JP2005085486A - Organic organic electroluminescent device, its driving method and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL device with color display function, having extended service life of a light emitting device and maintaining high luminance and high coloring of a screen for a long period of time. <P>SOLUTION: The organic electroluminescent device comprises first and second electrodes 10, 11 arranged oppositely to each other, first and second light emitting layers 12a, 12b held between the first and second electrodes 10, 11, having respective light emitting spectrums different to each other, and voltage applying means 13 capable of applying either positive or negative voltage to the first and second electrodes 10, 11. Voltage is applied to the organic electroluminescent device by inverting the polarity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescence device, a driving method thereof, and an electronic apparatus including the organic electroluminescence device.

  An organic electroluminescence device (hereinafter referred to as an organic EL device) is expected as a next-generation display device. The organic EL device has a light emitting element having a structure in which a light emitting layer containing a light emitting organic compound is sandwiched between an anode layer and a cathode layer. Holes injected from the anode layer side and holes injected from the cathode layer side. The light emission phenomenon is utilized when the organic compound is recombined in the light emitting layer and the organic compound is deactivated from the excited state.

As a color display method in the organic EL device, for example, there is a method in which sub-pixels are configured by sequentially arranging organic molecules that emit light of the three primary colors of light. As an example of such a color display method, functional layers having different emission colors are arranged horizontally across an insulating layer, and one of the layers is caused to emit light by switching a forward bias voltage and a reverse bias voltage. (For example, refer to Patent Document 1).
JP 2000-331781 A

By the way, in a polymer EL device using a polymer material, it is known that among the three primary colors of red, blue, and green, a blue light-emitting element has a short light emission lifetime (luminance half-life). When the colors are arranged in the horizontal direction as in the above method, for example, when the function of a blue light emitting element is deteriorated, there is no way to save the light emitting element, and the luminance in the display screen area including the light emitting element There is a problem that efficiency is lowered.
Accordingly, an object of the present invention is to extend the life of a light emitting element and maintain high luminance and color development on a screen for a long time in an organic EL device having a color display function.

  In order to solve the above problems, the present inventors have conducted intensive studies, and as a result, the materials forming the light-emitting layer have different mobilities for holes and electrons. It was found that the bonding position was biased. Therefore, a first light-emitting layer and a second light-emitting layer having different emission spectra are stacked, and the first and second light-emitting layers are operated by switching the polarities of the electrodes. I came to the view that I could do it.

  That is, the organic electroluminescence device of the present invention includes a first electrode and a second electrode arranged opposite to each other, a first electrode and a second electrode sandwiched between the first electrode and the second electrode, and having different emission spectra. And a voltage applying unit capable of applying a positive or negative voltage to each of the first light emitting layer and the second light emitting layer, and each of the first electrode and the second electrode. Features. If both positive and negative voltages can be applied, color can be developed in either the first light-emitting layer or the second light-emitting layer by reversing the polarity. Can be extended.

  The above-described organic electroluminescence device includes either an electron or a hole between the first electrode and the first light-emitting layer and between the second electrode and the second light-emitting layer. It is preferable that a carrier injection layer capable of acting also on the substrate is provided. The ability of the carrier injection layer to act on both electron and hole carriers effectively promotes the injection of electrons and holes from the electrode to the light-emitting layer even when the polarity of the electrode is reversed. Thus, the first light emitting layer and the second light emitting layer can be colored equally.

  The organic electroluminescence device is further provided between the first light emitting layer and the carrier injection layer on the first electrode side, and between the second light emitting layer and the carrier injection layer on the second electrode side, respectively. A carrier transport layer that can act on both carriers of electrons and holes may be provided. Since the carrier transport layer can also act on electrons and holes, both carriers are more efficiently transported between the electrode and the light emitting layer even when the polarity of the electrode is reversed.

The carrier transport layer preferably contains a hole transport compound and an electron transport compound. By adopting such a configuration, it is possible to ensure the action of electrons and holes in both layers, and when any of the first light emitting layer and the second light emitting layer is colored. Similar effects can be obtained.
In the organic electroluminescence device, the first electrode and the second electrode, the pair of carrier injection layers, and the pair of carrier transport layers are preferably made of the same material. By using the same material, the first light-emitting layer and the second light-emitting layer have the same light emission rate even if the manufacturing process is simplified and the polarity of the electrodes is reversed.

As a method of driving the organic electroluminescence device, a voltage can be applied with the polarity reversed to the first electrode and the second electrode that can inject electrons and holes. By reversing the polarity and applying a voltage, the recombination site of electrons and holes can be switched between the first light-emitting layer and the second light-emitting layer, and any layer can be colored. In addition, no complicated wiring is required, and there is no difficulty in manufacturing.
An electronic device provided with the above-described organic electroluminescence device is good because it can emit two colors per light emitting element without changing the film thickness, and the life of the light emitting element is long.

Hereinafter, although an embodiment of the present invention is illustrated and explained, the present invention is not limited to this.
FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of the present invention.
The organic EL device 1 shown in FIG. 1 is sandwiched between a first electrode 10 and a second electrode 11, which are arranged to face each other, and between the first electrode 10 and the second electrode 11, and different emission spectra. The first light-emitting layer 12a and the second light-emitting layer 12b, and the driving circuit (voltage applying means) 13 connected to the first electrode 10 and the second electrode 11 are configured. The drive circuit 13 is characterized by being able to apply a positive or negative voltage to each of the electrodes 10 and 11. A transparent substrate 14 is disposed below the second electrode 11, and the light emission phenomenon in the light emitting layers 12 a and 12 b reaches the observer through the transparent substrate 14.

As a material for forming the light emitting layers 12a and 12b, the first light emitting layer 12a and the second light emitting layer 12b are configured to have different emission spectra. For example, any combination of the three primary colors of red, blue, and green may be used.
As a material for forming a light emitting layer that emits red light, for example, CN-PPV shown as the following compound 1 is used.

  As the green light emitting layer material, for example, the following compound 2 is used.

  As the blue light emitting layer material, for example, F8 (polydioctylfluorene) shown as the following compound 3 is preferably used.

The electrodes 10 and 11 can transport both electrons and holes when the polarity is reversed. In order to maintain the carrier transport rate when the polarity is reversed, it is preferable to form both electrodes with the same material. Examples of the material forming the electrodes 10 and 11 include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO (zinc oxide), SnO (tin oxide), and the like.
When the electrodes 10 and 11 are formed of a transparent electrode material such as ITO, both the electrodes are transparent and suitable for a display such as a window glass.

The film thicknesses of the light emitting layers 12a and 12b are each preferably 10 to 150 nm, and the total film thickness of both layers is preferably 30 to 300 nm.
Each film thickness of the electrodes 10 and 11 is preferably 10 to 500 nm, and more preferably 50 to 200 nm. In consideration of symmetry when the polarity is reversed, it is desirable to form the first electrode 10 and the second electrode 11 with the same film thickness.

The light emitting layers 12a and 12b can be formed by sequentially applying the light emitting layers 12a and 12b on the electrode 11 by an ink jet (droplet discharge) method. At this time, since the forming material needs to be made into a solution, the above-described material may be appropriately dissolved in a solvent and discharged from an inkjet head. About the light emitting layers 12a and 12b, the compound which is the material for each color mentioned above can be made into the liquid material for light emitting layer formation by melt | dissolving in solvents, such as a cyclohexylbenzene, for example.
The electrodes 10 and 11 can be obtained by forming them using a known method such as sputtering and patterning them into a predetermined shape.

In this embodiment, a driving method of the organic EL device of the present invention will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view showing a case where a voltage is applied so that the first electrode 10 becomes an anode (a) and a case where a voltage is applied so that the second electrode 11 becomes an anode (b). is there.
As shown in FIG. 2A, for example, when a voltage is applied so that the first electrode 10 becomes an anode, recombination of electrons and holes is caused by the first electrode 10 and the first light emitting layer 12a. Occurs near the interface. On the other hand, when a voltage is applied so that the electrode 11 becomes an anode, the recombination occurs near the interface between the second electrode 11 and the second light emitting layer 12b, as shown in FIG.

In order to switch the polarity, for example, a positive voltage is applied to the first electrode 10 to make the first electrode 10 an anode, and conversely, the first electrode 10 is made a cathode, that is, the second electrode When the electrode 11 is used as an anode, a negative voltage may be applied to the first electrode 10.
With such a driving method, both the light emitting layers 12a and 12b can emit light. The color display method of the organic EL device using this effect will be described in detail later.

As shown in FIG. 3, the organic EL device of the present invention includes a carrier injection layer 15 between the first electrode 10 and the first light emitting layer 12a and between the second electrode 11 and the second light emitting layer 12b, 16 may be arranged. The carrier injection layers 15 and 16 can act on both carriers of electrons and holes.
The carrier injection layers 15 and 16 include metal halides such as LiF (lithium fluoride) and MgF2 (magnesium fluoride), and metal oxides such as Li2O (lithium oxide), MgO (magnesium oxide), and Al2O3 (aluminum oxide). An insulating layer made of or the like is formed. The thickness is preferably 0.1 to 10 nm, more preferably 5 nm or less. By forming such an ultra-thin insulating layer between the electrodes 10 and 11 and the light emitting layer 12, when the polarity is reversed, both carriers of electrons and holes are transferred from the electrodes 10 and 11 to the light emitting layer 12a. , B can be efficiently injected.

As a manufacturing method, when manufacturing the organic EL device 1 described above, the carrier injection layer 16 may be formed next to the second electrode 11 and the carrier injection layer 15 may be formed next to the light emitting layer 12a by a vacuum evaporation method.
The carrier injection layer 15 and the carrier injection layer 16 are preferably made of the same material. If both layers are formed of the same material, the manufacturing convenience is good, and a constant carrier injection efficiency can be maintained for any polarity. Therefore, the first light emitting layer 12a and the second light emitting layer 12 Equivalent color development efficiency can be obtained in the light emitting layer 12b.

Further, as shown in FIG. 4, the organic EL device described above includes a carrier transport layer 17 between the first light emitting layer 12a and the carrier injection layer 15 and between the second light emitting layer 12b and the carrier injection layer 16, respectively. , 18 may be included. The carrier transport layers 17 and 18 can act on electrons and holes, like the carrier injection layers 15 and 16.
The material forming the carrier transport layers 17 and 18 preferably contains an electron transport compound and a hole transport compound. Specifically, it is formed by dispersing an electron transporting compound in a hole transporting polymer (hole transporting compound) or dispersing a hole transporting compound in an electron transporting polymer (electron transporting compound).
Furthermore, it is preferable that both layers 17 and 18 are formed from the same material.

Examples of the hole transporting polymer include PVK (polyvinyl carbazole), and examples of the electron transporting compound include PBD (2- (4-Biphenylyl) -5- (4-tert-buthylphenyl) 1,3, Oxadiazole derivatives such as 4-oxadiazole).
Examples of the electron transporting polymer include MEH-PPV. Examples of the hole transporting compound include α-NPD (4,4′-bis [N- (1-napthyl) -N-phenyl-amino]. biphenyl). These compounds are preferably prepared so that the electron transport property: hole transport property is 1: 1.

As a manufacturing method, the above materials can be made into a solution using cyclohexylbenzene or the like as a solvent, and can be applied using an ink jet (droplet discharge) method. At that time, it is desirable that the film thickness be 5 to 500 nm, more preferably 100 nm or less.
By arranging such carrier transport layers 17 and 18, there is an effect of improving the carrier transport efficiency between the electrodes 10 and 11 and the light emitting layers 12 a and b.
As a method for manufacturing the carrier transport layers 17 and 18, a method using an inkjet is exemplified, but the method is not limited to this, and depending on the forming material, a method such as a vapor deposition method, a spin coating method, or a dip method may be used. Good.

  In the present embodiment, a back (bottom) emission type in which a transparent substrate 14 is provided below the second electrode 11 is used. However, in the organic EL device of the present invention, the transparent substrate is disposed above the first electrode 10. The top emission type is also applicable. Moreover, if both electrodes 10 and 11 are manufactured using transparent materials, such as ITO as mentioned above, it will become a display apparatus suitable for the display in places, such as a window glass and a windshield.

Next, an example of the color display method by the organic EL device described above is shown in FIG.
The pixel display area shown in FIG. 5 is composed of three parallel subpixels 3, 4, and 5. Each of the subpixels 3, 4, and 5 includes light emitting elements 30, 40, and 50 and driving circuits 31, 41, and 51 that drive the light emitting elements. The light emitting elements 30, 40, and 50 have at least a first electrode and a second electrode that are arranged opposite to each other, and two light emitting layers that are sandwiched between these electrodes and have different emission spectra. The drive circuits 31, 41, 51 can apply either positive or negative voltage to the light emitting elements to be connected.

In FIG. 5, when a forward bias voltage is applied, the light emitting elements 30, 40, and 50 are colored in R (red), G (green), and B (blue), respectively. On the other hand, when a reverse bias voltage is applied to the light emitting elements 30, 40, 50, G (green), B (blue), and R (red) are colored.
For example, it is assumed that the forward bias voltage is continuously applied, the B (blue) light emitting layer of the light emitting element 50 is consumed, and the luminance is lowered. The polarity applied to the electrode of the light emitting element 50 can be reversed, and the second light emitting layer R (red) can be colored. In accordance with this, the light-emitting elements 30 and 40 are also reversed in polarity and reverse-biased to obtain G (green) and B (blue) displays, respectively. Further, when it is not necessary to maintain the three primary colors, the forward bias may be continuously used in the light emitting elements 30 and 40. Also in this case, the luminance efficiency in the pixel display region shown in FIG. 5 can be maintained by utilizing the second light emitting layer R (red) of the light emitting element 50.

Finally, an example of the electronic device of the present invention will be described. FIG. 5 shows a mobile phone, which includes the above-described organic EL device. The mobile phone 2 includes a mobile phone body 20 and a color display unit 21 including the organic EL device. Since the color display unit 21 is composed of the organic EL device described above, it is an extremely thin film and can maintain good color development and high luminance for a long time.
The electronic device of the present invention includes a mobile phone and various other electronic display devices, such as a personal computer, a TV, a car navigation device, an electronic notebook, a calculator, electronic paper, a wristwatch type electronic device, and a touch panel. Equipment. The display device can be applied to both an active matrix and a passive matrix. Moreover, any organic material may be used among a low molecule and a polymer.

It is a schematic sectional drawing which shows an example of embodiment of the organic electroluminescent apparatus of this invention. It is a schematic sectional drawing which shows an example of embodiment of the organic electroluminescent apparatus of this invention. It is a schematic sectional drawing which shows an example of embodiment of the organic electroluminescent apparatus of this invention. It is a schematic sectional drawing which shows an example of embodiment of the organic electroluminescent apparatus of this invention. It is a schematic structure figure showing an example of an embodiment of an organic EL device of the present invention. It is a perspective view which shows an example of the electronic device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic electroluminescent apparatus, 10 1st electrode, 11 2nd electrode, 12a 1st light emitting layer, 12b 2nd light emitting layer, 13, 31, 41, 51 Drive circuit (voltage application means), 15, 16 Carrier injection layer, 17, 18 Carrier transport layer.

Claims (9)

  A first light-emitting layer and a second light-emitting layer, which are sandwiched between the first electrode and the second electrode, which are arranged opposite to each other, and which have a light emission spectrum different from each other; And an organic electroluminescence device comprising voltage applying means capable of applying a positive or negative voltage to each of the first electrode and the second electrode.   2. The organic electroluminescence device according to claim 1, wherein the first electrode and the second electrode are made of the same material.   Carriers that can act on both electrons and holes between the first electrode and the first light-emitting layer and between the second electrode and the second light-emitting layer. 3. The organic electroluminescence device according to claim 1, wherein an injection layer is provided.   4. The organic electroluminescence device according to claim 3, wherein the pair of carrier injection layers are made of the same material.   Between the first light-emitting layer and the carrier injection layer on the first electrode side and between the second light-emitting layer and the carrier injection layer on the second electrode side, either electrons or holes 5. The organic electroluminescence device according to claim 3, further comprising a carrier transport layer capable of acting on carriers.   6. The organic electroluminescent device according to claim 5, wherein the pair of carrier transport layers are made of the same material.   The organic electroluminescence device according to claim 5 or 6, wherein the carrier transport layer contains a hole transporting compound and an electron transporting compound.   A method for driving an organic electroluminescence device according to claim 1, wherein a voltage is applied to a first electrode and a second electrode that can inject electrons and holes by inverting the polarity. A driving method of an organic electroluminescence device, wherein the organic electroluminescence device is applied. An electronic apparatus comprising the organic electroluminescence device according to claim 1.

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