JP2003068449A - Drive circuit of organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit of organic EL element which has a specific constant current circuit and can maintain luminescence even if a minute short circuit occurs. SOLUTION: A zener diode Z, of which the break down voltage is 10 V, and a resistor R are added to a constant current circuit for driving the organic EL element L. When the power supply voltage of 20 V drive this, the voltage applied to the organic EL element becomes 13 V, then, the element emits light normally. In this case, since the voltage, which is applied to the zener diode side, is 7 V, current does not flow at all. By continuing the drive in this state until a short circuit occurs in somewhere in the elements, resistance of organic EL element becomes small and the applied voltage falls. If the voltage, which is applied to the element, becomes less than 10 V, the voltage, which is applied to the zener diode side, exceeds 10 V, and the current I', which is decided by the resistance, flows, and the voltage, which is applied to the organic EL element, is maintained to more than the voltage, which is necessary to maintain luminescence, for example 5 to 10 V, then, the luminescence is maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an organic EL element, which is provided with a specific constant current circuit and can sustain light emission even if a minute short circuit occurs.

[0002]

2. Description of the Related Art In an organic EL device driven by a constant current, a specific pixel stops emitting light due to a short circuit between an anode and a cathode, or almost all of the current flows through the short-circuited part, so that the entire device stops emitting light. There is (for example,
JP-A-11-40346). Further, due to moisture, oxygen, or the like, dark spots may be generated and grow especially when exposed to a high temperature atmosphere or during long-term use. There is a need for a simple device, operation, etc. for suppressing the occurrence of such pixel defects and dark spots, or for repairing a short-circuited portion. Furthermore,
It is desired to provide a driving method and the like that can directly emit light without repairing a short-circuited portion.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art. Even if there is a minute short circuit, it is possible to emit light as it is without repairing it. It is an object of the present invention to provide a drive circuit for an organic EL element having a specific configuration capable of driving an EL element.

[0004]

A drive circuit for an organic EL element of the present invention is characterized in that a zener diode and a resistor are added to a constant current circuit of an organic EL element driven by a constant current. Further, in the present invention, the organic EL element may include a substrate and an organic EL laminate formed by laminating an anode, an organic EL thin film, and a cathode on the surface of the substrate in this order. it can. In this case, the organic EL element includes a sealing member that seals the organic EL laminate, and a combustion-supporting gas generating agent is sealed in a space formed by the substrate and the sealing member. Can be

In the element provided with this driving circuit, it is possible to emit light as it is without repairing a minute short-circuited portion, and it is possible to continue the light emission. In a constant current driven organic EL element, when a short circuit occurs, the voltage required to flow a constant current may decrease, and the entire element may not emit light. Therefore, when a breakdown voltage is exceeded, a current suddenly flows, and a Zener diode that keeps the voltage almost constant regardless of the magnitude of the current and a resistor for controlling the current amount are arranged in series with the element. And add it to the constant current circuit. In this way, when the resistance of the element decreases due to a short circuit and the applied voltage decreases, the current determined by the resistance is almost equal to the breakdown voltage of the Zener diode.
It flows through the added Zener diode and resistance. As a result, the voltage applied to the device is maintained to the extent required for light emission, and light emission is continued as it is.

Further, in this drive circuit, when a short circuit occurs, the current flowing through the Zener diode and the resistor is applied to the element in addition to the current due to the constant current drive, so that the short circuit site generates heat and is oxidized. It may be repaired. After the short-circuited portion is repaired in this way, the normal constant current drive is resumed, and stable light emission is maintained.

The above-mentioned organic EL device of the present invention comprises a substrate, an organic EL laminate formed by laminating an anode, an organic EL thin film and a cathode on the surface of the substrate in this order, and the organic E layer.
The organic EL element can be provided with a sealing member that seals the L laminated body. Further, in this case, as the organic EL element, a substrate, an organic EL laminate formed by laminating an anode, an organic EL thin film and a cathode on the surface of the substrate in this order, and the organic EL laminate are sealed. In the organic EL element including the sealing member, the organic EL element in which the combustion supporting gas generating agent is enclosed in the space formed by the substrate and the sealing member can be used. This makes it possible to easily adjust the enclosed amount of the combustion-supporting gas generating agent for releasing the minimum necessary oxygen gas, suppress the occurrence of a short circuit, and prevent the element due to excess oxygen gas. It is possible to prevent deterioration. Moreover, if a combustion-supporting gas generating agent that absorbs water and releases oxygen gas is used, it is possible to more efficiently absorb moisture in the sealed space. This sealing member is formed of a sealing material made of glass, metal, or the like, and a bonding layer for bonding the sealing material to the peripheral edge of the substrate.

As the "flammable gas generating agent", a compound capable of releasing a combustion supporting gas capable of suppressing the occurrence of a short circuit when the element is used can be used. The combustion-supporting gas is usually an oxygen gas generated by decomposition of the combustion-supporting gas generating agent, and other gases that impair the characteristics of the organic EL thin film and electrodes that form the organic EL element due to the decomposition are also included. A combustion-supporting gas generating agent that does not generate is preferable. Further, as the combustion-supporting gas generating agent, without particularly heating,
In general, it is more preferable that the organic EL element easily emits a combustion-supporting gas such as oxygen gas at the environmental temperature in which the organic EL element is used. Further, from the viewpoint of ease of handling when enclosing and fixing in the sealed space, the combustion-supporting gas generating agent is preferably a solid such as powder or granules.

Examples of such combustion-supporting gas generating agents include peroxides such as sodium peroxide, potassium peroxide and zinc peroxide, and peroxodicarbonates such as sodium peroxodicarbonate and potassium peroxodicarbonate, and Ammonium peroxodisulfate, sodium peroxodisulfate,
Examples thereof include peroxodisulfates such as potassium peroxodisulfate and barium peroxodisulfate. Of these, most of the peroxy acid salts generate oxygen gas by absorbing moisture, and when used as a combustion-supporting gas generating agent, the water contained in the sealed space of the organic EL element is absorbed and the element is used. It is particularly preferable because it does not generate a decomposition product that impairs the characteristics of 1.

It is known that water is a cause of so-called dark spots and their growth over time.
The amount of water contained in the sealed space of the organic EL element is reduced by the combustion-supporting gas generating agent that generates oxygen gas by absorbing moisture. Therefore, in some cases, it is possible to reduce the amount of the hygroscopic agent, such as barium oxide powder or calcium oxide powder, that is normally enclosed in the sealed space. In addition, ammonium peroxodisulfate and the like are in powder form and are easy to handle when enclosing in a sealed space. After mixing with a hygroscopic agent, it is fixed on the inner surface of the encapsulant with a resin film or the like having moisture permeability, and enclosed. You can also do it.

Oxygen gas also has a high concentration and may contribute to the generation and growth of dark spots over a long period of time. Therefore, it is preferable that the amount of oxygen gas released from the combustion-supporting gas generating agent be the minimum amount necessary for suppressing the occurrence of short circuit. This amount of oxygen gas can be easily adjusted by adjusting the amount of the combustion-supporting gas generating agent to be an appropriate amount depending on the volume of the sealed space. The amount of oxygen gas is 0.1 when the sealed space is 100% by volume.
-5% by volume, particularly 0.5-2% by volume is preferable. If the oxygen gas amount is less than 0.1% by volume, the effect of suppressing the occurrence of a short circuit cannot be sufficiently obtained, and if it exceeds 5% by volume, dark spots may occur over time and growth may occur. Not preferable.

As a method of manufacturing the above organic EL device, for example, in an atmosphere containing 1 volume% or more of oxygen gas,
It is possible to energize the organic EL thin film formed on the substrate to generate heat at a short-circuited portion and oxidize it, and then seal the organic EL thin film in an inert gas atmosphere.

In this manufacturing method, the anode, the
An organic EL thin film having at least a light emitting layer and a cathode are formed in this order, and after repairing the short-circuited portion with oxygen gas, under an inert gas atmosphere such as nitrogen gas or argon gas,
The sealing material is attached to the peripheral edge of the substrate via the bonding layer, and the organic EL
The thin film and both electrodes are sealed. In this way, after repairing the short-circuited portion in advance, by sealing in an inert gas atmosphere, it is possible to prevent oxygen gas from entering the sealed space, and after repairing the short-circuited portion, The organic EL thin film and the like can be shielded from oxygen gas. Thereby,
The generation and growth of dark spots can be prevented more reliably. That is, according to the above manufacturing method, the short-circuited portion can be repaired in advance, and since oxygen gas is not mixed into the sealed space, the generation and growth of dark spots during use of the element can be prevented.

Electricity can be applied to the organic EL thin film in a closed space containing "1% by volume or more" of oxygen gas, and the device used is not particularly limited. The upper limit of oxygen gas concentration is not specified, but if the concentration is too high, organic E
Since it may impair the characteristics of the L element, it is preferably 20% by volume or less, particularly preferably 10% by volume or less. The oxygen gas concentration is 1 to 5% by volume, more preferably 1 to 2% by volume.
It is preferable that the oxygen gas concentration is within this range, and the short-circuited portion can be efficiently and sufficiently repaired.
If the oxygen gas concentration is less than 1% by volume, the short-circuited portion cannot be sufficiently repaired, or the repair requires a long time,
Not practical.

The voltage and current during energization are not particularly limited as long as they can heat the short-circuited portion and oxidize it to the extent that conduction is lost. It is preferable that the voltage and the current are high voltage and large current as compared with the normal driving of the organic EL element. By applying a high voltage and a large current for a short period of time, it is possible to efficiently perform repair without deteriorating the characteristics of the element. Furthermore, by setting higher voltage and current, it is possible to short-circuit a defective portion which has not yet been short-circuited, generate heat, oxidize and repair, and prevent occurrence of short-circuit during use in advance.

As a driving method of the organic EL element, for example, a high voltage is applied at the start of driving to cause the organic EL element to emit light, and then a predetermined constant current driving is performed.

With this driving method, light can be emitted as it is without repairing a minute short-circuited portion. If there is a short-circuited portion, current may flow intensively in that portion, and the entire organic EL element driven by constant current may not emit light. Therefore, a high voltage exceeding the voltage applied during constant current driving is applied at the start of driving. By doing so, a current exceeding the amount of current that can flow through the short-circuited portion flows through the other part of the element, and the element emits light. Then, a predetermined current flows, and the resistance value of the portion where the light emission is started decreases, so that the light emission is continued even after switching to the normal constant current drive after a certain period of time. That is, according to the above-mentioned driving method, even if there is a minute short circuit, it is possible to emit light by slightly changing the driving method at the start of driving, and it is possible to simply and inexpensively emit an element with a short circuit. You can

The above driving method requires an additional circuit for applying a high voltage at the start of driving, and in the driving circuit of the present invention, it is necessary to add a Zener diode and a resistor to the constant current circuit. . Therefore, the above-described driving method and the driving circuit of the present invention are both suitable for the segment type element having a smaller number of pixels than the dot matrix type element having a large number of pixels. In particular, the above driving method that requires a capacitor and a coil that are difficult to integrate is more suitable for a segment type element.

In the present invention, the organic EL device comprises a substrate and an organic EL laminate in which an anode, an organic EL thin film and a cathode are laminated in this order on the surface of the substrate. The organic EL thin film has at least a light emitting layer and may have a hole transport layer and an electron transport layer. Also,
A hole injection layer may be provided between the anode and the hole transport layer, and an electron injection layer may be provided between the electron transport layer and the cathode.

As the substrate, glass such as soda lime glass, synthetic resin such as polyethylene terephthalate, polyether sulfone and polycarbonate, and transparent material such as quartz can be used. Of these, a substrate made of glass is often used.

The light emitting layer can be formed of a light emitting material such as an aluminum quinolium complex and a benzoquinolinol Be complex. Further, a doping agent such as a quinacridone derivative or a DCM derivative can be added to these light emitting materials. The hole transport layer can be formed of a triphenylamine derivative or the like, and the electron transport layer can be formed of an aluminum quinolium complex, a hydroxyflavone Be complex, or the like. The hole injection layer can be formed of a copper phthalocyanine complex or the like, and the electron injection layer is
Fluoride or oxide of alkali metal such as LiF and Ba
It can be formed from a fluoride of an alkaline earth metal such as F ₂ .

The anode can be formed of a simple metal such as gold or nickel, or a metal compound such as ITO, CuI, SnO ₂ or ZnO. Of these, ITO is particularly preferable from the viewpoint of productivity, stable conductivity, and the like. The cathode can be formed of aluminum, Mg-Ag alloy, Na-K alloy, or the like. Each layer forming these organic EL laminates can be formed by a vacuum vapor deposition method, and can also be formed by various other methods such as a spin coating method, a casting method, a sputtering method and an LB method.

The organic EL laminate can be sealed by bonding a sealing material to the periphery of the substrate via a bonding layer. As the sealing material, one made of metal such as stainless steel, aluminum or an alloy thereof, glass such as soda lime glass, silicate glass, synthetic resin such as acrylic resin and styrene resin can be used. The bonding layer is formed by a cured body made of a thermosetting resin such as an epoxy resin or an acrylate resin, and a sealing resin such as a photocurable resin. Among these encapsulating resins, it is preferable to use an encapsulating resin that forms a cured body that is less likely to allow moisture and the like to permeate, in order to suppress a decrease in brightness and the like. Further, a photocurable resin that can relieve the thermal stress applied to the element and has a high curing speed is more preferable.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples. Reference Example 1 As shown in FIG. 1, a transparent substrate 1 made of glass, a transparent electrode 2 made of ITO, an organic EL thin film 3 having at least a light emitting layer, and a cathode 4 made of aluminum are formed on the surface of the transparent substrate 1. Organic E formed by sequentially stacking
The L laminated body, the sealing material 52 made of stainless steel, and the bonding layer 5 that bonds the sealing material 52 to the peripheral edge of the transparent substrate 1.
An organic EL element including the sealing member 5 composed of 1 and 1 was manufactured. The light emitting area of this element is 7.2 × 3.6 cm ² , and the volume of the sealed space 53 is 4 cm ³ .

As shown in FIG. 1, a moisture-permeable resin film 6 is formed on the periphery of the recess 54 on the inner surface of the sealing material 52 of this element, as shown in FIG.
Is attached. The recess 54 is filled with a mixed powder 7 of 0.2 g of barium oxide powder and 0.8 mg of ammonium peroxodisulfate powder. This ammonium peroxodisulfate is used as the bonding layer 5 when the device is used.
The total amount of oxygen gas generated from the enclosed 0.8 mg of ammonium peroxodisulfate is 4 × 10 ⁻² by absorbing moisture that has entered the sealed space 53 from the first and the like and releasing oxygen gas.
It will be cm ³ . Therefore, the concentration of oxygen gas contained in the sealed space 53 is about 1% by volume. This suppresses the occurrence of short circuit when the element is used.

Reference Example 2 An organic EL device was manufactured by performing a treatment for repairing a short circuit part in advance by the apparatus shown in FIG. 2 and then sealing it. Hereinafter, the steps will be described in order with reference to FIG. Under vacuum in the film forming chamber 8, the surface of the glass substrate 1 was
A transparent electrode 2 made of TO, an organic EL thin film 3 having at least a light emitting layer, and a cathode 4 made of aluminum were formed in this order (this is referred to as an intermediate product). When the intermediate product is driven with a constant current and there is a pixel that does not emit light due to a short circuit, the intermediate product is transferred to the vacuum processing chamber 9, and then a mixed gas of 1 volume% oxygen gas and 99 volume% nitrogen gas is introduced. Then, the internal pressure was set to 0.1 MPa.

The intermediate product is connected to the aging circuit 91, and a high voltage exceeding the voltage and current at the time of constant current driving is applied, a large current is caused to flow, the short-circuited portion is heated and oxidized (at the short-circuited portion, the cathode aluminum Is oxidized and becomes aluminum oxide and does not conduct electricity.) Repaired. The intermediate product was transferred to the sealing chamber 10, and the sealing chamber 10 was once put in a vacuum state to remove oxygen gas, and then nitrogen gas was introduced to make the internal pressure 0.1 MPa. An ultraviolet curable resin was applied to the peripheral edge of the glass substrate 1 and a glass or metal sealing material 52 was adhered thereto, and then the resin was cured and sealed to produce an organic EL element.

By producing the element by such a process, the short-circuited portion can be repaired in advance, and oxygen gas can be prevented from being mixed into the sealed space, so that a dark spot is generated during use. And its growth can also be prevented. In FIG. 2, P is a vacuum pump for bringing each processing chamber into a vacuum state, and O ₂ and N ₂
Are sources of oxygen gas and nitrogen gas, respectively,
These are connected to each processing chamber via a valve.

Reference Example 3 By discharging the electric charge accumulated in a capacitor,
The organic EL element was driven by a constant current circuit including a drive circuit capable of applying a high voltage, for example, a drive circuit of a fuel injection valve of a direct injection gasoline engine.
FIG. 3 schematically shows changes in voltage or current with time in this case. As described above, even if there is a minute short circuit due to the high voltage during discharge, the element emits light and the voltage is high, so that the brightness is higher than that during normal constant current driving. Thereafter, the voltage or current decreased, and after a certain period of time, even after switching to constant current driving from t ₀ , the light emitting element continued to emit light because the resistance of the element that once emitted light decreased. With this drive method,
By adjusting the capacity of the capacitor and the time for switching to the constant current drive, it is possible to drive the elements having different light emitting areas under optimum conditions.

Example 1 In a constant current circuit for driving the organic EL element L, as shown in FIG. 4, a Zener diode Z having a breakdown voltage of 10V was used.
And resistance R are added. When this was driven by a power supply voltage of 20 V, the voltage applied to the organic EL element was 13 V, and the element emitted light normally. In this case, since the voltage applied to the Zener diode side is 7V, no current flows at all.

When driving is continued in this state and a short circuit occurs somewhere in the element, the resistance of the organic EL element decreases,
The applied voltage drops. When the voltage applied to the element falls below 10V, the voltage applied to the Zener diode side exceeds 10V, and as shown in FIG.
Flows, and the voltage applied to the organic EL element is maintained at a voltage equal to or higher than the voltage required for light emission, for example, 5 to 10 V, and light emission is continued. On the other hand, as shown in FIG. 6, when the Zener diode and the resistor are not added, the voltage applied to the organic EL element due to the occurrence of the short circuit is lower than the voltage required for light emission,
For example, the voltage drops to 2V and the device stops emitting light.

It should be noted that the present invention is not limited to the above-mentioned embodiment, but various modifications can be made within the scope of the present invention according to the purpose and application. That is, in Reference Example 2,
The device, operation, etc. used are not limited as long as the short-circuited portion can be repaired in advance by such a process. Also,
In Reference Example 3 as well, another drive circuit may be used as long as a high voltage can be applied at the start of drive.

[0033]

According to the present invention, even when a short circuit occurs during use of the device, the device can continue to emit light,
In some cases, the short circuit site may be repaired

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing an organic EL element of Reference Example 1 in which a combustion-supporting gas generating agent is enclosed in a sealed space.

FIG. 2 is a schematic diagram showing an outline of an apparatus for performing sealing after repairing a short-circuited portion in Reference Example 2.

FIG. 3 is a graph showing a high voltage or a large current at the start of driving and a constant current driving thereafter with time in Reference Example 3;

FIG. 4 is a circuit diagram showing a constant current circuit to which a Zener diode and a resistor are added in the first embodiment.

FIG. 5 is a circuit diagram showing a state in which a current flows through a Zener diode and a resistor and a voltage required for light emission is continuously applied to the element.

FIG. 6 is a circuit diagram showing a constant current circuit to which a Zener diode and a resistor are not added.

[Explanation of symbols]

1; transparent substrate, 2; anode, 3; organic EL thin film, 4; cathode, 5; sealing member, 51; bonding layer, 52; sealing material, 5
3; Sealing space, 54; Recess, 6; Moisture permeable resin film, 7; Mixed powder, 8; Film forming chamber, 9; Restoration chamber, 9
1; Aging circuit, 10; Sealing chamber, L; Organic EL element, Z; Zener diode, R; Resistor.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 33/04 H05B 33/04 33/14 33/14 A 37/02 37/02 Z (72) Inventor Takashi Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Masahide Kosugi 1 Toyota Town, Toyota City, Aichi F Motor Vehicle Co., Ltd. F Term (reference) 3K007 AB08 BB01 DB03 FA02 GA00 3K073 AA43 AA69 BA01 CF01 CF12 CF21 CG45 CJ17 CJ18 5C080 AA06 BB01 DD09 DD18 DD28 DD29 FF03 FF08 HH09 JJ03 JJ05 JJ06

Claims (3)

[Claims] 1. A drive circuit for an organic EL element, wherein a zener diode and a resistor are added to a constant current circuit of the organic EL element driven by constant current. 2. The organic EL device comprises a substrate, and an organic EL laminate formed by laminating an anode, an organic EL thin film and a cathode in this order on the surface of the substrate.
A drive circuit for the organic EL element described. 3. The organic EL element includes a sealing member for sealing the organic EL laminate, and a combustion-supporting gas generating agent is sealed in a space formed by the substrate and the sealing member. The drive circuit for the organic EL element according to claim 2.