JP2007294266A - Organic electroluminescent element - Google Patents

Organic electroluminescent element Download PDF

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JP2007294266A
JP2007294266A JP2006121337A JP2006121337A JP2007294266A JP 2007294266 A JP2007294266 A JP 2007294266A JP 2006121337 A JP2006121337 A JP 2006121337A JP 2006121337 A JP2006121337 A JP 2006121337A JP 2007294266 A JP2007294266 A JP 2007294266A
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refractive index
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index layer
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JP4939104B2 (en
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Takeyuki Yamaki
健之 山木
Nobuhiro Ito
宜弘 伊藤
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Panasonic Electric Works Co Ltd
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Matsushita Electric Works Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element with light extraction efficiency improved. <P>SOLUTION: The organic EL element has a metal electrode 8, an electroluminescent layer 9, a transparent electrode 2, and a transparent base material 1 laminated, so made to take out light through the transparent base material 1. Two layers of a high-refraction index layer 10 and a low-refraction index layer 11 are provided between the transparent electrode 2 and the transparent base material 1, with the former 10 by the side of the transparent electrode 2 and the latter 11 by the side of the transparent base material 1. An optical film thickness and a refraction index of each layer are set as follows: (1) an optical film thickness of the transparent electrode 2 to be smaller than (1/2)λ, (2) an optical film thickness of the low-refraction index layer 11 to be larger than (1/2)λ, (3) an optical film thickness of the high-refraction index layer 10 to be larger than (1/8)λ and smaller (3/8)λ, (4) an optical distance from a face of the high-refraction index layer 10 at the side of the transparent base material 1 to a face of the metal electrode 8 at the side of the transparent base material 1 to be smaller than λ, and (5) a refraction index of the high-refraction index layer 10 to be larger than (a refraction index of the transparent electrode 2 minus 0.2), provided, λ is a light emission wavelength, and the refraction index is one at the emission wavelength. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、各種ディスプレイ、表示素子、液晶用バックライト等に用いられる有機ＥＬ素子に関するものである。   The present invention relates to an organic EL element used for various displays, display elements, liquid crystal backlights, and the like.

近年、情報化社会の進展に伴って、各種のディスプレイが開発されている。このようなディスプレイに用いられる薄膜型の発光素子の代表的なものの一つとして、例えば有機ＥＬ（エレクトロルミネッセンス）素子からなる発光体がある。   In recent years, various displays have been developed with the progress of the information society. As a typical thin film type light emitting element used for such a display, there is a light emitting body made of, for example, an organic EL (electroluminescence) element.

図３は透明基材１の上にエレクトロルミネッセンス層や電極などからなる発光層１５を設けて形成される有機ＥＬ素子を概略的に示すものであり、発光層１５から発光される光は透明基材１を通して、透明基材１の露出表面から出射されることによって、外部に取り出されるようになっている。ここで図３に矢印で示すように、透明基材１の表面と空気との界面に小さい入射角で入射する一部の光は透明基材１の露出表面から外部に出射されるが、多くの光は透明基材１の露出表面と空気との界面で反射して、透明基材１内において端部に向かう方向に導波されたり、内部で消失されたりしてしまい、発光した光の２０％程度しか透明基材１の露出表面から取り出すことができない。この現象は、有機ＥＬ素子において光の取出効率を低く留めている大きな原因の一つである。   FIG. 3 schematically shows an organic EL device formed by providing a light emitting layer 15 composed of an electroluminescence layer, an electrode, or the like on a transparent substrate 1, and the light emitted from the light emitting layer 15 is a transparent substrate. By being emitted from the exposed surface of the transparent substrate 1 through the material 1, it is taken out to the outside. Here, as shown by arrows in FIG. 3, some of the light that enters the interface between the surface of the transparent substrate 1 and the air at a small incident angle is emitted from the exposed surface of the transparent substrate 1 to the outside. Is reflected at the interface between the exposed surface of the transparent base material 1 and the air, and is guided in the direction toward the end in the transparent base material 1 or disappears therein, and the emitted light Only about 20% can be taken out from the exposed surface of the transparent substrate 1. This phenomenon is one of the major causes that keep the light extraction efficiency low in the organic EL element.

そこで、このような現象を回避して透明基材１の露出表面からの光の取り出し効率を高めるための工夫が種々なされている。例えば、図４に概略的に示すように、透明基材１と発光素子１５との間に透明基材１より屈折率が小さい低屈折率層１７（例えば屈折率が１．３以下）を設けることが行なわれている。このようにすると、低屈折率層１７と透明基材１との界面で光を屈折させて、透明基材１の露出表面と空気との界面に入射する光の入射角が小さくなり、その結果、透明基材１の露出表面と空気との界面で反射される光の量が少なくなって透明基材１内における導波が抑制され、透明基材１の表面から外部に光を取り出す効率が高まるものである。   Therefore, various ideas have been made to avoid such a phenomenon and to increase the light extraction efficiency from the exposed surface of the transparent substrate 1. For example, as schematically shown in FIG. 4, a low refractive index layer 17 (for example, a refractive index of 1.3 or less) having a refractive index smaller than that of the transparent substrate 1 is provided between the transparent substrate 1 and the light emitting element 15. Has been done. In this way, light is refracted at the interface between the low refractive index layer 17 and the transparent substrate 1, and the incident angle of light incident on the interface between the exposed surface of the transparent substrate 1 and the air is reduced. The amount of light reflected at the interface between the exposed surface of the transparent substrate 1 and the air is reduced, the wave guide in the transparent substrate 1 is suppressed, and the efficiency of extracting light from the surface of the transparent substrate 1 to the outside is improved. It will increase.

このように低屈折率層の挿入によって透明基材１内での導波を実質的に消滅させることが可能で、その結果、光の取出効率を高めることができる。そして特許文献１では、このような低屈折層をシリカエアロゲルに代表される多孔質薄膜で形成するようにしている。しかし多孔質薄膜は機械強度が必ずしも十分ではないので、特許文献２では、この機械強度が十分ではないシリカエアロゲル薄膜の代わりに、低屈折率微粒子とバインダーからなる低屈折率層を有機ＥＬ素子に導入することが提案されている。   As described above, the insertion of the low refractive index layer can substantially eliminate the waveguide in the transparent substrate 1, and as a result, the light extraction efficiency can be increased. In Patent Document 1, such a low refractive layer is formed of a porous thin film typified by silica aerogel. However, since the mechanical strength of the porous thin film is not always sufficient, in Patent Document 2, instead of the silica airgel thin film having insufficient mechanical strength, a low refractive index layer composed of low refractive index fine particles and a binder is used as an organic EL element. It has been proposed to introduce.

しかしながら、有機ＥＬ素子はエレクトロルミネッセンス層を形成する発光層・ホール輸送層・ホール注入層や透明電極等の多層積層構造となっており、光の干渉（増幅・減衰）が発生するものであり、光の干渉を考慮せずに、低屈折率層を透明電極と透明基材との間に挿入しても十分な光取り出しの向上は得られない。   However, the organic EL element has a multilayer laminated structure such as a light emitting layer, a hole transport layer, a hole injection layer, and a transparent electrode that form an electroluminescence layer, and light interference (amplification / attenuation) occurs. Even if the low refractive index layer is inserted between the transparent electrode and the transparent substrate without considering the interference of light, sufficient light extraction cannot be improved.

また特許文献３では透明電極と低屈折率層の界面の全反射による光取り出しロスの改善方法が提案されている。すなわち、低屈折率層に散乱機能（光散乱微粒子）を付与し、界面の全反射によるロスを低減している。しかしながら、このように低屈折率層に光散乱微粒子（粒径５０ｎｍ以上）を導入すると、光散乱微粒子によって低屈折率層の表面粗さが大きくなり、その表面粗さが透明電極にも反映されることになって、有機ＥＬ素子としての信頼性を損なってしまうという問題があった。
特開２００１−２０２８２７号公報 特開２００３−２１６０６１号公報 特開２００４−２９６４３７号公報 Patent Document 3 proposes a method for improving light extraction loss due to total reflection at the interface between the transparent electrode and the low refractive index layer. That is, a scattering function (light scattering fine particles) is imparted to the low refractive index layer, and loss due to total reflection at the interface is reduced. However, when light scattering fine particles (particle size of 50 nm or more) are introduced into the low refractive index layer in this way, the surface roughness of the low refractive index layer is increased by the light scattering fine particles, and the surface roughness is also reflected in the transparent electrode. As a result, there is a problem that reliability as an organic EL element is impaired.
JP 2001-202827 A Japanese Patent Laid-Open No. 2003-216061 JP 2004-296437 A

上記のように、薄膜型の発光素子である有機ＥＬ素子においては発光した光を外部（大気中）に取り出す場合の取り出し効率を向上させることが難しく、取り出し効率の向上が課題となっているものである。   As described above, in an organic EL element which is a thin-film light emitting element, it is difficult to improve the extraction efficiency when the emitted light is extracted outside (in the atmosphere), and improvement of the extraction efficiency is a problem. It is.

本発明は上記の点に鑑みてなされたものであり、有機ＥＬ素子において、光の取り出し効率を向上させることを目的とするものである。   The present invention has been made in view of the above points, and an object of the present invention is to improve light extraction efficiency in an organic EL element.

本発明の請求項１に係る有機ＥＬ素子は、少なくとも金属電極、エレクトロルミネッセンス層、透明電極、透明基材をこの順に積層し、エレクトロルミネッセンス層で発光した光を透明基材を通して取り出すようにした有機ＥＬ素子において、透明電極と透明基材の間に高屈折率層及び低屈折率層の２層を、高屈折率層を透明電極の側に、低屈折率層を透明基材の側に配置して設け、上記各層の光学膜厚及び屈折率を下記のように形成して成ることを特徴とするものである。
・透明電極の光学膜厚が、（１／２）λより小さい
・低屈折率層の光学膜厚が、（１／２）λより大きい
・高屈折率層の光学膜厚が、（１／８）λより大きく且つ（３／８）λより小さい
・高屈折率層の透明基材の側の面から、金属電極の透明基材の側の面までの光学距離が、λより小さい
・高屈折率層の屈折率が、（透明電極の屈折率−０．２）より大きい
（但し、λはエレクトロルミネッセンス層で発光する光の波長、屈折率はこの発光波長における屈折率）
また請求項２の発明は、請求項１において、低屈折率層の屈折率が１．４０未満であることを特徴とするものである。 The organic EL device according to claim 1 of the present invention is an organic EL device in which at least a metal electrode, an electroluminescence layer, a transparent electrode, and a transparent substrate are laminated in this order, and light emitted from the electroluminescence layer is extracted through the transparent substrate. In an EL element, two layers, a high refractive index layer and a low refractive index layer, are arranged between the transparent electrode and the transparent substrate, the high refractive index layer on the transparent electrode side, and the low refractive index layer on the transparent substrate side. The optical film thickness and refractive index of each of the above layers are formed as follows.
The optical film thickness of the transparent electrode is smaller than (1/2) λ The optical film thickness of the low refractive index layer is larger than (1/2) λ The optical film thickness of the high refractive index layer is (1 / 8) Larger than λ and smaller than (3/8) λ · The optical distance from the transparent substrate side surface of the high refractive index layer to the transparent substrate side surface of the metal electrode is less than λ · High The refractive index of the refractive index layer is larger than (refractive index of transparent electrode -0.2) (where λ is the wavelength of light emitted from the electroluminescent layer, and the refractive index is the refractive index at this emission wavelength).
The invention of claim 2 is characterized in that, in claim 1, the refractive index of the low refractive index layer is less than 1.40.

本発明によれば、透明基材の正面方向への光の取り出しの効率は、高屈折率層と低屈折率層によって形成される誘電体ミラーと、金属電極によって形成される金属ミラーとの間の共振効果による光干渉を利用して高めることができ、また透明基材の斜め方向への光の取り出し効率は、低屈折率層の取り出し効果を利用して高めることができ、全方位方向でのトータルの外部取り出し効率を向上させることができるものである。   According to the present invention, the light extraction efficiency in the front direction of the transparent substrate is between the dielectric mirror formed by the high refractive index layer and the low refractive index layer and the metal mirror formed by the metal electrode. The light extraction efficiency in the oblique direction of the transparent substrate can be increased by using the light extraction effect of the low refractive index layer, and can be increased in all directions. The total external extraction efficiency can be improved.

以下、本発明を実施するための最良の形態を説明する。   Hereinafter, the best mode for carrying out the present invention will be described.

図１は有機ＥＬ素子の層構成の一例を示すものであり、透光性の透明基材１の上に透明導電膜からなる透明電極２を積層し、透明電極２の上にホール注入層３及びホ−ル輸送層４を積層すると共に、その上に有機発光層５が積層してある。さらにこの有機発光層５の上に電子輸送層６及び電子注入層７を積層し、その上に金属電極８が積層してある。通常、透明電極２が陽極、金属電極８が陰極として形成されるものであり、またホール注入層３・ホ−ル輸送層４・有機発光層５・電子輸送層６・電子注入層７によってエレクトロルミネッセンス層９が形成されるものである。そして本発明では、透明電極２と透明基材１の間に、高屈折率層１０及び低屈折率層１１の２層を、高屈折率層１０を透明電極２の側に、低屈折率層１１を透明基材１の側に配置して、挿入してある。ここで、低屈折率層１１は透明基材１よりも屈折率が低い層であり、高屈折率層１０は低屈折率層１１よりも屈折率が高い層である。   FIG. 1 shows an example of the layer structure of an organic EL element. A transparent electrode 2 made of a transparent conductive film is laminated on a translucent transparent substrate 1, and a hole injection layer 3 is laminated on the transparent electrode 2. In addition, a hole transport layer 4 is laminated, and an organic light emitting layer 5 is laminated thereon. Further, an electron transport layer 6 and an electron injection layer 7 are laminated on the organic light emitting layer 5, and a metal electrode 8 is laminated thereon. Usually, the transparent electrode 2 is formed as an anode and the metal electrode 8 is formed as a cathode, and the hole injection layer 3, the hole transport layer 4, the organic light emitting layer 5, the electron transport layer 6, and the electron injection layer 7 are used for electrolysis. The luminescence layer 9 is formed. In the present invention, between the transparent electrode 2 and the transparent substrate 1, two layers of a high refractive index layer 10 and a low refractive index layer 11, a high refractive index layer 10 on the transparent electrode 2 side, and a low refractive index layer. 11 is arranged on the transparent substrate 1 side and inserted. Here, the low refractive index layer 11 is a layer having a refractive index lower than that of the transparent substrate 1, and the high refractive index layer 10 is a layer having a refractive index higher than that of the low refractive index layer 11.

勿論、この層構成はあくまでも一例であり、例えばホール注入層３とホ−ル輸送層４の一方あるいは両方を備えない構成、電子輸送層６と電子注入層７の一方あるいは両方を備えない層構成などに形成することもでき、本発明の趣旨に反しない限り図１の層構成に限定されるものではない。   Of course, this layer configuration is merely an example. For example, a configuration in which one or both of the hole injection layer 3 and the hole transport layer 4 are not provided, or a layer configuration in which one or both of the electron transport layer 6 and the electron injection layer 7 are not provided. The layer structure is not limited to that shown in FIG. 1 unless it is contrary to the spirit of the present invention.

そして、エレクトロルミネッセンス層９の有機発光層５で発光した光の一部は、透明電極２と透明基材１を透過して、透明基材１の表面（外面）から取り出されるものであり、また発光した光の他の一部は、金属電極８のエレクトロルミネッセンス層９側の面が金属ミラー８ａとなって反射され、エレクトロルミネッセンス層９と透明電極２及び透明基材１を透過して、透明基材１の表面（外面）から取り出されるものである。   A part of the light emitted from the organic light emitting layer 5 of the electroluminescence layer 9 is transmitted through the transparent electrode 2 and the transparent base material 1 and taken out from the surface (outer surface) of the transparent base material 1. The other part of the emitted light is reflected by the surface of the metal electrode 8 on the side of the electroluminescence layer 9 serving as the metal mirror 8a, passes through the electroluminescence layer 9, the transparent electrode 2 and the transparent substrate 1, and is transparent. It is taken out from the surface (outer surface) of the substrate 1.

上記のように形成される有機ＥＬ素子にあって、光干渉（共振）を利用して透明基材１からの光の取り出し量を向上させるためには、透明電極２の透明基材１の側の面から金属電極８の金属ミラー８ａまでの光学距離と、高屈折率層１０と低屈折率層１１によって形成される誘電体ミラーのしみ込み光学距離の和が、エレクトロルミネッセンス層９の有機発光層５で発光される光の主たる波長をλとすると、（１／２）λのｍ倍（ｍは整数）になるように設計すれば、正面方向の共振効果を得ることができるので、透明基材１の正面方向（透明基材１の表面に対して垂直あるいは垂直に近い方向）での取り出し量を向上させることができる。ここで誘電体ミラーのしみ込み光学距離は、誘電体実効屈折率をＮｅｆｆ、高屈折率層１０と低屈折率層１１の屈折率差をΔｎとしたとき、（１／２）λ×（Ｎｅｆｆ／Δｎ）で求められる距離であり、誘電体実効屈折率は、高屈折率層１０と低屈折率層１１の屈折率の平均屈折率とほぼ同じ値である。しかし、透明基材１の斜め方向（透明基材１の表面に対して斜めの方向）での光の取り出し効率を向上させるためには、発光点から低屈折率層１１までの光学距離を限りなく小さくすることが必要であり、透明電極２の透明基材１の側の面から金属電極８の金属ミラー８ａまでの光学距離と誘電体ミラーのしみ込み光学距離の和はｍ＝２のλ、あるいはｍ＝３の（３／２）λ程度にすることが望ましく、ｍ＝２のλ程度が最も望ましい。   In the organic EL element formed as described above, in order to improve the amount of light extracted from the transparent substrate 1 by utilizing light interference (resonance), the transparent electrode 2 side of the transparent substrate 1 is used. The sum of the optical distance from the surface of the metal electrode 8 to the metal mirror 8a and the penetration optical distance of the dielectric mirror formed by the high refractive index layer 10 and the low refractive index layer 11 is the organic light emission of the electroluminescence layer 9. If the main wavelength of the light emitted from the layer 5 is λ, it is possible to obtain a resonance effect in the front direction by designing it to be m times (1/2) λ (m is an integer). The amount of take-out in the front direction of the substrate 1 (perpendicular or nearly perpendicular to the surface of the transparent substrate 1) can be improved. Here, the penetration optical distance of the dielectric mirror is (1/2) λ × (Neff, where Neff is the dielectric effective refractive index and Δn is the refractive index difference between the high refractive index layer 10 and the low refractive index layer 11. / Δn), and the dielectric effective refractive index is substantially the same as the average refractive index of the refractive indexes of the high refractive index layer 10 and the low refractive index layer 11. However, in order to improve the light extraction efficiency in the oblique direction of the transparent base material 1 (direction oblique to the surface of the transparent base material 1), the optical distance from the light emitting point to the low refractive index layer 11 is limited. The sum of the optical distance from the surface of the transparent electrode 2 on the transparent substrate 1 side to the metal mirror 8a of the metal electrode 8 and the penetration optical distance of the dielectric mirror is λ of m = 2. Alternatively, it is preferable to set m = 3 to about (3/2) λ, and m = 2 is most preferable.

このため本発明では、高屈折率層１０の透明基材１の側の面から、金属電極８の透明基材１の側の面までの光学距離をλより小さく形成してあり、透明基材１の正面方向と斜め方向のいずれの方向からの光の取り出し効率を向上させ、透明基材１からの光の取り出し量を向上させることができるものである。   Therefore, in the present invention, the optical distance from the surface of the high refractive index layer 10 on the transparent substrate 1 side to the surface of the metal electrode 8 on the transparent substrate 1 side is formed to be smaller than λ. 1 can improve the light extraction efficiency from either the front direction or the oblique direction, and can improve the light extraction amount from the transparent substrate 1.

尚、上記の光学距離は各膜の光学膜厚（実膜厚と上記の発光波長での屈折率との積）の総和であり、図１の構成の有機ＥＬ素子において、透明電極２の透明基材１の側の面から金属電極８の金属ミラー８ａまでの光学距離は、透明電極２・ホール注入層３・ホ−ル輸送層４・有機発光層５・電子輸送層６・電子注入層７の各実膜厚と屈折率との積の総和である。   The optical distance is the sum of the optical film thicknesses of each film (the product of the actual film thickness and the refractive index at the emission wavelength). In the organic EL device having the configuration shown in FIG. The optical distance from the substrate 1 side surface to the metal mirror 8a of the metal electrode 8 is as follows: transparent electrode 2, hole injection layer 3, hole transport layer 4, organic light emitting layer 5, electron transport layer 6, electron injection layer 7 is the sum of the products of the actual film thickness and the refractive index.

次に、透明電極２については、透明電極２を形成する代表的な透明電極材料であるＩＴＯ、ＩＺＯは屈折率が１．９〜２．０であり、屈折率が約１．７程度のエレクトロルミネッセンス層９よりも高く、光の取り出しに対する障壁層になってしまう。このため、光の取り出し効率を向上させるためには、透明電極２はなるべく薄く形成するのがよく、光学膜厚で（１／２）λより薄くすることが必要である。透明電極２の光学膜厚は、より好ましくは（１／４）λ程度、さらに好ましくは（１／８）λ程度である。光の取り出し効率のうえではこれより薄いことがより好ましいが、電極としての機能を考慮すると、透明電極２の光学膜厚は（１／８）λ程度が最も好ましい。   Next, as for the transparent electrode 2, ITO and IZO, which are representative transparent electrode materials forming the transparent electrode 2, have an index of refraction of 1.9 to 2.0, and have an index of refraction of about 1.7. It is higher than the luminescence layer 9 and becomes a barrier layer against light extraction. For this reason, in order to improve the light extraction efficiency, the transparent electrode 2 is preferably formed as thin as possible, and it is necessary to make the optical film thickness thinner than (1/2) λ. The optical film thickness of the transparent electrode 2 is more preferably about (1/4) λ, and further preferably about (1/8) λ. In terms of light extraction efficiency, it is more preferable to be thinner than this, but considering the function as an electrode, the optical film thickness of the transparent electrode 2 is most preferably about (1/8) λ.

次に、透明電極２と透明基材１との間に設ける高屈折率層１０と低屈折率層１１については、高屈折率層１０の屈折率は、透明電極２から高屈折率層１０に光が入りやすくするために、（透明電極２の屈折率−０．２）よりも大きくすることが必要である。また、高屈折率層１０の光学膜厚は、高屈折率層１０と低屈折率層１１とで形成される誘電体ミラーの反射率分散において、波長λのときに最高反射率になるのが最も好ましく、このため（１／８）λより厚く、かつ（３／８）λより薄く形成されるものであり、（１／４）λ程度の光学膜厚が最も望ましい。   Next, for the high refractive index layer 10 and the low refractive index layer 11 provided between the transparent electrode 2 and the transparent substrate 1, the refractive index of the high refractive index layer 10 is changed from the transparent electrode 2 to the high refractive index layer 10. In order to make light easy to enter, it is necessary to make it larger than (refractive index of the transparent electrode 2 -0.2). Further, the optical film thickness of the high refractive index layer 10 has the highest reflectance at the wavelength λ in the reflectance dispersion of the dielectric mirror formed by the high refractive index layer 10 and the low refractive index layer 11. Most preferably, it is thicker than (1/8) λ and thinner than (3/8) λ, and an optical thickness of about (1/4) λ is most desirable.

この高屈折率層１０の材質としては、発光波長の領域において吸収がないものが好ましく、透過率・透明性に優れたものが好ましい。例えば蒸着・スパッタ・ＣＶＤ等の気相法で形成される酸化チタン（屈折率２．４〜２．７）、酸化ジルコニウム（屈折率２．２）、酸化スズ（屈折率１．９〜２．１）等を使用することができる。   The material of the high refractive index layer 10 is preferably a material that does not absorb light in the emission wavelength region, and is preferably excellent in transmittance and transparency. For example, titanium oxide (refractive index 2.4-2.7), zirconium oxide (refractive index 2.2), tin oxide (refractive index 1.9-2. 1) etc. can be used.

また、低屈折率層１１の屈折率は、高屈折率層１０の屈折率より小さければ誘電体ミラーになるが、誘電体ミラーの反射率を高くし、かつ斜め方向の光取り出し効率を向上させるためには、１．４未満が好ましく、より好ましくは１．３５未満である。また低屈折率層１１の光学膜厚は、斜め方向の取り出し効率を向上させるためにも、１／２λよりも厚くする必要があり、λより厚くすることがより望ましい。   Moreover, if the refractive index of the low refractive index layer 11 is smaller than the refractive index of the high refractive index layer 10, it becomes a dielectric mirror. However, the reflectance of the dielectric mirror is increased and the light extraction efficiency in the oblique direction is improved. For this purpose, it is preferably less than 1.4, more preferably less than 1.35. Further, the optical film thickness of the low refractive index layer 11 needs to be thicker than 1 / 2λ, and more desirably thicker than λ, in order to improve the extraction efficiency in the oblique direction.

この低屈折率層１１の材質としては、発光波長の領域において吸収がないものが好ましく、透過率に優れたものが好ましい。例えば蒸着・スパッタ・ＣＶＤ法等の気相法で形成される酸化ケイ素（屈折率１．４〜１．５）、フッ化マグネシウムやフッ化リチウム等のフッ化金属（屈折率１．３５〜１．４）、あるいは液相法（ゾル・ゲル等）で形成されるシリカ・シリコーン系樹脂膜、フッ素樹脂膜、及び多孔質微粒子と樹脂の複合膜等を使用することができる。液相法はさまざまな微粒子との組み合わせにより、散乱性を有する膜を形成することができるものであり、散乱性を付与することで、より高効率な光取り出しを達成することが可能である。   The material of the low refractive index layer 11 is preferably a material that does not absorb in the emission wavelength region, and preferably has a high transmittance. For example, silicon oxide (refractive index: 1.4 to 1.5) formed by a vapor phase method such as vapor deposition, sputtering, or CVD method, or a metal fluoride such as magnesium fluoride or lithium fluoride (refractive index of 1.35 to 1). 4), or a silica / silicone resin film, a fluororesin film, a composite film of porous fine particles and a resin, etc. formed by a liquid phase method (sol, gel, etc.) can be used. In the liquid phase method, a film having scattering properties can be formed by a combination with various fine particles, and it is possible to achieve more efficient light extraction by imparting scattering properties.

次に、本発明を実施例によって具体的に説明する。尚、重量平均分子量の測定は東ソー社製「ＨＬＣ−８２２０」を用いたゲルパーミエーションクロマトグラフィー（ＧＰＣ）で行ない、被膜屈折率の測定はエリプソメーター（ＵＬＶＡＣ社製「ＥＭＳ−１」）を用いて発光波長λ＝６５０ｎｍで行なった。   Next, the present invention will be specifically described with reference to examples. The weight average molecular weight was measured by gel permeation chromatography (GPC) using “HLC-8220” manufactured by Tosoh Corporation, and the film refractive index was measured using an ellipsometer (“EMS-1” manufactured by ULVAC). The emission wavelength was λ = 650 nm.

（実施例１）
テトラエトキシシラン２０８質量部にメタノール３５６質量部を加え、さらに水１８質量部及び０．０１Ｎの塩酸１８質量部を加え、ディスパーを用いてよく混合することによって溶液を得た。得られた溶液を２５℃恒温槽中で２時間攪拌し、重量平均分子量が８５０のシリコーンレジン（テトラエトキシシランが加水分解して縮重合したもの）を得た。次に、このシリコーンレジンに、中空シリカ微粒子として中空シリカＩＰＡ分散ゾル（固形分：２０質量％、分散媒：イソプロピルアルコール、平均一次粒子径：約３５ｎｍ、外殻厚み：約８ｎｍ、触媒化成工業株式会社製）を、中空シリカ微粒子／シリコーンレジン（縮合化合物換算）の固形分質量基準で８０／２０となるように添加し、全固形分が１０質量％になるようにメタノールで希釈して、中空シリカ微粒子を含有するコーティング材を得た。尚、「縮合化合物換算」とはテトラエトキシシランに存在するＳｉがＳｉＯ２であるとしての重量である。 Example 1
A solution was obtained by adding 356 parts by mass of methanol to 208 parts by mass of tetraethoxysilane, further adding 18 parts by mass of water and 18 parts by mass of 0.01N hydrochloric acid, and mixing well using a disper. The obtained solution was stirred for 2 hours in a thermostatic bath at 25 ° C. to obtain a silicone resin having a weight average molecular weight of 850 (one obtained by hydrolyzing and polymerizing tetraethoxysilane). Next, to this silicone resin, hollow silica IPA dispersion sol (solid content: 20% by mass, dispersion medium: isopropyl alcohol, average primary particle size: about 35 nm, outer shell thickness: about 8 nm, Catalyst Chemical Industry Co., Ltd.) Company) is added so as to be 80/20 based on the solid mass of hollow silica fine particles / silicone resin (condensed compound equivalent), diluted with methanol so that the total solid content becomes 10% by mass, and hollow A coating material containing silica fine particles was obtained. The “condensed compound equivalent” is the weight assuming that Si present in tetraethoxysilane is SiO 2 .

次に透明基材１としてガラス板（屈折率１．５１）を用い、透明基材１の表面にこのコーティング材をスピンコーターで塗布して乾燥し、この塗布・乾燥を２回繰り返した後、２００℃で１０分間焼成することによって、実膜厚１０００ｎｍの低屈折率層１１を得た。この低屈折率層１１の屈折率は１．３０であり、光学膜厚は１３００ｎｍ（＝２λ）であった。   Next, a glass plate (refractive index 1.51) is used as the transparent substrate 1, and this coating material is applied to the surface of the transparent substrate 1 with a spin coater and dried. After this coating and drying are repeated twice, By baking at 200 ° C. for 10 minutes, a low refractive index layer 11 having an actual film thickness of 1000 nm was obtained. The refractive index of the low refractive index layer 11 was 1.30, and the optical film thickness was 1300 nm (= 2λ).

次に、ＤＣマグネトロンスパッタ法により、低屈折率層１１の上に酸化チタン（屈折率２．４５）を６５ｎｍの実膜厚で形成して高屈折率層１０を得た。この高屈折率層１０の光学膜厚は１６０ｎｍ（≒（１／４）λ）である。この時点での誘電体ミラー（透明基材／低屈折率層／高屈折率層）の反射率は、約３０％（波長６５０ｎｍ）であった。   Next, a high refractive index layer 10 was obtained by forming titanium oxide (refractive index 2.45) with a real film thickness of 65 nm on the low refractive index layer 11 by DC magnetron sputtering. The optical film thickness of the high refractive index layer 10 is 160 nm (≈ (1/4) λ). At this time, the reflectance of the dielectric mirror (transparent substrate / low refractive index layer / high refractive index layer) was about 30% (wavelength 650 nm).

さらにＤＣマグネトロンスパッタ法により、高屈折率層１０の上にＩＴＯ薄膜を実膜厚５０ｎｍで形成し、透明電極２を得た。この透明電極２の屈折率は２．０であり、光学膜厚は１００ｎｍ（＜＜（１／２）λ）であった。   Further, an ITO thin film having an actual film thickness of 50 nm was formed on the high refractive index layer 10 by DC magnetron sputtering to obtain a transparent electrode 2. The transparent electrode 2 had a refractive index of 2.0 and an optical film thickness of 100 nm (<< (1/2) λ).

次に、透明電極層上にＰＥＤＴ／ＰＳＳ（poly[3,4-(ethylenedioxy)thiophene]／poly(styrene sulfonate)）（スタルクヴィテック社製「Baytron P AI4083」、ＰＥＤＴ：ＰＳＳ＝１：６）をスピンコートで塗布し、１５０℃で１０分間焼成することにより、実膜厚５０ｎｍのホール注入層３を得た。ホール注入層３の屈折率は１．５５であり、光学膜厚は７８ｎｍであった。   Next, on the transparent electrode layer, PEDT / PSS (poly [3,4- (ethylenedioxy) thiophene] / poly (styrene sulfonate)) (“Baytron P AI4083” manufactured by Starck Vitec, PEDT: PSS = 1: 6) Was applied by spin coating and baked at 150 ° C. for 10 minutes to obtain a hole injection layer 3 having an actual film thickness of 50 nm. The refractive index of the hole injection layer 3 was 1.55, and the optical film thickness was 78 nm.

次に、ＴＦＢ（Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N-(4-sec-butylphenyl))diphenylamine)]）（アメリカンダイソース社製「Hole Transport Polymer ADS259BE」、屈折率１．７）をＴＨＦ溶媒に溶解した溶液を、ホール注入層３の上にスピンコーターで塗布してＴＦＢ被膜を作製し、これを２００℃で１０分間焼成することによって、実膜厚２０ｎｍのホール輸送層４を得た。このホール輸送層４の光学膜厚は３４ｎｍである。   Next, TFB (Poly [(9,9-dioctylfluorenyl-2,7-diyl) -co- (4,4 '-(N- (4-sec-butylphenyl)) diphenylamine)]) (manufactured by American Dice Source) A solution in which “Hole Transport Polymer ADS259BE”, refractive index 1.7) is dissolved in a THF solvent is applied onto the hole injection layer 3 by a spin coater to form a TFB film, which is baked at 200 ° C. for 10 minutes. As a result, a hole transport layer 4 having an actual film thickness of 20 nm was obtained. The hole transport layer 4 has an optical film thickness of 34 nm.

さらに、赤色高分子（アメリカンダイソース社製「Light Emittingpolymer ATS111RE」、屈折率１．７）をＴＨＦ溶媒に溶解した溶液を、ホール輸送層４の上にスピンコーターで塗布し、１００℃で１０分間焼成することによって、実膜厚が１３５ｎｍの発光層５を得た。この発光層５の光学膜厚は２３０ｎｍである。   Further, a solution obtained by dissolving a red polymer (“Light Emitting polymer ATS111RE” manufactured by American Dye Source, refractive index 1.7) in a THF solvent is applied onto the hole transport layer 4 with a spin coater, and is heated at 100 ° C. for 10 minutes. By firing, the light emitting layer 5 having an actual film thickness of 135 nm was obtained. The light emitting layer 5 has an optical film thickness of 230 nm.

最後に、真空蒸着法により、発光層５の上にアルミニウムを７００ｎｍの厚みで製膜して金属電極８を作製し、図２の層構成の有機ＥＬ素子を得た。   Finally, a metal electrode 8 was formed by depositing aluminum with a thickness of 700 nm on the light-emitting layer 5 by a vacuum vapor deposition method, to obtain an organic EL element having the layer structure of FIG.

このようにして得られた有機ＥＬ素子の高屈折率層１０の透明基材１側の面から金属電極８の透明基材１側の面までの光学距離Ｌは６０２ｎｍであり、λ（６５０ｎｍ）より薄くなるように設計されているものであった。   The optical distance L from the surface on the transparent substrate 1 side of the high refractive index layer 10 of the organic EL element thus obtained to the surface on the transparent substrate 1 side of the metal electrode 8 is 602 nm, and λ (650 nm) It was designed to be thinner.

（比較例１）
実施例１において、高屈折率層１０と低屈折率層１１を設けないようにした他は、実施例１と同様にして有機ＥＬ素子を作製した。 (Comparative Example 1)
In Example 1, an organic EL element was produced in the same manner as in Example 1 except that the high refractive index layer 10 and the low refractive index layer 11 were not provided.

（比較例２）
実施例１において、透明電極２を実膜厚２１３ｎｍに形成して、光学膜厚が４２５ｎｍ（＞（１／２）λ）になるようにした他は、実施例１と同様にして有機ＥＬ素子を作製した。 (Comparative Example 2)
In Example 1, an organic EL element was formed in the same manner as in Example 1 except that the transparent electrode 2 was formed to an actual film thickness of 213 nm and the optical film thickness was 425 nm (> (1/2) λ). Was made.

（比較例３）
実施例１において、低屈折率層１１を実膜厚１２０ｎｍに形成して、光学膜厚が１５６ｎｍ（≒（１／４）λ）になるようにした他は、実施例１と同様にして有機ＥＬ素子を作製した。 (Comparative Example 3)
In Example 1, the organic layer was formed in the same manner as in Example 1 except that the low refractive index layer 11 was formed to an actual film thickness of 120 nm and the optical film thickness was 156 nm (≈ (1/4) λ). An EL element was produced.

（比較例４）
実施例１において、高屈折率層１０の代わりに、二酸化ケイ素（屈折率１．４７）の層を光学膜厚で１６０ｎｍ（≒１／４λ）になるように形成した他は、実施例１と同様にして有機ＥＬ素子を作製した。 (Comparative Example 4)
In Example 1, instead of the high-refractive index layer 10, a layer of silicon dioxide (refractive index 1.47) was formed to have an optical film thickness of 160 nm (≈1 / 4λ). Similarly, an organic EL device was produced.

上記のように実施例１及び比較例１〜４で作製した有機ＥＬ素子において、透明電極２と金属電極８の間に直流電源を接続し、電流密度４０ｍＡ／ｃｍ２の条件下で発光させた。そして透明基材１の表面の発光スペクトルを色彩輝度計（トプコン社製「ＳＲ−３」、測定波長６００〜７００ｎｍ、１ｎｍピッチ)で測定した。測定は、透明基材１の表面の垂直線に対して０度（正面）、１０度、２０度、３０度、４０度、５０度、６０度、７０度、８０度の角度について行なった。そして正面の発光スペクトルの積分値（６００〜７００ｎｍ）を導出し、各角度における発光スペクトル積分値から発光球体・楕円体としての体積値を導出し、正面・全方位方向の光取り出し量を測定した。結果を、比較例１の有機ＥＬ素子の正面・全方位方向の光取り出しを基準とし、その相対比を求めて表１に示す。 In the organic EL elements produced in Example 1 and Comparative Examples 1 to 4 as described above, a direct current power source was connected between the transparent electrode 2 and the metal electrode 8, and light was emitted under conditions of a current density of 40 mA / cm 2 . . And the emission spectrum of the surface of the transparent base material 1 was measured with the color luminance meter ("SR-3" by Topcon Corporation, measurement wavelength 600-700 nm, 1 nm pitch). The measurement was performed at angles of 0 degrees (front), 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, and 80 degrees with respect to the vertical line on the surface of the transparent substrate 1. Then, the integrated value (600 to 700 nm) of the front emission spectrum was derived, the volume value as the light emitting sphere / ellipsoid was derived from the integrated emission spectrum value at each angle, and the light extraction amount in the front and all directions was measured. . The results are shown in Table 1 with respect to the light extraction in the front and omnidirectional directions of the organic EL element of Comparative Example 1 as a reference, and the relative ratios obtained.

Figure 2007294266
Figure 2007294266

表１にみられるように、実施例１のものは、正面・全方位いずれの方向においても光取り出し量が優れているものであった。   As seen in Table 1, the light extraction amount of Example 1 was excellent both in the front direction and in all directions.

本発明に係る有機ＥＬ素子の層構成の一例を示す概略図である。It is the schematic which shows an example of the layer structure of the organic EL element which concerns on this invention. 本発明に係る有機ＥＬ素子の層構成の他の一例を示す概略図である。It is the schematic which shows another example of the layer structure of the organic EL element which concerns on this invention. 従来例を示す概略図である。It is the schematic which shows a prior art example. 他の従来例を示す概略図である。It is the schematic which shows another prior art example.

符号の説明Explanation of symbols

１ 透明基材
２ 透明電極
８ 金属電極
９ エレクトロルミネッセンス層
１０高屈折率層
１１ 低屈折率層 DESCRIPTION OF SYMBOLS 1 Transparent base material 2 Transparent electrode 8 Metal electrode 9 Electroluminescent layer 10 High refractive index layer 11 Low refractive index layer

Claims (2)

少なくとも金属電極、エレクトロルミネッセンス層、透明電極、透明基材をこの順に積層し、エレクトロルミネッセンス層で発光した光を透明基材を通して取り出すようにした有機ＥＬ素子において、透明電極と透明基材の間に高屈折率層及び低屈折率層の２層を、高屈折率層を透明電極の側に、低屈折率層を透明基材の側に配置して設け、上記各層の光学膜厚及び屈折率を下記のように形成して成ることを特徴とする有機ＥＬ素子。
・透明電極の光学膜厚が、（１／２）λより小さい
・低屈折率層の光学膜厚が、（１／２）λより大きい
・高屈折率層の光学膜厚が、（１／８）λより大きく且つ（３／８）λより小さい
・高屈折率層の透明基材の側の面から、金属電極の透明基材の側の面までの光学距離が、λより小さい
・高屈折率層の屈折率が、（透明電極の屈折率−０．２）より大きい
（但し、λはエレクトロルミネッセンス層で発光する光の波長、屈折率はこの発光波長における屈折率） In an organic EL device in which at least a metal electrode, an electroluminescent layer, a transparent electrode, and a transparent base material are laminated in this order, and light emitted from the electroluminescent layer is extracted through the transparent base material, between the transparent electrode and the transparent base material Two layers, a high refractive index layer and a low refractive index layer, are provided with the high refractive index layer disposed on the transparent electrode side and the low refractive index layer disposed on the transparent substrate side. Is formed as follows, and is an organic EL element characterized by the above-mentioned.
The optical film thickness of the transparent electrode is smaller than (1/2) λ The optical film thickness of the low refractive index layer is larger than (1/2) λ The optical film thickness of the high refractive index layer is (1 / 8) Larger than λ and smaller than (3/8) λ · The optical distance from the transparent substrate side surface of the high refractive index layer to the transparent substrate side surface of the metal electrode is less than λ · High The refractive index of the refractive index layer is larger than (refractive index of transparent electrode -0.2) (where λ is the wavelength of light emitted from the electroluminescent layer, and the refractive index is the refractive index at this emission wavelength). 低屈折率層の屈折率が１．４０未満であることを特徴とする請求項１に記載の有機ＥＬ素子。   The organic EL element according to claim 1, wherein the refractive index of the low refractive index layer is less than 1.40.
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