JP2003115389A - Organic electroluminescent device - Google Patents

Abstract

(57) [Problem] To provide an organic electroluminescent device in which the luminous efficiency, electric characteristics, lifetime, contrast and the like of the device are improved. The organic electroluminescent device absorbs visible light that is located between the outside of the light emitting layer and the second electrode located in a direction other than the light extraction interface side of the organic electroluminescent device and passes through the inside of the organic electroluminescent device. Organic electroluminescent device provided with a first type intermediate layer capable of performing the following.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel organic electroluminescent device, and more particularly to a thin, lightweight, highly precise organic electroluminescent device having high efficiency.

[0002]

2. Description of the Related Art In recent years, with the widespread use of various mobile phones, mobile terminals, mobile computers, car navigation systems and the like, there is an increasing demand for a lightweight, high-definition, high-brightness and inexpensive small flat display.

In addition, flat displays such as space-saving desktop displays and wall-mounted televisions are becoming widespread in homes and offices in place of conventional CRT tube displays. In particular, due to the spread of high-speed Internet and the progress of digital broadcasting, hundreds to several gigabits /
Second-class digital signal transmission has been put to practical use both by wire and wireless, and we are moving to an era in which extremely large amounts of information are exchanged in real time.

Therefore, in addition to the lightness, the high definition, the high brightness and the low price, which are required in the past, the flat display is required to have a high-speed display capable of digital signal processing.

As such a flat panel display, a liquid crystal display (Liquid Crystal Display: LCD) is used.
And Plasma Display (Plasma Display: P
D), field emission display (Field
Emission displays (FEDs) and the like have been studied, but in addition to these various flat displays, organic electroluminescence devices (organic electroluminescense devices) have recently been added.
e: OELD) or organic light emitting diode (Organic)
A new type of flat panel display called a Light Emitted Diode (OLED) is attracting attention.

The organic electroluminescence device is a device for displaying by causing an electric current to flow through an organic compound sandwiched between a cathode and an anode to cause the fluorescent or phosphorescent organic molecule contained therein to emit light. .

Reference: "Remaining important issues and practical strategies for organic LED devices" edited by the Society for Organic Electronics Materials (Bunshin Publishing, 1999, pp. 1-11, Yoshiharu Sato, "Introduction Materials"・ Current status and problems of devices "), research on organic electroluminescent devices was conducted mainly in the past with a focus on organic semiconductor single crystals such as anthracene and perylene, but in 1987, Tang et al. Proposed a two-layer organic electroluminescent device in which a thin film of an organic compound and a thin film of a hole transporting organic compound are laminated (CW Tang).
and S. A. VanSlyke, Appl. Phys.
Lett. 51, 913, 1987), the emission characteristics can be significantly improved (emission efficiency 1.5 lm / W, drive voltage 10).
V, luminance 1000 cd / m ² ) is the starting point of the research.

After that, dye-doping technology and polymer OLE
Elemental technologies such as D, a low work function electrode, and a mask vapor deposition method have been researched and developed, and in 1997, a part of an organic electroluminescent element by a charge injection method called a simple matrix method was put into practical use. Furthermore, development of an organic electroluminescence device by a new charge injection method called an active matrix method is under consideration.

Such an organic electroluminescence device is driven by the following principle. That is, a fluorescent or phosphorescent organic light emitting material is thinned between a pair of electrodes, and electrons and holes are injected from the positive and negative electrodes.

In organic light-emitting materials, injected electrons are the lowest unoccupied molecular orbitals of light-emitting molecules (Lowest Unoccupied).
It becomes a one-electronized organic molecule (simply called an electron) that has entered into Molecular Oral (LUMO), and the injected holes are
Highest Occupied Molecular Orbital of Luminescent Molecules
One hole-forming organic molecule (referred to simply as a hole) that has entered the Molecular Orbital (HOMO) is formed, and moves in the organic material toward the counter electrode. When electrons and holes meet on the way, a singlet or triplet excited state of a light emitting molecule is formed, which emits light by deactivating while emitting light.

In general, many organic light-emitting materials are known, such as various laser dyes, which have high quantum efficiency for photoexcitation. However, when they are made to emit light by charge injection, many organic compounds are insulators. Therefore, the charge transport property of electrons and holes is low, and a high voltage of several hundreds V is required for an initial organic electroluminescence device. However, the organic electrophotographic photoconductor used as a photoconductor of a copying machine. Thin film that transports charges (holes) by utilizing the high charge transport performance of
The two-layer organic electroluminescent device of Tang described above has improved light emission characteristics by functionally separating it from a thin film that emits light. A three-layer type organic electroluminescent device in which the organic thin film has been reported has been reported.

In addition to this, a thin film having various functions such as a charge injection layer for improving the injection characteristics of holes and electrons into the organic material, and a hole stop layer for increasing the recombination probability of both are added. By doing so, a function-separated type and a multilayer film type organic electroluminescent device have been proposed.

However, the part which becomes the basis of the light emission is still the light radiation in the deactivation process of the excited state from the organic light emitting molecules contained in the organic light emitting layer.

In the series of charge flow such as injection, transport and recombination of positive and negative charges into the organic material, the first problem is the charge from the electrode (metal material) to the organic material. Injecting process.

At the junction between the conductive electrode and the insulating organic material, there is a potential barrier due to the difference in the electronic structure, and a certain amount of energy is required to cross the potential barrier and inject the charge. To be done.

In a material having a wide band width such as a metal or a semiconductor, the barrier can be overcome by one-step excitation, and its current can be explained by the Richardson-Schottky emission model.

However, in an insulating material having a narrow band width such as an organic material, it is necessary to make a diffusion motion before reaching the potential maximum at a position of depth x _m from the interface, and the current is one-dimensional. Follow the Onsager model.

Here, the size of the potential barrier at the interface plays an important role, and the current density increases as χ decreases in the case of electron injection and χ increases in the case of hole injection. . Therefore, in the actual material search, it is considered to provide a charge injection layer between the electrode and the organic layer, and an electron-injected cathode has an ultra-thin film of a low work function material or an alloy with an electrode material. (For example, Mg: A
g, Li: Al, Cs: Al, LiF / Al, MgO /
Ultra thin films of high work function materials (for example, Au, Pt, Se, CuPc, etc.) are being studied for anodes into which holes are injected.

Another important factor in considering the efficiency of another organic electroluminescent device is the light extraction efficiency. The light extraction efficiency refers to the ratio of the light generated inside the device to the outside of the device, which is finally extracted to the outside of the device.

References (NC Greenham, RH Frie
nd, D.D. D. C. Bradley, Adv. Mater. 6,
491, 1994), out of the light extraction efficiency, the light extraction efficiency from the light emitting layer thin film forming the organic electroluminescent device to the outside of the thin film is determined by the law of reflection and refraction of classical optics. When the rate is n, it is given by [ _Equation 1] η _ext = 1 / (2n ² ) ... (1).

The light emitting layer of many organic electroluminescent elements, or the glass substrate holding them has a refractive index of about 1.6, which is η _ext = 0.2. this is,
In the so-called thin film or glass substrate, the ratio of the light confined by total reflection is shown, but in addition to this, in an actual organic electroluminescent element, an antireflection film for preventing contrast deterioration due to external light, Since many films are multilayered, such as a protective film for preventing mechanical shocks and an ultraviolet protection film for preventing deterioration of element constituent materials due to external ultraviolet rays, the decrease in light extraction efficiency due to absorption and reflection of these films is integrated. To be done.

Among them, increasing the contrast of the organic electroluminescence device is a particularly important problem when it is used as a practical display device. Because the organic electroluminescent device is
The structure is sandwiched between a pair of electrodes. One of them is a transparent electrode for extracting light, and most of them are ITO (Ind).
The counter electrode is a metal thin film (Al, Mg, A) having a work function higher than that of the anode.
(g, Li, Ca, etc.) are often used and play the role of a total reflection mirror. For this reason, light that has entered the pixel portion from the outside is reflected by the counter electrode, so that it is difficult to see the light of the lit pixel.

As a method of increasing the contrast, Japanese Patent Application Laid-Open No.
000-113988), a nematic liquid crystal element subjected to uniaxial alignment treatment is used as a circularly polarizing element,
An antireflection structure combined with a wave plate has been reported.

Further, according to Japanese Patent Laid-Open No. 2000-347394, there is a method for achieving a high contrast by using a black partition wall having a low reflectivity and made of a photosensitive paste containing a low melting point glass which is blackened after firing. It has been reported. Similarly, with regard to high contrast using a black partition, JP-A-3-250583 and JP-A-3-27469.
4, JP-A-6-342692 or JP-A-2000-
It is reported in Japanese Patent No. 048964.

Further, Japanese Patent Laid-Open No. 2000-284703 has reported a method for increasing the contrast by placing a semi-transmissive member on the light extraction surface from the light emitting layer. Furthermore, according to Japanese Patent Laid-Open No. 2000-048964, the reflectance of the electrode on the side opposite to the light extraction surface of the organic electroluminescent element is reduced, and a transparent conductive layer or a light absorption layer is placed outside the electrode to achieve high contrast. A method for achieving this has been reported. All of these are intended to achieve high contrast by forming various optical structures outside the organic electroluminescent device.

[0026]

As described above, various techniques have been studied to improve the light extraction efficiency of the organic electroluminescent device. However, considering the light extraction efficiency of the organic electroluminescence device including the means for increasing the contrast, there are various problems.

For example, in the method in which the polarizing element and the quarter-wave plate are combined, 50% of the light generated inside the organic electroluminescent element is absorbed by the light absorption by the polarizing element and the wavelength dependence of the wavelength plate. Change in chromaticity characteristics due to gender,
There were problems such as viewing angle dependence.

Further, in the method using the black partition, there is a problem that in addition to the reduction of the pixel aperture ratio due to the partition formation, the reflection itself from the counter electrode is not reduced. Further, in the method of placing the semi-transmissive member on the light extraction surface, the external light and the internally generated light are absorbed, and sufficient contrast cannot be obtained.

Further, in the method of reducing the reflectance of the counter electrode on the light extraction surface and disposing the transparent conductive layer or the light absorbing layer on the outside thereof, the electric sheet resistance is increased by thinning the counter electrode,
There have been problems such as an increase in the total amount of total internal reflection of light inside the device due to optical waveguide to a transparent conductive layer or a light absorbing layer formed outside thereof, and blurring of pixel edges.

In view of the above, it is an object of the present invention to provide an organic electroluminescent device that solves the problems associated with improving the electrical characteristics.

[0031]

The summary of the present invention for achieving the above object is as follows.

An organic electroluminescent device capable of injecting and transporting both positive and negative charges and generating light by recombination of holes and electrons generated by the both charges, and included in the organic electroluminescent device. The first electrode on the light extraction surface side, which is at least light-transmissive, may include a luminescent material due to recombination or a fluorescent material that secondarily generates light by receiving light from the luminescent material. In the organic electroluminescent device having a structure in which the organic electroluminescent layer is sandwiched between the second electrodes facing each other, the organic electroluminescent device is provided between the second electrode and the outside of the light emitting layer located in a direction other than the light extraction interface side of the organic electroluminescent device. In addition, the organic electroluminescence device is characterized by further comprising a first-type intermediate layer capable of absorbing almost all visible light passing through the inside of the organic electroluminescence device.

The first type intermediate layer is formed between the anode and the light emitting layer, and the intermediate layer has a work function of -5.0e.
The organic electroluminescent device has a voltage of V or less.

Further, the first type intermediate layer is composed of C, Pt, W,
The organic electroluminescent device described above contains at least one of Se, Au, Cu, Os, Ni, Pd, Co, and Ge.

In the organic electroluminescent device, the first-type intermediate layer contains a negatively ionized atomic group or a substituent.

In addition, the above-mentioned organic electroluminescence device in which the first-type intermediate layer also has the function of the second electrode.

The organic electroluminescent element is an amorphous silicon thin film transistor, a polycrystalline silicon thin film transistor, or an organic electroluminescent element formed on a substrate on which the organic thin film transistor is formed.

After forming the above-mentioned organic electroluminescent device,
It is an organic electroluminescent device integrated with an amorphous silicon thin film transistor, a polycrystalline silicon thin film transistor, or a substrate on which an organic thin film transistor is formed.

The organic electroluminescent device of the present invention is capable of injecting holes from an anode electrode and electrons from a cathode electrode into a light emitting layer containing organic light emitting molecules, and the hole is formed inside the light emitting layer. In the organic electroluminescent device capable of emitting light by recombination of electrons with, the light emitting layer may be a single layer or a multilayer.

In addition to the organic light-emitting molecule that emits light by recombination of holes and electrons, the light-emitting layer can absorb light generated from the organic light-emitting molecule and generate another light. It may include a fluorescent substance (or a phosphorescent substance).

Further, the light emitting layer may contain a hole transporting substance or an electron transporting substance capable of increasing the mobility of holes or electrons inside the light emitting layer.

Further, the light emitting layer may contain a hole-trapping substance or an electron-trapping substance which traps holes or electrons at a specific spatial position or reduces the transportability.

The above organic light-emitting molecule, fluorescent substance (or phosphorescent substance), hole-transporting substance, electron-transporting substance, hole-trapping substance and electron-trapping substance may be contained in the same layer, or they may be separated. It may be separated into layers. Even when a layer containing these constituents is formed by being divided into a plurality of layers, they are collectively referred to as a light emitting layer in the present invention.

Further, between the light emitting layer of the present invention and an anode or a cathode for injecting holes or electrons into the light emitting layer, a hole injecting layer or electrons for improving injection efficiency of holes or electrons is provided. An injection layer may be provided.

Further, a light emitting layer, an anode, a cathode, a hole injection layer,
A substrate for holding the electron injection layer may be provided,
Intermediate layers other than those may be provided as appropriate.

As the intermediate layer, a reflection mirror or a partial transmission mirror for modulating the reflection characteristic of light, a filter for transmitting specific light, an optical switch for adjusting the emission timing of the light, and a phase characteristic of the light are adjusted. The wavelength plate, the diffusion plate for diffusing the emission direction of the light, the protective film for preventing the deterioration of the substance forming the element due to the external light, heat, oxygen, moisture and the like.

As these intermediate layers, a light emitting layer, an anode, a cathode, a hole injecting layer, an electron injecting layer and the like can be appropriately provided between the substrate and the outside thereof in such a specification that the device characteristics are not significantly deteriorated. The layer corresponding to the outermost surface from which light is extracted from the organic electroluminescent device will be referred to as an extracted outermost layer.

As the electroluminescent material which can be used in the present invention, various metal complex type luminescent materials (such as 8-quinolinol, benzoxazole, azomethine, and flavone as ligands, and Al and Be as central metals) can be used. , Z
n, Ga, Eu, Ru, Pt) and fluorescent dye-based luminescent materials (oxadiazole, pyrazoline, distyrylarylene, cyclopentadiene, tetraphenylbutadiene,
Bisstyrylanthracene, perylene, phenanthrene, oligothiophene, pyrazoloquinoline, thiadiazolopyridine, layered perovskite, p-sexiphenyl, spiro compound, etc.) can be used.

Further, various polymer materials such as polyphenylene vinylene, polyvinylcarbazole, polyfluorene, etc. are used as the light emitting material, or non-light emitting polymer materials such as polyethylene, polystyrene, polyoxyethylene, polyvinyl alcohol, It is also possible to mix or polymerize various light emitting materials or fluorescent materials with polymethyl methacrylate, polymethyl acrylate, polyisoprene, polyimide, polycarbonate, etc. as a matrix.

Further, various organic hole or electron transporting materials (triphenylamine etc.) can be interposed.
Furthermore, various hole or electron injection layers (for example, Li,
(Ca, Mg, Cs, CuPc, etc.) can be interposed, and can be appropriately selected according to the element structure.

The term "first-type intermediate layer" as used herein refers to an organic layer between at least a light-transmissive first electrode on the light extraction surface side (this is referred to as a front electrode) and a second electrode facing the first electrode. In an organic electroluminescent device having a structure in which an electroluminescent layer is sandwiched, the organic electroluminescent device is located between the outside of the light emitting layer located in a direction not on the light extraction interface side of the organic electroluminescent device and the second electrode (this is referred to as a back electrode). And an optical thin film layer capable of absorbing almost all visible light passing through the inside of the organic electroluminescence device.

In particular, a desirable arrangement for forming the first type intermediate layer is a structure in which the first type intermediate layer is formed between the light emitting layer and the back electrode.

Preferred examples of the C-containing substance that can be contained in the first type intermediate layer include graphite, fullerenes such as C ₆₀ and C ₇₀ , and carbon allotropes such as carbon nanotubes. It is possible to do so, and those doped with various ions are also effective.

Various organic thin film forming techniques such as spin coating, coating, casting, sputtering, vacuum deposition, molecular beam deposition, liquid phase epitaxy, etc. Atomic layer epitaxial method, roll method, screen printing method, inkjet method,
The electric field polymerization method, rubbing method, spraying method, water surface expansion method, Langmuir-Blodgett film method, etc. can be used.

In order to promote the orientation during or after the film formation, a crystalline substrate having an orientation regulating force on the substrate itself, an alignment film coated substrate, a physical or chemical surface treatment is used. A treated substrate or the like can be used. Further, as the molecular skeleton in the compound suitable for such an alignment treatment, one having liquid crystallinity in the alignment treatment process is desirable,
After orientation treatment, it is also effective to fix the orientation state by cooling the sample temperature below the glass transition temperature or forming a new chemical bond between molecules by the reaction by light or heat. .

As the substrate, a substrate made of an inorganic substance such as glass, silicon or gallium arsenide, a substrate made of an organic substance such as polycarbonate, polyethylene, polystyrene, polypropylene or polymethylmethacrylate, or a combination of both. Any substrate can be used.
These substrates can be formed by cutting and polishing from the base material, injection molding, or the like.

It is also possible to use a substrate on which a thin film transistor is formed in order to control the light emitting state. An organic electroluminescent layer may be formed on such a thin film transistor forming substrate, or a thin film transistor forming substrate and an organic electroluminescent layer may be formed. It is also possible to form the substrate on which is formed separately from each other, and then bond the two to be integrated.

Further, in the organic electroluminescent device of the present invention, various precision processing techniques can be used in order to produce a required optical device structure in the process of forming the device. For example, precision diamond cutting processing, laser processing, etching processing, photolithography, reactive ion etching, focused ion beam etching and the like can be mentioned. Further, it is also possible to arrange a plurality of processed organic electroluminescent elements in advance, to form a multi-layer structure, to connect between them with an optical waveguide, or to seal in that state.

It is also possible to store the device in a container filled with an inert gas or an inert liquid. Furthermore, a cooling or heating mechanism for adjusting the operating environment can coexist. Materials that can be used for such containers include copper, silver, stainless steel, aluminum,
Various metals such as brass, iron, chrome and their alloys, or
A composite material or ceramic material in which these metals are dispersed in a polymer material such as polyethylene or polystyrene can be used.

Further, styrofoam, porous ceramics, glass fiber sheet, paper and the like can be used for the heat insulating layer. In particular, it is possible to apply a coating for preventing dew condensation.

As the inert liquid to be filled inside, liquids such as water, heavy water, alcohol, low melting point wax, mercury and the like or a mixture thereof can be used. In addition, examples of the inert gas with which the inside is filled include helium, argon, nitrogen and the like. A desiccant may be added to reduce the humidity inside the container.

In addition, the organic electroluminescent device of the present invention may be subjected to a treatment for improving its appearance and characteristics and for prolonging its life after forming a product. Examples of such post-treatments include thermal annealing, radiation irradiation, electron beam irradiation, light irradiation, radio wave irradiation, magnetic force line irradiation, and ultrasonic wave irradiation.

Further, the organic electroluminescence device can be used for various purposes such as adhesion, fusion, electrodeposition, vapor deposition, pressure bonding, dyeing, melt molding, kneading, press molding and coating. It can be compounded using a suitable means.

Further, the organic electroluminescent device of the present invention can be mounted in high density in close proximity to an electronic circuit for driving, and integrated with an interface for transmitting / receiving signals to / from the outside, an antenna or the like. You can also

[0065]

BEST MODE FOR CARRYING OUT THE INVENTION The organic electroluminescent element of the present invention will be described based on Examples.

Example 1 First, an example of an organic electroluminescent device which is the basis of the present invention will be described with reference to FIG.

In the organic electroluminescent device of the present invention, as shown in FIG. 1A, the transparent electrode 2 is formed on the substrate 1, and the low work function cathode 3, the light emitting layer 4 and the hole transport layer are formed. 5,
The black layer 6 and the conductive layer 7 are sequentially stacked.

The substrate 1 can be made of glass or polymer, and the transparent electrode 2 can be made of ITO or IZO (Indium Zinc Oxide). For the low work function cathode 3, Al, In,
Mg: Ag, LiAl, Ca or the like is used as Alq in the light emitting layer 4.
3 [Aluminiumtris (8-hydroqu
indole)], distyrylarylene, polyparaphenylene vinylene, etc.
[N, N-diphenyl-N, N-bis (3-me
thylphenyl) -1,1-biphenyl-
4,4-diamine], α-NPD [4,4-bis
(N- (1-naphthyl) -N-phenylam
ino) biphenyl], PEDT: PSS: PX
T-mixed polymer [PEDT = poly (3,4-Ethyl
endioxythiophene), PSS = po
ly (4-stylenesulfonate), PX
T = poly (p-xylylene-α-tetra
hydrothiophenium)] and the like are used. The conductive layer 7 may be made of Al, Cr, Au, Ag, Ni or the like.

The transparent electrode 2 functions as a first electrode for extracting light, and the opposing conductive layer 7 functions as a second electrode.

Of particular importance here is the black layer 6,
It is formed between the light emitting layer 4 and the conductive layer 7, and absorbs almost all visible light. Furthermore, its work function is a low work function cathode 3.
It is desirable to have a lower work function than
It is desirable that the work function is lower than that of the transparent electrode 2 thereunder.

As shown in FIG. 1B, this structure includes a conductive layer 7, a black layer 6, a hole transport layer 5, a light emitting layer 4, a low work function cathode 3 and a transparent electrode 2 on a substrate 1. In addition, an inverted stacking structure may be used.

The difference in contrast with respect to the penetration of external light between the case where the black layer is used as the first type intermediate layer and the case where it is not used will be described with reference to FIGS.

FIG. 2A shows an element structure of an organic electroluminescent element when a black layer is not used (comparative example).

Here, the organic electroluminescence device is formed on the substrate 9 with the transparent electrode 10, the transparent electrode 11, the light emitting layer 12, the low work function cathode 13 and the conductive layer 14, and the light generated in the light emitting layer 12 is on the substrate side. The structure is taken out. In order to reduce the invasion and reflection of external light, it is necessary to form the polarizing plate 8 on the outside of the substrate 9. Although not specifically shown here,
A comparative example has a structure in which a polarizer and a quarter-wave plate are combined as the polarizing plate 8 and the light is absorbed by the polarizer when the entering light is reflected.

The light generated in the light emitting layer 12 isotropically generates light inside the light emitting layer. Of the light generated at an arbitrary point of the light emitting layer, for example, the position of the white circle in the light emitting layer 12 in FIG. 2B, the light directly generated on the substrate side is as it is.
1, passing through the transparent electrode 10 and the substrate 9, but assuming that there is no light attenuation up to that stage, when passing through the last polarizing plate 8, one component of the polarized light is absorbed, so the light is halved. turn into.

As shown in FIG. 2 (c), the light generated on the side opposite to the substrate reaches the low work function cathode 13 or the conductive layer 14, but is reflected by the metal surface toward the substrate side, and similarly, finally the polarizing plate. Finally, it reaches the outside of the device through 8. Even in this case, if there is no internal attenuation, the extracted light becomes 1/2. Therefore, as a whole, only 1/2 of the amount of light emitted from the light emitting layer can be extracted. Actually, there is a loss due to absorption and scattering inside, and in particular, the light reflected on the counter electrode side passes a longer optical distance, so the loss is larger than this.

On the other hand, as shown in FIG. 2D, one component of the polarized light is absorbed when the light enters the inside of the device from the outside, passes through the inside, is reflected by the counter electrode, and is then reflected by the device. When the polarized light is rotated when it goes out, the other component is also absorbed.

However, due to the wavelength characteristics of the wave plate and internal scattering, the polarization of the reflected light cannot be completely canceled out, and the light leaks out. Since this size increases as the amount of light penetrating from the outside increases, the contrast decreases when the environment in which the organic electroluminescent element is used is bright.

Next, the contrast in the case of the organic electroluminescent element of the present invention will be examined with reference to FIG. Here, a case where light is extracted from the substrate side (corresponding to FIG. 1A) will be described.

As shown in FIG. 3A, the organic electroluminescent device comprises a transparent electrode 16, a low work function cathode 17, a light emitting layer 18, a hole transport layer 19, a black layer 20, and a conductive layer 21 on a substrate 15. It is sequentially laminated.

Here, an arbitrary point in the light emitting layer 18 (see FIG.
Light isotropically generated from (b) is divided into light that directly travels to the substrate side as in (b) and light that travels to the counter electrode side as in (c). Of these, those that directly proceed to the substrate side are emitted to the outside of the device through the low work function cathode 17, the transparent electrode 16, and the substrate 15.

Here, ignoring the loss inside the element, the light in this direction can be extracted without being attenuated on the way.

On the other hand, since the light traveling to the counter electrode side is absorbed by the black layer 20, there is no component reflected and returned. Therefore, the amount of light extracted by the device is 1/2 of the light generated.
In this respect, the amount of extracted light is equivalent to that of the conventional element shown in FIG.

On the other hand, light entering from the outside (FIG. 3 (d))
On the other hand, similarly, since the light is absorbed when the light reaches the black layer 20, there is no component in which light is reflected and returned by the counter electrode. Of course, unlike the conventional type, the polarizing plate and the retardation plate do not compensate the reflected light, so the optical characteristics do not change depending on the wavelength of external light, the penetration angle, the environment (temperature, humidity, etc.), You can always remove the external light.

Next, the results of theoretical comparison of the degree of high contrast between the conventional element and the element of the present invention are shown in FIG.
Will be explained.

FIG. 4 shows the case of the conventional device (a, c) and the case of the device of the present invention (b, d). In FIG. 4, (a, b) shows that the external environment light amount IC is larger than the generated light amount IL. If larger,
(C, d) is a case where the external environment light amount IC is smaller than the generated light amount IL.

If half of the external environment light quantity IC is returned light, the contrast ratio of the element is given by IL / (IC / 2). If the IC is small, sufficient contrast can be obtained between when the element is on and when it is off.
The contrast decreases as the outside light becomes brighter. Therefore, the conventional device is limited in use at night or indoors where the surroundings are dark to some extent. On the other hand, the element of the present invention has no such influence and the contrast is constant.

Furthermore, when the amount of external environmental light increases and the amount of returned light exceeds the amount of generated light, the generated light is completely buried in the returned light of the external light in the conventional element, and lighting display cannot be performed. Therefore, a larger amount of generated light is required, which causes various problems such as an increase in element power consumption, heat generation, and reduction in element life.

On the other hand, in the device of the present invention, the contrast of the pixel portion is constant even if there is a large amount of ambient light, and it is possible to observe an image sufficiently outdoors.

Example 2 Next, a more specific manufacturing procedure of the present invention will be described. FIG. 5 shows the structural formulas of the materials of the light emitting layer and the hole transporting layer used in the organic electroluminescent device produced as an example.

An organic electroluminescent element made of a low molecular weight material and an organic electroluminescent element made of a high molecular weight material were produced. After purchasing commercially available products, sublimation purification was repeated twice. As the high molecular weight material and the low molecular weight material, Alq3 is used for the light emitting layer and α-NPD is used for the hole transporting layer.
Was used.

As a material, PPV [pol is used for the light emitting layer.
y (2- (4-decyloxy) phenyl-1,4-
phenylene vinylene, manufactured by Shimada Chemical Research Institute), and PEDOT [poly
(3,4-ethylenedioxythiophe
ne, manufactured by Bayer Co., Ltd.] was used for the low-molecular type by vacuum vapor deposition, and for the high-molecular type by spin coating.

As the polymer system, a commercially available product was used, PPV was used as a toluene solution, PEDOT was used as an aqueous dispersion solution of the commercially available product, which was filtered with a filter of 3 μm and 0.2 μm before spin coating, respectively. .

FIG. 6 is a block diagram showing an example of an apparatus for manufacturing an organic electroluminescence device of the present invention. The hole transport layer, the light emitting layer and the low work function cathode made of a low molecular weight material are a molecular beam vapor deposition apparatus (manufactured by Nichiden Anelva, model OMBE, IMBE-620).
It was formed by vapor deposition inside.

In the molecular beam deposition apparatus, the substrate holder is replaced,
A first growth for forming an exchange chamber for mounting, a pretreatment chamber capable of transporting a substrate in the exchange chamber and heating it up to 1300 ° C., a hole transport layer, an organic light emitting material layer and an inorganic barrier layer. Chamber, a second growth chamber for forming a metal electrode,
It is composed of an analysis room for analyzing the surface condition of the formed thin film by ESCA and AES.

The base pressure of each chamber is 1 except for the exchange chamber.
0 ^-10 Torr level, exchange room is 10 ^-9 Torr level,
The chambers are separated from each other by a gate valve, and the substrates can be moved together with the substrate holders under an ultrahigh vacuum, if necessary.

Further, the mounting of the substrate in the exchange chamber and the taking-out of the film-formed sample are carried out by the first and second partitions separated by the gate valve.
It is performed through the glove box and the installation room (Miwa Seisakusho). The substrate, the polymeric material, and the like are externally mounted from the mounting chamber, and after degassing or gas replacement, the substrates can be transferred into the first or second glove box partitioned by the gate valve.

Among them, the first glove box was a dry nitrogen atmosphere (dew point -89, dew point -90), from which water and oxygen were removed.
The temperature is kept at 0 ° C. and the oxygen concentration is 0.01 ppm), and spin coating of the polymer light emitting layer, preliminary drying of the substrate, and element sealing work are performed.

The second glove box is in an environment where the atmosphere is a normal atmosphere but is shielded from surrounding dust and the like (has a circulation type clean booth inside), in which the hole transport of the polymer material is carried out. The layer is spin-coated, its pre-dried, and the black layer is formed. Here, the substrates that have been constantly cleaned can be exchanged under atmospheric pressure, but under the environment of dry nitrogen from which oxygen and water have been removed. The vapor deposition was performed by moving the substrate to the first and second growth chambers as needed.

At the time of vapor deposition, while the corresponding growth chamber chamber was cooled with liquid nitrogen, the raw material preliminarily mounted in each growth chamber was heated to sublimate or vaporize, and vapor deposition was performed on the substrate to form a thin film.

The raw materials are organic substances in a quartz crucible (Nichiden Anelva), and inorganic substances in a boron nitride crucible (Shin-Etsu Chemical Co., Ltd.), placed in each growth chamber, placed in a vacuum state, and heated with a heater. To vaporize the raw material. A mechanical shutter is attached to the outlet of the crucible, and by opening the shutter for a predetermined time, the vaporized raw material is deposited on the substrate. The film thickness of the vapor-deposited raw material was measured by a crystal oscillator type film thickness meter placed near the substrate to form a thin film having a predetermined film thickness.

The substrate temperature is -90 ° C to 150 ° C.
It is possible to maintain a predetermined temperature within the range. Vapor deposition rate is 0.1 nm for low molecular weight light emitting layer and hole transport layer
/ S, and the low work function cathode material has a crucible temperature of about 30 nm / s. The vapor deposition procedure differs between the low molecular weight type and the high molecular weight type as follows.

First, in the case of a low molecular weight system, an element having the structure shown in FIG. Borosilicate glass (size 40 x
40 x 0.8 mm, double sided polishing) and IT on one side
The transparent electrode layer 2 was formed by patterning and etching O after sputter deposition. ITO film thickness is 100n
m was a polycrystalline ITO film formed at a substrate temperature of 200 ° C., and the sheet resistance was 20 Ω / □.

This was subjected to ultrasonic cleaning in a neutral detergent for 15 minutes, washed under running pure water for 1 hour, and then ultrasonically cleaned in pure water for 15 minutes twice, and then washed with acetone (Wako Pure Chemical Industries, Ltd.). Manufactured by special grade) for 15 minutes, and then isopropanol (Wako Pure Chemical Industries, special grade) for 15 minutes, and dried by blowing dry nitrogen. This was irradiated with an ultraviolet lamp for 5 minutes in a first glove box on a hot plate at 150 ° C.

Next, this substrate is used as a second glove box,
It was transported to the second vapor deposition chamber via the exchange chamber and the like. here,
As the low work function cathode 3 at a substrate temperature of 23 ° C., a vapor-deposited film of Al (made of rare metallics, purity 6N) 5 nm and LiF (made of rare metallics, purity 6N) 0.6 nm was used. It is widely used as a low work function cathode for Alq3 of the light emitting layer 4 to be deposited next.

Next, the sample was transported to the first vapor deposition chamber, Alq3 was 70 nm as the light emitting layer 4, and α- was used as the hole transport layer 5.
70 nm of NPD was vapor-deposited.

Next, a method of forming the black layer 6 and the conductive layer 7 on this will be described. Similarly, using cleaned borosilicate glass, Pt (made of rare metallic,
A black layer 6 was produced by sputtering-coating a 6 nm-purity 20 nm film, and subjecting the surface to platinum black by an electrolytic method. This was thoroughly dried in the first glove box and transported to the second glove box.

The sample previously vapor-deposited to the hole-transporting layer was also conveyed here, where both surfaces were pressed and the end surfaces were cured and sealed with an ultraviolet curable resin. First of all,
An element A of (a) type was produced.

As a comparison, the element without platinum black was transported to the second glove box with the sample vapor-deposited up to the hole transport layer 5 and then transported to another sputtering apparatus with a dedicated container, and 20 nm of Pt was similarly sputter coated. . This again the second
It was returned to the glove box, covered with a glass plate having the same thickness, and the end face was sealed with an ultraviolet curable resin (element B).

Next, a procedure for manufacturing an element using a polymer material will be described. Similarly, borosilicate glass (size 40 × 40 × 0.8 mm, double-sided polished) was used for the substrate 1. This is subjected to ultrasonic cleaning for 15 minutes in a neutral detergent, washed for 1 hour under running pure water, then ultrasonically cleaned for 15 minutes in pure water twice, and then ultrasonically cleaned for 15 minutes in acetone. Then
After ultrasonic cleaning in isopropanol for 15 minutes, it was dried by blowing dry nitrogen. This was irradiated with an ultraviolet lamp for 5 minutes in a first glove box on a hot plate at 150 ° C.

Here, as the conductive layer 7, a Pt (rare metallic, purity 6N) 20 nm sputter coat was separately prepared, and the black layer 6 was obtained by subjecting the surface of this to platinum black by an electrolytic method. . In addition, some of the samples were prepared as comparative examples without platinum blackening.

To these, PEDOT was spin-coated to 70 nm as the hole transport layer 5 in the first glove box, sufficiently dried and degassed, and then transported into the second glove box. Here, as the light emitting layer 4, PPV was spin-coated with 70 nm and dried sufficiently. This sample was transferred to the second vapor deposition chamber, and Ca (Aldrich) was used as the low work function cathode 3.
Made of Al (rare metallics, purity 6N) 5nm as a transparent electrode (2),
Similarly, an ultraviolet curable resin was sealed with a glass plate.

Of these, the one with platinum black is the element C,
Element D without platinum black was used. In the final sample, the light emitting layer area is sealed, and the ITO or Al anode and the cathode are drawn out to the outside, and a voltage can be applied to these electrodes from the outside using a blower.

Among these elements, in the elements B and D, which are comparative examples, an absorption type polarizing film and a quarter wavelength plate were attached to the light extraction surface to obtain the polarizing plate 8 in FIG.

Next, the evaluation of the emission characteristics of the produced organic electroluminescent device will be described. A diagram for measuring the effect of the manufactured device is shown in FIG.

With respect to the produced organic electroluminescent element 22,
Voltage supply and current measuring device 25 (Hewlett-Packard) for supplying voltage and measuring the amount of current flowing at the same time
dA, pA Meter / DC Voltage S
A voltage was applied from the source 4140B), and a current was caused to flow inside the device from the anode to the cathode, so that the device was electroluminescent.

The amount of light generated is determined by a luminance meter camera 23 installed in the front position of the central part of the element, and a luminance meter controller 24 (manufactured by Photoresearch, Spectra Pritchard Photo).
The brightness was measured by a meter, Model 1980A-PL). The brightness meter controller 24 and the voltage supply / current measuring device 25 are controlled and measured by a control personal computer 26. All measurements were performed at room temperature, and no particular temperature control was performed.

FIG. 8 is a graph showing typical luminance-applied voltage characteristics of the organic electroluminescent device of the present invention.

When voltage application is started, noise level light emission is initially observed, but the light emission amount increases rapidly from several V (about 3 V in the figure) (this voltage is set as the threshold voltage). Further, when a voltage is applied, the amount of light emission increases, but the brightness is 1
The voltage when it reached 00 cd / m ² was defined as the characteristic voltage.

Further, when the voltage is continuously applied, the maximum luminance is reached, but the dielectric breakdown of the element occurs in the vicinity thereof, and the element is destroyed. This voltage was defined as the breakdown voltage.

The performances of the fabricated devices were compared by using these four indexes, that is, the threshold voltage, the characteristic voltage, the maximum brightness and the breakdown voltage. In addition, in order to evaluate the influence of the environment (external light),
When the outside light was measured in a white lamp environment of 0, 10, 100 lm (lumens), the ratio of the measured light amount when the element was turned off to the light amount when the element was turned off was measured as a contrast ratio.

First, looking at the light emission characteristics of the elements (these are measured when the external light is 0 lm), the threshold voltage, the characteristic voltage, the breakdown voltage, and the maximum brightness are the same as those of the low molecular weight elements A and B, and the high molecular weight There was almost no characteristic difference between the element C and the element D.

On the other hand, looking at the influence of external light on the contrast ratio, the contrast ratios of the elements A and C of the present invention hardly changed as the measurement environment became brighter.
In the conventional devices B and D, the contrast decreased as the brightness increased.

As described above, by using the device of the present invention, an organic electroluminescent device has been shown in which the contrast ratio does not decrease even in a bright environment.

[0125]

[Table 1] [Embodiment 3] Next, an example in which an element having the same element structure and using the first type intermediate layer of a different material is produced will be described.
Here, various allotropes of carbon (C) were used for the first-type intermediate layer, and the effects of the light emission characteristics were compared.

As in Example 2, a glass substrate with ITO was used as the substrate, and PEDOT and PPV were sequentially spin-coated on the substrate to form a common hole transport layer and light emitting layer. After forming graphite powder and fullerene C ₆₀ thin films each having a thickness of about 60 nm by the following method as a first type intermediate layer thereon, an Al electrode was formed thereon in the same manner as in Example 2 to form an element. Sealed.

The graphite powder layer was formed by the following procedure. For the graphite powder, a commercially available product (manufactured by Wako Pure Chemical Industries, Ltd.) was prepared by crushing it in a mortar as finely as possible, and this was quickly mixed with silver paste at a ratio of 1: 1 and diluted to 10 wt% with acetone as a diluent solvent. Using this solution as a stock solution, the sample on which the light emitting layer had been formed was spin-coated in the glove box shown in Example 2. The electrode forming process after drying the solvent in the apparatus is the same as that in the second embodiment.

The fullerene C ₆₀ layer was formed by the following procedure. As a raw material, a commercially available fullerene C ₆₀ (manufactured by Tokyo Kasei Co., Ltd., purity: 99.9% or more) was set in the organic chamber of the molecular beam vapor deposition apparatus described in Example 2, and molecular beam vapor deposition was performed on the sample on which the light emitting layer was formed. Vacuum deposition (crucible temperature 480 ° C.) to a predetermined film thickness by using, and moving the sample as it is to the inorganic chamber of the molecular beam deposition apparatus to form an Al electrode,
Finally, the device was sealed.

Table 2 shows the organic electroluminescence characteristics of each element thus manufactured. It can be seen that although both graphite and C ₆₀ have lower emission intensities than those in Example 2, they still show a high contrast ratio.

[0130]

[Table 2] [Example 4] Next, the characteristics of the organic electroluminescent device in the case where a thin film layer in which various kinds of fine metal powders are dispersed are formed as the first-type intermediate layer, and the results of evaluating the contrast ratio will be described.

The fine metal powder used is W (Aldr
ich nanosize activated p
owder, purity 99.9% or more), Se (manufactured by Kojundo Chemical, purity 3N, powder diameter 10 μmφ), Au (Aldri
ch made nanosize activated pow
der, purity 99.9% or more, particle size 100 nmφ), C
u (manufactured by Kojundo Chemical, purity 4N, powder diameter 1 μmφ), Os
(High purity chemical, purity 3N), Ni (high purity chemical, purity 3N, powder diameter 2 to 3 μmφ), Pd (Aldrich
Made Palladium black), Co (Aldr
ich, purity 99.8% or more, particle size 2μmφ), Ge
(Manufactured by Kojundo Chemical Co., Ltd., purity 4N, powder diameter 10 μmφ) was used.

Since these metals are extremely highly active, they were handled in the glove box described in Example 2 from which water and oxygen were sufficiently removed.

As in Example 2, a glass substrate with ITO was used as the substrate, and PEDOT and PPV were sequentially spin-coated on the glass substrate to form a common hole transport layer and light emitting layer. On top of that, as the first type intermediate layer, various metal powders shown in the previous stage were dissolved in chloroform separately dehydrated with a metal sodium mirror, and polystyrene (manufactured by Aldrich,
A weight average molecular weight of 600,000) was mixed and dispersed in a ratio of metal 1: solution 10 in a weight ratio, and this was spin-coated in a glove box at 1000 rpm for 1 minute, and dried in the glove box for a whole day and night. Next,
An Al electrode was formed by vapor deposition in the same procedure, and similarly sealed to obtain an element.

Table 3 summarizes the characteristics of devices using these metal powders. It can be seen that in both cases, the emission intensity is lower than in the case of Example 2, but the contrast ratio is still high. However, when the metal particle size is large, the scattering property is high and the contrast is relatively low. In the future, performance improvement can be expected by making the particle size finer.

[0135]

[Table 3]

According to the present invention, by using a material having a higher work function as the anode, the luminous efficiency of the organic electroluminescence device can be improved.

Further, since the reflected light is prevented and the external optical film can be reduced, it is possible to obtain a display device having a high contrast even in the daytime or in a bright environment.

Further, since the active cathode serves as the lowermost layer, stabilization can be achieved, and since the black layer can be attached later, the manufacturing process is simplified, and the TFT substrate for driving the element can be separated. It becomes possible to composite the material formed in the process later.

Further, by improving the electric characteristics of the element, it is possible to lower the voltage for driving the element, increase the luminance, and extend the life of the element, and it is possible to increase the screen size and definition of the image display element.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic device configuration of an organic electroluminescent device of the present invention.

FIG. 2 is a configuration diagram of a comparative example element for explaining the effect of the organic electroluminescent element of the present invention.

FIG. 3 is a configuration diagram illustrating an organic electroluminescent device of the present invention.

FIG. 4 is a characteristic comparison diagram illustrating the effect of the organic electroluminescent device of the present invention.

FIG. 5 is a luminescent material used in the organic electroluminescent device of the present invention.
3 is a chemical structural formula of a hole transport material.

FIG. 6 is a configuration diagram showing an example of an apparatus for manufacturing an organic electroluminescent element of the present invention.

FIG. 7 is a diagram for measuring the effect of the organic electroluminescent device of the present invention.

FIG. 8 is a representative diagram of characteristics of the organic electroluminescent device of the present invention.

[Explanation of symbols]

1, 1 '... substrate, 2, 2' ... transparent electrode, 3, 3 '... low work function cathode, 4, 4' ... light emitting layer, 5, 5 '... hole transport layer, 6, 6' ... black layer , 7, 7 '... Conductive layer, 8 ... Polarizing plate, 9 ... Substrate, 10 ... Transparent electrode, 11 ... Hole transport layer, 1
2 ... Emitting layer, 13 ... Low work function cathode, 14 ... Conductive layer, 1
5 ... Substrate, 16 ... Transparent electrode, 17 ... Low work function cathode, 1
8 ... Emitting layer, 19 ... Hole transporting layer, 20 ... Black layer, 21 ...
Conductive layer, 22 ... Organic electroluminescent device, 23 ... Luminance camera, 24 ... Luminance controller, 25 ... Voltage supply / current measuring device, 26 ... Control personal computer.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 33/26 H05B 33/26 ZF term (reference) 3K007 AB02 AB06 AB11 AB17 BA06 BB07 CC02 DA01 DB03 EA00 EB00 5C094 AA06 AA10 AA24 AA31 AA43 BA03 BA27 CA19 DA12 DA13 DB01 DB04 DB05 EA04 EA05 EA10 EB02 ED20 FA02 FB01 FB20 GB10 5G435 AA02 AA17 BB05 CC09 EE32 EE41 FF14 KK05

Claims (7)

[Claims] 1. An organic electroluminescent device capable of injecting and transporting both positive and negative charges and generating light by recombination of holes and electrons generated by the both charges, and the organic electroluminescent device. And a fluorescent substance which is included in the above and emits light secondarily by receiving light from the luminescent substance or light from the luminescent substance, and at least the first electrode on the light extraction surface side which is light transmissive. In an organic electroluminescent device having a structure in which an organic electroluminescent layer is sandwiched between second electrodes facing each other, the second electrode and the outside of the light emitting layer positioned in a direction other than the light extraction interface side of the organic electroluminescent device. An organic electroluminescence device, characterized in that a first-type intermediate layer is provided between them and capable of absorbing almost all visible light passing through the inside of the organic electroluminescence device. 2. The organic electroluminescent device according to claim 1, wherein the first-type intermediate layer is formed between the anode and the light emitting layer, and the work function of the intermediate layer is −5.0 eV or less. 3. The first type intermediate layer is C, Pt, W, S
The organic electroluminescent element according to claim 1, which contains at least one of e, Au, Cu, Os, Ni, Pd, Co, and Ge. 4. The organic electroluminescent device according to claim 1, wherein the first-type intermediate layer contains a negatively ionized atomic group or a substituent. 5. The organic electroluminescent device according to claim 1, wherein the first-type intermediate layer also has a function of a second electrode. 6. The organic electroluminescent device according to claim 1, wherein the organic electroluminescent device is formed on an amorphous silicon thin film transistor, a polycrystalline silicon thin film transistor, or a substrate on which the organic thin film transistor is formed. element. 7. The organic electric field according to claim 1, which is integrated with an amorphous silicon thin film transistor, a polycrystalline silicon thin film transistor, or a substrate on which an organic thin film transistor is formed after forming the organic electroluminescent device. Light emitting element.