KR101401233B1 - Organic solar cell using nanocomposite of titania nanosheet and graphene - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to an organic solar cell using titania nanosheets and graphene, wherein the graphene and titania nanosheets are two-dimensional structures having a single atomic unit layer, and are very thin and excellent in physical stability due to the structure of nanosheet, Applicable to devices. In addition, since it has excellent electrical properties and chemical stability, when applied to an organic solar cell, electrons generated from the photoactive layer can be smoothly transferred to the electrode, and the chemical / physical stability is excellent. .

Description

[0001] The present invention relates to an organic solar cell using titania nanosheets and graphenes,

The present invention relates to an organic solar cell using titania nanosheets and graphene, and a manufacturing method thereof.

With the rapid development of the information electronics industry in recent years, the expected value of flexible elements that can be bent, folded, and curved as a next generation device is increasing.

Recently, organic solar cells based on plastic substrates and organic semiconductor materials are attracting attention. However, ITO, which is widely used as a transparent electrode, has a disadvantage in that it has poor physical stability, and therefore, a material to replace ITO is required to realize a flexible organic solar cell.

Patent Document 1 relates to a transparent electrode containing a graphene sheet, and it has become possible to obtain a transparent electrode having a very high conductivity, a low surface resistance and a low surface roughness by producing a transparent electrode using a graphene sheet . However, since the surface of graphene is basically hydrophobic, when the other material is deposited on the graphene, the adhesion force is weak and it does not rise well, which causes deterioration of materials. In the case of solar cells, since electrons and holes flow in the upper and lower parts of the device, if the adhesion between the materials and the interface is weak, the electrons and hole flow are interfered with, and the device characteristics are deteriorated. For this reason, the importance of the intermediate layer is great as a study of the interface improvement between graphene and the photoactive layer.

Non-Patent Document 1 relates to a dye-sensitized solar cell using a composite of graphene and TiO ₂ nanoparticles. Basically, a dye-sensitized solar cell is a device that applies the principle of photosynthesis of a plant, and is a solar cell that uses a pigment that absorbs light energy from a chloroplast in combination with a polymer. The basic structure of the dye-sensitized solar cell is composed of a transparent electrode coated on a transparent substrate, a porous TiO ₂ composed of nanoparticles bonded on the transparent electrode, a dye polymer coated with a monolayer on the surface of the TiO ₂ particle, An electrolytic solution for oxidation / reduction filling a space of 30 to 100 μm thickness, and a counter electrode for electrolyte reduction and a transparent substrate. The fundamental difference between this cell and conventional solar cell is that the process of absorption of solar energy and separation / transport of electron-hole pairs formed in this process occur simultaneously in the semiconductor due to the potential difference of the photoactive layer , Dye-sensitized solar cells are formed in semiconductor nanoparticles in such a way that the absorption of solar energy is caused by the dye, and the separation / transport of the generated electrons diffuses by the electron density difference. Specifically, when the sunlight is incident on the cell, the photoconductor that has passed through the transparent substrate and the transparent electrode is absorbed by the dye polymer. The dye is excited by the absorption of sunlight to generate electrons, and the generated electrons are transferred to the TiO ₂ conduction band and flow to the external circuit through the transparent electrode to transfer the electrical energy. The dye oxidized by the absorption of sunlight is returned to the original state by receiving electrons from the electrolyte solution. At this time, the electrolyte to be used mainly serves as an oxidation / reduction pair of I ^- / I ^{3 -} and receives electrons from the counter electrode and transfers the electrons to the dye. The process of generating and transporting electrons plays an important role in determining the performance of a battery. First, the time for the electrons excited from the dye to be injected into TiO ₂ must be shorter than the time for bonding with the hole and disappearing. One of the ways to improve the efficiency of the dye-sensitized cell is to increase the surface area of the TiO ₂ semiconductor oxide. Since the dye polymer has high efficiency when it is adsorbed to a semiconductor as a monolayer, the amount of sunlight absorbed becomes larger as the surface area of the semiconductor to which the dye polymer is adsorbed is wider. The nanoparticulate porous TiO ₂ layer having a large surface area has an irregular network structure, and thus the electrons injected from the dye can not be sufficiently transmitted to the transparent electrode. In this non-patent document 1, TiO _{2, which} is a semiconductor nanoparticle type in the dye-sensitized solar cell, is made to form a graphene complex to sufficiently transfer electrons from the transparent electrode to the transparent electrode. However, The use of a TiO ₂ composite having a pin and spherical nanoparticle form has the problem that the adhesive strength is weak and the characteristics and lifetime of the device become weak when applied to a flexible device.

Korean Patent Publication No. 2009-0028007 (Mar. 17, 2009)

Two-Dimensional Graphene Bridges Enhanced Photoinduced Charge Transport in Dye-Sensitized Solar Cells, ACS NANO, Vol. 4, No. 2, p887-894, Nailiang Yang et al

Accordingly, it is an object of the present invention to provide an organic solar cell applicable to a flexible solar cell and a method of manufacturing the same.

According to an aspect of the present invention, there is provided a photovoltaic cell including a lower electrode layer on which graphene is laminated on a substrate, a titania or nanosheet layer stacked on the lower electrode layer, a photoactive layer formed on the titania nanosheet layer, And an upper electrode layer formed on the upper electrode layer.

The present invention also relates to

Depositing graphene on the substrate to form a lower electrode layer;

Depositing a titania nanosheet on the lower electrode layer;

Forming a photoactive layer on the titania nanosheet;

Forming an upper electrode layer on the photoactive layer; And

The present invention provides a method of manufacturing an organic solar cell.

The present invention can improve the solar energy conversion efficiency by transferring electrons generated in the photoactive layer to the electrode smoothly when applied to an organic solar cell with excellent conductivity and physical / chemical stability using a transparent composite of graphene and titania nanosheet, It is expected that the applicability to flexible devices will be excellent.

Fig. 1 shows a titania nanosheet 1 having a size of several tens of 탆 ² and a titania nanosheet surface 2 after being laminated on a substrate.
2 is a schematic diagram of deposition of graphene and titania nanosheet on a substrate.
FIG. 3 is a schematic view of an organic solar cell designed on the basis of Griffin and titania nanosheets.

Hereinafter, the present invention will be described in detail.

The present invention relates to an organic electroluminescent device including a lower electrode layer on which graphene is laminated on a substrate, a titania nanosheet layer stacked on the lower electrode layer, a photoactive layer formed on the titania nanosheet layer, and an upper electrode layer formed on the photoactive layer It is about solar cells.

The substrate is not particularly limited as long as it is a substantially transparent substrate capable of emitting external light such as sunlight. Specifically, it is preferable to use a glass substrate or a plastic substrate. Specific examples of the plastic substrate include polyethylene terephthalate (PET), poly (ethylene naphthalate) PEN, polycarbonate (PC), polypropylene (PP) For example, polyimide (PI) or triacetyl cellulose (TAC).

The lower electrode (first electrode) layer may be replaced with graphene instead of conventional ITO, and may be formed of a single layer or a multilayer film.

The graphene is the thinnest and strongest of the existing materials. It is 100 times more electricity than copper and it can move electrons more than 100 times faster than monocrystalline silicon, which is mainly used as a semiconductor. Strength is more than 200 times stronger than steel and is twice as high thermal conductivity as diamonds with the highest thermal conductivity. It is excellent in elasticity and does not lose its electrical properties even when stretched or bent. Graphene can be rolled up to 5%, which means that ITO used as the surface material of the touch screen can easily be broken even if it is bent by only 2%, and the application area can be varied compared to the fact that the conductive conductivity is lost. It is also possible to grow a large area of cm ² .

Since the titania nanosheet has a large band gap of 3.5 eV, the titania nanosheet serves as a gate insulator (accelerating by direct acceleration through the titania nanosheet rather than passing slowly between the graphene and the photoactive layer, thereby improving the conductivity) And improves the adhesion of the graphene and the photoactive layer to improve the performance of the graphene. Since it is chemically very stable, it has a possibility to increase the lifetime when applied to an organic solar cell which is vulnerable to water and oxygen. Thickness is very thin, less than 1nm. One of the major features of the nanosheet form is that in a general bulk state, the grain is small in nm units. In the case of nanosheets, atoms are arranged two-dimensionally with a larger area than grain, Is very advantageous and has excellent physical strength.

When applied to an organic solar cell, it is expected that it will be more bendy and able to transfer electrons generated from the photoactive layer with excellent efficiency.

The graphene layer may be laminated as a single layer, or the titania nanosheet layer may be laminated as a single layer, or the titania nanosheet layer may be multilayered after lamination of a plurality of graphene layers. In addition, a single layer of graphene and a single layer of titania nanosheet may be alternately repeatedly laminated (refer to FIG. 2 (1) (2); (1) (2). (1), (2), (1), (2), and so on).

The photoactive layer may be a two-layer structure (D / A bi-layer) or a composite thin film (D + A) material having a thickness of about 100 nm and including an electron donor (D) blend structure can be used.

The photoactive layer preferably includes a p-type conductive polymer material including a [pi] -electron as an electron donor and a conductive polymer-electron accepting blend layer containing fullerene or a derivative thereof as an electron acceptor can do.

Specific examples of the conductive polymer used as the electron donor include P3HT (poly (3-hexylthiophene), polysiloxane carbazole, polyaniline, polyethylene oxide, poly (1-methoxy- Phenylene-vinylene), polyindole, polycarbazole, polypyridazine, polyisothianaphthalene, polyphenylene sulfide, polyvinylpyridine, polythiophene, polyfluorene, polypyridine, Derivatives, etc. However, the conductive polymer is not necessarily limited thereto. The conductive polymer may be a combination of two or more kinds of materials.

Specific examples of the electron acceptor include, but are not necessarily limited to, fullerene or a derivative thereof, nanocrystals such as CdSe, carbon nanotubes, nanorods, nanowires and the like.

The photoactive layer preferably comprises a mixture of P3HT as an electron donor and PCBM ([6,6] -phenyl-C61 butyric acid methyl ester) as a fullerene derivative as an electron acceptor, and the mixing weight ratio thereof is 1: 0.1 to 1: 2 is preferable.

The present invention is an organic solar cell in a reverse direction. Since electrons are dropped into the lower electrode, a hole transport layer may be further included between the upper electrode layer and the photoactive layer. The hole transport layer captures and transports holes generated in the photoactive layer. can do.

In the present invention, MoO ₃ may be used as the hole transport layer, but the present invention is not limited thereto.

The average thickness of the hole transporting layer may be suitably set according to the material, use, etc., and is not particularly limited, but is preferably from 5 to 2,000 nm. If it is outside the above range, it may be undesirable due to a decrease in hole transporting property or an increase in driving voltage.

The upper electrode (second electrode) layer may be formed of a material having a small work function to facilitate injection of electrons into the photoactive layer.

As the material of the upper electrode, metals such as aluminum, magnesium, calcium, sodium, potassium, indium, yttrium, lithium, silver, lead and cesium or a combination of two or more thereof may be used. Preferably, aluminum (Al) may be used for the upper electrode.

A buffer layer may be formed between the upper electrode layer and the photoactive layer and the buffer layer may be a mixed phase of zinc sulfide (ZnS) and zinc oxide (ZnO) or a single phase of ZnS1-xOx. The constituent material of the buffer layer can be controlled by controlling the ratio of sulfur to oxygen when preparing the Zn (S, O) thin film or by making the source material differently.

The present invention also relates to

Depositing graphene on the substrate to form a lower electrode layer;

Depositing a titania nanosheet on the lower electrode layer;

Forming a photoactive layer on the titania nanosheet;

Forming an upper electrode layer on the photoactive layer; And

The present invention relates to a method of manufacturing an organic solar cell.

First, graphene is laminated on a substrate to form a lower electrode layer. Specifically, graphene grown on a copper substrate in a large area by CVD is fixed to a rigid substrate below the copper substrate, and then a copper substrate is removed PMMA is deposited with a spin coater as a process to prevent wrinkling during processing. It is immersed in a copper etchant to remove copper and washed with DI-water. Carefully lift up the floating graphene on the flexible substrate. After drying in an oven, the organic substrate is fixed under a flexible substrate, and PMMA is coated with a spin coater to reduce wrinkles. Then, it is immersed in acetone to remove PMMA, and then dried. The organic substrate attached below is removed and used.

The titania nanosheets are separated into a single layer in a TBAOH solution and exist in the form of a colloidal solution. Since the single-layered titania nanosheets are negatively charged, they are dipped in PDDA (poly (diallyldimethylammonium)) solution, which is a polymer having a positive charge on the graphene prepared above, and surface-coated. The griffin coated with PDDA is immersed in a titania nanosheet colloid solution so that the titania nanosheets are deposited as a single layer by electrical attraction. After lamination to the desired thickness, the PDDA polymer material is removed by UV irradiation.

Alternatively, the graphene layer and the titania nanosheet layer may be alternately repeatedly deposited. Alternatively, the titania nanosheet layer may be formed in multiple layers after the graphene layer is multilayered.

The photoactive layer may be deposited or coated by a conventional deposition or coating method, for example, spraying, spin coating, dipping, printing, doctor blading, sputtering, or electrophoresis. But the method is not limited thereto.

The hole injection layer may be formed on the upper surface of the first electrode using a general deposition or coating method such as spraying, spin coating, dipping, printing, doctor blading, sputtering, or electrophoresis Or coated, and is not necessarily limited to these methods.

As the step of forming the upper electrode layer, a thin film deposition method such as sputtering, thermal deposition, or electron beam deposition may be used, but there is no limitation thereto

A buffer layer may be additionally formed between the upper electrode layer and the photoactive layer. The buffer layer may be formed by a known buffer layer growth method. Particularly preferably, the buffer layer may be formed by sputtering, evaporation, CVD (chemical vapor deposition), metalorganic chemical vapor deposition (MOCVD) Close-spaced sublimation (CSS), spray pyrolysis, chemical spraying, screen printing, non-vacuum liquid deposition, CBD (chemical bath deposition), VTD Vapor transport deposition, and electrodeposition may be used.

The organic solar cell using the characteristics of graphene and titania nanosheet according to the present invention is thin, has excellent physical / electrical properties, and is excellent in chemical stability, so that it is possible to drive the device with excellent persistence. Application of such graphene and titania nanosheets to organic solar cells results in improved solar energy conversion efficiency through flexible and more smooth electron transfer.

Claims (10)

Board;
A lower electrode layer on the substrate;
A titania nanosheet layer on the lower electrode layer;
A photoactive layer on the titania nanosheet layer; And
And an upper electrode layer on the photoactive layer,
Wherein the lower electrode layer is a laminated graphene.
Organic solar cell using titania nanosheets and graphene. The method according to claim 1,
Characterized in that the laminated graphene is a single film or a multilayer film.
Organic solar cell using titania nanosheets and graphene. The method according to claim 1,
Wherein the thickness of the titania nanosheet layer is 1 nm or less.
Organic solar cell using titania nanosheets and graphene. 3. The method according to claim 1 or 2,
Wherein the titania nanosheet layer is a single film or a multilayer film.
Organic solar cell using titania nanosheets and graphene. 5. The method of claim 4,
Wherein the graphene and the titania nanosheet layer are alternately laminated when the multilayer film is a multilayer film or multilayered films of titania nanosheets are laminated after the multilayer film laminate of graphene is laminated.
Organic solar cell using titania nanosheets and graphene. The method according to claim 1,
Further comprising a hole transport layer between the upper electrode layer and the photoactive layer.
Organic solar cell using titania nanosheets and graphene. The method according to claim 6,
And the thickness of the hole transporting layer is 5 to 2000 nm.
Organic solar cell using titania nanosheets and graphene. Preparing a substrate;
Depositing graphene on the substrate to form a lower electrode layer;
Depositing a titania nanosheet layer on the lower electrode layer;
Forming a photoactive layer on the titania nanosheet layer;
And forming an upper electrode layer on the photoactive layer.
(METHOD FOR MANUFACTURING ORGANIC SOLAR CELL USING TITANIA NANO SHEET AND GRAPHIN). 9. The method of claim 8,
Forming a lower electrode layer by laminating graphene on the substrate,
1) fixing graphene grown on a copper substrate in a large area by CVD with a rigid substrate beneath the copper substrate;
2) removing the copper substrate;
3) preventing wrinkle formation by depositing PMMA with a spin coater;
4) dipping in a copper etchant to remove copper and washing with deionized water (DI water);
5) drying in an oven;
6) fixing the glass substrate under the substrate and coating PMMA with a spin coater to reduce wrinkles;
7) removing PMMA using acetone and then drying;
8) removing the glass substrate under the substrate,
(METHOD FOR MANUFACTURING ORGANIC SOLAR CELL USING TITANIA NANO SHEET AND GRAPHIN).
9. The method of claim 8,
Wherein the step of laminating the titania nanosheet layer on the lower electrode layer comprises:
Dipping the lower electrode layer made of the graphene in a PDDA solution, which is a polymer having a positive charge, to perform surface coating;
Laminating a titania nanosheet with an electric attraction by dipping in a titania nanosheet colloid solution; And
UV irradiation to remove the PDDA.
(METHOD FOR MANUFACTURING ORGANIC SOLAR CELL USING TITANIA NANO SHEET AND GRAPHIN).

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