Patent Application
20200312929
The present disclosure relates to an organic EL light-emitting element (organic electroluminescent light-emitting element) and a method of manufacturing the same.
An organic EL light-emitting element is formed such that a thin layer of organic material containing an organic light-emitting substance is sandwiched between an anode and a cathode. This organic thin layer is formed by a vapor deposition method or a coating method. In a method of manufacturing of a vapor-deposition type organic thin layer, a supporting substrate (a substrate to be vapor-deposited) and a deposition mask are arranged overlapped, an organic material is vapor-deposited in vacuum through an opening of the deposition mask, and a thin layer is formed on the supporting substrate. In general, low molecular weight compounds are used as an organic material for a vapor-deposition type organic material. On the other hand, in a method of manufacturing of a coated-type organic EL light-emitting element, a thin layer is formed on a supporting substrate using a solution for, for example, a printing process such as a screen printing, an ink-jet process. An organic EL light-emitting element which is produced by a coating process can be produced at a lower manufacturing cost compared to an organic EL light-emitting element which is produced by a vapor-deposition process since, for example, it does not require an expensive vapor mask or equipment for high vacuum process, and an efficiency in use of an organic material in a coating process is higher than a vapor-deposition process. However, it is difficult to produce a good quality thin layer using a coating process since low molecular weight compounds tend to be easily crystalized. Therefore, polymer compounds having a high amorphous property have been used as an organic material in the coating process. For example, Patent Document 1 describes a polymer compound containing a specific repeating unit as an organic material for a coated-type organic EL light-emitting element, which can be used as a light-emitting material or charge transport material. A polymer compound used in a coating process usually contains at least a number of several tens or more of such repeating units.
As mentioned above, a polymer compound is used for an organic material for a coated-type organic EL light-emitting element. However, in the conventional coated-type organic EL light-emitting element, it is difficult to coat an organic material in a minute dot pattern since a size of a droplet of the organic material is hardly reduced even using an ink-jet method. An attempt has been made to have a coating solution within a pixel by devising an insulation bank arrangement when the display apparatus is large-sized and the pattern formation has large area, for example, a size of each pixel for the display apparatus is a long-side length of 210 μm or more and a short-side length of 70 μm or more.
However, an area for each pixel of the display apparatus becomes very small with the reduced weight, size, and thickness and the high definition of the recent electronic apparatus such as a portable device, making unable to separately coat on each pixel even using an ink-jet method, since the droplet spreads across more than one pixels. Also, the purification of polymer compounds is difficult, and it is hard to obtain highly purified polymer compounds. Therefore, when the polymer compounds are used for an organic EL light-emitting element, a luminescent color purity, a light emission efficiency, a brightness and so on might be reduced. Further, if the molecular weight of the polymer compound becomes too high, forming a homogeneous layer may become difficult due to a gelation of polymer compounds.
Further, it has been generally known that the low molecule weight compounds have a higher light emission efficiency and longer light emission life compared to the polymer compounds, and also have many variations in color and have superior performance in especially blue light emission. However, a coating solution containing a low molecule weight compound has a high fluidity, thereby the coating solution spreads right after being ejected from a discharge nozzle of the ink jet apparatus, making it difficult to form a liquid drop of good quality, and, since the low molecule weight compounds tend to be easily crystalized as described above, a layer of a low molecule material is formed in such a way that the material is inhomogeneously distributed, and thus it is difficult to use low molecule weight compounds for a conventional method of manufacturing a coated-type organic EL light-emitting element.
As described above, when the polymer compounds are used for an organic material, it is difficult to prepare a small liquid drop. Therefore, when a pixel size becomes small, a problem arises that a separate coating with high definition on an electrode of the small pixel is unable to be carried out even using an ink-jet method. Further, the difficulty has been enhanced in selectively coating a small-sized desired area with the organic material, depending on a droplet diameter of a liquid drop to be ejected, while a technique for manufacturing an organic layer with smaller size and higher definition for, for example, display apparatus for a smartphone is demanded. The inventors have found that the reason a size of coating solution cannot be reduced attributes a molecular weight of an organic material, and that the molecular weight of an organic material should be 5000 or less, preferably 3000 or less and the organic material should be an oligomer of the organic material.
The present invention has been made in view of such circumstances as mentioned above, and an object of the present invention is to provide an organic EL light-emitting element having an organic layer with a small size and a high definition pattern and a second electrode with a thin thickness so that the element can be used for a top emission structure, using an inexpensive printing method for the organic layer formation, and a manufacturing method thereof.
An organic EL light-emitting element according to the first embodiment of the present application comprises a substrate, a first electrode provided on a surface of the substrate, an insulation bank formed to surround at least part of the first electrode, an organic layer formed on the first electrode surrounded by the insulation bank, and a second electrode formed on the organic layer, wherein the insulation bank has a forward tapered shape and a hydrophilic surface, a thickness of the second electrode is from 10 nm or more and 25 nm or less, and the organic layer is a coated-type organic layer comprising an oligomer of an organic material.
A method of manufacturing an organic EL light-emitting element according to the second embodiment of the present application comprises forming a first electrode on a surface of a substrate, forming an insulation bank to surround at least part of the first electrode, forming a coated-type organic layer on an area of the first electrode surrounded by the insulation bank, and forming a second electrode on the organic layer, wherein the second electrode is formed of a translucent material, wherein the insulation bank is formed so as to have a height of from 0.5 μm or more and 1 μm or less from a surface of the first electrode, and the organic layer is formed by applying a droplet of a liquid composition comprising an oligomer of an organic material using an ink-jet process.
According to the first embodiment of the present application, an organic EL light-emitting element is formed with a coated-type organic layer containing an oligomer of an organic material, thereby it is not necessary to subject an insulation bank to a liquid repellent treatment. Thus, a deterioration of the organic layer by fluorine which is contained in a material for a liquid repellent property or introduced in a material by a surface treatment does not occur. Further, there is no need to form an insulation bank in a reversed tapered shape, preventing an occurrence of a stepwise disconnection of a second electrode. This enables to form a second electrode with a thin thickness of, for example, from 10 nm or more and 25 nm or less. This can provide a top emission type, coated-type organic EL light-emitting element. Further, according to the second embodiment of the present application, a coating solution containing an oligomer of an organic material is used and thus a small-sized liquid droplet is ejected and dropped using an ink-jet process. This enables a selective and precise coating of even a small light-emitting area surrounded by an insulation bank having a low height with an organic material, and prevents an occurrence of a stepwise disconnection of a second electrode having a thin thickness, and provides an organic EL light-emitting element in which a coated-type organic layer is formed in a high definition pattern. Consequently, a small, high-definition organic EL light-emitting element can be obtained at a low cost and a small, high-definition display apparatus can be manufactured inexpensively.
The invention will be further described below. The embodiments described below are intended only to provide an example of the disclosure and the invention is not limited to certain embodiments described below.
As illustrated in
The term “coated-type organic layer” is used herein to refer to the organic layer prepared by drying a coated layer formed by coating process, for example, a coated layer of an organic material formed using a dispenser and a coated layer formed by a printing process such as a screen printing or an ejection of organic material drops by ink-jet process. When a shape of a sidewall of the insulation bank 23, which forms an opening, is formed such that a spacing between sidewalls of the insulation bank 23 in a vertical cross sectional view is increased from a surface of the first electrode 22 toward a top surface of the insulation bank 23, the shape of the insulation bank 23 is referred to herein as “forward tapered shape”. The term “hydrophilic” is used herein to refer to not only a property specifically obtained through a hydrophilic treatment but also a lack of a liquid repellent property which might be obtained using a material with a liquid repellent property or through a liquid repellent treatment.
As described above, the conventional, coated-type organic EL light-emitting element has a problem that the element cannot be formed in a small-sized light-emitting area. When coating an organic material on an area of the electrode, which will constitute each pixel, by, for example, ink-jet process for manufacturing a display apparatus, it is necessary to adjust a physical property of a coating solution ejected from a nozzle of ink-jet apparatus and optimize a ejecting speed of a liquid drop of a coating solution when ejected and a printing condition of an ink-jet apparatus, however, the inventors have found out that among those a size of a liquid drop of a coating solution when being ejected is an important factor to determine a possible size of an area to which an organic layer is provided, and that it is very important to adjust a size of a liquid drop to a desirable size at a pattern forming using an ink-jet process. With a conventional coating solution, a volume of a liquid drop when a coating solution of an organic material being ejected using an ink-jet process is about 5 pL to 30 pL in average, and it is impossible to reduce the volume of a coating solution per one drop to 1 pL or less. However, as a result of the inventors' extensive studies, the inventors found out that the reason why a size of the conventional liquid drop cannot be reduced is attributed to a polymer with a high molecular weight. The inventors found out that a droplet of 0.05 to 1 pL can be obtained by using an oligomer having a molecular weight of 5000 or less.
As a result of further extensive studies of inventors, the inventors found out that a size of a liquid drop is largely affected by a molecular weight of an organic material. In other words, the inventors ascertain that the reason why small droplets cannot be formed is attributed to a fact that a solute (an organic material) in the conventional coating solution is a polymer compound having a high degree of polymerization and a large molecular weight of 10000 or more. It is considered that a size of a liquid drop is affected by a concentration of an organic material in a coating solution (a solubility of an organic material in a solvent) or a viscosity of a coating solution, however, the inventors conducted a test under the condition in which a concentration is as high as possible, yet a dropping of the solution is enable to be conducted.
As a result, the inventors found out that when a molecular weight is 300 or more and 5000 or less, preferably about 3000 or less, more preferably 500 or more and 1000 or less, a liquid droplet volume per one drop can be set to about 0.05 pL to about 1 pL. The inventors conducted various studies with different polymerization methods and tested various compounds with a smaller molecular weight, i.e. a smaller degree of polymerization, and, as a result, the inventors found out that a liquid drop with the above-mentioned size can be obtained by using an organic material having a certain polymerization degree, which can form an oligomer (generally around or less than an icosamer), preferably an dimer to decamer.
As described above, for the conventional, coated-type organic EL light-emitting element, an element having a light-emitting area of 70 μm×70 μm or less as a minimum size cannot be formed. The fact that a length of the one side of the area with a minimum size is 70 μm means a liquid drop will overflow from the area that has a size equal to or smaller than that minimum size. Therefore, a pixel size corresponding to a 20-inch QHD display, which is, a size of 70 μm×210 μm, is a limit size of the area that can be formed in the conventional, coated-type organic EL light-emitting element. Even with this size of light-emitting area, various improvements as described above to an insulation bank were needed. The exemplary organic EL light-emitting element according to the present application will be described in the followings by referring to
In the conventional, coated-type organic EL light-emitting element having such a structure, when the organic EL light-emitting elements are arranged in matrix form in a display apparatus, a coating solution overflows an opening 23a of the insulation bank 23 and spreads to neighboring light-emitting areas since a liquid droplet volume per one drop ejected by an ink-jet process is large, as described above. The following attempts have been made to avoid this problem.
For example, an attempt to increase a height h of an insulation bank 23 from a first electrode 22 (see
Further, another attempt, in which an insulation bank 23 is formed in a reversed tapered shape (the shape in which a spacing between sidewalls of the insulation bank 23 in a vertical cross sectional view is decreased from a surface of the first electrode 22 toward a top surface of the insulation bank 23, i.e. a reversed shape of a forward tapered shape) has been also made in the conventional, coated-type organic EL light-emitting element in order to prevent a coating solution from spreading over a neighboring light-emitting area. However, making such a reversed tapered shape is difficult, and further, it causes a problem that a stepwise disconnection of a second electrode 27 which is formed across an entire surface of an organic layer 26 and top surface of the insulation bank 23, as described above, may occur more frequently. Therefore, a stepwise disconnection problem of the second electrode 27 will become even severe compared to in the above-described attempt to increase a height of the insulation bank 23, and thus, in this kind of light-emitting element, it is necessary to form a second electrode 27 much thicker, for example, with a thickness of at least 1 pm or more. Further, since the stepwise disconnection problem of the second electrode 27 will be prompted unless a metal material having excellent coating characteristics is used as a material of a second electrode 27, only a limited number of materials, such as Al formed so as to have an increased thickness, can be used for the second electrode 27 for the conventional, coated-type organic EL light-emitting element.
On the other hand, in an exemplary embodiment according to the present application, by using an organic material with a smaller degree of polymerization, which is neither a polymer compound nor a low molecule weight compound and has a molecular weight of 300 or more and 5000 or less, preferably about 3000 or less, more preferably 500 or more and 1000 or less, in other words, by using an organic material of an oligomer, preferably an oligomer from a dimer to a decamer, as an organic material to be dissolved in a coating solution, a small liquid drop of a coating solution having a volume per one drop of about 0.05 pL or more and about 1 pL or less was obtained. This enables to make a height h of an insulation bank 23 smaller since there is no possibility that a coating solution 25a overflows an opening 23a even if the size of an area to which a coated layer will be formed is small (see,
Consequently, the second electrode 27 was formed with a thin thickness, for example, with a thickness of about 5 to 30 nm, preferably 10 nm or more and 25 nm or less without causing a stepwise disconnection problem. In the presently illustrated embodiment, this makes it possible for a light-emitting element to be formed either as a top emission type light-emitting element or as a bottom emission type light-emitting element. Because the conventional, coated-type organic EL light-emitting element was realized only as a bottom emission type light-emitting element, the presently illustrated embodiment of the present application is significantly advantageous when producing a top emission type light-emitting element, which is never obtained with the conventional, coated-type organic EL light-emitting element using a polymer compound.
Further, according to an exemplary embodiment of the present application, the insulation bank 23 is formed to have a low height, and thus, a width of an insulation bank between neighboring pixels can be formed small, thereby a pixel with very high definition, such as a pixel with a size of 10 μm square at minimum, can be arranged with a high definition pattern, for example, with a small pixel pitch, such as, for example, 25 μm pitch. Further, since the height of an insulation bank 23 is low, light emissions from a light-emitting layer in oblique directions are not blocked. This may improve a problem of poor viewing angle characteristics which the conventional, coated-type organic EL light-emitting element has.
Still another attempt which makes the surface of an insulation bank 23 which is exposed inside an opening 23a and the top surface of an insulation bank 23 liquid repellent has been made to avoid the problem the conventional, coated-type organic EL light-emitting element has, in that a liquid droplet volume per one drop ejected by an ink-jet process is large and a coating solution overflows an opening 23a of the insulation bank 23, spreading to areas of neighboring light-emitting elements. With such a liquid repellent treatment, a dripped coating solution is likely repelled by the insulation bank 23 even when the volume of the dripped coating solution is larger than a volume in the opening 23a, and the coating solution is pulled into a spherical shape due to a surface tension of the coating solution, raised in the vertical direction and kept in an opening 23a, without overflowing the insulation bank 23 and spreading to areas of neighboring light-emitting elements from a small light-emitting area. To obtain such a liquid repelling property, an insulation bank 23 is need to be either formed by a fluorine resin containing fluorine, for example a polyamide containing fluorine, or a silicone resin, or subjected to plasma treatment for treating a surface of the insulation bank 23 by, for example, CF4 based gas, both of which can be a difficult work and may increase a manufacturing cost. There is also a possibility that the fluorine gas may negatively affect the organic layer, and a deterioration of the organic layer 26 may be caused by an effusion of fluorine after the element was formed. Further, it seems difficult to completely prevent the wetting spread of the coating solution to the neighboring light-emitting areas.
However, in the presently illustrated embodiment, a small-sized liquid drop was able to be formed, as described above, and thus, the organic layer 26 was formed successfully and precisely, even when an area to which the coated layer will be formed is small, for example, even in a light-emitting area having a much smaller size compared to the conventional size of 70 μm×210 μm, such as a small-sized light-emitting area of about 10 μm×10 μm. Therefore, there is no need to subject a surface of the insulation bank 23 to a liquid repellent treatment. This is because a liquid drop of a coating solution containing an oligomer of an organic material according to the presently illustrated embodiment can be kept in an opening 23a and does not overflow even when the surface of the insulation bank 23 does not have a liquid repelling property. In other words, according to the presently illustrated embodiment, there is no need to form an insulation bank 23 using a fluorine resin containing fluorine or a silicone resin, and a plasma treatment of a surface of the insulation bank 23 by CF4 based gas is also not necessary. Not only that this makes a manufacturing process of an element very simple, but also it can exclude an adverse influence that may be caused by an effusion of fluorine from the insulation bank 23 or by a surface treatment using a fluorine-based gas. For example, it may be preferable to use a non-fluorine-based resin containing no fluorine, such as polyimide-based resin containing no fluorine for an insulation bank 23. This may achieve a life prolongation of the elements. Further, in the presently illustrated embodiment, not only is there no need to conduct a liquid repellent treatment, but also an insulation bank 23 may be even formed so as to have a hydrophilic property. A resin having a hydrophilic property as referred herein involves a resin with no liquid repellent property as well as a resin to which no specific treatment, i.e. no liquid repellent treatment, has been conducted, and this may be advantageous because when an inside of an opening 23a of the insulation bank 23 is formed to have a hydrophilic property, a dripped coating solution may be easily spread up to a peripheral portion of a first electrode 22. The insulation bank 23 may be formed by a particularly hydrophilic material such as polyimide or polyamide, or a surface of the insulation bank 23 may be modified to have a hydrophilic property by treatments such as plasma surface treatment, UV irradiation treatment, ozone treatment. The first electrode 22 can be totally covered with a coated layer, up to a peripheral portion of the first electrode 22. This may exclude a possibility of an occurrence of short circuit between the first electrode 22 and the second electrode 27 which is formed on an organic layer 26 after a formation of the organic layer 26 from a coated layer.
As described above, the inventors found out that by applying a compound, which has a molecular weight of about 300 or more and 5000 or less, preferably about 3000 or less, more preferably about 500 or more and 1000 or less and a degree of polymerization similar to the degree the oligomers have, as an organic material for an coated-type organic layer 26, a coating solution can drip as a small droplet which has a volume per one drop of about 0.05 pL or more and 1 pL or less and a nearly spherical shape to an opening 23a of the insulation bank 23 which has a hydrophilic surface and a forward tapered shape. Even when the area of a surface of the first electrode 22 exposed in the opening 23a is, for example, 100 μm2 or more and 2500 μm2 or less, preferably 1200 μm2 or less, more preferably 850 μm2 or less, or, 520 μm2 or more and 850 μm2 or less, in other words, 17 μm×50 μm or less for a high definition panel of a medium or large size, or 25 μm×25 μm or less for a high definition panel of a small size, such as a hand-held display apparatus, or a small area where a length of one side is about 10 μm, a coated-type organic layer can be obtained on that area by an ink-jet process. As a result, even a light-emitting element to be used for a small, high definition display apparatus such as a smartphone can be formed as a coated-type organic layer. Therefore, an organic EL light-emitting element according to the presently illustrated embodiment can form a pixel of the organic EL display apparatus, which has a resolution around 500 ppi or a higher pixel density for an apparatus with a size of the smartphone. Further, it was found that a concentration of solute in the coating solution can be increased to about 10 mass % to 30 mass %, and thus the organic layer was formed efficiently in the small light-emitting area. Further, since an insulation bank 23 with a height of about 1 μm or less can be formed to have a forward tapered shape, even when a second electrode 27 formed by a thin layer having a thickness of about 5 to 30 nm is formed across an entire surface of an organic layer 26 and top surface of the insulation bank 23, a stepwise disconnection of the second electrode 27 hardly occurs, providing a satisfactory and continuously formed second electrode 27. Also, it provides a high light-transmitting property through a second electrode, and thus a top emission type organic EL display element with a high quality can be formed. Further, since the light-emitting layer is surrounded by a lower insulation bank 23, compared to the conventional, coated-type organic EL light-emitting element, the viewing angle characteristics can be improved. In addition, since the height of the insulation bank 23 is low, a stabilized insulation bank 23 can be formed even when a width of an insulation bank member is not wide, and thus a spacing between the neighboring pixels can be small. This enables to make a pitch between pixels narrow. Further, this enables to form an insulation bank 23 with a small taper angle θ, an occurrence of a stepwise disconnection of the second electrode may be further prevented. Therefore, a high definition, coated-type organic EL light-emitting element with a second electrode 27, which is a thin layer with a thickness sufficient to obtain a light transmitting property, can be produced. Further, according to the presently illustrated embodiment, an insulation bank 23 can be formed in a forward tapered shape, and thus a protection layer 28 can be also coated on the second electrode 27 without a risk of stepwise disconnection. In other words, a protection layer 28 which has a good sealing performance enough to satisfactory prevent a penetration of water and/or oxygen into the organic layer 26. Therefore, according to the presently illustrated embodiment, an organic EL light-emitting element having a high reliability, in which a deterioration due to a penetration of water and/or oxygen into the organic layer 26 will be hardly occurred, can be obtained.
An upper limit of a size of the area to which an organic layer 26 according to the presently illustrated embodiment is formed is not limited to the ones described above. A coating solution containing an oligomer according to the presently illustrated embodiment is suitably applicable to an area having a similar size to the conventional, coated-type organic EL light-emitting element. When the area to be coated is large, a cross-sectional area of an ejecting port of a nozzle will be increased so that even a large area may be formed in a relatively short time. Thus, the above-mentioned length for one side of the pixel having a rectangular shape is merely an example and a size of the area may be any sizes that correspond to a various pixel shapes for the desired display apparatus. When the shape of an area to be coated is a rectangular shape, and if a length of one side of the rectangular shape is too small (a width of the rectangle is too narrow), it becomes impossible to apply a liquid drop to the area precisely. Therefore, when a shape of the area to which an organic layer 26 will be formed has a rectangular shape, it may be preferable that a short side of the rectangle is 10 μm or more. In other words, a squared value of this lower limit of a length of the short side will be a lower limit of a size of a pixel which can be formed by the presently illustrated embodiment. It should be appreciated that a shape of the area to which an organic layer 26 will be formed, i.e. a shape of a pixel, is not limited to a rectangular shape or a square shape, and may be a round shape, elliptic shape, or polygon.
In the presently illustrated embodiment, as described above, even when a coating solution 25a is coated to a small light-emitting area surrounded by an insulation bank 23 having a hydrophilic surface, there is no risk for a coating solution 25a to overflow an insulation bank 23. As a result, an organic layer was formed successfully by a coating process even on an area of the light-emitting area formed with the above described high definition pattern without an occurrence of color mixing problem. Since the surface of an insulation bank 23 is hydrophilic, the organic layer 26 evenly fills a space from a bottom of an opening 23a to a sidewall of an opening 23a. This makes it possible to obtain an organic layer 26 with an improved flatness, preventing an occurrence of a luminance unevenness or a light emission color unevenness. Also, by forming an insulation bank 23 to have a height h of 0.5 μm or more and 1 μm or less, an occurrence of a stepwise disconnection problem is further prevented, providing a second electrode 27 which is formed across an entire surface of an organic layer 26 and top surface of the insulation bank 23 to have a thickness of 10 nm or more and 25 nm or less.
An organic layer 26 may include one or more organic layers such as a hole transport layer or an electron transport layer, other than a light-emitting layer. In case where the organic layer 26 is formed with a plurality of layers, a material for each layer should be an organic material containing an oligomer as mentioned above. Further, an organic layer 26 according to the presently illustrated embodiment may further include an optional layer between the organic layer 26 and a first electrode 22 or a second electrode 27, or between each of the organic layers when the organic layer 26 is formed by one or more organic layers. Further, a TFT (not indicated) or a planarization layer (not indicated) and so on may be formed on a substrate 21. It should be noted that an organic EL light-emitting element shown in
An organic EL light-emitting element according to the presently illustrated embodiment may be applicable to an illumination apparatus by sealing one or more organic EL light-emitting elements with an envelope (a covering layer) which has at least a translucent front surface, or to a display apparatus by arranging a plurality of light-emitting elements in matrix form. When applied to an illumination apparatus, light-emitting elements of three colors, red (R), green (G) and blue (B) are enclosed in one envelope, providing a white light emitting illumination apparatus. A white light or a light of any other desirable colors emitting illumination apparatus may be also formed by covering a monochromatic light emitting element by a fluorescent resin.
When applied to a display apparatus, sub-pixels of three colors, R, G and B are formed respectively for each pixel (one pixel) arranged in matrix form, providing a full-color display apparatus. In this case, a size of each sub-pixel is about one-thirds of the size of one pixel, and its area is smaller than the area of one pixel. A material for an organic layer for each sub-pixel and a planar shape of a sub-pixel could be different each other, however, a layered structure formed with, for example, a first electrode 22, an organic layer 26, a second electrode 27 is same, and thus a sub-pixel is herein described as one light-emitting element (one pixel) without distinguishing a sub-pixel from a pixel. An arrangement of the pixels is not particularly limited, and the pixels may be arranged, for example, in a mosaic arrangement, a delta arrangement, a stripe arrangement, a pentile arrangement. In each pixel, a first electrode 22 of an organic EL light-emitting element is connected to a driving element, and a predetermined color corresponding to each pixel is emitted by the on-off control of each pixel and various luminescent colors are realized by mixing different colors.
A substrate 21 may be a support substrate formed with, for example, a glass plate, a polyimide film. In case where the substrate 21 does not need to be translucent, a metal substrate or a ceramics substrate may be used as well. When applied to a display apparatus, though
An insulation bank 23, which is formed by, for example, a silicon oxide, a silicon nitride, a silicon oxynitride, acrylic resin, polyimide resin or a novolak-type phenol resin, is formed around a first electrode 22 which constitutes each pixel, as described in
In either case, it is important to form a layered structure in which the first electrode 22 and the second electrode 27, which is formed after a formation of the organic layer 26, are never in contact with one another (inducing a leakage). Therefore, as described above, it may be preferable that an organic layer 26 is provided in an area surrounded by an insulation bank 23 so as to cover an entire surface of the first electrode 22 which is exposed in an opening 23a of the insulation bank 23. A second electrode 27 may be formed on the organic layer 26. However, an organic layer 26 may be formed on the first electrode 22 to have a size smaller than the size of the first electrode 22 without covering an entire surface of the first electrode 22, and a second electrode 27 may be formed on the organic layer 26 to have a size further smaller than the size of the organic layer 26.
Among the coated-type organic layers 26, organic materials each correspond to a color from R, G, and B may be used for each of light-emitting layers. However, a light-emitting layer may be formed using the same material, and a color filter may be provided on the surface of the light-emitting layer to obtain a color R, G, or B through a color filter. Further, the organic layer 26 other than a light-emitting layer may include a hole transport layer or an electron transport layer, or a layered structure thereof. In case where a light-emitting property is considered the most important, it may be preferable to coat a material suitable for a light-emitting layer separately for forming a hole transport layer or an electron transport layer. However, when using a coating process, it is possible to form an organic EL light-emitting element with a coated-type organic layer 26 which includes a fewer number of layers by mixing organic materials each of which forms respective layers.
For example, in order to form the organic layer 26, as described, for example, in
With a dropping of a coating solution 25a, a coated layer 25 is formed as described in
As described above, in the presently illustrated embodiment, the element is a top emission type in which a light is emitted from the surface of the element which is the opposite to the surface including a substrate 21 in FIGs, and thus a second electrode 27 formed on the organic layer 26 is formed of a translucent material such as a thin eutectic layer composed of magnesium and silver. A material such as aluminum may be also used. It should be noted that in case where the element is a bottom emission type in which a light is emitted through the substrate 21, a material such as ITO, In3O4 may be used for a first electrode 22 and a metal having a small work function such as Mg, K, Li, Al may be used for a second electrode 27. On the surface of the second electrode 27 a protection layer (a covering layer) 28 (see
As described above, since the organic material for an organic layer 26 according to the presently illustrated embodiment is an oligomer, for example, with a polymerization degree of 2 to 10, having a molecular weight of 300 to 5000, the organic material has a solubility to a solvent sufficient to be applied for a coating solution 25a for ink-jet process which is ejected from a nozzle of ink-jet apparatus to form a coated layer 25 by coating. A concentration of the oligomer in the coating solution 25a according to the presently illustrated embodiment may be adjusted to a concentration which enables to form an organic layer 26 with a desirable thickness, and it can be, for example, about 10 mass % to 30 mass %. Further, since the oligomer has the above described polymerization degree, only the oligomer having a desirable polymerization degree can be isolated and purified after the synthetic reaction by a purification method such as a separation by a chromatography including a column chromatography and gel permeation chromatography, a reprecipitation, a recrystallization. In the presently illustrated embodiment, the oligomer which is highly purified and has no molecular weight distribution can be used as an organic material for the organic layer 26, and thus, the color purity and brightness can be enhanced when such an organic material is applied to an organic EL light-emitting element compared to the element where an organic material containing a polymer compound which is not easily purified and difficult to be obtained as a highly purified compound is used. Also, to use an oligomer of the organic material as an organic material may prevent a crystallization or aggregation of the organic material when being coated, and thus, a stability of a layer of the organic layer 26 to be formed may be increased compared to the layer formed from the organic material containing a low molecule weight compound which is, for example, crystalized easily in general. If a crystallization or aggregation of the organic material occurs in the organic layer, a brightness of the area in which a crystallization or aggregation occurs and a layer thickness is relatively increased is relatively decreased because an amount of the current to be injected is reduced compared to the area in which such a crystallization or aggregation does not occur, possibly causing variation in the distribution of the light emission intensity within a pixel. Also, there would be a possibility that the lifetime of the element itself may be shortened because of a deterioration occurred in the area having a thin thickness due to a concentration of current in the area having a relatively thin thickness. The occurrence of this kind of problems can be prevented by using an oligomer of the organic material of the exemplary embodiment of the present application for an organic layer 26 of the light-emitting element. Therefore, an organic EL light-emitting element with a high definition having a long lifetime and superior light emission intensity can be provided by a method for manufacturing a coated-type element using a relatively inexpensive printing method.
In one embodiment of the present application, an organic layer 26 of the organic EL light-emitting element may include one or more organic materials which have a superior property such as a hole transport property or an electron transport property, in addition to the light-emitting organic material, as described above. For example, a coating solution 25a containing a composition formed by mixing an oligomer of an organic material which is a light-emitting material and a compound having a hole transport property or an electron transport property may be used for a formation of the organic layer 26. An oligomer of different kinds of organic materials, for example, an oligomer as a light-emitting material and an oligomer having a hole transport property, may be mixed and used to form an organic layer 26 through a coating process. It should be noted that a combination of the materials is not limited to those described above. This may enable to reduce a number of layers in the organic layer 26 of the organic EL light-emitting element. This may improve a flatness of the organic layer 26 and prevent an occurrence of a display unevenness such as a luminance unevenness or a light emission color unevenness when the organic layer 26 emits light.
Referring to a flowchart in
When applying the light-emitting element to an organic EL display apparatus, as described above, a driving TFT, for example, which forms a driving circuit on the substrate 21, is formed with an amorphous semiconductor, for example, by a usual method using a lithography process, for example. It is planarized by, for example, using a polyimide resin to planarize irregularities of the surface. The first electrode 22 is formed in matrix form according to an arrangement of each pixels on its surface. This first electrode 22 is also formed by forming the above described material for electrode on the entire surface and being subjected to a patterning process (S1).
Subsequently, the insulation bank 23 is formed (S2). This insulation bank 23 may be formed by an inorganic material such as a silicon oxide, a silicon nitride, a silicon oxynitride, or, if a thicker layer is required, it may be formed in a short time by using a resin material such as acrylic resin, polyimide resin or novolak-type phenol resin. The exemplarily examples of a preferable material may include a photosensitive resin material among the above described resin materials, especially a photosensitive polyimide resin. For example, an insulation bank 23, which is formed of a cured material of a photosensitive resin material and includes an opening 23a that exposes at least a part of the first electrode inside thereof as illustrated in
Forming a boundary portion between a sidewall of an opening 23a and a top surface of an insulation bank 23 to have a rounded shape may be advantageous because even when a second electrode 27 is formed by a thin layer, the second electrode 27 can be formed satisfactory and continuously on an entire surface of an organic layer 26 and top surface of the insulation bank 23 without causing a stepwise disconnection. Therefore, in the presently illustrated embodiment, it may be preferable that a top surface of the insulation bank and a side surface of the insulation bank does not form a sharp edge. In other words, it may be preferable that a corner part provided between a top surface of the insulation bank and a side surface of the insulation bank is formed to have a curvature of 1×106 or more and 2×108 or less. Forming an insulation bank to have this curvature may prevent an induction of a discontinuous point at a corner part to a second electrode 27 when forming a second electrode 27 and a problem that a thickness of the second electrode 27 formed at the corner part is reduced. A thin layer with a uniform layer thickness may be formed continuously. A corner part of this type may be obtained through a long etching process using an isotropic etchant when forming an insulation bank 23. An additional heat treatment may be further conducted to make the corner part provided between a top surface of the insulation bank 23 and a side surface of the insulation bank 23 have a more gradual curve shape to obtain this range of curvature. It should be noted that a curvature referred herein means the reciprocal of radius of curvature, and the radius of curvature referred herein means the radius of the circular arc which approximates the curve at that point.
The insulation bank 23 may be formed by a hydrophilic material, or, the surface of the insulation bank 23 may be formed to have a hydrophilic property by conducting a surface modifying treatment, such as UV irradiation treatment, ozone treatment, plasma surface treatment, to the surface of the insulation bank 23 exposed inside the opening 23a. These may improve a wettability of a coating solution to the insulation bank 23 and a coating solution being dropped_inside an opening 23a spreads up to a peripheral portion of a first electrode 22 and the organic layer 26 evenly fills a space from a bottom of an opening 23a to a sidewall of an opening 23a, forming an organic layer 26 with an excellent flatness.
Subsequently, a coating solution 25a of the above mentioned organic material is ejected from a nozzle 31 by an ink-jet process, as illustrated in
In particular, as illustrated in
Subsequently, a eutectic layer composed of magnesium and silver, for example, is formed by, for example, a vapor-deposition on the entire surface to form a second electrode 27 which is formed of a translucent material on the organic layer 26 (S4). In the organic EL light-emitting element according to the presently illustrated embodiment, the second electrode 27 serves as a cathode. An example of the material which constitutes a second electrode 27 is as described above, and the second electrode 27 is formed of a thin metal layer to have a thickness of 10 nm or more and 25 nm or less, which is a thickness sufficient to obtain a light transmitting property. The second electrode 27 is formed on the entire surface including the top surface of the insulation bank 23, since it is formed as a common electrode for each pixel.
Next, a protection layer 28 which serves as a seal layer to prevent a penetration of water and/or oxygen from the outside is formed on the second electrode 27. This protection layer 28 may be an inorganic layer formed of, for example, Si3N4 or SiO2, which has no hygroscopic property and may be formed by bonding to a substrate 21 (not indicated) in such a way to entirely cover the second electrode 27 and organic layer 26 and so on. Consequently, the organic EL light-emitting element of the embodiment of the present application is completed (see
As described above, by using an organic material containing an oligomer of the organic material as an organic material for the organic layer 26 of the organic EL light-emitting element, a coated-type organic layer 26 can be provided excellently on an small-sized area on the electrode and the second electrode 27 can be formed to have a thickness of 10 nm or more and 25 nm or less. Accordingly, a display unevenness such as a thickness unevenness can be reduced, and an organic EL light-emitting element with a high definition pattern having a superior light-emission property can be obtained at a low cost and, in addition, can be produced as a top emission type.
(1) An organic electroluminescent light-emitting element according to the first embodiment of the present application includes a substrate, a first electrode provided on a surface of the substrate, an insulation bank formed to surround at least part of the first electrode, an organic layer formed on the first electrode surrounded by the insulation bank, and a second electrode formed on the organic layer, wherein the insulation bank has a forward tapered shape and a hydrophilic surface, a thickness of the second electrode is from 10 nm or more and 25 nm or less, and the organic layer is a coated-type organic layer comprising an oligomer of an organic material.
According to the organic EL light-emitting element of the exemplary embodiment of the present application, a volume per one drop of a liquid drop of a liquid composition to be ejected form a nozzle of the ink-jet apparatus to form a coated layer can be small since the organic material to form a coated-type organic layer contains an oligomer, and thus, there is no possibility that a liquid composition overflows the insulation bank and spreads to the electrodes of neighboring pixels. This enables a high definition pattern formation of pixels by coating process. Further, since the surface of the insulation bank is formed to have a hydrophilic property, a dripped coating solution ejected to form a coated layer may be easily spread onto a surface of the insulation bank, enabling to form the organic layer which evenly fills up to a sidewall of an opening of the insulation bank. The organic layer with an excellent flatness can be formed on the first electrode. Further, the second electrode is formed by a thin layer, providing a light transmitting property through the second electrode.
(2) It may be preferable that the organic EL light-emitting element is a top emission type wherein an emitted light is taken out from a surface including the second electrode. Since the second electrode is a thin layer having a thickness of 10 nm or more and 25 nm or less, the second electrode can be formed with a thin thickness similar to the one wherein the organic layer is formed by vapor deposition method, and a light can be taken out efficiently from a top surface including the second electrode.
(3) It may be preferable that a height of the insulation bank from a surface of the first electrode is from 0.5 μm or more and 1 μm or less. With this range of height, a width of an insulation bank member can be formed narrow, enabling to make a pitch between pixels narrow. As a result, high definition pixels can be realized with a high definition pattern with a small pixel pitch such as 25 μm. Further, a deterioration of the viewing angle characteristics can be improved since there is no risk that light emissions in oblique directions are blocked by the insulation bank having a high height.
(4) It may be preferable that a curvature of a corner part provided between a top surface of the insulation bank and a side surface of the insulation bank is from 1×106 or more and 2×108 or less. This enables to form a thin layer of the second electrode, which is formed on an entire surface of an organic layer and top surface of the insulation bank, without causing a stepwise disconnection.
(5) It may be preferable for a top emission type light-emitting element that the second electrode is formed of aluminum or of a eutectic layer composed of magnesium and silver.
(6) Further, a method of manufacturing an organic EL light-emitting element of the second embodiment of the present application includes forming a first electrode on a surface of a substrate, forming an insulation bank to surround at least part of the first electrode, forming a coated-type organic layer on an area of the first electrode surrounded by the insulation bank, and forming a second electrode on the organic layer, wherein the second electrode is formed of a translucent material, wherein the insulation bank is formed so as to have a height of from 0.5 μm or more and 1 pm or less from a surface of the first electrode, and the organic layer is formed by applying a droplet of a liquid composition comprising an oligomer of an organic material using an ink-jet process.
According to the method of manufacturing an organic EL light-emitting element of the second embodiment of the present application, even when a size of pixel is small, an organic EL light-emitting element with an organic layer having an excellent flatness can be formed with a high definition pattern on a pixel electrode by a coating process. Therefore, a small-sized, high definition organic EL light-emitting element having the second electrode which is formed of a translucent material can be manufactured easily and inexpensively.
(7) It may be preferable that the method further includes conducting a surface treatment such that a corner part provided between a top surface of the insulation bank and a side surface of the insulation bank has a curved shape because this enables to form a thin layer of the second electrode on an entire surface of an organic layer and top surface of the insulation bank without causing a stepwise disconnection.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/042624 | 11/28/2017 | WO | 00 |
