JP5326744B2 - Organic thin film solar cell and method for producing the same - Google Patents

Description

  The present invention relates to an organic thin film solar cell and a method for manufacturing the same.

  In order to increase the conversion efficiency value of the organic thin film solar cell, it is important to appropriately control the electrical connection state between the photoelectric conversion layer made of the organic thin film and the electrode. For example, it has been reported that a high conversion efficiency value can be obtained by performing heat treatment after forming an aluminum (Al) electrode on a photoelectric conversion layer by a vacuum deposition method (see Non-Patent Document 1). This is considered to be because a stable bonding state is formed between the electron-accepting material and the Al electrode by the heat treatment.

  In order to increase the conversion efficiency value, it has been proposed to chemically bond a conductive polymer contained in a photoelectric conversion layer and having a terminal modified with a substituent (see Patent Document 1). .) Alternatively, it has been proposed to modify the electrode with an organic molecule whose terminal is modified with a group having the same structure as the conductive polymer contained in the photoelectric conversion layer (see Patent Document 2). The manufacturing process of these organic thin film solar cells is performed in a vacuum or in an inert gas in order to prevent photooxidation of an organic layer such as a photoelectric conversion layer.

  In addition, in organic electroluminescence devices having a structure similar to that of organic thin-film solar cells, high charge injection is achieved by including a reactive organic compound or its reaction product between the organic layer containing the charge injection transport material and the electrode. It has been reported that characteristics are obtained (see Patent Document 3).

  Each of the above prior arts improves the performance by appropriately controlling the electrical connection state between the organic thin film and the electrode. However, the conversion efficiency realized by the above prior art is small, and further improvement of the conversion efficiency value is necessary for practical use.

JP 2006-032636 A JP 2006-344741 A JP 2006-019678 A

W. Ma et al., Advanced Functional Materials (Adv. Func. Mater.), 2005, Vol. 15, p. 1617

  In view of the above problems, an object of the present invention is to provide an organic thin film solar cell having high photoelectric conversion efficiency and a method for producing the same.

    According to the first aspect of the present invention, the first electrode on the substrate, the photoelectric conversion layer containing the electron donating material and the electron accepting material on the first electrode, and formed on the surface of the photoelectric conversion layer, oxygen There is provided an organic thin-film solar cell including an oxygen-added layer to which is added and (d) a second electrode formed on the surface of the oxygen-added layer.

    According to the second aspect of the present invention, a step of forming a first electrode on a substrate, a step of forming a photoelectric conversion layer containing an electron donating material and an electron accepting material on the first electrode, and photoelectric conversion An organic process comprising: exposing a layer to a gas containing oxygen to form an oxygen-added layer in which oxygen is added to the surface of the photoelectric conversion layer; and (d) forming a second electrode on the surface of the oxygen-added layer. A method of manufacturing a thin film solar cell is provided.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide an organic thin film solar cell with high photoelectric conversion efficiency, and its manufacturing method.

It is sectional drawing which shows an example of the organic thin film solar cell which concerns on embodiment of this invention. It is process sectional drawing (the 1) which shows an example of the manufacturing method of the organic thin-film solar cell which concerns on embodiment of this invention. It is process sectional drawing (the 2) which shows an example of the manufacturing method of the organic thin film solar cell which concerns on embodiment of this invention. It is process sectional drawing (the 3) which shows an example of the manufacturing method of the organic thin film solar cell which concerns on embodiment of this invention. It is process sectional drawing (the 4) which shows an example of the manufacturing method of the organic thin film solar cell which concerns on embodiment of this invention. It is process sectional drawing (the 5) which shows an example of the manufacturing method of the organic thin film solar cell which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  As shown in FIG. 1, the organic thin film solar cell according to the embodiment of the present invention includes a substrate 10, a first electrode 12 on the substrate 10, a hole extraction layer 14 on the first electrode 12, and a hole extraction layer 14. The upper photoelectric conversion layer 16, the oxygen addition layer 18 provided on the surface of the photoelectric conversion layer 16, and the second electrode 20 provided on the surface of the oxygen addition layer 18 are provided. The photoelectric conversion layer 16 includes an electron donating material and an electron accepting material.

  The photoelectric conversion layer 16 has a bulk heterojunction in which an electron donating material and an electron accepting material are mixed, or a heterojunction in which an electron accepting material film is stacked on an electron donating material film. In order to increase the photoelectric conversion efficiency, a bulk heterojunction is desirable. In addition, it is desirable to use an electron-donating material and an electron-accepting material whose ends are not modified. This is because if the electron-donating material and the electron-accepting material whose ends are modified are used, the crystallinity of the photoelectric conversion layer becomes poor, the conductivity is deteriorated, and the photoelectric conversion efficiency is lowered.

  The film thickness of the photoelectric conversion layer 16 is, for example, in the range of 0.2 nm to 3000 nm, preferably in the range of 1 nm to 600 nm. When the film thickness of the photoelectric conversion layer 16 is thicker than 3000 nm, the volume resistance of the photoelectric conversion layer 16 may increase. On the other hand, if the film thickness is less than 0.2 nm, light may not be sufficiently absorbed or a short circuit may occur between the electrodes.

The electron donating material of the photoelectric conversion layer 16 is not particularly limited as long as it has a function as an electron donor, but it is preferable that the film can be formed by a wet coating method. Among these, an electron donating conductive polymer material is preferable. The conductive polymer is a so-called π-conjugated polymer, which is composed of a π-conjugated system in which double bonds or triple bonds containing carbon-carbon or hetero atoms are alternately linked to single bonds, and exhibits semiconducting properties. It is. In addition, since the conductive polymer material can be easily formed by a wet coating method by using a coating solution in which the conductive polymer material is dissolved or dispersed in a solvent, a large-area organic thin film solar cell As an electron-donating material, for example, polythiophene (P3HT), polyphenylene, polyphenylene vinylene, polysilane, polycarbazole, polyvinyl carbazole, porphyrin, polyacetylene, polypyrrole, Polymer materials such as polyaniline, polyfluorene, polyvinylpyrene, polyvinylanthracene, and derivatives thereof, and copolymers thereof, or phthalocyanine-containing polymers, carbazole-containing polymers, and organometallic polymers are used. Among the above, thiophene-fluorene copolymer, polyalkylthiophene, phenylene ethynylene-phenylene vinylene copolymer, phenylene ethynylene-thiophene copolymer, phenylene ethynylene-fluorene copolymer, fluorene-phenylene vinylene copolymer A thiophene-phenylene vinylene copolymer is preferably used. These electron donating materials can form a heterojunction in which the energy level difference of the lowest unoccupied molecular orbital (LUMO) is appropriate for many electron accepting materials.

The electron-accepting material of the photoelectric conversion layer 16 is not particularly limited as long as it has a function as an electron acceptor, but is preferably a film that can be formed by a wet coating method. Examples of the electron-accepting material include polyphenylene vinylene, polyfluorene, and derivatives thereof, and polymer materials such as copolymers thereof, carbon nanotube (CNT), phenyl C61-butyric acid methyl ester (PCBM), and the like. Fullerene derivatives, cyano (CN) group or trifluoromethyl (CF ₃ ) group-containing polymers, and (CF ₃ ) group-substituted polymers.

The first electrode 12 is not particularly limited as long as it is a conductive material, but is preferably selected appropriately in consideration of the irradiation direction of light, the work function of the material forming the second electrode 20 described later, and the like. . For example, when the second electrode 20 is a conductive material having a low work function, the first electrode 12 is preferably a conductive material having a high work function. Examples of the conductive material having a high work function include gold (Au), silver (Ag), cobalt (Co), nickel (Ni), platinum (Pt), conductive carbon (C), indium tin oxide (ITO), and oxidation. tin (SnO _2), fluorine (F) SnO ₂ doped with, such as zinc oxide (ZnO). Moreover, when making the board | substrate 10 side into a light-receiving surface, it is preferable to make the 1st electrode 12 into a transparent electrode, In this case, what is generally used as a transparent electrode can be used. Specifically, indium zinc oxide (IZO), ITO, Al-doped ZnO, zinc tin oxide (ZnSnO), or the like is used.

  The total light transmittance of the first electrode 12 is 85% or more, preferably 90% or more, and more preferably 92% or more. When the substrate 10 is a light receiving surface, if the total light transmittance of the first electrode 12 is 85% or more, the first electrode 12 can sufficiently transmit light, and the photoelectric conversion layer 16 efficiently transmits light. Can be absorbed. The first electrode 12 may be a single layer, or may be a laminate of materials having different work functions. The film thickness of the first electrode 12 is in the range of 0.1 nm to 500 nm, preferably in the range of 1 nm to 300 nm. When the film thickness is less than 0.1 nm, the sheet resistance of the first electrode 12 becomes too large, and it becomes difficult to sufficiently transmit the generated photocharge to the external circuit. On the other hand, when the film thickness is thicker than 500 nm, the total light transmittance is lowered and the photoelectric conversion efficiency is lowered.

  The second electrode 20 is not particularly limited as long as it has conductivity. However, it is preferable to select the second electrode 20 in consideration of the light irradiation direction, the work function of the material forming the first electrode 12, and the like. For example, when the first electrode 12 is a transparent electrode, the second electrode 20 may not be transparent. Further, when the first electrode 12 is made of a material having a high work function, the second electrode 20 is preferably made of a material having a low work function. Specifically, materials having a low work function include lithium (Li), indium (In), Al, calcium (Ca), magnesium (Mg), samarium (Sm), terbium (Tb), ytterbium (Yb), Zirconium (Zr), lithium fluoride (LiF), or the like is used.

  The second electrode 20 may be a single layer, or may be a laminate of materials having different work functions. The film thickness of the second electrode 20 is in the range of 0.1 nm to 500 nm, preferably in the range of 1 nm to 300 nm. When the film thickness is less than 0.1 nm, the sheet resistance of the second electrode 20 becomes too large, and it becomes difficult to sufficiently transmit the generated photocharge to the external circuit. On the other hand, when the film thickness is thicker than 500 nm, the light transmittance is lowered, and the photoelectric conversion efficiency may be lowered.

  The hole extraction layer 14 provided between the first electrode 12 and the photoelectric conversion layer 16 easily extracts holes generated in the photoelectric conversion layer 16 to the first electrode 12 that is a hole extraction electrode. Is for. Thereby, since the hole extraction efficiency from the photoelectric conversion layer 16 to the first electrode 12 is increased, the photoelectric conversion efficiency can be improved.

  The hole extraction layer 14 is not particularly limited as long as it is a material that stabilizes the extraction of holes from the photoelectric conversion layer 16. Specifically, doped polyaniline, polyphenylene vinylene, P3HT, polypyrrole, polyparaphenylene, polyacetylene, conductive organic compounds such as triphenyldiamine (TPD), or electron donation such as tetrathiofulvalene, tetramethylphenylenediamine, etc. An organic material or the like that forms a charge transfer complex composed of an organic compound and an electron-accepting compound such as tetracyanoquinodimethane or tetracyanoethylene is used. Moreover, metal thin films, such as Au, In, Ag, palladium (Pd), can also be used. Furthermore, the metal thin film may be formed alone or in combination with the above organic material. In particular, polyethylenedioxythiophene (PEDOT) and TPD are preferably used.

  The thickness of the hole extraction layer 14 is preferably in the range of 10 nm to 200 nm when an organic material is used, and preferably in the range of 0.1 nm to 5 nm when a metal thin film is used.

  When the second electrode 20 is a hole extraction electrode, the hole extraction layer 14 is formed between the photoelectric conversion layer 16 and the second electrode 20. Further, the hole extraction layer 14 may be omitted.

  The material and thickness of the substrate 10 are not limited as long as the first electrode 12 can be formed on the surface. As the substrate 10, a plate-like or film-like resin, glass or the like is used. For example, when the substrate 10 side is the light receiving surface, transparent resin such as polyethylene naphthalate (PEN) or polycarbonate (PC), glass, or the like is used for the substrate 10.

  A conventional organic thin film solar cell is manufactured in an inert gas in order to prevent deterioration of the photoelectric conversion layer due to moisture. The second electrode is directly provided on the surface of the photoelectric conversion layer. On the other hand, in the embodiment of the present invention, oxygen is added by exposing the surface of the photoelectric conversion layer 16 to a gas containing oxygen, and the oxygen addition layer 18 in which the photoelectric conversion layer 16 is modified by oxygen is formed. Yes. The second electrode 20 is provided on the surface of the oxygen addition layer 18. The presence of the oxygen addition layer 18 can substantially reduce the potential barrier between the second electrode 20 and the photoelectric conversion layer 16. Thus, by providing the oxygen addition layer 18 between the second electrode 20 and the photoelectric conversion layer 16, the electrical connection state between the second electrode 20 and the photoelectric conversion layer 16 can be improved. As a result, charges generated in the photoelectric conversion layer 16 can be efficiently taken out to the external circuit.

  Next, the manufacturing method of the organic thin-film solar cell concerning embodiment of this invention is demonstrated using process sectional drawing shown in FIGS. In addition, a manufacturing process is implemented in inert gas except an oxygen addition layer formation process.

As shown in FIG. 2, an ITO film is formed on the surface of a substrate 10 on which a silicon oxide (SiO ₂ ) thin film is formed by a physical vapor deposition (PVD) method or the like by a reactive ion plating method using a pressure gradient plasma gun or the like. Is deposited. After forming the ITO film, the first electrode 12 is formed by patterning by photolithography and etching.

  The substrate 10 is a PEN film having a thickness of about 125 μm. The first electrode 12 is a transparent electrode having a film thickness of about 150 nm and a sheet resistance of about 20Ω / □. The conditions for reactive ion plating of the ITO film are: power of about 3.7 kW, oxygen partial pressure of about 73%, film formation pressure of 0.3 Pa, film formation rate of about 150 nm / min, and substrate temperature of about 20 ° C. It is. Next, the substrate 10 on which the first electrode 12 is formed is cleaned using acetone, a substrate cleaning solution, isopropanol (IPA), or the like.

  As shown in FIG. 3, a conductive polymer paste in which poly- (3,4-ethylenedioxythiophene) is dispersed is formed on the first electrode 12 by spin coating. The formed conductive polymer paste is dried at about 150 ° C. for about 30 minutes to form the hole extraction layer 14. The film thickness of the hole extraction layer 14 is about 100 nm.

  P3HT and PCBM are dissolved in a solvent such as chlorobenzene to prepare a coating solution having a solid content concentration of about 1.4% by weight. As shown in FIG. 4, the prepared coating solution is applied onto the hole extraction layer 14 at a rotational speed of about 600 rpm by spin coating to form the photoelectric conversion layer 16.

As shown in FIG. 5, the photoelectric conversion layer 16 is exposed to a gas containing oxygen (O ₂ ), for example, the atmosphere, and the oxygen-added layer 18 to which oxygen is added is formed on the surface of the photoelectric conversion layer 16. Air exposure conditions range from 10 minutes to 2 hours at room temperature of about 20 ° C.

  As shown in FIG. 6, the second electrode 20 is formed by forming a film of Al on the surface of the oxygen addition layer 18 by a vacuum deposition method. The film thickness of the second electrode 20 is about 100 nm.

  Next, the substrate 10 on which the first electrode 12, the hole extraction layer 14, the photoelectric conversion layer 16, the oxygen addition layer 18, and the second electrode 20 are formed is heated and dried on a hot plate having a temperature of about 150 ° C. Thereafter, the second electrode 20 is sealed with a sealing glass material, an adhesive sealing material, or the like. Thus, an organic thin film solar cell is manufactured.

In the oxygen addition layer forming step, the atmosphere is used as a gas containing oxygen. However, the gas containing O ₂ is not limited to the atmosphere, and may be, for example, dry air or a gas obtained by mixing O ₂ with an inert gas such as argon (Ar) or nitrogen (N ₂ ). In particular, dry air can be prepared at low cost, and the manufacturing cost of the organic thin-film solar cell can be reduced.

The solar cell characteristics of each organic thin-film solar cell having the oxygen addition layer 18 formed by exposure to dry air and air were evaluated. Moreover, the solar cell characteristic of the organic thin film solar cell of the conventional structure without the oxygen addition layer manufactured by implementing all the manufacturing processes in inert gas as a comparative example was evaluated. Regarding the solar cell characteristics, the current-voltage characteristics were measured using a pseudo-sunlight (output: 100 mW / cm ² ) of air mass (AM) 1.5 as an irradiation light source and a current voltage source such as a source measure unit. From the measured current-voltage characteristics, the series resistance and photoelectric conversion efficiency of the organic thin film solar cell were evaluated.

The organic thin film solar cell in which the oxygen-added layer 18 is formed using dry air has a series resistance of about 4.2 Ω / cm ² and a photoelectric conversion efficiency of about 2.7%. The series resistance of the organic thin film solar cell in which the oxygen-added layer 18 is formed using the atmosphere is about 5.1 Ω / cm ² and the photoelectric conversion efficiency is about 2.5%. On the other hand, the organic thin film solar cell of the comparative example has a series resistance of about 10.1 Ω / cm ² and a photoelectric conversion efficiency of about 2.1%. As described above, in the organic thin film solar cell having the oxygen addition layer 18 according to the embodiment of the present invention, the organic thin film solar cell is substantially reduced by reducing the potential barrier between the second electrode 20 and the photoelectric conversion layer 16. It has been confirmed that the series resistance of the battery is reduced and the photoelectric conversion efficiency is increased. The exposure time with the above dry air and air was about 2 hours.

  Moreover, the relationship between the exposure time of dry air and air | atmosphere and a photoelectric conversion efficiency value was confirmed. In the case of dry air, even if the exposure time was about 2 hours and about 5 hours, the photoelectric conversion efficiency was not much different. On the other hand, in the case of the atmosphere, the photoelectric conversion efficiency was reduced by about 35% when the exposure time was about 5 hours as compared with the case where the exposure time was about 2 hours. Although the oxygen-added layer is formed by exposure to the atmosphere and the photoelectric conversion efficiency increases, the deterioration of the photoelectric conversion layer 16 due to moisture contained in the air also proceeds at the same time. For this reason, the photoelectric conversion efficiency decreases when exposed to the atmosphere for a long time. As described above, as the gas containing oxygen, dry air containing no moisture is desirable.

(Other embodiments)
Although the embodiments of the present invention have been described as described above, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 10 ... Substrate 12 ... 1st electrode 14 ... Hole extraction layer 16 ... Photoelectric conversion layer 18 ... Oxygenation layer 20 ... 2nd electrode

Claims (7)

A first electrode on the substrate;
On the first electrode, a photoelectric conversion layer containing an electron donating material and an electron accepting material;
An oxygen-added layer formed on the surface of the photoelectric conversion layer and added with oxygen;
The organic thin film solar cell; and a second electrode of conductivity formed in contact with the oxygenation layer surface.   The organic thin-film solar cell according to claim 1, further comprising a hole extraction layer provided between the first electrode and the photoelectric conversion layer.   The organic thin-film solar cell according to claim 1 or 2, wherein the electron-donating material is polythiophene having an unmodified terminal, and the electron-accepting material is a fullerene derivative having an unmodified terminal.   The said 2nd electrode is aluminum, The organic thin-film solar cell of any one of Claims 1-3 characterized by the above-mentioned. Forming a first electrode on a substrate;
Forming a photoelectric conversion layer containing an electron-donating material and an electron-accepting material on the first electrode;
Exposing the photoelectric conversion layer to a gas containing oxygen to form an oxygen-added layer in which oxygen is added to the surface of the photoelectric conversion layer;
And a step of forming a conductive second electrode in contact with the surface of the oxygen-added layer.   The method for producing an organic thin film solar cell according to claim 5, wherein the gas containing oxygen is dry air.   The method for producing an organic thin-film solar cell according to claim 5, further comprising a step of forming a hole extraction layer on the first electrode before forming the photoelectric conversion layer.

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