JP2009238593A - Light-emitting element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a light-emitting element with a finely film-formed organic layer. <P>SOLUTION: The organic layer is formed with the use of surfactant-containing coating liquid containing polyethylene dioxythiophene, polystyrene sulfonate and a surfactant. The organic layer is a hole transport layer. The organic layer is formed by coating the surfactant-containing coating liquid in the spin coat method. It is preferrable that the surfactant is contained until fall of surface tension of the coating liquid reaches a saturated state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting device and a method for manufacturing the same.

  A general structure of an organic electroluminescence light emitting element is, for example, as shown in Patent Document 1, in which an anode electrode, an organic layer such as a hole transport layer, a light emitting layer, and a cathode electrode are stacked in this order. Formed.

  As a hole transport material for forming the hole transport layer, for example, a mixture of polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS) is used.

  However, the mixture of PEDOT and PSS has a strong surface tension. Therefore, when the coating liquid is applied, if there are irregularities or foreign matters on the surface to be coated, pinholes or the like that can cause dark spots are generated in the hole transport layer due to the influence thereof.

JP 2003-297585 A

The present invention has been made in view of such problems, and an object of the present invention is to provide a light-emitting element having an organic layer in which pinholes and the like are not easily generated, and a method for manufacturing the light-emitting element.
Another object of the present invention is to provide a light emitting device having a well-formed organic layer and a method for manufacturing the light emitting device.

In order to achieve the above object, a method of manufacturing a light emitting device according to the first aspect of the present invention includes
It has an organic layer forming step of forming an organic layer using a surfactant-containing coating liquid containing polyethylene dioxythiophene, polystyrene sulfonic acid, and a surfactant.

  The organic layer can also be a hole transport layer.

  In the organic layer forming step, the surfactant-containing coating solution can be applied by a spin coating method.

  Further, the surfactant can be contained until the surface tension of the coating solution is saturated.

  It is also possible that the surfactant is a nonionic surfactant.

In order to achieve the above object, a light emitting device according to the second aspect of the present invention is
A first electrode;
An organic layer disposed on the first electrode and formed by coating using a surfactant-containing coating solution containing polyethylene dioxythiophene, polystyrene sulfonic acid, and a surfactant;
A light emitting layer disposed on the organic layer;
And a second electrode disposed on the light emitting layer.

  A light-emitting element formed by the method for manufacturing a light-emitting element according to the present invention has a well-formed organic layer.

[Light emitting element]
First, a light emitting device 800 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, the light emitting device 800 according to the present embodiment includes an insulating substrate 110, an anode electrode 120, a hole transport layer 190 as an organic layer, an organic electroluminescence (EL) light emitting layer 140, and The cathode electrode 160 and the sealing glass 170 are included. Here, the organic layer is a light emission auxiliary layer that assists the light emission of the light emitting layer 140, and is a layer made of an organic material. The light emitting method of the light emitting element 800 is a bottom emission type.

  As will be described later, the hole transport layer 190 is formed using a surfactant-containing coating solution in which a surfactant is contained in a coating solution containing polyethylene dioxythiophene and polystyrene sulfonic acid. As will be described later, the coating solution can be applied by spin coating.

  On the insulating substrate 110, a plurality of anode electrodes 120 made of ITO (Indium Tin Oxide) are provided. A region corresponding to the anode electrode 120 is a pixel. An insulating film 130 is formed around each anode electrode 120, and a hole transport layer 190 and an organic EL light emitting layer 140 are deposited on each anode electrode 120 surrounded by the insulating film 130. A cathode electrode 160 is stacked on each organic EL light emitting layer 140 and the insulating film 130. Further, the insulating substrate 110 is bonded to the sealing glass 170 by a sealing member 150 provided on the periphery thereof, and the space between the insulating substrate 110 and the sealing glass 170 is sealed.

[Method for Manufacturing Light-Emitting Element]
Next, a method for manufacturing the above-described light emitting element 800 will be described.

  First, an ITO film is formed on the insulating substrate 110 with a uniform thickness by sputtering or vapor deposition. Then, in the ITO film formation, a phenol novolac resin or the like is used as a resist, and by photolithography, a plurality of anode electrodes 120 are arranged on the insulating substrate 110 in the vertical direction and the horizontal direction at predetermined intervals. Is formed by patterning. The thickness of the anode electrode 120 is 30 nm to 100 nm. And after apply | coating photosensitive resin, exposure and image development are performed. Thereafter, firing is performed to form an insulating film 130 opening on each anode electrode 120.

  Next, the anode electrode 120 is cleaned and lyophilic by oxygen plasma treatment or UV ozone treatment. By performing this oxygen plasma treatment or UV ozone treatment, the surfactant-containing coating solution for coating the anode electrode 120 spreads over the entire anode electrode 120, and it becomes easy to form a uniform film thickness.

  Next, the surfactant-containing coating liquid is applied onto the lyophilic anode electrode 120 by, for example, a spin coating method, an ink jet method for discharging a plurality of separated droplets, or a nozzle printing method for discharging a continuous liquid flow. Apply.

  The surfactant-containing coating solution is a coating solution containing polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS) represented by Chemical Formula 1 and containing a surfactant.

  Various surfactants can be used. For example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, and the like can be used.

Among these, nonionic surfactants can be preferably used. This is because nonionic surfactants are easy to use because they are not easily affected by water hardness or electrolytes. Here, the nonionic surfactant is a surfactant having a hydrophilic group that does not ionize when dissolved in water.
For this reason, the nonionic surfactant does not generate free ions, and it is possible to avoid mixing ionic impurities into the organic layer that may deteriorate the light emission characteristics as compared with the ionic surfactant.

  As the nonionic surfactant, various types such as an ester type, an ether type, and an ester / ether type can be used. As the ester type, for example, glycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester and the like can be used. As the ether type, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, and the like can be used. As the ester / ether type, fatty acid polyethylene glycol, fatty acid polyoxyethylene sorbitan, or the like can be used.

  After discharging the surfactant-containing coating liquid containing the surfactant onto the lyophilic anode electrode 120, the hole transport layer is dried on a hot plate under a temperature condition of 100 ° C. or higher. 190 is formed.

  By making the coating liquid containing polyethylenedioxythiophene and polystyrene sulfonic acid contain a surfactant, the surface tension of the surfactant-containing coating liquid is lowered. For this reason, even if there is unevenness on the surface to be coated, it is difficult to be affected by the unevenness, the film surface becomes smooth, and pinholes and the like are hardly generated.

  Next, an organic EL light emitting layer forming coating solution is applied on the formed hole transport layer 190. The application is desirably performed in a nitrogen gas atmosphere. The organic EL light emitting material may change its characteristics when it comes into contact with oxygen, water vapor or the like. Therefore, it becomes possible to make the characteristic change of the organic EL light emitting material difficult to occur by applying in a nitrogen gas atmosphere.

  After the coating liquid for forming the organic EL light emitting layer is applied, the organic EL light emitting layer is removed by drying with a hot plate in a nitrogen atmosphere or drying with a sheathed heater in vacuum to remove the residual liquid. 140 is formed.

  Thereafter, a cathode electrode 160 having a thickness of, for example, 100 nm is provided on the organic EL light emitting layer 140. The cathode electrode 160 is formed by, for example, resistance heating vapor deposition, electron beam vapor deposition, or sputtering.

  Then, a sealing glass 170 is formed on the upper electrode 160. Thereby, the light emitting element 800 shown in the above-described embodiment is formed.

In addition, although the structure which provides the positive hole transport layer 190 as an organic layer was shown in the above-mentioned embodiment, this invention is not limited to this embodiment. It is possible to provide a hole transport layer as the organic layer, and it is also possible to form both a hole transport layer and a hole injection layer as the organic layer. Note that a pixel circuit including a transistor connected to the anode electrode 120 may be provided in the insulating film 130. Further, it is not necessary to separate the hole transport layer 190 for each pixel, and the hole transport layer 190 may be continuously formed across the insulating film 130. In particular, when the hole transport layer 190 is continuously formed on a plurality of pixels by a spin coating method, the insulating film 130 is not necessarily required.
Further, the light emitting element 800 can be applied to an exposure device of a display device or a printing device.

(Reduction of surface tension)
As Example 1, PEDOT / PSS (coating solution containing polyethylene dioxythiophene and polystyrene sulfonic acid) contains Kao Emulgen 105 (nonionic surfactant) as a surfactant containing polyoxyethylene lauryl ether. Thus, a surfactant-containing coating solution was prepared. In addition, HLB of Kao Emulgen 105 was 9.7.
In Example 2, PEDOT / PSS (coating solution containing polyethylene dioxythiophene and polystyrene sulfonic acid) contains Kao Emulgen 109P (nonionic surfactant) as a surfactant and contains a surfactant. A coating solution was prepared. In addition, HLB of Kao Emulgen 109P was 13.6.

In Example 1, surfactant-containing coating was applied for each of cases where the addition amount of Kao Emulgen 105 was 0 wt%, 0.005 wt%, 0.025 wt%, 0.05 wt%, 0.1 wt%, and 0.5 wt%. The surface tension of the liquid was examined.
Similarly, in Example 2, the amount of Kao Emulgen 109P added is 0 wt%, 0.005 wt%, 0.025 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, respectively. The surface tension of the surfactant-containing coating solution was examined. These results are shown in Table 1.

  In Example 1 and Example 2, the relationship between the surface tension and the surfactant addition amount (addition amount of Kao Emulgen) is shown in FIG. In both Example 1 and Example 2, the surface tension decreased as the addition amount increased. However, when the addition amount is about 0.05 wt% or more, the surface tension is hardly decreased, the surface tension is almost saturated, and even if a surfactant is further added, the surface tension is hardly decreased. It was. From this, it was found that the surfactant is preferably contained until the decrease in the surface tension of the coating solution is saturated.

(Number of dark spots)
Next, as Example 3, a surfactant-containing coating solution containing 0.05 wt% of Kao Emulgen 105 was prepared, and was discharged onto the lyophilic anode electrode by a spin coating method and dried at 100 ° C. or higher. To form a hole transport layer. Then, blue, green, and red organic EL light emitting layers were formed on the formed hole transport layer to form a light emitting element 800.
As Example 4, a surfactant-containing coating solution containing 0.05 wt% of Kao Emulgen 109P was prepared, and a light emitting device 800 was formed in the same manner as in Example 3.
As a comparative example, a light emitting element 800 was formed in the same manner as in Example 3 for PEDOT / PSS to which no surfactant was added.

  Then, in Example 3, Example 4, and Comparative Example, the number of dark spots in the 2 × 2 mm light emitting region was examined. The results are shown in Table 2.

  In Example 3, the number of dark spots was reduced in each of the blue, green, and red colors compared to the comparative example. Further, in Example 4, the number of dark spots was reduced in each color of blue and red as compared with Example 3. From this point, it is considered that the surface tension of the PEDOT / PSS containing the surfactant is lowered, and even if there are irregularities on the surface to be coated, it is considered that dark spots are hardly generated.

It is sectional drawing explaining the cross section of the light emitting element which concerns on embodiment. It is a figure explaining the relationship between the addition amount of surfactant, and the surface tension of surfactant containing coating liquid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 110 ... Insulating substrate, 120 ... Anode electrode, 140 ... Organic electroluminescent light emitting layer, 160 ... Cathode electrode, 170 ... Sealing glass, 190 ... Hole transport layer, 800 ... Light emitting element

Claims (6)

Using a surfactant-containing coating liquid containing polyethylene dioxythiophene, polystyrene sulfonic acid and a surfactant, and having an organic layer forming step of forming an organic layer,
A method for manufacturing a light-emitting element. The organic layer is a hole transport layer,
The method for manufacturing a light-emitting element according to claim 1. In the organic layer forming step, the surfactant-containing coating solution is applied by a spin coating method.
The method for manufacturing a light-emitting element according to claim 1 or 2. The surfactant is contained until a decrease in the surface tension of the coating solution is saturated.
The method for manufacturing a light-emitting element according to claim 1, wherein: The surfactant is a nonionic surfactant;
The method for manufacturing a light-emitting element according to claim 1, wherein: A first electrode;
An organic layer disposed on the first electrode and formed by coating using a surfactant-containing coating solution containing polyethylene dioxythiophene, polystyrene sulfonic acid, and a surfactant;
A light emitting layer disposed on the organic layer;
A second electrode disposed on the light emitting layer.
A light emitting element characterized by the above.

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