This nonprovisional application is based on Japanese Patent Application No. 2005-155980 filed with the Japan Patent Office on May 27, 2005, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to methods of fabricating thin-film solar cell, and such thin-film solar cell, and particularly to methods of fabricating thin-film solar cell capable of reducing a leak current at a perimeter thereof, and such thin-film solar cell.
2. Description of the Background Art
Various types of solar cell converting the energy of sunlight directly to electrical energy have been practically used. Among others, a thin-film solar cell that employs thin amorphous silicon film is actively being developed as it is readily processed at low temperature and increased in area to have a large area and can hence be fabricated inexpensively.
Thin-film solar cell 1 is fabricated for example as follows: Initially on transparent insulator substrate 2 transparent electrode layer 3 is deposited and thereafter laser-scribed to remove a portion of transparent electrode layer 3 to form the first isolation groove 6 to divide transparent electrode layer 3 into a plurality of such layers isolated. Subsequently, on transparent electrode layer 3 divided into the plurality of such layers isolated, plasma CVD is employed to deposit in order a p layer, an i layer and an n layer of thin amorphous silicon film to form photoelectric conversion semiconductor layer 4. Then photoelectric conversion semiconductor layer 4 is laser-scribed to remove a portion of photoelectric conversion semiconductor layer 4 to form contact line 7 to divide photoelectric conversion semiconductor layer 4 into a plurality of such layers isolated. Subsequently, back surface electrode layer 5 is deposited to fill contact line 7 and also cover photoelectric conversion semiconductor layer 4. Finally, photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 are laser-scribed to form the second isolation groove 8 dividing photoelectric conversion semiconductor layer 4 into a plurality of such layers isolated and back surface electrode layer 5 into a plurality of such layers isolated. Thin-film solar cell 1 shown in
If the trimming method with a conventional laser scribing method is adopted, however, a portion of the transparent electrode layer volatilized by the irradiation of the fundamental harmonic of the YAG laser light adheres on a vertical cross section of the photoelectric conversion semiconductor layer. This forms a leak path between the transparent electrode layer and the back surface electrode layer, and the leak path passes a leak current resulting in the thin-film solar cell having reduced conversion efficiency.
Accordingly, the purpose of the present invention is to provide a method of fabricating a thin-film solar cell capable of reducing a leak current caused at a perimeter of the thin-film solar cell, and such thin-film solar cell.
The present invention provides a method of fabricating a thin-film solar cell including a transparent electrode layer, a photoelectric conversion semiconductor layer and a back surface electrode layer deposited on a transparent insulator substrate in this order, and the method includes the steps of: irradiating a first laser light from a side of the transparent insulator substrate to remove the photoelectric conversion semiconductor layer and the back surface electrode layer at a region irradiated with the first laser light; and irradiating a second laser light from the side of the transparent insulator substrate to remove the transparent electrode layer, the photoelectric conversion semiconductor layer and the back surface electrode layer at a region outer than the region irradiated with the first laser light.
In the present method of fabricating the thin-film solar cell the first laser light can be a second harmonic of YAG laser light.
Furthermore in the present method of fabricating the thin-film solar cell the second laser light can be a fundamental harmonic of YAG laser light.
Furthermore the present invention provides a thin-film solar cell including a transparent electrode layer, a photoelectric conversion semiconductor layer and a back surface electrode layer deposited on a transparent insulator substrate in this order, wherein the thin-film solar cell has a perimeter with the transparent electrode layer protruding outer than the photoelectric conversion semiconductor layer and the back surface electrode layer.
In the present thin-film solar cell preferably the transparent electrode layer protrudes by a length of at least 100 μm and at most 1000 μm.
Thus the present invention can provide a method of fabricating a thin-film solar cell capable of reducing a leak current caused at a perimeter of the thin-film solar cell, and such thin-film solar cell.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
Hereinafter an embodiment of the present invention will be described. Note that in the figures, identical reference characters denote identical or like components.
FIGS. 1(a)-1(h) are schematic cross sections illustrating one preferred example of a method of fabricating a thin-film solar cell in accordance with the present invention. Initially, as shown in
Then, as shown in
Then, as shown in
Herein, the thin amorphous silicon film can be thin-film formed of a hydrogenated amorphous silicon-based semiconductor (a-Si: H) having a dangling bond of silicon terminated by hydrogen, and the thin microcrystalline silicon film can be implemented by thin-film formed of a hydrogenated, microcrystalline silicon-based semiconductor (μc-Si: H) having a dangling bond of silicon terminated by hydrogen.
Furthermore, photoelectric conversion semiconductor layer 4 can have a thickness for example of at least 100 nm and at most 600 nm.
Furthermore, the technique employed to deposit photoelectric conversion semiconductor layer 4 employed in the present invention is not limited to a particular technique. For example, photoelectric conversion semiconductor layer 4 can be deposited by plasma-CVD.
Then, as shown in
Then, as shown in
While back surface electrode layer 5 may be formed of a single or plurality of layers of thin metallic film alone, introducing the transparent conductive film between the single or plurality of layers of thin metallic film and photoelectric conversion semiconductor layer 4 is preferable as such can prevent metal atoms from diffusing from the thin metallic film into photoelectric conversion semiconductor layer 4 and also provide a tendency to increase the sunlight reflectance of the thin metallic film. Furthermore, the technique employed to deposit back surface electrode layer 5 is not limited to a particular technique. For example, back surface electrode layer 5 can be sputtered.
Then, as shown in
Then, a first laser light is irradiated from a side of transparent insulator substrate 2 so that a portion of photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 that is irradiated by the first laser light is volatilized and thus removed to form a removed portion 9. Herein, the first laser light can be implemented for example by a second harmonic of YAG laser light (wavelength: 532 nm). The second harmonic of YAG laser light has a tendency to be transmitted through transparent insulator substrate 2 and transparent electrode layer 3 and absorbed into photoelectric conversion semiconductor layer 4. As such, if the second harmonic of YAG laser light is employed as the first laser light, photoelectric conversion semiconductor layer 4 can selectively be heated, and by the heat, photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 adjacent thereto can be volatilized. Note that the second harmonic of YAG laser light preferably has an intensity that does not damage transparent electrode layer 3.
Note that in the present invention the YAG laser refers to an Nd: YAG laser, and the Nd: YAG laser is formed of yttrium aluminum garnet (Y3Al5O12) crystal including neodymium ion (Nd3+). The YAG laser oscillates a fundamental harmonic of YAG laser light (wavelength: 1064 nm), and that wavelength is halved to obtain the second harmonic of YAG laser light (wavelength: 532 nm).
Finally, from a side of transparent insulator substrate 2, a second laser light is irradiated at a region outer than that irradiated with the first laser light, and, as shown in
Thus, in accordance with the present invention, at a region irradiated with the first laser light, transparent electrode layer 3 can remain unremoved and photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 alone can be removed. Thus, as shown in
The thus fabricated, present thin-film solar cell includes transparent electrode layer 3, photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 deposited on transparent insulator substrate 2 in this order, and the thin-film solar cell at a perimeter thereof has transparent electrode 3 protruding outer than photoelectric conversion semiconductor layer 4 and back surface electrode layer 5.
Herein, with reference to
Initially, as shown in
Then, a fundamental harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 to laser-scribe and thus remove a portion of transparent conductive layer 3 in a strip to form, as shown in
Then, plasma CVD was employed to deposit a p layer formed of a boron-doped, hydrogenated amorphous silicon-based semiconductor (a-Si: H), then an i layer formed of an undoped, hydrogenated amorphous silicon-based semiconductor (a-Si: H), and then an n layer formed of a phosphorus-doped, hydrogenated, microcrystalline silicon-based semiconductor (μc-Si: H) to provide photoelectric conversion semiconductor layer 4 as shown in
Subsequently a second harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 to irradiate transparent electrode layer 3 at an intensity that does not damage transparent electrode layer 3 to laser-scribe and thus remove a portion of photoelectric conversion semiconductor layer 4 in a strip to form, as shown in
Then, ZnO and silver were sputtered successively to deposit transparent conductive film and thin metallic film, respectively, to provide back surface electrode layer 5 as shown in
Then, a second harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 to laser-scribe and thus remove a portion of photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 in a strip to form, as shown in
Then the second harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 to irradiate a perimeter of photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 to laser-scribe and thus remove a portion of layers 4 and 5 in a strip to provide removed portion 9 of 1000 μm in width as shown in
Finally, a region outer than removed portion 9 was irradiated with a fundamental harmonic of YAG laser light from a side of transparent insulator substrate 2 to laser-scribe and thus remove transparent electrode layer 3, photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 at the irradiated portion in a strip having a width of 11 mm as measured from an outer side to fabricate the thin-film solar cell of the first example. The thin-film solar cell of the first example had the transparent electrode layer with a protrusion having length L, as shown in
Then, the thin-film solar cell of the first example was measured for leak current at a perimeter thereof by applying reverse bias voltage for each cell, and measured for conversion efficiency with a solar simulator. The result is shown in Table 1. As shown in Table 1, the thin solar cell of the first example provided a leak current of 12 mA at the perimeter, and a conversion efficiency of 10.9%.
Except that the steps shown in FIGS. 1(g) and 1(h) were not performed and a fundamental harmonic of YAG laser light was irradiated from a side of a transparent insulator substrate to remove a transparent electrode layer, a photoelectric conversion semiconductor layer and a back surface electrode layer all at once as shown in
More specifically, initially, as shown in
Then, a fundamental harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 to laser-scribe and thus remove a portion of transparent conductive layer 3 in a strip to form, as shown in
Then, plasma CVD was employed to deposit a p layer formed of a boron-doped, hydrogenated amorphous silicon-based semiconductor (a-Si: H), then an i layer formed of an undoped, hydrogenated amorphous silicon-based semiconductor (a-Si: H), and then an n layer formed of a phosphorus-doped, hydrogenated, microcrystalline silicon-based semiconductor (μc-Si: H) to provide photoelectric conversion semiconductor layer 4 as shown in
Subsequently a second harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 at an intensity that does not damage transparent electrode layer 3 to laser-scribe and thus remove a portion of photoelectric conversion semiconductor layer 4 in a strip to form, as shown in
Then, ZnO and silver were sputtered successively to deposit transparent conductive film and thin metallic film, respectively, to provide back surface electrode layer 5 as shown in
Then, a second harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 to laser-scribe and thus remove a portion of photoelectric conversion semiconductor layer 4 and back surface electrode layer 5 in a strip to form, as shown in
Finally the second harmonic of YAG laser light was irradiated from a side of transparent insulator substrate 2 to laser-scribe and thus remove the perimeter of transparent electrode layer 3, photoelectric conversion semiconductor layer 4 and back surface electrode layer 5, all at once, in a strip to provide removed portion 9 of 1000 μm in width as shown in
The thin-film solar cell of the first comparative example was then measured for leak current at a perimeter thereof, and measured for conversion efficiency in the same method as applied to the thin-film solar cell of the first example and under the same conditions as applied to the thin-film solar cell of the first example. The result is indicated in Table 1. As shown in Table 1,
As is also apparent from Table 1, the thin-film solar cell of the first example at its perimeter has provided a smaller leak current than that of the first comparative example and as a result has increased in conversion efficiency.
Thus the present invention can provide a method of fabricating a thin-film solar cell capable of reducing a leak current at a perimeter of the thin-film solar cell, and such thin-film solar cell.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.
Number | Date | Country | Kind |
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2005-155980 (P) | May 2005 | JP | national |