KR20050054945A - Organic electroluminescence device and organic electroluminescence display - Google Patents

Abstract

An organic EL device comprises a transparent substrate (31), and over the substrate (31), an anode (32), a hole injection layer (33), a hole transport layer (34), a luminescent layer (35), an electron transport multilayer body (36), a cathode-side electron transport layer (37), and a cathode (38) all formed in a multilayer structure. The electron transport multilayer body (36) has a structure in which electron transport layers (36A, 36B) of two types having different electron affinities are alternated. By increasing the electron current injected from the cathode (38), the electron current and the hole current are balanced, thereby enhancing the luminous efficiency.

Description

Organic electroluminescent device and organic electroluminescent display {ORGANIC ELECTROLUMINESCENCE DEVICE AND ORGANIC ELECTROLUMINESCENCE DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to optoelectronic devices and flat panel displays using optoelectronic devices, and more particularly to organic electroluminescent devices and organic electroluminescent displays.

In recent years, market needs have gradually shifted from conventional large-sized, CRT (brown tube) displays to thin, lightweight flat displays. As a flat display, a liquid crystal display and a plasma display are put into practical use, and it is put to practical use as a home television receiver, the monitor for personal computers, etc.

In recent years, the electroluminescent display (henceforth "EL display"), especially organic electroluminescent display is attracting attention as a next generation flat display. The organic EL device constituting the organic EL display has been 10V or less since the report of a stacked device in which each organic thin film of hole transporting and electron transporting is laminated (CW Tang and SA VanSlyke, Applied Physics Letters vol. 51, 913 (1987)). As a large area light emitting device that emits light at low voltage of, attention has been actively studied. Compared with a liquid crystal monitor, organic electroluminescent display is a natural light emission type, and since it can be thinned without requiring a backlight, the structure is simple and a flexible display can be manufactured, and it is expected that the application range will expand. On the other hand, in practical use, the organic electroluminescent display has left a problem to lengthen lifetime.

1 is a schematic cross-sectional view of a conventional organic EL device. As shown in FIG. 1, the organic EL element 10 includes a transparent anode 12, a hole injection layer 13, a hole transport layer 14, a light emitting layer 15, and an electron transport layer on a transparent insulating substrate 11. 16), the cathode 18 is formed in this order. In the organic EL element 10, holes are injected from the transparent anode 11 into the hole injection layer 13, electrons are injected from one cathode 19, and holes and electrons are recombined and emitted from the light emitting layer 15. By the energy, the organic phosphor contained in the light emitting layer 15 is excited and emits light. Since the luminance is determined by the recombination amount of holes and electrons to be recombined per hour, and the luminous efficiency is expressed by the luminance with respect to the consumption current, the better the balance between the amount of electrons contributing to the emission and the amount of holes, the higher the luminous efficiency.

In the organic EL element 10, the transparent anode 12 is formed of indium tin oxide (ITO), and the surface of the ITO is subjected to oxidation treatment by UV ozone, oxygen plasma, or the like, and the work function of the hole injection layer. By matching with the ionization potential, the hole injection barrier from the transparent anode 12 to the hole injection layer 13 is reduced to increase the amount of hole current.

On the other hand, Li, Mg, alloys Al-Li, Mg-Ag, and the like, which are metals having a low work function, having a small electron injection barrier to the electron transport layer 16 are used for the cathode 18. In recent years, a metal fluoride such as LiF / Al is introduced as an electron injection layer so that even if single Al is used for the cathode 18, a device using a single work alloy of low work function metal such as Li, Mg, or an alloy thereof as the cathode It is known to exhibit an electron injection capability into an organic film equivalent to, and to exhibit a value equal to or greater than that of using a work function metal having a low work function metal as a cathode (LS Hung, CW Tang Tang, and MG Mason). , Applied Physics Letters vol. 70 (2), 152 (1997)).

However, even when such a low work function metal, an alloy, or an electron injection layer such as LiF is introduced into the cathode 18, the amount of electron current reaching the light emitting layer 15 is small compared to the amount of hole current, and thus the amount of electron current and hole Due to the imbalance of the amount of current, a hole current that does not contribute to light emission is wasted, and there is a problem that the light emission efficiency cannot be sufficiently improved.

In addition, when the luminous efficiency is low, in order to obtain sufficient luminance, it is necessary to increase the voltage to be applied and flow more current. When the voltage is excessively applied, the anode 12, the hole injection layer 13, and the cathode ( The chemical reaction easily occurs at the interface between the 18) and the electron transport layer 16, and the hole injection layer 13 and the electron transport layer 16 are deteriorated to degrade the function, thereby leading to device destruction. Therefore, there is a problem that the device life cannot be sufficiently secured.

Further, Japanese Laid-Open Patent Publication No. 2002-43063 discloses that the formation of a multilayer electron transport region improves the injection of the carrier into the light emitting layer or lowers the operating voltage. However, in this publication, the specific structure is not disclosed about the structure of a multilayer electron transport region.

[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-43063

[Patent Document 2] Japanese Patent Application Laid-Open No. 2001-357975

1 is a cross-sectional view of a conventional organic EL device.

2 is a cross-sectional view of a device structure according to the present invention.

FIG. 3 is a I-V characteristic diagram of the device structure shown in FIG. 2. FIG.

4 is a cross-sectional view of an organic EL device of a first embodiment of the present invention.

5 is an energy diagram of the organic EL device of the first embodiment;

6 is a diagram for explaining a method for obtaining an energy gap.

7 is a view for explaining a method for obtaining an ionization potential.

8 is a diagram showing characteristic values of an electron transporting layer and a hole transporting layer used in an organic EL device according to Examples and Comparative Examples.

9 is a diagram showing the layer configuration and evaluation results of the organic EL elements according to the first to third examples and the first to second comparative examples.

Fig. 10 is a diagram showing the layer structure and evaluation results of the organic EL elements according to the fourth to fifth examples and the third to fourth comparative examples.

11 is an exploded perspective view of an organic EL display of a second embodiment of the present invention.

<Description of the code>

31: Substrate

32: anode

33: hole injection layer

34: hole transport layer

35: light emitting layer

36: electron transport laminate

37: cathode transport layer

38: cathode

36A1, 36A2: first electron transport layer

36B1 and 36B2: second electron transport layer

50: organic EL display

Therefore, an object of the present invention is to provide a novel and useful organic electroluminescent device and an organic electroluminescent display that solve the above problems.

The more specific subject of this invention is providing the organic electroluminescent element which is excellent in luminous efficiency and long life is possible.

According to one aspect of the invention,

An anode, a light emitting layer formed on the anode, a carrier transporting laminate formed on the light emitting layer, and a cathode formed on the carrier transporting laminate,

The carrier transport laminate is formed by alternately stacking a first carrier transport layer and a second carrier transport layer,

The first carrier transport layer and the second carrier transport layer is provided with an organic electroluminescent device, characterized in that the electron transport properties are different from each other.

Here, electron transportability is determined by the electron affinity, ionization potential, energy gap, etc. of the organic material which forms a 1st carrier transport layer and a 2nd carrier transport layer.

According to the present invention, the carrier transport laminate in which the first carrier transport layer and the second carrier transport layer having different electron transport properties are alternately stacked between the light emitting layer and the cathode can increase the amount of electron current injected into the light emitting layer. As a result, the organic electroluminescent device of the present invention has a high luminous efficiency and a long lifetime by balancing the electron current amount and the hole current amount.

The first carrier transport layer and the second carrier transport layer have different electron affinity. As the electron affinity between the first carrier transport layer and the second carrier transport layer is different from each other, multiple quantum wells can be formed to increase the amount of electron current. Moreover, electron affinity is represented by the energy difference of the energy of the conductor lower end of a material which comprises a carrier transport layer, etc., and a vacuum level, and is represented by a positive value.

According to another aspect of the present invention, there is provided an organic electroluminescent display provided with any one of the above organic electroluminescent elements.

According to the present invention, an organic electroluminescent display having a high luminous efficiency and a long lifetime can be realized.

First, the process by which the inventors of the present invention have been achieved will be described. The inventors of the present invention perform the experiments described below to form an electron transporting laminate in which an electron transporting layer having different electron transporting properties is alternately formed between a light emitting layer and a cathode, thereby increasing the injectable current density. Got.

2 is a cross-sectional view of the device structure according to the present invention used in this experiment. Referring to FIG. 2, the device structure 20 includes a substrate 21, an anode 22 formed on the substrate 21, and two different electron transport layers 26A and 26B alternated on the anode 22. The electron transport stack 25 is stacked with a negative electrode side electron transport layer 27 stacked on the electron transport stack 26, and a cathode 28 formed on the cathode side electron transport layer 27. . Al is used for the anode 22 and LiF / Al is used for the cathode 28. In addition, TYE704 (trade name of Toyo Ink Co., Ltd.) is used for the cathode-side electron transport layer 27. In the electron transport laminate 26, the first electron transport layer 26A1, the second electron transport layer 26B1, and the first electron transport layer 26A2 and the second electron transport layer 26B2 are alternately stacked in this order. It is. Here, TYE704 is used for the first electron transport layer 26A, and TYG201 (trade name manufactured by Toyo Ink Co., Ltd.) is used for the second electron transport layer 26B. TYG201 (trade name of Toyo Ink Co., Ltd.) is known as a green light emitting material, but can also be used as an electron transporting layer. The same device, that is, the device structure of repeating number N = 0, was produced except for the device structure of N = 1, 3, 4, and the electron transport laminated body for comparison. The thickness of the electron transport laminated body 26 (shown in {}) and the cathode side electron transport layer 27 is shown below. In addition, the cathode-side electron transport layer 26 was formed in each element structure in order to make the electron injection barrier from the cathode the same condition.

N = 0: TYG201 (80 nm)

N = 1: {[TYG201 (30 nm) / TYE704 (30 nm)] ₁ } / TYG201 (20 nm)

N = 3: {[TYG201 (10 nm) / TYE704 (10 nm)] ₃ } / TYG201 (20 nm)

N = 4: {[TYG201 (7.5 nm) / TYE704 (7.5 nm)] ₄ } / TYG201 (20 nm)

In order to measure the amount of current flowing through the electron transport laminate 25, a direct current of 0 to 10 V was applied every 0.5 V between the anode 22 and the cathode 28, and the amount of current flowing through the device was measured with an ammeter.

FIG. 3 is a diagram showing I-V characteristics of the element structure shown in FIG. 2. Referring to FIG. 3, when the devices of N = 0 and N = 1 are compared, the amount of current which is almost equal or N = 1 is slightly smaller. On the other hand, at N = 3 and N = 4, it can be seen that the amount of current is greatly increased and is increased as the number of repetitions is increased. Therefore, the electron current amount can be increased by repeatedly stacking two electron transport layers 25A and 25B having different electron transport properties, and by increasing the number of stacked layers, a sufficient amount of electron current balanced with the hole current amount can be flowed. It is inferred that multiple quantum wells are formed by alternately stacking electron transport layers having different electron affinity, and the amount of electron current is increased by the multiple quantum well effect. The reason why the amount of current does not increase in the case of N = 1 is assumed to be that no multiple quantum wells are formed in N = 1.

As mentioned above, this inventor came to invention of the organic electroluminescent element provided with the electron carrying laminated body which laminated | stacked the different electron carrying layer.

(1st embodiment)

EMBODIMENT OF THE INVENTION Hereinafter, the organic electroluminescent element of embodiment which concerns on this invention is demonstrated, referring drawings.

4 is a cross-sectional view of an organic EL device according to an embodiment of the present invention. FIG. 5 is an example of an energy diagram of the organic EL element of this embodiment shown in FIG. In FIG. 5, Ea represents electron affinity, Eg represents an energy gap, and Ip represents an ionization potential. 4 and 5, the organic EL element 30 of the present embodiment includes a transparent substrate 31, an anode 32, a hole injection layer 33, and a hole transport layer 34 on the substrate 31. ), The light emitting layer 35, the electron transport stack 36, the cathode side electron transport layer 37, and the cathode 38 are formed in this order.

As the board | substrate 31, transparent insulating substrates, such as glass and quartz, semiconductor substrates, such as Si, films, such as PET and PEN, resin substrates, such as PVA, etc. can be used, for example. Alternatively, a TFT (thin film transistor) for controlling the on / off of the organic EL element may be formed in a matrix on these substrates. The thickness of the substrate 31 is appropriately selected depending on the material of these substrates, and is approximately 200 µm to 1000 µm.

The anode 32 is formed of a conductive material such as Al on the substrate 31 by vapor deposition or sputtering, and Au, Cr, Mo, or the like having a large work function is suitable from the viewpoint of hole injection properties. However, when light is emitted from the anode side, it is formed of a transparent material such as ITO or indium oxide.

The hole injection layer 33 and the hole transport layer 34 are made of a material having a high HOMO, that is, a small ionization potential. Typical examples include copper phthalocyanine (CuPc), m-MTDATA of a starburst amine, 2-TNATA, TPD, α-NPD, and the like. Moreover, in order to perform more hole injection between an anode and a hole transport layer, you may form a hole injection layer. As the hole injection layer, m-MTDATA and 2-TNATA of the above-described copper phthalocyanine (CuPc) and starburst amine can be used.

In addition, it is preferable that the hole transport layer 34 has a smaller electron affinity for the light emitting layer 35. Electrons can be accumulated in the light emitting layer, so that the space electron density in the light emitting layer can be increased. Specifically, as shown in FIG. 5, the relationship between the electron affinity Ea ₃₄ of the hole transport layer ₃₄ and the electron affinity Ea ₃₅ of the light emitting layer is set to Ea ₃₄ <Ea ₃₅ , and the height BR ₃₄ (= Ea ₃₅ -Ea _34). To form an energy barrier.

Moreover, you may form by laminating | stacking the positive hole transport layer from which ionization potential differs. By forming an energy barrier with respect to the holes, the amount of hole current can be suppressed and the balance with the amount of electron current can be achieved.

As the light emitting layer 35, metal complex system materials such as Alq3 (tris (8-hydroxyquinolio) aluminum), Znq2, Balq2, and dye-based materials such as PZ10 and EM2 are used. Moreover, what doped the pigment | dyes, such as rubrene and TPB, with host materials, such as Alq3, can be used.

The cathode side electron transport layer 37 is made of the same material as the electron transport layer constituting the electron transport laminate 36 described later. In particular, it is preferable that the cathode-side electron transport layer 37 has the same or larger size of the energy gap than the electron transport layer constituting the electron transport stack 36. Light emission in the cathode-side electron transport layer 37 can be prevented.

As the cathode 38, a metal such as Li having a small work function, an alloy thereof Mg-Ag, Al-Li, or the like can be used. Moreover, you may use the cathode which introduce | transduced the electron injection layer, such as a metal fluoride, like LiF / Al.

The electron transport laminate 36 has a configuration in which the first electron transport layer 36A and the second electron transport layer 36B having different electron transport properties are alternately stacked. Here, different electron transport property means that HOMO, LUMO (lowest molecule orbital), electroconductivity, etc. differ. In the present embodiment, the first electron transport layer 36A and the second electron transport layer 36B will be described below with different electron affinity.

The first electron transport layer 36A and the second electron transport layer 36B include a metal chelate of 8-hydroxyquinoline, a metal thioxynoid compound, an oxadiazole metal chelate, triazine, 4, 4'-bis (2, 2-diphenylvinyl) biphenyl and the like can be used. Among the metal chelates of 8-hydroxyquinoline, suitable are Alq3 (tris (8-hydroxyquinolinate) aluminum, Balq (bis (8-hydroxyquinolato)-(4-phenylphenolato) aluminum, bis PBD, etc. In addition, suitable among the metal thioxynoid compounds include bis (8-quinolinethiolato) zinc, bis (8-quinolinethiolato) cadmium, tris (8-quinolinethiolato) gallium, tris ( 8-quinolinethiolato) indium, etc. In addition, suitable among oxadiazole metal chelates is bis [2- (2-hydroxyphenyl) -5-phenyl-1, 3, 4-oxadiazolato. ] Zinc, bis [2- (2-hydroxyphenyl) -5-phenyl-1, 3, 4-oxadiazolato] beryllium, bis [2- (2-hydroxyphenyl) -5- (1-naph Til) -1,3,4-oxadiazolato] zinc, bis [2- (2-hydroxyphenyl) -5- (1-naphthyl) -1,3,4-oxadiazolato] beryllium and the like Can be mentioned.

The first electron transport layer 36A and the second electron transport layer 36B use Ea _{A as} the electron affinity of the first electron transport layer 36A and the electron affinity of the second electron transport layer 36B as the material of the electron transport layer described above. _{When it is set to B} , the relationship of electron affinity is selected so that Ea _A <Ea _B. In the selection of a material having such a relationship, the electron affinity may be determined using the measurement method described later.

Electrons are circulated from the cathode 38 toward the light emitting layer 35. In the electron transport stack 36, for example, these two layers are formed at the interface of the first electron transport layer 36A2 from the second electron transport layer 36B2. An energy barrier BR ₂ is formed by the difference E _B2 -E _A2 of the electron affinity to form a well type potential. Similarly, the energy barrier BR ₁ is formed from the second electron transport layer 36B1 to the first electron transport layer 36A1 to form a well type potential. Therefore, it is inferred that multiple quantum wells are formed and the amount of electron current is increased.

The film thickness of the first electron transport layer 36A and the second electron transport layer 36B is appropriately selected depending on the number of repetitions of the first electron transport layer 36A and the second electron transport layer 36B, and is preferably 2 nm to 50 nm (preferably Preferably 5 nm to 20 nm). When the thickness is larger than 50 nm, the thickness of the whole organic EL element becomes excessive, the appropriate applied voltage becomes excessively large, and an electrochemical reaction easily occurs at the interface between the anode or cathode and the hole injection layer or cathode side electron transport layer in contact with them. This adversely affects the lifetime of the organic EL device. In addition, when it is thinner than 2 nm, it becomes difficult to form a continuous film, and the periodicity of the well type potential is disturbed.

The film thicknesses of the first electron transport layer 36A and the second electron transport layer 36B are each set to a predetermined film thickness in the above range. The periodicity of the multiple quantum wells is good. In addition, the film thickness of the 1st electron carrying layer 36A and the 2nd electron carrying layer 36B may be the same film thickness, and may differ.

The thin film of the first electron transport layer 36A may be thinner than the second electron transport layer 36B. Since the first electron transport layer 36A has a small electron affinity, the first electron transport layer 36A functions as a barrier layer. However, the electron current amount can be further increased by thinning the barrier layer.

The number of repetitions of the first electron transport layer 36A and the second electron transport layer 36B is set to 2 to 10 (preferably 2 to 4). When larger than 10, the thickness of the organic EL element becomes excessive, and when smaller than 2, multiple quantum wells cannot be formed.

In addition, energy gaps, ionization potentials, and electrical affinity such as electron transport layers and hole transport layers were determined by the following measurement conditions and measurement methods.

Energy gap Eg measured the light absorption spectrum, and made energy of the long wavelength end of an optical absorption spectrum into energy gap Eg. Specifically, under the same conditions as those for forming each layer of the organic EL device, the electron transporting layer or the like to be measured was formed as a thin film having a thickness of about 50 nm alone. Using a spectrophotometer device (Hitachi Seisakusho Co., Ltd., spectrophotometer U-4100) capable of measuring the light absorption spectrum, the light was irradiated to the thick film in the air and in the visible region, and the light absorption spectrum (wavelength dependence) was measured. Measured.

6 is a characteristic diagram showing a light absorption spectrum. Referring to FIG. 6, the wavelength of the intersection point CP1 of the straight line which extrapolated the linear part LN1 of the edge of the long wavelength side of a light absorption spectrum by linear approximation to the long wavelength side, and the extrapolation of the straight line part BG1 of the background by linear approximation to the short wavelength side Was converted into energy to obtain an energy gap Eg.

Ionization potential Ip made the threshold energy of photoelectron emission measured by the ultraviolet photoelectron analysis into ionization potential Ip. Specifically, using a thick film formed in the same manner as the thick film used for the measurement of the energy gap Eg, by using an atmospheric atmosphere type ultraviolet photoelectric analysis device (manufactured by Risen Keiki Co., Ltd., product name: AC-1), ultraviolet light is absorbed into the thin film. The number of photoelectrons emitted by the irradiation was measured and determined from the relationship between the energy of incident ultraviolet rays and the number of photoelectrons. As for measurement conditions, the energy range of incident ultraviolet rays is 3.8-6.2 eV, and an ultraviolet intensity is 20 kW.

7 is a characteristic diagram showing an example of the relationship between the square root of the number of photoelectrons and the energy of incident ultraviolet rays. Referring to Fig. 7, the energy of the intersection point CP2 of the straight line extrapolated by the straight line approximation to the low-energy straight line portion LN2 and the straight line extrapolated to the higher energy side by the linear approximation than the straight line portion in the background is ionized potential Ip. It was set as.

In addition, electron affinity Ea was calculated | required by the difference (Ea = Ip-Eg) of the ionization potential Ip and energy gap Eg calculated | required above.

Using this method, the energy gap, ionization potential, and electrical affinity can be measured for individual electron transport materials to select a combination of electron transport layers constituting the electron transport laminate.

It is a figure which shows the measured value of the energy gap, ionization potential, and electrical affinity of the electron carrying layer and the hole transporting layer which comprise the organic electroluminescent element of the Example which concerns on this invention and the comparative example which do not follow this invention demonstrated below. . The Example and comparative example which were performed based on the measured value shown in FIG. 8 are shown below.

[First Embodiment]

On the glass substrate, ITO was used to form an anode having a thickness of 150 nm by sputtering, and the surface of the anode was irradiated with UV light for 20 minutes in an oxygen atmosphere to perform UV ozone treatment. Subsequently, 2-TNATA (thickness 40 nm) as a hole injection layer, (alpha) -NPD (thickness 10 nm) as a hole transport layer, and TYG201 (thickness 20 nm) as a light emitting layer were formed sequentially.

Next, as an electron transport laminated body, the tank of TYE704 (thickness 15nm) and TYG201 (thickness 15nm) was formed repeatedly from TYE704 twice. Furthermore, TYE704 (thickness 20 nm) was further formed on the electron carrying laminated body, and finally the negative electrode which consists of LiF / Al was formed.

In the organic EL device of this embodiment, green light emission was observed at a voltage of 3V or more. When a voltage of 10 V was applied, luminance of 913 mA / m 2 and emission efficiency of 8.40 mA / A were obtained.

Second Embodiment

The organic EL device of this embodiment is the same as that of the first embodiment except that the pair of TYE704 (thickness 10 nm) and TYG201 (thickness 10 nm) is repeated three times as an electron transport laminate.

In the organic EL device of this embodiment, green light emission was observed at a voltage of 3V or more. When the voltage of 10V was applied, luminance of 1075 kW / m 2 and luminous efficiency of 9.70 kW / A were obtained.

Third Embodiment

The organic EL device of this embodiment is the same as the first embodiment except that the pair of TYE704 (thickness 7.5 nm) and TYG201 (thickness 7.5 nm) is repeated four times as the electron transport laminate.

In the organic EL device of this embodiment, green light emission was observed at a voltage of 3V or more. When voltage 10V was applied, luminance 1017 mA / m 2 and light emission efficiency 8.89 mA / A were obtained.

[First Comparative Example]

The organic EL device of this comparative example is similar to the first embodiment except that TYG201 (50 nm thick) was formed as a light emitting layer, and the electron transport layer was used as one layer made of TYG201 (thickness 50 nm) instead of the electron transport laminate. .

In the organic EL device of this comparative example, green light emission was observed at a voltage of 3V or more. When voltage 10V was applied, luminance 967 mA / m 2 and light emission efficiency 8.25 mA / A were obtained.

Second Comparative Example

The organic EL device of this comparative example is similar to the first embodiment except that a pair of TYE704 (thickness 30 nm) and TYG201 (thickness 30 nm) was formed as an electron transport laminate.

In the organic EL device of this comparative example, green light emission was observed at a voltage of 4V or more. When voltage 10V was applied, luminance 750 kW / m 2 and luminous efficiency 7.48 kW / A were obtained.

It is a figure which shows the laminated constitution and evaluation result of 1st-3rd Example and a 1st-2nd comparative example. Referring to FIG. 9, when the number of repetitions of the stacks of the TYE704 and the TYG201, which are the electron transport stacks, is 2 or more, the number of repeats is 1 when the electron transport stack is one layer as in the first comparative example, or as in the second comparative example. In comparison with the case, it can be seen that the luminous efficiency is increased. In addition, it is inferred that the organic EL device of the second embodiment has the maximum luminous efficiency, so that the electron current amount and the hole current amount are balanced. Also from the viewpoint of the luminescence brightness, it can be seen that the organic EL element of the second embodiment is maximized.

Next, the Example and comparative example which substituted TYG201 by Alq3 among TYE704 and TYG201 which comprise an electron carrying laminated body are demonstrated.

[Example 4]

The organic EL device of this embodiment is the same as the second embodiment except that Alq3 (thickness 10 nm) is used instead of TYG201 (thickness 10 nm) as the electron transport laminate, and the number of repetitions is three.

In the organic EL device of this embodiment, green light emission was observed at a voltage of 5V or more. When voltage 10V was applied, luminance 994 kW / m 2 and luminous efficiency 7.52 kW / A were obtained.

[Example 5]

The organic EL device of this embodiment is similar to the fourth embodiment except that the thickness of each layer of the electron transport laminate is 7.5 nm and the number of repetitions is four.

In the organic EL device of this embodiment, green light emission was observed at a voltage of 5V or more. When voltage 10V was applied, luminance 1021 mA / m 2 and luminous efficiency 7.44 mA / A were obtained.

Third Comparative Example

The organic EL device of this comparative example is the fourth embodiment except that the electron transport layer is one layer made of Alq3 (thickness 30 nm) instead of the electron transport laminate, and the electron transport layer in contact with the cathode is TYG201 (thickness 50 nm). Same as

In the organic EL device of this comparative example, green light emission was observed at a voltage of 5 V or more. When voltage 10V was applied, luminance 1058 mA / m 2 and light emission efficiency 6.68 mA / A were obtained.

Fourth Comparative Example

The organic electroluminescent element of this comparative example is the same as that of 4th Example except having made the thickness of each layer of an electron carrying laminated body into 30 nm, and setting the number of repetitions to 1.

In the organic EL device of this comparative example, green light emission was observed at a voltage of 5 V or more. When voltage 10V was applied, luminance 1005 mA / m 2 and light emission efficiency 6.75 mA / A were obtained.

It is a figure which shows the laminated constitution and evaluation result of 4th-5th Example and 3rd-4th Comparative Example. Referring to FIG. 10, when the number of repetitions of lamination of TYE704 and Alq3, which are electron transport stacks, is 3 or more, the number of repeats is 1 when the electron transport stack is one layer as in the third comparative example or as in the fourth comparative example. It can be seen that the luminous efficiency is increased compared to the case.

In addition, when the examples of the same repetition number of the organic EL elements of the second to third embodiments and the fourth to fifth embodiments are compared, the organic EL elements of the second to third embodiments in which the TYG201 layer and the TYE704 layer are laminated In comparison with the organic EL devices according to the fourth to fifth embodiments in which the Alq3 layer and the TYE704 layer are laminated, the luminous efficiency of the comparative example (the second comparative example and the fourth comparative example, respectively) of which the number of repetitions is 1 It can be seen that the improvement rate is high. As a reason for this, as shown in Fig. 8, the difference in electron affinity between the Alq3 layer and the TYE704 layer is 0.10 eV, whereas the difference in electron affinity between the TYG201 layer and the TYE704 layer is 0.23 eV, which is a combination of the TYG201 layer and the TYE704 layer. It is inferred that this multiple quantum well is more sufficiently formed, and as a result, a more significant multiple quantum well effect has occurred.

(2nd embodiment)

It is an exploded perspective view of the organic electroluminescent display of 2nd Embodiment of this invention. Referring to FIG. 11, the organic EL display 50 includes a glass substrate 51, a cathode 51 formed in a stripe shape on the glass substrate, and an anode formed in a stripe shape perpendicular to the cathode 51. 54 and a laminate 53 formed between the cathode 52 and the anode 54. In addition, although not shown, the organic EL display 50 is made of a driving circuit for driving a voltage applied between the cathode and the anode, a sealing material for preventing exposure to water vapor or oxygen, and the like.

The organic EL display 50 can emit a desired region by applying a voltage to the cathode 52 and the anode 54 of the desired region. The characteristic of the organic electroluminescent display 50 is that the cathode 52, the laminated body 53, and the anode 54 are comprised with the organic electroluminescent element of this invention mentioned above. Therefore, the organic EL display which is excellent in luminous efficiency and long life can be achieved.

As mentioned above, although the preferable Example of this invention was described in detail, this invention is not limited to this specific embodiment, A various deformation | transformation and a change are possible within the scope of this invention as described in a claim.

For example, in the present embodiment, an organic EL element may be formed sequentially on the substrate from the anode side, or may be formed from the cathode side.

According to the present invention, in the organic electroluminescent device, by forming an electron transport laminate in which electron transport layers having different electron transport properties are alternately stacked on the cathode side of the light emitting layer, an organic electroluminescent device having excellent luminous efficiency and long lifespan is possible. A luminescence device can be provided.

Claims (11)

An anode, a light emitting layer formed on the anode, a carrier transporting laminate formed on the light emitting layer, and a cathode formed on the carrier transporting laminate, The carrier transport laminate is formed by alternately stacking a first carrier transport layer and a second carrier transport layer, And said first carrier transport layer and said second carrier transport layer have different electron transport properties. The method of claim 1, The first carrier transport layer and the second carrier transport layer is an organic electroluminescent device, characterized in that the electron affinity is different from each other. The method of claim 1, The said carrier transport laminated body is laminated | stacked alternately in the range of 2-10 of a 1st carrier transport layer and a 2nd carrier transport layer, The organic electroluminescent element characterized by the above-mentioned. The method of claim 1, An organic electroluminescent device, wherein each of the first carrier transport layer and the second carrier transport layer has a predetermined film thickness. The method of claim 1, The first carrier transport layer has an electron affinity smaller than that of the second carrier transport layer, and the film thickness is the same as or smaller than that of the second carrier transport layer. The method of claim 1, An organic electroluminescent device, wherein one of the first carrier transport layer and the second carrier transport layer is made of the same material as the light emitting layer. The method of claim 1, Further comprising an electron transport layer between the carrier transport laminate and the cathode, An organic electroluminescent device, characterized in that the electron transport layer has an energy gap equal to or larger than the larger of the first carrier transport layer and the second carrier transport layer. The method of claim 1, The carrier transport stack further comprises a third carrier transport layer, An organic electroluminescent device, wherein a first carrier transporting layer, a second carrier transporting layer, and a third carrier layer are sequentially stacked repeatedly. The method of claim 1, Further comprising a hole transport layer between the anode and the light emitting layer, The hole transport layer is an organic electroluminescent device, characterized in that the electron affinity is greater than the light emitting layer.  The method of claim 9, Further comprising another hole transport layer between the anode and the light emitting layer, The hole transport layer and the other hole transport layer is made of alternately stacked, The hole transport layer and the other hole transport layer is an organic electroluminescent device, characterized in that the ionization potential is different from each other. The organic electroluminescent display provided with the organic electroluminescent element of any one of Claims 1-10.