JP5727772B2 - Solar cell - Google Patents

Description

  The present invention relates to a solar cell, and more particularly, to a solar cell with improved photoelectric conversion efficiency by improving the transmittance of sunlight.

  When energetic particles called photons contained in sunlight hit the pn junction interface, electrons and holes are generated by the photovoltaic effect, and electrons move toward the n layer and holes move toward the p layer. A solar cell is an element that takes out electrons generated by the photovoltaic effect with the upper electrode and the back electrode and converts light energy into electric energy.

  As an example of such a solar cell, a crystalline silicon solar cell forms a back electrode made of a metal film or the like on the back surface side of a pn-junction semiconductor element, and on the light receiving surface side, a finger electrode, A bus bar electrode is formed. The finger electrode is, for example, an elongated electrode having a width of several hundreds to several tens of μm extending along the light receiving surface side of the semiconductor substrate, and a large number of such finger electrodes are arranged. Further, the bus bar electrode is formed so as to intersect with such a large number of finger electrodes, and is connected to a power line that takes out electrons collected by the finger electrodes to the outside.

  Conventionally, such finger electrodes and bus bar electrodes have been constituted by a metal film obtained by forming a highly conductive metal material, for example, a paste containing Ag in a predetermined pattern on one surface side of a semiconductor element (for example, a patent) Reference 1).

JP 2006-237363 A

  However, since the finger electrode described above is formed of a metal film that does not transmit light, sunlight (natural light) incident on this portion does not reach the semiconductor element and thus does not contribute to power generation, resulting in loss. On the other hand, in order to reduce such a loss, when the aperture ratio is increased by narrowing the width of the finger electrode, the resistance of the finger electrode is increased and the current collection performance is lowered.

  The present invention has been made in view of the above problems, and provides a solar cell that achieves high power generation efficiency by increasing the amount of sunlight reaching a semiconductor element while sufficiently securing the current collecting property by finger electrodes. Objective.

In order to solve the above problems, some embodiments of the present invention provide the following solar cell.
That is, the solar cell of the present invention includes a semiconductor element including at least a p-type semiconductor layer and an n-type semiconductor layer, a bus bar electrode extending along at least one side of the semiconductor element, and a plurality of crossing the bus bar electrode. A finger electrode, wherein at least one of the finger electrodes has two regions formed of different materials, and the two regions are transparent conductors. And a second region formed of a conductive metal that is disposed between the first region and the bus bar electrode and electrically connects the first region and the bus bar electrode. .

Among previous SL finger electrodes, at least one finger electrodes may be configured of a transparent conductive material over the entire area.
Moreover, you may further provide the wiring formed by the transparent conductor which cross | intersects the said finger electrode and extends substantially in parallel with the said bus-bar electrode.

The wiring in the connection section of the front Symbol first region and the second region may be configured to intersect the finger electrodes.
Further, the wiring before Symbol second region may be configured to intersect the finger electrodes.

A plurality of bus bar electrodes may be formed so as to extend substantially in parallel to each other, and at least an end portion in the extending direction of the finger electrodes may be formed of a transparent conductor.
Moreover, the said finger electrode may make the said bus-bar electrode adjacent to conduct.

The finger electrodes may be electrically connected between the bus bar electrodes adjacent in the second region.
The plurality of finger electrodes may be arranged such that finger electrodes having the second region and finger electrodes formed of a transparent conductor are adjacent to each other over the entire region.

  According to the solar cell of the present invention, when the sunlight is incident, the sunlight reaches the semiconductor element from between the finger electrodes arranged in a comb-like shape. The sunlight that has entered the region formed by the above can also pass through this region and reach the semiconductor element.

  Of the sunlight incident on the current collecting electrode that has not been able to contribute to power generation (photoelectric conversion) because it is conventionally formed of a metal film or the like, the sunlight incident on the region formed by the transparent conductive material also enters the semiconductor element 18. Therefore, it is possible to achieve a solar cell with improved power generation efficiency while maintaining a high current collection capability by using a bus bar electrode made of a metal material and a finger electrode made of at least a part of a transparent conductive material. It becomes possible.

It is sectional drawing which shows one Embodiment of the solar cell of this invention. It is a top view which shows the one surface side in the solar cell of FIG. It is explanatory drawing which shows the effect | action in one Embodiment of the solar cell of this invention. It is sectional drawing which shows the solar cell of 2nd embodiment. It is sectional drawing which shows the solar cell of 3rd embodiment. It is sectional drawing which shows the solar cell of 4th embodiment. It is sectional drawing shown in steps about an example of the manufacturing method of the solar cell of this invention.

  Hereinafter, an embodiment of a solar cell according to the present invention will be described with reference to the drawings. The present embodiment is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified. In addition, in the drawings used in the following description, in order to make the features of the present invention easier to understand, there is a case where a main part is shown in an enlarged manner for convenience, and the dimensional ratio of each component is the same as the actual one. Not necessarily.

(First embodiment)
FIG. 1 is a cross-sectional view along the thickness direction of a single crystal silicon solar cell which is an embodiment of the solar cell of the present invention.
For example, a single crystal silicon solar cell (hereinafter simply referred to as a solar cell) 10 includes a substrate (n-type semiconductor layer) 11 constituting an n-type semiconductor layer. On one surface (sunlight incident surface) 11a side of the substrate (n-type semiconductor layer) 11, a p-type semiconductor layer 13 and a transparent conductive film 14 are sequentially stacked. Among these, the substrate (n-type semiconductor layer) 11 and the p-type semiconductor layer 13 constitute a semiconductor element 18.
On the other hand, a metal electrode film (back surface electrode) 16 is sequentially stacked on the other surface (back surface) 11b side of the substrate 11.

  The substrate (n-type semiconductor layer) 11 may be made of, for example, a silicon single crystal wafer. The p-type semiconductor layer 13 only needs to be made of, for example, a thin film of amorphous silicon (a-Si) or microcrystal silicon (μc-Si). Moreover, the layer doped so that it might become a p-type semiconductor may be sufficient.

The transparent conductive film 14 may be composed of a light-transmitting conductive thin film, for example, an ITO (indium oxide-tin) film, a ZnO (zinc oxide) film, a TO (tin oxide) film, or the like. In addition, the transparent conductive film 14 on the sunlight incident surface side is formed with a texture for the prism effect and the light confinement effect for extending the optical path of the incident sunlight in order to improve the conversion efficiency of light energy. It is also preferable to do this.
The metal electrode film 16 may be made of, for example, an Ag (silver) film.

  In the solar cell 10 configured as described above, when energetic particles called photons contained in sunlight enter the semiconductor element 18 and reach the pn junction interface between the substrate (n-type semiconductor layer) 11 and the p-type semiconductor layer 13, Electrons and holes are generated by the photovoltaic effect, and electrons move toward the substrate (n-type semiconductor layer) 11 and holes move toward the p-type semiconductor layer 13. Due to the electrons generated by the photovoltaic effect, a potential difference is generated between the transparent conductive film 14 and the metal electrode film (back electrode) 16. Thereby, light energy can be converted into electric energy (photoelectric conversion).

  The transparent conductive film 14 has a larger electric resistance than a metal film or the like, and it is difficult to use the transparent conductive film 14 as an electrode for extracting power. For this reason, a current collecting electrode (upper electrode) 21 serving as an electrode on the incident surface side is formed on the one surface 14 a side of the transparent conductive film 14.

FIG. 2 is a plan view showing one surface side (sunlight incident surface side) in the solar cell of FIG. 1.
The collector electrode (upper electrode) 20 includes a bus bar electrode 21 and a plurality of finger electrodes 22 intersecting with the bus bar electrode 21.
The bus bar electrode 21 is made of, for example, a metal layer that is a good conductor such as Ag, collects electrons flowing into the finger electrode 22 described later, and outputs the collected electrons to the outside. The bus bar electrode 21 may be, for example, an Ag film that is formed to have a width of 0.05 to 2 mm and a thickness of about 0.5 to 40 μm.

  The finger electrodes 22 are elongate electrodes extending in a direction intersecting with the bus bar electrode 21 at, for example, a right angle, and a plurality of finger electrodes 22 are formed on both sides along the extending direction of the bus bar electrode 21. The finger electrode 22 is formed to have a width of 0.05 to 0.1 mm and a thickness of 0.5 to 40 μm, for example.

The finger electrode 22 has two regions formed of different materials, ie, a first region 22a formed of at least a transparent conductor and a second region 22b formed of a conductive metal. In other words, as shown in FIG. 2 and FIG. 4 described later, at least one of the finger electrodes 22 includes a first region 22a formed of a transparent conductor, and the first region 22a and the bus bar. The second region 22b is formed of a conductive metal that is disposed between the electrodes 21 and electrically connects the two.
The first region 22a may be made of a transparent conductor, for example, ITO (indium tin oxide), ZnO (zinc oxide), TO (tin oxide), or the like. In this embodiment, for example, ITO is used. On the other hand, the second region 22b may be made of a conductive metal such as Ag (silver), Al (aluminum) Au (gold) Cu (copper), or the like. In this embodiment, for example, Ag is used.

  The finger electrode 22 is formed with a second region 22b made of Ag having a predetermined length, for example, 10 to 50 mm from a portion electrically connected to the bus bar electrode 21, and an end portion of the second region 22b. The first region 22a made of ITO extends, for example, in a length of 2 to 10 mm toward the periphery of the solar cell 10.

The operation of the solar cell 10 having such a configuration will be described. It demonstrates using FIGS. 1-3.
FIG. 3 is an explanatory diagram for explaining the operation of the solar cell according to the embodiment of the present invention.
The solar cell 10 causes sunlight (natural light) S to enter from the incident surface side, that is, the side on which the collecting electrode (upper electrode) 20 is formed. Then, photoelectric conversion is performed by sunlight S that reaches the semiconductor element 18 through the transparent conductive film 14 to generate electric power. When such sunlight S is incident, the sunlight S reaches the semiconductor element 18 from between the finger electrodes 22 arranged in a comb-like shape. Further, of the finger electrodes 22, ITO which is a transparent conductive material The sunlight Sa incident on the first region 22 a formed by the above can also pass through the first region 22 a and reach the semiconductor element 18.

  The first region formed by ITO, which is a transparent conductive material, among the sunlight S incident on the current collecting electrode (upper electrode) that could not contribute to power generation (photoelectric conversion) because it was conventionally formed of a metal film or the like The sunlight Sa incident on 22 a can pass through the first region 22 and reach the semiconductor element 18. Accordingly, the current collecting electrode (upper electrode) 20 is formed by the first region 22a formed of the transparent conductive material while maintaining a high current collecting ability by the bus bar electrode 21 formed of the metal material and the second region 22b of the finger electrode 22. It is possible to realize the solar cell 10 that allows a part of the sunlight S incident on the light to pass therethrough to improve the power generation efficiency.

Next, an example of a method for manufacturing such a solar cell will be described.
FIG. 7 is a cross-sectional view showing an example of a method for manufacturing a solar cell according to the present invention in stages.
In manufacturing the solar cell 10, first, for example, a p-type single crystal silicon substrate 101 having a thickness of about 200 μm and a 125 mm square having a textured structure by texture etching is prepared (FIG. 7A). A paint containing phosphorus (P) is applied to the surface 101 a of 101. Next, the silicon substrate 101 is heat-treated at, for example, 900 ° C. for 10 minutes to form an n-type diffusion layer 102 having a thickness of about 0.5 μm near the surface of the silicon substrate (FIG. 7B). .

  Next, an aluminum layer 104 is formed with a thickness of about 2 μm by sputtering in the region where the back electrode of the back surface 101b of the silicon substrate 101 is to be formed. Alternatively, an aluminum paste with a thickness of 40 μm may be applied by screen printing to a region where the back electrode of the back surface 101b of the silicon substrate 101 is to be formed, and then dried at 150 ° C. for 10 minutes. As a result, the aluminum layer 104 is formed in a predetermined pattern on the back surface 101b of the silicon substrate 101 (FIG. 7C).

Next, an ITO film is formed on the surface of the diffusion layer 102 of the silicon substrate 101 to a thickness of about 800 mm at about 200 ° C. using a sputtering apparatus to form an ITO film 107 (FIG. 7D).
Thereafter, an ITO paste is applied to the area where the finger electrodes on the surface side are to be formed, for example, by screen printing, application by an ink jet printer, and the like in vacuum at 230 ° C. for 30 minutes under a reduced pressure of 1 × 10 ⁻³ Pa. First firing is performed. Next, the atmosphere is returned to the atmosphere, and second baking is performed in air at 230 ° C. for 30 minutes. Next, an Ag paste is printed on the surface of the area where the grid and finger electrodes are formed by screen printing, and baked at 200 ° C. for 20 minutes. By such two-stage firing, the solar cell 10 including the finger electrodes 108 made of ITO and the bus bar electrodes 109 made of Ag can be formed (FIG. 7E).

(Second embodiment)
FIG. 4 is a plan view showing one surface side (sunlight incident surface side) in the solar cell of the second embodiment of the present invention.
In the solar cell 30 of this embodiment, a collecting electrode (upper electrode) 31 is formed on one surface side (sunlight incident surface side) of the semiconductor element 18. The current collecting electrode 31 includes a bus bar electrode 32 and a plurality of finger electrodes 33 intersecting with the bus bar electrode 32.
The bus bar electrode 32 is formed of a metal layer that is a good conductor such as Ag. The finger electrodes 33 are elongate electrodes extending in a direction intersecting with the bus bar electrode 32 at a right angle, for example, and a plurality of finger electrodes 33 are formed on both sides along the extending direction of the bus bar electrode 32.

  The finger electrode 33 is formed of a first finger electrode 33a including at least a first region 22a formed of a transparent conductor and a second region 22b formed of a conductive metal, and a transparent conductor over the entire region. The second finger electrode 33b including the first region 22a. The first finger electrodes 33 a and the second finger electrodes 33 b are alternately formed along the extending direction of the bus bar electrode 32.

  According to the solar cell 30 of the second embodiment, the second finger electrode 33b composed of the first region 22a formed of a transparent conductor over the entire area is used to make the solar cell 30 in comparison with the solar cell 10 of the first embodiment. The light transmissive area is further increased, and the power generation efficiency can be further increased.

(Third embodiment)
FIG. 5 is a plan view showing one surface side (sunlight incident surface side) in the solar cell of the third embodiment of the present invention.
In the solar cell 40 of this embodiment, a collecting electrode (upper electrode) 41 is formed on one surface side (sunlight incident surface side) of the semiconductor element 18. The current collecting electrode 41 includes a bus bar electrode 42 and a plurality of finger electrodes 43 intersecting with the bus bar electrode 42.
The bus bar electrode 42 is formed of a metal layer that is a good conductor such as Ag. The finger electrodes 43 are elongate electrodes extending in a direction intersecting with the bus bar electrode 42 at a right angle, for example, and a plurality of finger electrodes 43 are formed on both sides along the extending direction of the bus bar electrode 42.

  The finger electrode 43 is formed of a first finger electrode 43a composed of at least a first region 22a formed of a transparent conductor and a second region 22b formed of a conductive metal, and a transparent conductor over the entire region. The second finger electrode 43b is formed of the first region 22a. Such first finger electrodes 43 a and second finger electrodes 43 b are alternately formed along the extending direction of the bus bar electrodes 42.

  Further, a wiring (finger electrode connection wiring) 45 constituting the collecting electrode (upper electrode) 41 is formed. The wiring (finger electrode connection wiring) 45 is formed substantially in parallel with the bus bar electrode 42 so as to connect a portion of the first finger electrode 43a where the first region 22a and the second region 22b are connected. The wiring 45 may be formed entirely of a transparent conductor, for example, ITO, and may be formed, for example, by sandwiching the bus bar electrode 42 therebetween.

  According to the solar cell 40 of the third embodiment, the wiring (finger electrode connection wiring) 45 increases the electrical conductivity between the plurality of finger electrodes 43 and also has a highly conductive metal film (second region 22b). This has the effect of spreading the high current collecting property due to the tip direction of the finger electrode 43. Therefore, it is possible to realize a solar cell that further increases the area through which sunlight can be transmitted to increase power generation efficiency and ensure high current collection.

  In addition, the wiring (finger electrode connection wiring) 45 in the third embodiment is preferably formed of a conductive metal such as Ag in addition to being formed of a transparent conductive film such as ITO. Whether the wiring 45 is made of a transparent conductive material or a conductive metal such as Ag is selected as appropriate depending on the purpose of further increasing the conductivity (collecting power) or increasing the transmittance of sunlight (opening ratio). It should be done.

(Fourth embodiment)
FIG. 6 is a plan view showing one surface side (sunlight incident surface side) in the solar cell of the fourth embodiment of the present invention.
In the fourth embodiment, an example of forming the collecting electrode (upper electrode) 51 in the large-area solar cell 50 is shown. In the solar cell 50 of the fourth embodiment, a collecting electrode (upper electrode) 51 is formed on one surface side (sunlight incident surface side) of the semiconductor element 18. The current collecting electrode 51 includes a plurality of bus bar electrodes 52 and a plurality of finger electrodes 53 intersecting with the bus bar electrodes 52.

  In the plurality of bus bar electrodes 52, for example, two bus bar electrodes 52 are formed in parallel to each other. The bus bar electrode 52 is formed of a metal layer that is a good conductor, such as Ag, and is formed so that the width of one end portion thereof gradually decreases in the length direction.

  The finger electrodes 53 are elongate electrodes extending in a direction perpendicular to the two bus bar electrodes 52, and a plurality of finger electrodes 53 are formed on both sides along the extending direction of the bus bar electrodes 52. The finger electrode 53 is formed of a first finger electrode 53a composed of at least a first region 22a formed of a transparent conductor and a second region 22b formed of a conductive metal, and a transparent conductor over the entire region. And the second finger electrode 53b including the first region 22a. Then, the first finger electrode 53a and the second finger electrode 53b are, for example, the extension direction of the bus bar electrode 52 in the ratio of three first finger electrodes 53b to one first finger electrode 53a. It is formed along.

  Among these finger electrodes 53, some of the first finger electrodes 53a are second regions 22b formed of a conductive metal so that two adjacent bus bar electrodes 52 are connected (conductive) to each other. Is formed.

  Further, a wiring (finger electrode connection wiring) 55 constituting the current collecting electrode (upper electrode) 51 is formed. This wiring (finger electrode connection wiring) 55 is formed substantially parallel to the bus bar electrode 52 so as to cross the plurality of arranged finger electrodes 53 and to connect the finger electrodes 53 to each other. The wiring 55 should just be comprised from the transparent conductor, for example, ITO, and the wiring 55 should just be formed in multiple numbers, for example, six in this embodiment.

  According to the solar cell 50 of the fourth embodiment, the finger electrode 53 is arranged so as to cover the wide light receiving surface of the solar cell 50, and at least the first region 22a formed of a transparent conductor, and the conductive metal The first finger electrode 53a composed of the second region 22b formed in (1) can increase the solar light transmission area while ensuring the current collecting property, thereby realizing a solar cell with excellent power generation efficiency.

  Further, the wiring (finger electrode connection wiring) 55 enhances the electrical conductivity between the plurality of finger electrodes 53 and at the same time enhances the current collecting property of the finger electrode 53 by the metal film (second region 22b) having excellent electrical conductivity. It has the effect of spreading in the tip direction. Therefore, it is possible to realize a solar cell that further increases the area through which sunlight can be transmitted to increase power generation efficiency and ensure high current collection.

The present applicant verified the effect according to an embodiment of the present invention.
Two types of solar battery cells with a square light-receiving surface, 125 mm square and 50 mm square, respectively. Each of the finger electrodes is formed of a metal film (comparative example (conventional example))
・ Each finger electrode has only the tip region formed of ITO (Example 1)
The first finger electrode in which the tip region of the finger electrode is formed of ITO and the second finger electrode in which the entire finger electrode is formed of ITO are alternately arranged, and further, the ITO is arranged so as to cross these finger electrodes. (Example 2) provided with wiring formed by
The power generation efficiency in Example 1 and Example 2 when the comparative example was 100% was determined.
These verification results are shown in Table 1.

  According to the results shown in Table 1, in Example 1 and Example 2 of the present invention, sunlight reaching the semiconductor element by forming part or all of the finger electrodes with a light-transmitting conductive material such as ITO. It was confirmed that the amount of light increased and the power generation efficiency improved.

  DESCRIPTION OF SYMBOLS 10 ... Solar cell, 11 ... Board | substrate, 13 ... p-type semiconductor layer, 20 ... Current collecting electrode (upper electrode), 21 ... Bus-bar electrode, 22 ... Finger electrode, 22a ... 1st area | region, 22b ... 1st area | region.

Claims (9)

A sun including at least a semiconductor element including at least a p-type semiconductor layer and an n-type semiconductor layer, a bus bar electrode extending along at least one surface side of the semiconductor element, and a plurality of finger electrodes intersecting with the bus bar electrode A battery,
Of the finger electrodes, at least one finger electrode has two regions formed of different materials, and the two regions are a first region formed of a transparent conductor, and the first region And a bus bar electrode, and a second region formed of a conductive metal that electrically connects the two.   The solar cell according to claim 1, wherein at least one finger electrode of the finger electrodes is made of a transparent conductor over the entire region.   3. The solar cell according to claim 1, further comprising a wiring made of a transparent conductor that intersects the finger electrode and extends substantially parallel to the bus bar electrode.   The solar cell according to claim 3, wherein the wiring intersects the finger electrode at a connection portion between the first region and the second region.   The solar cell according to claim 3, wherein the wiring intersects the finger electrode in the second region.   6. The bus bar electrode according to claim 1, wherein a plurality of the bus bar electrodes are formed so as to extend substantially in parallel to each other, and at least an end portion in the extending direction of the finger electrodes is formed of a transparent conductor. A solar cell according to claim 1.   The solar cell according to claim 6, wherein the finger electrode conducts the bus bar electrodes adjacent to each other.   The solar cell according to claim 7, wherein the finger electrode conducts the bus bar electrodes adjacent to each other in the second region.   9. The plurality of finger electrodes, wherein finger electrodes having the second region and finger electrodes formed of a transparent conductor are arranged so as to be adjacent to each other over the entire region. Solar cell.

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