JP2010147257A - Organic el device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL device that is thinned while ensuring moisture barrier properties, and suppresses the occurrence of short circuit by self repairing. <P>SOLUTION: An organic EL element 3 includes a translucent electrode 4, a functional layer 7 formed on the translucent electrode 4 and including at least an organic light emitting layer, and a back electrode 9 formed on the functional layer 7. A barrier layer 8 having at least the moisture barrier properties are formed between the functional layer 7 and the back electrode 9 or in the back electrode 9. The barrier layer 8 has a film thickness of ≤50 nm. The barrier layer 8 is formed between the functional layer 7 and the back electrode 9, and has a conduction band energy level of 2.0-5.5 eV. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic EL (electroluminescence) element, and particularly relates to reduction of display failure and suppression of voltage drop due to a short circuit of an organic EL element.

  Conventionally, as a light emitting element, a transparent electrode made of ITO (Indium Tin Oxide) or the like, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and the like on a translucent support substrate made of a glass material. There is known an organic EL element configured by sequentially laminating an organic layer and a back electrode made of aluminum (Al) or the like (see, for example, Patent Document 1).

  An organic EL panel using an organic EL element has recently attracted attention as a self-luminous flat display device, has less viewing angle dependency than a liquid crystal display device, has a high contrast ratio, and can be thinned. R & D is being carried out in various places because of such advantages.

On the other hand, in the organic EL element, dark areas and dark spots that become non-light emitting parts are generated and grow by adsorbing moisture. Therefore, the organic EL element is sealed by bonding the sealing substrate to the support substrate, Further, a method such as disposing a hygroscopic agent that captures moisture in the sealed space is employed (see, for example, Patent Document 2). However, the method of including the hygroscopic agent is disadvantageous in reducing the thickness because of the physical thickness of the hygroscopic agent. On the other hand, as a method advantageous for thinning, a method of forming a barrier film made of silicon dioxide (SiO ₂ ), silicon nitride (SiN) or the like on the organic EL element by PE-CVD method or sputtering method has been conventionally used. It is known (see, for example, Patent Document 3).

On the other hand, in the manufacture of organic EL elements, the electrodes are short-circuited due to defects in the manufacturing process, high leak sites, etc. due to the structure in which both electrodes are stacked, resulting in a non-light emitting portion, resulting in a reduction in display quality. For example, Patent Document 4 discloses a self-repairing method in which a reverse bias voltage is applied during a non-light-emission period in order to eliminate a portion (defective part) that causes a short circuit as a solution to the problem. Yes. Further, for example, Patent Document 5 discloses a technique such as repair aging in which a defective portion is removed (destroyed) in advance by applying a reverse bias voltage before product shipment so that a short circuit does not occur.
JP 2000-68057 A JP 2002-198170 A JP-A-5-36475 JP 2003-282249 A JP 2005-91717 A

  However, in the so-called film sealing that covers the organic EL element with a barrier film to prevent intrusion of moisture, there is a problem that the self-repair is not sufficiently performed in the above-described self-repair or repair aging. In other words, self-repair is achieved by the back electrode at the defective part being dissolved, vaporized or scattered by Joule heat, but when the barrier film is formed on the back electrode, the back electrode must be removed together with the barrier film. Without Joule heat. For this reason, there is a problem that a short circuit occurs due to the failure of self-repair and as a result, the display quality deteriorates.

  In view of such a problem, an object of the present invention is to provide an organic EL element that can secure moisture barrier properties and can be thinned, and further can perform self-repair and suppress occurrence of a short circuit.

  In order to solve the above problems, the present invention includes a translucent electrode, a functional layer formed on the translucent electrode and including at least an organic light emitting layer, and a back electrode formed on the functional layer. An organic EL element provided, wherein a barrier layer having at least a moisture barrier property is formed between the functional layer and the back electrode.

  The barrier layer has a thickness of 50 nm or less.

  The barrier layer is formed between the functional layer and the back electrode, and has a conduction band energy level of 2.0 to 5.5 eV.

  The barrier layer is formed between the functional layer and the back electrode, and the back electrode is formed so as to be in contact with the barrier layer, and a work function thereof is higher than a conduction band energy level of the barrier layer. It has a low metal layer.

  The barrier layer is formed in the back electrode, and the back electrode has a metal layer that is formed so as to sandwich the barrier layer and whose work function approximates the conduction band energy level of the barrier layer. It is characterized by that.

  The barrier layer is made of nitride or oxide.

  The present invention relates to an organic EL element, which can secure a moisture barrier property and can be thinned, and further can perform self-repair and suppress occurrence of a short circuit.

  FIG. 1 is a diagram showing a first embodiment in which the present invention is applied to a passive drive type organic EL panel 1. The organic EL panel 1 is formed by forming an organic EL element 3 on a support substrate 2 and applies self-repair by applying a reverse bias voltage in order to eliminate a portion (defective part) that causes a short circuit of an electrode. Is what you do. The self-repairing method may be a method in which a reverse bias voltage is applied during a non-emission period in driving of the organic EL panel 1, and a repair aging in which a reverse bias voltage is applied in the manufacturing process of the organic EL panel 1. You may perform a process. Further, a sealing member that hermetically covers the organic EL element 3 is provided on the support substrate 2, but the sealing member is omitted in FIG. 1.

  The support substrate 2 is made of a rectangular transparent glass material and is an electrically insulating substrate.

  As shown in FIGS. 1 and 2, the organic EL element 3 includes a plurality of light-transmitting electrodes 4 that are formed in a line and serve as signal electrodes, an insulating layer 5, a partition wall 6, a functional layer 7, and a barrier layer. 8 and a back electrode 9 which is formed in a plurality of lines so as to intersect the translucent electrode 4 and serves as a scanning electrode. In the organic EL element 3, the intersection of the translucent electrode 4 and the back electrode 9 becomes a light emitting pixel, and a plurality of the light emitting pixels are arranged in a matrix to form a display area (light emitting area) for performing a predetermined display. The electrodes 9 are sequentially scanned to emit light. In this embodiment, the translucent electrode 4 serves as an anode that supplies holes, and the back electrode 9 serves as a cathode that supplies electrons.

  The translucent electrode 4 serves as an anode for injecting holes into the functional layer 7, and after forming a translucent conductive material such as ITO on the support substrate 2 by means of sputtering or the like, It is formed in a plurality of lines so as to be substantially parallel to each other by a photolithography method or the like.

  The insulating layer 5 is made of, for example, a polyimide-based electrically insulating material, and is formed on the translucent electrode 4 so as to be positioned between the translucent electrode 4 and the back electrode 9. It has an opening to be exposed. The insulating layer 5 prevents a short circuit between the translucent electrode 4 and the back electrode 9 serving as electrodes and makes the outline of each light emitting pixel clear.

  The partition wall 6 is made of, for example, a phenol-based electrically insulating material and is formed on the insulating layer 5. The partition wall portion 6 is formed by means such as photolithography so that the cross section thereof has an overhang shape such as a reverse taper shape with respect to the insulating layer 5. A plurality of partition walls 6 are formed at equal intervals in a direction orthogonal to the translucent electrode 4. The partition wall 6 forms the functional layer 7, the barrier layer 8, and the back electrode 9 in a line shape by overhanging when the functional layer 7, the barrier layer 8, and the back electrode 9 are formed from above by a vapor deposition method, a sputtering method, or the like. A structure to be separated is obtained.

  The functional layer 7 includes a plurality of layers having at least an organic light emitting layer and is formed on the translucent electrode 4. In the present embodiment, the functional layer 7 is formed by sequentially laminating a hole injection layer, a hole transport layer, an organic light emitting layer, an electron transport layer, and an electron injection layer by means such as vapor deposition. The organic light emitting layer may be a laminate of a plurality of layers.

The barrier layer 8 is formed on the functional layer 7 (the electron injection layer in the first embodiment) and has at least a moisture barrier property that blocks moisture. In the first embodiment, the barrier layer 8 is formed by layering silicon nitride (SiN) by means such as sputtering, vacuum deposition using EB (electron beam), or CVD capable of forming a thin film. . As the barrier layer 8, a nitride such as silicon nitride oxide (SiON), or an oxide such as zirconium oxide (ZrO ₂ ), hafnium oxide (HfO ₂ ), or titanium oxide (TiO ₂ ) may be used.

  The back electrode 9 serves as a cathode for injecting electrons into the functional layer 7, and in the first embodiment, aluminum (Al) is formed into a plurality of lines by means such as sputtering or vacuum deposition. It becomes. Each line of the back electrode 9 is formed so as to intersect (intersect) each line of the translucent electrode 4 substantially at a right angle. Further, the back electrode 9 is electrically connected to the connection wiring portion 10. The connection wiring part 10 is formed with the translucent electrode 4, and consists of ITO of the same material. As the back electrode 9, a metallic conductive material having a higher conductivity than the translucent electrode 4 is used. In addition, magnesium (Mg), cobalt (Co), lithium (Li), gold (Au), copper (Cu), zinc (Zn), or an alloy thereof may be used.

  In the organic EL element 3 according to the first embodiment, the barrier layer 8 having a moisture barrier property is formed between the functional layer 7 and the back electrode 9, so that the organic EL element 3 is sealed in a sealing space for sealing the organic EL element 3. Intrusion of moisture into the organic EL element 3 can be suppressed without providing an adsorbent, and the organic EL panel 1 can be thinned without the physical thickness of the adsorbent as in the prior art. Become. In addition, since a physical film that covers the back electrode 9 is not formed as in the prior art, application of the reverse bias voltage can sufficiently eliminate the defective portion, and the self-repair can be carried out satisfactorily to prevent short-circuiting. Occurrence can be suppressed.

  Here, when SiN which is an insulating material is used for the barrier layer 8, it can be considered that the barrier layer 8 inhibits carrier conduction to the functional layer 7. The light emission of the organic EL element 3 was confirmed by setting the thickness to several nm to 50 nm. This is because, for example, SiN is a material having a high non-dielectric constant of about 5.3 to 7 and a small voltage drop, and the organic EL element 3 normally emits light at 0.4 MV / cm to 0.8 MV / cm. Since a strong electric field is applied to cause light emission, SiN or the like tends to generate Fowler-Nordheim Tunneling current (hereinafter referred to as FN tunnel current), and this FN tunnel current seems to contribute to light emission. Therefore, in particular, if a material having a high relative dielectric constant and a conduction band energy level that approximates the work function of the back electrode 9 is used for the barrier layer 8, good device characteristics (such as luminance, light emission efficiency, or lifetime) can be obtained. Obtainable. In the first embodiment, the work function of Al used for the back electrode 9 is 4.3 eV, and it is particularly desirable that the conduction band energy level of the barrier layer 8 be 2.0 to 5.5 eV. SiN, SiON, ZrO2, HfO2, and TiO2 have a high relative dielectric constant, and their conduction band energy levels are about 2.8 eV, 2.0 to 2.8 eV, 3.8 eV, 3.7 eV, and 5 eV from the vacuum level, respectively. .2 eV, which satisfies this condition.

  Next, a second embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the part same as the above-mentioned 1st embodiment, or an equivalent part, and detailed description is abbreviate | omitted.

  The second embodiment is different from the first embodiment in that the back electrode 9 serving as a cathode has a laminated structure of a first metal layer 9a and a second metal layer 9b.

  The first metal layer 9a is formed on the barrier layer 8, and in the second embodiment, calcium (Ca) is formed in layers by means such as vacuum deposition. The first metal layer 9a has a low work function, and in particular, the work function is preferably lower than the conduction band energy level of the barrier layer 8. In the second embodiment, Ca used for the first metal layer 9 a has a work function of 2.6 eV, which is higher than the conduction band energy level (2.8 eV) of SiN used for the barrier layer 8. Low and satisfies this condition. In addition, Li, cesium (Cs), barium (Ba), Mg, indium (In), or the like may be used as the first metal layer 9a.

  The second metal layer 9b is formed on the first metal layer 9a. In the second embodiment, Al is formed in layers by means such as sputtering or vacuum deposition. In addition, Mg, Co, Li, Au, Cu, Zn, or alloys thereof may be used for the second metal layer 9b.

  In the organic EL element 3 in the second embodiment, similarly to the first embodiment described above, moisture enters the organic EL element 3 without providing an adsorbent in the sealing space for sealing the organic EL element 3. Thus, there is no physical thickness of the adsorbent as in the prior art, and the organic EL panel 1 can be made thinner. In addition, since a physical film that covers the back electrode 9 is not formed as in the prior art, application of the reverse bias voltage can sufficiently eliminate the defective portion, and the self-repair can be carried out satisfactorily to prevent short-circuiting. Occurrence can be suppressed.

  The second metal layer 9b is formed to prevent oxidation because the first metal layer 9a is made of a material that is easily oxidized, such as Ca, and the conduction characteristics of the back electrode 9 can be kept good. . If the prevention of oxidation is not taken into consideration, the back electrode 9 may be formed of only the first metal layer 9a without forming the second metal layer 9b.

  Next, a third embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same part as the above-mentioned 1st, 2nd embodiment, or an equivalent part, and detailed description is abbreviate | omitted.

  The third embodiment is different from the first and second embodiments in that the back electrode 9 serving as a cathode has a laminated structure of a first metal layer 9a and a second metal layer 9b, and the barrier layer 8 is It is the point formed in the 1st metal layer 9a.

  The first metal layer 9a is formed on the functional layer 7, and in the third embodiment, Ca is formed in layers by means such as vacuum deposition. The first metal layer 9a is formed so as to sandwich the barrier layer 8 between its lower layer (functional layer 7 side) and upper layer (second metal layer 9b side). Specifically, first, the lower layer of the first metal layer 9 a is formed on the functional layer 7, the barrier layer 8 is formed on the lower layer of the first metal layer 9 a, and the first metal is formed on the barrier layer 8. By forming the upper layer of the layer 9a, the barrier layer 8 can be provided in the first metal layer 9a. In such a structure, it is desirable that the work function of the first metal layer 9 a approximates the conduction band energy level of the barrier layer 8. In the third embodiment, Ca used for the first metal layer 9a has a work function of 2.6 eV, which is close to the conduction band energy level (2.8 eV) of SiN used for the barrier layer 8. Therefore, this condition is satisfied.

  The organic EL element 3 according to the third embodiment can be applied to the organic EL element 3 without providing an adsorbent in the sealing space for sealing the organic EL element 3 as in the first and second embodiments. Intrusion of moisture can be suppressed, and there is no physical thickness of the adsorbent as in the prior art, and the organic EL panel 1 can be thinned. In addition, since a physical film that covers the back electrode 9 is not formed as in the prior art, application of the reverse bias voltage can sufficiently eliminate the defective portion, and the self-repair can be carried out satisfactorily to prevent short-circuiting. Occurrence can be suppressed.

  The second metal layer 9b is formed to prevent oxidation because the first metal layer 9a is made of a material that is easily oxidized, such as Ca, and the conduction characteristics of the back electrode 9 can be kept good. . If the prevention of oxidation is not taken into consideration, the back electrode 9 may be formed of only the first metal layer 9a without forming the second metal layer 9b.

Hereinafter, specific examples of the present invention will be described with further examples. First, as an evaluation method, whether self-repair has been made (whether a defective part has been eliminated) can be determined by whether or not a destruction mark (hereinafter referred to as a repair mark) formed by self-repair is formed. . The repair mark is a so-called pinhole which is a non-light emitting part, but the size of the pinhole is about several μm to several tens of μm, so it is not a size recognizable with the naked eye, but as an organic EL panel. It does not reduce the display quality. If the back electrode and the transparent electrode are not in contact with each other when the repair mark is formed, the repair is successful, and no display defect due to a short circuit or the like is caused. Hereinafter, as a method for evaluating the conventional example and the example, light was emitted for 250 hours at a high temperature of about 80 ° C. by a module driving method to which a reverse bias voltage of 20 V was applied. Then, repair marks by self-healing are generated with moderate distribution in the panel, the repair mark occurrence rate is 0.02 to 0.05 pieces / mm ² , and the size of the repair marks is several μm to several tens μm. The degree of self-healing was judged. As for the moisture barrier property, the organic EL panel is sealed with a sealing member without arranging a member for removing moisture such as a hygroscopic agent, and the amount of dark area and dark spots after the above-mentioned 250 hours of light emission are approximated. Judged by quantity.

As a first conventional example, the dot size is 0.5 × 0.5 mm, the scanning line (back electrode) is 32 lines, and the signal line (translucent electrode) is 80 lines. The hole injection layer of MoO ₃ as the functional layer is 50 nm, the hole transport layer, the organic light emitting layer, the electron transport layer, and the electron injection layer are formed by vacuum deposition, and Al is used as the back electrode by vacuum deposition. A passive drive type organic EL panel A formed with a film thickness of 100 nm was produced. As a result of carrying out the above-described evaluation method for the organic EL panel A, as shown in FIG. 5, although a sufficient function was confirmed with respect to self-healing properties, the dark area and dark spots covered the entire area with respect to moisture barrier properties. A sufficient function could not be confirmed.

  In addition, as a second conventional example, a passive drive organic EL panel B similar to the first conventional example is manufactured except that a barrier film made of SiN is formed by sputtering to cover the back electrode. did. As a result of performing the above-described evaluation method for the organic EL panel B, as shown in FIG. 5, although the amount of dark area and the amount of dark spot are within the allowable range with respect to the moisture barrier property, a sufficient effect has been confirmed, but self-repairability In regard to, the occurrence rate of repair marks did not satisfy the above-mentioned criteria, and the short-circuit occurrence rate was about 60%, and a sufficient effect could not be confirmed.

As a first example, the passive drive type is the same as the first conventional example except that the barrier layer 8 is formed between the functional layer 7 and the back electrode 9 as shown in the first embodiment. An organic EL panel C was prepared. In the organic EL panel C, SiN was formed as the barrier layer 8 with a film thickness of 50 nm by sputtering. As a result of performing the above-described evaluation method for the organic EL panel C, as shown in FIG. 5, sufficient effects were confirmed for both the self-repairing property and the moisture barrier property. In addition, about the 1st Example, the result that an element characteristic was inferior to the 1st, 2nd conventional example was obtained, but this can be improved by further optimizing the material of the barrier layer 8. It is thought that. For example, if TiO ₂ whose conduction band energy level is higher than the work function of Al is used for the barrier layer 8, it is presumed that good device characteristics can be obtained for the same organic EL panel C.

  Further, as a second example, a barrier layer 8 is formed between the functional layer 7 and the back electrode 9 as shown in the above-described second embodiment, and the first and second metals are formed as the back electrode 9. A passive drive type organic EL panel D similar to that of the first conventional example was manufactured except that the layers 9a and 9b were provided. In the organic EL panel D, SiN is formed as a barrier layer 8 on the functional layer 7 with a film thickness of 50 nm by a sputtering method, and Ca is formed as a first metal layer 9a with a film thickness of 20 nm by a vacuum evaporation method. As the metal layer 9b, Al was formed with a film thickness of 80 nm by a vacuum deposition method. As a result of performing the above-described evaluation method on the organic EL panel D, as shown in FIG. 5, sufficient effects were confirmed in both the self-repairing property and the moisture barrier property. Further, the organic EL panel E has significantly improved device characteristics as compared with the first embodiment. This is because the first metal layer 9a whose work function is lower than the conduction band energy level of the barrier layer 8 on the side in contact with the barrier layer 8 of the back electrode 9 is not a FN tunnel current, but a band theory. It is presumed to show a suitable electric conduction form.

  Furthermore, as shown in the third embodiment, as a third example, the first and second metal layers 9a and 9b are provided as the back electrode 9, and a barrier layer is provided in the first metal layer 9a. Except for forming 8, a passive drive organic EL panel E similar to the first conventional example was produced. The organic EL panel E is formed by forming Ca as a lower layer of the first metal layer 9a on the functional layer 7 with a film thickness of 20 nm by a vacuum deposition method, and forming SiN as a barrier layer 8 with a film thickness of 50 nm by a sputtering method. As the upper layer of the first metal layer 9a, Ca was formed in a film thickness of 20 nm by a vacuum evaporation method, and Al was formed as a second metal layer 9b in a film thickness of 60 nm by a vacuum evaporation method. As a result of performing the above-described evaluation method for the organic EL panel E, as shown in FIG. 5, sufficient effects were confirmed for both the self-repairing property and the moisture barrier property. The back electrode 9 includes a barrier layer 8 and has a laminated structure of a lower layer of the first metal layer 9a, a barrier layer 8, an upper layer of the first metal layer 9a, and a second metal layer 9b. The upper second metal layer 9b was reached, and as a result, no short circuit occurred. This is because the barrier layer 8 is relatively thin and the Ca used in the first metal layer 9a is easily vaporized, and the Ca is easily oxidized and oxidized to form an insulator. This is because current does not occur even when the electrode 4 is contacted. Further, the organic EL panel E has significantly improved device characteristics as compared with the first embodiment. This is presumably because the conduction band energy level of the barrier layer 8 is close to the work function of the first metal layer 9a, so that carriers move to the lower layer of the first metal layer 9a by applying an electric field and emit light. The

  It is clear from this evaluation result that by applying the present invention, the moisture barrier property can be secured and the thickness can be reduced, and further, self-healing can be performed to suppress the occurrence of a short circuit.

1 is an overview diagram showing an organic EL panel according to an embodiment of the present invention. The schematic cross section which shows the organic EL element same as the above. The schematic cross section which shows the organic EL element which is 2nd embodiment of this invention. The schematic cross section which shows the organic EL element which is 3rd embodiment of this invention. The figure which shows the evaluation result which compared the Example and conventional example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic EL panel 2 Board | substrate 3 Organic EL element 4 Translucent electrode 5 Insulating layer 6 Partition part 7 Organic layer 8 Barrier layer 9 Back electrode 9a 1st metal layer 9b 2nd metal layer 10 Connection wiring part

Claims (6)

An organic EL device comprising: a translucent electrode; a functional layer formed on the translucent electrode and including at least an organic light emitting layer; and a back electrode formed on the functional layer,
An organic EL device, wherein a barrier layer having at least a moisture barrier property is formed between the functional layer and the back electrode or in the back electrode. The organic EL element according to claim 1, wherein the barrier layer has a thickness of 50 nm or less. 2. The organic EL element according to claim 1, wherein the barrier layer is formed between the functional layer and the back electrode and has a conduction band energy level of 2.0 to 5.5 eV. The barrier layer is formed between the functional layer and the back electrode, and the back electrode is formed in contact with the barrier layer and has a work function lower than a conduction band energy level of the barrier layer. It has a layer, The organic EL element of Claim 1 characterized by the above-mentioned. The barrier layer is formed in the back electrode, and the back electrode has a metal layer that is formed so as to sandwich the barrier layer and whose work function approximates the conduction band energy level of the barrier layer. The organic EL device according to claim 1, wherein The organic EL element according to claim 1, wherein the barrier layer is made of a nitride or an oxide.

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