JP2011107290A - Device and method for driving organic el panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for driving an organic EL panel, to more reliably restore the luminance of an organic EL element, with high stability over time. <P>SOLUTION: The device includes organic EL elements E11 to Emm formed by holding an organic light-emitting layer between a pair of electrodes S1 to Sm and D1 to Dn on a support substrate. A driving voltage is applied between the electrodes S1 to Sm and D1 to Dn to turn on the organic LE elements E11 to Emm. The device for driving an organic EL panel has a period for applying a voltage in a direction opposite to that of the driving voltage to between the electrodes S1 to Sm and D1 to Dn when the organic EL elements E11 to Emm are not turned on, and a period where a potential difference between the electrodes S1 to Sm and D1 to Dn is less than an absolute value of a light emission start voltage. The period for applying the voltage in a direction opposite to that of the driving voltage between both the electrodes S1 to Sm and D1 to Dn is at least 30% or more of the period where the potential difference between the electrodes S1 to Sm and D1 to Dn is less than the absolute value of the light emission start voltage. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a driving apparatus and a driving method for an organic EL panel including an organic EL element in which an organic light emitting layer is sandwiched between a pair of electrodes on a support substrate.

  Conventionally, as an organic EL panel, for example, an organic layer having at least an organic light emitting layer includes an anode (first electrode) made of ITO (Indium Tin Oxide) or the like, and a cathode (second electrode) made of aluminum (Al) or the like. A light-emitting display unit is known in which an organic EL element sandwiched between two layers is formed as a light-emitting pixel in a matrix on a light-transmitting support substrate (see, for example, Patent Document 1). Such an organic EL element emits light by injecting holes from the anode and injecting electrons from the cathode, and the holes and electrons recombine in the organic light emitting layer. The organic EL element has a so-called diode characteristic in which current does not easily flow from the cathode side to the anode side.

  The organic EL panel as described above is, for example, a passive matrix organic EL panel that controls light emission of the organic EL element by passive driving (line-sequential driving) in which an anode is a data line and a cathode is a common line.

JP-A-8-315981 JP 2001-093663 A

  Here, it is known that the organic EL element is a passive matrix type organic EL panel, and when the light is continuously emitted at a constant current, the light emission luminance is attenuated with time. If there is a difference between the two, there is a problem that image sticking and luminance unevenness occur and display quality deteriorates. On the other hand, as disclosed in Patent Document 2, a method of applying a voltage that recovers luminance at a timing after the organic EL element is turned on is known.

  However, the method disclosed in Patent Document 2 is necessary to be able to recover the luminance, although the timing of applying a voltage that recovers the luminance and resetting the charge stored in the organic EL element is specified. The voltage application conditions are not clear, and there is a problem that the effect of recovering luminance cannot be obtained with certainty.

  SUMMARY OF THE INVENTION In view of the above-described problems, the present invention has an object to provide a driving device and a driving method for an organic EL panel that can more reliably recover the luminance of an organic EL element and that is highly stable over time. To do.

  In order to solve the above-described problems, the present invention includes an organic EL element in which an organic light emitting layer is sandwiched between a pair of electrodes on a support substrate, and a driving voltage is applied between the electrodes to apply the organic EL element. A period in which a voltage opposite to the driving voltage is applied between the electrodes when the organic EL element is not lit, and a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage. An organic EL panel driving device provided, wherein a potential difference between the electrodes is less than an absolute value of the light emission start voltage during a period in which a voltage opposite to the driving voltage is applied between the electrodes. It is characterized by being at least 30% or more with respect to the period.

  Further, a period during which a voltage opposite to the driving voltage is applied between the electrodes is set to at least 100% or more with respect to a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage. Features.

  Further, the electrodes are set to the same potential during a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage.

  In addition, a plurality of the organic EL elements are provided, and each of the organic EL elements is lit by passive driving.

  In order to solve the above-described problems, the present invention includes an organic EL element in which an organic light emitting layer is sandwiched between a pair of electrodes on a support substrate, and a driving voltage is applied between the electrodes to apply the organic EL element. A period in which the element is turned on and a voltage in the direction opposite to the drive voltage is applied between the electrodes when the organic EL element is not lit, and a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage; A method of driving an organic EL panel in which a voltage difference between the electrodes in a direction opposite to the drive voltage is applied between the electrodes, and a potential difference between the electrodes is less than an absolute value of the light emission start voltage. It is characterized by being at least 30% or more with respect to the period.

  In addition, a period in which a voltage in the direction opposite to the driving voltage is applied between the electrodes is set to at least 100% or more with respect to a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage. It is characterized by.

  Further, the electrodes are set to the same potential during a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage.

  In addition, a plurality of the organic EL elements are provided, and each of the organic EL elements is lit by passive driving.

  The present invention provides at least a period in which a voltage in the direction opposite to the drive voltage that affects the luminance life of the organic EL element is applied to a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage. A driving device and a driving method for an organic EL panel with high display quality with little deterioration in luminance over time even when high reliability is required so that luminance recovery can be obtained more reliably by specifying 30% or more Can be realized.

  Further, the period during which the voltage in the direction opposite to the driving voltage is applied is at least 100% or more with respect to the period in which the potential difference between the two electrodes is less than the absolute value of the light emission start voltage. Brightness recovery can be obtained.

  According to the present invention, the luminance of the organic EL element can be recovered more reliably, and the stability can be improved over time.

The figure which shows the drive device of the organic electroluminescent panel which is embodiment of this invention. The figure which shows an example of the drive waveform in the drive device of an organic EL panel same as the above. The figure which shows the time-dependent characteristic at the time of leaving an organic electroluminescent panel. The figure which shows the time-dependent characteristic at the time of reverse bias voltage application of an organic electroluminescent panel. The figure which shows the time-dependent characteristic at the time of the leaving of an organic electroluminescent panel, and the repetition of reverse bias voltage application. The figure which shows the relationship between the ratio of the reverse bias voltage application period with respect to the same electric potential period, and a luminance lifetime. The figure which shows the measurement result of the brightness | luminance lifetime of the Example of this invention.

  Hereinafter, an organic EL panel driving apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, the drive device for the organic EL panel 1 includes an organic EL panel 1, a cathode drive circuit 2, an anode drive circuit 3, and a display controller 4.

  The organic EL panel 1 includes pixels E11 to Emn, which are organic EL elements each having an organic light emitting layer sandwiched between an anode and a cathode on a support substrate, arranged in a matrix. The pixels E11 to Emn are provided at intersections between a plurality of scanning lines S1 to Sm that are provided in the horizontal direction and serve as cathodes, and drive lines D1 to Dn that are provided as a plurality and are orthogonal to the scanning lines S1 to Sm. ing. The pixels E11 to Emn are represented by an equivalent circuit composed of a diode component and a parasitic capacitance component arranged in parallel, but in order to prevent the drawing from becoming complicated, the pixels E11 to Emn are illustrated with only a diode in FIG. ing.

  The cathode drive circuit 2 includes a plurality of scan switches 21 to 2m corresponding to the scan lines S1 to Sm. The scanning switches 21 to 2 m selectively connect the scanning lines S <b> 1 to Sm to the common potential Vc or the ground potential (0 V) based on a control signal from the display controller 4. The scanning lines S1 to Sm are sequentially selected in one frame period, the scanning lines S1 to Sm that are selected have a ground potential, and the scanning lines S1 to Sm that are not selected have a common potential Vc. The common potential Vc is set such that a potential difference from a driving voltage applied from a constant current source A, which will be described later, is less than the absolute value of the light emission start voltage of the pixels E11 to Enm. And the same potential.

  The anode drive circuit 3 allows a constant current source A that individually supplies a drive current corresponding to each drive line D1 to Dn, and a drive current from the constant current source A can be connected to each drive line D1 to Dn. It comprises drive switches 31 to 3n. Switching of each of the drive switches 31 to 3n is determined based on a control signal from the display controller 4.

  The display controller 4 sequentially turns on the scanning switches 21 to 2m to sequentially scan the scanning lines S1 to Sm and performs passive driving to turn on / off each of the drive switches 31 to 3n. Display characters, figures, etc. on panel 1.

  Next, a method for driving the organic EL panel 1 will be described by taking as an example a case where the pixel E11 connected to the scanning line S1 and the drive line D1 is turned on in one frame period. FIG. 2 shows drive waveforms of the scan lines S1 to Sm and the drive line D1.

  In one frame period, the scanning lines S1 to Sm are sequentially selected from the scanning line S1, and become the ground potential when selected, and become the common potential Vc when not selected. The drive line D1 is connected to the constant current source A when the scanning lines S1 to Sm are selected, and is connected to the ground potential for a predetermined period while the selection of the scanning lines S1 to Sm is switched. At this time, during a period t1 in which the scanning line S1 is selected and the drive line D1 is connected to the constant current source A, a forward drive voltage is applied between the electrode lines S1 and D1, and the pixel E11 is lit. In the period t2 in which the scanning line S1 is not selected and the drive line D1 is at the ground potential, a voltage Vc (hereinafter referred to as a reverse bias voltage) Vc opposite to the drive voltage is applied between the electrode lines S1 and D1. Is applied, and the pixel E11 is not lit. In the period t3 when the scanning line S1 is not selected and the drive line D1 is connected to the constant current source A, the pixel E11 is not lit, and the potential difference between the electrode lines S1 and D1 is the absolute value of the light emission start voltage. It becomes less than the value, and the pixel E11 is not lit. Similarly, when the other pixels E12 to Enm are lit, the periods t1 to t3 are provided.

  The feature of this embodiment is that the ratio between the period t2 and the period t3 is adjusted as appropriate, and the period t2 in which the reverse bias voltage Vc is applied between the electrode lines S1 to Sm and D1 to Dn in one frame period. In addition, the potential difference between the electrode lines S1 to Sm and D1 to Dn is at least 30% (t2 / t3 ≧ 0.3) with respect to the period t3 in which the light emission start voltage is less than the absolute value.

  Here, in general, in the manufacturing process of the organic EL panel, a reverse bias energization process is performed in which a reverse bias voltage is applied between both electrodes, and then the organic EL panel is in a state where the potential difference between the electrodes is less than the absolute value of the light emission start voltage. It is known that the luminance of the organic EL element when left for a predetermined time is attenuated at the beginning of light emission and then stabilized as shown in FIG. Such characteristics are particularly prominent when left in a high temperature environment of about 60 ° C. or higher, and FIG. 3 shows a case where it is left in a temperature environment of 85 ° C. On the other hand, the luminance of the organic EL element when the reverse bias energization process is not performed in the manufacturing process and the reverse bias voltage is applied for a predetermined time after the manufacturing can be greatly increased in the initial stage of light emission and then stabilized as shown in FIG. Are known. This is because when the potential difference between the two electrodes of the organic EL element is less than the absolute value of the light emission starting voltage when left standing, the organic molecules are relatively easily thermally stabilized, but a reverse bias voltage is applied from the stable state. It is presumed that the organic molecules sometimes change to a thermally activated state due to the potential difference between the electrodes.

  The inventor of the present application has confirmed that such a characteristic is observed even when the neglected state and reverse bias voltage application are alternately repeated, and it has been confirmed by an experiment that the behavior is almost reversible (see FIG. 5). The standing was performed under a temperature environment of 85 ° C. In FIG. 5, the luminance of the organic EL element attenuates when left unattended and increases when a reverse bias voltage is applied. As a result, it has been confirmed that the luminance life of an organic EL panel that emits light with a certain luminance changes not only with the light emission time but also with the standing time and the reverse bias voltage application time in each frame period of light emission driving as described above. It was done.

  Next, in order to investigate in detail how much the standing time and the reverse bias voltage application time have an influence on the light emission lifetime, the inventor of the present application has a potential difference between the electrode lines S1 to Sm and D1 to Dn in this embodiment. The ratio of the period t3 during which the reverse bias voltage Vc is applied between the electrode lines S1 to Sm and D1 to Dn is changed to 85 ° C. The life characteristics when driven in a temperature environment were investigated. FIG. 6 shows the relationship between the ratio of the period t2 to the period t3 and the luminance life (initial luminance ratio arrival time of 80%) when all the pixels E11 to Enm are turned on. In the period t3, both electrode lines S1 to Sm and D1 to Dn are set to the same potential. According to FIG. 6, it can be seen that the luminance life is greatly improved when the ratio of the period t2 to the period t3 is around 30 to 60%. The reason for exhibiting such characteristics is considered as follows. As described above, the pixels E11 to Enm, which are organic EL elements, exhibit luminance degradation when left standing, while the luminance recovers when the reverse bias voltage Vc is applied. Accordingly, when the ratio of the period t2 that is the reverse bias voltage application time to the period t3 that is the neglected time is small, the speed of luminance deterioration due to neglecting exceeds the speed of the luminance recovery by applying the reverse bias voltage Vc. The luminance life of the is shortened. In FIG. 6, this corresponds to the region where the ratio of the period t2 to the period t3 is less than 30%. On the other hand, when the ratio of the period t2 to the period t3 is further increased, the speed of luminance recovery by application of the reverse bias voltage Vc is higher than the speed of luminance deterioration due to being left. Therefore, as the ratio of the period t2 to the period t3 increases, the luminance life of the organic EL panel 1 gradually increases. In FIG. 6, this corresponds to a region where the ratio of the period t2 to the period t3 is about 30 to 60%. Further, when the ratio of the period t2 to the period t3 is further increased, the speed of luminance recovery by application of the reverse bias voltage Vc is further increased than the speed of luminance deterioration due to being left. However, as shown in FIG. 4, the luminance of the pixels E11 to Emn becomes constant after recovering to some extent, and thereafter the luminance life is further improved even if the ratio of the period t2 to the period t3 is increased. It becomes. In FIG. 6, this corresponds to the region where the ratio of the period t2 to the period t3 is 60% or more.

  As apparent from FIG. 6, in the driving apparatus and driving method for the organic EL panel 1 as in the present embodiment, the period t2 during which the reverse bias voltage Vc is applied between the electrode lines S1 to Sm and D1 to Dn is set. In addition, the potential difference between the electrode lines S1 to Sm and D1 to Dn is at least 30% or more with respect to the period t3 in which the light emission start voltage is less than the absolute value, thereby recovering the luminance of the pixels E11 to Enm and high reliability. Even when the property is required, the luminance life of the organic EL panel 1 can be improved and the stability over time can be enhanced. Further, in order to more reliably recover the luminance, the ratio of the period t2 to the period t3 is set to 60% or more, and in order to more efficiently recover the luminance, the ratio of the period t2 to the period t3 is set to 100% or more. Is desirable.

  FIG. 7 shows the measurement results of the luminance life of Examples 1 and 2 in which the driving method of the present invention was performed in a temperature environment of 85 ° C. In Example 1, the reverse bias voltage Vc is applied between the electrode lines S1 to Sm and D1 to Dn for the period t3 in which the potential difference between the electrode lines S1 to Sm and D1 to Dn is less than the absolute value of the light emission start voltage. The ratio of the applied period t2 was about 30%. In Example 1, the luminance life was about 2000 hours. In Example 2, the reverse bias voltage Vc is applied between the electrode lines S1 to Sm and D1 to Dn for the period t3 in which the potential difference between the electrode lines S1 to Sm and D1 to Dn is less than the absolute value of the light emission start voltage. The ratio of the applied period t2 was about 60%. In Example 2, the luminance life was about 2500 hours or more. In Examples 1 and 2 in which the driving method of the present invention was implemented, the luminance life was about 2000 hours or more, and the life was clearly improved. It is clear from FIG. 7 that the stability over time can be improved by implementing the present invention.

  The present invention relates to an organic EL panel driving apparatus and driving method, and is particularly suitable for a passive driving organic EL panel driving apparatus and driving method.

1 Organic EL Panel 2 Cathode Drive Circuit 3 Anode Drive Circuit 4 Display Controller

Claims (8)

An organic EL element having an organic light emitting layer sandwiched between a pair of electrodes on a support substrate, a driving voltage is applied between the electrodes to light the organic EL element, and the organic EL element is not lit An organic EL panel drive device comprising a period in which a voltage opposite to the drive voltage is applied between the electrodes and a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage. And
A period in which a voltage opposite to the driving voltage is applied between the electrodes is set to at least 30% or more of a period in which a potential difference between the electrodes is less than an absolute value of the light emission start voltage. An organic EL panel drive device. A period in which a voltage in the direction opposite to the driving voltage is applied between the electrodes is set to at least 100% or more with respect to a period in which a potential difference between the electrodes is less than an absolute value of the light emission start voltage. The driving device for an organic EL panel according to claim 1. 2. The organic EL panel drive device according to claim 1, wherein the potential between the electrodes is set to the same potential during a period in which a potential difference between the electrodes is less than an absolute value of the light emission start voltage. The organic EL panel driving device according to claim 1, comprising a plurality of the organic EL elements, wherein each of the organic EL elements is lit by passive driving. An organic EL element having an organic light emitting layer sandwiched between a pair of electrodes on a support substrate, a driving voltage is applied between the electrodes to light the organic EL element, and the organic EL element is not lit A method for driving an organic EL panel, which sometimes includes a period in which a voltage opposite to the driving voltage is applied between the electrodes and a period in which the potential difference between the electrodes is less than the absolute value of the light emission start voltage,
A period during which a voltage in the direction opposite to the drive voltage is applied between the electrodes is set to at least 30% or more with respect to a period in which a potential difference between the electrodes is less than an absolute value of the light emission start voltage. A method for driving an organic EL panel, which is characterized. A period in which a voltage in the direction opposite to the driving voltage is applied between the electrodes is set to at least 100% or more with respect to a period in which a potential difference between the electrodes is less than an absolute value of the light emission start voltage. The driving method of the organic EL panel according to claim 5. 6. The method of driving an organic EL panel according to claim 5, wherein the potential between the electrodes is set to the same potential during a period in which a potential difference between the electrodes is less than an absolute value of the light emission start voltage. The organic EL panel driving method according to claim 5, comprising a plurality of the organic EL elements, and lighting each of the organic EL elements by passive driving.

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