JP2921382B2 - Organic hole transport membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic hole transport film having excellent hole transport properties and durability.

[0002]

2. Description of the Related Art As an organic electroluminescence device using various functional organic materials, instead of the conventional single-layer structure device, an organic material having excellent hole transportability is used. A layered structure in which respective layers such as a hole transport layer, an electron transport layer made of an organic material having an excellent electron transport property, and a light emitting layer made of an organic light emitting material are appropriately combined is becoming mainstream.

In the organic EL device having the above-mentioned laminated structure, aromatic tertiary amines such as triphenylamine, phthalocyanines, and polysilanes are known as a hole transporting material constituting the hole transporting layer. In particular, the following equation (1):

[0004]

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N, N'-diphenyl-N,
Aromatic tertiary amines represented by N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (hereinafter referred to as "TPD") have high hole transport ability. It is preferably used. For example, the hole mobility of TPD is 10 ⁻³ [cm] at an electric field strength of 5 × 10 ⁵ [V / cm].
² / V · sec].

The hole transport layer is formed by forming these hole transport materials alone or dispersing them in a binder film made of a suitable thermoplastic resin such as polycarbonate. As described above, the organic electroluminescence device including the hole transport layer made of the hole transport material having a high hole transport ability has excellent initial light emission luminance and light emission efficiency. However, the organic electroluminescent element has a problem that the luminous efficiency deteriorates and the luminous brightness decreases in a very short period of time after the start of use, and the improvement of luminous life and stability is a major issue.

One of the causes is that the above-mentioned conventional hole transporting materials are all low molecular, and have a melting point, a glass transition temperature,
It is considered that the crystallization temperature and the like are low (for example, the glass transition temperature Tg of TPD = 63 ° C.) and the thermal properties are not sufficient. In other words, the hole transporting material having low molecular weight and insufficient thermal properties is liable to be deteriorated by itself or to form an exciplex with the light emitting material due to Joule heat generated when an electric current is applied to the device. Therefore, as these phenomena occur, the luminous efficiency of the device deteriorates, and the luminous brightness decreases.

In the organic electroluminescence device, in order to increase the carrier injection efficiency, the interface between each organic layer and the interface between the organic layer and the electrode layer must be finished as smooth as possible. Although the organic layer is amorphous, the low molecular weight hole transporting material has a low crystallization temperature, so the generation of Joule heat or
Alternatively, molecular aggregation is likely to occur due to, for example, being left in the air for a long time. For this reason, due to crystallization of the hole transporting material contained in the hole transporting layer, the interface between the hole transporting layer and another layer loses smoothness, the carrier injection efficiency decreases, and the luminous efficiency of the device deteriorates. As a result, the light emission luminance decreases.

These phenomena occur particularly remarkably in the hole transport layer having a structure in which the hole transport material is formed as a single layer. However, the hole transport layer has a structure in which the hole transport material is dispersed in a binder film made of a thermoplastic resin. The same occurs in the transport layer. The reason for this is that the thermal properties of the thermoplastic resin itself that constitutes the binder film, especially the glass transition temperature is rather low, though not as high as that of the hole transport material. It is possible to exercise freely.

[0010] Poly-N-vinylcarbazole (hereinafter referred to as "P
VK ”) is a polymer and is known to have a hole transporting property.
The level is several steps lower than that of a low-molecular-weight hole transport material. The organic electroluminescence element preferably has a high hole mobility of 10 ⁻⁵ [cm ² / V · sec] or more at an electric field strength of 5 × 10 ⁵ [V / cm] (PVK).
Is 1 at an electric field strength of 5 × 10 ⁵ [V / cm].
0 ^-6 [cm ² / V · sec], glass transition temperature Tg = 224
° C).

Therefore, recently, in order to provide an organic electroluminescence device having excellent luminous efficiency, luminous brightness and stability, various studies have been made mainly on a hole transporting material constituting a hole transporting layer. An organic electroluminescence device using a hole transport material having a structure has been proposed. For example, Japanese Patent Laid-Open No. 5-2
No. 5,473, the use of a specific fluorenyl diphenylamine derivative described in the publication as a hole transport material, low-voltage driving, high emission intensity,
It has been reported that an organic electroluminescent element having excellent durability and the like can be obtained (see, for example, page 4, column 6, lines 44 to 49 of the publication).

In Japanese Patent Application Laid-Open No. H5-152072, specific oxadiazole-based compounds having a plurality of oxadiazole rings (compounds 1 to 14 exemplified on pages 2 to 5 of the same publication) are disclosed. It has been reported that an organic electroluminescent device having excellent durability can be obtained by using the oxadiazole-based compound as a hole transporting material because such a compound is excellent in film-forming properties and hard to be crystallized ( For example, see page 6, column 10, lines 20 to 35 of the publication.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 5-194943, the compound represented by the formula (I) or (II)
It has been reported that a long-life organic electroluminescence device can be obtained by using a specific distyrylbenzene derivative having a high glass transition temperature and a high melting point as a hole transport material (for example, page 3, column 4 of the publication). (See lines 2-6).

Since the hole transport materials disclosed in the above publications have better heat resistance than conventional hole transport materials such as TPD, the organic electroluminescent devices using these hole transport materials are better than the conventional ones. Stability is improved. However, since all of these compounds are compounds having a smaller molecular weight than polymers such as PVK, at present, the stability has not been secured to such an extent that an organic electroluminescence device can be put to practical use. Some of these hole transporting materials also have a problem that their hole transporting ability is lower than that of a conventional hole transporting material such as TPD.

The present invention has been made in view of the above circumstances, and has an organic hole which has both sufficient durability and high hole transportability, and which can contribute to improvement of the durability of an organic electroluminescence element. It is intended to provide a transport membrane.

[0016]

In order to solve the above problems, the present inventors have studied the structure of an organic hole transport film. As a result, when a hole transporting material having a high hole transporting ability is dispersed in an organic binder having a crosslinked structure crosslinked by light or heat, the organic hole transporting having both sufficient durability and high hole transporting ability is obtained. The inventors have found that a film can be obtained, and have completed the present invention.

[0017] That the organic hole-transporting layer of the present invention is an organic hole transport membrane halls transporting material in an organic binder is dispersed with a crosslinked structure, the organic hole-transporting
An organic binder having a cross-linking property and a hole transport material
And a coating solution containing a coating material on a base to form a film,
It is characterized by being a crosslinked and cured organic binder . The organic hole transport film of the present invention having the above-described structure has excellent thermal characteristics as a whole, such as a high glass transition temperature because the organic binder constituting the film has a crosslinked structure.

The hole transporting material is trapped in the crosslinked structure of the organic binder having excellent thermal characteristics as described above, so that crystallization due to molecular aggregation does not occur. Moreover, since the hole transporting material dispersed in the organic binder does not need to consider the thermal characteristics of the hole transporting material itself, as is apparent from the structure of the film, a material having particularly excellent hole transporting ability such as the TPD described above should be used. Can be appropriately selected and used.

Therefore, the organic hole transport film of the present invention is
It will have both sufficient durability and high hole transport ability. Hereinafter, the present invention will be described. As the organic binder having a cross-linked structure, which constitutes the organic hole transport film of the present invention, a cured product of a curable resin which is cured by light or heat, etc., may be mentioned, and is particularly cured by irradiation with light such as ultraviolet light or visible light. A cured product of a photocurable resin is suitably used.

In the case of a thermosetting resin, the hole transport material is deteriorated by heat at the time of curing, or the hole transport material is agglomerated and crystallized in an organic binder before curing, thereby impairing the smoothness of the film surface. There is a risk. On the other hand, in the case of a photo-curable resin, it can be cured without applying heat, and thus the above-mentioned problems can be prevented as much as possible.

The curable resin constituting the organic binder, which is cured by heat or light, is not limited thereto, but includes, for example, silicone resin, phenoxy resin, phenol resin, ketone-formaldehyde resin,
Various conventionally known curable resins such as an epoxy resin, a melamine resin, an alkyd resin, an unsaturated polyester resin, a curable acrylic resin, and a curable polycarbonate resin can be used. An excellent curable acrylic resin or silicone resin is preferably used. These can be used alone or in combination of two or more.

The hole transporting material dispersed in the resin binder having a crosslinked structure, which is a cured product of the above-mentioned curable resin, is not limited thereto. For example, aromatic tertiary amines, phthalocyanine And various kinds of conventionally known hole transporting materials such as polysilanes, those having excellent hole transporting ability as described above can be selectively used. In particular, aromatic tertiary amines represented by TPD represented by the above formula (1) can be mentioned as a hole transport material suitable for the present invention.

In the two-component organic hole transporting film according to the present invention, in addition to the hole transporting ability of the hole transporting material itself, the intermolecular distance of the hole transporting material molecules dispersed in the film is not limited. It is known that it greatly affects the hole transport ability. That is, the smaller the intermolecular distance of the hole transport material molecules, the greater the hole transport ability of the entire film. Therefore, in the present invention, by adjusting the proportion of the hole transporting material in the film, and changing the intermolecular distance of the hole transporting material molecules, it is possible to set the hole transporting ability of the entire film to an arbitrary value. it can.

The proportion of the hole transporting material is not particularly limited in the present invention, but is preferably in the range of 10 to 70% by weight in the film (weight ratio).
When the proportion of the hole transporting material is less than the above range, even if the hole transporting material itself has excellent hole transporting ability, the hole transporting ability of the whole film may be insufficient. Conversely, when the ratio of the hole transport material exceeds the above range, the ratio of the organic binder is relatively reduced, and the thermal characteristics of the entire film is reduced, or the hole transport material is aggregated and crystallized. Or it may become easier.

When the organic hole transporting film of the present invention is used, for example, as a hole transporting layer of an organic electroluminescence device, the above-mentioned electric field strength of 5 × 10
^{Since a} hole transport layer having a high hole mobility of 10 ^-5 [cm ² / V · sec] or more at ⁵ [V / cm] and capable of withstanding Joule heat during light emission of the device is formed, a hole transport material is used. Of the total film is 40 to 40% in the above range.
The content is more preferably 60% by weight, and even more preferably about 50% by weight.

The thickness of the organic hole transporting film of the present invention is not particularly limited, and various thickness ranges can be selected according to the use of the film. To secure the thickness, a thickness of about 10 to 10000 nm is preferable. In particular, when the organic hole transporting film of the present invention is used as a hole transporting layer of an organic electroluminescence device, it is more preferably in the above range, particularly preferably in the range of 10 to 200 nm, and about 40 to 50 nm. Is more preferred.

In order to adjust the film thickness, the concentration of the coating solution and the conditions for coating may be changed. In order to produce the organic hole transport film of the present invention, first, a crosslinkable resin and a hole transport material before curing are mixed in a predetermined ratio, and the mixture is dissolved in a common solvent to prepare a coating solution. . Next, this coating solution is applied on a suitable base by a conventionally known coating method such as a spin coating method or a dip coating method, and the solvent is dried and removed to form a film.

When the curable resin is cured by applying light or heat to the formed coating film, the organic hole transporting film of the present invention in which the hole transporting material is dispersed in an organic binder having a crosslinked structure is obtained. can get. The solvent used for the coating liquid is not particularly limited as long as it can dissolve both the crosslinkable resin and the hole transport material before curing, but in consideration of removal from the coating film after film formation, the solvent has a relatively high boiling point. An organic solvent having a low pH is suitably used. Examples of the solvent include, but are not limited to, dichloromethane,
Dichloroethane, tetrahydrofuran, acetonitrile, acetone, methanol, ethanol, carbon tetrachloride,
Examples include carbon disulfide, benzene, toluene, hexane, octane and the like.

The organic hole transporting film of the present invention is, for example,
It is suitably used as a photoconductive thin film for an electrophotographic photosensitive drum, or as a hole transport layer of an organic electroluminescence element. When the organic hole transport film of the present invention is used as a hole transport layer in an organic electroluminescence device, the configuration other than the hole transport layer is not particularly limited, and even if it has a conventional two-layer structure,
Alternatively, it may have a multilayer structure of three or more layers. In short, various layer configurations can be applied.

Layers other than the hole transporting layer that constitute the device having a multilayer structure include, for example, an electron transporting layer and a light emitting layer. The material constituting these layers is not particularly limited, and various materials conventionally used for each layer can be used. Each of the above layers can be formed by a vapor phase growth method such as a vacuum evaporation method or a solution coating method. In addition, each of the above layers may include other components not directly related to the function of the layer, such as a binder resin, a curing agent, a curing catalyst, an antioxidant, an ultraviolet absorber, and other various additives. The thickness of each layer is not particularly limited, and may be the same as in the related art.

The specific layer constitution of the organic electroluminescence element is not particularly limited, but the organic binder constituting the hole transport layer is made of ITO glass or IT glass.
Excellent adhesion to substrates such as O-film,
Considering that the hole transport layer is formed exclusively by a solution coating method, etc., the hole transport layer and the electron transport layer
In the case of an element having a layered structure, as shown in FIG. 3, ITO (indium-tin-tin) formed on the surface of the glass substrate 1 or the like is used.
On an anode 10 made of a transparent conductive material such as oxide).
It is preferable that two layers of the hole transport layer 2 and the electron transport layer 3 are laminated in this order.

In the above figures, reference numeral 4 denotes a cathode made of a metal deposited film of Mg / Ag or the like, and B denotes a power supply for applying a drive voltage to the device.

[0033]

The present invention will be described below based on examples and comparative examples. Example 1 TPD represented by the above formula (1) as a hole transport material
And an acrylic photocurable resin [OPTKLEB HV2 (trade name, manufactured by Adel Co.), which is a raw material of an organic binder having a cross-linked structure, in a weight ratio of 1:
The mixture was dissolved at a ratio of 1 and the resulting mixture was dissolved in 6 times the amount of dichloroethane to prepare a coating solution for an organic hole transport film.

Next, an ITO having a sheet resistance of 15Ω / □ is used.
(Indium-tin-oxide) coated glass substrate (Asahi Glass Co., Ltd., ITO film thickness 1500-1600 °) I
The coating solution was applied on the TO film by a spin coating method, and then dried to obtain a coating film. The spin coating conditions were a substrate rotation speed of 6000 rpm, and the amount of the coating solution dropped was 4 drops.

Next, 10 minutes from the substrate surface in a nitrogen atmosphere.
From a 650W halogen lamp set at a distance of cm
The coating film on the substrate was irradiated with visible light twice for 2 minutes to crosslink and cure the photocurable resin in the coating film, thereby producing an organic hole transport film. Observation of the obtained organic hole transporting film with a scanning electron microscope revealed that the film thickness was 40 nm from cross-sectional observation. From the surface observation, it was also confirmed that the organic hole transport film had a smooth surface.

Further, the organic hole transport film of Example 1 was
A change in surface state when heated in air under a heating condition of 100 ° C. was observed by an atomic force microscope (AFM). Then, when the change of the RMS factor, which is the root mean square of the surface roughness, was recorded as a parameter of the surface state, as shown in FIG. 1 (a), the change in the RMS factor remained 150 hours after the start of heating. I didn't see it. From this, the organic hole transport film of Example 1 was heated to TP
It was confirmed that D did not aggregate and crystallize and had excellent durability.

Then, on the organic hole transporting film of Example 1, the formula (2):

[0038]

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Tris (8-quinolinolate) represented by
An aluminum (III) complex (hereinafter referred to as “Alq”)
A film was formed by a vacuum evaporation method, an electron transporting layer was laminated, and magnesium and silver were co-deposited thereon at a deposition rate ratio of 10: 1 to form a film having a thickness of 200 nm and Mg / Ag = 10/1 (mol). Ratio) to form a Mg / Ag electrode layer, and as shown in FIG.
On the ITO film (anode) 10 of the TO coated glass substrate 1,
An organic electroluminescence device in which the hole transport layer 2, the electron transport layer 3, and the Mg / Ag electrode layer (cathode) 4 were laminated in this order was obtained. The conditions for the Alq deposition were as follows: ultimate vacuum: 2 ×
10 ^-5 Torr, substrate temperature: room temperature, deposition rate: 2-4Å /
Seconds, the thickness of the electron transport layer was 50 nm. The size of the light emitting region was a square having a length of 0.5 cm and a width of 0.5 cm.

Using the ITO film 10 of the organic electroluminescence device as an anode and the Mg / Ag electrode layer 4 as a cathode, a DC electric field is applied from a power source B between both electrodes at room temperature and in the air to emit light, and the light emission luminance is obtained. Was measured using a luminance meter (LS-100 manufactured by Minolta Co., Ltd.). As a result, a green light emission with a luminance of 7000 cd / m ² was observed from the electron transport layer 3 at a driving voltage of 12 V.

COMPARATIVE EXAMPLE 1 A TPD represented by the above formula (1) and a formula (3) as a linear thermoplastic resin:

[0042]

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And a bisphenol A-type polycarbonate represented by the following formula (1) in a weight ratio of 1: 1, and this mixture was dissolved in dichloroethane to obtain a solid content concentration of 10 g / liter for an organic hole transport membrane. A coating solution was prepared. Next, this coating solution was applied on the same ITO-coated glass substrate by the dip coating method, and then dried to produce an organic hole transport film having a thickness of about 50 nm. The conditions for dip coating were a pulling rate of the substrate of 10 cm / min.

The change of the surface state when the organic hole transporting film of Comparative Example 1 was heated in air at 100 ° C. was measured by using the RMS factor as a parameter of the surface state in the same manner as in Example 1. When recorded and evaluated, as shown in FIG. 1 (b), the RMS factor increased linearly with the lapse of time, and especially at the lapse of 42 hours, the RMS factor increased 9 times the original value. Was observed. From this, the organic hole transport film of Comparative Example 1 was heated to TP
It was confirmed that D was aggregated and crystallized.

Example 2 A TPD represented by the above formula (1) and a thermosetting silicone resin (SH805 manufactured by Toray Silicone Co., Ltd.), which is a raw material of an organic binder having a crosslinked structure, were
It is blended at a weight ratio of 1: 1.
It was dissolved with 6 times the amount of dichloroethane to prepare a coating solution for an organic hole transport film.

Next, this coating solution was applied on the same ITO-coated glass substrate by the spin coating method, and dried to obtain a coating film. The spin coating conditions were as follows: the substrate rotation speed was 6000 rpm, and the amount of the applied solution was 4 drops.
Drops. Next, in a nitrogen atmosphere, the mixture was heated to 250 ° C. and held for 1 hour to cure the silicone-based resin, thereby producing an organic hole transport film.

When the obtained organic hole transporting film was observed with a scanning electron microscope, it was found from a cross-sectional observation that the film thickness was 40 nm. From the surface observation, it was also confirmed that the organic hole transport film had a smooth surface. The change in surface state when the organic hole transporting film of Example 2 was heated in air at 100 ° C. under heating conditions was measured in Example 1.
Similarly to the above, when the RMS factor as a parameter of the surface state was recorded and evaluated, as shown in FIG. 2, the RMS factor 65 hours after the start of heating was within twice the original value. From this, the organic hole transport film of Example 2 was
It was confirmed that the TPD did not agglomerate or crystallize due to heating and was excellent in durability.

Therefore, an electron transport layer (Al) was formed on the organic hole transport film of Example 2 in the same manner as in Example 1.
q layer) and an Mg / Ag electrode layer were formed in this order to obtain an organic electroluminescence device having a layer configuration shown in FIG. The size of the light emitting region was a square having a length of 0.5 cm and a width of 0.5 cm. ITO of the above-mentioned organic electroluminescence element
Using the film 10 as an anode and the Mg / Ag electrode layer 4 as a cathode, a DC electric field is applied from a power source B between the two electrodes at room temperature and in the air to emit light. −
100), a driving voltage of 12 V
Green light emission with a luminance of 5000 cd / m ² from the electron transport layer 3 was observed.

[0049]

As described in detail above, the organic hole transporting film of the present invention has a structure in which a hole transporting material is dispersed in an organic binder having a cross-linked structure, and thus has sufficient durability and high hole transporting properties. It has both noh and ability. Therefore, according to the present invention, for example, there is a possibility that the durability of the organic electroluminescence element can be improved.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are the sum of squares of the surface roughness as parameters of the surface state when the organic hole transport films of Example 1 and Comparative Example 1 are heated in air, respectively. RM that is
It is a graph which shows a time-dependent change of S factor.

FIG. 2 is a graph showing a change with time of an RMS factor, which is a root-mean-square of surface roughness, as a parameter of a surface state when the organic hole transport film of Example 2 is heated in air.

FIG. 3 is a cross-sectional view showing an example of a layer configuration of an organic electroluminescence device using the organic hole transport film of the present invention as a hole transport layer.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinobu Ueba 1-3-1 Shimaya, Konohana-ku, Osaka-shi In the Osaka Works of Sumitomo Electric Industries, Ltd. (56) References JP-A-7-85973 (JP, A) JP-A-7-192874 (JP, A) JP-A-5-134430 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 33/22

Claims (1)

(57) [Claims] 1. A halls transporting material in an organic binder having a crosslinked structure is an organic hole-transporting layer which is dispersed, the organic hole transport layer is an organic binder having a crosslinkable
And a coating solution containing a hole transport material
Cloth, film formation, cross-linking and curing of the organic binder
The organic hole transport layer, characterized in that the at it.