JP2015090799A - Organic el element, and image display device and illumination device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL element that suppresses the occurrence of SPP mode light and suppresses the absorption of light in a metal layer, and an image display device and an illumination device including the same.SOLUTION: An organic EL element 10 of the present invention is an organic EL element provided in order with a first electrode 2, an organic layer 3 including a luminescent layer, a second electrode 4, a low refractive index layer 5, a high refractive index layer 7, and a metal layer 6, where the second electrode 4 is composed of translucent conductive material, and the refractive index of the high refractive index layer 7 is higher than the refractive index of the low refractive index layer 5.

Description

  The present invention relates to an organic EL element, and an image display device and an illumination device including the organic EL element.

Organic EL elements have features such as a wide viewing angle, high-speed response, clear self-luminous display, etc., and they are thin, lightweight, and have low power consumption. It is expected as a pillar of
Organic EL elements are classified into a bottom emission type in which light is extracted from the support substrate side and a top emission type in which light is extracted from the opposite side of the support substrate, depending on the direction in which the light generated in the organic light emitting layer is extracted. .

In a bottom emission type organic EL element, light incident on the transparent substrate out of the light emitted from the light emitting layer passes through the transparent substrate and is extracted outside the element. Of the light emitted from the light emitting layer, a small incident angle that is less than the critical angle at the interface between a transparent substrate (for example, glass (typical refractive index: 1.52)) and air (refractive index: 1.0). Light incident at (the angle formed by the incident light and the normal of the incident interface) is refracted at the interface and extracted outside the device. In this specification, these lights are called external mode lights.
On the other hand, of the light emitted from the light emitting layer, the light incident on the interface between the transparent substrate and air at an incident angle larger than the critical angle is totally reflected at the interface and is not taken out of the device, and finally Can be absorbed by the material. In the present specification, this light is referred to as substrate mode light.
Further, of the light emitted from the light emitting layer, a critical angle is formed at the interface between the transparent electrode made of a transparent conductive oxide (for example, indium tin oxide (ITO (typical refractive index: 1.82))) and the transparent substrate. Light incident at a large incident angle is also totally reflected at the interface and is not extracted outside the device, but can be finally absorbed by the material, and in this specification, this light is referred to as waveguide mode light.
Further, when a metal layer such as a metal cathode is present in the organic EL element, out of the light emitted from the light emitting layer, the light enters the metal layer and is coupled with free electron vibration on the metal surface, and surface plasmon polariton (SPP; The light trapped on the surface of the metal electrode as a surface plasmon polariton) is not taken out of the device but can be finally absorbed by the material. In the present specification, this light is referred to as SPP mode light.

The light extraction efficiency of the organic EL element (ratio of the light extracted outside the element with respect to the light emitted from the light emitting layer) is generally limited to about 20% (for example, Patent Document 1). That is, about 80% of the light emitted from the light emitting layer is lost, and it is a big problem to reduce these losses and improve the light extraction efficiency.
Here, the extraction of the substrate mode light can be dealt with by providing a light diffusion sheet or the like on the transparent substrate (for example, Patent Document 2), but the reduction and extraction of the waveguide mode light and the SPP mode light, particularly the SPP mode light. It can be said that research has just begun on the reduction and removal of odors.

  As a countermeasure against SPP mode light, it has not been sufficiently studied yet, but the light captured as SPP on the metal surface is captured by the Otto type arrangement of metal layer / low refractive index medium / high refractive index medium. It has been proposed to extract the SPP mode light into a high refractive index medium.

JP 2008-210717A JP 2011-243625 A

However, in the Otto type arrangement, the captured SPP mode light cannot be completely extracted. This will be described with reference to FIG.
FIG. 1 is a diagram schematically showing an Otto type organic EL element 90. On the substrate 91, an anode 92, an organic layer 93, a cathode 94, a low refractive index layer 95, and a metal layer 96 are sequentially laminated. Here, the refractive index of the organic layer 93 or the cathode 94 is larger than the refractive index of the low refractive index layer 95. At this time, the metal layer 96 / the low refractive index layer 95 / the organic layer 93 or the cathode 94 is an Otto type arrangement of metal / low refractive medium / high refractive index medium.

First, the principle of capturing light as SPP mode light on the metal surface will be described before the description of taking out the SPP mode light captured on the metal surface. In the Otto type organic EL element, there are two processes in which light is captured on the surface of the metal layer 96 (interface with the low refractive index layer 95).
The first process is a process in which light emitted from the organic layer 93 is directly captured by the metal layer 96, as indicated by an arrow A1. Since the light emitted from the organic layer 93 can be regarded as a dipole that vibrates the light emitter, the dipole exchanges energy with the SPP mode light existing on the surface of the metal layer 96 through the dipole field of the light emitting point. As a result, light is captured as SPP mode light (arrow A2) on the surface of the metal layer 96 (hereinafter referred to as process 1). It is well known that such energy transfer from a dipole to SPP mode light occurs when a light emitting molecule and a metal layer are close to each other in a general organic EL element.

The second process is a process supplemented by the metal layer 96 via the evanescent wave in the low refractive index layer 95. Next, this will be described.
In an Otto type arrangement composed of a metal layer / low refractive index medium / high refractive index medium, if the real part of the in-plane direction component of the layer of the wave number of the SPP mode light generated on the surface of the metal layer is k ′ _sp The dispersion relation is determined by the real part ε ₁ of the relative dielectric constant of the metal layer and the relative dielectric constant ε ₂ of the low refractive index medium in contact with the surface of the metal layer, and is approximately given by the following equation (1) (k ₀ Is the wave number of light in vacuum at the peak wavelength of light emitted from the light emitting layer).

The magnitude of the in-plane direction component of the light propagating through the high refractive index medium at the propagation angle θ is expressed by Expression (2), where ε ₃ is the relative dielectric constant of the high refractive index medium.

Therefore, when ε ₃ is sufficiently large, the wave number of the SPP mode light on the surface of the metal layer and the dispersion curve of the propagating light are placed at the position of the angular frequency of the emitted light by appropriately selecting the angle θ in Equation (2). It is possible to have an intersection (hereinafter, θ at this time is referred to as θ ₃ ). In this case, the mode of the propagating light in the high refractive index medium and the SPP mode can be coupled to exchange energy with each other, so that the SPP mode light on the surface of the metal layer can be extracted into the high refractive index medium as propagating light. become. In other words more specifically, SPP mode light generated in the metal layer surface, through the electromagnetic field of its leaking to the low-refractive medium side, cause energy transfer to the high refractive index medium, high refractive index at an angle theta ₃ It becomes propagating light propagating in the medium.

Therefore, like the organic EL element 90, for example, the metal layer 96 (real part ε ₁ of relative permittivity) / low refractive index in the vicinity of the organic layer 93 (relative permittivity ε ₃ ) in order from the side far from the organic layer 93. When the layer 95 (relative dielectric constant ε ₂ ) is provided, the SPP mode light excited on the surface of the metal layer 96 has a predetermined angle θ ₃ via an evanescent wave generated in the low refractive index layer 95 in the Otto type arrangement structure. As a result, propagating light radiated into the organic layer 93 can be extracted into the organic layer 93.

However, the combination of the SPP mode light and the propagation light mode in the organic layer 93 is not only the extraction from the SPP mode light but also the process in which the light in the organic layer 93 is trapped on the surface of the metal layer 96 as SPP. Also means that it can occur at the same time.
That is, when light propagating through the organic layer 93 is incident on the interface between the high refractive index medium (the organic layer 93 or the cathode 94) and the low refractive index layer 95 at a predetermined angle θ ₃ and totally reflected, the light enters the low refractive index layer. An evanescent wave is generated, and this evanescent wave exchanges energy with the SPP mode light existing on the surface of the metal layer 96, so that propagating light in the organic layer 93 is captured as SPP mode light on the surface of the metal layer 96. (Hereinafter referred to as process 2).
Note that light totally reflected at an angle other than the predetermined angle θ also generates an evanescent wave in the low refractive index layer 95. The dispersion curve of the evanescent wave and the dispersion curve of the SPP mode light are at each frequency position of the emitted light. Since there is no intersection, energy cannot be exchanged.

That is, in the Otto-type arrangement, SPP mode light generated in the process 1 (arrow A2) is through the electromagnetic field of the SPP mode light (arrow A3), is extracted to the organic layer 93 at a predetermined angle theta ₃ (arrow A4) . A part of the light thus extracted can be extracted to the outside through the anode 92 and the substrate 91 (arrow A4e).
On the other hand, the light (arrow A4 ′) reflected back to the organic layer 93 side without being taken out to the outside enters the low refractive index layer 95 side and is captured again as SPP mode light by the process 2 (arrow A5). It can be dissipated as heat while propagating on the layer surface (arrow A6). Further, the light propagating from the light emitting point to the organic layer 93 instead of being converted into the SPP mode light is also captured as the SPP mode again by the process 2 at the propagation angle θ ₃ (arrows B1 and B1 ′). (Arrows B2, B3).
Therefore, the Otto type arrangement has a problem that it is impossible to extract all the generated SPP mode light.

  The present invention has been made in view of the above circumstances, an organic EL element capable of suppressing the generation of SPP mode light and suppressing the absorption of light in a metal layer, and an image display device and an illumination device including the organic EL element. The purpose is to provide.

  By introducing a second electrode side structure having a high refractive index layer having a higher refractive index than the low refractive index layer between the low refractive index layer and the metal layer, the light captured as SPP mode light is suppressed. In addition, the light absorption in the metal layer was also suppressed.

In order to solve the above-mentioned problems, the present invention having the outline adopts the following configuration.
(1) An organic EL element comprising a first electrode, an organic layer including a light emitting layer, a second electrode, a low refractive index layer, a high refractive index layer, and a metal layer in this order. An electrode is made of a light-transmitting conductive material, and the refractive index of the high refractive index layer is higher than the refractive index of the low refractive index layer.
(2) The organic EL element according to (1), wherein a refractive index of the high refractive index layer is higher than that of the organic layer.
(3) The organic EL element according to any one of (1) to (2), wherein the high refractive index layer has a thickness of 10 to 300 nm.
(4) The organic EL element according to any one of (1) to (3), wherein a refractive index of the low refractive index layer is further lower than a refractive index of the organic layer.
(5) The organic EL element according to (4), wherein the refractive index of the low refractive index layer is lower than the refractive index of the second electrode.
(6) The organic EL element according to any one of (1) to (5), wherein the first electrode has a refractive index modulation structure on a side opposite to the organic layer.
(7) The organic EL element according to (6), wherein the refractive index modulation structure is any one of a diffraction grating, a lens, and a photonic crystal.
(8) The organic EL device according to any one of (1) to (5), wherein a diffusion scatterer is provided on the side of the first electrode opposite to the organic layer.
(9) An image display device comprising the organic EL element according to any one of (1) to (8).
(10) An illumination device comprising the organic EL element according to any one of (1) to (8).

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of SPP mode light can be suppressed, and the organic EL element which can also suppress the light absorption in a metal layer, and an image display apparatus and an illuminating device provided with the same can be provided.

It is the cross-sectional schematic diagram which showed typically the cross section of the organic EL element 90 of Otto type | mold arrangement | positioning. It is a cross-sectional schematic diagram for demonstrating the organic EL element which concerns on one Embodiment of this invention. 'The relationship between the _sp and the wave number k of the evanescent wave, the wave number k of the SPP mode light in the organic EL device 10 of the present invention' the wave number k of the SPP mode light in the organic EL element 90 of the Otto type arrangement wavenumber k of _'sp and evanescent wave It is the figure which showed this relationship typically. The figure which showed typically the film thickness direction distribution of the electromagnetic field amplitude of SPP using the organic EL element 10 (FIG.4 (b)) of this invention and the organic EL element 90 (FIG.4 (a)) of Otto type | mold arrangement | positioning. It is. It is the cross-sectional schematic diagram which showed typically the modification concerning the 1st electrode side structure of the organic EL element which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram for demonstrating an example of the image display apparatus provided with the organic EL element of this invention. It is a cross-sectional schematic diagram for demonstrating an example of the illuminating device provided with the organic EL element of this invention. It is a cross-sectional schematic diagram which shows the model structure of the organic EL element of this invention used by simulation. Of the model structure of the organic EL element of the present invention used in the simulation, it is a schematic cross-sectional view specifically showing the metal layer side from the light emitting point, and in the example, the thickness of the high refractive index layer 7 is constant FIG. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element 10 shown in FIG. 9 by the computer simulation using FDTD method. Of the model structure of the organic EL element of the present invention used in the simulation, it is a schematic cross-sectional view specifically showing the metal layer side from the light emitting point, and in the example, the thickness of the low refractive index layer 5 is constant FIG. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element shown in FIG. 11 by the computer simulation using the FDTD method. Of the model structure of the organic EL element of the present invention used in the simulation, it is a schematic cross-sectional view specifically showing the metal layer side from the light emitting point, and in the example, the thickness of the high refractive index layer 7 is constant, and the cathode It is a cross-sectional schematic diagram when 4 is made of metal. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element 10 shown in FIG. 13 by the computer simulation using FDTD method. Of the model structure of the organic EL device of the present invention used in the simulation, it is a schematic cross-sectional view specifically showing the metal layer side from the light emitting point, and in the example, the thickness of the low refractive index layer 5 is constant, and the cathode It is a cross-sectional schematic diagram when 4 is made of metal. It is a figure which shows the result of having calculated | required the light extraction efficiency of the organic EL element 10 shown in FIG. 15 by the computer simulation using FDTD method.

Hereinafter, the structure of an organic EL element to which the present invention is applied, an image display apparatus and an illumination apparatus including the organic EL element will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. . In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately changed and implemented without changing the gist thereof.
Any of the so-called bottom emission structure and top emission structure may be applied to the organic EL element of the present invention.
In the present invention, one of the first electrode and the second electrode is an anode and the other is a cathode. In the following description, a configuration in which the first electrode is an anode and the second electrode is a cathode will be described as an example.
Moreover, the organic EL element of this invention may be provided with the layer and structure which are not described below in the range which does not impair the effect of this invention. For example, a refractive index modulation structure or the like may be used on the first electrode side (substrate, first electrode, and organic layer) in order to efficiently extract guided mode light in a direction perpendicular to the substrate.

(Structure of organic EL element)
FIG. 2 is a schematic cross-sectional view for explaining an example of an organic EL element according to an embodiment of the present invention. The organic EL element shown in FIG. 2 includes a substrate 1, an anode (first electrode) 2, an organic layer 3 including a light emitting layer, a cathode (second electrode) 4, a low refractive index layer 5, and a high refractive index. An organic EL element 10 having a layer 7 and a metal layer 6 in this order, the cathode 4 is made of a translucent conductive material, and the refractive index of the high refractive index layer 7 is higher than the refractive index of the low refractive index layer 5. high.
When comparing the refractive indexes of the structure on the cathode 4 side as described above, the refractive index of the organic layer 3 means the average refractive index of all the layers including the light emitting layer made of the organic EL material.

すなわち、ε_１＜０であることに注意すると、金属層６に隣接する層が低屈折率層５である場合の式（１）と比較して、ε_ｈ＞ε_２であることから、ＳＰＰモード光の波数がｋ’_ｓｐに比べ大きくなっていることが分かる。 First, in order to clarify the difference between the conventional Otto type organic EL element 90 and the organic EL element 10 of the present invention, the light capture by the process 1 and the process 2 is performed in the organic EL element 10 of the present invention. Explain how it behaves like this. Hereinafter, for comparison with the organic EL element 90, the low refractive index layer 5 and the metal layer 6 of the organic EL element 10 are made of the same members as the low refractive index layer 95 and the metal layer 96 of the organic EL element 90, respectively. Considering the case, the real part of the relative permittivity is set to ε ₁ and ε ₂ , respectively.
3, 'the relationship between the _sp and the wave number k of the evanescent wave, the wave number k of the SPP mode light in the organic EL device 10 of the present invention' the wave number k of the SPP mode light in the organic EL element 90 of the Otto type arrangement _'sp and evanescent It is the figure which showed typically the relationship of the wave number k of a wave.
In the organic EL device 90 of the Otto type arrangement, the wave number k _'sp of the SPP mode light is represented by the formula (1), each table in-plane component of the wavenumber k of the propagation light in the organic layer 3 is the formula (2) Is done. If the dielectric constant epsilon ₃ of the organic layer 3 is sufficiently large, the dispersion curve of the formula (1) and (2), the propagation angle such as to have a point of intersection with angular frequency omega ₀ of the emitted light as shown in FIG. 3 theta ₃ exists, and the energy of light propagating in the organic layer at the propagation angle θ ₃ is captured as SPP mode light.
On the other hand, the organic EL element 10 of the present invention introduces the high refractive index layer 7 between the low refractive index layer 5 and the metal layer 6 so that the wave number of the SPP mode light generated on the surface of the metal layer 6 is It is determined by the real part ε ₁ of the relative dielectric constant of the metal layer 6 and the relative dielectric constant ε _h of the high refractive index layer 7 in contact with the surface of the metal layer 6 and is approximately given by the following equation (3) (k ₀ is Wave number of light in vacuum at the peak wavelength of light emitted from the light emitting layer).

That is, when attention is paid to ε ₁ <0, since ε _h > ε ₂ compared to the formula (1) in the case where the layer adjacent to the metal layer 6 is the low refractive index layer 5, SPP it can be seen that the wave number of the mode light is larger than that of the k _'sp.

That is, the wave number k ″ _sp of the SPP mode light in the organic EL element of the present invention increases as shown by the dispersion curve in FIG. 3, and the dispersion curve of light propagating in the organic layer 3 (formula (2)) and Any crossing angle θ no longer has an intersection.
That is, the SPP mode and the propagating light mode in the organic layer 3 are not combined, and the propagating light in the organic layer 3 is not captured as SPP mode light on the surface of the metal layer 6 by the process 2.

となる。したがって、金属層／低屈折率層界面から距離ｚの低屈折率層９５中でのＳＰＰの電磁場振幅Ｓ_１は、ｚ＝０での値を１として近似的に

となる。ただし、各界面におけるフレネル反射の影響は無視する。
同様に、有機ＥＬ素子１０において、高屈折率層／低屈折率層界面から距離ｚの低屈折率層中におけるＳＰＰの電磁場振幅Ｓ_２は、ｚ＝０での値を１として近似的に

となる。
ここで前述したようにｋ’_ｓｐ＜ｋ’’_ｓｐであるから、有機ＥＬ素子１０の低屈折率層中における電磁場振幅（図４（ｂ））の方が、有機ＥＬ素子９０の低屈折率層中の電磁場振幅（図４（ａ））より急激に減衰していることがわかる。さらに、有機ＥＬ素子１０では金属層６表面のＳＰＰモードは有機層３中の伝播光モードと結合していないので、ＳＰＰモードの電磁場は有機層３中でエバネッセント波となり、指数関数的に急激に減衰する。一方、有機ＥＬ素子９０においては金属層９６表面のＳＰＰモードと有機層９３中の伝播光モードが結合しているため、有機層９３中の電磁場はエバネッセント波とならず、指数関数的な減少は起こらない。すなわち、有機ＥＬ素子１０では、有機層中の発光点に達するＳＰＰの電磁場が非常に小さく抑えられている。このために、低屈折率層と金属層の間に高屈折率層を有する有機ＥＬ素子１０では、過程１による発光点からＳＰＰへのエネルギー移動が有機ＥＬ素子９０に比べて大きく抑制される。 FIG. 4 is a diagram schematically showing the distribution in the film thickness direction of the electromagnetic field amplitude of the SPP using the organic EL element 10 of the present invention and the organic EL element 90 of the Otto type arrangement.
Since the organic EL element 10 of the present invention has a high refractive index layer between the low refractive index layer and the metal layer, trapping in the SPP by the process 1 is also suppressed. This will be described.
In the organic EL element 90, the vertical direction component of the wave number in the low refractive index layer 95 of the SPP propagating on the surface of the metal layer 96 is determined by using the in-plane direction component k ′ _sp of the wave number.

It becomes. Therefore, the electromagnetic field amplitude S ₁ of the SPP in the low refractive index layer 95 at a distance z from the metal layer / low refractive index layer interface is approximately set to 1 at z = 0.

It becomes. However, the influence of Fresnel reflection at each interface is ignored.
Similarly, in the organic EL element 10, the electromagnetic field amplitude S ₂ of the SPP in the low refractive index layer of the distance z from the high refractive index layer / low refractive index layer surface is approximately the value at z = 0 as 1

It becomes.
Because here is the k _'sp <k'_'sp as described above, towards the field amplitude (FIG. 4 (b)) in the low refractive index layer of the organic EL element 10, a low refractive index of the organic EL element 90 It can be seen that the field decays more rapidly than the amplitude of the electromagnetic field in the layer (FIG. 4A). Further, in the organic EL element 10, since the SPP mode on the surface of the metal layer 6 is not coupled with the propagation light mode in the organic layer 3, the electromagnetic field of the SPP mode becomes an evanescent wave in the organic layer 3 and exponentially increases rapidly. Attenuates. On the other hand, in the organic EL element 90, since the SPP mode on the surface of the metal layer 96 and the propagating light mode in the organic layer 93 are combined, the electromagnetic field in the organic layer 93 does not become an evanescent wave, and the exponential decrease does not occur. Does not happen. That is, in the organic EL element 10, the electromagnetic field of the SPP reaching the light emitting point in the organic layer is suppressed to be very small. For this reason, in the organic EL element 10 having the high refractive index layer between the low refractive index layer and the metal layer, the energy transfer from the light emitting point to the SPP by the process 1 is greatly suppressed as compared with the organic EL element 90.

  As shown here, in the organic EL element 10 of the present invention, by introducing the second electrode structure provided with the high refractive index layer 7, light is transmitted through the surface of the metal layer 6 in the process 1 and process 2 paths. Are not captured as SPP mode light. That is, in the organic EL element 90 having the conventional Otto type arrangement structure, a part of the light captured in the path of the process 2 is lost, but in the organic EL element 10 of the present invention, the processes 1 and 2 are originally performed. Since light is not captured by the surface of the metal layer 6 through the path, it is possible to efficiently extract light without losing light.

It is considered that the effect of suppressing the above-described process 1 and process 2 can be obtained even in an organic EL element in which the high refractive index layer 7 is formed between the metal layer 6 and the cathode 4 and does not have the low refractive index layer 5. However, in such an organic EL element, light emitted from the light emitting point of the organic layer 3 to the cathode side is incident on the surface of the metal layer 6 and reflected as it is, and is returned to the organic layer 3 side as propagating light. The effect of suppressing the process 1 and the process 2 is small.
On the other hand, in the organic EL element 10 of the present invention, reflection by total reflection can be used at the interface between the cathode 4 and the low refractive index layer 5 by introducing the low refractive index layer 5.
Metal reflection loses part of its light due to absorption, but in the case of total reflection, there is almost no loss because it reflects all incident light.
That is, the second electrode structure in which the high refractive index layer 7 and the low refractive index layer 5 are introduced between the cathode 4 and the metal layer 6 not only eliminates the light trapped on the surface of the metal layer 6 but also reflects it. Loss can be reduced and light can be extracted more efficiently.

(Configuration of each layer)
The organic EL element 10 according to the present invention includes a bottom emission type (when the substrate 1 is on the opposite side of the organic layer 3 when viewed from the anode 2) and a top emission type (when viewed from the metal layer 6 on the side opposite to the low refractive index layer 5). The present invention can be applied to any of the organic EL elements.
When applied to the bottom emission type, the substrate 1 is a light-transmitting substrate and usually needs to be transparent to visible light. Here, “transparent to visible light” means that it is only necessary to transmit visible light having a wavelength emitted from the light emitting layer, and it is not necessary to be transparent over the entire visible light region. A smooth substrate having a transmittance in visible light of 400 to 700 nm of 50% or more is preferable. Further, the transmittance is more preferably 70% or more.
Specific examples of the material constituting the substrate 1 include glass and polymer. Examples of the glass include soda lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the polymer include polycarbonate, acrylic, polyethylene terephthalate, polyethylene naphthalate, polyether sulfide, and polysulfone.
Even when the emitted light is not visible light, it is necessary to be transparent at least in the emission wavelength region as in the case of visible light. The transmittance is preferably 50% or more and more preferably 70% or more with respect to the wavelength at which light emission has the maximum intensity.
In order to apply to the top emission type, an opaque material can be used in addition to the same as described above. Specifically, for example, Cu, Ag, Au, Pt, W, Ti, Ta, Nb, Al alone, an alloy containing these elements, or a metal material such as stainless steel, Si, SiC, AlN, GaN, Nonmetallic materials such as GaAs and sapphire, and other substrate materials usually used in top emission type organic EL elements can be used. In addition, in order to release heat generated due to light emission of the element, it is preferable to use a material having high thermal conductivity for the substrate.

  The thickness of the substrate 1 is not particularly limited depending on the required mechanical strength, but is preferably 0.01 mm to 10 mm, more preferably 0.05 mm to 2 mm.

The anode 2 is an electrode for applying a voltage between the anode 4 and injecting holes into the organic layer 3 from the anode 2, and is made of a metal, an alloy, a conductive compound, or a mixture thereof having a high work function. It is preferable to use a material, and it is preferable to use a material having a work function of 4 eV or more and 6 eV or less so that the difference from the HOMO (Highest Occupied Molecular Orbital) level of the organic layer 3 in contact with the anode 2 does not become excessive. The material of the anode 2 is not particularly limited as long as it is a translucent and conductive material. For example, transparent inorganic oxidation such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and zinc oxide is possible. , PEDOT: PSS, conductive polymer such as polyaniline and conductive polymer doped with any acceptor, conductive light transmissive material such as carbon nanotube, thin film metal, metal nanowire formed in thin film, these Can be mentioned. Here, the anode 2 can be formed on the substrate 1 by, for example, a sputtering method, a vacuum deposition method, a coating method, or the like.
Although the thickness of the anode 2 is not specifically limited, For example, it is 10-2000 nm, Preferably it is 50-1000 nm. If the thickness is less than 10 nm, the sheet resistance of the anode 2 increases. If the thickness is more than 2000 nm, the flatness of the organic layer 3 cannot be maintained, and the transmittance of the anode 2 decreases.

The organic layer 3 may include a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, and the like in addition to a light emitting layer made of an organic EL material. As a material of the light emitting layer, any material known as a material for an organic EL element can be used.
The hole injection layer is a layer that assists hole injection from the anode 2 to the organic layer 3, and its ionization energy is usually as low as 5.5 eV or less. Such a hole injection layer is preferably a material that injects holes into the organic layer 3 with a lower electric field strength. However, the material to be formed is not particularly limited as long as it can perform the above functions, and is well known. Any one can be selected and used. The hole transport layer is a layer that transports holes to the light emitting region and has a high hole mobility. The material to be formed as such a hole transport layer is not particularly limited as long as it can perform the above function, and any material can be selected and used from known materials.
The electron injection layer is a layer that assists electron injection from the cathode 4 to the organic layer 3. As such an electron injection layer, a material that injects electrons into the organic layer 3 with a lower electric field strength is preferable. However, the material to be formed is not particularly limited as long as it can perform the above-described function. Any one can be selected and used. The electron transport layer is a layer that transports electrons to the light emitting region and has a high electron mobility. The material for forming such an electron transport layer is not particularly limited as long as it can perform the above function, and any material can be selected and used from known materials.

The organic layer 3 may be formed by a dry process such as an evaporation method or a transfer method, or may be formed by a wet process such as a spin coating method, a spray coating method, a die coating method, or a gravure printing method.
Although the thickness of the organic layer 3 is not specifically limited, For example, it is 50-2000 nm, Preferably it is 100-1000 nm. If it is thinner than 50 nm, extinction other than SPP coupling occurs, such as a decrease in internal quantum efficiency due to punch-through current and lossy surface wave mode coupling due to metal layer 6, and if it is thicker than 2000 nm, it is driven The voltage rises.

The cathode 4 is an electrode for injecting electrons into the light emitting layer, and it is preferable to use a material made of a metal, an alloy, a conductive compound, or a mixture thereof having a small work function. It is preferable to use a work function of 1.9 eV or more and 5 eV or less so that the difference from the LUMO (Lowest Unoccupied Molecular Orbital) level does not become excessive.
As a material of the cathode 4, it is necessary to use a light-transmitting conductive material in order to form a cathode side structure having an Otto type arrangement. Therefore, the same anode material as described above can be used.
Although the thickness of the cathode 4 is not specifically limited, For example, it is 30 nm-1 micrometer, Preferably it is 50-500 nm. When the thickness is less than 30 nm, the sheet resistance increases and the driving voltage increases. When the thickness is greater than 1 μm, damage due to heat and radiation during film formation and mechanical damage due to film stress accumulate in the electrode and the organic layer. .

The low refractive index layer 5 is provided on the surface of the cathode 4 opposite to the organic layer 3, and is preferably made of a material having a refractive index lower than that of the organic layer 3.
When the refractive index of the low refractive index layer 5 is smaller than that of the organic layer 3, even when a metal is used for the cathode 4, the low refractive index layer 5 / cathode 4 / organic layer 3 is low refractive index medium / metal / high refractive index. Since the medium has a Kretschmann arrangement, the SPP mode light captured at the interface of the low refractive index layer 5 of the cathode 4 can be extracted.
The low refractive index layer 5 is preferably made of a material having a refractive index lower than that of the translucent conductive material constituting the cathode 4.
When light emitted from the light emitting layer propagates to the cathode 4 side and reaches the interface between the cathode 4 and the low refractive index layer 5, total reflection occurs when incident at an angle greater than the critical angle, and metal reflection at the metal layer 6 occurs. Can reduce the loss of light.

The material of the low refractive index layer 5 is not particularly limited as long as it is a material having a refractive index lower than that of the organic layer 3. For example, when the average refractive index of all the layers of the organic layer 3 is 1.72. SOG satisfying this refractive index, metal fluoride such as magnesium fluoride (MgF ₂ (typical refractive index 1.38)), polytetrafluoroethylene (PTFE (typical refractive index 1.35)), etc. Organic fluorine compounds, silicon dioxide (SiO ₂ (typical refractive index 1.45)), various low-melting-point glasses, and porous materials. Further, the low refractive index layer 5 is composed of a layer including an air layer, and may have a refractive index lower than that of the translucent conductive material constituting the cathode 4.

The metal layer 6 is provided on the opposite side of the cathode 4 from the organic layer 3 via a low refractive index layer 5 and a high refractive index layer 7.
As the material of the metal film 6, it is sufficient that the emitted light generated in the organic layer 3 can be reflected to the anode side, so that almost any single metal or alloy can be used, but the real part of the relative complex dielectric constant is absolutely A material having a large negative value is preferable. Examples of such materials include simple substances such as Au, Ag, Cu, Zn, Al, Mg, alkali metals and alkaline earth metals, alloys of Au and Ag, alloys of Ag and Cu, and alloys such as brass. It is done. Further, the metal layer 6 may have a laminated structure of two or more layers.
Although the thickness of the metal layer 6 is not specifically limited, For example, it is 20-2000 nm, Preferably it is 50-500 nm. If it is thinner than 20 nm, the reflectance is lowered and the front luminance is lowered. If it is thicker than 2000 nm, heat, radiation damage, and mechanical damage due to film stress during film formation accumulate in the electrode and the organic layer.

The material for the high refractive index layer 7 is not particularly limited as long as the material has a higher refractive index than that of the low refractive index layer 5.
For example, when the low refractive index layer 5 is made of magnesium fluoride (MgF2, refractive index 1.38), the material of the high refractive index layer 7 is SOG having a refractive index higher than 1.38 (typical refractive index: 1.1 to 2.0), silicon oxide (typical refractive index: 1.45) including silica (SiO ₂ ) and magnesium oxide (MgO) (typical refractive index: 1.74), Oxides including zinc oxide (ZnO) (typical refractive index: 2.02), nitrides including aluminum nitride (AlN), aluminum oxynitride (AlON) and silicon oxynitride Selected from oxynitrides, polyethylene naphthalate (PEN (typical refractive index: 1.77)), polymer compounds such as melamine resins, and the like. In addition, a porous material, a mixture thereof, or a material in which fine particles of an inorganic material are dispersed in a transparent medium can be used.
When the refractive index of the low refractive index layer 5 is lower than 1.38, in addition to the above materials, for example, magnesium fluoride (MgF ₂ ) (typical refractive index: 1.38) Selected from metal halides, polytetrafluoroethylene (PTFE (typical refractive index: 1.35)) and other fluororesins, polymethyl methacrylate (typical refractive index: 1.49) Can be used.

The film thickness of the high refractive index layer 7 is preferably 10 nm to 300 nm, more preferably 20 to 100 nm, and even more preferably 30 to 60 nm. If the thickness is 10 nm or less, the thickness of the high refractive index layer is thin, so that k ″ _sp is not sufficiently large, and a part of the light trapped on the surface of the metal layer 6 is generated through the path of the process 1 and the process 2. The extraction efficiency decreases. If it is 300 nm or more, light is guided through the high refractive index layer 7 and the light extraction efficiency is lowered.

The organic EL device according to the present invention has the SPP mode light extracted to the organic layer by the second electrode side structure on the first electrode side (the substrate, the first electrode, the organic layer, and the outside of the device) without using the waveguide mode. Refractive index modulation structure such as concave and convex shape, multiple microlenses, diffraction grating, photonic crystal, reflection structure, etc. and diffusion with low refractive index region and high refractive index region randomly distributed to efficiently guide to the substrate A first electrode side structure such as a scatterer may be used.
FIG. 5 shows a modification of the anode (first electrode) side structure of the organic EL element 10 shown in FIG. FIG. 5A shows an example in which a refractive index modulation structure composed of translucent materials 17 and 18 having different refractive indexes is used between the substrate 1 and the anode 2. When the modulation structure has periodicity, it functions as a diffraction grating and a photonic crystal structure, so that guided mode light can be extracted efficiently. FIG. 5B shows an example in which a similar refractive index modulation structure is formed using a light-transmitting material 17 having a refractive index different from that of the anode 2. FIG. 5C is an example in which a similar refractive index modulation structure is formed using the anode 2 and the organic layer 3 having different refractive indexes. FIG. 5D shows an example of a similar refractive index modulation structure using the organic layer 3 and the dielectric layer 8 having different refractive indexes. FIG. 5 (e) and FIG. 5 (f) show the laminated structure of the organic layer 3 and the dielectric layer 8 / anode 2 having different refractive indexes, or the organic layer 3 and the dielectric layer 8 / anode having different refractive indexes. 2 / This is an example of a similar refractive index modulation structure using a part of the laminated structure of the substrate 1.
Note that, specifically, the refractive index modulation structure is a structure in which a plurality of refractive index interfaces formed by repeatedly disposing substances having different refractive indexes in at least one direction within the element surface are perpendicular to the element surface or It means a structure close to vertical.
The refractive index modulation structure may be a structure having periodicity or a non-periodic structure having no periodicity. When the refractive index modulation structure has periodicity, in addition to the refraction effect, a diffraction effect as a transmission diffraction grating (hereinafter sometimes simply referred to as “diffraction grating”) (refracted at a predetermined angle with respect to the element surface) Effect) and an effect as a photonic crystal (an effect of prohibiting in-plane waveguide of light of a specific frequency), it is possible to extract guided mode light in a direction perpendicular to the element surface.
In the case of an aperiodic structure, light incident on the first electrode side structure is diffracted in a random direction / phase, so that specific radiation angles are not emitted intensified. Therefore, by having such a structure on the first electrode side, it is possible to obtain a light distribution characteristic with high diffusibility (a gentle angle dependency).
That is, in the case where the first electrode side structure is a periodic structure, it is possible to obtain an alignment characteristic in which the light intensity at a specific radiation angle is increased by the effect of strengthening the emitted light by the diffraction grating, When the first electrode side structure is a non-periodic structure, highly diffusive alignment characteristics can be obtained. Therefore, the first electrode side structure can be selected to be a structure having periodicity or a non-periodic structure according to a required light distribution characteristic.

(Image display device)
Next, the image display apparatus 100 including the organic EL element will be described. An image display apparatus including the organic EL element 10 will be described. In addition, the organic EL element may have a bottom emission structure or a top emission structure, but in the following, an example of a bottom emission structure will be described.
FIG. 6 is a diagram illustrating an example of an image display device including the organic EL element.
The image display device 100 shown in FIG. 6 is a so-called passive matrix type image display device. In addition to the organic EL element 10, the anode wiring 104, the anode auxiliary wiring 106, the cathode wiring 108, the insulating film 110, and the cathode partition 112 are used. , A sealing plate 116 and a sealing material 118.

  In the present embodiment, a plurality of anode wirings 104 are formed on the substrate 1 of the organic EL element 10. The anode wirings 104 are arranged in parallel at a constant interval. The anode wiring 104 is made of a transparent conductive film, and for example, ITO can be used. The thickness of the anode wiring 104 can be set to 100 nm to 150 nm, for example. An anode auxiliary wiring 106 is formed on the end of each anode wiring 104. The anode auxiliary wiring 106 is electrically connected to the anode wiring 104. With this configuration, the anode auxiliary wiring 106 functions as a terminal for connecting to the external wiring on the end portion side of the substrate 1, and the drive circuit (not shown) provided outside via the anode auxiliary wiring 106. A current can be supplied to the anode wiring 104. The anode auxiliary wiring 106 is formed of, for example, a metal film having a thickness of 500 nm to 600 nm.

  A plurality of cathode wirings 108 are provided on the organic EL element 10. The plurality of cathode wirings 108 are arranged so as to be parallel to each other and orthogonal to the anode wiring 104. For the cathode wiring 108, Al or an Al alloy can be used. The thickness of the cathode wiring 108 is, for example, 100 nm to 150 nm. Further, similarly to the anode auxiliary wiring 106 for the anode wiring 104, a cathode auxiliary wiring (not shown) is provided at the end of the cathode wiring 108 and is electrically connected to the cathode wiring 108. Therefore, a current can flow between the cathode wiring 108 and the cathode auxiliary wiring.

  Further, an insulating film 110 is formed on the substrate 1 so as to cover the anode wiring 104. A rectangular opening 120 is provided in the insulating film 110 so as to expose a part of the anode wiring 104. The plurality of openings 120 are arranged in a matrix on the anode wiring 104. In the opening 120, the organic EL element 10 is provided between the anode wiring 104 and the cathode wiring 108. That is, each opening 120 becomes a pixel. Accordingly, a display area is formed corresponding to the opening 120. Here, the thickness of the insulating film 110 can be, for example, 200 nm to 1000 nm, and the size of the opening 120 can be, for example, 100 μm × 100 μm.

  The organic EL element 10 is located between the anode wiring 104 and the cathode wiring 108 in the opening 120. In this case, the anode 2 of the organic EL element 10 is in contact with the anode wiring 104 and the cathode 4 is in contact with the cathode wiring 108. The thickness of the organic EL element 10 can be set to 150 nm to 200 nm, for example.

  On the insulating film 110, a plurality of cathode partition walls 112 are formed along a direction perpendicular to the anode wiring 104. The cathode partition 112 plays a role for spatially separating the plurality of cathode wirings 108 so that the wirings of the cathode wirings 108 do not conduct with each other. Accordingly, the cathode wiring 108 is disposed between the adjacent cathode partition walls 112. As the size of the cathode partition 112, for example, the one having a height of 2 μm to 3 μm and a width of 10 μm can be used.

  In addition, the substrate 1 is bonded to each other through a sealing plate 116 and a sealing material 118. Thereby, the space in which the organic EL element 10 is provided can be sealed, and the organic EL element 10 can be prevented from being deteriorated by moisture in the atmosphere. As the sealing plate 116, for example, a glass substrate having a thickness of 0.7 mm to 1.1 mm can be used. The sealing plate 116 may not be transparent when light is extracted from the substrate 1 side as in the case of a bottom emission type element. On the other hand, when light is extracted from the sealing plate 116 side as in the case of the top emission type, the sealing plate 116 needs to be transparent to at least a part of the emission wavelength region.

  In the image display apparatus 100 having such a structure, a current can be supplied to the organic EL element 10 through a positive electrode auxiliary wiring 106 and a negative electrode auxiliary wiring (not shown) by a driving device (not shown) to cause the light emitting layer to emit light. Then, light can be emitted from the substrate 1 through the substrate 1. An image can be displayed on the image display device 100 by controlling the light emission and non-light emission of the organic EL element 10 corresponding to the above-described pixel by the control device.

(Lighting device)
Next, a lighting device using the organic EL element will be described. A lighting device including the organic EL element 10 will be described. In addition, the organic EL element may have a bottom emission structure or a top emission structure, but in the following, an example of a bottom emission structure will be described.
FIG. 7 is a diagram illustrating an example of an illumination device including the organic EL element 10 described above.
7 includes the organic EL element 10 described above, a terminal 202 installed on the substrate 1 of the organic EL element 10 and connected to the anode 2 (see FIG. 2), and the cathode 4 (see FIG. 2). And the lighting circuit 201 for driving the organic EL element 10 connected to the terminal 202 and the terminal 203.

  The lighting circuit 201 has a DC power source (not shown) and a control circuit (not shown) inside, and supplies a current by applying a voltage between the anode layer 2 and the cathode 4 of the organic EL element 10 through the terminal 202 and the terminal 203. To do. Then, the organic EL element 10 is driven, the light emitting layer is caused to emit light, light is emitted through the substrate 1, and used as illumination light. The light emitting layer may be made of a light emitting material that emits white light, and each of the organic EL elements 10 using light emitting materials that emit green light (G), blue light (B), and red light (R). A plurality of them may be provided so that the combined light is white.

(Manufacturing method of organic EL element)
Below, the manufacturing method of the organic EL element of each embodiment of this invention is mentioned as an example, respectively. It goes without saying that the steps and methods of the method for manufacturing an organic EL element of one embodiment can be applied to the methods for manufacturing an organic EL element of another embodiment, even if not specifically mentioned.

First, the anode 2 is formed on the substrate 1. A method for forming the anode 2 is not particularly limited. For example, in addition to a dry process such as a resistance heating vapor deposition method, an electron beam vapor deposition method, a sputtering method, an ion plating method, and a CVD method, various wet processes such as a coating method can be used. Can be used.
In addition, after the anode 2 is formed, the surface treatment of the anode 2 is performed to improve the performance of the overcoated layer (adhesion with the anode 2, surface smoothness, reduction of hole injection barrier, etc.). Can do. Specific examples of the surface treatment include high-frequency plasma treatment, sputtering treatment, corona treatment, UV ozone irradiation treatment, ultraviolet irradiation treatment, oxygen plasma treatment, and the like.

  Furthermore, the same effect as the surface treatment can be expected by forming an anode buffer layer (not shown) instead of or in addition to the surface treatment of the surface treatment of the anode 2. The anode buffer layer can be prepared by a wet process. Specific film forming methods include spin coating, casting, micro gravure coating, gravure coating, bar coating, roll coating, and wire bar. Examples of the coating method include a coating method, a dip coating method, a spray coating method, a screen printing method, a flexographic printing method, an offset printing method, and an inkjet printing method, an immersion method, and an electrochemical method.

  Next, the organic layer 3 is formed on the anode 2. A conventionally known method can be used to form the organic layer 3 and is not particularly limited. For example, methods such as a vacuum deposition method, a spin coating method, a casting method, and an LB method can be used.

  The cathode 4 can be formed by the same method as the anode 2 and is not particularly limited. For example, a resistance heating vapor deposition method, an electron beam vapor deposition method, a sputtering method, an ion plating method, a CVD method, or the like is used. Can do.

Although the formation method of the low refractive index layer 5 is not specifically limited, For example, resistance heating vapor deposition method, electron beam vapor deposition method, sputtering method, ion plating method, CVD method etc. can be used.
When the low-refractive index layer 5 is a low-refractive index layer including an air layer, for example, after the SOG layer is formed, the SOG material is left at a predetermined position in the SOG layer using photolithography. The low refractive index layer is formed by etching away the SOG layer so that the portion where the SOG layer is removed becomes an air layer.

  Although the formation method of the high refractive index layer 7 is not specifically limited, For example, resistance heating vapor deposition method, electron beam vapor deposition method, sputtering method, ion plating method, CVD method etc. can be used.

  Although the formation method of the metal layer 6 is not specifically limited, For example, a vapor deposition method and sputtering can be used.

  The present invention is not limited to the bottom emission structure, and may be formed on the substrate in order from the reflective layer 6 in the reverse order of the above-described steps.

  The organic EL element 10 can be manufactured by the above process. After these series of steps, it is preferable to attach a protective layer or a protective cover (not shown) for driving the organic EL element 10 stably for a long period of time and protecting the organic EL element 10 from external moisture, oxygen and the like. . As the protective layer, polymer compounds, metal oxides, metal fluorides, metal borides, silicon compounds such as silicon nitride and silicon oxide, and the like can be used. It is also possible to use a metal having a relatively large ionization tendency such as zinc as a sacrificial layer (a protective layer to be removed in a subsequent process). And these laminated bodies can also be used. Further, as the protective cover, a glass plate, a plastic plate whose surface has been subjected to low water permeability treatment, a metal, or the like can be used. It is preferable to adopt a method in which the protective cover is sealed by being bonded to the substrate 1 with a thermosetting resin, a photocurable resin, or frit glass. At this time, a predetermined space can be maintained by using a spacer, and it is preferable because the protective cover can be prevented from being touched by an external force to damage the organic EL element 10. Then, if an inert gas such as nitrogen, argon or helium, or various inert liquids such as perfluorocarbon is sealed in this space, it is easy to prevent the upper metal layer 6 from being oxidized. In particular, when helium is used, heat conduction is high, and thus heat generated from the organic EL element 10 when voltage is applied can be effectively transmitted to the protective cover, which is preferable. Further, by installing a desiccant such as barium oxide in this space, it becomes easy to suppress the moisture adsorbed in the series of manufacturing steps from damaging the organic EL element 10.

  Examples of the organic EL device of the present invention will be described below.

In the present invention, the effect on the light extraction efficiency of the organic EL element of each embodiment was confirmed by simulation. First, the finite difference time domain method (FDTD method) used for the simulation will be described. The FDTD method is an analysis method for tracking the time change of the electromagnetic field at each point in space by differentiating Maxwell's equation describing the time change of the electromagnetic field spatially and temporally. In order to calculate the light extraction efficiency of the organic EL element by the FDTD method, the light emission in the light emitting layer is regarded as the radiation from the minute dipole, and the intensity of the radiation is counted. More specifically, the frequency dependence is calculated using the ratio of the light extracted to the substrate with respect to the total radiation intensity of the dipole as the light extraction efficiency. Hereinafter, the calculation result of the light extraction efficiency is shown in a graph. Λ on the horizontal axis represents the frequency of the dipole as a wavelength in vacuum, and η on the vertical axis represents the light extraction efficiency. The same applies to the following drawings.
In order to simulate a light emission phenomenon close to reality, the calculation was performed with a dipole as a light emission source being random (dipole moment is random in all directions).

Example 1
FIG. 8 is a cross-sectional view showing a model structure of the organic EL element 10 used in the simulation. The SPP mode light extracted up to the organic layer is made into a waveguide mode by the second electrode side structure having a high refractive index layer having a higher refractive index than the low refractive index layer between the low refractive index layer and the metal layer. In order to efficiently lead to the substrate without introducing a refractive index modulation structure as an example of the first electrode side structure on the anode 2 side. Specifically, a dielectric layer 8 having a plurality of holes is provided between the anode 2 and the organic layer 3, and the organic layer 3 has at least a hole inner surface covering portion that covers the inner surface of the hole. The refractive index of the dielectric layer 8 is different from that of the inner surface covering portion of the hole portion, the anode 2 is provided with an anode hole portion communicating with the hole portion, and the organic layer 3 is further provided in the anode hole portion of the anode hole portion. The inner surface covering portion of the anode hole portion covering the side surface, and the layer portion disposed between the dielectric layer 8 and the inner surface covering portion of the hole portion and the cathode 4 are provided.
The substrate 1 is made of glass, and a refractive index of 1.52 is used. Assuming that the anode 2 and the cathode 4 are made of ITO, the refractive index is 1.82 + 0.009i at 550 nm, and other wavelengths are extrapolated by the Lorentz model. Further, 1.72 was used as the refractive index of the organic layer 3. The low refractive index layer 5 is made of magnesium fluoride (MgF ₂ ), and the refractive index is 1.38. Further, assuming that the metal layer 6 is made of silver (Ag), the refractive index is 0.125 + 3.34i at 550 nm, and other wavelengths are extrapolated by the Drude model. Further, assuming that the high refractive index layer 7 is made of titanium oxide (TiO ₂ ), the refractive index is 2.13 at 550 nm, and other wavelengths are extrapolated by the Lorentz model.
As the refractive index modulation structure on the anode 2 side, the structure shown in FIG. 5E (however, the organic layer 3 has a layered portion) was introduced. The dielectric layer 8 is made of silicon oxide (SiO ₂ ), and a refractive index of 1.45 is used.
The layer thickness of the anode 2, the layer thickness of the dielectric layer 8, and the distance in the film thickness direction from the light emitting point of the organic layer 3 to the dielectric layer 8 were 150 nm, 120 nm, and 80 nm, respectively. Regarding the thickness of the other layers, various changes were made in the following examination.
Further, in the refractive index modulation structure of the organic EL element 10, the holes communicating with the holes of the dielectric layer 8 and the anode holes of the anode 2 are circular in plan view, and the communicating holes are arranged in a square lattice pattern. The distance between the centers of adjacent anode hole portions was 1000 nm, the gap width between the anode hole portions was 400 nm, and the diameter of the anode hole portion was 600 nm. Since the current flows through the anode hole portion, in this embodiment, the center of the anode hole portion (the star-marked portion in FIG. 8) is used as the light emission point.
For comparison, the light extraction efficiency was also calculated for an Otto type organic EL element 90 in which the high refractive index layer 7 was not introduced. These Otto type organic EL elements 90 were also provided with the same refractive index modulation structure as the organic EL element 10 of the example.

In Example 1, as shown in FIGS. 9A to 9C, the film thickness of the high refractive index layer 7 was kept constant at 30 nm, and the film thickness of the low refractive index layer 5 was changed. Furthermore, for comparison, the light extraction efficiency of an Otto type organic EL element 90 in which the high refractive index layer 7 is not introduced as shown in FIGS. 9D to 9F was also calculated. However, in FIGS. 9A to 9F, the first electrode side structure on the anode 2 side is not shown, and only the configuration from the light emitting point to the metal layer 6 is drawn.
Here, FIG. 9A and FIG. 9D have a difference in whether or not the high refractive index layer 7 is provided, but the optical distance from the light emitting point of the organic layer 3 to the metal layer 6. (The value obtained by multiplying the distance by the real part of the refractive index) is the same. 9A and 9D are optically radiated directly from the light emitting point to the anode side and reflected from the metal layer 6 to the anode side after being emitted from the light emitting point to the cathode side. The shape of the interference pattern generated in the element by the traveling light is almost the same. For the same reason, FIG. 9 (b) and FIG. 9 (e), FIG. 9 (c) and FIG. 9 (f) show whether the optical distance is the same and whether or not the high refractive index layer 7 is provided. Have a difference.
Specifically, the thicknesses of the metal layer 6 and the cathode 4 were set to 100 nm and 50 nm, respectively, in all the elements shown in FIGS. The layer thickness of the low refractive index layer 5 and the shortest distance from the light emitting point of the organic layer 3 to the cathode 4 are as shown in FIGS.

FIG. 10 shows the result of calculating the light extraction efficiency of the organic EL element 10 shown in FIG. 9 by computer simulation using the FDTD method. The symbols in the figure correspond to the results of the light extraction efficiency of the organic EL element 10 with the symbols in FIG.
Comparing (a) and (d) in the graph of FIG. 10, the light extraction efficiency of (a) having the high refractive index layer 7 is improved as compared to (d) not having the high refractive index layer 7. Can be confirmed. Similarly, comparing (b) and (e), it can be seen that (b) improves light extraction efficiency, and (c) and (f) compare (c). That is, it can be seen that, when the optical distance is the same, by introducing the high refractive index layer 7, light can be extracted efficiently without losing light.

(Example 2)
In Example 2, as shown in FIGS. 11A to 11C, the film thickness of the low refractive index layer 5 was constant at 100 nm, and the film thickness of the high refractive index layer 7 was changed. Further, for comparison, the light extraction efficiency of an Otto type organic EL element 90 without introducing the high refractive index layer 7 was also calculated as shown in FIGS. However, in FIGS. 11A to 11F, the structure on the first electrode side on the anode 2 side is not shown, and only the structure from the light emitting point to the metal layer 6 is drawn.
Here, FIG. 11A and FIG. 11D have the same optical distance from the light emitting point of the organic layer 3 to the metal layer 6 (the value obtained by multiplying the distance by the real part of the refractive index). The difference is whether or not the high refractive index layer 7 is provided. Similarly, FIG. 11 (b) and FIG. 11 (e), FIG. 11 (c) and FIG. 11 (f) have the same optical distance, but whether or not the high refractive index layer 7 is provided. have.
Specifically, the thicknesses of the metal layer 6 and the cathode 4 were set to 100 nm and 50 nm, respectively, in all the elements shown in FIGS. The layer thickness of the high refractive index layer 7 was changed to 30 nm, 45 nm, and 60 nm, respectively, in FIGS. Further, the layer thickness of the low refractive index layer 5 and the shortest distance from the light emitting point of the organic layer 3 to the cathode 4 are as shown in FIGS.

FIG. 12 shows the result of calculating the light extraction efficiency of the organic EL element 10 shown in FIG. 11 by computer simulation using the FDTD method. The symbols in the figure correspond to the results of the light extraction efficiency of the organic EL element 10 with the symbols in FIG.
When comparing (a) and (d) of the graph of FIG. 12, it can be confirmed that (a) having the high refractive index layer 7 has improved light extraction efficiency. Similarly, comparing (b) and (e), it can be seen that (b) improves light extraction efficiency, and (c) and (f) compare (c). That is, it can be seen that when the optical distance is the same, the light can be extracted efficiently without loss of light by introducing the high refractive index layer 7.
In addition, the light extraction efficiency is improved in (a) where the film thickness of the high refractive index layer 7 is 30 nm as compared with (b) and (c). This is considered to be because if the thickness is 30 nm, light capture by the SPP mode light in the metal layer 6 can be sufficiently suppressed, and light guided in the high refractive index layer 7 can be reduced.

(Example 3)
In Example 3, calculation was performed by changing the layer thickness of the low refractive index layer 5 while keeping the high refractive index layer 7 constant as in Example 1, except that the cathode 4 was made of silver (Ag) in FIG. It was. The cathode 4 has a refractive index of 550 nm and 0.125 + 3.34i, and other wavelengths were extrapolated by the Drude model.
In addition, as shown in FIGS. 13A to 13C, the film thickness of the high refractive index layer 7 is constant at 30 nm, and the light extraction efficiency is calculated when the film thickness of the low refractive index layer 5 is changed. It is a graph. Furthermore, for comparison, the light extraction efficiency of an Otto type organic EL element 90 in which the high refractive index layer 7 is not introduced as shown in FIGS. 13D to 13F was also calculated. However, in FIGS. 13A to 13F, the first electrode side structure on the anode 2 side is not shown, and only the configuration from the light emitting point to the metal layer 6 is drawn.
Here, FIG. 13A and FIG. 13D have the same optical distance from the light emitting point of the organic layer 3 to the metal layer 6 (a value obtained by multiplying the distance by the real part of the refractive index). The difference is whether or not the high refractive index layer 7 is provided. Similarly, FIG. 13 (b) and FIG. 13 (e), FIG. 13 (c) and FIG. 13 (f) have the same optical distance, but whether or not the high refractive index layer 7 is provided. have.
Specifically, the film thicknesses of the metal layer 6 and the cathode 4 were 100 nm and 15 nm, respectively, in all the elements shown in FIGS. The layer thickness of the low refractive index layer 5 and the shortest distance from the light emitting point of the organic layer 3 to the cathode 4 are as shown in FIGS.

FIG. 14 shows the result of calculating the light extraction efficiency of the organic EL element 10 shown in FIG. 13 by computer simulation using the FDTD method. The symbols in the figure correspond to the results of the light extraction efficiency of the organic EL element 10 with the symbols in FIG.
Comparing (a) and (d) in the graph of FIG. 14, it can be confirmed that (a) having the high refractive index layer 7 has improved light extraction efficiency. Similarly, comparing (b) and (e), it can be seen that (b) improves light extraction efficiency, and (c) and (f) compare (c). That is, it can be seen that when the optical distance is the same, the light can be extracted efficiently without loss of light by introducing the high refractive index layer 7.

Example 4
In Example 4, as in Example 3, the thickness of the high refractive index layer 7 was kept constant with the low refractive index layer 5 being constant as in Example 2 except that the cathode 4 was made of silver (Ag) in FIG. The calculation was performed while changing.
In Example 4, when the film thickness of the low refractive index layer 5 is constant at 130 nm and the film thickness of the high refractive index layer 7 is changed as shown in FIGS. It is the graph which calculated extraction efficiency. Further, for comparison, the light extraction efficiency of an Otto type organic EL element 90 in which the high refractive index layer 7 is not introduced as shown in FIGS. 15D to 15F was also calculated. However, in FIGS. 15A to 15F, the first electrode side structure on the anode 2 side is not shown, and only the configuration from the light emitting point to the metal layer 6 is drawn.
Here, FIG. 15A and FIG. 15D have the same optical distance from the light emitting point of the organic layer 3 to the metal layer 6 (the value obtained by multiplying the distance by the real part of the refractive index). The difference is whether or not the high refractive index layer 7 is provided. Similarly, FIG. 15B and FIG. 15E, FIG. 15C and FIG. 15F have the same optical distance, but whether or not the high refractive index layer 7 is provided. have.
Specifically, the thicknesses of the metal layer 6 and the cathode 4 were set to 100 nm and 15 nm, respectively, in all the elements shown in FIGS. The layer thickness of the high refractive index layer 7 was changed to 30 nm, 45 nm, and 60 nm in FIGS. Further, the layer thickness of the low refractive index layer 5 and the shortest distance from the light emitting point of the organic layer 3 to the cathode 4 are as shown in FIGS.

FIG. 16 shows the result of calculating the light extraction efficiency of the organic EL element 10 shown in FIG. 15 by computer simulation using the FDTD method. The symbols in the figure correspond to the results of the light extraction efficiency of the organic EL element 10 with the symbols in FIG.
When comparing (a) and (d) of the graph of FIG. 16, it can be confirmed that (a) having the high refractive index layer 7 has improved light extraction efficiency. Similarly, comparing (b) and (e), it can be seen that (b) improves light extraction efficiency, and (c) and (f) compare (c). That is, it can be seen that when the optical distance is the same, the light can be extracted efficiently without loss of light by introducing the high refractive index layer 7.

  From these results, it is found that the high refractive index layer 7 is introduced regardless of whether the film thickness of the low refractive index layer 5 and the high refractive index layer 7 is changed or the material of the cathode 4 is changed. It can be seen that the light extraction efficiency is improved by the two-electrode structure.

DESCRIPTION OF SYMBOLS 10, 90 Organic EL element 1, 91 Substrate 2, 92 Anode 3, 93 Organic layer 4, 94 Cathode 5, 95 Low refractive index layer 6, 96 Metal layer 7 High refractive index layer 8 Dielectric layer 17, 18 Translucency Material 100 Image display device 104 Anode wiring 106 Anode auxiliary wiring 108 Cathode wiring 110 Insulating film 112 Cathode partition 116 Sealing plate 118 Sealing material 120 Opening 200 Lighting device 201 Lighting circuit 202 Terminal 203 Terminal

Claims (10)

An organic EL device comprising a first electrode, an organic layer including a light emitting layer, a second electrode, a low refractive index layer, a high refractive index layer, and a metal layer in order,
The second electrode is made of a translucent conductive material,
An organic EL element, wherein a refractive index of the high refractive index layer is higher than a refractive index of the low refractive index layer.   The organic EL element according to claim 1, wherein a refractive index of the high refractive index layer is higher than that of the organic layer.   The organic EL element according to claim 1, wherein the high refractive index layer has a thickness of 10 to 300 nm.   The organic EL element according to claim 1, wherein a refractive index of the low refractive index layer is further lower than a refractive index of the organic layer.   The organic EL element according to claim 4, wherein a refractive index of the low refractive index layer is lower than a refractive index of the second electrode.   6. The organic EL element according to claim 1, wherein the first electrode has a refractive index modulation structure on a side opposite to the organic layer.   The organic EL element according to claim 6, wherein the refractive index modulation structure is any one of a diffraction grating, a lens, and a photonic crystal.   6. The organic EL element according to claim 1, further comprising a diffusion scatterer on a side opposite to the organic layer of the first electrode.   An image display device comprising the organic EL element according to claim 1.   An illuminating device comprising the organic EL element according to claim 1.

Images