WO2014200034A1 - 有機エレクトロルミネッセンス素子の駆動方法 - Google Patents
有機エレクトロルミネッセンス素子の駆動方法 Download PDFInfo
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- WO2014200034A1 WO2014200034A1 PCT/JP2014/065510 JP2014065510W WO2014200034A1 WO 2014200034 A1 WO2014200034 A1 WO 2014200034A1 JP 2014065510 W JP2014065510 W JP 2014065510W WO 2014200034 A1 WO2014200034 A1 WO 2014200034A1
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2003—Display of colours
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/60—Circuit arrangements for operating LEDs comprising organic material, e.g. for operating organic light-emitting diodes [OLED] or polymer light-emitting diodes [PLED]
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
- H10K71/70—Testing, e.g. accelerated lifetime tests
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F21—LIGHTING
- F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
- F21Y2105/00—Planar light sources
- F21Y2105/10—Planar light sources comprising a two-dimensional array of point-like light-generating elements
- F21Y2105/14—Planar light sources comprising a two-dimensional array of point-like light-generating elements characterised by the overall shape of the two-dimensional array
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F21—LIGHTING
- F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
- F21Y2115/00—Light-generating elements of semiconductor light sources
- F21Y2115/10—Light-emitting diodes [LED]
- F21Y2115/15—Organic light-emitting diodes [OLED]
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2310/00—Command of the display device
- G09G2310/06—Details of flat display driving waveforms
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/04—Maintaining the quality of display appearance
- G09G2320/043—Preventing or counteracting the effects of ageing
- G09G2320/045—Compensation of drifts in the characteristics of light emitting or modulating elements
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/0626—Adjustment of display parameters for control of overall brightness
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/0666—Adjustment of display parameters for control of colour parameters, e.g. colour temperature
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
- G09G2330/04—Display protection
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/30—Devices specially adapted for multicolour light emission
- H10K59/32—Stacked devices having two or more layers, each emitting at different wavelengths
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
- Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
Definitions
- the present invention relates to a method for driving an organic electroluminescence element.
- organic electroluminescence element (organic EL element) has advantages such as less viewing angle dependency, a high contrast ratio, and a reduction in thickness as compared with a liquid crystal display device.
- organic EL element has advantages such as less viewing angle dependency, a high contrast ratio, and a reduction in thickness as compared with a liquid crystal display device.
- portable displays and portable rear displays using organic EL elements have been actively put on the market. Display using these organic EL elements is expected to be put on the market for large TVs due to its high visibility, and some plans for launch are reported. Yes.
- the organic EL element is a self-luminous light source and is a surface-emitting light source, it has been spotlighted as next-generation illumination and has been developed in various places as organic EL illumination.
- the organic EL element has RGB light emitting materials between the electrodes, and is prepared by arbitrarily adjusting and driving RGB light output, or by applying a layer design including the thickness of the organic layer.
- the emission color and emission color intensity can be freely changed.
- the organic EL element can emit light freely as a white color required for illumination use, for example, from a light bulb color such as a color temperature of 2000K or 3000K to a daylight white color such as 5000K or 6000K.
- a phosphorescent material it is possible to realize luminous efficiency equivalent to or exceeding that of LEDs and fluorescent lamps, and realization as thinning illumination is expected.
- an illumination or light source that changes colors by forming the RGB light emitting layer in a strip shape in the horizontal direction and changing the intensity ratio of each emitted color is also proposed.
- an illumination or light source that changes colors by forming the RGB light emitting layer in a strip shape in the horizontal direction and changing the intensity ratio of each emitted color is also proposed.
- the life (deterioration rate) of each light emitting layer is different. For this reason, the color tone of the light emission color of the organic electroluminescence element changes from the initial color tone over time. As a result, the display quality of the organic electroluminescence element is deteriorated over time.
- the present invention provides a method for driving an organic electroluminescence element capable of suppressing a decrease in display quality.
- the organic electroluminescence element driving method of the present invention is a driving method of an organic electroluminescence element in which a first current peak value is applied to a first light emitting layer and a second current peak value is applied to a second light emitting layer, A second current peak value having a current density lower than the first current peak value is applied to the second light emitting layer having a light emission efficiency lower than that of the first light emitting layer at the current density of the second current peak value, and the first light emitting layer is applied to the first light emitting layer. A first current peak value higher than the second current peak value is applied.
- the first current peak value having a high current density is applied to the first light emitting layer having a high light emission efficiency
- the low current density is applied to the second light emitting layer having a low light emission efficiency.
- Two current peak values are applied.
- luminance fall of a 1st light emitting layer can be accelerated
- produces with progress of time can be suppressed, and the change of the color tone of an organic electroluminescent element can be suppressed. Accordingly, it is possible to suppress a decrease in display quality of the organic electroluminescence element.
- FIG. 1 shows a configuration example of an organic EL element to which a driving method is applied.
- the organic EL element 10 shown in FIG. 1 includes a first electrode 14, a first light emitting functional layer 11, a second electrode 15, a second light emitting functional layer 12, a third electrode 16, and a third light emitting functional layer 13 on a substrate 19.
- the 4th electrode 17 has the structure laminated
- the first light emitting functional layer 11 has a light emitting layer having a green (G) emission color
- the second light emitting functional layer 12 has a light emitting layer having a red (R) emission color
- the layer 13 includes a light emitting layer having a blue (B) emission color.
- phosphorescent materials are used for the green light emitting layer and the red light emitting layer of the first light emitting functional layer 11 and the second light emitting functional layer 12, and a fluorescent material is used for the blue light emitting layer of the third light emitting functional layer 13. .
- the organic EL element 10 is formed with an outer dimension of 40 mm ⁇ 40 mm.
- the first electrode 14 is made of 300 nm ITO
- the second electrode 15 is made of 15 nm Al
- the third electrode 16 is made of 15 nm Al
- the fourth electrode 17 is made of 100 nm Al.
- the first light emitting functional layer 11 has a 30 nm MoO 3 hole injecting layer, a 50 nm ⁇ -NPD hole injecting layer, and a light emitting host material and a green light emitting color on the first electrode 14. It is formed of a phosphorescent material having a concentration of 3 to 5%, 30 nm of Alq3 as an electron transport layer of a luminescent dopant, and 1 nm of LiF as an electron injection material.
- the second light emitting functional layer 12 is a light emitting material having a red emission color on the second electrode 15 with 30 nm of MoO 3 as a hole injection layer, 50 nm ⁇ -NPD as a hole transport layer, and a light emitting host material as a light emitting layer. It is formed of a phosphorescent material having a dopant concentration of 3 to 5%, 30 nm of Alq3 as an electron transport layer, and 1 nm of LiF as an electron injection material.
- the third light emitting functional layer 13 is a light emitting material having a blue emission color on the third electrode 15 with 30 nm of MoO 3 as a hole injection layer, ⁇ -NPD of 50 nm as a hole transport layer, and a host material for light emission as a light emitting layer. It is made of a fluorescent material having a dopant concentration of 3 to 5%, 30 nm of Alq3 as an electron transport layer, and 1 nm of LiF as an electron injection material.
- FIG. 2 shows the efficiency characteristics of each light emitting functional layer of the organic EL element having the above configuration.
- the vertical axis indicates the luminous efficiency of each of the first light emitting functional layer 11, the second light emitting functional layer 12, and the third light emitting functional layer 13, and the current density applied to the horizontal axis. Yes.
- the light emission efficiency varies greatly depending on each light emitting functional layer.
- the first light emitting functional layer 11 and the second light emitting functional layer 12 made of a phosphorescent material have higher light emission efficiency even at a low current density than the third light emitting functional layer 13 made of a fluorescent material.
- the first light emitting functional layer 11 and the second light emitting functional layer 12 made of a phosphorescent material have a light emitting efficiency that is significantly lower than that of the third light emitting functional layer 13 by increasing the current density. Then, at a certain current density, the luminous efficiency is lower than or equal to that of the third light emitting functional layer 13 made of a fluorescent material.
- FIG. 3 shows driving waveforms when a conventional general driving method is used.
- the drive waveform shown in FIG. 3 shows the current density applied on the vertical axis and the application time on the horizontal axis for each of the first light emitting functional layer 11, the second light emitting functional layer 12, and the third light emitting functional layer 13. Yes.
- the application time to each light emitting functional layer is the same. That is, the application time to each light emitting functional layer is 1/3 duty of a frame frequency of 100 Hz. Independent light emission of 3.3 msec for each of RGB.
- the organic EL element 10 having the above configuration displays white 1,000 cd / m 2 with CIE chromaticity ⁇ 0.3, 0.3>, each color used at this time is displayed. current peak value is, 3.8 mA / m 2 green light emitting layer, 4.2 mA / m 2 red light emitting layer, a 22mA / cm 2 in the blue emitting layer.
- the organic EL element 10 having the above-described configuration has a light emission efficiency of about 4.9 cd / A for blue, about 21 cd / A for red, and about 25 cd / A for green.
- FIG. 4 shows a life deterioration characteristic indicating a decrease in luminance over time of the light emitting functional layer.
- each light emitting functional layer exhibits different luminance reductions as the driving time of the organic EL element elapses.
- the luminance decrease of the third light emitting functional layer 13 using the fluorescent material having low light emission efficiency is large, and the luminance decrease of the first light emitting functional layer 11 using the phosphorescent material having high light emission efficiency is small. That is, the lifetime of the third light emitting functional layer 13 is short, and the lifetime of the first light emitting functional layer 11 is long.
- the emission color changes from the initially set color tone with the passage of time.
- the emission luminance of blue which has a large decrease in luminance, is reduced, and the color tone initially set is changed to a color tone with reduced blue light, for example, from the initially set white color tone to a yellowish color tone.
- the emission color of the organic EL element changes with time, and the display quality deteriorates.
- the above-described decrease in luminance of the light emitting layer corresponds to the light emission efficiency shown in FIG. That is, the third light emitting functional layer 13 using a fluorescent material having low light emission efficiency needs to be driven at a high current density of 22 mA / cm 2 in the blue light emission layer in order to compensate for the low light emission efficiency. In contrast, the first light emitting functional layer 11 using a phosphorescent material having high light emission efficiency can be driven at a low current density of 3.8 mA / m 2 .
- the lifetime of the element varies depending on the applied current density, and the lifetime of the element is shorter when driven at a high current peak value, and the lifetime of the element tends to be longer when driven at a low current peak value. That is, in the organic EL element 10, the blue light emitting layer has a low luminous efficiency of about 4.9 cd / A and is driven at a high current density of 22 mA / cm 2 , so that the luminance is greatly reduced.
- the green light-emitting layer has a high luminous efficiency of about 25 cd / A and is driven at a low current density of 3.8 mA / m 2 , so that the luminance reduction is small.
- a high current peak value is applied to the light emitting layer with low light emission efficiency, and a low current peak value is applied to the light emitting layer with high light emission efficiency.
- the lifetime deterioration characteristics of the respective light emitting functional layers are different, and the emission color changes with time.
- the organic EL element having the light emitting function layers having different light emission efficiencies as described above as a method for matching the lifetimes of the light emitting function layers, for example, when forming the light emitting function layers in parallel by the RGB color separation method
- this method when only a green light emitting layer with high luminous efficiency is displayed, there is a problem that a non-lighting area is visually recognized, and it is a good light source for visual recognition such as a decorative organic EL illumination. Absent.
- the present invention applies a low current peak value to the light emitting functional layer having a low light emission efficiency and a high current peak value to the light emitting functional layer having a high light emitting efficiency, contrary to the above-described conventional driving method. Apply.
- a difference occurring in the life deterioration characteristics of each light emitting functional layer is suppressed. That is, it is possible to bring the luminance reduction rate with the passage of time of each light emitting functional layer closer and to suppress the change in color tone with the passage of time.
- Embodiment of Driving Method of Organic Electroluminescence Element An embodiment of a method for driving an organic electroluminescence element (organic EL element) of the present invention will be described. In this example, a method for driving an organic EL element having the same configuration as that shown in FIG. 1 used in the above description of the outline will be described. Moreover, the efficiency characteristics of each light emitting functional layer of the organic EL element are the same as those in FIG.
- FIG. 5 shows drive waveforms according to the drive method of this example.
- a fluorescent material having the highest current density applied to the first light emitting functional layer 11 that emits green light using a phosphorescent material having high light emission efficiency and low light emission efficiency is used.
- the current density applied to the blue light emitting third light emitting functional layer 13 used is minimized.
- the applied current density is set to a value between the first light emitting functional layer 11 and the third light emitting functional layer 13.
- the lifetime deterioration characteristics of the respective light emitting functional layers can be matched. Specifically, a relatively low current peak value is applied to a light emitting layer having a relatively low luminous efficiency, and a high current peak value is applied to a light emitting layer having a high luminous efficiency.
- the current peak value applied to each light emitting functional layer can be set as follows.
- the applied current peak value can be derived from the relationship between the current density and the luminous efficiency shown in FIG.
- the current peak value to be applied to the first light emitting functional layer 11 and the second light emitting functional layer 12 is determined in accordance with the third light emitting functional layer 13 having the lowest light emission efficiency.
- the current peak value to be applied to the third light emitting functional layer 13 is set.
- the current peak value applied to the third light emitting functional layer 13 is higher than the current density at which the light emitting efficiency of the third light emitting functional layer 13 and the light emitting efficiency of the first light emitting functional layer 11 are the same.
- the current peak value is smaller than the current density at which the light emission efficiency of the third light emitting functional layer 13 and the light emission efficiency of the second light emitting functional layer 12 are the same.
- the current peak value applied to the third light emitting functional layer 13 intersects the curve of the first light emitting functional layer 11 and the curve of the second light emitting functional layer 12 with the curve of the third light emitting functional layer 13 in FIG.
- the current peak value is set at a position where the current density is lower than the position.
- the current density applied to the third light emitting functional layer 13 is 22 mA / cm 2 .
- a current density that obtains the same light emitting efficiency as the light emitting efficiency of the third light emitting functional layer 13 determined as described above is obtained.
- a current peak value that is equal to or higher than the current density is set to a current peak value applied to the first light emitting functional layer 11.
- the current density applied to the first light emitting functional layer 11 is 120 mA / cm 2 .
- the current density at which the light emitting efficiency is the same as the light emitting efficiency of the third light emitting functional layer 13 determined as described above is obtained. Then, a current peak value that is equal to or higher than the current density is set to a current peak value to be applied to the second light emitting functional layer 12. For example, in this example, the current density applied to the second light emitting functional layer 12 is 95 mA / cm 2 .
- FIG. 6 shows a life deterioration characteristic indicating a decrease in luminance over time of an organic EL element using the above current peak value.
- the life deterioration characteristics of each light emitting functional layer of the organic EL element can be improved. That is, by applying a current peak value lower than that of the other light emitting functional layers to the light emitting functional layer having a low light emitting efficiency, the luminance of the light emitting functional layer having a low light emitting efficiency is moderately lowered and the life is extended.
- a current peak value higher than the current density applied to the light emitting functional layer having a low light emitting efficiency is applied to the light emitting functional layer having a high light emitting efficiency. This promotes a decrease in luminance. As a result, the life-deterioration characteristics of the respective light emitting functional layers are shifted in a direction that matches.
- the toning of the organic EL element is performed by adjusting the time for driving each light emitting functional layer.
- the color of the organic EL element is adjusted by adjusting the current density applied to the light emitting functional layer.
- toning of the organic EL element is performed by controlling the light emission time of each light emitting functional layer. As described above, when a high current peak value is applied to the first light emitting functional layer 11, the luminance of the first light emitting functional layer 11 is increased.
- the luminance of the third light emitting functional layer 13 is lowered.
- the decrease in luminance is compensated for by increasing the light emission time of the third light emitting functional layer 13 where the luminance decreases.
- the increase in luminance is offset by shortening the light emission time of the first light emitting functional layer where the luminance is increased.
- the light emitting functional layer tends to increase the luminance itself although the light emission efficiency decreases due to an increase in the applied current density.
- the first light emitting functional layer 11 and the second light emitting functional layer 12 are driven at a higher current density than the third light emitting functional layer 13.
- the luminance of the third light emitting functional layer 13 is low
- the luminance of the first light emitting functional layer 11 and the second light emitting functional layer 12 is high
- the organic EL element 10 is The desired color tone cannot be adjusted.
- the first light emitting functional layer 11 and the second light emitting functional layer 12 having relatively high current density and high luminance have a short light emission time, and the current density is low and the luminance is low.
- the light emission time of the three light emitting functional layers 13 is lengthened.
- the organic EL element 10 displays white 1,000 cd / m 2 with CIE chromaticity ⁇ 0.3, 0.3>
- the first light emitting functional layer 11 has 120 mA / cm 2 and the second light emitting functional layer. 12 is adjusted to apply a current of 95 mA / cm 2 and the third light emitting functional layer 13 is applied with a current of 22 mA / cm 2 .
- the lighting rates of the first light emitting functional layer 11, the second light emitting functional layer 12, and the third light emitting functional layer 13 are set to different application times. That is, the frame frequency is 100 Hz, the first light emitting functional layer 11 is lit for 0.3 msec, the second light emitting functional layer 12 is lit for 0.5 msec, and the third light emitting functional layer 13 is lit for 3.3 msec.
- changing the lighting rate may affect the life deterioration characteristics of the light emitting functional layer.
- the decrease in luminance is moderate because the lighting rate of the first light emitting functional layer is low and the light emission time is shortened.
- a current density at which the light emission efficiency of the first light emitting functional layer is lower than the light emission efficiency of the third light emitting functional layer that is, a current peak value higher than the above current density
- luminance reduction is achieved. It can be accelerated to match the life degradation characteristics.
- the lifetime deterioration characteristic of the organic EL element can be improved by considering the lighting rate for toning of the organic EL element.
- the driving method of the organic EL element of this embodiment even if each light emitting functional layer having different light emission efficiency is formed in the same organic EL element, the life deterioration characteristic is improved and the time from the initial chromaticity is improved. It is possible to prevent a change in color tone due to progress. And the display quality of an organic EL element can be improved.
- the frame frequency 100 Hz is used as the frame frequency, but a different frequency may be used.
- the non-lighting time becomes long, so that when a frame frequency of about 100 Hz is used, it looks like flicker.
- the frame frequency is as high as possible, such as 500 Hz.
- the duty driving of the organic EL element in which three light emitting functional layers are stacked is exemplified, but the number of light emitting functional layers, the duty ratio, etc. of the organic EL element are not particularly limited.
- the organic EL element to which the above driving method can be applied does not have to have a laminated structure, and may not have a laminated structure as long as the current peak value applied to each light emitting functional layer and the driving time can be controlled. Moreover, the structure which can drive a some light emission functional layer simultaneously may be sufficient.
- the driving method of the organic EL element when the light emitting area of each light emitting functional layer is the same and the light emitting efficiency of each light emitting functional layer is different is described. It is not limited to this.
- the organic EL element may have a configuration in which the area of the light emitting layer having a lower light emitting efficiency is larger than that of the light emitting layer having a high light emitting efficiency.
- the organic EL element may have a configuration in which the area of the light emitting layer having a lower light emitting efficiency is larger than that of the light emitting layer having a high light emitting efficiency.
- the lifetime deterioration characteristics can be matched by making the current peak value applied to the light emitting layer with high luminous efficiency larger than the current peak value applied to the light emitting layer with low luminous efficiency. That is, a technique for extending the life of a light emitting layer with low light emission efficiency by extending the area and matching the life deterioration characteristics of a light emitting layer with low light emission efficiency and a light emitting layer with high light emission efficiency by the driving method of the above-described embodiment. Can be used together.
- phosphor materials and fluorescent materials are used as materials, only phosphor materials or only fluorescent materials may be used.
- a current peak value corresponding to the light emission efficiency is applied as in the first light emitting functional layer (G) and the second light emitting functional layer (R) of the above-described embodiment.
- the life deterioration characteristics of the light emitting layers can be matched. The same applies to the case where only the fluorescent material is used or other combinations.
- the life deterioration characteristics depending on the material constituting each light emitting functional layer are described without consideration. Even when the life deterioration characteristics differ depending on the material used, as in the above-described embodiment, a low current peak value is applied to a material with a large decrease in brightness, and a high current peak value is applied to a material with a small decrease in brightness. By doing so, the life deterioration characteristics can be matched. And arbitrary toning becomes possible by controlling the application time to each light emitting functional layer.
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Abstract
Description
また、近年では、有機EL素子を利用した携帯ディスプレイや携帯背面ディスプレイ等も積極的に市場投入されている。これらの有機EL素子を利用したディスプレイは、視認性の高さから、大型テレビへの市場投入が期待され、一部投入計画が報道されるなどフラットパネルディスプレイでの市場投入に拍車がかかってきている。
有機EL素子は、電極間内にRGBの発各光材料を有し、RGBの発光出力を任意に調製して駆動することで、又は、有機層の厚さを含めた層設計を施すことで、発光色や発光色強度を自由に変えることが可能となる。このため、有機EL素子は、照明用途として要求される白色として、例えば、色温度2000Kや3000Kなどの電球色から、5000Kや6000Kなどの昼白色まで、自由に発光することが可能である。さらに、燐光材料を使用することで、LEDや蛍光灯と同等又はそれを超える発光効率を実現でき、薄型化照明としての実現が期待されている。
さらに、発光層を透明基板と垂直方向にスタックすることで開口率を増やし、調色することも提案されている(例えば、特許文献2参照)。
なお、説明は以下の順序で行う。
1.本発明の概要
2.有機エレクトロルミネッセンス素子の駆動方法の実施形態
本発明の具体的な実施形態の説明に先立ち、有機エレクトロルミネッセンス素子(有機EL素子)の駆動方法の概要について説明する。
図1に示す有機EL素子10は、基板19上に、第1電極14、第1発光機能層11、第2電極15、第2発光機能層12、第3電極16、第3発光機能層13、及び、第4電極17がこの順に積層された構成を有する。
本例では、第1発光機能層11に緑色(G)発光色を有する発光層を有し、第2発光機能層12に赤色(R)発光色を有する発光層を有し、第3発光機能層13に青色(B)発光色を有する発光層を有する。また、第1発光機能層11及び第2発光機能層12の緑色発光層と赤色発光層とにリン光材料を使用され、第3発光機能層13の青色発光層に蛍光材料が使用されている。
第1電極14は300nmのITO、第2電極15は15nmのAl、第3電極16は15nmのAl、第4電極17は100nmのAlで形成されている。
図2に示す効率特性は、縦軸に、第1発光機能層11、第2発光機能層12、及び、第3発光機能層13のそれぞれの発光効率、横軸に印加する電流密度を示している。
図2に示すように、各発光機能層に応じて発光効率が大きく異なる。特に、リン光材料で構成した第1発光機能層11と第2発光機能層12は、蛍光材料で構成した第3発光機能層13に比べて、低電流密度でも発光効率が高い。
また、リン光材料で構成した第1発光機能層11と第2発光機能層12は、電流密度を高くすることにより発光効率が、第3発光機能層13よりも大きく低下する。そして、ある程度の電流密度において、蛍光材料で構成した第3発光機能層13と同等の発光効率以下に低下している。
図3に示す駆動波形は、第1発光機能層11、第2発光機能層12、及び、第3発光機能層13のそれぞれについて、縦軸に印加する電流密度、横軸に印加時間を示している。
また、従来の一般的な駆動方法において、上記構成の有機EL素子10は、青色で約4.9cd/A、赤色で約21cd/A、緑色で約25cd/Aの発光効率を有する。
図4に示すように、従来の駆動方法を用いた場合には、有機EL素子の駆動時間の経過とともに、各発光機能層が異なる輝度低下を示す。上記有機EL素子10では、発光効率の低い蛍光材料を用いた第3発光機能層13の輝度低下が大きく、発光効率の高いリン光材料を用いた第1発光機能層11の輝度低下が小さい。つまり、第3発光機能層13の寿命が短く、第1発光機能層11の寿命が長い。
しかし、この方法では、発光効率の高い緑発光層だけを表示するような場合、非点灯域が視認されるなどの問題があり、装飾用の有機EL照明のような視認される光源としては芳しくない。
本発明の有機エレクトロルミネッセンス素子(有機EL素子)の駆動方法の実施形態について説明する。なお、本例では、上述の概要の説明において用いた、図1に示す構成と同様の構成の有機EL素子の駆動方法について説明する。また、有機EL素子の各発光機能層の効率特性も、上述の図2と同様である。
図5に示すように、本実施形態の駆動方法では、発光効率の高いリン光材料を用いた緑色発光の第1発光機能層11に印加する電流密度が最も大きく、発光効率の低い蛍光材料を用いた青色発光の第3発光機能層13に印加する電流密度を最も小さくする。発光効率が両者の間にある第2発光機能層12では、印加する電流密度を第1発光機能層11と第3発光機能層13との間の値とする。
印加する電流波高値は、上述の図2に示す電流密度と発光効率の関係から導くことができる。例えば、最も発光効率の低い第3発光機能層13に合わせて、第1発光機能層11と第2発光機能層12に印加する電流波高値を決める。
このように、第3発光機能層13に印加する電流密度を決めることにより、第3発光機能層13の発光効率が決まる。
図6に示すように、発光効率を基準にして電流密度を調整することにより、有機EL素子の各発光機能層の寿命劣化特性を改善することができる。
つまり、発光効率の低い発光機能層に、他の発光機能層よりも低い電流波高値を印加することにより、発光効率の低い発光機能層の輝度低下を緩やかにして長寿命化する。また、発光効率の低い発光機能層に印加される電流密度において、発光効率が高い発光機能層に対しては、発光効率の低い発光機能層に印加される電流密度よりも高い電流波高値を印加することにより輝度低下を促進する。
この結果、各発光機能層の寿命劣化特性が一致する方向に遷移する。
上述の概要で説明した方法では、発光機能層に印加する電流密度を調整することにより、有機EL素子の調色を行う。本実施形態では、発光機能層に印加する電流密度は、発光効率と寿命劣化特性とにより決められるため、印加する電流密度の調整による調色は難しい。従って、各発光機能層の発光時間を制御することにより、有機EL素子の調色を行う。
上述のように、第1発光機能層11に高い電流波高値を印加すると、第1発光機能層11の輝度は高くなる。また、第3発光機能層13の発光効率に低い電流波高値を印加すると、第3発光機能層13の輝度は低くなる。このため、輝度の低くなる第3発光機能層13の発光時間を長くすることにより、輝度の低下を補う。また、輝度が高くなる第1発光機能層の発光時間を短くすることにより、輝度増加分を相殺する。
これにより、発光効率に伴う寿命変化を各発光機能層で補い、各発光機能層で同等の寿命劣化特性を得ることができる。
このように、上述の発光効率と寿命劣化特性との関係に加えて、有機EL素子の調色のための点灯率を考慮することにより、有機EL素子の寿命劣化特性を改善することができる。
従って、有機ELディスプレイ等で一般的に広く採用されている、塗り分け法にて各発光機能層を並列に形成する際に、異なる発光効率有する有機発光層の発光面積又は開口率を変える素子形成方法においても、上述の実施形態の駆動方法を適用することにより、視認性を損なうことなく表示することが可能となる。
例えば、リン光材料のみを用いた場合にも、上述の実施形態の第1発光機能層(G)と第2発光機能層(R)とのように、発光効率に応じた電流波高値を印加し、印加時間を調整することにより、各発光層の寿命劣化特性を一致させることができる。蛍光材料のみを用いた場合や、その他組み合わせにおいても同様である。
Claims (6)
- 第1発光層に第1電流波高値を印加し、第2発光層に第2電流波高値を印加する有機エレクトロルミネッセンス素子の駆動方法であって、
前記第2電流波高値の電流密度において前記第1発光層よりも発光効率が低い前記第2発光層に、前記第1電流波高値よりも電流密度の低い前記第2電流波高値を印加し、
前記第1発光層に、前記第2電流波高値よりも高い前記第1電流波高値を印加する
有機エレクトロルミネッセンス素子の駆動方法。 - 前記第1電流波高値の印加時間が、前記第2電流波高値の印加時間よりも小さい請求項1に記載の有機エレクトロルミネッセンス素子の駆動方法。
- 前記第2電流波高値は、前記第1発光層と前記第2発光層との発光効率が一致する電流密度よりも小さい請求項1又は2に記載の有機エレクトロルミネッセンス素子の駆動方法。
- 前記第1発光層に、前記第2電流波高値での前記第2発光層の発光効率と同じ発光効率となる電流密度以上の前記第1電流波高値を印加する請求項1又は2に記載の有機エレクトロルミネッセンス素子の駆動方法。
- 同じ発光面積を有する前記第1発光層と前記第2発光層とに、前記第1電流波高値、前記第2電流波高値を印加する請求項1に記載の有機エレクトロルミネッセンス素子の駆動方法。
- 積層された前記第1発光層と前記第2発光層とに、前記第1電流波高値、前記第2電流波高値を印加する請求項1に記載の有機エレクトロルミネッセンス素子の駆動方法。
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US14/897,245 US9824623B2 (en) | 2013-06-13 | 2014-06-11 | Method for driving organic electroluminescent element |
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CN201480033033.4A CN105325057B (zh) | 2013-06-13 | 2014-06-11 | 有机电致发光元件的驱动方法 |
KR1020157034958A KR20160007587A (ko) | 2013-06-13 | 2014-06-11 | 유기 일렉트로루미네센스 소자의 구동 방법 |
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WO2017203787A1 (ja) * | 2016-05-26 | 2017-11-30 | コニカミノルタ株式会社 | 有機エレクトロルミネッセンス素子 |
WO2018083974A1 (ja) * | 2016-11-04 | 2018-05-11 | コニカミノルタ株式会社 | 有機エレクトロルミネッセンス素子、及び、発光装置 |
CN115019675A (zh) * | 2022-05-31 | 2022-09-06 | 武汉天马微电子有限公司 | 一种显示面板及显示装置 |
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EP3010310A1 (en) | 2016-04-20 |
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