KR101841274B1 - Organic electroluminescence element - Google Patents

Abstract

(Problem) A high luminous efficiency is obtained in an organic EL element emitting phosphorescence.
A light emitting layer 14 containing a light emitting material emitting phosphorescence and a first adjacent layer 13 and a second adjacent layer 13 disposed adjacent to the light emitting layer 14 with the light emitting layer 14 interposed therebetween, Wherein a first excitation triplet energy level of the luminescent material is higher than a first excitation energy level of the first luminescent material in the organic electroluminescence device, Emitting layer 14 is higher than the lowest energy level among the first excitation triplet energy levels of the plurality of materials constituting the adjacent layer and the second adjacent layer, And a metal member (20) for generating a resonance on the surface.

Description

[0001] ORGANIC ELECTROLUMINESCENCE ELEMENT [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence element (electroluminescence element) that generates light emission by application of an electric field, and more particularly to an organic electroluminescence element having a light emission layer that emits phosphorescence.

An organic electroluminescent (EL) device is a device in which a plurality of layers such as an electron transporting layer, a light emitting layer, and a hole transporting layer are laminated between a cathode and an anode, electrons and holes are injected from each electrode by applying a voltage between the electrodes, These are combined in the light emitting layer to emit light.

In the organic EL device, the light-emitting material of the light-emitting layer is excited by the recombination of holes and electrons to generate excitons. The exciton formation efficiency of the first excitation energy level (hereinafter referred to as "S1 level") is theoretically 25%, and the excitation generation efficiency of the first excitation energy level (hereinafter referred to as "T1 level") Is 75%. The light emission produced when returning from the S1 level to the base state is fluorescence, and the light emission when returning from the T1 level to the base state is phosphorescence. The T1 level can increase T1 production efficiency from 75% of the theoretical limit to 100% in principle by promoting intersection crossing at a point lower than the S1 level.

In other words, it is theoretically possible to dramatically increase the luminous efficiency by using phosphorescence over fluorescence. However, although the fluorescent EL device has been put to practical use in the present situation, the practical use of the phosphorescent EL device has not been progressed.

In the organic EL device, the external quantum yield is represented by the product of the quantum yield of PL, the hole electron balance factor, and the drawing efficiency. Therefore, in order to increase the external quantum yield, it is required to design the element configuration so as to increase the quantum efficiency of PL, the electron balance factor, and the drawing efficiency.

The organic EL element has a structure in which an electrode layer, a light emitting layer, and the like are laminated on a substrate, and light emitted from the light emitting layer is generally taken out through the transparent electrode. At this time, due to the influence of the refractive index of each layer, light incident at a critical angle or more in the layer interface at the light extraction side is totally reflected, is confined in the device, and can not be drawn out. For this reason, it is difficult to draw out emitted light with high efficiency, and in the case of a refractive index of a transparent electrode which is currently favorably used, such as ITO, the upper limit of the drawing efficiency is about 20%.

Regardless of the fluorescent EL and the phosphorescent EL, a material having a PL quantum yield of 1 (PL luminous efficiency 100%) is generally used as a practical EL element as a light emitting material.

On the other hand, in order to achieve high efficiency of EL emission, it is required that the excitation energy in the light-emitting layer does not scatter (energy does not move) to the layer adjacent to the light-emitting layer. This is because the luminous efficiency is lowered due to the scattering of the energy from the light emitting layer to the adjacent layer.

Therefore, in order to obtain high-efficiency light emission in the fluorescent EL device, it is a condition to select the materials constituting the light-emitting layer and the adjacent layer so that the S1 level of the light-emitting material becomes smaller than the lowest S1 level of the adjacent layer.

Similarly, in order to obtain high-efficiency light emission in the phosphorescent EL device, it is a condition that the material constituting the light emitting layer and the adjacent layer is selected so that the T1 level of the light emitting material becomes smaller than the lowest T1 level of the adjacent layer.

It is possible to relatively easily satisfy the condition that the excitation level of the luminescent material is lower than the excitation level of the adjacent layer in the currently practically used fluorescent EL device, A material having an S1 level higher than the S1 level of the light emitting material is used.

In addition, in the fluorescent EL device, a plasmon enhancement method for enhancing luminescence by disposing a metal in the vicinity of the fluorescent luminescent layer (for example, several tens of nanometers) in order to increase the luminous efficiency has been proposed in Non-Patent Documents 1 and 2 . This enhancement of the luminescence is caused by the fact that dipole radiation from the light emitting element causes plasmons (or localized plasmons) to be generated on the surface of the metal, and after the energy is absorbed, new light emission is re-emitted. However, as described above, in a practical fluorescent EL device of the present situation, it is general to use a fluorescent light emitting material whose PL quantum yield is close to 1, and from the point of satisfying the condition for increasing the hole electron balance factor, The effect of increasing the luminous efficiency is hardly obtained.

On the other hand, in phosphorescent EL devices, particularly blue and green phosphorescent EL devices, the T1 level of the materials for the hole transporting layer and the electron transporting layer, which are highly practical from the viewpoint of driving voltage and durability, is low (longer wavelength than green for light wavelength conversion) , It is difficult to satisfy the condition that the T1 level of the phosphorescent material is lower than the T1 level of the adjacent layer.

 Journal of Modern Optics (USA) vol. 45, pp. 616-699, 1998  Proc. SPIE (USA) Vol. 7032, 703224 (2008)

As described above, in the phosphorescent EL device, it is difficult to satisfy the condition that the T1 level of the phosphorescent material is lower than the T1 level of the adjacent layer, and therefore, high luminous efficiency can not be obtained. As well.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an organic EL element which generates phosphorescence capable of realizing high luminous efficiency.

The organic electroluminescence device of the present invention includes a light emitting layer containing a phosphorescent material and a plurality of layers including a first adjacent layer and a second adjacent layer disposed adjacent to the light emitting layer, An organic electroluminescence device in which a first excitation triplet energy level of the light emitting material is higher than a first excitation triplet energy level of a plurality of materials constituting the first adjacent layer and the second adjacent layer And a metal member for generating a plasmon resonance on the surface by the light emitted from the light emitting layer in the vicinity of the light emitting layer.

The distance between the metal member and the light emitting region is preferably 30 nm or less.

Preferably, the metal member is a metal film disposed between the plurality of layers. The metal film may be a solid film or may be a granular film (a film having a concavo-convex structure smaller than the wavelength of emitted light), but particularly an island structure film in which metal fine particles having a particle diameter of 5 nm or more are dispersed randomly, Do. Here, the particle diameter refers to the maximum length of the fine particles. That is, when the fine particles are spherical, it refers to the long diameter when the fine particles are in the shape of an elongated (rod-like) shape having an aspect ratio of the diameter, the major axis of the fine particles and the minor axis perpendicular thereto.

The material of the metal film may be a material that generates plasmon resonance by the emitted light and may be a metal such as Ag (silver), Au (gold), Cu (copper), Al (aluminum), Pt (platinum) Quot; main component " is defined as a component having a content of 80 mass% or more.

Among these materials, Ag or Au is particularly preferable.

It is preferable that at least one surface of the metal film is subjected to surface modification with a terminal end having a polarity such that the work function of the metal film approaches the work function of the layer adjacent to the metal film. When the work function of the metal film is smaller than the work function of adjacent layers on both sides of the metal film (on the cathode side), the terminal group is an electron donating group and is larger than the work function of adjacent layers on both sides of the metal film (On the anode side), the terminal group becomes an electron-withdrawing group.

Examples of the terminal group having a polarity include an electron donor having an electron donor or an electron attracting group having an electron attracting property. Examples of the electron donating group include an alkyl group such as a methyl group, an amino group and a hydroxyl group. , A carboxyl group, and a sulfo group.

The metal member may be a core-shell-type fine particle comprising at least one metal fine particle core and an insulator shell covering the metal fine particle core, and the core-shell fine particles are preferably dispersed in many layers in the vicinity of the light emitting region. Here, the core-shell-type fine particles may be present in the luminescent region. The particle size of the core fine particle metal fine particle core is preferably 10 nm or more and 1 占 퐉 or less, and the thickness of the insulator shell is preferably about 30 nm or less. Here, the " particle diameter " means the maximum diameter of the fine particles.

When the core-shell-type fine particles or the metal fine particles are fine particles having an elongated shape (rod-like shape) in which the aspect ratio of the major axis of the fine particles and the minor axis perpendicular thereto is larger than 1, It is preferable that the particle diameter of the fine particles is arranged to be oriented in a direction substantially perpendicular to the electrode surface.

A plurality of metal fine particle cores may be provided in the insulator shell.

It is preferable that the metal fine particle core is made of any one of Au, Ag, Al, Cu, and Pt, or an alloy containing them as a main component.

Insulators such as SiO ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , PbO, B ₂ O ₃ , CaO, and BaO can be preferably used as the material of the insulator shell.

The organic EL device of the present invention is characterized in that the plurality of layers have a layer thickness and a refractive index satisfying a resonance condition in which a region where the electric field strength of a standing wave due to light emitted from the light- .

(Effects of the Invention)

In the organic EL device emitting the phosphorescent light of the present invention, the first excitation triplet energy level of the light-emitting material is lower than the first excitation triplet energy level of the plural materials constituting the first adjacent layer and the second adjacent layer adjacent to the light- It is preferable that the dipole radiation from the light emitting layer is formed on the surface of the metal by a plasmon (or a metal ion) that has a higher energy level than the lowest energy level, but has a metal member that generates plasmon resonance on the surface by the light emitted from the light- It is possible to improve the luminous efficiency as a new luminous flux for re-emission is applied after absorbing the energy. That is, the luminescent device has a mode in which a luminescence transition by a new plasmon is added to the luminescent process of the luminescent device, and the effect of shortening the lifetime of the exciton can be exhibited, and the excitation energy in the luminescent layer It can be drawn out as light emission, and the luminous efficiency can be improved.

Therefore, the first excitation triplet energy level of the light-emitting material, such as green and blue phosphorescence, is set to the lowest energy level among the first excitation triplet energy levels of the plural materials constituting the first adjacent layer and the second adjacent layer adjacent to the light- It is possible to emit green and blue phosphorescence in practical use by enabling the device to emit light with higher efficiency than in the prior art.

In addition, since the acid of the excitation energy to the adjacent layer is suppressed, heat generation can be suppressed at the same time, and the durability of the device can be improved.

1 is a schematic diagram showing a structure of an organic EL device according to a first embodiment of the present invention.
2 is a schematic diagram showing a structure of an organic EL device according to a second embodiment of the present invention.
Fig. 3 is a view for explaining a work function adjusting film of the organic EL device of Fig. 2; Fig.
4 is a schematic diagram showing a structure of an organic EL device according to a third embodiment of the present invention.
5 is a schematic diagram showing a structure of an organic EL device according to a fourth embodiment of the present invention.

Embodiments of the present invention will be described with reference to the drawings.

≪ First Embodiment >

1 is a diagram schematically showing the structure of an organic electroluminescence device (EL element) 1 according to a first embodiment of the present invention.

The organic EL device 1 of the present embodiment basically includes an anode 11, a hole injecting layer 12, a hole transporting layer 13, a light emitting layer 14, an electron transporting layer 15, an electron injecting layer 16, (17). ≪ / RTI > The light emitting layer 14 contains a light emitting material that emits phosphorescence and emits phosphorescence by recombination of holes and electrons injected from the anode 11 and the cathode 17 in the light emitting layer 14.

The light emitting material contained in the light emitting layer 14 may be any material that emits phosphorescence, but it is particularly preferable to use a material having a PL quantum yield of about 1 at room temperature. Here, it is assumed that the PL quantum yield is 1 to 0.8, which is close to 1. Specifically, a metal complex having Ir or Pt can be preferably used, and examples thereof include the following compounds.

The first excitation triplet energy level (T1 level) of the luminescent material of the luminescent layer 14 in the device 1 constitutes the hole transport layer 13 and the electron transport layer 15 adjacent to the luminescent layer 14 Is higher than the lowest T1 level among the T1 levels of the material. Generally, each of the hole transporting layer and the electron transporting layer is composed of one or more materials, and each material has a unique T1 level. If there is only one material having a Tl level lower than the T1 level of the light emitting material in the adjacent layer, it can be said that the material is likely to be scattered to the adjacent layer of the excitation energy of the light emitting layer. The T1 level of the light-emitting layer may be larger than the T1 level of all the materials constituting the adjacent layers 13 and 15.

NPD, 2TNATA or the like can be used as the material of the practical hole transporting layer 13 that satisfies the above conditions, and BAlq, Alq3 or the like can be used as the material of the practical electron transporting layer 15 (see the chemical formula in the later embodiment .).

The " practical material " referred to herein is a material that does not significantly degrade in all aspects of the device driving voltage, luminous efficiency, and driving durability when applied to an EL device, It is a material that has been found in knowledge.

In the device 1, a metal film 20 as a metal member for generating plasmon resonance by the luminescent light is disposed in the vicinity of the luminescent region (luminescent layer 14). In order that the metal film 20 does not become a reflective material, it is preferable that the thickness is thin. When the metal film 20 is brought into contact with the light emitting layer 14 or at a distance d of less than 5 nm, charge transfer occurs directly from the light emitting layer 14 and light emission is attenuated, Is preferably separated by 5 nm or more. On the other hand, when the distance from the light emitting layer 14 is too far, the plasmon resonance due to the emitted light is not generated and the luminescent enhancing effect can not be obtained. Therefore, the distance d from the light emitting layer 14 is 30 nm or less desirable.

The metal film 20 may be a flat film or a film having a concavo-convex structure smaller than the wavelength of the emitted light, that is, a granular film having a surface in the form of a granule, or metal fine particles having a grain size of 5 nm or more, (Island) structure film in which a gap exists between the fine particles formed by dispersing the fine particles in an aqueous medium. In the case where the metal film is a flat film, the surface plasmon is induced on the surface of the metal film by the emitted light, but the recombination into the radiation mode hardly occurs and the ratio of disappearing as heat finally becomes large. On the other hand, when the metal film is an island structure film, the surface plasmon induced on the film surface by the luminescent light is recombined again in the radiation mode, and the efficiency of emitting the radiation is high.

The material of the metal film is not limited as long as plasmon resonance is generated by the emitted light and any one of Ag (silver), Au (gold), Cu (copper), Al In particular, silver is preferred as the emission wavelength is a visible wavelength, since silver from the plasma frequency can cause surface plasmon resonance in the visible range. For example, if it is infrared, gold is preferable.

Further, the above-described EL element is configured such that light is sequentially drawn out from the anode side on the substrate, for example, in order from the cathode side. Each layer other than the metal film can be formed by the lamination method used in the production of the conventional organic EL device. The metal film can be formed using, for example, a sputtering method, a vacuum deposition method, or the like.

The device 1 is configured such that the T1 level of the light emitting material of the light emitting layer 14 is smaller than the T1 of the material having the lowest T1 level among the materials constituting the hole transporting layer 13 and the electron transporting layer 15 adjacent to the light emitting layer 14, Therefore, when the excitation energy in the light emitting layer 14 is shifted from the T1 level of the light emitting material to the adjacent layer (the hole transporting layer 13 and / or the electron transporting layer 15) containing a material having a T1 level lower than the T1 level It is an easy layer composition. However, since the element 1 is provided with a metal film for generating plasmon resonance, the lifetime of the exciton can be shortened to promote the luminescence as phosphorescence, and the excitation energy can be suppressed from being scattered on the adjacent layer. That is, by providing the metal film 20, the emission of excitation energy can be suppressed and the luminous efficiency can be improved. At the same time, an effect of improving durability by shortening the excursion lifetime can also be expected.

≪ Second Embodiment >

The structure of the organic EL device 2 of the second embodiment is schematically shown in Fig. In addition, Fig. 2 also shows the potential energy of each layer. In the following embodiments, layers equivalent to those of the organic EL device 1 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

The organic EL device 2 of the present embodiment is different from the first embodiment in that the electron injection layer 16 is not provided and that the work function adjusting layer 25 is formed on one surface of the metal film 20 Of the organic EL device 1 shown in Fig. The work function adjustment layer 25 is a surface modification layer having a polar end terminal for bringing the work function of the metal film 20 close to the work function of a layer adjacent to the metal film 20 (here, the electron transport layer 15) Layer.

In Fig. 2, a black circle (●) represents an electron (e), and a white circle (○) represents a hole (h). 2, each layer is generally arranged such that its work function continuously changes from the anode 11 side and the cathode 17 side toward the light emitting layer 14, but the metal contained in the electron transport layer 15 The film 20 has a larger work function (lower potential energy) than the electron transport layer 15 and becomes an electron trap at the time of application of an electric field, so that the flow of electrons is inhibited and recombination in the light emitting layer 14 is impossible There is a possibility that light emission is not likely to occur.

Here, the work function adjusting layer 25 has a function of suppressing the electron trap of the metal film 20. [ The effective work function of the metal film 20 is made small (the position energy is made high) by the work function adjusting layer 25, that is, the original energy level E ₀ of the metal film 20 is set to Is effectively changed to the energy level (E ₁ ) so that the electrons e are moved to the light emitting layer side without being trapped in the metal film 20.

Fig. 3 shows an example of the work function adjustment layer 25. Fig. Here, it is assumed that the metal film 20 is made of Au. 3, the work function adjusting layer 25 is a SAM film (self-assembled monolayer film) formed by bonding a thiol or a disulfide with a terminal end having polarity to an Au film surface by Au reaction. 3 shows an example of a SAM film of benzenethiol (thiophenol) having a methyl group at the para position of a thiol group.

An alkyl group such as a methyl group is an electron donating group. When such an end group is present, the position energy of Au is increased by the electron donor, and the work function can be made small. Examples of the electron donating group include an alkyl group such as a methyl group, an amino group, and a hydroxyl group.

After the Au film is formed, the work function adjusting layer 25 can be formed by a general SAM fabrication method. In particular, a liquid phase method such as a coating method, a vapor deposition method, and a sputtering method can be used. The work function adjusting layer may be provided on both sides of the metal film 20 as well as on one side.

Here, an example in which the metal film 20 is provided in the electron transport layer 15 is described, but the metal film 20 may be provided in the hole transport layer 13 on the anode side. In this case, since the work function of the metal film 20 is smaller than the work function of the hole transport layer 13 (the position energy is high), the work function adjustment layer for lowering the position energy so as to be close to the work function of the hole transport layer 13 May be provided on at least one side of the metal film. In this case, the work function adjustment layer can effectively reduce the potential energy by providing the electron attracting device instead of the electron hole excitation shown in Fig. 3 as the terminal end thereof, and the work function of the metal film 20 can be lowered to the hole transporting layer 13, It is possible to approximate to. Examples of the electron withdrawing group include a nitro group, a carboxyl group, and a sulfo group.

In this way, since the work function adjusting layer (polarized molecular film) 25 for adjusting the work function of the metal film is provided, it is possible to suppress the adverse effect of the metal film on the movement of the electric charge when the electric field is applied. Therefore, it is possible to more effectively improve the phosphorescence emission efficiency and the device durability according to the plasmon enhancement.

In order to adjust the work function of the organic polymer forming the Schottky barrier and the metal electrode in the organic LED, the modification of the metal surface by the SAM having the electron donating group is called "Tuning the Work Function of Gold with Self-Assembled Monolayers Derived from X- [C 6 H 4 -C≡C-] nC 6 H 4 -SH (n = 0,1,2; X = H, F, CH 3, CF 3, and OCH 3 Quot ;, Robert W. Zehner et al, Langmuir 1999, 15, p.1121-1127. In addition to "Toda Toru, Journal of the Japanese Photographic Society, 70, 38 (2007)", it is described that the energy level of gold or silver is controlled by modifying the metal surface with an electron donor or electron attracting group to control the flow of electrons have.

The technique described in the above document may be applied to the metal film only if the energy level of the metal film is adjusted. However, there is a possibility that the effect of improving the luminous efficiency due to plasmon resonance may be deteriorated only by applying it directly. The present inventors have found an arrangement for adjusting the energy level of a metal film while fully utilizing the effect of improving the luminous efficiency by plasmon resonance, thereby realizing an electroluminescence device that realizes high luminous efficiency without lowering durability.

≪ Third Embodiment >

Fig. 4 schematically shows the configuration of the organic EL element 3 according to the third embodiment of the present invention.

4, the organic EL device 3 of the present embodiment includes an anode 11, a hole transporting layer 13, a light emitting layer 14, an electron transporting layer 15, a cathode 17 . Here, the core-shell-type fine particles 40 composed of the metal fine particle core 42 and the insulator shell 41 covering the metal fine particle core 42 are formed as a metal member that generates plasmon resonance by the light emitted from the hole transport layer 13 ). Here, the insulator shell 41 is made of a material having light transmittance to the emitted light. Here, the light transmittance means that the transmittance of the emitted light is 70% or more.

The translucent substrate 10 is not particularly limited, and flexible substrates such as glass, quartz, and polymers can be used.

The core-shell-type fine particles 40 are arranged in the vicinity of the light-emitting region (light-emitting layer 14) so as to generate plasmon resonance by the light-emitting light. The core shell-type fine particles 40 are not particularly limited as long as the contained metal fine particle cores 42 are disposed in a region where plasmon resonance occurs due to the emitted light. However, if the distance from the light emitting layer 14 to the metal fine particle core 42 is excessively large, the plasmon resonance due to the emitted light is hardly generated and an effective luminescence enhancing effect can not be obtained. And the distance d between the light emitting layer 14 and the light emitting layer 14 is preferably 30 nm or less. In the organic EL device of the present embodiment, since the metal fine particle core 42 is covered with the insulator shell 41, the metal fine particle core 42 can be disposed in the light emitting layer 14.

The material of the metal fine particle core 42 is not limited to Ag (silver) and may be Au (gold), Cu (copper), Al (Aluminum), Pt (platinum), and an alloy containing any of these metals as a main component (80% or more).

As the material of the insulator shell 41, an insulator such as SiO ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , PbO, B ₂ O ₃ , CaO, or BaO can be preferably used.

As described above, when the metal member is inserted into the laminate, the metal member may interfere with the movement of the charge. In the present embodiment, the core-shell-type fine particles 40 are used as a metal member in order to prevent this. The core-shell-type fine particles 40 are formed by using a dielectric such as SiO ₂ as the metal fine particle core 42, for example, as the insulator shell 41 of Ag fine particles. Since the metal fine particle core 42 contributing to plasmon resonance is covered with the insulator shell 41, even when an electric field is applied between both electrodes, charges (electrons or holes) are not trapped in the conductive chain Ag, And the effect of the plasmon resonance can be obtained in the light emitting layer. Therefore, it is possible to more effectively improve the phosphorescence emission efficiency and the device durability according to the plasmon enhancement.

An example of a manufacturing method of the EL element 3 of the present embodiment will be briefly described.

An anode 11 made of a transparent electrode such as ITO is formed on the transparent substrate 10 by vapor deposition. As the core-shell-type fine particles 40, Ag fine particles 42 having a particle size of 50 nm are coated with SiO ₂ (41) having a thickness of 10 nm. Subsequently, the core-shell-type fine particles 40 are dispersed in dichloromethane in which a tripelediamine derivative (TPD), which is a hole transporting material, is dissolved and applied on the positive electrode 11 by a spin coating method, The hole transport layer 13 is formed. Next, the light emitting layer 14 and the electron transport layer 15 are formed by vapor deposition, and finally the cathode 17 is formed.

Although the core-shell-type fine particles 40 are dispersed in the hole-transporting layer 13 in the above embodiment, the core-shell-type fine particles 40 may be arranged in any layer as long as it is a region generating plasmon resonance . Particularly, it is preferable because it is possible to generate plasmon resonance more effectively by being present in the light emitting layer.

In FIG. 4, a plurality of core-shell-type fine particles 40 are shown. However, even if the number of core-shell fine particles 40 is one, the effect of increasing the luminous efficiency by plasmon resonance can be obtained.

4 shows a configuration in which one metal fine particle core 42 is provided in the insulator shell 41. However, in the core shell type fine particles having a plurality of metal fine particle cores 42 in the insulator shell 41 good.

The particle diameter of the metal fine particle core 42 of the core shell-type fine particle 40 is not particularly limited as long as the size of the plasmons can be made organic, but it is preferably smaller than the wavelength of the emitted light, more preferably 10 nm or more and 1 μm or less Do.

It is preferable that the thickness of the insulator shell 41 is a film thickness which does not inhibit the localized plasmon induction in the metal fine particle core 42 by the emitted light. It is preferable that the distance between the luminescent layer 14 and the surface of the metal fine particle core is 30 nm or less in order to efficiently obtain the localized plasmon induction by the luminescent light in the luminescent layer 14. The position where the core- The layer configuration and the thickness of the insulator shell 41 are preferably designed to achieve more effective plasmon resonance. Here, the thickness of the insulator shell 41 is defined as an average distance between the surface of the insulator shell 41 and the surface of the metal fine particle core in a configuration in which only one metal fine particle core 42 is contained in the insulator shell 41. When a plurality of metal fine particle cores are provided in the insulator shell, the average value of the shortest distance between the surface of the insulator shell and the surface of each metal fine particle core is taken as the thickness of the insulator shell.

In another preferred embodiment, a plurality of so-called elongated fine particles having an aspect ratio of the major axis of the fine particles and the minor axis perpendicular thereto is greater than 1, and a plurality of the elongated core shell- And organic EL elements in which the fine particles have a short axis oriented in a direction substantially perpendicular to the electrode surface.

With this configuration, strong scattering light can be obtained on the side of the light extraction surface due to the shape anisotropy of the thin and long core-shell type fine particles, and higher drawing efficiency can be obtained.

In another preferred embodiment, the core-shell type fine particles 40 having a large diameter are arranged so that the metal fine particle core 42 is contained in the light emitting layer 14. As already described, by allowing the metal fine particle core 42 to exist in the light emitting layer 14, it is possible to more effectively achieve the luminescence transition by plasmon resonance.

≪ Fourth Embodiment &

The configuration of the organic EL device 4 according to the fourth embodiment of the present invention is schematically shown in Fig.

The organic EL element 4 of the present embodiment has almost the same layer structure as the organic EL element 1 of the first embodiment but the cathode 17 and the anode 11 are reflective portions that reflect the emitted light, And also that the metal film 20 is formed in the hole transporting layer 13. In this case,

In the element of this embodiment, the standing wave 19 is generated between the electrodes 11 and 17 by making the cathode 17 made of Ag (silver) and the anode 11 made of Cu (copper), thereby improving the directivity Effect can be produced. In addition, by matching the emission layer 14 with the emission wave 19a of the standing wave, the intensity of the electric field in the emission layer 14 can be maximized, and the emission efficiency can be maximized. Resonance conditions for achieving such a micro-cavity effect are given by the following formulas, and each of the layers 12 to 16 is designed to have a refractive index and a thickness satisfying the following formula. In addition, to in formula, λ ₀ is in a light emitting wavelength of the light, n _i is the refractive index, d _i is the thickness of each layer, φ ₁ and φ ₂ are each anode 11, a cathode 17 in the respective layers The phase difference due to reflection, and m is the degree of cavity.

In the microcavity type organic EL device as shown in Fig. 5, the light emitting layer 14 is formed at a position within 10% from a peak (peak) of the standing wave at which the electric field intensity is maximum, The film 20 is disposed. In this way, it is preferable that the metal film is disposed at a position close to the fold of the standing wave, that is, at a position where the electric field intensity by the standing wave is large, thereby effectively obtaining the plasmon resonance effect. In the design of the present embodiment, the cavity degree m = 1 is employed.

By virtue of such a configuration, the effect of the micro-cavity effect and the effect of the plasmon enhancement are superimposed, and the effect of improving the luminous efficiency, the directivity, and the durability can be obtained more remarkably.

As described above, in the element 4 of the present embodiment, the electrodes 11 and 17 are made of metal, and a cavity is formed between the electrodes to form a standing wave inside the element. The reflectance of the electrodes 11 and 17 constituting the reflection portion of the cavity with respect to the emitted light may be sufficient to form a standing wave. In the present embodiment, the thickness of the electrode on the light extraction side (here, the Cu anode 11) is adjusted so that the reflectance is about 30%, for example. The reflectance on the Ag cathode 17 side may be 90% or higher. Further, a transparent electrode may be provided as an electrode, and a reflective layer may be further formed on the outer side of the electrode. The reflective layer may be composed of a metal or dielectric multilayer film having an appropriate reflectance.

Also, in the EL elements of the first to third embodiments described above, the standing wave is generated in the element as a cavity between the electrodes 11 and 17, and the emission layer 14 and the standing wave are substantially aligned, Is designed to have a refractive index and a thickness satisfying the above-described resonance condition, it is possible to superimpose the effect of the plasma enhancement and the micro-cavity effect.

(Example)

Examples and comparative examples of the organic EL device 1 (see Fig. 1) of the first embodiment described above will be described.

&Quot; Example 1 "

The EL device of Example 1 was an ITO anode 11, a 2TNATA + 0.3% F4TCNQ (120 nm) hole injecting layer 12, a NPD (10 nm) hole transporting layer 13, a CBP-10% Ir (ppy) (20 nm) electron transporting layer 15, a LiF (1 nm) electron injection layer 16, an Al cathode 17 (15 nm) ) Are stacked in this order.

The light emitting material of the light emitting layer 14 is Ir (ppy) 3, and its T1 level is 2.5 eV. The metal film 20 is disposed in the electron transporting layer 15. The T1 level of the NPD constituting the hole transport layer 13 is 2.3 eV and the T1 level of the BAlq constituting the electron transport layer 15 is 2.3 eV and all are lower than the T1 level of the light emitting material.

Comparative Example 1

In the EL device of Comparative Example 1, the Ag metal film 20 was not provided in the device of Example 1. [

That is, in the device of Comparative Example 1, the ITO anode 11, 2TNATA + 0.3% F4TCNQ (120 nm) hole injection layer 12, NPD (10 nm) hole transport layer 13, CBP-10% Ir (ppy) Emitting layer 14, a BAlq (30 nm) electron transporting layer 15, an LiF (1 nm) electron injection layer 16, and an Al cathode 17 are sequentially laminated.

&Quot; Example 2 "

The EL device of Example 2 was fabricated in the same manner as in Example 1 except that the ITO anode 11, 2TNATA + 0.3% F4TCNQ (120 nm) hole injection layer 12, NPD (10 nm) hole transport layer 13, mCP + 15% Pt1 , A BAlq (10 nm) electron transporting layer 15, an Ag (14 nm) metal film 20, a BAlq (20 nm) electron transporting layer 15, a LiF (1 nm) electron injection layer 16, and an Al cathode 17, .

The light emitting material of the light emitting layer 14 is Pt1, and its T1 level is 2.7 eV. The metal film 20 is disposed in the electron transporting layer 15. The T1 level of the NPD constituting the hole transport layer 13 is 2.3 eV and the T1 level of the BAlq constituting the electron transport layer 15 is 2.3 eV and all are lower than the T1 level of the light emitting material.

Comparative Example 2

In the EL device of Comparative Example 2, the Ag metal film 20 was not provided in the device of Example 2. [

&Quot; Example 3 "

The EL device of Example 3 was fabricated in the same manner as in Example 1 except that the ITO anode 11, the 2TNATA + 0.3% F4TCNQ (120 nm) hole injection layer 12, the NPD (10 nm) hole transport layer 13, the mCP + 15% , A BAlq (10 nm) electron transporting layer 15, an Ag (14 nm) metal film 20, a BAlq (20 nm) electron transporting layer 15, a LiF (1 nm) electron injection layer 16, and an Al cathode 17, .

The light emitting material of the light emitting layer 14 is Pt2, and its T1 level is 2.5 eV. The metal film 20 is disposed in the electron transporting layer 15. The T1 level of the NPD constituting the hole transport layer 13 is 2.3 eV and the T1 level of the BAlq constituting the electron transport layer 15 is 2.3 eV and all are lower than the T1 level of the light emitting material.

[Comparative Example 3]

In the EL device of Comparative Example 3, the Ag metal film 20 was not provided in the device of Example 3 above.

The detailed chemical formulas and the T1 level of each material used in the above Examples and Comparative Examples are as follows. The T1 level of each material was determined from the peak wavelength of the phosphorescence spectrum of the vapor-deposited film at 77K.

The luminescence peak wavelength, emission lifetime, EL external quantum yield, and EL driving half life were measured for each of the devices of the above Examples and Comparative Examples. The PL quantum yields of the films of only the light emitting layers of Examples (Comparative Examples) 1 to 3 were measured, respectively. The measurement method for each is as follows.

<Luminescent lifetime>

Each device was irradiated with nitrogen laser light (wavelength: 337 nm, pulse width: 1 ns) as excitation light, and the light emission lifetime from each light emitting material was measured by a stream camera (C4334 manufactured by Hamamatsu Fotonics Co., Ltd.).

&Lt; Luminescence peak wavelength and EL external quantum yield >

A direct current was applied to each device by using a source major unit 2400 manufactured by Toyo Technica Co., Ltd. to emit light. The emission spectrum at that time was measured using a spectrometer SR-3 manufactured by Topcon Corporation, and the emission peak wavelength was determined. Based on the obtained spectrum, the external quantum efficiency at the current density of 0.25 mA / cm 2 and 25 mA / cm 2 of the device was calculated by the intensity conversion method for each wavelength.

<EL drive half life>

The DC current of each device was measured at a luminance of 2000 cd / m &lt; 2 &gt; and the time until the luminance reached 1000 cd / m &lt; 2 &gt;

&Lt; Pl Quantum Yield of Light Emitting Layer Film &

EXAMPLES (COMPARATIVE EXAMPLES) Films of only the light emitting layers 1 to 3 were formed on a quartz substrate, and the yield of PL quantum of each film was measured by using an absolute PL quantum yield measuring device (C9920-02 manufactured by Hamamatsu Fotonics Co., Ltd.) .

The measurement results are shown in Table 1 below.

As shown in Table 1, in each of the comparative examples, the emission lifetime is shortened, the external quantum efficiency is improved, the driving half life of the device is extended, and the characteristics are improved .

The EL device of the present invention can be suitably used for display devices, displays, backlights, electrophotography, illumination light sources, recording light sources, exposure light sources, reading light sources, markers, signs,

1, 2, 3, 4: organic EL element 11: anode
12: Hole injection layer 13: Hole transport layer
14: light emitting layer 15: electron transporting layer
16: electron injection layer 17: cathode
19: standing wave 19a: ship
20: metal film (metal member) 25: work function adjusting layer (surface modification)
40: core shell type fine particles (metal member) 41: insulator shell
42: metal fine particle core

Claims (8)

An organic electroluminescent device comprising a light-emitting layer containing a light-emitting material that emits phosphorescence, and a plurality of layers including a first adjacent layer and a second adjacent layer disposed adjacent to the light- As a Nessel element,
Wherein a first excitation triplet energy level of the light emitting material is higher than a lowest energy level of a first excitation triplet energy level of a plurality of materials constituting the first adjacent layer and the second adjacent layer,
And a metal member for generating a plasmon resonance on the surface by the light emitted from the light emitting layer at a position spaced by 5 nm or more and 30 nm or less from the light emitting layer, wherein the metal member is Au or Ag, Wherein the organic electroluminescence element is an organic electroluminescent element. delete The method according to claim 1,
Wherein the metal member is a metal film disposed between the plurality of layers. The method of claim 3,
Wherein the metal film is an island structure film in which a plurality of metal fine particles having a particle diameter of 5 nm or more are dispersed in a film form. The method of claim 3,
Wherein at least one surface of the metal film is subjected to a surface modification with a terminal having a polarity such that a work function of the metal film is made close to a work function of a layer adjacent to the metal film, . 5. The method of claim 4,
Wherein at least one surface of the metal film is subjected to a surface modification with a terminal having a polarity such that a work function of the metal film is made close to a work function of a layer adjacent to the metal film, . The method according to claim 1,
Wherein the metal member is a core-shell type fine particle comprising a metal fine particle core and an insulator shell covering the metal fine particle core. 8. The method according to any one of claims 1 to 7,
Wherein the plurality of layers have a layer thickness and a refractive index that satisfy a resonance condition in which a region where the electric field strength of a standing wave due to light emitted from the light emitting layer from the light emitting layer is maximized coincides with the light emitting layer, The Suns device.

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