JP2012009336A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element having increased light extraction efficiency.SOLUTION: The organic electroluminescent element 1 has a substrate 2, an optically transparent first electrode 3 formed on the substrate 2, an organic layer 4 including an organic luminescent layer 43, and a second electrode 5, in this order. The organic electroluminescent element is arranged so that the organic luminescent layer 43 has a refraction index of 1.6 or smaller, and the refraction index of the first electrode 3 is larger than that of the substrate 2 and smaller than that of the organic luminescent layer 43. Thus, the differences of refraction indices among materials of the substrate 2, first electrode 3 and organic luminescent layer 43 are reduced, whereby the loss attributed to reflections at their interfaces is suppressed.

Description

  The present invention relates to an organic electroluminescence element (hereinafter referred to as an organic EL element) used for a flat panel display, a backlight for a liquid crystal display, a light source for illumination, or the like.

  A structure of a conventional organic EL element (for example, see Non-Patent Document 1) is shown in FIG. This organic EL element 100 is configured by laminating a light-transmitting anode 11, an organic layer 14 including a hole transport layer 12 and an organic light emitting layer 13, and a cathode 15 in this order on a substrate 10. The surface of the substrate 10 opposite to the anode 11 is in contact with the atmosphere 16. When a voltage is applied, the anode 11 injects holes into the organic light emitting layer 13, the cathode 15 injects electrons into the organic light emitting layer 13, and these holes and electrons recombine within the organic light emitting layer 13. Then, excitons are generated by this recombination, and when the excitons transition to the ground state, photons are emitted and taken out through the anode 11 and the substrate 10.

  By the way, when light propagates from one medium to another medium having a different refractive index, reflection and transmission according to each refractive index occur at the interface of the medium according to Fresnel's law. The reflected light is reflected at another interface and is extracted out of the medium, but there is also light lost by absorption in the medium. According to Fresnel's law, the greater the difference in refractive index of each medium, the easier it is for reflection to occur. This reflection is called Fresnel reflection. In the organic EL element 100, among the light emitted from the light emitting source 13a in the organic light emitting layer 13 toward the atmosphere 16, the optical path L1 indicates the light extracted to the atmosphere 16, and the optical paths L1a, L1b, and L1c are Fresnel reflections at the interface. Shows the light to be.

  When light propagates from a medium with a high refractive index to a medium with a low refractive index, the critical angle is determined from Snell's law at the interface based on the refractive index between the media, and has an incident angle greater than the critical angle. The light is totally reflected at the interface and is confined and absorbed in a medium having a high refractive index. Of the light emitted from the light source 13a with an incident angle, the optical path L2 indicates light extracted to the atmosphere 16, and the optical paths L3 and L4 indicate light totally reflected at the interface.

  Here, the refractive index of each layer of the organic EL element 100 will be described. The substrate 10 is exclusively made of glass from the viewpoints of excellent transparency, strength, low cost, gas barrier layer, chemical resistance, and heat resistance, and the refractive index of general soda lime glass is about 1.52. It is.

  For the anode 11, indium tin oxide (ITO) or indium zinc oxide (IZO) in which indium oxide is doped with tin oxide is widely used because of its excellent transparency and electrical conductivity. Their refractive index varies depending on the composition, film forming method, crystal structure, etc., but ITO is approximately 1.7 to 2.3, IZO is approximately 1.9 to 2.4, Very expensive.

  The refractive index of the organic electroluminescent material (light emitting material), electron transporting material, hole transporting material, etc. used for the organic layer 14 is a π-conjugated bond system containing a large number of general benzene rings in its molecular structure. Since it is a material, the refractive index is about 1.6 to 2.0.

  Accordingly, in the organic EL element 100, the refractive index of each layer is in the relationship of the atmosphere 16 <substrate 10 <organic layer 14 <anode 11 in contact with the substrate 10. For this reason, the light emitted from the light emitting source 13a of the organic light emitting layer 13 in the organic layer 14 is lost due to Fresnel reflection at each interface from the viewpoint of Fresnel's law, and from the viewpoint of Snell's law, the substrate 10 Loss due to total reflection occurs at the interface between the anode 16 and the atmosphere 16 and at the interface between the anode 11 and the substrate 10. Due to such a loss, part of the light emitted from the light emitting source 13a is lost without being extracted to the atmosphere 16, and the light extraction efficiency of the organic EL element 100 is lowered.

Here, the loss light by total reflection is demonstrated. The refractive indexes of the atmosphere 16, the substrate 10, the anode 11, the hole transport layer 12, and the organic light emitting layer 13 are n ₁₆ , n ₁₀ , n ₁₁ , n ₁₂ , and n ₁₃ , respectively. The incident angles from the organic light emitting layer 13 to the hole transport layer 12, the hole transport layer 12 to the anode 11, the anode 11 to the substrate 10, and the substrate 10 to the atmosphere 16 are respectively θ _13-12 , θ _12-11 , θ _{11−. 10} and θ _10-16, and the exit angle from the substrate 10 to the atmosphere 16 is θ ₁₆ . From the Snell's law, the following equation 1 holds.

Focusing on the relationship between the organic light emitting layer 13 and the hole transport layer 12 having a lower refractive index than the organic light emitting layer 13, the substrate 10, and the atmosphere 16, the following mathematical formulas 2 to 4 are extracted from the above mathematical formula 1.

Based on the mathematical formulas 2 to 4, the critical angles θ _c12 , θ _c10 , and θ _c16 of the hole transport layer 12, the substrate 10, and the atmosphere 16 viewed from the organic light emitting layer 13 are the following mathematical formulas 5-7. Is required.

The formula in Formula 5-7, for example, _{n 13 = 1.8, n 12 =} 1.6, n 10 = 1.52, and substituting n 16 = 1.0, the critical angle θ _c12, θ _c10, θ _c16 is 63 °, 58 °, and 34 °, respectively. Light emitted from the light emitting source 13a of the organic light emitting layer 13 at the angle or more is confined in the organic light emitting layer 13, the anode 11 or the substrate 10 and becomes loss light. Therefore, the light extraction efficiency of the organic EL element 100 is lowered.

As a method of reducing the aforementioned loss light, a refractive index n ₁₃ of the organic light emitting layer 13 is lowered, thereby it is conceivable to increase the critical angle. In Non-Patent Document 1, as the method, SiO ₂ is mixed with the organic light emitting layer 13 formed by MEH-PPV (poly [2-methoxy-5- (2′-ethyl-hexyloxy) -p-phenylene vinylene]). The technique to do is shown. Since the refractive index of SiO ₂ is 1.6 and lower than MEH-PPV, mixing the SiO ₂ particles lowers the refractive index of the organic light-emitting layer 13 and the light extraction efficiency (quantum efficiency) is 1. It is improved 45 times.

However, even if SiO ₂ particles having a refractive index of 1.6 are mixed, the refractive index of the organic light emitting layer 13 does not become lower than 1.6, and the refractive index n ₁₀ = 1.52 of the substrate 10 and the refractive index of the atmosphere 16. It remains higher than n ₁₆ = 1.0. For this reason, the organic EL element 100 still has a lot of loss light confined in the substrate 10 and the anode 11 by total reflection, and the light extraction efficiency is lowered.

  Further, an organic EL element is known in which an intermediate layer having a refractive index larger than that of the substrate and smaller than that of the anode is formed between the substrate and the anode (see, for example, Patent Document 1). This organic EL element is intended to reduce the difference in refractive index between layers and to reduce total reflection at the interface between the substrate and the anode. However, in such an organic EL element, a difference in refractive index occurs between the substrate and the intermediate layer and between the intermediate layer and the anode. Therefore, loss occurs due to Fresnel reflection at the interface, and light extraction efficiency is increased. Becomes lower.

JP 2004-134158 A

Carter, S. A. et al, “Enhanced luminance in polymer composite light emitting devices,” Applied Physics Letters, 1997, 71 (9), p.1145

  The present invention solves the above-described conventional problems, and an object thereof is to provide an organic electroluminescence element capable of improving light extraction efficiency.

  The organic electroluminescence element of the present invention has a substrate, a light-transmitting first electrode formed on the substrate, an organic layer including an organic light emitting layer, and a second electrode in this order, The refractive index of the organic light emitting layer is 1.6 or less, and the refractive index of the first electrode is larger than the refractive index of the substrate and smaller than the refractive index of the organic light emitting layer. Features.

  In this organic electroluminescence element, it is preferable that the refractive index of the first electrode gradually changes from the refractive index of the substrate to the refractive index of the organic layer as it goes from the substrate side to the organic layer side. .

  In the organic electroluminescence element, it is preferable that the first electrode includes one or both of metal nanoparticles and metal nanowires and a transmissive material that holds them.

  In this organic electroluminescence element, the organic light emitting layer preferably contains a substance having a refractive index lower than that of the light emitting material constituting the organic light emitting layer.

  In this organic electroluminescence element, the substance having a refractive index lower than that of the light emitting material is preferably porous silica.

  In this organic electroluminescence element, it is preferable that at least one of the inside and the outside of the substrate has a scattering structure.

  In this organic electroluminescence element, the reflectance of the second electrode is preferably 90% or more.

  According to the organic electroluminescence device of the present invention, the refractive index difference between the materials of the substrate, the first electrode, and the organic light emitting layer is reduced, so that loss due to Fresnel reflection at each interface is suppressed, and light extraction efficiency is reduced. Will improve. Moreover, since the refractive index of the organic light emitting layer is 1.6 or less, which is lower than the conventional one, the loss due to total reflection is reduced, and the light extraction efficiency is improved.

Sectional drawing of the organic electroluminescent element which concerns on one Embodiment of this invention. Sectional drawing of the conventional organic electroluminescent element.

  An organic EL device according to an embodiment of the present invention will be described with reference to FIG. The organic EL element 1 includes a substrate 2, a light-transmissive first electrode 3 formed on the substrate 2, an organic layer 4 including an organic light emitting layer 43, and a second electrode 5 in this order. A scattering layer 6 is provided on the opposite side of the substrate 2 from the first electrode 3. Between the first electrode 3 and the organic light emitting layer 43, a hole injection layer 41 and a hole transport layer 42 are provided as constituent layers of the organic layer 4. The hole injection layer 41 and the hole transport layer 42 may be omitted as appropriate. In addition, a hole block layer, an electron transport layer, and an electron injection layer may be appropriately provided between the organic light emitting layer 43 and the second electrode 5. The refractive index of the organic light emitting layer 43 was 1.6 or less. The refractive index of the first electrode 3 was made larger than the refractive index of the substrate 2 and smaller than the refractive index of the organic light emitting layer 43.

  When a voltage is applied between the first electrode 3 and the second electrode 5, the first electrode 3 serves as an anode to inject holes into the organic light-emitting layer 43, and the second electrode 5 serves as a cathode to the organic light-emitting layer 43 with electrons. Inject. These holes and electrons are combined in the organic light emitting layer 43. Excitons are generated by this coupling, and light is emitted when the excitons transition to the ground state. This light is extracted from the upper surface of the substrate 2 through the first electrode 3 and the substrate 2 to the outside.

  The substrate 2 is formed by forming a light transmitting material into a plate shape, and is, for example, a rigid transparent glass plate such as soda glass or non-alkali glass, or a flexible transparent plastic plate such as polycarbonate or polyethylene terephthalate.

  The first electrode 3 includes metal nanoparticles and a permeable material that holds the metal nanoparticles. The refractive index of the first electrode 3 is changed from the refractive index of the substrate 2 to the organic by changing the mixing ratio of the metal nanoparticles and the transmissive material in an inclined manner from the substrate 2 side to the organic layer 4 side. The layer 4 is configured to gradually change to the refractive index. Metal nanowires may be used instead of metal nanoparticles or in combination with metal nanoparticles.

  The first electrode 3 is formed by performing spin coating, screen printing, dip coating, die coating, casting, spray coating, gravure coating, or the like, with a permeable material containing metal nanoparticles. The transparent material is a resin that transmits light, such as acrylic resin, polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylate, polycarbonate resin, polyurethane, polyacrylonitrile, polyvinyl acetal, Polyamide, polyimide, diacryl phthalate resin, cellulose resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, other thermoplastic resins, and two or more copolymers of monomers constituting these resins Can be mentioned.

  Metal nanoparticles and metal nanowires are conductive materials such as fine particles of metals such as silver and gold, indium-tin oxide (ITO), indium-zinc oxide (IZO), tin oxide, and the like. It consists of fine particles of metal oxide, a conductive polymer, a conductive organic material, a dopant (donor or acceptor) -containing organic layer, a mixture of a conductor and a conductive organic material (including a polymer), and the like.

  The hole injection layer 41 of the organic layer 4 is formed of a low molecular weight organic compound such as copper phthalocyanine (CuPc) or a polymer material such as polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT-PSS).

  The hole transport layer 42 comprises 4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NPD), N, N′-bis (3-methylphenyl)-(1,1 ′. -Biphenyl) -4,4'-diamine (TPD), 2-TNATA, 4,4 ', 4 "-tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (MTDATA), 4, 4'-N, N'-dicarbazole biphenyl (CBP), spiro-NPD, spiro-TPD, spiro-TAD, TNB, etc. as representative examples, triarylamine compounds, amine compounds containing carbazole groups, or fluorene It is formed by an amine compound containing a derivative.

  The organic light emitting layer 43 includes a light emitting material 44 and includes a substance 45 having a refractive index lower than that of the light emitting material 44. The light emitting material 44 is an organic electroluminescence material, for example, anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzoxazoline, bisstyryl, cyclohexane. Pentadiene, quinoline metal complex, tris (8-hydroxyquinolinato) aluminum complex, tris (4-methyl-8-quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, aminoquinoline metal complex, benzo Quinoline metal complexes, tri- (p-terphenyl-4-yl) amine, pyran, quinacridone, rubrene, and derivatives thereof, or 1-aryl-2,5-di (2-thieni ) Pyrrole derivative, distyryl benzene derivatives, distyryl arylene derivatives, styrylamine derivatives, and compounds or polymers such having a group consisting of luminescent compounds in a part of the molecule. Further, not only compounds derived from fluorescent dyes typified by the above-mentioned compounds, but also so-called phosphorescent materials such as iridium (Ir) complex, osmium (Os) complex, platinum (Pt) complex, europium (Eu) complex, etc. Materials, or compounds or polymers having these in the molecule can also be suitably used. These materials are appropriately selected and used as necessary.

  Since the light-emitting material 44 is a π-conjugated bond material containing many common benzene rings in its molecular structure, the refractive index is about 1.6 to 2.0. In order to set the refractive index of the organic light emitting layer 43 to 1.6 or less, the organic light emitting layer 43 includes a substance 45 having a refractive index lower than that of the light emitting material 44 constituting the organic light emitting layer 43. The substance 45 has a refractive index lower than 1.6, and is, for example, particles made of a metal such as silica, calcium carbonate, magnesium fluoride, or a metal oxide. The substance 45 is made of acrylic resin, polyethylene, polypropylene, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylate, polycarbonate resin, polyurethane, polyamide, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, other resins, Or a low molecular compound containing fluorine.

The substance 45 having a low refractive index is preferably a porous particle that includes voids in the particles and exhibits a lower refractive index due to the voids, among the above-described particles made of the metal or metal oxide. The porous particles are, for example, silica porous particles made of porous silica. The porous silica is hollow silica, nanoporous silica, mesoporous silica or the like. The refractive index of the porous silica can be obtained by the following formula from the porosity [%].
[Equation 8]
(Refractive index of silica) × (1−porosity / 100) + porosity / 100

  For this reason, in order to make the refractive index of porous silica low, the one where the porosity is high is preferable.

  Since the layer thickness of the organic light emitting layer 43 is generally several tens nm to several hundreds nm, the substance 45 having a low refractive index is preferably a fine particle having a particle diameter of 10 nm to 100 nm.

The second electrode 5 is a light reflective electrode that reflects light from the organic light emitting layer 43 toward the substrate 2. The reflectance of the second electrode 5 is preferably 90% or more. The electrode material of the second electrode 5 is, for example, a metal such as Al or Ag. From the Fresnel equation, the reflectance of Al at a wavelength of 650 nm is 80 to 82% and the reflectance of Ag is 96 to 97%. In order to make the reflectance 90% or more, Ag is preferable. The second electrode 5 may be configured as a laminated structure or the like by combining these metals and other electrode materials. Such a combination of electrode materials includes a laminate of an alkali metal and Al or Ag, a laminate of an alkali metal halide and Al or Ag, a laminate of an alkaline earth metal or rare earth metal and Al or Ag, Alloys of these metal species and other metals, specifically, for example, a laminate of sodium, sodium-potassium alloy, lithium, magnesium, barium, etc. and Al, a laminate of calcium and Ag, Examples thereof include a magnesium-silver mixture, a magnesium-indium mixture, an aluminum-lithium alloy, a LiF / Al mixture / laminated body, and an Al / Al ₂ O ₃ mixture.

  The scattering layer 6 is a scattering structure that scatters light, and a light extraction film having micro-order unevenness on the surface is in contact with the surface opposite to the surface on which the first electrode 3 of the substrate 2 is formed, that is, the atmosphere. It is formed by sticking to the surface. The uneven shape may be any shape that scatters light. For example, the cross-sectional shape is a hemisphere, a trapezoid, a triangle, or the like. Light extraction film materials are acrylic resin, polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylate, polycarbonate resin, polyurethane, polyacrylonitrile, polyvinyl acetal, polyamide, polyimide, diacrylphthalate resin Cellulose resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, and other resins. The scattering structure may be formed inside the substrate 2 by imprinting or the like.

  Four types of organic EL elements 1 as examples of the present invention and two types of organic EL elements as comparative examples were prepared.

  As the substrate 2, alkali-free glass (Corning "No. 1737") was used. The refractive index of the substrate 2 at a wavelength of 500 nm is 1.50 to 1.53 (≈1.50). Polyethylenedioxythiophene / polystyrene sulfonic acid (PEDOT-PSS) (“CLEVIOS (registered trademark) PH1000” manufactured by HC Starck, PEDOT: PSS = 1: 2.5) on the substrate 2 with a film thickness of about After applying with a spin coater to 300 nm, the first electrode 3 was obtained by heat treatment for 15 minutes on a hot plate in the atmosphere at 120 ° C. The refractive index of the first electrode 3 at a wavelength of 650 nm was 1.52 as measured by an optical thin film measurement system (“FilmTek” manufactured by SCI).

  Next, PEDOT-PSS (“CLEVIOS P AI4083” manufactured by HC Starck, PEDOT: PSS = 1: 6) is applied on the first electrode 3 with a spin coater so as to have a film thickness of about 30 nm. A hole injection layer 41 was obtained by baking at 10 ° C. for 10 minutes. The measured value of the refractive index of the hole injection layer 41 at a wavelength of 650 nm was 1.55.

  Next, TFB (Poly [(9,9-dioctylfluorenyl-2,7-diyl) -co- (4,4 '-(N- (4-sec-butylphenyl)) diphenylamine)]) (manufactured by American Dice Source) A solution in which “Hole Transport Polymer ADS259BE”) was dissolved in a THF solvent was applied onto the hole injection layer 41 with a spin coater so as to have a film thickness of 12 nm to prepare a TFB coating. This TFB film was baked at 200 ° C. for 10 minutes to obtain a hole transport layer 42. The measured value of the refractive index of the hole transport layer 42 at a wavelength of 650 nm was 1.7.

  Next, a red polymer ("Light Emitting polymer ADS111RE" manufactured by American Dye Source Co., Ltd.) and isopropanol-dispersed porous hollow silica fine particles ("Culture" CS60-IPA manufactured by Catalyst Kasei Kogyo), solid content 20% by mass A solution obtained by dissolving an average primary particle diameter of 60 nm and an outer shell thickness of about 10 nm in a THF solvent at a weight ratio of 4: 1 is applied on the hole transport layer 42 by a spin coater so that the film thickness becomes 70 nm. The organic light emitting layer 43 was obtained by baking at a temperature of 10 minutes. The measured value of the refractive index of the organic light emitting layer 43 at a wavelength of 650 nm was 1.60.

  Further, Ba (barium) (manufactured by High-Purity Chemical) was formed as an electron injection layer on the organic light emitting layer 43 to a thickness of 5 nm. Finally, Al (made by high-purity chemical) was vacuum-deposited to a thickness of 80 nm on the electron injection layer to form the second electrode 5.

  The board | substrate 2 in which each said layer was formed was put into the glove box of a dry nitrogen atmosphere with a dew point of -80 degrees C or less, and was conveyed, without exposing to air | atmosphere. On the other hand, a water absorbing agent (manufactured by Dynic) was attached to a glass sealing cap, and an ultraviolet curable resin sealing agent was applied to the outer periphery of the sealing cap in advance. Then, in the glove box, the sealing cap is bonded to the substrate 2 with a sealing agent so as to surround each layer, and the sealing agent is cured by irradiating with ultraviolet rays, whereby each layer is sealed with the sealing cap, and the organic EL element 1 Got.

  An organic EL element 1 was obtained in the same manner as in Example 1 except for the first electrode 3. For the first electrode 3, the mixing ratio of CLEVIOS (registered trademark) PH1000 and ITO nanoparticles having a particle diameter of about 40 nm (“NanoTek” (registered trademark) ITCW 15 wt% -G30 manufactured by CI Kasei) was set to 1: 0, 1: 0. 4, 1: 0.8, 1: 1.3, ITO: PEDOT / PSS aqueous solution dispersed with a solvent was applied onto the substrate 2 in order from a solution having a low concentration of ITO nanoparticles by spin coating. A pattern formation layer was formed so as to have a film thickness of 75 nm and heated on a hot plate in the atmosphere at 120 ° C. to obtain the first electrode 3. When the refractive index of the thin film in the first electrode 3 at a wavelength of 650 nm was measured by an optical thin film measurement system (“FilmTek” manufactured by SCI), 1.52, 1.54, 1.56 and 1.58.

  After sealing the substrate 2 on which each layer is formed, a light scattering sheet (“light up 100SXE” manufactured by Kimoto Co., Ltd.) is formed as a scattering layer 6 on the surface opposite to the surface on which the first electrode 3 of the substrate 2 is formed. Was pasted. Other than that was carried out similarly to Example 2, and obtained the organic EL element 1. FIG.

  On the organic light emitting layer 43, Ca (made by high-purity chemical) was formed as an electron injection layer with a film thickness of 5 nm. Then, Ag (manufactured by high-purity chemical) was vacuum-deposited with a film thickness of 80 nm on the electron injection layer to form the second electrode 5. Other than that was carried out similarly to Example 3, and obtained the organic EL element 1. FIG.

(Comparative Example 1)
An ITO film was sputtered directly on the surface of the substrate to form a first electrode. Then, a hole injection layer and a hole transport layer were formed directly on the first electrode in the same manner as in Example 1, and a red polymer (“Light Emittingpolymer ADS111RE” manufactured by American Dice Source) was dissolved in a THF solvent. The solution was applied on the hole transport layer with a spin coater so as to have a film thickness of 70 nm, and baked at 100 ° C. for 10 minutes to form an organic light emitting layer. When the refractive index at a wavelength of 650 nm was measured, the first electrode was 1.9 and the organic light emitting layer was 1.7. Furthermore, the 2nd electrode was formed and each layer was sealed with the sealing cap, and the organic EL element was obtained.

(Comparative Example 2)
An organic EL device was obtained in the same manner as in Example 1 except that the ITO film was directly sputtered on the surface of the substrate to form the first electrode.

(Evaluation test)
The test which evaluates light extraction efficiency was done about the organic EL element 1 of Examples 1-3 and Comparative Examples 1 and 2 which were produced as mentioned above. The results of the evaluation test are shown in Table 1 below.

  The refractive index of the organic light emitting layer 43 is 1.60 or less (≈1.60), the refractive index of the first electrode 3 is larger than the refractive index of the substrate 2 (≈1.50), and the organic light emitting layer 43 The organic EL elements 1 of Examples 1 to 4 having a value smaller than the refractive index are lighter than those of Comparative Examples 1 and 2 in which the first electrode is a conventional ITO (refractive index≈1.9). It was confirmed that the extraction efficiency was improved.

  Thus, according to Examples 1 to 4, that is, according to the organic EL element 1 of the present invention, the difference in refractive index among the materials of the substrate 2, the first electrode 3, and the organic light emitting layer 43 is reduced. Loss due to Fresnel reflection at the interface is suppressed, and light extraction efficiency is improved. Moreover, since the refractive index of the organic light emitting layer 43 is 1.6 or less, which is lower than the conventional one, the loss due to total reflection is reduced and the light extraction efficiency is improved.

  Since the organic light emitting layer 43 includes the substance 45 having a refractive index lower than that of the light emitting material 44, the refractive index of the organic light emitting layer 43 can be 1.6 or less. Further, by using the porous silica particles as the material 45 having a low refractive index, since the porous silica has a low refractive index, the refractive index of the organic light emitting layer 43 can be lowered, and the light extraction efficiency of the organic EL element 1 can be reduced. Will improve.

  As the refractive index of the first electrode 3 moves from the substrate 2 side to the organic layer 4 side, the refractive index of the substrate 2 gradually changes from the refractive index of the organic layer 4 (refractive index≈1.52 to 1.52). 1.58) The organic EL elements 1 of Examples 2 to 4 have improved light extraction efficiency as compared with Example 1 in which the refractive index of the first electrode 3 is constant (refractive index≈1.52). It was confirmed.

  As described above, according to the organic EL element 1 in which the refractive index of the first electrode 3 is gradually and gradually changed, the refractive index difference between the substrate 2 and the first electrode 3, and between the first electrode 3 and the organic layer 4. Since the difference in refractive index is reduced and loss due to Fresnel reflection at each interface is suppressed, the light extraction efficiency is improved.

  It was confirmed that the organic EL elements 1 of Examples 3 and 4 having the scattering layer 6 as the scattering structure have improved light extraction efficiency as compared with Example 2 having no scattering layer.

  Thus, according to the organic EL element 1 having the scattering layer 6 as the scattering structure, the total reflection caused by the refractive index step between the substrate 2 and the outside (atmosphere) is reduced, so that the light extraction efficiency is improved.

  In Example 4 in which the second electrode 5 is formed of Ag (reflectance of 90% or more), the light extraction efficiency is improved compared to Example 3 in which the second electrode 5 is formed of Al (with a reflectance of less than 90%). It was confirmed that

  As described above, according to the organic EL element 1 in which the reflectance of the second electrode 5 is 90%, light traveling in the direction of the second electrode 5 in the element is easily reflected in the direction of the substrate 2. Will improve.

  In addition, this invention is not restricted to the structure of said embodiment, A various deformation | transformation is possible in the range which does not change the summary of invention. For example, in the organic EL element 1, the first electrode 3 may be a cathode and the second electrode 5 may be an anode.

1 Organic electroluminescence device (organic EL device)
2 Substrate 3 First electrode 4 Organic layer 43 Organic light emitting layer 44 Light emitting material (organic electroluminescence material)
45 Low refractive index material (porous silica)
5 Second electrode 6 Scattering layer (scattering structure)

Claims (7)

In the organic electroluminescence device having a substrate, a light-transmitting first electrode formed on the substrate, an organic layer including an organic light emitting layer, and a second electrode in this order,
The organic light emitting layer has a refractive index of 1.6 or less,
An organic electroluminescence element, wherein a refractive index of the first electrode is larger than a refractive index of the substrate and smaller than a refractive index of the organic light emitting layer.   The refractive index of the first electrode gradually changes from the refractive index of the substrate to the refractive index of the organic layer as it goes from the substrate side to the organic layer side. Organic electroluminescence element.   The organic electroluminescence device according to claim 2, wherein the first electrode includes one or both of metal nanoparticles and metal nanowires, and a transmissive material that holds these.   The organic electroluminescent device according to claim 1, wherein the organic light emitting layer contains a substance having a refractive index lower than that of the light emitting material constituting the organic light emitting layer.   The organic electroluminescence device according to claim 4, wherein the substance having a refractive index lower than that of the light emitting material is porous silica.   The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device has a scattering structure in at least one of the inside and the outside of the substrate.   The organic electroluminescence device according to claim 1, wherein the reflectance of the second electrode is 90% or more.

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