JP5011401B2 - Organic light emitting layer material, organic light emitting layer forming coating liquid using organic light emitting layer material, organic light emitting element using organic light emitting layer forming coating liquid, and light source device using organic light emitting element - Google Patents

Description

  The present invention relates to an organic light emitting layer material, an organic light emitting layer forming coating solution using the organic light emitting layer material, an organic light emitting device using the organic light emitting layer forming coating solution, and a light source device using the organic light emitting device.

  In recent years, organic light emitting devices have attracted attention as next-generation planar light sources. This organic light-emitting device has excellent characteristics such as self-light emission, wide viewing angle, high-speed response characteristics, and high color rendering properties. For example, the organic light emitting device is configured by forming a transparent electrode such as ITO, an organic layer composed of a hole transport layer, a light emitting layer, an electron transport layer, and the like, and a low work function reflective electrode on a glass substrate. . The emitted light passes through the electrode and is taken out from the back side of the substrate.

  As a method for manufacturing the organic light emitting element, a vacuum deposition method, an ink jet method, a printing method, or the like is used. In the vacuum evaporation method, an organic material is heated and evaporated in a vacuum to form a film on a substrate. Since the film thickness, concentration, and the like can be controlled by the deposition rate and a laminated structure can be easily formed, an organic light-emitting element having a desired structure can be easily produced. However, there are problems such as low material utilization efficiency and difficulty in increasing the substrate size. Wet methods such as the inkjet method and the printing method have a difficulty in forming the laminated structure because it is essential to control the solubility of the lower material when forming the laminated structure, but the material utilization efficiency is high. Since it is easy to increase the area, it is expected as a low-cost manufacturing method.

  In order to use an organic light emitting device as a light source, white light emission is required. In order to realize high color rendering white light emission, an organic white light emitting element that emits light of three colors of red, blue, and green is required.

  As a method for producing an organic white light emitting device by a wet method, a method of mixing red, blue and green light emitting dopants in a light emitting layer is disclosed. For example, in Patent Document 1, white luminescence is realized by using polyvinyl carbazole as a host material of a light emitting layer and dispersing red, blue, and green dopants at low concentrations (0.01 to 5 mol%). .

JP-A-9-63770

  In the organic light emitting device manufactured by the conventional coating method, the green dopant concentration is 0.02 mol%, the red dopant concentration is very low, 0.02 mol% and 0.015 mol%, and it is difficult to control the dopant concentration. was there.

  An object of the present invention is to use an organic light emitting layer material that can easily emit white light, an organic light emitting layer forming coating solution using the organic light emitting layer material, an organic light emitting device using the organic light emitting layer forming coating solution, and an organic light emitting device. A light source device that has been provided.

  In order to solve the above-mentioned problems, the present invention is characterized by an organic light emitting device having a first electrode, a second electrode, and a light emitting layer disposed between the first electrode and the second electrode. The light emitting layer includes a host material, a red dopant, and a green dopant, and the red dopant has a concentration gradient in the light emitting layer.

  In addition, a feature of the present invention is a light emitting layer forming coating liquid used for the organic light emitting device, wherein the light emitting layer forming coating liquid includes a solvent, a host material, a red dopant, and a green dopant. It is a liquid.

  In addition, a feature of the present invention is a light emitting layer forming material used for the organic light emitting element, wherein the light emitting layer forming material is a light emitting layer forming material including a host material, a red dopant, a blue dopant, and a green dopant. is there.

  Moreover, the characteristics of this invention are light source devices provided with the said organic light emitting element.

  INDUSTRIAL APPLICABILITY According to the present invention, an organic light emitting layer material that can easily emit white light, an organic light emitting layer forming coating liquid using the organic light emitting layer material, an organic light emitting element using the organic light emitting layer forming coating liquid, and a light source using the organic light emitting element Equipment can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is sectional drawing of one Embodiment of the white light emitting element of this invention. 2 is an energy diagram of the white light emitting device of Example 1. FIG.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

Conventional methods have problems such as low luminous efficiency and difficulty in controlling the amount of dopant. The cause is energy transfer between dopants. The excitation energy of the luminescent dopant decreases in the order of blue dopant, green dopant, and red dopant. Therefore, energy transfer is likely to occur from the blue dopant to the green dopant and from the green dopant to the red dopant. When a structure having three color light emitting dopants in one light emitting layer is used, the three color light emitting dopants are close to each other. Therefore, energy transfer is likely to occur. In a state where energy transfer occurs, it is easy to move to the red dopant having the lowest excitation energy, so blue light emission becomes small, and highly efficient white light emission cannot be obtained.
Therefore, in order to cause sufficient blue light emission, it is necessary to significantly reduce the amount of green dopant and the amount of red dopant.

  Therefore, a light emitting layer according to an embodiment of the present invention includes a host material and a dopant having a substituent for localizing during film formation. The dopant is localized near the surface of the light emitting layer or the interface with the lower layer during film formation. Here, being localized in the vicinity of the electrode means that the concentration in the layer is high in the vicinity of the determined electrode. Therefore, a light emitting layer formed by a wet method has a function substantially equivalent to that of a light emitting layer in which three layers are stacked. By adopting such a structure, the distance between the light-emitting dopants having different emission colors becomes longer except near the interface. That is, energy transfer between dopants is less likely to occur. Therefore, it becomes easy to control the amount of dopant. Therefore, a white light emitting element can be easily formed.

  The present invention will be described in more detail with reference to specific examples. The following examples show specific examples of the contents of the present invention, and the present invention is not limited to these examples, but by those skilled in the art within the scope of the technical idea disclosed in this specification. Various changes and modifications are possible.

  FIG. 1 is a cross-sectional view of the white light emitting device of this example. This organic white light emitting element has an upper electrode 12 as a first electrode, a lower electrode 11 as a second electrode, and an organic layer 13. The lower electrode 11 may be used as the first electrode, and the upper electrode 12 may be used as the second electrode. 1 has a structure in which a lower electrode 11, an organic layer 13, and an upper electrode 12 are arranged in this order, and is a bottom emission type in which light emission of the light emitting layer 3 is extracted from the lower electrode 11 side. Here, the lower electrode 11 is a transparent electrode serving as an anode, and the upper electrode 12 is a reflecting electrode serving as a cathode. The organic layer 13 has a hole injection layer 1, a hole transport layer 2, a light emitting layer 3, an electron transport layer 8 and an electron injection layer 9. The laminated structure of the organic layer 13 is not necessarily as described above, and may be a single layer structure including only the light emitting layer 3. The organic layer 13 may have a laminated structure without the hole transport layer 2, and the electron transport layer 8 may have a laminated structure of an electron transport layer and a blocking layer. A light source device is obtained by providing the organic light emitting element in FIG.

  The light emitting layer 3 has host molecules and dopant molecules. The dopant molecule has a red dopant 5, a green dopant 6 and a blue dopant 7. The material for forming the light emitting layer 3 includes host molecules, a red dopant 5, a green dopant 6, and a blue dopant 7. However, as long as it becomes white light, the material for forming the light emitting layer 3 may include host molecules, red dopants 5 and blue dopants 7. In the light emitting layer 3, the red dopant 5 and the blue dopant 7 are biased in each region, forming a pseudo laminated structure. First, the configuration of the light emitting layer 3 will be described.

  As the red dopant 5, an iridium compound represented by the following formula was used.

  In addition to the above, an iridium complex represented by the following general formula is preferable.

  In the formula, X1 represents an aromatic heterocycle containing N, and X2 represents an aromatic hydrocarbon ring or an aromatic heterocycle. Examples of the aromatic heterocycle represented by X1 include quinoline ring, isoquinoline ring, pyridine ring, quinoxaline ring, thiazole ring, pyrimidine ring, benzothiazole ring, oxazole ring, benzoxazole ring, indole ring and isoindole ring. . Examples of the aromatic hydrocarbon ring or aromatic heterocycle represented by X2 include a benzene ring, naphthalene ring, anthracene ring, thiophene ring, benzothiophene ring, furan ring, benzofuran ring, and fluorene ring. Examples of Y1 and Y2 include a fluoroalkyl group, a perfluoroalkyl group, an alkyl group (the number of C is 10 or more), a perfluoropolyether group, and a siloxy group (—Si—O—Si—). The material of the red dopant 5 may have at least one of these functional groups, but may have a plurality of types. Since the functional groups of Y1 and Y2 have a function of reducing the surface energy, the red dopant 5 is localized on the surface of the light emitting layer on the side where the upper electrode exists by using this dopant. These functional groups may be directly introduced into the main skeleton as in (Chemical Formula 2), but may be introduced via an amide bond or an ester bond. As described above, the red dopant 5 has a concentration gradient in the light emitting layer 3.

Other than that, so-called phosphorescent dopants such as osmium complexes, europium complexes and platinum complexes having similar functional groups, and (E) -2- (2- (4- (dimethylamino) styryl) -6-methyl-4H-pyran- It may be a derivative of a compound such as 4-ylidene) malononitrile (DCM).

  The host material 4 of the light emitting layer 3 is, for example, mCP (1,3-bis (carbazol-9-yl) benzene. Other carbazole derivatives, fluorene derivatives, arylsilane derivatives, and the like can also be used as the host material. In order to obtain efficient light emission, it is preferable that the excitation energy of the host material 4 is sufficiently larger than the excitation energy of the blue dopant, which is measured using an emission spectrum.

  The host material 4 may be a mixture of several kinds of host materials. Even if a part of the host material 4 is substituted with a fluoroalkyl group, a perfluoroalkyl group, an alkyl group (the number of C is 10 or more), a perfluoropolyether group, or a siloxy group (—Si—O—Si—) Good. By mixing such a host material, a part of the host material 4 is easily localized on the surface of the light emitting layer 3 and coexists with the red dopant 5 on the light emitting surface. Thereby, aggregation of the red dopant 5 on the surface is less likely to occur, and more efficient light emission is possible.

  As a material for the green dopant 6, an iridium complex represented by the following formula was used.

  In addition, an iridium complex having two different ligands as represented by the following formula may be used instead of a coumarin compound or an iridium complex composed of almost the same type of ligand as described above.

  Although it is not necessary to use a special functional group for the green dopant 6, a dopant material with low objectivity is preferable from the viewpoint of imparting solubility. Moreover, you may have a substituent with a poor compatibility with the positive hole transport layer used as a base layer, a positive hole injection layer, or a lower electrode.

  As the blue dopant 7 material, an iridium complex having a substituent for attracting the base layer represented by the following formula was used.

The functional group for attracting the underlying layer during film formation varies depending on the type of the underlying layer. When the underlayer is a hole transport layer, examples thereof include an arylamino group, a carbazole group, and a hydrazone site that introduce a structure similar to that of the hole transport layer. When the underlayer is an electrode such as ITO or metal, for example, a hydroxy group (—OH), a thiol group (—SH), a carboxyl group (—COOH), a sulfo group (—SO ₃ H), I, Br , Cl, F, SCN, CN , NH 2, NO 2, bipyridyl group. The blue dopant 7 may have at least one of these functional groups, but may have a plurality of types. Further, when an oxide having a high specific gravity is mixed in the light emitting layer, a hydroxy group can be used. Moreover, when a base layer has a long-chain alkyl group, it is better to have a long-chain alkyl group. These groups may be directly introduced into the main skeleton as shown in (Chemical Formula 5), but may be introduced via an alkyl chain in consideration of the size of the molecule. Further, as the blue dopant 7, a perylene derivative or the like may be used.

  Other requirements will be described below. However, as the layer constituting the organic layer 13, the hole injection layer 1, the hole transport layer 2, the electron transport layer 8, and the electron injection layer 9 may be omitted as described above.

  As the hole injection layer 1, PEDOT (poly (3,4-ethylenedioxythiophene)): PSS (polystyrene sulfonate) was used. In addition, a polyaniline-based, polypyrrole-based or triphenylamine-based polymer material, or a material containing metal fine particles may be used. Moreover, a phthalocyanine compound often used in combination with a low molecular material system can also be applied.

  As the hole transport layer 2, an arylamine polymer was used. In addition, various polymers such as polyfluorene, polyparaphenylene, polyarylene, and polycarbazole can be used. Further, starburst amine compounds, stilbene derivatives, hydrazone derivatives, thiophene derivatives, and the like can be used. Alternatively, a polymer containing the above material may be used. Further, the present invention is not limited to these materials, and two or more of these materials may be used in combination.

  The electron transport layer 8 is a layer that supplies electrons to the light emitting layer 3. In this embodiment, the electron transport layer 8 is a laminate of bis (2-methyl-8-quinolinolato) -4- (phenylphenolato) aluminum (hereinafter referred to as BAlq) and tris (8-quinolinolato) aluminum (hereinafter referred to as Alq3). Structure was used. As the material for the electron transport layer 8, for example, BAlq, Alq3, oxadiazole derivatives, triazole derivatives, fullerene derivatives, phenanthroline derivatives, quinoline derivatives, triarylborane derivatives, or other single films can be used. Further, the electron transport layer 8 may have a laminated structure of a blocking material having a blocking function of holes and an excited state and an electron transport material. As a blocking material, BAlq, a phenanthroline derivative, a triazole derivative, a triarylborane derivative, or the like can be used. As the electron transport material, Alq3, oxadiazole derivatives, fullerene derivatives, quinoline derivatives, silole derivatives, and the like can be used.

The electron injection layer 9 is used to improve the efficiency of electron injection from the cathode to the electron transport layer 8.
In this example, lithium fluoride was used. In addition, magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride, magnesium oxide, and calcium oxide may be used.
Further, a mixture of an electron transport material and an alkali metal or an alkali metal oxide may be used. Alternatively, a mixture of an electron transport material and an electron donating material may be used. Of course, it is not limited to these materials, and two or more of these materials may be used in combination.

  As the lower electrode 11, ITO was used. As the anode material used for the lower electrode 11, any material having transparency and a high work function can be used, and conductive oxides such as ITO and IZO and metals having a large work function such as thin Ag can be applied. . In general, the electrode pattern can be formed on a substrate such as glass by using photolithography.

  As the upper electrode 12, Al was used. The cathode material used for the upper electrode 12 is a reflective electrode for injecting electrons into the light emitting layer 3 and reflecting the light from the light emitting layer 3, and specifically, Al, Mg: Ag alloy, Ag or the like is preferable. Used for.

The light emitting layer coating solution is obtained by dissolving the host material 4, the red dopant 5, the green dopant 6 and the blue dopant 7 in an appropriate solvent. When the blue dopant is not present, the light emitting layer coating liquid has a solvent, a host material, a red dopant, and a green dopant. In this example, the weight ratio of the host material 4, red dopant 5, green dopant 6 and blue dopant 7 was 100: 1: 5: 1, respectively. In terms of the molar concentration in the solid content, the red dopant is 0.46%, the green dopant is 2.9%, and the blue dopant is 0.5%. Tetrahydrofuran (THF) was used as the solvent. The solvent used here may be any solvent that dissolves each material, for example, an aromatic hydrocarbon solvent such as toluene, an ether solvent such as tetrahydrofuran, an alcohol, and a fluorine solvent. Further, a mixed solvent in which a plurality of the above-mentioned solvents are mixed for adjusting the solubility of each material and the drying speed may be used. For example, two kinds of solvents having different boiling points (first solvent and second solvent) are prepared, and the second solvent having a high boiling point is used as a poor solvent for the red dopant 5, whereby the film surface of the red dopant 5 Can help move to.
The solubility of the solvent is measured by a liquid chromatogram method.

  As a coating method for forming the light emitting layer, a spin coating method was used in this example. In addition, a casting method, a dip coating method, a spray coating method, a screen printing method, an ink jet printing method, and the like can be used.

  The bottom emission type element structure has been described above by way of example. However, if the upper electrode is a cathode and the lower electrode is an anode, a top emission type element structure in which the upper electrode is a transparent electrode may be used.

  When a positive potential was applied to the lower electrode side of the light emitting device of this example and a negative potential was applied to the upper electrode, white light emission of three colors of blue, green and red was obtained. An energy diagram of the element structure of this example is shown in FIG.

  When the red dopant 5 and the blue dopant 7 spontaneously phase-separate, the band diagram shown in FIG. 2 is obtained. In FIG. 2, the energy of the lowest empty orbit (LUMO) of the blue dopant 7 is between the light emitting layer 3 and the lower electrode 11 and is lower than the energy of the lowest empty orbit of the layer adjacent to the light emitting layer 3. Yes. The energy of the lowest unoccupied orbit is measured by a method of calculating and calculating an energy difference of HOMO (highest occupied orbit) -LUMO from an absorption spectrum, or a method of directly measuring by reverse photoelectron spectroscopy. In this case, electrons are injected from the electron transport layer 8 into the light emitting layer 3 and trapped by the blue dopant 7. On the other hand, holes are injected from the hole transport layer 2 into the blue dopant 7 and recombine light emission. Some holes move to the green dopant 6 and the red dopant 5, and recombine with electrons injected from the electron transport layer 8 to emit light. Thus, since an energy barrier for electrons exists between the hole transport layer 2 and the blue dopant 7, blue light emission occurs efficiently.

[Comparative Example 1]
A light emitting device was produced in the same manner as in Example 1 except that the following (Chemical Formula 6) was used as the red dopant 5 and the following (Chemical Formula 7) was used as the blue dopant 7. Only obtained. This is thought to be because energy transfer from the blue dopant 7 and the green dopant 6 to the red dopant 5 occurred because the green dopant 6 and the red dopant 5 were close to the blue dopant 7.

  The material constituting the light emitting layer is that the blue dopant 7 is (Chemical Formula 7), and the weight ratio of the host material 4, the red dopant 5, the green dopant 6 and the blue dopant 7 is 100: 1: 0.5: 10, respectively. A light emitting device was produced in the same manner as in Example 1 except that. In terms of the molar concentration in the solid content, the red dopant 5 is 0.45%, the green dopant 6 is 0.28%, and the blue dopant 7 is 5.5%. As a result, white light emission composed of red, green and blue light emission was obtained.

[Comparative Example 2]
When a light emitting device was produced in the same manner as in Example 2 except that (Chemical Formula 6) was used for the red dopant 5, blue and green light emission was weak, and only red strong light emission was obtained.

  A light-emitting element was fabricated in the same manner as in Example 1 except that the material constituting the light-emitting layer contained a material represented by the following formula (Formula 8) in addition to mCP as the host material 4.

  As a result, light emission with higher efficiency was obtained as compared with Example 1.

  A light-emitting element was fabricated in the same manner as in Example 2 except that the material constituting the light-emitting layer included the material represented by the following formula (Formula 8) in addition to mCP as the host material 4.

  As a result, light emission with higher efficiency than that of Example 2 was obtained.

  A light emitting device was produced in the same manner as in Example 1 except that the material constituting the light emitting layer was the following material (Chemical Formula 9) as the red dopant 5. From the light emitting element, white light emission of three colors of blue, green and red was obtained.

  The light-emitting element is the same as in Example 1 except that the material constituting the light-emitting layer is a material represented by the following formula (Formula 10) as the blue dopant 7 and that the light-emitting layer contains titania fine particles having a diameter of about 2 nm. Was made.

  From this element, white light emission consisting of three colors of red, green and blue was obtained.

DESCRIPTION OF SYMBOLS 1 Hole injection layer 2 Hole transport layer 3 Light emitting layer 4 Host material 5 Red dopant 6 Green dopant 7 Blue dopant 8 Electron transport layer 9 Electron injection layer 10 Substrate 11 Lower electrode 12 Upper electrode

Claims (14)

A first electrode;
A second electrode;
An organic light emitting device having a light emitting layer disposed between the first electrode and the second electrode,
The light emitting layer includes a host material, a red dopant, and a green dopant,
The organic light-emitting device, wherein the red dopant has a first substituent for localizing in the vicinity of the first electrode . The organic light emitting device according to claim 1,
The first substituent is an organic containing one or more functional groups among a fluoroalkyl group, a perfluoroalkyl group, an alkyl group (the number of C is 10 or more), a perfluoropolyether group, and a siloxy group. Light emitting element. The organic light emitting device according to claim 1 or 2 ,
The organic light-emitting device, wherein the red dopant is an iridium complex represented by the following ( Chemical Formula 2 ).
In the formula, X1 represents an aromatic heterocycle containing N, and X2 represents an aromatic hydrocarbon ring or an aromatic heterocycle. Y1 and Y2 each represents a fluoroalkyl group, a perfluoroalkyl group, an alkyl group (the number of C is 10 or more), a perfluoropolyether group, or a siloxy group. In the organic light emitting element according to any one of claims 1 to 3 ,
The light emitting layer includes a blue dopant;
The organic light emitting element and the blue dopant is characterized by having a second substituent for drawn to the second electrode. In the organic light emitting element according to any one of claims 1 to 4 ,
The second substituent is an arylamino group, carbazole group, an organic light emitting device characterized by comprising one or more functional groups of the hydrazone site. In the organic light emitting element according to any one of claims 1 to 4 ,
A hole transport layer is disposed between the second electrode and the light emitting layer;
The second substituent and comprising hydroxy group, carboxyl group, a sulfo group, I, Br, Cl, F , SCN, CN, NH 2, NO 2, one or more functional groups of the bipyridyl groups Organic light emitting device. The organic light emitting device according to any one of claims 1 to 6 ,
The organic light-emitting element, wherein the host material has the first substituent. A coating solution for forming a light emitting layer used in the organic light emitting device according to any one of claims 1 to 3 ,
The light emitting layer forming coating solution is a light emitting layer forming coating solution containing a solvent, a host material, a red dopant, and a green dopant. A coating solution for forming a light emitting layer used in the organic light emitting device according to any one of claims 4 to 7 ,
The light emitting layer forming coating liquid, a solvent, a host material, a red dopant, emission-layer-forming coating liquid which comprises a green dopant and a blue dopant. In the organic light emitting element according to any one of claims 1 to 7 ,
An organic light emitting device comprising metal oxide fine particles. An organic light emitting device according to any one of claims 4 to 7 ,
The energy of the lowest unoccupied molecular orbital of the blue dopant is between the second electrode and the light emitting layer, an organic light emitting device characterized by lower than the energy of the lowest unoccupied molecular orbital of the layer adjacent to the light emitting layer. A light emitting layer forming material used for the organic light emitting device according to any one of claims 1 to 3 ,
Emitting layer formation material, a host material, the light emitting layer formation material which comprises a red dopant and a green dopant. A light-emitting layer forming material used in the organic light-emitting device according to any one of claims 4 to 7 ,
Emitting layer formation material, a host material, a red dopant, the light emitting layer formation material which comprises a blue dopant and a green dopant. A light source device characterized in that it comprises an organic light-emitting device according to any one of claims 1 to 7.