JP2007317834A - Film-like solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible CIS solar cell with high conversion efficiency. <P>SOLUTION: In the film-like solar cell, lamination having at least an electrode layer and a chalcopyrite construction semiconductor thin film is formed on a substrate film where film thickness is 3 to 200 μm, a linear expansion coefficient is 1 to 10 ppm/°C, and tensile fracture strength of a longitudinal direction is 300 MPa or above in a polyimide film. In these materials, polycondensation is performed in aromatic diamineses and aromatic tetrapod carboxylic anhydrides, especially a polyimide benzo oxazole film in which polycondensation is performed in aromatic diamineses having a benzo oxazole structure, and the aromatic tetrapod carboxylic anhydrides. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a film-like CIS-based solar cell using a flexible and high-strength substrate film in which a laminate having at least an electrode layer and a chalcopyrite structure semiconductor thin film is formed on the film.

Conventionally, solar cells manufactured by processing single crystal silicon ingots, manufactured by processing polycrystalline silicon ingots, thin film solar cells represented by amorphous silicon solar cells, and thick film semiconductors as base materials Proposals have been made of laminated solar cells having two or more layers produced by printing and laminating them on top of each other, or combinations thereof. As a structure of a solar cell, the structure formed in order by forming an electrode layer, a photoelectric converting layer, and a (transparent) electrode layer on a base material is mentioned. The photoelectric conversion layer is a layer (including a case where it has a laminated structure) configured to convert solar energy into electric energy, and a layer made of a semiconductor such as a silicon-based semiconductor is widely known. Examples of the base material for the thin film solar cell and the thick film semiconductor include a stainless steel plate and a flexible base material. Attempts to form thin-film solar cells and thick-film solar cells using organic base materials have been made for a long time for the purpose of weight reduction, flexibility, and mass production. As an attempted solar cell, for example, there is a solar cell in which a metal foil is bonded to the surface of a fiber fabric substrate, and a silicon thin film is formed on the metal foil (see Patent Document 1).
JP 05-308143 A

In order to relieve the thermal stress applied to the film substrate when forming a thin film semiconductor, a production method using a support substrate in addition to the film substrate at the time of manufacturing a solar cell is proposed. In this manufacturing method, a heat-resistant base substrate to be a film substrate later is provided on a supporting substrate, and then an amorphous silicon layer having electrode layers laminated on both sides is formed on the heat-resistant base substrate. This is a method for manufacturing a thin-film solar cell, which includes subsequently peeling the heat-resistant base substrate from the support substrate (see Patent Document 2).
In addition to the above, for the purpose of improving the heat resistance of the film substrate itself, it has been proposed to produce a thin film solar cell using a heat resistant film having a specific composition and specific physical properties as a substrate ( (See Patent Documents 3 to 6). It has also been proposed to produce a polyimide film as a substrate (see Patent Document 7).
JP 05-315630 A Japanese Patent Laid-Open No. 11-029645 JP 11-245291 A JP 2001-127327 A Japanese Patent Laid-Open No. 2002-265643 JP 2003-179238 A

On the other hand, a CuInSe ₂ (CIS) film that is a compound semiconductor thin film (chalcopyrite structure semiconductor thin film) composed of a group I element, a group III element, and a group VI element, or Cu (In, Ga) Se in which Ga is dissolved. ₂ A solar cell using a (CIGS) film (hereinafter, both may be referred to as a solar cell using a CIS-based film), and both are described as Cu (In _1-X Ga _X ) Se ₂ However, this system is known to have a high energy conversion efficiency of 17% or more. Although CIS solar cells mainly use glass as a substrate, there are also reports of solar cells using flexible substrates.
A solar cell in which a CIS-based semiconductor thin film is formed on polyimide was introduced at the 25th Itriple Photovoltaic Power Generation Expert Meeting held in Washington, USA in 1996. Brunet M. Basol et al. Have been reported under the title "Flexible and Light Weight Copper Indium Diselenide Solar Cells."
Further, a solar cell in which a CIS-based semiconductor thin film is formed on stainless steel is disclosed in a publication “Progress in Photovoltaics: Research and Applications” No. 7, pages 311-316, “Progress in Photovoltaics: Research and Applications,” published in 1999. 7, 311-316 (1999) "is reported under the title" Progress Word 20% Efficiency in Cu (In, Ga) Se ₂ Polycrystalline Thin-Film Solar Cells ".
25th Photovoltaic Specialist Conference Proceedings, IEEE, Washington, DC, 157-162 (1996) Progress in Photovoltaics: Research and Applications, 7, 311-316 (1999)

Although the CIS solar cell formed on the flexible substrate has been reported conventionally, the conversion efficiency is lower than that using a glass substrate. In particular, the conversion efficiency of a CIS solar cell using a polyimide substrate is about 10%, which is significantly inferior to the conversion efficiency of 17% or more obtained by a CIS solar cell using a glass substrate. One of the main reasons for this is that the heating temperature in the film forming process is limited. When a substrate made of stainless steel is used, heating at a higher temperature than a glass substrate is possible. However, since the thermal expansion coefficient of stainless steel and the thermal expansion coefficient of the CIS-based semiconductor thin film are greatly different, there is a problem that the CIS-based semiconductor thin film is easily peeled off from the substrate. The CTE of SUS304 (Fe-18Cr8 ¥ -8Ni) is 17.3 ppm / K, which is about twice as large as that of the CIGS thin film. In order to suppress such peeling, it is important to optimize the film forming conditions such as the heating rate of the substrate, the heating temperature, and the heating time. Therefore, in order to manufacture a CIS solar cell exhibiting high conversion efficiency using a flexible substrate, it is often necessary to improve the film forming process and the heat treatment process.
In view of such circumstances, the present invention provides a polyimide substrate that can produce a CIS solar cell having flexibility and high conversion efficiency with high production efficiency, thereby providing flexibility and high conversion efficiency. An object is to provide a solar cell.

As a result of intensive studies, the present inventors have found that a polyimide film having specific physical properties has sufficient adhesion strength with a laminate including a chalcopyrite structure semiconductor thin film photoelectric conversion layer, and a dry film forming method of a chalcopyrite structure semiconductor thin film A film-like solar cell that is satisfactory for the preparation of a laminate film containing a chalcopyrite-structured semiconductor thin film in terms of thermal behavior, etc., has sufficient adhesion to the laminate such as a chalcopyrite-structured semiconductor thin film, and has very little wrinkling or peeling The inventors have found that the film-like solar cell panel obtained thereby can be satisfied as a highly reliable film-like solar cell that can withstand, for example, a heat history due to cooling and heating, and has reached the present invention.
That is, this invention consists of the following structures.
1. In a film-like solar cell in which a laminate having at least an electrode layer and a chalcopyrite structure semiconductor thin film is formed on a substrate film, the substrate film is obtained by polycondensing aromatic diamines and aromatic tetracarboxylic acid anhydrides. A film-like solar cell having a film thickness of 3 to 200 μm, a linear expansion coefficient of 1 to 10 ppm / ° C., and a tensile breaking strength in the longitudinal direction of 300 MPa or more.
2. The film-like solar cell according to 1 above, wherein the polyimide film is a polyimide benzoxazole film obtained by polycondensation of an aromatic diamine having a benzoxazole structure and an aromatic tetracarboxylic acid anhydride.
3. The roll for producing the film-like solar cell according to 1 or 2 wound up in a roll shape in which a laminate having at least an electrode layer and a chalcopyrite structure semiconductor thin film is formed on a long substrate film.

In the film-like solar cell in which a laminate having a chalcopyrite structure semiconductor thin film is formed on the substrate film of the present invention, the substrate film is a polyimide formed by polycondensation of aromatic diamines and aromatic tetracarboxylic anhydrides A film-like solar cell having a film thickness of 3 to 200 μm, a linear expansion coefficient of 1 ppm / ° C. to 10 ppm / ° C., and a tensile breaking strength in the longitudinal direction of 300 MPa or more is a specific polyimide that is a substrate film to be used The film has sufficient adhesion strength with a laminate including a chalcopyrite structure semiconductor thin film photoelectric conversion layer, and is suitable for producing a laminate film containing a chalcopyrite structure semiconductor thin film in the thermal behavior in a dry film forming method of the chalcopyrite structure semiconductor thin film. Satisfactory substrate film, such as chalcopyrite structure semiconductor thin film It is possible to provide a film-like solar cell that has sufficient adhesion to the laminate and has very little wrinkles or peeling, and the resulting film-like solar cell panel is heated by, for example, irradiation with sunlight, and low temperatures in winter It becomes a highly reliable film-like solar cell that can withstand a heat history due to cooling or the like, and has a great industrial significance.
Moreover, in the case of a glass substrate, production can only be performed in a single sheet form, and if the glass substrate becomes large, the loss of the movement time of the substrate, the loss such as the temperature rise time inevitably increases, and the size is inevitably increased. However, since film can be produced on a roll-to-roll basis, the productivity is improved and the apparatus can be made compact compared to a large area.

The polyimide film in the metallized polyimide film in the present invention is a polyimide film obtained by reacting aromatic diamines and aromatic tetracarboxylic acids,
Although it is not particularly limited as long as it is a polyimide film having a film thickness of 3 to 200 μm, a linear expansion coefficient of 1 ppm / ° C. to 10 ppm / ° C., and a tensile breaking strength in the longitudinal direction of 300 MPa or more, preferably the following fragrance A preferred example is a combination of an aromatic diamine and an aromatic tetracarboxylic acid (anhydride).
A. Combination with aromatic tetracarboxylic acid having pyromellitic acid residue and aromatic diamine having benzoxazole structure.
B. A combination of an aromatic diamine having a diaminodiphenyl ether skeleton and an aromatic tetracarboxylic acid having a pyromellitic acid skeleton.
C. A combination of an aromatic diamine having a phenylenediamine skeleton and an aromatic tetracarboxylic acid having a pyromellitic acid skeleton.
D. A combination of one or more of the above ABCs.
In particular, A. A combination for producing a polyimide film having an aromatic diamine residue having a benzoxazole structure, and a combination in which the aromatic diamine contains at least paraphenylenediamine and / or diaminodiphenyl ethers are preferable. A polyimide benzoate mainly composed of polyimide benzoxazole obtained by reacting an aromatic diamine having a benzoxazole structure that can be particularly preferably used in the present invention with an aromatic tetracarboxylic anhydride having a pyromellitic acid residue. The following compounds can be illustrated as aromatic diamines having a benzoxazole structure used in oxazole.

Among these, amino (aminophenyl) benzoxazole isomers are preferable from the viewpoint of ease of synthesis. Here, “each isomer” refers to each isomer in which two amino groups of amino (aminophenyl) benzoxazole are determined according to the coordination position (eg, the above “formula 1” to “formula 4”). Each compound described in the above. These diamines may be used alone or in combination of two or more.
In the present invention, it is preferable to use 70 mol% or more of the aromatic diamine having the benzoxazole structure.

The present invention is not limited to the above items, and the following aromatic diamines may be used. Preferably, the diamines do not have the benzoxazole structure exemplified below as long as the total aromatic diamine is less than 30 mol%. Is a polyimide film using one or two or more in combination.
Examples of such diamines include 4,4′-bis (3-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, and bis [4- (3-aminophenoxy) phenyl]. Sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine,

  3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide 4,4'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,4'- Diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, bis [4- (4-aminophenoxy) phenyl] methane, 1 , 1-Bi [4- (4-aminophenoxy) phenyl] ethane, 1,2-bis [4- (4-aminophenoxy) phenyl] ethane, 1,1-bis [4- (4-aminophenoxy) phenyl] propane, 1 , 2-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl ]propane.

  1,1-bis [4- (4-aminophenoxy) phenyl] butane, 1,3-bis [4- (4-aminophenoxy) phenyl] butane, 1,4-bis [4- (4-aminophenoxy) Phenyl] butane, 2,2-bis [4- (4-aminophenoxy) phenyl] butane, 2,3-bis [4- (4-aminophenoxy) phenyl] butane, 2- [4- (4-aminophenoxy) Phenyl] -2- [4- (4-aminophenoxy) -3-methylphenyl] propane, 2,2-bis [4- (4-aminophenoxy) -3-methylphenyl] propane, 2- [4- ( 4-aminophenoxy) phenyl] -2- [4- (4-aminophenoxy) -3,5-dimethylphenyl] propane, 2,2-bis [4- (4-aminophenoxy) -3,5-dimethylphen Le] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane,

1,4-bis (3-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) ) Biphenyl, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfoxide, bis [4- ( 4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 1,3-bis [4- (4-aminophenoxy) ) Benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (3 Aminophenoxy) benzoyl] benzene, 4,4′-bis [(3-aminophenoxy) benzoyl] benzene, 1,1-bis [4- (3-aminophenoxy) phenyl] propane, 1,3-bis [4- (3-aminophenoxy) phenyl] propane, 3,4'-diaminodiphenyl sulfide,

  2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, bis [4- (3-aminophenoxy) phenyl] methane, 1,1 -Bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bis [4- (3-aminophenoxy) phenyl] ethane, bis [4- (3-aminophenoxy) phenyl] sulfoxide, 4,4 '-Bis [3- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [3- (3-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-α) , Α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, bis 4- {4- (4-aminophenoxy) phenoxy} phenyl] sulfone, 1,4-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-trifluoromethylphenoxy) -α, α-dimethylbenzyl] benzene, 1,3 -Bis [4- (4-amino-6-fluorophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-methylphenoxy) -α, α-dimethylbenzyl Benzene, 1,3-bis [4- (4-amino-6-cyanophenoxy) -α, α-dimethylbenzyl] benzene,

  3,3′-diamino-4,4′-diphenoxybenzophenone, 4,4′-diamino-5,5′-diphenoxybenzophenone, 3,4′-diamino-4,5′-diphenoxybenzophenone, 3, 3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3 '-Diamino-4,4'-dibiphenoxybenzophenone, 4,4'-diamino-5,5'-dibiphenoxybenzophenone, 3,4'-diamino-4,5'-dibiphenoxybenzophenone, 3,3'- Diamino-4-biphenoxybenzophenone, 4,4′-diamino-5-biphenoxybenzophenone, 3,4 -Diamino-4-biphenoxybenzophenone, 3,4'-diamino-5'-biphenoxybenzophenone, 1,3-bis (3-amino-4-phenoxybenzoyl) benzene, 1,4-bis (3-amino- 4-phenoxybenzoyl) benzene, 1,3-bis (4-amino-5-phenoxybenzoyl) benzene, 1,4-bis (4-amino-5-phenoxybenzoyl) benzene, 1,3-bis (3-amino) -4-biphenoxybenzoyl) benzene, 1,4-bis (3-amino-4-biphenoxybenzoyl) benzene, 1,3-bis (4-amino-5-biphenoxybenzoyl) benzene, 1,4-bis (4-Amino-5-biphenoxybenzoyl) benzene, 2,6-bis [4- (4-amino-α, α-dimethylbenzyl) pheno Si] A part or all of the hydrogen atoms on the aromatic ring in the benzonitrile and the aromatic diamine are halogen atoms, alkyl groups having 1 to 3 carbon atoms or alkoxyl groups, cyano groups, or alkyl groups or alkoxyl group hydrogen atoms. Examples thereof include aromatic diamines substituted with a halogenated alkyl group having 1 to 3 carbon atoms, partially or entirely substituted with halogen atoms, or alkoxyl groups.

  The aromatic tetracarboxylic acids used in the present invention are, for example, aromatic tetracarboxylic anhydrides. Specific examples of the aromatic tetracarboxylic acid anhydrides include the following. Among them, pyromellitic acid of Chemical formula 14 can be preferably used, and 70 mol% or more of the wholly aromatic tetracarboxylic acids are preferably used.

  These tetracarboxylic dianhydrides may be used alone or in combination of two or more. In the present invention, one or two or more non-aromatic tetracarboxylic dianhydrides exemplified below may be used in combination as long as they are less than 30 mol% of the total tetracarboxylic dianhydrides. Examples of such tetracarboxylic acid anhydrides include butane-1,2,3,4-tetracarboxylic dianhydride, pentane-1,2,4,5-tetracarboxylic dianhydride, and cyclobutanetetracarboxylic acid. Acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, cyclohexane-1,2,4,5-tetracarboxylic dianhydride, cyclohex-1-ene-2,3 5,6-tetracarboxylic dianhydride, 3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohexane-3 -(1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride 1-ethylcyclohexane -(1,2), 3,4-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane- 1- (2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ′, 4′-tetracarboxylic dianhydride.

Bicyclo [2.2.1] heptane-2,3,5,6-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1 , 3-Dipropylcyclohexane-1- (2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ′, 4′-tetracarboxylic dianhydride, bicyclo [2.2.1] Heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] Oct-7-ene-2,3,5,6-tetracarboxylic dianhydride and the like. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  The solvent used when reacting (polycondensing) the aromatic diamines with aromatic tetracarboxylic acids (anhydrides) to obtain polyamic acid dissolves both the raw material monomer and the produced polyamic acid. Although it will not specifically limit if it carries out, A polar organic solvent is preferable, for example, N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N, N-dimethylformamide, N, N-diethylformamide, N, Examples thereof include N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoric amide, ethyl cellosolve acetate, diethylene glycol dimethyl ether, sulfolane, and halogenated phenols. These solvents can be used alone or in combination. The amount of the solvent used may be an amount sufficient to dissolve the monomer as a raw material. As a specific amount used, the mass of the monomer in the solution in which the monomer is dissolved is usually 5 to 40% by mass, The amount is preferably 10 to 30% by mass.

The polymerization reaction conditions for obtaining the polyamic acid may be conventionally known conditions. As a specific example, stirring and / or continuous in an organic solvent at a temperature range of 0 to 80 ° C. for 10 minutes to 30 hours. Mixing may be mentioned. If necessary, the polymerization reaction may be divided or the temperature may be increased or decreased. In this case, the order of adding both monomers is not particularly limited, but it is preferable to add aromatic tetracarboxylic acid anhydrides to the solution of aromatic diamines. The mass of the polyamic acid in the polyamic acid solution obtained by the polymerization reaction is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, and the viscosity of the solution is measured with a Brookfield viscometer (25 ° C.). From the viewpoint of the stability of liquid feeding, it is preferably 10 to 2000 Pa · s, and more preferably 100 to 1000 Pa · s. The reduced viscosity (ηsp / C) of the polyamic acid in the present invention is not particularly limited, but is preferably 3.0 dl / g or more, and more preferably 4.0 dl / g or more.
Vacuum defoaming during the polymerization reaction is effective for producing a high-quality polyamic acid organic solvent solution. Moreover, you may perform superposition | polymerization by adding a small amount of terminal blockers to aromatic diamines before a polymerization reaction. Examples of the end capping agent include compounds having a carbon-carbon double bond such as maleic anhydride. The amount of maleic anhydride used is preferably 0.001 to 1.0 mol per mol of aromatic diamine.

  The obtained polyamic acid solution was cast on an endless support to obtain a self-supporting polyimide precursor film (hereinafter also referred to as a green film) in which complete imidization had not progressed by drying or solvent removal. This is wound up or subsequently subjected to a treatment such as high temperature to advance imidization to obtain a polyimide film. As an imidization method by high-temperature treatment, a conventionally known imidation reaction can be appropriately used. For example, using a polyamic acid solution that does not contain a ring-closing catalyst or a dehydrating agent, the imidization reaction proceeds by subjecting it to a heat treatment (so-called thermal ring-closing method), or a polycyclic acid solution containing a ring-closing catalyst and a dehydrating agent. In particular, a chemical ring closing method in which an imidization reaction is performed by the action of the above ring closing catalyst and a dehydrating agent can be given.

In the chemical ring closure method, imidation can be completely performed by heating after forming a precursor complex having self-supporting property by partially proceeding imidization reaction of the polyamic acid solution.
In this case, the condition for partially proceeding with the imidization reaction is preferably a heat treatment for 3 to 20 minutes at 100 to 200 ° C., and the condition for allowing the imidization reaction to be completely performed is preferably 200 to 400 ° C. For 3 to 20 minutes.
The timing for adding the ring-closing catalyst to the polyamic acid solution is not particularly limited, and may be added in advance before the polymerization reaction for obtaining the polyamic acid. Specific examples of the ring-closing catalyst include aliphatic tertiary amines such as trimethylamine and triethylamine, and heterocyclic tertiary amines such as isoquinoline, pyridine, and betapicoline. Among them, heterocyclic tertiary amines are mentioned. At least one amine selected from is preferred. Although the usage-amount of a ring-closing catalyst with respect to 1 mol of polyamic acids does not have limitation in particular, Preferably it is 0.5-8 mol.
The timing of adding the dehydrating agent to the polyamic acid solution is not particularly limited, and may be added in advance before the polymerization reaction for obtaining the polyamic acid. Specific examples of the dehydrating agent include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride. Among them, acetic anhydride, benzoic anhydride, etc. Acids or mixtures thereof are preferred. Moreover, the usage-amount of the dehydrating agent with respect to 1 mol of polyamic acids is not particularly limited, but is preferably 0.1 to 4 mol. When a dehydrating agent is used, a gelation retarder such as acetylacetone may be used in combination.

As a specific method of imidization, the above-mentioned imidation reaction and imidization treatment can be used as appropriate, but preferably the maximum treatment temperature is 460 ° C. or higher and lower than 500 ° C., and 3 minutes or longer and 30 minutes or shorter. It is preferable to perform the high temperature imidization treatment for a time of
Although the thickness of a polyimide film and a polyimide benzoxazole film is not specifically limited, When considering using it for the board | substrate film of a film-like solar cell, it is 3-200 micrometers normally, Preferably it is 10-150 micrometers. This thickness can be easily controlled by the amount of the polyamic acid solution applied to the support and the concentration of the polyamic acid solution.
The polyimide film of the present invention is usually an unstretched film, but may be stretched uniaxially or biaxially. Here, the unstretched film refers to a film obtained without intentionally applying a mechanical external force in the surface expansion direction of the film by tenter stretching, roll stretching, inflation stretching, or the like.

  The polyimide film of the present invention must have a linear expansion coefficient of 1 ppm / ° C. to 10 ppm / ° C. and a tensile strength at break in the longitudinal direction of 300 MPa or more. In the case of a film outside this range, the chalcopyrite structure semiconductor It has sufficient adhesion strength with a laminate including a thin film photoelectric conversion layer, and can be a substrate film that can satisfy the production of a laminate film containing a chalcopyrite structure semiconductor thin film in the thermal behavior in a dry film forming method of a chalcopyrite structure semiconductor thin film. Therefore, it becomes impossible to provide a film-like solar cell that has sufficient adhesion to a laminate such as a chalcopyrite-structured semiconductor thin film and that has very little wrinkling and peeling. Can withstand heat history due to heating by irradiation and cold cooling in winter , Not be a reliable film-like solar cells.

In the film-like solar cell of the present invention, for the formation of the electrode and the semiconductor thin film, a method that is performed in accordance with the production method described in Patent Document 7 and the like was adopted. At least a first step of forming an electrode film on a flexible substrate film that is a heat-resistant polyimide film having the specific physical properties, and above the electrode film (that is, directly or indirectly on the electrode film) ) CuInSe ₂ (CIS) film which is a compound semiconductor thin film (chalcopyrite structure semiconductor thin film) composed of Group I element, Group III element and Group VI element, or Cu (In, Ga) Se _{2 in} which Ga is dissolved in this. Manufactured by a method including a second step of forming a (CIGS) film (hereinafter also referred to as a CIS-based film together) and a third step of forming the semiconductor thin film by heat-treating the thin film. The

  The heat treatment may include a temperature increasing process and a heat retaining process in this order, and the temperature of the thin film may be increased at a rate of 10 ° C./second or more in the temperature increasing process. According to this structure, the production | generation of the binary compound of an Ib group element and a VIb group element or the binary compound of an IIIb group element and a VIb group element can be suppressed. In the case of this configuration, it is also a preferable aspect that the thin film is maintained at a temperature of 450 ° C. or higher for 10 seconds to 300 seconds in the heat retaining process. According to this configuration, it is possible to form a semiconductor film suitable for the light absorption layer of the solar cell and to use a flexible substrate having low heat resistance. In addition, a heat retention process means the process of hold | maintaining the temperature of a target object to the temperature more than fixed temperature or the temperature in a fixed range. The heat treatment includes a first temperature rising process, a first heat retaining process, a second temperature rising process, and a second heat retaining process in this order, and in the first heat retaining process, the thin film is heated to 100 ° C. to 100 ° C. You may hold | maintain to the temperature within the range of 400 degreeC, and may hold | maintain the said thin film in temperature higher than a said 1st heat retention process in a said 2nd heat retention process. According to this configuration, thermal stress due to rapid heating can be alleviated, and the semiconductor thin film can be prevented from peeling from the substrate. In this configuration, it is preferable to raise the temperature of the thin film at a rate of 10 ° C./second or more in the second temperature raising process. Moreover, it is preferable to hold | maintain the said thin film at the temperature of 450 degreeC or more in the range of 10 second-300 second in a said 2nd heat retention process.

After forming the semiconductor film, a solar cell is manufactured by further stacking layers necessary for the solar cell (the same applies to the following embodiments). Although there is no particular limitation on the configuration and formation method of each layer, for example, as shown in FIG. 1, the window layer 6 and the upper electrode film 4 may be laminated in order to form the extraction electrodes 5 and 7. For the window layer 6, for example, a layer made of CdS, ZnO, Zn (O, S), ZnO: Al can be used, and for the upper electrode film 4, for example, an ITO film can be used. A buffer layer or the like may be formed between the window layer and the upper electrode film.
Further, since the semiconductor film 3, the upper electrode film 4, the window layer 6, and the upper electrode film 4 are not formed on the extraction electrode 7, the thin film is not formed by the baffle plate, the pattern is formed by mechanical scribing, and the pattern is formed by laser scribing. A known technique may be used as appropriate.

In the solar cell manufacturing method, in the first and second steps, the electrode film and the thin film may be formed while moving the substrate. In this case, the substrate may be moved using a first roll that feeds the substrate wound in a cylindrical shape and a second roll that winds the substrate fed from the first roll. preferable. According to this configuration, a semiconductor thin film can be continuously formed on a long substrate, and a solar cell can be manufactured with high productivity.
When actually making a solar cell, attach a protective film on the back of the film-like solar cell of the present invention, affix it to a plate, tile, glass, etc., and fix it with a transparent resin for surface protection. You may use it combining suitably the method which has broken with the existing solar cell panel, such as sticking.

Examples of the present invention will be described below, but the present invention is not limited thereto. In addition, the evaluation method of the physical property in the following examples is as follows.
1. Reduced viscosity of polyamic acid (ηsp / C)
A solution dissolved in N-methyl-2-pyrrolidone so that the polymer concentration was 0.2 g / dl was measured at 30 ° C. using an Ubbelohde type viscosity tube.
2. Film thickness of polyimide film The thickness of the film was measured using a micrometer (Finereuf, Millitron 1254D).

3. Tensile modulus, tensile breaking strength and tensile breaking elongation of polyimide film The film after drying was cut into strips having a length of 100 mm and a width of 10 mm in the longitudinal direction (MD direction) and the width direction (TD direction), respectively, and used as test pieces. Using a tensile tester (Shimadzu Autograph (trade name) model name AG-5000A), the tensile modulus, tensile breaking strength and tensile breaking elongation were measured under the conditions of a tensile speed of 50 mm / min and a distance between chucks of 40 mm. It was measured.
Each data value in the table is indicated by a value in the MD direction.

4). Linear expansion coefficient (CTE) of polyimide film
For the polyimide film to be measured, the dimensional change rate in the MD direction and the TD direction is measured under the following conditions, respectively, and the dimensional change rate at intervals of 30 ° C. to 45 ° C., 45 ° C. to 60 ° C.,. The temperature was measured, this measurement was performed up to 300 ° C., and the average value of all measured values was calculated as CTE. Data values in the table are shown as average values in the MD and TD directions.
Device name: TMA4000S manufactured by MAC Science
Sample length; 20mm
Sample width: 2 mm
Temperature rise start temperature: 25 ° C
Temperature rising end temperature: 400 ° C
Temperature increase rate: 5 ° C / min
Atmosphere: Argon

5). Conversion efficiency Conversion efficiency was performed under simulated sunlight with an intensity of 100 mW / cm ² and an air mass of 1.5.

6). Peeling from a laminated substrate film made of a semiconductor thin film, etc. At least 0.3 m of a laminated polyimide film made of a semiconductor thin film (film-like solar cell) is sampled and placed on a horizontal surface to be made of a semiconductor thin film. The peeling of the laminate was visually observed, and the case where peeling was not observed was judged as ◎, the case where peeling was slightly observed was judged as ○, and the case where peeling and wrinkles could be observed was judged as x.

7). Warpage during heating A laminated polyimide film made of a semiconductor thin film (film-like solar cell) was cut into a width of 5 mm and a length of 70 mm to form a cantilever. The supporting part was sandwiched between glasses. Fix the SUS plate with the scale on the free end of the cantilever so that you can read the warp, put it in the electric furnace, change the temperature from 100 ℃ to every 50 ℃, It was read visually. The maximum absolute value in the difference from the reading at room temperature was taken as the warp value.

[Synthesis Example 1]
(Polyamide acid polymerization-1) PMDA-DAMBO
<Polymerization of a polyamic acid composed of a diamine having a benzoxazole structure>
The inside of a reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod was purged with nitrogen, and then 500 parts by mass of 5-amino-2- (p-aminophenyl) benzoxazole (DAMBO) was charged. Next, after 8000 parts by mass of N, N-dimethylacetamide was added and completely dissolved, 485 parts by mass of pyromellitic dianhydride (PMDA) was added and stirred at a reaction temperature of 25 ° C. for 48 hours. A viscous polyamic acid solution was obtained. The solution obtained had a ηsp / C of 4.0 dl / g.

[Synthesis Example 2]
<Polyamide acid polymerization-2> PMDA-ODA
545 parts by mass of pyromellitic dianhydride and 500 parts by mass of 4,4′diaminodiphenyl ether (ODA) were dissolved in 8000 parts by mass of N, N-dimethylacetamide, and the reaction was carried out in the same manner while keeping the temperature at 20 ° C. or lower. A polyamic acid solution was obtained. The ηsp / C of the obtained solution was 2.2 and was dl / g.

[Synthesis Example 3]
<Polyamide acid polymerization-3> BPDA-PDA
As tetracarboxylic dianhydride, 398 parts by mass of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 147 parts by mass of paraphenylenediamine (PDA) were added to 4600 parts by mass of N, N-dimethyl. It melt | dissolved in the acetamide and it made it react similarly, keeping temperature at 20 degrees C or less, and obtained the polyamic-acid solution. The obtained solution had a ηsp / C of 3.0 dl / g.

[Synthesis Example 4]
<Polyamide acid polymerization-4>
In N, N-dimethylformamide, 4,4′-diaminodiphenyl ether was dissolved by supplying 60 mol% based on the total diamine, followed by sequentially supplying 40 mol% paraphenylenediamine and pyromellitic dianhydride, And stirred for about 1 hour. Finally, a polyamic acid solution having a polycarboxylic acid concentration of 20% by weight comprising a tetracarboxylic dianhydride component and a diamine component of about 100 mol% stoichiometry was prepared to obtain a polyamic acid solution. The obtained solution had a ηsp / C of 2.7 of dl / g.
This polyamic acid solution was ice-cooled, acetic anhydride and β-picoline were added and stirred.

[Examples 1 to 9, Comparative Examples 1 to 4]
As shown in Tables 1 to 3, the polyamic acid solution obtained in each synthesis example was mixed with 80% of the main polyamic acid and 20% of the subpolyamic acid. In Tables 1 to 3, when the subpolyamic acid column is "-", the case where only the main polyamic acid is used is shown. The mixed or unmixed polyamic acid is coated with a comma coater so that the width of the polyimide film is as shown in Tables 1 to 3 on one side of a stainless steel endless belt that is 600 mm wide and is a support. Then, it was dried at 110 ° C. for 30 minutes, peeled off from the support to obtain a green film as each polyimide precursor film, and each synthesis example shown as a surface coating layer in Tables 1 to 3 above and below this green film After coating with the polyamic acid of dip squeeze coating, or when the surface coating layer is “None” in Tables 1 to 3, the 600 mm wide green film was passed through a continuous heat treatment furnace purged with nitrogen without coating. First, second, and third stages of high temperature heating were applied to advance the imidization reaction. The first stage furnace is 150 ° C., and the second stage furnace is 200 ° C. The temperature of the furnace in the third stage is shown as heat treatment conditions in Tables 1-3. However, in Examples 1 to 6, the film was not stretched, but in Examples 7 to 9, the film was stretched 1.1 times in the longitudinal direction (MD direction). The film of Comparative Example 2 was formed by preparing a film having a thickness of 50 μm and then pressing it.
Then, the polyimide film of each example which exhibits brown was obtained by cooling to room temperature in 5 minutes. Measurement results such as physical properties of the obtained polyimide film are shown in Tables 1 to 3 (columns of tensile elongation at break).

Using the film obtained in each example as a substrate film, a film-like solar cell in which a laminate having at least an electrode layer and a chalcopyrite structure semiconductor thin film is formed as described below (actual film-like solar cell panel production) Roll for).
(First step) An electrode layer is formed on a substrate film. Although an insulating film such as a SiO ₂ film may be formed on the substrate film, the electrode layer is directly formed in this example or the comparative example. The electrode layer is a metal film or a transparent conductive film. For example, a Mo film can be used. In this example or a comparative example, first, a Mo film (film thickness: about 0.00 mm) is formed in an Ar atmosphere by sputtering. 8 μm) to form an electrode layer.
A sputtering apparatus for producing an electrode includes a feed roll (first roll), a take-up roll (second roll), and a Mo target disposed on the cathode. A polyimide substrate is wound around the delivery roll, and the substrate is delivered from here. The winding roll winds and stores the polyimide substrate that is fed from the feeding roll and on which the Mo film is formed. In this sputtering apparatus, a Mo film was formed on the polyimide substrate by sputtering in an Ar atmosphere while moving the polyimide substrate. The take-up roll containing the polyimide substrate on which the Mo film is formed is mounted on the film forming apparatus of FIG. 2 and functions as a feed roll.
(Second step) deposition in Na ₂ S films: after forming the (thickness of about 20 nm), and Cu is Ib group element, and In and Ga are IIIb group element, Se and a group VIb element A precursor semiconductor thin film (thickness: about 1.2 μm) made of was formed on the Na ₂ S film by vapor deposition.

The film forming apparatus of FIG. 2 includes a feed roll 1, a take-up roll 10, a Na ₂ S deposition source 4, a Cu deposition source 6, a Ga deposition source 7, an In deposition source 8, and Se. The vapor deposition source 9 is provided. The feed roll 1 feeds the polyimide substrate 2 on which the Mo film is formed, and the take-up roll 52 winds and stores the polyimide substrate 2 on which the Na ₂ S film 33 and the precursor thin film 34 are formed.
In the film forming apparatus, a Na ₂ S deposition source 4, a Cu deposition source 6, a Ga deposition source 7, an In deposition source 8, and a Se deposition source 9 are respectively set to 700 to 900 ° C., 1100 to 1300 ° C., The precursor thin film was formed by heating within the range of 850-950 degreeC, 800-900 degreeC, and 200-250 degreeC, and evaporating each element and compound. A take-up roll containing a polyimide substrate on which a precursor thin film is formed is mounted on a heat treatment apparatus and functions as a feed roll.
(Third step) Next, the precursor semiconductor thin film is heat-treated. The heat treatment in the third step may be performed in an atmosphere composed of at least one gas selected from the group consisting of nitrogen gas, oxygen gas and argon gas. In this example or the comparative example, in the nitrogen gas atmosphere And heat treated. In the heat treatment apparatus, heat treatment was performed using a heater heated to 500 ° C. while moving the polyimide film on which the precursor semiconductor thin film was formed. At this time, the atmosphere of the heat treatment chamber was an N ₂ gas (normal pressure) atmosphere, and the running speed of the polyimide film was 10 cm / min. The time required for an arbitrary point of the polyimide substrate to be heated from room temperature to 500 ° C. while moving was about 30 seconds, and the average temperature increase rate was 15 ° C./second or more. Moreover, the time maintained at 500 ° C. was about 1 minute 30 seconds. The temperature of the substrate is substantially equal to the temperature of the precursor thin film formed thereon.
The polyimide substrate after the heat treatment was not deformed or melted. By this heat treatment, the precursor semiconductor thin film became a Cu (In, Ga) Se ₂ film (semiconductor film) composed of a group Ib element, a group IIIb element, and a group VIb element and containing a trace amount of Na. From the X-ray diffraction pattern (XRD) of the obtained film, it was found that a thin film having a chalcopyrite structure oriented strongly at 112 was formed. Further, since no peak due to a different phase other than the chalcopyrite structure was observed, it was found that a single-phase Cu (In, Ga) Se ₂ film having excellent crystallinity was formed.

After forming the semiconductor film, a solar cell is manufactured by further stacking layers necessary for the solar cell. As shown in FIG. 1, the window layer 6 and the upper electrode film 4 were laminated in order to form extraction electrodes 5 and 7. As the window layer 6, a 0.1 μm thick layer made of ZnO was formed by sputtering. As the upper electrode film 4, an ITO film having a thickness of 0.1 μm was formed on the ZnO layer by sputtering. Thereafter, an extraction electrode was formed. The electrode film 2 in FIG. 1 is formed on the front surface of the substrate film 1, but in the second step, in the place where the right end of the film in the traveling direction is deposited, it is concealed by a baffle plate, and the exposed portion of the electrode is I made it.
In addition, the extraction electrode was produced only on the necessary portion by cutting out the roll and then attaching a stainless steel mask.
Each example film thus produced was used as a substrate film to obtain a roll for each film-like solar cell panel, and the results of evaluation were shown in Tables 1 to 3.

以上、本発明の実施の形態について例を挙げて説明したが、本発明は、上記実施の形態に限定されず本発明の技術的思想に基づき他の実施形態に適用することができる。

Although the embodiments of the present invention have been described above by way of examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

  The present invention relates to a film-like solar cell using a polyimide film which is a flexible substrate having a heat resistance lower than that of a steel plate or the like, and a roll for producing a film-like solar cell used for producing a flexible solar cell panel Since a flexible substrate can be rolled and manufactured, a large-area semiconductor thin film can be manufactured at high speed. Thus, by using the specific physical property polyimide film of the present invention, a semiconductor thin film suitable for the light absorption layer of the solar cell can be formed on the flexible polyimide film at high speed, and has flexibility and light weight. In addition, a CIS solar cell having a large area and high conversion efficiency with few defects can be efficiently produced.

Schematic diagram of solar cell in the present invention Schematic diagram of an example of semiconductor film manufacturing equipment

Explanation of symbols

1 substrate film 2 electrode film 3 semiconductor film 4 upper electrode film 5 and 5 'rolls 8 substrate film unwinding extraction electrode 6 window layer 7 9,11 roll 10 Na ₂ S evaporation sources 12 Cu evaporation source 13 Ga evaporation source 14 an In evaporated Source 15 Se evaporation source 16 Winding roll

Claims (3)

  In a film-like solar cell in which a laminate having at least an electrode layer and a chalcopyrite structure semiconductor thin film is formed on a substrate film, the substrate film is obtained by polycondensing aromatic diamines and aromatic tetracarboxylic acid anhydrides. A film-like solar cell having a film thickness of 3 to 200 μm, a linear expansion coefficient of 1 to 10 ppm / ° C., and a tensile breaking strength in the longitudinal direction of 300 MPa or more.   The film-like solar cell according to claim 1, wherein the polyimide film is a polyimide benzoxazole film obtained by polycondensation of an aromatic diamine having a benzoxazole structure and an aromatic tetracarboxylic acid anhydride.   The roll for film-form solar cell preparation of Claim 1 or 2 wound up by the roll shape formed by the lamination | stacking which has an electrode layer and a chalcopyrite structure semiconductor thin film at least on a long substrate film.

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