KR102245647B1 - Pedot:pss based electrode and method for manufacturing the same - Google Patents

Abstract

Preparing a PEDOT:PSS thin film formed on a substrate; Treating the thin film with a solution containing sulfuric acid or a sulfuric acid derivative in an amount of 75 to 100% by volume; Separating and washing the thin film from the solution; And drying the washed thin film at a temperature of 60 to 160° C., a method of manufacturing a PEDOT:PSS-based electrode, a PEDOT:PSS-based electrode manufactured thereby, and an organic electronic device employing the electrode. do.
According to the present invention, a PEDOT:PSS-based electrode capable of realizing electrical properties that can replace ITO while having the advantages of a conductive polymer such as processability, light weight, flexibility, simple coating process, and low production cost, a manufacturing method thereof, and An organic electronic device employing the electrode can be provided.

Description

PEDOT:PSS-based electrode and its manufacturing method {PEDOT:PSS BASED ELECTRODE AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a PEDOT:PSS-based electrode and a method of manufacturing the same. More specifically, it relates to a PEDOT:PSS-based electrode with improved electrical conductivity, a method of manufacturing the same, and an organic electronic device employing the same.

Flexible plastic electronic devices are light and flexible, and are a collection of science and technology that can be usefully used in the future ubiquitous era. One of the most important factors in the development of such electronic devices is the development of plastic transparent electrodes. Transparent electrodes are widely used in flat panel displays such as LCD, PDP, and OLED, touch screens, and thin-film solar cells.

The most representative transparent electrode currently in use is indium tin oxide (ITO), which exhibits excellent optical and electrical performance. However, ITO is not only difficult to be used in the field of next-generation bending devices because of its fragile properties, and because it uses a high-temperature evaporation process, there has been a limit to manufacturing high-performance transparent electrodes using a printing process. In addition, the development of a new transparent electrode is urgently due to the limited reserves of indium, the main raw material of ITO, and the resulting price increase.

As a transparent electrode to replace ITO, many studies have been conducted on carbon nanotubes, graphene, silver nanowires, and metal oxides, but the plastic transparent electrodes developed so far have remarkably low conductivity, so it is urgent to overcome this.

As another transparent electrode to replace ITO, conductive polymers are made of organic materials, and have the advantages of general plastics such as workability, light weight, flexibility, simple coating process, and low production cost. Because it is high, it is in the spotlight as a substitute for ITO. In addition, conventional alternative materials composed of organic materials must also require an expensive and complex deposition process in order to obtain electrical conductivity comparable to that of ITO, but conductive polymers have the advantage that low-temperature solution processes are possible.

However, in replacing ITO with a conductive polymer, the relatively low electrical conductivity of the conductive polymer has been a problem.

As a representative conductive polymer, PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) has high conductivity among conductive plastic materials, has good transmittance in the visible light region, and is environmentally friendly because it is soluble in water. It is one of the most widely used materials due to its possible solution process and excellent stability (Fig. 1), but it has a very low conductivity of 1 S/cm for use as a transparent electrode, compared to ITO (>5,000 S/cm). That's an absurd shame.

For the past decades, many studies have been conducted on the optical and electrical properties of PEDOT:PSS, and there have been attempts to improve the conductivity through various organic solvents, surfactants, and acid treatments. According to the recently published Non-Patent Document 1, there is a report that a 1.0 M sulfuric acid (H ₂ SO ₄ ) solution was dropped on a PEDOT:PSS thin film to obtain an electrical conductivity of 3,065 S/cm. However, not only does not present a specific mechanism for improving conductivity and an optimal manufacturing method, but also does not realize electrical properties that can replace ITO, there is a limit to practical commercialization.

Therefore, there is a need to develop a transparent electrode that realizes electrical properties that can replace ITO by presenting an optimal manufacturing method for improving the conductivity of a conductive polymer.

Yijie Xia, Kuan Sun, and Jianyong Ouyang, Solution-Processed Metallic Conducting Polymer Films as Transparent Electrode of Optoelectronic Devices, Advanced Materials 2012, 24, 2436-2440

One aspect of the present invention is a PEDOT:PSS-based electrode capable of realizing electrical properties that can replace ITO while having advantages such as processability, light weight, flexibility, simple coating process, and low production cost, and a method of manufacturing the same, and the electrode I would like to present an organic electronic device employing.

However, the problem to be solved by the present invention is not limited to the problems mentioned above, and other problems that are not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, one aspect of the present invention, the step of preparing a PEDOT:PSS thin film formed on a substrate; Treating the thin film at room temperature with a solution containing sulfuric acid or a sulfuric acid derivative in an amount of 75 to 100% by volume; And separating and washing the thin film from the solution, wherein the step of separating and washing the thin film includes removing sulfuric acid or a sulfuric acid derivative attached to the surface of the PEDOT:PSS thin film or desorbed from the PEDOT:PSS To remove PSS, it provides a method of manufacturing a PEDOT:PSS-based electrode.
In an embodiment of the present invention, it may further include drying the washed thin film at a temperature of 60 to 160°C.

Another aspect of the present invention is a substrate; And an electrode in the form of a PEDOT:PSS thin film formed on the substrate, wherein the PEDOT:PSS thin film has a molar ratio of PEDOT to PSS of 1.6 to 2.0, and a crystallinity of 40% or more. to provide.

Another aspect of the present invention is a substrate; A first electrode in the form of a PEDOT:PSS thin film formed on the substrate; A photoactive layer on the first electrode; And a second electrode positioned on the photoactive layer, wherein the PEDOT:PSS thin film has a molar ratio of PEDOT to PSS of 1.6 to 2.0, and a crystallinity of 40% or more. The device is provided.

According to the present invention, a PEDOT:PSS-based electrode capable of realizing electrical properties that can replace ITO while having the advantages of a conductive polymer such as processability, light weight, flexibility, simple coating process, and low production cost, and a manufacturing method thereof, and An organic electronic device employing the electrode can be provided.

1 is a diagram showing the chemical structure of PEDOT:PSS.
2A is a schematic diagram illustrating a rearrangement of a PEDOT:PSS structure through high concentration sulfuric acid treatment and a mechanism for improving conductivity accordingly.
2B is a diagram showing a method of post-treating a PEDOT:PSS thin film with sulfuric acid according to an embodiment of the present invention.
FIG. 3 is a graph showing changes in the electrical conductivity of PEDOT:PSS when the concentration of sulfuric acid is changed (a) and the drying temperature is changed (b).
4 is a diagram showing the results of X-ray structure analysis (a) and the molecular packing structure (b) of crystalline PEDOT:PSS when the concentration of sulfuric acid is varied.
5 is a BF (Bright Field)-TEM image and a HAADF-STEM image of a PEDOT:PSS thin film treated with various concentrations of sulfuric acid.
6 shows the structural formula (a) of various solvents for PEDOT:PSS treatment, sheet resistance values (b) of PEDOT:PSS treated with each of these solvents at various temperatures, and conductivity values of PEDOT:PSS treated with each of these solvents ( b) is the result.
7 shows absorption spectrum (a), molar ratio (b), charge density (c), crystallinity (d), and charge mobility (e) of PEDOT:PSS thin films treated with various concentrations of sulfuric acid. This is the result showing the change.
8 is a graph showing the relationship between the light transmittance versus the sheet resistance (a) and the light transmittance versus the wavelength (b) of a PEDOT:PSS-based electrode according to an embodiment of the present invention.
9 is a graph (b) showing a performance comparison (a) and a relationship between current density and voltage of a solar cell employing a PEDOT:PSS-based electrode and ITO as an electrode according to an embodiment of the present invention.
10(a) is a structure of a light emitting device employing a PEDOT:PSS-based electrode and ITO as electrodes according to an embodiment of the present invention.
10(b) is a performance comparison result of a light emitting device employing a PEDOT:PSS-based electrode and ITO as an electrode according to an embodiment of the present invention.
11 is a schematic diagram showing an organic electronic device according to an embodiment of the present invention.

Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present application. However, the present application may be implemented in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, parts not related to the description are omitted in order to clearly describe the present application.

Throughout this specification, when a member is positioned “on” another member, this includes not only the case where a member is in contact with the other member, but also the case where another member exists between the two members.

In the entire specification of the present application, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated. The terms "about", "substantially", "approximately", etc. to the extent used throughout this specification are used at or close to that value when manufacturing and material tolerances specific to the stated meaning are presented, To aid the understanding of the present application, accurate or absolute numerical values are used to prevent unreasonable use of the stated disclosure by unscrupulous infringers. As used throughout the specification of the present application, the term "step (to)" or "step of" does not mean "step for".

In the entire specification of the present application, the term "combination of these" included in the expression of the Makushi format refers to one or more mixtures or combinations selected from the group consisting of components described in the expression of the Makushi format, and the constituent elements It means to include one or more selected from the group consisting of.

In the present specification, terms such as “consisting of” or “comprising” should not be construed as necessarily including all of the various elements or various steps described in the specification, and some of the elements or some steps are included. It should be interpreted that it may not be, or may further include additional components or steps.

In the present specification, "%" representing the concentration of sulfuric acid or sulfuric acid derivative can be understood as "vol%" or "volume%" unless otherwise specified.

The present invention is a kind of conductive polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) post-treatment with sulfuric acid or a sulfuric acid derivative, and electrical properties such as low electrical conductivity, which have been pointed out as disadvantages of conventional conductive polymers. The present invention relates to a technology for using as an electrode that can replace ITO by remarkably improving the process of post-treatment with sulfuric acid or a sulfuric acid derivative, as shown in Fig. 2b.

First, a PEDOT:PSS thin film formed on a substrate is prepared.

Polyethylenedioxythiophene (PEDOT, poly(3,4-ethylenedioxythiophene)), a polythiophene-based conductive polymer, ^{has excellent electrical conductivity of 10 3} ~ 10 ⁶ S/cm, but it does not dissolve in water, so there is a problem that processability is poor. . Thus, polystyrenesulfonate (PSS, poly(styrenesulfonate)) having anionic properties was introduced as a dopant, so that it can exist as a stable dispersion in water as a composite of PEDOT/PSS, and has excellent thermal stability. In addition, in order to maintain the optimum dispersibility of PEDOT in water, the concentration of PEDOT and PSS solids is adjusted in the range of 1.0% to 1.5% by weight. Since the PEDOT is further mixed well with water, alcohol, or a solvent having a large dielectric constant, it can be easily coated by diluting with the solvent. Even when a coating film is formed, it exhibits excellent transparency compared to other conductive polymers such as polyaniline and polypyrrole.

Meanwhile, in forming PEDOT:PSS on the substrate, a dry process or a wet process may be used. Dry processes include sputtering and evaporation, and wet processes include dip coating, spin coating, roll coating, and spray coating. have. However, it is preferable to use a wet process in which PEDOT:PSS mixed in a solvent such as water, alcohol, acetonitrile, etc. is coated on a substrate in terms of printability, manufacturing cost, and low-temperature process possibility.

The thickness of the PEDOT:PSS thin film is 30 nm (light transmittance 94% and sheet resistance 80 Ω/sq) to 105 nm (light transmittance 83% and sheet resistance 26 Ω/sq) in terms of reducing sheet resistance.

The substrate may be selected from the group consisting of glass, quartz, Al ₂ O ₃ and SiC, but is not limited thereto. Preferably, glass or the like is used without fear of corrosion even under high-concentration acidic conditions, which will be described later.

The previously prepared PEDOT:PSS thin film is treated with a solution containing sulfuric acid or a sulfuric acid derivative in an amount of 75 to 100% by volume. In the solution, components other than sulfuric acid or a sulfuric acid derivative may be water, alcohols, acetonitrile, or a mixture of two or more thereof, but are not limited thereto. The method of treating the thin film with the solution is to expose the thin film to the solution, and methods such as spraying, coating, and immersion may be used, but the method of immersion is preferable in terms of simplicity of the process and maximization of reaction efficiency. . (In the following, the invention is limited to'immersion' as a treatment method.)

The sulfuric acid or sulfuric acid derivative _{may include a compound containing -SO 3} ^- or -SO ₃ H, but is not limited thereto. The PSS part present in PEDOT:PSS contains -SO ₃ ^- or -SO ₃ H, but it is thought that the interaction with PEDOT:PSS will be good if a solvent containing sulfuric acid or a sulfuric acid derivative having a similar functional group is used. Specifically, the sulfuric acid or sulfuric acid derivative is methanesulfonic acid, trifluoromethansulfonic acid, sulfuric acid (sulfuric acid), perchloric acid, benzenesulfonic acid, and paratoluenesulfonic acid. p-Toluenesulfonic acid), 4-Ethylbenzenesulfonic acid, 4-Sulfophthalic acid, p-Xylene-2-sulfonic acid hydrate, 5- Amino-1-naphthalenesulfonic acid (5-Amino-1-naphthalenesulfonic acid), 8-amino-2-naphthalenesulfonic acid (8-Amino-2-naphthalenesulfonic acid), 4-amino-2-naphthalenesulfonic acid (4-amino-2 -naphthalenesulfonic acid), taurine, 1,4-butanedisulfonic acid, sulfurous acid, bis (trifluoromethane) sulfonamide and 2 thereof It may be selected from the group consisting of a mixture of more than one species, but is not limited thereto. However, for convenience of explanation, in the present specification, a reaction mechanism is typically described using sulfuric acid.

Referring to FIG. 2A, a high concentration of sulfuric acid (H ₂ SO ₄ ) performs an autoprotolysis action so that two sulfuric acid (H ₂ SO ₄ ) molecules generate two ions as follows.

_{2H 2 SO 4 ↔ H 3 SO} 4 + + HSO 4 -

In the case of PEDOT:PSS, anionic PSS exists around PEDOT polymers that exhibit electrical conductivity due to intermolecular attraction. This PSS serves to improve the dispersibility in the solvent by preventing stacking of PEDOT. However, the low electrical conductivity PSS forms a non-conductive molecular chain around the PEDOT, so that the overall electrical conductivity of the electrode may be degraded. In the case of post-treatment with a solution containing ultra-high concentration of sulfuric acid or a sulfuric acid derivative in the present invention, anionic HSO ₄ ^- is surrounded by the PEDOT and cationic H ₃ SO ₄ ⁺ is surrounded by the PSS. The intermolecular force is weakened, leading to a "charge separated transition state".

That is, when PEDOT:PSS is treated with an ultra-high concentration of H ₂ SO ₄ , the two ions stabilize the separated state of the positively charged PEDOT and the negatively charged PSS. In this case, a dense PEDOT network is created due to the strong π-π stacked bond of PEDOT and the rigidity of the backbone. Significant changes follow in the morphological structure. Eventually, structural rearrangement occurs with crystalline PEDOT:PSS nanofibers (nanofibril).

The time to immerse the PEDOT:PSS thin film may vary depending on the type and concentration of sulfuric acid or sulfuric acid derivative, but referring to Table 1 to be described later, the immersion time varies from 1 minute to 1000 minutes for 100% by volume of sulfuric acid. Even so, the prepared PEDOT:PSS thin film showed good conductivity without significant change in performance. Therefore, it is considered that more than 1 minute will be sufficient for the reaction. In addition, as confirmed by the present researchers, the structure of PEDOT did not change even when immersed for one week, and there was no effect on the electrical conductivity, so the upper limit is not set.

In the case of other sulfuric acid derivative solutions or different concentrations, the appropriate immersion time may vary, but if the immersion time is too short, there is a risk that the time is insufficient for the PSS to be desorbed and the reproducibility is deteriorated.

In addition, it is preferable to use the sulfuric acid or sulfuric acid derivative at a relatively high concentration. The electrical properties of the electrode prepared using an aqueous solution of sulfuric acid or a sulfuric acid derivative contained in an amount of 75 to 100% by volume were relatively good. More preferably, it is preferable to use a solution containing sulfuric acid or a sulfuric acid derivative in an amount of 80 to 100% by volume. Most preferably, 100% by volume of sulfuric acid, that is, using pure sulfuric acid containing no solvent such as water, has the most excellent electrical properties. For reference, when the concentration is calculated in moles (M), it is 13.1M when the sulfuric acid is 70% by volume, 14.1M when the sulfuric acid is 75% by volume, 15.0 M when the sulfuric acid is 80% by volume, and 18.8M when the sulfuric acid is 100% by volume.

During the immersion process, excess uncoupled PSS and H ₂ SO ₄ or derivatives thereof desorbed from PEDOT:PSS may be attached to the surface of the substrate and PEDOT:PSS thin film, and washed with a sufficient amount of detergent. Can be removed. The cleaning agent may be water, but is not limited thereto, and among them, it is preferable to use deionized water. On the other hand, the minimum amount of PSS required to maintain the PEDOT:PSS structure is reorganized in PEDOT and acts as a counter ion.

PEDOT is a conductive material, but PSS is a non-conductive material, so it is believed that the electrical conductivity can be improved by leaving only the minimum PSS necessary to maintain the structure of PEDOT:PSS.

If the molar ratio of PEDOT:PSS of the PEDOT:PSS composite before the sulfuric acid treatment was about 1:2.0, the molar ratio of PEDOT:PSS after treatment and washing of 75 to 100% by volume of sulfuric acid was changed to about 1.6 to 2.0:1. , It was confirmed that the ratio of PSS was extremely low. This increase in the molar ratio of PEDOT:PSS can be expected to lead to an increase in charge density. According to the results of this study, the molar ratio of PEDOT:PSS was found to be approximately 2.0:1 in the case of showing the most optimal electrical properties.

In addition, if the crystallinity of PEDOT:PSS of the PEDOT:PSS composite before sulfuric acid treatment was about 15%, the crystallinity of PEDOT:PSS after treatment and washing of 75 to 100% by volume of sulfuric acid changed to 40% or more, and the ratio of PSS It was confirmed that the crystallinity was increased as this extremely decreased. Such an increase in the crystallinity of PEDOT:PSS can be expected to lead to an increase in the motility of the electric charge. (Fig. 7)

In terms of electrical conductivity, the crystallinity is preferably 40% or more, preferably 46% or more, more preferably 48% or more, and most preferably 50% or more. However, the higher the crystallinity, the better, so there is no particular upper limit.

The washed thin film is dried at a temperature of 60 to 160°C.

By hot air drying, vacuum drying, or ultraviolet (IR) drying of the substrate coated with the PEDOT:PSS composition, an electrode having a shape fixed to the substrate is formed.

PEDOT: Sulfuric acid, sulfuric acid derivatives, and water may exist in the place where PSS is desorbed from the PSS. If dried at too high temperature, there is a problem that these liquid substances evaporate before PEDOT is formed into crystals. When dried, it is believed that a liquid substance exists between PEDOTs and inhibits the π-π interaction. However, even at a low temperature, this problem can be reduced if the drying time is sufficiently long to be 10 minutes or more.

11 is a schematic diagram showing an organic electronic device 100 according to an embodiment of the present invention.

Referring to FIG. 11, a first electrode 120, a hole transport layer 130, a photoactive layer 140, an electron transport layer 150, and a second electrode 160 may be sequentially formed on the substrate 110. Here, the hole transport layer 130 and the electron transport layer 150 may be omitted. In addition, when the PEDOT:PSS of the present invention is used as an anode, there is an advantage that it is not necessary to separately provide a PEDOT:PSS functioning as a hole transport layer in the conventional ITO electrode.

The substrate 110 is used to support an organic electronic device and may be a _{light-transmitting inorganic substrate selected from glass, quartz, Al 2} O ₃ and SiC, but is not limited thereto, and the present invention uses a high concentration of strong acid. In this regard, it is preferable to use a material that is not corroded.

The first electrode 120 may be a light-transmitting electrode in the form of a PEDOT:PSS thin film manufactured in the present invention. This is a component that replaces the conventional ITO (Indium Tin Oxide) film.

The hole transport layer 130 easily transports holes supplied through an external circuit from the first electrode 120 to the photoactive layer 140 (in the case of an organic light emitting device), or generated in the photoactive layer 140. The hole can be easily transported to the first electrode 120 (in the case of an organic solar cell). In addition, the hole transport layer 130 may serve as a buffer layer to alleviate the surface roughness of the first electrode 120. In addition, the LUMO (Lowest Unoccupied Molecular Orbital) level of the hole transport layer 130 is higher than the LUMO level of the photoactive layer 140, and an electron blocking layer that prevents electrons from flowing from the photoactive layer 140 to the first electrode 120 It can also play a role as

In the case of an organic solar cell, the hole transport layer 130 includes poly(styrenesulfonate, hereinafter, PSS) and poly(3,4-ethylenedioxythiophene) (poly(3,4-ethylenedioxy-thiophene, Hereinafter, a mixture of PEDOT) may be used, but is not limited thereto.

The hole transport layer 130 of the organic light emitting device may include at least one selected from triphenylline, perylline, pyrene, tetracene, anthracene series, NPD series, TPD series, and photoconductive polymer, but is not limited thereto.

The photoactive layer 140 may be a light emitting layer or a photoelectric conversion layer. Here, the light-emitting layer refers to a layer that generates light by the combination of electrons and holes supplied from the outside, and the photoelectric conversion layer is the generation of electron-hole pairs (excitons) by light supplied from the outside and each charge Refers to the layer in which the separation occurs. When the photoactive layer 140 is composed of a light emitting layer or a photoelectric conversion layer, the organic electronic device 100 may be manufactured as an organic light emitting device or an organic solar cell, respectively.

Materials of the light emitting layer and the photoelectric conversion layer are not particularly limited, and various polymers or low molecular organic materials may be used.

For example, the material of the light-emitting layer is polyaniline-based, polypyrrole-based, polyacetylene-based, polyethylenedioxylthiophene (poly(3,4-ethylenedioxythiophene), PEDOT)-based, and polyphenylene. Vinylene (polyphenylenevinylene (PPV)), polyfluorene (polyfluorene), polyparaphenylene (PPP), polyalkylthiophene, polypyridine (PPy), polyvinylcarbazole (polyvinylcarbazole) or a copolymer thereof, or may be selected from an appropriate host/dopant-based material.

For example, as a material of the electron donor material of the photoelectric conversion layer, polythiophene-based, polyfluorene-based, polyaniline-based, polycarbazole-based, polyvinylcarbazole (polyvinylcarbazole)-based, polyphenylene-based, polyphenylvinylene-based, polysilane-based, polyisothianaphthanene-based, polythiazole-based, polybenzothia It may be a sol (polybenzothiazole)-based, polythiopheneoxide-based, or a copolymer thereof. As an example, the electron donor material is poly(3-hexylthiophene) (poly(3-hexylthiophene), P3HT), a kind of polythiophene, or PCPDTBT (poly [2,6- (4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCDTBT (poly[N-9″-heptadecanyl-2,7-carbazolealt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]) or PFDTBT ( poly(2,7-(9-(2'-ethylhexyl)-9-hexyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3' -benzothiadiazole))) In addition, for example, the electron acceptor material of the photoelectric conversion layer is C ₆₀ to C ₈₄ fullerene or a derivative thereof, perylene, polymer, or quantum dot The fullerene derivative may be PCBM, for example, PCBM(C ₆₀ )([6,6]-phenyl-C ₆₁ -butyric acid methyl ester) or PCBM(C ₇₀ )([6,6]- phenyl-C ₇₁ -butyric acid methyl ester).

The electron transport layer 150 easily transports electrons supplied through an external circuit from the second electrode 160 to the photoactive layer 140 (in the case of an organic light emitting device), or generated from the photoactive layer 140. It may serve to easily transport electrons to the second electrode 160 (in the case of an organic solar cell). In addition, the electron transport layer 150 may serve as a hole blocking layer that prevents holes generated in the photoactive layer 140 from flowing into the second electrode 150. The electron transport layer 150 may be, for example, a titanium oxide layer. The titanium oxide layer can prevent degradation of the device due to penetration of oxygen or water vapor into the photoactive layer 140, and an optical spacer for increasing the amount of light introduced into the photoactive layer 140. In addition to its role as a spacer), it can also play a role of a lifespan increase layer that increases the lifespan of an organic electronic device. The titanium oxide layer may be formed using a sol-gel method.

The second electrode 160 is an electrode having a smaller work function than the first electrode 120 and may be a metal or a conductive polymer electrode. As an example, the second electrode 160 is among Li, Mg, Ca, Ba, Al, Cu, Ag, Au, W, Ni, Zn, Ti, Zr, Hf, Cd, Pd, Cs, and alloys thereof. It may be any one metal electrode selected. When the second electrode 160 is a metal electrode, it may be formed by hot-air vapor deposition, electron beam deposition, sputtering, or chemical vapor deposition, or by applying a paste for forming an electrode including a metal and then heat treatment. However, it is not limited thereto.

Hereinafter, the present invention will be described in detail through examples. However, the following examples are only examples for explaining the present invention in more detail, and do not limit the scope of the present invention.

[Example]

Preparation Example 1: Preparation of PEDOT:PSS thin film

PEDOT:PSS (Clevios PH1000) was filtered through a hydrophilic syringe filter (0.45 μm) to remove large-sized particles. The filtrate was spin-cast on a 2×2 cm 2 glass or perforated silicon nitride-supported TEM substrate and dried at 120° C. for 15 minutes to form a large number of PEDOT:PSS thin films.

For post-treatment, at room temperature, the PEDOT:PSS thin film (<100 nm) was added to a sulfuric acid solution having a different concentration (10 to 100 vol%) _{of sulfuric acid (H 2} SO _{4) (Duksan Pure Chemicals, >95%).} Each was immersed while varying the immersion time (1 to 1000 minutes).

Then, after sufficiently washing the thin film with deionized water, it was dried for 10 minutes or more at various temperatures (60 ~ 120) ℃ to remove residual water.

In order to obtain a clear XRD pattern, a PEDOT:PSS thin film (>10 μm) was prepared by drop casting a filtered PEDOT:PSS solution on a silicon substrate according to the same process as described above. However, the detailed process conditions were adjusted as follows: the immersion time was increased to 3 hours, and the drying conditions were dried at 60-80°C for 1 hour and then dried at 120°C for 30 minutes to make the PEDOT:PSS thin film of the present invention Got it.

In addition, as a post-treatment solution, a sulfuric acid derivative solution other than sulfuric acid, i.e., trifluoromethanesulfonic acid (CF ₃ SO ₃ H) (Sigma-Aldrich Chemical Co., 98%), paratoluenesulfonic acid, bistrifluoromethanesulfonimide, Also in the benzenesulfonic acid and 4-sulfonephthalic acid solution, the PEDOT:PSS thin film was immersed for 10 minutes or more, respectively, and the remaining conditions were the same to obtain a PEDOT:PSS thin film.

Analysis Example 1: Characterization of PEDOT:PSS thin film

Characterization of the PEDOT:PSS thin film prepared in Preparation Example 1 was performed using the following method.

Sheet resistance was measured by a four-point probe method. Current was applied using a Keithley 2400 Source Meter unit, and voltage drop was measured using an HP 34401A multimeter. The thin film thickness was measured using a Surfcorder ET-3000 profilometer (Kosaka Laboratory Ltd.). XRD patterns were obtained using a Rigaku D/max-2500 diffractometer, TEM images were obtained using a Tecnai G ² F30 S-Twin microscope, and absorption spectra were obtained using a Perkin-Elmer Labmda 750 UV/Vis/NIR spectrophotometer. . Based on these data, the molar ratio, crystallinity, and conductivity of PEDOT to PSS of the PEDOT:PSS thin film obtained for each manufacturing condition are summarized in Table 1 below. However, since the data described in one sample No. may mean the average value of the measured values for samples manufactured under the same conditions, the actual measured data may exist within ±5% of the error range in the data shown in Table 1 below. For example, a molar ratio of PEDOT to PSS of 1.9 may mean about 2.0.

Sample
No. Sulfuric acid ratio
(vol%) Treatment temperature
(℃) Processing time
(minute) Molar ratio of PEDOT to PSS Crystallinity
(%) conductivity
(S/cm)
(medium) One pristine 120 10 0.53 15 1.13 2 10 120 10 0.59 16 70 3 20 120 10 0.65 18 117 4 30 120 10 0.62 20 320 5 40 120 10 0.59 22 730 6 50 120 10 0.56 24 1150 7 60 120 10 0.78 29 1420 8 70 120 10 1.3 36 1890 9 72.5 120 10 1.4 38 2030 10 75 120 10 1.6 40 2400 11 77.5 120 10 1.7 44 2500 12 80 120 10 1.8 46 3700 13 90 120 10 1.9 48 4000 14 100 120 10 1.9 51 4200 15 100 60 10 1.9 49 4010 16 100 80 10 1.9 47 3800 17 100 100 10 1.9 48 4050 18 100 140 10 1.9 47 3800 19 100 160 10 1.9 45 3400 20 100 120 One 1.9 51 4200 21 100 120 2 1.9 51 4200 22 100 120 3 1.9 51 4200 23 100 120 5 1.9 51 4200 24 100 120 8 1.9 51 4200 25 100 120 10 1.9 51 4200 26 100 120 12 1.9 51 4200 27 100 120 20 1.9 51 4200 28 100 120 30 1.9 51 4200 29 100 120 100 1.9 51 4200 30 100 120 1000 1.9 51 4200

Changes in electrical properties and structural changes were observed by treating the PEDOT:PSS thin film with various concentrations of sulfuric acid and sulfuric acid derivatives (FIGS. 3 and 4).

The conductivity increased as the concentration of the treatment solvent increased (sample No. 1 to 14 in Table 1). When the concentration of sulfuric acid was less than 60%, it showed an electrical conductivity of less than 1,500 S/cm, and at 75% it was 2400 S/cm. , 80% showed an electrical conductivity of 3,700 S/cm, and 100% of 4,380 S/cm (maximum measured value) (Table 1 and FIG. 3(a)). The conductivity rapidly increased in the range of 75 to 80% of sulfuric acid concentration, and this rapid increase in electrical conductivity means that a remarkable structural change occurred at the concentration of 80% or more of sulfuric acid.

As a result of observing the conductivity by varying the treatment solvent, the highest conductivity (sulfuric acid (1): 4,380 S/cm (maximum measured value)); trifluoromethanesulfonic acid (2): 3,600 S/cm; Paratoluenesulfonic acid (3): 2,160 S/cm; Bistrifluoromethanesulfonimide (4): 2,300 S/cm; Benzenesulfonic acid (5): 1,980 S/cm; 4-sulfonephthalic acid (6): 2,420 S/ cm) (Fig. 6(c)).

It was confirmed that not only sulfuric acid but also a sulfuric acid derivative having a sulfonic acid functional group lowered the sheet resistance of PEDOT:PSS and improved electrical conductivity (FIG. 6(b)).

The electrical conductivity also varies depending on the drying temperature (Sample Nos. 14-19 in Table 1), showing good results with a conductivity of 3,800 S/cm or more in the treatment temperature of 60-160°C. In addition, referring to FIG. 3(b), when dried at 110° C. and 120° C., electrical conductivity of 4,000 S/cm or more was shown. Drying at 120°C showed the best electrical conductivity, but drying at a lower or higher temperature lowered the electrical conductivity. This is because sulfuric acid or a sulfuric acid derivative or water may exist at the place where PSS is desorbed from PEDOT:PSS.If dried at too high temperature, there is a problem that these liquid substances evaporate before PEDOT is formed into crystals. When dried at, it is thought that a liquid substance exists between PEDOT and inhibits the π-π interaction.

Changes in electrical conductivity according to treatment time of the treatment solvent (ex. sulfuric acid) were observed (sample Nos. 20 to 30 in Table 1), but no change in conductivity was observed when 100% sulfuric acid was used as a solvent, and reproducibility was also observed. There was no big change. Therefore, it is judged that the treatment time of the solvent does not play a decisive role in increasing the conductivity.

4(a) shows the XRD pattern of a PEDOT:PSS thin film treated with sulfuric acid at various concentrations. When sulfuric acid was not treated (Pristine), the XRD pattern showed four characteristic peaks: 2θ=3.8° (d=23Å), 6.6° (d=13.4Å), 17.7° (d=5.0Å), 25.6˚(d=3.5Å)

2θ = 3.8˚ and 6.6˚ respectively correspond to the two separate lamellar stacking distance d(100) of PEDOT and PSS, and 2θ=17.7˚ and 25.6˚ respectively indicate the distance between the amorphous halo of PSS and PEDOT d(010). Corresponds to (Fig. 4(b)).

As the concentration of the treated sulfuric acid increased, the shape of the XRD pattern gradually changed. In the case of treatment with 20% and 50% sulfuric acid, the peaks at 2θ = 3.8° and 6.6° shifted to about 0.4° lower, and the intensity on the XRD data increased. This means that the lamellar lamination spacing was increased and the crystallinity was also improved.

However, consistent with the data on the electrical conductivity, significant changes were observed when 80% sulfuric acid was treated, 2θ = 4.4˚ and 6.2˚ (d ₍₁₀₀₎ ) and 2θ = 9.2˚ and 13.3˚ (d ₍₂₀₀₎ ), a strong peak was observed. And, when treated with 100% sulfuric acid, it showed strong peaks at 2θ = 6.2˚ and 2θ = 13.3˚. It is understood that the (010) absorption peak representing the distance between PEDOTs decreases as the concentration of treated sulfuric acid increases, resulting in an increase in the layered bond between PEDOTs, and it can be seen that crystallinity is greatly improved as the absorption peak of the (100) plane increases. . From these results, it can be seen that PEDOT:PSS increases crystallinity as the concentration of sulfuric acid increases, and favors two distinct lamellar lamination bonding of PEDOT and PSS.

In order to elucidate the structural change process of PEDOT:PSS according to the concentration of the treated sulfuric acid, BF (Bright Field)-TEM images and HAADF-STEM (High-Angle Annular Dark-Field Scanning Transmission Electron Microscope) images were observed (Fig. 5). ).

In the pristine samples, white PEDOT:PSS clumps can be observed in the grain structure, and in the 20% and 50% sulfuric acid treated samples, slightly expanded grains in a spatially dense state dominate. It was observed that, as the concentration of sulfuric acid increased to 80% or more, it can be observed that a rapid morphological conversion occurs from the grain structure to the nanofiber form. Samples treated with 100% sulfuric acid showed that the width of the nanofibers was approximately 10-15 nm.

This means that the strong acidity of sulfuric acid induces reconstitution of the PEDOT:PSS composite to form crystalline nanofibers, thereby forming an excellent PEDOT network.

The treatment of sulfuric acid also brought about a change in the composition of the PEDOT:PSS thin film, which could be confirmed by observing the absorption spectrum.

Referring to FIG. 7(a)), the strong absorption peak in the UV region is due to the influence of the phenyl group of the PSS, and the wide absorption band in the visible light and the IR region is related to the free charge of the PEDOT. As a result of treatment with 80% sulfuric acid, the two strong absorption peaks in the UV region were significantly reduced, but at lower energy (<3.0 eV) there was no change in absorption properties. This result means that, when PEDOT:PSS is treated with a high concentration of sulfuric acid, only PSS is selectively removed without affecting PEDOT. As described above, as the concentration of sulfuric acid increases, a "charge separated transition state is induced, and it can be presumed that PSS is separated from PEDOT:PSS. When treated with 100% sulfuric acid," More than 70% of PSS was removed.

This change in PSS content led to an increase in charge density (n ) (FIG. 7(c)) according to an increase in the molar ratio of PEDOT to PSS (FIG. 7(a)). The molar ratio (R _M ) of PEDOT to PSS in the sample not treated with sulfuric acid (R M) was PEDOT/PSS = 1/1.9 (corresponds to about 1/2.5 weight ratio (w/w)), but treated with 100% sulfuric acid. The molar ratio of PEDOT to PSS of one sample ( R _M ) was approximately PEDOT/PSS = 1/0.5 (corresponding to about 1/0.7 weight ratio (w/w)).

Referring to Table 1, when treated with 75% sulfuric acid, the molar ratio of PEDOT to PSS is 1.6, when treated with 80% sulfuric acid, the molar ratio of PEDOT to PSS is 1.8, and when treated with 100% sulfuric acid, the molar ratio of PEDOT to PSS is 1.8. The molar ratio of PEDOT to that was 1.9 (about 2.0).

The change in the PSS content is also due to an increase in the charge mobility (μ ) according to the improvement in the crystallinity (X _c ) (sample Nos. 1 to 14 in Table 1, Fig. 7(d)) (Fig. 7(d)). Followed. Therefore, structural changes such as an increase in crystallinity of PEDOT:PSS are considered to have an effect on an increase in electrical conductivity.

Referring to Table 1, when treated with 75% sulfuric acid, the crystallinity was 40%, when treated with 80% sulfuric acid, the crystallinity was 46%, and when treated with 100% sulfuric acid, the crystallinity was 51%.

In order to evaluate the performance of the prepared PEDOT:PSS thin film as an electrode, a figure of merit was calculated.

)는 다음의 식을 통해서 구할 수 있다.Performance index(

) Can be obtained through the following equation.

)를 계산할 수 있다. 도 8a를 참조하면, 황산 처리한 PEDOT:PSS의 다양한 박막두께에서 얻은 면저항 대 투과도 결과를 사각 점으로 나타내었고, 이로부터 위의 식을 피팅하여 곡선으로 나타내었으며 평균 성능지수=72.2를 얻을 수 있었다. 이 수치는 현재까지 보고된 전도성 고분자 박막의 성능지수 중 가장 높은 값에 해당한다. 참고로, %T=90%에서 면저항(Rs)은 46.1 Ω/sq이었다.
Here, Z ₀ is a constant, and substituting the transmittance (%T) and sheet resistance (Rs) based on the wavelength (λ) 550 nm, the figure of merit (

) Can be calculated. Referring to Figure 8a, the sheet resistance vs. transmittance results obtained at various thin film thicknesses of sulfuric acid-treated PEDOT:PSS are represented by square dots, from which the above equations were fitted and represented as curves, and an average figure of merit = 72.2 was obtained. . This number corresponds to the highest value among the performance indices of the conductive polymer thin film reported so far. For reference, at %T=90%, the sheet resistance (Rs) was 46.1 Ω/sq.

Preparation Example 2: Preparation of polymer solar cell

Using 100% sulfuric acid (H ₂ SO ₄ )-treated PEDOT:PSS thin film (sample No. 14) as an anode, glass/anode/PEDOT:PSS(30 nm)/PTB7:PC ₇₁ BM(90 nm)/Ca( A polymer solar cell having a structure of 20 nm)/Al (100 nm) was prepared.

For comparison, a polymer solar cell having the same structure was manufactured using ITO as an anode.

A PEDOT:PSS aqueous solution (Clevios P AI 4083) different from PEDOT:PSS used for the anode was used as a hole transport layer (HTL). HTL was spin-coated on each electrode and dried at 140° C. for 10 minutes. _{Then, a solution containing a mixture of PTB7 and PC 71} BM (1:1.5 by wt%) in chlorobenzene to which 3 vol% of 1,8-diiodooctane was added was prepared on the PEDOT:PSS layer. It was spin-cast on and dried for 10 minutes at 70° C. in a nitrogen-filled glove box. Finally, Ca and Al were deposited by thermal evaporation under high vacuum conditions (4> 10 ^{-7 Torr).}

Analysis Example 2: Characterization of a polymer solar cell

Table 2 shows the results of performance evaluation when the PEDOT:PSS thin film treated with 100 vol% sulfuric acid (Sample No. 14) and ITO were used as electrodes of an organic thin film solar cell, respectively.

The open-circuit voltage (V _oc ), short-circuit current (J _sc ), fill factor (FF), and photoelectric conversion efficiency (PCE) are all evaluated at a level that can replace the ITO electrode.

Anode V _oc (V) J _sc (mA cm ^-1 ) FF PCE (%) ITO 0.73 14.5 0.68 7.2 H ₂ SO ₄ -PEDOT:PSS 0.73 13.9 0.65 6.6

In the present invention, when the PEDOT:PSS thin film treated with 100% sulfuric acid was used as an anode, it exhibited a sheet resistance of 46.1 Ω/sq and a transmittance of 90% (550 nm absorption region) or more. As a result of fabricating an organic solar cell using such a plastic electrode, it was confirmed that the energy conversion efficiency was almost similar to that of using ITO (>95%), and as a result, it has a high possibility as a printed plastic electrode that can replace ITO. Is shown (Fig. 9).

Preparation Example 3: Preparation of a polymer light emitting device

Using 100% sulfuric acid (H ₂ SO ₄ )-treated PEDOT:PSS thin film (Sample No. 14) as an anode, glass/anode/aryl-substituted poly(para-phenylene vinylene) derivative (P-PPV)(60 nm) A polymer light emitting device having a structure of /Ca(20 nm)/Al(100 nm) was manufactured.

For comparison, ITO was used as an anode, and PEDOT:PSS (30 nm) was additionally coated with a hole transport layer (HTL) thereon, and a polymer light emitting device having the same structure was manufactured for the remainder.

HTL was spin coated and dried at 140° C. for 10 minutes.

P-PPV solution (0.5 wt%) dissolved in toluene on each electrode was spin-cast and dried in a nitrogen-filled glove box at 80° C. for 10 minutes. Finally, Ca and Al were deposited by thermal evaporation under high vacuum conditions (4 × 10 ^{-7 Torr).}

Analysis Example 3: Characterization of a polymer light emitting device

The LED structure is a structure in which a photoactive layer is coated on an ITO electrode coated with a PEDOT:PSS hole transport layer and Ca and Al are deposited (comparative example), or a 100% sulfuric acid-treated PEDOT:PSS electrode that simultaneously serves as a hole transport layer is photoactive. It is a structure in which Ca and Al are deposited after coating a layer (invention example). Figure 10a briefly shows the energy level of each layer.

The sulfuric acid-treated PEDOT:PSS electrode (PEDOT-H ₂ SO ₄ ) shows comparable LED electrode characteristics compared to the ITO electrode (FIG. 10b). In addition, the PEDOT:PSS electrode has the advantage that it does not require an additional hole transport layer, unlike the ITO electrode.

As described above, in the present invention, _{by controlling the concentration of sulfuric acid (H 2} SO ₄ ) or the sulfuric acid derivative, the processing temperature, and detailed manufacturing process conditions, crystallization of the PEDOT:PSS thin film is induced, thereby realizing electrical conductivity that can replace ITO. It was revealed that this was achieved through the desorption of PSS through the "transition state in which the charge was separated".

The PEDOT:PSS thin film of the present invention may be included in an electronic device and used, for example, a field effect transistor, a thin film transistor, an optical sensor, a light emitting device, a photodetector, a magneto-optical memory device, a flat panel display, a flexible device, and a solar device. It can be applied to various applications such as batteries, electroluminescence (EL) devices, photoluminescence (PL) devices, cathodeluminescence (CL) devices, supercapacitors, and electrochromic devices. In particular, it is expected to be used as a transparent electrode in photovoltaic devices such as solar cells and light emitting devices.

Claims (8)

Preparing a PEDOT:PSS thin film formed on a substrate;
Treating the thin film at room temperature with a solution containing sulfuric acid or a sulfuric acid derivative in an amount of 75 to 100% by volume; And
Separating and washing the thin film from the solution,
The step of separating and washing the thin film is to remove the sulfuric acid or sulfuric acid derivative attached to the surface of the PEDOT:PSS thin film or to remove the PSS desorbed from the PEDOT:PSS, PEDOT:PSS-based electrode manufacturing method. The method of claim 1,
After the step of separating and washing the thin film, further comprising the step of drying the washed thin film at a temperature of 60 to 160°C. The method of claim 1,
The time for treating the thin film in the solution is 1 minute or more. delete The method of claim 1,
The step of separating and washing the thin film is performed using water, a method of manufacturing a PEDOT:PSS-based electrode. The method of claim 1,
Treating the thin film with the solution is to immerse the thin film in a solution containing 75 to 100% by volume of the sulfuric acid or sulfuric acid derivative. The method of claim 1,
The sulfuric acid or sulfuric acid derivative is methanesulfonic acid, trifluoromethansulfonic acid, sulfuric acid (sulfuric acid), perchloric acid, benzenesulfonic acid, and p-Toluenesulfonic acid. acid), 4-Ethylbenzenesulfonic acid, 4-Sulfophthalic acid, p-Xylene-2-sulfonic acid hydrate, 5-amino-1 -Naphthalenesulfonic acid (5-Amino-1-naphthalenesulfonic acid), 8-amino-2-naphthalenesulfonic acid (8-Amino-2-naphthalenesulfonic acid), 4-amino-2-naphthalenesulfonic acid (4-amino-2-naphthalenesulfonic acid) ), Taurine, 1,4-Butanedisulfonic acid, Sulfurous acid, Bis (trifluoromethane) sulfonamide, and mixtures of two or more thereof Which is selected from the group consisting of, PEDOT: a method of manufacturing a PSS-based electrode. The method of claim 1,
The substrate is selected from the group consisting of glass, quartz, Al ₂ O ₃ and SiC, PEDOT: PSS-based electrode manufacturing method.

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