JPH1187749A - Solar cell and formation method for semiconductor film thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor film for a solar cell whose thickness and crystallinity are uniform and whose area is large, by a method wherein a part which becomes a high temperature when it is heated on a plate is coated with a paste in a small amount and a part which becomes a low temperature is coated with the paste in a large amount. SOLUTION: A CdTe powder as a semiconductor material is mixed with polypylene glycol so as to prepare a paste. A glass plate 10 is coated with the obtained paste so as to be dried in such a way that its central part is coated to be thin and that its peripheral part is coated to be thick, a coating film 11 is formed, and a source substrate is obtained. Then, the central part is first coated with the paste so as to be dried to a square shape, and a coating film 11a is formed. Then, the paste is printed on the outer circumferential part of the coating film 11a so as to be dried, and a coating film 11b is formed. In addition, the paste is printed on the outer circumferential part of the coating film 11b so as to be dried, and a coating film 11c is formed. As a result a homogeneous CdTe film can be obtained, and a semiconductor film for a solar cell whose area is large and whose quality is high can be formed stably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Cadmium telluride (hereinafter referred to as CdTe) has a high band gap (= 1.4 eV) matching the peak of the sunlight spectrum, and therefore has high theoretical conversion efficiency. Therefore, CdTe is suitable for a light absorbing layer of a solar cell. In addition, CdTe is a semiconductor showing a direct transition, and therefore has a large absorption coefficient. Therefore, thinning is possible and a solar cell can be manufactured at low cost.
On the other hand, cadmium sulfide (hereinafter referred to as CdS) has a large forbidden band width (= 2.42 eV). Therefore,
CdS is suitable for a window layer of a solar cell. For the above reasons, CdS / CdTe solar cells using CdTe for the light absorbing layer and CdS for the window layer are expected to achieve high conversion efficiency.

Hereinafter, as an example of a semiconductor film for a solar cell,
A method for forming a CdTe film will be described. CdS / Cd
In a method of manufacturing a Te solar cell, a CdTe film is generally formed on the surface of a CdS film. As a method for forming a CdTe film, a proximity sublimation method capable of obtaining a high-quality CdTe film has attracted attention. The proximity sublimation method is a type of vapor deposition method, and currently has the world's highest conversion efficiency (15.8).
%) Having been obtained. The proximity sublimation method is described in, for example, "HIGHEFFICIENCY C" by TL Chu et al.
dS / CdTe SOLAR CELLS FROM SOLUTION-GROWN CdS FILMS
(TheConference Record of the 22nd IEEE Photov
oltaic Specialists Conference (1991) Vol.2, p.952)
And so on. According to this method, a material (hereinafter, referred to as a source) for forming a CdTe film and a substrate are arranged close to each other at an interval of about 0.5 to 5 mm and heated under reduced pressure. Thus, the source is sublimated and then deposited on the substrate. According to this method, the sublimated source is rearranged and crystallized on the substrate arranged at a short distance about the mean free path, so that a CdTe film having high crystallinity can be obtained. Further, the film forming speed is high because the processing is performed under reduced pressure.

Conventionally, in the proximity sublimation method, generally, CdTe powder spread in a dish-like container has been used as a source. For example, in the above document,
Commercially available polycrystalline CdTe having a purity of 5N, or ground powder of a polycrystalline ingot of CdTe obtained by directly synthesizing constituent elements (Cd and Te) and a dopant (for example, antimony) is used. However, according to this method, the utilization rate of the source is low. CdTe powder used for the sauce is expensive. Therefore, recently, it has been studied to form a coating film by printing and drying a paste containing a mixed powder of Cd and Te on a heat-resistant plate, and to use the coating film as a source. According to this method, a semiconductor film can be formed with a high material utilization rate using an inexpensive material.

[0005] However, when a large-area semiconductor film is formed by any of the above methods, the thickness and crystallinity of the obtained film vary greatly. When a large-area semiconductor film is formed by the proximity sublimation method, the substrate on which the semiconductor film is to be formed and the plate on which the source is arranged need to have a large area. When a large-area substrate and plate are used, heat is easily released from the peripheral portion, while heat is easily stored in the central portion. Therefore, a temperature difference occurs in the plate, and the sublimation speed of the source varies. In addition, even if the temperature difference between the plates is suppressed, the vaporized semiconductor material existing in the gap between the substrate and the plate flows out to the outside, so that the deposition amount of the vaporized source varies. Variations in the sublimation rate and deposition amount of these sources cause variations in crystallinity as well as the thickness of the obtained film. Naturally, the conversion efficiency of a solar cell using such a semiconductor film greatly varies. Furthermore, it is very difficult to heat a large-area plate substrate uniformly. Also, even if the temperature difference of the plate is suppressed,
The source sublimated at the periphery of the coating film spreads further to the periphery thereof, so that the CdTe film at the periphery of the substrate becomes thin.
For this reason, it has been difficult to stably form a large-area semiconductor film with small variations in thickness and crystallinity.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a solar cell semiconductor film capable of obtaining a large-area solar cell semiconductor film having a uniform thickness and crystallinity. Another object of the present invention is to stably provide a large-area solar cell having high conversion efficiency.

[0007]

According to the method of forming a semiconductor film for a solar cell of the present invention, in a proximity sublimation method, a paste containing a semiconductor material is applied on a heat-resistant plate and dried to form a source film. When paste is heated on the plate, the paste becomes less at the place where the temperature becomes high, and is applied more at the place where the temperature becomes low. Further, the amount of paste applied to the center of the plate is made smaller than that applied to the periphery of the plate.
This makes it possible to correct variations in the thickness and crystallinity of the semiconductor film due to the temperature difference and the structure of the plate. Therefore, a high-quality semiconductor film can be obtained at any position in the substrate.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of forming a semiconductor film for a solar cell according to the present invention, a paste containing a semiconductor material is applied to a heat-resistant plate and dried to form a coating film containing the semiconductor material on the surface of the plate. And a step of disposing a substrate and a coating film on which a semiconductor film is to be formed close to and facing each other, and heating the substrate and the coating film to form a semiconductor film on the substrate, In the step of forming a coating film, more paste is applied to a part where the temperature becomes relatively high in the step of heating the plate than to a part where the temperature becomes low. According to this method, it is possible to correct the variation in the sublimation speed of the semiconductor material due to the temperature difference between the plates, and to obtain a large-area semiconductor film having a uniform thickness and crystallinity. Therefore, by using this semiconductor film, a solar cell with high conversion efficiency can be manufactured stably. In particular, a high-quality semiconductor film with a large area can be obtained, so that a module with high conversion efficiency in which cells are connected in series can be obtained.

In a preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, in the step of forming a coating film, the coating film having a relatively low temperature in the heating step is coated with the coating film having a relatively high temperature. Thicker than membrane. In another preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, in the step of forming a coating film, a plurality of small-area coating films are scattered, and the temperature of a portion that becomes relatively low in the heating step is reduced. The area ratio occupied by the coating film is made higher than the area ratio occupied by the coating film at the portion where the temperature becomes high. In still another preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, in the step of forming a coating film, the portions where the paste is not applied are scattered, and the portions where the temperature becomes relatively low in the heating step are reduced. The area ratio occupied by the coating film is made higher than the area ratio occupied by the coating film at the portion where the temperature becomes high.

According to another method of forming a semiconductor film for a solar cell of the present invention, a paste containing a semiconductor material is applied to a heat-resistant plate and dried to form a coating film containing the semiconductor material on the surface of the plate. And a step of disposing a substrate and a coating film on which a semiconductor film is to be formed in close proximity to each other, and forming a semiconductor film on the substrate by heating the substrate and the coating film. In the step of forming the paste, more paste is applied to the peripheral portion of the plate than in the central portion. According to this method, the vaporized semiconductor material existing between the substrate and the plate flows out from the peripheral portion,
Variations in film thickness and crystallinity due to the configuration, in which the peripheral portion becomes thin, can be corrected, and a large-area semiconductor film with uniform thickness and crystallinity can be obtained. By using the obtained semiconductor film, a solar cell with high conversion efficiency can be manufactured stably. In a preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, in the step of forming a coating film, the coating film at the peripheral portion of the plate is thicker than the coating film at the central portion. In another preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, in the step of forming a coating film, a plurality of small-area coating films are scattered, and the area ratio of the coating film on the peripheral portion of the plate is reduced. It is higher than the area ratio occupied by the coating film at the center. In still another preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, in the step of forming a coating film, the portions where the paste is not applied are scattered, and the area ratio occupied by the coating film on the peripheral portion of the plate is reduced. It is higher than the area ratio occupied by the coating film at the center.

In a preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, in the heating step, the temperature of the semiconductor material is set higher than the temperature of the substrate. This method is particularly effective for forming a cadmium telluride film.
At this time, a cadmium telluride film can be formed at lower cost by using a mixed powder obtained by pulverizing tellurium and cadmium, which is far less expensive than CdTe powder, as a semiconductor material. A transparent conductive film and a cadmium sulfide film as a window layer are sequentially formed on a light-transmitting substrate, and a cadmium telluride film is formed thereon by any of the methods described above. By sequentially forming a current collector and a positive electrode on this cadmium telluride film and then forming a negative electrode connected to the transparent conductive film, a solar cell with high performance and small variation can be obtained.

In another preferred embodiment of the method for forming a semiconductor film for a solar cell according to the present invention, the semiconductor material comprises an organometallic compound. By using an organometallic compound as a semiconductor material, a semiconductor film can be formed at a lower temperature and in the air than an inorganic material. According to this method, the metal compound which has been vaporized and molecularly separated can be regularly arranged on the substrate, and an extremely dense semiconductor film can be obtained. In the step of forming the semiconductor film, the temperature of the semiconductor material is lower than the temperature of the substrate. Thus, a dense semiconductor film can be formed over a substrate using a material whose decomposition temperature is higher than the temperature at which the organometallic compound is vaporized. This method is particularly effective for forming a cadmium sulfide film.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment of the method of forming a semiconductor thin film for a solar cell according to the present invention, a method for forming a CdS film 3 and a CdTe film 4 by proximity sublimation in the solar cell shown in FIG. explain. As the substrate 1, borosilicate glass, low alkali glass, white plate glass or soda lime glass is used. The surface of the substrate 1 is formed to a thickness of 100 by chemical vapor deposition (CVD) or sputtering.
A transparent conductive film 2 made of tin oxide, indium tin oxide (ITO), or the like having a thickness of 0 to 10000 angstroms is formed.
At this time, silica (SiO 2) is provided between the substrate 1 and the transparent conductive film 2 in order to prevent diffusion of an alkali component from the substrate 1.
₂ ) A film may be formed. CdS on transparent conductive film 2
After the film 3 is formed, C is further formed by the following proximity sublimation method.
A dTe film 4 is formed. Further, after the CdTe film 4 is formed, a carbon film 5 as an electrode for the CdTe film 4, a negative electrode 6 made of an AgIn film, and a positive electrode 7 made of an Ag film are formed to obtain a solar cell.

As a preliminary experiment, the length and the width are 350 m.
A pair of m glass substrates were closely opposed to each other, heated to 700 ° C., and maintained at the same temperature. FIG. 2 shows the surface temperature distribution of the glass substrate at this time. From FIG. 2, it can be seen that the peripheral portion of the glass substrate is lower by about 30 ° C. than the central portion.

In the following Examples 1 to 6, a method for forming a CdTe film will be particularly described.

Example 1 CdTe as a semiconductor material
The powder was mixed with propylene glycol to prepare a paste. As shown in FIGS. 3 (a) and 3 (b), the obtained paste is applied to a glass plate 10 having a length and a width of 350 mm with a thin center portion and a thick peripheral portion, followed by drying. The film 11 was formed to obtain a source substrate. First, one side of the plate 10 is 340 by screen printing in the center.
The paste was applied to a square of mm and dried to form a coating film 11a. Then, a width of 120 mm was applied to the outer periphery of the coating film 11a.
The same paste was printed and dried to form a coating film 11b. Further, the same paste having a width of 70 mm was printed and dried on the outer peripheral portion of the coating film 11b to form a coating film 11c.

On the other hand, a paste was prepared by mixing cadmium diethyldithiocarbamate, which is an organometallic complex containing Cd and S, with propylene glycol. The obtained paste was applied to a glass substrate 1 provided with a transparent conductive film 2 and dried, and then cadmium diethyldithiocarbamate was thermally decomposed to form a CdS film 3 having a thickness of 500 to 2,000 angstroms. As shown in FIG. 4, the substrate 1 and the source substrate 9 were arranged such that the CdS film 3 and the coating film 11 faced each other with a gap of 1 to 10 mm. Then, the substrate 1 is placed in a nitrogen atmosphere at 1 atm.
At a temperature of 00 to 650 ° C., the source substrate 9 is
CdTe film 4 was formed on the surface of substrate 1 by heating and holding at a temperature higher by 00 ° C. for 1 to 30 minutes.

The substrate 1 on which the CdTe film 4 is formed is
Were divided equally into 1 to 9 shown below, and using these, solar cells were respectively manufactured. However, in practice, a portion having a length and a width of 100 mm at the central portion of the equally divided substrate 1 was used. Then, a methanol-saturated solution of cadmium chloride was applied onto the CdTe film 4 of the substrate 1 and methanol was evaporated.
Heat treatment was performed at 400 ° C. for 30 minutes to grow grains in the CdTe film 4. Separately, carbon powder was mixed with polyvinyl butyral as a thickener to prepare a carbon paste. The obtained carbon paste was screen-printed on the CdTe film 4, dried and baked to form a carbon film 5. A paste is prepared by mixing a mixed powder of silver and indium with a urethane resin as a thickener,
This paste was screen-printed on the CdS film 3 and the carbon film 5, respectively, dried and baked to form the + side electrode 7 and the − side electrode 6.

Comparative Example 1 The same paste as that used in Example 1 was applied to the same plate 12 as that used in Example 1 by screen printing and dried. (B) As shown in FIG.
Was formed to obtain a source substrate. Using the obtained source substrate, a CdTe film was formed in the same manner as in Example 1. Furthermore, a CdS / CdTe solar cell was similarly produced using the obtained coating film.

The conversion efficiencies of the solar cells of Example 1 and Comparative Example 1 obtained as described above were expressed as AM: 1.5, 10
It was measured under the condition of 0 mW / cm ² . Table 1 shows the results.

[0021]

[Table 1]

From Table 1, it can be seen that the conversion efficiency of the solar cell of Comparative Example 1 is large, while the solar cell of Example 1 is small and exhibits high conversion efficiency. From this, it can be seen that a homogeneous CdTe film can be obtained by arranging more sources at the periphery of the plate where the temperature becomes low during film formation than at the center as in Example 1. In addition,
In this embodiment, since the CdTe film is formed by the batch process, a large amount of the source is arranged on the peripheral portion where the temperature is low. However, even when other methods, for example, a continuous furnace or the like are used, the temperature distribution of the source at the time of heating is used. The amount of paste applied may be controlled in consideration of the above.

Example 2 Pure water was added to Cd powder and Te powder, and wet pulverization was performed using a zirconia medium. Next, propylene glycol was mixed with the ground powder to prepare a paste. A CdTe film was formed in the same manner as in Example 1 using the obtained paste.

<< Embodiment 3 >> As shown in FIG.
The paste is applied to the same heat-resistant plate 14 as that used in the above in a dot pattern by screen printing,
It dried and the coating film 15 was formed. Here, while the coating film 15 on the peripheral portion of the plate 14 is formed into a square having a maximum of 10 mm on one side, the coating film 15 on the central portion is formed into a rectangular shape having a minimum of 1 mm on one side, and the area occupied by the coating film 15 on the peripheral portion. The ratio was higher than that of the central part. Here, the same paste as that used in Example 1 was used.

Example 4 A paste was screen-printed in the same pattern on a coating film 1c formed on the periphery of the source substrate similar to that used in Example 1 to form a coating film. A CdTe film was formed in the same manner as in Example 1 using the obtained source substrate.

Example 5 A paste was prepared in the same manner as in Example 2 by using a pulverized powder obtained by wet-pulverizing Cd powder and Te powder. A source substrate similar to that of Example 4 was manufactured using the obtained paste. A CdTe film was similarly formed using the obtained source substrate.

Embodiment 6 In the same dot-shaped pattern as that shown in Embodiment 3, the peripheral coating film is formed into a square having a maximum of 20 mm on a side, and the area ratio of the peripheral coating film to the square is measured. A source substrate that was even higher than that of Sample No. 3 was prepared. Using the obtained source substrate, CdT
An e film was formed.

The substrate on which the CdTe film was formed as described above was divided into nine parts as in Example 1, and a solar cell was fabricated at the center of each substrate. Table 2 shows the conversion efficiency of the obtained solar cell.

[0029]

[Table 2]

From Table 2, it can be seen that the solar cells of Examples 2 to 6 have the same characteristic variation among the solar cells using the CdTe film formed on the same substrate as in the solar cell of Example 1. It can be seen that it decreases. In the solar cells of Examples 2 and 5, both the starting materials for the CdTe film have a material cost of approximately 1/10 that of the CdTe powder.
In this case, d and Te are used alone. The solar cells of these examples are not much different in performance from the solar cells of other examples using CdTe powder as a starting material. Therefore,
By using simple substances of Cd and Te as starting materials, the cost can be significantly reduced. In the above embodiment, when Cd and Te are used as the starting materials, Cd and Te are wet-pulverized, but the same effect can be obtained by dry pulverization. However, in dry milling, it is necessary to pay attention to the rapid exothermic reaction between Cd and Te. Similar effects can be obtained by pulverization using a medium made of another material such as alumina. In each of the above embodiments, the film is formed in a nitrogen atmosphere, but may be formed in an atmosphere of an inert gas such as helium or argon, or hydrogen. The same effect can be obtained if the pressure is 2 atm or less.

In each of the solar cells of the above embodiments, Cd
Although the case where the CdTe film is formed on the S film has been described, similar effects can be obtained by using a CdZnS film instead of the CdS film.

Next, a method for forming a CdS film on a glass substrate will be described in the following examples.

Example 7 A paste obtained by mixing cadmium diethyldithiocarbamate and propylene glycol, which are organometallic compounds, on a heat-resistant plate similar to that used in Example 1 was used. Was printed and dried in the same three-layer structure pattern as the source substrate used in the above to form a coating film. Then, in the same manner as used in Example 1, the source substrate was opposed to the transparent conductive film at an interval of 1 to 10 mm while heating and holding the glass substrate on which the transparent conductive film was previously formed at 450 ° C. in the atmosphere. Then, a CdS film was formed on the transparent conductive film.

Example 8 A coating film was formed in a similar pattern on the coating film on the peripheral portion of the source substrate similar to that used in Example 7. Using this source substrate, a CdS film was formed on the substrate in the same manner as in Example 7.

Comparative Example 2 As a comparative example, a coating film having a uniform thickness was formed in the same manner as in Comparative Example 1 using the same paste. Using the obtained coating film, a CdS film was formed in the same manner as in Example 7.

The CdS film obtained as described above was divided into nine squares as shown in FIG. 5, and the thickness of the film at each central portion was measured. Next, a CdTe film was formed on these CdS films in the same manner as in Comparative Example 1, and a similar solar cell was produced using these films. The conversion efficiency of the obtained solar cell was measured. Table 3 shows the measurement results.

[0037]

[Table 3]

As shown in Table 3, in the solar cell of Example 7, a high conversion efficiency of 14% or more was obtained in any of 1 to 9, and the variation was reduced. Further, the thickness of the CdS film obtained in Example 8 at the peripheral portion of the substrate is larger than that of the film obtained in Example 7, and the variation between CdS films formed using the same substrate is further reduced. Has been improved. This effect is also evident in the conversion efficiency of the solar cell, where 14.5% or more is obtained over the entire area of the substrate, and the variation in solar cell characteristics is further reduced.

In the formation of the CdS film, the same effect can be obtained by using an organic metal compound other than cadmium diethyldithiocarbamate used in the above embodiment as long as the material contains Cd and S.

As described above, according to the present invention, a coating film formed by coating and drying a paste containing a semiconductor material on a heat-resistant plate is used as a source, and a portion where the temperature becomes high when heated on the plate is used. By applying a small amount of paste to a portion where the temperature is low, the sublimation amount of the source can be made constant over the entire surface of the plate. As a method of changing the area ratio occupied by the coating film, when a small area coating film is scattered as in Example 3, a coating film 17 having an arbitrary shape such as a circle as shown in FIG. May be formed. In addition, as shown in FIG.
9, the same effect can be obtained even if a portion where the plate 18 is exposed is provided therein. Further, by changing the density of the semiconductor material in the paste, the arrangement amount of the source can be similarly controlled, and the same effect can be obtained.

[0041]

According to the present invention, a large-area, high-quality semiconductor film for a solar cell can be formed stably. Therefore, it is possible to stably provide a solar cell having small variations in characteristics.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a solar cell according to one embodiment of the present invention.

FIG. 2 is a diagram showing a temperature distribution of a plate when a semiconductor film is formed.

FIG. 3 is a view showing a source substrate used in the embodiment;
(A) is a plan view, and (b) is a bb ′ cross-sectional view of (a).

FIG. 4 is a longitudinal sectional view showing an arrangement of a substrate and a source substrate when a CdTe film is formed in the example.

FIG. 5 shows sample numbers 1 to 9 of the formed semiconductor film.
It is a figure showing arrangement of.

6A and 6B are diagrams showing a source substrate used in a comparative example of the present invention, wherein FIG. 6A is a plan view, and FIG. 6B is a cross-sectional view taken along the line bb ′ of FIG.

7A and 7B are diagrams showing a source substrate used in another embodiment of the present invention, wherein FIG. 7A is a plan view and FIG. 7B is bb ′ of FIG.
It is a line sectional view.

FIG. 8 is a plan view showing a pattern of a coating film on a source substrate according to still another embodiment of the present invention.

FIG. 9 is a plan view showing a pattern of a coating film on a source substrate according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 transparent conductive film 3 CdS film 4 CdTe film 5 carbon film 6 − side electrode 7 + side electrode 8 substrate 9 source substrate 10 plate 11, 11a, 11b, 11c coating film 12 plate 13 coating film 14 plate 15 coating film 16 Plate 17 Coating 18 Plate 19 Coating

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Mikio Murono, 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery Industry Co., Ltd. (72) Miwa Tsuji 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery Industrial Co., Ltd.

Claims (15)

[Claims] A step of applying a paste containing a semiconductor material to a heat-resistant plate and drying the paste to form a coating film containing the semiconductor material on the surface of the plate; A step of disposing the coating film in close proximity to each other, and, by heating the substrate and the coating film, comprising a step of forming a semiconductor film on the substrate, in the step of forming the coating film, A method of forming a semiconductor film for a solar cell, wherein the paste is applied more in a portion where the temperature becomes relatively high in the step of heating the plate than in a portion where the temperature becomes low. 2. The solar cell according to claim 1, wherein, in the step of forming the coating film, the portion of the coating film where the temperature is relatively low in the heating step is thicker than the portion of the coating film where the temperature is high. A method for forming a semiconductor film for a battery. 3. In the step of forming the coating film, a plurality of small-area coating films are scattered, and the area ratio of the coating film in a portion where the temperature of the plate becomes relatively low in the heating step is the same. The method for forming a semiconductor film for a solar cell according to claim 1, wherein the area ratio of the coating film at a high temperature is higher than an area ratio. 4. In the step of forming the coating film, spots where the paste is not applied are scattered, and the area ratio of the coating film in a portion where the temperature of the plate becomes relatively low in the heating step is the same. The method for forming a semiconductor film for a solar cell according to claim 1, wherein the area ratio of the coating film at a high temperature is higher than an area ratio. 5. A step of applying a paste containing a semiconductor material to a heat-resistant plate and drying the paste to form a coating film containing the semiconductor material on the surface of the plate; A step of disposing the coating film in close proximity to each other, and, by heating the substrate and the coating film, comprising a step of forming a semiconductor film on the substrate, in the step of forming the coating film, A method for forming a semiconductor film for a solar cell, wherein the paste is applied more to the peripheral portion of the plate than to the central portion. 6. The method for forming a semiconductor film for a solar cell according to claim 5, wherein in the step of forming the coating film, the coating film at the peripheral portion of the plate is thicker than the coating film at the central portion. 7. In the step of forming the coating film, a plurality of small-area coating films are scattered, and the area ratio of the coating film at the peripheral portion of the plate to the area ratio of the coating film at the central portion is determined. 6. The method for forming a semiconductor film for a solar cell according to claim 5, wherein 8. In the step of forming the coating film, spots where the paste is not applied are scattered, and the area ratio of the coating film at the peripheral portion of the plate is determined by the area occupied by the coating film at the central portion. The method for forming a semiconductor film for a battery according to claim 5, wherein the ratio is higher than the ratio. 9. The method according to claim 1, wherein in the step of heating the substrate and the coating film, the temperature of the semiconductor material is higher than the temperature of the substrate. 10. The method for forming a semiconductor film for a solar cell according to claim 9, wherein the semiconductor film to be obtained is a cadmium telluride film. 11. The method according to claim 10, wherein the semiconductor material is a mixed powder obtained by pulverizing tellurium and cadmium. 12. The method according to claim 1, wherein the semiconductor material comprises an organometallic compound. 13. The method for forming a semiconductor film for a solar cell according to claim 12, wherein in the step of heating the substrate and the coating film, the temperature of the semiconductor material is lower than the temperature of the thin film forming substrate. 14. The method according to claim 13, wherein the semiconductor film to be obtained is a cadmium sulfide film. 15. A light-transmitting substrate, a transparent conductive film formed on the surface of the substrate, a cadmium sulfide film as a window layer formed on the transparent conductive film, and light formed on the cadmium sulfide film. A cadmium telluride film serving as an absorption layer, a current collector formed on the cadmium telluride film, a + side electrode electrically connected to the current collector, and electrically connected to the transparent conductive film A solar cell comprising a negative electrode, wherein the cadmium telluride film is formed on the cadmium sulfide film formed in advance by the method according to claim 1.