JP2010118488A - Solution for forming conductive high polymer film, method for forming conductive high polymer film, and organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a conductive high polymer film having an intended thickness and excellent in flatness and conductivity. <P>SOLUTION: As the conductive high polymer material, one or both of polyaniline having a weight-average molecular weight of 1,000 or more and 10,000 or less and a derivative are used and dissolved in a mixed solvent to obtain a solution for forming a thin film. The mixed solvent includes a first aprotic polarity solvent and a second solvent does not include a hydroxyl group and includes a boiling point of 50°C or above and less than 120°C, which is lower than that of the first solvent. The mixed ratio by weight of the first and the second solvent ranges from 1:3 to 10:1. The thin film obtained by drying the solution, for instance, is employed for a hole-injection layer of an organic EL element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to film formation of a conductive polymer film using polyaniline or a derivative thereof as a conductive polymer material.

  In an organic electroluminescence (electroluminescence: hereinafter referred to as EL) element, an organic layer is usually formed on an indium tin oxide (ITO) electrode, but the surface of the ITO electrode immediately after the formation has large irregularities. For this reason, the organic layer of the organic EL element formed on the ITO electrode is likely to be short-circuited during driving particularly in a high-temperature environment, which causes a decrease in the reliability of the element.

  In addition, when small particles adhere to the ITO electrode, the organic layer is thin, so the particles are likely to be insufficiently covered with the organic layer, reducing the reliability of the device, such as disconnection and dark spots. End up.

  In order to solve the above problem, a method of reducing the surface unevenness by polishing the surface of the ITO electrode can be considered. However, there is a new problem of polishing marks and abrasive residue, and there is a problem that it cannot be applied when a flexible substrate is used. Further, it cannot cope with adhered particles.

  A method of forming a hole injection layer on an ITO electrode by a coating method using a solution containing PEDOT (polyethylenedioxythiophene): PSS (polystyrene sulfonic acid), which is a conductive polymer, is proposed in Non-Patent Document 1, etc. Has been.

  However, PEDOT: PSS proposed in Non-Patent Document 1 is an acidic material and reduces the device lifetime.

  On the other hand, Non-Patent Document 2 and the like disclose a polymer organic EL element using polyaniline as a hole injection layer instead of PEDOT: PSS. When an organic EL device is formed by coating using a commercially available highly conductive polyaniline solution, improvement is expected in terms of device life. However, a particle dispersion solution is adopted, and the flatness of the coating film surface is poor, short circuit is easily caused, and the reliability of the element is lowered.

  Patent Documents 1 and 2 disclose a new polyaniline coating solution which is not a particle dispersion but a dissolution type, in order to solve the above-mentioned problem of the commercially available polyaniline solution used for coating.

JP 2002-151272 A WO2003 / 071559 Synthetic metals 87, pp. 171-174 (1997) Nature 357, pp. 477-479 (1992)

  In the solution-type polyaniline solution for film formation, polyaniline is usually dissolved in an aprotic polar solvent such as 1-methyl-2-pyrrolidone. However, since a solution using an aprotic polar solvent is unlikely to become a high-viscosity solution, it is necessary to prevent a short circuit, for example, when a solution film is formed on a glass substrate by a spin coating method using only an aprotic polar solvent. It is difficult to obtain a uniform film having a uniform thickness, for example, a thickness of 100 nm.

  Patent Document 1 and Patent Document 2 suggest that a solvent such as ethyl cellosolve or ethylene glycol is added. However, these solvents containing a hydroxy group act to lower the solubility by acting on the N atom of polyaniline.

に示されるような構造を持ち、特許文献１では、式中のｙで区切られたユニットを省略して溶解度を向上させている。しかし、このユニットｙを省略するとポリアニリンとして安定した導電率が得られにくい。 Here, the polyaniline has the following formula (2):

In Patent Document 1, the unit delimited by y in the formula is omitted to improve the solubility. However, when this unit y is omitted, it is difficult to obtain a stable conductivity as polyaniline.

  In Patent Document 2, the unit y of the chemical formula (2) is generated by firing in the presence of oxygen in order to obtain a stable conductivity. Therefore, it cannot be fired in an inert gas atmosphere such as in a glove box. However, a structure other than polyaniline, such as a metal layer or another organic layer of an organic EL element, is often desired to have an inert gas atmosphere upon firing.

  In the present invention, formation of a conductive polymer film having excellent flatness and conductivity and having a desired thickness is realized.

  The solution for forming a conductive polymer film according to the present invention is a conductive polymer film in which a conductive polymer material containing one or both of a polyaniline and a polyaniline derivative having a weight average molecular weight of 1,000 to 10,000 is dissolved in a mixed solvent. A solution for forming a molecular film, wherein the mixed solvent includes a first solvent having an aprotic polarity and a second solvent not containing a hydroxy group and having a boiling point lower than that of the first solvent, The boiling point of the two solvents is 50 ° C. or higher and lower than 120 ° C., and the mixing weight ratio of the first solvent and the second solvent is between 1: 3 and 10: 1.

式（１）において、
Ｒ１、Ｒ２、Ｒ３、Ｒ４は、それぞれＨ、Ｃ_ｎＨ_２ｎ＋１（ｎ＝１〜８）、Ｏ、Ｃ_ｎＨ_２ｎ＋１（ｎ＝１，２）のいずれか、
Ｒａ、Ｒｂは、それぞれ水素原子、アルキル基、アリール基、アルコキシ基、ヒドロキシ基のいずれかであり、
式（１）において、ｘで区切られたユニットと、ｙで区切られたユニットと、ｚで区切られたユニットが、高分子中にランダム状又はブロック状のいずれか又は両方の混合状態で配置され、かつ、２ｚ／（２ｘ＋ｙ＋２ｚ）は、０．００５から０．１の範囲にあり、ｙ／（２ｘ＋ｙ）は０．２から０．７の範囲にある。 In another aspect of the present invention, in the solution for forming a conductive polymer film, the polyaniline or a derivative of the polyaniline is a compound represented by the following formula (1):

In equation (1),
R1, R2, R3, R4 are each _{H, C n H 2n + 1} (n = 1~8), O, C n H 2n + 1 either (n = 1, 2),
Ra and Rb are each a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a hydroxy group,
In the formula (1), the unit delimited by x, the unit delimited by y, and the unit delimited by z are arranged in a polymer in a random state, a block shape, or both in a mixed state. 2z / (2x + y + 2z) is in the range of 0.005 to 0.1, and y / (2x + y) is in the range of 0.2 to 0.7.

  In another aspect of the present invention, in the solution for forming a conductive polymer film, the first solvent includes any one of 1-methyl-2-pyrrolidone, dimethylformamide, and dimethylacetamide.

  In another aspect of the present invention, in the solution for forming a conductive polymer film, the second solvent contains a cyclic ether compound.

  In another aspect of the present invention, in the solution for forming a conductive polymer film, the second solvent contains any one of tetrahydrofuran, tetrahydropyran, and dioxane.

  In another aspect of the present invention, in the solution for forming a conductive polymer film, the doping anion represented by A in the formula (1) is an organic sulfonic acid or an organic phosphoric acid.

In another aspect of the present invention, in the conductive polymer film forming solution, the conductive polymer film forming solution is formed with a thickness of 100 nm on an insulating substrate using the conductive polymer film forming solution. The electrical conductivity is 10 ⁻⁶ S / cm or more and 10 ⁻⁴ S / cm or less.

  In another aspect of the present invention, there is provided a method for forming a conductive polymer film, wherein any one of the above-described solutions for forming a conductive polymer film is disposed on a film formation target, and then the mixed solvent is subjected to heat treatment. Is evaporated to form a conductive polymer film on the film formation target.

  In another aspect of the present invention, in the method for forming a conductive polymer film, the solution for forming the conductive polymer film is disposed on the film formation target by a wet process.

  In another aspect of the present invention, in the method for forming a conductive polymer film, a vacuum drying process or a heat drying process at 120 ° C. or more and 250 ° C. or less is performed as the drying process.

In another aspect of the present invention, an organic electroluminescent device comprising a light emitting layer containing an organic material, a hole transport layer, and a hole injection layer between an electron injection electrode and a hole injection electrode. The hole injection layer is formed directly on the hole injection electrode, the hole injection layer is formed using the above-mentioned solution for forming a conductive polymer film, and The conductivity of the hole injection layer is 10 ⁻⁶ S / cm or more and 10 ⁻⁴ S / cm or less.

  In another aspect of the present invention, in the organic electroluminescent element, the light emitting layer includes either or both of a low molecular light emitting property and a high molecular light emitting organic material, and the hole transporting layer has a low molecular hole transporting property. It is desirable to include the organic material.

  By using the solution for forming a conductive polymer film of the present invention, a conductive polymer having excellent surface flatness and desired conductivity on various substrates such as a glass substrate, an ITO electrode, and a resin substrate. A film can be formed. In addition, it can be fired in any environment such as air or nitrogen gas atmosphere.

  Furthermore, by applying the conductive polymer film as in the present invention to an organic EL element, it is possible to form an organic EL element with a short life during driving and a long life and high reliability. For this reason, for example, it becomes possible to apply also to the use to the vehicle-mounted display element etc. which are highly requested | required of high reliability.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments (hereinafter, embodiments) of the invention will be described with reference to the drawings.

(Conductive polymer film and solution for thin film formation)
The conductive polymer film according to the present embodiment uses, as the conductive polymer material, either or both of polyaniline having a weight average molecular weight of 1000 or more and 10,000 or less and a polyaniline derivative. A solution obtained by dissolving this conductive polymer material in a mixed solvent is placed on a film formation target (formation surface) to form a solution layer, and then subjected to a drying treatment to volatilize the mixed solvent. A conductive polymer film having a thickness can be obtained.

  A so-called wet process method can be employed as a method for attaching the solution to the film formation target surface. For example, a coating method such as a spin coating method, a dip coating method, or a spray method, an ink jet method, a transfer, a LITI (laser- printing methods such as induced thermal imaging).

  The mixed solvent employed for dissolving the polyaniline or the polyaniline derivative includes a first solvent having an aprotic polarity and a second solvent having no hydroxy group and having a boiling point lower than that of the first solvent.

  The boiling point of the second solvent not containing a hydroxy group is preferably 50 ° C. or more and less than 120 ° C. It is more desirable that the temperature be 60 ° C. or higher and 110 ° C. or lower. When the second solvent has such a boiling point, the second solvent is faster than the first solvent and is appropriate when drying (baking) after the solution layer is formed on the film formation target surface by coating or the like. It can be evaporated at speed. For this reason, it is possible to prevent the additive solvent from remaining in the thin film while improving the flatness of the thin film surface, and to form a high-density thin film.

式（１）において、Ｒ１、Ｒ２、Ｒ３、Ｒ４は、それぞれＨ、Ｃ_ｎＨ_２ｎ＋１（ｎ＝１〜８）、Ｏ、Ｃ_ｎＨ_２ｎ＋１（ｎ＝１，２）のいずれかであり、互いに同じでも異なっていても良い。Ｒａ、Ｒｂは、それぞれ水素原子、アルキル基、アリール基、アルコキシ基、ヒドロキシ基のいずれかであり、互いには同じでも異なっていても良い。 The polyaniline or a derivative of the polyaniline is a compound represented by the following formula (1):

In the formula (1), R1, R2, R3, and R4 are H, C _n H _{2n + 1} (n = 1 to 8), O, C _n H _{2n + 1} (n = 1, 2), respectively. It can be the same or different. Ra and Rb are each a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a hydroxy group, and may be the same or different.

  In the above formula (1), the unit delimited by x, the unit delimited by y, and the unit delimited by z are arranged in a random or block state or a mixture of both. In the formula, 2z / (2x + y + 2z) is in the range of 0.005 to 0.1, and y / (2x + y) is in the range of 0.2 to 0.7.

  As described above, 2z / (2x + y + 2z) is in the range of 0.005 to 0.1, and y / (2x + y) is in the range of 0.2 to 0.7, so that polyaniline is aggregated in the solution. Can be prevented. For this reason, when a thin film is formed from a solution in which polyaniline is dissolved, a flat film surface can be obtained.

Furthermore, polyaniline or a derivative thereof includes a unit represented by y necessary for the expression of conductivity, and 2z / (2x + y + 2z) and y / (2x + y) satisfy the above conditions, whereby the conductivity is 10 ⁻⁶ S / A thin film having a thickness of cm to 10 ⁻⁴ S / cm can be stably formed.

  If the conductivity in this range can be achieved, the conductive polymer film according to the present embodiment can be used, for example, for an organic EL element to exhibit appropriate conductivity as described later.

  As 2z / (2x + y + 2z) and y / (2x + y) are larger, polyaniline is more likely to aggregate. However, both are important parameters for obtaining the non-aggregated state and conductivity of polyaniline by setting the range as in the present embodiment because of the parameters which are largely related to the conductivity when the film is formed into a thin film. A material represented by 2x = y is called emeraldine and can exhibit high conductivity and is suitable as a conductive thin film.

  Examples of the first solvent include aprotic polar 1-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide and the like.

  The second solvent is a solvent having no hydroxy group as described above, and for example, a cyclic ether compound solvent can be employed, and more specifically, tetrahydrofuran, tetrahydropyran, and dioxane are exemplified.

  The mixing weight ratio of the first solvent and the second solvent is preferably between 1: 3 and 10: 1. When only the first aprotic polar solvent is used as the solvent for the polyaniline or its derivative material, it is difficult to form a uniform film with a sufficient thickness because the viscosity of the solution is low.

  However, in the present embodiment, as in the above-mentioned weight mixing ratio, a second solvent having at least a hydroxy group is used as an additive solvent to the first solvent. The hydroxy group acts on the N atom of the polyaniline skeleton to lower the solubility. However, since the hydroxy solvent does not exist in the second solvent, the solubility of the polyaniline does not decrease even if added. In addition, a uniform film can be obtained by a coating method with a film thickness necessary for preventing a short circuit.

  In particular, the cyclic ether compound solvent as the second solvent has an oxygen atom and a high surface shape of the molecule in addition to the above-described properties, and thus has high affinity with ITO and a glass substrate, and is an aprotic polar solvent. Affinity with (first solvent) is also high. Therefore, for example, in coating formation by spin coating, the film thickness can be increased despite the low viscosity of the coating solution. The high wettability to the substrate and the low viscosity of the coating solution also have the effect of improving the coverage of particles and steps, so that the effect of preventing an element short circuit is great.

  Further, the solution for forming the conductive polymer film may contain a doping anion material as represented by A in Formula (1). Examples of the doping anion include organic sulfonic acids such as dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid and paratoluenesulfonic acid, and organic phosphoric acids such as bis (2-ethylhexyl) phosphoric acid. By adding an appropriate amount of doping anion to a solution containing polyaniline or its derivative material as represented by chemical formula (1), 2z / (2x + y + 2z) of polyaniline or its derivative is changed from 0 before addition to 0.005 to 0 after addition. .1 value can be controlled.

  As described above, the film forming method using the solution in which the conductive polymer film material according to this embodiment is dissolved is a wet process method such as a coating method or a printing method. Examples of the drying process for volatilizing the solvent after forming the solution layer include a thermal drying process and a vacuum drying process.

  The heat drying treatment is desirably performed in a dry gas atmosphere, but is not limited and may be performed in the air. The heat treatment temperature is preferably 120 ° C. or higher and 250 ° C. or lower, and more preferably 130 ° C. or higher and 200 ° C. or lower. With such a heat treatment temperature, a plastic substrate with low heat resistance can be employed in addition to a glass substrate as a substrate on which the conductive polymer film is formed. Further, when drying at such a temperature, as described above, the second solvent evaporates before the first solvent, and the flatness of the film and the density of the film are improved.

(Element structure)
Next, an element using the conductive polymer film according to this embodiment will be described. FIG. 1 shows a schematic cross-sectional structure of an element 100 when an organic light emitting element, for example, an organic electroluminescence (hereinafter, EL) element is adopted as this element. Hereinafter, an organic EL element will be described as an example of the element of the present embodiment. However, the element is not limited to the organic EL element, and can be used for an electronic device such as an organic electronic device.

  The organic EL element 100 according to this embodiment includes an organic layer on a substrate 10 between a hole injection electrode 12 that functions as an anode and an electron injection electrode 14 that functions as a cathode. In this embodiment, the organic layer has a three-layer structure including a hole injection layer 20, a hole transport layer 22, and a light emitting layer 24 containing an organic material from the hole injection electrode 12 side. The structure is not limited to the three-layer structure, and an electron transport layer 26 may be provided between the light emitting layer 24 and the electron injection electrode 14 as shown in FIG. Furthermore, you may have many layers.

  In the organic EL device 100 as shown in FIG. 1, holes are injected from the hole injection electrode 12 into the light emitting layer 24 through the hole injection layer 20 and the hole transport layer 22, and electrons are transferred from the electron injection electrode 14 to the electron transport layer. 26 is injected into the light-emitting layer 24 via. Holes and electrons recombine in the light emitting layer 24, and light emission occurs when the electrons excited by the recombination energy return to the ground state. In the organic EL element, this light is extracted to the outside of the element. Used as a type display device.

  In the present embodiment, as the hole injection layer 20 formed in contact with the hole injection electrode 12, a conductive polymer layer formed using the above-described solution for forming a conductive polymer film is employed. This hole injection layer 20 enhances the efficiency of hole injection from the hole injection electrode 12 and exhibits an electron blocking property so that electrons injected from the electron injection electrode 14 do not reach the hole injection electrode 12 and disappear. To do.

  The substrate 10 is a transparent substrate such as glass, but is not limited to glass, and various substrates such as a resin substrate with a barrier film and a metal substrate can be used.

  The hole injection electrode 12 may employ any conductive material that can form a transparent or translucent electrode. Specifically, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, zinc oxide, indium oxide, zinc aluminum oxide, zinc gallium oxide, titanium niobium oxide, etc. are used as oxides and stacked by sputtering or the like. can do. Among these, ITO is a material having advantages such as low resistance, solvent resistance, and excellent transparency.

  The hole injection electrode 12 may be formed by forming a translucent conductive layer by vapor-depositing a metal material such as aluminum, gold, or silver on the surface of a conductive layer such as ITO or on the substrate 10. Furthermore, the hole injection electrode 12 may be formed by using other methods.

  Further, the hole injection electrode 12 may be patterned into a shape required for a display or the like by etching after film formation, if necessary. For example, an individual shape for each pixel or a stripe shape for each row or column can be used. Note that the surface may be activated by UV treatment or plasma treatment.

  The conductive polymer layer is formed as the hole injection layer 20 on the hole injection electrode 12. First, a solution for forming a thin film (hereinafter simply referred to as a polyaniline solution) is prepared by dissolving either or both of the above-mentioned polyaniline or a derivative thereof in a mixed solvent, and the polyaniline solution is applied to a wet process such as a coating method or a printing method. It is deposited on the hole injection electrode 12 by the method.

  For example, in the case of a spin coating method which is a kind of coating method, a predetermined amount of a thin film forming solution is discharged onto the hole injection electrode 12, and then the solution layer is uniformly formed on the hole injection electrode 12 by a spin coater (not shown). A polyaniline solution layer is formed on the hole injection electrode 12 by spreading. Thereafter, a drying process is performed to evaporate the solvent from the solution layer, thereby obtaining a conductive polymer film including polyaniline or a derivative layer thereof. This conductive polymer film can be formed to a thickness of about 100 nm, for example.

  Moreover, as a drying method, a heat drying process, a vacuum drying process, etc. are employable. In the case of the thermal drying treatment, it is desirable to be performed in a dry gas atmosphere, but the present invention is not limited to this and may be performed in the air. The heat treatment temperature is preferably 120 ° C. or higher and 250 ° C. or lower, and more preferably 130 ° C. or higher and 200 ° C. or lower. Within such a temperature range, a flexible and lower heat-resistant plastic substrate can be adopted as the substrate 10 on which the organic EL element is formed, in addition to a glass substrate.

  After the formation of the hole injection layer 20, in this embodiment, a hole transport layer 22, a light emitting layer 24, and an electron transport layer 26 are sequentially formed as organic layers. Further, the electron injection electrode 14 can be further formed on the electron transport layer 26. Both the organic layer and the electron injection electrode 14 can be formed by vacuum deposition. Further, it can be formed by a method other than the vacuum deposition method. For example, when a polymer material such as a polymer light emitting material is used, it can be formed by employing a wet process method.

  The hole injection layer 20 can also adopt a laminated structure. As the first hole injection layer covering the hole injection electrode 12, the above polyaniline layer may be adopted, and a copper phthalocyanine (CuPc) layer or the like may be formed thereon as the second hole injection layer. Note that the second hole injection layer may be omitted.

  The hole transport layer 22 is preferably made of a material having a high hole mobility. For example, a high hole mobility can be realized by adopting a low molecular organic material such as triphenylamine tetramer (TPTE). . Further, the TPTE layer formed by the vacuum evaporation method has excellent flatness, high density, and good adhesion to the hole injection layer 20 and the upper light emitting layer 24 of the present embodiment.

The light emitting layer 24 can also employ a low molecular organic material, and can be formed using, for example, a quinolinol aluminum complex (Alq ₃ ) as a layer that serves as both the light emitting layer and the electron transport layer. In this case, methylated quinacridone (MeQd) (host material is, for example, the quinolinol aluminum complex) as a dopant material only in the region of the light emitting layer 24, and the light emitting layer 24 and the electron transport layer 26 can be formed continuously. it can. The light emitting layer 24 and the electron transport layer 26 can be formed of different materials.

  The hole transport layer 22, the light emitting layer 24, and the electron transport layer 26 can be formed using a polymer material. In this case, for example, the film can be formed by a wet process method as described above.

  The electron injection electrode 14 is desirably made of a material having a low work function, and in particular, the interface on the light emitting layer 24 side should have a low work function. Therefore, as the electron injection electrode 14, a stacked structure in which an electron injection layer is interposed between the metal electrode layer and the electron injection electrode 14 can be adopted. For example, a stacked structure using alkali metal or alkaline earth metal, alkali metal or alkaline earth metal as the electron injection layer, and aluminum or the like as the metal electrode layer can be employed. Alternatively, a laminated structure using an alkali metal or alkaline earth metal halide or the like as the electron injection layer and aluminum or the like as the metal electrode layer can be employed.

  Specifically, Al / Ca (light emitting layer side), Al / Ba (light emitting layer side), Al / Li (light emitting layer side), Al / LiF (light emitting layer side), Al / CsF (light emitting layer side), A laminated structure such as Al / CaF (light emitting layer side) or Al / Ca / LiF (light emitting layer side) can be employed. Moreover, these laminated structures can be formed, for example by a vacuum evaporation method.

  After the formation of the electron injection electrode 14, finally, a sealing member is bonded to the element forming side of the substrate 10 in an inert gas atmosphere such as dry nitrogen, and the element is sealed. It is desirable to perform the sealing process by bonding the sealing member in a glove box.

  As a sealing member, various things, such as a metal can, glass with low permeability of oxygen and water, a resin substrate with a barrier film, and a metal substrate can be used. Also, a method of sealing the element by forming a protective film (barrier film) having low permeability such as oxygen and hydrogen so as to cover the entire element from above the electron injection electrode 14 instead of bonding is adopted. May be.

  In addition, when the process for forming each layer is performed in different film forming chambers, and particularly when each layer is formed by vacuum deposition, transportation between processes is not particularly limited, but transportation in a dry atmosphere is required. Is desirable.

  The polyaniline layer 20 is prepared by dissolving polyaniline or a derivative material thereof in a mixed solvent containing a first solvent and a second solvent, as described in the above-mentioned item of the conductive polymer film and the solution for forming the conductive polymer film. It forms using the solution which added doping anion material.

  As described above, the polyaniline or a derivative material thereof preferably has a weight average molecular weight of 1000 or more and 10,000 or less in order to improve the solubility in a mixed solvent. The starting material polyaniline or a derivative material thereof is preferably a material represented by the above chemical formula (1) and having z of 0 and y / (2x + y) in the range of 0.2 to 0.7. A material having 2x + y) in the range of 0.4 to 0.6 is more desirable. Among them, a material (emeraldine) having a relationship of 2x = y showing high conductivity is preferable.

  The first solvent of the mixed solvent is an aprotic polar solvent, and the second solvent does not contain a hydroxy group and has a lower melting point than the first solvent. The mixing ratio of both solvents is also preferably between 1: 3 and 10: 1 as described above.

  As the doping anion material added to the solution, organic sulfonic acids such as dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid and paratoluenesulfonic acid, and organic phosphoric acids such as bis (2-ethylhexyl) phosphoric acid can be employed. By adding an appropriate amount of doping anion to the polyaniline solution, 2z / (2x + y + 2z) can be controlled from 0 before addition to a value of 0.005 to 0.1 after addition.

The polyaniline layer formed using the polyaniline solution thus prepared has a conductivity of 10 ⁻⁶ S / cm or more and 10 ⁻⁴ S / cm or less, and has an appropriate conductivity as the hole injection layer 20 of the organic EL element. Realized.

  Such conductivity can prevent the organic EL element using the polyaniline layer from increasing in voltage. In addition, it is possible to suppress power loss due to in-plane leakage current between electrodes having different polarities arranged in the substrate surface. The electrodes with different polarities in the substrate surface are, for example, electrodes formed in individual shapes for each pixel, or electrodes formed in stripes for each row or column, and the electrodes arranged in proximity to each other, This corresponds to the case where a potential difference is generated due to the relationship between the selected (current supply) pixel and the non-selected (current non-supply) pixel.

  In the organic EL element, when the potential difference between the hole injection electrode 12 and the electron injection electrode 14, that is, the applied voltage must be increased, there is inevitably a large potential difference between the selected pixel and the non-selected pixel in the hole injection electrode 12. appear. However, by adopting the polyaniline layer as in the present embodiment for the hole injection layer 20 and suppressing the increase in the voltage of the element, the potential difference between the electrodes having different polarities in the substrate plane is reduced, and the in-plane leakage current is reduced. Can be suppressed.

  In the passive matrix type (passive drive dot matrix type) display, the hole injection electrode 12 and the electron injection electrode 14 are formed in a stripe shape in a direction crossing each other, and at the intersection of both electrodes, the electrodes And an organic layer sandwiched between the layers. This passive matrix type display has a simple structure compared to an active matrix type display in which each pixel is provided with an active element such as a transistor element for individually controlling light emission by an organic EL element. It is necessary to increase the voltage applied to the organic EL element of the pixel. Therefore, in this passive matrix type display, power loss in the substrate surface is likely to be a problem, but with this embodiment, this power loss can be suppressed, and low-cost, low-voltage driving is possible. In addition, it becomes easy to obtain a highly reliable organic EL element and organic EL display device.

  In addition, since the film surface has high smoothness and excellent adhesion to the underlying hole injection electrode 12 and the substrate 10 such as glass, peeling after the formation of the element can be prevented, contributing to an improvement in element reliability. Moreover, the fact that a conductive polymer layer having a sufficient thickness of about 100 nm can be formed is very advantageous in improving the reliability of the device.

  Hereinafter, specific examples of the present embodiment will be described.

Example 1
As Example 1 according to the present embodiment, a method for preparing a polyaniline solution is shown. First, 10 g of undoped polyaniline (emeraldine base, weight average molecular weight 5000) manufactured by Aldrich was added to 183 g of 1-methyl-2-pyrrolidone solvent as the first solvent, and completely dissolved by applying ultrasonic waves at 60 ° C. A first solution was prepared. Next, a second solution was prepared by mixing 1.34 g of dodecylbenzenesulfonic acid as a doping anion material and 183 g of tetrahydrofuran as a second solvent.

  To the first solution in which the polyaniline material is dissolved in the first solvent, the dodecylbenzenesulfonic acid solution, which is the second solution, is gradually added with stirring by a dropping method, and heat treatment is performed at 60 ° C. for 4 hours. The third solution was prepared by dissolving 3% by weight of polyaniline.

  Finally, 378 g of 1-methyl-2-pyrrolidone solvent as the first solvent and 378 g of tetrahydrofuran as the second solvent were added to the third solution to obtain a polyaniline solution (polyaniline solution for forming a thin film) in which 1 wt% polyaniline was dissolved. .

  The state of polyaniline in the polyaniline solution is as follows. In the chemical formula (1), x is 0.25, y is 0.425, z is 0.0375, 2z / (2x + y + 2z) is 0.075, and y / (2x + y) was 0.46.

The polyaniline layer was formed as follows. That is, the polyaniline solution was used as a coating solution, and the spin coating method was used. The above polyaniline solution was applied on an ITO / glass substrate that had been subjected to UV / O ₃ treatment under conditions of 2000 rpm for 30 seconds, followed by heat treatment drying at 150 ° C. for 2 hours to obtain a polyaniline thin film having a thickness of 100 nm. .

A copper phthalocyanine (CuPc) layer was formed on the obtained polyaniline layer as a second hole injection layer of the organic EL element. The hole transport layer 22 is a triphenylamine tetramer (TPTE) layer, the light emitting layer 24 is a quinolinol aluminum complex (Alq ₃ ) layer doped with 2% of methylated quinacridone (MeQd), and the electron transport layer 26 is a quinolinol aluminum. A complex was formed. All of these organic layers were produced in-situ by vacuum deposition. Further, subsequently, lithium fluoride (LiF) as an electron injection layer of the electron injection electrode 14 and aluminum (Al) as a metal electrode layer were both laminated in order by a vacuum deposition method to obtain an element structure. Finally, the element structure was sealed with a sealing can to obtain an organic EL element according to Example 1.

  The film thickness of each layer is ITO: 150 nm, polyaniline: 100 nm, copper phthalocyanine: 10 nm, triphenylamine tetramer: 50 nm, methylated quinacridone-doped quinolinol aluminum complex: 40 nm, quinolinol aluminum complex: 20 nm, lithium fluoride 0.5 nm, Al: 100 nm.

(Comparative Example 1-1)
As Comparative Example 1-1, H.264 was used instead of the polyaniline layer. C. A PEDOT: PSS layer (thickness: 100 nm) was formed on the hole injection electrode 12 using a PEDOT: PSS (CLEVIO P CH8000) solution manufactured by Starck. Other configurations and formation conditions were the same as in Example 1, and an organic EL element according to Comparative Example 1-1 was produced.

(Comparative Example 1-2)
As Comparative Example 1-2, Example 1 was used except that a polyaniline layer was formed using a commercially available highly conductive polyaniline coating solution (Emeraldine salt, 0.5 wt.%, Conductivity ~ 1 S / cm thin film) manufactured by Aldrich. An element having the same configuration was produced.

(Evaluation)
A breakdown voltage V _br when a reverse voltage is applied to the elements of Example 1 and Comparative Examples 1-1 and 1-2, a forward current passed through the elements, and an initial luminance of 2400 cd / m ² at room temperature. In the case of current driving, the relative luminance (L / L ₀ ) and the voltage increase rate (dV / V ₀ ) with respect to the initial value after 100 hours were measured. The results are shown in Table 1 below.

  In Example 1 and Comparative Example 1-1, a high breakdown voltage was shown, but in Comparative Example 1-2, it was low. A high breakdown voltage means that the element is difficult to short-circuit, and Example 1 and Comparative Example 1 were found to be elements that are difficult to short-circuit.

  Further, in Example 1 and Comparative Example 1-2, the relative luminance was high and the voltage increase rate was low, whereas in Comparative Example 1, the opposite result was obtained. Therefore, Example 1 and Comparative Example 1-2 had a long life. It turned out to be an element. From the above results, only Example 1 satisfies all the characteristics, and the effect of the solution for forming a conductive polymer film according to this embodiment is shown.

(Example 2)
Next, as Example 2, an example in which the weight average molecular weight of the polyaniline used as the conductive polymer material in Example 1 is changed is shown. In Example 1 above, the weight average molecular weights of undoped polyaniline (emeraldine base) manufactured by Aldrich were changed to 1000, 5000, 10000, 20000, and 65000, respectively, and polyaniline solutions were prepared.

  As a result of passing the obtained polyaniline solution through a PTFE 0.45 μm filter, there was a problem when the weight average molecular weights were 1000 (Example 2-1), 5000 (Example 2-2), and 10000 (Example 2-3). It was possible to pass without. However, when the weight average molecular weight was 20000 (Comparative Example 2-1), a considerable resistance was passed, and when the weight average molecular weight was 65000 (Comparative Example 2-2), it did not pass at all.

  The ease of passing through the filter correlates with the generation of particles, and as can be seen from the results of Examples 2-1, 2-2, and 2-3, it is understood that the weight average molecular weight is preferably 10,000 or less. On the other hand, if the weight average molecular weight is less than 1000, crystallization is likely to occur when a thin film is formed. From the above, it was found that a weight average molecular weight of 1,000 or more and 10,000 or less is an appropriate condition without generation of particles.

(Example 3)
Next, as Example 3, a case where the boiling point of the cyclic ether compound solvent used as the second solvent is changed is shown.

  As the cyclic ether compound solvent of the second solvent shown in Example 1 above, furan (boiling point 31 ° C.), tetrahydrofuran (boiling point 66 ° C.), tetrahydropyran (boiling point 88 ° C.), dioxane (boiling point 101 ° C.), 1-benzofuran ( Polyaniline solutions each having a boiling point of 173 ° C. were prepared.

  Furthermore, a polyaniline thin film was formed by spin coating using this solution. The result of evaluating the flatness (arithmetic mean roughness) Ra of the film surface in this case with an atomic force microscope is shown in FIG. Each flatness Ra was 1.56 nm for furan, 0.52 nm for tetrahydrofuran, 0.63 nm for tetrahydropyran, 0.76 nm for dioxane, and 1.12 nm for 1-benzofuran. The flatness Ra is desirably 1 nm or less in order to obtain a high breakdown voltage. From the result of FIG. 2, it is understood that the boiling point of the second solvent is an appropriate condition between 50 ° C. and 120 ° C. it can.

Example 4
Example 4 shows an example in which the mixing weight ratio of the aprotic polar solvent used as the first solvent in Example 1 and the cyclic ether compound solvent used as the second solvent was changed.

  Under the same conditions as in Example 1, except that the mixing weight ratio of 1-methyl-2-pyrrolidone, which is an aprotic polar solvent, and tetrahydrofuran, which is a cyclic ether compound solvent, was changed between 1: 5 and 20: 1. A polyaniline solution was prepared. A polyaniline thin film was formed by spin coating using the obtained polyaniline solution.

  As a result of the formation of the polyaniline film, when the mixing weight ratio (first solvent: second solvent) is between 1: 5 and 1: 4, polyaniline remains undissolved, and coating methods such as spin coating, ink jet, transfer, etc. As a solution for use in printing methods such as

  Furthermore, when the mixing weight ratio was between 11: 1 and 20: 1, polyaniline aggregated during heat treatment drying after spin coating, and a uniform thin film could not be obtained. From the above, it can be understood that the appropriate mixing weight ratio of the first solvent and the second solvent is between 1: 3 and 10: 1.

(Example 5)
Example 5 shows an example in which the value of 2z / (2x + y + 2z) of the polyaniline material represented by the chemical formula (1) used in Example 1 is changed.

  2z / (2x + y + 2z) of the polyaniline material was changed to 0, 0.001, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, and others were the same as in Example 1 above. Organic EL elements were prepared under the same conditions.

FIG. 3 shows an element driving voltage when a current of 50 mA / cm ² is passed through each element. As shown in FIG. 3, when 2z / (2x + y + 2z) is less than 0.005, the drive voltage of the element rapidly increases as the conductivity decreases. On the other hand, at 0.2 or more, particles were generated in the coating solution, and a uniform polyaniline thin film could not be formed.

  From the above results, it can be understood that it is an appropriate condition that 2z / (2x + y + 2z) of the polyaniline material is in the range of 0.005 to 0.1 as in the present embodiment.

(Example 6)
Example 6 shows a case where the value of y / (2x + y) of the polyaniline material represented by the chemical formula (1) used in Example 1 is changed.

  A polyaniline thin film was prepared under the same conditions as in Example 1 except that y / (2x + y) of the polyaniline material was changed between 0 and 1.

When y / (2x + y) is 0 (the state in which the polyaniline thin film is completely reduced), the resulting polyaniline thin film has a conductivity of 6 × 10 ⁻⁸ S / cm. When (2x + y) is 1 (a state in which the polyaniline thin film is completely oxidized), particles are generated.

  On the other hand, when y / (2x + y) is 0.2 to 0.7, the problem that particles are generated does not occur. That is, it can be understood that it is an appropriate condition that y / (2x + y) is in the range of 0.2 to 0.7 as in the present embodiment.

(Example 7)
Next, as Example 7, a case where the conductivity of the polyaniline thin film is changed is shown.

In FIG. 3, the electrical conductivity of the polyaniline thin film when 2z / (2x + y + 2z) is 0.005 is 2 × 10 ⁻⁶ S / cm. On the other hand, the conductivity when 2z / (2x + y + 2z) is 0.001 is 5 × 10 ⁻⁸ S / cm. Therefore, it can be seen that the conductivity is desirably 10 ⁻⁶ S / cm or more.

In addition, when the conductivity is 10 ⁻⁴ S / cm or more, in a 2-inch (2-inch type) size passive matrix display, an in-plane leakage current between electrodes of different polarities arranged in the substrate surface is 1 μA. Thus, it has been found that the power loss increases.

From the above, it can be understood that the appropriate condition is that the electrical conductivity of the polyaniline thin film is 10 ⁻⁶ S / cm or more and 10 ⁻⁴ S / cm or less as in this embodiment.

It is a figure which shows schematic structure of the organic EL element which concerns on embodiment of this invention. It is a figure which shows the relationship between the surface flatness which concerns on Example 3, and the boiling point of a 2nd solvent. The value of the polyaniline according to Example 5 2z / (2x + y + 2z), a diagram showing the relationship of the element driving voltage at a current of 50 mA / cm ² to the organic EL device formed by a respective polyaniline.

Explanation of symbols

  10 substrate, 12 hole injection electrode, 14 electron injection electrode, 20 hole injection layer, 22 hole transport layer, 24 light emitting layer, 26 electron transport layer, 100 organic EL element.

Claims (11)

A conductive polymer film-forming solution in which a conductive polymer material containing either or both of a polyaniline having a weight average molecular weight of 1000 or more and 10,000 or less and a polyaniline derivative is dissolved in a mixed solvent;
The mixed solvent is
A first solvent of aprotic polarity;
A second solvent not containing a hydroxy group and having a boiling point lower than that of the first solvent;
Including
The boiling point of the second solvent is 50 ° C. or higher and lower than 120 ° C.,
A solution for forming a conductive polymer film, wherein a mixing weight ratio of the first solvent and the second solvent is between 1: 3 and 10: 1. In the solution for forming a conductive polymer film according to claim 1,
The polyaniline or the derivative of the polyaniline is a compound represented by the following formula (1):

In equation (1),
R1, R2, R3, R4 are each _{H, C n H 2n + 1} (n = 1~8), O, C n H 2n + 1 either (n = 1, 2),
Ra and Rb are each a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a hydroxy group,
In the formula (1), the unit delimited by x, the unit delimited by y, and the unit delimited by z are arranged in a polymer in a random state, a block shape, or both in a mixed state. And 2z / (2x + y + 2z) is in the range of 0.005 to 0.1, and y / (2x + y) is in the range of 0.2 to 0.7. Solution. In the solution for forming a conductive polymer film according to claim 1 or 2,
The solution for forming a conductive polymer film, wherein the first solvent contains any one of 1-methyl-2-pyrrolidone, dimethylformamide, and dimethylacetamide. In the solution for forming a conductive polymer film according to any one of claims 1 to 3,
The solution for forming a conductive polymer film, wherein the second solvent contains a cyclic ether compound. In the solution for forming a conductive polymer film according to any one of claims 1 to 3,
The solution for forming a conductive polymer film, wherein the second solvent contains any one of tetrahydrofuran, tetrahydropyran, and dioxane. In the solution for forming a conductive polymer film according to claim 1,
In the above formula (1), the doping anion represented by A is an organic sulfonic acid or an organic phosphoric acid. In the conductive polymer film forming solution according to claim 1,
The conductivity of the conductive polymer film is 10 ⁻⁶ S / cm or more and 10 ⁻⁴ S / cm or less when the conductive polymer film forming solution is used to form 100 nm on an insulating substrate. A solution for forming a conductive polymer film. A method of forming a conductive polymer film,
After arranging the solution for forming a conductive polymer film according to any one of claims 1 to 7 on a film formation target,
A method for forming a conductive polymer film, comprising evaporating the mixed solvent by a drying process to form a conductive polymer film on the film formation target. The method for forming a conductive polymer film according to claim 8,
The method for forming a conductive polymer film, wherein the solution for forming the conductive polymer film is disposed on the film formation target by a wet process. In the formation method of the conductive polymer film according to claim 8 or 9,
The method for forming a conductive polymer film, characterized by performing a vacuum drying process or a thermal drying process at 120 ° C. or higher and 250 ° C. or lower as the drying process. An organic electroluminescent device,
Between the electron injection electrode and the hole injection electrode,
Having three or more organic layers including a light emitting layer containing an organic material, a hole transport layer, and a hole injection layer;
The hole injection layer is formed directly on the hole injection electrode,
The hole injection layer is formed using the solution for forming a conductive polymer film according to any one of claims 1 to 6, and the conductivity of the hole injection layer is 10 ^-6 S / cm or more. The organic electroluminescent element characterized by being 10 < ^-4 > S / cm or less.

Images