JP2000133828A - Thin-film solar cell and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film solar cell together with a method for manufacturing it, wherein a shorting between solar cells or between a thin-film solar cell and a frame is prevented. SOLUTION: A zinc oxide film is formed on a translucent substrate 1, using a first mask where a specified width from the periphery of the substrate is covered, and after the first mask is removed, the zinc oxide film is etched by a specified thickness so that a transparent electrode 2 is formed only in a region which is not covered by the first mask, while uneveness is formed on its surface so that a photoelectric transfer active layer 3 and a rear-surface electrode 4 are sequentially formed on the transparent electrode 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin-film solar cell and a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, the following structures are known for thin-film solar cells. First, a transparent electrode such as SnO ₂ , ITO, or ZnO is formed on an insulating translucent substrate such as glass. A p layer, an i layer and an n layer made of an amorphous semiconductor
By stacking the layers in this order, a photoelectric conversion active layer is formed. Further, a structure is known in which a back electrode made of a metal thin film is laminated thereon. Apart from this structure,
An n layer made of an amorphous semiconductor on a metal substrate also serving as an electrode,
There is also known a structure in which a photoelectric conversion active layer is formed by laminating an i-layer and a p-layer in this order, and a transparent electrode is laminated thereon.

[0003] Of the above structures, the former structure has been developed because a light-transmitting substrate can also serve as a cover glass on the surface of a thin-film solar cell, and a plasma-resistant transparent electrode such as SnO ₂ has been developed. It has been widely used because a photoelectric conversion active layer made of an amorphous semiconductor can be stacked thereon by a plasma CVD method or the like, and is now the mainstream.

As a material of a transparent electrode of a thin-film solar cell,
Although SnO ₂ is common, ZnO has also been used. In addition, a technique has been reported in which the surface of a transparent electrode is made uneven to effectively use light inside the thin-film solar cell (for example, JP-A-6-204527). As a method for realizing a large area, a method of performing integration using a laser and connecting individual solar cells in series is generally adopted. In the structure obtained by this method, a strip-shaped transparent electrode is formed on an insulating translucent substrate such as a glass substrate, and a strip-shaped amorphous semiconductor is formed on the transparent electrode while being shifted from the transparent electrode. It has a structure in which an active layer is formed, and then a strip-shaped back electrode is formed thereon, shifted from the photoelectric conversion active layer.
This thin-film solar cell has a structure in which a plurality of solar cells including a set of transparent electrodes, a photoelectric conversion active layer, and a back electrode are provided, and the transparent electrode of one solar cell is in contact with the back electrode of an adjacent solar cell. have.

[0005]

A problem when integrating thin-film solar cells is that a leak current occurs between the solar cells. This leak current flows through the transparent electrode at the periphery of the portion functioning as a solar cell. For this reason, it has hitherto been necessary to form a trimming line having a width of about 1 mm for completely separating the solar cell and the transparent electrode at the periphery thereof. However, the formation of such a wide trimming line
If a laser is used at the same time as the formation of the solar cell, there is a problem that it takes a very long time. In addition, since it is necessary to scribe in both the X-axis direction and the Y-axis direction to form a trimming line, there is a problem that it takes time to move the laser and find the origin. Further, even if a trimming line is formed, it is difficult to completely prevent a short circuit because the line is not sufficiently thick.

Further, since a transparent electrode is present in the peripheral portion of the substrate, when a module is formed, insulation between the solar cell portion and the frame becomes a problem. Therefore, a module structure in which the metal constituting the frame directly contacts the substrate cannot be adopted. In addition, there has been a problem that insulation failure due to contact between the transparent electrode and the frame at the periphery of the substrate is likely to occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a structure in which a transparent electrode does not exist around the substrate of a thin film solar cell, and has a structure in which the above problem does not occur. And a method for producing the same.

[0008]

According to the present invention, a zinc oxide film is formed on a translucent substrate using a first mask covering a predetermined width from the periphery of the substrate, and the first mask is removed. After the zinc oxide film is etched to a predetermined thickness, a transparent electrode is formed only in a region not covered with the first mask, and irregularities are formed on the surface thereof, and a photoelectric conversion active layer and a back electrode are sequentially formed on the transparent electrode. A method of manufacturing a thin-film solar cell is provided. Further, according to the present invention, there is provided a thin-film solar cell obtained by the above method, comprising a transparent electrode, a photoelectric conversion active layer, and a back electrode on a light-transmitting substrate, wherein the transparent electrode is a predetermined electrode from the periphery of the substrate. A thin-film solar cell is provided which is formed in a region other than the width.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The process by which the present inventors have invented the present invention will be described below. FIG. 2 shows a schematic plan view of a conventional thin-film solar cell. In FIG. 2, 5 is a first scribe line, 6 is a transparent electrode made of SnO ₂ , 8
Is a trimming line.

Conventionally, the reason why the thin film solar cell is electrically separated from the peripheral portion by the trimming line 8 is that SnO ₂ is used as a material of the transparent electrode 6. This trimming line 8 is formed by performing scribe many times with a laser. That is, SnO ₂ is 6
It is formed into a film by normal pressure CVD at a high temperature of about 00 ° C. Therefore, since there is no mask that can withstand the temperature, the peripheral portion where the formation of the transparent electrode 6 is not desired cannot be covered by the mask. In addition, since SnO ₂ is chemically stable, it has been difficult to remove only unnecessary SnO _{2 in the} peripheral portion at low cost by etching.

However, S which has the above-mentioned disadvantages
The reason why nO ₂ was used as a material for the transparent electrode 6 was that
This is because there has been no means for forming minute unevenness equivalent to an electrode made of nO ₂ . That is, since the thin-film solar cell is thin, it is necessary to effectively scatter the light in the film and extend the optical path length of the light in the film in order to sufficiently absorb the incident light. For that reason, it is an important point to improve the efficiency to form minute irregularities on the surface of the transparent electrode.

On the other hand, the inventors of the present invention have developed a technique for forming a transparent electrode having fine irregularities equivalent to that of SnO ₂ over a large area uniformly and at a low temperature in a desired region by using zinc oxide. I found it. Therefore, it has become possible to form a transparent electrode made of ZnO only on the thin-film solar cell portion without forming a transparent electrode on the periphery of the translucent substrate, which has been difficult in the past. Specifically, in the structure of the present invention shown in FIG. 1, since the transparent electrode 2 is not formed in the peripheral portion, a trimming line 8 for separating the thin film solar cell from the peripheral portion as in the conventional structure of FIG. Need not be formed. Therefore, cells can be separated only by scribing with a laser in one direction, and the time required for the laser process can be greatly reduced.

Hereinafter, the present invention will be described. The method for manufacturing a thin-film solar cell of the present invention comprises a step of laminating a transparent electrode, a photoelectric conversion active layer, and a back electrode in this order on a translucent substrate. The light-transmitting substrate is not particularly limited as long as it has a light-transmitting property, and any substrate that can be used in the field can be used. In addition, since the light-transmitting substrate has electrodes formed thereon, it is preferable that at least the electrode formation surface be insulated. In particular, it is preferable to use a transparent and insulating substrate such as glass, quartz, and plastic. However, a conductive substrate can also be used by covering the electrode formation surface with an insulator.

A transparent electrode made of zinc oxide is formed on the transparent substrate. Here, the term “zinc oxide” includes the formula Z
Various compositions of zinc oxide included in n _1-x O _x (0 <X <1) are included. The thickness of the transparent electrode is 500-1200n
It is preferably in the range of m. Further, impurities such as Al and Ga may be doped for lowering the resistance. Of these,
Ga that can lower the resistance is preferable.

For the transparent electrode, a first mask is formed on the periphery of the light-transmitting substrate where formation of the transparent electrode is not desired, a zinc oxide film is formed using the first mask, and after removing the first mask, the zinc oxide is removed. By etching the film to a predetermined thickness, it can be formed only in the region not covered by the first mask. The formation of the zinc oxide film is not particularly limited, but is preferably performed at a temperature as low as possible (about 100 to 200 ° C.). Examples of such a method include a sputtering method, a vacuum evaporation method, an ion plating method, a CVD method, a spray coating method, and the like. Of these, the sputtering method is preferred.

The first mask may be formed on a translucent substrate, or the substrate holder may be used as a mask. By using the substrate holder as the first mask, a zinc oxide film can be formed more easily. Here, the area covered with the first mask varies depending on the size of the substrate, manufacturing equipment, forming method, and the like, but is preferably about 5 to 15 mm from the end of the light-transmitting substrate. Within this range, both the insulation of the peripheral portion of the thin-film solar cell and the power generation efficiency can be favorably compatible.

The first mask preferably has a thickness of 1 μm or less at an inner end of the translucent substrate. With this thickness, the appearance can be deteriorated, and the occurrence of interference fringes in the zinc oxide film that hinders scribing by laser can be prevented. A particularly preferred thickness is 1
０．２0.2 μm. Furthermore, the first mask may have a tapered shape that becomes thinner from the outside to the inside of the light-transmitting substrate. Here, the taper shape is usually 20 to 3
It preferably has a tilt of 0 °.

Further, the zinc oxide film is etched to a predetermined thickness after removing the mask, because a minute unevenness is formed on the zinc oxide film. As a result, light can be scattered inside the solar cell, and the optical path length of the light can be increased, and the short-circuit current can be improved by about 30% as compared with a case where there is no unevenness. Further, since the zinc oxide film easily goes around the periphery of the mask, a thin zinc oxide film is also formed in a portion where the film is not desired to be formed (this phenomenon is called mask blurring). This etching removes the thin zinc oxide film. If a thin-film solar cell is formed without removing it, an output distribution is generated due to mask blurring, and the characteristics are degraded, and a rainbow-colored pattern appears in the peripheral portion, causing a problem in appearance. Here, the predetermined thickness is usually 100
0-2000 °.

In general, when a certain film is formed by a sputtering method using a mask, a thin metal mask (having a thickness of 0.1 to 0.1 mm) is formed in order to prevent the wraparound as described above.
(About 0.5 mm). This metal mask has a problem in accuracy because the larger the size, the more likely it is to bend. In contrast, according to the present invention, a transparent electrode having a desired shape can be formed without using a metal mask.

The etching method is not particularly limited, but a wet etching method is preferred. Specifically, in the case of the wet etching method, it can be performed by immersion in an aqueous solution of acetic acid, hydrochloric acid, or the like. More specifically, for example, when using acetic acid as an etchant,
0.3 to 10 at room temperature. It can be carried out by immersing in a 20% by weight acetic acid aqueous solution for 20 to 180 seconds. When etching is performed under such conditions, unevenness can be formed on the surface of the zinc oxide film. By forming the unevenness, the optical path length of the light incident on the thin-film solar cell can be extended, so that the photoelectric conversion efficiency can be improved. The etching method for forming the irregularities is called a texture etching method.

Next, a photoelectric conversion active layer is formed on the transparent electrode. Here, the photoelectric conversion active layer is made of Si, Ge, S
Semiconductors such as iGe, SiC, SiN, GaAs, and SiSn can be used. Among them, it is preferable to use Si, SiGe or SiC. These semiconductors
It may have any crystal system of amorphous, single crystal, and polycrystal. The photoelectric conversion active layer usually has a two-layer structure of p-type and n-type or a three-layer structure of p-type, i-type and n-type by doping a predetermined impurity. The p-type and the n-type can be formed by doping predetermined impurities. Of these, it is preferable to use a three-layer structure having good conversion efficiency. The thickness of each of the p-type layer, i-type layer and n-type layer is 8 to 15 nm, 25 to 50 nm and 10 to 10 nm.
Preferably it is in the range of 30 nm.

The photoelectric conversion active layer may be a single layer, or may be a laminate of a plurality of photoelectric conversion active layers such as a tandem structure. The method for forming the photoelectric conversion active layer includes:
The method is not particularly limited, and a known method can be used.
For example, sputtering, ion plating,
CVD method and the like can be mentioned.

More specifically, it is preferable that a second mask is formed on a light-transmitting substrate, and the photoelectric conversion active layer is formed using the second mask. Here, as the second mask, it is preferable to use a mask whose opening is slightly larger than that of the first mask (about 5 mm larger in consideration of an error). By using this mask, a photoelectric conversion layer having a size that completely covers the transparent electrode can be formed. This makes it possible to form a structure in which the back electrode and the transparent electrode described below do not short-circuit in the peripheral portion.

When irregularities are formed on the surface of the transparent electrode, irregularities derived from the irregularities are also formed on the surface of the photoelectric conversion active layer. A back electrode is formed on the photoelectric conversion active layer. Here, it is preferable to use a metal having a relatively high reflectivity, such as Al or Ag, for the back electrode. The thickness of the back electrode is preferably in the range of 100 nm to 1 μm.

The method for forming the back electrode is not particularly limited.
Any of the known methods can be used. For example,
Sputtering method, ion plating method, CVD
Method, vapor deposition method and the like. Further, a transparent conductive film may be formed between the back electrode and the photoelectric conversion active layer in order to effectively use the light reflected on the back electrode. The thickness of the transparent conductive film is preferably in the range of 40 to 100 nm.

Here, the thin-film solar cell may be composed of a plurality of solar cells. As a method of forming a plurality of solar cells, for example, the following method is given.
First, the transparent electrode formed on the translucent substrate by the above method is divided into grooves having a desired shape by means of a laser or the like. The groove dividing the transparent electrode is called a first scribe line.

Next, a photoelectric conversion active layer is formed on the transparent electrodes. At this time, since the first scribe lines are also filled with the material of the photoelectric conversion active layer, insulation between the transparent electrodes can be ensured. . Next, the photoelectric conversion active layer is divided by forming a groove into a desired shape by means such as a laser. The groove dividing the photoelectric conversion active layer is also referred to as a second scribe line. It is preferable that the second scribe line partially overlaps with the first scribe line and is formed in parallel.

Further, a back electrode is formed on the photoelectric conversion active layer. At this time, since the second scribe line is also filled with the material of the back electrode, it is electrically connected to the transparent electrode of the adjacent solar cell. be able to. Thereafter, the solar cell can be formed by dividing the back electrode into a desired shape by forming a groove by means such as a laser. The groove dividing the back electrode is also referred to as a third scribe line. This third scribe line is
It is preferable that the scribe line does not overlap and is formed in parallel.

[0029]

An embodiment of the present invention will be described below with reference to FIG. First, a glass substrate (substrate size: 650 × 455 mm) was used as the insulating translucent substrate 1. On this, a transparent electrode 2 was formed with a thickness of 800 nm. The transparent electrode 2 used ZnO as its material. The transparent electrode 2 was formed by a sputtering method, and the film forming conditions were a substrate temperature of 150 ° C., an argon pressure of 2.3 Pa, and a power density of 2.5 W / cm ² .

At this time, sputtering is performed by using a substrate holder 7 which also serves as a mask for covering the peripheral portion of the substrate, as shown in FIG. 3, so that the transparent electrode 2 is not formed at a peripheral portion of about 1 cm as shown in FIG. Done. The substrate holder 7 has a thickness of 0.2 to 0.1 mm at the inner end of the translucent substrate.
A tapered shape having a thickness of 3 μm and a thin taper inward from a peripheral portion having an inclination of 20 to 30 ° was used.

Next, the transparent electrode 2 was patterned as described below. Transparent electrode 2 after patterning
Was formed into a plurality of strips by the first scribe line 5. The patterning was performed by scribing in only one direction using a laser as shown in FIG. The width of the strip was set to 1 cm or less in consideration of the resistance loss due to the sheet resistance of zinc oxide.

After this patterning, the substrate is immersed in a 0.5% by weight acetic acid aqueous solution (etching solution) maintained at a liquid temperature of 25 ° C. and allowed to stand for 210 seconds, thereby forming irregularities on the surface of the transparent electrode and masking. The thin zinc oxide film due to the blur was removed. Thereafter, the etching solution was washed away by washing the substrate with pure water. Next, a-S, which is an amorphous semiconductor, is formed on the transparent electrode 2 as the photoelectric conversion active layer 3.
i: H = p layer, a-Si: H = i layer and a-Si: H =
The n layers were sequentially laminated. The thickness of the p-layer was 10 nm, the thickness of the i-layer was 300 nm, and the thickness of the n-layer was 25 nm. At this time, the surface area for forming the photoelectric conversion active layer 3 was formed to be about 5 mm larger than the area for forming the transparent electrode 2 as shown in FIG.
The formation of the photoelectric conversion active layer 3 filled the first scribe line 5 with an amorphous semiconductor.

Thereafter, a second scribe line 5 a was formed on the photoelectric conversion active layer 3 in the same manner as the formation of the first scribe line 5. This second scribe line 5a
It was formed in the same direction as the first scribe line 5 so as not to overlap. Next, a back electrode 4 was formed on the photoelectric conversion active layer 3 to a thickness of 500 nm. Ag, which is a metal having a relatively high reflectance, was used for the back electrode 4. The second scribe line 5a is formed by the formation of the back surface electrode.
And electrically connected to the adjacent transparent electrode 2.

Next, a thin film solar cell was obtained by forming a third scribe line 5b on the back electrode 4 in the same manner as the first scribe line 5. Note that the third scribe line 5b is 100
It was formed with a width of about 40 μm at a place separated by about μm. The obtained thin-film solar cell had an AM of 1.5 (100 mW / cm
^{In 2} ), Isc: 0.527 A, Voc: 65.8
V, F.C. F. : 0.73, Pmax: 25.3W.

[0035]

According to the method for manufacturing a thin film solar cell of the present invention, when a transparent electrode made of zinc oxide is formed on a transparent substrate for forming a thin film solar cell, a zinc oxide film is formed around the substrate. By covering with a mask such as a substrate holder so as not to be performed, a configuration in which a leak current does not flow between individual solar cells can be formed. With this configuration, the number of laser scribing steps is reduced, and the processing time can be reduced.

Further, by forming the photoelectric conversion active layer one size larger than zinc oxide, a short circuit due to contact between the back electrode and the transparent electrode can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a schematic plan view when a transparent electrode is formed by a manufacturing method of the present invention.

FIG. 2 is a schematic plan view when a transparent electrode is formed by a conventional manufacturing method.

FIG. 3 is a schematic plan view when a translucent substrate is set on a substrate holder in the manufacturing method of the present invention.

FIG. 4 is a schematic plan view when a photoelectric conversion active layer is formed by the manufacturing method of the present invention.

FIG. 5 is a schematic perspective view of a thin-film solar cell of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 translucent substrate 2, 6 transparent electrode 3 photoelectric conversion active layer 4 back electrode 5 first scribe line 5 a second scribe line 5 b third scribe line 7 substrate holder 8 trimming line

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F051 AA05 BA11 CB27 FA02 FA13 FA16 FA19 GA03 GA05 5H032 AA06 AS16 BB00 BB05 EE02 EE07 HH06

Claims (6)

[Claims] 1. A method of forming a zinc oxide film on a light-transmitting substrate using a first mask covering a predetermined width from the periphery of the substrate, and etching the zinc oxide film to a predetermined thickness after removing the first mask. Forming a transparent electrode only in a region not covered by the first mask, forming irregularities on the surface thereof, and sequentially forming a photoelectric conversion active layer and a back electrode on the transparent electrode. Production method. 2. The method according to claim 1, wherein the substrate is placed on a substrate holder when the transparent electrode is formed, and the substrate holder also serves as the first mask. 3. The method according to claim 1, wherein the photoelectric conversion active layer is formed after being covered with a second mask having an opening larger than the first mask. 4. The method according to claim 3, wherein the substrate is placed on a substrate holder when the photoelectric conversion active layer is formed, and the substrate holder also serves as the second mask. 5. The method according to claim 1, wherein the transparent electrode is formed by a sputtering method under a temperature condition of 100 to 200 ° C. 6. A thin-film solar cell obtained by the method according to any one of claims 1 to 5, comprising a transparent electrode, a photoelectric conversion active layer, and a back electrode on a light-transmitting substrate, wherein the transparent electrode is the substrate. Characterized by being formed in a region other than a predetermined width from the periphery of the thin film solar cell.