JP2005347566A - Solar battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery in which characteristics such as conversion efficiency is improved and a method for manufacturing the solar battery. <P>SOLUTION: The solar battery comprises a first electrode layer, a second electrode layer, a p-type semiconductor layer arranged between the first and second electrode layers, and an n-type semiconductor layer arranged between the p-type semiconductor layer and the 2nd electrode layer. The p-type semiconductor layer is a compound semiconductor layer containing a group Ib element, a group IIIb element, a group VIb element, and Zn. The concentration of Zn contained in the p-type semiconductor layer has composition gradient so that the concentration is increased from the first electrode layer to the n-type semiconductor layer in the film thickness direction of the p-type semiconductor layer. It is defined that the electron affinity of the p-type semiconductor layer is χ1 (eV), and the electron affinity of the n-type semiconductor layer is χ2 (eV). Relation expressed by an expression 0≤(χ1-χ2)<0.5 is satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

A thin film solar cell using a compound semiconductor layer (chalcopyrite structure compound semiconductor thin film) composed of a group Ib element, a group IIIb element, and a group VIb element as a light absorption layer has been reported. For example, CuInSe ₂ (hereinafter also referred to as “CIS”) or Cu (In, Ga) Se ₂ (hereinafter also referred to as “CIGS”) in which Ga is dissolved in CIS is one type of the compound semiconductor. Can be mentioned. A thin film solar cell using the above CIS or CIGS as a light absorption layer (hereinafter also referred to as “CIS solar cell”) has high energy conversion efficiency and excellent properties such as no deterioration of conversion efficiency due to light irradiation or the like. It has been known. Compound semiconductors such as CIS and CIGS are p-type semiconductors, and a solar cell having a p-type semiconductor layer as a light absorption layer is obtained by forming an n-type semiconductor layer so as to be pn-junction with the p-type semiconductor layer. (For example, described in Patent Document 1).
Japanese Patent Laid-Open No. 08-330232

  However, when an n-type semiconductor layer is formed on a p-type semiconductor layer that is a light absorption layer, for example, on a CIGS thin film using a method such as sputtering, a stable pn junction is formed due to defects present on the surface of the CIGS thin film. There is a possibility that it cannot be formed. If the state of the pn junction is disturbed, sufficient solar cell characteristics (for example, conversion efficiency) may not be obtained.

  In view of such a situation, the present invention provides a solar cell in which a pn junction better than the conventional one is formed between a p-type semiconductor layer and an n-type semiconductor layer, which are light absorption layers, and is excellent in characteristics such as conversion efficiency. It is an object of the present invention to provide a manufacturing method thereof.

  The solar cell of the present invention includes a first electrode layer, a second electrode layer, a p-type semiconductor layer disposed between the first electrode layer and the second electrode layer, and the p-type. A solar cell including a semiconductor layer and an n-type semiconductor layer disposed between the second electrode layer, wherein the p-type semiconductor layer comprises a group Ib element, a group IIIb element, a group VIb element, and Zn. The concentration of Zn contained in the p-type semiconductor layer is increased in the film thickness direction of the p-type semiconductor layer from the first electrode layer toward the n-type semiconductor layer. When the electron affinity of the p-type semiconductor layer is χ1 (eV) and the electron affinity of the n-type semiconductor layer is χ2 (eV), χ1 and χ2 are expressed by the formula 0 ≦ ( (χ1-χ2) <0.5 is satisfied.

Next, the method for manufacturing a solar cell according to the present invention includes a first electrode layer, a second electrode layer, and a p-type semiconductor disposed between the first electrode layer and the second electrode layer. A method for manufacturing a solar cell, comprising: a layer; and an n-type semiconductor layer disposed between the p-type semiconductor layer and the second electrode layer,
(I) a step of sequentially stacking a first electrode layer and a p-type semiconductor layer on a substrate to form a first stacked body including the substrate, the first electrode layer, and the p-type semiconductor layer; ,
(Ii) doping the p-type semiconductor layer with Zn;
(Iii) The n-type semiconductor layer is stacked so that the p-type semiconductor layer doped with Zn is sandwiched between the first electrode layer and the n-type semiconductor layer, and the stacked n-type semiconductor layer is the p-type semiconductor layer. Laminating the second electrode layer so as to be sandwiched between the type semiconductor layer and the second electrode layer to form a second stacked body, and the p-type semiconductor layer includes a group Ib element and A compound semiconductor layer containing a group IIIb element and a group VIb element, and in the step (iii), an n-type semiconductor layer having an electron affinity of χ 2 (eV) is stacked. However, in the method for manufacturing a solar cell of the present invention, χ2 has the relationship represented by the formula 0 ≦ (χ1−χ2) <0.5 when the electron affinity of the p-type semiconductor layer is χ1 (eV). It is a positive numerical value that satisfies.

  ADVANTAGE OF THE INVENTION According to this invention, the solar cell excellent in characteristics, such as conversion efficiency, and its manufacturing method can be provided. In particular, according to the present invention, it is possible to provide a CIS or CIGS solar cell capable of increasing efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts may be denoted by the same reference numerals and overlapping description may be omitted.

  First, the solar cell of the present invention will be described.

  An example of the solar cell of the present invention is shown in FIG. A solar cell 1 shown in FIG. 1 includes a first electrode layer 12, a second electrode layer 16, and a p-type semiconductor layer 13 disposed between the first electrode layer 12 and the second electrode layer 16. And an n-type semiconductor layer 15 disposed between the second electrode layer 16 and the p-type semiconductor layer 13. Each layer is formed on the substrate 11. The p-type semiconductor layer 13 includes a group Ib element, a group IIIb element, a group VIb element, and Zn (zinc). The p-type semiconductor layer 13 is, for example, a compound semiconductor layer having a chalcopyrite crystal structure. Here, the composition gradient is such that the concentration of Zn contained in the p-type semiconductor layer 13 increases in the film thickness direction of the p-type semiconductor layer 13 from the first electrode layer 12 toward the n-type semiconductor layer 15. doing. Further, when the electron affinity of the p-type semiconductor layer 13 is χ1 (eV) and the electron affinity of the n-type semiconductor layer 15 is χ2 (eV), χ1 and χ2 are expressed by the equation 0 ≦ (χ1-χ2) <0. 5 is satisfied.

  By using such a solar cell, a solar cell in which the state of the pn junction formed between the p-type semiconductor layer 13 and the n-type semiconductor layer 15 is good (for example, there are few interface defects) is obtained. it can. For this reason, it can be set as the solar cell excellent in characteristics, such as conversion efficiency.

  In addition, the p-type semiconductor layer 13 is a light absorption layer, and the solar cell 1 of the present invention is a solar cell that generates photovoltaic power by light incident from the second electrode layer 16 side. The generated photovoltaic power is transmitted to the outside through the extraction electrode 17 electrically connected to the first electrode layer 12 and the extraction electrode 18 electrically connected to the second electrode layer 16. Can do.

  Further, in the solar cell 1 shown in FIG. 1, the first electrode layer 12, the p-type semiconductor layer 13, the n-type semiconductor layer 15 and the second electrode layer 16 are disposed on the substrate 11, but the present invention. In the solar cell, the substrate 11 is not necessarily required. At least the second electrode layer 16, the n-type semiconductor layer 15, the p-type semiconductor layer 13, and the first electrode layer 12 arranged in this order from the light incident side may be included, and the substrate 11 may be used as necessary. Can be omitted. Similarly to the substrate 11, the extraction electrodes 17 and 18 can be omitted if necessary. In addition, in the solar cell 1 of this invention, arbitrary layers may be arrange | positioned as needed between each layer mentioned above.

  In the solar cell of the present invention, the p-type semiconductor layer 13 is a compound semiconductor layer having a chalcopyrite structure containing a group Ib element, a group IIIb element, a group VIb element, and Zn. The form (state of each said element in the p-type semiconductor layer 13) in which the p-type semiconductor layer 13 contains said each element is not specifically limited. For example, the p-type semiconductor layer 13 may be a p-type compound semiconductor (I-III-VI compound semiconductor) containing a group Ib element, a group IIIb element, and a group VIb element, doped with Zn.

  The distribution of Zn in the p-type semiconductor layer 13 is, for example, a composition such that the Zn concentration increases in the thickness direction of the p-type semiconductor layer 13 from the first electrode layer 12 toward the n-type semiconductor layer 15. It only needs to be sloped. In particular, it is preferable that the concentration of Zn is substantially 0 in the vicinity of the main surface facing the first electrode layer 12 in the p-type semiconductor layer 13. By setting the Zn concentration to approximately 0, the state of the pn junction formed between the p-type semiconductor layer 13 and the n-type semiconductor layer 15 can be improved. When the I-III-VI compound semiconductor is the p-type semiconductor layer 13 doped with Zn, the doping amount of Zn in the p-type semiconductor layer 13 is the first electrode layer in the film thickness direction of the p-type semiconductor layer 13. It can be said that the gradient is increased from 12 toward the n-type semiconductor layer 15. Such a p-type semiconductor layer 13 can be obtained, for example, by the method for manufacturing a solar cell of the present invention described later. The composition gradient of Zn may be continuous or stepwise.

  In addition, as shown in FIG. 2, the p-type semiconductor layer 13 includes a first region 14b that contains relatively much Zn and a second region 14a that contains relatively little Zn, and the first region 14 b may be disposed in the vicinity of the main surface 22 facing the n-type semiconductor layer 15 in the p-type semiconductor layer 13. The state of the pn junction formed between the p-type semiconductor layer 13 and the n-type semiconductor layer 15 can be improved. In particular, it is preferable that the second region 14a does not substantially contain Zn. Such a p-type semiconductor layer 13 can be formed, for example, by the method for manufacturing a solar cell of the present invention described later. Although a specific description will be given later, for example, as shown in FIG. 4B, Zn may be doped from the main surface 22 of the p-type semiconductor layer. The distance doped with Zn (doping distance) can be the thickness d of the first region 14b shown in FIG. It can be said that the first region 14b is a Zn-doped layer described later. The thickness d of the first region 14b is, for example, in the range of about 3 nm to 30 nm.

  In other words, as shown in FIG. 3, the solar cell of the present invention is provided between the first electrode layer 12, the second electrode layer 16, and the first electrode layer 12 and the second electrode layer 16. P-type semiconductor layer 13 and n-type semiconductor layer 15 arranged between second electrode layer 16 and p-type semiconductor layer 13. Includes a first region (Zn-doped layer) 14b including a large amount of Zn and a second region 14a including a relatively small amount of Zn, and the first region 14b is disposed so as to face the n-type semiconductor layer 15. It can be said that there is.

Specific types of the Ib group element, IIIb group element, and VIb group element contained in the p-type semiconductor layer 13 are not particularly limited. For example, Cu (copper) is used as the Ib group element, and In (indium) is used as the IIIb group element. And at least one element selected from Ga (gallium) may contain at least one element selected from Se (selenium) and S (sulfur) as a VIb group element. More specifically, for example, CuInSe ₂ , Cu (In, Ga) Se ₂ , or a compound semiconductor in which a part of Se is substituted with S may be used. Such a solar cell is a CIS or CIGS solar cell, and can be a solar cell with more excellent conversion efficiency. The thickness of the p-type semiconductor layer 13 is, for example, in the range of about 0.4 μm to 3.5 μm. The shape of the p-type semiconductor layer 13 is not particularly limited and may be set arbitrarily. The shape of the other layers is not particularly limited as is the case with the p-type semiconductor layer 13.

The n-type semiconductor layer 15 can form a pn junction with the p-type semiconductor layer 13, the electron affinity of the p-type semiconductor layer 13 is χ1 (eV), and the electron affinity of the n-type semiconductor layer 15 is χ2 (eV). Sometimes, the composition and the like are not particularly limited as long as χ1 and χ2 satisfy the relationship represented by the expression 0 ≦ (χ1−χ2) <0.5. Among these, the n-type semiconductor layer 15 containing Zn, Mg, and O is preferable. In such a solar cell, a pn junction having a more ideal electron affinity can be formed between the p-type semiconductor layer 13 and the n-type semiconductor layer 15. For this reason, it can be set as the solar cell excellent in characteristics, such as conversion efficiency. As the n-type semiconductor layer 15 whose electron affinity is χ2, for example, when the p-type semiconductor layer 13 is Cu (In, Ga) Se ₂ , the n-type semiconductor layer 15 has a composition represented by the formula Zn _0.9 Mg _0.1 O. The semiconductor layer 15 is mentioned.

Although the specific composition of the n-type semiconductor layer 15 containing Zn, Mg, and O is not particularly limited, it is an n-type semiconductor layer having a composition represented by the formula Zn _1-x Mg _x A _y O. Is preferred. In the above formula, A is at least one element selected from Ca (calcium), Sr (strontium) and Ba (barium), and x is represented by the formula 0.05 ≦ x ≦ 0.35. Y is a numerical value that satisfies the relationship, and y is a numerical value that satisfies the relationship represented by the expression 0.00005 ≦ y ≦ 0.005. In such a solar cell, the electrical resistance of the n-type semiconductor layer 16 can be further reduced. For this reason, it can be set as the solar cell which is excellent in characteristics, such as the electrical conductivity as the whole battery, and conversion efficiency. In the above composition formula, a stoichiometric ratio is not necessarily established between oxygen and an element other than O (oxygen). For example, oxygen may be partially lost. Note that the thickness of the n-type semiconductor layer 15 may be in the range of 50 nm to 0.3 μm, for example.

  The material used for the board | substrate 11 is not specifically limited, What is necessary is just the material generally used for a solar cell. For example, a glass substrate, a stainless steel substrate, a polyimide substrate, or the like may be used. When the solar cell to be manufactured is an integrated type and the substrate is a conductive substrate (for example, a stainless steel substrate), a process of forming an insulating layer on the surface of the substrate or insulating the surface of the substrate Must be performed in advance.

The material used for the first electrode layer 12 is not particularly limited as long as it has conductivity. For example, a metal or semiconductor having a volume resistivity of 6 × 10 ⁶ Ω · cm or less may be used. Specifically, for example, Mo (molybdenum) may be used as the first electrode layer 12. The thickness of the first electrode layer 12 may be in the range of about 0.1 μm to 1 μm, for example.

  As the second electrode layer 16 disposed on the light incident side, for example, a light-transmitting conductive material may be used. The “translucency” here may be any translucency with respect to light in a band incident on the solar cell. Specifically, for example, indium tin oxide (ITO), ZnO, or a laminated film of these materials may be used. The thickness of the second electrode layer 16 may be in the range of about 0.1 μm to 0.3 μm, for example.

  The material used for extraction electrode 17 and 18 is not specifically limited, What is necessary is just the material generally used for a solar cell. For example, NiCr, Ag, Au, Al, etc. may be used.

  Next, the manufacturing method of the solar cell of this invention is demonstrated.

  The method for manufacturing a solar cell according to the present invention includes a first electrode layer, a second electrode layer, a p-type semiconductor layer disposed between the first electrode layer and the second electrode layer, and a p-type. It is a manufacturing method of the solar cell containing the n-type semiconductor layer arrange | positioned between the semiconductor layer and the 2nd electrode layer. The p-type semiconductor layer is a compound semiconductor layer that includes a group Ib element, a group IIIb element, and a group VIb element and has a chalcopyrite structure.

  An example of the manufacturing method of the solar cell of this invention is shown to Fig.4 (a)-FIG.4 (c).

  First, as shown in FIG. 4A, the first electrode layer 12 and the p-type semiconductor layer 13 are sequentially stacked on the substrate 11, and the substrate 11, the first electrode layer 12, and the p-type semiconductor layer 13 are stacked. Is formed (step (i)).

  Next, as shown in FIG. 4B, the p-type semiconductor layer 13 is doped with Zn (step (ii)).

  Next, as shown in FIG. 4C, the n-type semiconductor layer 15 is stacked so that the p-type semiconductor layer 13 doped with Zn is sandwiched between the first electrode layer 12 and the n-type semiconductor layer 15. . In the example shown in FIG. 4C, the n-type semiconductor layer 15 is stacked on the p-type semiconductor layer 13. The n-type semiconductor layer 15 to be stacked at this time has the formula 0 ≦ (χ1-χ2) when the electron affinity of the p-type semiconductor layer 13 is χ1 (eV) and the electron affinity of the n-type semiconductor layer 15 is χ2 (eV). ) <0.5 which satisfies the relationship represented by <0.5.

  Subsequently, the second electrode layer is stacked so that the stacked n-type semiconductor layer 15 is sandwiched between the p-type semiconductor layer 13 and the second electrode layer 16 to form a stacked body 23. In the example shown in FIG. 4C, the second electrode layer 16 is stacked on the n-type semiconductor layer 15.

  In such a manufacturing method, the p-type semiconductor layer 13 is doped with Zn in the step (ii) so that the p-type semiconductor layer 13 and the n-type semiconductor layer 15 stacked in the step (iii) are conventionally used. Can be formed (for example, with few interface defects). For this reason, the solar cell excellent in characteristics, such as conversion efficiency, can be manufactured. In addition, the solar cell obtained by the manufacturing method of the present invention is a solar cell in which the p-type semiconductor layer 13 is a light absorption layer and a photovoltaic power is generated by light incident from the second electrode layer 16 side. Moreover, in the manufacturing method of this invention, you may form the extraction electrodes 17 and / or 18 as needed. The solar cell 1 of the present invention as shown in FIG. 1 and / or FIG. 3 can be manufactured. The method of forming the extraction electrodes 17 and 18 is not particularly limited as long as each extraction electrode can be electrically connected to each electrode layer, and a general method may be used. Moreover, you may laminate | stack arbitrary layers between each layer which comprises a solar cell as needed.

  The material used for the board | substrate 11 is not specifically limited, What is necessary is just the material generally used for a solar cell. For example, a glass substrate, a stainless steel substrate, a polyimide substrate, or the like may be used. When the solar cell to be manufactured is an integrated type and the substrate is a conductive substrate (for example, a stainless steel substrate), a process of forming an insulating layer on the surface of the substrate or insulating the surface of the substrate Must be performed in advance.

For the lamination of the first electrode layer 12 in the step (i), a method generally used for manufacturing a solar cell may be used, and for example, a sputtering method, a vapor deposition method, or the like may be used. The material used for the first electrode layer 12 is not particularly limited as long as it has conductivity. For example, a metal or semiconductor having a volume resistivity of 6 × 10 ⁶ Ω · cm or less may be used. Specifically, for example, Mo (molybdenum) may be stacked as the first electrode layer 12. The shape of the 1st electrode layer 12 is not specifically limited, What is necessary is just to laminate | stack in arbitrary shapes according to a shape required as a solar cell. The laminated shape is the same for the layers other than the first electrode layer 12. The thickness of the 1st electrode layer 12 to laminate | stack should just be the range of about 0.1 micrometer-1 micrometer, for example.

For the lamination of the p-type semiconductor layer 13 in the step (i), a method generally used for manufacturing a solar cell may be used, and for example, a vapor deposition method or a selenization method may be used. The material used for the p-type semiconductor layer 13 is not particularly limited as long as the compound semiconductor has a chalcopyrite structure with a group Ib element, a group IIIb element, and a group VIb element as main constituent elements. Specifically, for example, the p-type semiconductor layer 13 including Cu (copper), at least one element selected from In and Ga, and at least one element selected from Se (selenium) and S (sulfur). What is necessary is just to laminate. More specifically, for example, CuInSe ₂ , Cu (In, Ga) Se ₂ , or a compound semiconductor in which a part of Se is substituted with S may be stacked as the p-type semiconductor layer 13. In such a manufacturing method, a CIS or CIGS solar cell can be obtained, and thus a solar cell with higher conversion efficiency can be manufactured. The thickness of the p-type semiconductor layer 13 to be stacked is, for example, in the range of about 0.4 μm to 3.5 μm.

  The region of the p-type semiconductor layer 13 doped with Zn in the step (ii) is not particularly limited. For example, a part of the p-type semiconductor layer 13 may be doped with Zn. For example, Zn is contained so that the concentration of Zn contained in the p-type semiconductor layer 13 becomes higher from the first electrode layer 12 side in the film thickness direction of the p-type semiconductor layer 13 (so as to have a concentration gradient). What is necessary is just to dope. In particular, as shown in FIG. 4B, Zn may be doped in the vicinity of the main surface 22 opposite to the main surface facing the first electrode layer 12 in the p-type semiconductor layer 13. preferable. By such a manufacturing method, a pn junction can be formed better between the p-type semiconductor layer 13 and the n-type semiconductor layer 15, so that a solar cell that is superior in characteristics such as conversion efficiency can be manufactured. it can. The vicinity of the main surface is, for example, the distance from the main surface 22 in the p-type semiconductor layer 13 in FIG. 4B (doping distance: d shown in FIG. 2 corresponds to the above distance), for example, The range is about 3 nm to 30 nm. The doping distance does not need to be constant throughout the p-type semiconductor layer 13 and may vary partially.

  When doping a part of the p-type semiconductor layer 13 with Zn, the step (ii) is a step of forming a Zn-doped layer inside the p-type semiconductor layer by doping Zn into the p-type semiconductor layer. It can be said that there is. At this time, it is preferable to form a Zn-doped layer in the vicinity of the main surface opposite to the main surface facing the first electrode layer in the p-type semiconductor layer. The thickness of the Zn doped layer to be formed may be the same as the doping distance described above. In this manufacturing method, for example, a solar cell as shown in FIG. 3 can be manufactured. In this case, the Zn-doped layer is a layer corresponding to the first region 14b shown in FIG.

  The amount of Zn doped into the p-type semiconductor layer 13 in the step (ii) is not particularly limited. In the region of the p-type semiconductor layer 13 doped with Zn, the doping amount of Zn may be in the range of, for example, about 1 (at%) to 15 (at%).

  The method of doping the p-type semiconductor layer 13 with Zn in the step (ii) is not particularly limited. For example, the p-type semiconductor layer 13 may be irradiated with Zn ions. At this time, the doping distance and the doping amount can be controlled by controlling the energy of the irradiated Zn ions.

  Alternatively, the p-type semiconductor layer 13 may be doped with Zn by bringing the solution containing Zn into contact with the p-type semiconductor layer 13. At this time, the doping distance and the doping amount of Zn can be controlled by controlling the concentration of the solution containing Zn, the time for which the solution and the p-type semiconductor layer 13 are brought into contact with each other. Moreover, in such a manufacturing method, Zn can be doped more uniformly. Further, the doping distance can be further reduced (that is, the region doped with Zn (for example, the Zn doped layer) in the p-type semiconductor layer 13 can be made thinner).

  More specifically, for example, the p-type semiconductor layer 13 may be doped with Zn by immersing the stacked body 21 formed in the step (i) in a solution containing Zn. In such a manufacturing method, Zn can be more easily doped, and thus a manufacturing method having excellent manufacturing cost can be obtained.

  The solution containing Zn is not particularly limited, and may be a solution containing Zn ions, for example. Specifically, for example, Zn sulfate (zinc sulfate), chloride (zinc chloride), iodide (zinc iodide), bromide (zinc bromide), nitrate (zinc nitrate) and acetate (zinc acetate) The aqueous solution of at least one compound selected from The concentration of the aqueous solution is not particularly limited. For example, the concentration of Zn ions in the aqueous solution may be in the range of 0.01 mol / L to 0.03 mol / L. In the above concentration range, a better Zn doped layer can be formed. In addition, the time which immerses the laminated body 21 in the solution containing Zn is not specifically limited, What is necessary is just to set arbitrarily according to required dope distance (or thickness of required Zn dope layer).

  For the lamination of the n-type semiconductor layer 15 in the step (iii), a method generally used for manufacturing a solar cell, for example, a vapor deposition method or a sputtering method may be used. The thickness of the n-type semiconductor layer 15 to be stacked may be in the range of 50 nm to 0.3 μm, for example.

  Especially, it is preferable to laminate | stack the n-type semiconductor layer 15 containing Zn, Mg, and O in process (iii). In such a manufacturing method, a pn junction having a more ideal electron affinity can be formed between the p-type semiconductor layer 13 and the n-type semiconductor layer 15. For this reason, the solar cell which is excellent in characteristics, such as conversion efficiency, can be manufactured.

Although the specific composition of the n-type semiconductor layer 15 containing Zn, Mg, and O is not particularly limited, it is an n-type semiconductor layer having a composition represented by the formula Zn _1-x Mg _x A _y O. Is preferred. In the above formula, A is at least one element selected from Ca, Sr and Ba, x is a numerical value satisfying the relationship represented by the formula 0.05 ≦ x ≦ 0.35, and y is The numerical value satisfying the relationship represented by the expression 0.00005 ≦ y ≦ 0.005. In such a manufacturing method, the electrical resistance of the n-type semiconductor layer 16 can be further reduced. For this reason, it is excellent in the electrical conductivity as the whole battery, and the solar cell which is excellent in characteristics, such as conversion efficiency, can be manufactured. Note that a stoichiometric ratio is not necessarily established between oxygen and an element other than O (oxygen). For example, oxygen may be partially lost.

  The method for laminating the n-type semiconductor layer 15 having the above composition is not particularly limited. For example, a sputtering method or a vapor deposition method may be used. According to the sputtering method or the vapor deposition method, the composition of the n-type semiconductor layer 15 to be stacked can be controlled relatively easily by changing the composition of the target (or vapor deposition source). Specifically, for example, a target including at least one element A selected from Ca, Sr, and Ba, Zn, Mg, and O may be used. A plurality of targets having different compositions may be used. In addition, the n-type semiconductor layer 15 may be formed using a target including the element A, Zn, and Mg in a weak oxidizing atmosphere. Even in this case, a plurality of targets having different compositions may be used.

  For the lamination of the second electrode layer 16 in the step (iii), a method generally used for manufacturing a solar cell, for example, a sputtering method may be used. As the second electrode layer 16 on the light incident side, for example, a light-transmitting conductive material may be stacked. Specifically, for example, indium tin oxide (ITO), ZnO, or a stacked film of these materials may be stacked. The thickness of the second electrode layer 16 to be laminated may be in the range of about 0.1 μm to 0.3 μm, for example.

  When the extraction electrodes 17 and / or 18 are further formed, the material used for the extraction electrodes 17 and 18 is not particularly limited as long as it is a material generally used for solar cells. For example, the extraction electrodes 17 and / or 18 may be formed by arranging NiCr, Ag, Au, Al, or the like. A generally used method may be used for the formation. When the extraction electrodes 17 and 18 are formed, a solar cell as shown in FIG. 1 and / or FIG. 3 can be manufactured.

  In the manufacturing method of the present invention, between step (ii) and step (iii), a step of heat-treating the stacked body 21 after doping the p-type semiconductor layer 13 with Zn in step (ii) (step (a)) ) May further be included. By performing the heat treatment, a better pn junction can be formed between the p-type semiconductor layer 13 and the n-type semiconductor layer 15.

  The heat treatment of the stacked body 21 is preferably performed in an inert gas atmosphere from the viewpoint of maintaining the composition of the formed stacked body 21. Specifically, for example, nitrogen gas, rare gas, or an atmosphere containing these gases may be used. For example, argon gas may be used as the rare gas. The temperature of heat processing is the range of 250 to 450 degreeC, for example, and the range of 300 to 400 degreeC is preferable. Although the heat treatment time varies depending on the heat treatment temperature, it may be, for example, in the range of about 5 minutes to 30 minutes. The method for applying heat to the stacked body 21 is not particularly limited, and may be performed, for example, by heating the substrate 11 or heating the entire stacked body 21.

  Moreover, you may perform the said heat processing with respect to the laminated body 23 formed in process (iii) after process (iii). The same effect as when the heat treatment is performed on the stacked body 21 can be obtained. In addition, when heat treatment is performed on the stacked body 23, the characteristics of the n-type semiconductor layer 15 can be further improved. For this reason, you may use together the heat processing with respect to the laminated body 21, and the heat processing with respect to the laminated body 23. FIG.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the following examples.

(Example 1)
In Example 1, Cu (In, Ga) to a thin film formed of Se ₂ by contacting a solution containing Zn ions and verify Zn can be doped Cu (In, Ga) to Se ₂ film.

First, a Mo film (thickness: 1 μm) is formed as a first electrode layer on a glass substrate by a vapor deposition method, and a Cu (In, Ga) Se ₂ film (as a p-type semiconductor layer is formed on the formed Mo film. 2 μm in thickness) was formed by multi-source deposition to form a laminate including a substrate, a first electrode layer, and a p-type semiconductor layer. Next, an aqueous solution containing zinc sulfate (ZnSO ₄ ), which is a compound (salt) containing Zn, was prepared. The concentration of Zn ions in the solution was 0.025 mol / L. Next, the prepared aqueous solution was kept at 85 ° C. in a thermostatic bath, and the laminate was immersed for about 3 minutes. During immersion, the main surface opposite to the main surface facing the first electrode layer in the p-type semiconductor layer (exposed surface in the p-type semiconductor layer) is in contact with the aqueous solution containing Zn. Become.

  Thereafter, the stacked body is taken out, and the main surface of the p-type semiconductor layer opposite to the main surface facing the first electrode layer (the surface on which the aqueous solution is in contact during immersion) is subjected to secondary ion mass spectrometry. Analysis using the method (SIMS). The results are shown in FIG. As shown in FIG. 5, the presence of Zn was confirmed in the range of about 20 nm from the main surface. That is, it was found that Zn could be doped by the above immersion in a doping distance range of about 20 nm. (It can be said that a Zn-doped layer having a thickness of about 20 nm could be formed in the p-type semiconductor layer).

(Example 2)
In Example 2, a solar cell as shown in FIG. 1 was produced and its characteristics were evaluated.

First, a Mo film (thickness: 1 μm) was arranged as the first electrode layer 12 on the glass substrate. The vapor deposition method was used for the arrangement of the Mo film. Next, using a vapor deposition method, a Cu (In, Ga) Se ₂ film (thickness: 2 μm) is arranged as the p-type semiconductor layer 13 on the Mo film, and the substrate, the first electrode layer, the p-type semiconductor layer, The laminated body containing was formed.

  Next, the same zinc sulfate solution as in Example 1 was prepared, and the formed laminate was immersed in the same manner as in Example 1.

  Next, the laminate was pulled up from the zinc sulfate solution, washed with pure water, and further heat-treated at 400 ° C. for 10 minutes in a nitrogen atmosphere.

Next, a Zn _0.9 Mg _0.1 O film (thickness: 100 nm) was formed as the n-type semiconductor layer 15 on the p-type semiconductor layer 13 in the stacked body by binary sputtering using a ZnO target and an MgO target. At this time, in an argon gas atmosphere (gas pressure 2.66 Pa (2 × 10 ⁻² Torr)), sputtering is performed by applying a high-frequency power of 200 W to the ZnO target and a high-frequency power of 120 W to the MgO target. Went.

Next, an ITO film (thickness: 100 nm), which is a light-transmitting conductive film, was formed as the second electrode layer 16 on the n-type semiconductor layer 15 by using a sputtering method. The ITO film was formed by applying a high frequency power of 400 W to the target in an argon gas atmosphere (gas pressure 1.07 Pa (8 × 10 ⁻³ Torr)). Finally, a NiCr film and an Ag film are stacked on the Mo film and the ITO film by using an electron beam evaporation method to form extraction electrodes 17 and 18, and a solar cell (sample 1) as shown in FIG. Was made.

  Separately from the solar cell (sample 1), a solar cell that was not immersed in an aqueous zinc sulfate solution (that is, not doped with Zn) was produced as a comparative example. It was produced in the same manner as Sample 1 except that immersion in the aqueous zinc sulfate solution was omitted.

The power generation characteristics were evaluated by irradiating the two types of solar cells thus produced with artificial sunlight of AM (Air Mass) 1.5 and 100 mW / cm ² .

In the comparative example, a short circuit current of 34.0 mA / cm ² , an open circuit voltage of 0.522 V, a fill factor (FF) of 0.391, and a conversion efficiency of 6.9% were obtained. In contrast, Sample 1 in which the p-type semiconductor layer is doped with Zn has a short circuit current of 34.3 mA / cm ² , an open circuit voltage of 0.523 V, a fill factor of 0.634, and a conversion efficiency of 11.4%. Obtained. Therefore, the effect of improving the power generation characteristics of the solar cell was confirmed by doping the p-type semiconductor layer with Zn.

  In Example 1 and Example 2, zinc sulfate was used as the compound containing Zn, but the same effect can be obtained when zinc chloride, zinc iodide, zinc bromide, zinc nitrate, zinc acetate, or the like is used. I was able to get it.

  As described above, according to the present invention, it is possible to provide a solar cell excellent in characteristics such as conversion efficiency and a manufacturing method thereof. In particular, according to the present invention, it is possible to provide a CIS or CIGS solar cell capable of increasing efficiency.

It is a schematic diagram which shows an example of the solar cell of this invention. It is a schematic diagram for demonstrating an example of a structure of the p-type semiconductor layer in the solar cell of this invention. It is a schematic diagram which shows another example of the solar cell of this invention. It is a schematic process diagram which shows an example of the manufacturing method of the solar cell of this invention. It is a figure which shows the result of the secondary ion mass spectrometry (SIMS) measured in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solar cell 11 Board | substrate 12 1st electrode layer 13 p-type semiconductor layer 14a 2nd area | region 14b 1st area | region 15 n-type semiconductor layer 16 2nd electrode layer 17, 18 Extraction electrode 21, 23 Laminated body 22 Main surface

Claims (18)

A first electrode layer; a second electrode layer; a p-type semiconductor layer disposed between the first electrode layer and the second electrode layer; the p-type semiconductor layer; and the second electrode layer. A solar cell comprising an n-type semiconductor layer disposed between the electrode layers,
The p-type semiconductor layer is a compound semiconductor layer containing a group Ib element, a group IIIb element, a group VIb element, and Zn;
The compositional gradient is such that the concentration of Zn contained in the p-type semiconductor layer increases in the thickness direction of the p-type semiconductor layer from the first electrode layer toward the n-type semiconductor layer. ,
When the electron affinity of the p-type semiconductor layer is χ1 (eV) and the electron affinity of the n-type semiconductor layer is χ2 (eV), χ1 and χ2 are expressed by the equation 0 ≦ (χ1-χ2) <0.5. A solar cell characterized by satisfying the indicated relationship. The p-type semiconductor layer includes a first region containing a relatively large amount of Zn and a second region containing a relatively small amount of Zn;
2. The solar cell according to claim 1, wherein the first region is disposed in the vicinity of a main surface facing the n-type semiconductor layer in the p-type semiconductor layer. The solar cell according to claim 2, wherein the second region substantially does not contain Zn. The solar cell according to claim 1, wherein the n-type semiconductor layer contains Zn, Mg, and O. The solar cell according to claim 4, wherein the n _- type semiconductor layer has a composition represented by the formula Zn _1-x Mg _x A _y O.
However, in the above formula,
A is at least one element selected from Ca, Sr and Ba,
x is a numerical value that satisfies the relationship represented by the formula 0.05 ≦ x ≦ 0.35,
y is a numerical value that satisfies the relationship represented by the expression 0.00005 ≦ y ≦ 0.005. 2. The solar cell according to claim 1, wherein the p-type semiconductor layer includes at least one element selected from In and Ga, at least one element selected from Se and S, and Cu. A first electrode layer; a second electrode layer; a p-type semiconductor layer disposed between the first electrode layer and the second electrode layer; the p-type semiconductor layer; and the second electrode layer. A method for producing a solar cell comprising an n-type semiconductor layer disposed between electrode layers,
(I) a step of sequentially stacking a first electrode layer and a p-type semiconductor layer on a substrate to form a first stacked body including the substrate, the first electrode layer, and the p-type semiconductor layer; ,
(Ii) doping the p-type semiconductor layer with Zn;
(Iii) The n-type semiconductor layer is stacked so that the p-type semiconductor layer doped with Zn is sandwiched between the first electrode layer and the n-type semiconductor layer, and the stacked n-type semiconductor layer is the p-type semiconductor layer. Forming the second laminate by laminating the second electrode layer so as to be sandwiched between the shaped semiconductor layer and the second electrode layer,
The p-type semiconductor layer is a compound semiconductor layer containing a group Ib element, a group IIIb element, and a group VIb element,
In the step (iii), an n-type semiconductor layer having an electron affinity of χ 2 (eV) is laminated.
However, χ2 is a positive numerical value satisfying the relationship represented by the formula 0 ≦ (χ1−χ2) <0.5 when the electron affinity of the p-type semiconductor layer is χ1 (eV). In the step (ii),
The method for manufacturing a solar cell according to claim 7, wherein Zn is doped in the vicinity of a main surface opposite to the main surface facing the first electrode layer in the p-type semiconductor layer. In the step (ii),
The method for manufacturing a solar cell according to claim 7, wherein the p-type semiconductor layer is doped with Zn by bringing a solution containing Zn into contact with the p-type semiconductor layer. In the step (ii),
The method for manufacturing a solar cell according to claim 9, wherein the p-type semiconductor layer is doped with Zn by immersing the first stacked body in a solution containing Zn. The method for producing a solar cell according to claim 9, wherein the solution containing Zn is an aqueous solution of at least one compound selected from Zn sulfate, chloride, iodide, bromide, nitrate and acetate. The method for manufacturing a solar cell according to claim 9, wherein a concentration of Zn ions in the Zn-containing solution is in a range of 0.01 mol / L to 0.03 mol / L. Between the step (ii) and the step (iii),
(A) The manufacturing method of the solar cell of Claim 7 which further includes the process of heat-processing the said 1st laminated body which doped Zn to the said p-type semiconductor layer. After the step (iii),
(A) The manufacturing method of the solar cell of Claim 7 which further includes the process of heat-processing the formed said 2nd laminated body. The method for manufacturing a solar cell according to claim 13 or 14, wherein a temperature of the heat treatment is in a range of 250C to 450C. In the step (i),
The method for manufacturing a solar cell according to claim 7, wherein a p-type semiconductor layer containing at least one element selected from In and Ga, at least one element selected from Se and S, and Cu is stacked. In the step (iii),
The method for manufacturing a solar cell according to claim 7, wherein an n-type semiconductor layer containing Zn, Mg, and O is stacked. The method for manufacturing a solar cell according to claim 17, wherein the n _- type semiconductor layer has a composition represented by the formula Zn _1-x Mg _x A _y O.
However, in the above formula,
A is at least one element selected from Ca, Sr and Ba,
x is a numerical value that satisfies the relationship represented by the formula 0.05 ≦ x ≦ 0.35,
y is a numerical value that satisfies the relationship represented by the expression 0.00005 ≦ y ≦ 0.005.

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