KR20160027883A - Pedot:pss based electrode and method for manufacturing the same - Google Patents

Abstract

Provided in the present invention are a method for manufacturing a PEDOT:PSS based electrode, a PEDOT:PSS based electrode manufactured by the method and an organic electronic device which adopts the electrode. The method comprises the steps of: preparing a PEDOT:PSS film formed in a base material; processing the film with a solution which contains sulfuric acid or a sulfuric acid derivative at 75 to 100 volumetric %; washing the film by separating the film from the solution; and drying the washed film at 60 to 160°C. According to the present invention, a method for manufacturing a PEDOT:PSS based electrode, a method of the same and an organic electronic device which adopts the electrode can be provided, thus having advantages of conductive polymers such as excellent workability, reduced weight, flexibility, simple coating process, low production costs, etc. and materializing electric properties capable of substituting ITO.

Description

PEDOT: PSS BASED ELECTRODE AND METHOD OF MANUFACTURING THE SAME

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

Flexible plastic electronic devices are a collection of science and technology that can be 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, due to its fragile nature, ITO is not only difficult to use in next-generation bending devices, but also uses a high-temperature deposition process, making it difficult to fabricate high-performance transparent electrodes using a printing process. In addition, the development of a new transparent electrode is urgently required due to the limitation of indium deposits, which are the main raw material of ITO, and thus the price increase.

Many studies have been made on transparent electrodes for replacing ITO with carbon nanotubes, graphenes, silver nano wires, metal oxides, etc. However, since plastic transparent electrodes developed so far have remarkably low conductivity, it is urgent to overcome them.

As another transparent electrode for replacing ITO, conductive polymer is made of organic material and has workability, lightness, flexibility, simple coating process and low production cost, which are advantages of general plastic. It is widely recognized as a substitute for ITO. In addition, existing alternative materials composed of organic materials also require a complicated and expensive deposition process in order to obtain electric conductivity equivalent to that of ITO. However, the conductive polymer has an advantage that a low-temperature solution process is possible.

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

Poly (3,4-ethylenedioxythiophene): Poly (styrenesulfonate) is a conductive plastic material that has high conductivity, good transparency in the visible region, and is environmentally friendly because it is dissolved in water. However, the conductivity is very low as 1 S / cm for use as a transparent electrode, which is comparable to that of ITO (> 5,000 S / cm), and it is one of the most widely used materials It is an absurd number.

There have been many studies on the optical and electrical properties of PEDOT: PSS over the past several decades and attempts have been made to improve the conductivity through the use of various organic solvents, surfactants and acids. According to the recently published Non-Patent Document 1, it is reported that 1.0 M sulfuric acid (H ₂ SO ₄ ) solution is dropped on the PEDOT: PSS thin film to obtain an electric conductivity of 3,065 S / cm. However, it does not provide concrete mechanism and optimal manufacturing method for improvement of conductivity, and does not realize electric characteristics that can replace ITO, and thus, practical commercialization is limited.

Therefore, it is necessary to develop a transparent electrode that realizes an electrical characteristic that can replace ITO by suggesting an optimal manufacturing method for improving the conductivity of the 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 relates to a PEDOT: PSS-based electrode capable of realizing electrical properties that can be substituted for ITO while having merits such as processability, light weight, flexibility, simple coating process and low production cost, Organic electroluminescent device.

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

According to an aspect of the present invention, there is provided a method of manufacturing a PEDOT: PSS thin film, comprising: preparing a PEDOT: PSS thin film formed on a substrate; Treating the thin film with a solution containing 75 to 100% by volume of sulfuric acid or a sulfuric acid derivative; Separating and washing the thin film from the solution; And drying the washed thin film at a temperature of 60 to 160 캜.

Another aspect of the invention relates to a substrate, comprising: a substrate; And a PEDOT: PSS thin film electrode 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 at least 40% to provide.

Another aspect of the present invention is a substrate, comprising: a substrate; A first electrode in the form of a PEDOT: PSS thin film formed on the substrate; A photoactive layer disposed on the first electrode; And a second electrode disposed on the photoactive layer, wherein the PEDOT: PSS thin film has a PEDOT: PEDOT molar ratio of 1.6 to 2.0 and a crystallinity of at least 40% Device.

According to the present invention, there is provided a PEDOT: PSS-based electrode capable of realizing an electrical property which is advantageous to a conductive polymer such as processability, light weight, flexibility, simple coating process and low production cost, An organic electronic device employing the electrode can be provided.

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

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly explain the present invention in the drawings, portions not related to the description are omitted.

Throughout this specification, when a member is " on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms " about, "" substantially, "and" roughly ", etc. used to the extent that they are used throughout the specification are used in their numerical values or in close proximity to their numerical values when the manufacturing and material tolerances inherent in the stated & Accurate or absolute numbers are used to prevent unauthorized exploitation by unscrupulous infringers of the disclosures referred to in order to facilitate understanding of the present disclosure. The word " step (or step) "or" step "used to the extent that it is used throughout the specification does not mean" step for.

Throughout this specification, the term "combination thereof" included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

The use of terms such as " comprising "or" comprising "in this specification should not be construed as necessarily including the various elements or steps described in the specification, including some or all of the steps Or may further include additional components or steps.

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

The present invention relates to a method of post-treating PEDOT: PSS (poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) as a conductive polymer with sulfuric acid or a sulfuric acid derivative, thereby lowering electric characteristics such as low electrical conductivity The present invention relates to a technique for dramatically improving the performance of an ITO electrode as a substitute for ITO. The process of post-treatment with a sulfuric acid or a sulfuric acid derivative is schematically shown in FIG.

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

Poly (3,4-ethylenedioxythiophene), a polythiophene conductive polymer, has an excellent electrical conductivity of 10 ³ to 10 ⁶ S / cm, but is insoluble in water, resulting in poor processability . PEDOT / PSS complex can be present as a stable dispersion in water by introducing anionic polystyrene sulfonate (PSS, poly (styrenesulfonate)) as a dopant, and has excellent thermal stability. In order to maintain the optimum dispersibility of PEDOT in water, the solid concentration of PEDOT and PSS is adjusted in the range of 1.0 wt% to 1.5 wt%. Since PEDOT is further mixed with water, alcohol or a solvent having a large dielectric constant, the PEDOT can be easily coated by diluting with the solvent. When the coating film is formed, the PEDOT exhibits excellent transparency as compared with other conductive polymers such as polyaniline and polypyrrole.

On the other hand, in forming PEDOT: PSS on a substrate, a dry process or a wet process can be used. Sputtering and evaporation are examples of the dry process. Dip coating, spin coating, roll coating, and spray coating are used as the wet process. have. However, it is preferable from the viewpoints of printability, manufacturing cost, and low-temperature processability that the PEDOT: PSS mixed in a solvent such as water, alcohols, acetonitrile or the like is coated on a substrate by a wet process.

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

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 which does not cause corrosion even in a high-concentration acidic condition described later is preferable.

The PEDOT: PSS thin film prepared above is treated with a solution containing 75 to 100% by volume of sulfuric acid or a sulfuric acid derivative. The components other than sulfuric acid or sulfuric acid derivatives in the solution 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 it is possible to use a method such as spraying, coating or immersion, but the method of immersion is preferable in terms of simplicity of the process and maximization of reaction efficiency . (Hereinafter, the present invention will be described in the context of 'immersion' as a treatment method.)

Examples of the sulfuric acid or sulfuric acid derivative include, but are not limited to, compounds containing -SO ₃ ^- or -SO ₃ H. The PSS present in PEDOT: PSS contains -SO ₃ ^- or -SO ₃ H. If a solvent containing sulfuric acid or sulfuric acid derivative with similar functional groups is used, interaction with PEDOT: PSS is considered to be good. Specifically, the sulfuric acid or the sulfuric acid derivative may be at least one selected from the group consisting of methanesulfonic acid, trifluoromethanesulfonic acid, sulfuric acid, perchloric acid, benzenesulfonic acid, paratoluenesulfonic acid p-toluenesulfonic acid, 4-ethylbenzenesulfonic acid, 4-sulfophthalic acid, p-xylene-2-sulfonic acid hydrate, 5- Amino-1-naphthalenesulfonic acid, 8-amino-2-naphthalenesulfonic acid, 4-amino-2-naphthalenesulfonic acid, -naphthalenesulfonic acid, taurine, 1,4-butanedisulfonic acid, sulfurous acid, bis (trifluoromethane) sulfonamide, and 2-thiophene- A mixture of two or more species, and mixtures thereof. It is not. However, for convenience of explanation, the reaction mechanism will be exemplified herein using sulfuric acid.

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

2H ₂ SO ₄ ↔ H ₃ SO ₄ ⁺ + HSO ₄ ^-

In the case of PEDOT: PSS, anionic PSS is present around the PEDOT polymer with electrical conductivity due to intermolecular attraction. These PSS prevent the stacking of PEDOT and improve the dispersibility to the solvent. However, PSS with a low electrical conductivity may form a nonconductive molecule chain around the PEDOT, which may cause the overall electrical conductivity of the electrode to deteriorate. In the present invention, when the solution is treated with a solution containing an ultra-high concentration of sulfuric acid or sulfuric acid derivative, the anionic HSO ₄ ^- is surrounded by the PEDOT and the cationic H ₃ SO ₄ ⁺ is surrounded by the PSS, The intermolecular force is weakened to lead to a "charge separated transition state ".

That is, when PEDOT: PSS is treated with ultra-high concentration of H ₂ SO ₄ , the two ions stabilize the separated states of positively charged PEDOT and negatively charged PSS. This results in a dense PEDOT network due to the strong π-π stacking of the PEDOT and rigidity of the backbone. As the amorphous PEDOT: PSS grains are formed into a crystalline nanofibril structure, Significant changes in morphology follow. As a result, structural reordering occurs with crystalline PEDOT: PSS nanofibers.

The time for immersing the PEDOT: PSS thin film may be varied depending on the type and concentration of the sulfuric acid or the sulfuric acid derivative. However, referring to Table 1 described later, in the case of 100 vol% sulfuric acid, Showed good conductivity without significant change in the performance of the prepared PEDOT: PSS thin film. Therefore, if the reaction time is longer than 1 minute, the reaction will be sufficient. Also, according to the results of the present inventors, the upper limit of the PEDOT was not determined because the PEDOT structure did not deform even after immersion for 1 week, and the electrical conductivity had no effect.

Even in the case of other sulfuric acid derivative solutions or in different concentrations, the proper immersion time may vary. However, if the immersion time is too short, there is a fear that the PSS is desorbed and the reproducibility is lowered.

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

In the immersion process, excess uncoupled PSS and H ₂ SO ₄ or derivatives thereof, which have desorbed from the PEDOT: PSS, may be attached to the surface of the substrate and the PEDOT: PSS thin film, washed with a sufficient amount of detergent Can be removed. The cleaning agent may be water, but is not limited thereto, and it is preferable to use deionized water. On the other hand, the minimum amount of PSS necessary for PEDOT: PSS structure retention is reformed into PEDOT and acts as a counter ion.

Since PEDOT is a conductive material and PSS is a nonconductive material, it is believed that the electrical conductivity can be improved by leaving only the minimum PSS necessary for maintaining the structure of PEDOT: PSS.

If the molar ratio of PEDOT: PSS in the PEDOT: PSS complex before the sulfuric acid treatment was about 1: 2.0, the molar ratio of PEDOT: PSS after 75 to 100 vol% sulfuric acid treatment and washing changed to about 1.6 to 2.0: 1 , And the ratio of PSS was extremely low. It can be expected that the increase of the molar ratio of PEDOT: PSS leads to the increase of the charge density. According to the results of the present study, the molar ratio of PEDOT: PSS was found to be about 2.0: 1 when the most optimal electrical properties were shown.

When the crystallinity of PEDOT: PSS in the PEDOT: PSS complex before the sulfuric acid treatment was about 15%, the crystallinity of the PEDOT: PSS after 75 to 100 volume% sulfuric acid treatment and washing changed to more than 40% It was confirmed that the increase of the crystallinity was achieved. It can be expected that the increase in the crystallinity of PEDOT: PSS leads to an increase in the mobility of the charge. (Fig. 7)

From the viewpoint of electric 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 degree of crystallinity is, the better.

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

The substrate coated with the PEDOT: PSS composition is subjected to hot-air drying, vacuum drying or ultraviolet (IR) drying to form an electrode having a shape fixed to the substrate.

Sulfuric acid or sulfuric acid derivatives and water may be present at the site where PSS is removed from PSS: PSS. However, when the PSS is dried at an excessively high temperature, there is a problem that such a liquid material evaporates before PEDOT is formed into crystals. It is believed that when dried, the liquid material exists between the PEDOTs and interferes with the π-π interaction. However, if the drying time is longer than 10 minutes at low temperature, this problem can be alleviated.

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 a 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, it is not necessary to separately provide PEDOT: PSS which functions as a hole transport layer in the conventional ITO electrode.

The substrate 110 may be a light-transmissive inorganic substrate selected from the group consisting of glass, quartz, Al ₂ O ₃ , SiC, and the like, but is not limited thereto. In the present invention, It is preferable to use a material which does not cause corrosion in the point.

The first electrode 120 may be a PEDOT: PSS thin film type light transmitting electrode manufactured according to the present invention. This is a substitute for a conventional ITO (Indium Tin Oxide) film.

The hole transport layer 130 can easily transport the holes supplied through the external circuit from the first electrode 120 to the photoactive layer 140 (in the case of an organic light emitting device) (In the case of an organic solar cell) to easily transport holes to the first electrode 120. [ In addition, the hole transport layer 130 may serve as a buffer layer for reducing the surface roughness of the first electrode 120. The LUMO (Lowest Unoccupied Molecular Orbital) level of the hole transport layer 130 is higher than the LUMO level of the photoactive layer 140 to prevent electrons from entering the first electrode 120 from the photoactive layer 140. [ As well.

The hole transport layer 130 may be formed of poly (styrenesulfonate) (PSS) and poly (3,4-ethylenedioxy-thiophene) (Hereinafter, referred to as PEDOT) may be used, but the present invention is not limited thereto.

The hole transport layer 130 of the organic light emitting device may include at least one selected from triphenylene, perylene, pyrene, tetracene, anthracene, NPD, TPD, and photoconductive polymers.

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. The photoelectric conversion layer is a layer in which electrons and holes (excitons) Is a layer in which separation occurs. When the photoactive layer 140 is formed of a light emitting layer or a photoelectric conversion layer, the organic electronic device 100 may be an organic light emitting device or an organic solar cell.

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

For example, the material of the light emitting layer may be one selected from the group consisting of polyaniline, polypyrrole, polyacetylene, poly (3,4-ethylenedioxythiophene), PEDOT, Polyphenylenevinylene (PPV), polyfluorene, polyparaphenylene (PPP), polyalkylthiophene, polypyridine (PPy), polyvinyl carbazole polyvinylcarbazole, copolymers thereof, or may be selected from suitable host / dopant materials.

For example, the material of the electron donor of the photoelectric conversion layer may be a polythiophene series, a polyfluorene series, a polyaniline series, a polycarbazole series, a polyvinyl carbazole series, polyvinylcarbazole type, polyphenylene type, polyphenylvinylene type, polysilane type, polyisothianaphthanene type, polythiazole type, polybenzothiazole type, A polybenzothiazole type, a polythiopheneoxide type, or a copolymer thereof. For example, the electron donor material may be poly (3-hexylthiophene) (P3HT), which is a kind of the polythiophene type, or PCPDTBT (poly [2,6- (2,1-b, 3,4-b '] dithiophene) -tallow-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 5 '- (4', 7'-di-2-thienyl-2 ', 1 ', 3 ' For example, the electron acceptor material of the photoelectric conversion layer may be a fullerene or a derivative thereof of C ₆₀ to C ₈₄ , a perylene, a polymer, or a quantum dot ) may be a fullerene derivative PCBM as, an _{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 can easily transport 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) And can easily transfer 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 to prevent 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 may prevent deterioration of the device due to penetration of oxygen or water vapor into the photoactive layer 140 and may prevent optical degradation of the photoactive layer 140 due to penetration of an optical spacer spacer), and can also serve as a lifetime enhancement layer that increases the lifetime of the organic electronic device. The titanium oxide layer may be formed using a sol-gel method.

The second electrode 160 may have a smaller work function than the first electrode 120, and may be a metal or a conductive polymer electrode. In one embodiment, the second electrode 160 is formed of a material selected from the group consisting of Li, Mg, Ca, Ba, Al, Cu, Ag, Au, W, Ni, Zn, Ti, Zr, Hf, Cd, Pd, And may be any one selected from metal electrodes. When the second electrode 160 is a metal electrode, the second electrode 160 may be formed by thermal vapor deposition, electron beam deposition, sputtering, or chemical vapor deposition, or may be formed by applying an electrode forming paste containing a metal, followed by heat treatment. However, the present invention is not limited thereto.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the following examples are only for illustrating 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 with a hydrophilic syringe filter (0.45 mu m) to remove large size particles. The filtrate was spin-cast on a 2 x 2 cm 2 glass or perforated silicon nitride supported TEM substrate and dried at 120 ° C for 15 minutes to form a plurality of PEDOT: PSS thin films.

The PEDOT: PSS thin film (<100 nm) was dissolved in a sulfuric acid solution (10 to 100 vol%) of sulfuric acid (H ₂ SO ₄ ) (Duksan Pure Chemicals,> 95% (1 to 1000 minutes).

 Then, the thin film was thoroughly washed with deionized water and then dried at various temperatures (60-120) ° C for 10 minutes or more to remove residual water.

In order to obtain a clear XRD pattern, a PEDOT: PSS thin film (> 10 mu m) was prepared by drop casting a filtered PEDOT: PSS solution onto 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, the drying conditions were drying at 60 to 80 ° C for 1 hour, and then drying at 120 ° C for 30 minutes to obtain the PEDOT: PSS thin film &Lt; / RTI &gt;

Further, as a post-treatment solution, a sulfuric acid derivative solution other than sulfuric acid, that is, trifluoromethanesulfonic acid (CF ₃ SO ₃ H) (Sigma-Aldrich Chemical Co., 98%), paratoluenesulfonic acid, bistrifluoromethanesulfonimide, PEDOT: PSS thin films were also prepared for benzenesulfonic acid and 4-sulfophthalic acid solutions for 10 min or more, respectively.

Analysis Example 1: Characterization of PEDOT: PSS thin film

The characteristics of the PEDOT: PSS thin film prepared in Preparation Example 1 were analyzed in the following manner.

The 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 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 the 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. Actual measurement data may be within ± 5% of the error range in the data of Table 1 below, since the data described in one sample No. may mean the average value of the measurements for samples manufactured under the same conditions. For example, the molar ratio of PEDOT to PSS, 1.9, may mean about 2.0.

Sample
No. Sulfuric acid ratio
(vol%) Treatment temperature
(° C) Processing time
(minute) The 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

The electrical properties and structural changes of PEDOT: PSS thin films treated with various concentrations of sulfuric acid and sulfuric acid derivatives were observed (FIGS. 3 and 4).

Conductivity increased as the concentration of the treatment solvent increased (Sample Nos. 1 to 14 in Table 1). Electrical conductivity of less than 1,500 S / cm at a sulfuric acid concentration of less than 60% and 2400 S / cm at 75% , 3,700 S / cm at 80% and 4,380 S / cm at 100% (maximum measured value) (Table 1 and Fig. 3 (a)). Concentration of sulfuric acid in the 75 ~ 80% area rapidly increased. The rapid increase of the conductivity indicates that a significant structural change occurred when the concentration of sulfuric acid was over 80%.

As a result of observing the conductivity with different treatment solvent, the highest conductivity (sulfuric acid (1): 4,380 S / cm (maximum value of measurement), trifluoromethanesulfonic acid (2): 3,600 S / cm when the concentration was 100% (3): 2,160 S / cm; bistrifluoromethanesulfonimide (4): 2,300 S / cm; benzenesulfonic acid (5): 1,980 S / cm; 4-sulfophthalic acid (6): 2,420 S / cm) (Fig. 6 (c)).

Sulfuric acid derivatives having sulfonic acid functional groups in addition to sulfuric acid also confirmed that the sheet resistance of PEDOT: PSS was lowered and the electric conductivity was improved (FIG. 6 (b)).

The electrical conductivity also varied with the drying temperature (Sample Nos. 14 to 19 in Table 1) and showed good results with conductivities above 3,800 S / cm at the treatment temperature range of 60-160 ° C. Also, referring to FIG. 3 (b), when dried at 110 ° C. and 120 ° C., electrical conductivity of 4,000 S / cm or more was shown. When dried at 120 ° C, it showed the best electrical conductivity. However, when dried at lower or higher temperature, the electrical conductivity decreased. This may be due to the presence of sulfuric acid or sulfuric acid derivatives or water in the place where PSS is desorbed from PEDOT: PSS. However, when it is dried at an excessively high temperature, there is a problem that the liquid material evaporates before PEDOT forms crystals. It is believed that the liquid material exists between the PEDOTs to inhibit the π-π interaction.

Although the change in the electrical conductivity with the treatment time of the treating solvent (ex. Sulfuric acid) was observed (Sample Nos. 20 to 30 in Table 1), no change in conductivity was observed when 100% sulfuric acid was used as a solvent, There was no big change. Therefore, it is considered that the treatment time of the solvent does not play a decisive role in increasing the conductivity.

4 (a) shows an XRD pattern of PEDOT: PSS thin films treated with various concentrations of sulfuric acid. When the sulfuric acid was not treated (Pristine), the XRD pattern showed four characteristic peaks: 2? = 3.8 占 d? 23 ?, 6.6 占 d? 13.4 ?, 17.7 占 d = 25.6 DEG (d = 3.5 ANGSTROM)

2θ = 3.8 ° and 6.6 ° correspond to the two separated lamellar lamination distances d (100) of PEDOT and PSS, respectively, and 2θ = 17.7 ° and 25.6 ° are the distance between the amorphous halo of PSS and PEDOT, d (010) (Fig. 4 (b)).

As the concentration of treated sulfuric acid increased, the shape of the XRD pattern gradually changed. When treated with 20% and 50% sulfuric acid, the peak at 2θ = 3.8˚ and 6.6˚ shifted to about 0.4˚ lower and the intensity of XRD data was increased. This means that the lamellar lamination interval is increased and the crystallinity is improved.

Consistent with the electrical conductivity data, however, significant changes were observed with 80% sulfuric acid treatment, with 2θ = 4.4˚ and 6.2˚ (d ₍₁₀₀₎ ), 2θ = 9.2˚ and 13.3˚ (d ₍₂₀₀₎ ), A strong peak was observed. When treated with 100% sulfuric acid, strong peaks were observed at 2θ = 6.2˚ and 2θ = 13.3˚. (010) absorption peaks indicating the distance between the PEDOTs decreased as the concentration of the treated sulfuric acid increased, and it was understood that the lamination bond between the PEDOTs increased, and the absorption peak of the (100) plane was increased, . These results show that PEDOT: PSS increases crystallinity with increasing sulfuric acid concentration and favored two distinct lamellar lamination bonds, PEDOT and PSS.

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

In the non-sulfuric acid pristine sample, white PEDOT: PSS masses can be observed in the grains structure and in the 20% and 50% sulfuric acid treated samples, the slightly expanded granules in the spatially dense state predominate And the abrupt morphological conversion of the nanoparticles to the nanofibril form can be observed as the concentration of sulfuric acid increases to 80% or more. The sample treated with 100% sulfuric acid showed that the width of the nanofibers was approximately 10 to 15 nm.

This means that the strong acidity of the sulfuric acid induces the reconstruction of the PEDOT: PSS complex to form crystalline nanofibers, forming a superior PEDOT network.

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

7 (a)), strong absorption peaks in the UV region depend on the phenyl group of PSS, and broad absorption bands in the visible region and IR region are related to the free charge of PEDOT. Treatment with 80% sulfuric acid resulted in a significant decrease in the two strong absorption peaks in the UV region, but no change in absorption characteristics at lower energy (<3.0 eV). These results indicate that treatment of PEDOT: PSS with sulfuric acid at high concentration selectively removes only PSS without affecting PEDOT. It can be assumed that as the concentration of sulfuric acid increases, "charge separated transition state" is induced and PSS is separated from PEDOT: PSS as described above. When treated with 100% sulfuric acid More than 70% PSS was removed.

This change in PSS content resulted in an increase in the charge density n (Fig. 7 (c)) with an increase in the mole ratio of PEDOT to PSS (Fig. 7 (a)). The molar ratio ( R _M ) of the PEDOT to the PSS in the non-sulfuric acid-treated sample (PSS) was PEDOT / PSS = 1 / 1.9 (corresponding to about 1 / 2.5 weight ratio (w / The molar ratio ( R _M ) of PEDOT to the PSS of one sample was approximately PEDOT / PSS = 1 / 0.5 (corresponding to about 1 / 0.7 weight ratio (w / w)).

As shown in Table 1, when the molar ratio of PEDOT to PSS was 1.6 and 80%, when sulfuric acid was treated with 75% of sulfuric acid, the molar ratio of PEDOT to PSS was 1.8, when treated with 80% And the molar ratio of PEDOT was 1.9 (about 2.0).

Changes in the PSS content is further determined by the degree (X _c) enhance the increase in charge carrier mobility (μ) according to the (sample No. 1 ~ 14, 7 (d ) is also shown in Table 1) (Fig. 7 (d)) of It continued. Therefore, structural changes such as increase in crystallinity of PEDOT: PSS seem to have affected the increase of electrical conductivity.

As shown in Table 1, in the case of treatment with 75% sulfuric acid, the crystallinity was 40% and the crystallinity was 46% when treated with 80% sulfuric acid and 51% when treated with 100% sulfuric acid.

A figure of merit was obtained to evaluate the performance of the PEDOT: PSS thin film thus produced as an electrode.

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

) Can be obtained by 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 when the transmittance (% T) and the sheet resistance (Rs) based on the wavelength (λ) 550 nm are substituted,

) Can be calculated. Referring to FIG. 8A, the sheet resistance versus permeability obtained from various thin film thicknesses of the sulfuric acid-treated PEDOT: PSS is shown by a square point, from which the above equation can be fitted and expressed as a curve and an average figure of merit = 72.2 . This value is the highest among the performance indexes of the conductive polymer thin films reported so far. For reference, the sheet resistance (Rs) was 46.1 Ω / sq at% T = 90%.

Production Example 2: Production of polymer solar cell

100% sulfuric acid (H ₂ SO ₄₎ - treated PEDOT: PSS thin film (Sample No. 14) for use as an anode glass / anode / PEDOT: PSS ( 30 nm) / PTB7: PC 71 BM (90 nm) / Ca ( 20 nm) / Al (100 nm) structure.

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 the PEDOT: PSS used for the anode was used as the 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% 1,8-diiodooctane was added was added to the PEDOT: PSS layer 0.0 > 70 C &lt; / RTI &gt; for 10 minutes 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 polymer solar cell

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

Open-circuit voltage (V _oc ), short-circuit current (J _sc ), fill factor (FF) and photoelectric conversion efficiency (PCE)

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, the sheet resistance showed a permeability of 46.1 Ω / sq and 90% (550 nm absorption region) or more. As a result of the fabrication of organic solar cell using such a plastic electrode, it was confirmed that the energy conversion efficiency is almost the same as that of using ITO (> 95%). As a result, (Fig. 9).

Production Example 3: Production of polymer light emitting device

(60 nm) glass / anode / aryl-substituted poly (para-phenylene vinylene) derivative (P-PPV) using a PEDOT: PSS thin film (Sample No. 14) treated with 100% sulfuric acid (H ₂ SO ₄ ) / Ca (20 nm) / Al (100 nm) structure.

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

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

A P-PPV solution (0.5 wt%) dissolved in toluene was spun-cast on each electrode 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 polymer light emitting device

The LED structure is a structure (comparative example) in which a photoactive layer is coated on an ITO electrode coated with a PEDOT: PSS hole transport layer (comparative example), or a photoactive Layer, and a structure in which Ca and Al are vapor-deposited. FIG. 10A briefly shows the energy levels of the respective layers.

The sulfuric acid-treated PEDOT: PSS electrode (PEDOT-H ₂ SO ₄ ) shows LED electrode characteristics comparable to the ITO electrode (FIG. 10B). The PEDOT: PSS electrode has the advantage that an additional hole transport layer is unnecessary unlike the ITO electrode.

Thus, in the present invention, by controlling the concentration of sulfuric acid (H ₂ SO ₄ ) or sulfuric acid derivative, the treatment temperature, and the detailed manufacturing process conditions, induction of crystallization of the PEDOT: PSS thin film achieves electric conductivity , And that this was accomplished through the desorption of PSS through the "isolated state of charge".

The PEDOT: PSS thin film of the present invention can be utilized in an electronic device, for example, a field effect transistor, a thin film transistor, an optical sensor, a light emitting element, a photodetector, a magneto- The present invention can be applied to various applications including batteries, EL (electroluminescence) devices, PL (photoluminescence) devices, CL (Cathodeluminescence) devices, supercapacitors, and electrochromic devices. In particular, it is expected to be used as a transparent electrode in an optical device such as a solar cell and a light emitting device.

Claims (8)

Preparing a PEDOT: PSS thin film formed on a substrate;
Treating the thin film with a solution containing 75 to 100% by volume of sulfuric acid or a sulfuric acid derivative; And
Separating the thin film from the solution and washing the PEDOT: PSS-based electrode. The method according to claim 1,
Further comprising the step of separating and washing said thin film, followed by drying said washed thin film at a temperature of 60 to 160 ° C. The method according to claim 1,
Wherein the time for treating the thin film in the solution is at least 1 minute. The method according to claim 1,
Wherein the step of separating and cleaning the thin film is for removing sulfuric acid or sulfuric acid derivative adhering to the surface of the PEDOT: PSS thin film or removing PSS desorbed from the PEDOT: PSS. The method according to claim 1,
Wherein the step of separating and cleaning the thin film is carried out using water. The method according to claim 1,
Wherein the treatment of the thin film with the solution is performed by immersing the thin film in a solution containing 75 to 100% by volume of the sulfuric acid or the sulfuric acid derivative. The method according to claim 1,
The sulfuric acid or sulfuric acid derivative may be at least one selected from the group consisting of methanesulfonic acid, trifluoromethanesulfonic acid, sulfuric acid, perchloric acid, benzenesulfonic acid, p-toluenesulfonic acid, acid, 4-ethylbenzenesulfonic acid, 4-sulfophthalic acid, p-xylene-2-sulfonic acid hydrate, Amino-2-naphthalenesulfonic acid, 8-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 &Lt; RTI ID = 0.0 &gt; PEDOT: PSS. &Lt; / RTI &gt; The method according to claim 1,
Wherein the substrate is selected from the group consisting of glass, quartz, Al ₂ O ₃ and SiC.

Images