JPH10294181A - Organic electroluminescence element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain an aging reduction rate of light emitting luminance and a generation rate of a light unremitting part, improve light emitting efficiency, reduce driving voltage, maintain a stable light emitting characteristic over a long period, and improved durability by constituting a hole transport layer mainly of an organic compound, and performing heating work on its part. SOLUTION: At least a light emitting layer 13 and a hole transport layer 12 are provided between an ITO anode 21 and a cathode 15 arranged on a glass substrate 10, and the light is emitted by electric energy. The hole transport layer 12 is an organic layer whose part is heat-treated. In heat treatment of here, it is important to be heat-treated further after a film is formed even when it is heated at film forming time like when the hole transport layer 12 is formed by vacuum evaporation while heating the substrate 10 by imparting heat after the hole transport layer 12 is formed as a film. In order to stabilize a thin film shape and prevent coagulation of a thin film by melting, a heat treatment temperature is set from a substrate temperature to a melting point at film forming time of the hole transport layer, and reduction in luminance and a dark spot are restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, a flat panel display, a backlight, a lighting, an interior, a sign, a signboard, an electrophotographic device, and the like.
The present invention relates to an organic electroluminescent device capable of converting electric energy into light and a method for manufacturing the same.

[0002]

2. Description of the Related Art Organic electroluminescent devices in which holes injected from an anode and electrons injected from a cathode recombine in an organic phosphor sandwiched between both electrodes to emit light have been actively researched in recent years. ing. This element has attracted attention because it is thin, can emit high-luminance light under low-voltage driving, and can emit multicolor light by selecting an organic fluorescent material.

[0003] The fact that organic electroluminescent devices emit light with high luminance at low voltage is disclosed in Kodak C.S. W. Tang et al. (Appl. Phys. Lett. 51
(12) 21, p. 913, 1987). A typical configuration of an organic electroluminescent device presented by a Kodak research group is a vacuum deposition of a hole transport layer made of an amine compound, a light emitting layer made of 8-hydroxyquinoline aluminum, and a Mg: Ag cathode sequentially on an ITO glass substrate. Provided at a drive voltage of about 10 V and 1000 cd
/ M ² green light emission was possible. Although the current organic electroluminescent device has a different configuration such as providing an electron transport layer in addition to the above-mentioned device components, it basically follows the configuration of Kodak Company.

A major problem with organic electroluminescent devices is durability. Although the cause of the insufficient durability of the device has not yet been completely elucidated, one of the causes is considered to be the change over time in the form of the organic layer. Amorphous thin films are often used for the organic layers that compose the organic electroluminescent element. However, partial aggregation and crystallization of the amorphous thin film occur due to structural relaxation after film formation and heat generation during element driving, and the thin film morphology is reduced. It often changed greatly compared to the initial state. This morphological change causes a disorder in the element structure, resulting in a decrease in luminous efficiency and an increase in non-light emitting portions.

[0005] The hole transport layer is an organic layer that greatly affects the durability of the organic electroluminescent device, and many improvements have been made so far, particularly on materials. As described above, the hole transport layer is required to have high hole transport characteristics and easy film formation of the amorphous thin film, and as described above, the temporal stability of the thin film form is required. The method is not yet known.

On the other hand, as disclosed in JP-A-3-173095 and JP-A-5-182664, an attempt to improve durability by using an organic layer having a crystalline structure instead of an amorphous thin film from the beginning. However, the durability required for practical use has not been obtained.

[0007]

As described above, when an attempt is made to improve the durability of the device by an approach from a hole transport material, the device has excellent hole transport characteristics and easy film formation, and
Even when using a hole transporting material that is expected to maintain a stable thin film form even from various viewpoints, an actually manufactured device often has poor durability. That is, although there is a hole transporting material having excellent characteristics, there is a big problem in that the conventional technology cannot sufficiently utilize the characteristics. In addition, in an approach using an organic film having a crystal structure, it is generally difficult to form an organic thin film having a uniform crystal structure, and a thin film having a microcrystalline structure is used. It is necessary to suppress the occurrence of an undesired leak current or the like due to the crystal grain boundaries, and there is a problem that available materials and element manufacturing conditions are limited.

As described above, the durability of the organic electroluminescent device is still insufficient, and it is necessary to make further efforts to obtain stable light emitting characteristics. The present invention solves such a problem,
It is an object of the present invention to provide an organic electroluminescent device having excellent durability and capable of maintaining stable light emitting characteristics for a long period of time, and a method for manufacturing the same.

[0009]

Means for Solving the Problems As a result of the present inventors' intensive efforts to achieve the above object, an organic electroluminescent device including a heat-treated hole transport layer exhibits particularly excellent durability. This led to the completion of the present invention.

That is, the organic electroluminescent device of the present invention is an organic electroluminescent device having a light emitting layer and a hole transport layer between a first electrode provided on a substrate and a second electrode facing the first electrode. Wherein the hole transport layer is mainly composed of an organic compound, and at least a part of the hole transport layer has been subjected to a heat treatment. "

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The organic electroluminescent device of the present invention comprises a light emitting layer and a hole transport layer between a first electrode provided on a substrate and a second electrode facing the first electrode. Is an element that emits light.

Here, the electric energy mainly indicates a direct current, but an alternating current or a pulse current can also be used.
The current value or the voltage value is not particularly limited. However, in consideration of the power consumption and durability of the element, the maximum luminance should be obtained with the lowest possible energy.

The first electrode and the second electrode need only have conductivity so that a current sufficient for light emission of the device can be supplied, and it is preferable that at least one electrode is transparent in order to extract light.

The use of a transparent electrode does not cause any major obstacle if the visible light transmittance is 30% or more, but it is more preferable if the transparent electrode has a visible light transmittance of 80% or more. Basically, it is preferable to have the same transmittance over the entire visible light range. However, if it is desired to change the color, it may be positively provided with absorption characteristics or interference characteristics. In that case, it is technically easy to change the color using a color filter or an interference filter. The material of the transparent electrode is often made of at least one element selected from indium, tin, gold, silver, zinc, aluminum, chromium, nickel, oxygen, hydrogen, and carbon, such as copper iodide and copper sulfate. Inorganic conductive substance, polythiophene,
It is also possible to use a conductive polymer such as polypyrrole and polyaniline, and there is no particular limitation.

Examples of the first electrode particularly desirable in the present invention include tin oxide and zinc oxide provided on a transparent substrate.
An anode such as indium oxide or indium tin oxide (ITO) can be given. In display applications where pattern processing is performed, ITO which is excellent in processability can be cited as a particularly suitable example. In order to improve conductivity, ITO may contain a small amount of metal such as silver and gold, and tin, gold, silver, zinc, indium, aluminum, chromium, nickel, and tantalum may be used as ITO guide electrodes. It is also possible to use as. Among them, chromium is a suitable metal because it can have both functions of a black matrix and a guide electrode. From the viewpoint of power consumption of the device, it is desirable that ITO has low resistance.
For example, if the sheet resistance value is 300Ω / □ or less, it functions as an element electrode. However, it is possible to supply about 10Ω / □ at present, and it is desirable to use a low resistance product.
The thickness of the ITO can be arbitrarily selected according to the resistance value, but is usually used in a range of usually 100 to 400 nm. The material of the transparent substrate is not particularly limited, and polyacrylate, polycarbonate, polyester, polyimide,
A plastic plate or film made of aramid or the like can be used, but a preferred example is a glass plate. Soda lime glass, non-alkali glass, or the like is used, and the thickness should be 0.5 mm or more since the mechanical strength may be maintained. In terms of the material, alkali-free glass with less ions eluted from the glass is preferable, but soda-lime glass coated with a barrier coat such as SiO ₂ is commercially available and can be used. I
The method for forming the TO film is not particularly limited, such as an electron beam method, a sputtering method, and a chemical reaction method.

With respect to the first electrode provided on the substrate, after processing such as pattern processing is performed as required, before the thin film layer constituting the organic electroluminescent element is formed. Preferably, a surface treatment is performed in addition to the usual organic solvent cleaning. This is because the surface of the first electrode is cleaned and activated in some cases, so that the manufactured organic electroluminescent element approaches an ideal state.
Suitable examples of the surface treatment method include UV ozone cleaning, acid / alkali treatment, and plasma treatment.
In particular, when a transparent anode such as ITO is used as the first electrode, a UV ozone treatment which can obtain a high cleaning effect by a relatively easy method can be exemplified as a more preferable surface treatment method.

In the present invention, a particularly desirable second electrode is a cathode, but the material thereof is not particularly limited as long as electrons can be efficiently injected into the organic layer. Therefore, it is possible to use a low work function metal such as an alkali metal, but considering the stability of the electrode, a metal such as platinum, gold, silver, copper, iron, tin, aluminum, magnesium and indium, or a metal such as these And an alloy with a low work function metal. In addition, the organic layer included in the organic electroluminescent element is previously doped with a small amount of a low work function metal in a small amount, or a thin layer of a metal salt such as lithium fluoride is formed on the organic layer. By forming a metal as a cathode, a stable electrode can be obtained while maintaining high electron injection efficiency. The method for forming these cathodes is also not particularly limited, such as a resistance heating evaporation method, an electron beam evaporation method, a sputtering method, and an ion plating method, but the present invention mainly uses a simple resistance heating evaporation method. .

Even if the first and second electrodes have a single-layer structure made of the same material, different materials may be used in the thickness direction.
It may have a laminated structure in which layers are stacked. For example, when the first electrode is an ITO anode, a thin metal film such as platinum or gold may be laminated on the ITO, or when the second electrode is a cathode, deterioration of the cathode due to moisture or oxygen is prevented. For this purpose, a cap layer can be laminated.

Examples of the laminated structure included in the organic electroluminescent device of the present invention include a hole transport layer / a light emitting layer or a hole transport layer / a light emitting layer / an electron transport layer. There is no particular limitation as long as the layer exists and at least a part of the hole transport layer is an organic layer subjected to a heat treatment. Therefore, each layer does not need to be a single layer. For example, two or more hole transport layers of different materials or of the same material but having different thin film forms may be laminated, and the same applies to the light emitting layer and the electron transport layer. In addition, a method of causing a part of the hole transport layer or the electron transport layer to emit light as it is, or a method of emitting light by doping a part of the hole transport layer or the electron transport layer with a luminescent organic molecule, is often used. In this case, the portion that actually controls light emission may be regarded as a light emitting layer, and the portion that mainly controls carrier transport may be regarded as a hole transport layer or an electron transport layer.

Materials used for the hole transport layer include:
N, N'-diphenyl-N, N'-di (3-methylphenyl) -1,1'-diphenyl-4,4'-diamine (TPD) and N, N'-diphenyl-N, N'-dinaphthyl -1,1′-diphenyl-4,4′-diamine (N
PD) and the like, N-isopropylcarbazole, N-substituted biscarbazolyl derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds, oxadiazole derivatives and quinacridone derivatives, and porphyrin derivatives and phthalocyanine derivatives for heterocyclic compounds Metal phthalocyanine derivatives typified by copper phthalocyanine; and in the polymer system, polycarbonate and styrene derivatives, polyvinyl carbazole, polysilane, polyaniline, polythiophene, and the like. Further, a material in which the monomer is bonded to a side chain of these polymers can also be used.

Although the present invention is not particularly limited to materials, it has excellent hole transport characteristics and film-forming easiness, and can be expected to exhibit the stability over time of the thin film form.
It is preferable that the hole transporting layer subjected to the heat treatment be made of an organic compound containing a carbazole ring. Further, since the effect of stabilizing the thin film form by the heat treatment is large, it is more preferable that the hole transport layer to be subjected to the heat treatment is made of an organic compound having a biscarbazolyl skeleton shown below.

[0022]

Embedded image (Where R1 and R2 are hydrogen, alkyl, halogen,
It is selected from aryl, aralkyl and cycloalkyl. The carbazolyl skeleton may have one or more substituents selected from alkyl, aryl, aralkyl, carbazolyl, substituted carbazolyl, halogen, alkoxy, dialkylamino, and trialkylsilyl groups. The materials used for the light emitting layer include anthracene and pyrene, which have been known as light emitters, and the aforementioned 8
-In addition to aluminum hydroxyquinoline, for example,
Bisstyrylanthracene derivatives, tetraphenylbutadiene derivatives, coumarin derivatives, oxadiazole derivatives, distyrylbenzene derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, oxadiazole derivatives, thiadiazopyridine derivatives, and polyphenylenevinylene derivatives in polymer systems , Polyparaphenylene derivatives, and polythiophene derivatives can be used. Further, as a dopant added to the light emitting layer, rubrene, quinacridone derivative, coumarin derivative,
Diazaindacene derivative, phenoxazone 660, DC
M1, perinone, perylene and the like can be used as they are.

As the material used for the electron transport layer, it is desirable to efficiently transport electrons injected from the cathode between the electrodes to which an electric field is applied. For this purpose, it is required that the material has a high electron affinity, a high electron mobility, a high stability, and a small amount of impurities serving as traps during production and use. As materials satisfying such conditions, 8-hydroxyquinoline aluminum, hydroxybenzoquinoline beryllium,
2- (4-biphenyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole (t-BuPB
Oxadiazole derivatives such as D), and oxadiazole dimer derivatives having improved thin film stability,
3, -bis (4-t-butylphenyl-1,3,4-oxazizolyl) biphenylene (OXD-1), 1,3,
-Bis (4-t-butylphenyl-1,3,4-oxadizolyl) phenylene (OXD-7), a triazole derivative, a phenanthroline derivative, and the like.

The organic materials used for the hole transporting layer, the light emitting layer, and the electron transporting layer can be used alone or as a mixture of two or more kinds. Vinyl chloride, polycarbonate, polystyrene, poly (N-vinylcarbazole), polymethyl methacrylate, polybutyl methacrylate, polyester, polysulfone, polyphenylene oxide,
Solvent-soluble resin such as polybutadiene, hydrocarbon resin, ketone resin, phenoxy resin, polysulfone, polyamide, ethyl cellulose, vinyl acetate, ABS resin, polyurethane resin, phenol resin, xylene resin, petroleum resin, urea resin, melamine resin, unsaturated It is also possible to use the resin dispersed in a curable resin such as a polyester resin, an alkyd resin, an epoxy resin and a silicone resin.

The organic layer such as the hole transporting layer, the light emitting layer and the electron transporting layer may be formed by a wet process such as a spin coating method or a dip coating method, a resistance heating evaporation method, an electron beam evaporation method, a sputtering method, or the like. A dry process such as a dry process can be used, and is not particularly limited, but generally, a vacuum deposition method such as a resistance heating evaporation method or an electron beam evaporation method is preferable in terms of characteristics. Since the thickness of the organic layer is also unconditionally shown because it is related to the resistance value, it is empirically selected from the range of 10 to 1000 nm.

Further, the whole or a part of the light emitting layer or the electron transporting layer, and in some cases, the hole transporting layer included in the organic electroluminescent device of the present invention may be made of a material other than an organic material. For example, SiC, GaN, ZnSe, Zn
S-based inorganic semiconductor materials and organic / inorganic composite materials can also be used.

In the organic electroluminescent device of the present invention, at least a part of the hole transporting layer is a heat-treated organic layer. Here, the heat treatment means applying heat after the hole transport layer is formed. Therefore, even when heating is performed during film formation, for example, a hole transport layer is formed by a vacuum evaporation method while heating a substrate, it is important to further perform heat treatment after film formation. Hereinafter, a specific description of the heat treatment will be given by exemplifying a specific element structure, but the present invention does not limit the element structure.

FIG. 1 shows a preferred device structure of the present invention.
The first electrode is a transparent anode, a hole transport layer exists on the side near the anode, the second electrode is a cathode, and the light emitting layer exists on the side near the cathode. Therefore, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are formed in this order on the anode.

When the hole transport layer is subjected to a heat treatment after the formation of the cathode, stress is applied to the entire device due to the presence of the cathode on the upper portion of the device, and the intended stabilization of the shape of the hole transport layer is hindered. Therefore, it is preferable to heat-treat the hole transport layer before forming the cathode. Basically, if a heat treatment is performed immediately after forming the target hole transport layer, that is, in a state where nothing is formed on the layer, the thin film morphology can be sufficiently stabilized. Therefore, the effect of the heat treatment can be sufficiently obtained. Further, in the case where the light-emitting layer needs to be subjected to heat treatment, the light-emitting layer may be formed and heat-treated after the hole-transport layer is subjected to heat treatment.

When two hole transport layers are present as shown in FIG. 2, heat treatment may be performed after forming both layers, and if necessary, the first hole transport layer may be used. May be heated, and then the film formation may be continued in the order of the second hole transport layer and the light emitting layer. As a matter of course, it is also possible to form the second hole transport layer after the first hole transport layer is subjected to the heat treatment, and to perform the heat treatment again. Known phthalocyanine derivatives, porphyrin derivatives, oligothiophene compounds and the like can be used for the first hole transporting layer in contact with the anode from the viewpoint of improving durability.

In particular, the effect of improving the luminous efficiency can be expected, such as recovering the defects introduced into the hole transport layer by the heat treatment and bringing the interface with the luminescent layer formed later to an ideal state. After heat-treating the hole-transporting layer, one or more other hole-transporting layers are formed on the hole-transporting layer using the same or different hole-transporting material as the hole-transporting layer. It is preferable to form a layer after the layer.

Since the temperature of the heat treatment depends on the material used for the hole transporting layer, it is difficult to specify the temperature, and in some cases, the temperature may be higher than the melting point of the material. However, it stabilizes the thin film morphology,
In order to prevent aggregation of the thin film due to melting, it can be said that the heat treatment temperature is preferably equal to or higher than the substrate temperature at the time of forming the hole transport layer and equal to or lower than the melting point of the hole transport layer. Furthermore, the organic layer constituting the hole transport layer is caused to shift its center of gravity, thereby stabilizing a sufficient thin film morphology. In addition, in order to prevent undesired crystallization of the amorphous thin film, the heat treatment temperature is set to be lower. More preferably, it is higher than the glass transition temperature of the layer and lower than the crystallization temperature of the hole transport layer.

The above-mentioned glass transition temperature, crystallization temperature, melting point, etc. are determined by, for example, the heat absorption and heat generation process of the hole transport layer or the material powder used for the hole transport layer by differential scanning calorimetry (DSC method). It can be measured by checking.

As a general heat treatment method, a method using an oven or a hot plate in an atmosphere of an inert gas such as nitrogen or argon may be mentioned. However, hot air or infrared rays may be used. The transport layer is not particularly limited as long as it can uniformly heat the transport layer at a desired temperature and minimize undesirable phenomena such as deterioration of the organic compound due to heating and contamination of the element with foreign substances. Therefore, depending on the material, heat treatment can be performed in an atmosphere in which oxygen, moisture, or the like exists. Further, heat treatment may be performed in a vacuum using heater heating, infrared rays, electromagnetic induction, or the like.

In particular, when forming a hole transporting layer or the like by a vacuum process such as a vacuum deposition method, it is possible to continuously form the light emitting layer and the subsequent layers without releasing the vacuum, thereby deteriorating the organic compound. Heat treatment in a vacuum can be said to be a preferable method because there is little chance of contamination or contamination of foreign matter. On the other hand, when the heat treatment is performed in a vacuum, a long time is often required for the subsequent decrease in the substrate temperature, which may increase the process time or induce crystallization of the hole transport layer. Therefore, in the case where the adverse effect of the release of the vacuum does not become a problem, it is rather preferable to release the vacuum after the step of forming the hole transport layer and then heat-treat the hole transport layer.

The heating time depends on the heating temperature, the heating treatment method, and the like, so that it is difficult to give an unambiguous indication. Basically, heating may be performed only for a time necessary for sufficiently stabilizing the form of the target hole transport layer, but may be optimized according to conditions.

Similarly, it is difficult to clearly indicate the rate of temperature rise / fall in the heat treatment. If the temperature lowering rate is too slow, undesirable crystallization of the amorphous thin film may be promoted, but empirically, 1 to 100 ° C./min. Choose between.

In the present invention, the organic electroluminescent device may be subjected to an aging treatment after the formation of the second electrode. This is a process for causing the element to emit light for a short time before the actual driving, and has the effect of preventing short-circuiting, a sharp decrease in luminance, and the like, and improving the long-term durability of the element. The aging condition is not particularly limited, but is preferably performed in a low-humidity atmosphere containing oxygen in order to suppress generation of dark spots while insulating a leak site in the device.

The organic electroluminescent device of the present invention shows excellent durability. The term “excellent durability” basically means that the rate of decrease in light emission luminance when the element is driven for a long time is small, but another important point is that a non-light-emitting portion called a dark spot is used. Also means that the occurrence rate is small. The heat treatment described above not only reduces the luminance reduction ratio of the element, but also has a significant effect of suppressing dark spots.

[0040]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 Bis (m-methylphenylcarbazole) was prepared as a hole transport material. According to measurement by the DSC method, the glass transition temperature was 90 ° C., the crystallization temperature was 168 ° C., and the melting point was 192 ° C.

ITO on glass substrate (1.1 mm thick)
Transparent electrode film (sheet resistance 15Ω / □, ITO film thickness 17
(0 nm, visible light transmittance: 88%) was patterned into a predetermined shape by an etching method, and washed with acetone, Semico Clean 56, pure water, isopropyl alcohol, and methanol. After surface-treating this ITO substrate with a UV ozone cleaning machine (manufactured by Sen Engineering Co., Ltd.), it was attached to a vacuum evaporation machine and evacuated. Under the conditions of a degree of vacuum of 3 × 10 ⁻⁴ Pa and a substrate temperature of room temperature, copper phthalocyanine was deposited as a hole transport layer to a thickness of 20 nm, and bis (m-methylphenylcarbazole) was deposited to a thickness of 100 nm. Once the substrate is removed, place the substrate on a hot plate under a nitrogen atmosphere,
The hole transport layer was heat-treated at 100 ° C. for 8 minutes. The substrate was returned to the vacuum evaporator again, and a tris (8-quinolinolato) aluminum (III) complex, which was both a light emitting layer and an electron transporting layer, was added under the conditions of a vacuum degree of 3 × 10 ⁻⁴ Pa and a substrate temperature of room temperature.
00 nm was deposited. After exchanging the deposition mask in a vacuum and exposing the organic layer to lithium vapor for doping (equivalent to a thickness of 0.5 nm), aluminum was deposited to a thickness of 200 nm to form a cathode. Thus, an organic electroluminescent device having a size of 5 × 5 mm was manufactured.

The device was driven to emit light in dry air at a constant current of 20 mA / cm ² (initial luminance: 528).
cd / m ² ), the luminance retention after 200 hours was 51%, and the area occupied by non-light-emitting portions (dark spots) was 1% or less.

COMPARATIVE EXAMPLE 1 An organic electroluminescent device was prepared and illuminated in the same manner as in Example 1 except that no heat treatment was performed (initial luminance: 530 cd / m ² ). 33
%, The area occupied by the non-light-emitting portion (dark spot) is about 15%
%was.

Example 2 Bis (4-methylnaphthylcarbazole) was prepared as a hole transport material. According to the measurement by the DSC method, the glass transition temperature was 158 ° C., and the crystallization temperature and the melting point were 280 ° C. or higher. An organic electroluminescent device was prepared and illuminated in the same manner as in Example 1 except that the hole transport layer was heated at 178 ° C. for 8 minutes (initial luminance: 612 cd / m ² ). The area occupied by 69% of the non-light-emitting portions (dark spots) was 1% or less.

COMPARATIVE EXAMPLE 2 An organic electroluminescent device was prepared and emitted (initial luminance of about 500 cd / m ² ) in the same manner as in Example 2 except that no heat treatment was performed. The retention dropped to 50%.

Example 3 Bis (phenylcarbazole) was prepared as a hole transport material. According to the measurement by the DSC method, the glass transition temperature was 93
° C, melting point was 205 ° C, and no crystallization temperature was detected. An organic electroluminescent device was prepared and illuminated in the same manner as in Example 1 except that the hole transport layer was heated at 113 ° C. for 8 minutes (initial luminance: 692 cd / m ² ). The area occupied by 64% and the non-light-emitting portion (dark spot) was 1% or less.

COMPARATIVE EXAMPLE 3 An organic electroluminescent device was prepared and illuminated in the same manner as in Example 3 except that no heat treatment was performed (initial luminance: 609 cd / m ² ). 40
%, Non-light-emitting area (dark spot) occupies approximately 5%
was.

Example 4 Bis (ethylcarbazole) was prepared as a hole transporting material. According to measurement by the DSC method, a glass transition temperature of 77
° C, crystallization temperature 160 ° C, melting point 191 ° C. An organic electroluminescent device was prepared and illuminated in the same manner as in Example 1 except that the hole transport layer was heat-treated at 97 ° C. for 8 minutes (initial luminance: 627 cd / m ² ). The area occupied by 54% and the non-light-emitting portion (dark spot) was 1% or less.

Comparative Example 4 An organic electroluminescent device was prepared and illuminated in the same manner as in Example 4 except that no heat treatment was performed (initial luminance: 579 cd / m ² ). 50
%, The area occupied by the non-light-emitting part (dark spot) is about 10
%was.

Example 5 An organic electroluminescent device was manufactured in the same manner as in Example 4,
/ Cm ² after aging treatment for emitting light for 2 hours at a constant current drive, the measurement was started (initial luminance 41
1 cd / m ² ), the luminance retention after 200 hours is 82%,
The area occupied by non-light-emitting portions (dark spots) was 1% or less.

Example 6 After the heat treatment of the hole transporting layer, the same hole transporting material, bis (ethylcarbazole), was deposited in vacuum in a thickness of 30 nm, and then the light emitting layer and subsequent layers were continuously formed. Example 4
When an organic electroluminescent device was prepared and emitted light in the same manner as in ( ¹ ), the initial luminance was 770 cd / m ² , the luminance retention after 200 hours was 62%, and the area occupied by the non-light-emitting portion (dark spot) was 1% or less. Was.

Example 7 An organic electroluminescent device was manufactured in the same manner as in Example 6,
/ Cm ² after aging treatment for emitting light for 2 hours at a constant current drive, the measurement was started (initial luminance 55%).
8 cd / m ² ), the luminance retention after 200 hours is 86%,
The area occupied by non-light-emitting portions (dark spots) was 1% or less.

Example 8 An organic electroluminescent device was prepared in the same manner as in Example 7, except that the device was heat-treated in a vacuum and the vacuum was not released during the process. 569
cd / m ² ), the luminance retention after 200 hours was 88%, and the area occupied by non-light-emitting portions (dark spots) was 1% or less. However, it took 12 hours or more to wait for the substrate temperature to return to normal film forming conditions (30 ° C. or lower) after the heat treatment.

Example 9 Bis (methylcarbazole) was prepared as a hole transport material. According to the measurement by the DSC method, the glass transition temperature was 78.
° C, crystallization temperature 143 ° C, melting point 204 ° C. An organic electroluminescent device was produced in the same manner as in Example 6, except that the hole transport layer was heat-treated at 98 ° C., 128 ° C., and 158 ° C. for 8 minutes, respectively. That is, after the heat treatment of the hole transporting layer, the same hole transporting material, bis (methylcarbazole), was vapor-deposited in a thickness of 30 nm in vacuum, and then the light emitting layer and subsequent layers were continuously formed. These elements were dried at 20 mA / cm in dry air.
The result of the light emission by the constant current drive ² shown in Table 1.

Comparative Example 5 Table 1 shows the results as in Example 9 except that no heat treatment was performed.

[0057]

[Table 1]

As the heat treatment temperature was increased, the effects of lowering the driving voltage, improving the luminance retention ratio, and suppressing the dark spot were recognized. In particular, at a processing temperature higher than the glass transition temperature of the hole transport layer by 50 ° C. or more (128 ° C. or more), the above effect is very large although the initial luminance (luminous efficiency) tends to slightly decrease. .

Example 10 The same results as in Example 9 were carried out except that after the organic electroluminescent device was produced, an aging treatment for emitting light at a constant current of 40 mA / cm ² for 2 hours was performed and then the measurement was started. It is shown in Table 2.

Comparative Example 6 Table 2 shows the results obtained in the same manner as in Example 10 except that the heat treatment was not performed.

[0061]

[Table 2]

As the heat treatment temperature increased, the effects of lowering the driving voltage, improving the luminance retention ratio, and suppressing dark spots were observed. In particular, it can be seen that the above effect is very large at a processing temperature higher than the glass transition temperature of the hole transporting layer by 50 ° C. or more (128 ° C. or more), and that the initial luminance (luminous efficiency) can be expected to be improved in some cases. .

[0063]

According to the organic electroluminescent device of the present invention, wherein the whole or a part of the hole transport layer is a heat-treated organic layer, the decrease rate of the luminous luminance with time and the non-luminous Since the occurrence rate of a portion (dark spot) can be suppressed to a low level, and improvement in luminous efficiency and lower driving voltage can be expected, it is useful for maintaining stable luminescent characteristics for a long period of time and realizing excellent durability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the organic electroluminescent device of the present invention.

FIG. 2 is a sectional view showing another example of the organic electroluminescent device of the present invention.

Claims (15)

[Claims] 1. An organic electroluminescent device having a light emitting layer and a hole transport layer between a first electrode provided on a substrate and a second electrode opposed thereto, wherein the hole transport layer is mainly An organic electroluminescent device comprising an organic compound, wherein at least a part of the hole transport layer has been subjected to a heat treatment. 2. The method according to claim 1, wherein the first electrode is a transparent anode, a hole transport layer exists on a side near the anode, and the second electrode is a cathode, and a light emitting layer exists on a side near the cathode. The organic electroluminescent device according to claim 1, wherein: 3. The organic electroluminescent device according to claim 2, wherein the first electrode is a transparent anode subjected to UV ozone treatment. 4. The organic electroluminescent device according to claim 1, wherein the hole transport layer is mainly composed of an organic compound containing a carbazole ring. 5. The method according to claim 1, wherein the hole transport layer is mainly composed of an organic compound having a biscarbazolyl skeleton.
4. The organic electroluminescent device according to any one of items 1 to 3, 6. A method according to claim 1, wherein a portion of said hole transport layer which is in contact with said anode comprises a phthalocyanine derivative.
5. The organic electroluminescent device according to any one of 5. 7. A method for producing an organic electroluminescent device in which a light emitting layer and a hole transport layer are present between a first electrode provided on a substrate and a second electrode facing the first electrode, wherein an organic compound is mainly used. A method for producing an organic electroluminescent device, wherein the hole transport layer is subjected to heat treatment after forming the hole transport layer. 8. A step of forming a hole transport layer on a transparent anode as a first electrode, a step of forming a light emitting layer on the hole transport layer, and a step of forming a second electrode on the light emitting layer. 8. A method for manufacturing an organic electroluminescent device according to claim 7, further comprising the step of: forming a cathode as a film, and heating the hole transport layer after the step of forming the hole transport layer. . 9. The organic electroluminescent device according to claim 8, wherein the hole transport layer is subjected to a heat treatment after the step of forming the hole transport layer and before the step of forming the light emitting layer. Method. 10. A heat treatment of the hole transport layer after the step of forming the hole transport layer and before the step of forming the light emitting layer, and further comprising the same or different hole transport material as the hole transport layer. 9. The method according to claim 8, wherein one or more other hole transport layers are formed on the hole transport layer by using. 11. The method for manufacturing an organic electroluminescent device according to claim 7, wherein the method for forming the hole transport layer is a vacuum evaporation method. 12. A method for forming a hole transport layer, which is a vacuum deposition method, wherein the vacuum is released after the step of forming the hole transport layer, and then the hole transport layer is heat-treated. Claim 7-
10. The method for manufacturing an organic electroluminescent device according to any one of 10). 13. The method according to claim 7, wherein the heat treatment is performed in a vacuum. 14. The organic electroluminescent device according to claim 7, wherein the heat treatment temperature is not lower than the substrate temperature at the time of forming the hole transport layer and not higher than the melting point of the hole transport layer. Production method. 15. The organic electroluminescent device according to claim 7, wherein the heat treatment temperature is higher than the glass transition temperature of the hole transport layer and lower than the crystallization temperature of the hole transport layer. Production method.