1. Field of the Invention
This disclosure relates to a solar cell, a solar cell module, and a method for manufacturing the solar cell, and particularly relates to a solar cell and a solar cell module which include single-crystal silicon substrates and to a method for manufacturing the solar cell.
2. Description of Related Art
A solar cell including a single-crystal silicon substrate has been conventionally known. Generally, the single-crystal silicon substrate used in the solar cell is obtained in such a way that a columnar single-crystal silicon ingot whose height direction is a growth direction in growth of the ingot is sliced along planes orthogonal to the grown direction. A semiconductor junction, electrodes, and the like are formed in the single-crystal silicon substrate and the solar cell is thus formed.
Moreover, the single-crystal silicon ingot is generally formed by Czochralski method or the like. The ingot formed by Czochralski method is known to have concentrically-symmetric defect distribution due to the manufacturing method thereof. This is disclosed in Fumio Shimura, “Semiconductor Silicon Crystal Technology”, Maruzen Publishing Co., Ltd published on September 30, Heisei 5 (1993), chapter 6, pp. 293 to 306, for example. Due to such concentric defect distribution, the single-crystal silicon substrate has concentric electrical characteristic distribution.
When a solar cell is formed by using a single-crystal silicon substrate having such concentric electrical characteristic distribution, the output of the solar cell decreases due to the existence of a portion having relatively poor electrical characteristics in the solar cell.
An object of an embodiment of the invention is to provide a solar cell, a solar cell module, and a method for manufacturing the solar cell which can suppress a decrease in output due to variation in electrical characteristics of a single-crystal silicon substrate.
A solar cell of a first aspect of the invention includes: a single-crystal silicon substrate having electrical characteristic distribution which is line symmetric with respect to a center line in a plan view and in which portions equidistant from the center line have an electrical characteristic substantially uniform in an extending direction of the center line in the plan view; a semiconductor junction formed by using the single-crystal silicon substrate; and an electrode.
A solar cell module of a second aspect of the invention includes solar cells electrically connected to one another in series, the solar cells each including: a single-crystal silicon substrate having electrical characteristic distribution which is line symmetric with respect to a center line in a plan view and in which portions equidistant from the center line have an electrical characteristic substantially uniform in an extending direction of the center line in the plan view; a semiconductor junction formed by using the single-crystal silicon substrate; and an electrode.
A method for manufacturing a solar cell of a third aspect of the invention includes the steps of: forming a single-crystal silicon ingot having concentric electrical characteristic distribution by crystal growth; slicing the single-crystal silicon ingot along a plane parallel to a growth direction of the single-crystal silicon ingot and thereby forming a single-crystal silicon substrate having electrical characteristic distribution which is line symmetric with respect to a center line and in which portions equidistant from the center line have an electrical characteristic substantially uniform in an extending direction of the center line; forming a semiconductor junction by using the single-crystal silicon substrate; and forming an electrode.
In the solar cell of the first aspect of the invention, the solar cell module of the second aspect, and the method for manufacturing a solar cell of the third aspect, the single-crystal silicon substrate having the electrical characteristic distribution described above is used. This can suppress variation in the electrical characteristics in the extending direction of the center line. Accordingly, the existence of a portion where the electrical characteristics are relatively poor in one solar cell can be suppressed by providing the electrode in the extending direction of the center line. Hence, a decrease in output of the solar cell can be suppressed.
An embodiment is described below based on the drawings.
First, description is given of a structure of solar cell module 1 using solar cells 23 of the embodiment with reference to
As shown in
A structure of a cross section taken along line 100-100 shown in
In the embodiment, as shown in
Moreover, as shown in
In each solar cell 23 of the embodiment, output characteristics of a region from which one of the finger electrode portions (finger electrode portions 235a and 236a) collects electricity are substantially identical to output characteristics of each of regions from which the other finger electrode portions collect electricity. In other words, a configuration of each solar cell 23 of the embodiment is equivalent to a configuration in which electricity generating elements having identical output characteristics are connected in parallel to the bus bar electrode portions (bus bar electrode portions 235b of electrode 235 and the bus bar electrode portion 236b of back electrode 236), continuously in the Y direction.
Electrode 235 of one solar cell 23 out of neighboring solar cells 23 is electrically connected to back electrode 236 of other solar cell 23 via tab electrodes 24a including a solder-plated copper wire or the like. Tab electrodes 24a are connected onto bus bar electrode portions 235b of electrodes 235 and the bus bar electrode portions (not illustrated) of back electrodes 236. Multiple (four in the embodiment) solar cells 23 are connected in series in the Y direction by tab electrodes 24a and each solar cell group 24 is thereby formed.
As shown in
Furthermore, each of L-shaped connection members 24b, 24c, 24e, and 24f is lead out from solar cell panel 2 through a notch in the back cover. An end portion of each of connection members 24b, 24c, 24e, and 24f is electrically connected to a terminal block (not illustrated) in terminal box 3.
Next, description is given of a manufacturing process of solar cells 23 of the embodiment. First, as shown in
Next, as shown in
Next, impurities are removed by cleaning each n-type single-crystal silicon substrate 231 and a texture structure (uneven shape) is formed by etching. Subsequently, i-type amorphous silicon layer 232 and p-type amorphous silicon layer 233 are sequentially deposited on n-type single-crystal silicon substrate 231 by using a CVD method. The semiconductor junction is thereby formed. Note that B, Al, Ga, and In which are group 3 elements can be given as an example of a p-type dopant used to form p-type amorphous silicon layer 233. p-type amorphous silicon layer 233 can be formed by mixing a compound gas including at least one of p-type dopants described above into a material gas such as SiH4 (silane) gas, during the formation of p-type amorphous silicon layer 233.
Next, transparent conductive film 234 made of indium oxide film is formed on p-type amorphous silicon layer 233 by using a PVD method. Then, Ag paste obtained by kneading silver (Ag) fine powder together with the epoxy resin is applied onto predetermined regions of the top surface of transparent conductive film 234 by using a screen printing method. At this time, the Ag paste is applied in such a way that, as shown in
Then, the Ag paste obtained by kneading the silver (Ag) fine powder together with the epoxy resin is applied onto the back surface of n-type single-crystal silicon substrate 231 by using the screen printing method. At this time, like in the formation of electrode 235, the Ag paste is applied in such a way that the bus bar electrode portions (not illustrated) extend in the extending direction of center line C and finger electrode portions 236a extend in the direction orthogonal to the extending direction of center line C. Thereafter, the Ag paste is hardened by being baked at about 200° C. for about 80 minutes. Thus, there is formed back electrode 236 including: finger electrode portions 236a which are formed in parallel to each other at predetermined intervals to extend in the X direction; and the bus bar electrode portions (not illustrated) which collect electric currents flowing though finger electrode portions 236a and which extend in the Y direction. Solar cells 23 of the embodiment are formed as described above.
Next, description is given of a manufacturing process of solar cell module 1 using solar cells 23 of the embodiment with reference to
Next, an EVA sheet eventually serving as the sealant, solar cells 23 connected by tab electrodes 24a, and another EVA sheet eventually serving as the sealant are disposed between the front cover made of glass and the back cover, in this order from the front cover side. Thereafter, thus-disposed parts are subjected to a vacuum laminating process while being heated and solar cell module 1 shown in
In the embodiment, variation in electrical characteristics in the extending direction of center line C can be suppressed by using n-type single-crystal silicon substrate 231 having electrical characteristic distribution which is line symmetric with respect to center line C in the plan view and in which portions equidistant from center line C have electrical characteristics substantially uniform in the extending direction of center line C, as described above. Accordingly, the existence of a portion where the electrical characteristics are relatively poor in one solar cell 23 can be suppressed by providing electrode 235 and back electrode 236 in the extending direction of center line C. Hence, a decrease in output of solar cell 23 can be suppressed.
In the embodiment, as described above, bus bar electrode portions 235b of electrode 235 and the bus bar electrode portions (not illustrated) of back electrode 236 are provided to extend, in the plan view, in the extending direction of the center line C in which the electrical characteristics are substantially uniform, and finger electrode portions 235a and 236a are provided to extend, in the plan view, in the direction intersecting the extending direction of center line C. Due to this, the portions equidistant, in the X direction, from any of bus bar electrode portions 235b of electrode 235 and the bus bar electrode portions (not illustrated) of back electrode 236 which extend along center line C have the electrical characteristics substantially uniform in the extending direction (direction Y) of bus bar electrode portions 235b of electrode 235 and the bus bar electrode portions of back electrode 236. Accordingly, collection of electricity can be performed with bus bar electrode portions 235b of electrode 235 and the bus bar electrode portions (not illustrated) of back electrode 236, in a direction in which the electrical characteristics are uniform. This can suppress a decrease in output of solar cell 23 which is caused by the existence of a portion where the electrical characteristics are relatively poor in solar cell 23.
In the embodiment, as described above, multiple finger electrode portions 235a and 236a are provided and the output characteristics of the regions respectively from which finger electrode portions 235a and 236a collect electricity are substantially identical to each other. This can suppress a decrease in output of solar cell 23 which is caused by the existence of a portion where the output characteristics are relatively poor in solar cell 23.
In the embodiment, the main surface of n-type single-crystal silicon substrate 231 is the (100) plane as described above. Accordingly, solar cell 23 can be manufactured by using n-type single-crystal silicon substrate 231 having the (100) plane as the main surface which has been conventionally used, and at the same time a decrease in output of solar cell 23 is suppressed.
In the embodiment, n-type single-crystal silicon substrate 231 whose electrical characteristics from one end to the other end in the extending direction of center line C are substantially uniform is used as described above. This can further suppress a decrease in output of solar cell 23.
Additionally, in the embodiment, high-level electrical characteristic region P and low-level electrical characteristic regions Q are substantially line symmetric with respect to center line C and low-level electrical characteristic regions Q are arranged outside high-level electrical characteristic region P when viewed from center line C as described above. A decrease in output of solar cell 23 which is caused by the existence of a portion where the electrical characteristics are relatively poor in solar cell 23 can be easily suppressed by such an arrangement of high-level electrical characteristic region P and low-level electrical characteristic regions Q, when electricity is collected in the extending direction (Y direction) of center line C.
In the embodiment, the electrical characteristics of n-type single-crystal silicon substrate 231 of neighboring ones of solar cells 23 are substantially identical to each other as described above. Accordingly, a decrease in output of entire solar cell module 1 formed by electrically connecting solar cells 23 in series can be easily suppressed.
In the embodiment, single-crystal silicon ingot 50 is sliced along the planes parallel to the growth direction (direction of arrow G) of single-crystal silicon ingot 50 and n-type single-crystal silicon substrates 231 can be thereby easily formed, n-type single-crystal silicon substrates 231 each having the electrical characteristic distribution which is line symmetric to center line C and in which the portions equidistant from center line C have the electrical characteristic substantially uniform in the extending direction of center line C.
Next, description is given of a comparison experiment to verify effects of the embodiment with reference to
In the comparison experiment, an output of a solar cell manufactured by using a single-crystal silicon substrate of an example obtained by the manufacturing method of the embodiment described above is compared with an output of a solar cell manufactured by using a single-crystal silicon substrate of a comparative example obtained by a conventional manufacturing method. Specifically, single-crystal silicon ingot 50 like one shown in
Then, voltage-current characteristics of solar cells A1 to A3 are compared respectively with voltage-current characteristics of solar cells B1 to B3.
As shown in
Moreover, as shown in
Furthermore, as shown in
The following reasons are conceivable as reasons for these results. Specifically, in each of solar cells A1 to A3 of the example, the single-crystal silicon substrate in which the portions equidistant from center line C have the electrical characteristics substantially uniform in the extending direction of center line C is used and the electrical characteristics are thus uniform in an extending direction of the bus bar electrode portions. Accordingly, there is no variation in characteristics along the bus bar electrode portions and an output of a portion with good characteristics is thus not hindered by an output of a portion with poor characteristics. Hence, loss (decrease) of output is suppressed. On the other hand, in each of solar cells B1 to B3 of the comparative example, the single-crystal silicon substrate in which the electrical characteristics are concentrically distributed is used. Accordingly, there is variation in electrical characteristics in the extending direction of bus bar electrode portions. Hence, an output of a portion with good characteristics is hindered by an output of a portion with poor characteristics and the output of the solar cell thereby decreases. Accordingly, it is assumed that solar cells A1 to A3 of the examples are improved in output (fill factor) compared to solar cells B1 to B3 of the comparative examples.
It should be understood that the embodiment disclosed herein is exemplary in all points and does not limit the embodiment. The scope of the embodiment is defined not by the descriptions of the embodiment but by claims and includes equivalents of claims and all modifications within the scope of claims.
For example, in the embodiment described above, description is given of the example using the single-crystal silicon substrate whose main surface is the (100) plane. However, the embodiment is not limited to this and may use a single-crystal silicon substrate using a different plane as a main surface.
In the embodiment described above, silicon (Si) is used as the semiconductor material. However, the embodiment is not limited to this and may use any of semiconductors including SiGe, SiGeC, SiC, SiN, SiGeN, SiSn, SiSnN, SiSnO, SiO, Ge, GeC, and GeN. In this case, these semiconductors may be crystalline or any one of amorphous and microcrystallite which include at least one of hydrogen and fluorine.
In the embodiment described above, description is given of the example in which the extending direction (X direction) of finger electrode portions 235a and 236a is substantially orthogonal to the extending direction (Y direction) of bus bar electrode portions 235b. However, the embodiment is not limited to this. Specifically, the extending direction of finger electrode portions 235a and 236a may be a direction obliquely intersecting the extending direction (Y direction) of bus bar electrode portions 235b.
The semiconductor junction of the embodiment can be also formed by thermally diffusing a dopant into the single-crystal silicon substrate. Moreover, the embodiment can be applied also to a back-junction-type solar cell.
Number | Date | Country | Kind |
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2010-145429 | Jun 2010 | JP | national |
This application is a continuation application of International Application No. PCT/JP2011/064549, filed on Jun. 24, 2011, entitled “SOLAR CELL, SOLAR CELL MODULE, AND METHOD FOR MANUFACTURING SOLAR CELL”, which claims priority based on Article 8 of Patent Cooperation Treaty from prior Japanese Patent Applications No. 2010-145429, filed on Jun. 25, 2010, the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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Parent | PCT/JP2011/064549 | Jun 2011 | US |
Child | 13721515 | US |