JP2005317563A - Sollar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery which ensures small environmental load and shows higher conversion efficiency in the solar battery using a compound semiconductor including the group Ib element, group IIIb element and group VIb element as the p-type semiconductor layer. <P>SOLUTION: The solar battery (1) comprises a first semiconductor layer (12) using a p-type semiconductor and a second semiconductor layer (13) using an n-type semiconductor. In this solar battery (1), the first semiconductor layer (12) and the second semiconductor layer (13) are coupled with the pn-joining method, the first semiconductor layer (12) includes the group Ib element, group IIIb element, and group VIb element; and the second semiconductor layer (13) is formed of three or more kinds of elements selected from a group including the elements of the third period and fourth period of the periodic table. Moreover, the lattice mismatching coefficient (%) calculated by ¾L<SB>1</SB>-L<SB>2</SB>¾/ä(L<SB>1</SB>+L<SB>2</SB>)/2}×100 is 3% or less when the lattice constant of the first semiconductor layer (12) is L<SB>1</SB>and the lattice constant of the second semiconductor layer (13) is L<SB>2</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solar cell, and more particularly to a solar cell using a compound semiconductor containing a group Ib element, a group IIIb element and a group VIb element for a p-type semiconductor layer.

Conventionally, CuInSe ₂ (hereinafter referred to as “CIS”), which is a compound semiconductor (chalcopyrite structure semiconductor) containing a group Ib element, a group IIIb element, and a group VIb element, or CuIn _{(1-X )} Ga _x Se ₂ (X is a real number between 0 <X <1, hereinafter referred to as “CIGS”) as a p-type semiconductor layer (hereinafter also referred to as “CIS solar cell”) However, it is known that it has the advantages of showing high energy conversion efficiency and little deterioration in conversion efficiency due to light irradiation or the like.

  A general method for producing a CIS solar cell will be described with reference to FIG. First, a first electrode layer 102 made of Mo or the like is formed on an insulating substrate 101 made of glass or the like by a vapor deposition method, a sputtering method, or the like. Next, a p-type semiconductor layer 103 made of CIS or CIGS is formed on the first electrode layer 102 by vapor deposition, sputtering, or the like. The p-type semiconductor layer 103 functions as a light absorption layer. Further, an n-type semiconductor layer 104 made of CdS is formed on the p-type semiconductor layer 103 by a chemical deposition method, an evaporation method, or the like, and is pn-junction with the p-type semiconductor layer 103. The n-type semiconductor layer 104 functions as a buffer layer. Then, a window layer 105 made of ZnO having a high electric resistance value is formed by a sputtering method or the like, and a second electrode layer 106 made of an indium oxide-tin oxide (hereinafter referred to as “ITO”) that is a transparent electrode is formed. It is formed by sputtering, chemical vapor deposition (CVD) or the like. Then, a first extraction electrode 108 and a second extraction electrode 109 are formed on part of the first and second electrode layers 102 and 106 by an electron beam evaporation method or the like, and the antireflection layer 107 is formed on the second electrode layer 106. Is formed by vapor deposition or the like, and the solar cell 100 is obtained.

In the solar cell 100, the interface between the p-type semiconductor layer 103 (CIS layer or CIGS layer) and the n-type semiconductor layer 104 (CdS layer) is a heterojunction, but the difference in lattice constant between the layers is small. Since the lattice mismatch rate between the layers is small, the solar cell 100 exhibits high conversion efficiency. Here, the lattice constants of the CIS layer and CIGS layer (composition ratio: In / Ga = 10/3) are 0.579 nm and 0.575 nm, respectively, and the lattice constant of the CdS layer is 0.582 nm. Even if any of the CIGS layers is used, the lattice mismatch rate between the layers is 2% or less. Note that the lattice mismatch rate in this specification is _expressed as | L _p −L _n | / [(L, where L _{p is} the lattice constant of the _p-type semiconductor layer and L _n is the lattice constant of the n-type semiconductor layer. _p + L _n ) / 2] × 100.

On the other hand, CIS solar cells not containing toxic Cd (that is, not using a CdS layer) have attracted attention from the viewpoint of preventing environmental pollution in recent years, and ZnO is used as an n-type semiconductor layer instead of the CdS layer. A solar cell using a layer or a mixed crystal compound semiconductor layer of ZnO, ZnS, and Zn (OH) ₂ has been reported (see, for example, Patent Document 1).
Japanese Patent No. 3249342

  However, in the solar cell described in Patent Document 1, for example, when a ZnO layer is used as the n-type semiconductor layer, the lattice constant of the ZnO layer is 0.325 nm, so the lattice mismatch rate with the CIS layer and the CIGS layer is 50% or more. In this case, the difference in lattice constant at the pn-junction hetero interface is large, that is, because the lattice mismatch rate is large, defects occur at the interface, and the frequency of carrier recombination at the junction interface during use increases. As compared with the case where the CdS layer is used, there is a possibility that the conversion efficiency, the fill factor FF, and the like are lowered.

  The present invention has been made to solve the above-mentioned problems, and in a solar cell using a compound semiconductor containing a group Ib element, a group IIIb element and a group VIb element for a p-type semiconductor layer, the environmental load is small, and A solar cell exhibiting high conversion efficiency is provided.

The solar cell of the present invention includes a first semiconductor layer using a p-type semiconductor and a second semiconductor layer using an n-type semiconductor, and the first semiconductor layer and the second semiconductor layer are pn-junctioned. The first semiconductor layer includes a group Ib element, a group IIIb element, and a group VIb element, and the second semiconductor layer includes a group consisting of elements in the third and fourth periods of the periodic table. When the lattice constant of the first semiconductor layer is L ₁ and the lattice constant of the second semiconductor layer is L ₂ , | L ₁ −L ₂ | / [(L ₁ + L ₂ ) / 2] × 100, the lattice mismatch rate (%) is 3% or less.

  According to the solar cell of the present invention, the second semiconductor layer is composed of three or more elements selected from the group consisting of the elements of the third period and the fourth period of the periodic table, and is toxic to the second semiconductor layer. Since high Cd is not included, a solar cell with a small environmental load can be realized. In addition, since the lattice mismatch rate between the first semiconductor layer and the second semiconductor layer is 3% or less, generation of defects at the heterojunction interface can be suppressed. Thereby, since the recombination frequency of the carrier at the joint interface at the time of use is reduced, the conversion efficiency can be improved.

The solar cell of the present invention includes a first semiconductor layer using a p-type semiconductor and a second semiconductor layer using an n-type semiconductor, and the first semiconductor layer and the second semiconductor layer are pn-junctioned. The pn junction can be formed, for example, by sequentially laminating a first semiconductor layer and a second semiconductor layer on an electrode layer made of Mo or the like by an evaporation method or the like. The first semiconductor layer is a compound semiconductor layer containing an Ib group element, an IIIb group element, and a VIb group element. For example, CIS, CIGS, CuInS _2, or the like described in the background art can be used. The second semiconductor layer is composed of three or more elements selected from the group consisting of elements in the third and fourth periods of the periodic table. Thereby, since the highly toxic Cd is not included in the second semiconductor layer, a solar cell with a small environmental load can be realized. As the semiconductor that can be used as the second semiconductor layer, a ternary compound semiconductor composed of three elements and a quaternary compound semiconductor composed of four elements are preferable. As the ternary compound semiconductor, a compound semiconductor represented by the general formula Zn _(1-X) M _X Se is preferable. However, X in the formula is a real number between 0 <X <1, and M in the formula is any one element of Mg and Mn. As the quaternary compound semiconductor, a compound semiconductor composed of Zn, Mg, S, and Se and a compound semiconductor composed of Zn, Mn, S, and Se are suitable.

In the solar cell of the present invention, when the lattice constant of the first semiconductor layer is L ₁ and the lattice constant of the second semiconductor layer is L ₂ , | L ₁ −L ₂ | / [(L ₁ + L ₂ ) / 2] The lattice mismatch rate (%) calculated by x100 is 3% or less. Thereby, since the recombination frequency of the carrier at the bonding interface at the time of use is reduced, the conversion efficiency can be improved.

Here, when CIS or CIGS is used as the first semiconductor layer and a compound semiconductor represented by the general formula Zn _(1-X) M _X Se is used as the second semiconductor layer, the lattice constant of the first semiconductor layer is 0. 561 to 0.579 nm, in order to satisfy the above condition, as the second semiconductor layer, when X in the formula is M is Mg: more than 0 and 0.52 or less, and M is Mn Case: A compound semiconductor that exceeds 0 and becomes 0.48 or less may be used. When CIS or CIGS is used as the first semiconductor layer and a compound semiconductor composed of Zn, Mg, S and Se is used as the second semiconductor layer, the composition ratio is Zn / Mg in order to satisfy the above condition. / S / Se = 0 to a real number that is 0.5 or less / a real number that is greater than 0 to 0.6 or less / a compound number that is 0.05 to 0.3 / 0.05 to 0.6 That's fine. When CIS or CIGS is used as the first semiconductor layer and a compound semiconductor composed of Zn, Mn, S and Se is used as the second semiconductor layer, the composition ratio is Zn / Mn in order to satisfy the above condition. / S / Se = 0 to a real number that is 0.5 or less / a compound number that is a real number that is greater than 0 to 0.6 or less / 0.1 to 0.3 / 0.1 to 0.6 That's fine.

Further, the thickness of the first semiconductor layer is preferably 1.0 to 3.0 μm. If it is less than 1 μm, it is difficult to absorb light, and a photocurrent may not be sufficiently obtained. On the other hand, if it exceeds 3 μm, the diffusion length of minority carriers is expected to be 1 to 3 μm, so electrons (carriers) generated in the vicinity of the back electrode film are recombined during movement, and a photocurrent cannot be obtained sufficiently. there is a possibility. Further, the thickness of the second semiconductor layer is preferably 3 to 15 nm. If the thickness is less than 3 nm, it is difficult to form a uniform pn junction. On the other hand, if it exceeds 15 nm, the tunnel current hardly flows. For example, in the case of the compound semiconductor represented by the general formula Zn _(1-X) M _X Se described above, the offset in the conduction band is 0.4 eV or more, and the film thickness must be 15 nm or less in order for the tunnel current to flow. I must.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. FIG. 1 to be referred to is a cross-sectional view of a solar cell according to an embodiment of the present invention.

  As illustrated in FIG. 1, a solar cell 1 according to an embodiment of the present invention includes a substrate 10, a first electrode layer 11, a first semiconductor layer 12, a second semiconductor layer 13 that are sequentially stacked on the substrate 10, The window layer 14, the second electrode layer 15, and the antireflection layer 16, and the first extraction electrode 17 and the second extraction electrode 18 formed on a part of the first and second electrode layers 11 and 15 are provided. . In the solar cell 1, light is incident from the antireflection layer 16 side when in use.

For the substrate 10, for example, glass, stainless steel, polyimide, or the like can be used. For the first electrode layer 11, for example, a metal layer such as Mo can be used, and the thickness is preferably 0.2 to 2 μm. For the first semiconductor layer 12 and the second semiconductor layer 13, it is preferable to use the compound semiconductor layer having the material and thickness described above. As the window layer 14, for example, a ZnO layer can be used, and the thickness is preferably 30 to 200 nm. The resistance value of the window layer 14 is preferably 1.0 × 10 ⁴ Ω · cm or more. The second electrode layer 15 is a transparent conductive layer. For example, ZnO—Al in which ZnO is doped with Al, ITO, or the like can be used, and the thickness is preferably 0.05 to 2 μm. The antireflection layer 16 is provided to prevent reflection of incident light at the interface with the second electrode layer 15. When the second electrode layer 15 is made of ITO or ZnO—Al, for example, MgF ₂ is used. be able to. Further, the thickness of the antireflection layer 16 is preferably 80 to 150 nm when the second electrode layer 15 is made of ITO or ZnO—Al. For the first and second extraction electrodes 17 and 18, for example, a metal layer in which a NiCr layer and an Au layer are laminated can be used, and a preferable thickness is 100 to 100 for both the first and second extraction electrodes 17 and 18. 300 nm. In addition, since the manufacturing method of the solar cell 1 is the same as the manufacturing method of the solar cell 100 demonstrated by background art, description is abbreviate | omitted.

  Examples of the present invention will be described below with reference to comparative examples that depart from the scope of the claims. In addition, this invention is not limited to this Example.

Example 1
As Example 1, a solar cell having a configuration excluding the antireflection layer 16 in the solar cell 1 (see FIG. 1) according to the embodiment of the present invention described above was manufactured. The material, thickness, and formation method of each layer are: substrate: glass (0.7 mm), first electrode layer: Mo (0.8 μm, formed by sputtering), first semiconductor layer: CIGS (2 μm, formed by multi-source deposition) Second semiconductor layer: Zn _0.68 Mn _0.32 Se (10 nm, formed by vapor deposition), window layer: ZnO (100 nm, formed by sputtering), second electrode layer: ITO (150 nm, formed by sputtering), first extraction electrode And a second extraction electrode: a metal layer (100 nm, formed by electron beam evaporation) in which a NiCr layer and an Au layer were laminated.

(Comparative Example 1)
As Comparative Example 1, Zn _0.68 Mn _0.32 Se used as the second semiconductor layer in the configuration of Example 1 was changed to a mixed crystal compound semiconductor of ZnO and ZnS, and the other conditions were the same as in Example 1. Produced. The composition ratio of the mixed crystal compound was ZnO / ZnS = 0.7 / 0.3.

(Evaluation)
For Example 1 and Comparative Example 1, photoelectric conversion characteristics were evaluated. The evaluation was performed by irradiating pseudo-sunlight of air mass (AM) 1.5, 100 mW / cm ² from the second electrode layer (transparent electrode layer) side. The results are shown in Table 1. In Table 1, the lattice constants of the first and second semiconductor layers were measured by an X-ray diffraction method.

As shown in Table 1, in Comparative Example 1, since the lattice mismatch rate does not satisfy the conditions of the present invention, the carrier recombination frequency at the junction interface increases, and the conversion efficiency Eff, compared with Example 1, The values of the open circuit voltage V _OC and the fill factor FF were lowered. From the above results, the solar cell of the present invention was able to obtain good photoelectric conversion characteristics by setting the lattice mismatch ratio (%) between the first semiconductor layer and the second semiconductor layer to 3% or less. .

  Since the environmental impact of the solar cell of the present invention is small, it can be installed in various places. Moreover, since conversion efficiency is high, an installation area can be made small compared with the conventional solar cell. Therefore, for example, solar cells that can be installed on roofs of various sizes for residential use can be provided.

It is sectional drawing of the solar cell which concerns on one Embodiment of this invention. It is sectional drawing of the conventional solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solar cell 12 1st semiconductor layer 13 2nd semiconductor layer

Claims (5)

a solar cell including a first semiconductor layer using a p-type semiconductor and a second semiconductor layer using an n-type semiconductor, wherein the first semiconductor layer and the second semiconductor layer are pn-junction,
The first semiconductor layer includes a group Ib element, a group IIIb element, and a group VIb element;
The second semiconductor layer is composed of three or more elements selected from the group consisting of elements in the third and fourth periods of the periodic table,
When the lattice constant of the first semiconductor layer is L ₁ and the lattice constant of the second semiconductor layer is L ₂ , it is calculated as | L ₁ −L ₂ | / [(L ₁ + L ₂ ) / 2] × 100. A solar cell having a lattice mismatch rate (%) of 3% or less. The solar cell according to claim 1, wherein the second semiconductor layer is made of a compound semiconductor represented by a general formula Zn _(1-X) M _X Se. [However, X in the formula is a real number between 0 <X <1, and M in the formula is any one element of Mg and Mn. ]   The solar cell according to claim 1, wherein the second semiconductor layer is made of Zn, Mg, S, and Se.   The solar cell according to claim 1, wherein the second semiconductor layer is made of Zn, Mn, S, and Se.   The thickness of the said 2nd semiconductor layer is 15 nm or less, The solar cell of any one of Claims 1-4.

Images