JP4444775B2 - Light emitting device - Google Patents

Description

The present invention relates to an organic EL (electroluminescence) light emitting element used for, for example, a planar light source and a display element, and more particularly, a plurality of light emitting structures each composed of a pair of electrodes and an organic compound layer group disposed therebetween. The present invention relates to a light emitting device using the laminated organic EL light emitting element.

  Conventionally, an organic EL comprising a transparent electrode formed on a transparent substrate, a counter electrode disposed so as to face the transparent electrode, and an organic compound layer group including at least a light emitting layer and disposed between the electrodes. Light emitting elements are known. In this organic EL element, when a current flows between the transparent electrode and the counter electrode, the light emitting layer included in the organic compound layer group emits light, and the emitted light is extracted through the transparent electrode and the transparent substrate. That is, in the organic EL light-emitting element, the intersection between the transparent electrode and the counter electrode is used as one light-emitting portion, and light emission and non-light emission can be controlled for each light-emitting portion. Note that if a mask having a minute opening is formed between the transparent electrode and the counter electrode, it is possible to narrow the light emitting region and define a minute pixel.

In addition, as one of this type of organic EL light emitting element, as shown in Patent Documents 1, 2, and 3, a stacked organic layer formed by laminating a plurality of light emitting structures composed of the above-described pair of electrodes and organic compound layer groups. An EL light emitting element is also known.
Japanese Patent Laid-Open No. 11-329748 JP 2003-045676 A JP 2000-238325 A

  By the way, since the light emission luminance of the organic EL light emitting element is proportional to the current density, it is necessary to set the current density high to obtain high luminance. In the case of an organic EL light-emitting element with high efficiency, high luminance can be obtained even if this current density is lowered, but the element material currently provided is still insufficient for realizing a significant increase in efficiency. .

  The stacked organic EL light-emitting devices described in Patent Documents 1 and 2 have a plurality of light-emitting structures stacked by arranging an intermediate electrode between a transparent electrode and a counter electrode, and the current density is kept low. It is intended to achieve brightness. However, in these stacked organic EL light emitting devices, the driving voltage is increased K times when the number of stacked layers of the light emitting structure is K as compared with a normal device having a light emitting structure. When this drive voltage is high, a booster circuit is required when the stacked organic EL light emitting element is applied to, for example, a portable display device, which is disadvantageous in terms of cost reduction and downsizing of the display device. .

  In addition, since the stacked organic EL light-emitting devices described in Patent Documents 1 and 2 basically supply current with two electrodes, a transparent electrode and a counter electrode, a phenomenon such as illegal short circuit or insulation in a part of the circuit. When this occurs, there is also a problem that the entire device is in a non-light emitting state.

  In order to cope with the above-described problem, the stacked organic EL light emitting device described in Patent Document 3 applies a pair of an anode and a cathode that overlap each other as an intermediate electrode, and each light emitting structure is dedicated to both ends. The anode and the cathode are provided. According to the configuration of Patent Document 3, it is possible to keep the driving voltage low and to control light emission and non-light emission for each light emitting structure. However, since the number of intermediate electrodes increases, the number of vapor deposition steps increases. This leads to a significant increase in cost of the stacked organic EL light emitting device. Further, in the configuration of Patent Document 3, since the number of intermediate electrodes is large, there is a problem that light absorption in them is large and light extraction efficiency is lowered.

The present invention has been made in view of the above circumstances, and it is possible to control the drive voltage low, control light emission and non-light emission for each light emitting structure, and have high light extraction efficiency and can be formed at low cost. an object of the present invention is to provide a light emission device.

The light emitting device according to the present invention comprises:
One transparent electrode, one or more translucent intermediate electrodes and one counter electrode are spaced apart from each other in this order;
An organic compound layer group formed by laminating a plurality of organic compound layers including at least a light emitting layer is disposed between two adjacent electrodes among the three kinds of electrodes,
In a group adjacent to each other in the organic compound layer group, a stacked organic EL light emitting element having a configuration in which the stacking order of the plurality of organic compound layers is opposite to each other ;
In the light emitting device including a drive circuit for passing a current between at least two adjacent electrodes among the three types of electrodes of the stacked organic EL light emitting element,
The drive circuit includes means for measuring a current value flowing between two adjacent electrodes among the three types of electrodes .

  When a plurality of the intermediate electrodes are provided, they are preferably formed from a common material. Furthermore, it is desirable that the intermediate electrode is formed of a material common to the counter electrode.

  In addition, it is desirable that a plurality of organic compound layer groups respectively disposed between two adjacent electrodes among the above three types of electrodes emit light of the same color.

In this light emitting device, the drive circuit has a function of setting the polarity of each of the three types of electrodes of the stacked organic EL light emitting element to any one of an anode, a cathode, and a non-connected state. Preferably, it is configured.

  In the stacked organic EL light emitting device according to the present invention, in the groups adjacent to each other in the organic compound layer group, the stacking order of the plurality of organic compound layers is opposite to each other. Can be used as an anode or a cathode for the organic compound layer group on both sides thereof. That is, for example, a transparent electrode (anode), a first intermediate electrode (cathode), a second intermediate electrode (anode), and a counter electrode (cathode) are provided, and a first organic compound layer group and a second organic compound layer are provided between the electrodes. In the configuration in which the group and the third organic compound layer group are arranged, the transparent electrode (anode) and the first intermediate electrode (cathode) feed power to the first organic compound layer group, and the first intermediate electrode (cathode) and the second Electric power is supplied to the second organic compound layer group with the intermediate electrode (anode), and electric power is supplied to the third organic compound layer group with the second intermediate electrode (anode) and the counter electrode (cathode). Specifically, the light emitting layer therein can emit light.

  Therefore, the stacked organic EL light emitting device according to the present invention is less expensive because the number of intermediate electrodes can be reduced as compared with the configuration of Reference 3 in which a pair of an anode and a cathode is provided as one intermediate electrode. Can be formed. Further, since the number of intermediate electrodes is small, light absorption in them can be suppressed to a low level, and high light extraction efficiency can be realized.

  The above will be described more specifically. Assuming that the number of stacked layers of the light emitting structure, that is, the number of organic compound layer groups is K, the number of electrodes is increased by (K−1) in the configuration of Patent Document 3 as compared with the stacked organic EL light emitting device according to the present invention. For example, when the number of stacked layers is 7, the number of intermediate electrodes is 6 in the stacked organic EL light emitting device of the present invention, but 12 in the configuration of Patent Document 3. In general, when an electrode is deposited, the metal electrode, the translucent electrode, and the organic material are generally deposited by changing the apparatus in order to avoid performance degradation due to mixing between them. Therefore, when the stacked organic EL light-emitting device of Patent Document 3 is manufactured, the number of times of moving the device in the process of manufacturing between the vapor deposition apparatuses is very large, whereas the stacked organic EL light-emitting device of the present invention is manufactured. In this case, the number of times is halved, so that the time required for production and materials used are greatly reduced, and a significant cost reduction effect can be obtained.

  Further, the transmittance of the electrode constituting the organic EL light emitting element is usually about 85%, and assuming that, the ratio of the light from the organic compound layer group farthest from the transparent electrode lost due to absorption at the electrode is While the structure of Patent Document 3 is 72%, in the case of the stacked organic EL light emitting device of the present invention, it is only 47%, and the light extraction efficiency is greatly improved.

  Further, in the stacked organic EL light emitting device of the present invention, as described above, since one organic compound layer group is uniquely supplied with a pair of electrodes on both sides thereof, the driving voltage is a pair of each. What is necessary is just to set it as the value which can be electrically fed to one organic compound layer group in the meantime for every electrode. That is, no matter how many layers of such a light emitting structure composed of a pair of electrodes and one organic compound layer group are stacked, the drive voltage does not have to be set high according to the number of stacked layers. The drive voltage can be kept low.

  The above will be described more specifically. When the number of stacking stages is 7, in the configurations shown in Patent Documents 1 and 2, the driving voltage is about 7 times and the current is about 1 compared with the stacked organic EL light emitting device of the present invention to obtain the same luminance. / 7. Usually, the driving voltage of the organic EL light-emitting element requires 0 to several V (volt), and therefore, in the configurations shown in Patent Documents 1 and 2, a voltage of ten and several V is required. Therefore, when considering application to a portable device or the like, it is necessary to boost the voltage of the battery. Since the efficiency of this type of booster circuit is about 50% to 80%, the use thereof increases the power consumption and greatly increases the element cost. Since the stacked organic EL light emitting device of the present invention can eliminate the need for such a booster circuit, the power consumption can be reduced correspondingly, and the cost can be reduced.

  Furthermore, in the laminated organic EL light emitting device of the present invention, as described above, one organic compound layer group is configured to emit light independently by a pair of electrodes on both sides thereof. Even if the electrode becomes unusable due to an improper short circuit, insulation, or the like, light emission can be continued using a light emitting structure composed of other normal organic compound layer groups and electrodes. That is, in the stacked organic EL light emitting device of the present invention, even if a certain organic compound layer group or electrode cannot be used due to an improper short circuit or insulation, the entire device does not become impossible to emit light at all.

  Therefore, the stacked organic EL light emitting device according to the present invention is driven and used so as to obtain a predetermined luminance by emitting only one organic compound layer group in a configuration in which, for example, three organic compound layer groups are provided. When one organic compound layer group becomes unable to emit light, another organic compound layer group is sequentially used to achieve a long life. Alternatively, only two of the three organic compound layer groups are driven to emit light to obtain a predetermined luminance, and when one of the used organic compound layer groups becomes unable to emit light, another one organic compound It is also possible to use a layer group, and if one of them becomes incapable of emitting light, the remaining one organic compound layer group can emit light at a higher current to obtain a predetermined luminance. .

  In addition, when a plurality of intermediate electrodes are provided, the work functions are equal to each other if they are formed of a common material. Therefore, different light-emitting structures composed of these intermediate electrodes emit light with the same luminance. Becomes easy. If the intermediate electrode is formed of the same material as the counter electrode, the light emitting structure including the intermediate electrode and the light emitting structure including the counter electrode emit light with the same luminance. It becomes easy to make.

  In addition, the plurality of organic compound layer groups respectively disposed between two adjacent electrodes among the above three types of electrodes may be configured to emit light of different colors depending on the application, or Although it may be configured to emit light of the same color, as described above, when the organic compound layer groups to be used are sequentially replaced one by one as the organic compound layer group goes down, the latter is set as the latter. Is convenient.

  On the other hand, the light emitting device according to the present invention includes a stacked organic EL light emitting element according to the present invention as described above and a current between at least two adjacent electrodes among the three types of electrodes of the stacked organic EL light emitting element. Therefore, at least one organic compound layer group of the stacked organic EL light emitting element can emit light.

  In the light emitting device according to the present invention, in particular, the drive circuit has a function of setting the polarity of each of the three types of electrodes of the stacked organic EL light emitting element to any one of an anode, a cathode, and an unconnected state. In the case of being configured to have, it is possible to arbitrarily select one or a plurality of organic compound layer groups to emit light. Therefore, according to the present light emitting device, as described above, the organic compound layer groups to be used are sequentially changed one by one as the organic compound layer groups are down, or the number of organic compound layer groups to be lit is changed. Is possible at will.

  In the light emitting device according to the present invention, in particular, if the drive circuit includes means for measuring a current value flowing between two adjacent electrodes among the three types of electrodes, the measured current value is obtained. Accordingly, it is possible to easily detect the state of the light emitting structure, such as whether or not the organic compound layer group is down.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a light emitting device according to an embodiment of the present invention. This light emitting device is composed of a stacked organic EL light emitting element 15 and a drive circuit 25 for driving the stacked organic EL light emitting element 15. In the figure, the layer structure of the stacked organic EL light emitting element 15 is schematically shown.

  First, the stacked organic EL light emitting element 15 will be described. The element 15 includes a transparent substrate 1, a transparent electrode 2 formed thereon, and an insulating layer 11 formed thereon and covering a portion other than a predetermined portion of the transparent electrode 2, and further sequentially thereon. First organic compound layer group 10a, first intermediate electrode 4a, second organic compound layer group 10b, second intermediate electrode 5a, third organic compound layer group 10c, third intermediate electrode 4b, fourth organic compound layer group 10d The fourth intermediate electrode 5b, the fifth organic compound layer group 10e, and the counter electrode 3 are formed. That is, the stacked organic EL light emitting device 15 of the present embodiment has four intermediate electrodes and five organic compound layer groups.

  The first organic compound layer group 10a is formed by laminating a hole injection layer 6a, a hole transport layer 7a, a light emitting layer 8a, and an electron transport layer 9a in this order from the transparent electrode 2 side. The second organic compound layer group 10b, the third organic compound layer group 10c, the fourth organic compound layer group 10d and the fifth organic compound layer group 10e are also the hole injection layer 6a, hole transport layer 7a and light emitting layer 8a, respectively. The same layers as those of the electron transport layer 9a are laminated. In the figure, each of the organic compound layer groups 10b, 10c, 10d and 10e is attached to each layer of the first organic compound layer group 10a. The symbol “a” is shown in place of “b”, “c”, “d”, and “e”, respectively. As shown in the drawing, the stacking order of the hole injection layer, the hole transport layer, the light emitting layer, and the electron transport layer is opposite to each other in the adjacent groups of the organic compound layer groups 10a to 10e.

  Hereinafter, an example of a method for producing the stacked organic EL element 15 having the above-described configuration will be described. First, the transparent electrode 2 is formed on the transparent substrate 1. As the material of the transparent electrode 2, a transparent conductor having a work function of 4.5 eV or more is usually used. More specifically, ITO (tin-doped indium oxide), IZO (zinc-doped indium oxide), ZnO (zinc oxide) and those doped with metal are preferably used.

Next, an insulating layer 11 is formed so as to completely cover the transparent electrode 2, and then an opening is formed in a predetermined region of the insulating layer 11 using a known photolithography process. As a material of the insulating layer 11, a general photoresist, photosensitive polyimide, SiO ₂ , SiN _x or the like is used. As the formation method, known spin coating, vapor deposition, sputtering, or the like can be appropriately employed. This insulating layer 11 is for defining a pixel area formed by the opposed portion unit of the transparent electrode 2 and the opposed electrode 3 within a predetermined range by the opening portion, and has a light shielding property. desirable. Moreover, when there is no need to define a pixel area as described above, it can be omitted.

  Next, each layer of the first organic compound layer group 10a is formed so as to cover all the openings of the insulating layer 11. In the first organic compound layer group 10a, as described above, the hole injection layer 6a, the hole transport layer 7a, the light emitting layer 8a, and the electron transport layer 9a are formed in this order from the transparent electrode 2 side. For forming these layers, for example, vapor deposition methods using metal masks, CVD methods, ink jet methods, and the like, all methods known as layer forming methods for organic EL light emitting elements are applicable.

  Next, the first intermediate electrode 4a is formed so as to cover all the openings of the insulating layer 11. The first intermediate electrode 4a and other intermediate electrodes are formed using a material having a work function as small as possible in order to improve the ease of electron injection. Examples of such materials include simple substances or compounds of alkali metals such as Ca, F, Li, and Na, or alloys such as Al: Li, Al: Se, Mg: Ag, and Mg: In. The first intermediate electrode 4a and other intermediate electrodes are preferably thin films of about 40 nm or less in order to ensure translucency.

  Next, the second organic compound layer group 10b is formed in the same manner as the first organic compound layer group 10a. As described above, the stacking order of the layers in the second organic compound layer group 10b is opposite to that in the first organic compound layer group 10a. That is, these layers are formed in the order of the electron transport layer 9b, the light emitting layer 8b, the hole transport layer 7b, and the hole injection layer 6b from the transparent electrode 2 side.

  Thereafter, the second intermediate electrode 5a, the third organic compound layer group 10c, the third intermediate electrode 4b, the fourth organic compound layer group 10d, the fourth intermediate electrode 5b, the fifth organic compound layer group 10e, and the counter electrode 3 are similarly used. By forming by the method, the stacked organic EL light emitting device 15 of the present embodiment is obtained.

  Next, the drive circuit 25 will be described. As shown in the figure, the drive circuit 25 includes a switching unit 20a connected to the transparent electrode 2, a switching unit 20b connected to the first intermediate electrode 4a, a switching unit 20c connected to the second intermediate electrode 5a, A switching unit 20d connected to the third intermediate electrode 4b; a switching unit 20e connected to the fourth intermediate electrode 5b; and a switching unit 20f connected to the counter electrode 3. Each of these switching units 20a to 20f can be selectively set to either a state in which each electrode is connected to the anode of the DC power source 21, a state in which the electrode is connected to the cathode, or a state in which neither electrode is connected (not connected). It is said that.

  Also, between the first intermediate electrode 4a and the switching unit 20b, between the second intermediate electrode 5a and the switching unit 20c, between the third intermediate electrode 4b and the switching unit 20d, and between the fourth intermediate electrode 5b and the switching unit 20e, Ammeters 22b, 22c, 22d, and 22e are respectively interposed between the anode terminals of the DC power supply 21 and the switching units 20a to 20f (before branching to the switching units 20a to 20f). Is also provided with an ammeter 23.

  The stacked organic EL light emitting element 15 is connected to the drive circuit 25 including the switching units 20a to 20f as described above, whereby any one or a plurality of the five organic compound layer groups 10a to 10e are DC-connected. It can be connected to the power source 21 to emit light. That is, for example, as shown in FIG. 1, the transparent electrode 2 is connected to the anode terminal of the DC power source 21, while all the intermediate electrodes 4a, 5a, 4b and 5b and the counter electrode 3 are connected to the cathode of the DC power source 21. By connecting to the terminal, it is possible to generate a potential difference only between the transparent electrode 2 and the first intermediate electrode 4a to feed power to the first organic compound layer group 10a, and to emit only the light emitting layer 8a. This light emission passes through the transparent electrode 2 and the transparent substrate 1 and is emitted outside the device. In this case, the current flowing through the first organic compound layer group 10a can be measured by the ammeter 22b.

  Further, for example, the switching unit 20a is operated from the state of FIG. 1 to connect the first intermediate electrode 4a to the cathode terminal of the DC power supply 21, and the switching units 20c and 20d are operated to operate the second intermediate electrode 5a and the third intermediate electrode 5a. By connecting the intermediate electrode 4b to the anode terminal of the DC power source 21, a potential difference is generated only between the first intermediate electrode 4a and the second intermediate electrode 5a to supply power to the second organic compound layer group 10b and to emit light. Only the layer 8b can emit light. In this case, the current flowing through the second organic compound layer group 10b can be measured by the ammeter 22b or 22c.

  Further, by operating the switching units 20c and 20d from the state of FIG. 1 to connect the second intermediate electrode 5a and the third intermediate electrode 4b to the anode terminal of the DC power source 21, the transparent electrode 2 and the first intermediate electrode 4a And a potential difference is generated between the first intermediate electrode 4a and the second intermediate electrode 5a to supply power to the first organic compound layer group 10a and the second organic compound layer group 10b, and the light emitting layers 8a And 8b can emit light. In this case, the total current flowing through the first organic compound layer group 10a and the second organic compound layer group 10b can be measured by the ammeter 22b.

  In this way, the first organic compound layer group 10a and the second organic compound layer group 10b can be supplied with power by sharing the first intermediate electrode 4a in the organic compound layer groups 10a and 10b. This is because the order is opposite to each other.

  As described above, when any one or more of the five organic compound layer groups 10a to 10e are selected to emit light, the organic compound layer group that does not emit light is stored as a backup, for example, light emission If the organic compound layer group being brought down goes down, it is possible to use the organic compound layer group stored as a backup in place of the downed one. In such a case, switching of the switching units 20b to 20f may be performed manually, or the driving current for each organic compound layer group indicated by the ammeters 22b to 22e and the total current indicated by the ammeter 23 It is also possible to define an abnormal current state in advance from the relationship and automatically switch the switching units 20b to 20f if an abnormal current state is detected.

  The stacked organic EL light emitting device of this embodiment can be formed at a lower cost because the number of intermediate electrodes can be reduced as compared with a configuration in which a pair of an anode and a cathode is provided as one intermediate electrode. Become. Further, since the number of intermediate electrodes is small, light absorption in them can be suppressed to a low level, and high light extraction efficiency can be realized.

  Furthermore, the stacked organic EL light emitting device of this embodiment has a configuration in which a single organic compound layer group 10a, 10b, 10c, 10d or 10e is independently fed with a pair of electrodes on both sides thereof. The driving voltage may be a value that can supply power to one organic compound layer group between each pair of electrodes. In other words, no matter how many light emitting structures are composed of such a pair of electrodes and one organic compound layer group 10a, 10b, 10c, 10d or 10e, the driving voltage is set high according to the number of layers. Since it does not have to be, it is possible to keep the drive voltage low.

  In addition, although the number of lamination | stacking of the organic compound layer group of this embodiment is 5, this number of lamination | stacking is not restricted to this example. However, considering the translucency of the electrodes and organic materials, it can be said that it is generally desirable to use 20 groups or less. The number of organic compound layer groups that emit light simultaneously is not limited to 1 or 2 described above, and an appropriate number can be set according to the application.

1 is a schematic configuration diagram showing a light emitting device according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Transparent electrode 3 Counter electrode 4a, 4b, 5a, 5b Intermediate electrode 6a, 6b, 6c, 6d, 6e Hole injection layer 7a, 7b, 7c, 7d, 7e Hole transport layer 8a, 8b, 8c, 8d, 8e Light emitting layer 9a, 9b, 9c, 9d, 9e Electron transport layer
10a, 10b, 10c, 10d, 10e Organic compound layer group
15 Stacked organic EL light emitting device
20a, 20b, 20c, 20d, 20e, 20f Switching unit
21 DC power supply
22b, 22c, 22d, 22e, 23 Ammeter
25 Drive circuit

Claims (5)

One transparent electrode, one or more translucent intermediate electrodes and one counter electrode are spaced apart from each other in this order;
An organic compound layer group formed by laminating a plurality of organic compound layers including at least a light emitting layer is disposed between two adjacent electrodes among the three kinds of electrodes,
In the group adjacent to each other in said organic compound layer group, and the stacked organic EL light emitting device which have a structure in which lamination order of the plurality of organic compound layers are opposite to each other,
In the light emitting device including a drive circuit for passing a current between at least two adjacent electrodes among the three types of electrodes of the stacked organic EL light emitting element,
The light emitting device, wherein the drive circuit includes means for measuring a current value flowing between two adjacent electrodes among the three types of electrodes. The light emitting device according to claim 1, wherein a plurality of the intermediate electrodes are provided and are formed of a common material. The light emitting device according to claim 1, wherein the intermediate electrode is made of a material common to the counter electrode. 4. The structure according to claim 1, wherein a plurality of organic compound layer groups respectively disposed between two adjacent electrodes among the three types of electrodes emit light of the same color. 5. The light emitting device according to claim 1. Claim 1, wherein the driving circuit, the polarity of each of the three electrodes of the stacked organic EL device, an anode, and having a function of setting in any of the states of the cathode and unconnected 5. The light emitting device according to any one of 4 to 4 .

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