JPH02181975A - Film solar cell - Google Patents

Abstract

PURPOSE:To improve a photoelectric converting efficiency and to decrease optical deterioration of an a-Si layer in comparison with conventional film solar cells by providing a photoelectric converting element on one face of an achromatic and transparent polyimide film substrate, that has been treated with plasma. CONSTITUTION:A polyimide film 1 used as a substrate should be an achromatic and trasparent one for the purpose of improving conversion efficiency of a photoelectric converting element and a thickness thereof is adjusted in a range from 10 to 100mum. Among achromatic and transparent polyimide films, preferably used is a film which presents a total transmittance of 80% or more and a yellowness index of 25 or less when it has a thickness of 50mum. Such achromatic and transparent polyimide film may be principally composed of polyimide having a repeated unit represented by the general formula (1). Such polyimide can be obtained typically from a reaction between aromatic tetracarbonic acid dianhydride and aromatic diamine.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention uses a colorless and transparent polyimide film as a substrate, and irradiates light from the substrate side to suppress photodeterioration of amorphous silicon and improve photoelectric conversion efficiency. The present invention relates to a film solar cell that has improved reliability by improving adhesive strength between the substrate and the transparent electrode.

<Prior art> Amorphous silicon (hereinafter referred to as A-8T) solar cells are used as built-in power supplies in electronic products such as calculators and watches, external power supplies in TVs and radios, and batteries for preventing discharge of storage batteries. Although it is commonly used as an auxiliary power source for chargers and the like, in recent years there has been a demand for A-8F solar cells to be thinner and lighter due to their use as thin calculators and portable external power sources.

Based on this background, aluminum plates, stainless steel plates, etc. are being considered in place of conventional glass plates as substrates for A-8T solar cells, but it is important to make them thinner, lighter, and more flexible. Polymer film substrates are seen as promising because of their ability to Since heat resistance is required for such a core polymer film substrate, a polyimide film typified by Kapton is usually used.

However, since the polyimide film described above lacks light transmittance, when the polyimide film is used as a substrate for an a-3i solar cell, it is necessary to have a structure as shown in FIG. 1. That is, a metal electrode 2 is formed on a polyimide substrate l, and on top of that a p-type a-8i (p layer) 3, an intrinsic a-8
i (i layer) 4 and n-type a-8i (n layer) 5 are laminated in sequence,
A transparent electrode 6 is formed thereon, and a transparent resin layer 7 is further provided for surface protection. Then, light enters from the transparent resin layer side and passes through the a-8i in the order of n layer → i layer → p layer. This order of passage of light is opposite to that of conventional glass plate substrates, which is unfavorable in terms of photoelectric conversion efficiency, and it is known that the photodegradation of a-8t becomes severe and reliability is lacking. On the other hand, attempts have also been made to reverse the formation order of the a-8t layers in FIG. 1 and change the order in which light enters from the p layer to the i layer to the n layer.
In this case, the a-8t film 'Jt is lowered and satisfactory characteristics cannot be obtained.

Therefore, when a normal polyimide substrate is used, since the substrate has poor light transmittance, light cannot enter from the substrate side, but instead enters from the opposite side.

Due to this method of introducing light, as mentioned above, the current situation is that satisfactory characteristics regarding photoelectric conversion efficiency and photodegradation cannot be obtained.

Therefore, it is conceivable to use a colorless and transparent polyimide film as a substrate of an fa-Si solar cell, and to have a configuration as shown in FIG. 2. That is, a transparent electrode 6 is formed on a colorless transparent polyimide substrate 8, a p layer, an i layer, and an n layer are sequentially laminated thereon, a metal electrode 2 is formed thereon, and a protective resin layer 9 is formed.
The configuration is to provide a. Light enters from the transparent polyimide substrate side, and in the a-Si layer, the light passes through the layers from the p layer to the i layer to the n layer. The order in which this light passes is exactly the same as in the case of conventional glass plate substrates, and this prevents the reduction in photoelectric conversion efficiency and the photodeterioration of A-3T, which were problems in the A-8T solar cell with the configuration shown in Figure 1. This makes it possible to obtain flexible film solar cells with performance comparable to that of glass substrates.

<Problem to be solved by the invention> However, in solar cells using a colorless and transparent polyimide film as a substrate as described above, the adhesion between the polyimide substrate and the transparent electrode may not be sufficient, and problems may occur during the manufacturing process or during use. Peeling at the interface? It has the potential to cause As a method to compensate for such a lack of adhesive strength, methods have been proposed in which the surface of the substrate is subjected to matte treatment, or the substrate contains an amorphous inorganic filler to form protrusions on the surface of the substrate in hopes of creating an anchor effect.

However, with this method, a sufficient anchoring effect cannot be expected, and sharp protrusions are formed on the substrate surface, which can damage the transparent electrode and the A-8T layer, leading to loss of functionality due to the sheet carbon. Sometimes there are.

Means for Solving the Problems> Therefore, the present inventors conducted repeated studies to improve the adhesive force between the substrate and the transparent substrate in an A-8T solar cell using a colorless transparent polyimide film as the substrate. It was discovered that by applying a specific treatment, the adhesive strength could be improved without impairing the function as a solar cell, and the present invention was completed.

Particularly, the present invention provides a film solar cell in which a photoelectric conversion element is provided on the treated surface of a colorless and transparent polyimide film substrate that has been subjected to plasma treatment on one side, and a colorless and transparent polyimide film substrate in which a large number of microspherical protrusions are formed on one side. A film solar cell is provided in which a photoelectric conversion element is provided on a protrusion-formed surface of a polyimide film substrate.

The polyimide film used as the substrate of the film solar cell of the present invention is colorless and transparent from the viewpoint of improving the conversion efficiency of the photoelectric conversion element. The thickness of the film affects light transmittance and conversion efficiency, so it is preferably 10 to 10
Adjust to a range of 0 μm. If the thickness is less than 10 μm, the mechanical strength is insufficient, and pinholes are likely to occur when the film explodes, which is unfavorable in terms of reliability.
On the other hand, if the thickness exceeds 100 μm, the light transmittance decreases, resulting in poor conversion efficiency, and the film becomes less flexible, which is not preferable.

The above-mentioned polyimide film is colorless and transparent, but in the present invention, one having a total light transmittance of 80 inches or more and a yellowness index of 25 or less when the thickness is 50 μm is preferably used from the viewpoint of photoelectric conversion efficiency.

Such a colorless and transparent polyimide film has the following general formula: F3 A mono- to tetra-nuclear component whose aromatic nucleus is meta-substituted, or a di- to tetra-nuclear component whose aromatic nucleus is meta-substituted and rose-substituted containing a purple oro group. It is an ingredient. ) A polyimide having the repeating unit shown as the main component is used, and such a polyimide can typically be obtained by a reaction between an aromatic tetracarboxylic dianhydride and an aromatic diamine.

The aromatic tetracarboxylic dianhydride is 3,3
', 4.4'-biphenyltetracarboxylic dianhydride, 2. 3.3', 4'-biphenyltetracarboxylic dianhydride, 3.3', 4.4'-diphenylsulfone tetracarboxylic dianhydride, 2.2-bis(3,
Examples include 4-dicarboxyphenyl)hexafluoropropane dianhydride, which may be used alone or in appropriate combinations.

Further, as the aromatic diamine, aromatic mononuclear diamine/
Examples include m-phenylenediamine, m-tolylenediamine, 4,6-! /methyl-m-7 ethylenediamine,
2,4-diaminomesitylene, 4-chloro-m-phenylenediamine, 3. Examples include 5-diaminobenzoic acid and 5-nitro-m-phenylenediamine. Examples of aromatic dinuclear diamines include 3.3'-diaminodiphenyl ether s3*3'-d aminodiphenyl sulfone, 3<3'-diaminodiphenylsulfoxy)', 3.3'-diaminodiphenylsulfide,
3.3'-diaminodiphenylmethane, 3.3'-diaminobenzophenone, 3.3'-diaminobiphenyl,
Examples include 2,2-bis(3-aminophenoxy)hexafluoropropane and 2,2-bis(4-aminophenoxy)hexafluoropropane. Examples of aromatic trinuclear diamines include 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenyl)benzene, 1. Examples include 3-bis(3-aminophenyl)benzene. As the aromatic tetranuclear diamine, bis[4
-(3-aminophenoxy)phenyl]sulfone, bis(4-(3-aminophenoxy)phenyl diether),
4.4'-bis(3-aminophenoxy)biphenyl,
2.2-bis(4-(3-aminophenoxy)phenyl]propane, 2.2-bis(4-(3-aminophenoxy)phenyl)hexafluoropropane, 2,2-bis(4-(4- Examples include aminophenoxy)phenyl]hexafluoropropane.These can be used alone or in appropriate combinations.

The polyimide obtained from the above-mentioned components is colorless and transparent and has the above-mentioned total light transmittance and yellowness index, and preferably contains at least 80 molti, preferably 95 molti or more in the film-forming composition. Therefore, in the present invention, other polyimides made of aromatic tetracarboxylic dianhydride and aromatic diamine can be mixed within a range that does not significantly reduce the photoelectric conversion efficiency in terms of total light transmittance and yellowness index values.

As such aromatic tetracarboxylic dianhydride,
Pyromellitic dianhydride, 3.3'-benzophenonetetracarboxylic dianhydride, 4.4'-oxycyphthalic dianhydride, 4.4'-bis(3゜4-dicarboxyphenoxy)diphenylsulfone dianhydride things, 2.3, 6.7
-Naphthalenetetracarboxylic dianhydride, 1,2,5.
6-naphthalenetetracarboxylic dianhydride, 1,4,5
．． Examples include 8-naphthalenetetracarboxylic dianhydride, which can be used alone or in combination. In addition, other aromatic diamines include p-fuynylene diamine, 2,5-tolylene diamine, benzidine, a
, 3'-dimethylbe/shicine, 4.4'-diaminodiphenyl ether, 3.4'-diaminodiphenyl ether, 4.4'-diaminodiphenylsulfone, 4.4'
-Diamino diphenyl sulfoxide, 4.4'-diaminodiphenylsulfide, 4.4'-diaminodiphenylmethane, 4.4'-diaminobenzophenone, 2,2
-bis(4aminophenyl)furopane, 3.3'-dimethoxy-4,4'-diaminodiphenylmethane, 3°3
7-dimethyl-4,4'-diaminodiphenylmethane,
1,4-bis(4-aminophenoxy)benzene, 4.
4'-diaminoterphenyl, bis[4-(3-7minophenoxy)phenyl]sulfone, bis-(4-(4-
Examples include aminophenoxy)phenyl]ether, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, and these may be used alone or in combination. Can be used.

The polyimide film serving as the substrate of the film solar cell of the present invention is produced, for example, by the following method.

A polyamic acid is synthesized by reacting the above-mentioned aromatic tetracarboxylic dianhydride and aromatic diamine in an organic solvent at a temperature of 80°C or less, and this polyamic acid solution is used to form a desired shape. form a mold, in the air,
In an inert gas or vacuum, the organic solvent is completely removed under a temperature condition of 50 to 350"C, and at the same time, the polyamic acid is dehydrated and ring-closed to synthesize a polyimide. Also, the polyamic acid is synthesized by acetic anhydride/pyridine mixed fi A chemical imidization method involves immersing it in a solution to simultaneously remove the solvent and imidize it, or a method in which polyamic acid is isolated by reprecipitation in a poor solvent, and then dehydrated and ring-closed by heating or chemical imidization to form polyimide. It is also possible to imidize the polyamic acid solution by heating it as it is to 100°C or higher.If the polyimide obtained is not soluble in the reaction solvent, it can be isolated as a precipitate. However, if it is soluble, it remains in solution form, so it can be isolated by reprecipitation in a poor solvent, as in the case of polyamic acid, or it can be isolated by forming a polyimide solution into a desired shape. However, it can also be obtained by removing the organic solvent in air, in an inert gas, or in vacuum at a temperature of 50 to 200''C. Fi filtration and washing is necessary when isolating by reprecipitation.

Suitable organic solvents include N,N-' dimethylformamide, N,N-dimethylacetamide, diglyme, triglyme, cresol, halogenated phenol, methyl cellosolve acetate, dioxane, and tetrahydrofuran, but especially N,N- Dimethylacetamide is preferred.

These organic solvents may be used alone or in combination of two or more. Since these organic solvents have relatively low boiling points, there is no problem that they decompose during imidization by heating and the decomposed products remain in the polyimide and cause coloring. N-methyl-2- is a commonly used solvent for polyimide polymerization.
Although pyrrolidone is available, this solvent is not preferred because it is known that it decomposes when heated to high temperatures, and its decomposed products remain in polyimide, causing coloration.

Note that when using the suitable organic solvents exemplified above,
Solvents such as ethanol, toluene, benzene, xylene, and nitrobenzene may be used alone or in a mixture of two or more to the extent that the colorless transparency of the polyimide film is not impaired.

As mentioned above, when producing a colorless and transparent polyimide film, the logarithmic viscosity (N) of polyamic acid is

(measured at 30°C at a concentration of 0.5 f/dl in N-dimethylacetamide) is preferably adjusted to be in the range of 0.5 to 5.0. Particularly suitable is 0.7 to 3.
It is 0. If the logarithmic viscosity is too low, the mechanical strength of the resulting polyimide film will decrease, which is undesirable.

On the other hand, if the logarithmic viscosity is too high, it becomes difficult to cast the polyamic acid solution when shaping it into an appropriate shape. From the viewpoint of workability, the concentration of the polyamic acid solution is also desirably set to 5 to 40% by weight, preferably 15 to 30% by weight.

The above logarithmic viscosity is calculated using the following formula, and the time in the formula is measured using a capillary viscometer.

to: Falling time of solvent (seconds) tl: Falling time of solution (seconds) C: Concentration Cf/di) When polyamic acid is imidized to form polyimide in this way, the resulting polyimide has a logarithmic viscosity from the viewpoint of properties. (at a concentration of 0.597 dl in 97% sulfuric acid at 30 °C)
(measured by ) is preferably set within the range of 0.5 to 5.0. The most preferred range is 0.7 to 3.0.

The polyamic acid solution thus obtained was cast onto a mirror-finished support to a constant thickness.
The polyamic acid is imidized by gradually heating at a temperature of 0 to 350° C. to promote desolvation and dehydration and ring closure, thereby obtaining a polyimide film. The heating step for removing the organic solvent and imidizing the polyimide film from the polyamic acid solution may be carried out under vacuum (reduced pressure) or an inert gas atmosphere, or at 400'C for a short time.
It is also possible to improve the properties of the polyimide film obtained by further heating the film.

Also, when using a polyimide solution, it can be obtained by casting the polyimide solution onto a support to a certain thickness in the same manner as above, and heating it at a temperature of 50 to 200"C to remove the solvent. can.

The heating process for such desolvation is performed under vacuum (under reduced pressure).
The colorless and transparent polyimide film obtained as described above is used as a substrate, but in the present invention, fine irregularities or spherical fillers are formed on one side of the lid film by plasma treatment. A micro spherical protrusion made of metal is formed to improve the adhesion with the transparent electrode.

Plasma treatment of a polyimide film as a substrate is performed using a plasma irradiation device under an inert atmosphere such as nitrogen gas or argon gas, or an active atmosphere such as an oxygen/freon mixed gas. -The effect can be obtained in a shorter time if the inside of the shell is under an active atmosphere. Irradiation dose is 100~sooow
The output should be in the range of 1 to 1000 minutes. If the irradiation amount is too small, the plasma treatment will not be performed sufficiently, and if the irradiation amount is too large, the effect will be saturated, resulting in poor economic efficiency.

On the other hand, methods for forming a large number of microspherical protrusions include a method in which the spherical filler is dispersed in an organic solvent in advance during the synthesis of the polyamic acid and the synthesis reaction is carried out, and a method in which the spherical filler is directly added to the solution of the synthesized polyamic acid. Alternatively, there is a method in which it is added after being dispersed in a small amount of an organic solvent, and a more uniform dispersion state can be achieved by ultrasonic irradiation. By imidizing the polyamic acid solution in which the θ-shaped filler is dispersed and forming it into a film as described above, microspherical protrusions are formed on the surface of the film.

The number of protrusions formed should be in the range of 100,000 to 100,000 per 1 mm2 of the film substrate, and the height should be 0 to improve adhesive strength.
．． The spherical filler for forming the protrusions is preferably a heat-resistant inorganic filler that does not undergo heat-induced deterioration or dimensional change, since temperatures of about 250 to 350°C are applied when producing the polyimide film. Organic fillers are used. Further, a substantially colorless or white filler is preferable so as not to impede light transmittance.

Examples of materials for fillers include silica, glass, zirconia, silicone resin,
Examples include resin and polyimide resin.

The particle size of the spherical filler can be determined in consideration of the thickness of the polyimide film substrate, and if the particle size is too large, the film properties may not be obtained.
Furthermore, if the particle size is too small, the formation of protrusions will be reduced. Generally, it is desirable that the particle diameter of the spherical filler falls within the range of 1150 to 115 times the thickness of the polyimide film substrate. Regarding the particle size distribution, although the particle sizes do not necessarily have to be uniform, if the maximum particle size exceeds 1/2 of the thickness of the polyimide film substrate, it becomes difficult to obtain the characteristics as a film.

To obtain the film solar cell of the present invention using a colorless and transparent polyimide film treated on one side as a substrate as described above, the following steps are followed, for example.

First, as a first step, transparent electrodes are formed on a colorless and transparent polyimide film substrate. An indium-tin oxide film (commonly called an ITO film) is preferably used for this purpose, but
It can be formed by a vapor deposition method or a sputtering method. The thickness of the transparent electrode is 0.01 to 1.0 μm.
If it is less than 0.01 μm, the desired conductivity cannot be obtained, and if it exceeds 1.0 μm, the transparency of the transparent electrode will be impaired, which is not preferable.

As a second step, an a-8i layer which becomes a photoelectric conversion element is formed on the transparent electrode. In addition to the a-81 thin film deposited in the order of p-type → i-type → n-type as the a-8i layer, p
Form a -SiC (amorphous silicon carbide) → Form i a-4Si-
Various materials can be used, such as an a-8t thin film deposited in the 4n type a-8t order. These a-8t deposition methods include sputtering method, glow discharge method,
There are various methods such as photo-CVD method and ion blating method.

For example, in the case of glow discharge, a colorless and transparent polyimide film substrate with transparent electrodes formed on a substrate holder heated to a temperature of 200 to 300°C? 13. The substrate holder is used as one electrode, and the opposite electrode is placed between the substrate holder and the opposite electrode.
Supplies high frequency power of 56 MHz. For example, p-type a-
To form an 8t thin film, diborane (Bz Ha
) to form an n-type a-8i thin film, phosphine (PH3) may be introduced into the silane. Note that the above a-8t thin film refers to hydrogenated a-3t and fluorinated a-8t.
says.

As a third step, a metal electrode is formed on the a-8i thin film obtained as described above. Examples of the metal electrode include aluminum, nickel, titanium, chromium, iron, stainless steel, and nickel-chromium alloy FK, and can be formed by an appropriate method such as vapor deposition or sputtering.

As a fourth step, lining with resin is performed for the purpose of protecting the a-8i layer and the metal electrode. The resin used for this purpose is not particularly limited as long as it has moisture resistance and flexibility, and epoxy resins, urethane resins, acrylic resins, polyimide resins, and the like can be suitably used.

<Effects of the Invention> As described above, since the film solar cell of the present invention uses a colorless and transparent polyimide film for the substrate, light rays do not come from the substrate side. The photoelectric conversion efficiency is increased, and the photodegradation of the A-8I layer is also less than that of conventional film solar cells.

Furthermore, since the substrate is subjected to specific processing, the adhesive strength at the interface with the transparent electrode (or some A-8T layers) is improved, preventing functional failure due to interfacial peeling during solar cell manufacturing or use. This eliminates this problem, allowing stable production and use.

In addition, when microspherical protrusions made of spherical filler are provided on a substrate, although the light transmittance slightly decreases, the haze rate increases significantly due to the unevenness of the surface, causing a light confinement effect and photoelectric conversion. Conversion efficiency is improved.

<Examples> Examples will be shown below to further specifically explain the present invention.

In addition, the abbreviations described in the table below mean the following compounds.

s-B PDA: 3.3', 4.4'-bisz
Nyltetracarboxylic dianhydride 6F-DA: 2,2-bis(3,4-dicarboxymphenyl)hexafluoropropanide anhydride 3.3'-BAPS: Bis(4-(3-aminophenoxy)phenyl) Enyldisulfone 3,3'-DDS: (bis(3-aminophenyl)sulfone X-10: Nippon Shokubai Chemical Co., Ltd. silica spherical powder N
S silica ~6 Using N,N-dimethylacetamide as a solvent, the aromatic diamine and aromatic dicarboxylic dianhydride shown in Table 1 were mixed at a concentration of 0.2 mol and 30% at room temperature.
A polyamic acid solution was obtained by reacting for a period of time. Table 1 shows the results of measuring the logarithmic viscosity of this polyamic acid at 0.5 f/dt and 30''C.

This polyamic acid solution was cast onto a support to form a liquid film, dried at 100°C in a hot air circulation dryer, and when the amount of residual solvent fell below 30%, heating was started and the final The imidization reaction was completed by heating to 300"C to obtain a colorless and transparent polyimide film having a thickness of 30 .mu.m.

Then, under the plasma irradiation atmosphere shown in Table 1, 300W
Plasma treatment was performed for 60 minutes at .

The total light transmittance and yellowness index of the polyimide film treated with plasma in this manner are also listed in Table 1.

A thickness of 50 mm was deposited on this polyimide film substrate by vapor deposition.
After providing a 0x ITO conductive thin film, it was held in a holder with a beater in an internal electrode type high frequency (13, s 6 MHz) glow discharge device, and diluted with hydrogen to 10 ml while keeping it at around 250 °C. 5000p with silane and hydrogen
Diborane (B2H8) diluted to pm was mixed and introduced into a glow discharge device. 1 and vacuum degree 0-2 T
A 150λ thick p-type a-
A 8t layer was provided. Subsequently, the same reaction was carried out by introducing only the above hydrogen-diluted silane, and a non-doped thickness of 50 mm was obtained.
oA i-form a-8iJfjk was deposited. Furthermore, phosphine (
PH3) was mixed and introduced into a glow discharge device to provide a 500X n-type a-8t layer doped with phosphorus. In this way, IT
A photoelectric conversion element consisting of p-type, i-type, and n-type a-8t thin films was formed via an O film.

Subsequently, this was held in a vacuum evaporation apparatus, and an aluminum conductive thin film having a thickness of 0.1 μm was deposited by a conventional evaporation method.

Next, after taking it out from the apparatus, the aluminum electrode was coated with an epoxy resin as a backing material to a thickness of 50 μm to protect it.

Finally, the solar cell was separated from the support, and the obtained a-8
AMI is the photoelectric conversion efficiency of T-film solar cells.

Measurement was performed by irradiating light from the colorless and transparent polyimide film substrate side with a 100 mW/d solar simulator.
The results are shown in Table 1. In addition, after being left in an atmosphere of 121°C and 12 atm for one week, a peel test was performed and the adhesion was kW.
The results are shown in Table 1. Comparative Examples 1 to 3 Polyimide films and solar cells were produced in the same manner as in Examples 1 to 3, except that no plasma treatment was performed.

The results are also listed in Table 1.

Examples 7 to 12 Using the aromatic tetracarboxylic dianhydride and aromatic diamine shown in Table 2, 0.5% by weight of the filler listed in the same table (based on the weight of the produced polyimide) 1 - N as a solvent , N-
A colorless and transparent polyimide film was obtained in the same manner as in the previous example, except that it was uniformly dispersed in dimethylacetamide using an ultrasonic oscillator. The total light transmittance and haze rate were measured and are also listed in Table 2.

Using this polyimide film as a substrate, a photoelectric conversion element was formed in the same manner as in the above example to produce a solar cell.

The photoelectric conversion efficiency and adhesion were measured and the results are shown in Table 2.

Comparative Examples 4 to 6 Polyimide films and solar cells were produced in the same manner as Examples 7 to 9 except that no filler was blended.

The evaluation results are also listed in @2 table.

As is clear from Tables 1 and 2, the products of the present invention have better adhesion between the substrate and the transparent electrode, compared to the comparative products.

Furthermore, as is clear from Table 2, the polyimide film containing filler has a high haze rate, exhibits a light trapping effect due to surface irregularities, and improves photoelectric conversion efficiency.

FIG. 3 shows the measurement results of the three-dimensional surface roughness of the colorless transparent polyimide film obtained in Example 12. The measured area was 0.5-, and the maximum value of the protrusion in the zm (height) direction was about 0°4 μm. Moreover, it can be seen that there are several hundred protrusions with a diameter of 0.01 to 1 μm when converted to 1 −. Furthermore, the protrusions are well dispersed throughout, and no coarse protrusions due to filler aggregation are observed.

FIG. 4 shows a scanning electron micrograph of the polyimide film obtained in Example 12. This clearly shows that the protrusions are spherical and that the filler does not directly appear on the film surface, but rather pushes up the polyimide skin.

No. figure Hand vE Nefu Seisho (spontaneous) Heisei 1 year August

Claims (6)

[Claims] (1) A film solar cell in which a photoelectric conversion element is provided on the treated side of a colorless and transparent polyimide film substrate that has been subjected to plasma treatment on one side. (2) A film solar cell in which a photoelectric conversion element is provided on the protrusion-forming surface of a colorless and transparent polyimide film substrate with a large number of microspherical protrusions formed on one side. (3) The film solar cell according to claim (2), wherein 100,000 to 100,000 microspherical protrusions are formed per 1 mm^2 of the substrate. (4) The film solar cell according to claim (2) or (3), wherein the microspherical protrusions have a height of 0.01 to 1 μm. (5) The film solar cell according to claim (1) or (2), wherein the polyimide film has a total light transmittance of 80% or more and a yellowness index of 25 or less when the thickness is 50 μm. (6) Polyimide film has a general formula, ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, R_1 has ▲Mathematical formulas, chemical formulas, tables, etc.▼,
▲There are mathematical formulas, chemical formulas, tables, etc.▼, ▲Mathematical formulas, chemical formulas,
There are tables, etc. ▼ or ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, and R_
2 is 1 in which the aromatic nucleus bonded to the nitrogen atom is meta-substituted
˜4-tetranuclear components, or meta- and para-substituted di- to tetranuclear components containing perfluoro groups. The film solar cell according to claim 1 or 2, which is a film containing a polyimide having a repeating unit represented by the formula (1) or (2).