JP2002134267A - Electric field light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make enable to extract a portion of a light, which can not be taken out outside because the light emitted from a luminescence layer of an electric field light emitting device, is totally reflected by an interface, using a hologram. SOLUTION: In the electric field light emitting device, which emits light from a light emitting point 7 in the luminescence layer 4 between two electrodes, when voltage is impressed between the two electrodes 2, 5, of which the one is transparent, a volume type hologram layer 10' is arranged, which changes a light emitting component 9 incident to the interface on the outside of the transparent electrode 2 above a critical angle, into the light, which incident at an angle smaller than the critical angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to a thin-film organic electroluminescent device having a high external luminous efficiency and being bright for a display device.

[0002]

2. Description of the Related Art Organic electroluminescent devices (organic EL devices)
As shown in a typical configuration in FIG.
A transparent electrode 2 of O or the like is formed, a hole injection layer 3 and a light emitting layer 4 are laminated thereon in this order, and a cathode electrode 5 is formed on the light emitting layer 4. A voltage is applied from a power source 6 between the transparent electrode 2 and the cathode electrode 5 to inject holes and electrons from the hole injection layer 3 and the cathode electrode 5, and they are recombined in the light emitting layer 4 to form activators. The energy excites the phosphor in the light emitting layer 4 to emit light from the light emitting point 7. Usually, in the organic EL element, the light emitting point 7
Is emitted to the outside through the transparent substrate 1 and is recognized as a display only when it enters the eyes of the observer.

[0003]

However, since the light generated in the light emitting layer 4 has no directionality and is emitted isotropically and uniformly from the light emitting point 7, the light obtained by the light emission is obtained. Of the light, only the light 8 emitted at an angle smaller than the critical angle with respect to the surface of the transparent substrate 1 as shown in FIG. 6, and the light 9 exceeding the critical angle is transparent as shown in FIG. The light is totally reflected on the surface of the substrate 1 and can only go out from the end face of the transparent substrate 1 and is not used effectively. Light emitted from the light-emitting layer 4 to the back surface opposite to the transparent substrate 1 is also reflected by the cathode electrode 5 on the back surface, and similarly,
Only light with an angle within the critical angle of is emitted outward.

The light extraction efficiency of the organic EL element is about 2
It is only 0%, which is the largest factor limiting the external luminous efficiency of the organic EL device.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an electroluminescent device in which light emitted from a light emitting layer is totally reflected at an interface and cannot be extracted to the outside. The object is to make it possible to take out light by using a hologram so as to enhance the external light emission efficiency and enable a bright display.

[0006]

According to the electroluminescent device of the present invention that achieves the above object, when a voltage is applied between two electrodes, at least one of which is transparent, the light emission in the light emitting layer between the two electrodes is achieved. An electroluminescent device that emits light from a point, characterized in that a volume hologram layer that converts a luminescent component incident on the interface at a critical angle or more to an interface at an angle smaller than the critical angle is disposed outside the transparent electrode. It is.

In this case, the volume hologram layer can be made of a transmission hologram.

In this case, it is desirable that the volume hologram layer is composed of a multilayer laminated hologram or a multiple recording hologram.

The volume hologram layer is composed of a two-layer laminated hologram, two volume holograms are double-recorded on each layer, and the interference fringes of the two hologram layers are arranged so as to intersect each other. Is desirable.

An organic electroluminescent device having a charge injection layer and a light emitting layer between two electrodes, at least one of which is transparent, wherein the volume hologram layer is disposed between the substrate and the transparent electrode. It can be.

Also, between two electrodes, both of which are transparent,
An organic electroluminescent device having a charge injection layer and a light emitting layer,
It is also possible to adopt a configuration in which a volume hologram layer is arranged on the back surface side of a transparent electrode provided on the back surface of the light emitting layer, and a reflection layer is provided on the opposite side of the volume hologram layer from the transparent electrode.

In this case, the volume hologram layer is desirably made of a reflection hologram.

The volume type hologram layer is composed of a multilayer hologram or a multiplex hologram.
It is preferable that the hologram is composed of a two-layered hologram, two volume holograms are double-recorded in each layer, and the interference fringes of the two hologram layers are arranged so as to cross each other.

In the present invention, a volume hologram layer for converting a light-emitting component incident on the interface at a critical angle or more into the interface at an angle smaller than the critical angle is disposed outside the transparent electrode. A luminous component that cannot be extracted outside can be extracted because the light is incident at an angle of an angle or more and is totally reflected, so that the external luminous efficiency of the electroluminescent element can be greatly increased, and a bright display or the like can be achieved. .

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic principle of the present invention is to use a transparent electrode to effectively use light emitted at an angle of a critical angle or more with respect to the interface of the transparent layer on the display side of the electroluminescent device. On the side, a volume hologram layer for converting the light into light having an angle smaller than the critical angle is provided, and the external emission efficiency is increased by increasing the external extraction ratio.

As is well known, a volume hologram is a hologram in which interference fringes having a difference in refractive index are recorded in a volume hologram photosensitive material such as a photopolymer.
It has a function of selectively diffracting incident light, and has relatively high wavelength selectivity and angle selectivity of diffraction efficiency.

Therefore, as shown in FIG. 1, a volume of light 9 emitted from the light emitting point 7 to the right side of the figure at an angle exceeding the critical angle with respect to the surface of the transparent substrate 1 is diffracted in an angle direction smaller than the critical angle. The hologram layer 10 is provided between the transparent electrode 2 and the transparent substrate 1 so that the light 9 is diffracted by the volume hologram layer 10 and can be extracted to the outside. Since the volume hologram layer 10 has a high angle selectivity of the diffraction efficiency as described above, the light 8 emitted at an angle equal to or less than the critical angle is not diffracted by the volume hologram layer 10 and is similar to the conventional case (FIG. 6). ). Therefore, the external luminous efficiency is increased by the amount of the light 9 emitted to the right side of FIG. 1 at an angle exceeding the critical angle and diffracted by the volume hologram layer 10.

FIG. 1 shows a case of an organic EL device, similar to FIG. 6, in which a transparent electrode 2 such as ITO is formed on a volume hologram layer 10 on a transparent substrate 1 and a hole injection layer is formed thereon. 3, a light emitting layer 4 is laminated in this order, a cathode electrode 5 is formed on the light emitting layer 4, a power source 6 is connected between the transparent electrode 2 and the cathode electrode 5, and a voltage can be applied from the power source 6. Holes and electrons are injected from the hole injection layer 3 and the cathode electrode 5, and they recombine in the light emitting layer 4 to form activators, and this energy excites the phosphor in the light emitting layer 4 to emit light. 7 emits light.

In the case of FIG. 1, the light 9 'emitted from the light emitting point 7 to the left side of the figure at an angle exceeding the critical angle with respect to the surface of the transparent substrate 1 is the angle of the diffraction efficiency of the volume hologram layer 10. No diffraction due to selectivity. Therefore, as shown in FIG. 2, it is desirable to provide a double recording volume hologram layer 10 ′ that diffracts such light 9 ′ similarly to light 9 between transparent electrode 2 and transparent substrate 1. This double-recording volume hologram layer 10 'is composed of two interference fringes, which are the same as the interference fringes of the volume hologram layer 10 of FIG. 1, and interference fringes obtained by rotating the interference fringes by 180 ° around the normal of the hologram layer. It has the effect of diffracting the light 9 with one interference fringe and the light 9 'with the other interference fringe, and the light 8 having an angle smaller than the critical angle is not diffracted by any interference fringes. It is transparent. Alternatively, as the volume hologram layer 10 ', FIG.
May be obtained by stacking two volume hologram layers 10. However, in that case, the other volume hologram layer 10 is formed by being rotated by 180 ° about the normal line of the hologram layer of the one volume hologram layer 10 and overlapped. As described above, by using the double recording or the two-layer laminated volume hologram layer 10 ′, the light 9 radiated at an angle exceeding the critical angle to the left and right in FIG. Luminous efficiency is higher.

The above is an example in which the light 9, 9 'radiated at an angle exceeding the critical angle with respect to the surface of the transparent substrate 1 on the left and right of the surface of FIG. 2 can be extracted to the outside. Light components emitted at angles exceeding the critical angle also exist on the front and back sides of the surface. In order to diffract the light component in the same manner so that it can be extracted outside, as shown in FIG. 3, the volume hologram layer 1 similar to the volume hologram layer 10 'in FIG.
If the 0 "is superimposed on the hologram layer by rotating relative to the normal of the hologram layer by 90 [deg.] So that the interference fringes are perpendicular to each other, all directions around the axis (normal) can be obtained. Light emitted at an angle exceeding the critical angle can be extracted to the outside.

In the embodiments of FIGS. 1 to 3 described above, the volume hologram layers 10, 10 ', and 10 "are all disposed between the transparent substrate 1 and the transparent electrode 2.
The same effect can be obtained by disposing it on the surface side (opposite side of the transparent electrode 2). However, if the distance between the light emitting layer 4 and the hologram layer is increased, the light 8 not diffracted by the hologram layer
And the diffracted light 9, 9 'becomes large, the display becomes difficult to see, and the resolving power decreases. Therefore, the volume type hologram layers 10, 10', 10 "
It is desirable to dispose it close to

An example of a method (photographing method) of the above-described volume hologram layers 10, 10 'will be described with reference to the layout diagram of FIG. The light emitted from the laser 20 is split by the half mirror 21 into two light beams,
The light reflected by 1 has its beam diameter expanded by a beam expansion system 23 and passes through a prism 24 as object light 25 that travels in the direction of the diffracted light by the volume hologram layers 10 and 10 ′. Light that is made incident on the volume hologram photosensitive material 11 such as a photopolymer provided on the back surface and transmitted through the half mirror 22 passes through mirrors 22 and 22 ′, and the beam diameter is expanded by a beam expanding system 23 ′. The two luminous fluxes 25 and 26 interfere with the volume hologram photosensitive material 11 as reference light 26 traveling in the direction of the light 9 via the prism 24, so that the volume hologram layer 10 Is taken.
Thereafter, by rotating the photosensitive material 11 around the normal line n by 90 ° and recording another interference fringe in the same manner, a volume hologram layer 10 ′ is produced.

Light emission from the light emitting point 7 in the light emitting layer 4 is isotropically emitted as described above. Therefore, as shown in FIG. 5, among the light emitted from the light emitting point 7, the light 18, 19, 19 'emitted to the cathode electrode 5' side on the back surface is included.
Also exists. The component 18 that proceeds in the front direction of the back surface in it is
When the light is specularly reflected on the back surface, the angle is equal to or smaller than the critical angle with respect to the surface of the transparent substrate 1 as in the case of the component 8. On the other hand, the components 19 and 19 ′ traveling obliquely on the rear surface have an angle equal to or larger than the critical angle with respect to the surface of the transparent substrate 1, like the components 9 and 9 ′, when specularly reflected on the rear surface. .

Therefore, the cathode electrode 5 'on the back side is also a transparent electrode, and the reflection type volume hologram layers 12, 12' are arranged on the back side of the cathode electrode 5 ', and the reflection layer 13 is further provided on the back side.

Here, the volume hologram layer 12 emits light 1 radiated at an angle exceeding the critical angle with respect to the surface of the transparent substrate 1 when specularly reflected from the light emitting point 7 to the left and right sides of the figure on the back surface.
9, 19 'are reflection-type volume hologram layers that diffract in the direction of an angle smaller than the critical angle on the reflection side, like the volume hologram layer 10', a double recording volume hologram layer or a two-layer stack. It is composed of a volume hologram layer.
Reference numeral 8 denotes a light which is transmitted without being diffracted. The volume hologram layer 12 ′ is formed by rotating a reflection type volume hologram layer similar to the volume hologram layer 12 by 90 ° relatively around the normal line of the hologram layer. A reflection-type volume hologram layer that diffracts light radiated at an angle exceeding the critical angle with respect to the surface of the transparent substrate 1 when specularly reflected on the front and back surfaces of the transparent substrate 1 toward the reflection side in an angle direction smaller than the critical angle. It is.

Therefore, the light 19 radiated from the light emitting point 7 to the back side in all directions at an angle exceeding the above critical angle,
19 ′ is diffracted toward the front side by the volume hologram layers 12 and 12 ′ in an angle direction smaller than the critical angle and is extracted to the outside. Hologram layers 12 and 1
The light passes through 2 ′, is specularly reflected by the reflection layer 13 on the back surface, enters the surface of the transparent substrate 1 at an angle equal to or smaller than the critical angle, is extracted outside, and is used for display or the like with high external luminous efficiency.

In order to fabricate the reflection type volume hologram layers 12 and 12 ', for example, it is possible to take an image by a two-beam interference method as shown in FIG.
The object beam 25 and the reference beam 26 are converted into a volume hologram photosensitive material 1
1 must be incident from opposite sides.

In the above, in the case of FIG. 3, the light emitted at an angle exceeding the critical angle to the front side of the surface of the light emitting layer 4 can be taken out, and in the case of FIG. Although it is a configuration that allows light emitted at an angle exceeding the critical angle to the back side of the device to be extracted to the outside, it is possible to achieve higher external luminous efficiency by configuring both at the same time. it can.

Although the above embodiments have been described on the premise of an organic EL device, the electroluminescent device to which the volume hologram layer of the present invention can be applied is not limited to this, and is also applicable to an inorganic EL device. What can be done will be clear from that principle.

Although the electroluminescent device of the present invention has been described based on the principle and the embodiments, the present invention is not limited to the embodiments and the like, and various modifications are possible.

[0031]

As is clear from the above description, according to the electroluminescent device of the present invention, the luminous component incident on the interface outside the transparent electrode at a critical angle or more at the interface is converted into the light incident at an angle smaller than the critical angle. Since the volume hologram layer to be converted is arranged, it is possible to extract light-emitting components that cannot be extracted outside because they are incident on the interface at an angle greater than the critical angle and are totally reflected. Efficiency can be greatly increased, and bright display and the like can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view of an organic electroluminescent device according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of an organic electroluminescent device according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view of an organic electroluminescent device according to another embodiment of the present invention.

FIG. 4 is an arrangement diagram for explaining a method of manufacturing a volume hologram layer used in the configurations of FIGS. 1 to 3;

FIG. 5 is a cross-sectional view of an organic electroluminescent device according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a typical configuration of an organic electroluminescent device.

[Description of Signs] 1 ... Transparent substrate 2 ... Transparent electrode 3 ... Hole injection layer 4 ... Emission layer 5 ... Cathode electrode 5 '... Transparent cathode electrode 6 ... Power supply 7 ... Emission point 8 ... Light emitted at an angle smaller than the critical angle 9, 9 ': light emitted at an angle exceeding the critical angle 10, 10', 10 ": transmissive volume hologram layer 11: volume hologram photosensitive material 12, 12 ': reflection volume hologram layer 13 ... Reflecting layer 18: Light emitted at an angle smaller than the critical angle 19, 19 '... Light emitted at an angle exceeding the critical angle 20 ... Laser 21 ... Half mirror 22, 22' ... Mirror 23, 23 '... Beam expanding system 24 ... Prism 25: Object light 26: Reference light n: Normal line

Claims (9)

[Claims] 1. An electroluminescent element which emits light from a light emitting point in a light emitting layer between two electrodes, at least one of which is transparent, when a voltage is applied between the two electrodes, wherein a critical voltage is applied to an interface outside the transparent electrode. An electroluminescent device, comprising a volume hologram layer for converting a luminous component incident at an angle or more into light incident at an angle smaller than a critical angle. 2. The electroluminescent device according to claim 1, wherein said volume hologram layer is formed of a transmission hologram. 3. The electroluminescent device according to claim 2, wherein the volume hologram layer is formed of a multilayer hologram or a multiplexed hologram. 4. The volume hologram layer is composed of a two-layer laminated hologram, two volume holograms are double-recorded on each layer, and the interference fringes of the two hologram layers are arranged so as to intersect each other. The electroluminescent device according to claim 2, wherein: 5. An organic electroluminescent device having a charge injection layer and a light emitting layer between two electrodes, at least one of which is transparent, wherein the volume hologram layer is disposed between the substrate and the transparent electrode. The electroluminescent device according to any one of claims 1 to 4, wherein: 6. An organic electroluminescent device having a charge injection layer and a light emitting layer between two electrodes both of which are transparent, wherein a volume hologram layer is provided on the back side of the transparent electrode provided on the back side of the light emitting layer. The electroluminescent device according to claim 1, wherein a reflective layer is provided on a side of the volume hologram layer opposite to the transparent electrode. 7. The electroluminescent device according to claim 1, wherein said volume hologram layer is made of a reflection hologram. 8. The electroluminescent device according to claim 7, wherein said volume hologram layer is formed of a multilayer laminated hologram or a multiplexed hologram. 9. The volume hologram layer is composed of a two-layer hologram, two volume holograms are double-recorded on each layer, and interference fringes of the two hologram layers are arranged so as to intersect each other. The electroluminescent device according to claim 2, wherein: