JP2014086345A - Electroluminescence element and luminaire using electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescence element in which angular dependence and wavelength dependence of emission intensity distribution can be reduced while reducing plasmon loss, and to provide a luminaire using the electroluminescence element.SOLUTION: An electroluminescence element 1A comprises: a transparent electrode layer 11 composing a first transparent electrode; a first transparent thin film metal layer 13 composing a second transparent electrode; an electroluminescent layer 12 sandwiched between the transparent electrode layer 11 and the first transparent thin film metal layer 13; a first transparent dielectric layer 14 provided on the first transparent thin film metal layer 13 on the reverse side of the electroluminescent layer 12; a second transparent thin film metal layer 15 provided on the first transparent dielectric layer 14 on the reverse side of the first transparent thin film metal layer 13; a second transparent dielectric layer 16 provided on the second transparent thin film metal layer 15 on the reverse side of the first transparent dielectric layer 14; and a light reflection layer 30 provided on the second transparent dielectric layer 16 on the reverse side of the second transparent thin film metal layer 15.

Description

  The present invention relates to an electroluminescent element and an illumination device using the electroluminescent element.

  2. Description of the Related Art In recent years, surface light sources with high luminous efficiency using electroluminescent elements such as light emitting diodes (LEDs), organic EL (Electro-Luminescence), and inorganic ELs have attracted attention. The electroluminescent element is composed of an electroluminescent layer sandwiched between a planar cathode and an anode. In general, the anode is often a transparent electrode, and the cathode is often a metal light reflecting electrode. When one of them is composed of a metal light reflecting electrode, light is extracted from the anode side of the transparent electrode and used as a single-sided light emitting device.

  At that time, the plasmon loss generated in the light reflecting electrode made of metal becomes a large light extraction efficiency loss factor. Plasmon loss is a phenomenon in which energy is deactivated when emitted light excites surface plasmons on a metal surface.

  On the other hand, a semitransparent electrode is used as a cathode to improve the front luminance, a buffer layer is provided on the semitransparent electrode, and a metal reflective layer is provided on the buffer layer. A light emitting element is disclosed in Japanese Patent Application Laid-Open No. 2005-71919 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-272855 (Patent Document 2).

JP-A-2005-71919 JP 2003-272855 A

  In the electroluminescent elements disclosed in Patent Document 1 and Patent Document 2, since the distance between the electroluminescent layer and the metal reflective layer can be increased, it has an effect of reducing plasmon loss.

  However, when the electroluminescent element having the above structure is applied to, for example, white illumination, particularly when a white organic EL element is applied to the electroluminescent element, a strong angle dependency of emission intensity occurs. In illumination applications, it is necessary to eliminate the angular dependence and wavelength dependence of the emission intensity.

  The present invention has been made in view of the above problems, and provides an electroluminescent element and an electroluminescent element thereof capable of reducing the angle dependence and wavelength dependence of the emission intensity distribution while reducing plasmon loss. It aims at providing the used illuminating device.

  In the electroluminescent element based on this invention, the transparent electrode layer which comprises a 1st transparent electrode, the 1st transparent thin film metal layer which comprises a 2nd transparent electrode, the said transparent electrode layer, and the said 1st transparent thin film metal layer An electroluminescent layer sandwiched between, a first transparent dielectric layer provided on the opposite side of the first transparent thin film metal layer from the side on which the electroluminescent layer is provided, and the first transparent dielectric layer. A second transparent thin film metal layer provided on the opposite side to the side on which the first transparent thin film metal layer is provided, and a side opposite to the side on which the first transparent dielectric layer is provided of the second transparent thin film metal layer. And a light reflecting layer provided on the opposite side of the second transparent dielectric layer from the side on which the second transparent thin film metal layer is provided.

  In another embodiment, the optical film thickness of the first transparent dielectric layer and the optical film thickness of the second transparent dielectric layer are not more than one quarter of the peak wavelength of the emission wavelength of the electroluminescent layer. .

  In another embodiment, the refractive index of the first transparent dielectric layer is higher than the refractive index of the electroluminescent layer.

  In the illuminating device based on this invention, it has an electroluminescent element in any one of the above-mentioned.

  According to the present invention, it is possible to provide an electroluminescent element and an illuminating device using the electroluminescent element that can reduce the angle dependency and the wavelength dependency of the emission intensity distribution while reducing the plasmon loss. Make it possible.

3 is a plan view of the electroluminescent element in the first embodiment. FIG. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 showing the minimum configuration for realizing the electroluminescent element in the first embodiment. FIG. 6 is a cross-sectional view showing the structure of an organic EL electroluminescence element in Embodiment 2. FIG. 6 is a cross-sectional view showing a specific configuration of an organic EL electroluminescent element in Embodiment 3. 5 is a cross-sectional view showing a specific configuration of an organic EL electroluminescent element in Comparative Example 1. FIG. It is a figure which shows the result of having calculated the reflectance of wavelength 520nm about the organic electroluminescent electroluminescent element in Embodiment 3. FIG. It is a figure which shows the result of having calculated the reflectance of wavelength 520nm about the organic electroluminescent electroluminescent element in the comparative example 1. FIG. FIG. 6 is a cross-sectional view showing a specific configuration of an organic EL electroluminescent element in a fourth embodiment. 6 is a cross-sectional view showing a specific configuration of an organic EL electroluminescent element in Comparative Example 2. FIG. It is a figure which shows the result of having calculated the reflectance of wavelength 520nm about the organic electroluminescent electroluminescent element in Embodiment 4. FIG. It is a figure which shows the result of having calculated the reflectance of wavelength 520nm about the organic electroluminescent electroluminescent element in the comparative example 2. FIG. It is a figure which shows the reflectance (0 degree reflection) which looked at the light reflection layer from the electroluminescent layer in each organic EL electroluminescent element in Embodiment 3, Embodiment 4, Comparative Example 1, and Comparative Example 2. FIG. FIG. 10 is a cross-sectional view showing a specific configuration of an organic EL electroluminescent element in a fifth embodiment. It is a figure which shows schematic structure of the white illuminating device in Embodiment 6. FIG. It is a figure which shows schematic structure of the white illuminating device in Embodiment 7. FIG.

  An electroluminescent element and an illumination device using the electroluminescent element in each embodiment based on the present invention will be described below with reference to the drawings. In each embodiment described below, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. The same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated. In addition, it is planned from the beginning to use the structures in the embodiments in appropriate combinations.

(Embodiment 1)
With reference to FIG. 1 and FIG. 2, the electroluminescent element 1 in Embodiment 1 is demonstrated. FIG. 1 is a plan view of the electroluminescent element 1 in the present embodiment, and FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1, showing the minimum configuration for realizing the electroluminescent element 1 in the present embodiment. FIG. In addition, sectional drawing in each embodiment shown below is a cross section equivalent to the II-II arrow line in FIG.

  The electroluminescent element 1 according to the present embodiment includes a substrate 10, a transparent electrode layer 11 constituting a first transparent electrode provided on one surface side of the substrate 10, and a first transparent thin film metal layer constituting a second transparent electrode. 13, the electroluminescent layer 12 sandwiched between the transparent electrode layer 11 and the first transparent thin film metal layer 13, and the first transparent thin film metal layer 13 provided on the side opposite to the side where the electroluminescent layer 12 is provided. A first transparent dielectric layer 14, a second transparent thin film metal layer 15 provided on the opposite side of the first transparent dielectric layer 14 from the side on which the first transparent thin film metal layer 13 is provided, and a second transparent thin film metal layer 15 The second transparent dielectric layer 16 provided on the side opposite to the side on which the first transparent dielectric layer 14 is provided, and the side of the second transparent dielectric layer 16 on which the second transparent thin film metal layer 15 is provided are opposite to each other. And a light reflection layer 30 provided on the side.

  In the electroluminescent device 1 having the above-described configuration, the first transparent thin film metal layer 13 and the first transparent dielectric layer 14 constitute a first buffer layer, and the second transparent thin film metal layer 15 and the second transparent dielectric layer 16. Constitutes the second buffer layer.

  As described above, in the electroluminescent element 1, the electroluminescent layer 12 is sandwiched between the transparent electrode layer 11 (first transparent electrode) and the first transparent thin film metal layer 13 (second transparent electrode). For example, as shown in FIG. 2, a configuration in which the transparent electrode layer 11 is an anode and the first transparent thin film metal layer 13 is a cathode is conceivable. Conversely, a configuration in which the transparent electrode layer 11 is a cathode and the first transparent thin film metal layer 13 is an anode is also possible. In the following description, the transparent electrode layer 11 is used as an anode, and the first transparent thin film metal layer 13 is used as a cathode.

  By applying a voltage between the transparent electrode layer 11 and the first transparent thin film metal layer 13, electrons are accelerated and injected into the electroluminescent layer 12, and the kinetic energy of the electrons is converted into photons in the electroluminescent layer 12. Thus, light is extracted to the transparent electrodes of both the transparent electrode layer 11 and the first transparent thin film metal layer 13.

  Generally, in order to facilitate electron injection, different materials are used for the transparent electrode layer 11 (first transparent electrode) and the first transparent thin film metal layer 13 (second transparent electrode). For example, a thin film metal electrode (Ag, Al, Au, Cu, etc.) having a work function suitable for electron injection is used on the cathode side, and a transparent oxide semiconductor electrode having a work function suitable for hole injection on the anode side ( ITO (mixture of indium oxide and tin oxide), IZO (mixture of indium oxide and zinc oxide), etc.) are used.

  A thin film metal electrode is excellent in electron transport properties, but since it has a low optical transmittance, when it is used as a transparent electrode, a film thickness of several nm to several tens of nm is suitable for increasing the transmittance. In addition, a transparent electrode using a transparent oxide semiconductor is characterized by a large sheet resistance per thickness and a high transmittance compared to a thin film metal electrode. Therefore, when a transparent oxide semiconductor is used as a transparent electrode, the sheet resistance is lowered. Therefore, the film thickness of 100 nm to 200 nm is suitable.

  When the same kind of transparent electrode is used for the transparent electrode layer 11 (first transparent electrode) and the first transparent thin-film metal layer 13 (second transparent electrode), the electron injection performance is reduced and the driving voltage is increased, resulting in luminous efficiency. Is undesirable. Therefore, different materials are used for the transparent electrode layer 11 (first transparent electrode) and the first transparent thin film metal layer 13 (second transparent electrode), and one electrode has improved electron injection property, while the other electrode It is desirable to improve the hole injection property.

  The first transparent thin film metal layer 13 and the second transparent thin film metal layer 15 are light-transmitting thin films made of a thin film metal. How thin the light can be transmitted can be expressed using the imaginary part of the refractive index. When the refractive index n and the extinction coefficient κ are used, the phase change φ and the transmittance T that occur when passing through a medium having a film thickness d (nm) are expressed by the following (Equation 1).

Here, λ is the wavelength of light in vacuum. From Expression (1), the distance Ld at which the light intensity attenuates to e ^1/2 is expressed as shown in the following (Expression 2).

  The first transparent thin film metal layer 13 is desirably thinner than Ld represented by the formula (2) in order to have sufficient transmittance.

The first transparent dielectric layer 14 and the second transparent dielectric layer 16 are layers made of a dielectric. The definition of the dielectric will be described below. Whether the object is a metal that contains many free electrons and does not transmit much light, or a dielectric that contains few free electrons and transmits light, can be examined using the complex relative permittivity. The complex relative dielectric constant ε _c is an optical constant related to interface reflection, and is a physical quantity expressed as in the following (formula 3) using the refractive index n and the extinction coefficient κ.

Here, P is polarization, E is an electric field, ε ₀ is a dielectric constant in vacuum, and i is an imaginary unit. From (Equation 3), it can be seen that the smaller the refractive index n and the larger the extinction coefficient κ, the smaller the real part of the complex relative dielectric constant. This shows the effect that the phase of the polarization response is shifted by the vibration of the electrons with respect to the vibration of the electric field.

  When the real part of the complex relative dielectric constant represented by (Equation 3) becomes negative, it means that the electric field oscillation and the polarization response are reversed, and this is a characteristic of the metal. Conversely, when the real part of the complex relative permittivity is positive, the direction of the electric field and the direction of the polarization response coincide with each other, indicating a polarization response as a dielectric. In summary, a medium having a negative real part of the complex relative dielectric constant is a metal, and a substance having a positive real part of the complex relative dielectric constant is a dielectric.

  In general, the smaller the refractive index n and the larger the extinction coefficient κ, the more the material vibrates. A material having a high electron transporting property tends to have a small refractive index n and a large extinction coefficient κ. In particular, in the metal electrode, the refractive index n is about 0.1, whereas the extinction coefficient κ has a large value of 2 to 10, and the rate of change with respect to the wavelength is large. Therefore, even when the refractive index n is the same between two different metal electrodes, if the extinction coefficient κ is greatly different, there will be a large difference in electron transport performance between the two different metal electrodes. .

Next, the desirable film thickness of the first buffer layer will be described. From (Equation 1), the thickness of the first transparent dielectric layer 14 d (nm), when the refractive index was n _d, between the first transparent thin metal layer 13 and the second transparent thin metal layer 15 The phase change of the light reciprocated in (1) is expressed by the following (formula 4) including the phase change of reflection.

  Since this is less likely to cause interference if this is 2π or less, (Equation 5) is a desirable film thickness of the first transparent dielectric layer 14. That is, the film thickness (optical film thickness) of the first transparent dielectric layer 14 is preferably equal to or less than ¼ of the peak wavelength of the emission wavelength of the electroluminescent layer 12. The same applies to the thickness of the second transparent dielectric layer 16 in the second buffer layer.

  For example, when a light emitting wavelength of the electroluminescent layer 12 is 550 nm and a transparent dielectric layer having a refractive index n = 1.7 is used, the film thickness is desirably 80 nm or less.

(Embodiment 2)
Next, the electroluminescent element in this embodiment will be described using a more specific example. As a specific configuration, the present embodiment will be described using an organic electroluminescent element (organic EL) that emits light in a visible light region (wavelength 400 nm to 800 nm). Note that this embodiment is not limited to an organic EL that emits visible light, and is common to all electroluminescent elements in which an electroluminescent layer is sandwiched between transparent electrodes. For example, an inorganic electroluminescent element or an element that emits infrared light It may be.

  FIG. 3 shows an organic EL electroluminescent element 1A according to the second embodiment. FIG. 3 is a cross-sectional view showing the structure of the organic EL electroluminescent element 1A in the present embodiment. In the organic EL electroluminescent element 1A in the present embodiment, a configuration in which a metal thin film having a good electron injection property is used as the first transparent thin film metal layer 13 and a transparent oxide semiconductor having a good hole injection property is used as the transparent electrode layer 11 is considered. . Examples of the transparent oxide semiconductor include (ITO (mixture of indium oxide and tin oxide), IZO (mixture of indium oxide and zinc oxide), ZnO, and InGaO3). The transparent electrode layer 11 is provided on the substrate 10.

  In this case, the transparent electrode layer 11 as the first transparent electrode is the anode, and the first transparent thin film metal layer 13 as the second transparent electrode is the cathode. As the electroluminescent layer 12A sandwiched between the transparent electrode layer 11 (first transparent electrode) and the first transparent thin film metal layer 13 (second transparent electrode), any fluorescent material and phosphorescent material known as organic EL materials are used. be able to.

  If necessary, a hole transport layer may be provided on the anode side of the electroluminescent layer 12A, or an electron transport layer may be provided on the cathode side of the electroluminescent layer. As the material for the electroluminescent layer 12A, it is preferable to use an organometallic complex as the material for the organic EL element from the viewpoint of preferably obtaining the effect of improving the external quantum efficiency of the element and extending the light emission lifetime.

  Further, the metal involved in complex formation is preferably any one metal belonging to Groups 8 to 10 of the periodic table, Al or Zn, and in particular, the metal is Ir, Pt, Al or Zn. Is preferred.

  A first transparent dielectric layer 14 is provided on the opposite side of the first transparent thin film metal layer 13 (second transparent electrode) from the electroluminescent layer 12A. The first transparent thin film metal layer 13 and the first transparent dielectric layer 14 form a first buffer layer. Similarly, a second transparent thin-film metal layer 15 is provided on the opposite side of the first transparent dielectric layer 14 from the first transparent thin-film metal layer 13 (outside as viewed from the electroluminescent layer 12A). A second transparent dielectric layer 16 is provided on the opposite side of the thin metal layer 15 from the first transparent dielectric layer 14. The second transparent thin film metal layer 15 and the second transparent dielectric layer 16 form a second buffer layer. Further, a light reflecting layer 30 is provided on the opposite side of the second transparent dielectric layer 16 from the second transparent thin film metal layer 15.

  Hereinafter, with reference to FIG. 4, the desirable material of each layer of the organic EL electroluminescent element 1A will be described. FIG. 4 is a cross-sectional view showing a material configuration of the organic EL electroluminescent element 1A. Particularly in the present embodiment, the refractive index n and the extinction coefficient κ of each layer are important. The substrate (resin substrate) 10 uses a material having a refractive index n of 1.5.

  As the transparent electrode layer 11, in addition to the above-described transparent oxide semiconductor, a conductive resin that can be formed at a low cost using a coating method may be used for the transparent electrode. As the conductive resin material used as the electron transporting electrode, a fullerene derivative such as a perylene derivative or PCBM (phenyl C61 butyric acid methyl ester) can be considered.

  For example, in the case of PCBM, the optical constant of visible light is (refractive index n = 2.2, extinction coefficient κ = 0.25), and the electrode reflectance viewed from the electroluminescent layer 12A is a refractive index of 1.5. Higher than resin. The conductive resin material used as the hole transporting electrode is PEDOT (Poly (3,4-ethylenedioxythiophene)) / PSS (Poly (4-styrenesulfonate)), P3HT (Poly (3-hexylthiphene)), P3OT (Poly ( 3-octylthiophene), P3DDT ((Poly (3-dodecylthiophene-2,5-Diyl)))), F8T2 (a copolymer of fluorene and bithiophene) and the like.

  For example, in the case of PEDOT / PSS, the optical constant of visible light is (refractive index n = 1.5, extinction coefficient κ = 0.01), and the electrode reflectance viewed from the electroluminescent layer 12A is the refractive index of 1. It becomes a value equivalent to the resin of 5, and the reflectance is lower than PCBM.

  Furthermore, in order to increase the electrical conductivity of the transparent electrode layer 11, a metal mesh, a metal nanowire, a metal nanoparticle, or the like may be used in combination. In this case, since the electron conductivity of the electrode using the metal nanowire is increased, the average refractive index tends to be low, and the reflectance viewed from the electroluminescent layer 12A tends to be high.

  As the material of the first transparent thin film metal layer 13 and the second transparent thin film metal layer 15, a metal material having a certain reflectance is suitable. For example, aluminum (Al) and silver (Ag) are desirable. In another example, gold (Au) which has an advantage that is not easily oxidized can be considered. Another material is copper (Cu), which is characterized by good conductivity.

  In addition, platinum, rhodium, palladium, ruthenium, iridium, osmium, and the like are listed as materials that have good thermal and chemical properties and are not easily oxidized even at high temperatures and do not cause chemical reaction with the substrate material. An alloy using a plurality of metal materials may be used. In particular, MgAg and LiAl are often used as thin film transparent metal electrodes.

  As materials for the first transparent dielectric layer 14 and the second transparent dielectric layer 16, it is preferable to use the transparent oxide semiconductors and conductive resins exemplified as the material for the transparent electrode layer. When the transparent oxide semiconductor exemplified as the material of the transparent electrode layer or a conductive resin is used for the transparent dielectric layer, the transparent thin film metal layer and the transparent dielectric layer function as a transparent electrode. There is an advantage that the surface resistance can be reduced and the in-plane luminance variation can be reduced.

In addition, a general dielectric material can be used as the material of the first transparent dielectric layer 14 and the second transparent dielectric layer 16. Examples of materials include TiO ₂ (refractive index n = 2.5), SiOx (refractive index n = 1.4 to 3.5), and the like. Examples of other dielectric materials include diamond, calcium fluoride (CaF), silicon nitride (Si ₃ N ₄ ), and the like. Moreover, as a glass material which can be used as a transparent member, a commercially available one having a refractive index of 1.4 to 1.8 is known.

Examples of the resin material include vinyl chloride, acrylic, polyethylene, polypropylene, polystyrene, ABS, nylon, polycarbonate, polyethylene terephthalate, polyvinylidene fluoride, Teflon (registered trademark), polyimide, phenol resin, and the refractive index is 1.4 to There is 1.8. There is also a technique for controlling the refractive index to be increased or decreased by mixing nanoparticles or the like, and the refractive index can be made close to 1 in a plastic material mixed with hollow nanosilica. It is also possible to realize a refractive index close to 2 by mixing particles of a high refractive index material such as TiO ₂ with a resin.

  Other methods for controlling the refractive index of the transparent member include a method using a photonic crystal provided with a dielectric periodic structure or a plasmonic crystal having a fine metal structure. The transparent member may be an inert gas such as nitrogen, a fluid, or a gel.

  As the material of the light reflecting layer 30, the metal materials exemplified as the materials of the first transparent thin film metal layer 13 and the second transparent thin film metal layer 15 can be used. In addition, the dielectric multilayer film mirror and the photonic crystal are reflected light. It may be used as a layer. When a dielectric multilayer mirror or a photonic crystal is used as the light reflecting layer, there is an advantage that plasmon loss in the light reflecting layer can be completely eliminated.

(Embodiment 3)
Below, with reference to FIG. 4 and FIG. 5, the electroluminescent element in this Embodiment is demonstrated, contrasting with the structure in a comparative example. 4 is a cross-sectional view showing a specific configuration of the organic EL electroluminescent element 1A in Embodiment 3, and FIG. 5 is a cross-sectional view showing a specific configuration of the organic EL electroluminescent element 100 in Comparative Example 1. As shown in FIG.

  When an organic material is used as the electroluminescent layer 12A, it typically has a refractive index between 1.6 and 1.8 in the visible light region. When using Alq3 (film thickness 50 nm) that emits light at a central wavelength of 520 nm and a hole transport layer (α-NPD, film thickness 50 nm) as the material of the electroluminescent layer 12A, the average of the electroluminescent layer 12A at a wavelength of 520 nm The refractive index is 1.8. Alq3 is tris (8-quinolinolato) aluminum, and α-NPD is 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl.

  Examples of materials and refractive indexes used for each member will be described at a wavelength of 520 nm. A resin film (acrylic resin) having a refractive index of 1.5 is used as the resin substrate 10. As the transparent electrode layer 11, ITO (refractive index n = 1.8, extinction coefficient κ = 0.007), which is a transparent oxide semiconductor electrode, is used. Ag (refractive index n = 0.13, extinction coefficient κ = 3.1) is used as the first transparent thin film metal layer 13 and the second transparent thin film metal layer 15.

As a specific film forming procedure, a resin substrate 10 having a refractive index of 1.5 is prepared, and an ITO thin film having a thickness of 100 nm is laminated on the resin substrate 10 as a transparent electrode layer 11. On the transparent electrode layer 11, laminated with α-NPD (50nm) as the electroluminescent layer 12A and the _Alq 3 (50 nm) in this order.

α-NPD is laminated between the transparent electrode layer 11 and Alq ₃ as a hole transport layer, and the first transparent thin film metal layer 13 is laminated on the Alq ₃ . Next, a thin Ag electrode (film thickness t1 = 15 nm) is laminated as the first transparent thin film metal layer 13, and then a conductive resin (refractive index 1.7, film thickness t2 =) is formed as the first transparent dielectric layer 14. 35 nm).

  Further, a thin Ag electrode (film thickness t3 = 20 nm) is laminated as the second transparent thin film metal layer 15 on the first transparent dielectric layer 14, and the second transparent thin film metal layer 15 is covered with the second transparent thin film metal layer 15. As the dielectric layer 16, a conductive resin (refractive index n = 1.7, film thickness t4 = 75 nm) is laminated. Next, Ag (film thickness t10 = 100 nm) as the light reflecting layer 30 is laminated on the second transparent dielectric layer 16. Thereby, the organic EL electroluminescent element 1A in the present embodiment is completed.

  The configuration of the organic EL electroluminescent element 1A shown in FIG. 4 satisfies the condition of (Formula 5). What is important when the light emitted from the electroluminescent layer 12A goes out is the reflectance on the light reflecting layer 30 side viewed from the electroluminescent layer 12A. FIG. 5 shows an organic EL electroluminescence device 100 employing a configuration that does not employ the structure of the present invention. In the organic EL electroluminescent element 100 of Comparative Example 1 shown in FIG. 5, the second transparent thin film metal layer 15 is not provided, and the transparent dielectric layer 20 is provided between the first transparent thin film metal layer 13 and the light reflecting layer 30. As a conductive resin (refractive index 1.7, film thickness t20 (= t2 + t4) = 110 nm) is provided. Other configurations are the same as those of the organic EL electroluminescent element 1A.

  FIG. 6 and FIG. 7 show the results of calculating the reflectance at a wavelength of 520 nm for the organic EL electroluminescent element 1A in the present embodiment shown in FIG. 4 and the organic EL electroluminescent element 100 in Comparative Example 1 shown in FIG. Show. FIG. 6 is a diagram showing the results of calculating the reflectance at a wavelength of 520 nm for the organic EL electroluminescent element 1A in the present embodiment, and FIG. 7 shows the wavelength for the organic EL electroluminescent element 100 in Comparative Example 1 at a wavelength of 520 nm. It is a figure which shows the result of having calculated the reflectance.

  6 and 7, TE (Transverse Electric Wave) indicates the case of S wave, and the case where the electric field vibration of light is parallel to the substrate (perpendicular to the paper surface in FIGS. 4 and 5). TM (Transverse Magnetic Wave) indicates a case of a P wave, and indicates a case where the magnetic field wave is parallel to the substrate (perpendicular to the paper surface in FIGS. 4 and 5). The same applies hereinafter.

  As a result of comparing FIG. 6 and FIG. 7, in the organic EL electroluminescent element 1 </ b> A according to the present embodiment, by reducing the effect of light interference between the first transparent thin film metal layer 13 and the light reflecting layer 30. While the angle dependency of the reflectance as viewed from the electroluminescent layer 12A is small (see FIG. 6), in the case of the organic EL electroluminescent element 100 in Comparative Example 1, the first transparent thin film metal layer 13 and the light It can be seen that the effect of light interference with the reflective layer 30 is increased, and the angle dependency of the reflectance viewed from the electroluminescent layer 12A is large (see FIG. 7).

(Embodiment 4)
In order to obtain a configuration suitable for a white organic EL electroluminescent element, characteristics at a plurality of wavelengths as well as a single color are important. Below, with reference to FIG. 8 and FIG. 9, the electroluminescent element in this Embodiment is demonstrated, contrasting with the structure in a comparative example. FIG. 8 is a cross-sectional view showing a specific configuration of the organic EL electroluminescent element 1B in Embodiment 4, and FIG. 9 is a cross-sectional view showing a specific configuration of the organic EL electroluminescent element 200 in Comparative Example 2.

  The configuration of the organic EL electroluminescent element 1B in the present embodiment shown in FIG. 8 satisfies the condition of (Equation 5). The difference from the configuration of the organic EL electroluminescent element 1A in the third embodiment shown in FIG. 4 is that the third transparent thin film metal layer 17 and the first transparent metal layer 17 are arranged between the second transparent dielectric layer 16 and the light reflecting layer 30. 3 transparent dielectric layers 18 are provided. Other configurations are the same. The third transparent thin film metal layer 17 and the third transparent dielectric layer 18 constitute a third buffer layer.

  The first buffer layer is composed of a thin film Ag (t1 = 15 nm) as the first transparent thin film metal layer 13 and a conductive resin (t2 = 30 nm) as the first transparent dielectric layer 14, and the second buffer layer is The thin film Ag (t3 = 15 nm) as the second transparent thin film metal layer 15 and the conductive resin (t4 = 30 nm) as the second transparent dielectric layer, and the third buffer layer is the third transparent thin film metal layer 17 is composed of a thin film Ag (t5 = 15 nm) as 17 and a conductive resin (t6 = 60 nm) as the third transparent dielectric layer 18.

  The organic EL electroluminescent element 200 as Comparative Example 2 shown in FIG. 9 does not include the second transparent thin film metal layer 15 and the third transparent thin film metal layer 17, and includes the first transparent thin film metal layer 13 and the light reflecting layer 30. Between them, a conductive resin (refractive index 1.7, film thickness t20 (= t2 + t4 ++ t6) = 120 nm) is provided as the transparent dielectric layer 20. Other configurations are the same as those of the organic EL electroluminescent element 1B.

  As in the case of the third embodiment, the reflectance at a wavelength of 520 nm is calculated for the organic EL electroluminescent element 1B in the present embodiment shown in FIG. 8 and the organic EL electroluminescent element 200 in the comparative example 2 shown in FIG. The results are shown in FIG. 10 and FIG. FIG. 10 is a diagram showing the result of calculating the reflectance at a wavelength of 520 nm for the organic EL electroluminescent element 1B in the present embodiment, and FIG. 11 shows the wavelength for the organic EL electroluminescent element 200 in Comparative Example 2 at a wavelength of 520 nm. It is a figure which shows the result of having calculated the reflectance.

  As a result of comparing FIG. 10 and FIG. 11, in the organic EL electroluminescent device 1 </ b> B in the present embodiment, by reducing the effect of light interference between the first transparent thin film metal layer 13 and the light reflecting layer 30. While the angle dependency of the reflectance as viewed from the electroluminescent layer 12A is small (see FIG. 10), in the case of the organic EL electroluminescent element 100 in Comparative Example 1, the first transparent thin film metal layer 13 and the light It can be seen that the effect of light interference with the reflective layer 30 is increased, and the angle dependency of the reflectance as viewed from the electroluminescent layer 12A is large (see FIG. 11).

  FIG. 12 shows the organic EL electroluminescent element 1A in the third embodiment, the organic EL electroluminescent element 1B in the fourth embodiment, the organic EL electroluminescent element 100 in the comparative example 1, and the organic EL electroluminescent element in the comparative example 2. For 200, the reflectance (0 degree reflection) when the light reflecting layer 30 is viewed from the electroluminescent layer 12A is shown. In the case of the comparative example 1 and the comparative example 2, it can be seen that the reflectance is largely reduced centering on the wavelength of 560 nm to 600 nm (green), and the white light emission is not sufficiently obtained.

  On the other hand, in the organic EL electroluminescent element 1A according to the third embodiment and the organic EL electroluminescent element 1B according to the fourth embodiment, although the reflectance is decreased at a wavelength of 520 nm or less, the blue (470 nm) is the center. Since the light having a hue centered on green (520 nm) and the light having a hue centered on red (630 nm) are reflected, the wavelength dependency is reduced and white light can be emitted.

(Embodiment 5)
FIG. 13 shows a configuration of an organic EL electroluminescent element 1C according to the fifth embodiment. FIG. 13 is a cross-sectional view showing a specific configuration of the organic EL electroluminescent element 1C. The configuration of the organic EL electroluminescent element 1C in the present embodiment shown in FIG. 13 satisfies the condition of (Equation 5). The difference from the configuration of the organic EL electroluminescent device 1A in the third embodiment shown in FIG. 4 is that the first transparent dielectric layer 14A and the second transparent dielectric layer 16A are electrically conductive with a refractive index n = 1.7. In this point, an ITO film is used instead of the conductive resin. The refractive index n of the first transparent dielectric layer 14A is 1.9, and the refractive index n of the second transparent dielectric layer 16A is 1.7. Other configurations are the same.

  By adopting this configuration, the refractive index (n = 1.9) of the first transparent dielectric layer 14A in contact with the first transparent thin film metal layer 13 is equal to or higher than the refractive index (n = 1.7) of the electroluminescent layer 12A. I have to. Plasmon loss may also occur in the first transparent thin-film metal layer 13, but as shown in FIG. 13, the refractive index of the first transparent dielectric layer 14A close to the electroluminescent layer 12A is higher than that of the electroluminescent layer 12A. When the height is increased, the rate at which the light from the electroluminescent layer 12A is absorbed by the first transparent thin film metal layer 13 due to the effect that the center of plasmon mode in the first transparent thin film metal layer 13 approaches the first transparent dielectric layer 14A. Can be reduced and the luminous efficiency can be improved.

  As mentioned above, in each embodiment based on this invention, in electroluminescent element 1, 1A, 1C in Embodiment 1-3, the buffer layer comprised by a transparent dielectric material layer and a transparent thin film metal layer In the electroluminescent element 1B according to the fourth embodiment, the case where three buffer layers each composed of a transparent thin film metal layer and a transparent dielectric layer are provided is described. However, the present invention is not limited to this configuration.

  According to the present invention, the effect of light interference can be reduced by laminating at least two buffer layers composed of a transparent dielectric layer and a transparent thin film metal. In addition, it is possible to reduce the angle dependence and wavelength dependence of the emission intensity distribution while reducing the plasmon loss by separating the distance between the electroluminescent layer and the metal reflective layer. A white illumination device using such an electroluminescence element can realize uniform light emission with high efficiency. In order to further enhance the effect of the present invention, fine particles having a refractive index different from that of the transparent dielectric layer may be dispersed in the transparent dielectric layer. In this case, the angle dependency and the wavelength dependency of the reflectance of the reflective electrode viewed from the electroluminescent layer can be further reduced due to the scattering effect.

(Embodiment 6)
The white illumination device 1000 using the organic EL electroluminescent element having the configuration shown in each of the above embodiments will be described below. FIG. 14 shows a schematic configuration of the white illumination device 1000 in the present embodiment. A white illumination device 1000 according to the present embodiment is a ceiling illumination device using the organic EL electroluminescence element 1100 according to each of the above embodiments on a ceiling 1200 of a room.

  The white lighting device 1000 according to the present embodiment is thin and can realize uniform light emission at various angles, so that it is possible to produce a soft space. Further, since light is emitted at various angles, an effect that it is difficult to make a shadow is obtained.

(Embodiment 7)
Hereinafter, another white illumination device using the organic EL electroluminescent element having the configuration shown in each of the above embodiments will be described. FIG. 15 shows a schematic configuration of white illumination apparatus 2000 in the present embodiment. The white lighting device 2000 in the present embodiment is a lighting stand, and the organic EL electroluminescence element 2200 in each of the above embodiments is used for the head 2100 portion.

  Also in the white illumination device 2000 according to the present embodiment, since it is thin and uniform light emission can be realized at various angles, it is possible to produce a soft space. In addition, since light is emitted at various angles, it is difficult to produce a shadow, so that the hand can be illuminated brightly.

  As described above, according to the electroluminescent element and the illuminating device using the electroluminescent element in the present embodiment, the electric field having a configuration that reduces the plasmon loss that has conventionally occurred in the metal electrode using the transparent electrode, the buffer layer, and the reflective layer. Although the light emitting element exists, there is a problem that the angle dependency of the reflectance viewed from the substrate side occurs due to the interference of light. In the embodiment based on the present invention, by providing two or more buffer layers composed of the transparent thin film metal layer and the transparent dielectric layer, the angle dependency of the emission intensity is reduced while reducing the plasmon loss generated in the metal electrode. A small electroluminescent element can be realized.

  In addition, although the electroluminescent element in each embodiment of this invention and the illuminating device using the electroluminescent element were demonstrated, embodiment disclosed this time is an illustration and restrictive at no points. Should be considered. Therefore, the scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Electroluminescent element, 10 board | substrate (resin board | substrate), 11 transparent electrode layer, 12, 12A electroluminescent layer, 13 1st transparent thin film metal layer, 14, 14A 1st transparent dielectric layer, 15 2nd transparent thin film metal layer, 16, 16A Second transparent dielectric layer, 17 Third transparent thin film metal layer, 18 Third transparent dielectric layer, 20 Transparent dielectric layer, 30 Light reflecting layer, 1000, 2000 White illumination device, 1100 Ceiling.

Claims (4)

A transparent electrode layer constituting the first transparent electrode;
A first transparent thin film metal layer constituting a second transparent electrode;
An electroluminescent layer sandwiched between the transparent electrode layer and the first transparent thin film metal layer;
A first transparent dielectric layer provided on the opposite side of the first transparent thin film metal layer from the side on which the electroluminescent layer is provided;
A second transparent thin film metal layer provided on the opposite side of the first transparent dielectric layer from the side on which the first transparent thin film metal layer is provided;
A second transparent dielectric layer provided on the opposite side of the second transparent thin film metal layer from the side on which the first transparent dielectric layer is provided;
A light reflection layer provided on the opposite side of the second transparent dielectric layer from the side on which the second transparent thin film metal layer is provided;
An electroluminescent device comprising:   2. The optical film thickness of the first transparent dielectric layer and the optical film thickness of the second transparent dielectric layer are one-fourth or less of a peak wavelength of an emission wavelength of the electroluminescent layer. Electroluminescent element.   3. The electroluminescent element according to claim 1, wherein a refractive index of the first transparent dielectric layer is higher than a refractive index of the electroluminescent layer.   The illuminating device which has an electroluminescent element of any one of Claim 1 to 3.

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