JP2002260859A - Lighting equipment - Google Patents

Abstract

(57) [Problem] To use an organic light-emitting element as a lighting device, the organic light-emitting element has a very high green light-emitting efficiency, but has a poor red light-emitting efficiency, and cannot be white-balanced when used as a white light source. There were challenges. SOLUTION: By stacking a green or yellow light emitting element on the back surface of a red light emitting element, a surface emitting lighting device with good white balance can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight for a display such as a liquid crystal display and an illumination such as a room illumination.

[0002]

2. Description of the Related Art A conventional light source has a spherical or rod-like shape such as a bulb using a filament and a lamp utilizing a discharge phenomenon. Therefore, when used as a lighting fixture, it mainly reflects light emitted upward and reflects light downward. It can be classified into two types: direct illumination provided with a reflective surface to be transmitted to the camera, and indirect illumination provided with a reflective surface to diffuse light or reduce glare. On the other hand, an electroluminescence (EL) panel has a feature of surface light emission, and is expected to be developed as a new lighting by using this.

In recent years, reports have been made on organic light-emitting devices using an organic material as a light-emitting material (for example, see the related paper Applied Physics Letters, vol. 51, p. 913, 1).
987). Organic light emitting devices have the feature of surface emission,
Particularly recently, organic light-emitting devices with a high efficiency exceeding 40 lm / W have been reported (for example, Spring Meeting of the Japan Society of Applied Physics, 31a-H-3, 2000).

[0004] Various light emission colors are possible for the organic light emitting device depending on the material design of the light emitting material. In order to develop a display device, a pixel is finely separated like a CRT, and red, green, and blue light emitting layers are formed in each pixel, or a color conversion color filter is attached to a blue only light emitting element. There is a method to attach. Furthermore, a high-definition display device can be realized by laminating light emitting elements having light emitting pixels of one color on each substrate as disclosed in Japanese Patent Application No. 5-205478. At the same time, blue, green,
By arranging red light and light having a short emission wavelength from long light, a display device with high color purity is enabled.

[0005]

However, in the development of lighting devices, organic light-emitting devices have very high green luminous efficiency, but have poor red luminous efficiency, and have a white balance when used as a white light source. There was a problem that there was not.

[0006]

In order to solve the above-mentioned problem, we have not only made the red light-emitting element, which is insufficient in efficiency, emit EL light, but also the red light-emitting material of the red light-emitting element absorbs and emits light on the back surface.
Light-emitting elements having a spectrum capable of emitting light are stacked and PL
By using a lighting device configured to extract light emission, a surface-emitting lighting device with good white balance has been provided.

Specifically, according to the invention of claim 1 of the present application, a driving means for generating a current, a pair of transparent electrodes on a transparent substrate which emits light according to the current, and at least a space between the transparent electrodes A lighting device including at least two light-emitting elements each having a light-emitting layer, the lighting means stacking a second light-emitting element capable of converting an emission spectrum of the first light-emitting element on a light extraction side. A lighting device is provided.

According to the invention of claim 2 of the present application, a driving means for generating a current, a pair of transparent electrodes on a transparent substrate which emits light according to the current, and a light emitting device having at least a light emitting layer between the transparent electrodes A lighting device having at least two stacked elements, wherein each of the light emitting elements has a different emission color, and has a green or yellow light emitting element on the back surface of the red light emitting element. Is provided.

According to a third aspect of the present invention, the illuminating means according to the first or second aspect is such that a blue light-emitting element, a red light-emitting element, and a green light-emitting element are sequentially stacked from the light extraction surface.

According to a fourth aspect of the present invention, the illuminating means according to any one of the first to third aspects has a reflection layer on a side opposite to the light extraction surface.

According to a fifth aspect of the present invention, the reflective layer according to the fourth aspect has an uneven shape.

According to a sixth aspect of the present invention, the light emitting layer according to any one of the first to fifth aspects is made of an organic material.

According to a seventh aspect of the present invention, a hole transport layer is laminated on the light emitting layer according to any one of the first to sixth aspects.

An eighth aspect of the present invention is to laminate an electron transporting layer on the light emitting layer according to any one of the first to seventh aspects.

According to the ninth aspect of the present invention, a driving means for generating a current, a pair of transparent electrodes on a transparent substrate which emits light in response to the current, and at least a light emitting layer between the transparent electrodes are provided. A lighting device comprising a plurality of light emitting elements having different emission colors, wherein a light emitting area of a red light emitting element is a light emitting area of a light emitting element other than red. A lighting device is provided, wherein the lighting device is larger than the lighting device.

According to a tenth aspect of the present invention, a green or yellow light emitting element is laminated on the back surface of the red light emitting element according to the ninth aspect.

Claim 11 of the present application claims claim 9 or claim 10.
The lighting means described in (1) has a reflection layer on the side opposite to the light extraction surface.

According to a twelfth aspect of the present invention, the reflective layer according to any one of the ninth to eleventh aspects has an uneven shape.

According to a thirteenth aspect of the present invention, the light emitting layer according to any one of the ninth to twelfth aspects is made of an organic material.

According to a fourteenth aspect of the present invention, a hole transport layer is laminated on the light emitting layer according to any one of the ninth to thirteenth aspects.

According to a fifteenth aspect of the present invention, an electron transport layer is laminated on the light emitting layer according to any one of the ninth to fourteenth aspects.

[0022]

Embodiments of the present invention will be described below.

The lighting device according to the present embodiment is realized by stacking light-emitting elements having different emission colors on different substrates. As a preferred form of stacking, it is preferable to stack a green light emitting element that the red light emitting material easily absorbs on the back surface of the inefficient red light emitting element. Alternatively, stacking yellow light-emitting elements having green and red spectral components is preferable because the red component can be enhanced. When the Stokes shift of the red light emitting material of the red light emitting element is large and blue light can be effectively converted to red, a blue light emitting element may be used on the back surface. As a specific form, the layers are stacked in order from the light extraction side, such as blue / red / green, blue / red / yellow, blue / green / red / yellow, blue / yellow / red / green, red / blue / green, etc. An example is given below.

In the approach to the white light emission of the organic light emitting element, there is a method of mixing light emitting materials emitting different emission colors in the same light emitting layer to whiten the light. Since the light-emitting elements having colors are formed on different substrates, they are independently operated and turned on, so that high luminous efficiency can be achieved at a low operation voltage.
As a specific example, FIG. 1 is a cross-sectional view of a blue / red / green stacked lighting device.

The emission spectrum when a DC voltage is applied to the lighting apparatus of FIG. 1 is shown by a solid line in FIG.

In FIG. 2, the broken line is the emission spectrum of the lighting device stacked in the order of blue / green / red. Green is slightly absorbed by the red light emitting element and converted to red.
By adopting the configuration shown in FIG. 1, it is possible to improve the balance with green light emission by adding photoluminescence (PL) light emission to red light, which was insufficient only by EL light emission, and to realize a high-quality white light source. Reached.

As a method of improving red light emission with poor efficiency, there is a method of making the light emitting area of the red light emitting element larger than the light emitting areas of the light emitting elements other than red. FIG. 3 shows an example of a specific embodiment.

FIG. 4 shows another example.

In the present embodiment, since the red light emission is improved by the light emitting area, the order of lamination is not particularly limited, but a green or yellow light emitting element is considered in consideration of the balance with green having high light emitting efficiency. May be laminated on the back surface. Further, the present invention is not limited to red light, and is effective for a light emission color with low efficiency as compared with light emission with high efficiency such as green light such as blue and purple. Preferably, each light emitting area is determined in inverse proportion to the efficiency ratio. According to the illumination device having the above-described configuration, not only a high-quality white light source can be realized, but also illumination of various color tones can be performed since the illumination device is operated independently.

As the light emitting element used in the lighting device according to the present embodiment, a light emitting element having a general structure can be used. Therefore, in addition to the anode / hole transport layer / light-emitting layer / electron transport layer / cathode (DH configuration), anode / hole transport layer / light-emitting layer / cathode (SH-A configuration), anode / light-emitting layer / electron transport layer / cathode (SH-B configuration), anode / light-emitting layer / cathode (single-layer configuration), etc. are possible.

The substrate used for the light emitting element constituting the lighting device according to the present embodiment may be any substrate that can carry the laminated thin film having the above-described basic configuration, and these basic configurations are all laminated on the substrate. . When light is extracted from the side facing the substrate, there is no particular limitation on the material, form, and the like. When taking out light from the substrate side, any transparent or translucent material may be used so as to take out light emission generated in each of the above layers,
Glass such as Corning 1737 or polyester or other resin film is used.

By making the electrodes transparent or translucent, the light emitting element can have a laminated structure and can emit surface light. Usually, the anode serving as a hole injection electrode has I
In many cases, a TO (indium tin oxide) film is used. Other examples include tin oxide, Ni, Au, Pt, and Pd.
In order to improve the transparency or reduce the resistivity of the ITO film, sputtering, electron beam evaporation,
A film forming method such as ion plating is employed.
The film thickness is determined from the required sheet resistance value and visible light transmittance. However, since the driving current density of the light emitting element is relatively high, the light emitting element is used with a thickness of 100 nm or more to reduce the sheet resistance value. Often. The ITO film, tin oxide, Ni, Au, P
In addition to the t and Pd thin films, MgAg proposed by Tang et al.
A thin film of an alloy, a thin film of an AgPdCu alloy, or the like can be used. When the light-emitting element is formed of an organic material, a phthalocyanine derivative such as dilithium phthalocyanine or a buffer layer such as a pyrazabol derivative is preferably provided because the organic layer may be damaged. It is more preferable to include a metal having a low work function and a low electron injection barrier, such as Li, Na, K, Mg, and Ca. Further, the electrode of the light emitting element located opposite to the light extraction side may have a reflective layer. As a material for forming the reflection layer, a metal is preferable, and in particular, Al, Ag, N
A metal having a relatively large work function and being stable, such as i or Bi, is preferable. The reflective layer may be smooth or may have an uneven shape for improving contrast. Further, the reflective layer may function as a cathode, an alloy of a metal having a small work function and a metal having a large work function such as MgAg, LiAl, or a metal having a low work function may be formed on the organic layer side. For the purpose of protecting this low work function metal, a metal having a large work function may be laminated thickly, or a laminated electrode such as Li / Al or LiF / Al may be used. For forming these cathodes, a vapor deposition method or a sputtering method is preferable.

As a material constituting the hole transport layer, a derivative having triphenylamine as a basic skeleton is preferable. For example, a tetraphenylbenzidine compound, a triphenylamine trimer, and a benzidine dimer can be given.
Also, a triphenyldiamine derivative or MTPD
(N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine, commonly called TPD). In particular, triphenylamine tetramer is preferable.

As a material constituting the electron transport layer, tris (8-quinolinolato) aluminum (hereinafter, Alq) is preferable. Other examples include metal complexes such as tris (4-methyl-8-quinolinolato) aluminum, 3- (2'-benzothiazolyl) -7-diethylaminocoumarin, and the like. The electron transport layer preferably has a thickness of 10 to 1000 nm.

Materials constituting the light emitting layer of the present embodiment include, in addition to the above Alq and its derivatives, low molecular materials such as 4,4′-bis (2,2-diphenylvinyl) biphenyl and tetraphenylporphine; Polymer materials such as poly (p-phenylenevinylene) and polyfluorene can be used. Further, a light emitting material such as a laser dye may be doped in order to improve luminous efficiency and to change the color of eight colors, such as tris (2-phenylpyridine) iridium,
A phosphorescent heavy metal complex such as 2,3,7,8,12,13,17,18-octaethyl-21H23H-porphine platinum (II) may be used. In order to improve the hole transporting ability and the electron transporting ability in the light emitting layer, the above hole transporting material and the electron transporting material may be mixed and exist. Further, an inorganic phosphor or the like may be used, and the composition may be formed by being dispersed in a polymer matrix or the like.

For each of the above-described hole transport layer, electron transport layer, and light emitting layer, it is desirable to form a homogeneous film in an amorphous state, and it is preferable to form the film by a vacuum evaporation method. Furthermore, by forming each layer continuously in a vacuum, by preventing impurities from adhering to the interface between each layer, it is possible to improve characteristics such as lower operating voltage, higher efficiency, and longer life. it can. In forming each of these layers by a vacuum deposition method, when a plurality of compounds are contained in one layer, it is preferable to co-deposit each boat containing the compounds by individually controlling the temperature. You may. Further, as other film forming methods, a solution coating method, Langmuir Blodget (L
The method B) can be used. In the solution coating method, each compound may be dispersed in a matrix material such as a polymer.

[0037]

As described above, according to the lighting device of the present invention, the red light-emitting element, which is particularly inefficient, can be replaced by the red light-emitting element.
In addition to emitting L light, a light emitting element having a spectrum that can be absorbed and emitted by the red light emitting element of the red light emitting element is laminated on the back surface thereof, and PL emission is also taken out. By making it larger than the light emitting area of the light emitting element, not only can a white light source with good white balance be provided,
Since they are operated independently, illumination with high efficiency and various color tones can be performed, and a novel surface-emitting type lighting device can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a blue / red / green laminated lighting device.

FIG. 2 shows an emission spectrum.

FIG. 3 is a cross-sectional view of a stacked lighting device.

FIG. 4 is a cross-sectional view of another laminated lighting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3B Blue light emitting layer 3R Red light emitting layer 3G Green light emitting layer 11 Blue light emitting element 12 Red light emitting element 13 Green light emitting element

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hisanori Sugiura 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Terms (reference) 3K007 AB00 AB04 BA05 CB01 DA01 DB03 EB00

Claims (15)

[Claims] And a driving means for generating an electric current, a pair of transparent electrodes disposed on a transparent substrate, and at least two light emitting elements disposed between the transparent electrodes. The wavelength region and a part or all of the light absorption wavelength region of the light emitting layer included in the second light emitting element are the same wavelength region, and the second light
A lighting device, comprising: a light emitting element. 2. The lighting device according to claim 1, wherein the first light emitting element emits green or yellow light and the second light emitting element emits red light. 3. A light emitting color of the first light emitting element is in a blue area, a light emitting color of the second light emitting element is in a red area,
The lighting device according to claim 1, further comprising a third light emitting element having a light emission color in a green region in a light emitting direction of the second light emitting element. 4. The lighting device according to claim 1, wherein a reflection layer is provided on a side opposite to a light emitting direction of the lighting device. 5. The lighting device according to claim 4, wherein the reflection layer has an uneven shape. 6. The lighting device according to claim 1, wherein the light emitting layer of the light emitting element is made of an organic material. 7. The lighting device according to claim 1, wherein a hole transport layer is laminated on a light emitting layer of the light emitting element. 8. The lighting device according to claim 1, wherein an electron transporting layer is laminated on a light emitting layer of the light emitting device. 9. A driving means for generating a current, a pair of transparent electrodes disposed on a transparent substrate, and at least two light emitting elements disposed between the transparent electrodes, wherein light emission of the at least two light emitting elements is provided. A lighting device, wherein the first light-emitting element having a different color and emitting light in a red region has a larger emission area than the second light-emitting element having a shorter emission wavelength than the red region. 10. A third light emitting element having a light emitting color in a green or yellow region instead of the second light emitting element on the side opposite to the light emitting direction of the first light emitting element having a light emitting color in a red region. The lighting device according to claim 9, wherein the lighting device is a lighting unit in which are stacked. 11. The lighting device according to claim 9, further comprising a reflective layer on the opposite side of the light emitting direction of the lighting device. 12. The lighting device according to claim 9, wherein the reflection layer has an uneven shape. 13. The lighting device according to claim 9, wherein the light emitting layer of the light emitting element is made of an organic material. 14. The lighting device according to claim 9, wherein a hole transport layer is laminated on a light emitting layer of the light emitting element. 15. The lighting device according to claim 9, wherein an electron transporting layer is laminated on a light emitting layer of the light emitting device.