KR100752620B1 - White organic electroluminescent device and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a white organic electroluminescent device and a method for manufacturing the same, the white organic electroluminescent device comprising: a first electrode formed on a substrate; A first blue light emitting layer formed on the first electrode; A red light emitting layer formed on the first blue light emitting layer; A second blue light emitting layer formed on the red light emitting layer; And a second electrode formed on the second blue light emitting layer. As a result, white luminescent properties with high purity can be obtained, and mass production is good by a simple process.

White light emitting layer, first blue light emitting layer, second blue light emitting layer, red light emitting layer

Description

White Organic Emitting Device and The Method of Manufacturing The Same

FIG. 1A illustrates a structure of a triwave white organic electroluminescent device according to the related art, and FIG. 1B illustrates light emission characteristics of FIG. 1A.

FIG. 2A illustrates a structure of a two-wavelength white organic EL device according to the related art, and FIG. 2B illustrates light emission characteristics of FIG. 2A.

3 is a schematic laminated structure of a white organic electroluminescent device according to an embodiment of the present invention.

4 is a schematic laminated structure of a white organic electroluminescent device according to another embodiment of the present invention.

5A through 5C are graphs of light emission characteristics of the organic light emitting diode according to the above-described embodiment.

* Reference numbers for major components *

31, 41: substrate 32, 42: first electrode

33, 43: hole injection layer 34, 44: hole transport layer

35, 45: light emitting layer 35a, 45a: first blue light emitting layer

35b, 45b: red light emitting layer 35c, 45c: second blue light emitting layer

36, 47: electron transport layer 37, 48: electron injection layer

38 and 49: second electrode 46: hole barrier layer

The present invention relates to a white organic electroluminescent device and a method of manufacturing the same, and more particularly, to a good white organic electroluminescent device and a method of manufacturing the same by improving the color purity by using a simple process.

Recently, the display industry is pursuing small size, light weight and thin film using thin film, and demanding high resolution. In response to these demands, research into display devices using LCDs or organic electroluminescent properties using glass substrates has been conducted to realize miniaturization and thinning using plastic or metal thin films as substrates. In order to realize the next generation plastic display, the organic EL device technology has been attracting attention as the most realistic device fabrication technology existing, and research on this has been concentrated.

FIG. 1A illustrates a structure of a triwave white organic electroluminescent device according to the related art, and FIG. 1B illustrates light emission characteristics of FIG. 1A. FIG. 2A illustrates a structure of a two-wavelength white organic EL device according to the related art, and FIG. 2B illustrates light emission characteristics of FIG. 2A. Referring to the drawings, the white organic EL devices 10 and 20 may include the first electrodes 12 and 22, the hole injection layers 13 and 23, the hole transport layers 14 and 24, and the substrate 11 and 21. Light emitting layers 15 and 25, hole barrier layers 16 and 26, electron transport layers 17 and 27, electron injection layers 18 and 28, and second electrodes 19 and 29. Referring to FIG. 1A, the light emitting layer 15 includes a blue light emitting layer 15a, a green light emitting layer 15b, and a red light emitting layer 15c, and the light emitting layer 25 includes a blue light emitting layer 25a and an orange light emitting layer 25b. do. The operating principle of the organic electroluminescent elements 10 and 20 made of organic materials is to apply current or voltage to both electrodes 12, 22, 19 and 29 formed at both ends of the light emitting layers 15 and 25 having light emission characteristics. Derivation of luminescent properties. The organic EL device may be implemented in various colors according to the type of material constituting the light emitting layer.

In particular, in order to fabricate an organic EL device having a white light emitting property, a light emitting material having a light emitting material having three light colors of red (R), green (G), and blue (B) is laminated as a light emitting layer. Or light emitting materials having mutual complementary relations. In general, the three-wavelength white organic electroluminescent device (see FIG. 1A) stacking the three primary light emitting layers (R, G, B) has excellent color purity, but is not easy to fabricate because a plurality of light emitting layers must be stacked. It is not easy to control and has a disadvantage of low luminous efficiency. In addition, in the case of directly stacking red, green, and blue of the three-wavelength white organic electroluminescent devices, color stability is inferior depending on the applied current or time due to energy potential (see FIG. 1B). In order to solve this problem, a barrier layer can be inserted between the light emitting layers to increase color stability.

On the other hand, the light emitting layer of the two-wavelength white organic electroluminescent device in which the light emitting materials having the complementary color relationship are laminated is formed of, for example, a combination of sky blue and red or blue and orange. The two-wavelength white organic electroluminescent device (see FIG. 2a) has the advantage of being easier to manufacture and higher efficiency than the three-wavelength white organic electroluminescent device, but green has lower luminous characteristics than red and blue (see FIG. 2b). Since color reproducibility is not good, it is difficult to apply in applications requiring high color purity and color reproducibility such as display lighting.

In addition, when manufacturing a conventional two-wavelength or three-wavelength white organic electroluminescent device, a method of widening the color reproduction range by doping the light emitting layer is used. In this case, since the color change is severe depending on the doping concentration of the light emitting layer, Doping control is an important factor in fabrication. Specifically, in order to increase the color purity and fairness of the light emitting layer, the doping concentration of the red light emitting material should be increased. Generally, when the doping concentration is high, the light emitting efficiency decreases, and energy transfer occurs from the red dopant to the neighboring light emitting layer, thereby improving white characteristics. There is a problem in that it is not easy to obtain, and color reproducibility is deteriorated with time.

The present invention has been devised to solve the above problems, and an object of the present invention is to provide a white organic electroluminescent device having improved purity by forming a red light emitting layer doped with a red light emitting material between blue light emitting layers.

It is also an object of the present invention to provide a white organic electroluminescent device having improved productivity only by doping a red light emitting layer.

In order to achieve the above object, according to an aspect of the present invention, a white organic electroluminescent device comprises a first electrode formed on a substrate; A first blue light emitting layer formed on the first electrode; A red light emitting layer formed on the first blue light emitting layer; A second blue light emitting layer formed on the red light emitting layer; And a second electrode formed on the second blue light emitting layer.

Preferably, a hole injection layer is formed on the first electrode, a hole transport layer is formed on the hole injection layer, the electron transport layer is formed on the second blue light emitting layer, and the electrons are formed on the second blue light emitting layer. It further includes an electron injection layer formed between the transport layer and the second electrode. And a regular wall layer formed between the second blue light emitting layer and the electron transport layer. The first blue light emitting layer and the second blue light emitting layer include a blue host and a blue dopant having blue light emission characteristics, and the blue host and the blue dopant constituting the first and second blue light emitting layers are the same blue light emitting material or each other. Another blue light emitting material is used. The red light emitting layer is formed using a red dopant having red light emission characteristics with the blue host. The blue host used for the red light emitting layer is the same as any one of the blue light emitting materials of the blue host used for the first and second blue light emitting layers. The concentration of the red dopant used in the red light emitting layer is 2 to 10% by mass of the blue host. The red light emitting layer has a thickness of 0.5 nm to 10 nm. At least one of the first electrode and the second electrode is a transparent electrode.

On the other hand, according to another aspect of the invention, forming a first electrode on the substrate; Forming a hole injection layer on the first electrode; Forming a hole transport layer on the hole injection layer; Forming a first blue light emitting layer on the hole transport layer; Forming a red light emitting layer on the first blue light emitting layer; Forming a second blue light emitting layer on the red light emitting layer; Forming an electron transport layer on the second blue light emitting layer; Forming an electron injection layer on the electron transport layer and forming a second electrode on the electron injection layer.

The method may further include forming a hole barrier layer between the second blue light emitting layer and the electron transport layer. The hole barrier layer is formed in a thickness range of 1 to 5nm. In the forming of the red light emitting layer, the red light emitting layer is formed by doping a blue host having blue light emission characteristics and a red dopant having red emission characteristics. In the forming of the red light emitting layer, the concentration of the red dopant used in the red light emitting layer is 2 to 10% by mass of the blue host. In the forming of the red light emitting layer, the red light emitting layer is formed in a thickness range of 0.5 nm to 10 nm. In the forming of the first electrode and the forming of the second electrode, at least one of the first electrode and the second electrode is formed as a transparent electrode.

Hereinafter, a white organic electroluminescent device according to the present invention will be described in detail with reference to the drawings showing an embodiment of the present invention.

3 is a schematic laminated structure of a white organic electroluminescent device according to an embodiment of the present invention. Referring to FIG. 3, the white organic EL device 30 includes a substrate 31, a first electrode 32 formed on the substrate 31, a hole injection layer 33, a hole transport layer 34, and a light emitting layer ( 35), an electron transport layer 36, an electron injection layer 37 and a second electrode 38. The light emitting layer 35 includes a first blue light emitting layer 35a, a red light emitting layer 35b, and a second blue light emitting layer 35c.

In order to manufacture the white organic electroluminescent element 30 of the above structure, the board | substrate 31 is prepared first. The substrate 31 uses a glass substrate or a plastic substrate having transparency. The first electrode 32 is formed on the substrate 31. The first electrode 31 also uses a lot of transparent conductive metal oxide. The first electrode 32 deposited on the substrate 31 is patterned according to the shape of the light emitting layer 35 to be formed later.

The hole injection layer 33 is formed on the first electrode 32 to improve the hole injection characteristics from the first electrode 32. On the hole injection layer 33, a hole transport layer 34 for efficiently moving holes injected into the hole injection layer 33 is formed. A light emitting layer 35 having a multi-layer structure for expressing white is formed on the hole injection layer 33. Specifically, a first blue light emitting layer 35a is formed on the hole injection layer 33. The first blue light emitting layer 35a includes a blue host and a blue dopant, and typical blue light emitting materials of the blue host are DPVBi and NPB, and blue light emitting materials of the blue dopant are DSA-amine and Perylene.

The red light emitting layer 35b is formed on the first blue light emitting layer 35a, and the second blue light emitting layer 35c is formed on the red light emitting layer 35b. The red light emitting layer 35b is formed by doping a red dopant which can exhibit red light emission characteristics using a material used in the blue light emitting layer as a host. At this time, the red dopant doped in the red light emitting layer 35b is selected and doped in the range of 2 to 10% by weight, the thickness is generally formed in the range of 0.5 to 10nm. When selecting the above-described doping concentration and the thickness of the red light-emitting layer 35b, it is appropriately selected with the reduction in color purity in mind. Specifically, when the red dopant is heavily doped in the red light emitting layer 35b, the efficiency of the organic EL device decreases, and energy transition occurs from neighboring light emitting layers 35a and 35c having a higher energy gap than red, thereby causing red. Since the light emission characteristics are enhanced, color purity may be degraded. Accordingly, in order to overcome this, the doping concentration of the red dopant is increased and the thickness of the red light emitting layer 35b is relatively reduced compared to the total thickness of the light emitting layer 35, so that the red light emitting layer 35b and the other light emitting layers 35a and 35c adjacent to each other. It controls the amount of red light generated by the energy transfer to.

Next, a second blue light emitting layer 35c is formed on the red light emitting layer 35b. The second blue light emitting layer 35b includes a blue dopant and a blue host, and typical blue light emitting materials of the blue host are DPVBi and NPB, and typical blue light emitting materials of the blue dopant are DSA-amine and Perylene. The thickness of the light emitting layer 35 may be 20 nm to 100 nm by combining the first blue light emitting layer 35a, the red light emitting layer 35b, and the second blue light emitting layer 35c. When the thickness of the light emitting layer 35 is 20 nm and the red light emitting layer is 1 nm, the thickness of any one of the first and second blue light emitting layers 35a and 35c and the thickness of the red light emitting layer 35b are different from each other. It becomes the blue light emitting layer thickness. For example, it is a 1st blue light emitting layer (Xnm) / red light emitting layer (1 nm) / 2nd blue light emitting layer (20-X-1 nm). The red light emitting layer may be introduced in any thickness depending on the efficiency ratio of the blue light emitting layer and the red light emitting layer. The first blue light emitting layer 35a and the second blue light emitting layer 35c may be selected and formed from the above materials. In this case, both layers may be formed of the same material or may be formed of different materials. Can be.

The electron transport layer 36 is formed on the second blue light emitting layer 35c. The electron injection layer 37 is formed on the electron transport layer 36, and the second electrode 38 is formed on the electron injection layer 37. The first electrode 31 and the second electrode 38 may be formed as transparent electrodes, and when the first electrode 31 is formed as a transparent electrode, the second electrode 38 may be formed as an opaque electrode to emit back light. Can be manufactured in a structure. In the case where the first electrode 31 is formed of an opaque electrode and the second electrode 38 is formed of a transparent electrode, it has a top emission structure. On the other hand, when both the first electrode 31 and the second electrode 38 are formed of a transparent electrode, it is a double-sided light emitting structure capable of double-side light emission. As described above, the white organic EL device 30 is manufactured through the above-described manufacturing process.

4 is a schematic laminated structure of a white organic electroluminescent device according to another embodiment of the present invention. Referring to FIG. 4, the white organic EL device 40 includes a substrate 41, a first electrode 42 formed on the substrate 41, a hole injection layer 43, a hole transport layer 44, and a light emitting layer ( 45), a hole barrier layer 46, an electron transport layer 47, an electron injection layer 48, and a second electrode 49. Hereinafter, only the light emitting layer 45 and the refined wall layer 46, which are characteristic components of the present embodiment, will be described in detail, and other components will be described with reference to the description of the embodiment of FIG. 3.

First, the light emitting layer 45 includes a first blue light emitting layer 45a, a red light emitting layer 45b, and a second blue light emitting layer 45c. Representative materials of the first blue light emitting layer 45a include DPVBi, NPB, and the like, and dopants include DSA-amine, Perylene, and the like.

A red light emitting layer 45b is formed on the first blue light emitting layer 45a, and a second blue light emitting layer 45c is formed on the red light emitting layer 45b. The red light emitting layer 45b is formed by doping a red dopant capable of exhibiting red light emission characteristics using a blue light emitting material as a host. At this time, the red dopant doped in the red light emitting layer 45b is selected in the range of 2 to 10% by weight, and the thickness is formed in the range of 0.5 to 10nm. When doping the red dopant in a high concentration it is easy to control the doping concentration can proceed the process simply. When doping the red dopant at a high concentration, the efficiency of the device decreases, and energy transfer occurs from the neighboring light emitting layer having a higher energy gap than red, thereby enhancing the red light emission characteristics. Is not easy. Accordingly, in order to facilitate the fabrication of the white organic electroluminescent device 40, the doping concentration of the red dopant may be increased, but the thickness of the red light emitting layer 45b may be reduced compared to the total thickness of the light emitting layer 45. The amount of red light generated by energy transfer to other adjacent light emitting layers is controlled.

Next, a second blue light emitting layer 45c is formed on the red light emitting layer 45b. Representative materials of the second blue light emitting layer are DPVBi, NPB, and the like, and dopants are DSA-amine, Perylene, and the like. The first blue light emitting layer 45a and the second blue light emitting layer 45b may use the same material or different materials. The light emitting layer 45 may have a thickness of 20 nm to 100 nm by combining the first blue light emitting layer 45a, the red light emitting layer 45b, and the second blue light emitting layer 45c.

For example, when the total thickness of the light emitting layer 45 is 20 nm and the red light emitting layer is 1 nm, the remaining thickness except for the thickness of any one of the first and second blue light emitting layers 45a and 45c and the thickness of the red light emitting layer 45b is obtained. The thickness is the thickness of one blue light emitting layer. That is, the first blue light emitting layer (X nm) / red light emitting layer (1 nm) / second blue light emitting layer (20-X-1 nm). The red light emitting layer may be introduced in any thickness depending on the efficiency ratio of the blue light emitting layer and the red light emitting layer.

The hole barrier layer 46 is formed on the second blue light emitting layer 45c. The hole barrier layer 46 blocks the movement of holes from the first electrode 41 to the upper part of the light emitting layer, thereby controlling color change of the light emitting layer. It is preferable that the hole barrier layer 46 has a thickness that enables excitons to transfer poster energy from the light emitting layer to the electron transport layer and is deposited to be thinner than the poster transition radius to obtain light emission characteristics in the electron transport layer. In FIG. 1, a regular wall layer 46 is formed in a thickness range of 1 nm to 5 nm.

5A through 5C are graphs of light emission characteristics of the organic light emitting diode according to the above-described embodiment. 5A to 5C, the horizontal axis represents wavelength and the vertical axis represents standard light emission intensity. In order to confirm the uniformity of white light emission characteristics of the white organic electroluminescent device, an experiment is performed in which the amount of current applied per unit area of the light emitting layer is different. Proceeded.

First, in the present experiment, FIG. 5A shows a case in which 2.5 mA (㎃ / cm 2) is applied per unit area, FIG. 5B shows a case in which 10 mA (㎃ / cm 2) is applied per unit area, and FIG. 5C shows 20 mA (㎃ / ㎠) per unit area. A graph of light emission characteristics was obtained according to the case of applying. In the case of the graph (a), the graph (b), and the graph (c), all show the same emission intensity at the same wavelength and show the same color coordinates (0.31, 0.31). As a result, when the white organic electroluminescent device is manufactured by using the method of manufacturing the white organic electroluminescent device according to the present invention, even when the current is applied differently, the emission characteristics (luminescence intensity, color coordinate, etc.) are very stable. It can be seen that the characteristics can be obtained.
Although the present invention has been described with reference to the embodiments illustrated in the accompanying drawings, it is merely an example, and those skilled in the art may understand that various modifications and equivalent other embodiments are possible. There will be.

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As described above, the red light emitting layer doped with a high concentration of the red dopant is thinly formed between the blue light emitting layers to maintain the color balance of red and blue to obtain pure white light emitting characteristics. In addition, only a step of doping the red light-emitting layer can obtain a high purity white light-emitting characteristic, thereby simplifying the process and improving productivity.

Claims (16)

A first electrode formed on the substrate; A first blue light emitting layer formed on the first electrode; A red light emitting layer formed on the first blue light emitting layer; A second blue light emitting layer formed on the red light emitting layer; And A second electrode formed on the second blue light emitting layer White organic electroluminescent device comprising a. The method of claim 1, A hole injection layer formed on the first electrode, a hole transport layer formed on the hole injection layer and formed under the first blue light emitting layer, an electron transport layer formed on the second blue light emitting layer, and the electron transport layer and the The white organic electroluminescent device further comprising an electron injection layer formed between the second electrode. The method of claim 2, The white organic electroluminescent device further comprising a regular wall layer formed between the second blue light emitting layer and the electron transport layer. The method of claim 3, The first blue light emitting layer and the second blue light emitting layer include a blue host and a blue dopant having blue light emission characteristics, and the blue host and the blue dopant constituting the first and second blue light emitting layers are the same blue light emitting material or each other. White organic electroluminescent element using another blue light emitting material. The method of claim 4, wherein The red light emitting layer is formed of a white organic electroluminescent device using a red dopant exhibiting red light emission characteristics with the blue host. The method of claim 5, The blue host used in the red light emitting layer is the same material as any one of the blue light emitting material of the blue host used in the first and second blue light emitting layer. The method of claim 5, The concentration of the red dopant used in the red light emitting layer is 2 to 10% mass ratio of the blue host. The method of claim 5, The thickness of the red light emitting layer is 0.5nm ~ 10nm white organic electroluminescent device. The method of claim 1, At least one of the first electrode and the second electrode is a transparent electrode. Forming a first electrode on the substrate; Forming a hole injection layer on the first electrode; Forming a hole transport layer on the hole injection layer; Forming a first blue light emitting layer on the hole transport layer; Forming a red light emitting layer on the first blue light emitting layer; Forming a second blue light emitting layer on the red light emitting layer; Forming an electron transport layer on the second blue light emitting layer; Forming an electron injection layer on the electron transport layer Forming a second electrode on the electron injection layer Method of manufacturing a white organic electroluminescent device comprising a. The method of claim 10, And forming a hole barrier layer between the second blue light emitting layer and the electron transporting layer. The method of claim 11, The hole barrier layer is a method of manufacturing a white organic electroluminescent device is formed in the thickness range of 1 ~ 5nm. The method according to claim 10 or 11, wherein And forming the red light emitting layer by doping a blue host having blue light emission characteristics and a red dopant having red emission characteristics. The method of claim 13, wherein the forming of the red light emitting layer The concentration of the red dopant used in the red light emitting layer is a method of manufacturing a white organic electroluminescent device is 2 to 10% mass ratio of the blue host. The method of claim 13, wherein the forming of the red light emitting layer The red light emitting layer is a method of manufacturing a white organic electroluminescent device is formed in a thickness range of 0.5nm ~ 10nm. The method of claim 10, In the forming of the first electrode and the forming of the second electrode The manufacturing method of the white organic electroluminescent element which forms at least one of the said 1st electrode and the said 2nd electrode as a transparent electrode.

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