Patent Application
20090128005
The present invention relates to an organic electroluminescent element (organic EL element) and a manufacturing method thereof.
Recent computerization and progress of the IT technology have been tremendous, and development of a luminescent element that emits light, a solar battery that absorbs light to subject the light to energy conversion, and further, liquid crystal-series and electrochromic-series light modulation elements in each of which a light transmittance is varied depending on ON-OFF of a voltage has been accelerated.
In each of these elements, an anode and a cathode are arranged on both surfaces thereof. In particular, when light is desired to be made incident onto or emitted from the element, a configuration is adopted, in which, by using a transparent electrode, light generated in the element is efficiently emitted to the outside, or light from the outside is made incident into the inside of the element.
Basically, the element represented by an organic EL element, the solar battery, the light modulation element, and a transistor element (FET element) allows the anode and the cathode to sandwich both surfaces of at least one type of functional thin film therebetween, and is composed as a sandwich type. When each element is viewed from a mechanical viewpoint, motion of charged carriers (electrons, holes) on interfaces between the two electrodes and the functional thin film, or on an interface between the functional thin film and the functional thin film, that is, on such an interface between different types of materials is positively utilized, and an electronic function or an optical function are exerted.
As an example of the above-described element, a description will be made below of an organic electroluminescent element that has got into the limelight recently.
When a voltage is applied between the anode 22 and the cathode 24, holes from the anode 22 side, and further, electrons from the cathode 24 side are injected into the light-emitting layer 23 beyond heights Δø of potential barriers in the respective contact interfaces thereof. Then, a mechanism is formed, in which the injected electrons and holes are recombined in the light-emitting layer 23, and the light is thereby emitted. Then, the light thus emitted is emitted from the transparent substrate 21 side formed of a light transmitting material.
First, there is proposed a method of fixing the anode in advance, and inserting a buffer layer between the anode and the light-emitting layer, in which an ionization potential of the buffer layer is an intermediate value between both thereof (refer to “Talk About Organic EL (original title is in Japanese), p. 49, edited by Nikkan Kogyo Shimbun, Ltd.).
Second, there is proposed a method of fixing the anode in advance, and selecting a light-emitting layer of which magnitude of the ionization potential is relatively close to the magnitude of the ionization potential ø2 of the anode.
Third, there is proposed a method of fixing the light-emitting layer in advance, and selecting an anode of which magnitude of the ionization potential is relatively close to the magnitude øH of the ionization potential of the light-emitting layer.
However, the above-described three methods have individually had problems.
In the first method, when the buffer layer is inserted, such an energy difference between the anode and the light-emitting layer can be varied in stages. Accordingly, as for the anode side, the holes as carriers thereof can easily go beyond the height Δø of the potential barrier. However, the magnitude ø of the ionization potential of the buffer layer cannot be arbitrarily controlled, and in addition, processes caused by coating and curing the buffer layer concerned are also increased, resulting in rising of cost. Accordingly, the first method has not been practical.
The second method has had a problem in that, when a light-emitting material is selected while focusing on the magnitude ø of the ionization potential, an emission color cannot be freely selected, or high light emission efficiency cannot be obtained, either.
In the third method, it has been extremely difficult to select such an anode of which magnitude of the ionization potential is close to the magnitude øH of the ionization potential of the light-emitting layer while satisfying low resistance, high light transmittance, electrode pattern formability such as etching property, and surface flatness, which are required for the anode. In addition, besides an ITO (Indium Tin Oxide) electrode that is most commonly used, as the anode for which transparent conductivity is required, electrodes of ATO (Antimony doped Tin Oxide), FTO (Fluorine doped Tin Oxide), ZnO (Zinc Oxide) are known; however, these electrodes have also had similar problems to those of the ITO electrode.
It has been desired to develop a functional element in which the height ø of the potential barrier on the contact interface between the anode and the cathode or the light-emitting layer is controlled as described above, and to make a display using the functional element commercially viable. However, in actual, based on physical values (ionization potentials) intrinsic to metal and oxide semiconductors, and further, to the functional thin film, the respective layers have not been able to help but being used in combination.
Moreover, as a conventional technology, there has been disclosed an organic EL element having a chemical doping layer in which a compound having property as a Lewis acid is doped into an organic compound is provided between the anode and the light-emitting layer (refer to Japanese Patent Unexamined Publication No. 2001-244079). However, since a process of providing the chemical doping layer is increased in the manufacturing process, this results in the rising of cost in a similar way to the above-described first method, and the disclosed organic EL element has not been practical. Moreover, in Japanese Patent Unexamined Publication No. 2001-244079, a configuration is adopted, in which a third layer (chemical doping layer) is provided between an anode layer and a hole transport layer. When the third layer as described above is formed, this does not contribute to a resistance decrease of the element at all, but on the contrary, there is a possibility that the third layer may function as a series resistor, and resistance between the anode layer and the hole transport layer may be increased. Moreover, there is also a possibility that the presence of the third layer may bring a decrease of the light transmittance. The decrease of the light transmittance leads to an optical loss when the light generated in the light-emitting layer is emitted to the outside through the anode transparent electrode and the transparent substrate, thereby causing a decrease of the emission brightness.
The present invention has been made in order to solve the above-described problems. It is an object of the present invention to provide an organic EL element that realizes the low-voltage drive and a long lifetime, and to provide a manufacturing method of the organic EL element, in which a manufacturing process is simple, and further, a cost reduction is achieved.
An organic electroluminescent element according to a first aspect of the present invention, includes: a substrate; a first electrode formed on the substrate; an organic light-emitting layer formed on the first electrode to be brought into contact with the first electrode; and a second electrode formed on the organic light-emitting layer, characterized in that an ion-doped surface onto which hydrogen ions or hydroxide ions are doped as dopant is provided in a vicinity of a contact interface between the first electrode and the organic light-emitting layer.
A manufacturing method of an organic electroluminescent element according to a second aspect of the present invention, includes the steps of: forming a first electrode on a substrate; adhering an aqueous solution containing hydrogen ions or hydroxide ions onto the first electrode, and doping the hydrogen ions or the hydroxide ions onto a surface of the first electrode; forming an organic light-emitting layer on the surface of the first electrode, onto which the hydrogen ions or the hydroxide ions are doped; and forming a second electrode on the organic light-emitting layer, characterized in that, when the hydrogen ions are doped onto molecules on the contact interface, negatively charged anions are adsorbed onto a surface of the first electrode, and an electric double layer is thereby formed, and when the hydroxide ions are doped onto the molecules on the contact interface, a concentration of the hydroxide ions is increased, and an ionization potential of the first electrode is thereby decreased.
A surface treatment method according to a third aspect of the present invention is characterized in that an electrode is immersed into an acidic solution containing hydrogen ions or into an alkaline solution containing hydroxide ions, the hydrogen ions or the hydroxide ions are doped onto a surface of the electrode, and an ionization potential of the surface of the electrode is thereby controlled.
a) to 3(c) are views showing states of the anode when hydrogen ions are doped onto a surface of the anode of the organic EL element according to the embodiment of the present invention:
a) is an explanatory view explaining how to measure photoelectrons flying out of the surface of the anode; and
a) to 13(c) are schematic views for explaining a decrease of the surface resistivity owing to the acidic solution treatment;
An organic EL element 1 according to an embodiment of the present invention is shown in
Then, the present invention is characterized in that an ion-doped surface (by an amount of several molecules) 4 onto which hydrogen ions (H+) are doped as dopant is provided in the vicinity of an interface formed in such a manner that the anode 3 and the organic light-emitting layer 5 are brought into contact with each other. As described above, the ion-doped surface 4 is formed on the contact interface between the anode 3 and the organic light-emitting layer 5, and a concentration of the hydrogen ions in the vicinity of the contact interface is increased. In such a way, an ionization potential of the anode 3 is increased, and when viewed from a hole side, a potential barrier ø of the contact interface between the anode 3 and the organic light-emitting layer 5 is lowered.
In
In accordance with a document, the ionization potential ø2 of the ITO electrode (anode 3) is approximately 4.5 eV to 4.7 eV, and an ionization potential of the PPC (organic light-emitting layer 5) is approximately 5.2 eV to 5.5 eV. When a consideration is made based on both values, the potential barrier ø of the contact interface between the anode 3 and the organic light-emitting layer 5 is estimated to be 0.5 eV to 1.0 eV. When a large potential barrier ø occurs on the contact interface between the anode 3 and the organic light-emitting layer 5, in order to obtain desired emission brightness, a high voltage must be applied between the anode 3 and the cathode 6, and holes or electrons must be injected positively. However, when the high voltage is applied between the anode 3 and the cathode 6, light emission stability and an emission lifetime in the organic light-emitting layer 5 are decreased, and the organic light-emitting layer 5 cannot reach a practical level. However, it is considered that, as in the present invention, the ion-doped surface 4 onto which the hydrogen ions (H+) are doped is formed on the contact interface between the anode 3 and the organic light-emitting layer 5, whereby a value of the ionization potential ø2 of the anode 3 is increased, and the emission brightness and the emission lifetime are enhanced. Note that the term “ionization potential” is used for the ITO as the material of the anode 3, and the ionization potential is defined to be energy necessary to take out the electrons from a neutral atom to the outside. Note that the ITO is a semiconductor, and in a strict sense, it is appropriate to use therefor not the “ionization potential” but a term “work function”. However, since both of the terms have basically the same conception, the term “ionization potential” is used here.
Next, a description will be made of functions and effects when the hydrogen ions (H+) are doped onto the surface of the anode 3 based on
First, a description will be made of the reason that an ionization potential IP2 of the anode 2 is increased when a surface of each sample is immersed into the acidic solution and the hydrogen ions (H+) are doped thereonto. Note that, though the reason is not clear at present, it is considered that the above-described phenomenon of increase occurs based on the following mechanism. Moreover, though the ionization potential of the electrode is expressed as Ip in the band structure shown in
In
A description will be specifically made of the examination in
By using a photoelectric spectrometer (AC-2, made by Riken Keiki Co., Ltd.), the ionization potential of the surface of the anode 3, on which the hydrogen ions (H+) are doped and the electric double layer 10 is formed, can be measured in the atmosphere. As shown in
Note that, on the above-described ion-doped surface 4, as shown in FIG. 6, the hydrogen ions 8 are present in the vicinity of the contact interface B of the anode 3 and the organic light-emitting layer 5. Specifically, the hydrogen ions 8 can be sometimes present on the contact interface B as denoted by reference numeral 8a, can be sometimes mainly present in the organic light-emitting layer 5 as denoted by reference numeral 8b, and further, can be mainly present in the anode 3 as denoted by reference numeral 8c. However, in the present invention, if a state is where the hydrogen ions 8 are in contact with the contact interface B, the ionization potential of the anode 3 can be increased.
The description has been made above of the organic EL element 1 in which the hydrogen ions are doped in the vicinity of the interface between the anode 3 and the organic light-emitting layer 5, whereby the ion-doped surface 4 is formed. However, in the present invention, an ion-doped surface in which hydroxide ions are doped onto an interface between the cathode and the organic light-emitting layer may be formed.
A longitudinal cross-sectional view of the organic EL element 13 in which the hydroxide ions are doped onto the contact interface between the cathode and the organic light-emitting layer is shown in
Then, in the present invention, an ion-doped surface (by an amount of several molecules) 16 onto which the hydroxide ions (OH—) are doped as the dopant may be provided in the vicinity of an interface formed in such a manner that the cathode 15 and the organic light-emitting layer 17 are brought into contact with each other. As described above, the ion-doped surface 16 onto which the hydroxide ions are doped is formed on the contact interface between the cathode 15 and the organic light-emitting layer 17, and a concentration of the hydroxide ions in the vicinity of the contact interface is increased. In such a way, an ionization potential of the cathode 15 is decreased, and a potential barrier ø of the contact interface between the cathode 15 and the organic light-emitting layer 17 is lowered. Note that, in a similar way to the hydrogen ions shown in
Next, a description will be specifically made of changes of the ionization potential Ip when the treatment is performed by using several types of acidic solutions or alkaline solutions based on
Data obtained by measuring the ionization potential Ip2 on the surface of the electrode (PEDOT:PSS) when PEDOT:PSS is used as the electrode, H2SO4 and HCl are used as the acidic solutions, and treatment concentrations at the time of the acidic treatment are changed is shown in
As shown in
Moreover, as shown in
Moreover, besides to the concentration (pH) at the time of the acidic solution treatment, the value of the ionization potential is varied also in response to the treatment temperature and the treatment time, which become factors to control the ion doping. Since the value of the ionization potential is varied in response to the treatment time or the treatment temperature, it is necessary to appropriately set the respective conditions in order to obtain a desired ionization potential. In
Note that, though the example of using H2SO4 and HCl as the acidic solutions has been mentioned in
Specifically, the organic electroluminescent element of the present invention includes the ion-doped surface onto which the hydrogen ions are doped as the dopant, and can select the proton acid, the Lewis acid, and a mixture thereof as the hydrogen ions. Then, preferably, the proton acid is at least one selected from among H2SO4, HCl, HNO3, HF, HClO3, FSO3H, and CH3SO3H, and the Lewis acid is at least one selected form among BF3, PF5, AsF5, SbF5, and SO3.
Moreover, it turned out that, when the surface of the electrode or the surface of the organic light-emitting layer was subjected to the acidic solution treatment to dope the hydrogen ions (H+) thereonto, surface resistivity of the surface of the electrode or of the organic light-emitting layer became small. Specifically, as shown in
From a result that strengths of OH and O in the inside of the electrode film are lowered, which is obtained by the data of
From the above-described points, it is considered that this phenomenon emerges in such a manner that the ions are directly doped onto the surface of the electrode or the surface of the organic light-emitting layer. Moreover, a configuration is adopted, in which the ions are directly doped, and more specifically, a configuration is adopted, in which a third layer is not present as in the conventional technology, and therefore, is not detected as an obvious layer thickness. In such a way, the decrease of the light transmittance within the visible light range is not recognized, either, and a merit is also generated, that the electrode or the organic light-emitting layer is usable as a transparent conductive film or a transparent electrode.
Note that the invention described in Japanese Patent Unexamined Publication No. 2001-244079 is one including a separate (independent) ion-doped layer from the functional thin film, in which the ion-doped layer is stacked on the functional thin film. Specifically, in Japanese Patent Unexamined Publication No. 2001-244079, it is described that the chemical doping layer is formed of an evaporation film or a solution coating layer, that a thickness thereof is 50 angstrom or more, and so on, in which the chemical doping layer is formed as a separate body from the light-emitting layer. When the chemical doping layer becomes the independent layer as described above, there occur such problems that a thickness of the stacked body is increased, and that the electric resistance is increased by an increase of the interface. Meanwhile, the invention of this application is one to dope the hydrogen ions or the hydroxide ions onto the molecules on the contact interface. Therefore, unlike the invention described in Japanese Patent Unexamined Publication No. 2001-244079, according to the present invention, functions and effects will be exerted, that the thickness of the functional thin film can be thinned, and the surface resistivity of the functional thin film can be reduced.
Next, a description will be made of the case of doping the hydroxide ions (OH−) by implementing the treatment by using the alkaline solution.
Data obtained by measuring the ionization potential Ip2 on the surface of the electrode (PEDOT:PSS) when PEDOT:PSS is used as the electrode, NaOH and NH3 are used as the alkaline solutions, and treatment concentrations at the time of the alkaline treatment are changed is shown in
As shown in
Moreover, it turned out that, when the concentration (pH) was increased to make the alkalinity strong in this solution treatment, the surface resistivity R of the surface of the electrode or the surface of the light-emitting layer became large. Although a mechanism of the above is not clear, either, this is probably considered to be because, when the treatment concentration is increased, the molecular structure of the electrode material itself or the organic light-emitting layer material itself is changed. Specifically, this is considered to be because, in the case of performing the NaOH treatment, Na is bonded to a terminal end of the molecular structure of the electrode or the organic light-emitting layer, whereby the molecular structure is changed.
Moreover, when the ionization potential of the electrode surface onto which the hydroxide ions as the dopant are not doped is defined as Ip1, and the ionization potential of the electrode surface onto which the hydroxide ions are doped is defined as Ip3, it is preferable that a difference Ip3-Ip1 between both thereof become smaller than 0. This means that the treatment using the alkaline solution reduces the ionization potential Ip3 of the electrode surface after the treatment more than the ionization potential Ip1 of the electrode surface before the treatment. Accordingly, a merit is generated, that the ionization potential of the cathode itself of the organic EL element can be arbitrarily controlled.
Next, a description will be made of composition materials of the organic EL elements 1 and 13.
As the electrodes (anodes and cathodes), it is preferable to use transparent electrodes in which an average light transmittance in the visible light range is 60% or more. In the case of using the transparent electrodes, it becomes possible for the organic EL elements to easily emit the light. As such transparent electrodes, a metal thin film, an oxide semiconductor, and an organic material thin film, which are to be shown below, can be mentioned. Note that, while the electrode material just needs to be selected in response to the usage purpose, low resistance can be obtained even under the room temperature (25° C.) in accordance with these transparent electrodes.
The metal thin film has a reflection peak (plasma reflection) intrinsic to the metal in the visible light range, and accordingly, does not always have high transparency. However, the metal thin film is low in resistance and excellent in stability, and accordingly, is frequently applied to a region brought by a high added value. As a material of the metal thin film, there can be mentioned at least one selected from among Au, Ag, Cu, Ni, Cr, Zn, In, Al, Sn, Pb, Pt, Pd, Ti, and mixtures thereof. From among those as illustrated above, it is preferable to select Au, Ag, Cu, or Pt from a viewpoint of the practical use. Note that it is possible to form the metal thin film by using the vacuum evaporation, the electron beam evaporation, the ion plating, or the sputtering method.
As the oxide thin film, it is preferable to use at least one selected from among inorganic oxides of tin oxide (SnO2), indium tin oxide (ITO), and zinc oxide (ZnO), and composites thereof, which is excellent in balance between the transparency and the specific resistance in the visible light range. Among them, ITO is widely used as the transparent electrode. This is because ITO is low in surface resistance and high in light transmittance, and further, it is easy to form a circuit pattern thereon by etching. On the contrary, ITO having such excellent property has a large disadvantage as will be described below. Since ITO is a ceramic thin film, flexibility thereof is insufficient. Moreover, it is difficult to form the ITO thin film on an organic material or an organic thin film, which is inferior in heat resistance, and accordingly, ITO cannot sometimes be composed as an element. Moreover, the ITO thin film is formed by mainly using the vacuum process (for example, the sputtering method, the ion plating method, the evaporation method, and the like), and accordingly, a deposition rate thereof is slow, and in addition, a large capital investment becomes necessary, and the rising of cost is inevitable. Accordingly, as the electrode, it is preferable to use an organic material thin film to be described below.
As the organic material thin film, it is preferable to use a thin film of a π-conjugated substance. In accordance with the π-conjugated substance, the low surface resistance and the high light transmittance can be made compatible with each other by a function of π electrons in a conjugated double bond. Such π-conjugated substances are broadly classified into ones with low molecular weights and ones with high molecular weights in accordance with molecular weights thereof, and just need to be appropriately selected in response to the configuration of the element or the deposition process.
As such low-molecular-weight π-conjugated substances, there can be mentioned at least one selected from porphyrin, phthalocyanine, triphenylamine, quinacridon, and derivatives thereof. Phthalocyanine may be one that does not contain metal, or may be a complex with copper, magnesium, or the like.
As such high-molecular-weight π-conjugated substances, there can be mentioned at least one selected from polypyrrole, polyacetylene, polyaniline, polythiophene, polyisothianaphthene, polyflan, polyselenophene, polytellurophene, polythiephene vinylene, polyparaphenylene vinylene, and derivatives thereof. Moreover, from a viewpoint of enhancing the conductivity, it is preferable to use a material in which the doping treatment is implemented for a π-conjugated polymer. In such a way, the material is low in resistance and excellent in light transmittance, and further, can exhibit desired optical functions such as color emission and photoelectromotive force.
Furthermore, as the organic material thin film, there may be used at least one selected from among polyethylenedioxythiophene (PEDOT), polypropylene oxide (PO), and derivatives thereof, which are soluble in water or an organic solvent. In such a way, it is easy to handle the organic material thin film, and in addition, it becomes easy to appropriately use a variety of printing methods therefor. In particular, polyethylenedioxythiophene (PEDOT):polystyrene sulfonate (PSS) among polyethylenedioxythiophenes (PEDOTs) functionally combines the low surface resistivity R and the high transmittance, and is soluble in the water or the organic solvent to be dispersible thereinto, and accordingly, is preferable as the electrode material. Note that the light transmittance in the visible light range must be decided in consideration for a relationship between a film thickness and light absorption amount of each π-conjugated substance.
Specifically, in the organic electroluminescent element of the present invention, at least one of the first electrode and the second electrode is any of the metal thin film, the oxide thin film, and the organic material thin film. Then, it is preferable that the metal thin film be formed of at least one element selected from among Au, Ag, Cu, Ni, Cr, Zn, In, Al, Sn, Pb, Pt, Pd, Ti, and the mixtures thereof. It is preferable that the oxide thin film be formed of at least one selected from among tin oxide, indium tin oxide, zinc oxide, and the composites thereof. Moreover, it is preferable that the organic material thin film be formed of the material containing the π-conjugated substance. Specifically, it is preferable that the above-described π-conjugated substance be the polymer soluble in the water or the organic solvent, and in detail, it is preferable that the π-conjugated substance be at least one selected from polypyrrole, polyaniline, polythiophene, polyacetylene, polyisothianaphthene, and the derivatives thereof, which are subjected to the doping treatment, or at least one selected from among polyethylenedioxythiophene, polypropylene oxide, and the derivatives thereof.
Moreover, for an organic material thin film made of other than the above-described π-conjugated substance, a material containing conductive nanoparticles and polymer resin having the light transmittance may be used. As the conductive nanoparticles, for example, there can be mentioned one of an element selected from among Au, Ag, Pt, Pd, Ni, Cu, Zn, Al, Sn, Pb, C, and Ti, or a compound containing an element selected from thereamong. It is preferable to set a particle diameter of the conductive nanoparticles roughly to 50 nm or less. When the particle diameter is set at 50 nm or less, the particle diameter of the conductive nanoparticles becomes smaller than the wavelength λ (380 to 780 nm) of the incident light in the visible light range, and the light transmittance is increased. Note that a shape of the conductive nanoparticles is not limited to the illustrated particulate shape, and may be needle-like and stick-like. In order to exhibit the light transmittance as described above, dispersibility of the conductive nanoparticles in the polymer resin becomes extremely important. When the conductive nanoparticles are mutually coagulated, the particle diameter thereof becomes larger, and the size thereof does not reach the size of the above-described wavelength λ of the incident light or less. Accordingly, the light transmittance is damaged by a scattering function that is based on the Rayleigh scattering and the Mie scattering. Moreover, roughness of the electrode surface is also increased. Furthermore, in any transparent electrode made of the metal thin film, the oxide thin film, and the organic material thin film, a film thickness thereof should be decided based on the balance between the light transmittance and the surface resistivity, and is not uniquely decided. However, roughly speaking, a film thickness of several ten nanometers to several hundred nanometers is at a practical level.
When the emission light is emitted to the outside of the element as in the organic EL element, it is preferable to increase a light transmittance of the substrate. As a substrate material that is highly light-transmittable, there can be mentioned glass, ceramics, and polymer resin. Note that a shape of such a substrate material is not particularly limited, and may be plate-like, film-like, linear, and variously three-dimensional.
Note that, with regard to a light transmittance of the substrate, it is also necessary to set the transmittance of the substrate in consideration for a thickness and surface flatness of the substrate, and further, for the transmittances, reflectances and absorptions of all the materials composing these elements. Light reflections on front and back surfaces of the substrate itself are generated by approximately 8% to 10% in total. Accordingly, preferably, an average transmittance of the substrate in the visible light range is set at 80% or more, more preferably, 85% or more. When the average light transmittance of the substrate is increased, a loss caused by the scattering and absorption of the light can be reduced to the minimum, and accordingly, the light generated from the organic light-emitting layer can be efficiently emitted through the substrate to the outside.
With regard to the substrate, besides the above-described light transmittance, anisotropy of a refractive index in the polymer resin also becomes a problem. This is because, when the anisotropy of the refractive index occurs, this affects an emitting direction of the light. Specifically, when birefringence Δn exceeds 0.1, it becomes difficult to emit the light to a required direction, resulting in an optical loss, and this is not preferable in practical use. Accordingly, it is preferable that the birefringence be set at 0.1 or less. Moreover, when the organic EL element is formed into a curved surface or a three-dimensional shape, flexibility of the substrate is required, and accordingly, it is preferable that the substrate be formed of a polymer resin film. As such a polymer resin film having the light transmittance, which is applicable to the substrate, there can be mentioned one selected from among polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polymethylmethacrylate (PMMA), polyethersulfone (PES), and derivatives thereof.
Next, a description will be made of a surface treatment method according to the embodiment of the present invention. Note that this surface treatment method is a method for forming the above-described ion-doped surface.
In the surface treatment method of the present invention, the acidic solution containing the hydrogen ions or the alkaline solution containing the hydroxide ions is adhered onto the electrode surface, the hydrogen ions or the hydroxide ions are doped onto the surface of the electrode, and the ionization potential of the electrode surface is controlled.
Describing in more detail, first, the surface of the substrate (of glass, ceramics, polymer resin, or the like) having the light transmittance is cleaned. As a cleaning method of the surface, a publicly known method can be used, and for example, there can be mentioned degreasing by a neutral detergent, and ultrasonic cleaning by an organic solvent (ethyl alcohol and the like).
After the surface of the substrate is cleaned, a PEDOT:PSS (of which ratio is 1:1.6) solution as the material of the transparent electrode is coated on the surface of the substrate by a thin-film forming method, thereafter, heat treatment is performed to cure the solution, and the transparent electrode is formed on the substrate having the light transparency. Here, a wet method should be used as the thin-film forming method, and as the wet method, there can be mentioned the casting method, the spin-coat method, the dip method, the spray method, and various printing methods (ink-jet method, gravure printing method, screen printing method). For example, in the case of using the spin-coat method, an appropriate amount of the PEDOT:PSS (of which ratio is 1:1.6) solution is dropped onto the glass substrate under the room temperature, and thereafter, a film with a predetermined thickness is formed by a spin coater while arbitrarily setting the number of revolutions thereof (for example, at 1,500 rpm). Thereafter, under the atmospheric pressure, the heat treatment for 10 minutes is performed at 200° C. to cure the solution. In such way, the transparent electrode as the PEDOT:PSS thin film can be formed on the glass substrate. Note that it is preferable to use the printing method in terms of the industrial production. In this case, after the electrode is pattern-printed on the substrate, the solution is cured, thus making it possible to form a transparent electrode pattern on the substrate.
Moreover, the acidic solution containing the hydrogen ions or the solution containing the hydroxide ions is prepared, and into the solution, the substrate on which the transparent electrode is formed is immersed for several seconds to several hundred seconds. In such a way, either the hydrogen ions or the hydroxide ions are ion-doped onto the surface of the transparent electrode. Thereafter, the treated surface is subjected to rinsing treatment by ultrapure water, and thereafter, is subjected to heat treatment at 200° C. for 20 minutes, and an ion-doped surface is thereby formed on the surface of the transparent electrode. In such a way, a series of the treatments is completed. For example, the immersion time when the H2SO4 solution is used as the acidic solution should be approximately 600 seconds, and the immersion time when the NaOH solution is used as the alkaline solution should be approximately 15 seconds. Note that treatment conditions (treatment solution concentration, immersion time, temperature) when the ions are doped should be appropriately set in response to the material, thickness, surface roughness or the like of the electrode or the organic light-emitting layer. Note that the above-described “immersion” incorporates a meaning that a surface of a sample is simply wetted by the acidic solution or the alkaline solution.
In accordance with the surface treatment method described above, there can be obtained a member including the electrode and the organic light-emitting layer, and further including the ion-doped surface in which either the hydrogen ions or the hydroxide ions are doped in the vicinity of the contact interface between the electrode and the organic light-emitting layer.
In the surface treatment of the present invention, not only the ionization potential of the surface of the electrode or the organic light-emitting layer can be arbitrarily controlled, but also it becomes possible to decrease the surface resistivity (increase the conductivity). A description will be made that the surface treatment method of the present invention can be extended to other various purposes.
The present invention is applied to the element represented by the organic EL element, the solar battery, the light modulation element, and the transistor (FET element). A point of the present invention is in that motions of the carriers (electrons, holes) on a bonded interface between different types of materials are positively utilized. It is obvious that the treatment method of the present invention is extremely effective for such an element as described above and a unit (aggregate) using the same. For example, when the present invention is extended to the organic EL element and a display member using the same, in addition to performance enhancements such as voltage reduction, lifetime elongation, and transmittance enhancement, it becomes possible to reduce the materials for use, to simplify the manufacturing process, and further, to reduce cost in the future by applying an all-wet process.
A description will be made of a manufacturing method of the organic EL element according to the embodiment of the present invention.
In the manufacturing method of the organic EL element according to the first invention, first, the surface of the substrate is cleaned. A cleaning method of the substrate is similar to the above-described method. After the cleaning, the first electrode is formed on the substrate. Specifically, the first electrode is formed by a wet thin-film forming method by using a material containing the π-conjugated substance soluble in the water or the organic solvent, and the first electrode is made as the above-described member. Here, the wet thin-film forming method is also similar to the above-described method.
Next, the ion-doped surface is formed, in which either the hydrogen ions or the hydroxide ions are doped onto the first electrode surface of the member. As a method of doping the hydrogen ions or the hydroxide ions, there can be employed a method of adhering the acidic solution containing the hydrogen ions or the alkaline solution containing the hydroxide ions onto the member. As a method of adhering the acidic solution or the alkaline solution onto the member, there can be mentioned a method of immersing the member into the solution, or exposing the member to an atmospheric gas thereof. For example, in the case of using, as the acidic solution, a solution containing the proton acid (H2SO4, HCl, HNO3, HF, HClO3, FSO3H, CH3SO3H) or the Lewis acid (BF3, PF5, AsF5, SbF5, SO3), it is preferable to set the solution concentration pH thereof at 0.5 to 6.5, and to perform the acidic treatment. Meanwhile, in the case of using, as the alkaline solution, a solution containing at least one selected from among NaOH, KOH, NH3, and the derivatives thereof, it is preferable to set the solution concentration pH thereof at 7.5 to 12.0, and to perform the alkaline treatment.
Thereafter, the surface subjected to the acidic treatment or the alkaline treatment as described above is washed and dried, and thereafter, the organic light-emitting layer is formed on the first electrode on which the ion-doped surface is formed. Specifically, the organic light-emitting layer is formed by using the wet thin-film forming method by using the material containing the π-conjugated substance soluble in the water or the organic solvent.
Moreover, the second electrode is formed on the organic light-emitting layer, and the organic EL element is made. Specifically, the second electrode is formed by the wet thin-film forming method by using the material containing the π-conjugated substance soluble in the water or the organic solvent.
In accordance with the above-described manufacturing method of the organic EL element, the formation of the electrodes (anode, cathode) and the organic light-emitting layer and the ion doping treatment can be brought together into a continuous wet process. Therefore, in comparison with the conventional vacuum evaporation method, the manufacturing process can be simplified, and further, the cost can be reduced to a large extent.
Specifically, the manufacturing method of the organic electroluminescent element according to the present invention is characterized in that the first electrode is the anode, the hydrogen ions are doped in the doping step, and further, the solution is at least one solution selected from among the proton acid, the Lewis acid, and the mixture thereof. Moreover, preferably, the proton acid is at least one selected from among H2SO4, HCl, HNO3, HF, HClO3, FSO3H, and CH3SO3H, the Lewis acid is at least one selected from BF3, PF5, AsF5, SbF5, and SO3, and the concentration pH of the solution is 0.5 to 6.5. Moreover, another manufacturing method of the organic electroluminescent element according to the present invention is characterized in that the first electrode is the cathode, the hydroxide ions are doped in the doping step, and further, the solution is at least one solution selected from among NaOH, KOH, NH3, and the derivatives thereof. Then, preferably, the concentration pH of the solution is 7.5 to 12.0.
Moreover, preferably, the first electrode is formed by the wet thin-film forming method by using the material containing the π-conjugated substance soluble in the water or the organic solvent, the organic light-emitting layer is formed by the wet thin-film forming method by using the material containing the π-conjugated substance soluble in the water or the organic solvent, and the second electrode is formed by the wet thin-film forming method by using the material containing the π-conjugated substance soluble in the water or the organic solvent. Furthermore, in the doping step, preferably, the substrate and the first electrode are immersed into the solution, whereby the solution is adhered onto the surface of the first electrode, and preferably, the step of washing and drying the surface of the first electrode is provided after the doping step and before the forming step of the organic light-emitting layer.
Moreover, the organic EL element manufacturing by the above-described manufacturing method can be driven at a low voltage since the ion-doped surface is provided between the electrode and the organic light-emitting layer in order to control the potential barrier. As a result, the long lifetime of the organic EL element can be realized. Furthermore, when the substrate or the electrode in the organic EL eminent is composed of the above-described transparent material having the high light transmittance, the emitting direction of the light can be arbitrarily set. As a result, it also becomes possible to apply the organic EL element as the display member and an illumination member by selecting the composition materials in response to the usage purpose.
A description will be specifically made below of the present invention by using Examples; however, the present invention is not limited to the illustrated Examples.
First, a quartz glass substrate was subjected to ultrasonic washing by ethyl alcohol, thereafter, an appropriate amount of the PEDOT:PSS (of which ratio was 1:1.6) was dropped onto the glass substrate under the room temperature, and was coated thereon by the spin coater with the number of revolutions of 1,500 rpm. In such a way, a thin film was formed. Thereafter, the thin film was subjected to heat treatment at 200° C. for 10 minutes, and was cured. In such a way, a member A was obtained, in which a transparent electrode with a film thickness of 100 nm was formed on the glass substrate.
Next, an acidic solution of H2SO4 with a solution concentration pH of 5.0 was prepared, the member A was immersed into the acidic solution of H2SO4, and the hydrogen ions were doped onto a surface of the member A. Thereafter, the surface of the member A was subjected to rinsing treatment by ultrapure water five times, and the member A was subjected to heat treatment at 200° C. for 600 seconds. In such a way, a sample was made, in which an ion-doped surface was formed on the transparent electrode of the member A.
In Example 1-2 to Example 1-5, samples in each of which the ion-doped surface was formed on the transparent electrode were made by using a similar method to that of Example 1-1 except that the concentration pH of the acidic solution of H2SO4 was changed at the time of the treatment by the acidic solution. The concentrations of the acidic solutions of H2SO4 in Example 1-2 to Example 1-5 were sequentially set at pH 3.0, pH 1.3, pH 0.6, and pH 0.2.
In Comparative example 1, the member A made in Example 1-1 without performing the treatment by the acidic solution was used as a sample.
In Example 2-1, a sample in which the ion-doped surface was formed on the transparent electrode was made by using a similar method to that of Example 1-1 except that an acidic solution of HCl with the concentration pH of 5.0 was used at the time of the treatment by the acidic solution.
In Example 2-2 to Example 2-5, samples in each of which the ion-doped surface was formed on the transparent electrode were made by using a similar method to that of Example 2-1 except that the concentration pH of the acidic solution of HCl was changed at the time of the treatment by the acidic solution. The concentrations pH of the acidic solutions of HCl in Example 2-2 to Example 2-5 were sequentially set at pH 3.0, pH 1.3, pH 0.6, and pH 0.2.
In Comparative example 2, the member A made by using a similar method to that of Example 1-1 without performing the treatment by the acidic solution was used as a sample.
In Example 3-1, a sample in which the ion-doped surface was formed on the transparent electrode was made by using a similar method to that of Example 1-1 except that an acidic solution of CH3SO3H with the solution concentration pH of 5.0 was used at the time of the treatment by the acidic solution.
In Example 3-2 to Example 3-5, samples in each of which the ion-doped surface was formed on the transparent electrode were made by using a similar method to that of Example 3-1 except that the concentration pH of the acidic solution of CH3SO3H was changed at the time of the treatment by the acidic solution. The concentrations pH of the acidic solutions of CH3SO3H in Example 3-2 to Example 3-5 were sequentially set at pH 3.0, pH 1.3, and pH 0.2.
In Comparative example 3, the member A made by using a similar method to that of Example 1-1 without performing the treatment by the acidic solution was used as a sample.
In Example 4-1, a sample in which the ion-doped surface was formed on the transparent electrode was made by using a similar method to that of Example 1-1 except that an acidic solution of BF3 with the solution concentration pH of 5.0 was used at the time of the treatment by the acidic solution.
In Example 4-2 and Example 4-3, samples in each of which the ion-doped surface was formed on the transparent electrode were made by using a similar method to that of Example 4-1 except that the concentration pH of the acidic solution of BF3 was changed at the time of the treatment by the acidic solution. The concentrations of the acidic solutions of BF3 in Example 4-2 and Example 4-3 were sequentially set at pH 3.0 and pH 1.3.
In Comparative example 4, the member A made by using a similar method to that of Example 1-1 without performing the treatment by the acidic solution was used as a sample.
In Example 5-1, first, the member A was made by using a similar method to that of Example 1-1.
Next, an alkaline solution of NaOH with the solution concentration pH of 7.5 was prepared. Then, the member A was immersed into the alkaline solution of NaOH for 15 seconds, and the hydroxide ions were doped onto the surface of the member A. Thereafter, the surface of the member A was subjected to rinsing treatment by ultrapure water five times, and the member A was subjected to heat treatment at 200° C. for 600 seconds. In such a way, a sample was made, in which an ion-doped surface was formed on the transparent electrode of the member A.
In Example 5-2 and Example 5-3, samples in each of which the ion-doped surface was formed on the transparent electrode were made by using a similar method to that of Example 5-1 except that the concentration pH of the alkaline solution of NaOH was changed at the time of the treatment by the acidic solution. The concentrations of the alkaline solutions of NaOH in Example 5-2 and Example 5-3 were sequentially set at pH 10.0 and pH 12.1.
In Comparative example 5, the member A made by using a similar method to that of Example 1-1 without performing the treatment by the alkaline solution was used as a sample.
In Example 6-1, a sample in which the ion-doped surface was formed on the transparent electrode was made by using a similar method to that of Example 5-1 except that an alkaline solution of NH3 with the solution concentration pH of 7.2 was used at the time of the treatment by the alkaline solution.
In Example 6-2 and Example 6-3, samples in each of which the ion-doped surface was formed on the transparent electrode were made by using a similar method to that of Example 6-1 except that the concentration pH of the alkaline solution of NH3 was changed at the time of the treatment by the alkaline solution. The concentrations of the alkaline solutions of NH3 in Example 6-2 and Example 6-3 were sequentially set at pH 10.0 and pH 12.1.
In Comparative example 6, the member A made by using a similar method to that of Example 1-1 without performing the treatment by the alkaline solution was used as a sample.
First, a quartz glass substrate was subjected to ultrasonic washing by ethyl alcohol, and thereafter, an ITO thin film was formed on the glass substrate by using the magnetron sputtering method. In such a way, a member B was obtained, in which a transparent electrode with a film thickness of 100 nm was formed on the glass substrate.
Thereafter, the member B was immersed into an alkaline solution of NaOH with the solution concentration pH of 7.5, and a sample in which an ion-doped surface was formed on the transparent electrode was made by using a similar method to that of Example 5-1.
In Example 7-2, a sample in which the ion-doped surface was formed on the transparent electrode was made by using a similar method to that of Example 7-1 except that the concentration pH of the alkaline solution of NaOH was changed to 12.0 at the time of the treatment by the alkaline solution.
In Comparative example 7, the member B made by using a similar method to that of Example 7-1 without performing the treatment by the alkaline solution was used as a sample.
First, a quartz glass substrate was subjected to ultrasonic washing by ethyl alcohol, and thereafter, an Au thin film was formed on the glass substrate by using the vacuum evaporation method. In such a way, a member C was obtained, in which a transparent electrode with a film thickness of 100 nm was formed on the glass substrate.
Thereafter, the member C was immersed into an alkaline solution of NaOH with the solution concentration pH of 10.0, and a sample in which an ion-doped surface was formed on the transparent electrode was made by using a similar method to that of Example 5-1.
In Comparative example 8, a member A made by using a similar method to that of Example 8 without performing the treatment by the alkaline solution was used as a sample.
For the respective samples made according to the above-described Example 1 to Example 8 and Comparative example 1 to Comparative example 8, the ionization potentials were measured in the atmosphere by using the photoelectric spectrometer (AC-2, made by Riken Keiki Co., Ltd.). Moreover, the resistivities of the respective samples were actually measured by the 4-point probe method (JIS K7194).
Measurement results of the respective samples of Example 1 to Example 4 and Comparative example 1 to Comparative example 4 are shown in Table 1, and measurement results of the respective samples of Example 5 to Example 8 and Comparative example 8 are shown in Table 2. Note that the ionization potentials of the respective Examples treated by the acidic solutions were defined as Ip2, the ionization potentials of the respective Examples treated by the alkaline solutions were defined as Ip3, and the ionization potentials of the members A, the members B, and the member C, which are not treated by the acidic solutions or the alkaline solutions, were defined as Ip1.
Note that, in Comparative example 1 to comparative example 6, the members A manufactured by using the manufacturing method of Example 1 were used as the samples; however, since trial production dates in the respective Comparative examples are different from one another, the values of the ionization potentials are different from one another. As opposed to this, in the same experimental systems (for example, Example 1-1 to Example 1-5 and Comparative example 1), the sample making was performed in the same day, and comparison was made for the respective Examples and Comparative example. Also in other experimental systems, the trial production date is the same in the same experimental system.
As shown in Table 1, in Examples in which the hydrogen ions were doped, the values of the ionization potentials became larger in comparison with Comparative examples in which the hydrogen ions were not doped. Moreover, Examples showed a tendency that the resistivities also became low and the conductivities became high. In particular, when comparison was made for Example 1-1 to Example 1-5 which were the same experimental systems, a tendency was shown, that the value of the ionization potential became larger as pH of the acidic solution containing the hydrogen ions was being reduced, and further, a tendency was shown, that the value of the resistivity became low and the conductivity became high. It turned out that a similar tendency was shown also in other experimental systems.
Moreover, as shown in Table 2, in Examples in which the hydroxide ions were doped, the values of the ionization potentials became smaller in comparison with Comparative examples in which the hydroxide ions were not doped. In particular, when comparison was made for Example 5-1 to Example 5-3 as the same experimental systems, a tendency was shown, that the value of the ionization potential became lower as pH of the alkaline solution was being increased. It turned out that a similar tendency was shown also in other experimental systems.
The entire contents of Japanese Patent Application 2005-51987 (filing date: Feb. 25, 2005) are incorporated herein by reference.
The description has been made above of the contents of the present invention along the embodiment and the examples; however, it is self-evident for those skilled in the art that the present invention is not limited to the description of these, and that various modifications and improvements are possible.
In accordance with the organic EL element according the present invention, the ion-doped surface is formed between the electrode and the organic light-emitting layer, and the potential barrier on the contact interface between the electrode and the organic light-emitting layer is controlled. Accordingly, the low-voltage drive is made possible, and the long lifetime can be achieved.
In accordance with the manufacturing method of the organic EL element according to the present invention, the element configuration becomes simple, the manufacturing process is also simple, and the further cost reduction can be achieved.
In accordance with an article using the organic EL element according to the present invention, a low-voltage drive thereof is made possible, and a long lifetime thereof can be achieved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-051987 | Feb 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP06/03430 | 2/24/2006 | WO | 00 | 10/25/2007 |
