JP2014191980A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, when there is incidence of light from an anode layer having high refractive index to a transparent substrate interface having low refractive index, the transmitted amount of light of the transparent substrate decreases due to total reflection, and the problem that the efficiency of light extraction decreases due to total reflection at an interface between a glass substrate and air.SOLUTION: Provided is an organic electroluminescent element 10 characterized in that at least a high refractive index resin layer 8 having a refractive index in the range from 1.6 to 2.0, an anode layer 2, a light scattering electrode 9, an electroluminescent layer 7, and a cathode layer 6 are laminated on a transparent substrate 1 in the order stated, wherein the light scattering electrode 9 is patterned in a desired shape.

Description

  The present invention relates to an organic electroluminescence element, and more particularly to a layer structure for improving the extraction efficiency of emitted light.

  An organic electroluminescence element (hereinafter referred to as an organic EL element) used for illumination or display is a self-light-emitting element in which an organic fluorescent material is sandwiched between electrodes facing each other at about 2000 mm or less. Organic fluorescent materials include low molecular weight materials and high molecular weight materials, but the principle of light emission is the same. Holes injected from the anode into the LOMO of the fluorescent material and electrons injected from the cathode into the HOMO Utilizes fluorescence or phosphorescence upon recombination. Expectations are growing as the next generation display devices and flat light sources for liquid crystal displays.

  The configuration of the organic EL element 20 is shown in FIG. 3. On the transparent glass substrate 1, the anode layer 2, the hole transport layer 3, the fluorescent light emitting layer 4, the electron transport layer 5, the cathode layer 6, and the protective film 14. Etc. The anode layer 2 is a transparent electrode from which light can be extracted, and usually ITO (indium tin composite oxide) is used. The hole transport layer 3 is an organic layer that facilitates injection of holes from the ITO electrode 2 into the fluorescent light emitting layer. The cathode 6 is a layer for injecting electrons into the fluorescent light-emitting layer 4 (hereinafter simply referred to as a light-emitting layer), which is a metal such as magnesium or an alloy of lithium and silver, and an alkali metal material having a small work function is used. .

  In addition, the hole injection layer 3 and the electron transport layer 5 are not only transporting the respective carriers, but are also multilayered by adding a functional layer (interlayer layer) for blocking the opposite charge. There are many. In any case, in order to improve the tunneling of holes and electrons, the thickness of each layer is very thin in the range of 100 to 1000 mm.

  For colorization, phosphors with different fluorescent colors are arranged in a predetermined pattern, white light emission is dispersed using a color filter, or a red light emission layer and a green light emission layer are separately deposited on a blue light emission layer. There is a method for color conversion.

  Although the protective film 14 covering the cathode layer 6 is originally unnecessary, the performance of the cathode electrode material and each of the organic layers described above is extremely deteriorated due to the influence of moisture and oxygen. It is installed as a barrier so as not to penetrate into the aforementioned layer. In general, after coating with an epoxy resin or the like, an inorganic film is laminated or covered with a cover glass containing a hygroscopic agent for further completeness.

  In the low molecular system and the high molecular system, the element manufacturing method is different in nature, but in the low molecular system, each layer is sequentially deposited on the glass substrate with a transparent electrode so as to have a predetermined thickness by vapor deposition. In the polymer system, a hole transport material and a conjugated polymer material are separately adjusted to ink in a solvent, and printing or dropping from a fine nozzle is employed. For this reason, low molecular weight systems are difficult to increase in size because it is necessary to mask-deposit RGB phosphors in a predetermined pattern, and are suitable for small and medium-sized displays, while high molecular weight systems are large because printing technology can be applied. It is said to be advantageous for the production of displays. However, there is no clear barrier to the adoption of materials and construction methods according to size, and ultimately it depends on cost.

By the way, in the organic EL element, as can be seen from FIG. 3, the light 13 emitted from the phosphor has a hole transport layer 3, an anode layer 2, and a transparent layer that support the phosphor layer 4 with the metal electrode 6 behind. It comes out through a multilayer medium called the substrate 1. In this situation, all of the light emitted from the phosphor 4 cannot be extracted in the front direction. One cause is that the singlet excited state of the phosphor does not contribute to light emission due to non-radiative deactivation when interacting with the adjacent cathode layer (metal electrode) 6 (Non-patent Document 1).

Japanese Patent Laid-Open No. 9-272863 JP-A-5-159881

A. N. Safonov et al., Synthetic Metals, 116, 145 (2001).

  On the other hand, the light 13 passing through the multilayer medium is modulated by the mutual refractive index relationship and the thickness. There is a problem that the transmission wavelength varies due to interference, or cannot be extracted as light guided in the layer due to total reflection. In particular, when light enters from a layer having a high refractive index to a layer having a low refractive index, total reflection may occur depending on the incident angle, and the total reflected light may be guided through the medium and emitted from the edge. Disappear. There is a problem that the amount of light that can be extracted forward is only about 20% of the light emitted by the phosphor.

  The refractive index of the electron transport layer 5 / the light emitting layer 4 / the hole transport layer 3 is approximately 1.7 to 1.8 when the refractive index difference between the layers is ignored, and the refractive index of the anode layer 2 (ITO) is 2 .About.2.2, that of the glass substrate 1 is about 1.45, and air is 1, so that the light extraction efficiency by total reflection at the interface between the anode layer 2 and the glass substrate 1 and at the interface between the glass substrate and air It can be said that the decline of is serious.

  Therefore, the present invention has a problem that the amount of light transmitted through the transparent substrate is reduced due to total reflection when entering from the high refractive index anode electrode to the low refractive index transparent substrate interface, and the total reflection at the glass substrate / air interface. Therefore, it was an object to improve the problem that the light extraction efficiency decreases. That is, an object of the present invention is to provide an interface configuration of an organic electroluminescence element that can suppress total reflection involving both surfaces of a transparent substrate.

  In order to achieve the above object, the invention according to claim 1 is provided on a transparent substrate, at least a high refractive index resin layer having a refractive index in the range of 1.6 to 2.0, an anode layer, a light scattering electrode, an electro The organic electroluminescence element is characterized in that a luminescence layer and a cathode layer are laminated in this order.

  The invention according to claim 2 is the organic electroluminescence device according to claim 1, wherein the light scattering electrode is patterned into a desired shape.

  The invention according to claim 3 is the organic electroluminescent element according to claim 2, wherein the surface of the light scattering electrode is substantially flush with the surface of the anode layer.

Invention of Claim 4 has an organic insulating layer which protects the said light-scattering electrode, It is set as the organic electroluminescent element of any one of Claims 1-3 characterized by the above-mentioned. .

  According to a fifth aspect of the present invention, in the organic electroluminescent element according to any one of the first to fourth aspects, the high refractive index resin layer contains fine particles made of an inorganic substance. It is what.

  According to the first aspect of the present invention, the light emitted from the high refractive index transparent substrate to the low refractive index air side and the light incident from the anode layer to the transparent substrate have total reflection components. The probability that the component is re-reflected by the conductive light scattering electrode is increased. Since the re-reflected light is extracted from the transparent substrate, there is an effect that the light extraction efficiency is increased.

  According to the second aspect of the present invention, the position of the light scattering electrode can be controlled by patterning, and there is an effect that it is possible to select a site with little visual influence. At the same time, the effect of lowering the resistance of the anode electrode can be expected.

  According to the invention described in claim 3, since the electrode surface is flat as a whole, adverse effects on the hole transport layer, the light emitting layer, and the like due to the unevenness are reduced.

  In the invention according to claim 4, the surface irregularities of the light scattering electrode are covered with a protective layer and made flat. As a result, leakage current due to surface irregularities can be reduced.

  According to the fifth aspect of the present invention, fine particles made of an inorganic material are dispersed in a high refractive index resin layer, and the ratio of transmitted light scattered in the layer is increased, so that the light extraction efficiency is increased. Can be expected.

It is a figure of the cross-sectional view explaining an example of the organic EL element structure which becomes this invention. It is a figure of the cross-sectional view explaining another example of the organic EL element structure which becomes this invention. It is a figure of the cross-sectional view explaining the structure of the conventional organic EL element. It is a top view photograph for demonstrating the form and arrangement | positioning aspect of a light-scattering electrode.

  As shown in FIG. 3, the organic EL element basically includes a transparent substrate 1, an anode layer 2 (generally ITO), an organic light emitting layer 7 (a hole transport layer 3, a light emitting layer 4, an electron transport layer 5, etc. ) And the cathode layer 6. The organic light emitting layer 7 illustrates a layer structure in which the hole transport layer 3, the light emitting layer 4, and the electron transport layer 5 are laminated in this order, but there is no other than the light emitting layer, or it is not shown but added In some cases, the functional layer is also included. The light emitting layer 4 may also serve as the hole transport layer 3.

The light 11 emitted from the organic light emitting layer 7 is dissipated due to various causes. However, the optical loss targeted by the present invention is transparent from the anode layer 2 (refractive index: n ₁ ) having a high refractive index and having a low refractive index. The total reflection component when entering the substrate 1 (generally a glass substrate having a refractive index n ₂ ) and the total reflection component at the interface between the transparent substrate 1 and the air layer.

In the present invention, in order to reduce the loss, first, as shown in FIG. 1, the anode layer 2 (ITO electrode having a refractive index n _{1 of} about 2.0 or more) and the transparent substrate 1 (refractive index n ₂ is 1). High refractive index resin layer 8 having a refractive index n satisfying the relationship of n ₁ >n> n ₂ so that the difference in refractive index of the glass substrate (about .45) changes stepwise without being discontinuous. The structure is inserted between the anode layer 2 and the transparent substrate 1.

  The refractive index n of the high refractive index resin layer 8 is preferably in the range of 1.6 to 2.0, which is an intermediate value between the refractive indexes of the transparent substrate 1 and the anode layer 2. For the high refractive index resin layer 8, a resin having a refractive index of the binder resin of about 1.4 to 1.6 (typical acrylic resin) is used. In this case, titanium oxide or oxide having a diameter of about 50 nm is used. It is obtained by dispersing a predetermined amount of zirconia fine particles. Further, fine particles having a diameter of about 0.4 to 1.5 μm made of an inorganic substance such as titanium oxide or silicon oxide are dispersed in the resin layer. Thereby, the component scattered in the resin layer 8 increases, and the light extraction efficiency in the front direction increases.

  In the present invention, in addition to the insertion of the high refractive index resin layer 8, a light scattering electrode 9 is laid on the anode layer 2 as shown in FIG. Alternatively, as shown in FIG. 2, the resin layer 8 or the anode layer 2 is dug down by the thickness of the light scattering electrode 9 so that the surfaces of the anode layer 2 and the light scattering electrode 9 are flush with each other. It is a housed configuration. In this case, since the actual thickness of the light scattering electrode 9 is relatively thicker than that of the anode layer 2 or the high refractive index resin layer 8, the thickness of the light scattering electrode 9 is thicker than that of FIG. It is drawn.

  As shown in FIG. 4, it is desirable that the light scattering electrode 9 is periodically laid on the anode 2 in a stripe shape (or a matrix shape or a dot shape). It is done. The light scattering electrode 9 is conductive, but silver particles having a diameter of about 2 μm are laid so as to have a thickness of 2 to 6 μm and a line width of 10 to 100 μm.

  The light scattering electrode 9 has a function of re-reflecting light totally reflected at the interface between the transparent substrate 1 and air and at the interface between the anode layer 2 and the transparent substrate 1 in various directions. Alternatively, it has a function of irregularly reflecting light emitted from the light emitting layer side. When embedded in the high-refractive index resin layer 8 (see FIG. 2), it has a function of scattering light guided through the resin to the end face method, and in either case, the forward light extraction efficiency is increased. There is an effect.

  The present invention can be applied regardless of whether the light emitting layer 7 is a low molecular weight light emitting layer 7 or a light emitting layer 7 based on a conjugated polymer. The value of the refractive index is described. As the hole transport material 3, TPD (n = 1.8 to 1.9) is used in a low molecular system, PEDOT-PSS (n = 1.5) is used in a high molecular system, and aluminum is used in a low molecular system as an organic light emitting material 4. There is quinoline (n = 1.8 to 1.9) and PPV (n = 2.0) in the polymer system. Although both have chromatic dispersion, the wavelength λ is a value for light of approximately 0.5 μm.

  As the transparent substrate 1 used in the present invention, a glass substrate, a quartz substrate, a plastic substrate or the like can be used, but a glass substrate excellent in transparency, strength, heat resistance, chemical resistance, and workability is most preferable. The refractive indexes of the glass substrate and the quartz substrate are both about 1.45 if slight wavelength dispersion is ignored. The difference in refractive index from the air layer is about 0.4, which is a cause of a decrease in extraction efficiency due to total reflection.

  First, on the glass substrate 1, a high refractive index resin layer 8 that is transparent in the visible region having a refractive index in the range of 1.6 to 2.0 is formed. A resin having a refractive index intermediate between the refractive index of the glass substrate 1 and the refractive index of the ITO electrode (preferably a combination having a refractive index difference of 0.3 or less) is desirable. .8), episulfide (˜1.7), acrylic (˜1.6), polyimide (˜1.75), triazine, silsesquio and other resins can be used as appropriate. The thickness of the resin layer 8 is set within a range of 1 to 3 μm and not colored. The high refractive index resin layer 8 can be produced by dissolving in an appropriate solvent and then applying and drying. The resin layer may be a photoresist formed by adding a photopolymerization initiator or the like so that it can be patterned by a photolithography method.

Moreover, the uneven | corrugated shape 11 is formed in the surface of the glass substrate 1 by the sandblasting method etc.,
A light scattering effect can be imparted. The unevenness preferably has a pitch of about the wavelength of light, and is preferably about 0.5 to 1 μm. If there is unevenness, the total reflection effect can be reduced by changing the angle of light incident from the resin side. Unevenness can also be formed on the surface of the glass substrate by wet etching.

  As another configuration, as shown in FIG. 2, fine particles made of an inorganic material such as titanium oxide or zirconia having a diameter of about 0.4 to 1.5 μm may be dispersed in the high refractive index resin layer 8. Absent. As described above, fine particles of inorganic material having a diameter of about 50 nm may be dispersed in the high refractive index resin layer 8.

Next, the anode _{2 made} of ITO (n ₂ = about 2.0 to 2.1) is provided on the high refractive index resin layer 8. As an electrode material, in addition to ITO, transparent electrode materials such as IZO (indium zinc composite oxide), tin oxide, zinc oxide, indium oxide, and aluminum oxide composite oxide can be used. ITO is preferable because it has high transparency and high transparency. ITO is sputtered on a substrate with a thickness of 0.1 to 0.3 μm and then annealed at 230 ° C. to lower the resistance.

  Next, the light scattering electrode 9 is periodically formed on the ITO 2. The light scattering electrode 9 can be patterned in accordance with a printing method or a photolithography method or the like using a paste material in which silver particles having a diameter of about 2 μm are dispersed in an acrylic resin. The light scattering electrode 9 preferably has high reflectance and turbidity. The surface of the light scattering electrode 9 is preferably flush with the surface of the anode layer 2, but for this purpose, a recess is formed on the ITO surface. Although the recess may be formed in the ITO by photoetching, the recess may be formed in the resin layer 8 in advance, and then the ITO and the light scattering electrode 9 may be laminated.

  After forming the base electrode as described above, the hole transport layer 3 is formed. The hole transport layer 3 is installed to lower the injection barrier so that holes are easily injected from the ITO transparent electrode 2 to the organic light emitting layer 4.

Examples of the low molecular hole transport material composing the hole transport layer 2 include TPD which is a triphenylamine dimer and starburst amine obtained by binding these in a starburst form. In any case, it is desirable to exhibit an amorphous state and to exhibit a high glass temperature so as not to crystallize.
It is formed by vacuum deposition at a low pressure of 10 ⁻⁴ Pa or less.

  In addition to the above organic compounds, the hole transport material composing the hole transport layer 2 includes inorganic oxides such as vanadium oxide (VOx), molybdenum oxide (MoOx), nickel oxide (NiOx), etc. Is mentioned. These materials can be formed by various deposition methods such as sputtering and resistance heating.

  As the polymer-based hole transport material, a polyaniline derivative, a polythiophene derivative, a polyvinylcarbazole (PVK) derivative, poly (3,4-ethylenedioxythiophene) (PEDOT-PSS), or the like may be used. These materials are dissolved or dispersed in a solvent and formed as a hole transport material ink by various coating methods such as letterpress printing, gravure printing, reverse offset printing, spin coater, bar coater, roll coater, die coater, gravure coater, etc. can do.

An interlayer layer (not shown) can be formed on the hole transport layer 3. Interlayer functions as an electron blocking layer that blocks electrons moving from the organic light-emitting layer to the anode side and increases the charge coupling probability in the organic light-emitting layer, by contact between the excited organic light-emitting material and the hole transport layer It is installed for the purpose of preventing quenching and preventing a decrease in luminous efficiency due to a chemical reaction between an organic light emitting material and a hole transport material.

  The material used for the interlayer can be a polymer material such as polyarylene, polyarylene vinylene, or polyfluorene, or a mixture of these polymer materials with low molecules such as aromatic amines. In particular, poly (2,7- (9,9-di-n-octylfluorene) -alt- (1,4-phenylene-((4-sec-butylphenyl) amino) -1,4-phenylene) ( In order to avoid color mixing with the organic light-emitting layer, the interlayer is usually subjected to a heat treatment at about 200 ° C. for 10 minutes or more before forming the organic light-emitting layer. Insolubilized.

Next, the organic light emitting layer 4 is formed.
Examples of the low molecular weight system include electron-transporting metal complexes such as aluminum quinoline, benzoxazole Zn complex, and benzoquinolinol Be complex, and dye-based materials used for adjusting the emission color by doping them. Examples of the dye system include distyrylarylene derivatives, pyrazoquinoline derivatives, and oxadiazole derivatives. These also preferably have a high glass transition temperature.

  In the case where a separate coating is required for a polymer system, a relief printing method, a gravure printing method, a printing method such as a reverse offset printing method, an ink jet method or the like can be used. Examples of organic light emitting materials include coumarin, perylene, pyran, anthrone, porphyrene, quinacridone, N, N′-dialkyl substituted quinacridone, naphthalimide, N, N′-diaryl substituted pyrrolopyrrole, iridium. Examples include complex-based luminescent dyes dispersed in polymers such as polystyrene, polymethyl methacrylate, and polyvinyl carbazole, and polyarylene-based, polyarylene vinylene-based, and polyfluorene-based polymer materials. However, it is not limited to these.

  These organic light emitting materials are dissolved or stably dispersed in a solvent to form an organic light emitting ink. Examples of the solvent for dissolving or dispersing the organic light emitting material include toluene, xylene, acetone, anisole, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, or a mixed solvent thereof. Among them, aromatic organic solvents such as toluene, xylene, and anisole are preferable from the viewpoint of the solubility of the organic light emitting material. Moreover, surfactant, antioxidant, a viscosity modifier, a ultraviolet absorber, etc. may be added to organic luminescent ink as needed.

  Finally, the cathode layer 6 is formed of a stripe or solid electrode. As the material of the cathode layer 6, those according to the light emission characteristics of the organic light emitting layer 7 can be used. For example, simple metals such as lithium, magnesium, calcium, ytterbium and aluminum, and stable metals such as gold and silver can be used. And alloys thereof. Alternatively, a conductive oxide such as indium, zinc, or tin can be used.

  Although not shown in FIG. 1, an electron transport layer 5 such as an alkali metal fluoride (LiF) or an oxide can be formed thinly between the cathode 6 and the light emitting layer 4. Electron injection efficiency is improved and light emission efficiency is also improved. Examples of a method for forming these cathodes and related layers include a method for forming by vacuum evaporation using a mask.

The organic EL element can have a laminated structure in which layers such as a hole blocking layer, an electron transport layer, and an electron injection layer are selected as necessary in addition to the hole transport layer, the interlayer layer, and the organic light emitting layer.
The laying of the high refractive index layer according to the present invention is applied regardless of the detailed laminated structure of the organic light emitting layer 7 described above.

  In addition, since the refractive index of the glass substrate is larger than the refractive index of air, there is also a mode in which the glass substrate is guided and dissipates from the edge of the glass substrate. In order to suppress this, a film having a lower refractive index than the glass substrate may be formed on the glass substrate, or a light scattering film may be laid.

1. Transparent substrate (glass substrate)
2. Anode layer (ITO transparent electrode)
3, hole transport layer 4, light emitting layer 5, electron transport layer 6, cathode layer (metal electrode)
7, organic light emitting layer 8, high refractive index resin layer 9, light scattering electrodes 10 and 20, organic EL element,
11, outgoing light 12, fine particles 13, reflection component (outgoing light) (substrate / air interface)
14. Protective film

Claims (5)

  A high refractive index resin layer having a refractive index in the range of 1.6 to 2.0, an anode layer, a light scattering electrode, an electroluminescence layer, and a cathode layer are laminated on the transparent substrate in this order. Organic electroluminescence device.   The organic electroluminescence element according to claim 1, wherein the light scattering electrode is patterned into a desired shape.   3. The organic electroluminescence device according to claim 2, wherein the surface of the light scattering electrode is substantially flush with the surface of the anode layer.   The organic electroluminescent element according to claim 1, further comprising an organic insulating layer that protects the light scattering electrode.   The organic electroluminescence element according to any one of claims 1 to 4, wherein the high refractive index resin layer contains fine particles made of an inorganic substance.