JP2002216973A - Light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white light emitting device which can be simply and easily manufactured at a low cost and further in which there is no problem in its life and reliability. SOLUTION: In the light emitting device wherein an electric field applying light emitting layer is pinched between a pair of electrodes either of which has an light permeation at least and the light is discharged outside through the light permeating electrode, the other electrode has a light reflectivity or light reflection treatment. Between the electrodes, at least the electric field applying light emitting layer and a light excitation light emitting layer wherein the light is excited by light emission from the electric field applying light emitting layer and wherein the light of a different wavelength is emitted are laminated, and the electric field applying light emitting layer is arranged in a close vicinity of the light permeating electrode to emit light outside, and the light excitement light emitting layer is arranged in a close vicinity of the opposing electrode having the light reflectivity or the light reflection treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-luminous light emitting device such as an electroluminescence (EL) device and a display device using the same.

[0002]

2. Description of the Related Art Electroluminescent (EL) elements and light emitting diode (LED) elements are
Since it does not generate heat, it is promising as a light-emitting element capable of high energy conversion efficiency. In addition, there has been considered an unprecedented application field utilizing the characteristics of no heat generation and thinness. It is also considered to manufacture a display device such as a liquid crystal using them, and development is being conducted.

[0003] When these are used for illumination, it is important to realize sufficient white light emission at all times. In the case of a display device, color display can be performed by a color filter system widely used in liquid crystals as long as sufficient white light emission is obtained, as well as monochrome. Therefore, since obtaining white light emission is important, many studies have been made so far.

The technical report of the Institute of Electronics, Information and Communication Engineers, OME94-78 (1995), p1, by Sato describes in detail the development of white light emission of organic EL. Organic EL is EL or L
Among the EDs, the development of materials is very active, especially as a pure light-emitting element for lighting or as a display device, because of the wide potential of material development, low voltage operation, and easy upsizing. ing.

According to Sato, a method for obtaining white light emission is as follows. 1. Single layer type mixed with RGB dyes 2. Layered type of RGB light emitting layer Broadening of the emission spectrum using exciplex formation at the interface between the hole transport layer and the light emitting layer is mentioned. Sato tries to achieve white light emission using the three primary colors of RGB light, but this may be two colors having a complementary color relationship. For example, blue and yellow.

In the method of mixing dyes to obtain white light emission, it is not easy to make the emission life of various types of dyes the same. Inevitable.

The structure of the laminated type is described in the above-mentioned Sato's paper, but a light emitting layer, which is usually one layer, is laminated between electrodes in multiple layers. As a result, the applied electric field per layer decreases, and the operating voltage increases. Also, since it is not easy to make the light emitting life of each light emitting layer the same,
It is conceivable that even in the initial stage, even if the color is white, it is a factor that the luminescent color changes with the lapse of time.

The above-mentioned exciplex is a dimer composed of different types of atoms and molecules. At the interface between the carrier transport layer and the light emitting layer, the excited state atoms or molecules and the ground state atoms or molecules are bonded. Is formed,
For this reason, it is difficult to completely control the generation and disappearance,
The method using the exciplex formation is the method with the most reliability problem.

There are several other methods for achieving white light emission. Hereinafter, for the sake of simplicity, the description will be made not with three colors but with two complementary colors. FIG. 2 is an example of a sectional view of these white light emitting elements. 2 is a light-transmitting substrate, 3 and 11 are transparent electrodes, and 4 is a counter electrode. Reference numeral 5 denotes a light emitting layer that emits light of one of complementary colors, and reference numeral 10 denotes a light emitting layer that emits light of the other of the complementary colors. This is a method in which the light emitting layers 5 and 10 are sandwiched by electrodes and laminated. 8 and 12 are light emitting layers 5 and 10 respectively.
, And white light emission is realized by mixing these colors.

In this case, unlike Sato et al., An increase in the operating voltage can be avoided, but the operation circuit becomes complicated, and the feasibility is poor especially for use as a display device. The light emitting layer 10
Must be light transmissive for both substrates. Inorganic EL or the like by AC operation is possible, but in organic EL of DC operation in which electrons and holes are injected to operate, it is difficult to inject electrons by the light transmissive electrode and it is difficult to realize. In addition, since the operation circuit becomes complicated, the cost naturally increases.

FIG. 3 shows another example of these white light emitting elements. Reference numeral 13 denotes a photoexcitation light-emitting layer in which the complementary color 14 is photoexcited by the light emission 8 from the light-emitting layer 5. This device, in which a photoexcited light emitting layer is disposed close to a light transmitting electrode, is disclosed in
It is described in 74974. In this method in which the photoexcited light emitting layer is arranged on the light extraction side, it is necessary to adjust the fluorescence quantum efficiency of the photoexcited light emitting layer to around 50%. However, the fluorescence quantum efficiency of many photoexcited light emitters is very large and close to 100%. Therefore, as a result, the photo-excited complementary color 14 becomes stronger,
It is difficult to obtain white light emission.

FIG. 4 shows another example of these white light emitting elements. Reference numeral 13 denotes a photoexcitation light-emitting layer in which the complementary color 14 is photoexcited by light emission 8 from the light-emitting layer 5 as in FIG. By processing the photoexcited light emitting layer into a fine shape, the light emission 8 and 14 appear mixed to the observer, and white light emission is obtained. However, in this method, it is inevitable that the photoexcited light emitting layer 14 is finely patterned, and the production is complicated and the production cost is increased.

[0013]

In various applications, white light-emitting elements have been demanded, and various EL-LEDs can be easily and inexpensively manufactured despite various proposals. Actually, a structure having no problem in terms of life and reliability has not been obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a white light-emitting device which can be easily and inexpensively manufactured and has no problem in terms of life and reliability. And

[0015]

In order to achieve the above object, a light emitting device according to the present invention has an electric field application light emitting layer sandwiched between a pair of electrodes, at least one of the electrodes being light transmissive and having a light transmissive property. In a light-emitting device that emits light to the outside through a conductive electrode, the other electrode is light-reflective or light-reflected, and at least an electric field applied light-emitting layer and A light-excited light-emitting layer that emits light of a different wavelength, which is light-excited by light emission, is laminated, the electric field-applied light-emitting layer is disposed close to a light-transmitting electrode that emits light to the outside, and the light-excited light-emitting layer is light-reflective. Alternatively, it is characterized by being arranged close to a counter electrode subjected to reflection processing.

Further, in the light emitting device according to the present invention, the laminate including the electric field applied light emitting layer and the photoexcited light emitting layer sandwiched between the electrodes is a semiconductor compound, and the electric field applied light emitting layer is more than the photoexcited light emitting layer. The light-excited light-emitting layer has a stronger electron-transport property than the electric-field-applied light-emitting layer, and the light-transmissive electrode that emits light to the outside is a positive electrode, and the light-reflective or reflective electrode is a counter electrode. Is operated as a negative electrode.

Further, the light emitting device according to the present invention is characterized in that the light emission of the electric field applied light emitting layer and the light emission of the photoexcited light emitting layer have a complementary color relationship, and emits white light to the outside by mixing these colors.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The light emitting device of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a structural sectional view of the light emitting device 1 of the present application. 2 is a light transmitting substrate, 3 is a light transmitting electrode, 4
Is a counter electrode. The counter electrode 4 is a light-reflective electrode made of metal or the like or a light-reflective electrode.

In a carrier injection type device such as an organic EL device, a metal having a low work function such as Al (aluminum) is suitable for at least one electrode in order to inject electrons at a high efficiency. Strong reflectivity.

In an AC electric field element such as an inorganic EL element, it is desirable that both electrodes are equivalent, and therefore, it is preferable that the opposite electrode is also a transparent electrode. In this case, a method of imparting light reflectivity by performing metal evaporation on the outside of the electrode or the like is used.

Reference numeral 5 denotes an electric-field-applied light-emitting layer that emits light of one of complementary colors, and reference numeral 6 denotes a light-excited light-emitting layer in which complementary light 9 is photoexcited by light emission 8 from the light-emitting layer 5. Light emitted from the light emitting center 7 in the light emitting layer 5 is emitted not only to the transparent electrode side but also to the reflective electrode side with the same intensity. Therefore, the emitted light reaches the light-excited light-emitting layer 6 and, after exciting the light emission 9, is reflected by the counter electrode 4 and emitted to the transparent electrode side. Light emission 8 and light emission 9 having two complementary colors are mixed to obtain white light emission.

FIG. 5 is an energy diagram of each layer and electrodes of the white light emitting device of the present invention. As shown in FIG. 5, the layer 5 (electroluminescent layer) on the light transmissive electrode side has a hole transporting property, and the layer 6 (photoexcited light emitting layer) on the light reflective electrode side has an electron transporting property and serves as a hole blocking layer. By stacking and combining the materials in the order of energy, only the layer 5 emits light when an electric field is applied, eliminating the reliability problem due to the difference in the lifetime of the plurality of light emitting layers as in the conventional example. .

In FIG. 5, the vertical direction indicates the energy order, and schematically shows the movement of holes 15 and electrons 16. If the difference between the LUMO levels of both the hole transporting and electron transporting layers is large and the difference between the HOMO levels of the layer 6 on the light reflective electrode side is sufficiently low, the holes 15 are blocked by the layer 6,
Carrier recombination occurs only in the layer 5 to emit light.

Further, unlike FIG. 3, white light emission with high purity can be obtained even if many photoexcited luminous bodies having high fluorescence quantum efficiency are used. Further, as shown in FIG. 4, fine processing of the luminous body is not required, so that the luminous body can be simply and inexpensively manufactured.

Since the photoexcited light emitting layer 6 is excited by the light emission 8 from the electroluminescent layer 5, the energy of the light emission 8 must be higher than that of the light emission 8. That is, the wavelength of the light emission 8 must be shorter than the wavelength of the light emission 9. As the wavelength at which white light is emitted by color mixture in a complementary color relationship, it is preferable that the light emission 9 be blue and the light emission 9 be yellow or orange.

Since stable white light emission can be easily obtained in this manner, the electrodes 3 and 4 are processed into fine dot shapes in the same manner as liquid crystal or the like, and a plurality of color filter coloring layers corresponding to the electrode structure are added. A color display device can be manufactured by connecting a driver circuit for applying an information signal.

Next, the present application will be described in more detail based on embodiments. Note that the present application is not limited to this embodiment.

Example 1 As a first example of the present invention, an electric field applied light emitting device 1 shown in FIG. 1 was manufactured. Glass as the transparent substrate 2, ITO as the transparent electrode 3, and opposing reflective electrode 4
Was used as MgAg.

A hole transporting PVK (polyvinyl carbazole) of 400 ° on the ITO substrate, and a TAZ (triazole) acting as a hole blocking layer with an electron transporting property of 100% are deposited on the ITO substrate.
ÅLaminated. The device was completed by vapor-depositing MgAg and finally sealing the device so that it was immersed in moisture.

When a voltage was applied with ITO being positive polarity and MgAg being negative polarity, the current density was 0.5 mA / m2.
Blue light emission with a luminance of 100 cd / m ² or more could be confirmed from a place exceeding m ² , but white light emission was not obtained. It is known that blue light emission is emitted from PVK, and it was confirmed that only PVK emitted light in the PVK / TAZ laminated structure.

When rubrene, which is a yellow pigment, was mixed at 1.5% with TAZ in the same configuration, white light emission was confirmed.
By arranging a fluorescent dye layer having a complementary color relationship with the light emission from the light emitting layer on the reflective electrode side, white light emission could be obtained by light emission from the light emitting layer and light emission by photoexcitation.

Furthermore, color display could be performed by combining a white light emission according to the present invention with a color filter. According to the invention of the present application, it has become possible to easily and inexpensively produce a white light-emitting element having no color change over time.

[0033]

According to the present invention, it is possible to easily and inexpensively manufacture a white light-emitting element having no change in color over time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a light emitting device of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a conventional light emitting element.

FIG. 3 is a cross-sectional view illustrating a configuration of a conventional light emitting device.

FIG. 4 is a cross-sectional view illustrating a configuration of a conventional light emitting device.

FIG. 5 is a diagram showing an energy diagram of a light emitting device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light emitting element 2 Substrate 3 Transparent electrode 4 Counter electrode 5 Electric field application light emitting layer 6 Photoexcitation light emitting layer 7 Light emission center 8, 9 Light emission 15 Hole 16 Electron

Claims (3)

[Claims] 1. A light emitting device in which an electric field application light emitting layer is sandwiched between a pair of electrodes, at least one of the electrodes is light transmissive and emits light to the outside through the light transmissive electrode. Alternatively, a light reflection treatment is performed, and at least an electric field applied light emitting layer and a light excited light emitting layer that emits light of a different wavelength and are photoexcited by light emission from the electric field applied light emitting layer are laminated between the electrodes. Wherein the electric field applied light emitting layer is disposed close to a light transmissive electrode which emits light to the outside, and the light excited light emitting layer is disposed close to a light reflective or reflection-treated counter electrode. apparatus. 2. A laminate comprising an electric field applied light emitting layer and a photoexcited light emitting layer sandwiched between electrodes is a semiconductor compound. The electric field applied light emitting layer has a stronger hole transporting property than the photoexcited light emitting layer. The light-excited light-emitting layer has a higher electron-transporting property than the electric-field-applied light-emitting layer.
2. The light emitting device according to claim 1, wherein the opposing electrode which has been subjected to light reflection or reflection processing is operated as a negative electrode. 3. The light emitting device according to claim 1, wherein the light emission of the electric field application light emitting layer and the light emission of the photoexcited light emitting layer have a complementary color relationship, and white light is emitted outside by mixing these colors.