JP5196724B2 - Organic EL display - Google Patents

Description

  The present invention relates to an organic EL (Electroluminescent) display.

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

  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 the organic EL element having such a configuration, when a voltage or current is applied between the transparent electrode and the metal electrode and a current is passed through the light emitting layer, the light emitting layer emits light, and light emitted from the light emitting layer is transmitted to the transparent electrode. And is released to the outside. In general organic EL elements, it is known that the emission intensity increases as the current flowing in the light emitting layer increases.

  By the way, since a normal organic EL display is required to emit light with high luminance, high luminance was obtained by applying a high voltage to the organic EL element and increasing the current density flowing in the light emitting layer. However, this method has a drawback that power consumption is large.

  In order to solve such a problem, there has been proposed an EL display in which 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. (For example, Patent Document 1).

Japanese Patent Laid-Open No. 2003-59651

  However, in the EL display proposed in Patent Document 1, only the condition that the light emission efficiency is increased with respect to the entire range of the voltage or current applied to the organic EL element is adopted, and it corresponds to the light emission condition at the time of moving image display. Thus, the power consumption was not reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for reducing power consumption when displaying a moving image on an organic EL display.

In order to solve the above-described problems, the invention of claim 1 is an organic EL display that displays a moving image, and is opposed to each other with an organic layer composed of one or more layers including a light emitting layer interposed therebetween. A plurality of organic EL elements each having a first electrode and a second electrode are provided, and 1/3 to 1/2 of the maximum light emission luminance which is the maximum value in the range of light emission luminance in the preset organic EL element . In the luminance range, the organic EL element is set to have the maximum luminous efficiency.

  Further, the invention of claim 2 is the organic EL display according to claim 1, wherein the organic EL element in a luminance range of 1/3 to 1/2 of a preset maximum light emission luminance of the organic EL element. The emission efficiency is set to be 80% or more of the maximum emission efficiency of the organic EL element.

  The invention of claim 3 is the organic EL display according to claim 1 or claim 2, wherein the plurality of organic EL elements emits light of a first color; A second organic EL element that emits light of a second color different from the first color; and a third organic EL element that emits light of a third color different from the first and second colors; And at least one of the first to third organic EL elements has a maximum luminous efficiency within a luminance range of 1/3 to 1/2 of a preset maximum emission luminance. It is set as follows.

  The invention according to claim 4 is the organic EL display according to claim 3, wherein at least one of the first to third organic EL elements is set to a preset maximum emission luminance. The luminous efficiency in a luminance range of 1/3 to 1/2 of the above is set to be 80% or more of the maximum luminous efficiency.

  The invention according to claim 5 is the organic EL display according to claim 3 or claim 4, wherein all of the first to third organic EL elements are set to 1/3 of a preset maximum emission luminance. To ½ of the luminance range, each of which is set so that the light emission efficiency is maximized.

  The invention of claim 6 is the organic EL display according to claim 5, wherein for all of the first to third organic EL elements, 1/3 to 1/2 of the preset maximum emission luminance. The light emission efficiency in the luminance range is set so as to be 80% or more of the maximum light emission efficiency.

<Terminology>
In this specification, “light emission efficiency” refers to the current density (for example, unit: ampere per square meter [A / m 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 ]), and the brightness is divided by the current density. Further, the light emission efficiency is shown by appropriately setting the maximum value of the light emission efficiency of the organic EL element as 1 as a reference value.

  According to the first aspect of the present invention, since the light emission efficiency is set to be the maximum within the luminance range of 1/3 to 1/2 of the maximum light emission luminance, it is frequently used when displaying moving images. Luminous efficiency for the luminance range is improved, and power consumption when displaying a moving image can be reduced.

  According to the second aspect of the present invention, the light emission efficiency is the maximum light emission efficiency even when light having any luminance included in the luminance range of 1/3 to 1/2 of the maximum light emission luminance is emitted. By setting it to be 80% or more, it is possible to broadly improve the light emission efficiency for the luminance range that is frequently used when displaying moving images, so that power consumption when displaying moving images is reliably reduced. Can do.

  According to the invention described in claim 3, among the three types of organic EL elements that emit light of different colors, the organic EL element that emits light of at least one kind of color has a maximum light emission luminance of 1. By setting so that the light emission efficiency is maximized within the luminance range of / 3 to 1/2, the light emission efficiency in the luminance range that is frequently used at the time of moving image display is improved. Power consumption can be reduced.

  According to the invention described in claim 4, among the three types of organic EL elements that emit light of different colors, the organic EL element that emits light of at least one kind of color has a maximum emission luminance of 1. By setting the luminous efficiency in the luminance range from / 3 to 1/2 to be 80% or more of the maximum luminous efficiency, it is possible to broadly improve the luminous efficiency in the luminance range that is frequently used when displaying moving images. Therefore, it is possible to reliably reduce power consumption when displaying a moving image.

  In addition, according to the invention described in claim 5, the luminous efficiency is maximized within a luminance range of 1/3 to 1/2 of the maximum emission luminance for all three types of organic EL elements that emit light of different colors. By setting so as to become, it is possible to greatly reduce the power consumption when displaying a moving image.

  According to the sixth aspect of the present invention, the emission efficiency is maximized in the luminance range of 1/3 to 1/2 of the maximum emission luminance for all three types of organic EL elements that emit light of different colors. By setting it to be 80% or more of the efficiency, it is possible to broaden the light emission efficiency for the luminance range that is frequently used when displaying moving images. Can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Configuration of organic EL display>
FIG. 1 is a cross-sectional view schematically showing a configuration of an organic EL display 21 according to an embodiment of the present invention. The organic EL display 21 is a top emission type, and as shown in FIG. 1, a glass substrate (hereinafter referred to as “substrate”) 23 which is a transparent substrate, an element portion 25 formed on the substrate 23, An adjustment layer 26 formed on the element portion 25 and a sealing film 27 formed so as to cover the entire element portion 25 from above the adjustment layer 26 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.

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

  The adjustment layer 26 is for adjusting the light transmission characteristics of the first to third organic EL elements 51r, 51g, and 51b. The sealing film 27 is for sealing the organic layer 33, the second electrode 35, and the like, and is formed so as to completely cover a region where the element portion 25 of the organic EL display 21 is formed. . 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 a part of the light emitted from the organic layer 33 to the organic layer 33 side, and is constituted by a reflective electrode (opaque electrode) such as Al, for example.

  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 formed of a semi-transparent electrode, the second electrode 35 needs to have optical characteristics that allow visible light to pass therethrough. Therefore, such optical characteristics are realized by reducing the film thickness of the electrode. Here, examples of suitable materials for the transparent electrode include ITO and IZO. Suitable materials for the translucent electrode include alkali metals such as Li, alkaline earth metals such as Mg, Ca, Sr, Ba, Al, Si, Ag, and the like.

  As shown in FIG. 2, the organic layer 33 includes, in order from the substrate 23 side, a charge injection layer 41 for injecting holes or electrons, a charge transport layer 43 for transporting holes or electrons, A light emitting layer 45 that emits EL light, a charge transport layer 47 for transporting electrons or holes, and a charge injection layer 49 for injecting electrons or holes are provided. In the present embodiment, the organic layer 33 is formed in a five-layer structure, but various layer structures such as a two- to four-layer structure are adopted depending on various conditions.

  The configuration and material of the organic layer 33 are, for example, the reflection characteristics (opaque, translucent or transparent) and polarity (which one is on the anode side) of the first and second electrodes 31 and 35, and the organic layer 33. It is determined according to the type of emission color (red, green, blue) or the like. As a specific example, for example, a material such as Alq3 (aluminum quinolyl complex) emits green light and has excellent electron transport properties. Therefore, in the element unit 25 that emits green light, the light emitting layer and the electron transport are used. The layer may be composed of a single material such as Alq3. In addition, when a transparent electrode is used, a metal electron injection layer is often used.

<Relationship between luminous brightness and luminous efficiency>
FIG. 3 illustrates the relationship between the light emission luminance and the light emission efficiency of a general organic EL element. In FIG. 3, the horizontal axis indicates the light emission luminance, and the vertical axis indicates the light emission 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 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”. Note that “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 at a constant current.

  By the way, when an organic EL display is used for applications such as a videophone and a digital TV, it is expected that the frequency of displaying a moving image is increased. In general, when a moving image is displayed, a luminance range (gradation) of about 1/2 to 1/3 from the low luminance side in a gradation range (that is, luminance range) that can be displayed (that is, used) by the display. Range) is most often used.

  Therefore, the inventors of the present application have the luminous efficiencies of the first to third organic EL elements 51r, 51g, and 51b in the luminance range of 1/2 to 1/3 from the low luminance side in the luminance range to be used. By adjusting so as to improve the power consumption, it was created to reduce power consumption when displaying moving images on the organic EL display 21.

<Adjustment of luminous efficiency>
FIG. 4 shows the relationship between the light emission luminance and the light emission efficiency of the organic EL display 21 according to the embodiment of the present invention, that is, the light emission luminance range of 1/2 to 1/3 from the low luminance side in the luminance range to be used. 5 illustrates the relationship between the light emission luminance and the light emission efficiency when the light emission efficiency of the organic EL elements 51r, 51g, 51b is adjusted to be maximum. In FIG. 4, 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 each set to 1, which is the light emission luminance and the light emission efficiency. A curve Cv1 showing the relationship is shown. In FIG. 4, a predetermined light emission luminance range (light emission luminance = 0.3 to 0.00) that substantially corresponds to the light emission luminance range (light emission luminance = 1/3 to 1/2) frequently used during moving image display. 5) is hatched. Further, for comparison, the curve Cv shown in FIG. 3 is indicated by a broken line.

  As shown in FIG. 4, the organic EL elements 51r, 51g, and 51b according to the present invention have lower maximum efficiency luminance Spk compared to the relationship between the luminance and luminous efficiency (curve Cv) shown in FIG. Shifting to the 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 light emission luminance range (light emission luminance = 0.3 to 0.5) that is frequently used during moving image display. As described above, by adjusting so that the light emission efficiency at the light emission luminance = 0.3 to 0.5 is increased, the power consumption at the time of moving image display can be reduced.

  Further, for example, the light emission efficiency is 80% (that is, 0.8) or more of the maximum light emission efficiency in the entire region of light emission luminance = 1/2 to 1/3 (that is, light emission luminance = 0.3 to 0.5). By adjusting in this way, it is possible to reliably reduce power consumption when displaying a moving image. Further, from the viewpoint of reducing power consumption, the light emission efficiency is 90% of the maximum light emission efficiency (that is, 0%) in the entire light emission luminance = 1/2 to 1/3 (that is, light emission luminance = 0.3 to 0.5). .9) It is more preferable to adjust so that it may become more than. Further, when the moving image is displayed, if the frequency of use of the light emission luminance is substantially equal over the entire luminance range of 0.3 to 0.5, the maximum efficiency luminance is set to the approximate center of the light emission luminance = 0.3 to 0.5. It is preferable to adjust the value to a value in the vicinity of emission luminance = 0.4.

  By the way, as a factor for shifting the maximum efficiency luminance of each organic EL element 51r, 51g, 51b to the lower luminance side, that is, adjusting the peak shape of the curve indicating the relationship between the emission luminance and the emission efficiency, the organic layer 33 is configured. The thickness of each layer to be processed, the mobility of carriers, the concentration of impurities, and the like can be given.

  Here, factors relating to the adjustment of the maximum efficiency luminance (that is, the peak shape of a curve indicating the relationship between the light emission luminance and the light emission efficiency) for each of the organic EL elements 51r, 51g, 51b will be briefly described.

  FIG. 5 is a diagram illustrating a potential diagram for the organic EL elements 51r, 51g, and 51b. Here, as an example, Al 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 the charge transport is The layer 47 is configured as an electron transport layer and the charge injection layer 49 is configured as an electron injection layer.

  When light is emitted from such organic EL elements 51r, 51g, and 51b, as shown by arrows in FIG. 5, holes are emitted from the first electrode 31 side to the hole injection layer 41, the hole transport layer 43, and the light emission. While proceeding in the order of the layer 45, 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 on the light emitting surface EM of the light emitting layer 45.

Meanwhile, there is an external quantum efficiency eta _phi Representative ones showing the luminous efficiency of the organic EL element. The external quantum efficiency eta _phi, against injected electrons number shows the number of photons emitted in the organic EL element externally in the ratio, the higher the external quantum efficiency eta _phi, photon number is increased. And external quantum efficiency (eta) _phi is shown by the following Formula (1).

In Expression (1), γ represents a carrier balance factor (charge balance), η _r represents exciton generation efficiency, η _f represents emission quantum efficiency from the exciton, and η _ext represents external extraction efficiency (light extraction efficiency). . That is, the external quantum efficiency eta _phi, carrier balance factor gamma, exciton generation efficiency eta _r, luminescence quantum efficiency eta _f, and consists of four products in external extraction efficiency eta _ext. Among these four values, the three values of exciton generation efficiency η _r , emission quantum efficiency η _f , and external extraction efficiency η _ext are basically values even if the current value flowing through the organic EL element changes. Does not change. On the other hand, the value of the carrier balance factor γ changes with a change in the current value flowing through the organic EL element. Therefore, as shown in FIGS. 3 and 4, the change in the carrier balance factor γ causes the peak of the light emission efficiency with respect to the change in the light emission luminance.

  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 γ.

  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, 2) the carrier mobility in the organic layer 33, 3) Carrier density in the organic layer 33 by doping, 4) space charge limited current (SCLC), and the like.

  1) Regarding the height of the charge injection barrier, the ease with which charges (holes or electrons) reach the light emitting surface EM depends on the height of the barrier. Generally, in the organic layer used in the organic EL element, holes are more easily injected, so for example, by appropriately changing the material constituting the electron injection layer 49, the height of the charge injection barrier is adjusted, If electrons are easily injected, the maximum efficiency luminance can be shifted to the low luminance side.

  2) The mobility of carriers in the organic layer 33 can be adjusted by doping the organic layer 33 with impurities that hinder 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.

  3) The carrier density in the organic layer 33 by doping is improved by doping. 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, resulting in maximum The efficiency luminance can be shifted to the low luminance side.

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

In Equation (2), μ is the carrier mobility, ε ₀ is the vacuum dielectric constant, ε is the dielectric constant of the organic thin film, V is the applied voltage, and L is the thickness of the organic layer.

  As is clear from equation (2), the current value J 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.

  As described above, in the organic EL display 21 according to the embodiment of the present invention, the organic EL element is set so that the luminous efficiency is maximized within the luminance range of 1/3 to 1/2 of the maximum luminous luminance. Yes. By adopting such a configuration, light emission efficiency for a luminance range that is frequently used during moving image display is improved, so that power consumption during moving image display can be reduced.

  In particular, the light emission efficiency in a luminance range of 1/3 to 1/2 of 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 light emission efficiency in the luminance range frequently used during moving image display is widely improved. As a result, it is possible to reliably reduce power consumption when displaying a moving image.

  Further, all of the organic EL elements 51r, 51g, 51b that emit light of three different colors of RGB so that the light emission efficiency is maximized within a luminance range of 1/3 to 1/2 of the maximum light emission luminance. Is set. For this reason, the power consumption at the time of performing a moving image display can be reduced significantly. Furthermore, the light emission efficiency in the luminance range of 1/3 to 1/2 of 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, it is possible to widely increase the light emission efficiency for a luminance range that is frequently used during moving image display, and thus it is possible to reliably and significantly reduce power consumption when performing moving image display.

<Modification>
As mentioned above, although embodiment of this invention was described, this invention is not limited to the thing of the content demonstrated above.

  For example, in the above embodiment, the organic EL elements 51r. 51g. 51b is adjusted so that the maximum efficiency luminance appears in the range of light emission luminance frequently used during moving image display. However, the present invention is not limited to this. For example, for organic EL elements of at least one color of RGB Further, adjustment may be made so that the maximum efficiency luminance appears within the range of light emission luminance that is frequently used during moving image display.

  In the above embodiment, the organic EL display 21 that can emit three colors of RGB has been described. However, the present invention is not limited to this, and light of at least one color such as a monochrome organic EL display is used. By applying the present invention to an organic EL display that can emit light, it is possible to reduce power consumption when displaying a moving image.

<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 keeping the total film thickness of the second hole injection layer and the hole transport layer at 350 mm. The configuration of each layer is as follows.

(a) Anode (first electrode)
Material: Aluminum Film thickness: 500mm
(b) First hole injection layer Material: NiOx Film thickness: 50 mm
(c) Second hole injection layer Material: CuPc Film thickness: 180 mm or 140 mm
(d) Hole transport layer Material: α-NPD Film thickness: 170 mm or 210 mm
(e) Light emitting layer Host material: CBP Guest material: Btp2Ir (acac)
Total film thickness: 350mm Concentration of guest material with respect to host material: 5wt%
(f) Hole blocking layer Material: BAlq Film thickness: 100 mm
(g) Electron transport layer Material: Alq Film thickness: 150 mm
(h) Electron injection layer Material: LiF
Film thickness: 5mm
(i) Cathode (second electrode)
Material: Mg: Ag (Mg-Ag alloy)
Film thickness: 200 mm.

  6 shows the above-described embodiment (Example 1: film thickness of the second hole injection layer 180 Å-hole transport layer 170 Å, Example 2: film thickness of the second hole injection layer 140 Å-holes. It is the figure which measured the current density at the time of light emission, and light emission brightness | luminance, and plotted the relationship between light emission brightness | luminance and light emission efficiency about the structure of the film thickness of a transport layer (210mm). In FIG. 6, the black square mark and the polygonal line L1 connecting the black square mark indicate the result according to the configuration of the first embodiment, and the white diamond mark and the polygonal line L2 connecting the white diamond mark are related to the configuration of the second embodiment. Results are shown. Further, in FIG. 6, for comparison, a comparative example in which the thicknesses of the second hole injection layer and the hole transport layer are changed from the configurations of Examples 1 and 2 (Comparative Example 1: of the second hole injection layer). Also shown are the results relating to the constitution of film thickness of 100Å-hole transport layer thickness of 250 層, comparative example 2: second hole injection layer thickness of 20Å-hole transport layer thickness of 330Å). Note that 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. Show.

Here, 900 cd / m ² is set as the maximum light emission luminance, and the range of light emission luminance frequently used when displaying moving images is 1/3 to 1/2 of the maximum light emission luminance, that is, 300 to 450 cd / m ^2. It will be described as being in the range.

As shown in FIG. 6, the maximum efficiency luminance of Example 1 (the light emission brightness when the light emission efficiency is maximized) is 308 cd / m ² , and the maximum efficiency brightness of Example 2 is 383 cd / m ² , and at the time of moving image display The maximum efficiency luminance was included in the frequently used emission luminance range (300 to 450 cd / m ² ). In contrast, the maximum efficiency luminance of Comparative Example 1 is 537 cd / m ² , and the maximum efficiency luminance of Comparative Example 2 is 757 cd / m ^2. m ² ) did not include the maximum efficiency luminance.

  In this way, by frequently 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, it is frequently used when displaying moving images. It is possible to adjust so that the maximum efficiency luminance is included in the range of the emission luminance used in the above.

<Example in which the maximum luminance is adjusted by the presence of the hole injection layer>
In this embodiment, an organic layer in which an anode, a first hole injection layer, a second hole injection layer, a third hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode are stacked in this order. An EL element was produced. The configuration of each layer is as follows.

(a) Anode (first electrode)
Material: Aluminum Film thickness: 500mm
(b) First hole injection layer Material: TiOx Film thickness: 10 mm
(c) Second hole injection layer Material: CFx Film thickness: 15 mm
(d) Third hole injection layer Material: CuPc Film thickness: 225 mm
(e) Hole transport layer Material: α-NPD Film thickness: 100 mm
(f) Light emitting layer Host material: CBP Guest material: FIrpic
Total film thickness: 270 mm Concentration of guest material relative to host material: 5 wt%
(g) Electron transport layer Material: Alq Film thickness: 240mm
(h) Electron injection layer Material: LiF
Film thickness: 5mm
(i) Cathode (second electrode)
Material: Mg: Ag (Mg-Ag alloy)
Film thickness: 200 mm.

  FIG. 7 is a graph plotting the relationship between the light emission luminance and the light emission efficiency by measuring the current density and the 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. 7, a white diamond mark and a broken line L3 connecting the white diamond marks indicate the results of the configuration of Example 3. Furthermore, in FIG. 7, the result concerning the structure of the comparative example (comparative example 3: no 3rd hole injection layer) which excluded the 3rd hole injection layer from the structure of Example 3 is also shown for the comparison. ing.

Here, 600 cd / m ² is set as the maximum light emission luminance, and the range of light emission luminance frequently used when displaying moving images is 1/3 to 1/2 of the maximum light emission luminance, that is, 200 to 300 cd / m ^2. It will be described as being in the range.

As shown in FIG. 7, the maximum efficiency luminance of Example 3 was included in the light emission luminance range (200 to 300 cd / m ² ) frequently used during moving image display. On the other hand, the maximum efficiency luminance of Comparative Example 3 was present on the higher luminance side than the light emission luminance range (200 to 350 cd / m ² ) frequently used during moving image display.

  Thus, by interposing the third hole injection layer in the organic EL element and shifting the maximum efficiency brightness to the low brightness side, the maximum efficiency brightness is within the range of the light emission brightness frequently used at the time of moving image display. Can be adjusted to be included.

It is sectional drawing which shows the structure of the organic electroluminescent display which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the organic electroluminescent display which concerns on embodiment of this invention. It is a figure which illustrates the relationship between the light-emitting luminance of a general organic EL element, and luminous efficiency. It is a figure which illustrates the relationship between the light emission luminance after adjustment, and light emission efficiency. It is a figure which shows the potential diagram of an organic EL element. It is a figure which shows the relationship between the light-emitting luminance and luminous efficiency of the Example and comparative example of this invention. It is a figure which shows the relationship between the light-emitting luminance and luminous efficiency of the Example and comparative example of this invention.

Explanation of symbols

21 Organic EL Display 25 Element Unit 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)
51b Third organic EL element 51g Second organic EL element 51r First organic EL element EM Light emitting surface Spk Maximum efficiency luminance

Claims (6)

An organic EL display for displaying moving images,
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;
The light emission efficiency of the organic EL element is maximized within a brightness range of 1/3 to 1/2 of the maximum light emission brightness, which is the maximum value of the light emission brightness range in the preset organic EL element. A carrier balance factor is set , and the carrier balance factor is (1) a height of a charge injection barrier from the first and second electrodes to the organic layer, (2) carrier mobility in the organic layer, (3) An organic EL display which is adjusted by carrier density in the organic layer by doping or (4) space charge limited current (SCLC) to determine a peak of light emission efficiency with respect to a change in light emission luminance .
The organic EL display according to claim 1,
The light emission efficiency of the organic EL element in a preset luminance range of 1/3 to 1/2 of the maximum light emission brightness of the organic EL element is set to be 80% or more of the maximum light emission efficiency of the organic EL element. Organic EL display characterized by being made.
The organic EL display according to claim 1 or 2, wherein
A plurality of organic EL elements that emit light of a first color; a second organic EL element that emits light of a second color different from the first color; A third organic EL element that emits light of a third color different from the first and second colors,
One or more organic EL elements among the first to third organic EL elements are configured such that the luminous efficiency is maximized within a preset luminance range of 1/3 to 1/2 of the maximum emission luminance. An organic EL display that is set.
The organic EL display according to claim 3,
With respect to one or more organic EL elements among the first to third organic EL elements, the light emission efficiency in a luminance range of 1/3 to 1/2 of the preset maximum light emission luminance is 80% or more of the maximum light emission efficiency. An organic EL display that is set to be
The organic EL display according to claim 3 or 4, wherein
All of the first to third organic EL elements are set so that the light emission efficiency is maximized within a luminance range of 1/3 to 1/2 of the preset maximum light emission luminance. Organic EL display.
The organic EL display according to claim 5,
All of the first to third organic EL elements were set such that the light emission efficiency in a luminance range of 1/3 to 1/2 of the preset maximum light emission luminance was 80% or more of the maximum light emission efficiency. An organic EL display characterized by that.

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