WO2007088861A1

WO2007088861A1 - Organic el display and image display device using same

Info

Publication number: WO2007088861A1
Application number: PCT/JP2007/051519
Authority: WO
Inventors: Chiaki Domoto
Original assignee: Kyocera Corporation
Priority date: 2006-01-31
Filing date: 2007-01-30
Publication date: 2007-08-09

Abstract

[PROBLEMS] To provide a technology for reducing power consumption or drive voltage in an organic EL display. [MEANS FOR SOLVING PROBLEMS] An organic EL display for displaying moving pictures is provided with an organic layer composed of one more layers including a light emitting layer; and a plurality of organic EL elements, each of which has first and second electrodes which face each other by having the organic layer in between. A peak where the emission efficiency of the organic EL element becomes maximum is set within a luminance range of 1/3 to 1/2 of a previously set maximum emission luminance of the organic EL element. Furthermore, in the organic EL display, within an emission luminance range of 90%-110% of the previously set maximum emission luminance of the organic EL element, a peak where the emission efficiency of the organic EL element becomes maximum is set.

Description

Specification

Organic EL display and image display device using the same

Technical field

The present invention relates to an organic EL (Electroluminescent) display and an image display device using the same.

Background art

Conventionally, an organic EL display using an organic EL element using electroluminescence has been known.

[0003] As an organic EL element, for example, there is one in which a transparent electrode and a metal electrode are arranged to face each other with an organic layer including a light emitting layer interposed therebetween. In an organic EL device having such a configuration, when a voltage or current is applied between a transparent electrode and a metal electrode and current is passed through the light emitting layer, the light emitting layer emits light, and light emitted from the light emitting layer is transparent. It passes through the electrode and is emitted to the outside. In general organic EL devices, it is known that the emission intensity increases as the current flowing in the emission layer increases.

[0004] By the way, since an ordinary organic EL display is required to emit light with high luminance, a high voltage is applied to the organic EL element to increase the current density flowing in the light emitting layer, thereby emitting light with high luminance. However, this method had the disadvantage of high power consumption.

[0005] To solve this problem, the voltage or current applied to the organic EL element is set to a voltage or current value at which the luminous efficiency of the organic EL element is 80% or more of the maximum value. Devices have been proposed (for example, Patent Document 1).

Patent Document 1: Japanese Patent Laid-Open No. 2003-59651

Patent Document 2: Japanese Patent Application Laid-Open No. 2002-72629

Disclosure of the invention

Problems to be solved by the invention

[0006] However, the organic EL element proposed in Patent Document 1 only adopts the condition of the voltage or current applied to the organic EL element so as to increase the light emission efficiency. Therefore When such an organic EL device was applied to an organic EL display, it was not enough to reduce power consumption in accordance with the light emission conditions during video display.

[0007] In addition, in an organic EL display, a voltage required for light emission at the maximum gradation is determined. Therefore, if no measures are taken to reduce the required voltage, power consumption is reduced. This increases the amount and the size of the power supply circuit such as a booster circuit.

Means for solving the problem

[0008] The first aspect of the present invention is an organic EL display, comprising: an organic layer comprising one or more layers including a light emitting layer; and first and second electrodes facing each other across the organic layer. A plurality of the organic EL elements, and the plurality of the organic EL elements display a moving image, and are within a preset luminance range of 1Z3 to 1Z2 of the organic EL element. The peak where the luminous efficiency is maximized is located.

[0009] The second aspect of the present invention is an organic EL display, comprising an organic layer comprising one or more layers including a light emitting layer, and first and second electrodes facing each other with the organic layer interposed therebetween. The organic EL element has the maximum luminous efficiency within a preset range of 90% to 110% of the maximum emission luminance of the organic EL element. The peak is located.

The invention's effect

[0010] According to the first aspect of the present invention, the peak at which the luminous efficiency is maximized is located within the preset luminance range of 1Z3 to 1Z2 of the maximum emission luminance of the organic EL element. The luminous efficiency of the luminance range that is frequently used in can be improved, and the power consumption when displaying moving images can be reduced.

[0011] Further, according to the second aspect of the present invention, the peak at which the luminous efficiency is maximized is located within the range of 90% to 110% of the preset maximum emission luminance, whereby the organic emission Since the voltage required for the EL element can be reduced, the voltage required for the organic EL display can be reduced. As a result, it is possible to reduce the size of the power supply circuit that supplies power to the organic EL element, thereby contributing to the downsizing of the image display device.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] <Terminology>

In this specification, “luminescence efficiency” means the current density (for example, unit: ampere per square meter [AZm ² ]) flowing through the organic EL element and the luminance of the light emitted from the organic EL element (for example, Unit: candela per square meter [cd / m ² ]), measured by luminance divided by current density. In addition, the light emission efficiency is shown by taking the maximum value of the light emission efficiency of the organic EL element as the reference value 1 as appropriate.

[0014] Configuration of organic EL display>

FIG. 1 is a cross-sectional view schematically showing the configuration of the organic EL display 21 according to the first and second embodiments. This organic EL display 21 is a top emission type, and as shown in FIG. 1, a transparent glass substrate (hereinafter abbreviated as “substrate”) 23 and an element portion 25 formed on the substrate 23, The adjustment layer 26 formed on the element portion 25 and the sealing film 27 formed so that the upper force of the adjustment layer 26 also covers the entire element portion 25 are provided. The element unit 25 includes a first electrode 31, an organic layer 33, and a second electrode 35 in order from the substrate 23 side. The first and second electrodes 31 and 35 are opposed to each other with the organic layer 33 interposed therebetween.

In addition, since the organic EL display 21 emits color light, as shown in FIG. 2, the first to third colors corresponding to the colors red (R), green (G), and blue (B) are provided. A plurality of organic EL elements 51r, 51g, 51b are provided. In FIG. 2, the sealing film 27 is omitted for convenience of illustration. The organic layer 33 of the first to third organic EL elements 51r, 51g, 51b is made of a material suitable for emitting light of each wavelength of red, green, and blue, as will be described later. .

The adjustment layer 26 is for adjusting the light transmission characteristics of the first to third organic EL elements 51r, 51g, 51b. The sealing film 27 is for sealing the organic layer 33, the second electrode 35, etc., and is formed so as to completely cover the region where the element portion 25 of the organic EL display 21 is formed. Yes. The sealing film 27 is formed of a light-transmitting insulating material such as SiNx.

The configuration of the element unit 25 will be described. The first electrode 31 reflects at least part of the light emitted from the organic layer 33 to the organic layer 33 side. For example, the first electrode 31 is a reflective electrode such as A1. (Opaque electrode).

[0018] The second electrode 35 is made of a conductive material that transmits light. The second electrode 35 can be a semi-transparent electrode or a transparent electrode. However, when the second electrode 35 is composed of a semi-transparent electrode, it needs to have an optical characteristic that allows visible light to pass therethrough. Therefore, such optical characteristics are realized by reducing the thickness of the electrode. Here, examples of suitable materials for the transparent electrode include ITO and IZO. Suitable materials for the semitransparent electrode include alkali metals such as Li, alkaline earth metals such as Mg, Ca, Sr, and Ba, Al, Si, and Ag.

[0019] As shown in Fig. 2, the organic layer 33 includes a charge injection layer 41 for injecting holes or electrons and a charge transport layer for transporting holes or electrons in this order. 43, a light emitting layer 45 for emitting EL, a charge transport layer 47 for transporting electrons or holes, and a charge injection layer 49 for injecting electrons or holes. In the present embodiment, various layer structures such as a two- to four-layer structure are adopted depending on various conditions.

[0020] The configuration and material of the organic layer 33 are, for example, the reflection characteristics (non-transparent, translucent or transparent) and polarity (which is the anode side, etc.) of the first and second electrodes 31, 35, and It is determined according to the type of luminescent color of the organic layer 33 (red, green, blue). As a specific example, for example, a material such as Alq (aluminum quinolyl complex) emits green light and has an electron transport property.

Three

Therefore, in the element unit 25 that emits green light, the light emitting layer and the electron transport layer may be made of a single material such as Alq. When using a transparent electrode,

Three

In many cases, a metal electron injection layer is used.

[0021] <Relationship between luminous brightness and luminous efficiency>

Fig. 3 illustrates the relationship between the luminance and luminous efficiency of a typical organic EL device. In FIG. 3, the horizontal axis represents the luminance and the vertical axis represents the luminous efficiency. The maximum value of the light emission efficiency and the maximum value of the light emission luminance to be used (hereinafter referred to as “maximum light emission luminance”) are set to 1 as the reference value, and a curve Cv indicating the relationship between the light emission luminance and the light emission efficiency is shown. Has been. In the case of an organic EL element capable of color display, the light emission luminance is set in advance so as to be the maximum light emission luminance when displaying the brightest white color. As shown in FIG. 3, when the light emission luminance is a value Spk smaller than the maximum light emission luminance, the light emission efficiency becomes maximum (peak value). Hereinafter, the maximum value of the light emission efficiency is referred to as “maximum light emission efficiency”, and the light emission luminance at which the maximum light emission efficiency is realized is referred to as “maximum efficiency luminance”. The “light emission efficiency” is obtained by dividing the light emission luminance by the current density, and thus indicates the efficiency with which light is emitted with respect to a constant current.

[0023] By the way, when an organic EL display is used in applications such as videophones and digital televisions, it is predicted that the frequency of displaying moving images will increase. In general, when displaying a moving image, the luminance range (gradation level) from 1Z3 to LZ2 from the low luminance side in the gradation range (that is, luminance range) that the display can display (that is, the display is used). Range) is most often used.

[0024] Therefore, the inventors of the present application have determined that the first to third organic EL elements 51r, 51g, and 51b have a light emission effect within the light emission luminance range of 1Z2 to LZ3 from the low luminance side in the luminance range to be used. By adjusting to improve the rate, we have created a reduction in power consumption when displaying video on the OLED display 21.

[0025] FIG. 4 is a schematic diagram showing a simplified circuit configuration of a general organic EL element. Note that the detailed circuit configuration of the organic EL element is generally configured by combining multiple circuits such as transistors, but in FIG. 4, in order to prevent the complexity of the diagram, The outline of the circuit configuration of a simple organic EL device is shown.

[0026] As shown in FIG. 4, the current density flowing in the light-emitting diode 51 corresponding to the organic EL element by the transistor 200 constituted by a TFT circuit or the like with a constant power supply voltage V applied by the power supply circuit 100 Can be adjusted.

Incidentally, the organic EL element requires the highest current density (hereinafter also referred to as “maximum current density”) at the maximum light emission luminance. Therefore, it is necessary to multiply the power supply voltage V so that the maximum current density can be obtained.

[0028] Therefore, the inventors of the present application improve the light emission efficiency of the first to third organic EL elements 51r, 51g, and 51b at the maximum value (maximum light emission luminance) in the luminance range to be used. By adjusting in such a way, the voltage required for the organic EL display 21 was reduced. And by reducing this required voltage, power supply circuits such as booster circuits It was also created to reduce the size and power consumption.

[0029] (First embodiment)

FIG. 5 shows the relationship between the light emission luminance and the light emission efficiency of the organic EL display 21 according to the first embodiment, that is, from the low luminance side of the used luminance range to the organic light emitting luminance range from 1Z3 to: LZ2. The relationship between the light emission luminance and the light emission efficiency when the light emission efficiency of the EL elements 51r, 51g, and 5 lb is adjusted to the maximum is illustrated. In FIG. 5, as in FIG. 3, the horizontal axis shows the light emission luminance and the vertical axis shows the light emission efficiency, and the maximum light emission efficiency and the maximum light emission luminance are the reference values of 1, respectively. The curve Cvl showing the relationship with is shown. In addition, in Fig. 5, the range of light emission luminance (light emission luminance = 1Z3 to LZ2) that is frequently used when displaying moving images is almost the same as the range of light emission luminance (light emission luminance = 0.3 to 0.5). Hatched. Furthermore, for comparison, the curve Cv shown in FIG. 3 is indicated by a broken line.

[0030] As shown in FIG. 5, the organic EL elements 51r, 51g, and 51b according to the present embodiment have a maximum efficiency as compared with the relationship between the light emission luminance and the light emission efficiency (curve Cv) shown in FIG. Luminance Spk is shifted to the lower luminance side. The light emission efficiency shows a peak value (maximum light emission efficiency) in a predetermined light emission luminance range (light emission luminance = 0.3 to 0.5) frequently used during moving image display. That is, the maximum efficiency luminance Spk is included in a predetermined emission luminance range (emission luminance = 0.3-0.5) that is frequently used when displaying moving images. As described above, by adjusting the light emission efficiency so that the light emission luminance is 0.3 to 0.5, the power consumption when displaying a moving image can be reduced.

[0031] Further, for example, in the entire region of emission luminance = 1Z3 to: LZ2 (that is, emission luminance = 0.3 to 0.5), the emission efficiency is 80% (that is, 0.8) or more of the maximum emission efficiency. By adjusting in this way, it is possible to more efficiently reduce power consumption when displaying a moving image. Furthermore, from the viewpoint of reducing power consumption, the luminous efficiency is 90% of the maximum luminous efficiency (ie, 0.9) over the entire range of luminous brightness = 1Z3 to: LZ2 (ie, luminous brightness = 0.3 to 0.5). It is more preferable to adjust so that it may become the above. In addition, when moving images are displayed, if the frequency of light emission luminance is approximately the same over the entire luminance range of 0.3 to 0.5, the maximum efficiency It is preferable to adjust the degree to a value in the vicinity of emission luminance = 0.4, which is a substantially central value of emission luminance = 0.3 to 0.5.

[0032] By the way, as a factor that shifts the maximum efficiency luminance of each organic EL element 51r, 51g, 5 lb to the lower luminance side, that is, a factor that adjusts the peak shape of the curve indicating the relationship between the emission luminance and the emission efficiency, The thickness of each layer constituting the organic layer 33, the mobility of carriers, the concentration of impurities, and the like can be mentioned.

[0033] Here, the factors relating to the adjustment of the maximum efficiency luminance (that is, the peak shape of the curve indicating the relationship between the luminous intensity and the luminous efficiency) for each of the organic EL elements 5 lr, 5 lg, and 5 lb are briefly described. Explained.

FIG. 6 is a diagram illustrating a potential diagram for the organic EL elements 51r, 51g, and 5 lb. Here, as an example, A1 is used as the first electrode 31, Ca is used as the second electrode 35, the charge injection layer 41 is a hole injection layer, the charge transport layer 43 is a hole transport layer, and a charge transport The layer 47 is configured as an electron transport layer, and the charge injection layer 49 is configured as an electron injection layer.

When such organic EL elements 51r, 51g, and 51b emit light, as indicated by arrows in FIG. 6, holes are introduced from the first electrode 31 side to the hole injection layer 41, the hole transport layer. The process proceeds in the order of 43 and the light emitting layer 45. On the other hand, electrons proceed in the order of the electron injection layer 49, the electron transport layer 47, and the light emitting layer 45 from the second electrode 35 side. Then, light is generated by combining holes and electrons in the light emitting surface EM of the light emitting layer 45.

[0036] By the way, the external quantum efficiency 7? Is a representative example of the luminous efficiency of the organic EL device.

Φ

The This external quantum efficiency of 7? Is emitted outside the organic EL device with respect to the number of injected electrons.

Φ

The number of photons is shown as a percentage. The higher the external quantum efficiency 7 ?, the greater the number of photons. So

Φ

The external quantum efficiency 7? Is expressed by the following equation (1).

Φ

[Equation 1] φ = γ 7? R 7? F 7? Ext · '·, 1) [0037] In equation (1), γ is the carrier balance factor (charge balance), η is the exciton generation efficiency, r? Is the emission quantum efficiency from the exciton, and η is the external extraction efficiency (light extraction efficiency) . In other words, the external quantum efficiency η is the carrier balance factor γ, exciton generation efficiency η, light emission

r It consists of four products: quantum efficiency 7) and external extraction efficiency 7}. And these four values

f ext

Of these, the three values of exciton generation efficiency 7 ?, emission quantum efficiency 7 ?, and external extraction efficiency 7?

r f ext

Even if there is a change in the current flowing through the organic EL element, the value basically does not change. On the other hand, the value of the carrier balance factor γ changes with changes in the current value flowing through the organic EL element. Therefore, as shown in FIGS. 3 and 5, this change in the carrier balance factor γ causes a peak in luminous efficiency with respect to the change in emission luminance.

[0038] Therefore, it is considered that the light emission efficiency with respect to the light emission luminance can be made desired by appropriately adjusting the carrier balance factor y.

[0039] Here, as factors for changing the carrier balance factor γ, 1) the height of the charge injection barrier from the first and second electrodes 31 and 35 to the organic layer 33, and 2) the carrier in the organic layer 33 Mobility, 3) carrier density in the organic layer 33 due to doping, and 4) space charge limited current (SCLC).

[0040] 1) Regarding the height of the charge injection barrier, the ease with which charges (holes or electrons) reach the light emitting surface depends on the height of the barrier. In general, in an organic layer used in an organic EL element, holes are more easily injected. For example, the height of the charge injection barrier is adjusted by appropriately changing the material constituting the electron injection layer 49. If the electrons are easily injected, the maximum efficiency luminance can be shifted to the low luminance side. If it is difficult to inject electrons, the maximum efficiency luminance can be shifted to the high luminance side.

[0041] 2) The carrier mobility in the organic layer 33 can be adjusted by doping the organic layer 33 with an impurity that inhibits the flow of charges. For example, each layer on the path through which holes move (hole injection layer 41, hole transport layer 43, etc.) is doped with impurities to reduce carrier mobility, thereby relatively moving electrons. As a result, the maximum efficiency luminance can be shifted to the lower luminance side. For example, by reducing the impurities doped in each layer (hole injection layer 41, hole transport layer 43, etc.) on the path through which holes move, the mobility of carriers is increased, thereby increasing the mobility of electrons. As a result, the movement of holes can be promoted relatively, and as a result, the maximum efficiency luminance can be shifted to the high luminance side.

[0042] 3) The carrier density in the organic layer 33 by doping is improved by doping. o For example, by improving the mobility of each layer (electron injection layer 49, electron transport layer 47, etc.) on the path along which electrons move, the movement of electrons relative to holes is promoted. The maximum efficiency luminance can be shifted to the low luminance side. For example, by improving the mobility of each layer (hole injection layer 41, hole transport layer 43, etc.) on the path through which holes move, the movement of holes relative to electrons is promoted. As a result, the maximum efficiency luminance can be shifted to the high luminance side.

[0043] 4) The space charge limited current is expressed by the following formula (2) when no trap exists in the organic layer (organic semiconductor).

[Equation 2]

[0044] In Equation (2), is the carrier mobility, ε is the dielectric constant of the vacuum, and ε is the dielectric constant of the organic thin film

0

, V is the applied voltage, and L is the thickness of the organic layer.

[0045] As is clear from Equation (2), the current town is inversely proportional to the cube of the film thickness. For this reason, for example, by appropriately adjusting the film thickness of each layer constituting the organic layer 33 while keeping the film thickness of the organic layer 33 constant, the hole flow is inhibited while the electron flow is promoted. be able to . As a result, the maximum efficiency luminance can be shifted to the low luminance side. Further, by appropriately adjusting the thickness of each layer constituting the organic layer 33 while keeping the thickness of the organic layer 33 constant, the flow of holes can be promoted while inhibiting the flow of electrons. . As a result, the maximum efficiency luminance can be shifted to the high luminance side.

[0046] It should be noted that the power efficiency in the organic EL display is the voltage efficiency of the external quantum efficiency 7?

Φ

Therefore, adjusting the external quantum efficiency 7?

Φ

Can be improved. The voltage efficiency is determined by factors such as the voltage efficiency in organic EL elements and the voltage drop in TFT circuits.

[0047] As described above, in the organic EL display 21 according to the first embodiment, the peak at which the luminous efficiency is maximized is positioned in the luminance range of 1Z3 to 1Z2 where the organic EL element has the maximum luminous luminance. Is set. By adopting such a configuration, the luminous efficiency is improved over the luminance range that is frequently used during video display. Power consumption can be reduced.

[0048] In particular, the light emission efficiency in the maximum light emission luminance range of 1Z3 to 1Z2 is set to be 80% or more (preferably 90% or more) of the maximum light emission efficiency. For this reason, the luminous efficiency is widely improved in the luminance range that is frequently used when displaying moving images. As a result, it is possible to more effectively reduce power consumption when performing moving image display.

[0049] In addition, for all of the organic EL elements 5lr, 51g, and 51b that emit light of three different colors of RGB, the peak with the highest luminous efficiency is within the luminance range of 1Z3 to 1Z2 of the maximum luminous luminance. Is set to be located. For this reason, it is possible to significantly reduce the power consumption when displaying moving images. Furthermore, the light emission efficiency in the luminance range of 1Z3 to 1Z2 with the maximum light emission luminance is set to be 80% or more (preferably 90% or more) of the maximum light emission efficiency. For this reason, the luminous efficiency for the luminance range frequently used during moving image display can be broadly increased, so that the power consumption during moving image display can be greatly reduced. As a result, it can contribute to the miniaturization of the power supply circuit and the battery.

[0050] <Modification>

As described above, the force described in the first embodiment. The present invention is not limited to the content described above.

[0051] For example, in the first embodiment, for all three colors of organic EL elements 5 lr. 51g. 51b, the maximum efficiency luminance appears within the light emission luminance range frequently used when displaying moving images. For example, for an organic EL element of at least one of RGB colors, the maximum efficiency luminance will appear within the emission luminance range that is frequently used during video display. You can adjust it.

[0052] Further, in the first embodiment, the power described with reference to the organic EL display 21 capable of emitting three colors of RGB is not limited to this. For example, at least such as a monochrome organic EL display By applying the present invention to an organic EL display that can emit one or more colors of light, it is possible to reduce power consumption when displaying a moving image. Example 1

<Example in which maximum luminance is adjusted by changing film thickness> In this example, an organic EL device in which an anode, a first hole injection layer, a second hole injection layer, a hole transport layer, a light emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode are stacked in this order. Was made. Here, the film thicknesses of the second hole injection layer and the hole transport layer were changed while maintaining the total film thickness of the second hole injection layer and the hole transport layer at 350A. The configuration of each layer is as follows.

(a) Anode (first electrode)

Material: Aluminum Kum

Film thickness: 500 A

(b) First hole injection layer

Material: NiO

Film thickness: 50 A

(c) Second hole injection layer

Material: CuPc

Film thickness: 180A or 140A

(d) Hole transport layer

Material: a-NPD

Film thickness: 170A or 210A

(e) Light emitting layer

Host material: CBP

Guest material: Btp Ir (acac)

2

(English mark 3 self: bis [2— (2f—benzothienyl) pyridinato—N, 3f] cetylacetonato) lndium (III))

Total film thickness: 350 A Concentration of guest material with respect to host material: 5 wt%

(1) Hole blocking layer

Material: BAlq Film thickness: 100 Λ

(g) Electron transport layer

Material: Alq Film thickness: 150A

(h) Electron injection layer

Material: LiF Film thickness: 5 A

(0 cathode (second electrode)

Material: Mg: Ag (Mg—Ag alloy)

Film thickness: 200 A

Figure 7 shows the above example (Example 1: Second hole injection layer thickness 180A—Hole transport layer thickness 170A, Example 2: Second hole injection layer thickness 140A—Hole FIG. 6 is a diagram plotting the relationship between the light emission luminance and the light emission efficiency by measuring the current density and the light emission luminance during light emission for the configuration of the transport layer thickness 210A). In FIG. 7, the black square mark and the polygonal line L1 connecting the black square marks indicate the results of the configuration of Example 1, and the white rhombus mark and the polygonal line L2 connecting the white rhombus marks are the configuration of Example 2. The result concerning is shown. Further, in FIG. 7, for comparison, a comparative example in which the film thicknesses of the second hole injection layer and the hole transport layer are changed from the configuration of Example 2 (Comparative Example 1: film thickness of the second hole injection layer). Also shown are the results for 100A—hole transport layer thickness 250A, comparative example 2: second hole injection layer thickness 20A—hole transport layer thickness 330A). The black triangle mark and the broken line C1 connecting the black triangle marks indicate the results according to the configuration of Comparative Example 1, and the white circle mark and the broken line C2 connecting the white circle marks indicate the results according to the configuration of Comparative Example 2.

[0055] Here, 900 cdZm ² is set as the maximum light emission luminance, and the range power of the light emission luminance that is frequently used during video display. The maximum light emission luminance is 1Z3 to: LZ2, that is, the range of 300 to 450 cdZm ² It will be explained as a thing.

[0056] As shown in FIG. 7, the maximum efficiency luminance of Example 1 (emission luminance when the luminous efficiency is maximum) is 308 cdZm ² , and the maximum efficiency luminance of Example 2 is 383 cd / m ^2. The maximum efficiency luminance was included in the emission luminance range (300 to 450 cdZm ² ) frequently used during display. In contrast, the maximum efficiency brightness of Comparative Example 1 is 537 cd / m ² , and the maximum efficiency brightness of Comparative Example 2 is 757 cdZm ^2. m ² ) did not include maximum efficiency luminance.

[0057] As described above, by appropriately changing the thicknesses of the second hole injection layer and the hole transport layer while keeping the total film thickness of the second hole injection layer and the hole transport layer constant, a moving image can be obtained. Adjustment can be made so that the maximum efficiency luminance is included in the range of the emission luminance frequently used during display. <Example in which the maximum efficiency brightness is adjusted by the presence of the hole injection layer>

In this example, the anode, the first hole injection layer, the second hole injection layer, the third hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the cathode were laminated in this order. An organic EL device was fabricated. The configuration of each layer is as follows.

[0059] (a) Anode (first electrode)

Material: Aluminum-Kum Film thickness: 500 A

(b) First hole injection layer

Material: TiO Film thickness: 10A

(c) Second hole injection layer

Material: CF Film thickness: 15A

(d) Third hole injection layer

Material: CuPc Film thickness: 225 A

(e) Hole transport layer

Material: α-NPD Film thickness: 100Λ

(ί) Light emitting layer

Host material: CBP Guest material: FIrpic

Total film thickness: 270 A Concentration of guest material relative to host material: 5 wt%

(g) Electron transport layer

Material: Alq Film thickness: 240 Λ

(h) Electron injection layer

Material: LiF

Film thickness: 5 A

(0 cathode (second electrode)

Material: Mg: Ag (Mg—Ag alloy)

Film thickness: 200 A

Fig. 8 is a graph plotting the relationship between light emission luminance and light emission efficiency by measuring the current density and light emission luminance at the time of light emission for the configuration of the above example (Example 3: with a third hole injection layer). It is. In FIG. 8, the white rhombus mark and the broken line L3 connecting the white rhombus marks are the configurations of Example 3. The result concerning is shown. Further, in FIG. 8, for comparison, the results of the comparative example (Comparative Example 3: no third positive hole injection layer) obtained by removing the third positive hole injection layer from the configuration of Example 3 are also shown. It shows.

[0060] Here, 600 cdZm ² is set as the maximum light emission luminance, and the range power of the light emission luminance that is frequently used when displaying moving images The maximum light emission luminance of 1Z3 to: LZ2, that is, 200 to 3

The description will be made assuming that the range is OOcdZm ² .

As shown in FIG. 8, the maximum efficiency luminance of Example 3 was included in the range of light emission luminance (200 to 300 cdZm ² ) frequently used during moving image display. In contrast, the maximum efficiency luminance of Comparative Example 3 was higher than the emission luminance range (200 to 350 cdZm ² ) frequently used during moving image display.

[0062] In this way, by interposing the third hole injection layer in the organic EL element and shifting the maximum efficiency luminance to the low luminance side, the maximum is within the range of the emission luminance frequently used when displaying moving images. Adjustments can be made to include efficient luminance.

[0063] (Second Embodiment)

FIG. 9 shows the relationship between the light emission luminance and the light emission efficiency of the organic EL display 21 according to the second embodiment, that is, the light emission efficiency of the first to third organic EL elements 51r, 51g, 51b in the vicinity of the maximum light emission luminance. The relationship between the light emission luminance and the light emission efficiency in the case where adjustment is made so as to maximize is shown.

In FIG. 9, as in FIG. 3, the horizontal axis indicates the light emission luminance, and the vertical axis indicates the light emission efficiency. The maximum light emission efficiency and the maximum light emission luminance are set to 1 as the reference values, respectively. A curve Cvl showing the relationship between luminance and luminous efficiency is shown. Furthermore, for comparison, the curve Cv shown in FIG. 3 is indicated by a broken line.

[0065] As shown in FIG. 9, the first to third organic EL elements 51r, 51g according to the present embodiment are compared with the relationship (curve Cv) between the light emission luminance and the light emission efficiency shown in FIG. In 51b, the maximum efficiency brightness Spk is shifted to the high brightness side. The light emission efficiency shows a peak value (maximum light emission efficiency) at the maximum light emission luminance (light emission luminance = 1). In other words, at the maximum emission brightness, the first to third organic EL elements 51r, 51g, 51b are set to have the maximum luminous efficiency. ing.

As described above, by improving the light emission efficiency at the maximum light emission luminance, the voltage required for the organic EL display 21 can be reduced.

Here, as shown in FIG. 9, an example is shown in which the light emission efficiency is set to be maximum at the maximum light emission luminance (light emission luminance = 1), but the present invention is not limited to this. For example, if the peak that maximizes the luminous efficiency is positioned within the luminous luminance range of 90% to 110% of the maximum luminous luminance, the luminous efficiency at the maximum luminous luminance can be improved. The voltage required for the organic EL display 21 can be reduced. However, in terms of the viewpoint of reducing the voltage required for the organic EL display 21 as much as possible, the luminous efficiency of the first to third organic EL elements 51r, 51g, and 51b is maximized at the maximum emission luminance. It is most preferable that the maximum light emission brightness and the maximum efficiency brightness Spk, which are preferable to be set, completely match. However, since such adjustment is very complicated, the difference Δ Spk between the maximum efficiency brightness Spk and the maximum light emission brightness of each color should be such that the relationship B <R <G holds. preferable. The blue organic EL element 51b has a short wavelength in R GB, and has low luminous efficiency. This is because it is preferable to make the maximum light emission brightness and the maximum efficiency brightness Spk that have low viewing sensitivity closest to each other. On the other hand, is the green organic EL element 5 lg good in luminous efficiency? Due to its good viewing sensitivity, the demand for bringing the maximum light emission brightness and the maximum efficiency brightness Spk close to each other is the lowest among RGB. Therefore, if the relationship of B <R <G is established for the difference Δ Spk between the maximum efficiency brightness Spk and the maximum light emission brightness, the peak position of the light emission efficiency considering the characteristics for each color and Become. As a result, it is possible to keep power consumption low while maintaining high productivity of organic EL displays.

[0068] As described above, in the organic EL display 21 according to the second embodiment, each of the organic EL elements 51r, 51g, 51b has an emission luminance within the range of 90% to 110% of the maximum emission luminance. The peak where the luminous efficiency of the EL element is maximized is set! By adopting such a configuration, it is possible to reduce the voltage required for each organic EL element 51r, 51g, 5 lb. Therefore, the voltage required for the organic EL display 21 can be reduced. .

[0069] In addition, it may be applied to a display mounted on a mobile phone or a screen of a personal computer. For example, still images are often displayed on these screens, and high gradation (high luminance) is frequently used at that time. Considering such applications, it is possible to reduce power consumption by increasing the light emission efficiency at high luminance as described above.

[0070] Further, by reducing the applied voltage, it is possible to reduce the size of a power supply circuit such as a booster circuit and a battery, which is effective when an organic EL display is mounted on a small device such as a cellular phone. is there.

[0071] Further, in particular, when the maximum luminous brightness is set so that the luminous efficiency of each organic EL element 51r, 51g, 51b is maximized, the voltage required for each organic EL element 51r, 51g, 51b is further increased. It can be effectively reduced. That is, the voltage required for the organic EL display 21 can be reduced more effectively.

[0072] Further, in the organic layer 33, when the emission luminance is lower than the maximum efficiency luminance, the number of holes is larger than the number of electrons (hole-rich state). For example, an organic layer that is vulnerable to holes (the electron transport layer 47 and the electron injection layer 49 in FIG. 6) is easily deteriorated by the penetration of holes, but the hole between the light-emitting layer 45 and the electron transport layer 47 By providing a hole blocking layer that prevents the invasion of the electrons, the electron transport layer 47 and the electron injection layer 49 can be prevented from deteriorating. On the other hand, for example, organic layers that are vulnerable to electrons (the hole transport layer 43 and the hole injection layer 41 in FIG. 6) are easily deteriorated by the intrusion of electrons, but there is almost no material that forms the electron blocking layer. Therefore, when the entire organic layer 33 is viewed, if the number of electrons is larger than the number of holes (electron rich state), the electrons are transferred to the hole transport layer 43 and the hole injection layer 41. Due to the invasion, the organic layer 33 is likely to deteriorate. In this regard, in the organic EL display 21 according to the second embodiment, the peak of the luminous efficiency is set to a relatively high luminance side (in FIG. 9, near the maximum luminous luminance) as shown in FIG. Deterioration of the organic layer 33 is suppressed.

[0073] <Modification>

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the thing of the content demonstrated above.

[0074] For example, in the second embodiment, for all of the first to third organic EL elements 51r, 51g, 51b, the luminous efficiency is within a range of 90% to 110% of the maximum luminance. Although the maximum setting is set, it is not limited to this. For example, the first to third organic EL elements 5 Even if at least one of the organic EL elements of lr, 51g, and 51b is set so that the luminous efficiency is maximized within the range of 90% to 110% of the maximum luminance, the organic EL The voltage required on the display can be reduced.

[0075] However, for example, when different power supply circuits are provided for the first to third organic EL elements 51r, 51g, and 5 lb, the first to third organic EL elements 51r, 51g, For all 51b, setting the maximum luminous efficiency within the range of 90% to 110% of the maximum emission luminance reduces the required voltage and power consumption for the OLED display 21 as a whole. In addition, it is preferable to further reduce the size of the power supply circuit.

[0076] Further, for example, even if at least one of the first to third organic EL elements 51r, 51g, 51b is set so that the light emission efficiency is maximized at the maximum light emission luminance, The voltage required for OLED displays can be further reduced.

[0077] However, for example, when different power supply circuits are provided for the first to third organic EL elements 51r, 51g, and 5 lb, the first to third organic EL elements 51r, 51g, For all 51b, it is more effective to reduce the required voltage and power consumption and to reduce the size of the power circuit for the entire OLED display 21 by setting the luminous efficiency to be the maximum at the maximum luminance. Is preferable.

[0078] When an organic EL display is mounted on a small device such as a mobile phone, the first to third organic EL elements 51r, 51g, 51b are used to reduce the size of the power circuit. On the other hand, a common power supply circuit may be used. In each of the organic EL elements 51r, 51g, 51b, of the first to third organic EL elements 51r, 51g, 51b, due to the material type of the organic layer 33, the energy of the wavelength of light, etc. For example, the voltage required for light emission in the third organic EL element 51b may be the highest.

[0079] A case where the voltage required for light emission of the third organic EL element 51b among the first to third organic EL elements 51r, 51g, 51b is the highest will be described. Here, it is assumed that the brightness of the light of the highest gradation (that is, white light) of the organic EL display 21 is 200 cdZm ² .

[0080] To obtain 200 cdZm ² of white light, the maximum brightness of B color light emitted from one pixel is 50 cdZm ² , and the maximum brightness of R color light emitted from one pixel is 60 cdZm ² , Maximum brightness of the G color light emitted from the pixels is required only 90cdZm ^2.

[0081] Then, in order to obtain B light of 50 cdZm ² , the third organic EL that actually emits light, taking into account the proportion of time the element is emitting light (duty) and the aperture ratio of the pixel Element 51b needs to emit 1428 cdZm ² of light. In other words, the maximum emission luminance of the third organic EL element 5 lb needs to be about 1430 cd / m ² .

[0082] As shown in FIG. 10, each pixel has a characteristic of repeating light emission and non-light emission, and the element emits light! The ratio of time is duty. As shown in Fig. 11, one pixel is divided into three RGB light-emitting areas, and the portions that emit light of each color are even smaller. The aperture ratio is the proportion of one pixel that emits light of one color. Here, assuming that the duty is about 44% and the aperture ratio is 8 (= [1Z3] X 24)%, the maximum emission brightness of the third organic EL element 5 lb is 1430 (= 50 X [100 / 44] X [100/8]) cd / m ² is calculated. Further, by the same calculation, the maximum light emission luminance force S 1 714 cdZm ^{2 of} the first organic EL element 51r is calculated, and the maximum light emission luminance of the second organic EL element 51g is calculated as 2570 cd / m 2.

[0083] Furthermore, since the voltage efficiency when the third organic EL element 51b emits light at the maximum emission luminance (1430 _C dZm ² ) is about 170 cdZm ² ZV, a driving voltage of about 8.4 V is required. . In addition, the voltage efficiency when the first organic EL element 51r emits light at the maximum light emission luminance (1714 cdZm ² ) is about 230 cdZm ² ZV, so a driving voltage of about 7.5 V is required. Furthermore, since the voltage efficiency when the ^second organic EL element 51g emits light with the maximum light emission luminance (2570 cdZm ² ) is about 395 cdZm ² ZV, a driving voltage of about 6.5 V is required.

Therefore, in such a configuration, the highest drive voltage (about 8.4 V) with respect to the third organic EL element 5 lb among the first to third organic EL elements 51r, 51g, 51b. Is required.

[0085] When a common power supply circuit is used for the first to third organic EL elements 51r, 51g, 5 lb, the first to third organic EL elements 51r, 51g, 51b The third organic EL element, which requires the highest voltage for at least the maximum light emission luminance, is 5 lb, and emits light within the range of 90% to 110% of the maximum light emission luminance. If the efficiency is set to the maximum, the voltage of the common power supply circuit can be easily reduced. As a result, the common power supply circuit can be downsized. In this case, the battery is connected to the common power circuit. Can be connected. Even if the common power supply circuit is not used for the first to third organic EL elements 51r, 51g, and 51b, the third organic EL element that requires the highest voltage at least for the maximum emission luminance even in the case. For 5 lbs, 90% of maximum emission brightness: L If the emission efficiency is set within the range of 10%, the required voltage and power consumption can be reduced, and the power supply circuit Can be miniaturized. In this case, the first power supply circuit used for the first organic EL element 51r, the second power supply circuit used for the second organic EL element 51g, and the third organic EL element 51b A third power supply circuit used in common and a notch connected in common to the third power supply circuit

In the second embodiment, among the first to third organic EL elements 51r, 51g, 51b, the third organic EL element 51b requires the highest voltage at the maximum light emission luminance. The organic EL elements 51r and 51g are not limited and may require the highest voltage at the maximum light emission luminance. In such a case, the other organic EL elements 51r and 51g are first adjusted for the peak position of the luminous efficiency.

[0087] In the second embodiment, the power described with reference to the organic EL display 21 capable of emitting three colors of RGB is not limited to this. For example, at least, for example, a monochrome organic EL display By applying the present invention to an organic EL display capable of emitting one or more colors of light, the voltage required for the organic EL display can be reduced.

Example 2

In this example, an organic EL device was fabricated in which an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode were laminated in this order. The configuration of each layer is as follows.

[0089] (a) Anode (first electrode)

Material: ITO

(b) Hole injection layer

Material: CuPc Film thickness: 50 A

(c) Hole transport layer

Material: a-NPD Film thickness: 230 A (d) Light emitting layer

Material: Alq (Host material): Rubrene (Doping material)

Three

Alq: Rubrene = 99 mass%: 1 mass%

Three

Film thickness: 240 A

(e) Electron transport layer

Material: Alq Film thickness: 200 Λ

(ί) Electron injection layer

Material: LiF Film thickness: 5A

(g) Cathode (second electrode)

Materials: Mg: Ag (Mg—Ag alloy), Mg: Ag = 90% by mass: 10% by mass FIG. 12 shows the emission luminance of the configuration of the above example by measuring the current density and emission luminance during light emission. It is the figure which showed the relationship between and luminous efficiency. In FIG. 12, curve C1 shows the results for the configuration of the example.

[0090] In FIG. 12, for comparison, the total film thickness of the organic layers is maintained while maintaining the ratio of the materials and thicknesses (that is, the basic element structure) constituting each organic layer based on the configuration of the example. Of Comparative Example 1 in which the total thickness of the organic layer was about 1.60 times, and Comparative Example 3 in which the total thickness of the organic layer was about 2.00 times. The result which concerns on a structure is shown. Curve C2 shows the result of the configuration of Comparative Example 1, curve C3 shows the result of the configuration of Comparative Example 2, and curve C4 shows the result of the configuration of Comparative Example 3. .

Here, it is assumed that 1430 cdZm ² is set as the maximum light emission luminance.

[0092] As shown in FIG. 12, the maximum efficiency luminance (emission luminance when the luminous efficiency is maximized) of the example is about 1430 cdZm ² , and the maximum emission luminance and the maximum efficiency luminance are approximately the same. . In contrast, the maximum efficiency luminance of Comparative Example 1 is 1119 cdZm ² , the maximum efficiency luminance of Comparative Example 2 is 886 cdZm ² , the maximum efficiency luminance of Comparative Example 3 is 640 cdZm ² , and the maximum efficiency luminance is The light emission efficiency at the maximum light emission brightness near the maximum light emission brightness is slightly low.

[0093] Thus, the materials constituting each organic layer and the ratio of thickness (ie, basic element structure) By reducing the total film thickness of the organic layer while maintaining the value, it is possible to change the maximum efficiency luminance so that the maximum light emission luminance and the maximum efficiency luminance can be substantially matched.

FIG. 13 is a graph plotting the relationship between the maximum efficiency luminance and the drive voltage required at the maximum light emission luminance for the configuration of the above-described example. Figure 13 shows the results for the configuration of the plot P1 force example. In addition, FIG. 13 shows the results relating to the configurations of Comparative Examples 1 to 3 for comparison. Plot P2 shows the result of the configuration of Comparative Example 1, Plot P3 shows the result of the configuration of Comparative Example 2, and Plot P4 shows the result of the configuration of Comparative Example 3. Further, FIG. 13 also shows the results relating to the configuration having the total film thickness between the example and the comparative example 1. Fig. 14 shows a table showing the relationship among film thickness, drive voltage at maximum light emission luminance, and maximum efficiency luminance for Comparative Examples 1 to 3 and other configurations where the total film thickness of the example is 1. Show.

As shown in FIG. 13, the closer the maximum efficiency luminance is to the maximum light emission luminance, the lower the drive voltage required for the maximum light emission luminance.

Brief Description of Drawings

FIG. 1 is a cross-sectional view showing a configuration of an organic EL display according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of the organic EL display according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating the relationship between light emission luminance and light emission efficiency of a general organic EL element.

FIG. 4 is a schematic diagram showing a simplified circuit configuration of an organic EL display.

FIG. 5 is a diagram illustrating the relationship between the adjusted light emission luminance and light emission efficiency.

FIG. 6 is a diagram showing a potential diagram of an organic EL element.

FIG. 7 is a graph showing the relationship between light emission luminance and light emission efficiency in Examples and Comparative Examples of the present invention.

FIG. 8 is a diagram showing the relationship between light emission luminance and light emission efficiency in Examples and Comparative Examples of the present invention.

FIG. 9 is a diagram exemplifying a relationship between adjusted light emission luminance and light emission efficiency.

FIG. 10 is a graph showing the proportion of time during which an organic EL element emits light.

FIG. 11 is a diagram showing a ratio of light emitting areas in a pixel.

FIG. 12 is a graph showing the relationship between light emission luminance and light emission efficiency in Examples and Comparative Examples. FIG. 13 is a diagram showing the relationship between the maximum efficiency luminance and the necessary voltage in Examples and Comparative Examples.

FIG. 14 is a diagram showing the relationship among film thickness, drive voltage at maximum light emission luminance, and maximum efficiency luminance for Examples and Comparative Examples.

Explanation of symbols

21 OLED display

23 Board

25 Element section

26 Adjustment layer

27 Sealing film

31 First electrode

33 Organic layer

35 Second electrode

41 Charge injection layer (hole injection layer)

43 Charge transport layer (hole transport layer)

45 Light emitting layer

47 Charge transport layer (electron transport layer)

49 Charge injection layer (electron injection layer)

51h) Third organic EL device

51g Second organic EL device

51r First organic EL device

51 Light emitting diode

100 power supply

V Supply voltage

EM light emitting surface

Spk maximum efficiency brightness

Claims

The scope of the claims

[1] OLED display,

A plurality of organic EL elements each having an organic layer including one or more layers including a light emitting layer and first and second electrodes facing each other across the organic layer;

The plurality of organic EL elements display a moving image,

Within the preset luminance range of 1Z3 to 1Z2 of the maximum emission luminance of the organic EL element,

An organic EL display having a peak where the luminous efficiency of the organic EL element is maximized.

[2] The organic EL display according to claim 1,

The organic EL element is set so that the luminous efficiency of the organic EL element in the preset luminance range of 1Z3 to 1Z2 is 80% or more of the maximum luminous efficiency of the organic EL element. EL display.

[3] The organic EL display according to claim 1,

The plurality of organic EL elements emit a first organic EL element that emits light of a first color, a second organic EL element that emits light of a second color different from the first color, and the first organic EL element. A third organic EL element that emits light of a third color different from the first and second colors,

For one or more of the first to third organic EL elements, the organic light emitting element having a peak at which the luminous efficiency is maximum is within a preset luminance range of 1Z3 to 1Z2. EL display.

[4] The organic EL display according to claim 3,

With respect to one or more of the first to third organic EL elements, the light emission efficiency in the luminance range from 1Z3 to 1Z2 of the preset maximum light emission brightness is 80% or more of the maximum light emission efficiency. OLED display set to.

[5] The organic EL display according to claim 3,

For all of the first to third organic EL elements, an organic EL display in which a peak with the highest luminous efficiency is located within a preset luminance range of 1Z3 to 1Z2.

[6] The organic EL display according to claim 5, An organic EL display that is set so that the light emission efficiency in the luminance range of 1Z3 to 1Z2 of the preset maximum light emission luminance is 80% or more of the maximum light emission efficiency for all of the first to third organic EL elements.

[7] OLED display,

The organic EL element displays a video,

An organic EL display in which a peak at which the emission efficiency of the organic EL element is maximum is located within a preset luminance range of 0.3 to 0.5 of the maximum emission luminance of the organic EL element.

[8] OLED display,

A plurality of organic EL elements each having an organic layer including one or more layers including a light emitting layer and first and second electrodes facing each other with the organic layer interposed therebetween,

An organic EL display in which a peak at which the luminous efficiency of the organic EL element is maximized is located within a preset range of 90% to 110% of the maximum luminous intensity of the organic EL element.

[9] The organic EL display according to claim 8,

For one or more of the first to third organic EL elements, the light emission efficiency of the organic EL element is within a range of 90% to: L 10% of the preset maximum light emission luminance. An organic EL display with a peak where is the largest.

[10] The organic EL display according to claim 9,

Among the first to third organic EL elements, an organic EL element that requires the highest voltage with a preset maximum emission brightness has an emission brightness of 90% to 110% of the preset maximum emission brightness. An OLED display with a peak that maximizes luminous efficiency within the range.

[11] The organic EL display according to claim 9,

An organic EL display in which a peak at which light emission efficiency is maximum is located within a predetermined range of 90% to 110% of the maximum light emission luminance for all of the first to third organic EL elements.

[12] The image display device according to claim 9,

The first color is red, the second color is green, and the third color is blue. The maximum light emission luminance predetermined for each of the first to third organic EL elements, and the organic color The difference Δ Spk from the emission luminance at which the luminous efficiency of the EL element is maximized is smaller in the third organic EL element than in the first and second organic EL elements, and the second organic EL element An image display device set smaller than each of the first organic EL elements.

[13] In the image display device,

The organic EL display according to claim 9, a first power supply circuit that supplies power to the first organic EL element, a second power supply circuit that supplies power to the second organic EL element, And a third power supply circuit for supplying electric power to the third organic EL element.

[14] In the image display device,

An image display device comprising: the organic EL display according to claim 9; and a power supply circuit that supplies power to the organic EL elements in common.

[15] In the image display device according to claim 13,

An image display device further comprising a knotter commonly connected to the first to third power supply circuits.

[16] The image display device according to claim 14,

An image display device further comprising a battery connected to the power supply circuit.