JP2011061016A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element having a stable luminescent region. <P>SOLUTION: The organic electroluminescent element 10 is formed by sandwiching organic layers 3 including a luminescent layer 6 between a pair of electrodes comprising a positive electrode 2 and a negative electrode 3. A luminescent dopant material included in a luminescent layer 6 has a concentration gradient in accordance with a relationship between electron mobility and hole mobility of the luminescent dopant material included in the luminescent layer 6 in the thickness direction of the luminescent layer 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence element.

  In recent years, self-luminous display devices using organic electroluminescence (hereinafter referred to as organic EL) have been developed as display devices that replace liquid crystal display devices.

  An organic EL element has a structure in which a light-emitting layer containing a light-emitting compound is sandwiched between a cathode and an anode, and excitons are generated by injecting electrons and holes into the light-emitting layer and recombining them. The device emits light by utilizing light emission (fluorescence / phosphorescence) when the exciton is deactivated. This organic EL element can emit light at a voltage of several volts to several tens of volts, and is a self-luminous type, so it has a wide viewing angle, high visibility, and is a thin-film type completely solid element. Therefore, it attracts attention from the viewpoint of space saving and portability.

  In such an organic EL element, in order to suppress chromaticity change due to aging and deterioration of the peripheral compound due to injection of holes or electrons into the peripheral compound of the light emitting layer, the light emitting region is stably stabilized in the light emitting layer. It is important to control. For example, Patent Document 1 discloses an organic EL element in which a light emitting region control layer for controlling a light emitting region is formed in a light emitting layer. In the organic EL element disclosed in Patent Document 1, a light emitting region is controlled in each light emitting layer by arranging a light emitting region control layer containing a hole transport material and an electron transport material between two light emitting layers. is doing.

  By the way, the conventional organic EL element is of a type called “heterojunction” composed of different types of organic multilayer thin films, whereas in recent years, a new type of organic EL element called “homojunction” has been developed. Yes. In the homojunction organic EL element, a layer structure including layers such as an electron transport layer, a hole transport layer, and a light emitting layer is realized by adding (doping) another substance into a single host material. Although the homojunction type organic EL element has a much simpler structure, it is expected as an organic EL element having the same efficiency as the heterojunction type.

JP 2007-299645 A (published November 15, 2007)

Hayato Hayato and three others, “Bis (carbazolyl) benzodifuran: A High-Mobility Ambipolar Material for Homojunction Organic Light-Emitting Diode Devices ], [Online], May 21, 2009, Advanced Materials, Internet <URL: http://www3.interscience.wiley.com/journal/122394710/abstract?CRETRY=1&SRETRY=0>

  However, in the homojunction organic EL element, control of the light emitting region is a particularly important issue.

  That is, in the homojunction organic EL element, the host material that forms a layer structure including layers such as an electron transport layer, a hole transport layer, and a light emitting layer is a single material. It is difficult to ensure the balance of hole transport properties, and it is difficult to control the light emitting region. In addition, since the light emitting layer of the homojunction organic EL element is formed by doping a light emitting material in the host material, the boundary of the light emitting region tends to be ambiguous. For this reason, in the homojunction organic EL element, chromaticity change due to aging, deterioration of peripheral compounds in the light emitting layer, and the like are likely to occur.

  On the other hand, in the technique disclosed in Patent Document 1, since the light emitting region control layer is provided to control the light emitting region, there is a problem that the layer structure is complicated and the thickness thereof is increased. In addition, since the light emitting region control layer described in Patent Document 1 can emit light even inside thereof, it cannot be said that the light emitting region is sufficiently controlled.

  Under such circumstances, there is a demand for an organic EL element in which the light emitting region is stably controlled with a simpler configuration.

  This invention is made | formed in view of the said subject, The objective is to provide the organic electroluminescent element which stabilized the light emission area | region by simpler structure.

  An organic electroluminescence element according to the present invention (hereinafter referred to as an organic EL element) is an electroluminescence element in which an organic layer including a light emitting layer is sandwiched between a pair of electrodes consisting of an anode and a cathode in order to solve the above-described problems. The light emitting dopant material contained in the light emitting layer has a concentration gradient in the thickness direction of the light emitting layer according to the relationship between the electron mobility and the hole mobility of the light emitting dopant material. Yes.

  In the above configuration, the light emitting region can be controlled to the light emitting layer by utilizing the difference between the electron mobility and the hole mobility of the light emitting dopant material in the light emitting layer. That is, the movement balance of electrons and holes in the light emitting layer is preferably adjusted, and electrons and holes can be efficiently recombined in the central portion of the light emitting layer, so that high light emission efficiency can be realized. Further, holes and electrons can be confined in the light emitting layer. Therefore, an organic electroluminescence device having a light emitting region stabilized in the light emitting layer is provided.

  Moreover, in the said structure, dope density | concentrations differ in a light emitting layer, and a light emitting layer is divided into the hole transport layer side with a large hole mobility, and the electron transport side with a large electron mobility. For this reason, even if the light emitting layer compound or the peripheral compound deteriorates during aging, the recombination probability of electrons and holes in the light emitting layer remains high. Therefore, the light emitting region is not likely to fluctuate greatly. Therefore, according to the above configuration, the light emitting region is not shifted due to aging, so that the chromaticity shift is less likely to occur and the life of the organic EL element is extended.

  In general, the mobility of a host (an organic compound not containing a heavy element metal (may include P or Si)) and the mobility of a phosphorescent dopant (a metal complex such as an Ir complex) having high emission efficiency In general, the organic EL device according to the present invention can be widely applied.

  Moreover, in the said structure, since it is not necessary to provide a light emission area | region control layer like patent document 1, it can be said that it is a simple structure. Therefore, the layer structure of the organic EL element according to the present invention can be easily manufactured, and the cost can be reduced during mass production.

  In the organic EL device according to the present invention, the hole mobility of the light emitting dopant material is larger than the electron mobility, and the concentration of the light emitting dopant material in the light emitting layer decreases from the anode toward the cathode. May be.

  In the light-emitting layer having the concentration gradient as described above, holes injected from the anode into the organic layer proceed in the light-emitting layer, but the concentration of the light-emitting dopant material decreases as it goes toward the cathode. The closer to the cathode, the more limited the movement.

  According to the above configuration, since electrons and holes can be efficiently recombined in the central portion of the light emitting layer, the light emitting region can be stabilized in the light emitting layer with a simple configuration.

  In the organic EL device according to the present invention, the electron mobility of the light emitting dopant material is larger than the hole mobility, and the concentration of the light emitting dopant material in the light emitting layer decreases from the cathode toward the anode. May be.

  In the light emitting layer having the concentration gradient of the light emitting dopant as described above, electrons injected from the cathode into the organic layer proceed in the light emitting layer, but the concentration of the light emitting dopant material decreases as it goes toward the cathode. In addition, the movement is limited as it approaches the anode.

  According to the above configuration, since electrons and holes can be efficiently recombined in the central portion of the light emitting layer, the light emitting region can be stabilized in the light emitting layer with a simple configuration.

  In the organic EL device according to the present invention, the electron mobility and the hole mobility of the light emitting dopant material are equal, and the concentration of the light emitting dopant material in the light emitting layer is from the central portion of the thickness of the light emitting layer. It may decrease towards the anode and the cathode.

  In the light-emitting layer having the concentration gradient of the light-emitting dopant material as described above, the holes injected from the anode and the charge injected from the cathode are both carried to the central portion of the thickness of the light-emitting layer, and recombination at the central portion. Probability increases.

  According to the above configuration, since electrons and holes can be efficiently recombined in the central portion of the light emitting layer, the light emitting region can be stabilized in the light emitting layer with a simple configuration.

  Moreover, it is preferable that the host material of the said organic layer consists of a single kind.

  With the above configuration, the layer structure of the organic EL element according to the present invention can be more easily manufactured, and cost reduction during mass production can be realized.

  In the organic EL device according to the present invention, the concentration of the light emitting dopant material in the light emitting layer is preferably in the range of 10% to 30% with respect to the host material in the light emitting layer.

  According to the above configuration, the light emitting region can be effectively stabilized in the light emitting layer.

  The present invention relates to an electroluminescence device in which an organic layer including a light emitting layer is sandwiched between a pair of electrodes consisting of an anode and a cathode, and the light emitting dopant material contained in the light emitting layer is an electron mobility of the light emitting dopant material. Provided is an organic electroluminescence device that has a simple structure and has a stable light emitting region in the light emitting layer because it has a concentration gradient in the thickness direction of the light emitting layer in accordance with the relationship between the light emitting layer and the hole mobility. There is an effect that can be.

It is sectional drawing which shows schematically the organic EL element which concerns on one Embodiment of this invention.

  The organic electroluminescent element (organic EL element) of the present invention is an electroluminescent element in which an organic layer including a light emitting layer is sandwiched between a pair of electrodes consisting of an anode and a cathode, and the light emitting dopant contained in the light emitting layer The material is characterized by having a concentration gradient in the thickness direction of the light emitting layer according to the relationship between the electron mobility and the hole mobility of the light emitting dopant material.

  Specifically, the hole mobility of the light emitting dopant material is larger than the electron mobility, and the concentration of the light emitting dopant material in the light emitting layer decreases from the anode toward the cathode.

  Alternatively, the electron mobility of the light emitting dopant material is larger than the hole mobility, and the concentration of the light emitting dopant material in the light emitting layer decreases from the cathode toward the anode.

  Alternatively, the electron mobility and the hole mobility of the light emitting dopant material are equal, and the concentration of the light emitting dopant material in the light emitting layer decreases from the center of the thickness of the light emitting layer toward the anode and the cathode. .

  In the present invention, the meaning of “decrease” means that the total decreases, and may decrease stepwise or gradually.

  Moreover, it is preferable that the density | concentration of the light emission dopant material with respect to a host material changes in the range of 10% or more and 30% or less.

  Note that in this specification, the concentration of the light emitting material in the light emitting layer can be calculated from the attenuation coefficient and refractive index difference between the host compound and the dopant compound by a spectroscopic ellipsometer. Moreover, the light emitting layer itself can be dissolved in a solvent and determined by an HPLC (liquid chromatography) apparatus.

  In the present invention, “the electron mobility and the hole mobility in a light-emitting dopant material are equal” does not necessarily require a completely identical value, and the difference in mobility between holes and electrons is within one digit. If there is, it is considered that the electron mobility and the hole mobility are equal.

  In the present invention, what is meant by “the central portion of the thickness of the light emitting layer” may be a region within a certain range including the center in the film thickness direction of the light emitting layer.

In addition, the organic EL element according to the present invention can employ, for example, the following configuration (1) or (2), but is not limited thereto, and may be appropriately determined according to the purpose and the like. In addition, the layer structure shown below has shown the organic material layer formed between an anode and a cathode.
Layer structure (1): Hole transport layer / light emitting layer / electron transport layer layer structure (2): Hole transport layer / block layer / light emitting layer / electron transport layer layer structure (3): Hole transport layer / light emitting layer / Block layer / electron transport layer layer configuration (4): hole transport layer / block layer / light emitting layer / block layer / electron transport layer Hereinafter, with reference to FIG. 1, an organic EL employing the configuration of (1) above The element will be described as this embodiment. FIG. 1 is a cross-sectional view showing a schematic configuration of an organic EL element 10 according to an embodiment of the present invention.

  As shown in FIG. 1, in the organic EL element 10 according to the present embodiment, an anode 2, an organic material layer 3, and a cathode 4 are laminated in this order on a substrate 1 serving as a base.

  As the substrate 1, a transparent glass substrate or the like can be used. However, a top emission type organic EL element does not require translucency in the substrate. Therefore, a semiconductor substrate such as a silicon wafer may be used as the substrate 1.

  The anode 2 only needs to have a function as an electrode for supplying holes to the organic material layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the organic EL element. Can be appropriately selected. As the anode 2, for example, indium tin oxide (ITO) is preferably used.

  The periphery of ITO may be patterned so as to be surrounded by an organic insulating film. In this case, the organic insulating film is not limited, but a polyimide resin material or the like is preferably used.

  The cathode 4 only needs to have a function as an electrode for injecting electrons into the organic compound layer, and the shape, structure, size and the like are not particularly limited, and are appropriately determined depending on the use and purpose of the light-emitting element. You can choose. As the cathode 4, for example, aluminum is preferably used.

  The organic material layer 3 is roughly divided into a hole transport layer 5 on the anode 2 side, a light emitting layer 6, and an electron transport layer 7 on the cathode 4 side.

  Here, the present invention can also be applied to both heterojunction type and homojunction type organic EL elements.

  When the organic EL element 10 is a heterojunction organic EL element, the host material contained in each of the hole transport layer 5, the light emitting layer 6, and the electron transport layer 7 is appropriately selected from known host materials. Can do.

  On the other hand, when the organic EL element 10 is a homojunction organic EL element, the host material of the organic material layer 3 is made of a single kind of material. The hole transport layer 5, the light emitting layer 6, and the electron transport layer 7 are formed by adding a dopant corresponding to each layer to a single type of host material.

However, the host material contained in the light-emitting layer 6 (in the case of the homojunction type, the organic material layer 3) includes electron mobility and hole mobility, both in the heterojunction type and the homojunction type. It is preferable to use materials that are both high and comparable. If the electron mobility and hole mobility of the host material are both 1 × 10 ⁻⁴ cm ² / V · sec or more, it is possible to reduce the voltage of the device. Examples of the host material for the organic material layer 3 include 2-methyl-9,10-di (2-naphthyl) anthracene (MADN) and bis (carbazolyl) benzodifuran (CZBDF).

  The hole transport layer 5 is a layer having a function of receiving holes from the anode 2 side and transporting them to the cathode side, and contains an electron-accepting dopant (p-dopant). As the p-dopant, for example, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinone dimethane (F4TCNQ) can be used.

  The electron transport layer 7 is a layer having a function of receiving electrons from the cathode 4 side and transporting them to the anode side, and contains an electron donating dopant (n-dopant). As the n-dopant, for example, a metal such as cesium (Cs) can be used.

  The light emitting layer 6 is a layer having a function of providing a hole and electron recombination field to emit light, and contains a light emitting dopant material (light emitting dopant). As a luminescent dopant, either one of a hole mobility and an electron mobility may be high, and both may be comparable. Specifically, examples of the light emitting dopant of the light emitting layer 6 include Ir complex, Pt complex, Eu complex, Au complex, Re complex, Ru complex, and Cu complex.

Moreover, Ir (dpbic) ₃ , Ir (ppy) ₃ etc. are mentioned as a light emission dopant with a hole mobility larger than an electron mobility. In this case, the hole mobility is preferably 1 × 10 ⁻⁴ cm ² / V · sec or more and the electron mobility is preferably 1 × 10 ⁻⁴ cm ² / V · sec or less. Furthermore, electron mobility as the hole mobility greater than the light emitting dopant, Alq _3, and the like. In this case, the electron mobility is preferably 1 × 10 ⁻⁴ cm ² / V · sec or more and the hole mobility is preferably 1 × 10 ⁻⁴ cm ² / V · sec or less. Further, the difference between the electron mobility and the hole mobility of the light-emitting dopant having the same electron mobility and hole mobility may be within one digit, but it is 1 × 10 ⁻⁴ cm ² / V · sec or less. More preferably.

  In addition, although a light emitting dopant may mix and use multiple types, a single type is preferable.

  The light emitting dopant contained in the light emitting layer 6 has a concentration gradient in the thickness direction (film thickness direction) of the light emitting layer 6 according to the relationship between the hole mobility and the electron mobility of the light emitting dopant used. Specifically, when the hole mobility of the light emitting dopant is μh and the electron mobility is μe, the light emitting dopant of the light emitting layer 6 has a concentration gradient as described below.

  When μh> μe, the concentration of the light-emitting dopant in the light-emitting layer 6 is highest on the anode 2 side and decreases from the anode 2 side toward the cathode 4 side.

  When μh <μe, the concentration of the light-emitting dopant in the light-emitting layer 6 is highest on the cathode 4 side and decreases from the cathode 4 side toward the anode 2 side.

  When μh≈μe, the concentration of the light-emitting dopant in the light-emitting layer 6 is highest at the center of the light-emitting layer 6 and decreases toward the anode 2 side and the cathode 4 side.

  Moreover, it is preferable that the density | concentration of the light emission dopant in the light emitting layer 6 changes in the range of 10% or more and 30% or less with respect to a host material.

  In a normal organic EL device, the concentration of the light-emitting dopant in the light-emitting layer is generally about 5% to 10% with respect to the host material. In the present invention, as described above, the light emission position can be suitably controlled by making a change in a larger range than usual. Further, if it is 30% or more, the interaction between the dopants becomes large, and the deactivation of light emission occurs. Therefore, it is preferably 30% or less.

  Further, the concentration of the light-emitting dopant in the light-emitting layer 6 may be decreased in a stepwise manner, or may be decreased step by step through a plurality of steps.

  For example, when μh> μe, the concentration of the light-emitting dopant in a certain region on the anode side in the light-emitting layer 6 may be 30%, and the concentration of the light-emitting dopant in the remaining region on the cathode side in the light-emitting layer 6 may be 10%. . Alternatively, the concentration of the luminescent dopant may gradually decrease from 30% to 10% from the anode side toward the cathode side.

  For example, when μh <μe, the concentration of the light-emitting dopant may be arranged opposite to the case where μh> μe.

  For example, when μh≈μe, the concentration of the light-emitting dopant is 10% in a certain region on the anode side in the light-emitting layer 6, and the concentration of the light-emitting dopant is 30% in the central region of the light-emitting layer 6. The concentration of the luminescent dopant may be 10% in the remaining cathode-side region of the layer 6. Alternatively, in a certain region on the anode side in the light emitting layer 6, the concentration of the light emitting dopant gradually increases from 10% to 30% from the anode side to the cathode side, and in the remaining cathode side region in the light emitting layer 6. May gradually decrease from 30% to 10% from the anode side toward the cathode side.

  In addition, as a method of forming the light emitting layer in which the dope concentration changes in an inclined manner, the method is not limited to this, but an in-line method (substrate conveyance, deposition source fixation) can be used.

  According to the above configuration, the light emitting region can be stably controlled in the light emitting layer 6 with a simpler configuration.

  In addition, when providing a block layer further with respect to the said structure, a block layer should just be comprised from the same material as the host material of the light emitting layer 6. FIG.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example.

Example 1
First, a silicon semiconductor film was formed on a glass substrate by plasma CVD, and a crystallization process was performed to form a polycrystalline silicon semiconductor film. Subsequently, the polycrystalline silicon thin film was etched to form a plurality of island patterns. On the plurality of island patterns, a gate insulating film and a gate electrode layer were sequentially formed, and patterning was performed by an etching process. Subsequently, a source region and a drain region were formed on each island of the island-shaped polycrystalline silicon semiconductor film by doping to produce a plurality of TFTs. Further, an interlayer insulating film having a function as a planarizing layer was formed, and an ITO pixel electrode was formed through a through hole. A polyimide resin layer was used as a single layer as the organic insulating film, and was patterned so as to surround the periphery of the ITO pixel electrode. Thereafter, the substrate was ultrasonically cleaned and baked under reduced pressure at 200 ° C. for 3 hours. The anode was formed by the above process.

  Next, the following organic material layers (hole transport layer / light emitting layer / electron transport layer) were deposited on the anode by vacuum deposition. Note that MADN was used as a host material for the organic material layer.

  First, as a hole transport layer, a layer in which 20% of F4TCNQ as a p-dopant was doped with respect to MADN was formed to 40 nm.

Next, green phosphorescent dopant (μh = 3.0 × 10 ⁻³ cm ² / V · sec and μe = 4.0 × 10 ⁻⁴ cm ² / V · sec with respect to MADN by co-evaporation. Then, a layer doped with 30% of an Ir complex (hereinafter referred to as “Ir complex A”) having a hole mobility μh larger than the electron mobility μe is formed to a thickness of 15 nm, and then the amount of co-deposition of Ir complex A is changed. Then, a layer of 15 nm doped with 10% of Ir complex A with respect to MADN was formed, thereby forming a light emitting layer.

The hole mobility and electron mobility can be obtained by measuring values at 10 ⁵ V / cm by the Time of Flight (TOF) method.

  Finally, as an electron transport layer, a layer in which Cs which is an n-dopant was doped by 30% was formed to 40 nm with respect to MADN.

  After the organic material layer is formed, lithium fluorine (LiF) is formed with a thickness of 0.5 nm by a vacuum evaporation method (deposition rate 1 Å / sec), and aluminum (Al) is formed with a thickness of 100 nm as a cathode. did.

  In the organic EL device of Example 1, the Ir complex A is present in the light emitting layer at two levels so as to decrease from the anode side toward the cathode side.

(Example 2)
Example 2 differs from Example 1 in that the organic material layer includes a block layer. Below, the formation process of an organic material layer is demonstrated and other description is abbreviate | omitted.

  In Example 2, the following organic material layers (hole transport layer / block layer / light emitting layer / block layer / electron transport layer) were deposited on the anode by a vacuum deposition method. Note that MADN was used as a host material for the organic material layer.

  First, as a hole transport layer, a layer in which 20% of F4TCNQ as a p-dopant was doped with respect to MADN was formed to 30 nm.

  Next, only 10 nm of MADN was formed as a block layer.

  Next, 15 nm of a layer in which 30% of Ir complex A, which is a green phosphorescent dopant, is doped to MADN is formed by co-evaporation, and then only the amount of co-deposition of Ir complex A is changed. A layer doped with 10% was formed to 15 nm. Thus, a light emitting layer was formed.

  Next, only 10 nm of MADN was formed as a block layer again.

  Finally, as an electron transport layer, a layer in which 30% of Cs which is an n-dopant was doped with respect to MADN was formed to 30 nm.

(Example 3)
Example 3 differs from Example 1 in that the organic material layer includes a block layer and that the Ir complex A is present in a gradient concentration in the light emitting layer. Below, the formation process of an organic material layer is demonstrated and other description is abbreviate | omitted.

  In Example 3, the following organic material layers (hole transport layer / block layer / light emitting layer / block layer / electron transport layer) were deposited on the anode by vacuum deposition. Note that MADN was used as a host material for the organic material layer.

  First, as a hole transport layer, a layer in which 20% of F4TCNQ as a p-dopant was doped with respect to MADN was formed to 30 nm.

  Next, only 10 nm of MADN was formed as a block layer.

  Next, 30 nm of a layer doped with Ir complex A, which is a green phosphorescent dopant, was formed on MADN by co-evaporation. At this time, the doping concentration of Ir complex A with respect to MADN was changed in an inclined manner from 30% to 10% by an in-line method. Thus, a light emitting layer was formed.

  Next, only 10 nm of MADN was formed as a block layer again.

  Finally, as an electron transport layer, a layer in which 30% of Cs which is an n-dopant was doped with respect to MADN was formed to 30 nm.

Example 4
In Example 4, unlike in Examples 1 to 3, in the light emitting layer, μh = 3.0 × 10 ⁻² cm ² / V · sec and μe = 4.0 × 10 ⁻² cm ² / V · sec. Ir complex (hereinafter referred to as Ir complex B), which is a green phosphorescent dopant having the same hole mobility μh and electron mobility μe, is used. That is, in Example 4, the Ir complex B has the highest concentration in the central portion of the light emitting layer.

  Below, the formation process of an organic material layer is demonstrated and other description is abbreviate | omitted.

  In Example 4, the following organic material layers (hole transport layer / block layer / light emitting layer / block layer / electron transport layer) were deposited on the anode by a vacuum deposition method. Note that MADN was used as a host material for the organic material layer.

  First, as a hole transport layer, a layer in which 20% of F4TCNQ as a p-dopant was doped with respect to MADN was formed to 30 nm.

  Next, only 10 nm of MADN was formed as a block layer.

  Next, 30 nm of a layer doped with Ir complex B, which is a green phosphorescent dopant, was formed on MADN by co-evaporation. At this time, the doping concentration of Ir complex B with respect to MADN was varied by an in-line method. Specifically, the first 15 mm was changed in an inclined manner from 10% to 30%, and the subsequent 15 mm was changed in an inclined manner from 30% to 10%. Thus, a light emitting layer was formed.

  Next, only 10 nm of MADN was formed as a block layer again.

  Finally, as an electron transport layer, a layer of 30 nm doped with 30% of Cs as an n-dopant was formed with respect to MADN.

(Example 5)
In Example 5, as in Example 4, Ir complex B, which is a green phosphorescent dopant having substantially the same hole mobility μh and electron mobility μe, is used. Example 5 differs from Example 4 in that the concentration gradient of Ir complex B is not a gradient but is stepwise.

  Below, the formation process of an organic material layer is demonstrated.

  In Example 5, the following organic material layers (hole transport layer / block layer / light emitting layer / block layer / electron transport layer) were deposited on the anode by a vacuum deposition method. Note that MADN was used as a host material for the organic material layer.

  First, as a hole transport layer, a layer in which 20% of F4TCNQ as a p-dopant was doped with respect to MADN was formed to 30 nm.

  Next, only 10 nm of MADN was formed as a block layer.

  Next, 30 nm of a layer doped with Ir complex B, which is a green phosphorescent dopant, was formed on MADN by co-evaporation. At this time, by changing only the co-deposition amount of Ir complex A, the doping concentration of Ir complex A with respect to MADN is 10% in the first 10 mm, 30% in the next 10 mm, and 10 mm in the last 10 mm. Again 10%. Thus, a light emitting layer was formed.

  Next, only 10 nm of MADN was formed as a block layer again.

  Finally, as an electron transport layer, a layer of 30 nm doped with 30% of Cs as an n-dopant was formed with respect to MADN.

(Comparative Example 1)
In Comparative Example, an organic EL device was produced in the same manner as in Example 1 except that 30 mm of a layer obtained by doping 15% of Ir complex A into MADN was formed as the light emitting layer.

(Measurement of drive voltage, current efficiency, CIE chromaticity)
A voltage was applied so that the obtained organic EL elements of Examples 1 to 5 and the organic EL element of the comparative example emitted light at 1000 cd / m ² , and the driving voltage, current efficiency, and CIE chromaticity at this luminance were measured. did. Moreover, the chromaticity shift | offset | difference in T70 at the time of 1000 cd / m < ² > light emission in each organic EL element was measured, and also the lifetime at the time of 1000 cd / m < ² > light emission was measured.

Note that the chromaticity deviation, a dark room, under the condition of a constant current value, at 1000 cd / ^{m 2} light emission, and performs the chromaticity measurement under conditions in which the luminance is deteriorated to 700 cd / ^{m 2,} compared to the initial state The CIE chromaticity x and y were measured and the difference was shown.

  The obtained results are shown in Table 1. In addition, since Example 4 and 5 differ from Examples 1-3 and Comparative Example 1 in the material of a light emission dopant, the characteristic and lifetime cannot be compared.

  In Examples 1 to 3, the performance was improved compared to Comparative Example 1 in terms of current efficiency, chromaticity shift, and lifetime. Therefore, in Comparative Example 1, the movement to the outside of the light emitting layer (F4TCNQ or Cs) is likely to occur and the light emission efficiency is lowered, whereas in Examples 1 to 3, light emission is suppressed in the light emitting layer. It became clear that.

  In addition, the life of Example 2 was kept longer than that of Example 1. Therefore, it has been clarified that by avoiding contact between the light emitting layer and the hole transport layer or the electron transport layer, deterioration of the interface between layers is suppressed and the life is extended.

  Further, the life of Example 3 was kept longer than that of Example 2. Therefore, it has been clarified that when the concentration of the light emitting dopant in the light emitting layer is changed in an inclined manner, the light emitting region is controlled more efficiently.

  In addition, Examples 4 and 5 showed the same excellent performance as Examples 1-3.

  The present invention can be used as organic electroluminescence that can be mass-produced at low cost.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Organic material layer 4 Cathode 5 Hole transport layer 6 Light emitting layer 7 Electron transport layer 10 Organic EL element

Claims (6)

An electroluminescence element having an organic layer including a light emitting layer sandwiched between a pair of electrodes consisting of an anode and a cathode,
The light-emitting dopant material contained in the light-emitting layer has a concentration gradient in the thickness direction of the light-emitting layer according to the relationship between the electron mobility and the hole mobility of the light-emitting dopant material. element.   The hole mobility of the light emitting dopant material is larger than the electron mobility, and the concentration of the light emitting dopant material in the light emitting layer decreases from the anode toward the cathode. Organic electroluminescence device.   The electron mobility of the light emitting dopant material is larger than a hole mobility, and the concentration of the light emitting dopant material in the light emitting layer decreases from the cathode toward the anode. Organic electroluminescence device.   The electron mobility and hole mobility of the light emitting dopant material are equal, and the concentration of the light emitting dopant material in the light emitting layer decreases from the center of the thickness of the light emitting layer toward the anode and the cathode. The organic electroluminescent element according to claim 1.   The organic electroluminescent element according to any one of claims 1 to 4, wherein the organic layer has a single host material.   The concentration of the light-emitting dopant material in the light-emitting layer is in the range of 10% to 30% with respect to the host material in the light-emitting layer. Organic electroluminescence element.

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