JP4806982B2 - Polyimide film and method for producing the same - Google Patents

Description

  The present invention relates to a polyimide film having a specific concavo-convex structure on at least one surface and a method for producing the same. More specifically, when used as a substrate, the light incident on the concavo-convex structure on the film surface can be used effectively. The present invention relates to a film for a solar cell or a film provided with a concavo-convex structure for improving adhesiveness and a method for producing the same.

Conventionally, ceramics and metals have been used as materials for substrates of electronic components such as flexible solar cells, information communication equipment (broadcast equipment, mobile radio, portable communication equipment, etc.), radar, high-speed information processing devices, and the like. Although a substrate made of ceramic has heat resistance, ceramics are not flexible and cannot be thinned, so the fields that can be used are limited.
For this reason, studies have been made to use a film made of an organic material as a base material for an electronic component, and a film made of polyimide has been proposed.

A polyimide film is used as a substrate for solar cells. For example, by forming an electrode layer on the surface of a polymer film such as a polyimide film and forming a chalcopyrite compound thin film on the electrode layer, a flexible solar cell having higher conversion efficiency than that using an a-Si thin film can be obtained. (See Patent Document 1). Further, the thickness of the polyimide produced by the reaction of biphenyltetracarboxylic acid and an aromatic diamine component containing phenylenediamine is 10 to 250 μm, and the maximum roughness of at least one film surface is 50 nm or less, The linear expansion coefficient is 5 to 20 × 10 ⁻⁶ cm / ° C., the tensile elastic modulus is 450 kgf / mm ² or more, the tensile breaking elongation is 15% or more, and the specific end resistance is 11 to 22 kg / 20 mm. / 10 μm and a residual volatile matter amount of 0.5% by weight or less, a solar cell using a silicon thin film as a substrate on an aromatic polyimide film (see Patent Document 2), insulating fine particles having a particle size of 0.1 to 1 μm Random or block consisting of a solar cell (see Patent Document 3), pyromellitic acid, and oxydianilines with a polyimide resin layer containing Alternatively, on a light-transmitting plastic substrate such as a solar cell (see Patent Document 4), polyethersulfone, polyimide, etc., which is made from an alternating copolymerized polyamic acid and has a polyimide film having a thermal expansion coefficient of 10 ppm / ° C. or more as a substrate. In addition, a thin film solar cell in which a transparent conductive film, a photoelectric conversion layer, and a back electrode layer are sequentially stacked is disclosed (see Patent Document 5, for example).
JP 05-259494 A Japanese Patent Laid-Open No. 11-029645 JP 2000-091606 A JP 2003-073473 A JP 2005-129713 A

A film made of polyimide is excellent in heat resistance and has the advantage that the film can be thin because it is tough. On the other hand, it has poor adhesion, and a large amount of fillers and lubricants are added to give surface irregularities. As a result, the flexibility of the corners is impaired, and the productivity is damaged.
Losing light by reflection because it absorbs irradiated light and converts it into electricity results in loss of conversion efficiency, and improving this point is an important factor for increasing conversion efficiency.
For this reason, it has been devised so that light reflected from the surface is incident again by forming minute irregularities on the surface, and a structure called texture has been used (Patent Document 6, However, it is necessary to perform an etching process in order to form the structure.
A material having a texture on the base side has also been proposed (see Patent Document 7). However, since a thin film layer is used as a texture, the process becomes long and expensive.
Thus, the film for solar cell base materials provided with the concavo-convex structure for heat resistance, adhesiveness, flexibility, and effective use of light has not yet been obtained sufficiently.
JP 05-291597 A JP 07-263729 A

The conventional polyimide film is excellent in heat resistance and tough, but in order to give a surface uneven structure, a prescription of adding insulating fine particles having a particle diameter of 0.1 to 1 μm has been adopted. I have to stay in it. Addition of a large amount of large particles has a significant effect on productivity, and it has been extremely difficult to efficiently provide a desired surface uneven structure.
The present invention is a solar cell that has excellent heat resistance of a polyimide film, retains tough properties, imparts an arbitrary surface uneven structure to a polyimide film at low cost, has excellent adhesion, and imparts an arbitrary surface structure It is an object of the present invention to provide a polyimide film useful for the above substrate.

  As a result of intensive studies, the present inventors obtained a polyimide precursor film by casting a polyamic acid on a support, and in a method for producing a polyimide film obtained by heat-treating and / or imidizing the polyimide precursor film, A concavo-convex structure having a depth of 1 μm to 50 μm is formed in advance on a support, a polyamic acid is cast on the support to obtain a polyimide precursor film, and the polyimide precursor film is heat-treated and / or imidized. Thus, the inventors have found that it is possible to obtain a polyimide film having a concavo-convex structure in which one surface of the film has a depth of 1 μm to 50 μm in the film thickness direction, and the present invention has been achieved.

That is, this invention consists of the following structures.
1. Polyimide obtained by reacting an aromatic diamine and an aromatic tetracarboxylic acid on a support to obtain a polyimide precursor film, and a polyimide obtained by heat-treating and / or imidizing the polyimide precursor film A polyimide film, wherein at least one surface of the film has a concavo-convex structure having a depth of 1 μm to 50 μm in the film thickness direction.
2. 2. The polyimide film according to claim 1, wherein the surface opposite to the surface having the uneven structure of the film does not have an uneven structure having a depth of 1 μm to 50 μm in the film thickness direction.
3. 1. A polyamic acid is obtained by reacting an aromatic diamine having a benzoxazole structure with an aromatic tetracarboxylic acid. Or 2. The polyimide film as described.
4). 1 above. ~ 3. A solar cell comprising a photoelectric conversion layer on any of the polyimide films described above.
5. Polyimide obtained by reacting an aromatic diamine and an aromatic tetracarboxylic acid on a support to obtain a polyimide precursor film, and a polyimide obtained by heat-treating and / or imidizing the polyimide precursor film A method for producing a film, in which a concavo-convex structure having a depth of 1 μm to 50 μm is formed in advance on a support, and a polyamic acid is cast on the support to obtain a polyimide precursor film. This polyimide precursor A method for producing a polyimide film, characterized in that a film is heat treated and / or imidized to obtain a polyimide film having a concavo-convex structure in which one side of the film has a depth of 1 μm to 50 μm in the film thickness direction.
6). 4. A polyamic acid is obtained by reacting an aromatic diamine having a benzoxazole structure with an aromatic tetracarboxylic acid. The manufacturing method of the polyimide film of description.

  The polyamic acid obtained by reacting an aromatic diamine and an aromatic tetracarboxylic acid according to the present invention is cast on a support to obtain a polyimide precursor film, and the polyimide precursor film is heat-treated and / or imidized. A polyimide film is obtained by forming a concavo-convex structure having a depth of 1 μm to 50 μm in advance on a support, casting a polyamic acid on the support, and obtaining a polyimide precursor film, This polyimide precursor film is heat-treated and / or imidized to obtain a polyimide film having a concavo-convex structure in which one side of the film has a depth of 1 μm to 50 μm in the film thickness direction. One surface of the film obtained by the method has a concavo-convex structure having a depth of 1 μm to 50 μm in the film thickness direction. The polyimide film can be manufactured at low cost without any hindrance to productivity, and the uneven structure having a depth of 1 μm to 50 μm leads to effective use of light rays in the solar cell, and an arbitrary surface uneven structure It can exhibit an excellent effect in improving adhesiveness and is extremely useful industrially.

In the production of a polyimide film, a polymerization reaction is performed by first subjecting an aromatic diamine and an aromatic tetracarboxylic acid to a ring-opening polyaddition reaction in a solvent to obtain a polyamic acid solution, and then a polyimide precursor from the polyamic acid solution. This is done by forming a green film as a film, followed by dehydration condensation (imidization).
In the present invention, among these aromatic diamines, aromatic diamines having a benzoxazole structure are particularly preferred diamines. Examples of the diamine having a benzoxazole structure particularly preferably used in the present invention include the following.

  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-bis [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-dimethylphenyl] 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-sia) Phenoxy)-.alpha., alpha-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′-dibi Phenoxybenzophenone, 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, , 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-bi) Phenoxybenzoyl) benzene, 2,6-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzonitrile and some or all of the hydrogen atoms on the aromatic ring in the aromatic diamine are halogen atoms, Some or all of the hydrogen atoms of the alkyl group or alkoxyl group having 1 to 3 carbon atoms, the cyano group, or the alkyl group or alkoxyl group are halo. Aromatic diamines which are substituted with an alkyl halide group or an alkoxyl group having 1 to 3 carbon atoms and the like in emissions atoms.

  The tetracarboxylic acid used in the present invention is preferably an aromatic tetracarboxylic anhydride. Specific examples of the aromatic tetracarboxylic acid anhydride include the following.

これらのテトラカルボン酸二無水物は単独で用いてもよいし、二種以上を併用してもよい。本発明においては、全テトラカルボン酸二無水物の３０モル％未満であれば下記に例示される非芳香族のテトラカルボン酸二無水物類を一種又は二種以上、併用しても構わない。

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 polymerizing an aromatic diamine (monomer) and an aromatic tetracarboxylic acid (monomer) to obtain a polyamic acid can be used as long as it dissolves both the monomer as a raw material and the polyamic acid to be produced. Although not particularly limited, polar organic solvents are preferred, such as N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, Examples thereof include 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.

Conventionally known conditions may be applied for the polymerization reaction for obtaining the polyamic acid (hereinafter also simply referred to as “polymerization reaction”). As a specific example, in a temperature range of 0 to 80 ° C., 10 Stirring and / or mixing continuously for 30 minutes. 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 an aromatic tetracarboxylic acid (anhydride) to the aromatic diamine solution. 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 2.0 dl / g or more, more preferably 3.0 dl / g or more, still more preferably 5.0 dl / g or more. preferable.

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 diamine 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.
In order to form a polyimide film from the polyamic acid solution obtained by the polymerization reaction, a polyimide precursor film (also referred to as a green film) is obtained by coating the polyamic acid solution on a support and drying, and then, A method of imidizing the green film by subjecting it to a heat treatment can be mentioned.

The support to which the polyamic acid solution is applied only needs to have sufficient rigidity to form the polyamic acid solution into a film, and the surface is metal (more preferably, stainless steel that does not rust and has excellent corrosion resistance), plastic Or a drum-like rotating body.
A method using a polymer film having appropriate rigidity is also a preferred embodiment.
The surface of the metal support may be plated with metal such as Cr, Ni, or Sn.
The surface of the support can be provided with any surface uneven structure depending on the required surface uneven structure of the film, and the surface uneven structure on the support may be applied to the entire surface of the support or may be partially applied. Alternatively, it may be directly applied to the drum or belt-like rotating body support, or a film or metal may be bonded and used. The depth of the concavo-convex structure is preferably 1 μm to 50 μm, more preferably 2 μm to 30 μm, still more preferably 3 μm to 20 μm.
Application of the polyamic acid solution to the support includes, but is not limited to, casting from a slit base, extrusion through an extruder, squeegee coating, reverse coating, die coating, applicator coating, wire bar coating, etc. Conventionally known solution coating means can be appropriately used.

The above polyimide film can be provided with a lubricant in the polyimide to give fine irregularities on the film surface to improve the slipperiness of the film (particularly the surface opposite to the surface imparting the surface irregular structure). .
As the lubricant, inorganic or organic fine particles having an average particle diameter of about 0.03 μm to 1 μm can be used. Specific examples include titanium oxide, alumina, silica, calcium carbonate, calcium phosphate, calcium hydrogen phosphate, calcium hydrogen pyrophosphate. , Magnesium oxide, calcium oxide, clay mineral and the like. As these polyimide films, unstretched films are preferably applied, but uniaxial or biaxially stretched films can also be used.
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 film-like solar cell using the film of the present invention as a substrate as a preferred embodiment of the present invention is formed by forming a laminate including a photoelectric conversion layer made of a semiconductor on the above-described film base. The said laminated body has a photoelectric converting layer which converts the energy of sunlight into an electrical energy as an essential structure, and usually further has an electrode layer etc. for taking out the obtained electrical energy.
Hereinafter, a laminated structure in which a photoelectric conversion layer is sandwiched between a pair of electrode layers will be described as a typical example of the laminated body formed so as to constitute a film-like solar cell. However, the laminated structure formed in the present invention is not limited to the embodiment described below, and the structure of the laminated body of the solar cell of the prior art may be referred to as appropriate, and a protective layer and known auxiliary means are added. Is also good.
One electrode layer (hereinafter also referred to as a back electrode layer) of the pair of electrode layers is preferably formed on one main surface of the film substrate. The back electrode layer is obtained by laminating a conductive inorganic material by a method known per se, for example, a CVD (Chemical Vapor Deposition) method or a sputtering method. Examples of conductive inorganic materials include metal thin films such as Al, Au, Ag, Cu, Ni, and stainless steel, and In ₂ O ₃ , SnO ₂ , ZnO, Cd ₂ SnO ₄ , ITO (adding Sn to In ₂ O ₃ Oxide semiconductor-based conductive materials and the like. The thickness of the back electrode layer is not particularly limited, and is usually about 30 to 1000 nm. Preferably, the back electrode layer is a metal foil film.

The photoelectric conversion layer that converts sunlight energy into electrical energy is a layer made of a semiconductor, and is usually a layer made of a silicon-based semiconductor. Examples of the silicon-based semiconductor include a thin film silicon layer, an amorphous silicon layer, and a polycrystalline silicon layer. The photoelectric conversion layer may be a laminate having a plurality of layers made of different semiconductors.
The thin film silicon layer is a silicon layer obtained by a plasma CVD method, a thermal CVD method, a sputtering method, a cluster ion beam method, a vapor deposition method, or the like.
The amorphous silicon layer is a layer made of silicon having substantially no crystallinity. The lack of crystallinity can be confirmed by not giving a diffraction peak even when irradiated with X-rays. Means for obtaining an amorphous silicon layer are known, and examples of such means include a plasma CVD method and a thermal CVD method.
The polycrystalline silicon layer is a layer made of an aggregate of microcrystals made of silicon. The above amorphous silicon layer is distinguished by giving a diffraction peak by irradiation with X-rays. Means for obtaining a polycrystalline silicon layer are known, and such means include means for heat-treating amorphous silicon.
The photoelectric conversion layer used in the present invention is not limited to a silicon-based semiconductor layer, and may be, for example, a thick film semiconductor layer. The thick film semiconductor layer is a semiconductor layer formed from a paste of titanium oxide, zinc oxide, copper iodide or the like.
The means for constituting the semiconductor material as the photoelectric conversion layer may refer to a known method as appropriate. For example, an a-Si (n layer) of about 20 nm is formed by performing high-frequency plasma discharge in a gas in which phosphine (PH ₃ ) is added to SiH ₄ at a temperature of 200 to 500 ° C., followed by SiH _4. An a-Si (i layer) of about 500 nm can be formed with gas alone, and then diborane (B ₂ H ₆ ) can be added to SiH ₄ to form a p-Si (p layer) of about 10 nm. .

Of the pair of electrode layers sandwiching the photoelectric conversion layer, an electrode layer (hereinafter also referred to as a current collecting electrode layer) provided on the side opposite to the film substrate is formed by solidifying a conductive paste containing a conductive filler and a binder resin. It may be an electrode layer or a transparent electrode layer. As the transparent electrode layer, an oxide semiconductor material such as In ₂ O ₃ , SnO ₂ , ZnO, Cd ₂ SnO ₄ , ITO (In ₂ O ₃ added with Sn) can be preferably used.
Thus, a transparent electrode / p-type a-Si / i-type a-Si / n-type a-Si / metal electrode / polyimide benzoxazole film having a surface concavo-convex structure surface, which is a preferred embodiment of the present invention, are laminated in this order. A film-like solar cell is obtained. Alternatively, the p layer may be a-Si, the n layer may be polycrystalline silicon, and a thin and doped a-Si layer may be inserted between them. In particular, when an a-Si / polycrystalline silicon hybrid type is used, the sensitivity to the sunlight spectrum is improved.
In manufacturing a solar cell, an antireflection layer, a surface protective layer, or the like may be added in addition to the above structure.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited by a following example. 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 The film thickness was measured using a micrometer (Millitron 1254D manufactured by Fine Reef Co., Ltd.).

3. Tensile modulus, tensile rupture strength, and tensile rupture elongation of a film A test piece obtained by cutting a base film to be measured into a strip of 100 mm × 10 mm in the longitudinal direction (MD direction) and the width direction (TD direction) It was. Using a tensile tester (manufactured by Shimadzu Corp., Autograph (registered trademark) model name AG-5000A) under the conditions of a tensile speed of 50 mm / min and a distance between chucks of 40 mm, the tensile modulus and tension in each of the MD and TD directions. Strength and elongation at break were measured.

4). Film linear expansion coefficient (also called CTE)
For the film to be measured, the stretch rate in the MD direction and the TD direction is measured under the following conditions, and the stretch rate / temperature at intervals of 30 ° C. to 45 ° C., 45 ° C. to 60 ° C.,. This measurement was performed up to 300 ° C., and the average value of all measured values was calculated as CTE. The meanings of the MD direction and the TD direction are as described above.
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

8). Photoelectric conversion characteristic It measured with the solar simulator made from Oriel which adjusted the conversion efficiency to AM = 1.
9. Depth of film surface uneven structure Using a stylus type surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd.) according to JIS B0601-1994, the shape of the film surface with the shape formed is measured to confirm the depth of the uneven structure. did. Ten point average roughness (Rz: 5 points from the highest peak and 5 points from the lowest valley bottom for each reference length) with a radius of 2 μm and a measurement evaluation length of 0.8 mm. The depth of the protrusion was measured.

(Examples 1-4)
(Preparation of polyamic acid solution)
After the inside of a reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod was purged with nitrogen, 500 parts by mass of 5-amino-2- (p-aminophenyl) benzoxazole was added. Next, 5000 parts by mass of N-methyl-2-pyrrolidone was added and completely dissolved, and then 485 parts by mass of pyromellitic dianhydride was added and stirred at 25 ° C. for 53 hours. A polyamic acid solution was obtained. The reduced viscosity (ηsp / C) was 5.1 dl / g.

(Manufacture of polyamic acid green film)
This polyamic acid solution is coated on a stainless steel belt formed by intimately forming a square pyramid having a height of 7 μm and a bottom surface of 7 μm × 7 μm, and dried under predetermined conditions using a continuous drying furnace having three zones. did. The polyamic acid film (also referred to as polyimide precursor film or green film) that became self-supporting after drying was peeled from the stainless steel belt to obtain green films of the respective examples.

(Production of polyimide benzoxazole film)
The obtained green film was passed through a continuous heat treatment furnace having three compartments and purged with nitrogen, and heated to advance the imidization reaction. In contrast to the stainless belt support having a concavo-convex structure of a square pyramid having a height of 7 μm, a concavo-convex structure having a depth of 6.3 μm was formed on the film surface.

(Manufacture of film-like solar cells)
A stainless steel target having a thickness of 1000 nm was formed on each of the films using a stainless steel target in a sputtering apparatus. Next, a film in which a stainless steel layer was formed was placed between the counter electrode and the support electrode in the vacuum reactor, and the inside of the reactor was once evacuated to 10 ⁻⁵ Torr, and the temperature of the support electrode was raised to 350 ° C. Then, while applying a 15MHz RF voltage of 30W to the counter electrode and the supporting electrode, SiH ₄ and argon gas was introduced into the reactor was pre-sputtered in an argon atmosphere of 3 mTorr, then diluted to 10% with hydrogen gas Similarly, a PH ₃ gas diluted to 1% with hydrogen gas was simultaneously introduced to form a 25 nm n-type amorphous silicon layer on the stainless steel layer in an atmosphere of 1 Torr. Next, only SiH ₄ is introduced, an i-type amorphous silicon layer having a thickness of 500 nm is laminated on the n-type amorphous silicon layer, and further a mixture containing 1% B ₂ H ₆ in SiH ₄ gas. A p-type amorphous silicon layer having a thickness of 25 nm was formed on the i-type amorphous silicon layer by introducing a gas.
Next, the film on which the pin type amorphous silicon layer was formed was mounted in a vacuum deposition apparatus, and an indium tin oxide layer having a thickness of 100 nm was deposited by an electron beam method to form a hetero electrode layer. Finally, a 100 nm palladium layer was vacuum-deposited in a comb shape on it. The film-like solar cell of each Example was obtained as described above. In the production process of the film-like solar cell, there was no problem that the film substrate was deformed by heat or wrinkles were produced, and a solar cell with excellent flatness was obtained.

(Comparative example)
In each of the above-described embodiments, a flat stainless steel bell that does not form a square weight at all is used in place of the stainless steel belt in which a square pyramid having a height of 7 μm and a bottom surface of 7 μm × 7 μm is closely formed. In the same manner as above, a polyimide benzoxazole film was obtained to obtain a film-like solar cell.
Table 1 summarizes the evaluation results of the film-like solar cells of each Example and Comparative Example.

表中、ＭＤ；フィルムの長さ方向、ＴＤ；フィルムの幅方向をそれぞれ示す。

In the table, MD represents the film length direction, and TD represents the film width direction.

  A method for producing a polyimide film obtained by heat-treating and / or imidizing a polyimide precursor film obtained by casting a polyamic acid on a support according to the present invention, wherein the depth of the support is 1 μm to 50 μm in advance. A certain concavo-convex structure is formed, and a polyamic acid is cast on the support to obtain a polyimide precursor film. The polyimide precursor film is heat-treated and / or imidized, and one surface of the film is deepened in the film thickness direction. Polyimide film having a concavo-convex structure with a thickness of 1 μm to 50 μm can be manufactured at low cost without any hindrance to productivity, and the concavo-convex structure with a depth of 1 μm to 50 μm is effective use of light rays in solar cells. Non-slip using a specific surface structure that can be used to improve the adhesiveness And it shall be used in special applications, industrially very useful.

Claims (3)

A polyamic acid obtained by reacting an aromatic diamine having a benzoxazole structure and an aromatic tetracarboxylic acid is cast on a support to obtain a polyimide precursor film, and the polyimide precursor film is subjected to heat treatment and / or A polyimide film obtained by imidization, wherein one surface of the film has a concavo-convex structure having a depth of 1 μm to 50 μm in the film thickness direction, and is opposite to the surface having the concavo-convex structure of the film However, it does not have the uneven structure whose depth is 1 micrometer-50 micrometers in a film thickness direction, The polyimide film for solar cell substrates characterized by the above-mentioned. A solar cell comprising a photoelectric conversion layer provided on the polyimide film according to claim 1. A polyamic acid obtained by reacting an aromatic diamine having a benzoxazole structure and an aromatic tetracarboxylic acid is cast on a support to obtain a polyimide precursor film, and the polyimide precursor film is subjected to heat treatment and / or imide. A method for producing a polyimide film obtained by forming a concavo-convex structure having a depth of 1 μm to 50 μm in advance on a support, and casting a polyamic acid on the support to obtain a polyimide precursor film The polyimide precursor film is heat-treated and / or imidized, and one surface of the film has a concavo-convex structure having a depth of 1 μm to 50 μm in the film thickness direction, and is opposite to the surface having the concavo-convex structure of the film Is characterized by obtaining a polyimide film having no concavo-convex structure having a depth of 1 μm to 50 μm in the film thickness direction. Method for manufacturing a solar cell substrate for the polyimide film that.