JPH0918033A - Thin film solar battery and its manufacturing method - Google Patents

Abstract

PURPOSE: To provide a excellent thin film solar battery and its manufacturing method causing no warping at all due to the difference in the thermal expansion coefficient even if a solar battery material is formed on a different kind of substrate. CONSTITUTION: The crystals formed as continuous layers on a substrate 10 are grown through the intermediary of mask layers 13 having many holes 12 juxtaposed at specific intervals so that insular crystals 16 swelling up from the insides of respective holes 12 of the mask layers 13 may be formed in the state not in contact with the other insular crystals 16.

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 and a method for producing the same.

[0002]

2. Description of the Related Art As a solar cell, a silicon solar cell is widely used because it has little influence on the environment, has a high energy conversion efficiency, and has stable power generation characteristics. As such a silicon solar cell, for example, as shown in FIG. 8, an impurity (for example, phosphorus) is thermally diffused at a high temperature on the surface of a single crystal silicon substrate 1 to form an n-type diffusion layer 2, and an electrode is formed. After forming 3, S on it
A single crystal silicon solar cell obtained by forming an antireflection film 4 such as iO ₂ is well known.

[0003]

However, in the above-mentioned single crystal silicon solar cell, the single crystal silicon substrate 1 is used.
However, since the material cost becomes high, it has been attempted to use a low-cost dissimilar substrate (metal substrate such as SUS) in place of the single crystal silicon substrate 1 and form a thin film of Si thereon. However, when the Si film is formed to a thickness (50 to 100 μm) required for use as a solar cell, the substrate and the Si are greatly different in thermal expansion coefficient, so that a large warp may occur in the substrate. found. When the warp occurs, it causes a large loss in the yield in the subsequent device manufacturing, and since stress remains in the Si thin film, countless crystal defects occur and the electrical characteristics deteriorate. As described above, the thin film solar cell obtained by depositing Si or the like on a different substrate has poor quality, and improvement thereof is strongly desired.

The present invention has been made in view of the above circumstances, and is an excellent thin film solar cell in which the above-mentioned warpage does not occur even though a solar cell material is formed on a different substrate. Its purpose is to provide the manufacturing method.

[0005]

In order to achieve the above object, the present invention provides a seed crystal layer formed on a conductive substrate, and a mask layer having a large number of holes arranged at predetermined intervals on the seed crystal layer. , Further, island-shaped crystals that grow from inside the holes of the mask layer and rise above the holes and crystallize into islands are formed in a state in which they do not contact each other, and At least the surface portion of the crystal is formed in the diffusion layer,
A thin-film solar cell, in which a transparent conductive layer extending over each of the island-shaped crystal diffusion layers is formed thereon, is defined as a first gist, and a diffusion layer is formed on an insulating transparent substrate via the transparent conductive layer. , There is formed a mask layer on which a large number of holes are arranged at predetermined intervals, and further, island-like crystals grown from inside the holes of the mask layer and rising above the holes and crystallized into islands are It is formed without contact with other island crystals,
The second gist is a thin-film solar cell in which a conductive layer extending over each of the island crystals is formed thereon.

Further, a step of forming a seed crystal layer on a conductive substrate, a step of forming a mask layer thereon, a hole having an opening width of 10 to 100 μm, and a distance of 100 from each other in the mask layer. A step of forming a large number of films at equal intervals to several hundreds of μm, and growing a crystal film on the mask layer by a liquid phase epitaxy method to form island-shaped crystals rising from the inside of the mask layer above the hole with each other. Of the island crystals, a step of forming a diffusion layer on at least the surface of each of the island crystals, and a step of forming a conductive layer across the diffusion layers of each of the island crystals. The method of manufacturing a thin-film solar cell according to the third aspect, a step of forming a conductive layer on an insulating transparent substrate, a step of forming a diffusion layer thereon, a step of forming a mask layer thereon, The mask layer has an opening width of 10 to 100 μm. A large number of holes are formed at equal intervals such that the distance between them is 100 to several 100 μm, and a crystal film is grown on the mask layer by a liquid phase growth method, and the holes are formed in the holes of the mask layer above the holes. A method for producing a thin-film solar cell, comprising: a step of obtaining island-shaped crystals that rise up in a state where they do not come into contact with other island-shaped crystals; and a step of forming a conductive layer that extends over each of the island-shaped crystals. To do.

[0007]

That is, according to the present invention, the crystal that has conventionally been formed as a continuous layer on a substrate is grown through a mask layer in which a large number of holes are arranged at a predetermined interval, so that each hole in the mask layer is Obtained as an island-shaped crystal that rises upward from
Moreover, each island crystal is obtained in a state where it does not come into contact with another adjacent island crystal. Therefore, the respective island-shaped crystals exist in a dispersed state as “dots” which are not continuous with the substrate, and the structure easily expands following the thermal expansion of the substrate. Therefore, even if a low-cost substrate is used and the substrate and the crystal film are thermally expanded at different rates at a high temperature, the laminated body does not warp significantly, which is advantageous for device fabrication. Further, since the residual stress in the crystal film is small, crystal defects, which have been a problem in the past, can be significantly reduced, and a high-quality solar cell having excellent electrical characteristics can be obtained. Furthermore, since island-shaped crystals are scattered and minute projections are repeated on the crystal surface, it is possible to suppress light reflection without performing a texturing process. For this reason, the texture processing step which has been conventionally required becomes unnecessary, and the manufacturing cost can be significantly reduced.

Next, the present invention will be described in detail.

The thin-film solar cell of the present invention is provided with a unique island crystal, and the manufacturing method thereof includes the following two manufacturing methods.

The first manufacturing method is a method for manufacturing a thin film solar cell, for example, as follows. That is, first, as shown in FIG. 1, a low-cost conductive substrate (SUS, carbon, etc.) 10 is prepared, and a vacuum chemical epitaxy method (Vaper Chemical Epi) is formed on the surface of the substrate 10.
taxy, hereinafter abbreviated as "VCE"), chemical vapor deposition (Ch
A thin film made of a semiconductor material is formed by using an electronic vapor deposition (hereinafter abbreviated as “CVD”) method or a sputtering method. This semiconductor thin film becomes the seed crystal layer 11.

The seed crystal layer 11 has a thickness of 0.1.
From the viewpoint of crystal growth, it is preferable to set the thickness to 10 μm, especially 0.5 to 1.0 μm. Further, as the semiconductor material forming the seed crystal layer 11, in addition to Si, G
There are various semiconductor materials that can be used as materials for solar cells, such as aAs and InP.

Next, on the surface of the seed crystal layer 11, as shown in FIG.
As shown in, a mask layer 13 having a large number of holes 12 having a predetermined size is formed at a predetermined interval. The mask layer 13 can be obtained by using, for example, a sol-gel method by screen printing. That is, first, a predetermined catalyst is added to a solution containing tetraethoxysilane and mixed at 20 to 50 ° C. for hydrolysis to obtain a tetrahydroxysilane solution. Next, the mask layer 13 is formed by screen plate making.
A layer of the above-mentioned tetrahydroxysilane solution is formed on the portion to be formed. The thickness of this layer is about 1 to 40 μm. When this is treated at 80 to 500 ° C. for about 30 minutes, the above tetrahydroxysilane is dehydrated to form a SiO ₂ film. In this way, the mask layer 13 can be obtained. Alternatively, the mask layer 13 made of a SiO ₂ film may be formed by using the thermal CVD method, and then the holes 12 at predetermined intervals may be formed by etching.

The thickness of the mask layer 13 is 3000 Å
10 μm, especially 0.5 to 1 μm,
It is preferable from the viewpoint of crystal growth. The holes 12 formed in the mask layer 13 are made of Si as described below.
It is a window necessary for growing a crystal in an island shape, and its opening shape may be a square shape as shown in the drawing, a circular shape, or another shape. The size of the opening is 1 (width in the case of square holes, width in the case of round holes, diameter in the case of round holes, and the same for other shapes).
It is necessary to set it to 0 to 100 μm. If the opening of the hole 12 is smaller than the above range, it is not easy to machine the hole, and each island-shaped crystal obtained by growing from this hole becomes very small. This is because the antireflection effect is reduced. On the contrary, if the opening of the hole 12 is larger than the above range, the island crystal becomes too large, the antireflection effect becomes small, and the yield in the subsequent device manufacturing process decreases.
In addition, the interval for forming the holes 12 depends on the size of the holes, but is usually 1 for each hole pitch (indicated by P in FIG. 2).
It is necessary to set it to be from 00 to several 100 μm. If the hole pitch is narrower than the above range, adjacent crystals may come into contact with each other before the crystals grow sufficiently in an island shape. Conversely, if the hole pitch is wider than the above range, it takes a long time for crystal growth. At the same time, the antireflection effect of light decreases.

The mask layer 13 is not necessarily made of Si.
Need not be formed by O _2, those that have been oxidized to form a material of the seed crystal layer 11, or TiO _2, Si ₃ N ₄ or the like,
Materials conventionally used as surface stabilizing film forming materials in solar cells can be appropriately used.

Next, a crystal film (P type) made of a semiconductor material is formed on the mask layer 13. The film forming step is preferably performed by a liquid phase epitaxial growth method (Liquid Phase Epitaxy, hereinafter abbreviated as “LPE”) in which the film forming rate is highly dependent on the plane orientation.
As an example of the LPE, as shown in FIG. 3, a substrate 10 on which the mask layer 13 is formed is melted in a solvent in a film forming raw material 14 (schematically shown in the drawing) in a melting tank 15. A well-known method is to immerse the substrate in the melt bath 15 to cool the inside of the melting tank 15 to precipitate crystals on the surface of the mask layer 13 of the substrate 10. When the crystal is grown in this manner, the crystal is formed as shown in FIG.
As shown in FIG. 3, the mask layer 13 grows from inside each hole 12, rises above the opening of the hole 12, and gradually forms an island shape. Therefore, the film formation ends when the island crystals 16 do not contact each other. For this purpose, it is preferable to set the height of the island crystal 16 (indicated by H in FIG. 4) to 10 to 100 μm.

The island crystal 16 is preferably made of the same material as the seed crystal layer 11.

Next, the conventionally known thermal diffusion method,
As shown in FIG. 5, a portion of the surface of the island crystal 16 having a predetermined thickness is formed in the N type diffusion layer 17 by the atmospheric pressure CVD method, the plasma CVD method, or the like. The thickness of the diffusion layer 17 is appropriately set, but is usually about 0.1 to 0.5 μm. The dopant to be diffused is the island crystal 1
It is appropriately selected according to the material of No. 6.

Then, as shown in FIG. 6, a film of ITO, SnO ₂ or the like is formed on the diffusion layer 17 by a vacuum deposition method, a sputtering method, an atmospheric pressure CVD method or the like to form a transparent conductive layer 18. obtain. This transparent conductive layer 18 becomes a surface electrode.
The thickness of the transparent conductive layer 18 is also set as appropriate,
Usually, it is about 500 to 1000Å.

The thin film solar cell thus obtained is
Since the island-shaped crystals 16 exist in a dispersed state as points without contacting each other, the low-cost conductive substrate 1
The structure is such that it easily expands following the thermal expansion of 0.
Therefore, under high temperature, the substrate 10 and the island-shaped crystal 16 are
Despite having different thermal expansion coefficients from each other, a large warpage does not occur, which is advantageous for device fabrication. Moreover, since the residual stress in the island-shaped crystal 16 is small, crystal defects, which have been a problem in the past, can be significantly reduced, and a high-quality solar cell having excellent electrical characteristics can be obtained. Further, the presence of the island crystals 16 causes the surface to repeat minute projections. Therefore, as shown in FIG. 6, when light irradiation is performed as shown by an arrow, the effect of preventing light reflection is high and the texture treatment is performed. It has the advantage that there is no need to apply.

On the other hand, the second manufacturing method is a method for manufacturing a thin film solar cell, for example, as follows. That is, first, a substrate is prepared similarly to the first manufacturing method, but in this case, an insulating transparent substrate (quartz plate, glass plate, etc.) 20 is prepared as a low-cost substrate (see FIG. 7). Then, a film of ITO, SnO ₂ or the like is formed on the surface of the substrate 20 by a vacuum deposition method, a sputtering method or the like to form the transparent conductive layer 2
Get 1. This transparent conductive layer 21 becomes a surface electrode. The thickness of the transparent conductive layer 21 is set as appropriate,
Usually, it is set to about 500 to 1000Å.

Next, on the transparent conductive layer 21, VC
An N-type semiconductor material (such as Si doped with P as a dopant) is formed into a film by the E method, the CVD method, or the like, and is used as the diffusion layer 22. The thickness of the diffusion layer 22 is appropriately set according to the type of semiconductor material forming the layer.
In the case of i, it is about 0.3 μm. In addition, this diffusion layer 2
2 also serves as a seed crystal for the subsequent film formation.

Next, the first layer is formed on the diffusion layer 22.
In the same manner as in the above manufacturing method, a mask layer 13 having a large number of holes 12 formed at predetermined intervals is formed. Then, similarly to the first manufacturing method, an island-shaped crystal 16 made of a semiconductor material is formed on the mask layer 13 and further formed on the surface thereof.
Al, Ag by vacuum deposition method, screen printing method, etc.
A film such as is formed to obtain the conductive layer 23. This conductive layer 23
Is the back electrode. The thickness of the conductive layer 23 is appropriately set, but is usually about 40 to 100 μm.

The thin film solar cell thus obtained is
Unlike the thin film solar cell obtained by the first manufacturing method,
The back surface side (lower side in FIG. 7) of the insulative transparent substrate 20 serves as a light receiving surface, and the function and effect thereof are the same as those obtained by the first manufacturing method.

Next, an embodiment will be described.

[0025]

[Example 1] Steel substrate (thickness 1 mm x 10 cm
A silicon film having a thickness of 1 μm was formed on the (10 cm) by a sputtering method to obtain a seed crystal layer. The sputtering target used had a boron concentration of 1 × 10 ²⁰ , and the obtained seed crystal had a boron concentration of 5 × 10 ¹⁹ to 1 × 10 ²⁰ . The reason for increasing the boron concentration of the seed crystal is to reduce the contact resistance with the steel substrate.

A mask layer (thickness: 1 μm) was formed on the seed crystal layer by the sol-gel screen printing method described above. The size of the mask openings was 100 μm and the pitch was 200 μm. Then, using tin as a solvent, silicon was crystal-grown from the mask opening by the LPE method. That is, the substrate treated as described above is immersed in a saturated silicon tin solution at 1100 ° C.,
By lowering the temperature at a rate of 1 ° C./min to deposit silicon, an island crystal of silicon was obtained. In the preliminary experiment repeated using the mask layer, the bond between the island-shaped crystals was observed about 70 minutes after the start of the temperature drop. Therefore, in this example, the crystal growth time was set to 60 minutes. The laminated substrate thus obtained had almost no warpage and was negligible.

Then, this laminated substrate was washed by a predetermined method, and a diffusion layer of about 0.3 μm was formed by a thermal diffusion method (diffusion temperature 850 ° C., processing time 30 minutes, diffusion source POCl ₃ ). After that, the oxide film was removed with hydrofluoric acid, and ITO was deposited to a thickness of 500 Å by a sputtering method to form a transparent conductive film. Hereinafter, the intended thin film solar cell was obtained according to a usual method. The thin film solar cell had an energy conversion efficiency of about 9%. When the thin-film solar cell was observed with a scanning electron microscope, pyramid-shaped projections of island crystals were regularly formed on its surface.

[0028]

Example 2 Quartz substrate (thickness 1 mm × 10 cm × 1
An ITO film of about 500 cm was formed by sputtering to form a transparent conductive film. Next, a seed crystal layer and a diffusion layer of about 0.3 μm were formed by the atmospheric pressure CVD method. The P concentration of the diffusion layer was set to about 1 × 10 ²⁰ . Further, the gas is monosilane (Si
H ₄ ) and phosphine (PH ₃ ) for doping.

Next, an oxide film (thickness 3000 Å) to be a mask layer is formed by an oxidation method, and the size is 100 μm and the pitch is 200 μm according to a usual IC etching technique.
m openings were formed. Next, in the same manner as in Example 1 above, an island-shaped silicon crystal was grown by the LPE method,
Then, an aluminum electrode was formed by a screen printing method to obtain a desired thin film solar cell. This thin film solar cell had an energy conversion efficiency of about 10%. When the thin-film solar cell was observed with a scanning electron microscope, pyramid-shaped projections of island crystals were regularly formed on the surface, as in Example 1.

[0030]

As described above, according to the present invention, by growing a crystal, which was conventionally formed as a continuous layer on a substrate, through a mask layer in which a large number of holes are arranged at predetermined intervals,
It is obtained as an island-shaped crystal that rises upward from each hole of the mask layer, and each island-shaped crystal is obtained in a state where it does not come into contact with another adjacent island-shaped crystal.
Therefore, the respective island-shaped crystals exist in a dispersed state as “dots” which are not continuous with the substrate, and the structure easily expands following the thermal expansion of the substrate. Therefore, even if a low-cost substrate is used and the substrate and the crystal film are thermally expanded at different rates at a high temperature, the laminated body does not warp significantly, which is advantageous for device fabrication. Further, since the residual stress in the crystal film is small, crystal defects, which have been a problem in the past, can be significantly reduced, and a high-quality solar cell having excellent electrical characteristics can be obtained. Furthermore, since island-shaped crystals are scattered and minute projections are repeated on the crystal surface, it is possible to suppress light reflection without performing a texturing process. Therefore, the manufacturing cost can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a process explanatory diagram according to an embodiment of the present invention.

FIG. 2 is a process explanatory diagram according to an embodiment of the present invention.

FIG. 3 is a process explanatory diagram according to an embodiment of the present invention.

FIG. 4 is a process explanatory diagram according to an embodiment of the present invention.

FIG. 5 is a process explanatory diagram according to an embodiment of the present invention.

FIG. 6 is a process explanatory diagram according to an embodiment of the present invention.

FIG. 7 is a process explanatory diagram according to another embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a configuration of a conventional, general silicon solar cell.

[Explanation of symbols]

 10 Substrate 11 Seed Crystal Layer 12 Hole 13 Mask Layer 16 Island Crystal 17 Diffusion Layer 18 Transparent Conductive Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Go Matsuda 2-6-6 Chikko Shinmachi, Sakai City, Osaka Prefecture 40 Daido Hokusan Co., Ltd.

Claims (4)

[Claims] 1. A seed crystal layer is formed on a conductive substrate, a mask layer in which a large number of holes are arranged at a predetermined interval is formed on the seed crystal layer, and a hole is formed on each of the holes in the mask layer. Of island-shaped crystals rising in the shape of an island above each other are formed in a state where they do not contact each other, and at least the surface portion of each of the island-shaped crystals is formed in the diffusion layer,
A thin-film solar cell, in which a transparent conductive layer straddling each of the island-shaped crystal diffusion layers is formed thereon. 2. A diffusion layer is formed on an insulating transparent substrate via a transparent conductive layer, a mask layer having a large number of holes arranged at predetermined intervals is formed thereon, and the mask layer is further formed thereon. The island-shaped crystals that grow from inside each hole and rise above the hole and crystallize in an island shape are formed in a state where they do not contact each other, and a conductive layer that extends over each of the island crystals is formed thereon. A thin film solar cell characterized by being formed. 3. A step of forming a seed crystal layer on a conductive substrate, a step of forming a mask layer thereon, a hole having an opening width of 10 to 100 μm, and a distance of 1 from each other in the mask layer.
And a step of forming a large number of crystal films on the mask layer by a liquid phase epitaxy method so as to form island-shaped crystals rising from the inside of the mask layer above the hole. A step of obtaining a state without contact with other island crystals, a step of forming a diffusion layer on at least a surface portion of each island crystal, and a step of forming a conductive layer extending over the diffusion layer of each island crystal. A method of manufacturing a thin-film solar cell, which is characterized by being provided. 4. A step of forming a conductive layer on an insulating transparent substrate, a step of forming a diffusion layer thereon, a step of forming a mask layer thereon, and an opening width of 10 in the mask layer.
~ 100μm holes, the mutual spacing is 100 ~ several 100μ
m, and forming a large number of crystal films on the mask layer by a liquid phase epitaxy method so as to form island-like crystals rising from the inside of the mask layer above the holes to the other islands. A method of manufacturing a thin film solar cell, comprising: a step of obtaining a state without contacting the island-shaped crystal; and a step of forming a conductive layer extending over each of the island-shaped crystals.