JP2008191539A - Driving device of organic el element, and driving method of organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device and a driving method of an organic EL element which shows stabilized light emission color even when temperature rise or a change with the passage of time takes place. <P>SOLUTION: There is provided the driving device of the organic EL element 1 for supplying a constant current at a prescribed duty ratio. The driving device includes a state detection means 2 which detects at least either of driving time or ambient temperature, and a control means 3 which changes the set value of the constant current of the organic EL element 1 so as to keep the light emission color of the organic EL element 1 based on the detection result of the state detection means 2 and changes the duty ratio of the current supply in order to maintain the light emission luminance of the organic EL element 1 according to the set value. The driving device has a memory unit 4 which memorizes the current adjustment data indicating a relation between at least either of the driving time or the ambient temperature and the set value. The control means 3 reads out the set value from the current adjustment data based on the detection result of the state detection means 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic EL (electroluminescence) element, and more particularly to a driving device and a driving method thereof.

  Conventionally, as a light-emitting element, a transparent electrode made of ITO (Indium Tin Oxide) or the like serving as an anode, a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport on a translucent support substrate made of a glass material. An organic EL element is known which is formed by sequentially laminating an organic layer composed of layers and the like and a non-translucent back electrode composed of aluminum (Al) as a cathode.

  Further, as a problem of a display device using an organic EL element, it is possible to efficiently obtain light of a predetermined color. As an organic EL element that obtains light of a predetermined color, for example, an element formed by laminating a light emitting layer exhibiting at least two kinds of different light emission colors on a host material as disclosed in Patent Document 1 is known. Yes. Such an organic EL element can obtain white light emission by color mixing, for example, by laminating a blue light emitting layer and a yellow light emitting layer.

However, such an organic EL element has a problem that the luminescent color obtained by temperature change or change with time changes. This is because the movement speed or movement efficiency of electrons and holes changes due to deterioration of the material due to temperature change or change over time, and the region where electrons and holes recombine changes in the light emitting layer. It is thought that there is. When the light emitting layer has a stacked structure, the recombination region changes, so that the light emitting region of the light emitting layer changes so as to be biased toward the light emitting layer in contact with the hole transport layer and is separated from the hole transport layer. The luminance of the light emitting layer is reduced. As a result, the balance of the color mixture in the light emitting layer is lost, the light emission color obtained is changed, and the light emission of the target color cannot be obtained.
JP 2000-68057 A JP 2002-352958 A

  As a method for solving such a problem, a method in which the light emitting layer is a single layer and at least two kinds of light emitting materials having different light emission wavelengths (showing different light emission colors) are doped in the light emitting layer (for example, patents). Reference 2). In such an organic EL element, since a plurality of types of light emitting materials are contained in the single light emitting layer, even if there is a change in the light emitting region, the emission color does not change.

  However, in such an organic EL element, in order to manufacture a desired organic EL element, it is necessary to manage the doping ratio of the light emitting material in detail, resulting in a decrease in yield and a complicated manufacturing process. There was room for improvement.

  In view of such problems, an object of the present invention is to provide a driving apparatus and a driving method for an organic EL element that exhibits a stable emission color even when a temperature change or a change with time occurs.

  In order to solve the above problems, the present invention provides an organic EL element driving apparatus that supplies a constant current at a predetermined duty ratio, the state detecting means for detecting at least one of driving time and ambient temperature, Based on the detection result of the state detection means, the set value of the constant current is changed to maintain the emission color of the organic EL element, and current supply is performed to maintain the emission luminance of the organic EL element according to the set value. And a control means for changing the duty ratio.

  A storage unit that stores current adjustment data indicating a relationship between at least one of a driving time and an ambient temperature and the set value; and the control unit is configured to control the current adjustment data based on a detection result of the state detection unit. The set value is read out from.

  Further, the organic EL element has a plurality of light emitting layers having different emission colors.

  In order to solve the above-described problems, the present invention provides a driving method for an organic EL element that supplies a constant current at a predetermined duty ratio, and includes a detection result of a state detection unit that detects at least one of driving time and ambient temperature. And changing the set value of the constant current to maintain the light emission color of the organic EL element, and changing the duty ratio of the current supply to maintain the light emission luminance of the organic EL element according to the set value. It is characterized by.

  Further, current adjustment data indicating a relationship between at least one of driving time or ambient temperature and the set value is stored in a storage unit, and the set value is read from the current adjustment data based on a detection result of the state detection unit. It is characterized by.

  Further, the organic EL element has a plurality of light emitting layers having different emission colors.

  The present invention relates to a driving apparatus and a driving method for an organic EL element, and can exhibit a stable emission color even when a temperature change or a change with time occurs.

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

  In FIG. 1, the organic EL element driving apparatus according to the first embodiment of the present invention includes an organic EL element 1, a state detection unit 2, a control unit 3, a storage unit 4, a current setting unit 5, It is mainly composed by.

  The organic EL element 1 is formed by laminating a translucent first electrode 12, an organic layer 13, and a second electrode 14 on a support substrate 11. The light transmitted through the electrode 12 is taken out. A substantially concave sealing member 15 is joined to the support substrate 11 so as to cover the organic layer 13 and the like. In the present embodiment, the organic EL element 1 emits white light.

  The support substrate 11 is a translucent glass substrate having a rectangular shape.

  The first electrode 12 is formed by layering a light-transmitting conductive material such as ITO (Indium Tin Oxide) on the support substrate 1 by a sputtering method or the like, and patterning it into a predetermined shape by, for example, a photolithography method. Become. In the present embodiment, the first electrode 12 serves as an anode, and holes are injected into the organic layer 13.

  The organic layer 13 is formed on the first electrode 12 and includes a plurality of layers having at least a light emitting layer. For example, in this embodiment, the organic layer 13 is formed by depositing a hole injection layer, a hole transport layer, a first light emitting layer, a second light emitting layer, a first electron transport layer, a second electron transport layer, and an electron injection layer. And the like are sequentially stacked by such means. The first light emitting layer emits amber light, the second light emitting layer emits blue light, and the organic EL element 1 obtains white by mixing colors.

  The second electrode 14 is an electrode disposed on the side facing the light emitting display surface, and a low resistance conductive material such as aluminum (Al) or magnesium silver (Mg: Ag) is deposited by means such as vapor deposition. It is formed by laminating layers having a film thickness of about 50 to 200 nm.

  The sealing member 15 is bonded to the support substrate 11 via an adhesive (not shown). For example, flat glass is formed into a substantially concave shape by a processing method such as cutting or etching. The sealing member 15 covers the organic EL element 1 together with the support substrate 11 and suppresses deterioration of the organic EL element 1 due to moisture or the like. A hygroscopic agent that adsorbs moisture may be disposed in the space covered by the sealing member 15.

  The state detection means 2 monitors the state of the organic EL element 1, and in this embodiment comprises a temperature sensor 2a and a timer 2b. The temperature sensor 2 a detects the ambient temperature of the organic EL element 1 as the state detection means and outputs a detection signal to the control means 3. The temperature sensor 2a is composed of, for example, a thermistor disposed on the support substrate 11. The timer 2b measures the drive time (light emission time) of the organic EL element 1 as the state detection means and outputs a time signal to the control means 3. For example, the timer 2b measures the time from turning on and off the power switch. Or the drive time is measured by measuring the number of times the power is turned on.

  The control means 3 is mainly composed of a microcomputer, and includes a CPU for executing a predetermined program, a ROM in which the program is stored, a RAM in which calculation results are temporarily stored, and the organic EL element 1. A drive circuit for outputting a PWM (Pulse Width Modulation) control signal at a predetermined duty ratio for driving light emission, a state detection means 2, an interface unit for inputting a display signal, and the like are provided. Further, the control unit 3 reads a constant current set value from a storage unit 4 (to be described later) according to the detection result of the state detection unit 2, and sends the constant current through a current setting unit 5 (to be described later) according to the read set value. Supplied to the organic EL element 1.

  The storage unit 4 is composed of a nonvolatile memory such as an EEPROM or a flash memory, and stores at least current adjustment data indicating the relationship between the ambient temperature, drive time, and constant current set value. FIG. 3 is a diagram showing the relationship between the current value of the organic EL element 1 and the emission color. The organic EL element 1 can change the emission color by changing the supplied current value as shown in FIG. That is, as the current adjustment data, the optimum constant current setting value for maintaining the emission color with respect to the change in ambient temperature and the driving time obtained from the sample having the same configuration as the organic EL element 1 is stored in advance. Yes.

  The current setting means 5 is mainly composed of, for example, a comparator and a resistance variable means, and changes the set value of the constant current by changing the resistance value in accordance with the control signal from the control means 3, and the PWM A constant current is supplied to the organic EL element 1 at a predetermined duty ratio based on the control signal.

  Next, a method for driving the organic EL element 1 by the control means 3 will be described.

  FIG. 4 is a diagram showing the relationship between the ambient temperature and drive time of the organic EL element 1 and the emission color. In the organic EL element 1, as shown in FIG. 4A, the x value and y value in the CIE chromaticity coordinates change depending on the ambient temperature, and the emission color changes. In addition, as shown in FIG. 4B, the organic EL element 1 changes the x- and y-values in the CIE chromaticity coordinates depending on the driving time, and the emission color changes.

  The control means 3 calculates the ambient temperature and driving time based on the detection results of the temperature sensor 2a and the timer 2b, and reads and sets the optimum constant current setting value from the storage unit 4 according to the ambient temperature and driving time. Determine the value. Further, the duty ratio of the current supply is determined so as to maintain the light emission luminance of the organic EL element 1 according to the determined set value. That is, since the light emission luminance of the organic EL element 1 is determined by the amount of current per unit time, by changing the duty ratio according to the change of the current value (set value), the current amount per unit time is maintained. The light emission luminance of the organic EL element 1 can be maintained. FIG. 5 is a diagram illustrating an example of a driving waveform of the organic EL element 1. FIG. 5A shows a case where the organic EL element 1 is driven with a duty ratio of 100%. The crest value a is determined by the supplied current value. The amount of current per unit time t is obtained from the area of the drive waveform (crest value × on-time of the drive waveform). When the peak value of the drive waveform is set to a peak value b that is twice the peak value a (that is, when the constant current setting value is changed to twice), as shown in FIG. By setting the ratio to 50%, the amount of current per unit time t can be made the same as before the change of the set value, and the light emission luminance can be maintained. In addition, since the organic EL element has a characteristic that the light emission luminance changes according to the ambient temperature and the driving time, it is more preferable that the change of the duty ratio is determined in consideration of the light emission luminance characteristic.

  According to this embodiment, it becomes possible to suppress the change in the emission color of the organic EL element 1 due to the change in the ambient temperature and the driving time by the driving method. Therefore, the effects of the present invention can be achieved without causing a reduction in yield and complication of production as compared with the conventional method of improving the organic layer of the organic EL element. FIG. 6 is a diagram illustrating a change in emission color of the organic EL element 1 with respect to the ambient temperature and the driving time when the organic EL element 1 is driven by the driving method according to the present embodiment. As shown in FIG. 6, it is obvious that both the x value and the y value in the CIE chromaticity coordinates are suppressed with respect to changes in the ambient temperature and driving time, and the present invention has a sufficient effect.

The block diagram which shows the electric constitution of the drive device of the organic EL element which is embodiment of this invention. The schematic cross section which shows the organic EL element same as the above. The figure which shows the relationship between the luminescent color of an organic EL element same as the above, and an electric current value. The figure which shows the relationship between the luminescent color of an organic EL element same as the above, ambient temperature, and drive time. The figure which shows an example of the drive waveform of an organic EL element same as the above. The figure which shows the relationship between the luminescent color of an organic EL element same as the above, ambient temperature, and drive time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic EL element 2 State detection means 2a Temperature sensor 2b Timer 3 Control means 4 Memory | storage part 5 Current setting means 11 Support substrate 12 1st electrode 13 Organic layer 14 2nd electrode 15 Sealing member

Claims (6)

A drive device for an organic EL element that supplies a constant current at a predetermined duty ratio,
State detecting means for detecting at least one of driving time and ambient temperature;
Based on the detection result of the state detection means, the set value of the constant current is changed to maintain the emission color of the organic EL element, and the current is supplied to maintain the emission luminance of the organic EL element according to the set value. And a control means for changing the duty ratio of the organic EL element. A storage unit that stores current adjustment data indicating a relationship between at least one of driving time or ambient temperature and the set value;
2. The organic EL element driving apparatus according to claim 1, wherein the control unit reads the set value from the current adjustment data based on a detection result of the state detection unit. The organic EL element driving apparatus according to claim 1, wherein the organic EL element includes a plurality of light emitting layers having different emission colors. A driving method of an organic EL element that supplies a constant current at a predetermined duty ratio,
Changing the set value of the constant current to maintain the emission color of the organic EL element based on the detection result of the state detection means for detecting at least one of the driving time or the ambient temperature,
A driving method of an organic EL element, wherein a duty ratio of current supply is changed in order to maintain light emission luminance of the organic EL element according to the set value. Current adjustment data indicating a relationship between at least one of driving time or ambient temperature and the set value is stored in the storage unit;
The organic EL element driving method according to claim 4, wherein the set value is read from the current adjustment data based on a detection result of the state detection unit. The organic EL element driving method according to claim 4, wherein the organic EL element includes a plurality of light emitting layers having different emission colors.

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