JP4782791B2 - White organic electroluminescent device using three primary colors - Google Patents

Description

  The present invention relates to a white organic electroluminescent device, and more particularly to an organic electroluminescent device that generates white light by three-color light emission.

  The organic electroluminescent element has the advantages that the light emitting layer forming material is made of an organic substance and emits light by itself, so that it has superior brightness, driving voltage and response speed characteristics and can be multicolored compared to the inorganic electroluminescent element. . Further, when applied to a color display element, it is excellent in color development, is light and thin, and has many advantages as an information display element for portable information communication equipment.

  Among the methods for realizing a color organic electroluminescent device, there is a method using white light. In this case, a color filter is used, but an RGB light emitting layer is used while finely moving a finely patterned metal mask. The defect rate is lower than that of the independent vapor deposition method in which the vapor deposition is sequentially performed and the production process is simple.

  A white organic electroluminescent device using blue and red light emission has the structure of FIG. That is, the anode 1 is formed on the substrate, and the hole transport and blue light emitting layer 10, the hole limiting and red light emitting layer 11, the electron transport layer 12 and the cathode 9 are sequentially stacked on the anode 1, or the hole transport is performed. In addition, the blue light emitting layer 13, the red light emitting layer 14, the hole limiting layer 15, the electron transport layer 16, and the cathode 9 are sequentially stacked to obtain white light.

  These two types of structures have a similar driving principle, and the driving mechanism is as follows.

  When a voltage is applied between the anode 1 and the cathode 9, holes injected from the anode 1 move to the red light emitting layer (11, 14) via the hole transport layer (10, 13), and a high HOMO. The movement to the cathode side is restricted by the hole limiting layer 15 having a (Highest Occupied Molecular Orbital: the highest level orbital filled with electrons) level.

  On the other hand, electrons are injected from the cathode 9 into the red light emitting layer (11, 14) via the electron transport layers 12 and 16, and the interface between the hole transport layer (10, 13) and the red light emitting layer (11, 14) and Carriers recombine on the bulk to generate excitons. While the generated excitons make a transition in the ground state, light is emitted, and blue light is formed in the hole transport layers (10, 13), and red light is formed in the light emitting layers (11, 14) to display white. .

  It is difficult to arbitrarily adjust the distribution of red and blue excitons of an organic electroluminescent device operated according to the driving principle as described above, and the white color purity can be adjusted by largely changing the distribution according to the applied voltage. There is a disadvantage that it is difficult. Furthermore, white is realized with only two colors of blue light emitted by exciton formation in the hole transport layer (10, 13) and red light emitted by exciton generation in the light emitting layer (11, 14), and low efficiency is achieved. Even when a color filter is used, it is difficult to apply to a color display element.

  FIG. 2 shows an energy level structure of a white organic electroluminescent device using three light emitting layers. First, the anode 1 is formed, and a hole transport layer 18, a blue light emitting layer 19, a green light emitting layer 20, and a red light emitting layer 21 are sequentially formed on the anode 1, and then an electron transport layer 22 and a cathode 9 are laminated. Is done.

  The driving principle of the white organic electroluminescent device having such a structure is as follows.

  When a voltage is applied between the anode 1 and the cathode 9, holes and electrons are injected from the anode 1 and the cathode 9. The injected holes and electrons form excitons via the hole transport layer 18 and the electron transport layer 22, and the formed excitons are arbitrarily distributed in the three light emitting layers (19, 20, 21). Emits light while transitioning in the ground state.

  A white organic electroluminescent device that operates according to such a driving principle also has a low luminous efficiency because it is difficult to adjust excitons that contribute to RGB light emission and to match the color purity of white. Further, there is a structural restriction that the blue light emitting layer 19 must always be positioned closer to the anode 1 side than the green 20 and red light emitting layer 21 from the viewpoint of energy level.

  The technical problem to be solved by the present invention is to solve the above-mentioned problems, and to provide an organic electroluminescence device that emits three colors of red, green, and blue uniformly to generate high-efficiency white light. is there.

  In order to solve the technical problem, the present invention uses a white adjustment layer and an exciton confinement structure.

  Specifically, an anode, a hole injection layer formed on the anode, a hole transport layer formed on the hole injection layer, a plurality of light emitting layers formed on the hole transport layer, At least one organic material layer formed between two predetermined layers of the plurality of light emitting layers and having an electron blocking effect, an electron transport layer formed on the light emitting layer, and a cathode formed on the electron transport layer The organic electroluminescent element containing is provided.

  At this time, it is preferable that at least one of the plurality of light-emitting layers has an energy level lower than two adjacent layers on both sides to form an exciton confinement structure, and the plurality of light-emitting layers are green. It is preferable that the light emitting layer, the red light emitting layer, and the blue light emitting layer are formed, and the green light emitting layer is located between the hole transport layer and the red light emitting layer to form an exciton confinement structure.

  Preferably, the plurality of light emitting layers include a green light emitting layer, a red light emitting layer, and a blue light emitting layer, and at least one organic material layer having an electron blocking effect is located between the red light emitting layer and the blue light emitting layer.

  Or an anode, a hole injection layer formed on the anode, a hole transport layer formed on the hole injection layer, a plurality of light emitting layers formed on the hole transport layer, and the light emitting layer An electron transport layer formed on the electron transport layer and a cathode formed on the electron transport layer, wherein at least one of the light emitting layers has a lower energy level than two adjacent layers on both sides thereof. An organic electroluminescent element forming an exciton confinement structure is provided.

  At this time, it is preferable to further include at least one organic material layer formed between two predetermined layers of the plurality of light emitting layers and having an electron blocking effect.

  Embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily carry out the embodiments. However, the present invention can be realized in various and different forms, and is not limited to the embodiments described here.

  3A is a cross-sectional view illustrating a layer structure of a white organic electroluminescent device according to an embodiment of the present invention, and FIG. 3B is a diagram illustrating an energy level structure of the white organic electroluminescent device according to an embodiment of the present invention.

  As shown in FIG. 3A, the white organic electroluminescent device according to the embodiment of the present invention includes an anode 1, a hole injection layer 2, a hole transport layer 3, a green light emitting layer 4, and a red light emitting layer 5 on an insulating substrate 100. , White adjustment layer 6, blue light emitting layer 7, electron transport layer 8, and cathode 9 are sequentially stacked.

  Here, the white adjustment layer 6 formed between the blue light-emitting layer 7 and the red light-emitting layer 5 adjusts the red (R), green (G), and blue (B) emission generation ratio when the thickness is adjusted. be able to. The white adjustment layer 6 adjusts the red, green, and blue emission ratios by appropriately blocking the progress of electrons entering through the cathode 9, the electron transport layer 8, and the blue emission layer 7.

  The green light emitting layer 4 has a lower LUMO (Lower Unoccupied Molecular Orbital) level compared to the hole transport layer 3 and the red light emitting layer 5 disposed on both sides of the green light emitting layer 4. The exciton confinement structure 17 is formed to increase the efficiency of green light emission.

  In the organic electroluminescent device according to the embodiment of the present invention, one or more of the hole transport layer 3, the light emitting layers 4, 5, 7 and the electron transport layer 8 may include a dopant capable of emitting light by hole-electron bonding. . At this time, as the dopant, coumarin 6 (Coumarin 6), rubrene, 4- (dicyanomethylene) -2-methyl-6- (P-dimethylaminostyryl) -4H-pyran (English name: 4) having the following structural formula. -(Dicianomethylene) -2-methyl-6- (P-dimethylaminostyryl) -4H-pyran: DCM), 4- (dicyanomethylene) -2-t-butyl-6- (1,1,7,7-tetramethyl) Jurolidyl-9-enyl) -4H-pyran (English name: 4- (dicyanomethylene) -2-t-butyl-6- (1,1,7,7-tetramethyldiolidyl-9-enyl) -4H-pyran: DCJTB ), Perylene, key used to realize blue color Cridon, 2-methyl-6-2-2,3,6,7-tetrahydro-1H, 5H-benzoquinolizin-9-yl) ethenyl) -4H-pyran-4-ylidene) propane-dinitrile (English name: 2) -Methyl-6- (2- (2,3,6,7-tetrahydro-1H, 5H-benzoquinizin-9-yl) ethenyl) -4H-pyran-4-ylidene) propane-dinitrile: DCM2) be able to.

  As a phosphorescent dopant, red 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum (English name: 2,3,7,8,12,13,17,18-Octaethyl) -21H, 23H-porphine platinum (PtOEP), blue iridium (III) bis [4,6-di-fluorophenyl) -pyridinato-N, C2 ′] picolinate (English name: iridium (III) bis [(4,6 -Di-fluoropheny) -pyridinato-N, C2 '] picolineate: Firric). The dopant content is 1 to 20 wt% with respect to the host forming materials of the hole transport layer 3, the light emitting layers (4, 5, 7) and the electron transport layer 8.

  The host materials for forming the light emitting layers (4, 5, 7) are as follows.

  Aluminum tris (8-hydroxyquinoline) (English name: Aluminum tris (8-hydroxyquinoline)) is used as a host material of the green light emitting layer 4.

  As a host material of the red and / or yellow light-emitting layer 5, (N, N-bis (naphthalen-1-yl) phenyl) -N, N-bis (phenyl) benzidine (English name: N, N′-bis (naphthalen- 1-yl) phenyl) -N, N′-bis (phenyl) benzidine (NPB) and 4,4′-bis (carbazol-9-yl) biphenyl (English name: 4,4′-bis (carbazol)) which is a phosphorescent host -9-yl) biphenyl: CBP).

  As a host material of the blue light emitting layer 7, 4,4′-bis (2,2-diphenyl-ethen-1-yl) -diphenyl (English name: 4,4′-bis (2,2-diphenyl-ethen-1-) yl) -diphenyl: DPVBi). The material for forming the blue light emitting layer 7 is a low molecular weight 4,4 "-bis (2,2-diphenylvinyl-1-yl) -p-terphenylene (English name: 4,4" -bis (2,2 -Diphenylvinyl-1-yl) -p-terphenylene: DPVTP), spiro-DPVBi, etc. can also be used.

  Such a light emitting layer (4, 5, 7) is formed by mixing with the dopant material to increase efficiency and change color.

  The thickness of the light emitting layer (4, 5, 7) is preferably about 100 to 500 mm depending on the contribution to white, and the range varies depending on the characteristics of the material used.

  As a material for forming the hole injection layer 2 and the hole transport layer 3, a material having a triphenylamine group having hole transport properties is used, and 4,4 ′, 4 ″ -Tris (N -3-methylphenyl-N-phenyl-amino) -triphenylamine (English name: 4,4 ', 4 "-Tris (N-3-methylphenyl-N-phenyl-amino) -triphenylamine: m-MTDATA) and N , N-bis (naphthalen-1-yl) phenyl) -N, N-bis (phenyl) benzidine (English name: N, N′-Bis (naphthalen-1-yl) phenyl) -N, N′-bis (phenyl) Benzidine: NPB) or the like is used. The hole injection layer 2 formed on the anode 1 is preferably about 400 to 1500 mm, and the thickness of the hole transport layer 3 is preferably about 100 to 500 mm.

  In the organic electroluminescent device according to the embodiment of the present invention, a substrate used in a normal organic EL device is used as the insulating substrate 100. However, a glass substrate excellent in transparency, surface smoothness, ease of handling, and waterproofness or It is preferable to use a transparent plastic substrate.

  As the anode 1 forming material, indium tin oxide (ITO), tin oxide, zinc oxide, etc., which is transparent and excellent in conductivity, is used, and the thickness is formed to 1000 to 2000 mm.

  Materials for forming the cathode 9 include lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), and magnesium-silver (Mg). Using a metal such as -Ag), the thickness of the film is formed in the range of 500 to 5000 mm.

  Here, the cathode 9 is formed of lithium fluoride (LiF) having a high reactivity and a small work function value in a thickness of 5 to 20 mm, and aluminum having a large work function value in a thickness of 1000 to 2000 mm. It is preferable to form a double layer in terms of device stability and efficiency.

As the electron transporting material forming the electron transport layer 8, tris (8-quinolinolate) -aluminum (Alq ₃ ) having the following structural formula is used, and the thickness of the electron transport layer 8 film is preferably in the range of 100 to 1000 mm.

  N, N′-bis (naphthalen-1-yl) phenyl) -N, N′-bis (phenyl) benzidine (NPB (= α-NPD)) is used as a material for forming the white adjustment layer 6. The thickness is preferably about 10 to 30 mm.

  FIG. 3B is a view illustrating a structure of an organic electroluminescent device according to an embodiment of the present invention according to energy levels.

  A white light-emitting layer 6 having an electron blocking effect is interposed between the red light-emitting layer 5 and the blue light-emitting layer 7, and a green light-emitting layer 4 having a low LUMO level is formed between the hole transport layer 3 and the red light-emitting layer 5. Then, a quantum well is formed to form an exciton confinement structure 17.

  At this time, the thickness of the white adjusting layer 6 is preferably about 10 to 30 mm according to the contribution of light emission, and the amount of electrons accumulated at the interface is injected by the energy barrier by adjusting the thickness to be injected into the red light emitting layer. 5 and the amount of electrons reaching the green light emitting layer 4 can be adjusted within an appropriate range.

  In order to form the exciton confinement structure 17, the green light emitting layer 4 must be formed between the hole transport layer 3 having a well-shaped energy level structure and the red light emitting layer 5.

  The white organic electroluminescent device according to the embodiment of the present invention has the above order, that is, anode / hole injection layer / hole transport layer / green light emitting layer / red light emitting layer / white light emitting layer / blue light emitting layer / electron. The transport layer / cathode is formed in this order, but a yellow light-emitting layer may be formed instead of the red light-emitting layer.

  Here, among the organic films sequentially stacked on the anode 1, the red or yellow light emitting layer 5 and the white adjusting layer 6 may be exchanged with each other depending on the arrangement of energy levels and the host material used. Good. That is, as shown in FIG. 4, the anode, the hole injection layer, the hole transport layer, the green light emitting layer, the white color adjusting layer, the red light emitting layer, the blue light emitting layer, the electron transport layer, and the cathode may be formed in this order. .

  Further, in order to realize a white organic electroluminescence device having high blue light emission efficiency, the light emission efficiency of the blue light emitting layer 7 is increased between the blue light emitting layer 7 and the electron transport layer 23 as shown in FIG. The light emission enhancing layer 23 may be further included. The light emission enhancement layer 23 is composed of multiple layers such as a blue light emitting layer / n-type layer, a blue light emitting layer / p type layer, and a blue light emitting layer / n type layer / p type layer.

  In the white organic electroluminescent device according to the embodiment of the present invention, the excitons generated when the organic electroluminescent device operates using the white adjusting layer 6 are R, G, and B light emitting layers (5, 4, 7). The maximum luminous efficiency of each independent color can be obtained without depending largely on the R, G, B element structure (doping concentration, thickness of the light emitting layer) by adjusting and distributing in accordance with the white contribution. Further, the color purity can be easily changed by adjusting the thickness of the white adjustment layer 6.

  A conventional white element has a hole blocking layer (HBL; reference numerals 11 and 15 in FIG. 1) and a light emitting layer (in FIG. 1). In contrast to obtaining white light by inducing light emission on the interface and bulk between 1 and 11, 14), the white adjustment layer 6 in the present invention adjusts the electron distribution by the electron blocking effect. The excitons that are not used in the blue light-emitting layer 7 contribute to red 5 and green 4.

  In the case of using an HBL material as shown in FIG. 1, the blue light emitting layer (10, 13) must always be placed in front of the anode 1 from the viewpoint of energy level in order to satisfy the light emission mechanism. There are structural limitations in which (11, 14, 21) must be located rearward. However, the white organic electroluminescent device according to the embodiment of the present invention does not have such a structural limitation.

  In addition, the hole transport layer 5 that greatly affects the lifetime of the organic element is doped to contribute to light emission, so that the hole transport layer 5 is exposed to the charge transporting body and is deteriorated due to heat and a lifetime decrease phenomenon. Can be eliminated by an energy transfer phenomenon between the host and the guest, and thus has a structural feature more advantageous for the lifetime of the device.

  The exciton confinement structure 17 is for solving the conventional problem in which only green light emission mainly occurs when the green light emitting layer 4 is placed on the anode 1 side. In the present invention, the exciton confinement structure 17 is used. By doing so, it is possible to prevent such a phenomenon, and it is possible to realize three-color white light by blue 4 and red 5 and green 4 emission. The exciton confinement effect is made possible by the exciton confinement structure 17 that confines excitons injected into the green light emitting layer 4 by dropping them in the quantum well. Therefore, it is possible to overcome the low contribution of green light, which is one of the problems of not only conventional light emitting devices using HBL but also light emitting devices that stack three color light emitting layers to induce white light. it can. In addition, by using the quantum well structure, it is possible to limit the surplus excitons that are not used for blue and red light emission only to the green light emission contribution, and to prevent the non-light emission contribution to the anode 1 side, which may cause a decrease in lifetime. It is advantageous.

  Hereinafter, more specific examples will be presented in consideration of the thickness and material content of each layer.

  The following examples are presented only for the understanding of the present invention, and the present invention is not limited to the following examples.

  The reference numerals in the following description of the embodiments are based on the reference numerals in FIG. 3A.

[First embodiment]
On the glass substrate 100, ITO is deposited to a thickness of 1800 mm to form the anode 1, and m-MTDATA is vacuum-deposited thereon to form the hole injection layer 2 to a thickness of 400 mm.

  Next, NPB is vacuum-deposited on the hole injection layer 2 to form a hole transport layer 3 having a thickness of 100 mm.

  Thereafter, Alq3 and coumarin 6 are simultaneously vacuum deposited on the hole transport layer 3 to form a green light emitting layer 4 having a thickness of 180 mm. At this time, the content of Alq3 was 99% by weight and the content of coumarin 6 was 1.0% by weight.

  Next, NPB and DCM are simultaneously vacuum-deposited on the green light emitting layer 4 in the same manner to form a red light emitting layer 5 having a thickness of 120 mm. At this time, the content of NPB was 96% by weight, and the content of DCM was 4.0% by weight.

  Next, NPB is vacuum-deposited on the red light emitting layer 5 to form a white adjustment layer 6 that can adjust the distribution of excitons. The thickness of the formed white adjustment layer 6 was 17 mm.

  DPVBi is vacuum-deposited on the white control layer 6 to form the blue light-emitting layer 7, and Alq3 is vacuum-deposited on the blue light-emitting layer 7 to form the electron transport layer 8. At this time, the formed thickness was 180 mm for the blue light emitting layer 7 and 120 mm for the electron transport layer 8.

  Further, LiF is vacuum-deposited on the electron transport layer 8 to form a LiF electron injection layer having a thickness of 10 mm, and Al is vacuum-deposited on the LiF electron injection layer to form an Al layer having a thickness of 2000 mm. A cathode 9 is formed.

  In the organic electroluminescent device manufactured by such a method, a part of the organic light emitting device is a blue light emitting layer 7 made of DPVBi due to the electron blocking effect that appears when the white adjusting layer 6 is formed between the red light emitting layer 5 and the blue light emitting layer 7. Light is emitted, and part of the red light-emitting layer 5 doped with DCM emits orange-red light, and the rest contributes to green light emission by the coumarin which is the green light-emitting layer 4 due to the exciton confinement structure.

  FIG. 4 is a view illustrating an emission spectrum, color coordinates, and efficiency characteristics of an organic electroluminescent device manufactured according to the first embodiment of the present invention.

  Referring to the emission spectrum of FIG. 4, it is easily confirmed that the three colors R, G, and B contribute equally to white light emission with peaks near 455 nm, 510 nm, and 590 nm corresponding to the three colors R, G, and B. it can. The color coordinates of the white light emitted at this time are (0.33, 0.38), and the light emission efficiency is 6.1 cd / A and 2.3 lm / W.

[Second Embodiment]
The red light-emitting layer 5 was formed by simultaneously vacuum-depositing NPB and rubrene to be 97% by weight of NPB and 3% by weight of rubrene, and the thickness of the white control layer 6 was changed to 19 mm to adjust the color purity. Except for, an organic electroluminescent device is manufactured by the same method as in the first embodiment.

  Accordingly, in the second embodiment, excitons partially contribute to yellow-orange light emission by rubrene of the red light emitting layer 5, and the color purity is adjusted by changing the thickness of the white adjusting layer 6 to remain in blue and green light emission. Child contributes.

  FIG. 5 is a view showing an emission spectrum, color coordinates, and efficiency characteristics of an organic electroluminescent device manufactured according to the second embodiment of the present invention.

  Referring to the spectrum of FIG. 5, all three colors of R, G, and B contribute to color emission with maximum wavelength peaks of 455 nm, 511 nm, and 560 nm. At this time, the color coordinates are (0.28, 0.36), and the luminous efficiency is 6.8 cd / A, 2.5 lm / W.

[Third embodiment]
An organic electroluminescent element is manufactured by the same method as in the second embodiment except that the thickness of the white color adjusting layer 6 is changed to 17 mm.

  The role of the white adjustment layer 6 is to adjust the distribution of electrons that contribute to light emission as mentioned above, which means to adjust the distribution of excitons. Therefore, when the thickness of the white adjustment layer 6 formed between the red light emitting layer 5 and the blue light emitting layer 7 is reduced, the electron blocking effect is reduced and the contribution of the blue light emitting layer 7 is reduced. The contribution of the red light emitting layer 5 is increased. That is, the contributions of green and yellow become larger and the color coordinates change to the longer wavelength side.

  FIG. 6 is a view showing an emission spectrum, color coordinates, and efficiency characteristics of an organic electroluminescent device manufactured according to the third embodiment of the present invention.

  Referring to the spectrum of FIG. 6, it can be seen that this fits well with this expectation, and the color coordinates at this time are (0.31, 0.40), and the luminous efficiency is 7.1 cd / A, 2.3 lm / W. Indicates.

[First comparative example]
An organic electroluminescence device having no exciton confinement structure as compared with the structures of the first to third embodiments of the present invention was manufactured and its characteristics were confirmed.

  An ITO electrode (anode) having a thickness of 1800 mm was formed on a glass substrate, and m-MTDATA was vacuum-deposited thereon to form a hole injection layer having a thickness of 400 mm. Next, NPB was vacuum-deposited on the hole injection layer to form a hole transport layer having a thickness of 100 mm.

  Thereafter, NPB and rubrene were simultaneously vacuum deposited on the hole transport layer to form a 140 mm thick green light emitting layer. At this time, the content of NPB is 97% by weight and the content of rubrene is 3.0% by weight.

  Next, 17 白色 white adjustment layer capable of adjusting the exciton distribution was formed on the green luminescent layer, and Alq3 and coumarin 6 were simultaneously vacuum deposited to form a 100 Å thick red luminescent layer. At this time, the content of Alq3 is 99% by weight and the content of coumarin 6 is 1.0% by weight.

  Further, DPVBi was vacuum deposited on the red light emitting layer to form a 180 mm thick blue light emitting layer.

  Thereafter, an electron transport layer 150 Å is formed on the blue light-emitting layer, LiF is vacuum deposited on the electron transport layer to form a 10 Å thick LiF electron injection layer, and then Al is vacuum deposited on the LiF electron injection layer. Then, an organic EL device was manufactured by forming an Al electrode with a thickness of 2000 mm.

  FIG. 7 is a view showing an emission spectrum, color coordinates, and efficiency characteristics of an organic electroluminescence device manufactured according to the first comparative example.

  Referring to the spectrum of FIG. 7, in the spectrum of the first comparative example in which the exciton confinement effect cannot be expected, the peak in the blue region is significantly reduced, and only the peak in the yellow-green region contributes mainly to obtain white. could not. The color coordinates at this time were (0.37, 0.54) and a light yellow color appeared.

[Second Comparative Example]
Compared with the structures of the first to third embodiments of the present invention, an organic electroluminescent device not forming the white adjusting layer 6 was manufactured and its characteristics were confirmed.

  An ITO electrode (anode) having a thickness of 1800 mm was formed on a glass substrate, and m-MTDATA was vacuum-deposited thereon to form a hole injection layer having a thickness of 370 mm. Next, NPB was vacuum-deposited on the hole injection layer to form a hole transport layer having a thickness of 100 mm. A green light emitting layer and a red light emitting layer were formed without a white adjusting layer thereon. The green light-emitting layer was deposited by mixing NPB and rubrene at 97% by weight to 3% by weight, and the red light-emitting layer was formed by vacuum-depositing DPVBi to a thickness of 200 mm.

  Also, LiF was vacuum-deposited on the electron transport layer 160 Å and the electron transport layer to form a LiF electron injection layer having a thickness of 10 、, and then Al was vacuum-deposited on the LiF electron injection layer to form a 2000 Å thick Al electrode. An organic electroluminescent device was manufactured by forming

  FIG. 8 is a diagram illustrating an emission spectrum, color coordinates, and efficiency characteristics of an organic electroluminescent device manufactured according to a second comparative example.

  Referring to FIG. 8, when no white adjustment layer is formed, all excitons are distributed in rubrene, which is a green light emitting layer, and emit yellow light. That is, no blue light emission occurred because the white adjustment layer that enables blue light emission by the electron blocking effect was not formed. Therefore, the color coordinates are (0.46, 0.47).

  Meanwhile, Table 1 summarizes the results of evaluating the luminance efficiency, the maximum luminance, the quantum efficiency, and the color coordinate characteristics of the organic electroluminescent devices manufactured according to the first to third examples and the first and second comparative examples. It was shown to.

  From Table 1, the organic electroluminescence devices of the first to third examples using the exciton confinement structure and the white adjustment layer of the present invention do not apply either the exciton confinement structure or the white adjustment layer. It was found that white light emission due to three-color light emission contribution was possible as compared with the first and second comparative examples.

  The preferred embodiments of the present invention have been described in detail above, but the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the claims. Forms are also within the scope of the present invention.

  In the organic electroluminescent device of the present invention, the distribution of excitons can be arbitrarily adjusted by introducing a white adjustment layer, and white light can be realized by the contribution of three colors (R, G, B) by the exciton confinement structure. Is possible. As a result, it is easier to adjust the color than the conventional white organic electroluminescent device, which is manufactured depending on the color purity rather than the maximum efficiency of the multiple light emitting layers, or realized by the contribution of different colors. Since the efficiency can be utilized, a highly efficient white element can be manufactured, and white light including all three colors is generated. Therefore, it is easy to convert to a color display using a color filter.

1 is a diagram illustrating an energy level structure of a conventional organic electroluminescent device that obtains white light by laminating blue and red light emitting layers. 1 is a diagram illustrating an energy level structure of a conventional organic electroluminescent device that obtains white light by stacking three light emitting layers. 1 is a cross-sectional view illustrating a layer structure of a white organic electroluminescent device according to an embodiment of the present invention. 1 is a diagram illustrating an energy level structure of a white organic electroluminescent device according to an embodiment of the present invention. 3 is a diagram illustrating an energy level structure of a white organic electroluminescent device according to another embodiment of the present invention. 3 is a diagram illustrating an energy level structure of a white organic electroluminescent device according to another embodiment of the present invention. 1 is a diagram illustrating an emission spectrum of an organic electroluminescent device manufactured according to various embodiments of the present invention. 1 is a diagram illustrating an emission spectrum of an organic electroluminescent device manufactured according to various embodiments of the present invention. 1 is a diagram illustrating an emission spectrum of an organic electroluminescent device manufactured according to various embodiments of the present invention. 2 is a diagram illustrating an emission spectrum, color coordinates, and efficiency characteristics of an organic electroluminescent device manufactured according to two comparative examples. 2 is a diagram illustrating an emission spectrum, color coordinates, and efficiency characteristics of an organic electroluminescent device manufactured according to two comparative examples.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode 9 Cathode 2 Hole injection layer 3, 18 Hole transport layer 4, 20 1st light emitting layer (green)
5, 21 Second light-emitting layer 6 White adjustment layer (White Balancing Layer)
7, 19 Third light emitting layer (blue)
23 emission enhancement layer 8, 12, 16, 22 electron transport layer 10, 13 hole transport and blue light emission layer 11 hole restriction and red light emission layer 14 red light emission layer 15 hole restriction layer 17 exciton confinement structure )

Claims (15)

anode,
A hole injection layer formed on the anode;
A hole transport layer formed on the hole injection layer;
A plurality of light emitting layers formed on the hole transport layer;
At least one organic layer formed between predetermined two layers of the plurality of light emitting layers and having an electron blocking effect;
An electron transport layer formed on the light emitting layer;
A cathode formed on the electron transport layer,
The plurality of light emitting layers includes a green light emitting layer, a red light emitting layer, and a blue light emitting layer,
The green light emitting layer is formed on the hole transport layer, and the red light emitting layer is formed on the green light emitting layer, and the green light emitting layer has a lower LUMO energy level than two adjacent layers on both sides thereof. An organic electroluminescence device characterized by having an exciton confinement structure.   The plurality of light emitting layers include a green light emitting layer, a red light emitting layer, and a blue light emitting layer, and at least one organic material layer having an electron blocking effect is located between the red light emitting layer and the blue light emitting layer. The organic electroluminescent element according to claim 1.   The organic electroluminescent device according to claim 2, wherein at least one of the hole transport layer, the plurality of light emitting layers, and the electron transport layer has 0.1 to 5 wt% of a dopant. .   Examples of the dopant include coumarin 6, rubrene, 4- (dicyanomethylene) -2-methyl-6- (P-dimethylaminostyryl) -4H-pyran (DCM), 4- (dicyanomethylene) -2-t-butyl- 6- (1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran (DCJTB), perylene, quinacridone, DCM2 and phosphorescent dopants 2,3,7,8,12,13 , 17,18-octaethyl-21H, 23H-porphine platinum (PtOEP), iridium (III) bis [4,6-di-fluorophenyl) -pyridinato-N, C2 ′] picolinate (Firpic) The organic electroluminescence device according to claim 3, wherein the organic electroluminescence device is used.   The organic electroluminescent device of claim 1, wherein each of the green light emitting layer, the red light emitting layer, and the blue light emitting layer has a thickness of 100 to 500 mm. The green light-emitting layer contains aluminum tris (8-hydroxyquinoline) as a main material, and the red light-emitting layer has (N, N-bis (naphthalen-1-yl) phenyl) -N, N-bis (phenyl) as a main material. ) Benzidine (NPB) and phosphorescent host 4,4′-bis (carbazol-9-yl) biphenyl (CBP),
The blue light-emitting layer is mainly composed of 4,4′-bis (2,2-diphenyl-ethen-1-yl) -diphenyl (DPVBi), 4,4 ″ -bis (2,2-diphenylvinyl-1-yl). The organic electroluminescent device according to claim 5, wherein the organic electroluminescent device comprises at least one of) -p-terperylene (DPVTP) and spiro-DPVBi.   The organic electroluminescent device of claim 1, wherein the hole injection layer has a thickness of 400 to 1500 mm, and the hole transport layer has a thickness of 100 to 500 mm.   The hole injection layer and the hole transport layer are mainly composed of 4,4 ′, 4 ″ -tris (N-3-methylphenyl-N-phenyl-amino) -triphenylamine (MTDATA) and N, N— The organic electroluminescent device according to claim 7, comprising at least one of bis (naphthalen-1-yl) phenyl) -N, N-bis (phenyl) benzidine (NPB).   The organic electroluminescent device of claim 1, wherein the electron transport layer has a thickness of 100 to 1000 mm.   The organic electroluminescent device of claim 1, wherein the at least one organic material layer having an electron blocking effect has a thickness of 10 to 30 mm.   The at least one organic layer having an electron blocking effect is N, N′-bis (naphthalen-1-yl) phenyl) -N, N′-bis (phenyl) benzidine (NPB (= α-NPD)) as a main material. The organic electroluminescent device according to claim 10, comprising:   The organic electroluminescent device according to claim 1, wherein the anode has a thickness of 1000 to 2000 and is made of at least one of indium tin oxide (ITO), tin oxide, and zinc oxide.   The cathode has a thickness of 500 to 5000 mm, lithium (Li), lithium fluoride (LiF), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium- The organic electroluminescent device according to claim 1, comprising indium (Mg-In), magnesium-silver (Mg-Ag), and at least one of them.   The organic electroluminescent device of claim 13, wherein the cathode comprises a double layer of a lithium fluoride (LiF) layer having a thickness of 5 to 20 mm and an aluminum layer having a thickness of 1000 to 2000 mm.   The plurality of light emitting layers include a green light emitting layer, a red light emitting layer, and a blue light emitting layer, and are formed between the blue light emitting layer and the electron transport layer to increase luminous efficiency, and are formed of an n-type layer and a p-type layer. The organic electroluminescence device according to claim 1, further comprising a light emission enhancement layer including at least one of the above and a blue light emission layer.

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