JP2015109178A - Organic electroluminescent device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent (organic EL) device which enables the achievement of a higher extraction efficiency by suppressing the reduction in the amount of light passed through a glass substrate owing to total reflection when light from an organic luminescent layer is incident on the glass substrate of a low refraction index from an ITO transparent electrode higher in refraction index.SOLUTION: An organic electroluminescent device comprises a glass substrate, and at least a light scattering layer, a positive electrode layer (ITO transparent electrode), an organic luminescent layer, a negative electrode layer which are laminated on the glass substrate in turn. The light scattering layer has one of a structure like a square pattern of a go board, a honeycomb structure, and circular structure, and has a pitch of 20-200 μm, a thickness of 0.5-3.0 μm, and a cross-section angle of 10-80 degrees.

Description

  The present invention relates to an organic electroluminescence element, and more particularly to a structure that improves the light extraction efficiency of an organic EL element.

  Organic electroluminescence elements (organic EL elements) are applied to displays for mobile phones and digital cameras, and lighting devices because of their advantages such as a wide viewing angle due to self-emission, high-speed response, and thin and light weight.

  An organic EL element generally has a structure in which a hole transport layer, a light-emitting layer, and an electron transport layer are sandwiched between electrodes. An electric field is applied between the electrodes, and electrons and holes are injected to generate excitons in the light-emitting layer. It produces light by generating and recombining. The exciton has a singlet state and a triplet state, the generation probability of the singlet state and the triplet state is 1: 3, and even when a phosphorescent material that uses triplet state emission is used. The luminous efficiency is up to 75%.

  Furthermore, the hole transport layer, the light emitting layer, and the electron transport layer are each composed of an organic layer, and the refractive index is approximately 1.7, the ITO transparent electrode is approximately 2.1 to 2.2, and the glass substrate is 1.4. Since about 1.5 and air is 1.0, total reflection occurs at the interface of the organic EL element, and the light that can actually be extracted to the outside of the element is about 20% of the emitted light. Is about 15%.

As a method for improving the extraction efficiency, for example, a method is disclosed in which light traveling in the direction of the element side surface is reflected forward by total reflection in which a reflection surface is formed on the element side surface (Patent Document 1).
In addition, for example, a method of changing the traveling direction of light by refraction and diffraction using a diffraction grating or a zone plate is disclosed (Patent Document 2). However, none of these methods has significantly improved the light extraction efficiency.

JP 2005-327522 A Japanese Patent No. 2911183

  In the present invention, when light from the organic light emitting layer is incident on a glass substrate lower than the ITO transparent electrode having a high refractive index, the amount of transmitted light of the glass substrate is reduced due to total reflection, and high extraction efficiency is obtained. An organic electroluminescence (organic EL) device is provided.

As a means for solving the above problems, the invention according to claim 1 is formed by sequentially laminating at least a light scattering layer, an anode layer (ITO transparent electrode), an organic light emitting layer, and a cathode layer on a glass substrate. An organic electroluminescence device,
The light scattering layer is formed of any one of a grid structure, a honeycomb structure, and a circular structure, and has a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, and a cross-sectional angle of 10 to 80 degrees. It is an organic electroluminescence device.

  The invention according to claim 2 is characterized in that the light scattering layer is made of a high refractive index resin having a refractive index in the range of 1.6 to 2.0. It is.

  The invention according to claim 3 is characterized in that the light scattering layer contains fine particles having a refractive index of 1.5 to 1.6 and a particle size of 0.7 to 1.5 μm. It is an organic electroluminescent element as described in above.

  According to the invention described in claim 1 of the present invention, in an organic electroluminescence device comprising, on a glass substrate, at least a light scattering layer, an anode layer (ITO transparent electrode), an organic light emitting layer, and a cathode layer are sequentially laminated. By forming a light scattering layer between the glass substrate and the ITO transparent electrode, it is possible to reduce the proportion of the light that is totally reflected and increase the light extraction efficiency in the front direction.

  Further, the light scattering layer has a shape of any one of a grid structure, a honeycomb structure, and a circular structure, with a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, and a cross-sectional angle of 10 to 80 degrees. By this, the light of the light emitting layer which deviated from the front direction can be scattered, and it has the effect of making it turn to a front direction again, and can suppress the leakage of the light to the horizontal direction of a glass substrate. Moreover, it can form easily by making the said light-scattering layer into said shape.

  Moreover, according to invention of Claim 2, it is a high refractive index resin of the range of refractive index 1.6-2.0 which is worth the middle of each refractive index in the middle of a glass substrate and an ITO transparent electrode. By forming the light scattering layer, the refractive index changes stepwise, the ratio of light that is totally reflected can be reduced, and the light extraction efficiency in the front direction can be increased.

  According to the invention described in claim 3, the light scattering layer has a refractive index of 1.5 to 1.6, a particle size in a high refractive index resin having a refractive index of 1.6 to 2.0. By including fine particles of 0.7 to 1.5 μm, scattering is more likely to occur, the ratio of light that is totally reflected can be reduced, and the light extraction efficiency in the front direction can be increased.

It is a section schematic diagram showing one embodiment of an organic EL device of the present invention. It is a cross-sectional schematic diagram which shows one Embodiment of the conventional organic EL element.

  As shown in FIG. 2A, a conventional organic EL element is generally formed by sequentially laminating an anode layer 3 (ITO transparent electrode), an organic light emitting layer 4 and a cathode layer 5 on a glass substrate 1. In this configuration, as described above, the hole transport layer, the light emitting layer, and the electron transport layer constituting the organic light emitting layer 4 are each composed of an organic layer having a refractive index of approximately 1.7, and the ITO transparent electrode 3 is 2 Since the glass substrate 1 is about 1.4 to 1.5 and the air is 1.0, total reflection occurs at the interface of the organic EL element. That is, as shown in FIG. 2B, the light emitted from the light emitting layer is totally reflected by the glass substrate 1, so that the light moves laterally with respect to the glass substrate 1 (lateral leakage of light), As a result, there is a problem that the amount of light transmitted in the front direction of the glass substrate 1 is reduced.

  The present invention is for solving the above-described problems, and the present invention will be specifically described below with reference to the drawings.

  As shown in FIG. 1A, the organic EL device of the present invention is formed by sequentially laminating at least a light scattering layer 2, an anode layer (ITO transparent electrode) 3, an organic light emitting layer 4 and a cathode layer 5 on a glass substrate 1. It is characterized by comprising.

  The light scattering layer 2 has a grid structure, a honeycomb structure, or a circular structure with a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, and a cross-sectional angle of 10 to 80 degrees. For example, it is characterized by having a honeycomb structure as shown in FIG.

  The glass substrate 1 used for this invention will not be specifically limited if it is excellent in terms of transparency, strength, heat resistance, chemical resistance, workability and the like.

  The light scattering layer 2 according to the present invention is made of a high refractive index resin having a refractive index in the range of 1.6 to 2.0, and has a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, and a cross-sectional angle of 10 to 10. It has one of 80-degree grid structure, honeycomb structure, and circular structure, and reduces the ratio of total reflection of light emitted from the organic light emitting layer, thereby increasing the light extraction efficiency in the front direction. effective.

  Specifically, the light scattering layer 2 according to the present invention includes a refractive index (about 1.4 to 1.5) of the glass substrate 1 and a refractive index (about 2.1 to 2.2) of the ITO transparent electrode 3. The refractive index is changed stepwise by being made of the high refractive index resin having a refractive index in the range of 1.6 to 2.0, which reduces the ratio of light that is totally reflected. The light extraction efficiency in the direction can be increased. Therefore, if the refractive index of the high refractive index resin forming the light scattering layer 2 is out of the above range, the refractive index between the ITO transparent electrode 3 and the glass substrate 1 cannot be changed step by step. The light extraction efficiency in the direction cannot be increased.

  The shape of the light scattering layer 2 is a grid structure having a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, a cross-sectional angle of 10 to 80 degrees between the glass substrate and the side surface of the light scattering layer, a honeycomb structure, By making one of the circular structures, as shown in FIG. 1 (c), the light emitted from the light emitting layer deviating from the front direction is scattered, which has the effect of directing again toward the front direction. Light leakage in the direction can be suppressed. When the grid structure, honeycomb structure, or circular structure that forms the light scattering layer 2 has a pitch of less than 20 μm and the cross-sectional angle between the glass substrate and the side surface of the light scattering layer is less than 10 degrees, a continuous flat film is obtained. An effective scattering effect cannot be obtained, and the light extraction efficiency in the front direction cannot be increased. On the other hand, if the pitch exceeds 200 μm, the pitch gap becomes too wide and the effect of the light scattering layer 2 is lost. On the other hand, if the film thickness is less than 0.5 μm, the light scattering layer 2 is too thin and the effect of the shape is lost.

  Examples of the high refractive index resin having a refractive index of 1.6 to 2.0 include thiourethane resins, episulfide resins, acrylic resins, polyimide resins, triazine resins, and silsesquio resins.

  The light scattering layer disperses fine particles having a refractive index of 1.5 to 1.6 and a particle size of 0.7 to 1.5 μm in the high refractive index resin having a refractive index of 1.6 to 2.0. Therefore, it can scatter more efficiently. As such fine particles, silica fine particles are desirable. When the refractive index and particle size are out of the above ranges, the efficiency of scattering deteriorates or scattering does not occur.

  Using the high refractive index resin and fine particles, a method of forming a grid structure, honeycomb structure, or circular structure with a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, and a cross-sectional angle of 10 to 80 degrees. Hereinafter, the light scattering layer 2 having a honeycomb structure shown in FIG. 1B will be described as an embodiment.

For example, separately, a honeycomb structure having a smooth surface with a metal plate (for example, a copper plate) having a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, and a cross-sectional angle of 10 to 80 degrees between the glass substrate and the side surface of the light scattering layer. Is directly engraved to produce a matrix of the light diffusion layer 2. Next, using the ultraviolet curable composition made of the high refractive index resin having a refractive index of 1.6 to 2.0, the uneven shape of the matrix is sufficiently filled with the uneven shape, and Apply so that the outermost surface is uniform. Next, the glass substrate 1 is stacked on the glass substrate 1 so that an air layer is not formed as much as possible. In this state, the ultraviolet light is irradiated from the glass substrate side to complete the curing, and the mother mold is peeled to form the light diffusion layer 2. Can do.

  The ultraviolet curable composition contains the high refractive index resin and a photopolymerization initiator, and a solvent may be used for adjusting the viscosity of the composition. When a solvent is used, it is necessary to dry the coating film before stacking the glass substrate 1. Note that the photopolymerization agent and the solvent are not particularly limited. Further, a release agent or the like may be used in advance on the mother die in order to facilitate the separation between the mother die and the glass substrate.

  As another method for forming the light scattering layer 2, for example, an electron beam curable resin composition made of the high refractive index resin is uniformly applied to a transparent film substrate such as polyethylene terephthalate (PET). It is also possible to obtain a fine pattern directly by drawing (exposure and curing) with an electron beam drawing apparatus after adhering a glass substrate thereon, and then peeling and developing.

  The anode layer (ITO transparent electrode) 3 according to the present invention is preferably provided with a thickness of 0.1 to 0.2 μm by a sputtering method. In addition to ITO, a transparent electrode material such as IZO (indium / zinc composite oxide), tin oxide, zinc oxide, indium oxide, and aluminum oxide composite oxide can be used as the anode layer 3. ITO is preferable because it is resistant to solvents, has high solvent resistance, and has high transparency.

  As the organic light emitting layer 4 according to the present invention, a known layer in which a hole transport layer, a light emitting layer, and an electron transport layer used for illumination are sequentially laminated can be used. The forming method is not particularly limited, and a known printing method or the like can be used.

  The hole transport layer is for lowering the injection barrier so that holes are easily injected from the ITO transparent electrode 2 to the light emitting layer. Examples of the low molecular weight hole transport material include triphenylamine dimer (TPD) and starburst amine obtained by binding these in a starburst form. All of them are in an amorphous state and preferably have a high glass transition temperature so as not to crystallize. As the polymer hole transport material, polyaniline derivatives, polythiophene derivatives, polyvinylcarbazole derivatives, and the like can be used.

  The light emitting layer includes low molecular weight materials such as an aluminum quinoline, a benzoxazole Zn complex, and an electron transporting metal complex such as a benzoquinolinol Be complex, and a dye material used for adjusting the emission color by doping them. Examples of the dye system include distyrylarylene derivatives, pyrazoquinoline derivatives, oxadiazole derivatives, and the like.

  Also, an organic light emitting material dispersed in a polymer material can be used. For example, organics such as coumarin, perylene, pyran, anthrone, porphyrene, quinacridone, N, N'-dialkyl substituted quinacridone, naphthalimide, N, N'-diaryl substituted pyrrolopyrrole, iridium complex Examples thereof include a material in which a light emitting material is dispersed in a polymer material such as polystyrene, polymethyl methacrylate, and polyvinyl carbazole.

  An appropriate solvent is added to the organic light-emitting material and the polymer material as described above, and a stably dispersed organic light-emitting ink is prepared, and a light-emitting layer is formed by various printing methods and coating methods. In addition, a surfactant, an antioxidant, a viscosity modifier, an ultraviolet absorber, and the like may be added as necessary to adjust the organic light emitting ink.

  The electron transport layer is for transporting electrons injected from the cathode to the light emitting layer. Examples of the material for forming the electron transport layer include quinoline, perylene, triazole, oxazole, oxadiazole, and derivatives and metal complexes thereof.

  The organic light-emitting layer 4 according to the present invention is formed by sequentially laminating the hole transport layer, the light-emitting layer, and the electron transport layer described above, and various materials constituting these and formation of each layer The method is not particularly limited.

  Examples of materials that can be used for the cathode layer 5 according to the present invention include simple metals such as lithium, magnesium, calcium, ytterbium, and aluminum, and alloys of these with stable metals such as gold and silver. Alternatively, a conductive oxide such as indium, zinc, or tin can be used. These electrode materials can be selected according to the light emission characteristics of the organic light emitting layer 4. The shape of the cathode layer 5 may be a stripe shape or a solid shape.

  As described above, the organic EL element of the present invention is provided with a light scattering layer having a refractive index that is intermediate between the refractive indexes between the glass substrate and the ITO transparent electrode. Due to the effects of the refractive index and the shape, the light extraction efficiency in the front direction of the light emitted from the light emitting layer can be improved.

  The organic EL device of the present invention can be used for a backlight for liquid crystal, a light source for illumination, electrical decoration, a light source for signage, and the like.

1 Glass substrate 2 Light scattering layer 3 Anode (ITO transparent electrode)
4 Organic light emitting layer 5 Cathode 6 Path of light emitted from the light emitting layer 10 Organic EL element

Claims (3)

An organic electroluminescent device comprising a glass substrate and at least a light scattering layer, an anode layer (ITO transparent electrode), an organic light emitting layer, and a cathode layer sequentially laminated,
The light scattering layer is formed of any one of a grid structure, a honeycomb structure, and a circular structure, and has a pitch of 20 to 200 μm, a film thickness of 0.5 to 3.0 μm, and a cross-sectional angle of 10 to 80 degrees. Organic electroluminescence device.   2. The organic electroluminescence device according to claim 1, wherein the light scattering layer is made of a high refractive index resin having a refractive index of 1.6 to 2.0.   The organic light-emitting device according to claim 1, wherein the light scattering layer contains fine particles having a refractive index of 1.5 to 1.6 and a particle size of 0.7 to 1.5 μm.