JP3619681B2 - Solar cell and manufacturing method thereof - Google Patents

Description

【００３２】
同表から明らかに、本発明太陽電池の方が集電極の抵抗値が減少したためにＦ．Ｆ．（曲線因子）が向上し、高い光電変換効率が得られた。
【００３３】
以上の如く、本発明によれば光電変換特性が良好で、量産性の良い太陽電池を提供できる。
【００３４】
尚、以上の実施の形態においてはアモルファス太陽電池について説明したが、本発明はこれに限らず非晶質半導体層上に形成された透明導電層及び櫛形状の集電極を有する太陽電池であれば如何なる構造の太陽電池に対しても適用することができる。この例としては、例えば、ｎ型（ｐ型）の結晶シリコン或いは多結晶シリコン基板とｐ型（ｎ型）の非晶質半導体層とからなる半導体接合を備え、ｐ型（ｎ型）の非晶質半導体層上に透明導電層を介して集電極を備えた構造の太陽電池がある。
【００３５】
図３は斯かる本発明の別の実施形態に係る太陽電池の素子構造断面図であり、ｎ型の結晶系シリコン基板１０の一主面上に厚さ１００Å程度のｉ型の非晶質シリコン層１１を介してｐ型の非晶質シリコン層１２が形成されており、このｐ型の非晶質シリコン層１２上に透明導電層１３及び集電極１４が積層されている。
【００３６】
また、結晶系シリコン基板１０の他の主面上には厚さ１００Å程度のｉ型の非晶質シリコン層１１を介してｎ型の非晶質シリコン層１５が形成されており、このｎ型の非晶質シリコン層１５上に透明導電層１３及び集電極１４が積層されている。
【００３７】
斯かる構成の太陽電池においても、透明電極層１３の集電極１４と接する表面部分に、他の表面部分よりも抵抗の小さい低抵抗領域１６を備えることで、同様の効果を奏する。
【００３８】
尚、本実施の形態にあっては結晶系シリコン基板１０の両主面上に非晶質半導体層１２，１５、透明導電層１３及び集電極１４を備えた構造となっているが、これに限らずどちらか一方の主面上にのみ非晶質半導体層、透明導電層及び集電極を備えた構造の太陽電池についても本発明を適用できるのは言うまでもない。
【００３９】
また、本発明に係る透明導電層は、ＺｎＯから構成することが好ましい。即ち、ＺｎＯは膜中の酸素量を微量に変化させるだけでそのシート抵抗を５０〜１２０ｋΩ／□以上にまで大幅に変化させることができる。従って、低抵抗領域と他の表面部分との間の抵抗の差を大きくできるので、電界メッキを用いて集電極を形成する際の選択性が向上し、より微細なパターンを有する集電極を形成することが可能となる。このため、太陽電池の有効面積が増大し、光電変換効率の向上した太陽電池が得られる。
【００４０】
【発明の効果】
以上説明した如く、本発明によれば、透明導電層の集電極と接する表面部分に、他の表面部分よりも抵抗の小さい低抵抗領域を備えるので、抵抗の小さい電界メッキによる集電極を使用することができる。この結果、量産性に優れ、光電変換特性の向上した太陽電池を提供できる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る太陽電池の素子構造断面図である。
【図２】本発明の他の実施形態に係る太陽電池の素子構造断面図である。
【図３】本発明の別の実施形態に係る太陽電池の素子構造断面図である。
【図４】従来の太陽電池の素子構造断面図である。
【符号の説明】
１…基板、２…裏面電極、３…アモルファス半導体層、４…透明導電層、
５…集電極、６…低抵抗領域[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar cell with good characteristics and a method for manufacturing the solar cell, and particularly relates to a structure and a method for manufacturing a surface-side collector electrode.
[0002]
[Prior art]
Solar cells capable of directly converting sunlight into electrical energy are expected as an alternative energy source for petroleum. Examples of solar cell types include single crystal silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon solar cells. In the case of single crystal silicon, the production cost is high because a high-temperature process of 1000 ° C. or higher is used. high. In addition, since single crystal silicon or polycrystalline silicon is an indirect transition type, the light absorption coefficient is small, and a film thickness of at least several hundred μm or more is required to absorb incident sunlight, which increases the material cost. In contrast, an amorphous semiconductor material typified by amorphous silicon can be manufactured by a low-temperature process of about 200 ° C., and since it is a direct transition type, the required film thickness can be as small as several thousand mm, which reduces the cost. It is expected as a solar cell material.
[0003]
As the structure of an amorphous solar cell using such an amorphous semiconductor material, as shown in the element structure cross-sectional view of FIG. 4, Ag or Ag is formed on a substrate 1 having an insulating surface such as plastic or a stainless plate coated with an insulating surface. A structure having a back electrode 2 made of a metal such as Al, an amorphous semiconductor layer 3 having a pin junction inside, a transparent conductive layer 4 made of ITO, and a comb-shaped collector electrode 5 made of Ag is known.
[0004]
In the amorphous solar cell having such a structure, in order to increase the efficiency, the area of the collecting electrode 5 serving as an ineffective portion is reduced by using a material having a small specific resistance such as Ag or copper. For example, the specific resistance of silver is 1.62 × 10 ⁻⁶ Ωcm, and the specific resistance of copper is 1.72 × 10 ⁻⁶ Ωcm, while that of aluminum is 2.75 × 10 ⁻⁶ Ωcm, zinc Then, it is 5.9 × 10 ⁻⁶ Ωcm.
[0005]
As a method for forming these collector electrodes, methods such as vapor deposition, plating, and printing are used in the case of a conventional crystalline solar cell. Among them, the vapor deposition method can deposit high-quality metals and have good ohmic contact with semiconductors, but the deposition rate is low, the throughput is low due to the use of a vacuum process, and a specific pattern is formed. Have problems such as the need for masking.
[0006]
In the case of plating, electroless plating of Ni is generally performed, but there are problems that it is easy to peel off and a mask is required.
[0007]
The printing method has the characteristics that it is most easily automated and has high mass productivity, and a method of performing screen printing of Ag paste, sintering at high temperature, and contacting is performed. In addition, in order to lower the resistance, it is also considered to perform plating or solder coating on the printed electrode.
[0008]
[Problems to be solved by the invention]
In the case of an amorphous solar cell, any of the above-mentioned methods has been studied, but practically, the printing method is excellent in mass productivity and put into practical use. However, in the case of an amorphous solar cell, problems such as diffusion of conductive impurities in the p and n layers occur at high temperatures, so that it cannot be sintered like a crystalline solar cell, resulting in a highly resistive electrode. . That is, since the conductive paste of silver contains a polymer resin as a binder, the specific resistance is about 4 × 10 ⁻⁵ Ωcm, which is one digit higher than that of pure silver. Therefore, in order to reduce the resistance without changing the area of the collecting electrode, it is desirable to increase the thickness of the electrode. However, if the thickness is to be increased, it is necessary to increase the viscosity of the conductive paste, and the screen is clogged. For this reason, the thickness of the electrode practically produced by screen printing is 10 μm to 20 μm. Therefore, the collector electrode produced by screen printing has to be wide in order to reduce the resistance, and thus the loss of the effective area is large.
[0009]
Also, the plating method can be used in the same manner as the crystal system, and for example, a method of forming an electrode on the transparent conductive layer of a solar cell by a plating method is disclosed (Japanese Patent Laid-Open No. 60-66426).
[0010]
However, in this method, it is necessary to provide a resist patterning film in order to prevent plating on portions other than the collector electrode, and it is necessary to remove the resist film after forming the collector electrode, which makes the manufacturing process complicated. is there.
[0011]
An object of the present invention is to solve the above-described problems in a solar cell using an amorphous semiconductor and to provide a solar cell with good mass productivity and photoelectric conversion characteristics.
[0012]
[Means for Solving the Problems]
In order to solve such a problem, the solar cell of the present invention is a solar cell including a transparent conductive layer and a collector electrode on an amorphous semiconductor layer, and on the surface portion of the transparent conductive layer in contact with the collector electrode, It has a low resistance region whose resistance is smaller than that of the other surface portion, and the other surface portion has a resistance higher than that of the inner region of the transparent conductive layer.
[0013]
In addition, the manufacturing method of the present invention includes a step of forming a transparent conductive layer on an amorphous semiconductor layer, and lowering a resistance of a surface portion corresponding to a region where the collector electrode of the transparent conductive layer is formed, thereby forming a low resistance region. Forming the collector electrode on the low-resistance region, and forming the collector electrode by an electroplating method.
[0014]
Alternatively, the step of forming a transparent conductive layer on the amorphous semiconductor layer and the surface portion other than the surface portion on which the collector electrode of the transparent conductive layer is formed have high resistance, and the surface portion is changed to another surface. And a step of forming a collector electrode on the low resistance region, wherein the collector electrode is formed by electroplating. Features.
[0015]
Furthermore, a step of forming a low-resistance first transparent conductive layer on the amorphous semiconductor layer, and a step of forming a high-resistance second transparent conductive layer on the first transparent conductive layer; Reducing the resistance of the surface portion corresponding to the region where the collector electrode of the second transparent conductive layer is formed to form a low resistance region; and forming the collector electrode on the low resistance region. The collector electrode is formed by an electroplating method.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a sectional view of an element structure showing the structure of a solar cell according to the first embodiment of the present invention. In the figure, parts having the same functions as those in FIG.
[0017]
The solar cell of the present embodiment is different from the conventional solar cell shown in FIG. 4 in that a low resistance region 6 having a resistance smaller than that of other surface portions is formed on at least a surface portion of the transparent conductive layer 4 in contact with the collector electrode 5. It is in the point prepared.
[0018]
According to such a configuration, there is a resistance difference between the surface portion of the transparent conductive layer 4 in contact with the collector electrode 5 and the other surface portion. The collector electrode 5 can be formed by depositing a plating metal and electrolytic plating. This eliminates the need for a resist pattern formation and removal process as in the prior art, and is excellent in mass productivity. Furthermore, since a low-resistance collector electrode is obtained by using electroplating, the photoelectric conversion characteristics are improved by reducing the resistance component of the collector electrode. The low resistance region 6 may be provided not only on the surface portion of the transparent conductive layer 4 as described above, but also in the region up to the amorphous semiconductor layer 3, but at least the surface portion includes the low resistance region 6. Then, the collector electrode 5 can be formed by electroplating.
[0019]
As described above, when the low resistance region 6 is formed on the surface portion of the transparent conductive layer 4 in contact with the collector electrode 5, the composition of the transparent conductive layer on the surface portion may be controlled. That is, a conductive oxide having translucency such as ITO, ZnO, SnO ₂ used as a transparent conductive layer for solar cells has its electrical and optical characteristics adjusted by adjusting the oxygen content. Can be controlled. Specifically, both the resistivity and light transmittance can be increased by increasing the oxygen content, and both the resistance and light transmittance can be decreased by decreasing the oxygen content. Can do.
[0020]
Therefore, after the transparent conductive layer 4 is formed, only the surface portion in contact with the collecting electrode 5 is reduced to reduce the amount of oxygen, thereby making this surface portion a low resistance region having a smaller resistance than the other surface portions. . For this purpose, it is sufficient to irradiate only a predetermined surface portion in a hydrogen atmosphere and selectively reduce the laser beam. Alternatively, only the surface portion may be exposed using a mask, and the surface portion may be selectively reduced by being exposed to hydrogen plasma in this state. The surface portion of the transparent conductive layer reduced as described above has a reduced light transmittance as described above, but this portion exists directly under the collecting electrode 5 and originally has no incident light. Since it is an invalid area, no particular problem occurs.
[0021]
Alternatively, after the formation of the transparent conductive layer 4, the surface portion other than the surface portion in contact with the collector electrode is oxidized to increase the amount of oxygen, thereby increasing the resistance compared to the internal region, thereby changing the surface portion in contact with the collector electrode. It can be set as a low resistance area | region where resistance is smaller than the surface part. For this purpose, a mask is provided so that only the other surface portions described above are exposed, and a method of selectively oxidizing by exposure to oxygen plasma, or similarly using a mask, irradiating ultraviolet rays in an oxygen or ozone atmosphere, A selective oxidation method can be used. In particular, in the method of irradiating ultraviolet rays in an ozone atmosphere, ozone becomes atomic oxygen having a strong oxidizing action when irradiated with ultraviolet rays, so that the oxidation effect of the transparent conductive layer is enhanced. Since the light transmittance of the other surface portion of the transparent conductive layer oxidized as described above increases as described above, the amount of light incident on the amorphous semiconductor layer can also be increased. It becomes possible to further improve the conversion characteristics. In this case, the photogenerated carriers generated in the amorphous semiconductor layer 3 are collected by the collector electrode 5 via the inner region of the transparent conductive layer 4 and the low resistance region 6, thereby increasing the resistance. It is necessary to limit the portion to be applied to the surface portion as described above, and the resistance of the inner region of the transparent conductive layer 4 needs to be kept low.
[0022]
Furthermore, in the former method in which a predetermined surface portion of the transparent conductive layer is selectively reduced in resistance to form a low resistance region, other surface portions originally have low resistivity, so that plating is performed during electroplating. Metals can also deposit on other surface portions.
[0023]
On the other hand, according to the latter method of selectively increasing the resistance of the other surface portion of the transparent conductive layer 4, the resistivity of the other surface portion can be extremely increased. Can also be suppressed.
[0024]
In addition, as shown in FIG. 2, the transparent conductive layer 4 is composed of a low-resistance first transparent conductive layer 4A on the amorphous semiconductor layer 3 side and a high-resistance second transparent conductive layer 4B on the collector electrode side. Then, the portion of the second transparent conductive layer 4B where the collector electrode 5 is formed may be selectively reduced to a depth reaching the first transparent conductive layer 4A to form the low resistance region 6. In this case, since the light transmittance of the second conductive layer 4B is increased, the amount of light incident on the amorphous semiconductor layer can be increased, and the photoelectric conversion efficiency of the solar cell can be further improved. . In the case of the present embodiment, when the low resistance region 6 is provided only on the surface portion of the second transparent conductive layer 4B, the second transparent conductive layer 4B has a high resistance, so that the inner region generates light. Since the resistance component is increased when carriers are collected, the low resistance region 6 needs to be provided up to the region reaching the first transparent conductive layer 4A as described above.
(Example)
As an example of the present invention, a solar cell having the structure shown in FIG. 1 was manufactured through the following steps.
[0025]
First, a back electrode 2 made of Ag having a thickness of about 1 μm is formed on a stainless steel substrate 1 whose surface is insulation-coated with SiO ₂ by sputtering, and thickened by plasma CVD on the back electrode 2. An amorphous semiconductor layer 3 was formed by sequentially stacking an n-type a-Si layer having a thickness of about 200 mm, an i-type a-Si layer having a thickness of about 3000 mm, and a p-type a-SiC layer having a thickness of about 100 mm.
[0026]
Next, a transparent conductive layer 4 made of ZnO having a thickness of about 700 mm was formed on the amorphous semiconductor layer 3 by sputtering using a ZnO target doped with 5% Al. Sputtering was performed in an Ar atmosphere at a temperature of 150 ° C., an RF power of 20 mW / cm ² , and 4 × 10 ⁻³ Torr, and a transparent conductive layer 4 having a sheet resistance of 50 to 80Ω / □ was obtained.
[0027]
Next, the other surface portion of the transparent conductive layer 4 except the surface portion corresponding to the portion where the collector electrode 5 is formed was selectively exposed to oxygen plasma using a mask to be oxidized. The sheet resistance of the portion subjected to the oxidation treatment was 120 kΩ / □.
[0028]
As described above, a low resistance region having a smaller resistance than other surface portions was formed on the surface portion of the transparent conductive layer 4 on which the collecting electrode 5 is formed.
[0029]
Thereafter, electroplating was performed in a plating bath using a mixed solution of nickel sulfate, nickel chloride and boric acid to form a collector electrode 5 made of Ni having a thickness of about 10 μm in 15 minutes.
[0030]
The photoelectric conversion characteristics of the solar cell of the present invention produced as described above and the conventional solar cell in which the collector electrode was formed by the screen printing method were measured. The results are shown in Table 2.
[0031]
[Table 1]

[0032]
As apparent from the table, the solar cell of the present invention has a lower resistance value of the collector electrode, so F. (Curve factor) was improved, and high photoelectric conversion efficiency was obtained.
[0033]
As described above, according to the present invention, it is possible to provide a solar cell with good photoelectric conversion characteristics and good mass productivity.
[0034]
In addition, although the amorphous solar cell was demonstrated in the above embodiment, this invention is not restricted to this, If it is a solar cell which has the transparent conductive layer and comb-shaped collector electrode which were formed on the amorphous semiconductor layer The present invention can be applied to a solar cell having any structure. As this example, for example, a semiconductor junction comprising an n-type (p-type) crystalline silicon or polycrystalline silicon substrate and a p-type (n-type) amorphous semiconductor layer is provided, and a p-type (n-type) non-layer is provided. There is a solar cell having a structure in which a collector electrode is provided on a crystalline semiconductor layer via a transparent conductive layer.
[0035]
FIG. 3 is a cross-sectional view of the element structure of a solar cell according to another embodiment of the present invention, and an i-type amorphous silicon having a thickness of about 100 mm on one main surface of an n-type crystalline silicon substrate 10. A p-type amorphous silicon layer 12 is formed through the layer 11, and a transparent conductive layer 13 and a collector electrode 14 are laminated on the p-type amorphous silicon layer 12.
[0036]
An n-type amorphous silicon layer 15 is formed on the other main surface of the crystalline silicon substrate 10 via an i-type amorphous silicon layer 11 having a thickness of about 100 mm. A transparent conductive layer 13 and a collector electrode 14 are laminated on the amorphous silicon layer 15.
[0037]
Also in the solar cell having such a configuration, the same effect can be obtained by providing the low resistance region 16 having a smaller resistance than the other surface portion on the surface portion in contact with the collecting electrode 14 of the transparent electrode layer 13.
[0038]
In the present embodiment, the amorphous semiconductor layers 12 and 15, the transparent conductive layer 13, and the collector electrode 14 are provided on both main surfaces of the crystalline silicon substrate 10. Needless to say, the present invention can also be applied to a solar cell having a structure including an amorphous semiconductor layer, a transparent conductive layer, and a collector electrode only on one of the principal surfaces.
[0039]
The transparent conductive layer according to the present invention is preferably composed of ZnO. That is, ZnO can significantly change the sheet resistance to 50 to 120 kΩ / □ or more simply by changing the amount of oxygen in the film to a small amount. Therefore, since the difference in resistance between the low resistance region and the other surface portion can be increased, the selectivity when forming the collector electrode using electroplating is improved, and a collector electrode having a finer pattern is formed. It becomes possible to do. For this reason, the effective area of a solar cell increases and the solar cell with improved photoelectric conversion efficiency is obtained.
[0040]
【The invention's effect】
As described above, according to the present invention, the surface portion in contact with the collector electrode of the transparent conductive layer is provided with the low resistance region having a smaller resistance than the other surface portions, so that the collector electrode by electric field plating having a low resistance is used. be able to. As a result, it is possible to provide a solar cell having excellent mass productivity and improved photoelectric conversion characteristics.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an element structure of a solar cell according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of an element structure of a solar cell according to another embodiment of the present invention.
FIG. 3 is a cross-sectional view of an element structure of a solar cell according to another embodiment of the present invention.
FIG. 4 is a cross-sectional view of an element structure of a conventional solar cell.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Back electrode, 3 ... Amorphous semiconductor layer, 4 ... Transparent conductive layer,
5 ... collector electrode, 6 ... low resistance region

Claims (8)

A solar cell comprising a transparent conductive layer and a collector electrode on an amorphous semiconductor layer,
The solar cell according to claim 1, wherein the transparent conductive layer has a low resistance region having a lower resistance than other surface portions at a surface portion in contact with the collector electrode. The solar cell according to claim 1, wherein the other surface portion has a higher resistance than an inner region of the transparent conductive layer. Forming a transparent conductive layer on the amorphous semiconductor layer;
Forming a low resistance region by reducing the resistance of the surface portion corresponding to the region where the collector electrode of the transparent conductive layer is formed;
Forming a collector electrode on the low resistance region;
A method for producing a solar cell, comprising: The method of manufacturing a solar cell according to claim 3, wherein the collector electrode is formed by an electroplating method. Forming a transparent conductive layer on the amorphous semiconductor layer;
Increasing the resistance of other surface portions other than the surface portion on which the collector electrode of the transparent conductive layer is formed, and making the surface portion a low resistance region having a smaller resistance than the other surface portions;
Forming a collector electrode on the low resistance region;
A method for producing a solar cell, comprising: 6. The method of manufacturing a solar cell according to claim 5, wherein the collector electrode is formed by an electroplating method. Forming a low-resistance first transparent conductive layer on the amorphous semiconductor layer;
Forming a high resistance second transparent conductive layer on the first transparent conductive layer;
Forming a low resistance region by reducing the resistance of the surface portion corresponding to the region where the collector electrode of the second transparent conductive layer is formed;
Forming a collector electrode on the low resistance region;
A method for producing a solar cell, comprising: The method of manufacturing a solar cell according to claim 7, wherein the collector electrode is formed by an electroplating method.

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