JP2007234241A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element that is not only capable of achieving step simplification and cost-reduction when forming a light-emitting layer, but also capable of improving light-emission efficiency. <P>SOLUTION: The organic EL element 1 is composed so that a green light-emitting layer, a red light-emitting layer, and a blue light-emitting layer are formed by a three-color-tone system. The organic EL element is also composed so as to have the blue light-emitting layer B, the red light-emitting layer R, and the green light-emitting layer G as the light-emitting layer for respectively forming a blue light-emitting region 11, a red light-emitting region 12, and a green light-emitting region 13. The green light-emitting layer G has a green light-emitting layer extension G1 provided so as to cover a face on the cathode side of the red light-emitting layer R in the red light-emitting region 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic EL (electroluminescence) element, and in particular, a structure in which a red light emitting layer, a green light emitting layer, and a blue light emitting layer for forming red, green, and blue light emitting regions are respectively formed by a thin film forming method. The present invention relates to an organic EL element having

  A display composed of organic EL elements has a wide viewing angle, a high contrast, a fast response speed, and can be easily reduced in weight and thickness. Accordingly, the organic EL element is expected to be applied as a display for portable devices. However, since the portable device is driven by a battery, the display is required to have low power consumption. In addition, as the price of portable devices decreases, there is a demand for cost reduction of displays.

  When configuring a display with organic EL elements, there are three types of full-color methods: a method combining white light emission and a color filter, a method combining blue light emission and a color conversion filter, and a RGB color separation method. It has been.

  Among the above three methods, the RGB coating method can make use of the characteristics of the organic EL element using the organic light emitting material. In this method, it is possible to use a bright luminescent color possessed by the organic luminescent material itself. Therefore, NTSC color reproducibility can be enhanced in full color display.

  For example, in a method combining white light emission and a color filter, the color reproducibility is limited by the performance of the color filter, so the color reproducibility is as low as 40 to 50%. In contrast, the RGB color separation method can achieve high color reproducibility such as 70 to 100%. Such color reproducibility is at the same level as CRT and PDP (plasma display panel), and therefore, a very vivid image can be displayed.

  The organic EL display manufacturing method using the RGB coating method is configured by forming individual light emitting layers in the light emitting regions of the three primary colors R (red), G (green), and B (blue). ing. In this case, the red light emitting layer, the green light emitting layer, and the blue light emitting layer were each formed by a thin film forming method such as a vapor deposition method using a shadow mask. Therefore, the three primary colors have to be applied separately, in other words, each light emitting layer has to be individually deposited using a mask. Therefore, the operation of aligning each mask on the substrate on which the light emitting layer is formed is complicated, and there is a risk of mask displacement. When mask displacement occurs, color displacement occurs on the screen and image quality is significantly impaired.

  Therefore, the RGB three-color coating method requires three fine shadow masks and has to position the three shadow masks with high accuracy. For this reason, an expensive fine shadow mask must be prepared, and the three shadow masks must be positioned with high accuracy, which requires time for positioning and tends to be complicated. . Therefore, the cost of the organic EL element may be increased.

As an organic EL element obtained by the three-color coating method, the following Non-Patent Document 1 discloses the organic EL element shown in FIG. In the organic EL element 101, a hole injection layer 104, a hole transport layer 105, a light emitting layer 106, and an electron transport layer 107 are disposed between the anode 102 and the cathode 103. In the light emitting layer 106, a red light emitting layer 106a, a green light emitting layer 106b, and a blue light emitting layer 106c are formed by a three-color coating method. Here, the red light emitting layer 106a is formed in the red light emitting region, and the green light emitting layer 106b is formed in the green light emitting region, and the blue light emitting layer 106c is not only the blue light emitting region but also one side of the other two color light emitting layers. Is also formed to cover. According to this structure, the blue light emitting layer 106c may be formed in the entire region where the light emitting layer is formed. Therefore, it is only necessary to use two types of masks: a mask for forming the red light emitting layer 106a and a mask for forming the green light emitting layer 106b. That is, the number of masks used can be reduced from 3 to 2.
H. D. Kim, K. J. Yoo, M. H. Kim, S. T. Lee and H. K. Chung, “Challenges to Am-oled Technology for Mobile Display”, IDW / AD'05, pp 267-270, (2005)

  In the organic EL element 101 described in Non-Patent Document 1, the number of masks to be used can be reduced, thereby reducing costs and improving productivity.

  However, when an organic EL element is used as a display, not only cost reduction but also improvement in luminous efficiency is strongly demanded to achieve low power consumption as described above.

  An object of the present invention is an organic EL element obtained by a three-color coating method excellent in color reproducibility in view of the current state of the prior art, and not only can reduce costs and improve productivity, It is an object of the present invention to provide an organic EL device that is excellent in luminous efficiency and can achieve low power consumption.

  An organic EL device according to the present invention includes an anode, a cathode, and a light emitting layer disposed between the anode and the cathode, and each of the light emitting layer includes a red light emitting region, a blue light emitting region, and a green light emitting region. A green light-emitting layer having a red light-emitting layer, a blue light-emitting layer, and a green light-emitting layer for forming the green light-emitting layer so as to cover the cathode-side surface of the red light-emitting layer in the red light-emitting region The green light emitting layer is formed so as to reach not only the green light emitting region but also the red light emitting region.

  Usually, the energy level of the lowest unoccupied molecular orbital (LUMO) of the host material used in the red light emitting layer is lower than the LUMO energy level of the host material in the green light emitting layer. Accordingly, in the portion where the green light emitting layer extension is stacked on the red light emitting layer, the electrons that have moved from the cathode side to the green light emitting layer extension are trapped by the red light emitting layer, and the recombination region becomes the red light emitting layer. It will be localized. Further, since the excitation energy of electrons in the green light emitting layer is larger than the excitation energy of electrons in the red light emitting layer, excitons generated in the red light emitting layer hardly move to the green light emitting layer side. On the other hand, the hole transport layer located on the anode side has blue fluorescence, and this excitation energy is larger than the excitation energy in the red light emitting layer. Therefore, excitons in the red light emitting layer are unlikely to move to the hole transport layer side. Therefore, excitons are effectively confined in the red light emitting layer, and the light emission efficiency of the red light emitting layer is effectively increased.

  In the present invention, more preferably, the green light emitting layer further has a second green light emitting layer extension that covers the cathode side surface of the blue light emitting layer, and the green light emitting layer comprises a green light emitting region and the red light. It is formed in all the light emitting areas which consist of a light emitting area and the blue light emitting area.

  In this case, since a mask is not required when forming the green light emitting layer, the number of masks to be used can be reduced from three to two, and cost can be reduced and productivity can be improved. .

  In addition, when the green light emitting layer second extension covers the cathode side surface of the blue light emitting layer, the LUMO of the host material of the green light emitting layer and the LUMO of the host material of the blue light emitting layer are substantially the same, Electrons that have moved from the cathode side are quickly moved to the blue light emitting layer. Since the hole transport layer is located on the surface of the blue light-emitting layer opposite to the side where the green light-emitting layer second extension is laminated, the electrons are transferred to the hole transport layer side in the blue light-emitting layer. The electron concentration increases in the hole transport layer side region of the blue light emitting layer. Therefore, the recombination region is localized in the region near the interface of the blue light emitting layer with the hole transport layer. Therefore, light emission occurs only from the blue light emitting layer, and no green light emission occurs, and the light emission efficiency in the blue light emitting layer is improved.

  In the present invention, preferably, the light emitting layer is composed of a plurality of thin films formed by a thin film forming method using a mask. In this case, since the green light emitting layer may be formed so as to have the green light emitting layer extension, or the green light emitting layer extension and the green light emitting layer second extension as described above, the number of masks to be used is reduced. Alternatively, the mask alignment process can be simplified.

  In the organic EL device according to the present invention, preferably, the area of the green light emitting region is smaller than the areas of the blue light emitting region and the red light emitting region. Usually, the green light emitting area is made smaller than the light emitting areas of the other two colors. This is because green has the highest visibility. However, in the light emitting region having the smallest area, color misregistration easily occurs when the light emitting layer is formed by the thin film formation method. However, in the present invention, the green light emitting layer has a relatively large region so as to have the green light emitting layer extension. What is necessary is just to form. Therefore, color misregistration hardly occurs.

  In the organic EL element according to the present invention, the green light emitting layer has a green light emitting layer extension, and the green light emitting layer extension is provided so as to cover the cathode side surface of the red light emitting layer in the red light emitting region. . Therefore, after forming the blue light emitting layer and the red light emitting layer, when forming the green light emitting layer, the mask for forming the green light emitting layer is the same as the mask used when the red light emitting layer is formed. It suffices to position only along the edge with the light emitting region, and the mask for forming the green light emitting layer does not need to be positioned with high accuracy in other portions. Therefore, the positioning operation can be simplified, the cost can be reduced, and color misregistration hardly occurs.

  In addition, the light emission efficiency of the red light emitting layer is enhanced by overlapping the green light emitting layer on the red light emitting layer. Accordingly, it is possible to provide an organic EL element that has high luminous efficiency and can reduce power consumption.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

(Abbreviations and contents of materials used)
The meaning and structure of the abbreviations of the materials used in the following examples are as follows.

(1) NPB
NPB is N, N′-di (1-naphthyl) -N, N′-diphenylbenzidine and has the following structure.

(2) TBADN
TBADN is 2-tertiary-butyl-9,10-di (2-naphthyl) anthracene and has the following structure.

(3) BCP
BCP is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline and has the following structure.

(4) HAT-CN6
HAT-CN6 is hexaazatriphenylenehexacarboxylic nitrile and has the following structure.

(5) Compound R
Compound R is dibenzotetraphenylperifuranthene and has the following structure.

(6) C545T
C545T is 10- (2-benzothiazolyl) -2,3,6,7-tetrahydro-1,1,7,7-tetramethyl1-1H, 5H, 11H- [1] benzopyrano [6,7,8, ij] quinolinidin-11-one, which has the following structure.

(7) TBP
TBP is 2,5,8,11-tetra-tertiary-butylperylene and has the following structure.

Example 1
FIG. 1A is a schematic front sectional view showing an organic EL element according to Example 1 of the present invention, and FIG. 1B is a front view schematically showing a light emitting layer thereof.

  The organic EL element 1 is formed by laminating a plurality of thin films on a substrate 2 by a thin film forming method. In this embodiment, the substrate 2 is made of a glass substrate. However, as the substrate 2, a TFT substrate may be used to form an active display type organic EL display.

  An anode 3 is formed by forming an ITO film on a substrate 2 made of a glass substrate by a thin film forming method. On the anode 3, as a hole injection layer, a CFx film having a thickness of 1.5 nm and a HAT-CN6 film having a thickness of 5 nm were formed. That is, the hole injection layer 6 was formed by a laminated film of a CFx (fluorocarbon) film and a HAT-CN6 film.

  Next, a hole transport layer 7 made of a 30 nm NPB film was formed on the hole injection layer 6 by vacuum deposition.

  Thereafter, a light emitting layer 5 described later was formed on the hole transport layer 7 by vapor deposition.

  Here, as the light emitting layer 5, the blue light emitting layer B is formed in the blue light emitting region 11, the red light emitting layer R is formed in the red light emitting region 12, the red light emitting layer R is formed, and then the green light emitting layer G is green light emitting. The film was formed not only on the region 13 but also in the red light emitting region 12 so as to have the green light emitting layer extension G1 laminated on the cathode side of the red light emitting layer R, that is, the surface on the electron transport layer side.

  For the blue light-emitting layer B, TBADN was used as the host material, and TBP at a ratio of 2% by weight with respect to the host material was used as the blue light-emitting dopant material. The red light-emitting layer R includes 70% by weight of rubrene as a hole transporting host material and 1% by weight of compound R as a red light emitting dopant with respect to a host material composed of 30% by weight of TBADN as an electron transporting host material. A material having a composition contained as a material was vapor-deposited to form a red light emitting layer R having a thickness of 40 nm. As the green light emitting layer G, a host material composed of 90% by weight TBADN as an electron transporting host material and 10% by weight NPB as a hole transporting host material is used as a 1% by weight green light emitting dopant material. A material having a composition containing C545T was formed by vapor deposition with a thickness of 40 nm. As shown in FIG. 1B, the green light emitting layer has a green light emitting layer extension G1, and the green light emitting layer extension G1 has a thickness of 40 nm, and the red light emission. It is laminated on one side of the layer R.

  After the light emitting layer 5 is formed, an electron transport layer 8 made of BCP having a thickness of 20 nm is formed by a vacuum deposition method, and these are stacked so that Li is 1 nm and Al has a thickness of 200 nm. The cathode 4 made of the laminated film was formed by vapor deposition. Details of the configuration of the organic EL device of Example 1 are shown in Table 1.

  With respect to the organic EL device obtained as described above, the driving voltage shown in the following Table 2 was applied from the anode 3 and the cathode 4, and the light emission characteristics were measured. Of the light emission characteristics, the red light emission characteristics are shown in Table 2 below. As is apparent from Table 2, at a driving voltage of 3.7 V, the chromaticity is (0.65, 0.35), the power (power) efficiency is 10.5 lm / W, and the luminous efficiency is 12. 3 cd / A.

(Example 2)
An organic EL device was produced in the same manner as in Example 1 except that the thickness of the BCP film as the electron transport layer 8 was changed from 20 nm to 5 nm. The emission characteristics were measured in the same manner as in Example 1. As to red emission, the driving voltage was 3.6 V, the chromaticity was (0.64, 0.35), and the power (power) efficiency was 9.5 lm. / W, and the light emission efficiency was 11.0 cd / A.

(Comparative Example 1)
An organic EL device was produced in the same manner as in Example 1, that is, according to the conventional three-color coating method, except that the green light emitting layer G did not have the green light emitting layer extension G1. Therefore, when the green light emitting layer G is manufactured, a mask using only the green light emitting region as an opening is used, and positioning is performed by the first mask for forming the blue light emitting region and the second mask for forming the red light emitting region. In addition, the third mask having the green light emitting region as an opening has to be positioned with high accuracy.

  The organic EL element of Comparative Example 1 obtained in this way was measured for light emission characteristics in the same manner as in Example 1. For red light emission, the driving voltage is 3.4 V, the chromaticity is (0.66, 0.34), the power (power) efficiency remains at 4.6 lm / W, and the light emission efficiency is also 4.9 cd / A. It was low.

  As described above, compared with Comparative Example 1, in Examples 1 and 2 in which the green light emitting layer extension G1 is laminated on one surface of the red light emitting layer R, the red light emitting efficiency and power efficiency are enhanced. This is considered to be due to the following reasons.

  That is, as shown in FIG. 3, the LUMO energy level of the red light emitting layer is lower than the LUMO energy level of TBADN of the green light emitting layer. Therefore, the electrons move as shown in FIG. 3 and are trapped in the red light emitting layer R, and the recombination region of electrons and holes is localized in the red light emitting layer. Moreover, since the excitation energy in the green light emitting layer is larger than the excitation energy in the red light emitting layer, excitons generated in the red light emitting layer hardly move to the green light emitting layer extension G1. Therefore, it is difficult for the excitons to shift to the green light emitting layer G or the green light emitting layer extension G1 to emit light. On the other hand, the hole transport layer, that is, NPB has blue fluorescence, and this excitation energy is larger than the excitation energy of the red light emitting layer R. Therefore, excitons in the red light emitting layer R do not move to the hole transport layer and emit blue light. Therefore, it is considered that the confinement efficiency of excitons in the red light emitting layer R is increased, the chromaticity in the red light emitting layer is hardly lowered, and the light emission efficiency is effectively increased.

(Example 3)
When forming the light emitting layer 5, a blue light emitting layer B having a thickness of 40 nm is formed by vapor deposition using TBADN as an electron transporting host material and 2 wt% TBP as a blue light emitting dopant material. A red light emitting layer R was formed in the same manner as in Example 1. Thereafter, the green light-emitting layer G contains 90% by weight of TBADN as an electron transporting host material, 10% by weight of NPB as a hole transporting host material, and 1% by weight of C545T is green with respect to 100% by weight of the host material. A green light emitting layer made of a composition containing the light emitting dopant material was formed so as to cover not only the green light emitting region G but also the surface of the blue light emitting layer B and the red light emitting layer R on the cathode side, that is, the electron transport layer side. Accordingly, the green light emitting layer G has a green light emitting layer extension G1 and a green light emitting layer second extension G2, as schematically shown in FIG. In this case, the thickness of the green light emitting layer G, the green light emitting layer extension G1, and the green light emitting layer second extension G2 was 40 nm.

  About other points, it carried out similarly to Example 1, and obtained the organic EL element. In forming the green light-emitting layer G, the green light-emitting layer G may be deposited so as to reach the entire light-emitting regions 11 to 13, and therefore a mask is not necessary when forming the green light-emitting layer G. Therefore, it is only necessary to prepare two masks for forming the blue light-emitting layer B and the red light-emitting layer R. The details of the structure of the organic EL device obtained in Example 3 are shown in Table 3 below.

  The light emitting characteristics of the organic EL device of Example 3 obtained as described above were evaluated in the same manner as in Example 1. As a result, in the blue light emission characteristics, when the driving voltage is 4.0 V, the chromaticity is (0.16, 0.24), the power (power) efficiency is 5.0 lm / W, and the light emission efficiency is 6 4 cd / A.

Example 4
An organic EL device was prepared and evaluated in the same manner as in Example 3 except that the thickness of the electron transport layer made of BCP was changed to 5 nm as shown in Table 3 below. As a result, for blue light emission, the driving voltage is 4.1 V, the chromaticity is (0.15, 0.21), the power (power) efficiency is 5.3 lm / W, and the light emission efficiency is 6.9 cd. / A.

(Comparative Example 2)
In the formation of the green light emitting layer G, an organic EL device was produced in the same manner as in Comparative Example 1, except that the green light emitting layer extension G1 and the green light emitting layer second extension G2 were not provided. The blue light emission characteristics of the organic EL device of Comparative Example 2 obtained in this manner were evaluated in the same manner as in Example 3. As a result, the driving voltage was 3.6 V, the chromaticity was (0.14, 0.10), the power (power) efficiency was 3.3 lm / W, and the blue light emission efficiency was 3.7 cd / A.

  Therefore, as is clear from the comparison between Comparative Example 2 and Examples 3 and 4, when the green light emitting layer second extending portion G2 is provided, in Examples 3 and 4, there is almost no decrease in chromaticity of blue light emission. It can be seen that power efficiency and light emission efficiency are improved. This is considered to be due to the following reason.

  That is, as shown in FIG. 4, in the portion where the green light emitting layer second extension G2 is laminated on the blue light emitting layer B, the LUMO energy level in the BCP as the electron transport layer and the green light emitting layer second Since the LUMO energy levels of TBADN which is the host material of the extension G2 and the blue light emitting layer are substantially equal, electrons from BCP move quickly to the blue light emitting layer B via the green light emitting layer second extension G2. On the other hand, the NPB LUMO as the hole transport layer has the same energy level as that of the TBADN LUMO, but has a hole transport property. Therefore, electrons remain on the TBADN film side at the interface between NPB and TBADN. Therefore, the electron concentration in the blue light emitting layer B in the vicinity of the interface between the blue light emitting layer B and the hole transport layer is increased, and the recombination region is localized in the vicinity of the interface of the blue light emitting layer B. Therefore, even if the green light emitting layer second extending portion G2 is laminated on the blue light emitting layer B, it is considered that light emission occurs only from the blue light emitting layer, and the light emission efficiency in the blue light emitting layer is enhanced.

  In Examples 1 to 4, the light emission characteristics of the green light emitting layer G are (0.32, 0.64) at a driving voltage of 3.5 V, and the power (power) efficiency is 11.0 lm / W and luminous efficiency were 12.1 cd / A. That is, the green light emitting layer R is inherently high in power efficiency and light emission efficiency.

  In the above Examples 1 to 4, the hole injection layer 6, the hole transport layer 7 and the electron injection layer 8 are formed of the specific material. However, the hole injection layer 6 and the hole transport layer 7 are formed of appropriate hole transport materials. Can be formed. The electron transport layer 8 can also be formed of an appropriate electron transport material. Further, the host material and the dopant material constituting the blue light-emitting layer B, the green light-emitting layer G, and the red light-emitting layer R are not limited to the above specific materials, and appropriate electron transporting host materials, host transporting host materials, and It can change so that the dopant material according to appropriate luminescent color may be included.

(A) is front sectional drawing which shows typically the organic EL element which concerns on Example 1 of this invention, (b) is a front view which shows typically the principal part of the light emitting layer. 6 is a front view schematically showing a light emitting layer of an organic EL element prepared in Example 3. FIG. The schematic diagram for demonstrating the reason for which the luminous efficiency of a red light emitting layer is improved in Example 1. FIG. FIG. 6 is a schematic diagram for explaining the reason why the light emission efficiency of the blue light emitting layer is improved in Example 3. Front sectional drawing which shows an example of the conventional organic EL element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Organic EL element 2 ... Substrate 3 ... Anode 4 ... Cathode 5 ... Light emitting layer 6 ... Hole injection layer 7 ... Hole transport layer 8 ... Electron transport layer 11 ... Blue light emitting region 12 ... Red light emitting region 13 ... Green light emitting region B ... Blue light emitting layer G ... Green light emitting layer G1 Green light emitting layer extension G2 Green light emitting layer second extension R Red light emitting layer

Claims (5)

A red light emitting layer for forming a red light emitting region, a blue light emitting region and a green light emitting region, respectively; Having a light emitting layer and a green light emitting layer,
The green light emitting layer has a green light emitting layer extension provided so as to cover the cathode side surface of the red light emitting layer in the red light emitting region, whereby the green light emitting layer is formed only in the green light emitting region. It is formed so that it may reach the said red light emission area instead, The organic EL element characterized by the above-mentioned.   The green light emitting layer further includes a green light emitting layer second extension that covers a surface of the blue light emitting layer on the cathode side, and the green light emitting layer includes the green light emitting region, the red light emitting region, and the blue light emitting region. The organic EL element according to claim 1, wherein the organic EL element is formed in all the light emitting regions.   The organic EL element according to claim 1, wherein the light emitting layer is composed of a plurality of thin films formed by a thin film forming method using a mask.   The organic EL element according to claim 1, wherein an area of the green light emitting region is smaller than areas of the blue light emitting region and the red light emitting region.   The organic EL element according to claim 1, wherein a host material of the green light emitting layer is made of an anthracene derivative.

Images