JP2006040784A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element in which a peak half-value width of a light emitting intensity is narrow and which has high brightness by a simple constitution. <P>SOLUTION: The organic EL element 10 includes: a multi-layered film mirror 12 constituted by laminating alternately thin films composed of two kinds of materials mutually different in the refractive index; a transparent electrode 14 formed sequentially on a surface of this multi-layered film mirror; a plurality of organic layers including at least one layer or more of the light emitting layers 15; a negative electrode layer 16; and a reflecting mirror. In the organic EL element 10, a fine resonator is constituted by the multi-layered film mirror and the reflecting mirror, and the organic EL element 10 is constituted so that a reflectivity of the multi-layered film mirror 12 is 80% or more, and so that the reflectivity of the reflection mirror becomes 85% or more and larger than the reflectivity of the multi-layered film mirror. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic EL element, and more particularly to an organic EL element having a microresonator structure composed of a semi-transmissive mirror and a reflective mirror.

  In recent years, organic EL elements that emit light by injecting electric current into an organic light emitting layer to convert electric energy into light energy have been developed as self-luminous display elements, especially organic hole transport composed of aromatic diamines. With the organic EL element including the layer and the organic light emitting layer made of an aluminum complex of 8-hydroxyquinoline, the light emission efficiency has been improved as compared with conventional electroluminescent elements using anthracene or the like.

  Further, for example, according to Patent Document 1 or the like, a device using a microresonator structure is disclosed for such an organic EL element, and the interference effect of light is used at a specific wavelength. Light having a relatively high emission intensity and a narrow spectral half width can be extracted.

An organic EL element having such a resonator structure is configured as shown in FIG. 8, for example.
That is, in FIG. 8, the organic EL element 1 includes a semi-transmissive mirror 3, a transparent electrode layer 4, a hole transport layer 5, an organic light emitting layer 6, and a reflective mirror that are sequentially formed on a transparent substrate 2 by a vacuum deposition method or the like. The cathode layer 7 also functions as

  The transparent substrate 2 is made of a transparent material such as glass or plastic and has a predetermined thickness.

As the transflective mirror 3, for example, a multilayer mirror constituted by alternately laminating two kinds of oxide, nitride or semiconductor thin films having different refractive indexes is mainly used.
Here, the transflective mirror 3 is specifically composed of, for example, a combination of TiO ₂ and SiO ₂ , SiN _x and SiO ₂ , Ta ₂ O ₅ and SiO ₂ , or GaAs and GaInAs.
In this way, by setting the thickness (optical length) of each thin film constituting the semi-transmissive mirror 3 to λ / 4 with respect to the wavelength λ of the light emitted from the light emitting portion, high reflectance can be obtained. Will be.

The transparent electrode 4 is made of, for example, nickel, gold, platinum, palladium or an alloy thereof, or a metal having a large work function such as tin oxide (SnO ₂ ) or copper iodide, an alloy or compound thereof, and a conductive material such as polypyrrole. In most cases, it is made of ITO and functions as an electrode on the anode side.

The hole transport layer 5 has a function of blocking electrons while facilitating the injection of holes from the transparent electrode 4 (anode) side.
The organic light emitting layer 6 has a function of facilitating injection of electrons from a cathode layer 7 described later.

  The cathode layer 7 is preferably made of a material effective for electron injection, for example, a metal material having a relatively low work function (low work function metal material) capable of improving the electron injection efficiency, such as aluminum, magnesium, A magnesium indium alloy, a magnesium aluminum alloy, a magnesium silver alloy, an aluminum lithium alloy, or the like is used. For example, the film can be formed by a so-called dry process such as a vacuum evaporation method or a sputtering method.

According to the organic EL element 1 having such a configuration, when a DC voltage is applied between the transparent electrode 4 and the cathode layer 7, holes injected from the transparent electrode 4 and electrons injected from the cathode layer 7 are changed. In the hole transport layer 5 and the organic light emitting layer 6 which are organic layers, electron-hole recombination is caused. As a result, electric energy is converted into light energy, and light is emitted from the organic light emitting layer 6.
Then, this light is emphasized by resonance by the microresonator constituted by the semi-transmissive mirror 3 and the cathode layer 7 functioning as a reflecting mirror, and is emitted to the outside of the organic EL element 1.

  At this time, the wavelength of the resonating light is determined depending on the distance between the semi-transmissive mirror 3 and the cathode layer 7 as a reflective mirror. Therefore, according to the wavelength of the light used, the film thickness of the transparent electrode 4 and the hole transport layer 5 and the organic light emitting layer 6 which are organic layers is adjusted, or between the transparent electrode 4 and the semi-transmissive mirror 3, By inserting a transparent buffer layer, it is possible to emphasize the desired wavelength of light and emit the light from the organic light emitting layer 6 of the organic EL element 1.

FIG. 9 is a graph showing an emission spectrum of the organic EL element 1 and the organic EL element not having the microresonator structure.
In FIG. 9, the emission spectrum of the organic EL element 1 denoted by reference symbols A and B has a microresonator structure with the semi-transmissive mirror 3 and the cathode layer 7 as the reflection mirror described above. The half width is relatively narrow, and the color purity is increased.
In addition, the peak intensity of the emission spectrum tends to be higher than the peak intensity of the organic EL element not shown in FIG. Further, when the observation angle with respect to the organic EL element 1 is changed from 0 degree to 20 degrees, the emission peak wavelength shifts to the short wavelength side as indicated by reference sign A to reference sign B.
Thereby, it turns out that light emission of various colors can be observed for every observation angle.

On the other hand, the organic layer 5 including the organic layers 5 and 6 includes, for example, trisaluminum (8-hydroxyquinolinato) aluminum (hereinafter referred to as Alq3), N, N′-diphenyl-N, N′-bis (3 -Methylphenyl) 1,1'-biphenyl-4-4'-diamine (hereinafter referred to as TPD) and other low molecular materials, and polyparaphenylene vinylene (PPV) and other high molecular materials. As a result, research and development of high-luminance light emission, multicolor light emission, and the like have been actively conducted, and some have been put into practical use.
Japanese Patent No. 3274527

  However, in the organic EL element 1 having such a configuration, apart from the selection of the organic material constituting the organic layer, the light emission with a relatively narrow half-value width is achieved by increasing the reflectance of the semi-transmissive mirror with respect to the microresonator. Although a spectrum can be obtained, as a result of the light being cut off by the half width, the luminance of the organic EL element as a whole is lowered, and efficient light emission cannot be obtained.

  In view of the above, an object of the present invention is to provide an organic EL element that has a simple configuration with a narrow peak emission half-value width and high luminance.

  According to the present invention, the above object is achieved by sequentially forming a multilayer mirror formed by alternately laminating thin films made of two kinds of materials having different refractive indexes and the surface of the multilayer mirror. The organic EL element includes a transparent electrode layer, a plurality of organic layers including at least one light emitting layer, a cathode layer, and a reflecting mirror, and the multilayer resonator and the reflecting mirror constitute a microresonator. The organic EL element is characterized in that the reflectance of the multilayer mirror is 80% or more, the reflectance of the reflection mirror is 85% or more, and larger than the reflectance of the multilayer mirror. Achieved.

  In the organic EL device according to the present invention, the reflectance of the reflection mirror is preferably 90% or more.

  In the organic EL device according to the present invention, preferably, the reflection mirror and the cathode layer are integrally formed of a metal thin film.

  In the organic EL device according to the present invention, the cathode layer is preferably configured as a translucent or transparent electrode separately from the reflection mirror.

  In the organic EL device according to the present invention, preferably, the cathode layer is composed of a semi-permeable film or a transparent conductive film made of a conductive metal, and the reflection mirrors have different refractive indexes on the cathode layer. A metal composed of silver, aluminum, gold, copper, rhodium, or an alloy thereof is formed on at least one dielectric layer made of a combination of two kinds of materials, preferably further formed on the dielectric layer. The reflection mirror has a reflectance of 90% or more.

According to the above configuration, the reflectance of the multilayer mirror is 80% or more, and the reflectance of the reflection mirror is 85% or more. The light emitted from the light emitting layer resonates by being efficiently reflected with a relatively high reflectance, thereby reducing the half-value width of the emission spectrum and increasing the emission intensity efficiently.
Here, the higher the reflectance of the multilayer mirror, the higher the emission intensity at the peak wavelength of the emission spectrum, but the luminance gradually decreases.
If the reflectance of the reflecting mirror is smaller than that of the multilayer mirror, the light emission intensity and luminance at the peak wavelength are greatly reduced.

  When the reflectance of the reflection mirror is 90% or more, the light emission intensity at the peak wavelength of the emission spectrum is further increased by further improving the reflection efficiency at the reflection mirror.

  When the reflecting mirror and the cathode layer are integrally formed of a metal thin film, the reflecting mirror and the cathode layer can inject electrons into the organic layer, and the higher the reflectance at the wavelength of the light used, the higher the reflectance. good. The reflection mirror can be made of silver, aluminum, gold, copper, rhodium and alloys thereof in accordance with the wavelength of light used. In addition, by setting the reflectance to 90% or higher, a high reflectance can be obtained with a simple configuration. There is no particular upper limit of the reflectance to be set, but if the reflectance is lower than this, the emission peak intensity and the luminance are lowered. Further, a metal having a low work function such as Li, Ca, Sr, or Cs, or a fluoride or oxide of a metal having a low work function such as LiF, CaF, or LiO is thinly formed on the organic layer as an electron injection layer, A reflective mirror and a cathode layer may be formed thereon. The thickness of the reflection mirror and the cathode layer may be a certain thickness that allows sufficient electron injection and does not decrease the reflectivity, and may be 100 nm or more. The upper limit is not limited, but is preferably about 100 to 500 nm.

  When the cathode layer is configured as a translucent or transparent electrode separately from the reflecting mirror, the reflecting mirror can be formed of an optimal material without considering conductivity. .

The cathode layer is made of a semi-permeable film made of a conductive metal or a transparent conductive film, and a reflection mirror is formed thereon. Examples of the translucent electrode material include silver and platinum. As the transparent electrode material, a transparent conductive film such as ITO, IZO, ZnO, SnO ₂ can be used. As the reflection mirror, a metal layer made of silver, aluminum, gold, copper, rhodium and alloys thereof can be used. When the reflectance of the reflection mirror is 90% or more, the resonance effect between the reflection mirror and the multilayer mirror is further enhanced, thereby further increasing the emission intensity and luminance at the peak wavelength of the emission spectrum. Will be.
Further, in order to obtain a higher reflectance than these metal materials, a structure in which at least one derivative layer composed of two kinds of combinations having different refractive indexes is formed, or silver, aluminum, A reflection mirror formed by depositing a metal layer made of gold, copper, rhodium, or an alloy thereof may be used. With this reflection mirror structure, a reflectance of 95% or more can be realized. In addition, the material used for the said multilayer film mirror is used for the material used for the dielectric material layer from which a refractive index differs.

  Thus, according to the present invention, the emission intensity at the peak wavelength of the emission spectrum can be increased even when the half-value width is narrow, as compared with the organic EL element having a conventional microresonator structure. Therefore, light emission with high luminance can be obtained.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 7.
The embodiments described below are preferable specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

FIG. 1 shows a configuration of an embodiment of an organic EL element according to the present invention.
In FIG. 1, an organic EL element 10 includes a transflective mirror 12 formed sequentially on a transparent substrate 11 by a vacuum deposition method, a transparent electrode 13 as an anode, a hole transport layer 14, an organic light emitting layer 15, and a reflecting mirror. The cathode layer 16 also functions as

  The transparent substrate 11 is made of a material such as transparent or translucent glass, PET, polycarbonate, amorphous polyolefin, or the like, and is formed to have a predetermined thickness in order to obtain a required strength.

As the semi-transmission mirror 12, for example, a multilayer mirror constituted by alternately laminating two kinds of oxide, nitride or semiconductor thin films having different refractive indexes is mainly used.
Here, the semi-transmission mirror 12 is specifically composed of, for example, a combination of TiO ₂ and SiO ₂ , SiN _x and SiO ₂ , Ta ₂ O ₅ and SiO ₂ , or GaAs and GaInAs. The semi-transmission mirror 12 further includes SiO, Al ₂ O ₃ , ZrO ₂ , Sb ₂ O ₃ , TiO, HfO ₂ , Y ₂ O ₃ , MgO, CeO ₂ , Nb ₂ O ₅ , MgF, SrF ₂ , It may be formed by appropriately selecting two kinds of combinations having different refractive indexes from BaF ₂ or the like.
In this way, the thickness (optical length) of each thin film of the multilayer mirror constituting the semi-transmissive mirror 12 is set to λ / 4 with respect to the wavelength λ of the light emitted from the light emitting unit. The reflectance will be obtained.

The transflective mirror 12 having such a configuration has a reflectance characteristic as indicated by a symbol A in FIG.
Here, the reflectance characteristics of the semi-transmissive mirror 12 are selected so that the high reflectance area covers the entire light emitting area of the light emitting characteristics (described later) of the organic light emitting layer 15 indicated by symbol B in FIG. Yes.
Further, the reflectance characteristic of the semi-transmissive mirror 12 has a reflectance of 80% or more in the wavelength range of light from the organic light emitting layer 15. When the reflectance is lower than this, the emission intensity at the peak wavelength is lowered.

The transparent electrode 13 is made of a conductive material having a large work function, and a transparent conductive film such as ITO, SnO ₂ , or ZnO is preferably used, but may be a semitransparent film such as gold.
Here, the transparent electrode 13 is preferably configured to have a transmittance of 80% or more with respect to the light from the light emitting portion, and the thickness is selected to be, for example, about 10 to 500 nm.

The hole transport layer 14 has a function of blocking electrons while facilitating injection of holes from the transparent electrode 13 (anode) side.
The hole transport layer 14 preferably has a high hole mobility, is transparent, and has good film formability. For example, a triphenylamine derivative such as TPD, or a polyolefin compound such as phthalocyanine or copper phthalocyanine. , Hydrazone derivatives, arylamine derivatives and the like are used.

The hole transport layer 14 may be divided into a first layer having a hole injection function and a second layer having a hole transport function, and provided separately.
In this case, the first layer has a function of facilitating injection of holes from the transparent electrode 13 (anode), and the second layer has a function of transporting holes and a function of blocking electrons.
The first layer and the second layer preferably each have a thickness of about 10 to 200 nm.

The organic light emitting layer 15 desirably has high luminous efficiency by recombination, good thin film properties, and no strong interaction at the interface with the transport material. For example, aluminum chelate complex (Alq3), distyryl Distyrylarylene (DSA) derivatives such as biphenyl derivatives (DPVBi), quinacridone derivatives, rubrene, coumarin, and perylene materials are used, and these materials are used as a single layer or a mixture of two or more types. obtain.
The organic light emitting layer 15 preferably has a thickness of about 10 to 200 nm, for example.
The organic light emitting layer 15 may be laminated in multiple layers.
Thereby, the organic light emitting layer 15 has an emission spectrum as indicated by a symbol B in FIG. 2, and its peak wavelength is 521 nm.

The cathode layer 16 can inject electrons into the organic layer and has a high reflectivity at the wavelength of light from the organic light emitting layer 15, such as silver, aluminum, gold, copper and rhodium, or these materials. Composed of alloy.
The cathode layer 16 has a reflectance of 85% or more, preferably 90% or more. If the reflectance is lower than this, the emission intensity and the luminance at the peak wavelength of the emission spectrum are lowered.
The cathode layer 16 is selected so that the reflectance as a reflecting mirror is higher than the reflectance of the semi-transmissive mirror (multilayer mirror) 12 described above at the wavelength of light from the organic light emitting layer 15. If the reflectance of the cathode layer 16 is lower than the reflectance of the semi-transmissive mirror 12, the emission intensity and luminance at the peak wavelength of the emission spectrum will be reduced.

  In addition, between the cathode layer 16 and the organic light emitting layer 15, a fluoride or oxide of a metal having a low work function such as Li, Ca, Sr, or Cs or a metal having a low work function such as LiF, CaF, or LiO is used. An electron injection layer made of a material may be formed on the organic light emitting layer 15.

  The cathode layer 16 has only to have a thickness that can sufficiently inject electrons into the organic light emitting layer 15 and does not decrease the reflectivity. For example, the cathode layer 16 has a thickness of about 100 to 500 nm. Yes.

The cathode layer 16 has a function as a reflection mirror. However, the present invention is not limited to this, and a reflection mirror may be provided separately from the cathode layer 16.
In this case, a semitransparent or transparent electrode (cathode) may be formed on the organic light emitting layer 15, and a reflection mirror may be formed thereon.
Here, the translucent electrode is made of a thin film such as silver or platinum, and the transparent electrode can be made of ITO, IZO, ZnO, SnO ₂ or the like.

On the other hand, the reflection mirror is composed of a metal film made of silver, aluminum, gold, copper, rhodium, or an alloy thereof.
Further, in order to further increase the reflectivity, the reflection mirror is formed by forming at least one dielectric layer composed of two kinds of combinations having different refractive indexes from each other, or silver, aluminum, It is configured by forming a metal film made of gold, copper and rhodium or an alloy thereof. Thereby, for example, a reflectance of 95% or more is obtained.

The material of the dielectric layers having different refractive indexes may be the same material as that used for the above-described semi-transmissive mirror (multilayer mirror) 12.
Also in this case, the above-described electron injection layer may be provided between the cathode and the reflection mirror.

The organic EL element 10 according to the embodiment of the present invention is configured as described above. When a DC voltage is applied between the transparent electrode 13 and the cathode layer 16, the transparent electrode 13 passes through the hole transport layer 14. The injected holes and the electrons injected from the cathode layer 16 cause electron-hole recombination in the organic light emitting layer 15 which is an organic layer. As a result, electric energy is converted into light energy, and light is emitted from the organic light emitting layer 15.
Then, the half-width of the peak wavelength is narrowed by the fact that only a specific wavelength is emphasized by resonance by the microresonator constituted by the semi-transmission mirror 12 and the cathode layer 16 functioning as a reflection mirror.

At this time, the reflectance of the semi-transmissive mirror 12 is 80% or more, and the reflectance of the cathode layer 16 is 85% or more, preferably 90% or more. Reflection efficiency is improved. Therefore, even if reflection is repeated in the microresonator composed of the semi-transmissive mirror 12 and the cathode layer 16, the optical loss is suppressed, so that the resonance effect is enhanced and the emission intensity at the peak wavelength is increased. Will be.
Moreover, since the reflectance of the cathode layer 16 (reflection mirror) is higher than the reflectance of the semi-transmissive mirror 12, the light extraction efficiency is improved, and the luminance of light from the organic EL element 10 is increased. become.

  The effects of the organic EL element 10 described above were evaluated by several experimental examples and a comparative example without a semi-transmissive mirror.

Experimental example 1

Six pairs of dielectric films with a combination of SiO ₂ (film thickness 94 nm) / TiO ₂ (film thickness 63 nm) were formed on a glass substrate by EB vapor deposition to produce a semi-transmissive mirror (multilayer mirror) 12. As shown in FIG. 3, the reflectance characteristics of the multilayer mirror 12 were 94% reflectance at the peak wavelength (521 nm) of the emission spectrum of the organic light emitting layer 15.
On the multilayer mirror 12, a transparent electrode 13 made of ITO was formed with a film thickness of 76 nm by sputtering to produce an ITO substrate. The resistance value of the transparent electrode 13 is 25Ω / □.

Subsequently, the ITO substrate is etched into a predetermined shape, then ultrasonically cleaned with acetone, isopropyl alcohol, etc., dried, further UV-O ₃ cleaned, set in a vacuum deposition tank, and 1 × 10 ^{− The} pressure was reduced to ⁵ Torr.
On this ITO substrate, first, α-NPD was deposited as a hole transporting layer at a rate of 0.2 to 0.4 nm / second to a film thickness of 111 nm, and subsequently a green light emitting layer was doped with a coumarin derivative Alq3. Is deposited to a thickness of 5 nm at a rate of 0.2 to 0.4 nm, and then Alq3 is deposited to a thickness of 69 nm at a rate of 0.2 to 0.4 nm as an electron transport layer, and further as an electron injection layer Li was deposited in a thickness of 1 nm, and silver was deposited in a thickness of 200 nm as a cathode layer.
Here, silver as a cathode had a reflectance of 96% at the peak wavelength of 521 nm.

Experimental example 2

In contrast to Experimental Example 1, a multilayer mirror was fabricated by depositing four sets of dielectric films by a combination of SiO ₂ (film thickness 94 nm) / TiO ₂ (film thickness 63 nm) by EB vapor deposition. The other conditions are the same as in Experimental Example 1.
In this case, the reflectance of the multilayer mirror at the peak wavelength of 521 nm was 84%.

Experimental example 3

In contrast to Experimental Example 1, a multilayer mirror was manufactured by forming three sets of dielectric films by a combination of SiO ₂ (film thickness 94 nm) / TiO ₂ (film thickness 63 nm) by EB vapor deposition. The other conditions are the same as in Experimental Example 1.
In this case, the reflectance of the multilayer mirror at the peak wavelength of 521 nm was 70%.

Experimental Example 4

In contrast to Experimental Example 1, a multilayer mirror was produced by depositing six sets of dielectric films by a combination of SiO ₂ (film thickness 94 nm) / TiO ₂ (film thickness 63 nm) by EB vapor deposition. The other conditions are the same as in Experimental Example 1.
In this case, the reflectance of the multilayer mirror at the peak wavelength of 521 nm was 98%.

Comparative Example 1

  On the other hand, the transparent electrode 13 was formed directly on the glass substrate without forming a dielectric film. The other conditions were the same as those of Experimental Example 1, but the organic EL element without a multilayer mirror, that is, without a microresonator structure was used.

Experimental Example 5

In contrast to Experimental Example 1, Al was deposited to a thickness of 200 nm as a cathode. The other conditions are the same as in Experimental Example 1.
In this case, the reflectance of the reflecting mirror at the peak wavelength of 521 nm was 91%.

Comparative Example 2

  On the other hand, the transparent electrode 13 was formed directly on the glass substrate without forming a dielectric film. The other conditions were the same as in Experimental Example 5, but the organic EL element without the microresonator structure was used.

Experimental Example 6

In contrast to Experimental Example 5, Al was deposited as a cathode at a film thickness of 200 nm at a degree of vacuum of about 5 × 10 ⁻⁵ Torr. Other conditions are the same as in Experimental Example 5.
In this case, the reflectance of the reflecting mirror at the peak wavelength of 521 nm was set to 85%.

Comparative Example 3

  On the other hand, the transparent electrode 13 was formed directly on the glass substrate without forming a dielectric film. The other conditions were the same as in Experimental Example 6, but the organic EL element without the microresonator structure was used.

Experimental Example 7

In contrast to Experimental Example 5, Al was deposited as a cathode at a film thickness of 200 nm at a degree of vacuum of about 5 × 10 ⁻⁵ Torr. Other conditions are the same as in Experimental Example 5.
In this case, the reflectance of the reflecting mirror at the peak wavelength of 521 nm was 71%.

Comparative Example 4

  On the other hand, the transparent electrode 13 was formed directly on the glass substrate without forming a dielectric film. The other conditions were the same as in Experimental Example 7, but the organic EL element without the microresonator structure was used.

  Thus, in Experimental Examples 1 to 7, as shown in the table of FIG. 4, the organic EL elements in which the reflectances of both the semi-transmissive mirror (multilayer mirror) and the cathode layer (reflective mirror) were changed respectively. Will be produced.

Here, based on the results of Experimental Examples 1 to 4, the case where the reflectance of the multilayer mirror is changed by fixing the reflectance of the reflecting mirror to 96% will be considered.
With respect to the organic EL elements produced in Experimental Example 1 and Comparative Example 1, the light emission characteristics when energized at 25 mA / cm ² are as shown in FIG.
That is, in the case of Experimental Example 1, due to the effect of the microresonator structure, a light emission characteristic with a narrow half-value width having a peak at 521 nm is obtained, a value of luminance 1550 cd / m ² and light emission intensity 0.365 W / m ² · sr at the peak wavelength. was gotten.
On the other hand, since the comparative example 1 does not have a microresonator structure, the luminance 2100 cd / m ² and the emission intensity 0.0673 W / m ² · sr at the peak wavelength were obtained.
Therefore, in Experimental Example 1, the ratio of the characteristics to Comparative Example 1 was 0.74 times higher in luminance and 5.42 times higher in emission intensity at 521 nm.
That is, by setting the reflectance of the multilayer mirror to 94% and the reflectance of the reflecting mirror to 96%, both the luminance and the emission intensity at the peak wavelength were high.

In comparison between Experimental Example 2 and Comparative Example 1, Experimental Example 2 has a light emission characteristic with a narrow half-value width having a peak at 521 nm, a luminance of 1909 cd / m ² , and an emission intensity of 0.234 W / m ^2. A value of sr was obtained.
Therefore, in Experimental Example 2, the ratio of the characteristics to Comparative Example 1 was 0.91 times the luminance and 3.47 times the emission intensity at 521 nm.
That is, by setting the reflectivity of the multilayer mirror to 84% and the reflectivity of the reflection mirror to 96%, the luminance increased from Experimental Example 1 and the emission intensity at the peak wavelength was slightly decreased. Both luminescence intensities were good and relatively high values. Here, the increase in luminance is due to the fact that the half-value width is slightly wider than that of Experimental Example 1.

Further, in comparison between Experimental Example 3 and Comparative Example 1, Experimental Example 3 has a light emission characteristic with a narrow half-value width having a peak at 521 nm, a luminance of 1921 cd / m ² , and an emission intensity of 0.128 W / m ² · peak wavelength. A value of sr was obtained.
Therefore, in Experimental Example 3, the ratio of the characteristics to Comparative Example 1 was 0.91 times the luminance and 1.90 times the emission intensity at 521 nm.
That is, by setting the reflectance of the multilayer mirror to 70% and the reflectance of the reflecting mirror to 96%, the luminance was equivalent to that of Experimental Example 2, and the emission intensity at the peak wavelength was further reduced.

In comparison between Experimental Example 4 and Comparative Example 1, Experimental Example 4 has a light emission characteristic with a narrow half-value width having a peak at 521 nm, a luminance of 790 cd / m ² , and an emission intensity of 0.199 W / m ² · peak wavelength. A value of sr was obtained.
Therefore, in Experimental Example 4, the ratio of the characteristics to Comparative Example 1 was 0.376 times the luminance and 2.96 times the emission intensity at 521 nm.
That is, the reflectance of the multilayer mirror is 98%, the reflectance of the reflection mirror is 96%, and the reflectance of the multilayer mirror is higher than the reflectance of the reflection mirror. As a result, the strength decreased.

Thus, from the measurement results of Experimental Examples 1 to 4, the relationship between the reflectance of the multilayer mirror, the luminance, and the emission intensity at the peak wavelength (521 nm) is as shown in FIG.
That is, as the reflectivity of the multilayer mirror increases, the emission intensity at the peak wavelength increases and the brightness tends to decrease gradually.However, if the reflectivity of the multilayer mirror is higher than the reflectivity of the reflection mirror, It can be seen that both the luminance and the emission intensity at the peak wavelength are greatly reduced.

Subsequently, based on the results of Experimental Examples 1, 5 to 7, the case where the reflectance of the multilayer mirror is fixed to 94% and the reflectance of the reflecting mirror is changed will be considered.
In comparison between Experimental Example 5 and Comparative Example 2, Experimental Example 5 has a light emission characteristic with a narrow half-value width having a peak at 521 nm, a luminance of 830 cd / m ² , and a light emission intensity of 0.149 W / m ² · sr at the peak wavelength. A value was obtained.
On the other hand, Comparative Example 2 did not have a microresonator structure, and thus the values of luminance 1922 cd / m ² and emission intensity at peak wavelength 0.0493 W / m ² · sr were obtained.
Therefore, in Experimental Example 5, the ratio of the characteristics to Comparative Example 2 was 0.43 times the luminance and 3.02 times the emission intensity at 521 nm.

In comparison between Experimental Example 6 and Comparative Example 3, Experimental Example 6 has a light emission characteristic with a narrow half-value width having a peak at 521 nm, a luminance of 504 cd / m ² , and an emission intensity of 0.0826 W / m ^2. A value of sr was obtained.
On the other hand, since the comparative example 3 does not have a microresonator structure, the luminance 1526 cd / m ² and the emission intensity 0.0374 W / m ² · sr at the peak wavelength were obtained.
Therefore, in Experimental Example 6, the ratio of the characteristics to Comparative Example 3 was 0.33 times the luminance and 2.21 times the emission intensity at 521 nm.

Further, in comparison between Experimental Example 7 and Comparative Example 4, Experimental Example 7 has a light emission characteristic with a narrow half-value width having a peak at 521 nm, a luminance of 292 cd / m ² , and an emission intensity of 0.0362 W / m ² · peak wavelength. A value of sr was obtained.
On the other hand, since the comparative example 4 does not have a microresonator structure, values of luminance 1483 cd / m ² and emission intensity 0.0372 W / m ² · sr at the peak wavelength were obtained.
Therefore, in Experimental Example 7, the ratio of the characteristics to Comparative Example 4 was 0.20 times the luminance and 0.97 times the emission intensity at 521 nm.

Thus, from the measurement results of Experimental Examples 1 and 5 to 7, the relationship between the reflectance of the cathode layer 16 (reflection mirror), the luminance, and the emission intensity at the peak wavelength (521 nm) is as shown in FIG. .
That is, the higher the reflectance of the cathode layer 16 (reflection mirror), the higher the emission intensity at the luminance and peak wavelength. Here, referring to the results of Experimental Example 4 (plotted in FIG. 7), when the reflectance of the reflecting mirror is lower than the reflectance of the multilayer mirror, the reflectance of both the reflecting mirror and the multilayer mirror is increased. However, it can be seen that the luminance and the peak wavelength do not increase so much. That is, when the reflectance of the multilayer mirror becomes higher than the reflectance of the reflection mirror, the increase rate of the luminance and peak intensity becomes small.
On the other hand, when the reflectance of the reflecting mirror is higher than the reflectance of the multilayer mirror, the increase rate becomes larger. In addition, when the reflectance of the reflection mirror is 85% or more, particularly 90% or more, the luminance and the emission intensity at the peak wavelength increase rapidly when the reflectance of the reflection mirror increases, but the reflectance of the reflection mirror is 90% or less. Then, the increase rate of the emission intensity at the luminance and peak wavelength is relatively small. Therefore, if the reflectance of the reflecting mirror is 85% or higher, it is possible to expect an increase in light emission intensity at good luminance and peak wavelength.

In the embodiment described above, the organic layer is composed of two layers of the hole transport layer 14 and the organic light emitting layer 15 in this order from the anode side. However, the organic layer is not limited to this, for example, the hole injection layer. , Hole transport layer, light-emitting layer, electron transport layer four-layer structure, hole injection layer, hole transport layer, three-layer structure of light-emitting layer, hole transport layer, light-emitting layer, electron transport layer three-layer structure Further, it is possible to use a multi-layered light emitting layer.
Here, the electron injection layer facilitates injection of electrons from the cathode layer into the organic layer.
Further, the electron transport layer has an electron transport function, and an aluminum chelate complex (Alq3), a distyrylbiphenyl derivative (DPVBi), an oxadiazole derivative, a bistyrylanthracene derivative, a benzoxazolethiophene derivative, and the like are used. Preferably, it has a film thickness of about 10 to 200 nm.

  Further, in the above-described embodiment, the structure from the anode layer to the cathode layer is a normal organic EL element, but it can also be applied to a light emitting element in which a plurality of light emitting units are stacked (hereinafter referred to as an MPE element). It is. FIG. 10 shows an application example, which is an element in which a microresonator is configured by forming a reflective mirror and a multilayer mirror on an element in which a plurality of organic EL elements are united through a layer forming an equipotential surface. The MPE element has a problem that the number of organic layers is larger than that of a normal organic EL element, and the light emission output decreases due to absorption by each organic layer. Therefore, the MPE element has a microresonator structure. In the case of the configuration, a decrease in light emission output becomes a greater problem. Therefore, the present invention is particularly useful even in an element in which the MPE element is configured to have a microresonator structure.

  As described above, according to the present invention, an organic EL element having a narrow peak emission half-value width and high luminance can be provided with a simple configuration.

It is a schematic sectional drawing which shows the structure of one Embodiment of the organic EL element by this invention. It is a graph which shows the reflectance characteristic of the semi-transmissive mirror (multilayer film mirror) in the organic EL element of FIG. 1, and the light emission characteristic of an organic light emitting layer. 6 is a graph showing the reflectance characteristics of a multilayer mirror according to Experimental Example 1. It is a graph which shows the reflectance of the multilayer film mirror in Example 1-7, and a reflective mirror. 5 is a graph showing light emission characteristics according to Experimental Example 1 and Comparative Example 1. It is a graph which shows the emitted light intensity in the brightness | luminance and peak wavelength with respect to the comparative example of Experimental example 1-Experimental example 4. FIG. It is a graph which shows the luminance ratio with respect to the comparative example of Experimental example 1, Experimental example 5-Experimental example 7, and the emitted light intensity ratio in a peak wavelength. It is a schematic sectional drawing which shows the structure of an example of the organic EL element provided with the conventional micro resonator structure. It is a graph which shows the light emission characteristic in the case of not having the light emission characteristic in the organic EL element of FIG. 8, and a micro resonator structure. It is a figure which shows one application example of a structure of the anode layer from the anode layer in embodiment by this invention.

Explanation of symbols

10 Organic EL Element 11 Transparent Substrate 12 Transflective Mirror (Multilayer Film Mirror)
13 Transparent electrode 14 Hole transport layer 15 Organic light emitting layer 16 Cathode layer (also used as reflection mirror)

Claims (5)

A multilayer mirror formed by alternately laminating thin films made of two kinds of materials having different refractive indexes, a transparent electrode layer sequentially formed on the surface of the multilayer mirror, and at least one light emitting layer An organic EL element including a plurality of organic layers, a cathode layer, and a reflection mirror, wherein a microresonator is configured by the multilayer mirror and the reflection mirror,
The multilayer mirror has a reflectance of 80% or more,
An organic EL element, wherein the reflectance of the reflection mirror is 85% or more and greater than the reflectance of the multilayer mirror.   The organic EL element according to claim 1, wherein a reflectance of the reflection mirror is 90% or more.   The organic EL element according to claim 1, wherein the reflection mirror and the cathode layer are integrally formed of a metal thin film.   The organic EL element according to claim 1, wherein the cathode layer is configured as a translucent or transparent electrode separately from the reflection mirror. The cathode layer is composed of a semi-permeable film or a transparent conductive film made of a conductive metal,
The reflection mirror is formed on at least one dielectric layer made of a combination of two kinds of materials having different refractive indexes on the cathode layer, and preferably further formed on the dielectric layer. Consists of a metal layer made of silver, aluminum, gold, copper, rhodium or their alloys,
6. The organic EL element according to claim 5, wherein the reflectance of the reflection mirror is 90% or more.

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