JP2002260852A - High-speed pulse el element drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high luminance light by raising the voltage to be impressed on the EL element. SOLUTION: This organic EL element which comprises an organic layer containing a luminous layer between a transparent electrode mirror as a positive electrode and a metal electrode mirror as a negative electrode and makes the luminous layer emit light by injecting an electron hole and an electron into the luminous layer from the above electrodes, and an organic EL element that is capable of luminescence wavelength selection, in which the thickness d between the positive electrode and negative electrode is set to satisfy the resonance conditions of light, m×λ/2=n×d (wherein m is integral number, λ is luminescence wavelength, n is refractive index unique to the organic layer), is used. The electrodes play the role of a flat-surface capacitor and generate pulse light by the charge that is charged and discharged to the capacitor by a bloom line form. Or the electric circuit that has incorporated this EL element is made a bloom line circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a high-speed pulse EL device driving device using an optical resonance type organic electroluminescent (EL) device.

[0002]

2. Description of the Related Art An electroluminescent device having an organic layer is a planar luminous body capable of emitting light electrically, and is used for a display device such as a front display of an automobile and a backlight of a liquid crystal display. I have. As an organic EL element, an optical resonance type organic EL element in which a light emitting element is provided between two reflecting mirrors is known (for example, Japanese Patent Application Laid-Open No. Hei 8-25).
0786, JP-A-11-288786).

[0003]

There is no restriction on the viewing angle.
Research and development of EL materials and device structures have been earnestly conducted with the aim of increasing the brightness, stabilizing, and improving the color tone of EL devices, which are expected as electroluminescent devices capable of low-voltage driving and high-speed response. No research and development has been conducted from the viewpoint of control and multifunctionalization of elements.

[0004] By increasing the voltage applied to the EL element, high-luminance light can be obtained, but as a result, the element is deteriorated because an overcurrent flows. Therefore, high brightness EL
In research and development of devices, research and development of EL materials having high luminous efficiency at low voltage have been generally performed.

In the conventional organic EL device, different light-emitting materials are used for each color, and light of a specific color such as red, green, and blue light, which are three primary colors of light (half-width of emission spectrum). In order to obtain light having a small value, a laser or an optical filter is used.

[0006]

In order to obtain light of a specific wavelength, research and development of an EL material which emits light of a specific color is generally performed in research and development of conventional EL devices.
That is, in order to obtain red, green, and blue light, which are the three primary colors of light, R & D on different luminescent materials for each color is being conducted.

The inventors of the present invention have proposed a method of saving the time and labor required for research and development of a light emitting material and reducing the man-hour and cost in manufacturing an optical element (that is, easily and freely without using an optical filter or the like). As a result, a new optical resonance structure was incorporated in the organic EL device, and the target light was successfully obtained.

Further, the present inventors have paid attention to the control of the current flowing through the element, and have searched for a technique for realizing the same. As a result, the Bloom line which has been conventionally known as a nitrogen laser charge supply circuit has been obtained. By using a circuit, a high voltage was applied to the EL element, and high-luminance light emission was realized by a pulse light generator having a high-speed response.

That is, the present invention comprises an organic layer including a light emitting layer between a transparent electrode mirror as an anode and a metal electrode mirror as a cathode, and injects holes and electrons from the electrode into the light emitting layer. An organic electroluminescent device that emits light from the light-emitting layer, and has a film thickness d between an anode and a cathode.
Is set to satisfy m × λ / 2 = n × d (m is an integer, λ is an emission wavelength, and n is a refractive index specific to an organic layer) which is a condition for resonance of light. A high-speed pulse EL element driving device characterized in that electrodes of an electroluminescent element play a role of a plane capacitor, and pulse light is generated by electric charges charged and discharged to and from the capacitor in a Bloom line format.

Further, the present invention comprises an organic layer including a light emitting layer between a transparent electrode mirror as an anode and a metal electrode mirror as a cathode, and injects holes and electrons from the electrode into the light emitting layer. An organic electroluminescent device that emits light from the light-emitting layer, wherein the film thickness d between the anode and the cathode is defined as m × λ / 2 = n × d (m is an integer, and λ is the emission wavelength , N is a refractive index specific to an organic layer). A high-speed pulse EL element drive characterized in that an electric circuit incorporating an organic electroluminescent element capable of selecting a light emission wavelength set so as to satisfy a Bloomline circuit is set. Device.

The high-speed pulse EL device driving device according to the present invention has the following features. 1. The three primary colors of light, red, green, and blue, can be extracted from one type of EL material. In other words, green from yellow-green light and red from orange light can be extracted without an optical filter. 2. Eliminates the need for optical filters for chromaticity adjustment. That is, man-hours and costs can be reduced.

3. High voltage (maximum 50V) for EL element
Can be applied. In a general steady voltage drive EL element,
At more than ten volts, the element is deteriorated, short-circuited and destroyed (20
There is no V). By applying this high voltage, high brightness (A
30000 cd / m ² when using lq3), high-speed response (1 ms including the rise and fall time of optical pulse)
Degree) realized. As for the high-speed response, the rise time of the pulse tends to be shorter as the applied voltage becomes higher (approximately 10 μs when 50 V is applied).

4. By using the bloom line circuit, light can be emitted ignoring the capacitor of the organic EL device. That is, pulse light with a fast rise can be generated. This is because the charge / discharge part is divided in the light emitting mechanism using the bloom line circuit. In other words, it means that the capacitors of the organic EL are also charged when the capacitors C1 and C2 are charged. If a pulse voltage is simply applied to the organic EL element, charging and discharging are performed simultaneously, and light emission is delayed by the time required for charging.

5. The amount of charge injected into the EL element can be controlled by changing the capacitance of the capacitor C2 in the circuit. That is, the brightness and the amount of light can be controlled. In addition, this function can reduce the deterioration of the element and realize high stability of the element. 6. By making the capacitor common to the electrode of the EL element, energy injection can be made smoother. (If the capacitor and the EL element are connected by wiring, electrical and temporal losses occur due to impedance of the wiring and the like. So it can be reduced).

[0015]

FIG. 1 shows a high-speed pulse EL according to the present invention.
FIG. 3 is a conceptual diagram showing a structure of an optical element in which an optical resonance structure is incorporated in an organic EL element used in an element driving device and the EL element is multifunctional. Anode A (2) in order from the lower glass substrate (1)
/ Anode B (3) / Anode buffer layer (4) / Hole transport layer (5)
/ Emission layer (6) / Electron transport layer (7) / Cathode buffer layer (8) /
It has a multilayer structure composed of a cathode (9). The anode buffer layer (4) and the cathode buffer layer (8) are provided as needed to efficiently inject holes and electrons from the electrodes, respectively.

The anode A, the anode B, and the cathode are metals that serve as electrodes and a mirror that reflects light at the same time. The anode A is a metal having a high transmittance (a certain degree of transmittance can be obtained by thinning even a metal film). Anode A is for increasing the strength of the electrode (depending on usage). The layers from the cathode to the anode may be reversed and stacked.

An organic layer including a light emitting layer is provided between a transparent electrode mirror as an anode B and a metal electrode mirror as a cathode, and holes and electrons are injected into the light emitting layer to cause the light emitting layer to emit light. In order to improve carrier injection efficiency and luminous efficiency, it is preferable to use gold having a high work function as the anode B and dope the luminescent layer with coumarin 6 by co-evaporation. The anode A uses a transparent conductive metal oxide film, for example, ITO.

In the structure of the optical element used in the high-speed pulse EL element driving device of the present invention, the film thickness d between the anode B and the cathode is set as follows.
M × λ / 2 = n × d (m is an integer, λ
Is the emission wavelength, and n is the refractive index specific to the organic layer). Since the film thickness increases as the integer m increases, about 1, 2, or 3 is selected. Resonance frequency ν (= 1
/ Λ) is determined by the distance d between the electrodes of the EL element and the refractive index n of the organic layer (mλ / 2 = nd). With this structure, an optical element whose emission wavelength can be selected is obtained. That is, the element for extracting green light and the element for extracting red have different film thicknesses and are separately manufactured. For example, in order to extract green (λ = 540 nm), d is 185 nm even at the minimum (m = 1), which is about twice the thickness of a general EL element (triple layer type).

As described above, the optical element used in the present invention is a thick-film element (the thickness depends on the resonance condition; about 200 to 600 nm, which varies depending on the wavelength of light to be generated), and has a structure in which light resonates. A specific light can be extracted. In addition, light from the light emitting layer can be adjusted by controlling the film thickness,
The anode can be taken out from either electrode.

A general EL element is only illuminated. Further, the film thickness d is as thin as about 100 nm in order to improve the injection of energy required for light emission (to reduce element resistance, increase space charge limiting current, etc.).

As described above, several problems occur with increasing the film thickness. As a solution, the present invention combines a Bloom line circuit with an organic EL element and
The electrode of the L element plays the role of a planar capacitor, and it has become possible to generate pulsed light by charges charged and discharged to and from the capacitor in a Bloom line format.

FIGS. 2A, 2B and 2C are perspective views showing a schematic structure of a high-speed pulse EL device driving apparatus according to the present invention. In FIG. 2A, a metal electrode 2 is arranged below an insulating layer (dielectric) 1, and two metal electrodes 4 and 5 are arranged with an organic layer 3 above the insulating layer. The electrode 4 functions as the capacitor C1, and the electrode 5 functions as the capacitor C2. The capacitors C1 and C2 are charged. When one of the capacitors is short-circuited, a potential difference is generated between the upper electrodes 4 and 5, and the other is charged. The carriers are injected into the organic layer 3 and the inside of the organic layer 3 becomes excited.

FIG. 2B shows an arrangement in which an upper electrode serving as a capacitor is not arranged on one plane, but an electrode 4 serving as a capacitor C1 and a capacitor C2 sandwiching an organic layer 3 therebetween.
5 is superimposed. Organic layer 6, Organic layer 7
Is an insulator provided for forming the organic layer 3, and also has a role of preventing a surface current (discharge) on a side surface of the organic layer 3. The portion of the organic layer 3 sandwiched between the two electrodes 4 and 5 formed as described above becomes a light emitting layer. By providing such a structure, the thickness of the light emitting layer can be arbitrarily controlled and the multilayer EL can be formed.
A device structure can be obtained, and high luminance and high efficiency can be realized.

Further, since the light emitting layer is sandwiched between the electrodes 4 and 5, it has an effect of confining the generated light in the light emitting layer and has an effect of protecting the organic layer 3 which is weak against oxygen and moisture. However, the areas of the cathode and the anode, which are the electrodes where the short circuit starts first, need to be the terminals for connecting to the oscillation circuit, so that the areas are about the same, and the two capacitor capacities are about the same. Therefore, the time constant in the charging / discharging transient phenomenon becomes substantially the same, the time required until the voltage generated between the light emitting layers reaches the maximum value becomes long, and it is not electrically efficient.

FIG. 2C shows that the organic layer 3 on the electrode 4 serving as the capacitor C1 is sandwiched between the organic layers 6 and 7, and the electrode 5 is superposed on the organic layer 3. Condenser C2
The electrode 5 serving as a part is located at the opposite edge of the end face from which the traveling wave is extracted, and its capacitance can be reduced. In addition, in such a structure, since the carriers accumulated in the capacitor are injected from the opposite edge direction, it is expected that the generated light has directivity and that the light traveling in the opposite edge direction is reflected by the cathode. Is done.

From the driving principle, the capacitance of the capacitor is C1
<< C2. The larger the capacity of C2 (for example, C2
(1 is about 0001 μF, C2 is about 1 μF) The charge injected into the organic layer 3 increases, and the organic layer 3 shines well. That is, the light amount can be adjusted not only by the voltage but also by the capacitance of C2. In addition, C1 serves as a stopper for the charge discharged from C2, and the smaller the capacity, the more effective. The reason will be described based on the driving circuit shown in FIG. The capacitor C
1 and C2 correspond to C1 and C2 on the drive circuit shown in FIG. It is also possible to replace only C2 with an external capacitor (depending on usage).

FIG. 3 shows a Bloom line circuit incorporating an organic EL element in the high-speed pulse EL element driving device of the present invention. A bloom line circuit has been conventionally used as a mechanism for injecting a large amount of electric charge into a device instantly as a device for injecting energy of a nitrogen laser or generating a pulse voltage.

In the circuit shown in FIG. 3, when the switch is off, a voltage is applied, and the capacitors C1 and C2 are charged. When the switch is turned on, discharge occurs and C
2 are injected into the EL device to emit light.

Referring to FIG. 3, p-channel FET
Below the transistor, there is an n-channel FET transistor. When a pulse voltage (rectangular voltage) is applied thereto, when the upper side is on, the lower side is switched off, and when the upper side is off, the lower side is switched on. The two capacitors are charged when the upper transistor is on and discharged when it is off. Upon discharge, the EL element emits light.

The discharge speed is related to the rise of EL, and the faster the discharge speed, the faster the rise.
The time required for discharging is determined by the product of the capacitance of the capacitor and the resistance of the circuit (C × R: time constant). Therefore, the discharge rate is C1
>> C2. This is because C2 has an overwhelmingly larger capacity than C1, and the discharge path of C2 has not only the resistance of R1 and the circuit itself, but also the extra resistance of the organic layer of the EL element. Here, R1 is 1Ω, and the resistance of the EL element changes from several tens kΩ to several hundreds Ω depending on the applied voltage. The resonance frequency (emission wavelength) does not depend on the capacitance and shape of C2. Further, the frequency of emitting light can be controlled by the frequency of a pulse voltage input to the transistor.

From the above, the phenomena at the time of discharging can be summarized as follows. The charge charged in C1 is overwhelmingly discharged earlier than C2. At that time, a voltage of almost V is generated between AB in FIG. 3 and the EL element emits light by the voltage. The amount of light emission at this time changes depending on the amount of charge determined by C2 × V and the applied voltage V, and the rise of light changes depending on V.

When a capacitor and an EL element are connected by a wiring, electrical and temporal losses occur due to the impedance of the wiring and the like. On the other hand, by sharing the capacitor with the electrode of the EL element, energy is injected. Can be made smoother. However, similar performance can be obtained even if a circuit is assembled by separating the optical element and the capacitor to emit light.

[0033]

EXAMPLES Example 1 of manufacturing a device

ITO (basic electrode) / Au (anode) / TP
D (hole transport layer) / Alq3 (light-emitting layer) / LiF (electron injection layer) / Al (cathode), and the thickness between Au and Al was designed and manufactured so that resonance conditions were satisfied. Where Li
F is lithium fluoride, and Alq3 is a quinolinol aluminum complex widely used as a light emitting material. As a comparative example, a well-known ITO / TPD / light-emitting material / MgA, which is generally called a triple layer, is used.
g of devices were fabricated. Here, ITO is glass coated with indium-tin oxide, and TPD is N, N'-diph.
ethyl-N, N '-(3-methylphenyl
l) -1,1'-biphenyl-4,4'-dia
mine.

In the fabrication of the device, first, the ITO substrate was etched to a width of about 2 mm with hydrogen gas generated by hydrochloric acid-Mg and used as a basic electrode. For cleaning, ethanol, detergent, pure water, acetone, trichloroethylene, and finally acetone vapor were used. Au as an anode on this substrate
400 °, TPD as a hole transport layer at 600 °, Alq3 as a light emitting material at 4900 °, and L as an electron injection layer.
iF was deposited at a thickness of 10 ° and Al as a cathode was deposited at a thickness of 1000 ° by a vacuum deposition method. Deposition of each layer is 10 ^-6 Torr
I went in.

At this time, the film thickness d between Au and Al is m × λ / 2 = nXd (m is an integer, λ is the emission wavelength, and n is the refractive index of the organic layer), which is the condition of light resonance. It was set to meet. In order to obtain a spectrum mainly having an emission wavelength of 540 nm, since the refractive index n is 1.46 (a value unique to the organic layer of this element), the integer m is 3, and the film thickness d is 55.
10 ° (= 600 + 4900 + 10). Substituting this value into the above equation gives λ = 5363Å = 536.3n
m.

As can be seen from the emission spectrum of FIG.
ITO with no Au layer and no light interference (reflection)
Compared with the spectrum obtained from the organic EL device having the structure of / TPD / Alq3 / LiF / Al, the spectrum obtained from the device of Example has light other than the expected wavelength removed,
The half width of the spectrum is reduced (filter effect).

This means that the color purity has increased. Also, the peak of the spectrum is about 540 from the graph.
nm, which proves that the resonance condition is satisfied. However, the drop in the spectrum around 640 nm is an area that cannot be measured due to the characteristics of the measuring device.

Element Production Example 2 Elements 1 and 2 were prepared under different resonance conditions. The processing of the substrate and the material constituting the element were the same as in Example 1, and only the film thickness of the organic layer was changed between the element 1 and the element 2. The structure is ITO / Au / TPD / Alq3 / LiF /
Al, and the thickness of the element 1 was 400 ° and 60 °, respectively.
0 °, 3200 °, 10 °, 1000 ° (m =
2). In the element 2, the film thickness was 400 °, 6 mm, respectively.
00, 4900, 10 and 1000 (m =
3). The peak wavelengths of the emission spectrum expected from this condition are 536 nm and 556 nm, respectively.

FIG. 5 shows emission spectra of the device 1 and the device 2. It can be seen from the spectrum shift that the resonance condition holds. However, the drop in the spectrum around 640 nm is an area that cannot be measured due to the characteristics of the measuring device. From FIG. 5, it can be seen that the wavelength as expected was obtained. From this result, it was proved that a spectrum having an arbitrary peak wavelength could be extracted by incorporating the resonance structure into the organic EL element (a specific color can be extracted). Further, it can be seen from the results that the refractive index n of the organic layer can be determined by measuring the spectra of two elements having different resonance conditions.

Example 1 Using the above-mentioned EL element, the EL
The device emitted light. Light emitted when a pulse voltage is applied to an EL device takes some time to reach a maximum intensity. This state was measured by a photodiode (FIG. 6A). The horizontal axis represents elapsed time, and the vertical axis represents applied voltage and emission intensity. Such a phenomenon occurs because the EL device itself has a capacitance. During the charging of the capacitance, carrier injection also occurs at the same time, which imposes a thermal load on the organic layer and is inefficient in terms of electrical. By using the bloom line circuit, the rise time of light emission can be improved.

FIG. 6B shows a signal observed when the EL element emits light using the circuit shown in FIG. FIG.
This indicates that an EL signal with a fast rise time is obtained. In the bloom line circuit, the carrier injected into the EL element is charged to C2. At this time, the EL
The capacitance of the element is also charged. As a result,
The blunting of the rise of EL as shown in FIG. 6A can be improved.

Further, as shown in FIG. 6B, the EL signal after the light emission peak gradually decreases in response to the discharge (discharge) of the applied voltage. This occurs because the amount of carriers injected over time decreases. Also,
This attenuation follows a time constant determined by the product of the capacitance of the capacitor C2 and the electrical resistance of the EL device and circuit.

When light is extracted as a pulse, light other than the peak of the signal is useless and should be eliminated even in view of electrical efficiency. This problem can be avoided by appropriately manipulating the frequency and pulse width of the pulse for controlling the switching. As the discharge time is shortened, the EL pulse width is reduced.

FIG. 7 shows the EL signals before the operation (a) and after the operation (b) when the discharge time was adjusted. However,
The measurement conditions are the same as in FIG. As shown in FIG.
It can be seen that a signal with a short fall time can be obtained. It has been found that the above-described method and operation can provide an EL pulse with fast rise and fall.

Embodiment 2 By driving an EL element using a Bloom line circuit, the driving voltage can be made higher than that of a commonly used driving method. In addition, the rise (response) time to the EL intensity peak tends to be shorter as the drive voltage is increased. FIG. 8 shows EL response time-drive voltage characteristics. However, the EL device emitted light using a Bloom line circuit (C ₂ = 100 nF), and the signal was measured by a photodiode.

The processing of the substrate of the EL device is the same as that of the first embodiment, and the structure is ITO (anode) / α-NPD.
(Hole transport layer 500Å) / Coumarin
e) Almq3 (light-emitting layer 500 °) / Almq3 (light-emitting layer 300 °) / LiF doped with 6 (21 mol%)
(Electron injection layer 10 °) / Al (cathode 600 °).

However, Almq3 is tris (4me
(thyl-8-quinolinolato) alum
inum (III), α-NPD is N, N′-di-
(Α-naphthyl) -N, N′-diphenyl
1-1,1'-biphenyl-4,4'-diam
ine. As shown in FIG. 8, as the driving voltage increases,
The response time of the organic EL tends to exponentially increase. At 50 V, the response time is about 10
μsec. become. From this result, it was proved that pulse light having a fast rise time can be generated by using the Bloom line circuit.

[0049]

As described above, the present invention realizes a high-speed pulsed organic EL device driving device which has a high response and can easily generate and control a specific wavelength and can obtain high luminance by high-voltage driving which can be controlled. The performance and manufacturing efficiency of an organic EL element used for a display device, a liquid crystal display, and the like can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a structure of an optical element having an optical resonance structure of a high-speed pulse EL element driving device according to the present invention.

FIG. 2 is a perspective view showing a schematic structure of a high-speed pulse EL element driving device according to the present invention.

FIG. 3 is an electric circuit diagram of the high-speed pulse EL element driving device of the present invention.

FIG. 4 is a graph showing emission spectra of Production Example 1 and Comparative Example 1 of an EL element.

FIG. 5 is a diagram showing an element 1 and an element 2 of Production Example 2 of an EL element.
3 is a graph showing an emission spectrum of the present invention.

FIG. 6 is a graph showing the result of measuring the relationship between the applied voltage and the EL signal of the device of Example 1.

FIG. 7 is a graph showing a result of measuring a relationship between a pulse frequency and a pulse width of an apparatus of Example 1 and an EL signal.

FIG. 8 is a graph showing the result of measuring EL response time-drive voltage characteristics of the device of Example 2.

Claims (2)

[Claims] 1. An organic layer including a light emitting layer between a transparent electrode mirror as an anode and a metal electrode mirror as a cathode, wherein holes and electrons are injected from the electrode into the light emitting layer to form the light emitting layer. Is an organic electroluminescent device that emits light. The film thickness d between the anode and the cathode is set to m × λ / 2 = n × d (m is an integer, λ is an emission wavelength, and n is an organic The electrode of the organic electroluminescent element, whose emission wavelength can be selected, is set so as to satisfy the refractive index of the layer. A high-speed pulse EL element driving device characterized by generating. 2. An organic layer including a light emitting layer between a transparent electrode mirror as an anode and a metal electrode mirror as a cathode, wherein holes and electrons are injected from the electrode into the light emitting layer to form the light emitting layer. And a film thickness d between the anode and the cathode is set to m × λ / 2 = n × d (m is an integer, λ is an emission wavelength, n
A high-speed pulse EL element driving device, wherein an electric circuit incorporating an organic electroluminescent element capable of selecting a light emission wavelength set so as to satisfy a refractive index unique to an organic layer is a Bloomline circuit.