JP2001015778A - Substrate for solar cell - Google Patents

Abstract

(57) Abstract: Provided is a solar cell substrate having excellent photoelectric conversion efficiency, insulation properties, light weight, and flexibility. SOLUTION: A solar cell substrate comprising a polyimide film laminated with a polyimide resin layer in which insulating fine particles are dispersed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substrate for a solar cell, and more particularly to a substrate for forming a thin film solar cell.

[0002]

2. Description of the Related Art At present, a glass substrate or a stainless steel substrate is generally used as a substrate for an amorphous Si solar cell. In order to improve the conversion efficiency of the amorphous Si solar cell, a method of forming fine irregularities on the surface of an insulating substrate has recently been proposed as a method of increasing the amount of absorbed sunlight (Japanese Patent Laid-Open No. 7-1995). No. 254721). Further, a heat-resistant substrate having a surface of a stainless steel plate provided with a polyimide resin film in which insulating fine particles are dispersed has been proposed (Japanese Patent Laid-Open No.
-329268).

[0003]

However, the use of a glass plate or a metal plate such as stainless steel as a substrate for a solar cell makes it possible to take advantage of the thin film and flexibility characteristic of an amorphous Si solar cell. There are drawbacks that can not be done. On the other hand,
When a solar cell is formed using a heat-resistant insulating film that can be made thin and thin, a light weight and flexibility can be obtained, but there is a problem that a conversion efficiency of sunlight into electricity is not sufficiently improved. is there.

[0004]

Under these circumstances, the present inventors have made intensive studies to provide a heat-resistant substrate which can solve the above-mentioned drawbacks of the prior art at once, and have completed the present invention. It is. The present invention is a solar cell substrate formed by laminating a polyimide resin layer in which insulating fine particles are dispersed on a polyimide film.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyimide film in the present invention is produced by casting and curing a resin solution of polyamic acid obtained by mixing an aromatic acid anhydride and an aromatic diamine, which is generally about 20 to 200 μm in thickness. Typical polyimide film, for example, pyromellitic anhydride (PMDA)
KAPTON, which is a condensate of 4,4 'oxydianiline (ODA) with biphenyltetracarboxylic anhydride (BPDA) and 4,4' oxydianiline (ODA)
And the trade name Iupirex-R, which is a condensate of biphenyltetracarboxylic anhydride (BPDA) and paraphenylenediamine (PPD). Since the polyimide film has heat resistance even when the substrate temperature rises to about 250 ° C. in the steps of sputtering and CVD in order to form a photoelectric conversion layer,
It satisfies the requirements as the base material of the solar cell substrate of the present invention.

The solar cell substrate of the present invention is obtained by laminating a polyimide resin layer in which spherical fine particles are dispersed on the surface of the above-mentioned polyimide film. The polyimide resin used in this polyimide resin layer is described in JP-A-10-32926.
No. 8, polyimides, polyamideimides, polyetherimides, and mixtures thereof, which are solvent-soluble. The polyimide-based resin also includes a mixture of a solvent-soluble resin such as polysulfone and polyether polysulfone as the second component. Specific examples of the polyimide resin include benzophenonetetracarboxylic dianhydride (BTDA)
And two aromatic diisocyanates, ie, 4,4
'-Diphenylmethane diisocyanate and 2,4-
Examples thereof include those obtained by copolymerizing tolylene diisocyanate, and those synthesized from biphenyltetracarboxylic dianhydride (BPDA) and aromatic diamine via polyamic acid. In addition, an aromatic diamine and an aromatic tetracarboxylic acid and / or a derivative thereof are applied as a solute on a polyimide film surface as a polyimide precursor solution in which a thermoplastic polyimide is dissolved in a solvent, followed by heat treatment to form a thermoplastic polyimide. And specifically, 4,4′-oxydianiline and / or 3,4′-oxydianiline
A combination of 4'-oxydianiline and 4,4'-oxydiphthalic acid and / or a derivative thereof, or 4,4 '
-Oxydianiline or 3,4'-oxydianiline,
And a combination of paraphenylenediamine with 4,4′-oxydiphthalic acid and / or a derivative thereof.

On the other hand, the insulating fine particles dispersed in the polyimide resin have an average particle diameter of 0.1 to 1.0 μm.
m is preferred. The wavelength of sunlight is 0.4-1.
In order to increase the optical path length in the range of 2 μm for increasing the absorption amount which is the object of the present invention, less than 0.1 μm or more than 1.0 μm is less preferable. Examples of the insulating fine particles to be used include calcium carbonate, alumina, silica, and titanium oxide. Among them, silica is preferably used. The amount of fine powder mixed into the polyimide resin varies depending on the type, average particle size, thickness of the coating, etc., but it is necessary to form fine irregularities on the surface of the layer to increase the amount of sunlight absorption. Is required, and the content is preferably 5 to 500% by weight based on the polyimide resin. If the compounding amount of the fine particles is less than 5% by weight, it is difficult to form fine irregularities on the surface of the layer, and if the compounding amount exceeds 500% by weight, pinholes are easily generated in the coating, which is not preferable.

As a method of laminating a polyimide resin layer in which spherical fine particles are dispersed on a polyimide film, usually,
A method in which a polyimide component is dissolved in a solvent and a solution in which the fine particle component is dispersed is applied to the surface of the polyimide film. Usable solvents include N-methylpyrrolidone, N, N'-dimethylformamide, o-methylphenol, m-methylphenol, p-methylphenol, o-chlorophenol, p-chlorophenol, 2,4-dichlorophenol Examples include phenol and diethylene glycol dimethyl ether. Among them, N-methylpyrrolidone and N, N'-dimethylformamide are preferred. The concentration of the resin in the coating liquid is preferably selected in the range of 1 to 25% by weight so as to obtain a viscosity such that the coating operation can be performed smoothly.

As a method of preparing a coating solution, a solution in which insulating fine particles are dispersed in a dilute solution of a polyimide resin is prepared. In order to improve dispersibility, a dispersant may be added to the solution. Examples of the coating method include a die coating method, a roll coating method, a flow coating method, and a doctor blade coating method. Among them, a die coating method and a roll coating method are preferably used, and the polyimide film is continuously applied while moving. By adjusting the resin concentration and viscosity of the coating liquid, the thickness of the wet coating film is adjusted to 5
The thickness is adjusted so that the thickness of the coating after coating and drying is preferably 1 to 20 μm. 1μ thickness
If it is less than m, it is difficult to form a uniform film thickness and
If it exceeds μm, the flexibility of the membrane is reduced, and it is not economical. As soon as the coating operation is completed, the coated thin film is heated and dried. In the method of heating and drying, the initial stage of drying is performed in a state where air is not applied, and the temperature is raised to about 300 ° C. to form a thin film in order to cure the polyimide resin when the solvent is scattered.

As described above, the solar cell substrate of the present invention is manufactured. Thereafter, a laminated structure for photoelectric conversion is formed on the substrate to manufacture a thin film solar cell. In this solar cell, the photoelectric conversion efficiency can be improved by increasing the optical path length of the sunlight incident from the minute unevenness formed on the substrate surface and increasing the absorption amount. Further, as a photoelectric conversion laminated structure, a metal electrode such as Ag or Al a-Si (p layer,
(i-layer, n-layer) A transparent electrode such as ITO and SnO ₂ is formed by sputtering and CVD in this order. At this time, the formation of fine irregularities on the surface of the solar cell substrate according to the present invention depends on the substrate and the metal electrode. This also has the effect of improving the adhesion.

[0011]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the following description unless it exceeds the gist. Example 1 A polyimide resin obtained by copolymerizing 3,3 ′, 4,4′-benzophenonetetracarboxylic anhydride (BTDA) with 4,4′-diphenylmethane diisocyanate and 2,4-tolylene diisocyanate was prepared by using dimethylformamide. To give a solution having a solid concentration of 15%. To this solution was added 250% by weight of spherical silica having an average particle diameter of 0.3 μm based on the solid content of polyimide, and the mixture was stirred and mixed by a sand mill. On the other hand, pyromellitic anhydride (PMD
A) and a polyimide film that is a condensate of 4,4 ′ oxydianiline (ODA) (trade name: KAPTON, width 300)
mm, thickness 75 μm) as a base material, and the above-mentioned solution for forming a thin film is wetted on one surface with a die coater to a film thickness of 50 μm.
And dried in a drying oven at 80 ° C. for 10 minutes. Thereafter, the coating coil was heated in a drying furnace from 80 ° C. to 300 ° C. in 30 minutes, and dried at 300 ° C. for 30 minutes. The thickness of the obtained polyimide resin layer was 5 μm.

Example 2 A polyimide film was prepared in the same manner as in Example 1 except that a spherical silica having an average particle size of 0.5 μm was added as a solution for forming a thin film by adding 300% by weight to the solid content of polyimide. Was prepared as a substrate. The thickness of the obtained polyimide resin was 7 μm.

APPLICATION EXAMPLES In Examples 1 and 2, and on the surface of a polyimide film having no fine particles laminated on the surface, first, an Ag film was formed as a metal electrode to a thickness of 2000 Å by sputtering. Further, an amorphous silicon film (photoelectric conversion layer) having a nip junction and a thickness of 5000 Å was formed on the metal electrode by a plasma CVD method. Finally, an ITO film was formed as a transparent electrode with a thickness of 600 angstroms by a sputtering method to produce a thin-film solar cell. The conversion efficiency of the solar cells obtained in Examples 1 and 2 was 30 to 50% higher than that of a solar cell using a polyimide film on which fine particles were not laminated.

[0014]

The solar cell substrate of the present invention is lightweight, excellent in flexibility, good in heat resistance, chemical resistance, electrical insulation, etc. and manufactured at low cost. Is possible. Further, in the solar cell substrate of the present invention,
Fine irregularities are formed on the surface of the polyimide resin layer in which the insulating fine particles laminated on the polyimide film are dispersed,
Since the incident light beam can be preferably diffusely reflected and confined on the surface of the insulating substrate, high photoelectric conversion efficiency can be achieved as a solar cell substrate.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // C08J 5/18 CFG C08J 5/18 CFG F term (reference) 4F071 AA60 AB18 AB21 AB26 AH12 BA03 BB02 BC01 4J002 CM041 DE146 DE236 DJ016 FD016 GF00 GQ00 5F051 AA05 BA15 CA15 DA04 GA03 GA05

Claims (2)

[Claims] 1. A solar cell substrate comprising a polyimide film and a polyimide resin layer in which insulating fine particles are dispersed. 2. The polyimide resin layer has an average particle size of 0.1.
The solar cell substrate according to claim 1, wherein the insulating fine particles of 1 to 1 µm are dispersed in 5 to 500% by weight.