JP2786600B2 - Thin film solar cell and method for manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film solar cell which can be easily formed into a module and which is advantageous in cost reduction, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, a thin-film solar cell has a structure in which a semiconductor thin film is sandwiched between two electrodes. A transparent electrode is used on the side on which light is incident, and a metal electrode is used on the other side. This metal electrode is made of low-resistance Al or Ag,
It also has a role of reflecting light transmitted through the semiconductor thin film without being absorbed by the semiconductor thin film in the reverse direction and contributing to photovoltaic current. On the other hand, SnO ₂ (tin oxide) and ITO (indium.
Although a transparent conductive film such as tin oxide) or ZnO (zinc oxide) is used, since the electrical resistivity is about 5 × 10 ⁻⁴ Ω · cm, which is about two orders of magnitude larger than that of the metal film, the generated current flows through the transparent electrode. Power loss occurs while flowing. This becomes more remarkable as the substrate area increases, and various structures have been devised to reduce the loss in order to reduce the power that can be extracted to the outside.

FIGS. 7 to 9 show the structure of a conventional thin-film solar cell. FIG. 7 shows an example in which a metal substrate (1) such as stainless steel is used as a first electrode, and an amorphous semiconductor such as amorphous silicon or CdS / CdTe or CdS / CuInS is used.
a polycrystalline semiconductor of the semiconductor thin film such as e ₂ (2) and a second
Transparent electrodes (3) are sequentially stacked, and a current collecting electrode (4) of a metal film is formed thereon. The collector electrode is also called a grid electrode and is formed in a tree shape at a constant pitch. However, since the incident light is blocked, the area of the collector electrode cannot be increased. For the formation, a mask having the same shape and a hole is used for a transparent electrode (3).
Metal is deposited by contacting the top
No film is formed where the mask is covered. ) Or a method of screen-printing a conductive paste in the same pattern, but all require alignment of the mask or screen with the substrate. FIG. 8 is also called an integrated solar cell, and is a cell in which many cells are connected in series. By the way, since the power loss due to the transparent electrode is proportional to the square of the flowing current, the current can be reduced by reducing the power generation area of a single cell.

[0004] Specifically, the loss on the substrate can be reduced by dividing the cell on the substrate into a number of small cells and connecting them in series. As shown in FIG. 8, the structure is such that a transparent electrode film (7), a semiconductor thin film (8) and a back metal electrode film (9) are sequentially stacked on a transparent substrate (6) such as glass or a polymer film. However, the formation method is generally performed by forming a film using a mask having a hole of a specific shape for each film, or performing laser etching after forming each film. In the figure, A, B, and C indicate areas where no transparent electrode film, semiconductor thin film, and back electrode film are present, respectively. The solar cell output can be taken out from the terminals (10) on both sides of the transparent electrode film. By the way, in a single cell of amorphous silicon, the photovoltaic power generated between the electrodes is about 0.7 V, but when three stages are connected in series as shown in the figure, an output of 2.1 V is obtained. That is, the current is 1/3 as compared with the case where the whole substrate is a single cell,
The voltage is tripled, the generated power is the same, and the loss is reduced to 1/9. (In this case, the areas of the invalid regions A, B, and C are ignored.) In this type of solar cell, it is necessary to align the mask and the laser beam in accordance with the underlying pattern.

In addition, a through-hole contact type as shown in FIG. 9 has been devised. FIG. 2B is a cross-sectional view thereof. Transparent electrode (first electrode) on transparent substrate (11)
(12), a semiconductor thin film (13), and a metal electrode (second electrode) (14) are sequentially stacked to form a cell. In order to form a through hole (15), a part of the cell is removed at regular intervals into a cylindrical shape.
6) and the back metal electrode (17) are laminated. The back metal electrode is electrically connected to the transparent electrode at the through hole. This through-hole serves as a bypass path, and positive charges generated on the transparent electrode side flow preferentially to the lower-surface metal electrode having lower resistance. FIG. 3C is a perspective sectional view of a through hole portion. Here, the insulating film (16) is represented as a transparent body. By arranging metal electrodes in parallel with the high-resistance transparent electrode and providing through-hole contacts at regular intervals, the back metal electrode functions as a current collecting electrode, thus reducing power loss due to the transparent electrode. it can. However, this through-hole contact type structure has a problem that the manufacturing process is complicated. First, after forming a cell, a portion where a through hole (15) is to be formed is removed in a cylindrical shape with a YAG laser, and then an insulating film (16) such as a polyimide resin is formed on the entire substrate. Subsequently, the insulating film at the center of the through hole is removed by etching using an excimer laser, and then a back metal electrode film (17) is formed to form a through hole contact. The output is obtained from the second electrode (14) and the terminal (18) of the back metal electrode. Also in this case, it is necessary to perform the laser processing position according to the pattern on the substrate. Such a complicated manufacturing process makes it difficult to obtain a high yield and increases the time required for manufacturing, which is disadvantageous for cost reduction. Further, the thickness of the metal electrode (14), which is the second electrode, is about 1 μm at the maximum and cannot be too large. This is because it is necessary to selectively laser-etch the semiconductor film (13) and the metal electrode (14) without damaging the underlying transparent electrode (12), so that the laser power density cannot be increased so much. That is, since the current that can be passed is naturally limited, there is a limit in increasing the area.

[0006]

As described above, a method of patterning each film constituting a thin film solar cell mainly includes a mask film formation and a laser etching method. In mask film formation, a mask plate is brought into close contact with the underlying film, so that an alignment step is required. Also, the film is easily damaged by contact with the mask, which causes a reduction in manufacturing yield, and laser etching. In the same method, it is necessary to align and process the irradiation laser beam with respect to the pattern shape of the underlying film, and it is necessary to carefully control the laser power so as not to damage the film, and There are problems such as the necessity of a step of removing etching debris, and these are factors that hinder cost reduction. In addition, the size of the mask is limited in mask formation, and the laser etching method requires a high-precision table that moves the substrate horizontally while keeping the substrate perpendicular to the laser beam. Naturalization had its limits. An object of the present invention is to provide a thin-film solar cell that can solve the above-mentioned problems, is easy to modularize, and is advantageous in reducing costs, and a method for manufacturing the same.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to activate the above-mentioned object, and a metal substrate provided with through holes at regular intervals is used as a first electrode. In a thin-film solar cell having a structure in which an amorphous or polycrystalline semiconductor thin film and a transparent conductive film as a second electrode are sequentially stacked on the main surface of the above, the other main surface of the metal substrate An object of the present invention is to provide a thin-film solar cell, characterized in that at least an insulating film and a metal film are sequentially stacked and the metal film is electrically connected to the transparent conductive film at least in the through hole. The present invention also provides a first step of forming an insulating film on the other main surface of the metal substrate, a second step of forming a large number of through-holes over the entire area of the metal substrate, and a step of forming a semiconductor on one main surface of the metal substrate. A third step of forming a film, and then a fourth step of forming a transparent conductive film on at least the semiconductor film, and subsequently, a metal film is formed on the insulating film, and the metal film and the transparent film are formed in a through hole. A method for manufacturing the thin-film solar cell, comprising a fifth step of electrically connecting the conductive film to a conductive film. Further, the present invention provides a first step of forming a large number of through holes over the entire area of the metal substrate, a second step of forming an insulating film on the other main surface of the metal substrate, and the third to fifth steps similar to the above.
The present invention also provides a method for producing the above-mentioned thin-film solar cell comprising the steps of: In the present invention, it is a particularly preferred embodiment that the insulating film is formed by anodic oxidation, ceramic plating, plasma CVD, sputtering, coating or thermal spraying.

[0008]

According to the present invention, one of the positive and negative charges (for example, positive charge) generated by light absorption in the semiconductor thin film reaches the transparent electrode serving as the second electrode, and then passes through the nearby transparent electrode. The current is collected to the back metal electrode through the hole. That is, the distance over which the charge moves in the transparent electrode is shortened, so that the voltage drop (power loss) is suppressed accordingly. The other charge (eg, a negative charge) flows in the metal substrate serving as the first electrode. By the way, if a large number of through holes are formed in the metal substrate in advance at regular intervals, the semiconductor thin film and the transparent conductive film can be formed on the light incident surface without aligning the insulating film and the back metal film on the other surface, respectively. It is possible to provide a thin-film solar cell that is low in cost, high in yield, low in loss, and easy to increase in area by simply forming a film.

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a structural diagram of a thin-film solar cell according to a first embodiment of the present invention. FIG. 3A is a top view, and FIG.
Is a sectional view taken along the line AA ', and (c) is a sectional perspective view. An amorphous or polycrystalline semiconductor thin film (22) and a transparent conductive film (23) are formed on one main surface (an upper light incidence surface in the figure) of a metal substrate (21) provided with through holes at regular intervals. Are laminated, and the metal substrate serves as the first electrode and the transparent electrode serves as the second electrode.
A cell is formed as the electrode of. Further, an insulating film (24) and a metal film (25) are laminated on the other main surface (lower side) of the metal substrate, and a through hole (contact hole) (26) is formed.
In, the metal film is electrically connected to the transparent conductive film and functions as a current collecting electrode of the second electrode.

FIG. 2 shows a manufacturing process of a thin-film solar cell according to a first embodiment of the present invention. Step (1) in FIG.
As shown in (1), a polymer film (20) is attached to one main surface of a metal substrate (21) made of stainless steel, iron, aluminum or the like to expose only the other main surface. A film (24) is formed. The insulating film is preferably made of ceramics (mainly metal oxides) that have high heat resistance and low outgassing in vacuum, and are preferably formed by anodic oxidation utilizing the conductivity of metal or ceramic plating which has been in the spotlight in recent years. Can be. Next, in step (3), a large number of through holes (26) are formed at regular intervals over the entire area of the metal substrate. In this case, after opening holes mainly by a laser processing method, a punching method, or a chemical etching method, the polymer film (20) is peeled off and the upper metal surface is exposed (not shown). At this time, if necessary, chemical etching can be performed on the metal surface to provide fine irregularities.

Subsequently, after a small mask (27) is placed at an appropriate position on the edge of the metal substrate, a semiconductor thin film (22) is formed. For this semiconductor thin film, an amorphous material such as amorphous silicon or a polycrystalline material such as CdS / CdTe or CdS / CuInSe ₂ can be used. The film formation method is as follows: amorphous silicon is a plasma CVD method, CdS / CdT
e, CdS / CuInSe ₂ can be formed by a sublimation method, an evaporation method, or a solution growth method. Next, a transparent conductive film (23) as a second electrode is formed (Step (4) in the figure). The transparent electrode made of this transparent conductive film is made of Sn
Oxides such as O ₂ , ITO, and zinc oxide can be formed by ion plating, sputtering, or the like. Subsequently, a metal film (25) is formed on the lower surface of step (5) in FIG.
Is formed by vapor deposition or sputtering. At this time, electrical connection is automatically made with the transparent conductive film on the inner wall surface of the through hole. Next, by removing the mask (27), the metal substrate (21) is partially exposed, and the lead wire (28) is connected thereto (see FIG. 1 (b)). The lead wire (28) of the counter electrode is also connected to the metal film (25). The polarity of the electrode is determined by the lamination order of the semiconductor film (22). The polarity is as shown when an n-type semiconductor is formed on the metal substrate side and the p-type semiconductor is formed on the transparent electrode side. It becomes reverse polarity.

Although the above-described anodic oxidation method and ceramic plating method for forming an insulating film are low-cost, they are liquid phase forming methods and need to cover one side with a polymer film or the like. On the other hand, if a plasma CVD method, a sputtering method, or a thermal spraying method is used, a single-sided film can be formed as shown in step (2) ′ of FIG. 2, so that a polymer film is unnecessary. In this case, as the insulating film, Si ₃ N ₄ , Si
C, SiO ₂ or Al ₂ O ₃ can be used. Similarly, a resin having high heat resistance such as polyimide and having relatively low outgassing in a vacuum is applied to one surface of a metal substrate using a roll coater, and then heated and cured to form an insulating film (coating method). Is also possible. The steps after step (3) 'in FIG. 2 are the same as the above-mentioned method.

[0013]

EXAMPLES Next, examples based on this manufacturing method will be described, but the present invention is not limited to these examples. [Example] A 100 mm x 100 mm x 0.2 mm thick stainless steel plate (SUS304) was used as a metal substrate.
After the surface is electrolytically polished and washed, the other (lower) main surface of the substrate is formed as an insulating film to a thickness of 5000 by a plasma CVD method.
The Si ₃ N ₄ film of Å was formed. The source gas is SiH
₄ (silane), NH ₃ (ammonia), N ₂ (nitrogen), and the flow rate of each was 100, 250, 2000 per minute.
cc. Further, the substrate temperature is 300 ° C., the RF power is 20
0 W. Next, YA is applied from one main surface (upper side) of the substrate.
A large number of holes were made by irradiating G laser light. At that time, by changing the spot diameter of the laser beam variously, the hole diameter is changed in the range of 50 μm to 500 μm,
In addition, the hole interval was varied in a range of 1 mm to 20 mm to perform processing.

Next, a mask for preventing deposition near the edge of the substrate.
Is placed on one main surface (upper side) of the substrate.
Amorphous silicon film by plasma CVD
A system film was formed by the following procedure. First, P-type amorphous
Silicon carbide (a-SiC) film with a thickness of 100 mm
did. The source gas is SiH_Four, CH_Four(Methane)
0.5% B as a topping gas_TwoH₆(Diborane)
The flow rates are 20, 30, and 20 cc per minute, respectively,
The temperature was 170 ° C. and the RF power was 10 W. Next, the buffer layer
As amorphous silicon carbide (a-SiC)
Was formed at a film thickness of 100 °. The source gas is SiH_Four, CH_Fouras well as
H_Two(Hydrogen) and the flow rate is 25, 25, 50 per minute respectively
0cc, substrate temperature 180 ° C, RF power 20W
there were. In addition, the amorphous layer
Fac silicon (a-Si) is deposited to a thickness of 4000mm.
Was. SiH as source gas_FourAnd the flow rate is 60 c / min.
c. Substrate temperature 170 ° C, RF power 10W
Was. In addition, n-type amorphous silicon is formed to a thickness of 150 mm.
Filmed. The source gas is SiH _Four, H_TwoOther doping gases
0.05% PH as_Three(Phosphine) was used. Flow rate
Is 30,500,300 cc / min.
The temperature was 170 ° C. and the RF power was 100 W. in this way
After forming a semiconductor film, ITO is used as a transparent conductive film.
A film having a thickness of 3000 mm was formed by a plating method. So
Was 10 Ω / □. Finally the trout prevention
After removing the mask, a vacuum is applied to Al on the insulating film on the other main surface of the substrate.
A film having a thickness of 5 μm was formed by an evaporation method.

A lead wire was attached to the thin-film solar cell thus prepared, and the output characteristics were measured under simulated sunlight (AM1.5 light irradiation intensity: 100 mW / cm ² ). The results shown in FIG. 6 were obtained. Was. FIG. 6 shows the dependence of the conversion efficiency of the thin-film solar cell of the present invention on the hole spacing. In the case where the hole diameter is 500 μm or less, the hole interval is 1 to 8 mm.
It turns out that the degree is optimal.

FIG. 3 is a sectional perspective view of a thin-film solar cell according to a second embodiment of the present invention. This is an insulating film (2
The fourth embodiment is different from the first embodiment in that 4) is formed up to the inner wall of the through hole (26). The purpose is that the semiconductor film (22) formed on the inner wall portion is thinner than the film formed on the main surface of the substrate, so that sufficient insulation resistance of the semiconductor film cannot be obtained and the metal film (21) is transparent. This is for preventing the conductive film (23) from being easily short-circuited. As a manufacturing method, as shown in FIG. 5, a through hole is first formed in a metal substrate, and then an insulating film is formed on one surface by the same method as described above.

FIG. 4 is a sectional perspective view of a thin-film solar cell according to a third embodiment of the present invention. Transparent conductive film (23)
Are different from the first and second embodiments in that are formed on both surfaces of the substrate. When a metal film is formed on a transparent conductive film, contact resistance occurs at the interface, but the value is inversely proportional to the contact area.
Therefore, as in the first and second embodiments, the through-hole (26)
Power loss due to contact resistance can be reduced by making contact with the entire lower surface of the substrate as shown in FIG. In this case, there is a sol-gel method as a method for forming a transparent electrode. In this method, after forming a semiconductor film, the entire substrate is dipped in an alkoxide solution of tin or indium, pulled up, dried, and fired. By doing this,
A transparent conductive film can be formed over the entire substrate, and then a metal film may be formed from below the substrate. The back metal electrode film can be formed to have a thickness of several tens μm or more by an electroplating method, a solder plating method, or the like, and the metal substrate serving as the first electrode has a thickness of several tens μm or more. A larger current can flow than the conventional structure, and the area can be easily increased.

In addition, a laser processing method can be used in the hole making step in the present invention, but it is only necessary to make holes at regular intervals in a metal substrate or a metal substrate having an insulating film formed on one side in the first step. In the conventional structure
There is no need for such alignment of the laser beam to the underlayer film pattern and close control of the laser power so as not to damage the underlayer film . As described above, according to the present invention, a large-area thin-film solar cell can be manufactured in a relatively short time by a simple manufacturing process as compared with the conventional structure.

[0019]

According to the present invention, the electric charge generated on the transparent electrode side is collected on the back metal film through the through hole provided in the metal substrate, thereby reducing the power loss due to the transparent electrode. Can be. Also, if a large number of through holes are provided at predetermined intervals on a metal substrate (or a metal substrate having an insulating film formed on one surface) in advance, the respective films of the semiconductor thin film, the transparent conductive film, and the (insulating film) back metal film can be formed. Can be manufactured simply by forming a film without the need for alignment.
It is possible to provide a thin-film solar cell that is low in cost, high in yield, low in loss, and easy to increase in area.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a thin-film solar cell showing one embodiment of the present invention. (A) Top view, (b) AA 'sectional drawing, (c) sectional perspective view.

FIG. 2 is a manufacturing process diagram of the thin-film solar cell according to the present invention.

FIG. 3 is a cross-sectional perspective view of a thin-film solar cell according to another embodiment of the present invention.

FIG. 4 is a cross-sectional perspective view of a thin-film solar cell showing still another embodiment of the present invention.

FIG. 5 is another manufacturing process diagram of the thin-film solar cell according to the present invention.

FIG. 6 is a graph showing the dependence of the conversion efficiency of the solar cell according to the present invention on the hole spacing.

FIG. 7 is a structural diagram of a conventional thin-film solar cell (grid electrode type). (A) Top view, (b) XX 'sectional drawing.

FIG. 8 is a structural view of a conventional thin-film solar cell (integrated type).
(A) Top view, (b) YY 'sectional drawing.

FIG. 9 is a structural diagram of a conventional thin-film solar cell (through-hole contact type). (A) Top view, (b) ZZ 'sectional view,
(C) Sectional perspective view.

[Explanation of symbols]

 21: Metal substrate 22: Semiconductor thin film 23: Transparent conductive film (transparent electrode) 24: Insulating film 25: Metal film (back metal electrode) 26: Through hole 28: Lead terminal

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-209822 (JP, A) JP-A-2-260663 (JP, A) JP-A-6-342924 (JP, A) JP-A-3-3 257874 (JP, A) Japanese Utility Model Showa 56-154172 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 31/04

Claims (11)

(57) [Claims] 1. A metal substrate provided with through holes at regular intervals is used as a first electrode, and an amorphous material is formed on one main surface of the metal substrate.
Alternatively, in a thin film solar cell having a structure in which a polycrystalline semiconductor thin film and a transparent conductive film as a second electrode are sequentially stacked, at least an insulating film and a metal film are sequentially stacked on the other main surface of the metal substrate. A thin-film solar cell having a structure in which the metal films overlap with each other and are electrically connected to the transparent conductive film at least in the through holes. 2. The thin-film solar cell according to claim 1, wherein the semiconductor thin film is made of amorphous silicon or CdS / CdTe or CdS / CuInSe ₂ . 3. The thin-film solar cell according to claim 1, wherein the transparent conductive film is made of tin oxide, indium tin oxide, or zinc oxide. 4. The thin-film solar cell according to claim 1, wherein the metal film is formed by vapor deposition of Al or Ag. 5. The insulating film is made of Si ₃ N ₄ , SiC, SiO ₂
Or thin-film solar cell according to claim 1 made of Al ₂ O _3. 6. The insulating film according to claim 1, wherein the insulating film is made of polyimide.
5. The thin-film solar cell according to any one of 4. 7. The thin-film solar cell according to claim 1, wherein the insulating film is formed up to the inner wall of the through hole. 8. The thin-film solar cell according to claim 1, wherein a transparent conductive film is formed also on the other main surface of the metal substrate. 9. A first step of forming an insulating film on the other main surface of the metal substrate, a second step of forming a large number of through holes over the entire area of the metal substrate, and a semiconductor on one main surface of the metal substrate. The method according to claim 1, comprising a third step of forming a film, a fourth step of forming a transparent conductive film on at least the semiconductor film, and a fifth step of forming a metal film on the insulating film. A method for manufacturing a thin-film solar cell. 10. A first step of forming a large number of through holes in the whole area of the metal substrate, a second step of forming an insulating film on the other main surface of the metal substrate, and a semiconductor on one main surface of the metal substrate. The method according to claim 1, comprising a third step of forming a film, a fourth step of forming a transparent conductive film on at least the semiconductor film, and a fifth step of forming a metal film on the insulating film. A method for manufacturing a thin-film solar cell. 11. The method for manufacturing a thin-film solar cell according to claim 9, wherein the formation of the insulating film is performed by an anodizing method, a ceramic plating method, a plasma CVD method, a sputtering method, a coating method or a thermal spraying method.