can be found theoretically from the energy level distribution of the organic layer. For example, in the case of an amorphous thin film, a distribution occurs in polarization energy with respect to electric charge due to non-uniformity of intermolecular distance and molecular orientation distribution. Therefore, the electron affinity and ionization potential have a spatial distribution, and the deviation is 0.2. This produces a Gaussian distribution of ~ 0.3 eV. For this reason, the difference of 1.4 eV gives an overlap at the base of this distribution, and the overlap width is located at 2.33 to 3.5σ from the center of the distribution, and erfc (2. 33) ^ 2 to erfc (3.5) ^ 2 having a density of states. This corresponds to a state density of 10 ¹⁵ to 10 ¹⁸ / cm ³ when the total state density is 10 ^ 22, and a carrier density of 10 ¹⁴ to 10 ¹⁷ / cm ³ required for organic EL light emission. From this, it can be seen that a sufficient carrier density can be generated within 1.4 eV.

  Here, in the case where the above configuration is reversed, holes are generated on the intermediate layer side, and electrons are generated in the light emitting unit on the adjacent anode side, the layer formed of a material having a shallow ionization potential on the intermediate layer side Alternatively, a layer containing the material is arranged, and a layer made of an insulating organic compound is arranged at the interface with the light emitting unit on the cathode side. In this case, if the difference in electron affinity between the shallow ionization potential layer and the layer in contact with the light emitting unit on the anode side is 1.4 eV or less, carriers can be generated, which is preferable.

  Also, when the difference between the deep electron affinity of the organic material constituting the organic layer and the ionization potential of the layer adjacent to the side opposite to the insulating organic material layer side of the organic layer becomes negative (for example, has a deep electron affinity) When the electron affinity of the layer becomes larger than the ionization potential of the hole transport layer), carriers are generated at the interface without applying an electric field. From the definition of electron affinity, ie, “(neutral molecule energy) − (anion molecule energy)” and the definition of ionization potential, ie, “(cation molecule energy) − (neutral molecule energy)”, both molecules Since anion and cation have lower energy than is neutral, carrier generation occurs spontaneously in a thermal equilibrium state. Therefore, even when the difference is negative as described above, the carrier generation effect is obtained, and thus the layer having the energy level relationship as described above can be used as the intermediate layer.

  It is sometimes misunderstood that this carrier is generated and both carriers are present as “a charge transfer complex is generated.” However, the charge transfer complex has binding energy to form a complex. Therefore, it is a well-known fact that this binding energy is larger than the difference between the electron affinity of the acceptor and the ionization potential of the donor, and it is clear from the above discussion. When this charge transfer complex is generated, in order to generate electrons and holes as free carriers from the charge transfer complex, it is necessary to give energy exceeding the binding energy. This is equivalent to giving a potential difference corresponding to the energy to a single molecule, and causes an increase in the applied voltage of the potential difference even when all the complexes are arranged at the interface. In the case of a mixed layer, when the charge transfer complex is distributed in the layer, the voltage rise is several times the molecular layer, and even a film thickness of about several nanometers has a potential difference of several volts or more. It becomes difficult to make it function.

  The important point as an intermediate layer is that in the case of the configuration of this example, electrons generated on the layer side having a deep electron affinity must be injected beyond the high barrier to the light emitting unit located on the anode side. It is to be realized by such a method. In the above-mentioned patent document 11, the present inventors can inject electrons into an electron transport layer having a shallow electron affinity rather than a deep electron affinity layer by disposing a thin layer of an insulating organic compound at this interface. It was found that series operation is possible equivalently. Furthermore, the present inventors have conducted intensive studies and found that the region adjacent to the intermediate layer of the light emitting unit and the region adjacent to the insulating organic layer of the organic layer (particularly n-type). )), The voltage loss in the intermediate layer is greatly reduced, and it is found that the device operates with a lower driving voltage, and the present invention has been achieved.

  As the organic substance having a deep electron affinity, a hexaazatriphenylene derivative (for example, HAT-CN6) is a preferable compound, but the organic substance to be used is not limited to this example. An n-type carrier for an organic substance having a deep electron affinity can be found in the organic substance, and a metallocene derivative can be preferably used, but is not limited thereto. The metal element contained in the metallocene derivative is not particularly limited, but Co (cobalt), Ni (nickel), and the like are preferably used.

  An n-type carrier for an organic substance having a deep electron affinity can be found from the organic substance, and an alkylamine derivative can be preferably used.

  In the present invention, the metallocene derivative can also be used in layers other than the intermediate layer. Specifically, for example, the metallocene derivative can be used by doping a heterocyclic compound that is an electron-transporting organic substance. . Therefore, the present invention also relates to an organic electroluminescent device characterized by having a layer containing a heterocyclic compound and a metallocene derivative as described above (second aspect of the present invention).

  Examples of the heterocyclic compound that is an electron-transporting organic substance include pyridine derivatives, triazine derivatives, phenanthroline derivatives, hexaazaphenylene derivatives, and the like, and one or more of these can be used in combination. .

Moreover, as an electron transport organic substance, phosphorus compounds, such as a compound represented by a following formula, etc. can also be used. Therefore, as described above, the present invention also relates to an organic electroluminescent device comprising a layer containing a metallocene derivative and a compound represented by the following formula (the third aspect of the present invention). Embodiment).

(In the formula, Ar ₁ , Ar ₂ , and Ar ₃ each independently represents an aryl group that may have a substituent.)

  The insulating organic material layer in the organic EL device of the present invention may be a single film made of only an insulating organic material, and may be an insulating organic material and an electron transporting organic material and / or an intermediate layer used for an electron transporting layer. A mixed film containing an organic substance having a deep electron affinity to be used may be used.

  According to the present invention, while avoiding the use of reducing substances such as alkali metals, which are essential for the structure of the conventional stack type organic EL device, the manufacturing process is greatly simplified, while the performance is almost the same as the conventional one. It is possible to realize a stack type organic EL element having a low driving voltage.

It is a schematic sectional drawing which shows the typical structure of the organic EL element which concerns on the 1st aspect of this invention. It is the schematic of the energy diagram which shows the typical structure of the organic EL element of this invention. 3 is a schematic cross-sectional view showing a laminated structure of an organic EL element produced in Example 1. FIG. It is the graph which plotted the voltage (V) -luminance (cd / m < ² >) about the organic EL element produced in Example 1 and Comparative Example 1. FIG.

  The organic EL device according to the first aspect of the present invention includes an anode, a cathode, a plurality of light emitting units including a light emitting layer located between the anode and the cathode, and the plurality of light emitting units. An intermediate organic layer, and the intermediate layer is adjacent to the insulating organic layer and an insulating organic layer provided at a site that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit. An organic layer, and a region adjacent to the intermediate layer of the light emitting unit and a region adjacent to the insulating organic layer of the organic layer are doped with the same type of carrier It is characterized by. Hereinafter, preferred embodiments of the organic EL element according to the first embodiment of the present invention will be described in detail. In the following description, overlapping description may be omitted.

  The organic EL element of the present invention includes n light emitting units (n is an integer of 2 or more). As shown in FIG. 1, the organic EL element 1 of the present embodiment is formed on a substrate 1 such as a glass substrate. The anode 2 formed in this order; the organic layer 3 composed of an organic material having a deep electron affinity; the first light emitting unit 4-1; the first insulating organic material layer 5-1 and a deep electron affinity. A first intermediate layer 7-1 including a first organic layer 6-1 composed of an organic substance; a second light emitting unit 4-2; a second insulating organic substance layer 5-2 and a deep electron affinity. And a second intermediate layer 7-2 composed of a second organic layer 6-2 made of an organic material, a third light emitting unit 4-3, and a cathode 7. The organic EL element 1 is omitted in FIG. 1, but the (n-1) th intermediate layer composed of the (n-1) th insulating organic material layer and the (n-1) th organic layer. And nth light-emitting unit.

  The first light emitting unit 4-1, the second light emitting unit 4-2, the third light emitting unit 4-3,... And the nth light emitting unit 4-n are collectively referred to as “light emitting unit 4”. The insulating organic layer 5-1, the second insulating organic layer 5-2, and the (n-1) th insulating organic layer 5- (n-1) are collectively referred to as an "insulating organic layer". There are things to do. In addition, the first organic layer 6-1, the second organic layer 6-2,... And the (n-1) th organic layer 6- (n-1) are collectively referred to as an “organic layer”. The intermediate layer 7-1, the second intermediate layer 7-2, and the (n-1) th intermediate layer 7- (n-1) may be collectively referred to as an "intermediate layer".

  In the organic EL element 1 shown in FIG. 1, the first intermediate layer 7-in each of the first light emitting unit 4-1, the second light emitting unit 4-2 and the third light emitting unit 4-3 is used. 1. Regions adjacent to the second intermediate layer 7-2 and the third intermediate layer (not shown) (ie, the first insulating organic material layer 5-1, the second insulating property) A carrier doped layer 8-15a doped with n-type carriers is formed in a region A) adjacent to the organic layer 5-2 and the third insulating organic layer (not shown). . Further, in the first organic layer 6-1 and the second organic layer 6-2, in the region B adjacent to the first insulating organic layer 5-1 and the second insulating organic layer 5-2, respectively. Also, a carrier doped layer 8-15b doped with n-type carriers of the same type as described above is formed.

  As described above, the organic EL element 1 of the present embodiment does not include any strong electron donating substance such as an alkali metal that quenches the luminescent organic substance contained in the light emitting unit 4. Further, in order to efficiently supply electronic charges into the light emitting unit 4, the low dielectric constant insulating organic material layer 5 is provided between the organic layer 6 made of an organic material having a deep electron affinity and the light emitting unit 4. It has a configuration.

As described above, the insulating organic material layer 5 in the organic EL device 1 of the present invention only needs to be composed of an insulating organic material having a low relative dielectric constant, and various organic compounds are used as the insulating organic material. It is expected. Among them, for example, the following formula:

Ca (dpm) ₂ (bis-di-pivaloyl-methanate-calcium) represented by the following formula:

And a metal complex having a β-diketone type ligand such as Mg (acac) ₂ (bis-acetylacetonato-magnesium).

  Further, for example, when the insulating organic material layer 5 is provided at a site where electronic charges move, it may be any layer that functions as an insulating layer with respect to the transport of electronic charges. ) A hole transporting organic material layer formed of a transporting organic material may be used.

  The n-type carrier (dopant) used for the carrier doped layers 8a-15a and 8-15b in contact with the anode 2 side and the cathode 7 side of the insulating organic layer 5 is not particularly limited, but a metallocene derivative is preferably used. be able to. Examples include decamethyl metallocene containing various metal elements, and examples of the metal elements contained therein include metals such as Co (cobalt), Ni (nickel), Mn (manganese), and Ru (ruthenium). However, it is not limited to these.

  The n-type carrier (dopant) used for the carrier doped layers 8-15a and 8-15b in contact with the anode 2 side and the cathode 7 side of the insulating organic layer 5 is not particularly limited, but an alkylamine derivative is preferably used. Can be used.

In the present embodiment, the organic material constituting the organic layer 6 (that is, an organic layer composed of an organic material having a deep electron affinity) in the intermediate layer 7 is an interface with an adjacent layer (for example, a hole transport layer), Any organic material that can form a site for generating electrons and holes may be used. Examples of organic substances having deep electron affinity that can be used here include the following formula:

The hexaazatriphenylene derivative (HAT-CN6) represented by these is mentioned. If HAT-CN6 is used and a hole transport layer (for example, a layer made of NPB) is laminated adjacent to the cathode 7 side, when a voltage is applied, carriers of electrons and holes are generated at the interface, and insulation is achieved. Good carrier injection can be performed to the light emitting unit 4 through the organic material layer 5.

  In addition, the organic EL element of this invention may have the structure containing the mixed layer of the said metallocene derivative and a heterocyclic compound (2nd aspect). As the heterocyclic compound, a hexaazaphenylene derivative such as HAT-CN6, a pyridine derivative, a triazine derivative, or a phenanthroline derivative can be used.

Furthermore, the organic EL device of the present invention includes the metallocene derivative and the following formula:

(Wherein, Ar ₁ , Ar ₂ , Ar ₃ each independently represents an aryl group which may have a substituent), and has a structure including a mixed layer with a phosphorus-containing compound (Third embodiment).

  In the organic EL device 1 of this embodiment shown in FIG. 1, as a material constituting the cathode 7, generally, a metal having a small work function, an alloy containing the metal, a metal oxide of the metal, or the like is used. . Specific examples include simple metals such as alkaline metals such as Li, alkaline earth metals such as Mg and Ca, rare earth metals such as Eu, and alloys of these metals with Al, Ag, In, and the like. It is done.

  Further, when adopting a configuration (see Japanese Patent Laid-Open Nos. 10-270171 and 2001-102175) using a metal-doped organic layer at the interface between the cathode 7 and the organic layer (not particularly limited). If the cathode 7 is a conductive material, its work function and other properties are not particularly limited.

  For example, using the techniques disclosed in Japanese Patent Application Laid-Open Nos. 11-233262 and 2000-182774, the organic layer in contact with the cathode 7 is at least one of alkali metal ions, alkaline earth metal ions, and rare earth metal ions. In the case of comprising an organometallic complex compound containing, a metal capable of reducing metal ions contained in the organometallic complex compound to a metal in a vacuum, such as Al, Zr, Ti, Si, etc. Reducible) metals or alloys containing these metals can also be used as the cathode material. Of these, Al, which is generally widely used as a wiring electrode, is preferable from the viewpoints of easiness of vapor deposition, high light reflectance, chemical stability, and the like.

  There is no restriction | limiting in particular as a material which comprises the anode 2, For example, transparent conductive materials, such as ITO (indium tin oxide) and IZO (indium zinc oxide), can be used. For example, in the case where the ITO film is formed by a sputtering method that does not damage the organic film using the method described in Japanese Patent Application Laid-Open No. 2002-332567, as in the case of the cathode 7, Japanese Patent Application Laid-Open No. 10-270171. If the metal-doped organic layer described in the publication is used for the electron injection layer, the transparent conductive material such as ITO or IZO described above can also be used for the cathode 7.

  Therefore, if both the cathode 7 and the anode 2 are transparent, the light-emitting unit 4 including the organic layer and the intermediate layer 7 are also transparent, so that a transparent organic EL element can be produced. Contrary to the case of a general organic EL element, the anode 2 is made of metal and the cathode 7 is a transparent electrode, so that light is extracted from the cathode 7 side instead of the substrate 1 side. An EL element can also be used. Further, regarding the order of forming each layer, it is not always necessary to start the formation (film formation) of the anode 2, and the formation may be started from the cathode 6.

  The light emitting unit 4 in the present embodiment can take various structures as in the case of a conventionally known organic EL element. For example, the light emitting unit 4 includes a combination of a light emitting layer and a hole transport layer and / or an electron transport layer. Various modes may be adopted as the combination.

The “light emitting layer” included in the light emitting unit 4 may be a conventional light emitting layer used in a conventional organic EL element, and the light emitting material constituting the light emitting layer is not particularly limited, and various fluorescent materials or phosphorescent materials are used. Any known material can be used. For example, the following formula:

And tris (8-quinolinolato) aluminum complex (Alq3) represented by

  The “hole transport layer” may be formed using a hole transport material that constitutes the hole transport layer of the conventional organic EL device, and is not particularly limited. For example, the ionization potential is smaller than 5.7 eV, and the hole transport property is That is, an organic compound having an electron donating property (electron donating substance) can be used. In general, it is desirable that the ionization potential is smaller than 5.7 eV in order for an organic compound having an electron donating property to easily enter a radical cation state.

For example, the general formula (I):

(In formula (I), Ar ₁ , Ar ₂ and Ar ₃ each independently represents an aromatic hydrocarbon group which may have a substituent) are preferably arylamine compounds. Of these, 4,4′-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl (NPB) is preferable.

  In addition to the arylamine compound, a pigment-based organic material containing a phthalocyanine compound that has been conventionally used as a hole injection material for organic EL elements may be used for the “hole transport layer”. Any material that can be generated can be appropriately selected and used.

  The “electron transport layer” may be formed using an electron transport material constituting the electron transport layer of the conventional organic EL device, and is not particularly limited. Generally, the electron transport material used in this embodiment is Among the electron transport materials used in the organic EL element, those having a relatively deep ionization potential are preferable. Specifically, it is preferable to use an electron transporting material having an ionization potential of at least about 6.0 eV. When an electron transporting material having a deep ionization potential is used as described above, the hole charge is difficult to move toward the electron transporting material, and the electron charge generated in the intermediate layer 7 is electrically neutralized as described above. The light emitting material can be surely excited to emit light without being summed.

  In addition, the electron affinity of the electron transporting substance used in the present embodiment is the difference between the electron affinity of the (strong) electron accepting substance used in the intermediate layer 7 and the electron affinity of the luminescent organic substance contained in the light emitting unit 6. It is preferably located between.

  In addition, as an electron transport substance (organic substance), for example, KLET02 manufactured by Chemipro Kasei Co., Ltd. can be used. The physical properties of the electron transport material (organic substance) manufactured by Chemipro Kasei Co., Ltd. are shown below (from Chemipro Kasei Co., Ltd. HP. Http://www.chemipro.co.jp/Yuki# EL / Products.html).

  As mentioned above, although the embodiment having a typical laminated structure (unit) of the organic EL element of the present invention has been described, the present invention can be modified in various ways within the scope of the technical idea of the present invention. Naturally, the invention whose design has been changed is also included in the present invention.

<Deformation mode>
For example, when the electron transport layer is adjacent to the insulating organic material layer in the organic EL device of the present invention, the electron transporting organic material constituting the electron transporting layer may be mixed in the insulating organic material layer. That is, the organic EL element of the present invention may have an insulating organic substance / electron transporting substance mixed layer instead of the insulating organic substance layer.

  In the organic EL device of the present invention, when an organic layer composed of an organic material having a deep electron affinity is adjacent to the insulating organic material layer, the insulating organic material layer has a deep electron affinity constituting the organic material layer. The organic substance which has this may be mixed. That is, the organic EL device of the present invention may have a mixed layer of an insulating organic substance and an organic substance having a deep electron affinity instead of the insulating organic substance layer. Even in such a configuration, an undesirable interaction between an electron transporting substance and an organic substance having a deep electron affinity may be avoided, and this can be confirmed by experiments as appropriate.

  In general, a light-emitting layer included in a light-emitting unit is often composed of a host material and a light-emitting substance dispersed in the host material, and the host material has an electron transporting property. It may be the same material as the substance. Therefore, in the organic EL device of the present invention, when the electron transport layer is adjacent to the light emitting layer, the light emitting layer and the electron transport layer are configured as a single layer integrally formed using the same material. May be.

  In the organic EL device of the present invention, when the hole transport layer is adjacent to the light emitting layer, the hole transport material may emit light or function as a host material for the light emitting layer. The layer and the hole transport layer may be formed as a single layer formed integrally. Furthermore, in this case, the luminescent material may be dispersed and mixed only in the portion near the cathode of the hole transport layer.

More specifically, the organic EL device of the present invention can have, for example, the following laminated structure.
a) Anode b) Organic layer composed of organic substance having deep electron affinity c) Hole transport layer d) Light emitting layer e) Electron transport layer f) Electron transport layer doped with n-type carrier g) Insulating organic layer h ) Organic layer doped with n-type carrier and composed of organic material with deep electron affinity i) Repeat b) to h)
-------------------------------
j) Cathode

Moreover, the organic EL element of this invention can also take the following laminated structure.
a) Anode b) Organic layer composed of organic material having deep electron affinity c) Hole transport layer d) Light emitting layer e) Electron transport layer f) n-type carrier doped electron transport layer g) Insulating organic material layer h) Repeat b) to g) above
-------------------------------
i) Cathode

  The organic EL device of the present invention has a laminated structure having a mixed layer of an organic substance having a deep electron affinity and a hole transporting substance (an organic substance having a deep electron affinity: a hole transporting substance) in the laminated structure as described below. You may have. The mixed layer can be formed by heating a plurality of vapor deposition sources separately to form a laminated film, or a plurality of vapor deposition sources can be heated simultaneously to form a mixed film (co-evaporation), the latter However, it is not limited to these.

Moreover, the organic EL element of this invention can also take the following laminated structures, for example.
a) anode b) mixed layer of organic matter / hole transport material having deep electron affinity c) hole transport layer d) light emitting layer e) electron transport layer f) n-type carrier doped electron transport layer g) insulating organic layer h ) Organic layer doped with n-type carrier and composed of organic material having deep electron affinity i) Repeat b) to h)
-------------------------------
j) Cathode

Moreover, the organic EL element of this invention can also take the following laminated structure.
a) Anode b) Organic / hole transport material mixed layer with deep electron affinity c) Hole transport layer d) Light-emitting layer e) Electron transport layer f) Electron transport layer doped with n-type carrier g) Insulating organic layer h ) Repeat b) to g)
-------------------------------
i) Cathode

  Further, in the above laminated structure, a laminated constitution part (“electron transport layer / insulating organic layer”) in which the electron transport layer and the insulating organic layer are adjacent to each other is divided into an electron transport layer and an electron transporting organic material / insulating organic material mixed layer. May be changed to an adjacent laminated component (“electron transport layer / electron transport organic compound / insulating organic compound mixed layer”). That is, the electron transporting organic material constituting the electron transporting layer may be mixed with the insulating organic material layer and used.

  Still further, the entire electron transport layer portion may be replaced in advance with an “electron transport organic compound / insulating organic compound mixed layer”, and further, “electron transport organic compound / insulating organic compound mixed layer / insulating organic compound layer” As described above, an insulating organic material layer may be laminated adjacent to the mixed layer.

  Still further, in the above-mentioned laminated structure, a laminated constitution part (“electron transport layer / insulating organic layer”) in which the electron transport layer and the insulating organic layer are adjacent to each other is divided into an electron transport layer, an insulating organic material, and a deep electron affinity. May be changed to an adjacent laminated component (“electron transport layer / insulating organic substance / organic mixed layer having deep electron affinity”). That is, an organic material having a deep electron affinity constituting the organic layer may be mixed with the insulating organic material layer. Even in such a configuration, an undesirable interaction between the electron transporting organic substance and the organic substance having a deep electron affinity may be avoided, and these can be confirmed by experiments as appropriate.

  In general, in a light-emitting layer, a light-emitting substance is often present dispersed in a host material, and the host material may be the same as an electron transporting substance. Therefore, in the organic EL device of the present invention, the stacked constituent portion where the light emitting layer and the electron transport layer are adjacent may be a single layer made of the same material.

  The hole transport material having the above laminated structure may constitute a light emitting layer or may function as a host material of the light emitting layer. In these cases, the “hole transport layer / light emitting layer / electron transport layer” laminated structure The part may be changed to a stacked constituent part of “hole transport layer (light emitting layer) / electron transport layer”. When the light-emitting substance is dispersed and mixed only in the portion near the cathode of the hole transport layer, the “hole transport layer / light-emitting layer / electron transport layer” layered structure is “hole transport layer / hole transport material / light-emitting material”. It may be changed to a layered configuration portion of “mixed layer / electron transport layer”.

  The structure of the basic unit of the organic EL element of the present invention has been described above. However, the organic EL element of the present invention may have a structure in which a plurality of these basic units are stacked. The organic EL element of the present invention as described above can be produced by a conventionally known method using a vacuum vapor deposition apparatus. In particular, when obtaining an organic EL device having a structure in which each layer other than the anode and the cathode is formed of an organic compound, the production can be easily carried out without making the process complicated.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1
As the organic EL element of Example 1, layers of materials and thicknesses shown in Table 1 below were sequentially laminated on a glass substrate 11 to produce an organic EL element 10 including the structure shown in FIG. 3 (shown in FIG. 1). The stacking order is the reverse of the stacking order). For the formation of each layer, a vacuum deposition machine manufactured by Eiko Co., Ltd. was used. The thickness of each layer is measured using a stylus type surface shape measuring device (DEKTAK3030), and for the characteristic evaluation of the obtained organic EL element, source meter 2400 manufactured by Keithley Instruments Co., Ltd. and Topcon Co., Ltd. Luminance meter BM-7.

  The structure of the first light emitting unit 18-1 is, in order from the cathode 12, the electron transport layer 18-1a (KLET02) / light emitting layer 18-1b (Alq3) / hole transport layer 18-1c (NPB). The configuration of the second light emitting unit 18-2 is, in order from the cathode 12 side, an electron transport layer 18-2a (KLET02) / light emitting layer 18-2b (Alq3) / hole transport layer 18-2c (NPB). .

In addition, regions adjacent to the first insulating organic material layer 16-1 and the second insulating organic material layer 16-2 in the first light emitting unit 18-1 and the second light emitting unit 18-2, respectively (that is, , The region adjacent to the electron transport layer 18-1a and the electron transport layer 18-2a) 21b (thickness 50 mm) and the region adjacent to the insulating organic layer among the organic layers composed of the organic material having deep electron affinity 21a (thickness 20 mm) and n-type carrier (dopant):

Decamethylcobaltene represented by the formula:

≪Comparative example 1≫
As an organic EL device of Comparative Example 1, a comparative organic EL device was produced in the same manner as in Example 1 except that no n-type carrier (dopant) was used.

[Evaluation test]
The direct current voltage was set to 0.1 V / 2 seconds or 0.5 V / 2 between the anode and the cathode of the organic EL device (Example 1) and the comparative organic EL device (Comparative Example 1) produced as described above. The voltage was applied stepwise at a rate of 2 seconds, and the luminance (green light emission from the light emitting layer) and current value after 1 second of voltage increase were measured. FIG. 4 shows a graph plotting voltage (V) -luminance (cd / m ² ). As shown in FIG. 4, the voltage of Example 1 is significantly lower than that of Comparative Example 1.

  From the above, it can be said that the organic EL element of the present invention can be used in a wide range of product fields that require light generation, such as various light sources and image display devices that are required to have low energy consumption.

Claims (11)

The anode,
A cathode,
A plurality of light emitting units including a light emitting layer located between the anode and the cathode;
An intermediate layer located between the plurality of light emitting units,
The intermediate layer is composed of an insulating organic material layer provided at a site that serves as a barrier against charge transfer from the intermediate layer to the light emitting unit, and an organic layer adjacent to the insulating organic material layer,
The region adjacent to the intermediate layer of the light emitting unit and the region adjacent to the insulating organic material layer of the organic layer are doped with the same type of carrier,
Organic electroluminescent element characterized by the above. The difference between the electron affinity of the organic material constituting the organic layer and the ionization potential of the layer adjacent to the side of the organic layer opposite to the insulating organic material layer side is 1.4 eV or less,
The organic electroluminescent element according to claim 1. The organic material constituting the organic layer contains a hexaazatriphenylene derivative;
The organic electroluminescent element according to claim 2. The carrier is n-type;
The organic electroluminescent element according to any one of claims 1 to 3. The carrier comprises a metallocene derivative;
The organic electroluminescent element according to claim 4. The carrier has the following formula:
(Wherein at least one of X ₁ , X ₂ and X ₃ is an alkyl group),
The organic electroluminescent element according to claim 4. The insulating organic layer includes an organometallic complex having a β-diketone type ligand;
The organic electroluminescent element according to claim 1, wherein:   An organic electroluminescent device comprising a layer containing a heterocyclic compound and a metallocene derivative. The metallocene derivative contains Co or Ni;
The organic electroluminescent element according to claim 8. The heterocyclic compound is a pyridine derivative, a triazine derivative, a phenanthroline derivative or a hexaazaphenylene derivative;
The organic electroluminescent element according to claim 8 or 9, wherein A metallocene derivative and the following formula:
(Wherein, Ar ₁ , Ar ₂ and Ar ₃ are each independently an aryl group which may have a substituent), and a layer containing
An organic electroluminescent device characterized by the above.