KR100836542B1 - Organic electroluminescence device capable of regulating chromaticity - Google Patents

Abstract

An object of the present invention is to provide an organic electroluminescence device which can adjust emission chromaticity while maintaining emission luminance constant. In addition, the organic electroluminescent device of the present invention uses an organic electroluminescent device having an organic electroluminescent layer that emits white of chromaticity according to a drive current density between electrodes, and an organic electroluminescent device. And a driving unit for controlling the driving current and controlling the current driving time per unit time in accordance with the chromaticity adjustment input. The driving unit controls the driving current to the first current value and the current driving time to the first time with respect to the first chromaticity adjustment input, respectively, and the driving current is greater than the first current value for the second chromaticity adjustment. With the two current values, the current driving time is controlled at a second time shorter than the first time, respectively, and the emission chromaticity is adjusted while keeping the emission luminance of the organic electroluminescent element almost constant. According to this, according to the chromaticity adjustment input for adjusting the emission chromaticity, the driving current value for the organic light emitting element is controlled to be adjusted to the emission chromaticity corresponding to the chromaticity adjustment input, and per unit time in response to the control of the driving current value. By adjusting the current driving time, the light emission luminance can be kept almost constant, and the adjustment to the desired light emission chromaticity is possible without changing the light emission luminance.

Organic Electroluminescence

Description

Chromaticity-adjustable organic electroluminescent device {ORGANIC ELECTROLUMINESCENCE DEVICE CAPABLE OF REGULATING CHROMATICITY}

Field of technology

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device capable of adjusting the chromaticity while emitting white light and keeping the luminance of the white constant.

Background

The organic electroluminescent (EL) element has a characteristic that it can emit light by itself by being driven by current (self-luminous) and can respond to current driving at high speed (high speed response), and application to a flat panel display device is expected. have. On the other hand, the organic EL element is thin, lightweight, and has a feature of emitting light uniformly in a large area, and can be applied to an illumination device.

The organic EL device has been reported since the report of a stacked device in which organic thin films of each of hole transporting and electron transporting are laminated (CW Tang and SA VanSlyke, Applied Physics Letters vol. 51, 913 (1987) (hereinafter referred to as Non-Patent Document 1)). Attention has been drawn to large area light emitting devices that emit light at the following low voltages. This laminated organic EL device basically has a laminated structure of a positive electrode / hole transport layer / light emitting layer / electron transport layer / negative electrode. In this case, as the light emitting layer, a structure in which the hole transporting layer or the electron transporting layer also functions as the light emitting layer may be possible as in the case of the two-layer device of Non-Patent Document 1. Moreover, in order to obtain the organic electroluminescent element of high luminous efficiency, in addition to the single film | membrane formed with one kind of material as a structure of a light emitting layer, the pigment | dye which doped a small amount of highly fluorescent dye pigment (guest material) in the host material which is a main component Doping films have been devised (CW Tang, SA VanSlyke, and CH Chen, Applied Physics Letters vol. 65, 3610 (1989) (hereinafter Non-Patent Document 2)).

Monochromatic display devices are proposed using organic EL elements (for example, Japanese Patent Application Laid-Open No. 2003-234181 (hereinafter, Patent Document 1)). According to this patent document 1, the organic electroluminescence display which has the pixel of the matrix which laminated | stacks a blue light emitting layer and a yellow light emitting layer between a hole injection layer and an electron injection layer, and emits white light is disclosed. Then, it is disclosed that luminance is adjusted by light emission pulse width modulation without changing the light emission chromaticity by keeping the driving voltage constant.

Disclosure of the Invention

However, Non-Patent Documents 1, 2 and Patent Document 1, which are the above-mentioned prior arts, do not disclose that the lighting device or the display device using white light emission can be adjusted to a desired chromaticity while keeping the light emission luminance constant.

Accordingly, an object of the present invention is to provide an organic electroluminescence device which can adjust the emission chromaticity while maintaining the emission luminance constant.

According to a first aspect of the present invention, an organic electroluminescent device having an organic electroluminescent layer that emits white of chromaticity according to a drive current density between electrodes, and the organic electroluminescent device are driven with a current, In accordance with the chromaticity adjustment input, has a drive unit for controlling the drive current and the control of the current drive time per unit time,

The driving unit controls the driving current to the first current value and the current driving time to the first time for the first chromaticity adjustment input, respectively, and the driving current to the first chromaticity adjustment than the first current value. With a large second current value, the current driving time is controlled at a second time shorter than the first time, respectively, and the emission chromaticity is adjusted while keeping the emission luminance of the organic electroluminescent element almost constant. It is an organic electroluminescent apparatus.

According to the first aspect, according to the chromaticity adjustment input for adjusting the emission chromaticity, the driving current value for the organic light emitting element is controlled to be adjusted to the emission chromaticity corresponding to the chromaticity adjustment input, and the control of the driving current value is supported. Accordingly, an organic electroluminescence device can be provided that can adjust a current driving time per unit time to maintain a substantially constant light emission luminance, and to allow adjustment to a desired light emission chromaticity without changing the light emission luminance. Such an organic electroluminescent device can be used as a lighting device or a backlight of a liquid crystal display device. The organic electroluminescent device can also be used as a light emitting segment of a segment display device.

In addition, although the chromaticity adjustment method by drive current adjustment was disclosed in this invention, you may perform chromaticity adjustment according to drive voltage adjustment. That is, since the voltage-current characteristic of the organic EL element is uniquely determined, the chromaticity adjustment is equally possible even if the voltage value is changed to be the current density to be controlled disclosed in the present invention.

Brief description of the drawings

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the organic electroluminescent apparatus in this embodiment.

2 is a structural diagram showing an example of a drive unit in the present embodiment.

3 is a diagram showing a relationship between the current density and the emission chromaticity of an organic EL layer.

4 is a diagram illustrating a relationship between current density and light emission luminance of an organic EL layer.

5 is a diagram illustrating an example of drive pulses of the organic EL element in the present embodiment.

6 is a configuration of an organic EL device in Embodiment 1;

7 is a configuration of an organic EL device in Embodiment 2;

Fig. 8 is a chart showing normalized average luminance and chromaticities x and y with respect to the current density and duty ratio of the started organic EL element.

9 is a diagram showing a structural formula of an organic material.

10 is a structural diagram illustrating another example of the drive unit in the present embodiment.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Hereinafter, embodiment example of this invention is described according to drawing.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the organic electroluminescent apparatus in this embodiment. This organic EL device comprises a cathode layer 12 made of a transparent electrode, for example, ITO, a cathode layer 24 made of, for example, aluminum, an anode layer 12, and a cathode formed on a transparent substrate 10. An organic EL element 100 having an organic EL layer that emits white formed between the layers 24, and a driving unit 26 connected to the anode layer 12 and the cathode layer 24 and supplying a driving current Id 26. ) The organic EL layer emitting white light is formed between the hole transport layer 14 for supplying holes from the anode layer 12, the electron transport layer 22 for supplying electrons from the cathode layer 24, and the transport layer. The light emitting layer which consists of the red light emitting layer 16, the blue light emitting layer 18, and the green light emitting layer 20 is provided. These layers 14 to 22 are formed by an organic material layer. By forming the hole transport layer 14 and the electron transport layer 22 between the electrode and the light emitting layer, high luminous efficiency can be provided.

The light emitting layer should just be able to obtain white light emission, and can emit white light by doping several pigment | dyes, for example, three types of red light emission, blue light emission, and green light emission in the light emitting layer. As shown in Fig. 1, the light emitting layer does not have to have a three-layer structure of a red light emitting layer, a blue light emitting layer, and a green light emitting layer, and as described later, red and blue, blue and green, or green and red in a single organic material layer. The light may be emitted. Further, all of red, blue, and green light may be emitted from a single organic material layer.

Moreover, it is good also as a light emitting layer common with the positive hole transport layer 14 and the electron carrying layer 22. FIG. That is, it is good also as a structure with a positive hole transport layer / light emitting layer, an electron carrying layer, a positive hole transport layer, a light emitting layer / an electron carrying layer.

2 is a structural diagram showing an example of a drive unit in the present embodiment. The drive unit 26 supplies a current source CS supplied to the organic EL element 100 and a drive switch SW for connecting the current source CS to the organic EL element 100 to supply a drive current Id. And a current control circuit 32 which controls the current value Id of the current source CS in accordance with the chromaticity adjustment input 28 and a conduction time of the drive switch SW in accordance with the chromaticity adjustment input 28. The drive time control circuit 34 and the chromaticity adjustment circuit 30 which controls the current control circuit 32 and the drive time control circuit 34 according to the chromaticity adjustment input 28 are provided. The current control circuit 32 controls the magnitude of the drive current Id of the current source CS, and the drive time control circuit 34 modulates the conduction drive signal S34 of the drive switch SW to the pulse width modulation PWM. do. The chromaticity adjustment circuit 30, the current control circuit 32, and the drive time control circuit 34 control the drive current Id corresponding to the adjusted emission chromaticity according to the chromaticity adjustment input 28. In addition, the drive switch SW is turned on at a drive time per unit time at which the light emission luminance is substantially constant in the controlled drive current Id.

When the area of the organic EL element 100 is constant, the drive current density can be changed by changing the drive current Id. As described later, the emission chromaticity can be changed in accordance with the change of the drive current density.

10 is a structural diagram illustrating a modification of the drive unit of FIG. 2. The difference from FIG. 2 is that the voltage source VS is formed instead of the current source, and the voltage control circuit 32V is formed instead of the current control circuit 32. That is, by controlling the voltage value of the voltage source VS by the voltage control circuit 32V, it is possible to change the drive current Id supplied to the organic EL element, thereby driving the EL element at a desired current density. The other operation is the same as that of FIG.

3 is a diagram showing a relationship between the current density and the emission chromaticity of an organic EL layer. When the current density supplied to the organic electroluminescent element shown in FIG. 1 was changed, it was discovered by this invention that the chromaticity of the white light which emits light changes as shown. That is, in the case of the organic EL element which emits RGB simultaneously, the emission chromaticity of the white light changes as the current density changes. In the example of FIG. 3, when the current density is reduced, the chromaticity is changed to (x, y) = (0.52, 0.45), while when the current density is increased, the chromaticity is changed to (x, y) = (0.25, 0.30). Doing. That is, depending on the current density, the chromaticity of emission changes between (x, y) = (0.52, 0.45) and (x, y) = (0.25, 0.30).

It is considered that the cause of the chromaticity change is that the light emission position in the organic EL layer changes with respect to the change in the drive current or the drive voltage and that the light emission start voltage of each light emission color is different. The organic electroluminescent device of this embodiment uses the organic electroluminescent element whose chromaticity of light emission white light changes with the drive current density corresponding to such a drive current or a drive voltage.

4 is a diagram illustrating a relationship between current density and light emission luminance of an organic EL layer. As shown in this figure, when the current density is changed in order to adjust the emission chromaticity, the emission luminance changes linearly accordingly. Therefore, in this embodiment, the drive unit supplies the drive current to the organic EL element by pulse driving. In the case where the current density is changed due to the adjustment of the emission chromaticity, in order to keep the emission luminance constant, the duty ratio of the driving pulse is changed in accordance with the changed current density to adjust the emission time per unit time, The luminous luminance per hour is kept constant. That is, when the current density is lowered, the duty ratio is increased to lengthen the light emission time of intermittent light emission, the luminance decrease accompanying the decrease in the current density is compensated for, and when the current density is increased, the duty ratio is lowered. The light emission time of intermittent light emission is shortened, and the brightness rise accompanying an increase of current density is compensated for.

5 is a diagram illustrating an example of drive pulses of the organic EL element in the present embodiment. Fig. 5A is a drive pulse in the case of controlling the current density low. The pulse width T (a) of the drive pulse is set long, and the duty ratio is set high. By using such a driving pulse, the light emission luminance per unit time is lowered at a low current density, but the time-averaged light emission luminance becomes a predetermined value by lengthening the light emission time per unit time. Fig. 5B is a drive pulse when the current density is controlled high. The pulse width T (b) of the drive pulse is set short, and the duty ratio is set low. By using such a driving pulse, the light emission luminance per unit time is increased at a high current density. However, by shortening the light emission time per unit time, the time averaged light emission luminance can be made equal to the predetermined value in Fig. 5A. In addition, since the change range of the emission chromaticity depends on the chromaticity change characteristic of the organic EL element, the element configuration may be optimized in advance so as to obtain a desired chromaticity change range.

As described above, in the present embodiment, when adjusting the emission chromaticity, the drive current density is controlled up and down in response to the adjustment input, and the pulse width of the drive pulse is controlled by the length in response to the control of the drive current density. do.

On the other hand, in the organic EL device of the present embodiment, when the emission luminance is adjusted, as shown in Fig. 2, in response to the emission luminance adjustment input 36, the current density is not changed, Adjust the pulse width. That is, the light emission luminance adjustment input for lowering the light emission luminance is controlled to shorten the pulse width of the drive pulse, and for the light emission luminance adjustment input for increasing the emission luminance, the pulse width of the drive pulse is controlled to be long. Accordingly, it is possible to adjust the light emission luminance corresponding to the light emission luminance adjustment input while maintaining the light emission chromaticity as the desired chromaticity.

As described above, in the organic EL device of the present embodiment, the emission chromaticity is independently adjusted to the emission luminance by the emission chromaticity adjustment input 28, and the emission luminance is independently adjusted by the emission luminance adjustment input 36 to the emission chromaticity. do.

For reference, chromaticity adjustment in the conventional organic EL display device will be described. In the conventional organic EL display device, an organic EL element emitting RGB light is formed for each pixel. Then, the red light emitting organic EL element, the blue light emitting organic EL element, and the green light emitting organic EL element are independently driven by current. Therefore, in order to emit white light, it is necessary to make all the organic EL elements of RGB emit light, and in order to adjust the chromaticity of the white light emission, the emission luminance of each organic EL element is adjusted, and the emission balance is adjusted. It is necessary to do it with white light chromaticity.

In the full-color liquid crystal display device, in order to adjust the chromaticity of the white color at the time of white display, the driving voltage to the liquid crystal layer in the RGB pixel is adjusted, and the transmission characteristic is adjusted to the desired chromaticity. Needs to be. In this way, the adjustment of the color temperature in the front white display in the organic EL display device or the liquid crystal display device is complicated.

On the other hand, in the organic EL device of the present embodiment, white light emission is possible with one organic EL element, and when the current density is changed, the light emission chromaticity is changed. Obtaining white light emission can be realized by a simple configuration.

[Example 1]

6 is a configuration diagram of an organic EL device in Embodiment 1; In the organic EL device of Example 1, the organic EL layer includes a hole injection layer 14A, a hole transport layer 14B, a red light emitting layer 16, a blue light emitting layer 18, a hole block layer 40, And an electron transporting layer and a green light emitting layer 42. The manufacturing method of this structure is as follows.

First, the glass substrate 10 in which the ITO electrode 12 was formed was ultrasonic-cleaned by water, acetone, and isopropyl alcohol, and after performing ultraviolet-ultraviolet (UV) ozone treatment, a vacuum vapor deposition apparatus (1x10 <^-6> torr) Substrate temperature is 140 nm on 2-TNATA (4,4 ', 4 "-tris (2-naphthylphenylamino) triphenylamine) as the hole injection layer 14A thereon. 10 nm of (alpha) -NPD (N, N'- dinaphthyl-N, N'- diphenyl- [1,1'-biphenyl] -4,4'- diamine) was formed as the hole transport layer 14B. On the double layers 14A and 14B, DCJTB (4-dicyanomethylene-6-cp-julolidinostyryl-2-tert-butyl-4H-pyran), which is a guest material, as a red light emitting layer 16, and Alq ₃ (tris, 8-hydroxyquinolinate) aluminum) was co-deposited layer (Alq ₃ 99 molecules for 1 molecule of deposition ratio DCJTB) 1 nm thereon, and the guest material t (bp) py (1) as a blue light emitting layer 18 thereon. , 3,6,8-tetrabiphenylpyrene) and host 20 nm of a layer on which co-deposited CBP (4,4'-bis (9-carbazolyl) -biphenyl) of a material (90 CBP to 10 molecules of deposition ratio t (bp) py) was deposited thereon 10㎚ BAlq as the layer 40, above the 30㎚ the Alq ₃ as a green light-emitting layer an electron transport layer cum (42), 0.5㎚ lithium fluoride thereon, and Al as a cathode was deposited 100㎚ the layer 24 thereon The lithium fluoride is for enhancing the electron injection function of the green light emitting layer and the electron transporting layer 42. The hole blocking layer 40 blocks a part of the holes supplied from the hole transporting layer 14B to the green light emitting layer 42. Has the function of reducing the number of supply holes.

Said organic material 2-TNATA, (alpha) -NPD, DCJTB, Alq3, t (bp) py, CBP, Balq is a material which consists of a structural formula shown in FIG.

Fig. 8 is a chart showing normalized average luminance and chromaticity x, y with respect to the current density and duty ratio of the organic EL element started. A diagram of the organic EL device of the first embodiment is shown in Fig. 8A. For the organic EL device produced as described above, the instantaneous current densities at the time of light emission were changed to 5 mA / cm 2, 50 mA / cm 2, and 500 mA / cm 2, and the corresponding driving duty ratio (light emission period: rest period) = (1 : 0), (1: 9), and (1:99) to drive. The relationship between the time average brightness normalized to the brightness | luminance at the current density of 5 mA / cm <2> at the time of this drive, and emission chromaticity is shown to FIG. 8 (a). As shown in this diagram, it is confirmed that the chromaticity can be adjusted by changing the current density, and the luminance can be maintained at a predetermined level by adjusting the duty ratio of the driving pulse in accordance with the change of the current density.

[Example 2]

7 is a configuration diagram of an organic EL device in Embodiment 2; In the organic EL device of Example 2, the organic EL layer is formed of a hole injection layer 14A, a hole transport layer 14B, a red and blue light emitting layer 44, a hole block layer 40, and an electron transport layer and green. The light emitting layer 42 is comprised. The manufacturing method of this structure is as follows.

First, the glass substrate 10 in which the ITO electrode was formed was ultrasonically cleaned with water, acetone, and isopropyl alcohol, and subjected to UV ozone treatment, and then using a vacuum deposition apparatus (1 × 10 ^-6 torr, substrate temperature at room temperature). Thus, 2-TNATA is formed as 140 nm as the hole injection layer 14A, and α-NPD is formed as the hole transport layer 14B thereon. On this double layer 14A, 14B, the layer which simultaneously deposited the blue guest material t (bp) py as a blue and red light emitting layer 44, DCJTB which is a red guest material, and CBP which is a host material (deposition ratio t (bp) py 10 molecules, CBP 89 molecules per DCJTB molecule) 20 nm, BAlq 10 nm thereon as the hole blocking layer 40 thereon, Alq ₃ 30 nm thereon as the green light emitting layer and the electron transporting layer 42 thereon Lithium fluoride was deposited at 0.5 nm and Al was deposited thereon as the cathode layer 24. The structural formula of each material is shown in FIG.

As shown in the diagram of Fig. 8 (b), the fabricated organic EL device changes the instantaneous current density at light emission to 5 mA / cm 2, 50 mA / cm 2, and 500 mA / cm 2, and the corresponding driving duty ratio is ( Light emission period: rest period) = (1: 0), (1: 9), (1:99) were changed to drive. The relationship between the time average brightness | luminance normalized by the brightness | luminance at 5 mA / cm <2> at the time of this drive, and emission chromaticity is shown in FIG. From this diagram, it is confirmed that the emission chromaticity can be adjusted while maintaining the luminance at a predetermined level.

As shown in FIG. 1, FIG. 5, and FIG. 6, the organic electroluminescent apparatus in this embodiment formed the organic electroluminescent layer which emits white light between a pair of electrode, and the white light of this organic electroluminescent layer is a drive current density. The chromaticity changes accordingly. By forming the organic EL element having such an organic EL layer in a predetermined area, a white lighting device can be provided. This white lighting device can be used, for example, as a lighting device instead of a fluorescent lamp. Alternatively, the white illumination device can be used as a backlight of a liquid crystal display device because thin, light and uniform surface emission can be achieved.

The organic EL device of the present embodiment can also be used in a segmented display device that selectively emits a plurality of segments to display English numerals and the like.

Industrial availability

According to the present invention, it is possible to provide an organic EL device which can be adjusted to a desired emission chromaticity while maintaining the emission luminance at a predetermined level. This organic EL device can be used both as a lighting device and as a display device.

Claims (14)

An organic electroluminescent device having an organic electroluminescent layer emitting white of chromaticity according to a drive current density between electrodes; And a drive unit for driving the organic electroluminescent device with a current and controlling the drive current and the control of the current drive time per unit time in accordance with a chromaticity adjustment input. The driving unit controls the driving current as the first current value and the current driving time as the first time for the first chromaticity adjustment input, and controls the driving current as the first current value for the second chromaticity adjustment. With a larger second current value, respectively, controlling the current drive time to a second time shorter than the first time, The organic electroluminescent layer emits red, blue, and green at the same time, the organic electroluminescence device. An organic electroluminescent device having an organic electroluminescent layer emitting white of chromaticity according to a drive current density between electrodes; A driving unit for driving the organic electroluminescent element at a predetermined driving voltage and controlling the driving voltage and controlling the voltage driving time per unit time in accordance with a chromaticity adjustment input; The driving unit respectively controls the driving current to the first current value and the voltage driving time to the first time with respect to the first chromaticity adjustment input, and for the second chromaticity adjustment, the driving current to the first current. Controlling the voltage driving time to a second time shorter than the first time, respectively, with a second current value greater than the value, The organic electroluminescent layer emits red, blue, and green at the same time, the organic electroluminescence device. delete delete The method of claim 1, The organic electroluminescent layer has a red light emitting layer, a blue light emitting layer, and a green light emitting layer. The method of claim 1, The organic electroluminescent layer has a red light emitting layer, and a blue and green light emitting layer, characterized in that the organic electroluminescent device. The method of claim 1, The organic electroluminescent layer comprises a red and a blue light emitting layer and a green light emitting layer. The method of claim 1, The organic electroluminescent layer comprises a red and green light emitting layer and a blue light emitting layer. The method of claim 1, The organic electroluminescent layer has a hole transport layer and an electron transport layer formed in contact with an electrode. The method of claim 1, The drive unit includes a current source, a drive switch connecting the current source to the organic electroluminescent element, a current control circuit for controlling the current value of the current source according to the chromaticity adjustment input, and a conduction time of the drive switch. An organic electro luminescence device having a drive time control circuit for controlling according to the chromaticity adjustment input. The method of claim 2, The drive unit includes a voltage source, a drive switch connecting the voltage source to the organic electroluminescent element, a voltage control circuit for controlling the voltage value of the voltage source according to the chromaticity adjustment input, and a conduction time of the drive switch. An organic electro luminescence device having a drive time control circuit for controlling according to the chromaticity adjustment input. The liquid crystal display device which has the organic electroluminescent apparatus of Claim 1 or 2 as a backlight means, and has a liquid crystal layer on the said organic electroluminescent apparatus. delete The method according to claim 1 or 2, Furthermore, the organic electroluminescent apparatus which has a hole block layer.

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