KR100790672B1 - Organic electroluminescence element and organic electroluminescence display - Google Patents

Abstract

The organic EL element 10 includes, on the substrate 11, the substrate 11, an anode 12, a hole injection layer 13, an electron transport suppression laminate 14, a light emitting layer 15, and an electron transport layer ( 16), the cathode 18 is formed in order, the hole injection layer 13 is comprised by the hole transport material doped with the acceptor, and the electron transport suppression laminated body 14 is the light emitting layer 15 From the side toward the hole injection layer 13, the first electron transport suppression layer 14A ₁ , the second electron transport suppression layer 14B ₁ , and the first electron transport suppression layer 14A ₂ are sequentially stacked and formed. have. Doping the acceptor into the hole injection layer 13 improves the conductivity, and reliably seals the electrons to the light emitting layer 15 by the first and second electron transport suppression layers 14A ₁ and 14B ₁ . The first and second electron transport suppression layers 14A ₁ and 14B ₁ are thinned to prevent the flow of hole currents from being inhibited. It is possible to improve the luminous efficiency and extend the lifespan.

Hole injection layer, electron passive layer, light emitting layer, electron affinity, carrier transport layer, energy barrier

Description

Organic electroluminescent element and organic electroluminescent display {ORGANIC ELECTROLUMINESCENCE ELEMENT AND ORGANIC ELECTROLUMINESCENCE DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to flat panel displays using optoelectronic devices and 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 and heavy weight CRT (brown tube) displays to thin and lightweight flat display devices. As a flat panel 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, as a next-generation flat display, an electroluminescent display ("EL display" hereafter), especially an organic EL display, attracts attention. 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 Tangand SA VanSlyke, Applied Physics Letters vol. 51, 913 (1987)). Attention has been focused on large-area light emitting devices that emit light at low voltages.

The stacked organic EL device basically has a configuration of an anode / hole transporting layer / light emitting layer / electron transporting layer / cathode. Among these, the electron transport layer may have a structure in which the light emitting layer also functions as in the case of the two-layer device of Tang and VanSlyke. As the anode, an electrode material having a large work function such as gold (Au), tin oxide (SnO ₂ ), indium tin oxide (ITO), or the like is used. As the cathode, Li, Mg, alloys Al-Li, Mg-Ag, and the like of a metal having a low work function having a small electron injection barrier to the electron transport layer are used.

By using various structures and organic materials of organic EL elements to date, luminance of about 1000 cd / m 2 has been obtained at a light emission voltage of 10 V at the beginning of use. However, when continuous driving of the organic EL element is performed, a decrease in luminescence brightness and an increase in driving voltage are observed due to changes over time, resulting in a short circuit.

The deterioration of the organic EL device is caused by the polarization of organic molecules for the crystallization of organic materials over time, the accumulation of space charges in the organic layer accompanying the organic material, and the dielectric polarization caused by application of a field in a certain direction. It is considered that the electrical properties of the polymer are deteriorated due to a change in the oxidation of the electrode or the like. In addition, when the power consumption is large, it is thought that the energy loss is changed to heat, thereby promoting deterioration of the organic material. Therefore, in order to prolong life, it is desirable to realize a highly efficient device in which high light emission luminance is obtained with low current and low power as much as possible.

Therefore, as a means for improving these high efficiency, the trial which improves durability by the examination from a material surface and the driving method of an EL element is made. For example, as disclosed in Japanese Patent Laid-Open No. 6-36877, two organic layers are alternately stacked to form a light emitting layer having an energy band of well type potential, and electrons that do not recombine in one light emitting layer, A method of increasing light emission efficiency by increasing the chance of emitting light by recombining holes in the next light emitting layer has been proposed. However, in this configuration, the high resistance characteristic of the organic layer causes the voltage drop and the generation of Joule heat in each organic layer, resulting in a decrease in luminous efficiency and lifetime of the organic EL element.

In order to solve this problem, as disclosed in JP-A-4-297076, it is proposed to increase the conductivity by doping the acceptor in the hole transport layer.

In this case, the conductivity can be improved to increase the amount of hole current and the amount of electron current. However, since the carrier is not confined sufficiently, the power consumption increases, resulting in a problem that the luminous efficiency and lifetime are lowered. This is because the size of the electron affinity of the acceptor is generally larger than that of the material of the hole injection transport layer, so that the energy barrier at the interface between the hole transport layer and the light emitting layer, which achieves the role of trapping electrons in the light emitting layer, becomes smaller. It is considered that the light emitting layer cannot be confined efficiently and the light emission efficiency is lowered.

As a means to solve this problem, a method of increasing the luminous efficiency by forming an electron injection suppressing layer for trapping electrons between the light emitting layer and the hole transporting layer is disclosed, as disclosed in Japanese Patent Laid-Open No. 2000-196140. Although the decrease in luminous efficiency is suppressed when the electron injection suppression layer is formed than when the hole transporting layer and the light emitting layer directly contact, there is a problem that electrons passing through the electron injection suppression layer exist. Such electrons can be suppressed by increasing the thickness of the electron injection suppressing layer, but at the same time, there is a problem that the flow of holes is suppressed and the luminance is lowered, and an EL characteristic that is not sufficiently satisfactory yet has not been obtained.

Patent Document 1: Japanese Patent Application Laid-Open No. 2000-196140

<Start of invention>

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 of long lifetime which is excellent in luminous efficiency and high luminous efficiency is maintained over a long term.

According to one aspect of the invention,

An organic electroluminescent device comprising an anode, a cathode formed above the anode, and a light emitting layer formed between the anode and the cathode and containing an organic light emitting material,

A hole injection layer comprising a hole transport material and an acceptor on the anode,

An organic electroluminescent device comprising an electron transport suppression laminate comprising a plurality of carrier transport layers between the hole injection layer and the light emitting layer and forming an energy barrier for electrons flowing from the light emitting layer to the hole injection layer. do.

According to the present invention, by forming a hole injection layer made of a hole transport material containing an acceptor, the conductivity of the hole injection layer is increased, and an energy barrier is formed by a plurality of carrier transport layers for electrons flowing from the light emitting layer to the hole injection layer. By providing an electron transport suppressing laminate, an increase in the amount of electron current from the light emitting layer due to the high conductivity of the hole injection layer to the hole injection layer is suppressed. Accordingly, the conductivity is improved, the sealing of the electrons to the light emitting layer is reliably performed by the plurality of carrier transporting layers, and the respective carrier transporting layers are thinned to prevent the flow of holes. As a result, it is possible to improve the luminous efficiency, and furthermore, it is possible to extend the lifespan.

The electron transport suppressing laminate has a first carrier transporting layer in contact with the anode side of the light emitting layer and a second carrier transporting layer in contact with the anode side of the first carrier transporting layer are alternately arranged in this order, and has an electron affinity. It has the relationship of Equation 1 below.

Here, in Equation 1, Ea _HT1 is the electron affinity of the first carrier transport layer, and Ea _HT2 is the electron affinity of the second carrier transport layer. At the interface between the first carrier transport layer and the second carrier transport layer, by providing an energy barrier to electrons, the amount of electron current flowing from the light emitting layer to the hole injection layer can be suppressed. In addition, electron affinity is represented by the energy difference (plus value) between the energy of the lower end of the conductor of the material which comprises a carrier transport layer, etc., and a vacuum level.

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.

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

FIG. 2 is a diagram showing an energy diagram of an organic EL element according to the first embodiment. FIG.

3 is a cross-sectional view of an organic EL device according to a modification of the first embodiment of the present invention.

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

5 is a diagram for explaining a method for obtaining an ionization potential.

6 is a diagram showing characteristic values of an electron transport suppression layer, a hole injection layer, and a light emitting layer used in the organic EL device according to the Examples and Comparative Examples.

Fig. 7 is a diagram showing the layer structure and evaluation results of main parts of the organic EL elements according to the first embodiment and the first to third comparative examples.

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

<Description of the code>

10, 20: organic EL element

11: substrate

12: anode

13: hole injection layer

14, 24: electron transport suppression laminate

14A, 24A: 1st electron transport suppression layer

14B, 24B: second electron transport suppression layer

15: light emitting layer

16: electron transport layer

18: cathode

30: organic EL display

<Best Mode for Carrying Out the Invention>

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

(1st embodiment)

1 is a cross-sectional view of an organic EL device according to an embodiment of the present invention. FIG. 2 is an energy diagram of the organic EL device of the present embodiment shown in FIG. 1. In FIG. 2, Ea represents electron affinity, Eg represents energy gap, and Ip represents ionization potential. 1 and 2, the organic EL element 10 of the present embodiment includes the anode 11, the hole injection layer 13, and the electron transport suppression stack on the substrate 11 and the substrate 11. The sieve 14, the light emitting layer 15, the electron carrying layer 16, and the cathode 18 are formed in this order.

In the organic EL element 10 of the present invention, the hole injection layer 13 is made of a hole transport material doped with an acceptor. The hole injection layer 13 is, for example, 2-TNATA (4, 4 ', 4' '-tris (2-naphthylphenylamino) triphenylamine), which is a hole transporting material, as a acceptor, and a halogenated metal compound, a halogen, and a platinum group element. Inorganic materials, such as metal, and the organic material which has a cyano group and a nitro group are added.

Specifically, a well-known material can be used as a hole transport material. In addition, there may be mentioned as an acceptor suitable, as the metal halide compound, FeCl _3, InCl _3, AsF _6, etc., as a halogen, Cl, Br, I, etc., a metal such as platinum group elements Au, Pt, W, Ir, etc. . In addition, as a suitable acceptor, as an organic material having a cyano group, TCNQ (7, 7, 8, 8, tetracyanoquinomimethane), F4-TCNQ (2, 3, 5, 6-tetrafluoro-7 Examples of organic materials having nitro groups such as, 7, 8, 8, tetracyanoquinodimethane) and TCNE (tetracyanoethylene) include TNF (trinitrofluorenone), DNF (dinitrofluorenone) and the like. Among these, TCNQ, F4-TCNQ, TCNE, TNF, and DNF are particularly preferable.

The content of the acceptor in the hole injection layer 13 is set to 0.01 vol% to 2.0 vol%, preferably 0.05 vol% to 1.0 vol% with respect to the hole transport material (100 vol%). If the amount is less than 0.01 vol%, the conductivity is not improved. If the amount exceeds 2.0 vol%, the amount of current increases and the power consumption increases. In particular, when F4-TCNQ is used as the acceptor, the content of the acceptor is preferably 0.05 vol% to 1.0 vol%.

The hole injection layer 13 can be formed using a vacuum process method such as a vacuum deposition method, a CVD method, a sputtering method, or a wet process method such as a spin coating method or a printing method.

In the organic EL device of the present invention, an electron transport suppression laminate 14 is provided between the hole injection layer 13 and the light emitting layer 15. The electron transport suppression layered body 14 is the first electron transport suppression layer 14A ₁ , the second electron transport suppression layer 14B ₁ , and the first electron from the light emitting layer 15 side toward the hole injection layer 13. The transport suppression layer 14A ₂ is formed by stacking sequentially. The first electron transport suppression layer 14A ₁ , 14A ₂ , and the second electron transport suppression layer 14B ₁ are made of a hole transport material, and are directed from the light emitting layer 15 side toward the hole injection layer 13 with respect to the electrons. The energy barrier is arranged to form.

It is preferable to have a relationship that one electron-transfer inhibiting layer (14A _1, 14A _2), and a second electron-transfer inhibiting layer (14B ₁₎ is expressed by equation (2) to.

Here, Ea _HT1 is the electron affinity of the first electron transport suppression layers 14A ₁ , 14A ₂ , and Ea _HT2 is the electron affinity of the second electron transport suppression layer 14B ₁ . Two first electron transport inhibiting layer (14A _1, 14A ₂₎ on, the first electron-transfer inhibiting layer (14A _1, 14A ₂₎ the size of the electron affinity is larger than the second inhibiting electron transport layer (14B ₁₎ formed between Therefore, the energy barrier BR ₁ is formed with respect to the electrons at the interface from the first electron transport suppression layer 14A ₁ to the second electron transport suppression layer 14B ₁ . Therefore, the amount of electron current from the light emitting layer 15 to the hole injection layer 13 is reduced.

Further, it is preferable to have the relationship shown in the light emitting layer 15 and the first equation (3) is to suppress an electron transport layer (14A _1).

Where, Ea is an electron affinity _EM, Ea _HT1 of the light-emitting layer 15 is the electron affinity of the first electron-transfer inhibiting layer (14A _1). An energy barrier BR ₂ is also formed at the interface between the light emitting layer 15 and the first electron transport suppression layer 14A ₁ to trap electrons in the light emitting layer 15. However, when only one layer of the first electron transport suppression layer 14A ₁ is present, the probability of electrons exceeding the energy barrier BR ₂ is high, and in order to reduce such probability, the thickness of the first electron transport suppression layer 14A ₁ is reduced. The thickness may be increased, but the voltage drop becomes large, which is not preferable in view of durability. It may also be a cause of lowering the amount of hole electron current. Thus, by made of a plurality of first and second electron transport inhibiting layer becomes, providing a plurality of energy barrier BR _1, inhibiting electron transport stack body 14 having the BR ₂ on the anode side of the light-emitting layer 15, a light emitting layer ( The amount of electron current directed from the 15 to the hole injection layer 13 can be effectively suppressed to increase the space electron density in the light emitting layer 15, thereby improving the luminous efficiency.

Hereinafter, the specific structure of the organic electroluminescent element which concerns on this embodiment is demonstrated.

As the board | substrate 11, 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. Or TFT (thin film transistor) which controls ON / OFF of organic electroluminescent element on these board | substrates may be formed in matrix form. Although the thickness of the board | substrate 11 is suitably selected by the material of these board | substrates, it is about 0.1 lmm-10 mm.

The anode 12 is formed of a conductive material such as Al on the substrate 11 by a vapor deposition method or a sputtering method. From the viewpoint of hole injection property, it is preferable to use Au, Cr or the like having a large work function. However, when light is emitted from the anode side, it is formed of a transparent material such as ITO or IZO (indium zinc oxide).

As the hole transport material of the hole injection layer 13, the first electron transport suppression layer 14A, and the second electron transport suppression layer 14B, a material having a high HOMO, that is, a small ionization potential is used. Typical examples include copper phthalocyanine (CuPc), m-MTDATA of starburst amine, 2-TNATA, TPD, α-NPD, and the like.

In addition, it is preferable that the ionization potentials of the first electron transport suppression layer 14A and the second electron transport suppression layer 14B are approximately equal from the viewpoint of increasing the amount of hole current. By forming an energy barrier low with respect to the hole, the amount of electron current can be suppressed without inhibiting the flow of the hole current.

In addition, another hole injection layer that does not contain an acceptor may be provided between the hole injection layer 13 and the anode 12. The other hole injection layer is made of a thin layer as compared with the hole injection layer 13, and is made of a material having an ionization potential almost equal to the size of the work function of the anode 12. The hole current can be easily flowed.

As the light emitting layer 15, 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 electron transport layer 16 includes 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. It is possible to use. Suitable metal chelates of 8-hydroxyquinoline include Alq 3, Balq (bis (8-hydroxyhydrate)-(4-phenylphenolate) aluminum), bis PBD and the like. In addition, suitable among the metal thioxynoid compounds include bis (8-quinolinthiolate) zinc, bis (8-quinolinthiolate) cadmium, tris (8-quinolinethiorate) gallium, tris (8-quinolinethiorate) indium Etc. can be mentioned. Further suitable among oxadiazole metal chelates are bis [2- (2-hydroxyphenyl) -5-phenyl-1, 3,4-oxadiazolate] zinc, bis [2- (2-hydroxyphenyl ) -5-phenyl-1, 3, 4-oxadiazolate] beryllium, bis [2- (2-hydroxyphenyl) -5- (1-naphthyl) -1, 3, 4-oxadiazolate ] Zinc, bis [2- (2-hydroxyphenyl) -5- (1-naphthyl) -1, 3, 4-oxadiazolate] beryllium, etc. are mentioned.

As the cathode 18, a metal such as Li having a small work function, an alloy thereof, Mg-Ag, Al-Li, or the like is used. Moreover, you may use the cathode which introduce | transduced the electron injection layer, such as a metal fluoride, like LiF / Al.

As shown in FIG. 2, electrons try to flow from the light emitting layer 15 toward the hole injection layer 13. However, at the interface between the first electron transport suppression layer 14A ₁ and the second electron transport suppression layer 14B ₁ , an energy barrier BR ₁ is formed by the difference Ea _HT1 -Ea _HT2 of the electron affinity of these two layers. . As a result, the flow of electrons is inhibited, the amount of electron current is suppressed, and electrons are sealed in the light emitting layer 15. Further, at the interface between the light emitting layer 15 and the first electron transport suppression layer 14A ₁ , an energy barrier BR ₂ is formed by the difference Ea _EM -Ea _HT1 of the electron affinity of these two layers. As a result, electrons are sealed in the light emitting layer 15 again. Therefore, the spatial electron density of the emission layer 15 may increase, thereby increasing the probability of recombination with holes.

In the organic EL device of the present embodiment, it is preferable that the relationship between the electron transporting layer 16 in contact with the cathode 18 side of the light emitting layer 15 and the ionization potential of the light emitting layer 15 has a relationship of the following formula (4).

Here, in Equation 4, Ip _EM is the ionization potential of the light emitting layer 15, Ip _ET is the ionization potential of the electron transport layer, and the ionization potential is the difference between the valence level (energy at the top of the valence band) and the vacuum level (plus Value). Holes can be confined in the light emitting layer 15 by forming an energy barrier BR ₃ for holes on the cathode 18 side of the light emitting layer 15. The probability of recombination with electrons can be increased by increasing the spatial hole density.

3 is a cross-sectional view of an organic EL device according to a modification of the present embodiment. In the drawings, parts corresponding to the parts described above are denoted by the same reference numerals and description thereof will be omitted.

Referring to FIG. 3, the organic EL element 20 of the present modification includes the anode 11, the hole injection layer 13, and the electron transport suppression laminate 24 on the substrate 11 and the substrate 11. The light emitting layer 15, the electron transport layer 16, and the cathode 18 are formed in this order. The electron transport suppression laminate 24 is directed from the light emitting layer 15 side toward the hole injection layer 13 from the first set of first electron transport suppression layer 24A ₁ and the second electron transport suppression layer 24B ₁ . N jojjae is composed of the first electron transport inhibiting layer (24A _N) and a second electron-transfer inhibiting layer (24B _N) of. Here, the number N of laminated | stacked is an integer of 2 or more, and in group _N , only 1st electron transport suppression layer 24A _N may be formed.

As the number N of stacked layers increases, the thickness of the first electron transport suppression layer 24A and the second electron transport suppression layer 24B is set to be thinner. It is preferable to set the total thickness of the electron transport suppression laminate 24 to 150 nm to 500 nm. If the thickness is larger than 500 nm, the electrical resistance becomes large and current cannot flow sufficiently, and if a high voltage is applied, the life of the organic EL element 20 is shortened. If the thickness is smaller than 150 nm, the amount of electron current flowing from the light emitting layer 15 side to the hole injection layer 13 cannot be sufficiently suppressed.

In particular, the thickness of the first electron transport suppression layer 24A and the second electron transport suppression layer 24B is set to 2 nm to 50 nm, more preferably 2 nm to 20 nm. By thinning the first electron transport suppression layer 24A and the second electron transport suppression layer 24B, the electrons are confined to the light emitting layer 15 and the flow of holes is prevented from being inhibited.

According to this modification, many electron barriers are formed in the electron transport suppression laminate 24 formed of the first electron transport suppression layer 24A and the second electron transport suppression layer 24B. As a result, the flow of electrons from the light emitting layer 15 to the hole injection layer 13 can be more reliably suppressed and the flow of holes can be prevented from being inhibited.

In addition, in the organic EL elements 10 and 20 according to the first embodiment and the modification, the electron transport suppression laminates 14 and 24 are composed of two kinds of electron transport suppression layers, but three or more types of electron transport You may be comprised by the suppression layer. For example, using a 3rd electron transport suppression layer other than a 1st electron transport suppression layer and a 2nd electron transport suppression layer, the 1st electron transport suppression layer in order toward the hole injection layer 13 from the light emitting layer 15 side. It is set as a 2nd electron transport suppression layer / 1st electron transport suppression layer / 2nd electron transport suppression layer / 3rd electron transport suppression layer / 1st electron transport suppression layer. The relationship of the electron affinity of these three types of electron transport suppression layers is set to the relationship of following formula (5).

In Equation 5, Ea _HT1 is an electron affinity of the first electron transport suppression layer, Ea _HT2 is an electron affinity of the second electron transport suppression layer, and Ea _HT3 is an electron affinity of the third electron transport suppression layer. An energy barrier is formed at the interface between the second electron transport suppression layer and the third electron transport suppression layer in addition to the interface between the first electron transport suppression layer and the second electron transport suppression layer. Energy barriers of different sizes can be formed in the inside to improve the suppression of electron flow.

The first electron transport suppression layers 14A and 24A or the second electron transport suppression layers 14B and 24B in contact with the cathode 18 side of the hole injection layer 13 have a relationship shown in the following equation (6). desirable.

In Equation 6, Ea _HT is an electron affinity of the first or second carrier transport layer in contact with the cathode 18 side of the hole injection layer 13, and Ea _HI is an electron affinity of the hole injection layer 13. When electrons flow from the light emitting layer 15 side to the hole injection layer 13, the flow of electrons can be suppressed by forming an energy barrier in front of the light emitting injection layer 13.

Moreover, in embodiment of this invention, energy gap, ionization potential, and electrical affinity of the electron transport suppression layer 14A, 14B, 24A, 24B, the light emitting layer 15, the electron transport layer 16, etc. are measured with the following measurement conditions and It calculated | required by the measuring method.

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, on the conditions similar to the conditions for forming each layer of the organic EL device, the electron transport layer or the like to be measured was formed as a thin film having a thickness of about 50 nm alone. Using a spectrophotometer apparatus (trade name: Spectrophotometer U-4100, manufactured by Hitachi, Ltd.) capable of measuring the light absorption spectrum, the film was irradiated with light in the ultraviolet-visible region to a thick film, and the light absorption spectrum (wavelength dependence) was measured. Measured.

4 is a characteristic diagram showing a light absorption spectrum. 4, the intersection of the straight line which extrapolated the linear part LN1 of the edge of the long wavelength side of the light absorption spectrum by linear approximation to the long wavelength side, and the straight line which extrapolated the background straight part BG1 to the short wavelength side by linear approximation. The wavelength of CP1 was converted into energy to make 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, ultraviolet light is irradiated to the thin film in the air by using an atmospheric atmosphere type ultraviolet photoelectron analyzer (trade name: AC-1, manufactured by Riken Instruments Co., Ltd.). The number of photoelectrons emitted 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 ultraviolet intensity is 20 nW.

5 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. 5, the energy of the intersection CP2 between the straight line extrapolated by the straight line approximation to the low energy side and the straight line extrapolated by the straight line approximation from the background straight line part to the high energy side Was the ionization potential Ip.

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

Using these methods, the energy gap, ionization potential, and electrical affinity can be measured for individual hole transport materials, and a combination of the first and second electron transport suppression layers or the light emitting layer constituting the electron transport suppression laminate can be selected. have.

Fig. 6 is a measurement of the energy gap, ionization potential, and electrical affinity of the electron transport suppression layer, the hole injection layer, and the light emitting layer constituting the organic EL device according to the present invention and the comparative example not according to the present invention described below. It is a figure which shows a value. The Example and comparative example which were performed based on the measured value shown in FIG. 6 are shown below.

[First Embodiment]

The organic electroluminescent element which concerns on a present Example consists of an electron transport suppression laminated body which consists of an ITO anode, a hole injection layer, and three layers of electron transport suppression layers, a light emitting layer, and a cathode on a transparent substrate.

The glass substrate having an ITO electrode was ultrasonically cleaned with water, acetone and isopropyl alcohol, and the surface of the anode was irradiated with UV light in the air for 20 minutes for UV ozone treatment. Subsequently, the vacuum deposition apparatus was used to set the vacuum degree 1 × 10 ⁻⁶ Torr and the substrate temperature at 20 ° C., and 2-TNATA and F4-TCNQ were respectively deposited at a deposition rate of 0.5 nm / s and 0.0005 nm / s as the hole injection layer. Were deposited simultaneously, and the thickness was 120 nm. That is, 2-TNATA was 100 vol%, and the content of F4-TCNQ was 0.1 vol%.

Then, the electron transport suppression laminated body which consists of three layers is formed. α-NPD is formed at a deposition rate of 0.1 nm / s at a thickness of 10 nm, followed by 2-TNATA at a deposition rate of 0.1 nm / s at a thickness of 10 nm, and α-NPD is formed at a deposition rate of 0.1 nm / s at 10 nm.

As the light emitting layer, Alq3 was deposited at 0.1 nm / s by 50 nm. Furthermore, an Al-Li alloy (Li: 0.5 mass%) was deposited thereon at 50 nm at a deposition rate of 0.02 nm / s to form an organic EL device according to the first embodiment. When the device was applied with a voltage of 6 V or more using ITO as the anode and Al-Li as the cathode, green light emission was observed.

[First Comparative Example]

As the hole injection layer, 2-TNATA was deposited at a deposition rate of 0.5 nm / s and a thickness of 130 nm, and the α-NPD layer was formed at a deposition rate of 0.1 nm / s and 20 nm in thickness in place of the electron transport suppression laminate. In the same manner as in Example 1, the organic EL device according to the first comparative example was formed.

Second Comparative Example

As the hole injection layer, 2-TNATA was deposited at a deposition rate of 0.5 nm / s and a thickness of 10 nm, and 2-TNATA and F4-TCNQ were simultaneously deposited at a deposition rate of 0.5 nm / s and 0.0005 nm / s, respectively. And the organic EL according to the second comparative example in the same manner as in the first example except that the α-NPD layer was formed at a deposition rate of 0.1 nm / s and a thickness of 20 nm in place of the electron transport suppression laminate with a thickness of 120 nm. The device was formed.

Third Comparative Example

An organic EL device according to Comparative Example 3 was formed in the same manner as in Example 1 except that the α-NPD layer was formed at a deposition rate of 0.1 nm / s and a thickness of 20 nm instead of the electron transport suppression laminate.

It is a figure which shows the laminated constitution and evaluation result of the principal part of the organic electroluminescent element of 1st Example and the 1st-3rd comparative example. Referring to FIG. 7, it can be seen that the luminous efficiency of the organic EL elements of the first embodiment is high relative to the organic EL elements of the first to third comparative examples. It is understood that the organic EL device of the first embodiment has lower light emission luminance than the second and third comparative examples, but also suppresses the current density and improves the light emission efficiency. The amount of electron current from the light emitting layer to the electron transport suppressing layer from the light emitting layer to the hole injection layer is suppressed by the electron transport suppressing laminate comprising α-NPD and 2-NATA (the difference in electron affinity is 0.23 eV), It is inferred that the probability of recombination with holes is improved by electrons trapped in the light emitting layer, thereby improving light emission efficiency.

(2nd embodiment)

8 is an exploded perspective view of an organic EL display of a second embodiment of the present invention. Referring to FIG. 8, the organic EL display 30 includes a glass substrate 31, a cathode 32 formed in a stripe shape on the glass substrate, and an anode formed in a stripe shape perpendicular to the cathode 32. 34 and a laminate 33 formed between the cathode 32 and the anode 34. In addition, although not shown, the organic electroluminescence display 30 is comprised from the drive circuit which drives the voltage applied between a cathode and an anode, the sealing container which prevents exposure to water vapor, etc ..

The organic EL display 30 can emit a desired region by applying a voltage to the cathode 32 and the anode 34 of the desired region. The characteristic of the organic electroluminescent display 30 is that the organic electroluminescent element which consists of the anode 34, the laminated body 33, and the cathode 32 is comprised by the organic electroluminescent element which concerns on 1st or 2nd embodiment mentioned above. will be. Therefore, an organic EL display having high luminous efficiency and long lifetime can be realized.

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

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

According to the present invention, in an organic electroluminescent device, an electron transport suppression laminate which enhances conductivity by doping an acceptor to a hole transport material of a hole injection layer, and forms an energy barrier with respect to electrons by a plurality of carrier transport layers. By providing on the anode side of the light emitting layer, it prevents the flow of electron current from the light emitting layer to the hole injection layer, traps electrons in the light emitting layer and prevents the flow of hole current from being impaired. An organic EL element and an organic EL display can be provided.

Claims (13)

An organic electroluminescent device comprising an anode, a cathode formed above the anode, and a light emitting layer formed between the anode and the cathode and comprising an organic light emitting material, A hole injection layer made of a hole transport material including an acceptor on the anode, An electron transport suppression laminate, comprising a plurality of carrier transport layers made of a hole transporting material, between the hole injection layer and the light emitting layer, and forming an energy barrier for electrons flowing from the light emitting layer to the hole injection layer. An organic electroluminescent device characterized by having. The method of claim 1, The electron transport suppressing laminate includes a first carrier transporting layer in contact with the anode side of the light emitting layer and a second carrier transporting layer in contact with the anode side of the first carrier transporting layer are alternately arranged in this order, Relationship between electron affinity and the following formula 1 [Equation 1]

(In Formula 1, Ea _HT1 is electron affinity of the first carrier transport layer, Ea _HT2 is electron affinity of the second carrier transport layer) An organic electroluminescent device characterized by having. The method of claim 2, The relationship between the electron affinity of the first carrier transport layer and the light emitting layer is represented by [Equation 2]

(Ea _HT1 is the electron affinity of the first carrier transport layer, Ea _EM is the electron affinity of the light emitting layer) An organic electroluminescent device characterized by having. The method of claim 2, The relationship between the first carrier transport layer or the second carrier transport layer in contact with the cathode side of the hole injection layer and the hole injection layer is represented by the following formula (3) [Equation 3]

(Equation 3, Ea _HT is the electron affinity of the first or second carrier transport layer in contact with the cathode side of the hole injection layer, Ea _HI is the electron affinity of the hole injection layer) An organic electroluminescent device characterized by having. The method of claim 1, Further having an electron transport layer between the light emitting layer and the cathode, The ionization potential of the electron transporting layer and the light emitting layer is represented by the following formula (4) [Equation 4]

(Equation 4, Ip _EM is the ionization potential of the light emitting layer, Ip _ET is the ionization potential of the electron transport layer) An organic electroluminescent device characterized by having. The method of claim 2, The film thickness of the said 1st carrier transport layer is equal to or larger than the film thickness of a 2nd carrier transport layer, The organic electroluminescent element characterized by the above-mentioned. The method of claim 2, The electron transport suppression laminate further has a third carrier transport layer, An organic electroluminescent device, wherein the first carrier transport layer, the second carrier transport layer, and the third carrier transport layer are regularly and repeatedly arranged. The method of claim 7, wherein The electron transport suppressing laminate includes a first carrier transporting layer in contact with the anode side of the light emitting layer, a second carrier transporting layer in contact with the anode side of the first carrier transporting layer, and a third carrier transporting layer in contact with the anode side of the second carrier transporting layer. And another first carrier transport layer in contact with the anode side of the third carrier transport layer, Relationship between electron affinity and equation 5 [Equation 5]

(Equation 5, Ea _HT1 is the electron affinity of the first carrier transport layer, another first carrier transport layer, and other first carrier transport layer, Ea _HT2 is the electron affinity of the second carrier transport layer, Ea _HT3 is the electron of the third carrier transport layer Affinity) An organic electroluminescent device characterized by having. The method of claim 1, Further having another hole injection layer between the anode and the hole injection layer, And the other hole injection layer is made of a hole transport material. An organic electroluminescent display comprising the organic electroluminescent element of any one of claims 1 to 9. The method of claim 1, The organic electroluminescent element of which the material of the said hole injection layer consists of 2-TNATA, and the said electron transport suppression laminated body consists of a laminated body of 2-TNATA and (alpha) -NPD. delete delete

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