JP6995569B2 - Organic EL element and display device and lighting device using it - Google Patents

Description

The present invention relates to an organic EL (electroluminescence) element that emits light by energizing an organic light emitting layer sandwiched between a pair of electrodes, and particularly a top emission type white light emitting organic EL element and the use thereof. Regarding the display device and lighting device that were used.

In recent years, self-luminous devices compatible with flat panels have attracted attention, and self-luminous devices include plasma emission display elements, field emission elements, EL elements, and the like. In particular, organic EL elements are being used in full-color display devices such as televisions, monitors for smartphones, and viewfinders for cameras, in addition to white lighting.
When manufacturing a full-color display device using an organic EL element, a method of painting different light emitting layers for each pixel (element) and a white organic EL element having a white light emitting layer are used to form a color filter of different colors. There is a method of painting each pixel separately. In the latter case where a white light emitting layer is used, white light emission is often obtained by mixing colors using two or more kinds of light emitting materials.
As the light emitting material of the white organic EL element, there are a case where a light emitting dopant material of two colors of yellow and blue is mainly used, and a case of using a light emitting dopant of three colors of red, green and blue. When using three colors of red, green, and blue light emitting dopants, when stacking three light emitting layers of red, green, and blue, and when using both red and green light emitting dopants, a red / green light emitting layer and a blue light emitting dopant are used. There are cases where two light emitting layers are laminated with a blue light emitting layer containing.
Patent Document 1 discloses a white organic EL device in which a red / green light emitting layer and a blue light emitting layer are laminated. In the white organic EL device of Patent Document 1, the hole transportability of the blue light emitting layer is set so that the difference in LUMO energy between the host material and the dopant material of the blue light emitting layer near the cathode is larger than the difference in HOMO energy. And the durability is improved. In this case, since the blue light emitting layer is hole transporting, electrons are trapped in the blue light emitting layer. Therefore, by stacking the blue light emitting layer on the side closest to the cathode, only the electrons not trapped in the blue light emitting layer are conducted to the red / green light emitting layer. On the other hand, the red / green light emitting layer has a hole trapping property that is generally used, and since it is formed on the anode side, holes are trapped and only the holes that are not trapped are conducted to the blue light emitting layer. Therefore, in the blue light emitting layer, light is emitted when the holes reach the place where the electrons are trapped, and in the green / red light emitting layer, light is emitted when the electrons reach the place where the holes are trapped.

Japanese Unexamined Patent Publication No. 2014-22205

Generally, in an organic EL device, a hole injection layer or a hole transport layer is provided between the anode and the light emitting layer, and an electron injection layer or an electron transport layer is provided between the cathode and the light emitting layer. Further, in a top-emission type organic EL element having the light extraction side on the side opposite to the substrate, it is common to arrange an anode on the substrate side and a cathode on the light extraction side.
In a top-emission type organic EL element, a light-transmitting conductive material such as ITO is sputtered and formed on the electrode on the light extraction side, but at that time, the member on the upper surface is damaged and desired light emission is achieved. The emission voltage applied to the element to obtain the amount increases. The damage during sputter film formation of the electrode is higher in the hole transporting material constituting the hole injecting layer or the hole transporting layer than in the electron transporting material constituting the electron injecting layer or the electron transporting layer. Therefore, it is preferable to arrange the cathode on the light extraction side.
Lithium fluoride is widely used as an electron injection material contained in the electron injection layer arranged in contact with the cathode, but lithium fluoride is reduced by depositing aluminum or the like on the electron injection material. Expresses electron injection function. When the cathode is placed on the substrate side, the cathode is formed and then the electron injection layer is formed to deposit aluminum and the like. Therefore, in the configuration where the electron injection layer and the electron transport layer are formed after the cathode is formed, the electron injection layer is formed. Lithium fluoride cannot be used. However, if the light extraction side is a cathode, there is no problem because the cathode is formed after the electron injection layer and the electron transport layer are formed, and the cathode is formed after the vapor deposition film such as aluminum is formed. Further, since the upper surface of the cathode when the cathode is sputter-deposited is a vapor-filmed film such as aluminum, damage to the electron injection layer and the electron transport layer is reduced.
Therefore, in the conventional top-emission type white organic EL element, it is common to arrange the cathode on the light extraction side. However, there is a problem that it is difficult to obtain the interference effect of light emission in the configuration in which the blue light emitting layer and the red / green light emitting layer are laminated and the blue light emitting layer is arranged on the cathode side as in Patent Document 1.
As a general top-emission type white organic EL element, from the substrate side, the reflecting electrode as an anode, the hole transport layer, the red / green light emitting layer, the blue light emitting layer, the electron transport layer, and the light extraction electrode as a cathode are in this order. The laminated configuration will be described.
When the optical distance from the reflective surface of the reflective electrode to the blue light emitting layer is set so that an interference effect such as λ / 4 can be obtained, the red / green light emitting layer has a longer emission wavelength (λ) than blue. The optical distance of the reflecting electrode from the reflecting surface is too short than λ / 4, and the interference effect cannot be obtained. On the contrary, when the optical distance from the reflective surface of the reflective electrode to the red / green light emitting layer is set so that an interference effect such as λ / 4 can be obtained, the optics from the reflective surface of the reflective electrode to the blue light emitting layer. The distance becomes too long than λ / 4, and it is difficult to obtain the interference effect of blue light emission.
In such a general top-emission type white organic EL element, if a hole-transporting blue light emitting layer is used, it is difficult to obtain the interference effect of both blue light emission and red and green light emission, and it is consumed. The problem is that the power consumption is high.
Further, if the optical distance from the reflective surface of the reflective electrode to the light emitting layer is set to λ / 4 and the optical distance from the light emitting layer to the light extraction electrode is also set to λ / 4, the film thickness of the entire organic compound layer becomes too thin. It may cause a short circuit or a leak. On the other hand, if the optical distance from the light emitting layer to the light extraction electrode is set to a thickness of about 3λ / 4 to suppress short circuits and leaks, there is a problem that the light emitting voltage becomes high because the film thickness of the electron transport layer becomes thick.
There is also a method in which the light extraction electrode is made of a transparent metal oxide such as ITO instead of a metal thin film such as Ag or MgAg, and the optical distance from the light emitting layer to the light extraction electrode is about 2λ / 4 thickness. There is another problem that the interference effect is reduced and the color purity of blue is deteriorated.
Therefore, the present invention obtains the interference effect of both blue emission and red emission or green emission in a top-emission type white emission organic EL element using a hole-transporting blue emission layer, and obtains an emission voltage. The purpose is to reduce it, reduce power consumption, and improve durability.

The first aspect of the present invention includes a substrate, a reflective electrode, an organic compound layer, and a light extraction electrode in this order.
The organic compound layer is formed between a first light emitting layer, a second light emitting layer arranged between the first light emitting layer and the light extraction electrode, and between the second light emitting layer and the light extraction electrode. The first light emitting layer has an arranged hole transport layer, and the first light emitting layer is an electron trap type light emitting layer that emits blue light, and the second light emitting layer emits light having a longer wavelength than the first light emitting layer. An organic EL element that is a light emitting layer
The reflective electrode is a cathode, and the light extraction electrode is an anode.
The optical distance from the reflective surface of the reflective electrode to the surface of the first light emitting layer on the light extraction side is the distance that enhances the blue light emitted by the first light emitting layer .
The optical distance from the surface of the first light emitting layer on the light extraction side to the reflection surface of the light extraction electrode is in the range of 3λ _B / 4 ± λ _B / 8 when the wavelength of the blue emission is λ _B. It is characterized by being.
The second aspect of the present invention is a display having a plurality of organic EL elements, blue, green, and red color filters arranged on the light extraction side of the organic EL element, and a switching element connected to the organic EL element. It is a display device, characterized in that the organic EL element is the organic EL element of the present invention.

In the present invention, high durability can be obtained by arranging the electron trap type blue light emitting layer on the cathode side. Furthermore, by arranging the cathode on the substrate side, it is possible to obtain a good interference effect in both blue light emission and red / green light emission while suppressing short circuits and leaks, and it is possible to obtain a good interference effect in the white light emission organic EL element. The voltage can be reduced. Further, since the hole transporting property is provided between the light emitting layer and the anode on the light extraction side, the light emitting voltage can be suppressed. Therefore, even if the hole injection layer and the hole transport layer on the upper surface are damaged when the anode on the light extraction side is formed, the emission voltage can be reduced as a whole, the power consumption is suppressed, and the durability is reduced. Can be improved. Therefore, it is possible to provide a display device and a lighting device having low power consumption and high durability.

It is sectional drawing of one Embodiment of the organic EL element of this invention. It is an energy band diagram of the blue light emitting layer of the organic EL element of this invention. It is sectional drawing of the embodiment of the display device of this invention.

The organic EL element of the present invention has a substrate, a reflective electrode, an organic compound layer, and a light extraction electrode in this order, and the organic compound layer includes a first light emitting layer, a first light emitting layer, and a light extraction electrode. It has a second light emitting layer arranged between the two. Further, the first light emitting layer is an electron trap type light emitting layer that emits blue light, and the second light emitting layer is a light emitting layer that emits light having a longer wavelength than the first light emitting layer. In the present invention, the reflective electrode is a cathode and the light extraction electrode is an anode, and the optical distance from the reflective surface of the reflective electrode to the surface of the first light emitting layer on the light extraction side is the blue light emitted by the first light emitting layer. It is characterized by a distance to strengthen each other. As the second light emitting layer, a light emitting layer that emits green light, red light, or both green and red is preferable.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The dimensions of each part of the drawing are different from the actual ones. Further, with respect to parts not particularly shown or described in the present specification, well-known or publicly known techniques in the art concerned shall be applied.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the present invention, in which a green / red light emitting layer 15 containing a red light emitting dopant and a green light emitting dopant and a blue light emitting layer 14 containing a blue light emitting dopant are shown on a substrate 10. The configuration is shown in which the two light emitting layers of and are laminated to form a white light emitting layer 18.

In the present embodiment, the reflective electrode 11 is provided on the substrate 10 as a cathode. The substrate 10 used may be either glass or resin, and when configuring a display device or a lighting device, a switching element (not shown) such as a TFT, a converter circuit (not shown), or the like is connected to the reflective electrode 11. To.
A reflective metal or the like is used for the reflective electrode 11, and Al, Ag, Ti, Cr and their alloys, TiN and the like can also be used as the metal, and even if a transparent metal oxide such as ITO is laminated and used. good.

It is preferable to form an electron injection layer 12 on the reflective electrode 11 in order to improve the electron injection property. As the electron injection layer 12, a mixture of an electron donating dopant and an electron transporting organic compound may be used. Further, the electron injection layer 12 may have an imidazolidene derivative and a carbene compound. As the electron donating dopant, an alkali metal, an alkaline earth metal, a rare earth metal, and a compound thereof can be used. The electron injection layer may be formed by containing an alkali metal compound in the electron transport material. More preferably, the alkali metal compound is a cesium compound. Further, more preferably, it is cesium carbonate.

In the present invention, a preferred method for forming the electron injection layer 12 is to co-deposit cesium carbonate and an electron transporting organic compound. As the electron-transporting organic compound, a conventionally known compound such as a phenanthroline compound can be used. In addition, cesium carbonate is decomposed during co-deposited deposition, and cesium suboxides such as (Cs ₁₁ O ₃ ) Cs ₁₀ and (Cs ₁₁ O ₃ ) Cs and Cs ₁₁ O ₃ derived from cesium carbonate are contained in the electron injection layer 12. May be formed. In addition, a coordination compound may be formed between cesium and an organic compound. Therefore, the electron injection layer 12 may contain a cesium suboxide or a cesium-coordinated organic compound in addition to cesium carbonate. When the cesium carbonate and the organic compound are co-deposited, the blending amount of cesium carbonate is preferably 1 to 10% by mass.

The film thickness of the electron injection layer 12 is preferably 10 nm or less. When it is 10 nm or less, when a plurality of reflective electrodes 11 are arranged to form a plurality of pixels and the electron injection layer 12 is formed across the plurality of pixels, the leakage current to the adjacent pixels can be suppressed, which is preferable.

When the electron injection layer 12 is not used, it is desirable that the reflective electrode 11 has electron injection properties, and the reflective metal contains any of an alkali metal, an alkaline earth metal, and a compound thereof as the electron injection material. It is preferable to let it. It is preferably cesium carbonate, and it is preferable to use a co-deposited product of Ag and cesium carbonate as the reflective electrode 11. The blending amount of cesium carbonate is preferably 1 to 10% by mass.

The electron transport layer 13 may be formed on the electron injection layer 12. As the electron transport layer 13 , a conventionally known electron transport organic compound such as a phenanthroline compound can be used, and the same or different from the electron transport organic compound used for the electron injection layer 12 can be used. good.

Although the blue light emitting layer 14 is formed on the electron transport layer 13, a hole block layer (not shown) may be inserted between the electron transport layer 13 and the blue light emitting layer 14.
The blue light emitting layer 14 contains a host material as a first organic compound (hereinafter referred to as “first host material”) and a blue light emitting dopant as a second organic compound having a content of 10% by mass or less. .. Then, assuming that the LUMO energy level of the first host material is Lh, the HOMO energy level is Hh, the LUMO energy level of the blue light emitting dopant material is Ld, and the HOMO energy level is Hd, the following equation ( It is preferable to satisfy a).
| Ld |> | Lh | and | Hd |> | Hh | ... (a)
The LUMO energy level and the HOMO energy level are based on the vacuum level, and in the case of a normal molecule, they take a negative value, but in the present invention, they are defined by the magnitude of the absolute value.

Further, in the present invention, a value measured by atmospheric photoelectron spectroscopy (“AC-2” manufactured by RIKEN Keiki Co., Ltd.) is used as the energy level of HOMO. The energy level of LUMO was obtained from the energy level of HOMO and the band gap obtained from the absorption edge in the visible light-ultraviolet absorption spectrum. That is, the LUMO energy level is the sum of the HOMO energy level and the bandgap.

FIG. 2 is an energy band diagram of the blue light emitting layer 14 in the organic EL device of the present invention. When electrons are injected into the blue light emitting layer 14 satisfying the above formula (a), the electrons are trapped in the energy level of LUMO of the blue light emitting dopant, but the blue light emitting dopant has 10 masses in the blue light emitting layer 14. Since it is as small as% or less, it becomes difficult for electrons to conduct. The blue light emitting layer 14 preferably contains 0.1% by mass or more of the blue light emitting dopant.

Further, when holes are injected, the holes are injected into the energy level of HOMO of the first host material, and the host material occupies a large part of the weight of the blue light emitting layer 14, so that this level. Conducts. Therefore, the blue light emitting layer 14 has a hole transporting property in which holes are more easily conducted than electrons. Since the hole-transporting blue light emitting layer 14 does not trap holes inside, the material is less likely to undergo oxidative deterioration even when continuously emitting light, and the drive durability characteristics are very high.

On the contrary, since the blue light emitting layer 14 is an electron trap type, theoretically, reduction deterioration is likely to occur. However, the organic material constituting the organic compound layer 19 is rarely detected as an actually reduced deterioration substance, and it is considered that the reduction deterioration of the organic material is much less likely to occur than the oxidative deterioration.

Further, in the present invention, since the reflective electrode 11 formed on the substrate 10 is used as a cathode, electrons can be injected when the blue light emitting layer 14 is arranged closest to the substrate 10. Then, the green / red light emitting layer 15 is formed on the blue light emitting layer 14. With this configuration, the optical distance from the reflective surface of the reflective electrode 11 to the surface of the blue light emitting layer 14 on the light extraction side is set to λ _B / 4 (λ _B is the blue emission wavelength), and the interference effect of blue emission is obtained. be able to. At the same time, the optical distance from the reflective surface of the reflective electrode 11 to the surface of the green / red light emitting layer 15 on the light extraction side is not too short by sandwiching the blue light emitting layer 14, and red and green light emission. The interference effect of can also be obtained. That is, since the emission wavelength (λ) is larger in red and green than in blue, the value of λ / 4 is larger in red and green than in blue, and the green / red emission layer is on the blue emission layer 14. By forming 15, it is possible to obtain the interference effect of both blue and red and green emission.

Further, in the present invention, since the anode serves as the light extraction electrode 17, holes are transported between the anode and the white light emitting layer 18, and the white light emitting layer 18 to the light extraction electrode 17 are compared with the case of normal electron transport. It is possible to suppress the voltage when the film thickness is increased. This is because the hole transport material generally used for organic EL has higher mobility than the electron transport material.

In the present invention, a pyrene derivative or the like is preferably used as the first host material constituting the blue light emitting layer 14, and other examples include a condensed ring compound. For example, fluorene derivative, naphthalene derivative, anthracene derivative, pyrene derivative, carbazole derivative, quinoxalin derivative, quinoline derivative and the like, organic aluminum complex such as tris (8-quinolinolate) aluminum, and organic zinc complex. Further, a triphenylamine derivative and the like can also be mentioned.
As the blue light emitting dopant, a fluoranthene derivative or the like is preferably used as a material satisfying the condition of the above formula (a).

In the present invention, the optical distance from the reflective surface of the reflective electrode 11 to the surface of the blue light emitting layer 14 on the light extraction side is adjusted to a distance that enhances the blue light emission of the blue light emitting layer 14. Specifically, it is preferable to adjust to about λ _B / 4 (λ _B is the emission wavelength of blue), and more preferably within the range of λ _B / 4 ± λ _B / 8. Here, in the present invention, blue refers to light emission having a peak wavelength of 430 nm to 480 nm in the emission spectrum. Further, red refers to a peak wavelength of the emission spectrum of 580 nm to 680 nm, and green refers to a peak wavelength of the emission spectrum of 500 nm to 570 nm.

Further, λ _B / 4 is represented by (λ _B / 4) × (2- (φ / π)) in consideration of the phase shift φ at the reflection electrode 11. Considering that the refractive index of the organic material from the reflective surface of the reflective electrode 11 to the surface of the blue light emitting layer 14 on the light extraction side is about 1.8, the actual film thickness L1 is preferably 55 nm or more and 65 nm or less. Become.
The optical distance from the reflective surface of the reflective electrode 11 to the surface of the green / red light emitting layer 15 on the light extraction side is also preferably adjusted to a distance that enhances green light emission or red light emission. Specifically, when the emission wavelength of green or red is λ _O , it is preferable to adjust the optical distance within the range of about λ _O / 4, specifically, λ _O / 4 ± λ _O / 8. ..

A green / red light emitting layer 15 is laminated on the blue light emitting layer 14. The green / red light emitting layer 15 in FIG. 1 is a light emitting layer containing both a green light emitting dopant and a red light emitting dopant in a second host material, but the green light emitting layer and the red light emitting layer are separately formed and laminated. May be. When the green light emitting layer and the red light emitting layer are laminated separately, it is preferable to stack the green light emitting layer on the blue light emitting layer 14 and the red light emitting layer on the green light emitting layer in this order because the interference effect is easily obtained. Further, the second host material may be the same as or different from the first host material.

As the second host material, the same material as that of the first host material is used, and a pyrene derivative or the like is preferably used. Further, as the green light emitting dopant and the red light emitting dopant, those conventionally known are used.

Although the hole transport layer 16 is formed on the green / red light emitting layer 15, an electron block layer (not shown) may be inserted between the hole transport layer 16 and the green / red light emitting layer 15. As the hole transport layer 16, a conventionally known hole transport material such as an arylamine derivative can be used.
A light extraction electrode 17 is formed on the hole transport layer 16 as an anode, but a hole injection layer (not shown) may be inserted between the hole transport layer 16 and the light extraction electrode 17. The light extraction electrode 17 is preferably a semi-transmissive metal thin film having a certain degree of reflectance and transparency, such as Ag or Ag alloy. It is preferable to use a thin film metal because the chromaticity can be adjusted by adjusting the interference.

In the present invention, the film thickness from the light emitting layer on the substrate 10 side, that is, the surface on the light extraction side of the blue light emitting layer 14 to the reflection surface (the surface on the substrate 10 side) of the light extraction electrode 17 is defined as L2.

As described above, in the present invention, the film thickness from the reflective surface of the reflective electrode 11 formed on the substrate 10 to the surface of the blue light emitting layer 14 on the light extraction side is defined as L1, and L1 has an interference effect of blue light emission. It is preferable that the optical distance is adjusted to be about λ _B / 4 so as to be obtained.
Further, in the present invention, it is preferable that L1 × 2 <L2 can suppress short circuits and leaks.
Further, in order to adjust the chromaticity of the extracted light, it is more preferable that L2 is approximately 3/4 times the wavelength λ at which the interference effect is desired, specifically, within the range of 3λ / 4 ± λ / 8. .. Therefore, since the emission peak wavelength from blue to green is 430 nm to 570 nm and the refractive index of the organic material is about 1.8, it is preferable that L2 is 180 nm or more and 240 nm or less. It is not preferable to increase L2 × 1.8 by λ / 4 times because the film thickness becomes too thin and short circuits and leaks are likely to occur.

In order to make the film thickness of L2 180 nm or more and 240 nm or less, it is preferable to set the film thickness of the hole transport layer 16 to be thicker than the green / red light emitting layer 15. At this time, the film of the hole transport layer 16 is set thick. The thickness needs to be 170 nm or more and 200 nm or less. In the present invention, since the organic compound layer on the light extraction side has not electron transport property but hole transport property having relatively high mobility, it is possible to suppress an increase in voltage even if the film thickness is increased.
Further, a protective film (not shown) such as SiN may be provided on the light extraction side of the light extraction electrode 17 as needed.

Next, a display device using the organic EL element of the present invention will be described with reference to FIG. 3 (a) and 3 (b) are schematic cross-sectional views of an embodiment of the display device of the present invention. The display device of the present invention has a plurality of organic EL elements of the present invention, blue, green, and red color filters, and a switching element connected to the organic EL element. FIG. 3 shows one repeating unit of red, green, and blue pixels.

In the display device of FIG. 3A, reflective electrodes 11R, 11G, and 11B corresponding to the red, green, and blue color filters are provided on the substrate 10. A switching element (not shown) such as a TFT is connected to the plurality of reflective electrodes 11R, 11G, and 11B in order to control the emission brightness. On the reflective electrodes 11R, 11G, 11B, the organic compound layer 19 and the light extraction electrode 17, as illustrated in FIG. 1, are commonly provided across the plurality of reflective electrodes 11R, 11G, 11B.

A protective film 21 such as SiN may be formed on the light extraction electrode 17. Red, green, and blue color filters 22R, 22G, and 22B are provided on the protective film 21 corresponding to each pixel, and at least red, green, and blue pixels 20R, 20G, and 20B are formed.
As a method of forming the color filters 22R, 22G, 22B, the color filters 22R, 22G, 22B corresponding to the pixel size are provided on another substrate, and the color filters 22R, 22G, 22B are bonded to the substrate 10 provided with the organic EL element of white light emission. You may. Further, as shown in FIG. 3, the color filters 22R, 22G, and 22B may be patterned on the protective film 21 by using a photolithography technique.

Further, in FIG. 3A, in the red, green, and blue pixels 20R, 20G, and 20B, the reflective electrodes 11R, 11G, and 11B have the same configuration, but in order to obtain a better interference effect of the light emitting layer, The configuration may be changed depending on the pixel. Specifically, as shown in FIG. 3B, the reflection electrodes 11B and 11G of the blue pixel 20B and the green pixel 20G are made of a light-reflecting metal, and the reflection electrode 11R of the red pixel reflects light. It is a laminate of a metallic metal layer 11Ra and a transparent metal oxide layer 11Rb. In this configuration, the optical distance from the reflective surface of the reflective electrode 11R (upper surface of the metal layer 11Ra) to the upper surface of the green / red light emitting layer (not shown) is relative to green by sandwiching the transparent metal oxide layer 11Rb. The red color is larger, and it becomes easier to obtain the interference effect of green and red at the same time.

The display device of the present invention can be used as an image display device such as a monitor of a television or a smartphone, a viewfinder of a camera, or the like.

Further, the lighting device of the present invention is characterized by having the organic EL element of the present invention and a converter circuit. The illuminating device may emit white, neutral white, or any other color from blue to red. The converter circuit is a circuit that converts an AC voltage into a DC voltage. Further, white has a color temperature of 4200 K, and neutral white has a color temperature of 5000 K. The illuminator may have a color filter.

Hereinafter, examples of the organic EL device of the present invention will be described, but the materials and device configurations used in the examples are preferable examples, but the present invention is not limited thereto.

(Example 1)
Ti (thickness 200 nm) was formed on the glass substrate as a reflective electrode, and UV / ozone cleaning was performed. Subsequently, it was attached to a vacuum vapor deposition apparatus (manufactured by ULVAC, Inc.) and exhausted to 1.33 × 10 ^-4 Pa. Next, a co-deposited film of cesium carbonate (3% by mass) and a phenanthroline derivative represented by the following structural formula (1) was formed on the reflective electrode with a film thickness of 7 nm to form an electron injection layer. Next, as the electron transport layer, only the phenanthroline derivative represented by the above structural formula (1) was formed into a film with a film thickness of 35 nm.

Next, as the blue light emitting layer, the pyrene derivative represented by the following structural formula (2) is used as the first host material, and the fluoranthene derivative represented by the following structural formula (3) is blended so as to contain 1% by mass as the blue light emitting dopant. Then, a 15 nm film was formed. The LUMO energy level Lh = 2.78 eV of the pyrene derivative structure, the HOMO energy level Hh = 5.72 eV, the LUMO energy level Ld = 3.06 eV of the fluoranthene derivative, and the HOMO energy level Hd =. It is 5.85 eV. Therefore, the condition of the above equation (a), that is, | Ld |> | Lh | and | Hd |> | Hh | is satisfied. The emission peak wavelength of the fluoranthene derivative is 440 nm.

Next, a green / red light emitting layer containing a green light emitting dopant and a red light emitting dopant at the same time was formed at 15 nm on the blue light emitting layer. Here, the pyrene derivative represented by the structural formula (2) was used as the second host material. Further, an anthracene derivative (4% by mass) represented by the following structural formula (4) was used as the green light emitting dopant, and a perylene derivative (0.5% by mass) represented by the following structural formula (5) was used as the red light emitting dopant. ..

Next, N, N'-α-dinaphthylbenzidine was formed into a film of 200 nm as a hole transport layer, and then an azatriphenylene derivative represented by the following structural formula (6) was formed into a film of 10 nm as a hole injection layer.

Further, Ag was formed into a film of 10 nm as a light extraction electrode by a vapor deposition method.

In the above configuration, the film thickness L1 from the reflective surface of the reflective electrode to the surface of the blue light emitting layer on the light extraction side is 57 nm, and if the refractive index of the organic material is 1.8, the optical distance is 102.6 nm. Become. Therefore, the emission peak wavelength of the blue emission dopant is within the range of 1/4 ± 1/8 times the emission peak wavelength of 440 nm, which is a condition for obtaining the interference effect of blue emission. Further, the film thickness from the reflective surface of the reflective electrode to the surface of the red / green light emitting layer on the light extraction side is 72 nm, and the optical distance is 130 nm. Therefore, since it is in the range of 1/4 ± 1/8 times the green emission wavelength (500 nm to 570 nm), it is a condition that the interference effect of green emission can be obtained. Further, since the optical distance of 130 nm is in the range of 1/4 ± 1/8 times the red emission wavelength (580 nm to 680 nm), it is a condition that the interference effect of red emission can be obtained.
Further, since the film thickness L2 from the surface of the blue light emitting layer on the light extraction side to the reflection surface of the light extraction electrode is 225 nm and L1 is 57 nm, L1 and L2 are preferable conditions of the present invention. × 2 <L2 is satisfied.
Further, when the refractive index of the organic material is 1.8, the optical distance corresponding to L2 is 405 nm, which is 3/4 times that of 540 nm, so that the interference effect of green light emission can be obtained.

Then, the substrate was conveyed in a vacuum to a plasma CVD apparatus (manufactured by ULVAC, Inc.), a film of SiN of 2 μm was formed to form a protective film, and an organic EL element emitting white light was obtained.

A voltage applying device (not shown) was connected to the obtained organic EL element, and its characteristics were evaluated by using the reflecting electrode 11 as a cathode and the light extraction electrode 17 as an anode. The current-voltage characteristics were measured with a micro ammeter "4140B" manufactured by Hured Packard, and the chromaticity was evaluated using "SR-3" manufactured by Topcon. The emission brightness was measured with "BM7" manufactured by Topcon Corporation.
As a result, the efficiency, voltage, and CIE chromaticity coordinates at 1000 cd / m ² display were 7.2 cd / A, 3.1 V, (0.36, 0.36), respectively, showing good characteristics.
Further, when a continuous drive test was performed at an initial luminance of 4000 cd / m ² , the luminance half time was 3000 h and the durability characteristics were also good.

(Example 2)
Example 1 except that Ag and cesium carbonate (3% by mass) were formed into a film of 200 nm as the reflective electrode 11 by a vapor deposition method, the electron injection layer 12 was not provided, and the film thickness of the electron transport layer 13 was changed to 42 nm. An organic EL element that emits white light was produced in the same manner as above.

When the obtained organic EL element was evaluated in the same manner as in Example 1, the same result as in Example 1 was obtained except that the voltage at 1000 cd / m ² display increased to 3.4 V.

(Comparative Example 1)
As the organic compound layer, the same as in Example 1 except that the hole injection layer, the hole transport layer, the green / red light emitting layer, the blue light emitting layer, the electron transport layer, and the electron injection layer were formed in this order from the substrate 10 side. An organic EL element that emits white light was produced. Regarding the film thickness, the hole injection layer was changed to 7 nm, the hole transport layer was changed to 35 nm, the electron transport layer was changed to 200 nm, and the electron injection layer was changed to 10 nm so that Example 1 and L1 and L2 had the same film thickness. ..

The characteristics of the obtained organic EL element were evaluated by the same method as in Example 1 except that the reflective electrode 11 was used as an anode and the light extraction electrode 17 was used as a cathode. As a result, the efficiency, voltage, and CIE chromaticity coordinates at 1000 cd / m ² display are 6.1 cd / A, 4.9 V, (0.35, 0.36), respectively, and the voltage is greatly increased. became.

In this example, the distance from the reflective surface of the reflective electrode to the surface of the blue light emitting layer on the light extraction side is 72 nm and the optical distance is 129.6 nm, which is 1/4 ± 1/8 of the emission peak wavelength of the blue light emitting dopant. It is within the double range, and the interference effect of blue light emission can be obtained. The distance from the reflective surface of the reflective electrode to the surface of the green / red light emitting layer on the light extraction side is 57 nm and the optical distance is 102.6 nm, which is 1/4 ± 1/8 times the red emission wavelength and the green emission wavelength. Within the range of, it is a condition that the interference effect of red light emission and green light emission can be obtained.

Further, when a continuous drive test was performed at an initial brightness of 4000 cd / m ² , the emission brightness decreased with a rapid voltage increase after 20 hours. It is considered that this is because, unlike the elements of Examples 1 and 2, the voltage rises due to the thick film thickness of the electron transport layer, which causes the temperature rise in the continuous drive test.

10: Substrate, 11: Reflective electrode, 14: Blue light emitting layer, 17: Light extraction electrode, 18: White light emitting layer, 19: Organic compound layer, 22R, 22G, 22B: Color filter

Claims (19)

It has a substrate, a reflective electrode, an organic compound layer, and a light extraction electrode in this order.
The organic compound layer is formed between a first light emitting layer, a second light emitting layer arranged between the first light emitting layer and the light extraction electrode, and between the second light emitting layer and the light extraction electrode. The first light emitting layer has an arranged hole transport layer, and the first light emitting layer is an electron trap type light emitting layer that emits blue light, and the second light emitting layer emits light having a longer wavelength than the first light emitting layer. An organic EL element that is a light emitting layer
The reflective electrode is a cathode, and the light extraction electrode is an anode.
The optical distance from the reflective surface of the reflective electrode to the surface of the first light emitting layer on the light extraction side is the distance that enhances the blue light emitted by the first light emitting layer .
The optical distance from the surface of the first light emitting layer on the light extraction side to the reflection surface of the light extraction electrode is in the range of 3λ _B / 4 ± λ _B / 8 when the wavelength of the blue emission is λ _B. An organic EL element characterized by being present. The first light emitting layer has a first organic compound and a second organic compound, and the LUMO energy level of the first organic compound is Lh, the energy level of HOMO is Hh, and the second The organic EL element according to claim 1, wherein when the LUMO energy level of the organic compound is Ld and the HOMO energy level is Hd, the following formula (a) is satisfied.
| Ld |> | Lh | and | Hd |> | Hh | ... (a) The light extraction electrode is a semi-transmissive metal thin film, the distance from the reflection surface of the reflection electrode to the light extraction side surface of the first light emitting layer is L1, and the light extraction side of the first light emission layer. When the distance from the surface to the reflection surface of the light extraction electrode is L2,
L1 × 2 <L2
The organic EL element according to claim 1 or 2, wherein the organic EL element satisfies the above conditions. The optical distance from the reflective surface of the reflective electrode to the surface of the first light emitting layer on the light extraction side is in the range of λ _B / 4 ± λ _B / 8 when the wavelength of the blue light emission is λ _B. The organic EL element according to any one of claims 1 to 3, wherein the organic EL element is characterized by the above. The organic EL element according to claim 4, wherein the distance from the reflective surface of the reflective electrode to the surface of the first light emitting layer on the light extraction side is 55 nm or more and 65 nm or less. Any of claims 1 to 5, wherein the optical distance from the reflective surface of the reflective electrode to the surface of the second light emitting layer on the light extraction side is a distance that enhances the light emitted by the second light emitting layer. The organic EL element according to item 1. The optical distance from the reflective surface of the reflective electrode to the surface of the second light emitting layer on the light extraction side is in the range of λ _O / 4 ± λ _O / 8, where the emission wavelength of the second light emitting layer is λ _O. The organic EL element according to claim 6, wherein the organic EL element is characterized in that. The organic according to any one of claims 1 to 7, wherein the distance from the surface of the first light emitting layer on the light extraction side to the reflection surface of the light extraction electrode is 180 nm or more and 240 nm or less. EL element. The organic EL device according to any one of claims 1 to 8, wherein the first light emitting layer and the second light emitting layer are in contact with each other. The organic EL element according to any one of claims 1 to 9, wherein the organic compound layer is in contact with the reflective electrode and has an electron injection layer containing cesium carbonate and an organic compound. The organic EL element according to claim 10, wherein the electron injection layer contains at least one of a cesium suboxide and a cesium-coordinated organic compound. The organic EL device according to claim 10 or 11, wherein the electron injection layer has a film thickness of 10 nm or less. The organic EL element according to any one of claims 1 to 12, wherein the reflective electrode contains cesium carbonate. The organic EL device according to claim 2, wherein the second organic compound contained in the first light emitting layer is a fluoranthene derivative. The first organic compound contained in the first light emitting layer is any one of a fluorene derivative, a naphthalene derivative, an anthracene derivative, a pyrene derivative, a carbazole derivative, a quinoxaline derivative, a quinoline derivative, an organic aluminum complex, an organic zinc complex, and a triphenylamine derivative. The organic EL element according to claim 2 or 14, wherein the organic EL element is characterized by the above. The organic EL element according to any one of claims 1 to 15, wherein the second light emitting layer emits green and red light. With multiple organic EL elements
A display device having a blue, green, and red color filters arranged on the light extraction side of the organic EL element and a switching element connected to the organic EL element.
The display device in which the organic EL element is the organic EL element according to any one of claims 1 to 16. The display device according to claim 17, wherein the organic EL element corresponding to the red color filter among the plurality of organic EL elements further has a transparent metal oxide layer between the reflective electrode and the organic compound layer. A lighting device comprising the organic EL element according to any one of claims 1 to 16 and a converter circuit connected to the organic EL element.

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