The present invention relates to an organic electroluminescent (EL) element that has a high luminous efficiency and can be used as a light source of an illuminating device, as well as a method for manufacturing the same.
Organic EL elements, which have inherent light emission capability and furthermore low power consumption, are not only used for pixels constituting display devices, but also have an excellent potential of being used as light-emitting elements in various types of illumination fixtures. If organic EL elements could be used as light-emitting elements in illumination fixtures, they would have better impact resistance and would be easier to handle than current incandescent light bulbs or fluorescent lamps, since organic EL elements are solid state elements, so that it would also become possible to realize illumination fixtures having special shapes that cannot be realized with current incandescent light bulbs or fluorescent lamps, leading to a wide range of applications.
However, with the structure of conventional organic EL elements, the light that is emitted from an organic light-emitting layer passes through the transparent substrate and other layers around it, and is attenuated to a level of 20% of the emitted light before reaching the outside. This is explained with reference to
Conventionally, such a microscopic uneven structure was fabricated using an etching process.
A microscopic uneven structure is disclosed for example in Yong-Jae Lee et al, Appl. Phys. Lett. 82 (2003) 3779 and M. Fujita et al, Electron. Lett. 39 (2003)1750.
However, when an etching process is used, the processing becomes complicated, and it becomes difficult to manufacture such a microscopic uneven structure at a low price.
Accordingly, it is an advantage of the present invention to provide an organic EL element as well as a method for manufacturing the same, with which the nanostructure can be manufactured at low cost using a nanoimprinting method not including an etching process, which can be used not only for applications as a pixel of a display device, but also as a light-emitting element of an illumination fixture.
In order to achieve this advantage, an organic electroluminescent element in accordance with a first aspect comprises:
a transparent substrate,
a sol-gel layer formed on the transparent substrate, the layer being made of a sol-gel material and having a microscopic unevenness (or roughness) in its surface,
a high refractive index material layer formed on the sol-gel layer by applying a high refractive index material to fill gaps in the unevenness of the sol-gel layer,
a first electrode formed on a multi-layer substrate (also referred to as “compound substrate” in the following) made of the transparent substrate, the sol-gel layer and the high refractive index material layer,
an organic solid light-emitting layer (also referred to as “light-emitting layer” in the following) including an organic light-emitting material formed on the first electrode, and
a second electrode formed on the light-emitting layer,
wherein the microscopic unevenness of the sol-gel layer is formed by nanoimprinting.
In accordance with a second aspect, in the organic electroluminescent element according to the first aspect,
the first electrode is a transparent electrode made of one selected from ITO, IZO and ZnO, or one selected from Au, Ag and Al, or an alloy including at least one metal selected from the group of Au, Ag and Al.
In accordance with a third aspect, in the organic electroluminescent element according to the first or second aspect,
the transparent substrate is a glass substrate.
In accordance with a fourth aspect, in the organic electroluminescent element according to any of claims the first to third aspect,
the refractive index of the sol-gel material is 1.30 to 1.60, and the refractive index of the high refractive index material used for planarizing the unevenness by applying it to the gaps in the unevenness of the sol-gel layer is 1.60 to 2.20.
In accordance with a fifth aspect, in the organic electroluminescent element according to any of the first to fourth aspects,
the microscopic unevenness of the sol-gel layer is formed by applying a sol-gel material to the transparent substrate, pressing and heating a die having a microscopic unevenness against the application surface, and separating the die, after the sol-gel material has been applied to the transparent substrate, and wherein the unevenness is planarized by applying a high refractive index material to the unevenness.
In accordance with a sixth aspect, in the organic electroluminescent element according to any of the first to fifth aspects,
the high refractive index material is an oxide of at least one metal selected from the group consisting of zirconium, aluminum, germanium and titanium.
In accordance with a seventh aspect, in the organic electroluminescent element according to any of the first to sixth aspects,
a difference H between valleys and peaks of the microscopic unevenness of the sol-gel layer is 10 nm to 10 μm, and a pitch W between valleys and peaks of the unevenness is 10 nm to 10 μm.
In accordance with an eighth aspect, in the organic electroluminescent element according to any of the first to seventh aspects,
a difference between the refractive index of the transparent substrate and the refractive index of the sol-gel layer is within a range of ±0.2, which is achieved by solidifying the sol-gel material after forming the microscopic unevenness in the sol-gel layer by pressing and heating a die having a microscopic unevenness against the sol-gel material, and separating the die.
In accordance with a ninth aspect, in the organic electroluminescent element according to any of the first to eighth aspects,
a difference between the valleys and peaks of the surface planarized by applying the high refractive index material is not greater than 20% of a difference H between valleys and peaks of the unevenness of the sol-gel layer.
In accordance with a tenth aspect, a method for manufacturing an organic electroluminescent element having a microscopic uneven structure made of a sol-gel material and a high refractive index material on a transparent substrate comprises.
a step of applying a sol-gel material on a transparent substrate;
a step of forming a sol-gel layer having a microscopic unevenness by pressing and heating a die having a microscopic unevenness against the applied sol-gel material, and separating the die,
a step of planarizing the unevenness by applying a high refractive index material on the microscopic unevenness, to form a high refractive index material layer,
and a step of layering a first electrode, an organic solid layer including an organic light-emitting material and a second electrode in that order on the planarized surface.
In accordance with an eleventh aspect, in the method for manufacturing an organic EL element according to the tenth aspect,
the first electrode is a transparent electrode made of one selected from ITO, IZO and ZnO, or one selected from Au, Ag and Al, or an alloy including at least one metal selected from the group of Au, Ag and Al.
In accordance with a twelfth aspect, in the method for manufacturing an organic EL element according to the tenth or eleventh aspect,
the transparent substrate is a glass substrate.
In accordance with a thirteenth aspect, in the method for manufacturing an organic EL element according to any of claims the tenth to twelfth aspects,
the refractive index of the sol-gel material is 1.30 to 1.60, and the refractive index of the high refractive index material is 1.60 to 2.20.
In accordance with a fourteenth aspect, in the method for manufacturing an organic EL element according to any of the tenth to thirteenth aspects,
the high refractive index material is an oxide of at least one metal selected from the group consisting of zirconium, aluminum, germanium and titanium.
In accordance with a fifteenth aspect, in the method for manufacturing an organic EL element according to any of the tenth to fourteenth aspects,
a difference H between valleys and peaks of the microscopic unevenness of the sol-gel layer is 10 nm to 10 μm, and a pitch W between valleys and peaks of the unevenness is 10 nm to 10 μm.
In accordance with a sixteenth aspect, in the method for manufacturing an organic EL element according to any of the tenth to fifteenth aspects,
a difference between the refractive index of the transparent substrate and the refractive index of the sol-gel layer is within a range of ±0.2, which is achieved by solidifying the sol-gel material after forming the microscopic unevenness in the sol-gel layer by pressing and heating a die having a microscopic unevenness against the sol-gel material, and separating the die.
In accordance with a seventeenth aspect, in the method for manufacturing an organic EL element according to any of the tenth to sixteenth aspects,
a difference between the valleys and peaks of the surface planarized by applying the high refractive index material is not greater than 20% of a difference H between valleys and peaks of the unevenness of the sol-gel layer.
With the subject matter of the first aspect, it is possible to improve the luminous efficiency of the organic EL element. This is explained with reference to the drawings.
On the other hand, in the case of the organic EL element according to the first aspect, there is little attenuation of the amount of light at the interface, the amount of light that is ultimately emitted to the outside of the organic EL element is increased, and the luminous efficiency is improved.
Then, when the light 111 passes through a second interface 108, which is the interface between a sol-gel layer 105 and the transparent substrate 106, it is attenuated and becomes the light 112, and the amount of light is reduced, but the degree of attenuation is lower than in the case of the conventional organic EL element. The reason why the degree of attenuation is lower is that the refractive index of the sol-gel layer 105 approximates the refractive index of the transparent substrate, and also lies in the effect of the uneven shape (or roughness) of the sol-gel layer. The light 112 that has passed through the second interface 108 passes through a third interface 109, which is the interface between the transparent substrate 106 and the outside, and becomes the light 113, which is emitted to the outside.
As explained above, with the subject matter of the first aspect, it is possible to suppress the attenuation of the light amount at the interfaces and to improve the overall luminous efficiency of the organic EL element by providing the sol-gel layer 105 and the high refractive index material layer 104.
It should be noted that, more specifically, the light 110 is that part of the light emitted in the light-emitting layer that has passed through the interface between the light-emitting layer 102 and the first electrode, but the attenuation at this interface is the same proportion in a conventional organic EL element as in the case of an organic EL element according to the present invention, so that for the sake of simplicity, this attenuation is ignored in the explanations of this specification.
In accordance with the second aspect, the same effect as with the first aspect can be attained also for an organic EL element in which the transparent electrode is made of one selected from ITO, IZO and ZnO, or one selected from Au, Ag and Al, or an alloy including at least one metal selected from the group of Au, Ag and Al.
In accordance with the third aspect, the same effect as with the first aspect can be attained also for an organic EL element in which the transparent substrate is made of glass.
In accordance with the fourth aspect, by setting the refractive index of the sol-gel material 1.30 to 1.60, and the refractive index of the high refractive index material used for filling the microscopic unevenness to 1.60 to 2.20, the difference between the refractive indices at the interface between the sol-gel layer made of sol-gel material and the transparent substrate can be made small, and also the difference between the refractive indices at the interface between the high refractive index material layer made of high refractive index material and the electrode can be made comparatively small. As a result, the optical transmittance at these interfaces can be improved.
In accordance with the fifth aspect, the same effect as with the first aspect can be attained also for an organic EL element in which the microscopic unevenness of the sol-gel layer is formed by applying a sol-gel material to the transparent substrate, pressing and heating a die having convex and concave portions corresponding to the concave and convex microscopic unevenness against the application surface, and separating the die, and in which a compound substrate is fabricated by planarizing the unevenness by applying/filling a high refractive index material to the unevenness (also referred to as “the nanoimprinting method” in the following). An organic EL element having a structure as shown in
Also in accordance with the sixth aspect, it is possible to attain the same effect as with the first aspect.
Also in accordance with the seventh aspect, it is possible to attain the same effect as with the first aspect.
Also in accordance with the eighth aspect, it is possible to attain the same effect as with the first aspect.
Also in accordance with the ninth aspect, it is possible to attain the same effect as with the first aspect.
In accordance with the tenth aspect, it is possible to attain the same effect as with the first aspect.
In accordance with the eleventh aspect, it is possible to attain the same effect as with the second aspect.
In accordance with the twelfth aspect, it is possible to attain the same effect as with the third aspect.
In accordance with the thirteenth aspect, it is possible to attain the same effect as with the fourth aspect.
In accordance with the fourteenth aspect, it is possible to attain the same effect as with the sixth aspect.
In accordance with the fifteenth aspect, it is possible to attain the same effect as with the seventh aspect.
In accordance with the sixteenth aspect, it is possible to attain the same effect as with the eighth aspect.
Also in accordance with the seventeenth aspect, it is possible to attain the same effect as with the ninth aspect.
Referring to the accompanying drawings, the following is an explanation of preferred embodiments of the present invention.
The sol-gel layer 106 is fabricated by so-called nanoimprinting using a sol-gel material, and is a nanostructure in which the difference H between the valleys and the peaks of a microscopic unevenness is for example 10 nm to 10 μm. Also the pitch W between the valleys and peaks of the unevenness is microscopic at 10 nm to 10 μm. The high refractive index material layer 104 is fabricated by coating a high refractive index material onto the sol-gel layer 105. A first electrode 103 functions as an anode or a cathode of the organic EL element. A light-emitting layer 102 serves as the light-emitting layer of the organic EL element and more specifically includes an electron transport layer, a light-emitting layer and a hole transport layer. A second electrode 101 functions as an anode or a cathode of the organic EL element. The portions that are arranged on top of the high refractive index material layer 104 may have the same structure as organic EL elements known in the art, and their manufacturing method may be the same as manufacturing methods known in the art. Accordingly, further explanations of their structure and manufacturing method are omitted.
The following is an explanation of a method for fabricating the sol-gel layer 105 and the high refractive index material layer 104.
First, the transparent substrate 106 is cleaned by ultrasonic cleaning or the like. Then, a sol-gel material is applied to the transparent substrate 106 (see
Next, a die 303 having a microscopic unevenness is pressed against the sol-gel material 105 (the numeral 105 is used for the sol-gel layer having a microscopic unevenness, but since also the state of the material not having this unevenness is physically the same, the same reference numeral 105 is used for it as well) and heated (see
The die 303 includes a microscopic unevenness, which is formed for example with a pitch of nm to 10 μm. The shape of this unevenness may be uniform, or it may be an irregular uneven shape instead of a constantly regular shape, as shown in
Moreover, as the conditions when pressing the die 303 against the sol-gel material 105 and heating it, a pressure of 10 to 2000 N/cm2 and a pressing time of 5 to 60 min is possible. As for the heating conditions, the heating temperature can be 18 to 500° C., and the press-heating time can be 5 to 60 min.
Next, after the sol-gel material 105 has solidified, the die 303 is separated from the sol-gel material 105 (
Next, a high refractive index material 104 (the numeral 104 is used for the high refractive index material, but since also the state of the material prior to shaping to the high refractive index material is physically the same, the same reference numeral 104 is used for it as well) is applied on the sol-gel layer 105, and its surface is planarized (see
It should be noted that the planarization is also important with regard to improving the reliability of the organic EL element according to the present invention.
The following is an explanation of a process for manufacturing an organic EL element according to the present invention by layering the first electrode 103, the light-emitting layer 102 and the second electrode 101 in that order on the compound substrate 120.
The method of layering, in order, the first electrode, the light-emitting layer 102, and the second electrode 101 on the compound substrate 120 fabricated by the process illustrated in
Firstly, the first electrode 103 is formed with, for example, ITO or IZO on the compound substrate 120, through film formation by sputtering (
The following is an explanation of the effect of the invention according to the present embodiment.
The effects of the invention according to the present embodiment lie in the aspect that the luminous efficiency of the organic EL element having a sol-gel layer and a high refractive index material layer as shown in
Then, a die 403 having a microscopic unevenness is pressed against the resist 402, and the thickness of a predetermined portion of the resist 402 is selectively reduced (see
Then, substrate including the residue is etched with a hydrofluoric acid based chemical (see
Compared to this conventional manufacturing method, the process shown in
Number | Date | Country | Kind |
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JP 2006-113761 | Apr 2006 | JP | national |