JPH04137392A - Driving method for organic electro-luminescence element and emission device making use of said driving method - Google Patents

Abstract

PURPOSE:To enable the same light emission in an AC driving system as in a DC driving system, while thermal deterioration is restrained, by specifying driving wave form in an AC driving system. CONSTITUTION:In order that time average brightness per second is equal to or more than standard brightness in the case of DC driving, light is emitted on condition that an equation of integral Ldt/integral dt >=L0 has to be satisfied, the interval of emission has to be less than the order of 30ms in order that the light can apparently be recognized as continuous emission, and driving wave form has to be used, which causes time for no emission to be equal to or more than temperature relaxing time within elements, and furthermore to be equal to or more than time for just before emission wherein L0 represents standard brightness in the case of DC driving, and L represents brightness in the case of repeating fluashing. This thereby prevents brightness from being lowered due to thermal generation within the elements, and the life of each element can thereby lengthened.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for driving an organic electroluminescent element and a light emitting device using the driving method, and particularly to a method for suppressing a decrease in brightness due to heat generation of the element and increasing the lifespan. The present invention relates to a method for driving an organic electroluminescent element that can achieve the following, and a light emitting device using the driving method.

[Prior Art and Problems to be Solved 1 Electroluminescent elements (EL elements) are characterized by high visibility because they emit light by themselves, and excellent impact resistance because they are completely solid-state elements. For this reason, various devices using inorganic and organic compounds are currently being proposed and attempts are being made to put them into practical use.

Among these devices, organic EL devices in particular are capable of significantly lowering the applied voltage, and therefore research and development are underway to utilize various organic materials as devices.

However, the above-mentioned organic EL element cannot operate (light emit light)
The problem is that it is not stable and deteriorates rapidly, making it impractical. That is, the deterioration of organic EL elements is largely due to heat generation during operation, and deterioration progresses more easily with a lower amount of heat generation than inorganic EL elements. Therefore, it is important to solve the problem of deterioration due to heat generation of the element during continuous driving and to suppress the decrease in brightness in order to extend the life of the organic EL element.

On the other hand, as conventional methods for driving EL elements, there are known direct current driving methods and alternating current driving methods.

The DC drive method is mainly a drive method for charge injection type light emitting devices, and its light emission principle is that holes and/or electrons are injected from the electrode into the organic multilayer part by voltage application, and both are not accelerated by a high electric field. It emits light by recombining in the light-emitting layer.

The AC drive method is mainly a drive method for collision-excited light emitting devices, and its light emission principle is that conduction electrons that already exist in the light emitting layer or electrons injected from the interface are accelerated by a high electric field. The emitted electrons excite the luminescent center, and the electrons and holes generated at this time emit light via the luminescent center.

In addition, Japanese Patent Application Laid-Open No. 2-15595 discloses a technique for AC driving a charge injection type light emitting element as one method for confirming light emission from the element.

In addition, Japanese Patent Application Laid-Open No. 189497/1989 describes AC thin film E
A technique for applying an asymmetrical AC voltage has been disclosed as an AC drive system for L-shaped EL elements (MIS-structured EL elements).

This method is a method for preventing a decrease in brightness by suppressing the accumulation of space charges.

Furthermore, the materials of the 129th study session of the 125th Photoelectric Interconversion Committee disclose a technique for pulse-driving an organic EL element (the light-emitting layer is made of aluminum chelate).

[Issue jII to be solved by the invention] However, the above-described method for driving an EL element has the following problems.

First, the direct current driving method of a charge injection type light emitting element has a problem in that, because it emits light continuously, the element is likely to deteriorate due to the light emission, resulting in a decrease in brightness.

Similarly, the AC drive method for collision-excited light emitting devices is
Since the electrodes have no polarity, this is a method for continuous light emission in principle.

Also, JP-A-2-15595, JP-A-62-1119
The techniques described in No. 497 and the above materials apply AC voltage to confirm whether the manufactured device has light-emitting ability or to examine the initial luminous efficiency, and are not intended to drive the device with AC. , I wanted to.

Specific conditions for AC driving a charge injection type light emitting device (
There is no disclosure regarding the conditions under which the apparent continuous light emission is recognized, the conditions for the average light emission brightness, etc., and the deterioration of the element when AC driving is continued.

2 In the field of light-emitting diodes, a technique for modulating and driving light-emitting diodes has been disclosed (Electronic Display Devices Chapter 7), but this technique is related to frequency or the lifetime of the injected carriers. It does not imply the present invention in any way.

The present invention was made in view of the above-mentioned circumstances, and
An object of the present invention is to provide a method for driving an organic electroluminescent element that can suppress reduction in brightness due to heat generation of the element and extend its life, and a light emitting device using the driving method.

In order to achieve the above object, the inventors of the present invention have conducted extensive research and have adopted an AC drive method as the drive method for organic EL elements, and by using a specific drive waveform, thermal deterioration can be suppressed. The present inventors have discovered that it is possible to emit light equivalent to that of direct current drive, and have completed the present invention.

[Means for Solving the Problems] That is, the method for driving an organic EL device according to claim 1 of the present invention provides an organic electroluminescent device having an organic multilayer portion including a light emitting layer made of an organic compound between an anode and a cathode. In the light emission drive of The light emitting drive waveform is designed to be driven using a light emission drive waveform that is shorter than the period recognized as , longer than the temperature relaxation time within the element, and longer than the immediately preceding light emission time.

Further, the light emitting device according to claim 2 includes an organic electroluminescent element having an organic multilayer portion including a light emitting layer made of an organic compound between an anode and a cathode, and a time average luminance per second that is a standard when performing DC drive. The light emission drive waveform is set so that the light emission drive waveform is equal to or higher than This configuration includes a drive source whose light emission drive waveform is set to be longer than the light emission time.

The present invention will be explained in detail below.

A third aspect of the present invention is to drive an organic EL element having an organic multilayer section including a light emitting layer made of an organic compound between an anode and a cathode using a specific drive waveform.

Here, it is preferable that the organic EL element be fabricated on a substrate. There are no particular limitations on the material of this substrate, and materials conventionally used for organic EL crystals, such as glass, transparent plastic, or quartz, can be used. In addition, the thickness of the substrate is
It is preferable that it is 10 times or more that of the element.

Materials for forming the electrode (anode or cathode) include gold, aluminum, indium, and magnesium.

Metals such as copper and #I, alloys and mixtures of these metals.

An alloy, a mixture electrode, or ITO (indium tin oxide; a mixed oxide of indium oxide and tin oxide) disclosed in JP-A No. 63-295695,
Transparent electrode materials such as 5n02 (stannic oxide), Z, and O (zinc oxide) are used.

In this case, it is preferable to use a metal with a large work function or an electrically conductive compound for the anode. It is preferable to use a metal or an electrically conductive compound with a small work function for the cathode.

It is preferable for at least one of these electrodes to be transparent or semi-transparent in order to increase the transmittance of the emitted light. This is preferable from the viewpoint of increasing the

The electrodes are formed by a known method such as a vapor deposition method or a sputtering method.

The organic multilayer part has at least a light emitting layer made of an organic compound, and the structure of this organic multilayer part is such that when it consists only of a light emitting layer (in this case, the organic multilayer part is a single layer), the light emitting layer/hole injection When it consists of a layer, when it consists of an electron transport layer/a light emitting layer, when it consists of an electron transport layer/a light emitting layer/a hole injection layer, in other cases (see JP-A No. 1-068387, etc.)
etc. The order of construction of this organic multilayer portion may be reversed depending on the electrode.

The light-emitting layer has an injection function, a transport function, and a light-emitting function.

Here, the injection function refers to a function that allows holes to be injected from an anode or a hole injection layer when an electric field is applied, and a function that allows electrons to be injected from a cathode or an electron injection layer.

Furthermore, the transport function refers to a function of moving (transporting) holes and electrons by the force of an electric field.

Furthermore, the light-emitting function is a function of providing a field for recombination of holes and electrons to cause light emission.

In this case, the thickness of the light-emitting layer, which may have a difference in hole-injecting ability and electron-injecting ability, is preferably within the range of 5n- to 51L hazy.

Although it is not necessary to provide a hole injection layer and an electron injection layer, it is preferable to provide them in order to improve the light emitting performance.

The hole injection layer is formed of a material that transports holes to the emissive layer at lower electric fields. The mobility of holes is 104 to 10'v
Under an electric field of /c■, at least 1O-6C 厘2/v-
It is preferable to have a value of sec.

The electron injection layer is formed of a material that transports electrons to the emissive layer at lower electric fields.

Note that the method for producing the organic EL element having the above structure is not particularly limited, but it is preferable to use a vapor deposition method because the organic EL element can be produced only by the vapor deposition method, which is more advantageous in terms of equipment and production time. .

The organic EL element having the above structure may be aged by applying a voltage between the anode and the cathode.

Aging here refers to applying a voltage to remove regions that generate leakage current, as well as removing holes and electrons accumulated within the device (Japanese Patent Application No. 2-117
(Refer to No. 885), thereby allowing the organic EL element to perform stable operation. The organic EL element used in the method of the present invention does not necessarily have to undergo this aging, but from the viewpoint of stabilizing the operation of the element. From this point of view, it is preferable to use a material that does not undergo aging.

In the method of the present invention, the organic EL element having the above structure is driven by a voltage (current) having a specific drive waveform.

Here, the organic EL element having the above structure emits light only when the anode is at a higher potential (forward potential) than the cathode.

When the opposite potential is generated or when the potential is zero, no light is emitted and no current flows. Therefore, when driving DC light, heat is constantly generated in the element.
This may cause deterioration of the element, shortening its lifespan.

Hereinafter, the driving waveform conditions in the method of the present invention will be explained in detail.

In the method of the present invention, it is necessary to use a light emission drive waveform in which the time average luminance per second is equal to or higher than the standard luminance when performing DC drive (waveform condition 1).

As mentioned above, the basic driving method for charge injection type organic EL elements is direct current, and "standard brightness when performing direct current driving" refers to the standard brightness in the case of direct current driving.

The value of "standard brightness when performing DC drive" varies depending on the emitted light color and application of the device, but it is generally about 100cd/■2 or the required characteristic, and when evaluating a single drop in the device, it is 100cd/2. It is appropriate to set it to 2.

Also, "time average luminance per second" is ]1! Indicates the time average value of luminance in the case of a drive that does not emit light continuously but repeatedly blinks (for example, AC drive or pulse drive). In other words, in the case of DC drive, the light emission is continuous, so it is usually expressed as "luminance". However, when one blink is repeated, the brightness value changes moment by moment, and there are times when no light is emitted, so the time average value of the brightness is taken and expressed as "time average brightness." Furthermore, since the method of the present invention includes cases where the brightness changes over - seconds, such expressions are used.

Then, this "time average luminance" is used for comparison with the luminance in the case of DC drive. Note that the brightness is measured by a brightness measuring device (for example, a photodiode, etc.) by causing the element to emit light.

A drive waveform that satisfies the waveform condition 1 above has a standard brightness when performing DC drive. Letting L be the luminance in the case of driving in which closing and blinking are repeated, it is expressed by the following equation (1).

5Ldt/Sdt≧L O------(t) The drive waveform only needs to satisfy the above equation (1), and the waveform is not particularly limited.

The time average brightness in the case of a drive that repeats blinking is the standard degree when performing a DC drive. In order to achieve the above, the brightness at peak emission should be equal to the standard brightness.

In order to do so, the drive waveform (in particular, the peak voltage (current); V*) is set.

The smaller the value of time-averaged luminance, the smaller the drop caused by heat generation. Therefore, in comparison with DC drive,
It is sufficient to achieve the same brightness as DC drive, so
The time average luminance is equal to the standard luminance L0 (S Ldt/
5dt=Lo)L/It is preferable to minimize the reduction in brightness due to heat generation.

However, the time average brightness is taken as the standard brightness. Even if it is made larger, the reduction in brightness due to heat generation can be reduced compared to the case of DC drive.

The above waveform condition 1 includes both light emission driving and no light emission as time passes, and since no heat is generated when no light is emitted, that is, when the current is 0 or very small, the heat accumulated in the element is Heat is dissipated by diffusion. Therefore, the temperature inside the element increases when it emits light, but when it does not emit light, the temperature rise is suppressed or the temperature decreases, so the temperature rise inside the element is milder than in the case of DC drive, and the element heat generation can be suppressed.

As mentioned above, the brightness during peak emission is the standard brightness in the case of DC drive. Since it has to be made larger, the electric power increases instantaneously, and the amount of heat generated at the moment of light emission is instantaneously larger than in the case of DC drive, but in general, brightness is proportional to the 1st to 2nd power of the current. Also, the current is proportional to the square of the voltage or more, that is, a small increase in voltage and current can result in a large increase in brightness, and since this is instantaneous, the temperature of the element increases as a whole. becomes smaller.

In addition, the drive waveform needs to be one that can be recognized as continuous light emission in appearance, and for this purpose, the light emission time needs to be shorter than the cycle that can be recognized as continuous light emission drive. (Waveform condition 2).

Here, "non-emission time" refers to the time when the element does not emit light or the time when it emits light at extremely low brightness. Specifically, the term "non-emission time" refers to the time when the element does not emit light or the time when it emits light at an extremely low intensity. This corresponds to the time when the light is off, the time when the light is emitted at a brightness that cannot be seen with the naked eye, or the time when the light is not emitted.

In addition, ``the period at which the apparent continuous light emission is recognized'' refers to the time period between the light emission and light emission of the hanging lamp, which is recognized as continuous light emission even though the blinking is repeated. In general, if the interval between light emissions is about 30 μS or less, it will be perceived by the naked eye as if the light is being emitted continuously.

Furthermore, it is necessary to use a driving waveform that is longer than the non-emission time or the temperature relaxation time in the element, and longer than the immediately preceding light emission time (waveform condition 3).
.

Here, the "temperature relaxation time" refers to the time when the application of voltage (or current) to the element is stopped as time 0, and then the temperature of the element or 1/e of the maximum temperature (e is the natural logarithm).
The time required to reach the value of

In this way, by making the non-emission time equal to or longer than the temperature relaxation time, it is possible to suppress the accumulation of heat within the element and suppress the temperature rise of the element.

In addition, the term "immediately preceding light emitting time" refers to the time during which light is being emitted just before a certain arbitrary non-emitting time 6 For example, as shown in FIG. 2, immediately before the non-emitting time t2. The light emission time is t□, and the light emission time immediately before the non-light emission time t4 is t3. Therefore, the condition for ``the non-emission time to be longer than the previous emission time'' is t□
<1. , or 1, < 1. Howar, such conditions are
This is necessary to suppress temperature rise.

Examples of drive waveforms that satisfy the above waveform conditions 1 to 3 include the waveforms shown in FIGS. 1(a) to 1(e).

FIGS. 1(a) and 1(b) show pulse rectangular waveforms. In this case, it is preferable that the frequency be 50H2 or more and the duty (load time) be 50% or less.

FIGS. 1(C) and (d) show a triangular waveform and an AC waveform, and FIG. 1(E) shows a superimposed waveform of a pulse waveform and an AC waveform.

Note that the driving waveform does not need to have a constant frequency in which the same waveform is repeated as shown in FIGS. 1(a) to (e), and may change over time. .

Next, a light emitting device according to a second invention will be explained with reference to the drawings.

FIG. 3 is a front view showing an example of the light emitting device of the present invention.

In the figure, 1 is an organic EL element, 2 is a metal electrode (cathode), 3 is a light emitting layer, 4 is an ITO electrode (anode), and 5 is a driving source.

The light emitting device according to the second invention includes at least an organic EL element 1
and a predetermined drive source 5.

Here, the organic EL element 1 is the same as in the case of the first invention described above.

Further, the predetermined drive source 5 refers to a drive source set to generate a specific drive waveform in the case of the first invention described above. Specifically, the function generator (5G-4511 Iwasaki Tsushinki Co., Ltd. II), the medium voltage generator (IflDO-BANDOFLINXU-1O
N GENERATOR) 0DEL FG-16
1 (NF CIRCUIT DESIGN BLOCK
A specific drive waveform can be generated using an arbitrary waveform generator such as one manufactured by CO, LTD.

In the light emitting device having the above configuration, a drive waveform is emitted from the drive lI5, whereby the organic EL element 1 emits light.

[Examples] Hereinafter, the present invention will be explained in more detail based on Examples.

Example 1 A transparent support substrate was prepared by forming an ITO electrode to a thickness of 1100 nm by vapor deposition on a glass substrate having a size of 25 x 75 x 1.1 l layers.

This transparent support substrate was fixed to a substrate holder of a commercially available Vapor S unit M (manufactured by Japan Vacuum Technology ■), and N,N'-diphenyl-N,N'-bis-(3-methyl phenyl)-[1,1'-biphenyl]-4,4'
- Put 2 (10 mg) of cyamine (TP[lA), put 200B of tris(8-quinolitool) aluminum (AM Q3) into a different resistance heating board made of molybdenum, and reduce the pressure in the vacuum chamber to lx l1l-'Pa. .

After that, the boat containing TPDA was heated to 215-220°C.
and TPDA at a deposition rate of 0.1 to 0.3 n/min.
A hole injection layer having a thickness of 60 nm was formed by vapor deposition on a transparent support substrate. The substrate temperature at this time was room temperature. Without taking this out of the vacuum chamber, Alq3 was placed on the hole injection layer from another boat as a light emitting layer.
A 0n layer was deposited. Vapor deposition conditions are boat temperature or 230℃
When the deposition rate is 0.01 to 0. [12 ns/s, substrate temperature was room temperature. This was taken out from the vacuum chamber, a stainless steel mask was placed on top of the light emitting layer, and it was again fixed to the substrate holder.

Next, 1 g of magnesium ribbon was placed in a Mori Latin resistance heating boat, and 500 mg of silver wire was attached to another tungsten basket. After that, open the vacuum chamber 2
After reducing the pressure to X IQ-'Pa, add silver to 0.1 nm/
At the same time, magnesium was started to be deposited from the other molybdenum boat using a resistance heating method at a deposition rate of 1.4 nm/s.

Under the above conditions, a 150n layer of a mixed metal electrode of magnesium and silver was deposited on the light emitting layer to serve as a counter electrode.

In the atmosphere, a DC electric field of 8.3X was applied to this device from Ov/cm using the ITO electrode as the anode and the metal electrode as the anode.
Aging was performed while applying up to 10' v/cm at intervals of 4.2 x 10' v/cm for 2 seconds each and measuring the voltage-current characteristics. Furthermore, the DC electric field was increased from Ov/c+s to -8.3X 10' v/cm by 4.2X 1G'
The voltage was applied for 2 seconds at v/Cm intervals, and aging was performed while measuring the voltage-current characteristics in the same manner. Thereafter, a DC electric field of 5.6 x 20'v/c was applied for 10 minutes to perform acing.

After the above steps, in a nitrogen atmosphere, frequency 1KH, DA L-Qi r-503, peak electric field 6.8x 10'V.
/C Otori-GV/am pulse rectangular waveform is generated by a voltage generator (
lll0DEL PG-161 (NF CIRCUIT
A voltage was applied using DESIGN BLO (:KC:O, manufactured by LTD) to cause the device to emit light.

Note that the time average luminance per second at the time of initial light emission was 100 cd/s''.

The device was allowed to emit light continuously under the above conditions, and the decrease in brightness was measured using a photodiode after 2 hours, 4 hours, and 50 hours. The results are shown in Table 1.

Example 2 The degree of luminance reduction was investigated in the same manner as in Example 1 except that the frequency condition of the pulse rectangular waveform was 200H. The results are shown in Table 1.

1. The degree of luminance reduction was investigated in the same manner as in Example 1 except that the frequency condition of the Yuyu pulse rectangular waveform was set to 50H8. The results are shown in Table 1.

014 The frequency condition of the pulse rectangular waveform is zoot, the duty condition is 30%, and the peak electric field condition is 9.2×1.
The degree of reduction in brightness was examined in the same manner as in Example 1 except that 05v/c■-0■/c soda was used. The results are shown in Table 1.

The degree of reduction in luminance of the device was examined in the same manner as in Example 1, except that the device was driven with a direct current electric field of 5.8 x 10'v/c. The results are shown in Table 1.

Forming a hole injection layer using 1-bis(4-di-p-trialuminophenol)cyclohexane (TPAC),
Peak electric field condition is 6.9X 10'v/cm-OV/a
The degree of luminance reduction was investigated in the same manner as in Example 1 except that m was used. The results are shown in Table 1.

Kl 1 The frequency condition of the pulse rectangular waveform is set to 2001. The degree of reduction in brightness was examined in the same manner as in Example 5 except that the paper was closed. The results are shown in Table 1.

Set the frequency conditions of the pulse rectangular waveform to 200) 1. The duty condition is 3oz, and the peak electric field condition is 9.1×10
The degree of luminance reduction was investigated in the same manner as in Example 5 except that the value was set to ``v/c proverb-OV/cm.The results are shown in Table 1.

The degree of luminance reduction of the device was examined in the same manner as in Example 5, except that the device was driven with a DC electric field of 6.7 x 10'v/c. The results are shown in Table 1.

A transparent support substrate was prepared by forming an ITO electrode into a film with a thickness of 100 r++w by vapor deposition on a glass substrate with a size of 25 mm x 75 x 1.1 layers.

This transparent support substrate was fixed to the substrate holder of a commercially available vapor deposition apparatus (manufactured by Japan Vacuum Technology ■), and N,N'-diphenyl-N,N'bis-(3-methylphenyl)- [1,1'-bihuenijishi]-4,4'
- Add 200g of diamine (TPDA) and place it on a different molybdenum resistance heating board.
p-tolylvinyl)xylene (DTVX) 200
The vacuum chamber was depressurized to LX 10-'Pa.

After (-17), the said boat containing TPDA is 215~2
Heating to 20°C, TPDA was deposited at a deposition rate of 1,1~[l
Deposited on a transparent support substrate with a film thickness of 70 nm.
A hole injection layer was formed. The substrate temperature at this time was room temperature. Without taking this out of the vacuum chamber, DTVX was deposited as a light-emitting layer in a 60 nm stack on the hole injection layer from another boat. The deposition conditions are boat temperature or 2.
The deposition rate was 35°C (Ll ~ 0.2 layers m/s), and the substrate temperature was room temperature. This was taken out of the vacuum chamber, a stainless steel mask was placed on top of the light emitting layer, and the substrate holder was placed again. Fixed.

Next, 1 g of magnesium ribbon was placed in a molybdenum resistance heating boat, and indium 5 (long) was placed in another tungsten basket.Then, the vacuum chamber was depressurized to 2x 10-'Pa, and indium was removed to 0.
．． At the same time, magnesium was started to be deposited from the other molybdenum boat by the resistance heating method at a deposition rate of 1.7 to 2.3 m/s.

Under the above conditions, a 150 ns a1 layer of a mixed metal electrode of magnesium and indium was deposited on the light emitting layer to serve as a counter electrode.

In the atmosphere, apply a DC electric field from Ov/c to 7.7X using the ITO electrode as the anode and the metal electrode as the cathode.
Aging was performed while applying up to 10' v/am at 4.2 x 10' v/cw+ intervals for 2 seconds each and measuring the voltage-current characteristics. Furthermore, the DC electric field was increased from Ov/am to -7,7X 10' v/css by 4.2x 10
'V/cmMi was applied for 2 seconds at intervals, and aging was performed while measuring the voltage-current characteristics in the same manner. After this,
Apply a DC electric field of 6.5X 10'v/c for 10 minutes,
Aging was performed.

After the above steps, in a nitrogen atmosphere, the frequency of 508, ,
Duty 4 50%, peak electric field 7.7X 1 (1
A pulse rectangular waveform of 'v/cm-OV/c■ was applied to cause the device to emit light. Note that the time average luminance per second at the time of initial light emission was 100 cd/m''.

The device was allowed to emit light continuously under the above conditions, and the decrease in brightness was measured using a photodiode after 2 hours, 4 hours, and 50 hours. The results are shown in Table 1.

The degree of luminance reduction of the device was examined in the same manner as in Example 8, except that the device was driven with a DC electric field of 7.2×10'v/c. The results are shown in Table 1.

[Hereinafter, blank spaces] As is clear from Table 1, according to the driving method of the present invention (Examples 1 to 8), in the case of DC voltage driving (Comparative Examples 1 to 3)
), the brightness decrease over time is smaller than that of

[Effects of the Invention] As explained above, according to the method for driving an organic EL element of the present invention and the light emitting device using this driving method, it is possible to suppress a reduction in brightness due to heat generation of the element and to extend the life of the element. can.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1(a) to (e) are diagrams showing aspects of driving waveforms used in the method for driving an organic EL element according to the first invention, and FIG. A waveform diagram to explain
FIG. 3 is a front view showing an example of a light emitting device according to the second invention.

Claims (2)

[Claims] (1) In light emission driving of an organic electroluminescent device having an organic multilayer part including a light emitting layer made of an organic compound between the anode and the pole, the time average brightness per second is higher than the standard brightness when driving with direct current. There is a light emission drive waveform such that the non-emission time in this light emission drive waveform is shorter than the period that is apparently recognized as continuous light emission drive, longer than the temperature relaxation time in the element, and longer than the immediately preceding light emission time. A method for driving an organic electroluminescent device, characterized in that it is driven using a certain light emission driving waveform. (2) An organic electroluminescent element having an organic multilayer part including a light-emitting layer made of an organic compound between an anode and a cathode, and an organic electroluminescent element that emits light so that the time average brightness per second is higher than the standard brightness when driving with direct current. Set the drive waveform, and emit light so that the non-emission time in this light emission drive waveform is shorter than the cycle that is recognized as continuous light emission drive, longer than the temperature relaxation time in the element, and longer than the previous light emission time. A light emitting device comprising a drive source having a set drive waveform.