JP2007013098A - Solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive solar battery with high conversion efficiency. <P>SOLUTION: The solar battery 10 consists of a transparent conductive substrate 1, a p-layer 2 made of Cu<SB>2</SB>O and an amorphous In-Ga-Zn-O n-layer 3 formed on the substrate 1 by sputtering, and a metallic electrode 4 provided on the n-layer 3. By using amorphous In-Ga-Zn-O as the n-layer 3; occurrence of discontinuation, a void or the like can be prevented on a joint interface between the n-layer 3 and the p-layer 2, thereby forming a good joint interface. In-Ga-Zn-O has large electron mobility even under the amorphous conditions. The n-layer 3 can be formed on the p-layer at a low temperature, resulting in preventing the interface from deteriorating. Therefore, large conversion efficiency can be attained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solar cell, and more particularly to a pn junction solar cell.

I. Conventional materials used for solar cells include silicon (single crystal Si, polycrystalline Si and amorphous Si), GaAs, CuInSe, and CdTe. Among these, silicon solar cells and GaAS solar cells have high conversion efficiency but are expensive. On the other hand, although CuInSe-based and CdTe-based solar cells are relatively inexpensive, materials such as selenium and cadmium are toxic. Therefore, environmental problems arise when they are mass-produced and widely spread.

II. Dye-sensitized solar cells using titanium dioxide have attracted attention as inexpensive and clean solar cells, and various proposals have been made (for example, JP-A-2003-123853). Titanium dioxide has a band gap of about 3.2 eV, so it hardly shows any response to visible light and is a material showing only response to ultraviolet light. Therefore, in the dye-sensitized solar cell, visible light response is improved by adsorbing an organic dye that absorbs visible light on the surface of titanium dioxide, and high conversion efficiency of about 10% at the maximum is realized. However, as a fundamental problem that the dye-sensitized solar cell has, the conversion efficiency greatly changes depending on the amount of dye adsorption, and it is necessary to use an electrolyte solution, so that packaging is difficult, Etc.

III. A transparent pn-junction solar cell for ultraviolet light composed of a combination of CuAlO ₂ / ZnO has been proposed. A pn junction solar cell composed of a combination of Cu ₂ O / ZnO has also been proposed. CuAlO ₂ or Cu ₂ O functions as a p layer and a light absorption layer, and ZnO functions as an n layer. Upon light irradiation, solar cell characteristics are exhibited by generating electrons and holes at the pn interface by photoexcitation.
JP 2003-123853 A

A problem with conventional pn junction solar cells is that large conversion efficiency cannot be obtained. The reason for this is that by laminating crystalline ZnO to crystalline CuAlO ₂ and Cu ₂ O, the bonding interface becomes rough, and discontinuities, voids, etc. are generated at the interface. It is thought that this is because a new interface is formed.

  Another problem is that it is difficult to reduce the cost. This is because it is necessary to perform a heat treatment during or after the formation of these solar cells, and thus it is impossible to form an n layer and a p layer on an inexpensive polymer substrate. Note that when ZnO as an n layer is formed by sputtering at a low temperature because a polymer substrate is used, the crystallinity of the ZnO film is deteriorated, the electron mobility is lowered, and the conversion efficiency is extremely deteriorated.

  An object of this invention is to provide the solar cell with high conversion efficiency.

The solar cell of the present invention (invention 1) is a pn junction solar cell in which a p layer and an n layer are stacked, the p layer is made of Cu ₂ O, and the n layer is an amorphous In—Ga—Zn It is characterized by comprising -O.

  The solar cell according to claim 2 is the solar cell according to claim 1, wherein the indium tin oxide substrate, the p layer formed on the indium tin oxide substrate, the n layer formed on the p layer, and an electrode formed on the n layer.

  A solar cell according to claim 3 is the solar cell according to claim 1, wherein the Cu plate, the p layer formed by oxidizing the surface of the Cu plate, the n layer formed on the p layer, and the n layer It has an electrode film made of indium tin oxide formed thereon and an electrode formed on the electrode film.

  The solar cell of claim 4 is characterized in that, in claim 1, the p layer or the n layer is formed on a polymer substrate.

  According to a fifth aspect of the present invention, in the solar cell according to any one of the first to fourth aspects, the p layer and the n layer are formed by a sputtering method, a reactive sputtering method, a CVD method, or an evaporation method.

  The solar cell according to claim 6 is the solar cell according to any one of claims 1 to 5, wherein In is 8 to 67 atm% and Ga is 1 to 55 atm when the total of In, Ga and Zn in the n layer is 100 atm%. %, Zn is 8 to 67 atm%.

  A solar cell according to a seventh aspect is characterized in that, in any one of the first to sixth aspects, the conversion efficiency of the solar cell is 0.67% or more.

  The solar cell according to claim 8 is characterized in that, in any one of claims 1 to 7, the p layer has an average particle diameter of 10 nm to 10 μm.

  In the solar cell of the present invention (invention 1), since amorphous In—Ga—Zn—O is used as the n layer, discontinuities, voids, and the like are present at the junction interface between the n layer and the p layer. Occurrence is prevented and a good bonding interface is formed, whereby a large conversion efficiency can be obtained.

  Further, In—Ga—Zn—O has a large electron mobility even in an amorphous state, so that electric power can be easily taken out, and high conversion efficiency can be obtained from this point.

Furthermore, since it is only necessary to form amorphous In—Ga—Zn—O, In—Ga—Zn—O can be formed over the p-layer at a low temperature. Therefore, without causing significant denaturation of grain growth such as Cu 2 _O in the p layer by heat when forming the n layer, the bonding interface between the p layer and the n layer is prevented from deteriorating, thereby A large conversion efficiency can be obtained.

Such a solar cell of the present invention was formed on the first electrode made of an indium tin oxide substrate, the p layer made of Cu ₂ O formed on the indium tin oxide substrate, and the p layer. You may have the said n layer which consists of In-Ga-Zn-O, and the 2nd electrode formed on this n layer (Claim 2).

Further, the solar cell of the present invention is formed on the first electrode made of a Cu plate, the p layer made of Cu ₂ O formed by oxidizing the surface of the Cu plate, and the p layer. An n-layer made of In-Ga-Zn-O; an electrode film made of indium tin oxide formed on the n-layer; and a second electrode formed on the electrode film. (Claim 3). As described above, by oxidizing the Cu plate, the first electrode and the p layer made of Cu ₂ O can be easily formed. Further, by forming an electrode film made of indium tin oxide between the n layer and the second electrode, the series resistance component can be greatly reduced, and as a result, conversion efficiency can be improved. I can do it.

  Further, since In—Ga—Zn—O is in an amorphous state and can be formed on the p layer at a low temperature, the p layer or the n layer may be formed on an inexpensive polymer substrate. 4). In this case, the cost of the solar cell can be reduced.

  The p layer and the n layer of this solar cell can be easily formed by sputtering, reactive sputtering, CVD, or vapor deposition.

As for the composition of the n layer, if the total of In, Ga and Zn in the n layer is 100 atm%, the electron transfer is such that In is 8 to 67 atm%, Ga is 1 to 50 atm%, and Zn is 8 to 67 atm%. The degree is high and an amorphous state can be easily obtained. Further, it has a sufficient visible light transmission property and does not obstruct the incidence of light to the Cu ₂ O layer that is the light absorption layer.

  This solar cell preferably has a conversion efficiency of 0.67% or more.

  When the average particle size of the p layer is 10 nm to 10 μm, the hole mobility is further high and the interfacial bonding property between the p layer and the n layer is also good.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a solar cell according to an embodiment. The solar cell 10 includes a transparent conductive substrate 1, a p layer 2 and an n layer 3 formed on the transparent conductive substrate 1 by sputtering, and a metal electrode 4 provided on the n layer 3.

  Conductive wires 6 are bonded to the surfaces of the transparent conductive substrate 1 and the electrodes 4.

As the transparent conductive substrate 1, a substrate made of a conductive material such as a conductive metal oxide thin film or metal is used. Preferable examples of the conductive metal oxide include In ₂ O ₃ : Sn (ITO), SnO ₂ : Sb, SnO ₂ : F, ZnO: Al, ZnO: F, and CdSnO ₄ .

  The thickness of the transparent conductive substrate 1 is generally 0.1 to 10 mm, and preferably 0.3 to 5 mm.

  Instead of the transparent conductive substrate 1, a substrate obtained by forming the transparent conductive substrate 1 on a transparent substrate may be used. In this case, as the transparent substrate, for example, glass such as alkali silicate glass, non-alkali glass, or quartz glass can be used. A polymer film substrate such as acrylic or PET can also be used. When these polymer substrates are used, the cost can be reduced. The thickness of the substrate is generally 0.1 to 10 mm, preferably 0.3 to 5 mm. The glass plate is preferably chemically or thermally strengthened.

The p layer 2 is Cu ₂ O. This Cu ₂ O has a function as a light absorption layer as well as a function as a p layer.

The average particle diameter of the deposited Cu ₂ O is preferably 10 nm to 10 μm. If the thickness is smaller than 10 nm, Cu ₂ O cannot sufficiently grow and crystallinity is deteriorated, so that the hole mobility in the p layer is reduced. On the other hand, if it is larger than 10 μm, the surface of the p layer becomes too rough, the bonding property between the p layer and the n layer is deteriorated, and the conversion efficiency is lowered. In addition, the leakage current component is also greatly increased.

The thickness of the p layer is, for example, 100 nm to 3 μm, preferably 300 nm to 1 μm. electron mobility of the p-layer is preferably 0.01~100cm ² / V · sec particular 1~100cm ² / V · sec.

The n layer 3 is In—Ga—Zn—O in an amorphous state. Since this amorphous In—Ga—Zn—O is uniform without forming grain boundaries, it is formed so as to uniformly cover the crystalline Cu ₂ O surface. As a result, the n layer and the p layer are formed. It is possible to prevent discontinuity, voids, and the like from occurring at the bonding interface with the layer, thereby forming a good bonding interface. Thereby, a large conversion efficiency can be obtained.

  Further, In—Ga—Zn—O has a large electron mobility even in an amorphous state, so that electric power can be easily taken out, and high conversion efficiency can be obtained from this point.

Furthermore, since it is only necessary to form amorphous In—Ga—Zn—O, In—Ga—Zn—O can be formed over the p-layer at a low temperature. Therefore, without causing significant denaturation of grain growth such as Cu 2 _O in the p layer by heat when forming the n layer, the bonding interface between the p layer and the n layer is prevented from deteriorating, thereby A large conversion efficiency can be obtained.

When the total of In, Ga, and Zn in the n layer is 100 atm%, it is preferable that In is 8 to 67 atm%, Ga is 1 to 55 atm%, and Zn is 8 to 67 atm%. In—Ga—Zn—O having such a composition can satisfy all of sufficient mobility of electrons, transparency of visible light, and bonding with a Cu ₂ O layer.

  The thickness of the n layer is, for example, 100 nm to 5 μm, preferably 300 nm to 1 μm.

The n layer is preferably formed under the condition that the temperature of the film formation surface is in the range of room temperature to 200 ° C. In this case, the bonding property between the n layer and the p layer is improved, and it is possible to prevent the Cu ₂ O in the p layer from being modified such as grain growth. A polymer substrate can be used as the substrate.

  As the metal electrode 4, platinum, Al, Cu, Ti, Ni or the like can be used.

In the present embodiment, a DC power source is used, the transparent conductive substrate 1 is placed in a mixed gas atmosphere of oxygen and argon, and sputtering is performed by applying a voltage to a Cu target. The sputtered Cu is oxidized on the surface of the transparent conductive substrate 1 or the like, and a Cu ₂ O layer is formed on the transparent conductive substrate 1. Next, sputtering is performed by applying a voltage to a target made of In—Ga—Zn. The sputtered In, Ga, and Zn are oxidized on the surface of the Cu ₂ O layer and the like, and an In—Ga—Zn—O layer is formed on the Cu ₂ O layer.

  Note that an In—Ga—Zn—O layer is formed using a plurality of types of targets having different compositions of at least one of In, Ga, and Zn instead of using one type of target composed of In—Ga—Zn. May be.

  Subsequently, the solar cell 10 is obtained by forming an electrode on the n layer made of In—Ga—Zn—O.

  The solar cell 10 thus obtained is preferably highly functional with a conversion efficiency of 0.67% or more.

In this embodiment mode, the p layer and the n layer are formed by reactive sputtering, but the p layer and the n layer are formed by sputtering using a Cu ₂ O target and an In—Ga—Zn—O target. May be performed. Alternatively, the p layer and the n layer may be formed by a CVD method, a vapor deposition method, or the like.

FIG. 2 is a schematic cross-sectional view of solar cells according to different embodiments. The solar cell 20 includes a Cu plate 21, a p layer 22 made of Cu ₂ O formed by oxidizing the surface of the Cu plate 21, and In—Ga—Zn formed on the p layer 22 by sputtering. It consists of an n layer 23 made of -O and an ITO (indium tin oxide) layer 25 and a metal electrode 24 provided on the ITO layer 25. The p layer 22 made of Cu ₂ O is formed by heat-treating the Cu plate 21 in the atmosphere. This solar cell 20 also has a high conversion efficiency.

  Examples 1 to 4 and Comparative Examples 1 and 2 will be described below, but the present invention is not limited to Examples 1 to 4.

<Example 1>
A p-layer made of Cu ₂ O and an n-layer made of In—Ga—Zn—O were formed in this order on the ITO glass substrate by reactive sputtering. The film forming conditions were as follows.
[P layer]
Target: Cu, ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa
Gas flow rate during film formation: Ar / O ₂ = 95/5 sccm, applied power: DC 50 W,
Deposition time: 30 minutes, film thickness: 350 nm
[N layers]
Target: InGaZn (In: Ga: Zn = 1: 1: 1 (atm%)),
Ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa,
Gas flow rate during film formation: Ar / O ₂ = 80/20 sccm,
Applied power: DC 50 W, film formation time: 30 minutes, film thickness: 300 nm

Al (thickness 100 nm) was formed on this n layer to form an electrode.
About the obtained solar cell, the conducting wire was joined to the ITO glass substrate and the Al electrode, and the conversion efficiency was measured using a solar simulator. The measurement was performed under the conditions of AM1.5 in an environment of 30 ° C. and in the atmosphere. The element size is 10 mm × 10 mm.
As a result, the conversion efficiency η was 1.9%.

<Example 2>
A 0.3 mm thick Cu plate was heat-treated at 450 ° C. for 6 hours in the atmosphere to form a p layer (thickness 350 nm) made of Cu ₂ O on the Cu plate surface. Next, an n layer and an ITO layer made of In-Ga-Zn-O are formed in this order on the p layer made of Cu ₂ O by using a reactive sputtering method, and an electrode made of Al is formed on the ITO layer. Formed. The n layer and the Al electrode were formed in the same manner as in Example 1. The ITO layer was formed by reactive sputtering under the following conditions.
[ITO layer]
Target: Indium tin oxide (In: Sn = 97: 3 atm%),
Ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa,
Gas flow rate during film formation: Ar / O ₂ = 95/5 sccm, applied power: DC 50 W,
Deposition time: 30 minutes, film thickness: 100 nm

About the obtained solar cell, the conducting wire was joined to Cu board and Al electrode, and the conversion efficiency was measured using the solar simulator similarly to Example 1. FIG.
As a result, the conversion efficiency η was 2.1%.

<Comparative Example 1>
A solar cell was obtained in the same manner as in Example 1 except that the n layer was ZnO. ZnO was formed by reactive sputtering under the following conditions.
[N layer (ZnO)]
Target: Zn, ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa,
Gas flow rate during film formation: Ar / O ₂ = 80/20 sccm, applied power: DC 50 W,
Deposition time: 30 minutes, film thickness: 280 nm

About the obtained solar cell, the conversion efficiency was measured using the solar simulator similarly to Example 1. FIG.
As a result, the conversion efficiency η was 0.2%.

<Example 3>
A p-layer made of Cu ₂ O and an n-layer made of In—Ga—Zn—O were formed in this order on the ITO glass substrate by reactive sputtering. The film forming conditions were as follows.
[P layer]
Target: Cu, ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa
Gas flow rate during film formation: Ar / O ₂ = 95/5 sccm, applied power: DC 50 W,
Deposition time: 30 minutes, film thickness: 350 nm
[N layers]
Target: InGaZnO (In: Ga: Zn: O = 1: 1: 1: 4-x (atm%)),
Ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa,
Gas flow rate during film formation: Ar / O ₂ = 80/20 sccm,
Applied power: DC 50 W, film formation time: 30 minutes, film thickness: 300 nm

Al (thickness 100 nm) was formed on this n layer to form an electrode.
About the obtained solar cell, the conducting wire was joined to the ITO glass substrate and the Al electrode, and the conversion efficiency was measured using a solar simulator. The measurement was performed under the conditions of AM1.5 in an environment of 30 ° C. and in the atmosphere. The element size is 10 mm × 10 mm.
As a result, the conversion efficiency η was 1.9%.

<Example 4>
A 0.3 mm thick Cu plate was heat-treated at 450 ° C. for 6 hours in the atmosphere to form a p layer (thickness 350 nm) made of Cu ₂ O on the Cu plate surface. Next, an n layer and an ITO layer made of In-Ga-Zn-O are formed in this order on the p layer made of Cu ₂ O by using a reactive sputtering method, and an electrode made of Al is formed on the ITO layer. Formed. The n layer and the Al electrode were formed in the same manner as in Example 3. The ITO layer was formed by reactive sputtering under the following conditions.
[ITO layer]
Target: Indium tin oxide (In: Sn = 97: 3 atm%),
Ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa,
Gas flow rate during film formation: Ar / O ₂ = 95/5 sccm, applied power: DC 50 W,
Deposition time: 30 minutes, film thickness: 100 nm

About the obtained solar cell, the conducting wire was joined to Cu board and Al electrode, and the conversion efficiency was measured using the solar simulator similarly to Example 3. FIG.
As a result, the conversion efficiency η was 2.1%.

<Comparative example 2>
A solar cell was obtained in the same manner as in Example 3 except that the n layer was ZnO. ZnO was formed by reactive sputtering under the following conditions.
[N layer (ZnO)]
Target: Zn oxide (Zn: O = 1: 1-x (atm%)),
Ultimate vacuum: 5.0 × 10 ⁻⁴ Pa, film forming pressure: 0.7 Pa,
Gas flow rate during film formation: Ar / O ₂ = 80/20 sccm, applied power: DC 50 W,
Deposition time: 30 minutes, film thickness: 280 nm

About the obtained solar cell, the conversion efficiency was measured using the solar simulator similarly to Example 1. FIG.
As a result, the conversion efficiency η was 0.2%.

It is typical sectional drawing of the solar cell which concerns on embodiment. It is typical sectional drawing of the solar cell which concerns on different embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent conductive substrate 2,22 p layer 3,23 n layer 4,24 Electrode 6 Conductor 10,20 Solar cell 21 Cu board 25 ITO layer

Claims (8)

In a pn junction solar cell in which a p layer and an n layer are stacked,
The p layer is made of Cu ₂ O;
The solar cell, wherein the n layer is made of amorphous In—Ga—Zn—O. The indium tin oxide substrate according to claim 1,
The p-layer formed on the indium tin oxide substrate;
The n layer formed on the p layer;
A solar cell comprising an electrode formed on the n layer. In claim 1, Cu plate;
The p layer formed by oxidizing the surface of the Cu plate;
The n layer formed on the p layer;
An electrode film made of indium tin oxide formed on the n layer;
A solar cell comprising an electrode formed on the electrode film.   2. The solar cell according to claim 1, wherein the p layer or the n layer is formed on a polymer substrate.   5. The solar cell according to claim 1, wherein the p layer and the n layer are formed by a sputtering method, a reactive sputtering method, a CVD method, or an evaporation method. In any one of Claims 1 thru | or 5, When the sum total of In, Ga, and Zn in the said n layer shall be 100 atm%,
In is 8 to 67 atm%,
Ga is 1 to 55 atm%,
Zn is 8 to 67 atm%
A solar cell characterized by being   The solar cell according to any one of claims 1 to 6, wherein the conversion efficiency of the solar cell is 0.67% or more.   8. The solar cell according to claim 1, wherein the p layer has an average particle diameter of 10 nm to 10 μm.

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