JP4406213B2 - Organic electroluminescence element, surface light source and display device - Google Patents

Description

【００６０】
このように作製した反射・屈折角に乱れを生じさせる領域（光散乱性色変換層）を形成する前の有機ＥＬ素子について、１３Ｖの直流電圧を印加したところ、１３．５ｍＡ／cm² の電流密度で素子に電流が通じ、発光が観測された。発光色は青色がかった白色をしており、ガラス基板の側面にみられる素子内に閉じ込められた導波光成分は青色であり、非常に強いものであった。
図５に示すように、市販の輝度計（トプコン社製の品名「ＢＭ９」）を用い、θ方向の素子の輝度を、０度〜８０度方向まで、１０度おきに測定した。正面０度の輝度値が１となるように規格化し、その角度分布を調べた。
結果は、０度：１．００に対し、１０度：１．０３、２０度：１．０６、３０度：１．１２、４０度：１．１５、５０度：１．１８、６０度：１．２１、７０度：１．２１、８０度：１．１５、となった。
【００６１】
この結果から、上記の有機ＥＬ素子は、本発明の式（１）の関係を十分に満たすものであった。また、この素子において、正孔と電子の再結合は、ほぼＴＡＺとＴＰＤの界面のＴＰＤ側で起こる。よって、本発明にいう正孔と電子の再結合発光領域の中心部と反射性電極との距離ｄはおよそ１０５ｎｍであった。
また、ガラス基板上に蒸着したＴＰＤ薄膜の蛍光スペクトルのピーク波長λはおよそ４５０ｎｍであった。また、分光エリプソメータを用いて測定したＴＰＤ薄膜の屈折率ｎはおよそ１．６８であった。よって、上記の有機ＥＬ素子は、本発明の式（２）の関係も満足するものであった。
【００６２】
＜光散乱性色変換層（反射・屈折角に乱れを生じさせる領域に発光性材料を含ませた層）の形成＞
緑色蛍光染料として、ＢＡＳＦ社製の「ＬｕｍｏｇｅｎＦ Ｙｅｌｌｏｗ−０８３」をジクロロメタンに０．２重量％の濃度で溶解させた。また、赤色蛍光染料として、ＢＡＳＦ社製の「ＬｕｍｏｇｅｎＦ Ｒｅｄ−３０５」をジクロロメタンに０．１５重量％の濃度で溶解させた。これらの溶液を１０ｇづつ等量混合し、その溶液中にマトリックス樹脂としてポリメタクリル酸メチルを６．５ｇ、拡散粒子としてアルミナ微粒子（昭和電工社製の「ＵＡ−５０３５」、平均粒径０．９μｍ）を１．３ｇ、加えて、十分に撹拌した。
この溶液を、剥離剤で処理したポリエチレンテレフタレートフィルムからなる厚さが５０μｍのセパレータ上に、アプリケータを用いて、キャスティングし、十分に乾燥したのち、キャストフィルムをセパレータから剥離して、厚さが５５μｍの光散乱性色変換層とした。
【００６３】
つぎに、前記のように作製した有機ＥＬ素子のガラス基板表面上に、上記の光散乱性色変換層を、アクリル系透明粘着剤を介して貼り合わせ、目的とする有機ＥＬ素子を作製した。この素子に前記同様に１３Ｖの電圧を印加して、１３．５ｍＡ／cm² の電流密度で素子に電流を通じたところ、白色発光が得られた。図６に、光散乱性色変換層形成前後の発光スペクトルを示した。図中、曲線−ｃは光散乱性色変換層形成前、曲線−ｄは光散乱性色変換層形成後、である。
【００６４】
比較例１
電子輸送層として、式（６）で表されるＡｌｑを４５ｎｍの厚さに形成した以外は、実施例１と同様にして、基本構成としての有機ＥＬ素子と、これに光散乱性色変換層を形成した有機ＥＬ素子を作製した。
この光散乱性色変換層の形成前後の有機ＥＬ素子に対して、８．３Ｖの電圧を印加し、同様に１０．５ｍＡ／cm² の電流密度で素子に電流を流して発光させ、実施例１と同様に評価した。
【００６５】
光散乱性色変換層形成前の有機ＥＬ素子は、発光色および導波光ともに青色であり、実施例１に比べて、導波光成分の強度は弱かった。また、θ方向の輝度分布は、０度：１．００に対し、１０度：１．００、２０度：０．９３、３０度：０．９３、４０度：０．８９、５０度：０．８９、６０度：０．７９、７０度：０．７９、８０度：０．７１、となった。
この結果から、光散乱性色変換層形成前のθ方向の輝度分布は、本発明の式（１）の関係を満足しなかった。また、Ａｌｑ層とＴＡＺ層の合計厚さ６０ｎｍという値も、本発明の式（２）の関係を満足しなかった。
光散乱性色変換層形成後の有機ＥＬ素子では白色発光が得られた。図１０に、光散乱性色変換層形成前後の発光スペクトルを示した。図中、曲線−ｅは光散乱性色変換層形成前、曲線−ｆは光散乱性色変換層形成後、である。
【００６６】
比較例２
電子輸送層として、式（６）で表されるＡｌｑを１４０ｎｍの厚さに形成した以外は、実施例１と同様にして、基本構成としての有機ＥＬ素子と、これに光散乱性色変換層を形成した有機ＥＬ素子を作製した。
この光散乱性色変換層の形成前後の有機ＥＬ素子に対して、１８．２Ｖの電圧を印加し、同様に１０．５ｍＡ／cm² の電流密度で素子に電流を流して発光させ、実施例１と同様に評価した。
【００６７】
光散乱性色変換層形成前の有機ＥＬ素子は、発光色および導波光ともに青色であり、実施例１に比べて、導波光成分の強度は弱かった。また、θ方向の輝度分布は、０度：１．００に対し、１０度：０．９５、２０度：０．８６、３０度：０．７７、４０度：０．７１、５０度：０．６３、６０度：０．５６、７０度：０．５２、８０度：０．４５、となった。
この結果から、光散乱性色変換層形成前のθ方向の輝度分布は、本発明の式（１）の関係を満足しなかった。また、Ａｌｑ層とＴＡＺ層との合計厚さ１５５ｎｍという値も、本発明の式（２）の関係を満足しなかった。
光散乱性色変換層形成後の有機ＥＬ素子では、白色発光が得られた。
【００６８】
つぎに、上記の実施例１および比較例１，２の各有機ＥＬ素子について、光散乱性色変換層形成後のθ方向の角度での実際の輝度値とさらに全光量を調べた。これらの結果は、表１に示されるとおりであった。
【００６９】
表１

【００７０】
上記の結果から明らかなように、本発明の実施例１の有機ＥＬ素子は、同じ素子電流（１０．５ｍＡ／cm² ）を通じた状態において、比較例１，２の有機ＥＬ素子に比べて、輝度および全光量ともに大きく、単位電流あたりの発光効率にすぐれていることがわかる。
また、実施例１の有機ＥＬ素子は、光散乱性色変換層形成前では、比較例１，２の有機ＥＬ素子とは異なり、正面より広角度になるほど輝度が大きい傾向を示していたが、光散乱性色変換層形成後は、比較例１，２の有機ＥＬ素子とほぼ同様に、正面より広角度になるほど輝度が低下する傾向を示した。
【００７１】
さらに、光散乱性色変換層形成前の発光強度は、実施例１の有機ＥＬ素子よりも、比較例１，２の有機ＥＬ素子の方が大きかったが、光散乱性色変換層形成後の発光強度は、上記と逆の結果となり、比較例１，２の有機ＥＬ素子よりも、実施例１の有機ＥＬ素子の方が大きくなった。
この結果は、実施例１では、正面輝度は低下するが、本来素子内部に閉じ込められて取り出すことのできない導波光成分を強め合うような基本構成として、これに空気層を介することなく光散乱性色変換層を形成したことにより、増強された導波光が全反射されることなく光散乱性色変換層に入射し、蛍光染料の励起光源として有効に利用されたことに基づくものである。
【００７２】
実施例２
実施例１において、光散乱性色変換層を形成する際に、拡散粒子を使用せず、光散乱性のない透明な蛍光フィルム（単なる色変化層）を作製した。この蛍光フィルムを、有機ＥＬ素子のガラス基板上に透明粘着剤を介して貼り合わせ、この上にさらに、反射・屈折角に乱れを生じさせる領域として、三角錐が多数配置されたコーナーキュープレンズシートを、透明粘着剤を介して貼り合せるようにした以外は、実施例１と同様にして、有機ＥＬ素子を作製した。
【００７３】
比較例３
電子輸送層として、式（６）で表されるＡｌｑを４５ｎｍの厚さに形成した以外は、実施例２と同様にして、有機ＥＬ素子を作製した。
【００７４】
上記の実施例２および比較例３の有機ＥＬ素子について、それぞれ、１０．５ｍＡ／cm² の電流密度で素子に電流を通じたときの輝度の角度分布を測定し、全光量を求めた。その結果、実施例２の有機ＥＬ素子では２４３（ｌｍ／ｍ² ）、比較例３の有機ＥＬ素子では１５９（ｌｍ／ｍ² ）となり、本発明の素子構成とすることにより、発光効率が高められることが確認された。
【００７５】
【発明の効果】
以上のように、本発明の有機ＥＬ素子は、白色ＬＥＤに応用されているように励起光源に青色、紫外光などの短波長の発光素子を用い、その励起光源を適宜の発光性材料で色変換する方式と同様に、発光性材料の添加量を調整するだけで、容易に白色をはじめとした任意の発光色を得ることができる。そればかりか、色変換層を形成する前は発光効率は低いが、本来素子内部に閉じ込められる導波光成分を増幅するように工夫しているため、空気層を介することなく色変換層を形成することで、立体角的に光量の多い増強された導波光成分がそのまま色変換層に入射し、これに分散された発光性材料の励起光源として有効に働く。
【００７６】
しかも、色変換層自体またはそれより出射面側を光の反射・屈折角に乱れを生じさせる領域とすることにより、励起発光した発光光が空気層界面で全反射し、導波光として内部に閉じ込められるのを抑制し、光の利用効率が損なわれないように工夫されているため、発光効率にすぐれた有機ＥＬ素子を提供することができる。このように有機ＥＬ素子の発光効率が向上することで、同じ明るさを得るために必要な駆動電流を小さくでき、素子の長寿命化につながる。また、励起光源にＥＬ発光光を用い、間接的に発光性材料を発光させ、しかも散乱させて外部に出射させるので、有機ＥＬ素子で問題となる素子劣化に伴うダークスポットの影響がほとんど現れなくなるという効果も得られる。
【図面の簡単な説明】
【図１】本発明の有機エレクトロルミネッセンス素子の一例を示す断面図である。
【図２】本発明および従来の有機エレクトロルミネッセンス素子の基本構成についての（光散乱性色変換層を形成する前の）特性図である。
【図３】本発明の有機エレクトロルミネッセンス素子の他の例を示す断面図である。
【図４】本発明の有機エレクトロルミネッセンス素子の別の例を示す断面図である。
【図５】実施例１の有機エレクトロルミネッセンス素子の特性の説明図である。
【図６】実施例１の有機エレクトロルミネッセンス素子の光散乱性色変換層を形成する前および後の発光スペクトルを示す特性図である。
【図７】本発明の有機エレクトロルミネッセンス素子の原理説明図である。
【図８】有機エレクトロルミネッセンス素子の発光領域を示す説明図である。
【図９】有機エレクトロルミネッセンス素子の輝度についての説明図である。
【図１０】比較例１の有機エレクトロルミネッセンス素子の光散乱性色変換層を形成する前および後の発光スペクトルを示す特性図である。
【符号の説明】
１ 支持基板
２ 透明電極（陽極）
３ 反射性電極（陰極）
４ 正孔輸送層
５ 電子輸送性発光層
６ 発光領域
７ 反射・屈折角に乱れを生じさせる領域
８ 発光性材料[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color conversion type organic electroluminescent element that uses emitted light emitted from a light emitting layer as an excitation light source and extracts the excited emitted light of a luminescent material as external light, and its emission efficiency, in particular, external extraction of emitted light. The present invention relates to an organic electroluminescence element having excellent efficiency, and also relates to a surface light source and a display device using the organic electroluminescence element and having high efficiency and low power consumption.
[0002]
[Prior art]
Electroluminescent elements and light-emitting diodes, which are provided with a light-emitting layer on the electrodes to obtain light emission, are used not only as display devices, but also for flat lighting, optical fiber light sources, liquid crystal display backlights, and liquid crystal projector backlights. Research and development is actively progressing as various light sources. In particular, the organic electroluminescence element is excellent in terms of light emission efficiency, low voltage driving, light weight, and low cost, and has attracted attention in recent years. In these light source applications, the greatest concern is the improvement of luminous efficiency, and improvements in device configuration, materials, driving methods, manufacturing methods, etc. are being studied with the aim of luminous efficiency comparable to fluorescent lamps.
[0003]
However, in an in-solid light-emitting device that extracts light from the light-emitting layer itself, such as an organic electroluminescence device, light emitted above the critical angle determined by the refractive index of the light-emitting layer and the refractive index of the output medium is totally reflected and confined inside. , Lost as guided light. In the calculation based on the classical law of refraction (Snell's law), assuming that the refractive index of the light emitting layer is n, the light extraction efficiency η for extracting the generated light to the outside is η = 1 / (2n²). If the refractive index of the light emitting layer is 1.7, η is about 17%, and 80% or more of the light is lost as guided light and lost in the side face direction of the device.
In addition, in the organic electroluminescence element, only the singlet excitons contribute to light emission among the excitons generated by recombination of electrons and holes injected from the electrodes, and the generation probability is 1/4. It is. That is, even if only this is taken into consideration, the efficiency is as low as 5% or less.
[0004]
In recent years, as a method for increasing the light emission efficiency of the light emitting layer itself, development of a light emitting material capable of obtaining light emission also from phosphorescence from triplet excitons (Japanese Patent Laid-Open No. 2001-313178) has been advanced, and quantum efficiency has been dramatically improved. There is also a possibility of improvement. However, even if the quantum efficiency can be improved, the light emission efficiency is reduced by multiplying the extraction efficiency. In other words, if the extraction efficiency can be improved, there remains room for a dramatic improvement in efficiency as a synergistic effect.
[0005]
In this way, in order to extract guided light to the outside, a region where the reflection / refraction angle is disturbed is formed between the light emitting layer and the exit surface, and Snell's law is broken, so that light that is originally totally reflected as guided light. It is necessary to change the transmission angle of the light or to give the light emission itself a light collecting property. However, it is not easy to form a region that emits all the guided light to the outside, and therefore, proposals have been made to extract as much guided light as possible.
[0006]
For example, as a method of improving the extraction efficiency, a method of improving the extraction efficiency by giving the substrate itself a light condensing property (Japanese Patent Laid-Open No. Sho 63-314795), or a light emitting layer formed with discotic liquid crystal A method of improving the front directivity of light itself (Japanese Patent Laid-Open No. 10-321371), a method of forming a three-dimensional structure, an inclined surface, a diffraction grating, etc. on the element itself (Japanese Patent Laid-Open Nos. 11-214162 and 11-214163) JP-A-11-283951) has been proposed.
However, these proposals have problems such as a complicated configuration and a reduction in luminous efficiency of the light emitting layer itself.
[0007]
Further, as a relatively simple method, a method has been proposed in which a light diffusing layer is formed and the light refraction angle is changed to reduce light in the total reflection condition.
For example, a method of using a diffusion plate in which particles having a refractive index distribution structure having different refractive indexes between the inside and the surface are dispersed in a transparent substrate (Japanese Patent Laid-Open No. 6-347617), a single particle on a translucent substrate Many methods have been proposed, such as a method using a diffusion member in which layers are arranged (Japanese Patent Laid-Open No. 2001-356207), a method of dispersing scattering particles in the same material as the light emitting layer (Japanese Patent Laid-Open No. 6-151061), and the like. .
In these proposals, characteristics are found in the characteristics of the scattering particles, the refractive index difference from the dispersion matrix, the dispersion form of the particles, the location where the scattering layer is formed, and the like.
[0008]
By the way, in an organic electroluminescence element, by applying an electric field, a hole injected from an anode and an electron injected from a cathode are recombined to form an exciton, and a fluorescent substance (or phosphorescent substance) emits light. Is used. Therefore, in order to increase the quantum efficiency, this recombination needs to be performed efficiently. A method generally used as the method is a method in which the element has a laminated structure. Examples of the laminated structure include a two-layer type of a hole transport layer / electron transporting light-emitting layer, and a three-layer type of hole transport layer / light-emitting layer / electron transport layer. In order to increase efficiency, a number of stacked elements having a double hetero structure have been proposed.
[0009]
In such a laminated structure, recombination occurs almost concentrated in a certain region.
For example, in the case of the two-layer type organic electroluminescence element, as shown in FIG. 8, a hole transport layer sandwiched between a pair of electrodes composed of a reflective electrode 3 and a transparent electrode 2 on a support substrate 1. 4 and the electron transporting light emitting layer 5 are concentrated in the region 6 on the electron transporting light emitting layer side by about 10 nm (Takuya, Ogawa et al, “IEICE TRANS ELECTRON” Vol. E85-C, No. 6, page 1239, 2002 report).
Further, the light generated in the light emitting region 6 is emitted in all directions. As a result, as shown in FIG. 9, there is an optical path difference between the light radiated in the light extraction surface direction on the transparent electrode 2 side and the light radiated and reflected on the reflective electrode 3 side and emitted in the light extraction surface direction. .
[0010]
In FIG. 9, the thickness of the electron transporting light emitting layer of the organic electroluminescence element is usually several tens to several hundreds of nanometers, which is on the order of visible light wavelength. Therefore, the light finally emitted to the outside causes interference and is strengthened or weakened depending on the distance d between the light emitting region and the reflective electrode.
In FIG. 9, only the radiated light in the front direction is described, but light in the oblique direction actually exists, and the interference condition varies depending on the angle of the radiated light depending on the distance d and the emission wavelength λ. As a result, light in the front direction can be intensified and light in the wide angle direction can be intensified, or vice versa. That is, the light emission luminance varies depending on the viewing angle. Of course, as the distance d increases, the light intensity changes significantly depending on the angle. Therefore, the film thickness is usually set so that the distance d is about 1/4 wavelength of the emission wavelength so that the light in the front direction strengthens each other.
[0011]
Further, when the distance d is thinner than about 50 nm, for example, in a reflective electrode in which a metal is usually used, light absorption becomes significant, and the emission intensity is reduced and the intensity distribution is affected. That is, in the organic electroluminescence element, the radiated light distribution changes remarkably depending on the distance d between the light emitting region and the reflective electrode, and the above-described waveguide light component also changes greatly accordingly.
Furthermore, the emission spectrum of the organic electroluminescence element has a broad characteristic over a relatively wide wavelength. Therefore, as a result of the wavelength range that is strengthened depending on the distance d being changed, the emission peak wavelength is changed. Also, depending on the distance d, the emission spectrum also changes depending on the viewing angle.
[0012]
In order to solve these problems, a proposal has been made to select a film thickness so as to suppress a phenomenon in which the emission color varies depending on the viewing angle (see Patent Document 1). However, there is no description about guided light, and the film thickness that can suppress the viewing angle dependency of the emission color by this proposal is clearly different from the scope of the present invention described later.
[0013]
For the above reason, in the classical calculation that about 80% of the emitted light is confined inside the device as guided light, the external extraction efficiency of the stacked organic electroluminescence device cannot be estimated correctly. That is, the guided light component also changes significantly depending on the element configuration. For example, M.M. H. According to a report by Lu et al. (J. Appl. Phys., Vol. 91, No. 2, p. 595, 2002), a guided wave component of an element configuration is calculated by a quantum theoretical calculation method considering a microcavity effect. Detailed research on changes is underway. Therefore, even if a light diffusion layer or the like is formed so as to break the total reflection condition, the actual effect is not as great as expected from the classical theory.
[0014]
On the other hand, a color conversion method has been proposed in which a light-emitting material that absorbs light emitted from an organic electroluminescence element and emits fluorescence in the visible light region is used for a filter (see Patent Documents 2 and 3). In this method, arbitrary visible light emission including white light emission can be taken out by adjusting the kind and addition amount of the luminescent material, the mixing ratio of the materials, and the like. In addition, when performing full color display in a display device, it is usually necessary to form red, green, and blue organic electroluminescence layers for each pixel. In the above method, all the pixels are used as the same organic electroluminescence layer. Full color display is possible by forming and separately using a color filter separately coated with red, green, and blue light-emitting materials. The manufacturing method of the color filter can directly apply the manufacturing technology cultivated with the color filter for the conventional liquid crystal display device, and the manufacturing cost can be reduced.
[0015]
However, when the light emitting material absorbs the excitation light of the organic electroluminescence device and emits light, the light is emitted in the solid as well as the efficiency is reduced due to the conversion efficiency, so most of the emitted light is guided light. The situation of being trapped inside is the same. In contrast, the conventional technique of dispersing particles having a refractive index different from that of the matrix in a region where the luminescent material is dispersed, or forming a light diffusion layer or a lens sheet on the luminescent material is used. Thus, it is possible to extract guided light to the outside to some extent.
[0016]
As described above, in the conventional technique, while taking advantage of the feature that any visible light emission can be obtained by the color conversion method, the change in the guided light component due to the element configuration is studied in detail, and then attention is paid to the improvement of the external extraction efficiency. Reports that have been studied in detail have not been made so far, and the present situation is that there is a strong desire for the appearance of highly efficient organic electroluminescence elements based on the above studies.
[0017]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-3081 (pages 2 to 4)
[Patent Document 2]
JP-A-3-152897 (pages 1 to 3)
[Patent Document 3]
JP-A-5-258860 (pages 1 to 3)
[0018]
[Problems to be solved by the invention]
In light of such circumstances, the present invention can efficiently extract lossy light that has been conventionally confined as guided light inside the organic electroluminescence element, and can take out any emitted light by a color conversion method. An object of the present invention is to provide a high-brightness organic electroluminescence element. Another object of the present invention is to provide a high-efficiency and low power consumption surface light source and display device using this organic electroluminescence element.
[0019]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors first obtained the following knowledge. This knowledge will be described with reference to FIG.
FIG. 7 is a schematic diagram showing only the upper hemisphere when the emitted light from the light emitting region 6 is emitted to the outside with respect to the two-layer type organic electroluminescence element shown in FIG. It is. Actually, there is also emitted light in the direction of the reflective electrode 3, which is omitted here.
In FIG. 7, the critical angle determined by the refractive index difference of the support substrate (glass substrate) 1 and the refractive index of the air layer is about 40 degrees. That is, light having an angle greater than 40 degrees is totally reflected at the glass / air interface and confined inside the device as guided light. On the paper, 40 degrees / 90 degrees, that is, nearly 45% of light appears to be emitted to the outside, but actual light emission is emitted in all directions. Therefore, from the solid angle relationship, the light quantity increases as the component becomes wider. This is why the luminous efficiency is calculated to be 20% or less by the classical calculation described above.
[0020]
When a color conversion layer containing a luminescent material is provided on the support substrate (glass substrate) 1 for the radiated light emitted in this manner and is made incident on this layer, the luminescent material is The emitted light is absorbed as an excitation light source to emit fluorescence or phosphorescence. The emission color of the fluorescence emission or phosphorescence emission can be arbitrarily selected by changing the type of the luminescent material to be used, and by using a plurality of luminescent materials and adjusting the addition amount, white luminescence can be obtained. It is also possible to obtain
Here, when the color conversion layer containing a luminescent material is composed of a normal region that does not disturb the reflection / refraction angle of light, the emitted light undergoes total reflection at the interface of the air layer and serves as guided light. The situation of being lost is no different.
[0021]
However, the inventors of the present invention, when the color conversion layer described above is composed of a light-scattering color conversion layer and is used as a region in which the reflection / refraction angle of light is disturbed, The light transmission angle is changed in the process until it is emitted, the light transmission angle changes, and the wide angle light that is originally confined inside the element can also be emitted outside the total reflection condition. The light thus scattered is totally reflected at the air interface, returned to the inside of the element, and while receiving the scattering again, the transmission angle is out of the total reflection condition and finally emitted to the outside. Found out to be.
[0022]
On the other hand, an optical interference effect occurs in an actual organic electroluminescence element. On the other hand, in the prior art, the element configuration is usually determined so that the light in the front direction that can be emitted to the outside strengthens. In this case, the guided light interferes so as to weaken the light. However, unlike the conventional case, the present inventors intentionally weaken the light in the front direction and determine the element configuration so as to intensify the wide-angle component light that is normally confined inside the element as guided light. It has been found that the luminous efficiency is remarkably improved by amplifying wide-angle light in which a large amount of light is distributed due to the angle and making this light incident on the light-scattering color conversion layer.
[0023]
In this way, when a light scattering color conversion layer is provided after forming an element structure in which the luminous efficiency of the ordinary organic electroluminescence element is reduced, the organic electroluminescence emission that is the excitation light is utilized to the maximum extent. Thus, the inventors have found that the excitation light can be efficiently extracted to the outside, and that a high-efficiency organic electroluminescence element is finally obtained.
In addition, the conventional organic electroluminescence device has a problem that the device is deteriorated by a very small amount of moisture and oxygen, and the light emission efficiency is lowered and a dark spot is generated starting from a minute defect. However, it has been found that this problem can also be avoided by the element configuration of the present inventors.
[0024]
Regarding dark spots, see, for example, J.A. In order to prevent this, the device is usually completely sealed, as described in detail in a report by McElvain et al. (J. Appl. Phys., Vol. 80, No. 10, p. 6002, 1996). However, it was not easy to completely prevent the occurrence of dark spots. This dark spot causes the appearance and visibility as a surface light source to be significantly reduced. However, in the above-described element configuration by the present inventors, even if some dark spots are generated, the light finally emitted to the observer side is the light emitting material dispersed in the light scattering color conversion layer. Most of the excitation light is scattered, and these are scattered several times and emitted to the outside, so that the effect of reducing visibility due to the occurrence of dark spots is hardly noticed.
[0025]
  The present invention has been completed based on the above findings.

  That is, according to the present invention, a pair of electrodes composed of at least one organic layer including a light emitting layer and a reflective electrode and a transparent electrode sandwiching the organic layer is a front surface of the emitted light emitted from the light extraction surface to the observer side. In the organic electroluminescence device formed so that the luminance value and the luminance value in the direction of 50 ° to 70 ° satisfy the relationship of the formula (1); the front luminance value <the luminance value in the direction of 50 ° to 70 °. Until the light is emitted from the light emitting layer to the observer through the transparent electrodeWithout going through the air layerA region that causes a disturbance in the reflection / refraction angle of light is provided, and the emitted light emitted from the light emitting layer is absorbed as an excitation light source in this region or between this region and the light emitting layer to emit fluorescence or phosphorescence. In the region containing at least one luminescent material and causing disturbance in the reflection / refraction angle of light, a transparent material or an opaque material having a different refractive index is dispersed and distributed in the transparent material. The present invention relates to an organic electroluminescence element (hereinafter simply referred to as an organic EL element) characterized by comprising a light diffusing portion.

  Further, in the present invention, as a particularly preferred embodiment of the organic EL device, the distance between the center of the recombination light-emitting region of holes and electrons and the reflective electrode is d (nm), and the fluorescence of the material used for the light-emitting layer is used. When the peak wavelength of the emission spectrum is λ (nm) and the refractive index of the organic layer between the light emitting layer and the reflective electrode is n, the formula (2); (0.3 / n) λ <d <( 0.5 / n) λ, which relates to an organic EL element that satisfies the relationship.
[0026]
  The present invention also provides,The present invention relates to a surface light source including the organic EL elements having the above-described configurations, and relates to a display device including the organic EL elements having the respective configurations.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an example of a two-layer type organic EL device of the present invention. This element has a structure in which a transparent electrode 2, a hole transport layer 4, an electron transport light emitting layer 5, and a reflective electrode 3 are sequentially laminated on a support substrate 1 as a basic structure. In other words, the organic layer composed of the hole transport layer 4 and the electron transporting light emitting layer 5 is sandwiched between a pair of electrodes composed of the transparent electrode 2 and the reflective electrode 3, and transports holes during operation. Recombination occurs in a region on the side of the electron-transporting light-emitting layer of about 10 nm from the interface layer between the layer 4 and the electron-transporting light-emitting layer 5, and light emission is concentrated in the illustrated light-emitting region 6.
In addition, in a three-layer type organic EL element different from the two-layer type, for example, a hole transport layer / light-emitting layer / electron transport layer, when a voltage is applied between the electrodes, holes from the anode and from the cathode Electrons are injected, these move through the respective carrier transport layers and recombine in the light emitting layer to generate excitons, and EL light emission occurs as described above.
[0028]
In the present invention, the basic configuration is such that, particularly, emitted light in the front direction is weakened, but guided light confined inside the device is strengthened. This will be described with reference to the characteristic diagram of FIG.
FIG. 2 shows the angular distribution of the luminance of the organic EL element consisting of only the basic configuration described above (before providing a light-scattering color conversion layer, which is a region in which the reflection / refraction angle is disturbed, which will be described later). The characteristic diagram measured every 10 degrees up to 80 degrees is shown. In the figure, curve -a is the one according to the present invention, and curve -b is the conventional one. The luminance value is shown as a relative value with the luminance value at 0 degrees at the front as 1.
However, in the basic configuration, the thickness of the transparent electrode 2 is 100 nm, the thickness of the hole transport layer 4 is 40 nm, and the thickness of the electron transporting light emitting layer 5 is 95 nm (according to the present invention) and 60 nm (conventional). Stuff). Further, the current passed through the element is measured by applying a voltage so that the current of the present invention is the same as that of the conventional one.
[0029]
From FIG. 2, the conventional luminance value is lower as the front luminance value, that is, the luminance value in the 0-degree front direction is higher and the angle is wider, whereas in the present invention, the front luminance value is low and wide. The luminance value increases as the angle increases. That is, the present invention is configured to satisfy the relationship of the formula (1); the front luminance value <the luminance value in the direction of 50 degrees to 70 degrees in the angle dependency of the luminance.
This relationship is achieved in the above example due to the difference in thickness of the electron-transporting light-emitting layer 5, but the material and thickness of the organic layer including the light-emitting layer 5 and the pair of electrodes are appropriately determined. By selecting, it can be achieved arbitrarily.
[0030]
In a more preferred embodiment of the present invention, the distance between the center of the hole-electron recombination light-emitting region 6 and the reflective electrode 3 is set to d (in this example, approximately the thickness of the electron-transporting light-emitting layer 5). The peak wavelength of the fluorescence emission spectrum of the material used for the light emitting layer (in this example, the electron transporting light emitting layer 5) is λ, and the organic layer between the light emitting layer and the reflective electrode 3 (in this example, When the refractive index of the electron-transporting light-emitting layer 5) is n, it is configured so as to satisfy the relationship of formula (2); (0.3 / n) λ <d <(0.5 / n) λ. It is particularly desirable that
For example, in the above example, if the peak light emission wavelength of the electron transporting light emitting layer 5 is blue light having a wavelength of 450 nm and the refractive index is 1.65, the distance d is 81.8 to 136.4 nm. It is desirable to be in the range.
[0031]
In the present invention, a basic configuration that satisfies the formula (1) and preferably satisfies the formula (2) is manufactured as described above, and an air layer is interposed between the light emitting layer and the observer-side emission medium. A region 7 that causes a disturbance in the reflection / refraction angle of light without any problem is provided, and the emitted light emitted from the light emitting layer is absorbed in the region 7 as an excitation light source to emit at least one type of fluorescent light or phosphorescent light. The region 7 is made into a light-scattering color conversion layer by including a light-emitting material 8.
[0032]
With this configuration, among the emitted light emitted from the light emitting layer, the light in the upper hemisphere on the paper passes through the transparent electrode and the support substrate and enters the light scattering color conversion layer, while the light in the lower hemisphere is reflected. After being reflected by the luminescent electrode, it enters the light scattering color conversion layer in the same manner. In this process, since an air layer having a low refractive index (refractive index = 1) is not interposed, emitted light can enter the light-scattering color conversion layer without undergoing total reflection (refractive index of the transparent electrode or the supporting substrate). Some light may be totally reflected.
[0033]
The incident light thus acts as an excitation light source for the luminescent material in this layer and is absorbed by the luminescent material. As a result, the luminescent material emits fluorescence or phosphorescence. At that time, the loss of light due to total reflection is minimized in the excitation light. In addition, the emission color of the above-described fluorescence emission or phosphorescence emission can be arbitrarily selected by changing the type of the luminescent material, and by adjusting the addition amount using a plurality of luminescent materials, Luminescence can also be obtained.
[0034]
In addition, the excitation emission light undergoes light scattering in the process until it is emitted to the outside, the light transmission angle changes, and wide-angle light that is originally confined inside the element can also be emitted outside the total reflection condition. become. In addition, the light that has been scattered so as to satisfy the total reflection condition is totally reflected at the air interface and returned to the inside of the element. Is emitted.
As described above, as a basic configuration of the organic EL element, the light in the front direction radiated from the light emitting layer is intentionally weakened, and the light of a wide angle component normally confined inside the element as guided light is strengthened. Since a wide angle light in which most of the light quantity is distributed is amplified and incident on the light scattering color conversion layer without passing through an air layer, it is finally extracted to the outside as described above. The excitation light emission has a very high light emission efficiency as compared with the prior art.
[0035]
In the present invention, the region 7 in which the reflection / refraction angle of light is disturbed can basically efficiently disturb the transmission angle of light at an angle greater than or equal to the total reflection angle to a transmission angle less than or equal to the total reflection angle. The formation method is not particularly limited as long as it is formed so that more guided light confined inside the element can be emitted to the outside. Conventionally proposed ones can be applied as they are.
[0036]
For example, as shown in FIG. 1, a light diffusible portion in which a transparent material or an opaque material having a refractive index different from that of the transparent material is dispersed and distributed may be formed in the transparent material. Specifically, there are those in which silica particles, titania particles, zirconia particles, plastic particles, liquid crystal particles, bubbles and the like are dispersed in glass or polymer.
There is no particular limitation on the refractive index, the refractive index difference, and the particle size of the particles. However, from the viewpoint of causing light scattering, the particle size is 0.1 μm to 10 μm, and the refractive index difference is 0.05 or more. Is preferred.
[0037]
Moreover, a lens structure can also be used suitably. A thin plate-like transparent material that changes the direction of light traveling straight by a plurality of lenses, prisms, V-grooves, etc. arranged or formed in a concentric shape, a plurality of parallel lines, a lattice shape, etc. Means. Specific examples include lenticular lens sheets, Fresnel lens sheets, corner cube lens sheets, fly eye lens sheets, cat eye lens sheets, double fly eye lens sheets, double lenticular lens sheets, radial lenticular lenses. Examples thereof include a sheet, a prism lens film, a micro prism lens film, a lens sheet obtained by changing the convex surface of these lens sheets to a concave surface, and a transparent sphere or a semi-transparent sphere arranged in a planar shape. Alternatively, the direction of light may be changed by carving a groove such as a V-shaped groove. The lens sheet may be made of glass or resin.
[0038]
Moreover, you may form a physical uneven surface in the support substrate surface or each interface. Specifically, it can be formed by matting the surface of the support substrate or thermally transferring a periodic uneven structure to the surface of the organic layer (polymer layer).
[0039]
In the present invention, the formation position of the region 7 that causes disturbance in the reflection / refraction angle of the light is not limited, and can be formed at any position.
For example, a diffusion film may be bonded to the surface of the support substrate 1 via an adhesive or an adhesive, or the support substrate 1 itself may have light diffusibility, or formed between the transparent electrode 2 and the support substrate 1. May be. When used for lighting applications with a relatively large light emitting area, it may be formed on the substrate surface. However, when the light emitting area is small as in a display device, transmission between the light emitting layer and a region that causes disturbance in the reflection / refraction angle. In order to reduce parallax due to distance, it is preferable to form the light-emitting layer as close as possible.
[0040]
In the present invention, as shown in FIG. 1, the luminescent material 8 is provided in the region 7 where the reflection / refraction angle of light on the support substrate 1 is disturbed, and a light scattering color conversion layer is provided. In addition to being configured, it can be provided as a color conversion layer having no light scattering property at an arbitrary position between the region 7 and the light emitting layer. It is desirable that the luminescent material is uniformly dissolved or dispersed in these color conversion layers.
[0041]
3 and 4 show the above example. In FIG. 3, a color conversion layer containing a light-emitting material 8 is provided between the support substrate 1 and a region 7 in which the reflection / refraction angle of light is disturbed. FIG. The substrate 1 itself is used as a color conversion layer by containing a luminescent material 8 therein. In both figures, the other configurations are the same as those in FIG. 1, and the same reference numerals as those in FIG. Even with these configurations, the same effects as those described above can be obtained.
[0042]
Further, the luminescent material may be included in both the inside of the region 7 that causes disturbance in the reflection / refraction angle of light and an arbitrary position between the region 7 and the light emitting layer, or different. A luminescent material may be included separately. Furthermore, the embodiment is arbitrary, such as forming a layer containing different luminescent materials as a laminated structure. For example, a laminated structure may be formed by pasting a film in which a light emitting material is dispersed in a transparent resin, or by applying a solution dissolved in a solvent. Each of these layers may be laminated directly, or may be bonded via a transparent adhesive or adhesive. Furthermore, a light-emitting material can be included in the pressure-sensitive adhesive or adhesive.
[0043]
In the present invention, the light-emitting material is not particularly limited as long as it is a material that absorbs ultraviolet light or visible light and emits light having a wavelength in the visible light region. Organic dyes, inorganic pigments, and the like that emit fluorescence such as emission from excited singlet, phosphorescence that emits light from triplet, and the like are used. It is desirable to use materials of blue, green and red as the emission wavelength alone or in combination. For example, examples of the organic fluorescent dye include the following blue phosphor, green phosphor, and red phosphor.
[0044]
The blue phosphor is not particularly limited as long as it is an organic compound having a fluorescence peak wavelength in a solution state of 380 nm or more and less than 480 nm. For example, the blue phosphor is selected from stilbene derivatives, distyrylarylene derivatives and tristyrylarylene derivatives It is desirable to contain at least one kind. Other blue phosphors include polycyclic aromatics such as anthracene, berylline, coronene, and alkyl-substituted products thereof.
[0045]
The green phosphor is not particularly limited as long as it is an organic compound having a fluorescence peak wavelength in a solution state of 480 nm or more and less than 580 nm. Specifically, 3- (2′-benzimidazolyl) -7-N, N-diethylaminocoumarin (coumarin 535), 3- (2-benzothiazolyl) -7-diethylaminocoumarin (coumarin 540), 2, 3, 5, 6, -1H, 4H-tetrahydro-8-trifluoromethylquinolidino- <9,9a, 1-gh> coumarin (coumarin 540A), 3- (5-chloro-2-benzothiazolyl) -7-diethylaminocoumarin ( Coumarin 34), 4-trifluoromethyl-piperidino [3,2-g] coumarin (coumarin 340), N-ethyl-4-trifluoromethyl-piperidino [3,2-g] coumarin (coumarin 355), N- Methyl-4-trifluoromethyl-piperidino [2,3-h] coumarin, 9-cyano-1,2,4,5-3H, 6H, 1 H- tetrahydro-1-benzopyrano [9,9al-gh] quinolizine-10-one (coumarin 377) coumarin compounds such as, xanthine dyes such as 2,7-dichloro-fluorenylmethyl Sen, tetracene, and the like quinacridone compounds.
[0046]
The red phosphor is not particularly limited as long as it is an organic compound having a peak wavelength in a solution state of 580 nm or more and 650 nm or less. Specific examples include dicyanomethylenepyran derivatives, dicyanomethylenethiopyran derivatives, fluorescein derivatives, and perylene derivatives that are used as red oscillation laser dyes described in European Patent No. 281381.
[0047]
These luminescent materials may be contained in a proportion of 0.1 to 10 mol%, preferably 0.5 to 5 mol%, with respect to the resin material constituting the color conversion layer. This amount is a concentration range for preventing concentration quenching.
In addition, the light emitting material does not absorb all the excitation light from the organic EL element, but absorbs a part of it and converts it into a longer wavelength color, and the excitation light source that has not been absorbed can be emitted to the outside as it is. Good. For example, white can be obtained by using blue as excitation light and adding an appropriate amount of an organic dye that emits yellow light, and by adding an appropriate amount of an organic dye that emits green and red light. These amounts may be appropriately adjusted so that the desired emission color can be obtained from the emission spectrum of excitation light emission, the absorption spectrum of the organic dye, the infrared spectrum, and the like.
[0048]
In the organic EL element of the present invention, there are no particular limitations on the organic material, electrode material, layer structure, and film thickness of each layer, which are basic structures, and the conventional technology can be applied as it is. The organic layer may be formed by vacuum deposition of a low molecular weight material, or a high molecular weight material may be formed by a coating method or the like, and is not particularly limited.
[0049]
Specifically, the anode / hole transport layer / electron transporting light-emitting layer / cathode, which is the above-described two-layer organic EL element, and the anode / hole transport layer, which is a three-layer organic EL element / Various configurations such as a light-emitting layer / electron transport layer / cathode, and an anode / light-emitting layer / cathode different from these stacked elements can be selected, and there is no particular limitation.
A structure in which a hole injection layer is provided at the anode interface or an electron injection layer at the cathode interface, or an electron block layer or a hole block layer for increasing recombination efficiency may be inserted. Basically, when a configuration, material, and formation method that increase the light emission efficiency are selected, strong EL light emission can be obtained with low power consumption, and the effects of the present invention can be further enhanced.
Of course, the material of the light-emitting layer is selected so that it efficiently functions as the excitation light of the light-emitting material. Basically, ultraviolet or blue light-emitting materials are used, but these are the characteristics of the excitation light and the light-emitting material. Therefore, it may be selected as appropriate.
[0050]
As the electrode material, an optimal material can be selected as appropriate. In a normal organic EL device, a transparent conductive film such as indium tin oxide (ITO) or tin oxide is used for the anode, and Mg and Ag are co-deposited at an atomic ratio of about 10: 1 for the cathode, An electrode, an Al electrode doped with a small amount of Li, and the like are applied from the viewpoint of improving the electron injection efficiency by lowering the work function of the cathode, but are not particularly limited.
[0051]
As the support substrate used in the present invention, a general substrate can be used regardless of the presence or absence of transparency. In addition to a method of using a glass substrate and extracting light emission to the glass substrate side through a transparent electrode, an opaque metal plate may be used for the support substrate, and light may be extracted from the opposite direction to the substrate.
In addition to using the anode as a transparent electrode, for example, forming a thin metal electrode that can maintain translucency of several nanometers to several tens of nanometers from the interface of the organic layer as a cathode, and then forming ITO, etc. Thus, the cathode may be a transparent electrode. Of course, a flexible material such as a polymer film may be used for the substrate, or the substrate itself may be formed with a region where the reflection / refraction angle of light is disturbed. Furthermore, as described above, the luminescent material can be dispersed in the substrate.
[0052]
In FIG. 1, FIG. 3 and FIG. 4, the region where the reflection and refraction angles of light are disturbed and the color conversion layer are formed directly on the support substrate and the transparent electrode. You may bond together through an agent and an adhesive agent. At that time, it is desirable to adjust the refractive index of these pressure-sensitive adhesives and adhesives in consideration of the refractive index of each layer so that the light emitted from the organic EL element is not lost by total reflection as much as possible.
[0053]
For example, in FIG. 1, a light-scattering color conversion layer in which a light-emitting material 8 is included in a region 7 where the reflection / refraction angle of light is disturbed is used on a support substrate (glass substrate) 1. In this case, the refractive index of the pressure-sensitive adhesive is desirably higher than the refractive index of the glass substrate and smaller than the refractive index of the light scattering color conversion layer. Thereby, total reflection does not occur at the interface of the glass substrate / adhesive and the adhesive / light scattering color conversion layer, and excitation light can be efficiently incident on the light diffusable color conversion layer. However, even if the refractive index of the pressure-sensitive adhesive does not satisfy the above relationship, if the refractive index difference is about 0.1 or less, there is no concern that the effects of the present invention will be significantly reduced.
[0054]
In the present invention, a surface light source characterized by comprising an organic EL element having such a structure as a light emitting element, and a display device comprising the organic EL element as a light emitting element are provided. it can. Accordingly, it is possible to provide a surface light source and a display device with high luminous efficiency and low power consumption.
[0055]
【Example】
  Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited only to the following examples.

  Of the “Examples 1 and 2” described below, “Example 1” shows an example of the organic EL element of the present invention included in the claims, and “Example 2” The example of the organic EL element as a reference example not included in the scope of claims is shown.
[0056]
Example 1
<Production of basic structure of organic EL element>
On one side of the glass substrate, an ITO ceramic target (In₂O_Three: SnO₂= 90 wt%: 10 wt%), an ITO film having a thickness of 100 nm was formed by a DC sputtering method to form a transparent electrode (anode).
Thereafter, ITO was etched using a photoresist to form a pattern so that the light emitting area was 15 mm × 15 mm. After ultrasonic cleaning, ozone cleaning was performed using a low-pressure ultraviolet lamp.
[0057]
Next, since blue light emission is used as excitation light, the literature [Junji. Kido et al. , Jpn. J. et al. Appl. Phys. Vol. 32, Part. 2, no. 7A, L917 to L920 (1993)], an organic layer was sequentially formed on the ITO surface by a vacuum deposition method with reference to the method.
First, as a hole injection layer, CuPc represented by the formula (3) was formed to a thickness of 15 nm at a deposition rate of 0.3 nm / s. Next, TPD represented by Formula (4) was formed to a thickness of 40 nm at a deposition rate of 0.3 nm / s as a hole transporting blue light emitting layer. Next, TAZ represented by the formula (5) was formed as a hole blocking layer at a deposition rate of 0.3 nm / s to a thickness of 15 nm. Finally, as the electron transport layer, Alq represented by the formula (6) was formed to a thickness of 90 nm at a deposition rate of 0.3 nm / s.
[0058]
Thereafter, Mg is co-deposited at a deposition rate of 1 nm / s and Ag is 0.1 nm / s to form MgAg with a thickness of 100 nm, and from the viewpoint of preventing oxidation of MgAg, 50 nm of Ag is further formed thereon. Thus, a reflective electrode (cathode) was obtained.
After taking out from the vacuum deposition device, drop the ultraviolet curable epoxy resin on the cathode electrode side, cover it with a slide glass, and when the epoxy resin spreads sufficiently, cure the epoxy resin using a high pressure ultraviolet lamp, The element was sealed.
[0059]
[Chemical 1]

[0060]
When a DC voltage of 13 V was applied to the organic EL element before forming the region (light-scattering color conversion layer) in which the reflection / refraction angle was produced in this way, 13.5 mA / cm was applied.²A current was passed through the device at a current density of and light emission was observed. The emission color was blueish white, and the guided light component confined in the element seen on the side surface of the glass substrate was blue and very strong.
As shown in FIG. 5, the luminance of the element in the θ direction was measured every 10 degrees from 0 degree to 80 degrees using a commercially available luminance meter (product name “BM9” manufactured by Topcon). Normalization was performed so that the luminance value at the front 0 degree was 1, and the angular distribution was examined.
The results are 0 degree: 1.00, 10 degree: 1.03, 20 degree: 1.06, 30 degree: 1.12, 40 degree: 1.15, 50 degree: 1.18, 60 degree: 1.21, 70 degrees: 1.21, and 80 degrees: 1.15.
[0061]
From this result, the organic EL element described above sufficiently satisfied the relationship of the formula (1) of the present invention. In this element, the recombination of holes and electrons occurs on the TPD side of the interface between TAZ and TPD. Therefore, the distance d between the central portion of the hole-electron recombination luminescent region and the reflective electrode referred to in the present invention was about 105 nm.
The peak wavelength λ of the fluorescence spectrum of the TPD thin film deposited on the glass substrate was about 450 nm. The refractive index n of the TPD thin film measured using a spectroscopic ellipsometer was about 1.68. Therefore, said organic EL element was also satisfying the relationship of Formula (2) of this invention.
[0062]
<Formation of a light-scattering color conversion layer (a layer in which a luminescent material is included in a region in which the reflection / refraction angle is disturbed)>
As a green fluorescent dye, “LumogenF Yellow-083” manufactured by BASF was dissolved in dichloromethane at a concentration of 0.2% by weight. As a red fluorescent dye, “Lumogen F Red-305” manufactured by BASF was dissolved in dichloromethane at a concentration of 0.15% by weight. Equal amounts of these solutions were mixed in an amount of 10 g, and 6.5 g of polymethyl methacrylate was used as a matrix resin in the solution, and alumina fine particles (“UA-5035” manufactured by Showa Denko KK, average particle size: 0.9 μm as diffusion particles). ) Was added and stirred well.
This solution was cast on a separator made of polyethylene terephthalate film treated with a release agent and having a thickness of 50 μm using an applicator. After sufficiently drying, the cast film was peeled off from the separator, and the thickness was reduced. A 55 μm light scattering color conversion layer was obtained.
[0063]
Next, on the glass substrate surface of the organic EL element produced as mentioned above, said light-scattering color conversion layer was bonded together through the acrylic transparent adhesive, and the target organic EL element was produced. A voltage of 13 V was applied to this element in the same manner as described above to obtain 13.5 mA / cm.²When a current was passed through the device at a current density of, white light emission was obtained. FIG. 6 shows emission spectra before and after forming the light scattering color conversion layer. In the figure, curve -c is before the light-scattering color conversion layer is formed, and curve -d is after the light-scattering color conversion layer is formed.
[0064]
Comparative Example 1
An organic EL element as a basic structure, and a light-scattering color conversion layer, as in Example 1, except that Alq represented by formula (6) was formed to a thickness of 45 nm as the electron transport layer. An organic EL element having the structure was prepared.
A voltage of 8.3 V was applied to the organic EL element before and after the formation of the light scattering color conversion layer, and similarly 10.5 mA / cm.²The device was caused to emit light by passing a current through the device at a current density of and evaluated in the same manner as in Example 1.
[0065]
The organic EL element before formation of the light-scattering color conversion layer was blue in both emission color and guided light, and the intensity of the guided light component was weaker than that in Example 1. Also, the luminance distribution in the θ direction is 0 degree: 1.00, 10 degrees: 1.00, 20 degrees: 0.93, 30 degrees: 0.93, 40 degrees: 0.89, 50 degrees: 0. .89, 60 degrees: 0.79, 70 degrees: 0.79, and 80 degrees: 0.71.
From this result, the luminance distribution in the θ direction before the formation of the light-scattering color conversion layer did not satisfy the relationship of the formula (1) of the present invention. Further, the value of the total thickness of 60 nm of the Alq layer and the TAZ layer did not satisfy the relationship of the formula (2) of the present invention.
White light emission was obtained in the organic EL element after the light scattering color conversion layer was formed. FIG. 10 shows emission spectra before and after forming the light scattering color conversion layer. In the figure, curve -e is before the light-scattering color conversion layer is formed, and curve -f is after the light-scattering color conversion layer is formed.
[0066]
Comparative Example 2
As an electron transport layer, an organic EL element as a basic structure and a light-scattering color conversion layer are formed in the same manner as in Example 1 except that Alq represented by the formula (6) is formed to a thickness of 140 nm. An organic EL element having the structure was prepared.
A voltage of 18.2 V was applied to the organic EL element before and after the formation of the light-scattering color conversion layer, and similarly 10.5 mA / cm.²The device was caused to emit light by passing a current through the device at a current density of and evaluated in the same manner as in Example 1.
[0067]
The organic EL element before formation of the light-scattering color conversion layer was blue in both emission color and guided light, and the intensity of the guided light component was weaker than that in Example 1. Also, the luminance distribution in the θ direction is 0 degree: 1.00, 10 degrees: 0.95, 20 degrees: 0.86, 30 degrees: 0.77, 40 degrees: 0.71, 50 degrees: 0. .63, 60 degrees: 0.56, 70 degrees: 0.52, 80 degrees: 0.45.
From this result, the luminance distribution in the θ direction before the formation of the light-scattering color conversion layer did not satisfy the relationship of the formula (1) of the present invention. Also, the value of the total thickness of 155 nm of the Alq layer and the TAZ layer did not satisfy the relationship of the formula (2) of the present invention.
In the organic EL element after the light scattering color conversion layer was formed, white light emission was obtained.
[0068]
Next, for each of the organic EL elements of Example 1 and Comparative Examples 1 and 2, the actual luminance value and the total amount of light at the angle in the θ direction after the light-scattering color conversion layer was formed were examined. These results were as shown in Table 1.
[0069]
Table 1

[0070]
As is clear from the above results, the organic EL device of Example 1 of the present invention has the same device current (10.5 mA / cm²), Both the luminance and the total light quantity are larger than those of the organic EL elements of Comparative Examples 1 and 2, and it can be seen that the luminous efficiency per unit current is excellent.
In addition, the organic EL element of Example 1 had a tendency that the luminance was larger as the angle was wider than the front, unlike the organic EL elements of Comparative Examples 1 and 2, before the light scattering color conversion layer was formed. After the light-scattering color conversion layer was formed, the luminance tended to decrease as the angle became wider from the front, as in the organic EL elements of Comparative Examples 1 and 2.
[0071]
Further, the emission intensity before forming the light-scattering color conversion layer was higher in the organic EL elements in Comparative Examples 1 and 2 than in the organic EL element in Example 1, but after the light-scattering color conversion layer was formed. As a result, the organic EL element of Example 1 was larger than the organic EL elements of Comparative Examples 1 and 2.
As a result, in the first embodiment, the front luminance is lowered, but the basic structure that reinforces the guided light component that is originally confined inside the element and cannot be taken out is a light scattering property without using an air layer. The formation of the color conversion layer is based on the fact that the enhanced guided light is incident on the light scattering color conversion layer without being totally reflected and is effectively used as an excitation light source of the fluorescent dye.
[0072]
Example 2
In Example 1, when forming a light-scattering color conversion layer, a transparent fluorescent film (simple color-changing layer) having no light-scattering property without using diffusing particles was produced. This fluorescent film is bonded to a glass substrate of an organic EL element via a transparent adhesive, and a corner cup lens sheet in which a large number of triangular pyramids are arranged on the glass substrate as a region where the reflection / refraction angle is disturbed. The organic EL element was produced in the same manner as in Example 1 except that the film was bonded via a transparent adhesive.
[0073]
Comparative Example 3
An organic EL device was produced in the same manner as in Example 2 except that Alq represented by the formula (6) was formed to a thickness of 45 nm as the electron transport layer.
[0074]
For the organic EL elements of Example 2 and Comparative Example 3 above, 10.5 mA / cm, respectively.²The angular distribution of luminance when current was passed through the device at a current density of 5 was measured to determine the total light quantity. As a result, in the organic EL element of Example 2, 243 (lm / m²), 159 (lm / m) for the organic EL device of Comparative Example 3²Thus, it was confirmed that the light emission efficiency can be improved by using the element configuration of the present invention.
[0075]
【The invention's effect】
As described above, the organic EL element of the present invention uses a light emitting element with a short wavelength such as blue or ultraviolet light as an excitation light source as applied to a white LED, and the excitation light source is colored with an appropriate luminescent material. Similar to the conversion method, it is possible to easily obtain any luminescent color including white by simply adjusting the addition amount of the luminescent material. In addition, the luminous efficiency is low before the color conversion layer is formed, but the color conversion layer is formed without going through the air layer because it has been devised to amplify the guided light component confined inside the element. Thus, the enhanced guided light component having a large solid light amount is incident on the color conversion layer as it is, and effectively works as an excitation light source for the luminescent material dispersed therein.
[0076]
In addition, by making the color conversion layer itself or the exit surface side of the color conversion layer a region where the reflection / refraction angle of light is disturbed, the excited emitted light is totally reflected at the air layer interface and confined as guided light. Therefore, an organic EL element having excellent luminous efficiency can be provided. Thus, by improving the light emission efficiency of the organic EL element, it is possible to reduce a driving current necessary for obtaining the same brightness, leading to a longer life of the element. In addition, since EL light is used as an excitation light source, the light emitting material is indirectly emitted, and then scattered and emitted to the outside, so that the influence of dark spots caused by element deterioration which is a problem in the organic EL element hardly appears. The effect is also obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of an organic electroluminescence element of the present invention.
FIG. 2 is a characteristic diagram (before forming a light-scattering color conversion layer) of the basic configuration of the present invention and a conventional organic electroluminescence element.
FIG. 3 is a cross-sectional view showing another example of the organic electroluminescence element of the present invention.
FIG. 4 is a cross-sectional view showing another example of the organic electroluminescence element of the present invention.
5 is an explanatory diagram of characteristics of the organic electroluminescence element of Example 1. FIG.
6 is a characteristic diagram showing emission spectra before and after forming a light-scattering color conversion layer of the organic electroluminescence element of Example 1. FIG.
FIG. 7 is a diagram illustrating the principle of the organic electroluminescence element of the present invention.
FIG. 8 is an explanatory diagram showing a light emitting region of an organic electroluminescence element.
FIG. 9 is an explanatory diagram of the luminance of the organic electroluminescence element.
10 is a characteristic diagram showing emission spectra before and after forming a light-scattering color conversion layer of the organic electroluminescence element of Comparative Example 1. FIG.
[Explanation of symbols]
1 Support substrate
2 Transparent electrode (anode)
3 Reflective electrode (cathode)
4 hole transport layer
5 Electron transporting light emitting layer
6 Light emitting area
7 Areas that cause disturbance in reflection and refraction angles
8 Luminescent materials

Claims (4)

A pair of electrodes composed of at least one organic layer including a light emitting layer and a reflective electrode and a transparent electrode sandwiching the organic layer has a front luminance value of emitted light emitted from the light extraction surface to the observer side and 50 degrees to In an organic electroluminescence device formed so that the luminance value in the 70-degree direction satisfies the relationship of the formula (1); front luminance value <brightness value in the direction of 50 degrees to 70 degrees, the emitted light is transparent from the light-emitting layer. A region that causes the reflection / refraction angle of light to be disturbed without going through the air layer before being emitted to the observer through the electrode, and emitting light within this region or between this region and the light emitting layer The region that absorbs the emitted light emitted from the layer as an excitation light source, includes at least one luminescent material that emits fluorescence or phosphorescence, and causes disturbance in the reflection / refraction angle of the light, With this in transparent material The organic electroluminescent device characterized by comprising a transparent material different in refractive index or opaque material from the light-diffusing site dispersed distribution.   The distance between the central part of the hole-electron recombination emission region and the reflective electrode is d (nm), the peak wavelength of the fluorescence emission spectrum of the material used for the light-emitting layer is λ (nm), and the light-emitting layer and reflectivity 2. The relationship according to claim 1, wherein the relationship of the formula (2); (0.3 / n) λ <d <(0.5 / n) λ is satisfied, where n is the refractive index of the organic layer in contact with the electrode. Organic electroluminescence device. A surface light source comprising the organic electroluminescence element according to claim 1 . A display device comprising the organic electroluminescence element according to claim 1 .

Images