JP2007266580A - Organic EL display and image display device using the same - Google Patents

Abstract

A technique for reducing power consumption or driving voltage in an organic EL display is provided.
A plurality of organic EL displays 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. And a peak at which the luminous efficiency of the organic EL element is maximized is set within a predetermined range of 90% to 110% of the maximum luminance of the organic EL element. Yes.
[Selection] Figure 5

Description

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

  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.

  Since a normal organic EL display is required to emit light with high luminance, high luminance is obtained by applying a high voltage to the organic EL element to increase the current density flowing through the light emitting layer.

Japanese Patent Laid-Open No. 2003-59651 JP 2002-72629 A

  However, in an organic EL display, a voltage required for light emission at the maximum gradation is determined. Therefore, unless a device for reducing the required voltage is applied, power consumption and boosting The size of a power supply circuit such as a circuit increases.

  This invention is made | formed in view of the said subject, and it aims at providing the technique which reduces the voltage required in an organic electroluminescent display.

  In order to solve the above problems, the invention of claim 1 is an organic EL display, wherein the organic layer is composed of one or more layers including a light emitting layer, and the first and A plurality of organic EL elements each having two electrodes, and the light emission efficiency of the organic EL element is maximum within a preset light emission luminance range of 90% to 110% of the maximum light emission luminance of the organic EL element. It is characterized in that the peak is located.

  The invention of claim 2 is the organic EL display according to claim 1, wherein the plurality of organic EL elements emit a first color light, and the first organic EL element emits light of a first color. A second organic EL element that emits light of a second color different from the color, and a third organic EL element that emits light of a third color different from the first and second colors, With respect to one or more organic EL elements among the first to third organic EL elements, the light emission efficiency of the organic EL element is maximum within a light emission luminance range of 90% to 110% of a preset maximum light emission luminance. A peak is located.

  The invention of claim 3 is the organic EL display according to claim 2, wherein the organic EL display that requires the highest voltage at a preset maximum emission luminance among the first to third organic EL elements. The element is characterized in that a peak where the light emission efficiency is maximum is located within a range of light emission luminance of 90% to 110% of the preset maximum light emission luminance.

  The invention of claim 4 is the organic EL display according to claim 2 or claim 3, wherein 90% to 90% of the preset maximum emission luminance is obtained for all of the first to third organic EL elements. A peak at which the luminous efficiency is maximized is located within a range of 110% emission luminance.

  According to a fifth aspect of the present invention, in the organic EL display according to any one of the second to fourth aspects, the first color is red, the second color is green, and the third color is blue. The difference ΔSpk between the maximum light emission luminance of the organic EL element that is predetermined for each of the first to third colors and the light emission luminance that maximizes the light emission efficiency of the organic EL element is the value of the first The first organic EL element is set smaller than the first organic EL element and smaller than the second organic EL element, and is set smaller than the second organic EL element in the first organic EL element.

  According to a sixth aspect of the present invention, in the image display device, the organic EL display according to any one of the second to fifth aspects, a first power supply circuit that supplies power to the first organic EL element, and the A second power supply circuit for supplying power to the second organic EL element, and a third power supply circuit for supplying power to the third organic EL element are provided.

  According to a seventh aspect of the present invention, in the image display device, the organic EL display according to any one of the second to fifth aspects and a power supply circuit that supplies power to the organic EL element in common are provided. Features.

  The invention according to claim 8 is the image display device according to claim 6, further comprising a battery connected in common to the first to third power supply circuits.

  The invention of claim 9 is the image display device according to claim 7, further comprising a battery connected to the power supply circuit.

  According to the first aspect of the present invention, it is necessary for the organic EL element because the peak at which the light emission efficiency is maximum is located within the light emission luminance range of 90% to 110% of the preset maximum light emission luminance. Therefore, the voltage required for the organic EL display can be reduced.

  According to the second aspect of the present invention, 90% to 110% of the preset maximum emission luminance is set for one or more organic EL elements that emit light of three different colors. The voltage required for the organic EL display can be reduced by positioning the peak at which the light emission efficiency is maximized within the range of the light emission luminance of%.

  According to the invention described in claim 3, among the three types of organic EL elements that emit light of different colors, the maximum light emission set in advance for the organic EL element that requires the highest voltage at the maximum light emission luminance. The voltage required for the organic EL display can be easily reduced because the peak at which the light emission efficiency is maximized is located within the light emission luminance range of 90% to 110% of the luminance.

  According to the invention described in claim 4, all of the three types of organic EL elements that emit light of different colors are within the range of 90% to 110% of the preset maximum emission luminance. By positioning the peak at which the luminous efficiency is maximized, the voltage required for the organic EL display can be more effectively reduced.

  According to the invention of claim 5, the difference ΔSpk between the maximum emission luminance predetermined for each of the red, green and blue organic EL elements and the emission luminance at which the emission efficiency of the organic EL element is maximized. Is set to be smaller in the blue organic EL element than in the red and green organic EL elements and smaller in the red organic EL element than in the green organic EL element. The peak position of the organic EL element is adjusted in consideration of the above characteristics. As a result, it is possible to keep power consumption small while maintaining high productivity of the organic EL display.

  According to the invention described in claim 6 or claim 7, the above-described organic EL display and a power supply circuit for supplying power individually or in common to the first to third organic EL elements are provided. For this reason, a small-sized image display device can be realized by downsizing the power supply circuit by reducing the power consumption of the organic EL display.

  Further, according to the invention described in claim 8 or claim 9, the battery further includes a battery connected to the power supply circuit. Therefore, the battery can be reduced in size by reducing the power consumption of the organic EL display, thereby reducing the size of the battery. An image display device can be realized.

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

<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 luminance is represented 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.

<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, as shown in FIG. 2, the first to third organic EL elements corresponding to the respective colors of red (R), green (G), and blue (B). A plurality of 51r, 51g, and 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, 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 according to 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 Alq ₃ (aluminum quinolyl complex) emits green light and has an excellent electron transport property. Therefore, in the element unit 25 that emits green light, a light emitting layer and an electron are used. The transport layer may be made of a single material such as Alq ₃ . 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.

  FIG. 3 shows an example in which the light emission efficiency becomes maximum (peak value) when the light emission luminance is a value Spk smaller than the maximum light emission luminance. 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.

  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 a plurality of circuits such as transistors, but in FIG. 4, in order to prevent complication of the diagram, a general organic configuration is used. The outline which simplified the circuit composition of EL element is shown.

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

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

  Therefore, the inventors of the present application adjust 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. Thus, it was created to reduce the voltage required in the organic EL display 21. In addition, by reducing the required voltage, it was also possible to reduce the size of power supply circuits such as a booster circuit and reduce power consumption.

<Adjustment of luminous efficiency>
FIG. 5 shows the relationship between the light emission luminance and the light emission efficiency of the organic EL display 21 according to an embodiment of the present invention, that is, the light emission 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 when the efficiency is adjusted to the maximum is illustrated.

  In FIG. 5, 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. Further, for comparison, the curve Cv shown in FIG. 3 is indicated by a broken line.

  As shown in FIG. 5, in the first to third organic EL elements 51r, 51g, and 51b according to the present embodiment, compared with the relationship (curve Cv) between the light emission luminance and the light emission efficiency shown in FIG. The maximum efficiency luminance Spk is shifted to the high luminance side. The light emission efficiency shows a peak value (maximum light emission efficiency) at the maximum light emission luminance (light emission luminance = 1). That is, the light emission efficiency of the first to third organic EL elements 51r, 51g, and 51b is set to the maximum at the maximum light emission luminance.

  Thus, the voltage required in the organic EL display 21 can be reduced by improving the light emission efficiency at the maximum light emission luminance.

  Here, as shown in FIG. 5, 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, the emission efficiency at the maximum emission luminance can be improved by adjusting the peak where the emission efficiency is maximum within the emission luminance range of 90% to 110% of the maximum emission luminance. The voltage required in the organic EL display 21 can be reduced. However, from the viewpoint of reducing the voltage required in the organic EL display 21 as much as possible, the light emission efficiency of the first to third organic EL elements 51r, 51g, 51b is set to be maximum at the maximum light emission luminance. It is more preferable that the maximum light emission luminance and the maximum efficiency luminance Spk completely match. However, since such adjustment is very complicated, it is preferable that the difference ΔSpk between the maximum efficiency luminance Spk and the maximum light emission luminance of each color satisfies the relationship of B <R <G. This is because the blue organic EL element 51b has a short wavelength in RGB, and has low luminous efficiency and low visibility, and it is preferable that the maximum light emission luminance and the maximum efficiency luminance Spk be closest to each other. On the other hand, since the green organic EL element 51g has good light emission efficiency and good visibility, the demand for bringing the maximum light emission luminance and the maximum efficiency luminance Spk closer to each other among RGB is the lowest. Therefore, if the relationship of B <R <G is established for the difference ΔSpk between the maximum efficiency luminance Spk and the maximum light emission luminance, the power consumption can be reduced while satisfactorily preventing the decrease in productivity of the organic EL display. It can be kept small.

  By the way, as a factor for shifting the maximum efficiency luminance of each organic EL element 51r, 51g, 51b, that is, a factor for adjusting the peak shape of the curve indicating the relationship between the emission luminance and the emission efficiency, Examples include a film thickness, carrier mobility, and impurity concentration.

  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. 6 is a diagram illustrating a potential diagram for the first to third 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, 51b, as shown by arrows in FIG. 6, holes are injected from the first electrode 31 side into 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 5, the change in the carrier balance factor γ causes a peak in luminous efficiency with respect to the change in 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 it is difficult to inject electrons, the maximum efficiency luminance can be shifted to the high 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, by reducing the impurities doped in each layer (hole injection layer 41, hole transport layer 43, etc.) on the path of movement of holes and increasing the mobility of carriers, It is possible to relatively promote the movement of holes, and as a result, the maximum efficiency luminance can be shifted to the high 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 (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.

  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 thickness of each layer constituting the organic layer 33 while keeping the thickness of the organic layer 33 constant, the flow of holes is promoted while inhibiting the flow of electrons. be able to. As a result, the maximum efficiency luminance can be shifted to the high luminance side.

The power efficiency of the organic EL display, since it is multiplied by the voltage efficiency to the external quantum efficiency eta _phi, by adjusting the external quantum efficiency eta _phi as described above, it is possible to improve the power efficiency. The voltage efficiency is determined by factors such as the voltage efficiency in the organic EL element and the voltage drop in the TFT circuit.

  As described above, in the organic EL display 21 according to the embodiment of the present invention, the organic EL elements 51r, 51g, and 51b are within the range of the light emission luminance of 90% to 110% of the maximum light emission luminance. Is set to maximize the luminous efficiency. By adopting such a configuration, the voltage required in each of the organic EL elements 51r, 51g, 51b can be reduced, so that the voltage required in the organic EL display 21 can be reduced. If the applied voltage can be reduced, the power consumption of the organic EL display 21 can be reduced as a result, considering that the power consumption is obtained by multiplying the voltage by the current.

  Also, considering application to mobile phone displays and personal computer screens, these screens often display still images, in which case high gradation (high brightness) is frequently used. . Considering such an application, the power consumption can be reduced by increasing the light emission efficiency at high luminance as described above.

  In addition, if the voltage to be applied may be low, the circuit for supplying the voltage (power supply circuit) and the battery connected to the power supply circuit can be reduced in size, and the organic EL display can be applied to a small device such as a cellular phone. Effective when installed.

  In particular, when the organic EL elements 51r, 51g, and 51b are set to have the maximum luminous efficiency at the maximum light emission luminance, the voltage required for each of the organic EL elements 51r, 51g, and 51b is more effectively obtained. Can be reduced. That is, the voltage required for the organic EL display 21 can be more effectively reduced.

  Further, the organic layer 33 is in a state where the number of holes is larger than the number of electrons (hole rich state) when the light emission luminance is lower than the maximum efficiency luminance. For example, an organic layer that is weak against holes (the electron transport layer 47 and the electron injection layer 49 in FIG. 6) easily deteriorates due to the penetration of holes, but no holes are formed between the light emitting layer 45 and the electron transport layer 47. By providing the hole blocking layer that prevents invasion, the electron transport layer 47 and the electron injection layer 49 can be prevented from deteriorating. On the other hand, for example, the organic layer that is weak against electrons (the hole transport layer 43 and the hole injection layer 41 in FIG. 6) is easily deteriorated by the penetration of electrons, but there is almost no material for forming 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. Because of the invasion, the organic layer 33 is likely to deteriorate. In this regard, in the organic EL display 21 according to the embodiment of the present invention, the peak of the luminous efficiency is set on the relatively high luminance side (in the vicinity of the maximum luminous luminance in FIG. 5) as shown in FIG. The deterioration of the organic layer 33 is suppressed.

<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.

  For example, in the above embodiment, the first to third organic EL elements 51r, 51g, 51b are all set so that the light emission efficiency is maximized within the light emission luminance range of 90% to 110% of the maximum light emission luminance. However, it is not limited to this. For example, for at least one of the first to third organic EL elements 51r, 51g, 51b, the light emission efficiency is maximum within a range of 90% to 110% of the maximum light emission luminance. Even if it sets so that it may become, the voltage required by an organic electroluminescent display can be reduced.

  However, for example, when different power supply circuits are provided for the first to third organic EL elements 51r, 51g, and 51b, for all of the first to third organic EL elements 51r, 51g, and 51b, When the light emission efficiency is set to the maximum within the light emission luminance range of 90% to 110% of the maximum light emission luminance, the organic EL display 21 as a whole reduces the required voltage and power consumption, and the power circuit and battery. It is preferable to further reduce the size of the device.

  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 becomes maximum at the maximum light emission luminance, the organic EL display The required voltage can be further reduced.

  However, for example, when different power supply circuits are provided for the first to third organic EL elements 51r, 51g, and 51b, for all of the first to third organic EL elements 51r, 51g, and 51b, Setting the luminous efficiency to be the maximum at the maximum luminous brightness makes it possible to more effectively reduce the required voltage and power consumption and reduce the size of the power supply circuit for the organic EL display 21 as a whole. Is preferable.

  Further, when an organic EL display is mounted on a small device such as a cellular phone, for example, for the first to third organic EL elements 51r, 51g, 51b, in order to reduce the size of the power supply circuit, One common power supply circuit may be used. In each of the organic EL elements 51r, 51g, 51b, among the first to third organic EL elements 51r, 51g, 51b, for example, due to the material type of the organic layer 33, the energy of the wavelength of the light, etc. In some cases, the voltage required for light emission in the third organic EL element 51b is the highest.

Thus, the case where the voltage required for light emission of the 3rd organic EL element 51b among the 1st to 3rd organic EL elements 51r, 51g, 51b becomes the highest will be described. Here, it is assumed that the luminance of light of the highest gradation (that is, white light) of the organic EL display 21 is 200 cd / m ² .

200 cd / m in order to obtain a ^second white light, one of the best luminance 60 cd / m ² of the R color lights maximum brightness of the B color light emitted from the pixel is emitted from 50 cd / m ^2, one pixel, 1 The maximum luminance of G color light emitted from one pixel is required to be 90 cd / m ² .

In order to obtain B light of 50 cd / m ² , the third organic EL element 51b that actually emits light in consideration of the ratio of time during which the element emits light (duty) and the aperture ratio of the pixel. There is a need to emit light of 1428 cd / m ² . That is, the maximum light emission luminance of the third organic EL element 51b needs to be about 1430 cd / m ² .

As shown in FIG. 7, each pixel has a characteristic of repeating light emission and non-light emission, and the ratio of the time during which the element emits light is duty. As shown in FIG. 8, one pixel is divided into three light-emitting areas of RGB, and the portions that emit light of each color are further reduced. The ratio of the portion that emits light of one color in one pixel is the aperture ratio. Here, assuming that the duty is about 44% and the aperture ratio is 8 (= [1/3] × 24)%, the maximum light emission luminance of the third organic EL element 51b is 1430 (≈50 × [100 / 44] × [100/8]) cd / m ² is calculated. Further, by the same calculation, the maximum light emission luminance of the first organic EL element 51r is calculated as 1714 cd / m ^2, and the maximum light emission luminance of the second organic EL element 51g is calculated as 2570 cd / m ² .

Furthermore, since the voltage efficiency when the third organic EL element 51b emits light at the maximum light emission luminance (1430 cd / m ² ) is about 170 cd / m ² / V, a driving voltage of about 8.4 V is required. Further, since the voltage efficiency when the first organic EL element 51r emits light at the maximum light emission luminance (1714 cd / m ² ) is about 230 cd / m ² / V, a driving voltage of about 7.5 V is required. Furthermore, since the voltage efficiency when the second organic EL element 51g emits light at the maximum light emission luminance (2570 cd / m ² ) is about 395 cd / m ² / V, a driving voltage of about 6.5 V is required.

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

  When a common power supply circuit is used for the first to third organic EL elements 51r, 51g, 51b, at least the maximum light emission luminance among the first to third organic EL elements 51r, 51g, 51b. If the third organic EL element 51b requiring the highest voltage in the above is set so that the light emission efficiency is maximized within the light emission luminance range of 90% to 110% of the maximum light emission luminance, 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, a battery may be connected to a common power supply circuit. Even when the common power supply circuit is not used for the first to third organic EL elements 51r, 51g, and 51b, the maximum light emission of the third organic EL element 51b that requires the highest voltage at least at the maximum light emission luminance. If the light emission efficiency is set to the maximum within the light emission luminance range of 90% to 110% of the luminance, the necessary voltage and power consumption can be reduced, and the size of the power supply circuit can be reduced. it can. In this case, for 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 that is used in this manner may be provided with a battery that is commonly connected to the third power supply circuit.

  In the above, among the first to third organic EL elements 51r, 51g, 51b, the third organic EL element 51b required the highest voltage in the maximum light emission luminance, but the present invention is not limited to this, and other organic EL elements The EL elements 51r and 51g 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 subjected to adjustment of the peak position of the luminous efficiency.

  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, the voltage required in the organic EL display can be reduced.

  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.

(a) Anode (first electrode)
Material: ITO
(b) Hole injection layer Material: CuPc Film thickness: 50 mm
(c) Hole transport layer Material: α-NPD Film thickness: 230 mm
(d) Light emitting layer Material: Alq ₃ (Host material): Rubrene (Doping material)
Alq ₃ : Rubrene = 99% by mass: 1% by mass
Film thickness: 240mm
(e) Electron transport layer Material: Alq Film thickness: 200 mm
(f) Electron injection layer Material: LiF Film thickness: 5 mm
(g) Cathode (second electrode)
Material: Mg: Ag (Mg-Ag alloy), Mg: Ag = 90 mass%: 10 mass%

  FIG. 9 is a diagram showing 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. In FIG. 9, the curve C1 shows the result according to the configuration of the example.

  Further, in FIG. 9, for comparison, the total film thickness of the organic layer is set to about 1 while maintaining the ratio of the materials and thicknesses (that is, the basic element structure) constituting each organic layer on the basis of the configuration of the example. Results of Comparative Example 1 in which the total film thickness of the organic layer is about 1.60 times, and Comparative Example 3 in which the total film thickness of the organic layer is about 2.00 times Is shown. The curve C2 indicates the result according to the configuration of the comparative example 1, the curve C3 indicates the result according to the configuration of the comparative example 2, and the curve C4 indicates the result according to the configuration of the comparative example 3.

Here, a description will be given assuming that 1430 cd / m ² is set as the maximum light emission luminance.

As shown in FIG. 9, the maximum efficiency luminance (emission luminance when the luminous efficiency is maximized) of the example is about 1430 cd / m ² , and the maximum emission luminance and the maximum efficiency luminance substantially coincide. In contrast, the maximum efficiency luminance of Comparative Example 1 is 1119 cd / m ² , the maximum efficiency luminance of Comparative Example 2 is 886 cd / m ² , and the maximum efficiency luminance of Comparative Example 3 is 640 cd / m ² , The maximum efficiency luminance is not near the maximum light emission luminance, and the light emission efficiency at the maximum light emission luminance is slightly low.

  In this way, the maximum efficiency luminance is changed by reducing the total film thickness of the organic layer while maintaining the ratio of the materials constituting each organic layer and the thickness (that is, the basic element structure), thereby changing the maximum luminance. The maximum efficiency luminance can be substantially matched.

  FIG. 10 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 embodiment. In FIG. 10, the plot P1 shows the result according to the configuration of the example. Moreover, in FIG. 10, the result which concerns on the structure of the said Comparative Examples 1-3 is shown for the comparison. In addition, the plot P2 shows the result concerning the configuration of Comparative Example 1, the plot P3 shows the result concerning the configuration of Comparative Example 2, and the plot P4 shows the result concerning the configuration of Comparative Example 3. Further, FIG. 10 also shows the result relating to the configuration having the total film thickness between the example and the comparative example 1. FIG. 11 shows a table showing the relationship between the film thickness, the driving voltage at the maximum light emission luminance, and the maximum efficiency luminance for Comparative Examples 1 to 3 and other configurations when the total film thickness of the example is 1. Show.

  As shown in FIG. 10, the driving voltage required for the maximum light emission luminance can be reduced as the maximum efficiency luminance is made closer to the maximum light emission luminance.

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 the schematic diagram which simplified and showed the circuit structure of the organic EL display. 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 ratio of the time when the organic EL element is light-emitting. It is a figure which shows the ratio of the light emission area which occupies in a pixel. It is a figure which shows the relationship between the light-emitting luminance and luminous efficiency of an Example and a comparative example. It is a figure which shows the relationship between the maximum efficiency brightness | luminance and required voltage of an Example and a comparative example. It is a figure which shows the relationship between the film thickness about the Example and a comparative example, the drive voltage at the time of the maximum light emission brightness | luminance, and the maximum efficiency brightness | luminance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Organic electroluminescent display 23 Substrate 25 Element part 26 Adjustment layer 27 Sealing film 31 1st electrode 33 Organic layer 35 2nd electrode 41 Hole injection layer (charge injection layer)
43 Hole transport layer (charge transport layer)
45 Light emitting layer 47 Electron transport layer (charge transport layer)
49 Electron injection layer (charge injection layer)
51 Light Emitting Diodes 51r, 51b, 51g Organic EL Element 100 Power Supply Spk Maximum Efficiency Brightness V Power Supply Voltage

Claims (9)

An organic EL display,
A plurality of organic EL elements each having an organic layer composed of 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, wherein a peak at which the light emission efficiency of the organic EL element is maximized is located within a range of 90% to 110% of the maximum light emission brightness of the organic EL element set in advance. The organic EL display according to claim 1,
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,
With respect to one or more organic EL elements among the first to third organic EL elements, the light emission efficiency of the organic EL element is maximum within a range of light emission luminance of 90% to 110% of the preset maximum light emission luminance. An organic EL display characterized in that a peak is located. The organic EL display according to claim 2,
Among the first to third organic EL elements, a range of 90% to 110% emission luminance of the preset maximum emission luminance for an organic EL element that requires the highest voltage with the preset maximum emission luminance. An organic EL display having a peak at which the luminous efficiency is maximized. The organic EL display according to claim 2 or 3, wherein
For all of the first to third organic EL elements, a peak where the light emission efficiency is maximum is located within a light emission luminance range of 90% to 110% of a preset maximum light emission luminance. EL display. The organic EL display according to any one of claims 2 to 4,
The first color is red, the second color is green, and the third color is blue;
The difference ΔSpk between the maximum light emission luminance of the organic EL element that is predetermined for each of the first to third colors and the light emission luminance that maximizes the light emission efficiency of the organic EL element is the first and the second values. An organic EL display that is smaller than the second organic EL element in the third organic EL element and smaller in the first organic EL element than the second organic EL element. In an image display device,
6. The organic EL display according to claim 2, a first power supply circuit for supplying power to the first organic EL element, and a second for supplying power to the second organic EL element. An image display device comprising: a power supply circuit; and a third power supply circuit that supplies power to the third organic EL element. In an image display device,
An image display device comprising: the organic EL display according to claim 2; and a power supply circuit for commonly supplying power to the organic EL element. The image display device according to claim 6,
An image display device further comprising a battery commonly connected to the first to third power supply circuits. The image display device according to claim 7,
An image display device further comprising a battery connected to the power supply circuit.

Images