JP2007335185A - Organic el element array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element array which is easily manufactured with high brightness and high efficiency. <P>SOLUTION: A bandpass filter layer is formed on the upper side of the organic compound layer of each organic EL element. A micro resonator structure is formed between the bandpass filter layer and a reflection layer formed below the organic compound layer. The organic EL element array is constituted so that only an emitted light having a predetermined color is transmitted through the bandpass filter layer and resonance is not generated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic EL element array in which a plurality of organic EL elements (hereinafter may be abbreviated as elements) are arranged.

  In recent years, research and development of a flat display device that is lightweight and consumes little power has been performed as a display device that can replace a cathode ray tube. Among these, a display device including an organic EL element array has been attracting attention as a display device that is self-luminous, has a high response speed, and can be driven with low power consumption. The organic EL element constituting the organic EL element array has a structure in which an organic compound layer is sandwiched between opposing electrodes. When a voltage is applied between both electrodes of the organic EL element, electrons injected from one electrode and holes injected from the other electrode recombine in the light emitting layer of the organic compound layer, and the generated recombination energy The organic light emitting molecules in the light emitting layer are excited. When the organic light emitting molecule in the excited state returns to the ground state, the organic EL element emits light by taking out the emitted energy as light. Among them, a configuration in which an element stacked on a TFT substrate is caused to emit light, and the light is extracted with high efficiency from a direction opposite to the substrate side on which the TFT drive circuit and wiring are formed (so-called top side), That is, development of a top emission type display device is in progress.

  Attempts have also been made to use the light interference effect in organic EL elements. For example, in Patent Document 1, an organic compound layer is sandwiched between a first electrode made of a light reflecting material and a second electrode made of a transparent electrode, and at least one of the second electrode or the light emitting layer of the organic compound layer is Discloses an element having a resonator structure for resonating light emitted from the light emitting layer. This element is configured such that the optical distance L of the resonator structure has a positive minimum value within a range satisfying the following expression.

(2L) / λ + Φ / (2π) = m (m is an integer)
L: optical distance of the resonator structure Φ: phase shift generated when light generated in the light emitting layer is reflected at both ends of the resonator structure λ: peak wavelength of the spectrum of light to be extracted out of the light generated in the light emitting layer

  In addition, microcavities that function as microresonator structures are formed in each element, and attempts have been made to extract light of a specific wavelength. By using this microresonator structure, light of a specific wavelength is selectively enhanced. be able to. For example, Patent Document 2 discloses an organic EL element array in which a plurality of organic EL elements are arranged. This organic EL element array has elements of a plurality of colors that emit light of different colors. A microresonator that repeatedly reflects the emitted light emitted from the light emitting layer of the organic compound layer within a predetermined optical length range for the specific at least one color element, thereby enhancing the selected wavelength of the emitted light. A structure is provided. The other elements of at least one color are configured to emit light emitted from the light emitting layer as it is without providing a microresonator structure.

International Publication No. WO01 / 039554 JP 2005-108737 A

  In order to construct an organic EL element array with the organic EL elements of Patent Document 1, it is necessary to coat the reflective layer, the hole transport layer, the light emitting layer, the electron transport layer, and the semi-transmissive layer for each element. Therefore, there is a problem that the number of processes increases when performing mask deposition. In addition, if there is an emission color that cannot improve efficiency even if a resonator structure with an optimal optical distance is provided, and there is a layer that absorbs a specific wavelength between the reflective layer and the semi-transmissive layer, the resonator By providing the structure, there is a problem that the efficiency is reduced.

  An object of the present invention is to provide an organic EL element array that has high brightness, high efficiency, and is easy to manufacture.

  As means for solving the problems of the background art described above, the organic EL element array according to the invention described in claim 1 is an organic EL element in which an organic compound layer is sandwiched between a first electrode and a second electrode. In the organic EL element array in which a plurality of are arranged, a band-pass filter layer is formed above the organic compound layer of each organic EL element. A microresonator structure is formed between the bandpass filter layer and a reflective layer formed below the organic compound layer, and only the emitted light of a predetermined color passes through the bandpass filter layer and resonates. It does not wake up.

  According to the present invention, an organic EL element that emits light of a predetermined color has a resonator structure in a form in which an organic compound layer is sandwiched between a lower reflective electrode and a bandpass filter layer. The band-pass filter layer has a property of transmitting only emitted light having a predetermined wavelength, and the emitted light transmitted through the band-pass filter is extracted outside the element without causing resonance in the resonator structure. Therefore, the emitted light transmitted through the bandpass filter layer can be extracted outside without being affected by absorption by the organic compound layer and loss due to reflection in the resonance region.

  By using the present invention, it is possible to separate the emission color that uses the interference effect by the resonator structure from the emission color that is not used. Further, since the band-pass filter layer does not need to be applied separately for each element, an organic EL element array having an optimum interference effect can be easily produced.

  In addition, compared with the case where each element is separately applied, the emission light of the element having no resonator structure need only be considered for strengthening the interference with the lower reflective layer, so that the process for element creation is greatly reduced. It is possible.

  Incidentally, when a resonator structure is also formed in an organic EL element that emits light other than the predetermined color, the resonator structure is formed above the organic compound layer. Therefore, the emitted light can be efficiently extracted without being absorbed in the organic compound layer or lost in the reflective layer.

<First Embodiment>
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic view of a top emission type organic EL element array having a microresonator structure in an element that emits red and green light. In the organic EL element array of this embodiment, a reflective anode electrode (first electrode) 11 and a hole transport layer 12 are formed on a substrate (not shown). Further, a blue light emitting layer 13B, a green light emitting layer 13G, a red light emitting layer 13R, an electron transport layer 14, an electron injection layer 15, a band pass filter layer 17, and a transparent cathode electrode (second electrode) 18 are formed. In an element that emits red and green light, a resonator structure using a multiple interference phenomenon is formed between the reflective anode electrode 11 and the band-pass filter layer 17 sandwiching the organic compound layer 16 and is enhanced by the resonator structure. Light is emitted from the transparent cathode electrode 18 side. Since the band-pass filter layer 17 has a characteristic of transmitting only blue emitted light, the blue emitted light is emitted as it is from the transparent cathode electrode 18 side without causing resonance.

  The organic EL element array shown in FIG. 1 has a very basic element configuration, and the configurations of the reflective anode electrode 11, the organic compound layer 16, the bandpass filter layer 17, and the transparent cathode electrode 18 are limited to this. is not. In order to improve hole injection between the reflective anode electrode 11 and the hole transport layer 12 in addition to the four layers of the hole transport layer 12, the light emitting layer 13, the electron transport layer 14, and the electron injection layer 15 as the organic compound layer 16. A structure in which a hole injection layer is provided on the surface is also possible. A configuration (bottom emission) in which the reflective anode electrode 11, the organic compound layer 16, the band pass filter layer 17, and the transparent cathode electrode 18 are stacked upside down and the light extraction direction is changed to the substrate side is also possible.

  The reflective anode electrode 11 is made of a material having a high work function, specifically, a transparent conductive metal oxide layer such as ITO or IZO in order to efficiently inject holes. A metal layer having a high reflectance, for example, chromium, silver, platinum, aluminum, or an alloy containing these is preferably formed thereunder. When the metal layer is formed, the interface between the metal layer and the conductive metal oxide layer corresponds to the lower reflective layer of the resonator structure. Incidentally, the reflectance of the reflective anode electrode 11 is preferably higher and is preferably 80% or more.

  The hole transport layer 12 is a layer that serves as a path when holes injected from the reflective anode 11 move to the light emitting layer 13. As the material of the hole transport layer 12, N, N′-di (naphthalen-1-yl) -N, N′-diphenyl-benzidine (N, N′-Di (naphthalene-1-yl) -N, N '-Diphenyl-benzidine (NPB), 4,4', 4 "-tris (3-methylphenylphenylamino) triphenylamine (4,4 ', 4' '-tris (3-methylphenylphenylamino) triphenylamine: MTDATA) , N, N′-diphenyl-N, N′-di (3-methylphenyl) -1,1′-bifinyl-4,4′-diamine (N, N′-diphenyl-N, N′-di (3 -Methylphenyl) -1,1'-biphenyl-4,4'-diamin: TPD) It is below.

  The light-emitting layer 13 (R, G, B) is a layer that recombines incoming electrons and holes to generate red, green, and blue light corresponding to the three primary colors of light. When electrons injected from the electron transport layer 14 and holes injected from the hole transport layer 12 recombine, the energy generated at that time excites the electrons of organic molecules present inside. When the excited electrons relax, light having a wavelength according to energy is emitted, and light emission can be obtained.

As a material of the light emitting layer 13 (R, G, B), an aluminum quinoline complex (Alq3) or a bis (benzoquinolite) beryllium complex (bis (10-hydroxybenzo [h] quinolinato) beryllium: Bebq ₂ ) containing a quinacridone derivative. ) And the like.

The electron transport layer 14 is a layer serving as a path when electrons injected from the transparent cathode electrode 18 move to the light emitting layer 13. Examples of the material for the electron transport layer 14 include an aluminum quinoline complex (Alq ₃ ), a bis (benzoquinolinolato) beryllium complex (bis (10-hydroxybenzo [h] quinolinato) beryllium: Bebq ₂ ), and the like.

  As the band-pass filter layer 17, a periodic grating having a sub-wavelength structure as shown in FIG. 2A can be used. Here, as an example, a large number of pyramidal pyramids are formed on the surface. A periodic grating having a subwavelength structure does not generate a diffracted wave, but the structure is equivalent to a medium having an average refractive index with respect to a light wave. That is, most of the occupation ratios of the medium 31 and the medium 32 are occupied by the medium 32 in the tip layer of the cone and the medium 31 in the root layer of the cone. As shown in FIG. 2B, the average refractive index gradually changes from the medium 32 to the value of the medium 31 in the depth direction. Since the reflection of light is caused by a rapid change in the refractive index, the light is hardly reflected with respect to the continuous refractive index change. For example, the IEICE Transactions 2000/3 Vol. J83-C No. 3 P.M. 173-181 describes a calculation example of the reflection characteristics of a pyramidal fine periodic grating. In the case of a fine structure in which the height of the quadrangular pyramid is 1.5 times the grating period, the reflectance is 0.1% or less when the wavelength is between 1.5 and 3 times the grating period. If the grating period 33 is a fine structure of 150 nm, it is possible to obtain a bandpass filter layer that does not reflect only blue visible light (wavelength: 450 nm). If a fine structure having a grating period 33 of 180 nm is used, it is possible to obtain a band-pass filter layer that does not reflect blue and green visible light (wavelength: 450 nm, wavelength: 530 nm). As a material of the bandpass filter layer 17, an alumina compound may be used.

  The transparent cathode electrode 18 is preferably a transparent conductive metal oxide such as ITO or IZO.

  Next, functions of the present embodiment will be described.

  It is set so as to function as a microresonator structure that repeatedly reflects on the upper surface of the reflective anode electrode 11 and the lower surface of the bandpass filter layer 17. Here, as for the optical distance between the reflective anode electrode 11 and the band pass filter layer 17, it is desirable that the optical path length + phase shift is an integral multiple of the specific wavelength. In the microresonator structure having the resonance region with the above optical distance, the emission light of a specific wavelength is repeatedly reflected, thereby increasing the probability that the emission light of a specific frequency is emitted and improving the efficiency.

  However, even if a microresonator structure having a resonance region with an optimal optical distance is formed, the efficiency is not always improved, and the efficiency deteriorates by providing a resonator structure for emitted light of a specific wavelength. Can also happen. For example, blue and green emitted light has a large absorption in the organic compound layer in the resonance region and a large loss in the reflection layer, so that it is difficult to obtain a sufficient efficiency improvement.

  FIG. 3 shows the wavelength dependency data of the transmittance and reflectance of the reflective electrode according to this embodiment. It can be seen that with this reflective electrode, the reflectance decreases as the wavelength decreases from around 500 nm, and a sufficient reflectance cannot be obtained in the blue wavelength region of 400 nm to 500 nm compared to red and green. Therefore, there is a possibility that the loss of blue light emission increases due to repeated reflection by the resonator structure and the efficiency is lowered.

  FIG. 4 shows wavelength dependency data of the transmittance and reflectance of the organic compound layer according to this embodiment. In this organic compound layer, it can be seen that the transmittance decreases as the wavelength is shortened from around 550 nm, and the transmittance decreases to about 60% in the blue wavelength region of 400 nm to 500 nm. For this reason, blue light emission may be absorbed repeatedly in the organic compound layer due to repeated reflection by the resonator structure, and the efficiency may be lowered.

  Therefore, in the present embodiment, a top emission type organic EL element array in which only the blue emission light (wavelength: 450 nm) is not reflected by the bandpass filter layer 17 is used. The band-pass filter layer 17 functions as a reflective layer for red and green light emission, and thus forms a resonator structure that enhances light by repeated reflection. On the other hand, since the blue emitted light is transmitted through the bandpass filter layer 17, the light emitted from the light emitting layer 13B can be taken out to the outside as it is. Since the blue emission light does not cause a resonance phenomenon, it is possible to avoid the light absorption in the organic compound layer 16 and the loss in the reflection layer, and to efficiently extract the emission light to the outside.

  The emitted light that passes through the bandpass filter layer 17 is not limited to blue, and emitted light of two or more colors may be transmitted. For example, if the bandpass filter layer having the fine concavo-convex structure shown in FIG. 2 is provided, if the grating period 33 is 150 nm, it is possible to obtain a bandpass filter layer that does not reflect only blue visible light (wavelength: 450 nm). . If a fine structure having a grating period 33 of 180 nm is used, it is possible to obtain a band-pass filter layer that does not reflect blue and green visible light (wavelength: 450 nm, wavelength: 530 nm). By adjusting the grating period 33, the ratio of transmission and reflection in the band-pass filter layer can be controlled, and an organic EL element array having excellent chromaticity and viewing angle can be obtained.

  The element that emits blue light does not need to consider the optical distance of the resonator structure, and only considers the relationship of strengthening with the light reflected by the reflective anode electrode 11. Since the film thickness of the layer above the light emitting region hardly affects the extraction of blue light, the organic compound layer 16 can be set to a film thickness optimal for the red or green resonator structure. It is not necessary to set the film thickness of 16.

  In the element that emits red and green light, the thickness of the organic compound layer 16 must be set so that the emitted light is reflected by the reflective anode electrode 11 and the bandpass filter layer 17 and functions as a microresonator structure. Don't be. The optimum resonance distance differs depending on the emission color, and the film thicknesses of the red and green organic compound layers 16 are configured so that the optical distance L of the resonator structure becomes a positive minimum value in a range satisfying the following expression. It is desirable.

(2L) / λ + Φ / (2π) = m (m is an integer)
L: optical distance of the resonator structure Φ: phase shift generated when light generated in the light emitting layer is reflected at both ends of the resonator structure λ: peak wavelength of the spectrum of light to be extracted out of the light generated in the light emitting layer

Second Embodiment
FIG. 5 shows a schematic diagram of a top emission type organic EL element array in which each element has a microresonator structure. The organic EL element array of this embodiment includes a reflective anode 11, a hole transport layer 12, a blue light emitting layer 13B, a green light emitting layer 13G, a red light emitting layer 13R, an electron transport layer 14, an electron injection layer 15, and a bandpass filter layer 17. And a transparent cathode electrode 18 and a semi-transmissive layer 19. A resonator structure using a multiple interference phenomenon is formed between the reflective anode electrode 11 and the bandpass filter layer 17, and light enhanced by the resonator structure is emitted from the transparent cathode electrode 18 side. If the periodic grating having the sub-wavelength structure described in [0022] is provided only on the electron injection layer 15 side as the band-pass filter layer 17, since it has a characteristic of transmitting only the blue emitted light, the blue emitted light is reflected. Instead, it enters the transparent cathode electrode 18 as it is. The blue emission light reflected by the transparent cathode electrode 18 is repeatedly reflected between the surface of the band-pass filter layer 17 where the periodic grating having the sub-wavelength structure is not formed and the semi-transmissive layer 19, and the light emission emission surface of the device Injected to the side.

  That is, red and green emitted light causes a resonance phenomenon between the reflective anode electrode 11 and the bandpass filter layer 17 with the organic compound layer 16 interposed therebetween, and is enhanced and emitted to the semi-transmissive layer 19 side. The blue emitted light that has passed through the bandpass filter layer 17 causes a resonance phenomenon between the semi-transmissive layer 19 and the band-pass filter layer 17, and the light is enhanced and emitted to the semi-transmissive layer 19 side. By forming a resonator structure for only blue light emission above the organic compound layer 16, light absorption by the organic compound layer 16 can be avoided and high luminance can be obtained.

  This embodiment shown in FIG. 5 is a very basic element configuration, and the configurations of the reflective anode electrode 11, the organic compound layer 16, the bandpass filter layer 17, the transparent cathode electrode 18, and the semi-transmissive layer 19 are the same. It is not limited. In order to improve hole injection between the reflective anode electrode 11 and the hole transport layer 12 in addition to the four layers of the hole transport layer 12, the light emitting layer 13, the electron transport layer 14, and the electron injection layer 15 as the organic compound layer 16. A structure in which a hole injection layer is provided on the surface is also possible. In addition, a configuration in which the reflective anode electrode 11 is changed to a transparent anode electrode and a bandpass filter layer, the bandpass filter layer and the transparent cathode electrode are changed to a reflective cathode electrode, and the light extraction direction is changed to the substrate side (bottom emission) is also possible. .

  This embodiment is effective when the organic compound layer 16 absorbs light of a specific wavelength and sufficient efficiency cannot be improved by the resonator structure. By forming the blue resonator structure above the organic compound layer 16, it is possible to enhance light by the resonator structure while avoiding light absorption by the organic compound layer 16.

  In the element that emits blue light, the resonator structure is not formed so as to sandwich the organic compound layer 16. Therefore, when the film thickness of the organic compound layer 16 is set, it is stronger than the light reflected by the reflective anode electrode 11. You only need to consider the relationship. Therefore, the organic compound layer 16 can be set to an optimum film thickness for the red or green resonator structure, and the film thickness of the organic compound layer 16 does not have to be set for each element.

  In the element that emits red and green light, the thickness of the organic compound layer 16 must be set so that the emitted light is reflected by the reflective anode electrode 11 and the bandpass filter layer 17 and functions as a microresonator structure. . In the element that emits blue light, the thickness of the transparent cathode layer 18 must be set so that the emitted light is reflected by the bandpass filter layer 17 and the semi-transmissive layer 19 and functions as a microresonator structure. It is desirable that the optimum resonance distance differs depending on the emission color, and that the film thickness of the resonance region is within a range satisfying the following expression, so that the optical distance L of the resonator structure is a positive minimum value.

(2L) / λ + Φ / (2π) = m (m is an integer)
L: optical distance of the resonator structure Φ: phase shift generated when light generated in the light emitting layer is reflected at both ends of the resonator structure λ: peak wavelength of the spectrum of light to be extracted out of the light generated in the light emitting layer

It is sectional drawing of the organic EL element array provided with the band pass filter layer. It is sectional drawing for demonstrating the band pass filter layer with a fine unevenness | corrugation. It is the data of the wavelength dependence of the transmittance | permeability of a reflective electrode and a reflectance concerning this embodiment. It is the data of the wavelength dependence of the transmittance | permeability and reflectance of an organic compound layer concerning this embodiment. It is sectional drawing of the organic EL element array which provided the resonator structure above the organic compound layer in blue light emission.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Reflective anode electrode 12 Hole transport layer 13R Red light emitting layer 13G Green light emitting layer 13B Blue light emitting layer 14 Electron transport layer 15 Electron injection layer 16 Organic compound layer 17 Band pass filter layer 18 Transparent cathode electrode 19 Transflective layer 31 Band pass filter layer Side medium 32 Medium 33 with different refractive index 33 Fine structure grating period

Claims (8)

In an organic EL element array in which a plurality of organic EL elements having an organic compound layer sandwiched between a first electrode and a second electrode are arranged,
A bandpass filter layer is formed above the organic compound layer of each organic EL element, and a microresonator structure is formed between the bandpass filter layer and a reflective layer formed below the organic compound layer. An organic EL element array, wherein only emitted light of a predetermined color passes through a band-pass filter and is emitted without causing resonance.   2. The organic EL element array according to claim 1, wherein the emitted light of a predetermined color to be resonated is emitted light having a large loss due to light absorption in the organic compound layer and reflection between the layers.   It has an organic EL element that emits red light, an organic EL element that emits green light, and an organic EL element that emits blue light, and emits red or green light. The organic EL element array according to claim 1, wherein a resonator structure is formed in the organic EL element shown.   2. The organic EL element array according to claim 1, wherein fine irregularities are formed on the band-pass filter layer.   The organic EL element array according to claim 4, wherein the unevenness of the band pass filter layer has a pitch of 0.166 μm or less.   6. The organic EL element array according to claim 4, wherein the unevenness of the bandpass filter layer contains alumina.   A resonator structure is formed above the bandpass filter layer, and the emitted light is resonated between the bandpass filter layer and a reflective layer formed above the bandpass filter layer. The organic EL element array according to claim 1 or 3.   It has an organic EL element that emits red light, an organic EL element that emits green light, and an organic EL element that emits blue light, and emits blue or green light. The organic EL device according to claim 7, wherein a resonator structure is formed between the bandpass filter layer and a reflection layer formed above the bandpass filter layer in the organic EL element shown. Element array.

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