JP2012247774A - Light-emitting device, display device and drive method of organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting device, a display device and a drive method of an organic electroluminescence element capable of preventing a failure due to a leak current and preventing the operating life of the device from being reduced due to such failure.SOLUTION: The light-emitting device comprises: an organic electroluminescence element that includes a first electrode, a luminous layer disposed over the first electrode and a second electrode disposed on the luminous layer; a drive circuit that drives the organic electroluminescence element by supplying a drive current across the first electrode and the second electrode; and drive stop means that stops driving the organic electroluminescence element when the value of the drive current is lower than a predetermined value.

Description

  Embodiments described herein relate generally to a light emitting device, a display device, and a method for driving an organic electroluminescent element.

  In recent years, organic electroluminescent elements (hereinafter also referred to as organic EL elements and OLEDs) have attracted attention for light emitting devices including illumination devices and flat light sources, and display devices. An organic electroluminescent element has a configuration in which a light emitting layer made of an organic material is sandwiched between a pair of electrodes of a cathode and an anode. When a voltage is applied to the device, electrons are injected from the cathode and holes are injected from the anode into the light-emitting layer, and electrons and holes are recombined in the light-emitting layer to generate excitons. Luminescence is obtained.

JP 2010-272271 A

  Foreign matter such as dust may adhere to the element panel during the manufacturing process of the organic electroluminescent element. In this case, there is a concern that the foreign matter adhering to the element panel may cause a leak current, resulting in the occurrence of a defect and eventually the element destruction. Therefore, it is desired to provide a light emitting device, a display device, and a method for driving an organic electroluminescent element that suppress the occurrence of a failure due to a leakage current and does not impair the device life due to such a failure.

  In order to achieve the above object, according to the embodiment, a first electrode, a light emitting layer disposed on the first electrode, and a second electrode disposed on the light emitting layer are provided. An organic electroluminescent element; a driving circuit for driving the organic electroluminescent element by supplying a driving current between the first electrode and the second electrode; and a value of the driving current is lower than a predetermined value. And a driving stop means for stopping the driving of the organic electroluminescent element.

FIG. 1 is a circuit diagram of the light emitting device according to the first embodiment. FIG. 2 is an external view showing the OLED panel according to Example 1-1. FIG. 3 is a cross-sectional view of the OLED panel according to Example 1-1. FIG. 4 is a cross-sectional view in the A-A ′ direction of the OLED panel according to Example 1-1. FIG. 5 is an external view showing the OLED panel according to Example 1-2. FIG. 6 is a cross-sectional view of the OLED panel 40 according to Example 1-2 in the B-B ′ direction. FIG. 7 is a diagram for explaining an assumed model of OLED degradation due to low current driving. FIG. 8 is a diagram for explaining element destruction. FIG. 9 is a graph showing current-voltage characteristics and current-luminance characteristics of normal and defective elements. FIG. 10 is a diagram illustrating an observation result of a leak occurrence portion using an optical microscope. FIG. 11 is an external view of the light emitting device according to the first embodiment. FIG. 12 is a diagram illustrating a display device according to the second embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit diagram of the light emitting device according to the first embodiment.
The light emitting device 1 includes an organic light-emitting diode (OLED) 10, a drive circuit that drives the OLED 10, and a circuit power supply (Vcc) that drives the drive circuit. As the circuit power supply (Vcc), for example, a battery such as a dry battery is assumed.

  The drive circuit shown in FIG. 1 constitutes a constant current circuit. In particular, in the present embodiment, the drive circuit that drives the OLED 10 is configured to monitor a current (drive current) that drives the OLED 10 and forcibly stop driving when the value of the drive current falls below a predetermined value. .

  Specifically, the emitter terminal of the transistor Q1 is connected to the positive terminal of the circuit power supply (Vcc). The collector terminal of the transistor Q1 is connected to the anode (anode) of the OLED 10. The cathode (cathode) of the OLED 10 is connected to the collector terminal of the transistor Q2. The emitter terminal of transistor Q2 is connected to resistor R1. The other end of the resistor R1 is connected to the negative terminal of the circuit power supply (Vcc). The output terminal of the operational amplifier (differential amplifier) AMP1 is connected to the base terminal of the transistor Q2. The non-inverting input terminal of the operational amplifier AMP1 is connected to the resistors R2 and R3. The inverting input terminal of the operational amplifier AMP1 is connected to the non-inverting input terminal of the operational amplifier AMP2. Resistors R4 and R5 are connected to the inverting input terminal of the operational amplifier AMP2. The output terminal of the operational amplifier AMP2 is connected to the base terminal of the transistor Q3. The emitter terminal of the transistor Q3 is connected to the base terminal of the transistor Q1 through a resistor. In the driving circuit shown in FIG. 1, the means for stopping the driving of the OLED 10 includes at least a transistor Q1, a transistor Q3, and an operational amplifier AMP2.

  During normal lighting, the operational amplifier AMP1 operates so that the reference voltage Vref2 input to the non-inverting input terminal of the operational amplifier AMP2 is equal to the voltage of the resistor R1 that detects the current flowing through the OLED 10, and the output current of the transistor Q2 is constant. Controlled. This is a normal operation as a constant current circuit, and a drive current is supplied between the terminals of the OLED 10.

The circuit power supply is assumed to be a battery such as a dry battery, for example, and the power supply voltage Vcc gradually decreases due to the discharge. With the drop in the power supply voltage Vcc, the collector of the transistor Q2 - emitter voltage _{V CE} is gradually lowered. Eventually, transistor Q2 enters the saturation region and is completely turned on. From this point, the drive circuit loses its current control function for voltage fluctuations and the like.

  When the power supply voltage Vcc further decreases, the current flowing through the OLED 10 also begins to decrease, and the voltage of the resistor R1 for detecting the output current decreases. The operational amplifier AMP2 monitors the current by monitoring the voltage of the resistor R1. That is, the voltage at the non-inverting input terminal of the operational amplifier AMP2 is equal to the voltage of the resistor R1, and the voltage at the inverting input terminal of the operational amplifier AMP2 is equal to the set reference voltage Vref1. The set reference voltage Vref1 is set in advance according to a predetermined lower limit current. This lower limit current corresponds to the lower limit value of the current that may flow through the OLED 10, that is, the lower limit value of the drive current. Setting the lower limit value of the drive current will be described in detail later.

  The operational amplifier AMP2 outputs a High or Low signal (ON / OFF signal) according to the potential difference between the non-inverting input terminal and the inverting input terminal. When the voltage of the resistor R1 falls below the set reference voltage Vref1, the operational amplifier AMP2 outputs a Low signal. As a result, the transistor Q3 is turned off, and further the transistor Q1 is turned off. Therefore, the entire drive circuit is turned off and the driving of the OLED 10 is stopped.

  The configuration shown in FIG. 1 is merely an example, and various modifications can be made within a range obvious to those skilled in the art. For example, in the above configuration, a function for forcibly stopping driving when the value of the driving current falls below a predetermined value is provided inside the driving circuit, but the function may be provided outside the driving circuit. Although the constant current circuit is used as the basic configuration of the drive circuit, the OLED 10 may be driven at a constant voltage. In other words, a constant voltage circuit may be used as a drive circuit for driving the OLED 10, and a function of forcibly stopping the circuit when the current flowing through the OLED 10 is monitored and becomes a predetermined current or less may be provided. Moreover, it is good also as a structure which can drive the light-emitting device 1 by switching from batteries, such as a dry cell, to alternating current power supply.

  An embodiment of the OLED 10 will be described. In the following Example 1-1, the OLED 10 is an OLED panel using a single organic electroluminescent element. In Example 1-2, the OLED 10 is an OLED panel in which a plurality of organic electroluminescent elements are connected in series. It is what.

<Example 1-1>
FIG. 2 is an external view showing the OLED panel according to Example 1-1. A first electrode pad portion 28 and a second electrode pad portion 29 for driving the OLED 10 are provided at the end of the light emitting area 2. The first electrode and the second electrode are a pair of electrodes, one being an anode (anode) and the other being a cathode (cathode). Here, the first electrode is an anode and the second electrode is a cathode. However, these may be reversed. Since the element substrate 20 is for supporting other members including the sealing substrate 26, it is preferable that the element substrate 20 has sufficient strength to hold a layer formed thereon. There is no restriction | limiting in particular about the shape of the element substrate 20, a structure, a magnitude | size, etc., It can select suitably according to a use, an objective, etc. The thickness of the substrate 20 is not particularly limited as long as it has sufficient strength to support other members.

  FIG. 3 is a cross-sectional view of the OLED panel according to Example 1-1.

  In this example, an alkali-free glass substrate was used as the element substrate 20. Specific examples of the material of the element substrate 20 include transparent or translucent quartz glass, transparent glass such as alkali glass and non-alkali glass, polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polypropylene, polyethylene, and amorphous polyolefin. And a polymer film made of a transparent resin such as a fluororesin, and transparent ceramics. A high refractive index glass substrate or plastic substrate having a refractive index of about 1.6 to 1.9 may be used.

  An indium tin oxide (ITO) layer 21 (first electrode) having a thickness of 110 nm is formed on the element substrate 20, and further, molybdenum (Mo) having a thickness of 50 nm, aluminum (Al) having a thickness of 600 nm, and A 50 nm-thick Mo film was laminated (Mo / Al / Mo layer 28). Here, the film thickness of the ITO layer 21 is determined by its resistance value, flatness, light extraction design, and the like, and varies depending on the element design. Similarly, the film thickness of each layer of the Mo / Al / Mo layer 28 varies depending on the element design. Although Mo / Al / Mo is used as the layer 28 here, an alloy such as Mo: Nb / Al: Nd / Mo: Nb may be used. That is, an alloy of molybdenum and niobium may be used instead of molybdenum, and an alloy of aluminum and neodymium may be used instead of aluminum. Alternatively, instead of the molybdenum, aluminum, and molybdenum layer 28, a layer of titanium, aluminum, and titanium (Ti / Al / Ti) may be used. The layer 28 is not necessarily a laminated film.

  A barrier layer such as a silicon oxynitride film (SiN) or a layer that improves light extraction efficiency by scattering, refraction, diffraction, or the like may be formed between the element substrate 20 and the ITO layer 21. Further, the stacking order of the ITO layer 21 and the Mo / Al / Mo layer 28 may be reversed.

  The Mo / Al / Mo layer 28 and the ITO layer 21 were patterned using a photolithography method. Subsequently, the insulating layer 22 was formed with a novolac positive resist. It is desirable that the insulating layer material used here has less moisture adsorption and is more resistant to pretreatment of organic EL deposition such as oxygen plasma treatment, and may be another resist, polyimide, acrylic, or the like.

  After the UV ozone cleaning, an organic layer 23 was formed, and then an Al cathode 24 (second electrode) having a thickness of 150 nm was vacuum deposited. Here, the moisture adsorbed by the insulating layer 22 may be evaporated by annealing in a vacuum or a glove box in a nitrogen atmosphere before vapor deposition. Further, oxygen plasma treatment or argon plasma treatment may be performed before vapor deposition. Note that the UV ozone cleaning treatment may be omitted when oxygen plasma treatment or argon plasma treatment is performed.

  FIG. 4 is a cross-sectional view in the A-A ′ direction of the OLED panel of FIG. 3 and shows details of the organic layer 23. The organic layer 23 has a plurality of layers such as an electron transport layer 32, an exciton block layer 33, a light emitting layer 34, a hole transport layer 35, and a hole injection layer 36, and is designed according to required specifications. The light emitting layer 34 includes a phosphorescent light emitting material or a fluorescent light emitting material. Also, the electron injection layer (LiF) is shown to be included in the Al cathode 24. The method for forming each layer is not limited to the vacuum deposition method, and an ink jet method, a slit coating method, a meniscus coating method, a gravure printing method, or the like may be used.

  After the deposition of the Al cathode 24, the Al cathode 24 was transported to a glove box in a nitrogen atmosphere so as not to be exposed to the atmosphere, and bonded to a glass 26 containing counterbore and sealed. An ultraviolet curable resin was used for the sealing material 27. The sealing method may be other methods, for example, film sealing using a SiN film or the like, frit sealing, or the like.

  In FIG. 3, 25 indicates a desiccant (getter), and 30 indicates auxiliary wiring. Reference numeral 31 denotes a light emitting area of the OLED panel according to Example 1-1.

  Although not shown, in order to increase the light extraction efficiency, a microlens sheet (φ30 μm microlens array manufactured by Optmate Co.) was attached to the surface of the element substrate 20 opposite to the surface on which the organic layer 23 was provided. The light extraction sheet may be one using scattering. Moreover, you may process a glass substrate directly instead of sticking a light extraction sheet | seat.

  A harness was soldered to the pad portions 28 and 29 of the first and second electrodes shown in FIG. 3, and the OLED panel of this example was connected to the drive circuit shown in FIG. In addition, you may connect an OLED panel and a drive circuit using a flexible printed circuit board (FPC).

<Example 1-2>
FIG. 5 is an external view showing the OLED panel according to Example 1-2. As shown in the figure, the OLED panel 40 is a single OLED panel in which a plurality of organic electroluminescent elements are connected in series. In Example 1-2, four organic electroluminescent elements 401 to 404 were connected in series. FIG. 6 is a cross-sectional view of the OLED panel 40 according to the present embodiment in the BB ′ direction. The plurality of light emitting units 41 to 44 (segments 1 to 4) correspond to the organic electroluminescent elements 401 to 404. As the OLED 10 shown in FIG. 1, the OLED 40 according to the embodiment 1-2 is applied, the current flowing through the OLED 40 is monitored in the drive circuit, and when the current falls below the lower limit current, the drive circuit is turned off and the drive of the OLED 40 is stopped. It is good also as composition to do.

  The inventors have found that leakage failure occurs when the OLED is driven at a low current. Hereinafter, the problem of leakage failure caused by driving the OLED 10 with a low current will be described.

  FIG. 7 is a diagram for explaining an assumed model of OLED degradation due to low current driving. As shown in FIG. 7A, the organic layer 23 is sandwiched between the first electrode (the pad portion) 21 and the second electrode (the pad portion) 24. As described above, the first electrode and the second electrode are a pair of electrodes, one being an anode (anode) and the other being a cathode (cathode). In general, the organic layer 23 is a thin film of about several tens to several hundreds of nm. As shown in FIG. 7B, when a foreign substance 50 such as dust or dirt adheres to the organic layer 23, the foreign substance 50 causes a leakage current as indicated by an arrow, for example. That is, since the organic layer 23 is a thin film, the first electrode 28 and the second electrode 29 are easily conducted by the foreign substance 50 and a short circuit (short) defect is likely to occur. If the area of the OLED is further expanded (large-area element is made), the probability of contamination of foreign matters increases in the manufacturing process and the like. This causes an increase in the number of “leak spots” in which a leakage current is generated by foreign matter.

  Here, in this embodiment, deterioration of the OLED due to low current driving is assumed as follows. That is, if there is a leakage current path in the same order as the current required for light emission in the low current (low voltage) region, no voltage is applied to the organic electroluminescence element, and only the leakage current flows. On the other hand, if the OLED is driven by a current (voltage) of a certain level or more, the leakage current path is burned out or voltage is applied to the entire element for some reason, the leakage phenomenon disappears and light emission starts.

  When only a leakage current flows when driving at a low current, a part such as a foreign substance that causes the heat generation generates heat, which may destroy the element.

  FIG. 8 is a diagram for explaining element destruction. This figure shows the change over time of the resistance value of the whole panel by a graph. The resistance of the entire panel is composed of normal resistance and / or defective part resistance. It is assumed that a defect occurs at the time (1) shown in FIG. Until now, the panel has emitted light almost uniformly over the entire surface. When a defect occurs, a bright spot with relatively high luminance is observed at that location. Thereafter, the normal resistance until the time point (1) starts to change to a resistance that causes a short circuit due to positive feedback of the current rise to the temperature rise. Then, the defective part is short-circuited in a short time from the time point (2) to (3), the element is destroyed, the resistance value is greatly reduced, and the panel does not emit light.

  In this embodiment, as described above, a deterioration model of OLED at the time of low current driving is assumed. According to the specific test results (to be described later) by the inventors of the present application, it was found that a leak phenomenon is likely to occur when an organic electroluminescent element is driven at a low current of 30 mA or less. Assuming that the leakage factor is due to foreign matter or the like attached to the organic layer as described above, such a phenomenon can be avoided if such foreign matter or the like can be completely removed in the manufacturing process of the OLED panel. It may be. However, for example, when a large OLED panel is manufactured by a low-cost facility such as a clean room whose air cleanliness is not so high, it may be difficult to completely remove foreign matters.

  As a countermeasure for preventing such element destruction, the OLED is driven by a current (voltage) of a certain level or more. In the configuration shown in FIG. 1, the driving current of the OLED 10 is monitored in the driving circuit, and when the lower limit current, that is, 30 mA is exceeded, the driving of the OLED 10 is stopped. Thereby, element destruction can be prevented beforehand. As described above, when a dry battery is assumed as a power source as shown in FIG. 1, the drive circuit constituting the constant current circuit is driven by the dry battery, and the OLED 10 is driven by the drive circuit. When the output voltage Vcc of the dry battery decreases, the drive circuit cannot maintain a constant current, and the drive current gradually decreases. If the use of the light emitting device 10 is continued without replacing the dry battery as it is, the OLED 10 will be driven at a current lower than 30 mA, and a leak failure may occur. However, in this embodiment, when the driving current falls below the lower limit current, that is, 30 mA, the driving of the OLED 10 is forcibly stopped. Note that the lower limit current does not need to exactly match 30 mA, and may be determined empirically with a predetermined range. That is, the lower limit current may be appropriately set to a value greater than 0 mA and not greater than 30 mA.

Here, the significance of driving the OLED at a certain voltage (current) or higher will be described based on the measurement results of the element characteristics.
FIG. 9 shows current-voltage characteristics and current-luminance characteristics of normal and defective elements. In the graph of FIG. 9, the curve D is for a defective element and the curve N is for a normal element. As shown in FIG. 9A, when the voltage is swept from −5 V to +10 V, a large leak current of about several hundred mA / cm ² flows in the defective element. However, as indicated by reference symbol C1, the leakage current decreases around + 8V, and changes so as to show substantially the same current and luminance (see FIG. 9C) as the normal element.

  On the other hand, when the voltage is swept from + 10V to −5V as shown in FIG. 9B, the current and brightness that are almost the same as those of the normal element are several hundreds around + 4V as indicated by reference numeral C2. It returns to the defective element characteristic in which a large leak current of about mA / cm 2 flows. As can be seen from FIG. 9 (d), the luminance starts to decrease significantly at this point. Such a behavior is a phenomenon often found when an organic EL element is manufactured in a clean room with a low cleanness. In the case of a general electronic device, defects such as leakage are more likely to occur when the voltage is high. However, in organic EL devices manufactured in a clean room with a low degree of cleanliness, low voltage causes leakage defects, and even if the same device has a high voltage, it exhibits the same characteristics as normal devices. It is a characteristic characteristic. The current-voltage characteristics of the organic EL element are non-linear, and the resistance is very high at a low voltage that does not emit light. Here, when there is a leak location due to foreign matter or dust, the current concentrates at the leak location because the resistance other than the leak location is high. On the other hand, the resistance of the organic EL element decreases with light emission, and becomes very small during high luminance light emission. At this time, it is considered that the resistance other than the leaked portion is lower than that of the leaked portion, current flows through the entire element, and the same characteristics as the normal element are exhibited.

  If driving is continued at a low voltage that does not emit light but emits light with low brightness, current will continue to flow through the leak location. If it does so, the temperature of a leak location will rise with Joule heat, the surrounding organic layer etc. will degenerate and will change to an irreversible leak location. An organic EL element is an element having a large area, and is a large area element of about several centimeters to several tens of centimeters, particularly for lighting applications. If even such a large-area element has such a leak portion, it becomes a defective product and the yield is remarkably reduced. Further, when taking measures such as increasing the cleanliness of the clean room in order to reduce the cause of foreign matter and dust, the manufacturing cost becomes high.

  On the other hand, according to the present embodiment, the device can be used in a normally operating region while avoiding driving the device with a low voltage that does not emit light as described above and that emits light with low luminance. Therefore, an element having some foreign matter or dust can be used as a non-defective product, leakage defects can be reduced while keeping the manufacturing cost low, and the yield can be greatly improved.

  In this embodiment, in addition to setting a lower limit to the drive current of the OLED and forcibly stopping the drive, attention is also paid to the speed of rise (and / or fall) of the drive current. That is, it is preferable that the time required for the drive current for driving the OLED by the drive circuit to rise to a constant current value (30 mA or more in the present embodiment) is within 2 milliseconds at the latest. Similarly, it is preferable that the time required for the driving current to fall from a constant current value (30 mA or more in the present embodiment) to zero by turning off the light is within 2 milliseconds at the latest. With such a configuration, it is possible to suppress the occurrence of leakage due to the OLED being driven with a low current and prevent element destruction. The rise / fall time need not be strictly 2 milliseconds, and may have a certain width. Although it depends on the cost of the parts to be selected, it is preferable to configure the drive circuit so as to operate at high speed so as to operate in about 2 milliseconds. In the configuration of the present embodiment shown in FIG. 1, the transistors Q1-Q3 and the operational amplifiers AMP1-2 are configured to rise / fall within 2 milliseconds. By setting the rise time or the fall time within 2 milliseconds, it is possible to suppress the occurrence of defects due to leakage current.

  In addition, in the conventional lighting device, it is general that the device rises / falls over a relatively long time. That is, it is preferable that the illumination is gradually turned on over a certain period of time or turned off slowly. Further, in consideration of the product cost, in the lighting device, as low-cost components as possible are selected for the drive circuit and the like. In this case, the rise time (fall time) of the constant current circuit is generally longer.

Hereinafter, the result of having performed the lighting drive test using the 150-mm-diameter transflective panel by the serial connection element shown in Example 1-2 is shown. The test time was set to 10 minutes, and ON (1 second) -OFF (1 second) lighting drive was performed. The brightness was measured at a viewing angle of BM-7 of 2.0. The following table shows luminance [cd / m ² ], actual luminance [cd / m], and pass / fail when the drive current [mA] is changed. The rise time of the drive current was 2 milliseconds. Leakage current was generated when the driving current was 5.8 mA or 22.6 mA (a circle mark is shown, a no mark is x).

  In FIG. 10, the result of having observed the leak occurrence location with the optical microscope is shown. As shown in FIGS. 4A and 4B, the destruction of the organic film was observed. This is considered to be because the element portion was heated by current concentration due to the generation of leakage current.

  FIG. 11 shows an external view of the light emitting device according to the first embodiment. 11A is a front view of the light emitting device, FIG. 11B is a back view, and FIG. 11C is a side view. In the figure, 101 is a light emitting area, 102 is a power switch, 103 is a stand, 104 is a screw hole, and 105 is a battery housing part. The stand 103 can be inserted into the screw hole 104 to support the housing.

(Second Embodiment)
As an example of the use of the organic electroluminescent element, there is a display device in addition to the above-described light emitting device. FIG. 12 is a circuit diagram showing a display device according to the second embodiment.
The display device 80 shown in FIG. 12 has a configuration in which pixels 81 are arranged in a circuit in which horizontal control lines (CL) and vertical signal lines (DL) are arranged in a matrix. The pixel 81 includes an organic electroluminescent element 85 and a thin film transistor (TFT) 86 connected to the organic electroluminescent element 85. One terminal of the TFT 86 is connected to the control line, and the other terminal is connected to the signal line. The signal line is connected to the signal line driving circuit 82. The control line is connected to the control line drive circuit 83. The signal line drive circuit 82 and the control line drive circuit 83 are controlled by the controller 84.

  When the drive current for driving the organic electroluminescent element 85 is monitored by the signal line drive circuit 82, the control line drive circuit 83 and / or the controller 84, and when the current falls below a certain current (for example, 30 mA as in the first embodiment). The driving of the organic electroluminescent element 85 is stopped.

  It is possible to prevent the occurrence of a leak failure due to the display device 80 being driven at a low current as the voltage of the battery driving the display device decreases. As in the first embodiment, in this embodiment, it is preferable that the rising / falling time of the drive current is within 2 milliseconds.

  According to the embodiments or examples described above, a light emitting device, a display device, and a method for driving an organic electroluminescent element that can suppress the occurrence of a defect due to a leakage current and do not impair the life of the device. Can be provided.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Light-emitting device, Q1-Q3 ... Transistor, AMP1, AMP2 ... Operational amplifier, R1-R5 ... Resistor, 10 ... Organic light emitting diode (OLED).

Claims (6)

An organic electroluminescent device comprising: a first electrode; a light emitting layer disposed on the first electrode; and a second electrode disposed on the light emitting layer;
A driving circuit for driving the organic electroluminescent element by supplying a driving current between the first electrode and the second electrode;
When the drive current rises, the time required to pass through the low voltage region including the extent that the organic electroluminescence element in the state where the drive current is low does not emit light to emit light with low luminance, and the drive current The light-emitting device is characterized in that the drive circuit controls the drive current so that at least one of the time required to pass through the low-voltage region becomes high speed when falling. The organic electroluminescent element has a spot where a leak current can occur,
When the drive current rises, the time required to pass through the low voltage region including the extent that the organic electroluminescence element in the state where the drive current is low does not emit light to emit light with low luminance, and the drive current 2. The light emitting device according to claim 1, wherein at least one of the time required to pass through the low voltage region is short enough not to generate a leakage current in the spot when the light falls.   When the drive current rises, the time required to pass through the low voltage region including the extent that the organic electroluminescence element in the state where the drive current is low does not emit light to emit light with low luminance, and the drive current 3. The light emitting device according to claim 2, wherein at least one of the time required to pass through the low voltage region is 2 milliseconds or less.   A display device using the light emitting device according to claim 1. A method for driving an organic electroluminescent device comprising: a first electrode; a light emitting layer disposed on the first electrode; and a second electrode disposed on the light emitting layer.
When the drive current rises, the organic electroluminescence device in a state where the drive current is low does not emit light, and the time required to pass through a low voltage region including a degree of light emission with low luminance is accelerated. A method for driving an organic electroluminescence device, comprising: supplying a driving current. A method for driving an organic electroluminescent device comprising: a first electrode; a light emitting layer disposed on the first electrode; and a second electrode disposed on the light emitting layer.
Raising the drive current to cause the organic electric field element to emit light;
Supplying the drive current so that the time required to pass through the low voltage region is faster when the drive current falls;
A method for driving an organic electroluminescent element, comprising:

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