JP3869984B2 - Driving method of light emitting element and driving method of light emitting device - Google Patents

Description

【００９１】
【化２】

【００９２】
【化３】

【００９３】
【化４】

【００９４】
【化５】

【００９５】
電子輸送層としては、例えば、トリス（８−キノリノール）アルミニウムを用いることができ、その他にも下記の材料を用いることができる。
【００９６】
【化６】

【００９７】
【化７】

【００９８】
【化８】

【００９９】
【化９】

【０１００】
また、以下に示されているようなドーパンド色素を電子輸送層、あるいは正孔輸送層にドーピングすることもできる。
【０１０１】
【化１０】

【０１０２】
また、陽極層４０１と基板１００との間に誘電層を設けることが好ましい。誘電層は、ＳｉＯ₂，ＳｉＯ等屈折率の異なる層の積層により特定の波長の反射透過率を高く（低く）することができる。あるいは単にハーフミラーを使用することも可能である。
【０１０３】
【発明の効果】
以上のべたように、本発明によれば、毎回順電圧の印加と逆電圧の印加を繰り返すのではなく、順電圧を複数回印加した後、逆電圧を印加することにより、発光に寄与しない過渡電流を低減し、発光素子やそれを用いた発光デバイスの消費電力の低減を可能とするものである。
【０１０４】
さらに本発明は、順電圧の印加と次なる順電圧の印加の間の期間において、逆電圧を印加しないときは発光素子の陰極と陽極を短絡、あるいは同電位にするのではなく、発光しないかその発光が無視しうる程度の順電圧に保持するか、あるいは陰極と陽極の間を開放することによって順方向過渡電流を低減し、発光素子やそれを用いた発光デバイスの消費電力の低減を可能とするものである。
【図面の簡単な説明】
【図１】本発明の第一の実施形態例において、駆動回路、及び有機ＬＥＤ素子に印加される電圧と、流れる電流とを示す図である。
【図２】本発明の第二の実施形態例において、駆動回路、及び有機ＬＥＤ素子に印加される電圧と、流れる電流とを示す図である。
【図３】図２の一部を拡大した図である。
【図４】本発明の第三の実施形態例として、有機ＬＥＤ素子を有する微小な画素を複数配列した有機ＬＥＤデバイスの等価回路を示す図である。
【図５】本発明の第三の実施形態例として、有機ＬＥＤ素子を有する微小な画素を複数配列した有機ＬＥＤデバイスの駆動タイミングを示す図である。
【図６】発光素子の一例を示す図である。
【図７】有機ＬＥＤ素子の従来の駆動タイミングを示す図である。
【図８】有機ＬＥＤ素子を有する微小な画素を複数配列した有機ＬＥＤデバイスの等価回路を示す図である。
【図９】有機ＬＥＤ素子を有する微小な画素を複数配列した有機ＬＥＤデバイスの従来の駆動タイミングを示す図である。
【図１０】従来の駆動法において、駆動回路、及び有機ＬＥＤ素子に印加される電圧と、流れる電流とを示す図である。
【図１１】図１０の駆動を繰り返し行ったときの、駆動回路、及び有機ＬＥＤ素子に印加される電圧と、流れる電流とを示す図である。
【符号の説明】
１１，２１，３１，４１ 有機ＬＥＤ素子
１２，２２，３２，４２ 保持容量
１００ 基板
４０１ 陽極層
４０２ 正孔輸送層
４０３ 電子輸送層
４０４ 陰極層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting element used for a copying machine, a printer, a display, a document illumination light source of an image reading apparatus, or the like, or a light emitting device in which a plurality of light emitting elements are arranged.
[0002]
[Prior art]
In recent years, organic thin-film light-emitting elements (organic LED elements) that can be formed in a thin film on a large-area substrate and can be driven by direct current have been developed. In addition, an organic LED device in which light-emitting portions composed of organic LED elements are arranged one-dimensionally or two-dimensionally is used as a light-emitting element device, and is applied to a copying machine, a printer, a display, a document illumination light source of an image reading apparatus, etc. It has been proposed.
[0003]
However, in some organic LED elements, when a forward voltage is applied continuously or intermittently, the emission luminance gradually decreases. Although this cause can be considered variously, as one factor, space charge accumulates in the organic layer in the vicinity of the interface of each layer constituting the organic LED element, thereby reducing the amount of charge injected into the organic layer. Alternatively, it is conceivable that the moving speed of charges conducted in the organic layer decreases.
[0004]
For the purpose of removing this accumulated space charge and preventing a decrease in light emission luminance, if a forward voltage is applied to the organic LED element for a certain period of time, a reverse voltage that reverses the polarity of the forward voltage each time is applied. There has been proposed a driving method in which an element is applied to recover the element.
[0005]
A timing diagram of this drive voltage is shown in FIG.
[0006]
In the figure, the vertical axis indicates the potential of the anode based on the potential of the cathode of the organic LED element. The horizontal axis indicates time. The forward voltage Vf is applied at time t0 and continues until time t1. At time t1, the applied voltage changes to the reverse voltage Vr and continues until time t2. The voltage applied again at time t2 is replaced with the forward voltage Vf. In this way, the forward voltage Vf and the reverse voltage Vr are repeatedly applied, thereby preventing the accumulation of space charge and preventing the light emission luminance from decreasing.
[0007]
An example of an equivalent circuit and an example of a driving method of an organic LED device in which a plurality of minute pixels having such organic LED elements are arranged to form a simple matrix are shown in FIGS.
[0008]
FIG. 8 is a diagram showing an equivalent circuit of the organic LED device.
[0009]
In this example, an organic LED device composed of four pixels, pixel 1, pixel 2, pixel 3, and pixel 4, is shown. The anodes of the organic LED elements 11 and 21 of the pixels 1 and 2 are both connected to the data signal line Y1. The anodes of the organic LED elements 31 and 41 of the pixels 3 and 4 are both connected to the data signal line Y2.
[0010]
On the other hand, the cathodes of the organic LED elements of the pixels 1 and 2 are connected to different selection signal lines X1 and X2, respectively. The cathodes of the organic LED elements of the pixels 3 and 4 are also connected to the selection signal lines X1 and X2, respectively.
[0011]
The data signal lines Y1 and Y2 are connected to a data signal circuit DATA having a signal source that operates respectively. Each signal source may act as a voltage source that generates a voltage signal, or may act as a current source that generates a current signal.
[0012]
On the other hand, the selection signal lines X1 and X2 are connected to the selection circuit SEL.
[0013]
FIG. 9 is a diagram showing the drive timing of the organic LED device in the example of FIG. 8, and the data signals data1 and data2 applied to the data signal lines Y1 and Y2, and the selection signal sel1 applied to the selection signal lines X1 and X2. , Sel2, and so on.
[0014]
At time t1, the selection signal sel1 applied to the selection signal line X1 is in a low potential state in which the selection signal sel1 is ON, and the sel2 applied to X2 is in a high potential state in which the selection signal sel1 is OFF. Then, a forward voltage corresponding to the signal is applied to each of the organic LED elements 11 and 31 of the pixel 1 and the pixel 3 connected to the selection signal line X1, and light is emitted at a luminance corresponding to the signal.
[0015]
At time t2, the selection signal sel2 applied to the selection signal line X2 is in a low potential state in which the selection signal sel2 is ON, and the sel1 applied to X1 is in a high potential state in which the selection signal sel2 is OFF. Then, a reverse voltage is applied to each of the organic LED elements 11 and 31 of the pixel 1 and the pixel 3 connected to the selection signal line X1, and at the same time as the light emission is completed, the accumulated space charge is removed and recovery is performed.
[0016]
At the same time, forward voltages corresponding to the signals are applied to the organic LED elements 21 and 41 of the pixels 2 and 4 connected to the selection signal line X2, and light is emitted at a luminance corresponding to the signals.
[0017]
At time t3, a high potential state is reached in which sel2 applied to the selection signal line X2 is OFF. Then, a reverse voltage is applied to each of the organic LED elements 21 and 41 of the pixel 2 and the pixel 4 connected to the selection signal line X2, and at the same time as the light emission is completed, the accumulated space charge is removed and recovery is performed.
[0018]
In this way, after the selection signal lines X1 and X2 or other selection signal lines (not shown) are successively scanned, at a time t4, sel1 applied to the selection signal line X1 is in a low potential state that is ON. .
[0019]
While repeating such an operation, each pixel constituting the organic LED device repeats light emission and recovery at a luminance corresponding to the data signal while gradually shifting the timing.
[0020]
[Problems to be solved by the invention]
However, the conventional driving method of the organic LED element or organic LED device that repeats the application of the forward voltage and the reverse voltage every time as described above gradually increases the charging and discharging of the capacitance parasitic on the organic LED element. However, there is a problem in that the invalid power that does not contribute to light emission is increased, resulting in an increase in power consumption.
[0021]
This is shown in FIG.
[0022]
FIG. 10 is a diagram illustrating a voltage Vdrv applied to the drive circuit, a current Idrv flowing through the drive circuit, a voltage Vled applied to the organic LED element, and a current Iled flowing through the organic LED element in the conventional driving method. is there.
[0023]
When the forward voltage Vf is applied at time t1, the capacitor parasitic in the organic LED element is charged in the forward direction, and a transient current Ift flows in the drive circuit. The transient current Ift is the largest at time t1, and eventually decays to settle to the steady current Ifc. This Ift is a current for causing the organic LED element to emit light. When the applied voltage is switched to the reverse voltage Vr at time t2, discharge is performed from the parasitic capacitance of the organic LED element, and then charging is performed in the reverse direction. Irt flows. The transient current Irt is the largest at time t2, and eventually decays to settle to the steady current Irc. Usually, since an organic LED element has a diode characteristic, Irc is very small. When the applied voltage is switched to the forward voltage Vf again at time t3, the forward transient current Ift flows again. By repeatedly applying the forward voltage Vf and the reverse voltage Vr in this way, a transient current and a steady current flow alternately in the drive circuit.
[0024]
FIG. 11 shows the voltage and current when this operation is repeated.
[0025]
As described above, in the driving method in which forward voltage application and reverse voltage application are repeated each time, forward and reverse transient currents that do not directly contribute to light emission increase.
[0026]
In addition, the forward transient current Ift and the reverse transient current Irt are each charged with a reverse polarity at the timing before it flows, and a large current value is required to reverse this. To do.
[0027]
In particular, when the luminous efficiency of the organic LED element is high or the required light emission luminance is low and the forward steady current Ifc may be small, the forward voltage application and the reverse voltage application are repeated frequently and the forward voltage is large. When the time from application to application of the reverse voltage is short, power due to these transient currents occupies a non-negligible portion of power consumption.
[0028]
There is a problem that this becomes a factor that hinders reduction in power consumption of the organic LED element and the organic LED device using the organic LED element.
[0029]
[Means for Solving the Problems]
The inventor of the present invention has reached the present invention as a result of intensive studies in view of the above-described conventional problems.
[0030]
  That is, the present invention relates to a method for driving a light-emitting element comprising at least an anode layer and a cathode layer on a substrate and one or more organic compound layers sandwiched between them, and a voltage for light emission as an electric field. The light emission voltage and the recovery voltage having the opposite polarity are applied, and the light emission voltage is applied to and released from the light emitting element a plurality of times, and then the recovery voltage is applied.And the application time of the recovery voltage is longer than one application time of the light emission voltage and shorter than the cumulative time of the application times.A driving method of a light emitting element characterized by the above.
[0033]
  In the driving method of the light emitting device of the present invention,The absolute value of the peak value of the recovery voltage is preferably larger than the absolute value of the average value within one application time of the light emission voltage.
[0034]
  Furthermore, the present invention provides a plurality of one-dimensional or two-dimensional light-emitting elements formed on a substrate by at least an anode layer and a cathode layer and one or more organic compound layers sandwiched therebetween. In a driving method of an arrayed light emitting device, the electric field has a light emission voltage and a recovery voltage having a polarity opposite to the light emission voltage, and the light emission is performed while scanning the arrayed light emitting elements. Voltage forofAppliedAnd releaseIs repeated a plurality of times, and then the recovery voltage is applied while scanning the arrayed light emitting elements, and the application time of the recovery voltage is less than one application time of the light emission voltage. The driving method of the light emitting device is characterized in that it is long and shorter than the cumulative time of the plurality of application times.
[0036]
  The present invention does not repeat the application of the forward voltage and the application of the reverse voltage every time.Application and releaseMultiple timesRepeatedThereafter, by applying a reverse voltage, a transient current that does not contribute to light emission is reduced, and power consumption of the light emitting element and the light emitting device using the light emitting element can be reduced.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings of the embodiments.
[0039]
FIG. 1 shows a voltage Vdrv applied to a driving circuit, a current Idrv flowing through the driving circuit, a voltage Vled applied to the organic LED element, and a current Iled flowing through the organic LED element in the first embodiment of the present invention. FIG.
[0040]
The forward voltage Vf is applied at time t1, and continues until time t2. At time t2, the applied voltage changes to the holding voltage Vh and continues until time t3. At time t3, the applied voltage is switched again to the forward voltage Vf. In this way, after the forward voltage Vf and the holding voltage Vh are repeatedly applied a plurality of times, the voltage applied at the time t4 is switched to the reverse voltage Vr. Here, the space charge accumulated so far is removed. After the reverse voltage Vr continues until time t5, the applied voltage is switched again to the forward voltage Vf at time t6. Such a cycle is repeated.
[0041]
Looking at the current in this process, when the forward voltage Vf is applied at time t1, the capacitor parasitic in the organic LED element is charged in the forward direction, and a transient current Ift flows in the drive circuit. The transient current Ift is the largest at time t1, and eventually decays to settle to the steady current Ifc. This Ifc is a current for causing the organic LED element to emit light.
[0042]
When the applied voltage is switched to the holding voltage Vh at time t2, discharge is performed from the parasitic capacitance of the organic LED element, and a reverse transient current Iht flows in the drive circuit. However, since the holding voltage is not zero but a forward voltage having a certain magnitude, the change amount of the applied voltage is small and the discharge current is small. In addition, charging in the reverse direction is not performed. Therefore, the sum of the transient current Iht becomes smaller than that when a reverse voltage is applied as in the prior art. The transient current Iht eventually decays and settles to the steady current Ihc, but Ihc is very small because the holding voltage Vh is set to a voltage close to or lower than the rising voltage in the diode characteristics of the organic LED element.
[0043]
When the voltage applied at time t3 is switched to the forward voltage Vf again, the forward transient current Ift flows again. However, since the parasitic capacitance of the organic LED element is not so discharged, the transient current Ift flowing at this time is also small. By repeatedly applying the forward voltage Vf and the holding voltage Vh in this way, the transient current and the steady current flow alternately in the drive circuit, but the ratio of the transient current is smaller than the steady current.
[0044]
After the forward voltage Vf and the holding voltage Vh are repeatedly applied in this way, the voltage applied at time t4 is switched to the reverse voltage Vr. At time t4, when the applied voltage is switched to the reverse voltage Vr, the parasitic capacitance of the organic LED element is discharged, and then charged in the reverse direction. Irt flows. At this time, the change amount of the applied voltage is large and the discharge current is large. In addition, charging in the reverse direction is also performed. Therefore, the sum of the transient current Irt becomes as large as the reverse transient current that flows when the reverse voltage is applied in the conventional example. The transient current Irt is the largest at time t4 and eventually decays to settle to the steady current Irc. Usually, since an organic LED element has a diode characteristic, Irc is very small.
[0045]
After the reverse voltage Vr continues until time t5, the applied voltage is switched to the forward voltage Vf again at time t5. At this time, since the discharge is performed from the parasitic capacitance of the organic LED element that has been charged in the reverse direction by the reverse voltage Vr, and then the forward charge is performed, the forward transient current Ift flows in the drive circuit. . At this time, the change amount of the applied voltage is large and the discharge current is large. In addition, forward charging is also performed. Therefore, the transient current Ift, which is the sum, becomes as large as the forward transient current that flows when the forward voltage is applied in the conventional example. However, since such a reverse voltage is applied only at a rate of one forward voltage application, the number of times that a large transient current flows is reduced, and the transient current that does not contribute to light emission can be reduced over the entire driving time. it can.
[0046]
  The application time of the reverse voltage from t4 to t5 is preferably as long as possible for the recovery effect, but it may be necessary to shorten such time that does not contribute to light emission as much as possible. In the present invention, since space charge relaxation can be expected to some extent while the holding voltage Vh is applied, the accumulated time of forward voltage application prior to reverse voltage applicationApply the reverse voltage application timeShortThe
[0047]
Furthermore, it can be expected that the recovery effect can be increased by setting the absolute value of the reverse voltage Vr higher than the absolute value of the average value of the forward voltage Vf even during a part of the reverse voltage application time.
[0048]
In this embodiment, the forward voltage Vf, the holding voltage Vh, and the reverse voltage Vr are constant voltages. However, even if Vf, Vh, and Vr are changed during each application time or for each application, Vf, Vh, and Vr are changed. The same effect can be expected.
[0049]
FIG. 2 shows a voltage Vdrv applied to the drive circuit, a current Idrv flowing through the drive circuit, a voltage Vled applied to the organic LED element, and a current Iled flowing through the organic LED element in the second embodiment of the present invention. FIG.
[0050]
In the present embodiment, the cathode and the anode are opened without being held at a specific potential by the external power source at the timing when the holding voltage is applied in the first embodiment.
[0051]
Looking at the current in this process, when the forward voltage Vf is applied at time t1, the capacitor parasitic in the organic LED element is charged in the forward direction, and a transient current Ift flows in the drive circuit. The transient current Ift is the largest at time t1, and eventually decays to settle to the steady current Ifc. This Ifc is a current for causing the organic LED element to emit light. When the gap between the cathode and the anode is opened at time t2, the charge accumulated in the parasitic capacitance of the organic LED element is discharged through the inside of the organic LED element, but no current flows through the drive circuit. Therefore, the transient current Iht becomes smaller than that in the first embodiment.
[0052]
FIG. 3 is an enlarged view of this portion.
[0053]
The discharge of the charge accumulated in the parasitic capacitance of the organic LED element through the inside of the organic LED element is gradually attenuated, and the voltage between the cathode and the anode of the organic LED element settles near the rising voltage in the diode characteristics of the organic LED element. When the voltage applied again at time t3 is switched to the forward voltage Vf, the forward transient current Ift flows again. However, since the parasitic capacitance of the organic LED element already holds the electric charge that the voltage between the cathode and the anode is held in the vicinity of the rising voltage in the diode characteristics of the organic LED element, the transient current Ift flowing at this time is also small. . By repeatedly applying and releasing the forward voltage Vf in this manner, a transient current and a steady current flow alternately in the drive circuit, but the ratio of the transient current is smaller than the steady current.
[0054]
After the forward voltage Vf is repeatedly applied and released in this manner, the voltage applied at time t4 is replaced with the reverse voltage Vr. At time t4, when the applied voltage is switched to the reverse voltage Vr, the parasitic capacitance of the organic LED element is discharged, and then charged in the reverse direction. Irt flows. At this time, the change amount of the applied voltage is large and the discharge current is large. In addition, charging in the reverse direction is also performed. Therefore, the sum of the transient current Irt becomes as large as the reverse transient current that flows when the reverse voltage is applied in the conventional example and the first embodiment. The transient current Irt is the largest at time t4 and eventually decays to settle to the steady current Irc. Usually, since an organic LED element has a diode characteristic, Irc is very small.
[0055]
After the reverse voltage Vr continues until time t5, the applied voltage is switched to the forward voltage Vf again at time t5. At this time, since the discharge is performed from the parasitic capacitance of the organic LED element that has been charged in the reverse direction by the reverse voltage Vr, and then the forward charge is performed, the forward transient current Ift flows in the drive circuit. . At this time, the change amount of the applied voltage is large and the discharge current is large. In addition, forward charging is also performed. Therefore, the transient current Ift, which is the sum, becomes as large as the forward transient current that flows when the forward voltage is applied in the conventional example. However, since such a reverse voltage is applied only at a rate of one forward voltage application, the number of times that a large transient current flows is reduced, and the transient current that does not contribute to light emission can be reduced over the entire driving time. it can.
[0056]
  Also in this embodiment example,As in the first embodiment, the reverse voltage application time from t4 to t5 is shorter than the cumulative time of forward voltage application prior to reverse voltage application.The
[0057]
Further, similarly to the first embodiment, the absolute value of the reverse voltage Vr is set higher than the absolute value of the average value of the forward voltage Vf even during a part of the reverse voltage application time. Can be expected to increase the recovery effect.
[0058]
In the present embodiment, the forward voltage Vf and the reverse voltage Vr are constant voltages. However, the same effect can be expected even if Vf and Vr are changed during each application time or for each application. .
[0059]
As a third embodiment of the present invention, an example of an equivalent circuit and an example of a driving method of an organic LED device in which a plurality of minute pixels having such organic LED elements are arranged to form a simple matrix are shown in FIGS. As shown in FIG.
[0060]
Such an organic LED device configured by arranging pixels in two dimensions is often used as a display device for computers, portable terminals, car navigation systems, and the like.
[0061]
FIG. 4 is a diagram showing an equivalent circuit of the organic LED device.
[0062]
In this example, an organic LED device composed of four pixels, pixel 1, pixel 2, pixel 3, and pixel 4, is shown. The anodes of the organic LED elements 11 and 21 of the pixels 1 and 2 are both connected to the data signal line Y1. The anodes of the organic LED elements 31 and 41 of the pixels 3 and 4 are both connected to the data signal line Y2.
[0063]
On the other hand, the cathodes of the organic LED elements of the pixels 1 and 2 are connected to different selection signal lines X1 and X2, respectively. The cathodes of the organic LED elements of the pixels 3 and 4 are also connected to the selection signal lines X1 and X2, respectively.
[0064]
Each of the organic LED elements 11, 21, 31, 41 is accompanied by a parallel capacitance or a storage capacitor 12, 22, 32, 42 provided for holding electric charges, which the organic LED element itself has.
[0065]
The data signal lines Y1 and Y2 are connected to a data signal circuit DATA having a signal source that operates respectively. Each signal source may act as a voltage source that generates a voltage signal, or may act as a current source that generates a current signal.
[0066]
On the other hand, the selection signal lines X1 and X2 are connected to the selection circuit SEL.
[0067]
FIG. 5 is a diagram showing the driving timing of the organic LED device of the example of FIG. 4, and the data signals data1 and data2 applied to the data signal lines Y1 and Y2 and the selection signal sel1 applied to the selection signal lines X1 and X2. , Sel2 and.
[0068]
At a time t1, a low potential state in which the selection signal sel1 applied to the selection signal line X1 is ON, and an open state in which sel2 applied to X2 is OFF. Then, a forward voltage corresponding to the signal is applied to each of the organic LED elements 11 and 31 of the pixel 1 and the pixel 3 connected to the selection signal line X1, and light is emitted at a luminance corresponding to the signal.
[0069]
At a time t2, a low potential state in which the selection signal sel2 applied to the selection signal line X2 is ON and an open state in which sel1 applied to X1 is OFF are set. Then, the anode and the cathode of each of the organic LED elements 11 and 31 of the pixel 1 and the pixel 3 connected to the selection signal line X1 are opened, and the charge accumulated in the parasitic capacitance or the holding capacitance of the organic LED element is the organic LED element. Discharge through the interior of the, and gradually ends the light emission.
[0070]
At the same time, forward voltages corresponding to the signals are applied to the organic LED elements 21 and 41 of the pixels 2 and 4 connected to the selection signal line X2, and light is emitted at a luminance corresponding to the signals.
[0071]
At time t3, an open state is established in which sel2 applied to the selection signal line X2 is OFF. Then, the anode and cathode of each of the organic LED elements 21 and 41 of the pixel 2 and the pixel 4 connected to the selection signal line X2 are opened, and the charge accumulated in the parasitic capacitance or the holding capacitance of the organic LED element is the organic LED element. Discharge through the interior of the, and gradually ends the light emission.
[0072]
In this way, after the selection signal lines X1 and X2 or other selection signal lines (not shown) are successively scanned, at a time t4, sel1 applied to the selection signal line X1 is in a low potential state that is ON. .
[0073]
While repeating such an operation, each pixel constituting the organic LED device repeats light emission and recovery at a luminance corresponding to the data signal while gradually shifting the timing.
[0074]
After such a display cycle is repeated n times, the following recovery cycle is driven.
[0075]
At time t4, the selection signal sel1 applied to the selection signal line X1 becomes a high potential state that is a recovery potential. Then, a reverse voltage is applied to each of the organic LED elements 11 and 31 of the pixel 1 and the pixel 3 connected to the selection signal line X1, the accumulated space charge is removed, and recovery is performed.
[0076]
At time t5, the selection signal sel2 applied to the selection signal line X2 becomes a high potential state that is a recovery potential. Then, a reverse voltage is applied to each of the organic LED elements 21 and 41 of the pixel 2 and the pixel 4 connected to the selection signal line X2, the accumulated space charge is removed, and recovery is performed.
[0077]
The selection signal sel1 applied to the selection signal line X1 may return to the open state at the timing of time t5. However, the longer the reverse voltage application time is, the higher the recovery effect is. It may return to the open state after a time or may be in a low potential state that is ON at the timing of forward voltage application in the next cycle.
[0078]
  In application to a display device or the like, image information is not displayed during this recovery cycle, which may cause image quality deterioration such as flicker and effective luminance reduction. In that sense, a shorter reverse voltage application time is better.Therefore, in this embodiment example,Set the reverse voltage application time longer than a single forward voltage and shorter than the cumulative time of forward voltage application in the cycle prior to reverse voltage application.The
[0079]
In this cycle, a reverse voltage is applied to each pixel constituting the organic LED device, and recovery is performed.
[0080]
After such a recovery cycle is performed once or m times, a display cycle is performed again.
[0081]
Also in the present embodiment example, since the reverse voltage is applied only at a rate of one forward voltage application, the number of times that a large transient current flows is reduced, and the transient current that does not contribute to light emission is reduced over the entire driving time. be able to. Such characteristics are particularly important when considering application to display devices of portable computers and portable terminals.
[0082]
In the present embodiment, the holding voltage is not applied to the organic LED element during the time between forward voltage application and forward voltage application in the display cycle, but an open state is set. This is to effectively use the charge accumulated in the parasitic capacitance or holding capacitance of the organic LED element. If such a thing is not minded, of course, the drive which applies a holding voltage to an organic LED element in the time between forward voltage application in a display cycle and forward voltage application is also possible.
[0083]
Further, in the driving of the recovery cycle, it is possible not to apply a forward voltage to the organic LED element at all, but to apply a reverse voltage after applying the forward voltage.
[0084]
Even if such a method is used, the reverse voltage is applied only at a rate of one forward voltage application, so the number of large transient currents decreases, reducing the transient current that does not contribute to light emission over the entire drive time. The effect that can be expected.
[0085]
As shown in FIG. 6, the light-emitting element used in the present invention includes at least an anode layer 401 and a cathode layer 404 on a substrate 100 and one or more organic compound layers sandwiched therebetween.
[0086]
The substrate 100 may be any substrate as long as the light emitting element can be formed on the surface. For example, glass such as soda lime glass, or a transparent insulating substrate such as a resin film is preferably used.
[0087]
A material having a high work function is desirable as the material of the anode layer 401. For example, ITO, tin oxide, gold, platinum, palladium, selenium, iridium, copper iodide, or the like can be used. On the other hand, the material of the cathode layer 404 is preferably a material having a small work function. For example, Mg / Ag, Mg, Al, In, or an alloy thereof can be used.
[0088]
The organic compound layer may have a single-layer structure or a multi-layer structure. For example, holes are injected from the anode layer 401 and electrons are injected from the cathode layer 404. The electron transport layer 403, and either the hole transport layer 402 or the electron transport layer 403 is a light emitting layer. In addition, a phosphor layer containing a phosphor may be provided between the hole transport layer 402 and the electron transport layer 403. Further, a mixed layer configuration that also serves as a hole transport layer, an electron transport layer, and a fluorescent layer is possible.
[0089]
As the hole transport layer 402, for example, N, N′-bis (3-methylphenyl) -N, N′-diphenyl- (1,1′-biphenyl) -4,4′-diamine can be used. In addition, the following organic materials can be used.
[0090]
[Chemical 1]

[0091]
[Chemical 2]

[0092]
[Chemical Formula 3]

[0093]
[Formula 4]

[0094]
[Chemical formula 5]

[0095]
As the electron transport layer, for example, tris (8-quinolinol) aluminum can be used, and in addition, the following materials can be used.
[0096]
[Chemical 6]

[0097]
[Chemical 7]

[0098]
[Chemical 8]

[0099]
[Chemical 9]

[0100]
Further, a dopant dye as shown below can be doped into the electron transport layer or the hole transport layer.
[0101]
Embedded image

[0102]
In addition, a dielectric layer is preferably provided between the anode layer 401 and the substrate 100. The dielectric layer is SiO₂The reflection transmittance of a specific wavelength can be increased (decreased) by stacking layers having different refractive indexes, such as SiO 2 and SiO 2. Alternatively, it is possible to simply use a half mirror.
[0103]
【The invention's effect】
As described above, according to the present invention, instead of repeating the application of the forward voltage and the application of the reverse voltage every time, a transient that does not contribute to light emission by applying the reverse voltage after applying the forward voltage a plurality of times. The current is reduced, and the power consumption of the light emitting element and the light emitting device using the light emitting element can be reduced.
[0104]
Further, according to the present invention, in the period between the application of the forward voltage and the application of the next forward voltage, when the reverse voltage is not applied, the cathode and the anode of the light emitting element are not short-circuited or set to the same potential, but do not emit light. The forward voltage is kept at a negligible forward voltage, or the cathode and anode are opened to reduce forward current transients, reducing the power consumption of light emitting devices and light emitting devices using them. It is what.
[Brief description of the drawings]
FIG. 1 is a diagram showing a voltage applied to a drive circuit and an organic LED element and a flowing current in the first embodiment of the present invention.
FIG. 2 is a diagram showing a voltage applied to a drive circuit and an organic LED element and a flowing current in the second embodiment of the present invention.
FIG. 3 is an enlarged view of a part of FIG. 2;
FIG. 4 is a diagram showing an equivalent circuit of an organic LED device in which a plurality of minute pixels each having an organic LED element are arranged as a third embodiment of the present invention.
FIG. 5 is a diagram showing driving timing of an organic LED device in which a plurality of minute pixels each having an organic LED element are arranged as a third embodiment of the present invention.
FIG. 6 illustrates an example of a light-emitting element.
FIG. 7 is a diagram showing conventional driving timing of an organic LED element.
FIG. 8 is a diagram showing an equivalent circuit of an organic LED device in which a plurality of minute pixels having organic LED elements are arranged.
FIG. 9 is a diagram showing conventional driving timing of an organic LED device in which a plurality of minute pixels having organic LED elements are arranged.
FIG. 10 is a diagram illustrating a voltage applied to a driving circuit and an organic LED element and a flowing current in a conventional driving method.
11 is a diagram showing a voltage applied to a drive circuit and an organic LED element and a flowing current when the drive of FIG. 10 is repeatedly performed.
[Explanation of symbols]
11, 21, 31, 41 Organic LED element
12, 22, 32, 42 Retention capacity
100 substrates
401 Anode layer
402 hole transport layer
403 Electron transport layer
404 Cathode layer

Claims (3)

  In a driving method of a light-emitting element including at least an anode layer and a cathode layer on a substrate and one or more organic compound layers sandwiched therebetween, a voltage for light emission as an electric field, A voltage having a reverse polarity and a voltage having a reverse polarity, applying and releasing the light emitting voltage to the light emitting element a plurality of times, and then applying the recovery voltage, and the recovery voltage. A method for driving a light-emitting element, wherein a voltage application time is longer than a single application time of the light emission voltage and shorter than a cumulative time of the plurality of application times. The driving method of a light emitting device according to claim 1, wherein the absolute value of the peak value of the voltage for the recovery, being greater than the absolute value of the average value in one of the application time of the voltage for emitting light. A light emitting device comprising a plurality of light emitting elements arranged in a one-dimensional or two-dimensional manner on a substrate, comprising at least an anode layer and a cathode layer, and one or more organic compound layers sandwiched therebetween. in the driving method, the voltage for emitting the electric field, and a voltage of the recovery voltage and polarity for emitting light to the contrary, the application of the voltage for emitting light while scanning the light emitting elements said array After the release is repeated a plurality of times, the recovery voltage is applied while scanning the arranged light emitting elements, and the application time of the recovery voltage is one application time of the light emission voltage. A driving method of a light emitting device, characterized by being longer and shorter than a cumulative time of the plurality of application times.

Images