JP2012146804A - Solar battery and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery which is easily manufactured and reduces the reflection of incident light at a boundary surface of a transparent electrode and a cover glass without impairing light permeability, and to provide a manufacturing method of the solar battery.SOLUTION: A solar battery 1 includes a back electrode layer 3, a light absorption layer 4 performing photoelectric conversion of incident light to obtain an electromotive force, and a transparent electrode layer 5 made of aluminum-doped zinc oxide on a substrate 2. The side of the transparent electrode layer 5, which is spaced apart from a boundary surface with the light absorption layer 4, has a higher aluminum content than the boundary surface side of the transparent electrode layer 5.

Description

  The present invention relates to a solar cell and a manufacturing method thereof.

  Conventionally, a thin film solar cell in which a back electrode, a light absorption layer, and a transparent electrode are laminated in this order on a substrate is known. Each layer of the back electrode, the light absorption layer, and the transparent electrode is formed on the substrate by, for example, sputtering. The thin-film solar cell is disposed in a space defined by a cover glass and a back sheet with the transparent electrode facing the cover glass, and a gap between the cover glass and the back sheet is ethylene-vinyl acetate. (EVA) Sealed with a sealing agent such as resin.

  In the thin-film solar cell, an electromotive force can be obtained by photoelectric conversion by a semiconductor such as a Si semiconductor or a compound semiconductor that forms the light absorption layer incident from the cover glass side through the transparent electrode. Here, the use of aluminum-doped zinc oxide (AZO) has been studied as the transparent electrode because it is less expensive than indium tin oxide (ITO) and the film-forming temperature can be lowered.

  However, the AZO electrode has a problem that the refractive index is about 2.0, which is larger than the refractive indexes of the cover glass and EVA resin are about 1.5. As a result, incident light is likely to be reflected at the interface between the AZO electrode and the EVA resin as the sealant, and the light incident on the light absorption layer may be reduced, and a sufficient electromotive force may not be obtained. .

  Therefore, an anti-reflection layer having an intermediate refractive index between the AZO electrode and the EVA resin is disposed to reduce reflection of incident light so that a larger electromotive force can be obtained. Can be considered. As the material of the antireflection layer, for example, SiO having a refractive index of 1.70 and inorganic oxides such as MgO having a refractive index of 1.75 are known (for example, see Patent Document 1).

JP 2001-284613 A

  However, in order to form the antireflection layer made of SiO or MgO on the AZO electrode, it is necessary to perform sputtering using a material different from that of the AZO. Therefore, the film forming conditions are changed according to each different material. There is an inconvenience that must be done.

  Therefore, the present invention eliminates such inconvenience, is easy to manufacture, and can reduce the reflection of incident light at the interface between the transparent electrode and the cover glass or EVA resin without impairing the light transmittance, and It aims at providing the manufacturing method.

  The inventors examined the relationship between the refractive index of AZO and the light transmittance. As a result, by setting the aluminum content of AZO to a specific range higher than that of AZO used as a normal transparent electrode, the refractive index is lower than that of AZO used as a normal transparent electrode without reducing light transmittance. And the present invention has been reached.

  Therefore, in order to achieve the above object, the solar cell of the present invention is a transparent electrode composed of a back electrode layer, a light absorption layer that photoelectrically converts incident light to obtain an electromotive force, and aluminum-doped zinc oxide. In a solar cell comprising an electrode layer, the transparent electrode layer is characterized in that the aluminum content on the side away from the interface is higher than that on the interface side with the light absorption layer.

  According to the solar cell of the present invention, the portion of the transparent electrode layer made of aluminum-doped zinc oxide that is separated from the interface side with the light absorption layer, that is, the aluminum content on the outer layer side is increased to increase the refraction of this portion. The rate is smaller than the interface side with the light absorption layer. As a result, the solar cell of the present invention is disposed in a space defined by the cover glass and the back sheet so that the transparent electrode layer faces the cover glass, and the gap between the cover glass and the back sheet is EVA. When sealed with a sealant such as resin, the difference in refractive index between the cover glass and EVA resin and the transparent electrode layer is reduced, and reflected light can be reduced.

  In the solar cell of the present invention, the transparent electrode layer may be configured such that the aluminum content continuously increases from the interface side with the light absorption layer toward the side away from the light absorption layer, and a plurality of aluminum contents different from each other. The aluminum content of each layer may be increased on the side farther from the interface than on the interface with the light absorption layer.

  In the solar cell of the present invention, when the transparent electrode layer is composed of a plurality of layers having different aluminum contents, the transparent electrode layer includes, for example, a first transparent electrode layer laminated on the light absorption layer; It can be made to consist of a 2nd transparent electrode layer laminated | stacked on a 1st transparent electrode layer and having much aluminum content rather than a 1st transparent electrode layer. At this time, the first transparent electrode layer has an aluminum content of 2% by mass or less of the entire first transparent electrode layer, and the second transparent electrode layer has an aluminum content of the second transparent electrode layer. It is preferable that it is the range of 3.0-5.0 mass% of the whole.

  The second transparent electrode layer can have a refractive index smaller than that of the first transparent electrode layer when the aluminum content is in the above range. The refractive index of the second transparent electrode layer cannot be made sufficiently small with respect to the first transparent electrode layer when the aluminum content is less than 3.0 mass% of the entire second transparent electrode layer. Sometimes. Further, the second transparent electrode layer may not be able to obtain sufficient light transmittance when the aluminum content exceeds 5.0 mass% of the entire second transparent electrode layer.

  The solar cell of the present invention includes a step of forming a back electrode layer on a substrate, a step of forming a light absorption layer that obtains an electromotive force by photoelectrically converting light incident on the back electrode layer, and the light absorption layer And a step of forming a transparent electrode layer made of aluminum-doped zinc oxide by sputtering using a zinc oxide target containing aluminum, wherein the sputtering includes a plurality of zinc oxide targets having different aluminum contents. Can be manufactured by a manufacturing method in which the zinc oxide target is sequentially changed from one having a low aluminum content to one having a high aluminum content under the same film forming conditions.

  According to the production method of the present invention, in the step of forming the transparent electrode layer made of aluminum-doped zinc oxide, a plurality of zinc oxide targets having different aluminum contents are sequentially replaced from those having a lower aluminum content to those having a higher aluminum content. Thus, the transparent electrode layer having a higher aluminum content on the side away from the interface than on the interface with the light absorption layer can be formed. According to the production method of the present invention, since any target is the same type of zinc oxide, layers having different aluminum contents can be produced under the same film-forming conditions without changing the sputtering conditions. The solar cell of the invention can be easily manufactured.

  In the manufacturing method of the present invention, the sputtering uses the first zinc oxide target containing predetermined aluminum to form the first transparent electrode layer, and then the first zinc oxide target under the same film forming conditions. It is preferable to form the second transparent electrode layer on the first transparent electrode layer using a second zinc oxide target having a higher aluminum content. By doing in this way, the 1st transparent electrode layer laminated on the above-mentioned light absorption layer, and the 2nd higher aluminum content than the 1st transparent electrode layer laminated on the 1st transparent electrode layer The transparent electrode layer composed of the transparent electrode layer can be easily formed.

Explanatory sectional drawing which shows the structure of the solar cell of this invention. Explanatory sectional drawing which expands and shows the principal part of the solar cell of this invention. The graph which shows the relationship between the refractive index and the electromotive force of the side spaced apart from the light absorption layer in the solar cell of this invention.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

  As shown to Fig.1 (a), the solar cell 1 of this embodiment has the back surface electrode layer 3, the light absorption layer 4, and the transparent electrode layer 5 laminated | stacked on the glass substrate 2 in this order. As shown in FIG. 1B, the solar cell 1 is disposed in a space defined by a cover glass 6 and a back sheet 7 to form a solar cell module 8. In the solar cell module 8, the solar cell 1 is disposed so that the transparent electrode 5 faces the cover glass 6, and an ethylene-vinyl acetate (EVA) resin or the like is provided in the gap between the solar cell 1 and the cover glass 6 and the back sheet 7. The sealing agent 9 is filled, and the solar cell 1 is sealed.

In the solar cell 1, the back electrode layer 3 is made of, for example, Mo, and the light absorption layer 4 is made of, for example, a chalcopyrite compound (CIGS) represented by the chemical formula Cu (InGa) Se ₂ , and photoelectrically converts incident light. Electromotive force can be obtained. The light absorption layer 4 includes a buffer layer (not shown) on the surface. The buffer layer is made of, for example, InS.

  In the solar cell 1 of this embodiment, the transparent electrode layer 5 is made of aluminum-doped zinc oxide (AZO). At this time, the transparent electrode layer 5 has a small aluminum content in a portion on the interface side with the light absorption layer 4 and a large aluminum content in a portion on the side away from the interface.

  Such a transparent electrode layer 5 is, for example, as shown in FIG. 2, a first transparent electrode layer 5a laminated on the light absorption layer 4 and a first transparent electrode layer 5a laminated on the first transparent electrode layer 5a. It can comprise from the 2nd transparent electrode layer 5b with much aluminum content rather than the transparent electrode layer 5a. In FIG. 2, the sealant 9 is omitted.

  The first transparent electrode layer 5a is made of, for example, AZO having an aluminum content of 2.0% by mass and has a refractive index of 2.0. On the other hand, the second transparent electrode layer 5b can be made to have a refractive index in the range of 1.70 to 1.80 by being made of AZO with an aluminum content in the range of 3.0 to 5.0% by mass. .

  Here, in the solar cell module 8, the refractive index of the cover glass 6 is about 1.5, and the refractive index of the sealant 9 is also about the same as that of the cover glass 6. Therefore, by forming the transparent electrode layer 5 from the first transparent electrode layer 5a and the second transparent electrode layer 5b, compared with the case where the aluminum content is composed only of AZO having an aluminum content of 2.0% by mass, the cover The difference in refractive index between the glass 6 and the sealant 9 can be reduced. Therefore, according to the solar cell 1, when it is set as the solar cell module 8, the reflected light in the interface with the cover glass 6 and the sealing agent 9 (represented by the cover glass 6 in FIG. 2) is reduced. Can do.

  Further, the second transparent electrode layer 5b is made of AZO having an aluminum content in the range of 3.0 to 5.0 mass%, so that the light transmittance is not impaired. Therefore, according to the solar cell 1 of the present embodiment, the photoelectric conversion efficiency in the light absorption layer 4 can be improved by 1% or more.

  The light transmittance of AZO is also related to the film thickness, and the second transparent electrode layer 5b preferably has a film thickness in the range of 60 to 150 nm. When the film thickness of the second transparent electrode layer 5b is outside the above range, the effect of improving the photoelectric conversion efficiency in the light absorption layer 4 by 1% or more may not be obtained.

  In the configuration shown in FIG. 2, the transparent electrode layer 5 is composed of a first transparent electrode layer 5 a made of AZO having an aluminum content of 2.0 mass% and a refractive index of 2.0. It consists of 0 to 5.0% by mass of AZO, and is composed of two layers with the second transparent electrode layer 5b having a refractive index in the range of 1.70 to 1.80. However, the transparent electrode layer 5 may be composed of three or more layers, and the aluminum content of each layer may be increased stepwise from the light absorption layer 4 side toward the cover glass 6 side. Further, the transparent electrode layer 5 may be a single layer, and the aluminum content may be continuously increased from the light absorption layer 4 side to the side facing the cover glass 6.

  Next, the manufacturing method of the solar cell 1 shown in FIG.1 and FIG.2 is demonstrated.

  When manufacturing the solar cell module 8, first, the back electrode 3 made of Mo is sputtered on the glass substrate 2, and is divided into a plurality of regions by irradiating a laser and scribing. Next, a Cu · Ga layer is sputtered on the divided back electrode 4, and an In layer is further sputtered on the Cu · Ga layer.

Next, the glass substrate 2 is heated to a temperature in the range of, for example, 400 to 600 ° C. in an H ₂ Se gas atmosphere, and the Cu · Ga / In layer is converted to Se to form CIGS. Next, a buffer layer made of InS is formed on the CIGS layer by a chemical bath deposition method, and a light absorption layer 4 made of the CIGS layer and the buffer layer is formed. Then, the light absorption layer 4 is scribed with a needle and divided into a plurality of regions corresponding to the divided back electrode 3.

  Next, the transparent electrode 5 made of AZO is formed on the light absorption layer 4 by sputtering. Here, when the transparent electrode 5 includes the first transparent electrode 5a and the second transparent electrode 5b, first, sputtering is performed using a zinc oxide target containing 2.0% by mass of Al, and the light absorption layer 4 On the top, the first transparent electrode 5a is formed to a predetermined thickness, for example, 520 nm. Next, the zinc oxide target is replaced with a zinc oxide target containing 3.0 to 5.0% by mass of Al, and sputtering is performed under the same film forming conditions as in the formation of the first transparent electrode 5a. The second transparent electrode 5b is formed on the first transparent electrode 5a to a thickness of 60 to 155 nm, for example, 80 nm.

  As a result, the solar cell 1 of this embodiment can be manufactured. After the solar cell 1 is disposed in a space defined by the cover glass 6 and the back sheet 7, it is sealed with a sealing agent 9 such as EVA resin in the usual manner, thereby the solar cell module 8 is Can be formed.

  Next, a solar cell in which the second transparent electrode layer 5b is formed on the first transparent electrode layer 5a made of AZO having an aluminum content of 2.0% by mass and having a refractive index of 2.0 and a film thickness of 520 nm. 1 was used to form a solar cell module 8 and the photoelectric conversion efficiency of the light absorption layer 4 was measured. Here, the second transparent electrode layer 5b is changed in the range of refractive index of 1.70 to 1.80 by changing the aluminum content of AZO in the range of 3.0 to 5.0% by mass. I made it. Further, the film thickness was varied in the range of 61 to 151 nm with respect to the second transparent electrode layer 5b having each refractive index.

  Photoelectric conversion efficiency of the light absorption layer 4 when the transparent electrode 5 is made of only the first transparent electrode layer 5a made of AZO having an aluminum content of 2.0% by mass and having a refractive index of 2.0 and a film thickness of 600 nm. The result is shown in FIG.

  From FIG. 3, according to the solar cell 1 of the present embodiment, the first transparent electrode layer 5 a is made of AZO having an aluminum content of 3.0 to 5.0 mass% and has a refractive index of 1.70 to 1. By forming the second transparent electrode layer 5b having a thickness of 1.80 and a thickness of 61 to 151 nm, the photoelectric conversion efficiency of the light absorption layer 4 is improved by 1% or more. Accordingly, the second transparent electrode layer 5b can reduce the reflection of incident light at the interface between the cover glass 6 and the sealant 9 and the transparent electrode layer 5, and can transmit light through the second transparent electrode layer 5b. It is clear that the sex is not impaired.

  DESCRIPTION OF SYMBOLS 1 ... Solar cell, 2 ... Glass substrate, 3 ... Back electrode layer, 4 ... Light absorption layer, 5 ... Transparent electrode layer, 5a ... 1st transparent electrode layer, 5b ... 2nd transparent electrode layer.

Claims (6)

On a substrate, a solar cell comprising a back electrode layer, a light absorption layer that photoelectrically converts incident light to obtain an electromotive force, and a transparent electrode layer made of aluminum-doped zinc oxide,
The solar cell, wherein the transparent electrode layer has a higher aluminum content on the side away from the interface than on the interface with the light absorption layer.   2. The solar cell according to claim 1, wherein the transparent electrode layer is composed of a plurality of layers having different aluminum contents, and the aluminum content of each layer is separated from the interface rather than the interface with the light absorption layer. A solar cell characterized by having more.   3. The solar cell according to claim 2, wherein the transparent electrode layer includes a first transparent electrode layer laminated on the light absorption layer, and a first transparent electrode layer laminated on the first transparent electrode layer. A solar cell comprising a second transparent electrode layer having a high aluminum content.   4. The solar cell according to claim 3, wherein the first transparent electrode layer has an aluminum content in a range of 2% by mass or less of the entire first transparent electrode layer, and the second transparent electrode layer has an aluminum content. It is the range of 3.0-5.0 mass% of the whole 2nd transparent electrode layer, The solar cell characterized by the above-mentioned. Forming a back electrode layer on the substrate;
Forming a light absorbing layer that photoelectrically converts light incident on the back electrode layer to obtain an electromotive force; and
And a step of forming a transparent electrode layer made of aluminum-doped zinc oxide by sputtering using a zinc oxide target containing aluminum on the light absorption layer.
The sputtering is performed by using a plurality of zinc oxide targets having different aluminum contents and sequentially changing the zinc oxide target from one having a low aluminum content to one having a high aluminum content under the same film-forming conditions. Battery manufacturing method.   6. The method for manufacturing a solar cell according to claim 5, wherein the sputtering is performed under the same film-forming conditions after forming the first transparent electrode layer using the first zinc oxide target containing predetermined aluminum. A method for producing a solar cell, comprising forming a second transparent electrode layer on a first transparent electrode layer using a second zinc oxide target having a higher aluminum content than that of one zinc oxide target.

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