JP2012142591A - Organic light-emitting layer material, coating liquid for forming organic light-emitting layer using organic light-emitting layer material, organic light-emitting element using coating liquid for forming organic light-emitting layer and light source device using organic light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic light-emitting element which emits white light while controlling the amount of dopant easily.SOLUTION: The organic light-emitting element comprises: a first electrode (12); a second electrode (11); and a luminous layer (3) disposed between the first and second electrodes. The luminous layer contains a host material (4), a red dopant material (5), a green dopant material (6), and a blue dopant material (7). The red dopant has a first functional group for moving to the first electrode side, and the green dopant has a second functional group for being attracted to the second electrode.

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.

  The manufacturing method of the organic LED is roughly divided into a vacuum deposition method and a coating method. Among them, the coating method has advantages such as easy formation of a large area and high material utilization efficiency. In order to use the coating method, it is necessary to reduce the number of layers of the organic LED, and it is required to make the light emitting layer a single layer.

  As an organic white light emitting device having a single light emitting layer, an organic white light emitting layer composed of a composition containing at least (a) a polymer and (b) an emission center forming compound is inserted between electrodes. An EL device, in which the composition contains an electron transporting material and a hole transporting material in a well-balanced manner, and the polymer has an emission color of blue or a shorter wavelength than that of the polymer. The luminescent center forming compound is present in a state where two or more of the luminescent center forming compounds are molecularly dispersed in the polymer, and each luminescent center forming compound emits light alone, and the colored light as the whole organic EL element is Patent Document 1 reports a single-layer white light-emitting organic EL device using two or more kinds of the luminescent center-forming compounds in combination so as to look white light.

JP-A-9-63770

  In the conventional organic light emitting device, the red dopant, the green dopant, and the blue dopant are not phase-separated, and there is a problem that it is difficult to emit white light while easily controlling the amount of the dopant.

  An object of the present invention is to provide an organic light emitting layer material that can easily control the amount of dopant, 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. It is providing the light source device using an element.

  In order to solve the above-described problems, the present invention is characterized in that an organic light-emitting element 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 blue dopant, and the red dopant is an organic light emitting element having a first functional group for moving to the first electrode side.

  In addition, a feature of the present invention is a light emitting layer forming coating solution used for the organic light emitting element, wherein the light emitting layer forming coating solution includes a solvent, a host material, a red dopant, and a blue 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.

  According to the present invention, an organic light emitting layer material capable of obtaining white light emission while easily controlling the amount of dopant, an organic light emitting layer forming coating solution using the organic light emitting layer material, and an organic layer using the organic light emitting layer forming coating solution A light source device using a light emitting element and an organic light emitting element can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is an energy diagram of each material in a white light emitting element. It is sectional drawing in one Embodiment of the organic light emitting element in this invention.

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

  In an organic light-emitting device manufactured by a conventional coating method, the green dopant concentration is very low, such as 0.02 mol%, and the red dopant concentration is 0.02 mol% and 0.015 mol%, which makes it difficult to control the dopant concentration. In addition, sufficient light emission efficiency cannot be obtained due to energy transfer between the dopants and insufficient carrier confinement in the light emitting region.

  FIG. 2 is a cross-sectional view of an organic white light emitting device according to an embodiment of the present invention. 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, the organic layer 13, and the upper electrode 12 are arranged in this order from the lower side of FIG. 2, and the organic white light emitting element of FIG. 2 is a bottom emission type that takes out light emitted from the light emitting layer 3 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 may have a single layer structure including only the light emitting layer 3 or a multilayer structure including any one or more of the electron injection layer 9, the electron transport layer 8, the hole transport layer 2 and the hole injection layer 1. The organic light emitting device in FIG. 1 is provided with a drive circuit, a housing, and the like, so that a light source device is obtained.

  The light emitting layer 3 includes host molecules and dopant molecules. The dopant molecule includes a red dopant, a green dopant, and a blue dopant. The material for forming the light emitting layer 3 includes a host molecule, a red dopant, a green dopant, and a blue dopant. However, as long as it becomes white light, the material for forming the light emitting layer 3 may include a host molecule, a red dopant, and a blue dopant. In the light emitting layer 3, each dopant material is biased to each region, and forms a pseudo laminated structure. First, the structure of the light emitting layer will be described.

<Phase separation>
When a red dopant, a green dopant, and a blue dopant are mixed in order to emit white light in a single light emitting layer, different color dopants are present in the surroundings. Excitation energy moves to adjacent molecules with a certain probability. For example, when a green dopant or a red dopant is present adjacent to a blue dopant, the excitation energy moves from the blue dopant to the low energy side of the green dopant or the red dopant, making white light emission difficult. Therefore, each dopant is spontaneously phase-separated in the light emitting layer so that low energy dopants are not adjacent to each other, so that even in a coating type white light emitting element, highly efficient white light emission is possible. In this case, white light emission can be obtained even at a high dopant concentration. As a method of spontaneous phase separation, the present invention is realized by adding an appropriate functional group to each light-emitting dopant.

<Host material>
As the host material, it is preferable to use a carbazole derivative, a fluorene derivative, an arylsilane derivative, or the like. In order to obtain efficient light emission, it is preferable that the excitation energy of the host material is sufficiently larger than the excitation energy of the blue dopant. The excitation energy is measured using an emission spectrum.

<Red dopant>
Examples of the main skeleton of the red dopant material 5 include rubrene, (E) -2- (2- (4- (dimethylamino) styryl) -6-methyl-4H-pyran-4-ylidene) malononitrile (DCM) and its derivatives. Iridium complexes (such as Bis (1-phenylisoquinoline) (acetylacetonate) iridium (III)), osmium complexes, and europium complexes. Among them, the iridium complex represented by (Chemical Formula 1) is more preferable in terms of light emission characteristics, and more preferable is one having an acetylacetonate moiety. 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. When the upper electrode is a cathode and the lower electrode is an anode, the red dopant is preferably on the light emitting layer (on the surface side). Here, the red dopant has a first functional group for moving to the upper electrode side. As a result, the red dopant is unevenly distributed and localized on the upper electrode side in the light emitting layer 3. Examples of the first functional group Y1 or Y2 added to the acetylacetonate site for transfer to the film surface during film formation include a fluoroalkyl group, a perfluoroalkyl group, and an alkyl group (however, the number of C is 10 or more) And perfluoropolyether groups and siloxy groups (—Si—O—Si—). The red dopant material 5 may have at least one of these functional groups, but may have a plurality of types. These groups may be directly introduced into the main skeleton as in (Chemical Formula 2) and (Chemical Formula 3), but may be introduced through an amide bond or an ester bond as in (Chemical Formula 4).

<Green dopant>
Examples of the main skeleton of the green dopant material 6 include coumarin and derivatives thereof, and iridium complexes (Tris (2-phenylpyridine) iridium (III): hereinafter Ir (ppy) 3, etc.). When the upper electrode is a cathode and the lower electrode is an anode, the green dopant is preferably in the lower part of the light emitting layer. Here, the green dopant has a second functional group to be attracted to the lower electrode or the hole transport layer. The second functional group for attracting the underlying layer during film formation varies depending on the type of the underlying layer. In the case where the underlayer is a hole transport layer, examples thereof include a phenylamino group, an oxazole group, a carbazole group, and a hydrazone site that introduce a structure similar to that of the hole transport layer. The green dopant material 6 may have at least one of these functional groups, but may have a plurality of types. 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 green dopant material 6 may have at least one of these functional groups, but may have a plurality of types. 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.

<Blue dopant>
Examples of the main skeleton of the blue dopant material 7 include perylene and iridium complexes (Bis (3,5-difluoro-2- (2-pyridyl) phenyl- (2-carboxypyridyl) iridium (III)): FIrpic and the like). A functional group need not be added to the blue dopant, but a structure having a poor affinity with the underlayer may be introduced in order to more positively perform phase separation.

<Containment of carrier>
Consider a case where the red dopant material 5, the green dopant material 6 and the blue dopant material 7 spontaneously phase-separate to form a pseudo laminated structure shown in FIG. The arrangement of each dopant is green / blue / red from the anode side in consideration of carrier conduction from the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) energy of each dopant. HOMO energy is measured by photoelectron spectroscopy. The LUMO energy is measured by a method for calculating and calculating an energy difference of HOMO-LUMO from an absorption spectrum, or a method for directly measuring by reverse photoelectron spectroscopy. When the energy difference between HOMO and LUMO of the host material is large and HOMO and LUMO of each dopant are located between them and have an appropriate dopant concentration, carrier conduction is performed by hopping the level of each dopant. When the absolute value of the LUMO energy of the blue dopant material 7 is sufficiently larger than the absolute value of the LUMO energy of the green dopant material 6, electrons that have propagated on the LUMO of the blue dopant material 7 are hopped into the LUMO of the green dopant material 6. Since the probability is low, it is confined to the blue dopant. Further, when the HOMO energy difference between the blue dopant material 7 and the green dopant material 6 is relatively small, holes that have propagated on the HOMO of the green dopant material 6 can be propagated by hopping of the blue dopant material 7 to the HOMO. As a result, the propagated carriers (electrons and holes) recombine on the blue dopant material 7 and emit blue light as it is, or the excitation energy moves to the green dopant material 6 to emit green light. On the other hand, holes can be confined between the red dopant material 5 and the electron injection layer 9, and red light is obtained by injecting and recombining electrons. And even when excitation energy moves from the blue dopant material 7 or the green dopant material 6, red light emission is obtained.

  Thus, in the present invention, since carriers can be confined in the vicinity of each dopant, the luminous efficiency of each color is increased, and as a result, a highly efficient white light-emitting element can be realized.

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

  The hole injection layer 1 is preferably a conductive polymer such as PEDOT (poly (3,4-ethylenedioxythiophene)): PSS (polystyrene sulfonate). In addition, polypyrrole-based or triphenylamine-based polymer materials can be used. Further, phthalocyanine compounds and starburst amine compounds that are often used in combination with low molecular weight materials are also applicable.

  As the hole transport layer 2, a starburst amine compound, a stilbene derivative, a hydrazone derivative, a thiophene derivative, or the like can 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. Examples of the material for the electron transport layer 8 include bis (2-methyl-8-quinolinolato) -4- (phenylphenolato) aluminum (hereinafter referred to as BAlq) and tris (8-quinolinolato) aluminum (hereinafter referred to as Alq3). , Oxadiazole derivatives, triazole derivatives, fullerene derivatives, phenanthroline derivatives, quinoline derivatives, and the like can be used.

  The electron injection layer 9 is used to improve the electron injection efficiency from the cathode to the electron transport layer. Specifically, lithium fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride, magnesium oxide, and aluminum oxide are desirable. Of course, the material is not limited to these materials, and two or more of these materials may be used in combination.

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

  The cathode material used for the upper electrode 12 is a reflective electrode for reflecting light from the light emitting layer 3, and specifically, a laminate of LiF and Al, an Mg: Ag alloy, or the like is preferably used. Moreover, it is not limited to these materials, For example, Cs compound, Ba compound, Ca compound etc. can be used instead of LiF.

  The coating liquid is obtained by dissolving a host material, a red dopant, a green dopant, and a blue dopant in an appropriate solvent. When the green dopant is not present, the coating liquid has a solvent, a host material, a red dopant, and a blue dopant. The solvent used here may be any solvent that dissolves each material such as an aromatic hydrocarbon solvent such as toluene, an ether solvent such as tetrahydrofuran, alcohols, 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 types 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. Can move. The solubility of the solvent is measured by a liquid chromatogram method.

  Examples of the coating method for forming the light emitting layer include spin coating, casting, dip coating, spray coating, screen printing, and ink jet printing. The light emitting layer is formed using one of these methods.

  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.

  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.

Example 1
<Synthesis of Exemplified Compound 1>
In order to make the white light emitting device of the first embodiment according to the present invention, first, a red dopant material represented by the structural formula (1) which is a main constituent member of the present invention was synthesized.

(Synthesis of (Chemical Formula 6))
(Chemical 6), which is an intermediate necessary for the synthesis of (Chemical 2) and (Chemical 3), was synthesized according to the following procedure.

A 200 ml three-necked flask was mixed with a solution of 0.718 g of phenylisoquinoline in 30 ml of ethoxyethanol and a solution of 0.418 g of iridium chloride in 10 ml of water. Thereafter, the mixture was refluxed at 120 ° C. for 10 hours under a nitrogen atmosphere, and then cooled to room temperature. The solution was evaporated to dryness, and the resulting solid was washed with alcohol to obtain (Chemical Formula 6).

(Synthesis of (Chemical Formula 2))
(Chemical Formula 2) was synthesized according to the following procedure.

  Intermediate A 0.959 g, 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione 0.512 g, sodium carbonate 0.25 g in a 200 ml three-necked flask Then, 30 ml of ethoxyethanol was added, and the mixture was refluxed at 115 ° C. for 10 hours under a nitrogen atmosphere, and then cooled to room temperature. The solution was evaporated to dryness and the resulting solid was washed with water and hexane. Silica gel column chromatography was performed using an ethyl acetate / hexane mixed solvent as a mobile phase to obtain (Chemical Formula 2). The molecular weight of (Chemical Formula 2) was 897 as measured by a mass spectrometer.

  When (Chemical Formula 2) was dissolved in dichloromethane and the fluorescence spectrum was evaluated, it showed red emission with a peak wavelength of 617 nm.

  A mixed film was formed on a quartz substrate by spin coating using (Chemical Formula 2) and mCP as a host molecule. The solvent was THF, the solid content concentration was 1 wt.%, And the exemplified compound 1 was 10 wt.% With respect to mCP. When the contact angle measurement with respect to the water of the obtained coating film was performed, it was 92.1 degrees. The contact angle measurement is performed by the θ / 2 method, the tangent method, or the curve fitting method. The contact angles of the single films of mCP and (Chemical Formula 2) produced simultaneously as reference samples were 80.6 ° and 96.7 °, respectively. Since the amount of change in the contact angle with respect to the mixing ratio is large, it is considered that (Chemical Formula 2) is not uniformly dispersed in the mCP but distributed more on the surface.

(Synthesis of (Chemical Formula 3))
(Chemical Formula 3) was synthesized according to the following procedure.

  In a 200 ml three-necked flask, 0.959 g, 1,1,1,2,2,3,3,7,7,8,8,9,9,9-tetradecafluoro-4,6- Nonanedione (0.706 g), sodium carbonate (0.25 g) and butoxyethanol (30 ml) were added, and the mixture was refluxed at 150 ° C. for 20 hours under a nitrogen atmosphere, and then cooled to room temperature. The solution is evaporated to dryness, and the resulting solid is dissolved in dichloromethane and filtered. The filtrate is separated and washed with dichloromethane / water, and the dichloromethane solution is taken out and evaporated to dryness. After the obtained solid content was washed with hexane, alumina column chromatography was performed using dichloromethane as a mobile phase to obtain (Chemical Formula 3).

<Preparation of organic light emitting device>
As a first example of the present invention, a white light emitting device having the structure shown in FIG. 2 was produced. An ITO electrode was formed on the lower electrode, and PEDOT was formed on the hole injection layer by spin coating. A polymer material was used for the hole transport layer. The organic light emitting layer is mCP (1,3-bis (carbazol-9-yl) benzene) as a host material, and the blue dopant is iridium complex (Bis (3,5-difluoro-2- (2-pyridyl) phenyl- (2 -Carboxyridyl) iridium (III))), and the above synthesized (Chemical Formula 2) was used as a red dopant. The weight ratio of each material was 100: 5: 1. These host material, blue dopant material and red dopant material were dissolved in THF to prepare a coating solution. The solid component concentration of the coating liquid was set to 1 wt. The density | concentration of the red dopant with respect to the solid component in a coating liquid was 0.46 mol%. The concentration of red dopant is measured by a liquid chromatograph. Using this coating liquid, an organic light emitting layer was formed by spin coating. Subsequently, BAlq and Alq3 layers were formed as an electron transport layer by a vacuum deposition method. Next, a laminate of LiF and Al was formed as the upper electrode, and the target organic light emitting device was produced.

  When voltage was applied to the produced organic light emitting device, light emission from both the red dopant and the blue dopant was confirmed from the EL spectrum, and white light emission was confirmed. On the other hand, when an organic light emitting device was produced under the same conditions using a material containing no fluoroalkyl group as a red dopant, it was confirmed that the intensity of blue light emission decreased and the intensity of red light emission increased.

(Example 2)
A second embodiment will be described. As a coating liquid for forming a light emitting layer, mCP as a host material, Bis (3,5-difluoro-2- (2-pyridyl) phenyl- (2-carboxypyridyl) iridium (III)) as a blue dopant, and as a red dopant (Chemical Formula 2), (Chemical Formula 5) or Ir (ppy) 3 dissolved in THF was used as a green dopant. The rest is the same as in the first embodiment.

When a voltage was applied to the organic white light-emitting device produced using (Chemical Formula 5) as the green dopant, light emission from the red dopant, the green dopant, and the blue dopant was confirmed. On the other hand, when Ir (ppy) 3 was used as the green dopant, the emission intensity of the blue dopant and the green dopant with respect to the red dopant was low.

DESCRIPTION OF SYMBOLS 1 Hole injection layer 2 Hole transport layer 3 Light emitting layer 4 Host material 5 Red dopant material 6 Green dopant material 7 Blue dopant material 8 Electron transport layer 9 Electron injection layer 10 Substrate 11 Lower electrode 12 Upper electrode 13 Organic layer

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 blue dopant,
The organic light-emitting device having a first functional group for moving the red dopant toward the first electrode. The organic light emitting device according to claim 1,
The first functional group is one or more functional groups selected from a fluoroalkyl group, a perfluoroalkyl group, an alkyl group (the number of C is 10 or more), a perfluoropolyether group, and a siloxy group. An organic light emitting device. 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 1).
(Wherein X1 represents an aromatic heterocycle containing N, and X2 represents an aromatic hydrocarbon ring or an aromatic heterocycle. Y1 and Y2 represent a fluoroalkyl group, a perfluoroalkyl group, an alkyl group, and a perfluoropolyether. Represents a 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 green dopant;
The organic light-emitting device having a second functional group for attracting the green dopant to the second electrode. The organic light emitting device according to claim 4,
The second functional group is a hydroxy group (—OH), a thiol group (—SH), a carboxyl group (—COOH), a sulfo group (—SO ₃ H), I, Br, Cl, F, SCN, CN, An organic light-emitting device that is one or more functional groups selected from NH ₂ , NO _2, and bipyridyl groups. The organic light emitting device according to claim 4,
A hole transport layer is disposed between the second electrode and the light emitting layer;
The organic light emitting device, wherein the second functional group is one or more functional groups selected from a phenylamino group, an oxazole group, a carbazole group, and a hydrazone moiety. The organic light emitting device according to any one of claims 4 to 6,
The organic light emitting device wherein the absolute value of the lowest empty orbit energy of the blue dopant is larger than the absolute value of the lowest empty orbit energy of the green dopant. In the organic light emitting element according to any one of claims 1 to 7,
The light emitting layer is an organic light emitting device manufactured by a coating method. 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 liquid is a light emitting layer forming coating liquid containing a solvent, a host material, a red dopant, and a blue 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 is a light emitting layer forming coating liquid containing a solvent, a host material, a red dopant, a blue dopant, and a green dopant. In the light emitting layer formation coating liquid of Claim 9 or 10,
The solvent used for the light emitting layer forming coating solution contains a first solvent and a second solvent,
The boiling point of the first solvent is higher than the boiling point of the second solvent;
Said 1st solvent is a coating liquid for organic light emitting layer formation which is a poor solvent with respect to the said red dopant. A light emitting layer forming material used for the organic light emitting device according to any one of claims 1 to 3,
The light emitting layer forming material is a light emitting layer forming material containing a host material, a red dopant, and a blue dopant. A light-emitting layer forming material used in the organic light-emitting device according to any one of claims 4 to 7,
The light emitting layer forming material is a light emitting layer forming material containing a host material, a red dopant, a blue dopant, and a green dopant.   A light source device provided with the organic light emitting element as described in any one of Claims 1 thru | or 8.