JP2009277917A - Organic luminescent device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic light emitting element which is low-cost and has high reliability and a long lifetime. <P>SOLUTION: The organic light emitting element 100 has at least a light emitting layer 26 between a hole implantation electrode 12 and an electron implantation electrode 14, a vacuum deposition layer of a monomeric material is formed as a hole transport layer 20 between the hole implantation electrode 12 and the light emitting layer 26, and the light emitting layer 26 that uses a polymeric material as a light emitting material is formed covering the hole transport layer 20. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic light emitting element using a polymer light emitting material.

  A self-luminous element such as an EL (electroluminescence) element is capable of emitting light with high luminance, reducing power consumption, and reducing the thickness of the device, and has attracted attention as a next-generation display device and light source device. In an organic EL element which is a kind of self-luminous element, an organic material is used for a light emitting layer provided between a hole injection electrode and an electron injection electrode, and the degree of freedom of emission color is high. On the other hand, there are problems such as low durability due to the fact that the light emitting layer is a very thin film and the coverage is low, and the durability of the organic material itself is low, in order to increase durability R & D is underway.

  In such an organic EL element, a low molecular organic EL element using a low molecular material as a light emitting organic material and a high molecular organic EL element using a high molecular material have been proposed. In the case of a low molecular organic EL device, low molecular organic materials are used not only for the light-emitting layer but also for the hole transport layer and the electron transport layer, and each layer can be sequentially laminated on the substrate by a vacuum deposition method or the like. it can. Such low molecular organic EL devices have already been put into practical use, and their reliability is being improved not only for the individual low molecular materials used but also for the entire device.

  On the other hand, in an EL element using a polymer material as a light-emitting material, a method such as coating or printing can be adopted as a method of laminating the polymer material on the substrate. In addition, since a single polymer organic material often has both a light emitting function and a carrier transport function, it is easy to obtain an organic EL element having a simple configuration in which a single layer of a polymer organic material layer is formed between electrodes. It has become. In addition, since the polymer organic material can be formed by the printing method as described above, it is easy to pattern the polymer organic material for each of the RGB pixels.

  There are also attempts to employ both low-molecular organic materials and high-molecular organic materials in organic EL devices. For example, in Patent Document 1, a first electrode is formed on a substrate, a first organic film layer is formed from a low molecular light emitting material on the first electrode, and a polymer electron transport material is formed on the first organic film layer. An organic EL element in which a second organic film layer to be formed is formed and a second electrode is formed on the second organic film layer is shown. In this organic EL element, the first and second organic film layers are not laminated in order on the first electrode, but the second organic film layer and the first organic film are arranged in order from the film side on the donor film separately adopted. And a first organic film layer (low molecular light emitting material layer) and a second organic layer film (polymer electron transport) on the first electrode of the substrate by laser thermal transfer (LITI) method from the donor film. Material) at the same time.

  In patent document 2, it is an organic EL element provided with the functional layer which contains a light emitting layer at least between the 1st electrode and the 2nd electrode, Comprising: As a functional layer, the light emitting layer using the polymeric organic material from the 1st electrode side It has been proposed to provide an electron transport layer formed of a low molecular organic material on the light emitting layer. Further, it has been proposed that a hole injection / transport layer using a polymer organic material is formed between the first electrode and the light emitting layer in the same manner as the light emitting layer, and hole injection / transport using a polymer organic material is proposed. The layer and the light emitting layer are formed by an ink jet printing method.

  Patent Document 3 is an organic EL element in which a hole injection / transport layer and a light emitting layer are laminated from the anode side between the anode and the cathode. A polymer material is used for the hole injection / transport layer. Is formed by a wet method. It has been proposed to use a low-molecular light-emitting material for the light-emitting layer and to laminate it using a wet method.

  In Patent Document 4, a light emitting medium laminate is provided between the first electrode layer and the second electrode layer, and the light emitting medium laminate includes a low molecular material layer made of a low molecular material having a weight average molecular weight of 1000 or less. And a layer formed as a polymer material layer made of a polymer material having a weight average molecular weight of 1000 or more. Furthermore, at least one low molecular material layer and at least one high molecular material layer are laminated so that their surfaces are in contact with each other, that is, the high molecular material layer and the low molecular material layer are alternately arranged. It is stated that the laminated structure can suppress the occurrence of crystallization and aggregation on the surface of the low molecular material layer.

Japanese Patent Laid-Open No. 2005-63977 JP 2005-285617 A JP 2006-190759 A JP 2007-242816 A

  As described above, the low-molecular organic EL element can form an organic EL element having high temperature durability and a long lifetime. However, the film formation using the vacuum evaporation method needs to be evaporated in a vacuum chamber, and in the case of forming a different light emitting layer for each RGB pixel, patterning using an evaporation mask is required. Further, as a single low molecular weight organic material, a material having all functions of hole transport, light emission, and electron transport has not been developed, and it is necessary to form a device by stacking multiple layers. For this reason, a large-scale apparatus in which a number of vacuum deposition apparatuses (vacuum deposition chambers) are connected is required, and the manufacturing cost tends to be very high.

  On the other hand, in the polymer type organic EL device, the vacuum vapor deposition process is only the cathode forming process, and other than that, a non-vacuum process can be used, so that the manufacturing cost can be reduced. Further, as described above, patterning is easy, which is advantageous in terms of reducing manufacturing costs. However, an organic EL element using a polymer organic material has many problems in terms of low high-temperature durability, short life, voltage increase due to driving, and the like as compared with a low-molecular organic EL element.

  As in Patent Documents 1 to 4, in the organic EL element, there is a possibility that the advantage of polymer / low molecule can be obtained by using both the low molecular material and the high molecular material. When aiming at practical application, there are many problems such as durability and stability, and suppression of voltage rise. In particular, durability, particularly durability under high temperature, high humidity environment, etc., cannot satisfy the requirements even if a polymer / low molecular laminate structure is simply adopted.

  The present invention provides an organic light-emitting device that is low-cost, has high-temperature durability, and has a long lifetime.

  The present invention relates to an organic light emitting device having at least a light emitting layer between a hole injection electrode and an electron injection electrode, and a vacuum deposition layer of a low molecular material as a hole transport layer between the hole injection electrode and the light emitting layer. The light emitting layer using the polymer material as the light emitting material is formed so as to cover the hole transport layer.

  In another aspect of the present invention, in the organic light emitting device, the polymer material of the light emitting layer has an average molecular weight of 10,000 or more, and the molecular weight of the low molecular material of the hole transport layer is 700 or more and 2000 or less. .

  In another aspect of the present invention, in the organic light emitting device, a coating layer or a printing layer of the polymer material is formed as the light emitting layer, and the low molecular material of the hole transport layer has a glass transition point, or In the case of a material having no glass transition point, the melting point is equal to or higher than the drying temperature performed after the light emitting layer is applied or printed.

  In another aspect of the present invention, in the organic light-emitting device, the hole transport layer has a glass transition of the low molecular material of the hole transport layer before the light-emitting layer is laminated on the hole transport layer. When there is no glass transition point or higher, the heat treatment is performed at a temperature higher than the melting point.

  In another aspect of the present invention, in the organic light-emitting device, a sublimation temperature in vacuum deposition of the low molecular material is 300 ° C. or higher at a vacuum degree of 1 Pa.

  In another aspect of the present invention, in the organic light emitting device, the low molecular material is a triphenylamine derivative material. For example, the triphenylamine derivative material can have a symmetrical central structure. The triphenylamine derivative material can be a starburst amine.

  In another aspect of the present invention, the light emitting layer is a layer containing the polymer material laminated on the hole transport layer by a coating method or a printing method, and the hole transport layer includes at least two layers. The low-molecular material of the first layer on the side in contact with the light-emitting layer of the hole transport layer is provided with a laminated structure, and the coating method or the low-molecular material of the second layer covered with the first layer The solubility with respect to the solvent substance used as a solvent of the said polymeric material in a printing method is low.

  In another aspect of the invention, the thickness of the first layer of the hole transport layer is thinner than the thickness of the second layer.

  In another aspect of the invention, the first layer is a vacuum deposition layer formed on the second layer.

  In another aspect of the present invention, the solvent of the polymer material includes any one kind of toluene, xylene, anisole, methylanisole, dimethylanisole, tetralin, ethyl benzoate, methylbenzoate, or two or more kinds. .

  In another aspect of the present invention, the hole transport layer is formed by patterning the low molecular material into a shape corresponding to a deposition mask.

  In another aspect of the present invention, the organic light emitting device is driven with a duty ratio of 1/3 or less during one frame period, or a display in one frame period is provided between a hole injection electrode and the electron injection electrode. DC driving is performed in which a predetermined DC voltage corresponding to the light emission luminance is supplied during the period.

  According to the present invention, in an organic light emitting device, a vacuum evaporation layer of a low molecular hole transport material is used as a hole transport layer, and a light emitting layer using a polymer material as a light emitting material is formed by covering the hole transport layer. It is possible to obtain an organic EL device which is low in cost and has high temperature durability and a long lifetime. For example, it can be suitably employed in applications that require durability under high temperature and high humidity environments such as in-vehicle display elements. Further, since it can be manufactured at a low cost, it can also be adopted for a segment type display element or the like that is strongly required to be inexpensive.

  As a result of the inventors' research, in organic light-emitting devices using polymer materials, PEDOT: PSS (poly (3,4-ethylenedioxythiophene) -poly- (styrenesulfonate), which is currently proposed as a polymer hole transport functional material, is proposed. It was found that the deterioration of the device was caused by instability of the polymer hole transport material such as)). However, in the present invention, as the hole transport layer, the high temperature durability of the organic light emitting device as described above by using a low molecular hole transport layer formed by a vacuum deposition method having high temperature durability and stable characteristics. It is possible to improve the lifetime and the voltage rise accompanying driving. In addition, the light-emitting layer manufacturing cost can be reduced as compared with the case where all layers are formed by vacuum deposition in a low molecular weight organic light-emitting device having a multilayer laminated structure between electrodes. As a result, it is possible to form an organic EL element that can be suitably used as an in-vehicle display element.

  By using a material having a molecular weight of 700 or more as a low-molecular material for the hole transport layer, it is difficult to dissolve in a solvent used for forming a light-emitting layer made of a polymer material, and exhibits some solubility. In addition, it becomes easy to suppress the diffusion of the low molecular weight material into the light emitting layer.

  In the present invention, as the low-molecular material of the hole transport layer, a material having a glass transition point or a melting point equal to or higher than the temperature of the drying treatment for volatilizing the solvent after coating or printing of the polymer material of the light-emitting layer is adopted. By doing so, the characteristic deterioration in the light emitting layer drying process can be prevented.

  In the present invention, before laminating the light-emitting layer on the hole transport layer, heat treatment is performed at a temperature equal to or higher than the melting point of the low-molecular material of the hole transport layer, or when there is no glass transition point. Further, it is possible to further improve the durability of the hole transport layer in forming the light emitting layer, for example, the durability to the solvent used for forming the light emitting layer.

  Moreover, the current efficiency of the organic EL device can be improved by reducing the driving voltage by forming a structure in which a low molecular hole transport layer that is soluble in a solvent is laminated under a low molecular hole transport layer that is insoluble in a solvent. Is possible.

  Furthermore, the first layer low molecular weight material in contact with the light emitting layer of the hole transport layer is more resistant to the solvent used when forming the high molecular weight material of the light emitting layer than the second layer low molecular weight material covered by the first layer. By using a material with low solubility, the solvent resistance of the hole transport layer can be improved at a low cost.

  In the present invention, the use of a low molecular material for the first layer, which is often expensive due to high solvent resistance, by making the thickness of the hole transport layer of the first layer thinner than that of the second layer While reducing the amount, it is possible to achieve both the improvement of the solvent property of the hole transport layer and the reduction of the production cost.

  The organic light emitting device of the present invention is driven with a duty ratio of 1/3 or less during one frame period, or according to light emission luminance during a display period within one frame period between a hole injection electrode and an electron injection electrode. The DC drive to which the predetermined DC voltage is supplied is performed. By adopting such a driving method, alteration at the interface between the light emitting layer of the high molecular material and the hole transport layer of the low molecular material can be suppressed, and it is easy to prevent the decrease in luminance and extend the device life. Become.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments (hereinafter, embodiments) of the invention will be described with reference to the drawings. FIG. 1 shows a schematic cross-sectional structure of an organic EL element 100 employed as an example of the organic light emitting element according to this embodiment.

  The organic EL element 100 includes at least a light emitting layer 26 using a polymer light emitting material between a hole injection electrode 12 functioning as an anode and an electron injection electrode 14 functioning as a cathode. In the present embodiment, at least a hole transport layer 20 is formed between the light emitting layer 26 and the hole injection electrode 12, and a hole injection / transport low molecular material is formed in the hole transport layer 20 by vacuum deposition. The deposited film is adopted.

  After the hole transport layer 20 is laminated on the anode 12 by vacuum vapor deposition, a polymer light emitting material is formed on the hole transport layer 20 as a light emitting layer 26 by a coating method or a printing method. On the light emitting layer 26, the cathode 14 is laminated | stacked by the vacuum evaporation method, for example. After forming the device 100 up to the cathode 14, a sealing can (not shown) is finally bonded to the device forming side of the substrate 10 in a dry nitrogen atmosphere and sealed.

  The substrate 10 is a transparent substrate such as glass, but is not limited to glass, and various substrates such as a resin substrate with a barrier film and a metal substrate can be used.

  The anode 12 can be any conductive material capable of forming a transparent or translucent electrode. Specifically, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, zinc oxide, indium oxide, zinc aluminum oxide, zinc gallium oxide, titanium niobium oxide, and the like are used as oxides and stacked by sputtering or the like. can do. Among these, ITO is a material having advantages such as low resistance, solvent resistance, and excellent transparency.

  A semi-transparent conductive layer may be formed by vapor-depositing a metal material such as aluminum, gold or silver on the surface of a conductive layer such as ITO or on the substrate 10, or an organic semiconductor such as polyaniline is used. And may be used as an anode. Furthermore, the anode 12 may be formed using other methods.

  Further, the anode 12 may be patterned into a shape required in a display or the like by etching after film formation, or may be activated by UV treatment or plasma treatment, if necessary.

  The cathode 14 is preferably made of a material having a low work function, and in particular, the interface with the light emitting layer 26 is desired to have a low work function. For example, an alkali metal or an alkaline earth metal, an alkali metal or an alkaline earth metal is used. A laminate of a metal electrode such as aluminum, a laminate of an alkali metal or alkaline earth metal halide and a metal electrode such as aluminum, or the like can be used. Specifically, Al / Ca (light emitting layer side), Al / Ba (light emitting layer side), Al / Li (light emitting layer side), Al / LiF (light emitting layer side), Al / CsF (light emitting layer side), A laminated structure such as Al / CaF (light emitting layer side) or Al / Ca / LiF (light emitting layer side) can be employed, and these laminated structures can be formed by, for example, a vacuum deposition method.

  The material of the low molecular hole transport layer 20 will be described in detail later, but the hole transport layer 20 is excellent in purity, density, and flatness by forming a low molecular material using a vacuum deposition method. High quality film can be obtained.

  As a method for forming the hole transport layer 20, in addition to the vacuum deposition method, a printing method such as an ink jet method, a general pressing transfer method and a laser transfer (LITI) method, a coating method such as spin coating, and vapor phase growth are used. There are also laws. However, the film quality of the hole transport layer 20 is important from the viewpoint of improving the high temperature and high humidity durability of the organic EL element. As described above, from the viewpoint of the purity, density, flatness, etc. of the film, the vacuum evaporation method is used. It is most desirable to use

  Further, after the low molecular material is deposited by vacuum deposition, heat treatment is performed before the light emitting layer 26 using the polymer material is formed as will be described later. By this heat treatment, the surface serving as the interface with the hole transport layer 20, particularly the light emitting layer 26, can be made smooth and dense, and the resistance (solvent resistance) to the solvent used for forming the light emitting layer can be improved. Can do.

  The heat treatment temperature is set to a temperature equal to or higher than the glass transition point of the low molecular weight material of the hole transport layer 20 or in the case of a material having no glass transition point. Note that the heat treatment may be performed in a vacuum deposition film formation chamber or may be performed separately by being transported to a heating unit. In any case, in order to prevent deterioration of low molecular materials due to oxygen, moisture, etc., non-oxidation is performed. It is desirable to heat in an atmosphere, for example, in an atmosphere of an inert gas such as nitrogen gas or argon gas.

  In vacuum deposition, when it is necessary to pattern the hole transport layer 20 into a desired shape for each pixel, for example, an opening is formed in a target pattern between the deposition source and the substrate to be deposited. The deposited vapor deposition mask is disposed, and the low molecular hole transport layer 20 is patterned simultaneously with the vapor deposition.

  As a method for forming the light emitting layer 26 using a polymer material formed on the hole transport layer 20, a so-called wet treatment method can be employed. This wet treatment is a method in which a polymer material is dispersed in a solvent and this solvent is adhered to the surface to be formed, such as a spin coating method, a dip coating method, a spraying method, an ink jet method as described above, Examples thereof include transfer and printing methods such as the LITI method.

  Although the conveyance between each process at the time of forming each layer of the organic EL element 100 demonstrated above is not specifically limited, It is desirable to convey in a dry atmosphere.

  In addition to sealing with a sealing can, the element sealing method includes a sealing method in which a glass or a film with a barrier is bonded to the element forming side of the substrate 10, or a protective thin film such as a silicon nitride film is formed on the cathode 14. A method of sealing the element from the outside by forming it so as to directly cover the entire rear substrate can be applied. Although such a sealing process and the film-forming process of the polymer light emitting layer 26 are not limited, they can be performed, for example, in a glove box.

  Next, the hole transport layer 20 and the light emitting layer 26 will be specifically described.

(Low molecular hole transport material)
The molecular weight of the low molecular hole transport material is preferably 700 or more and 2000 or less. When the molecular weight is 700 or more, even when a small amount is dissolved in the solvent of the polymer light emitting material dispersion for coating or printing the polymer material, diffusion of the low molecular material into the light emitting layer can be suppressed. . When the molecular weight is 2000 or less, when a film is formed by a vacuum vapor deposition method, it is easy to heat vapor deposit this material.

  Further, after the polymer material of the light emitting layer 26 is laminated, a solvent drying process is performed, and in this drying process, heating is performed to about 120 ° C. If the temperature in the drying step is higher than the melting point of the hole transport layer 20 when the low molecular material has no glass transition point or no glass transition point, in the drying step, an increase in interface roughness due to aggregation of the low molecular material, The mixing of the material and the polymer material occurs, and the device characteristics deteriorate. In the present embodiment, a material having a glass transition point or a melting point equal to or higher than the solvent drying temperature after application of the polymer material, for example, 120 ° C. or higher is used as the low molecular material of the hole transport layer 20.

  Furthermore, in this embodiment, since a low molecular material is used as the hole transport layer 20, it is necessary that the material has a high hole transport property. As an example, it is desirable to employ a triphenylamine derivative material. Specific examples of this triphenylamine derivative material include, but are not limited to, compounds shown in the following chemical formulas (1) to (4).

  The triphenylamine derivative material as described above can form the low molecular hole transport layer 20 by a vacuum deposition method. The glass transition temperature Tg of the exemplified triphenylamine derivative material is 143 ° C. for TPT of chemical formula (1), 131.8 ° C. for TBPB of chemical formula (2), and 133 for Spio-1-TAD of chemical formula (3). In the case where the temperature and the t-Bu-TBATA in the chemical formula (4) are 203 ° C. and these materials are used for the hole transport layer 20, the heat treatment after vacuum deposition is set to Tg or more of these materials to be used. As described above, if the heating temperature in the heating and drying step after stacking the polymer light emitting layer 26 is 120 ° C., for example, any of the above materials has a glass transition temperature equal to or higher than the heating temperature, and the drying step Thus, alteration of the hole transport layer 20 can be prevented.

  Among the above-mentioned triphenylamine derivative materials as the low-molecular hole transport layer material, the material having the center of symmetry has a molecular shape that is relatively close to a sphere, and when it is made into a thin film, the molecules are easily arranged and the solvent resistance is improved. Therefore, it is preferable. Among these, starburst amine is particularly preferable because molecules are easily arranged and a thin film excellent in solvent resistance is formed. The triphenylamine derivative materials represented by the chemical formulas (1) to (4) all have a portion in which the triphenylamine is arranged in a star shape.

  As described above, the molecular weight of the low molecular hole transport material is preferably 2000 or less.

  T-Bu-TBATA in the above chemical formula (4) has a molecular weight of 1540. On the other hand, the compound represented by the chemical formula (5) has the same basic skeleton as t-Bu-TBATA but has a molecular weight of 2165. In addition to the influence of the specific molecular structure, as in the chemical formulas (4) and (5), when the basic skeleton is the same and the molecular weight is increased, the evaporation temperature for performing vacuum deposition tends to increase. In fact, the temperature at which the compound of the chemical formula (5) is deposited needs to be higher than the t-Bu-TBATA of the chemical formula (4).

  Here, in this embodiment, in vacuum vapor deposition of a low molecular material, the sublimation temperature is 300 ° C. or higher at a vacuum degree of 1 Pa. Therefore, when the molecular weight exceeds 2000, the efficiency of vapor deposition is reduced and the sublimation temperature is further increased. Thus, not only the sublimation occurs due to heating, but also molecular decomposition may occur. When the decomposition occurs, the hole transport ability is adversely affected, leading to an increase in the driving voltage of the organic EL element. Therefore, it is preferable to employ a material having a molecular weight of 2000 or less.

(Multilayer structure of hole transport layer)
The hole transport layer 20 is a multilayer of two or more layers, the side in contact with the light emitting layer 26 is a first layer, and the lower layer covered with the first layer is a second layer, and at least the first layer and the second layer are different. Low molecular hole transport materials can be employed.

  For example, as the low-molecular material of the first layer, at least a material having low solubility (poorly soluble) in a solvent substance used as a solvent for the polymer material is used, and the second layer is hardly soluble in a solvent substance. It is also possible to adopt materials that are not present.

  When a single layer structure is adopted as the hole transport layer 20, it is required that the material of the hole transport layer 20 has resistance to dissolution of the polymer material of the light emitting layer 26 in a solvent. On the other hand, in the case of a multilayer structure, if at least the first layer in contact with the light emitting layer 26 has this dissolution resistance, the second layer's low molecular weight material covered by the first layer has a low dissolution resistance even if the dissolution resistance is low. Elution of low molecular weight materials can be prevented. For this reason, the freedom degree of selection of the material of a 2nd layer is high. That is, if a material that is hardly soluble in a solvent substance is used for the first layer that is in contact with the light emitting layer 26, it is possible to use a material that is not particularly poorly soluble as the material for the second layer. In this case, the multilayered hole transport layer 20 has a relationship that the solubility of the first layer is lower than the solubility of the second layer in the polymer light-emitting material solvent of the second layer.

  As an example, a triphenylamine derivative material as shown in the above chemical formulas (1) to (4) is adopted for the first layer, but as an example, the α shown in the following chemical formula (6) is used for the second layer. Although well known as a low molecular hole transport material such as -NPB, a material having low solvent resistance can be employed.

  Α-NPB of the above chemical formula (6) has a molecular weight of 588 and a glass transition temperature of 98 ° C. Even when this material is used for the second layer, a highly stable organic EL device can be obtained. Of course, the low-molecular hole transport material of the second layer is not limited to this α-NPB. For example, it is possible to obtain an organic EL element having excellent durability by adopting a material that can form a stable film having excellent hole transportability and excellent purity, density, and flatness by vacuum deposition. it can.

  In the multilayer structure of the hole transport layer 20, the first layer can be formed thinner than other layers (for example, the second layer). The thickness of the first layer should be at least thick enough to prevent elution of the second layer when it is not resistant to the solvent of the polymer light emitting layer 26. The thickness may be less than, for example, 10 nm. As described above, the low-molecular hole transport material of the first layer that is hardly soluble in the solvent of the polymer light emitting layer 26 (for example, a triphenylamine derivative material such as the above-mentioned starburst amine) has a high molecular weight, Often expensive. However, by forming it as thin as possible to the extent that an effect of preventing elution is obtained, it is possible to minimize the amount of material used and suppress an increase in manufacturing cost.

  As in the case of a single layer, each layer of the hole transport layer 20 having a multilayer structure is preferably formed by a vacuum deposition method from the viewpoint of the purity, density, and flatness of the film. In this case, the boundary between the second layer and the first layer is not necessarily clear. From the laminated region of only the second layer component, the mixed region gradually with the first layer component by co-evaporation, only the first layer component A layer structure in which the stacking region and the concentration change stepwise may be used.

(Hole injection layer)
In the organic EL element 100 of FIG. 1, a hole injection layer may be further provided between the hole transport layer 20 and the anode 12 described above. As a material for the hole injection layer, a material having a smaller hole injection barrier from the anode 12 than the hole transport layer 20 can be used, so that the efficiency of hole injection into the light emitting layer 26 can be increased, and the drive voltage can be reduced. To do.

  Examples of the material for the hole injection layer include copper phthalocyanine, Tetracanoethylene, 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane, 2- [4-((Bis (2-hydroxyethyl) aminophenylene) ) -2,5-cyclohexadiene-1-yldiene] malonitril, 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone, 2,6-Dimethylbenzoquinone, polyaniline and the like.

  Note that these hole injection layers can also be formed by a vacuum deposition method with high film formation quality.

(Other examples of hole transport layer materials)
In addition to the above chemical formulas (1) to (4), the material of the single layer structure of the hole transport layer 20 or the material of the first layer in contact with the light emitting layer 26 in the case of the multi-layer structure is as follows. Using compounds (TCTA, (DNA) PP, TFLFL, TNFL, NPB-CH ₂ -NPB, (PTB) DNPP, s-TPT, TBATA material) as shown in chemical formula (14) from (7), respectively Is possible.

(Polymer light emitting material)
The polymer light-emitting material desirably has an average molecular weight of 10,000 or more in consideration of surface flatness after coating and formation of a low element driving voltage. As the polymer light emitting material, for example, a polyfluorene (PF) polymer, a polyphenylene vinylene (PPV) polymer, a polyvinyl carbazole (PVK) polymer, or the like can be used, and a fluorescent dye or a phosphorescent dye can be used. Those dispersed in the polymer, polystyrene polymer, polythiophene polymer, polymethyl methacrylate polymer, or the like can also be used.

  Further, as other polymers, polysilane polymers such as polyphenylene ethynylene (PPE) polymers, polyphenylene (PP) polymers, polyparaphenylene (PPP) polymers, polymethylphenylsilane (PMPS), etc. It is also possible to adopt. These polymers may be used alone, or may be used as a mixture of two or more, or may be used as a mixture with a low molecular material or the like.

  Examples of solvents for these high molecular organic light emitting materials include toluene, xylene, acetone, anisole, methylanisole, dimethylanisole, tetralin, ethyl benzoate, methyl benzoate, methyl ethyl ketone, cyclohexanone, methanol, ethanol, isopropyl alcohol, and ethyl acetate. , Butyl acetate, water or the like, or a single or mixed solvent (solvent) can be used. A light emitting layer solution is prepared by dissolving in these solvents, and the obtained light emitting layer solution is adhered onto the hole transport layer 20 by wet treatment such as a coating method or a printing method as described above. Thereafter, the polymer light emitting layer 26 can be formed so as to cover the hole transport layer 20 by removing the solvent by drying.

  Among these solvents, aromatic solvents such as toluene, xylene, anisole, methylanisole, dimethylanisole, tetralin, ethyl benzoate, and methyl benzoate are particularly easy to handle due to the high solubility of the polymer organic light-emitting material. Therefore, it is a more preferable solvent. In addition, as a coating method, a spin coating method, a dip coating method, a spray method, or the like can be used, and as a printing method, a method such as an ink jet method or a transfer method can be used.

  As an example of the polyfluorene-based polymer, a poly [9,9-di- (2'-ethylhexylfluorenyl-2,7'-diyl)] polymer light-emitting material, which is a kind of light-emitting material, can be given. This luminescent material can be dissolved in, for example, a xylene solvent.

  As an example of the polyphenylene vinylene-based polymer, a poly (2-methyl-5- (2'-ethylhexyloxy) -1,4-phenylene vinylene) polymer light-emitting material, which is a kind of light-emitting material, can be given. This luminescent material can also be dissolved in, for example, a xylene solvent.

  The polyvinyl carbazole-based polymer material can be used by, for example, mixing with 2- (4-Biphenylyl) -5-phenyl-1,3,4-oxadiazole low molecular material and dissolving in a solvent. As the solvent in this case, for example, dichloroethane can be used.

  In addition, after forming the light emitting material layer on the hole transport layer 20 using any polymer and a solvent in which the polymer is dissolved, a drying process for removing the solvent is performed. The drying process is performed at about 120 ° C. in a non-oxidizing atmosphere such as an inert gas such as nitrogen gas or argon gas.

  FIG. 2 shows an example of a display using the organic EL element according to this embodiment. The organic EL device according to the present embodiment can be manufactured at a low cost and has extremely high durability in a high temperature and high humidity environment. For this reason, it is very useful as an in-vehicle display as an example, and FIG. 2 shows an example of this in-vehicle segment type display.

  A display is roughly classified into an active matrix type in which each pixel has a switching element and a passive matrix type in which no switching element is provided. The passive matrix type has a method in which the anode and the cathode are formed in a stripe shape so as to be orthogonal to each other with the light emitting layer interposed therebetween, or one of the anode and the cathode has a shape that is displayed from the beginning, and the other is There is a segment system which is a common electrode and has a shape displayed by a pixel (a segment type display may be distinguished from a passive matrix type display).

  In such a segment type display and a passive matrix type display using a striped electrode (for example, 1/3 duty ratio) with a small number of pixels, the EL element formed in each pixel has almost the entire period in one field period, or 1 The display period continues to be selected for a period of about / 3 period.

  For this reason, during each display period, a constant voltage corresponding to the display content is supplied to the EL element of each pixel. In the case of an active matrix display, a constant voltage is supplied to the EL element during the display period depending on the circuit configuration in the pixel. The EL element according to the present embodiment can display with high reliability for a long time in a driving method (DC driving) in which a constant voltage is applied during such a display period.

  Examples and comparative examples of this embodiment will be described below with reference to the element configuration shown in FIG.

[Example 1]
As Example 1 of this patent, an ITO electrode having a thickness of 150 nm was formed on the glass substrate 10 as the anode 12. Next, as the hole transport layer 20, t-Bu-TBATA represented by the chemical formula (4) was formed to a thickness of 60 nm by vacuum deposition.

  Next, a light emitting layer solution in which an ADS233YE polymer light emitting material manufactured by American Dye Source was dissolved in a xylene solvent was used, and this solution was formed on the hole transport layer 20 as a polymer light emitting layer by spin coating to a thickness of 100 nm. After a solvent drying step, an Al / Ca electrode was formed as a cathode 14 on the light emitting layer 26 by a vacuum deposition method.

  Finally, a metal can and a glass substrate on which the organic EL element 100 was formed were bonded with a photo-curing resin in a glove box, and a sample in which the organic EL element was sealed was created.

  As Comparative Example 1, a sample was prepared under the same conditions as in Example 1 except that a PEDOT: PSS polymer material layer formed to 100 nm by a spin coating method was used as the material of the hole transport layer 20.

FIG. 3 shows the time dependence of the drive voltage ratio with respect to the initial drive voltage when the organic EL elements of Example 1 and Comparative Example 1 are driven at a constant current at a current density of 50 mA / cm ² . In Comparative Example 1, the drive voltage ratio increased by 20% or more in 10 hours, whereas in Example 1, even when driven for 100 hours, it did not exceed 20% and stable drive characteristics were obtained.

FIG. 4 shows the time dependence of the emission luminance ratio with respect to the initial luminance when the devices of Example 1 and Comparative Example 1 are driven at a constant current at a current density of 50 mA / cm ² . In Comparative Example 1, the luminance was reduced by half in 10 hours, whereas in Example 1, the luminance decreased only by about 20% even when driven for 10 hours, and it can be understood that stable light emission characteristics were obtained.

  Further, it was found that even when driven under an environment of 85 ° C., Example 1 can be durable for a longer time than Comparative Example 1, and is excellent in high-temperature durability. Therefore, the organic EL element having the structure of Example 1 can be suitably used as an element for applications in which high temperature durability is strongly required, for example, in-vehicle applications.

[Example 2]
As Example 2, an organic EL element was produced under the same conditions as in Example 1 except that TBPB represented by the chemical formula (2) was used as the material of the hole transport layer 20. FIG. 5 shows the time dependence of the drive voltage ratio with respect to the initial drive voltage when the devices of Example 2 and Comparative Example 1 are driven at a constant current at a current density of 50 mA / cm ² .

  In Example 2, it can be seen that the rate of voltage increase due to driving is suppressed as compared with Comparative Example 1, and stable driving characteristics are obtained. Moreover, the light emission characteristic and high temperature durability showed the same tendency. From this result, it was shown that even if the materials were different, the effect could be obtained if the conditions as in Example 1 were satisfied.

[Example 3]
As Example 3, t-Bu-TBATA represented by the chemical formula (4) was used as the material of the hole transport layer 20, and an organic EL element was prepared under the same conditions as in Example 1 above. .

  Specifically, an ITO electrode having a thickness of 150 nm was formed on a glass substrate, and t-Bu-TBATA of the chemical formula (4) was formed to 60 nm as the hole transport layer 20 by a vacuum deposition method. As the polymer light-emitting layer 26, a poly [9,9-di- (2′-ethylhexylfluorenyl-2,7′-diyl)] polymer light-emitting material, which is a kind of polyfluorene-based light-emitting material, was dissolved in a xylene solvent. It formed in thickness of 100 nm with the spin coat method using the light emitting layer liquid.

  After the drying process of the solvent, an Al / Ca electrode is formed on the light emitting layer 26 by vacuum deposition, and finally the metal can and the glass substrate on which the element is formed are bonded with a photo-curing resin in the glove box. A sample in which the fabricated element was sealed was prepared.

FIG. 6 shows the time dependency of the drive voltage ratio with respect to the initial drive voltage when the elements of Example 3 and Comparative Example 1 are driven at a constant current density of 50 mA / cm ² . In Comparative Example 1, it increased by 20% or more in 10 hours, whereas in Example 3, even when driven for 100 hours, it did not exceed 20% and stable driving characteristics were obtained.

[Example 4]
In Example 4, an ITO electrode having a thickness of 150 nm was formed on the glass substrate 10 as the anode 12, and a material represented by the chemical formula (4) was used as the hole transport layer 20 to a thickness of 60 nm by a vacuum deposition method.

  As the light-emitting layer 26, a coating solution in which a poly (2-methoxy-5- (2′-ethylhexyloxy) -1,4-phenylenevinylene) polymer light-emitting material, which is a kind of polyphenylene vinylene-based light-emitting material, is dissolved in a xylene solvent. The film was formed to a thickness of 100 nm by spin coating. After the solvent drying step, an Al / Ca electrode is formed on the light emitting layer 26 as a cathode 14 by a vacuum deposition method, and finally a glass substrate on which a metal can and an element are formed in a glove box A sample was prepared by laminating the film with a photo-curing resin and sealing the fabricated element.

FIG. 7 shows the time dependence of the drive voltage ratio with respect to the initial drive voltage when the elements of Example 4 and Comparative Example 1 are driven at a constant current at a current density of 50 mA / cm ² . In Comparative Example 1, it increased by 20% or more in 10 hours, whereas in Example 4, even when driven for 100 hours, it did not exceed 20% and stable driving characteristics were obtained.

[Example 5]
As Example 5, an ITO electrode having a thickness of 150 nm was formed as an anode 12 on a glass substrate, and t-Bu-TBATA represented by the chemical formula (4) was formed as a hole transport layer 20 by a vacuum evaporation method to a thickness of 60 nm. As the light emitting layer 26, spin coating is performed using a coating solution in which 2- (4-Biphenylyl) -5-phenyl-1,3,4-oxadiazole low molecular material and Polyvinylcarbazole polymer material are dissolved in a dichloroethane solvent with an equal weight. The thickness was 100 nm by the method. After performing the solvent drying step, an Al / Ca electrode is formed on the polymer light emitting layer 26 by a vacuum deposition method, and finally a glass can on which a metal can and an element are formed in a glove box is a photo-curing resin. The sample which bonded together and sealed the preparation element was prepared.

FIG. 8 shows the time dependence of the drive voltage ratio with respect to the initial drive voltage when the devices of Example 5 and Comparative Example 1 are driven at a constant current density of 50 mA / cm ² .

  In Comparative Example 1, it increased by 20% or more in 10 hours, while in Example 5, stable driving characteristics were obtained without exceeding 20% even when driven for 30 hours.

[Example 6]
As Example 6, a sample in which a material represented by the chemical formula (4) was formed at a deposition rate of 5 nm / min was prepared as the hole transport layer 20 under the same conditions as in Example 1. As Comparative Example 2, a sample in which the material represented by the above chemical formula (5) was formed at a deposition rate of 5 nm / min as the hole transport layer 20 under the same conditions as in Example 1 was prepared.

When Example 6 and Comparative Example 2 were driven at a current density of 50 mA / cm ² , the drive voltage of Comparative Example 2 was 30% higher than that of Example 6. The molecular weight of t-Bu-TBATA represented by the chemical formula (4) is 1540, whereas the molecular weight of the compound of the chemical formula (5) is 2165. For this reason, the sublimation temperature for vapor-depositing the compound of chemical formula (5) needs to be higher than that of the compound of chemical formula (4), and this sublimation temperature exceeds the decomposition temperature of the material of chemical formula (5). It is thought that the characteristics of the hole transport layer deteriorated and the voltage increased.

  Therefore, if the molecular weight of the low molecular weight material exceeds 2000, the deposition temperature (sublimation temperature) may exceed the decomposition temperature. Therefore, the molecular weight of the low molecular weight material is preferably 2000 or less. Can understand.

It is a figure which shows schematic sectional structure of the organic EL element which concerns on embodiment of this invention. It is a figure which shows an example of the display using the organic EL element which concerns on embodiment of this invention. It is a figure which shows the time dependence of the drive voltage ratio with respect to the initial stage drive voltage at the time of carrying out the constant current drive of the organic EL element which concerns on Example 1 and the comparative example 1 by the current density of 50 mA / cm < ² >. It is a figure which shows the time dependence of the light emission luminance ratio with respect to initial luminance at the time of carrying out the constant current drive of the organic EL element which concerns on Example 1 and the comparative example 1 by 50 mA / cm < ² > of current density. It is a figure which shows the time dependence of the drive voltage ratio with respect to the initial stage drive voltage at the time of carrying out the constant current drive of the organic EL element which concerns on Example 2 and Comparative Example 1 by 50 mA / cm < ² > of current density. It is a figure which shows the time dependence of the drive voltage ratio with respect to the initial stage drive voltage at the time of carrying out the constant current drive of the organic EL element which concerns on Example 3 and the comparative example 1 with a current density of 50 mA / cm < ² >. It is a figure which shows the time dependence of the drive voltage ratio with respect to the initial stage drive voltage at the time of carrying out the constant current drive of the element of Example 4 and the comparative example 1 by 50 mA / cm < ² > of current density. It is a figure which shows the time dependence of the drive voltage ratio with respect to the initial stage drive voltage at the time of carrying out the constant current drive of the element of Example 5 and the comparative example 1 by 50 mA / cm < ² > of current density.

Explanation of symbols

  10 substrate, 12 hole injection electrode (anode), 14 electron injection electrode (cathode), 20 low molecular hole transport layer, 26 polymer light emitting layer, 100 organic EL device.

Claims (14)

In an organic light emitting device comprising at least a light emitting layer between a hole injection electrode and an electron injection electrode,
Between the hole injection electrode and the light emitting layer, a vacuum vapor deposition layer of a low molecular material is formed as a hole transport layer,
An organic light-emitting element, wherein the light-emitting layer using a polymer material as a light-emitting material is formed so as to cover the hole transport layer. The organic light emitting device according to claim 1,
The polymer material of the light emitting layer has an average molecular weight of 10,000 or more,
The organic light emitting device, wherein the low molecular weight material of the hole transport layer has a molecular weight of 700 or more and 2000 or less. The organic light-emitting device according to claim 1 or 2,
As the light emitting layer, a coating layer or a printing layer of the polymer material is formed,
The low molecular weight material of the hole transport layer has a glass transition point or, in the case of a material having no glass transition point, a melting point equal to or higher than a drying temperature that is executed after the light emitting layer is applied or printed. An organic light emitting device characterized. In the organic light emitting element according to any one of claims 1 to 3,
In the hole transport layer, before the light emitting layer is laminated on the hole transport layer, the glass transition point of the low molecular material of the hole transport layer or higher than the melting point when there is no glass transition point. An organic light-emitting element that is heat-treated at a temperature. In the organic light emitting element according to any one of claims 1 to 4,
An organic light-emitting element, wherein a sublimation temperature in vacuum deposition of the low molecular material is 300 ° C. or higher at a vacuum degree of 1 Pa. In the organic light emitting element according to any one of claims 1 to 5,
The organic light-emitting device, wherein the low-molecular material is a triphenylamine derivative material.   The organic light-emitting device according to claim 6, wherein the triphenylamine derivative material has a symmetrical central structure.   The organic light-emitting device according to claim 7, wherein the triphenylamine derivative material is a starburst amine. The organic light-emitting device according to any one of claims 1 to 8,
The light emitting layer is a layer containing the polymer material laminated on the hole transport layer by a coating method or a printing method,
The hole transport layer has a laminated structure of at least two layers,
The low molecular weight material of the first layer on the side of the hole transport layer in contact with the light emitting layer is higher in the coating method or the printing method than the low molecular weight material of the second layer covered with the first layer. An organic light emitting device having low solubility in a solvent substance used as a solvent for a molecular material.   10. The organic light emitting device according to claim 9, wherein a thickness of the first layer of the hole transport layer is thinner than a thickness of the second layer.   10. The organic light emitting device according to claim 8, wherein the first layer is a vacuum deposition layer formed on the second layer. 11. In the organic light emitting element according to any one of claims 8 to 11,
The organic light-emitting element characterized in that the solvent of the polymer material includes one or more of toluene, xylene, anisole, methylanisole, dimethylanisole, tetralin, ethyl benzoate, and methyl benzoate .   The organic light emitting device according to any one of claims 1 to 12, wherein the hole transport layer is formed by patterning the low molecular material into a shape corresponding to a deposition mask. In the organic light emitting element according to any one of claims 1 to 13,
The element is driven with a duty ratio of 1/3 or less during one frame period, or a predetermined DC corresponding to the light emission luminance during a display period within one frame period between the hole injection electrode and the electron injection electrode. An organic light-emitting element, wherein DC driving is performed to which voltage is supplied.

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