JP6415317B2 - Manufacturing method of solar cell - Google Patents

Description

  The present invention relates to a method for manufacturing a solar cell.

  In recent years, a solar cell including a compound semiconductor containing a chalcogen element (for example, S or Se) as a light absorption layer is known.

  As a light absorption layer containing a chalcogen element, for example, an I-III-VI group compound semiconductor or an I- (II-IV) -VI group compound semiconductor has attracted attention.

Among the I-III-VI group compound semiconductors, those using a chalcopyrite-structured I-III-VI group compound semiconductor containing Cu, In, Ga, Se, and S are called CIS-based thin film solar cells. Examples of typical light absorption layer materials include Cu (In, Ga) Se ₂ , Cu (In, Ga) (Se, S) ₂ , CuInS ₂ , and Cu (In, Ga) S ₂ . Those containing Ga in particular are also called CIGS thin film solar cells.

Among the I- (II-IV) -VI group compound semiconductors, those using chalcogenide type I- (II-IV) -VI group compound semiconductors containing Cu, Zn, Sn, S or Se are CZTS. Typical examples include Cu ₂ ZnSnS ₄ , Cu ₂ ZnSnSe ₄ , and Cu ₂ ZnSn (S, Se) ₄ .

  Solar cells equipped with these light absorption layers use materials that are relatively inexpensive and easy to obtain, are relatively easy to manufacture, and have a large absorption coefficient in the visible to near-infrared wavelength range. Since photoelectric conversion efficiency is expected, it is regarded as a promising candidate for next-generation solar cells.

  The above-described compound semiconductor containing a chalcogen element is used as a light absorption layer having p-type conductivity. In a solar cell, a first electrode layer, a p-type light absorption layer, an n-type buffer layer, and a second electrode are formed on a substrate. It is formed by sequentially laminating layers.

  A solar cell equipped with a compound semiconductor containing a chalcogen element as a light absorption layer has a high potential, but the currently realized photoelectric conversion efficiency is lower than the theoretical value, and further progress in manufacturing technology etc. It has been demanded.

International Publication No. 03/066944 Pamphlet

  For example, it has been proposed to improve the photoelectric conversion efficiency of converting light energy into electric energy by adding an alkali metal element to the light absorption layer.

  Patent Document 1 discloses that after a first electrode layer is immersed in an aqueous solution of a compound containing an alkali metal element and dried to form an alkali layer on the first electrode layer, a p-type light absorption layer, an n-type buffer layer, It has been proposed to form a solar cell by sequentially laminating a second electrode layer.

  In Patent Document 1, an alkali layer is formed on a first electrode layer using a compound containing a plurality of types of sodium (Na), and the photoelectric conversion efficiency of each solar cell is measured. It has been reported that the conversion efficiency is different.

  This suggests that higher photoelectric conversion efficiency can be obtained by selecting an appropriate kind of alkali metal element compound.

  In this specification, it is an object to provide a method for manufacturing a solar cell with high photoelectric conversion efficiency using a compound containing potassium (K) as an alkali metal element.

  According to the method for manufacturing a solar cell disclosed in this specification, a first step of forming a first electrode layer on a substrate, and a compound-based light absorption having p-type conductivity on the first electrode layer. A second step of forming a layer; a third step of forming a buffer layer having n-type conductivity on the compound-based light absorption layer; and a tetraoxide compound containing at least potassium on the surface of the buffer layer. A fourth step of attaching, and a fifth step of forming a second electrode layer on the buffer layer.

  According to the solar cell manufacturing method disclosed in the present specification described above, a solar cell with high photoelectric conversion efficiency can be obtained.

It is a figure which shows the solar cell formed using the manufacturing method of the solar cell disclosed to this specification. It is a figure which shows the manufacturing process (the 1) of one Embodiment of the manufacturing method of the solar cell disclosed to this specification. It is a figure which shows the manufacturing process (the 2) of one Embodiment of the manufacturing method of the solar cell disclosed to this specification. It is a figure which shows the manufacturing process (the 3) of one Embodiment of the manufacturing method of the solar cell disclosed to this specification. It is a figure which shows the manufacturing process (the 4) of one Embodiment of the manufacturing method of the solar cell disclosed to this specification. It is a figure which shows the photoelectric conversion efficiency of an Example and a comparative example.

  Hereinafter, a preferred embodiment of a solar cell and a method for manufacturing a solar cell disclosed in the present specification will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a diagram showing a solar cell formed using the method for manufacturing a solar cell disclosed in this specification.

  The solar cell 10 of this embodiment includes a substrate 11, a first electrode layer 12 disposed on the substrate 11, and a compound-based light absorption layer 13 having p-type conductivity disposed on the first electrode layer 12. A buffer layer 14 having n-type conductivity and high resistance disposed on the compound-based light absorption layer 13, and a transparent n-type conductivity second electrode layer disposed on the buffer layer 14. 15.

  Next, a preferred embodiment of the method for manufacturing the solar cell 10 described above will be described below with reference to FIGS.

  First, as shown in FIG. 2, the first electrode layer 12 is formed on the substrate 11. As the substrate 11, for example, a glass substrate such as blue plate glass or low alkali glass, a metal substrate such as a stainless plate, or a polyimide resin substrate can be used.

  As the first electrode layer 12, for example, a metal conductive layer made of a metal such as Mo, Cr, or Ti can be used. The thickness of the 1st electrode layer 12 can be 0.1-1 micrometer, for example. The first electrode layer 12 is formed using, for example, a sputtering method (DC, RF).

  Next, as shown in FIG. 3, a compound light absorption layer 13 having p-type conductivity is formed on the first electrode layer 12. A compound semiconductor containing a chalcogen element (for example, S or Se) can be used as the compound light absorption layer 13.

As a compound semiconductor containing a chalcogen element, for example, a CIS-based compound semiconductor formed from a I-III-VI group compound (which can also be expressed as a I-III-VI group ₂ compound), or I- (II-IV)- A CZTS compound semiconductor formed of a Group VI compound semiconductor (which can also be expressed as an I _2- (II-IV) -VI Group ₄ compound semiconductor) can be used.

In the case of a CIS compound semiconductor, for example, copper (Cu) can be used as the group I element. As the group III element, for example, gallium (Ga) or indium (In) can be used. As the group VI element, for example, selenium (Se) or sulfur (S) can be used. Specifically, examples of the CIS compound semiconductor include Cu (In, Ga) Se ₂ , Cu (In, Ga) (Se, S) ₂ , and CuInS ₂ .

  As a method for forming a CIS compound semiconductor, for example, (1) a method of forming a metal precursor film of a group I element and a group III element and forming a compound of the metal precursor film and a group VI element; And a method of forming a film containing a group I element, a group III element, and a group VI element by using a method.

In the case of a CZTS-based compound semiconductor, for example, copper (Cu) can be used as the group I element. As the group II element, for example, zinc (Zn) can be used. As the group IV element, for example, tin (Sn) can be used. As the group VI element, for example, selenium (Se) or sulfur (S) can be used. Specifically, Cu ₂ (Zn, Sn) Se ₄ , Cu ₂ (Zn, Sn) S ₄ , or a mixed crystal of Cu ₂ (Zn, Sn) (Se, S) is used as the CZTS compound semiconductor. ₄ is mentioned.

  As a method of forming a CZTS compound semiconductor, for example, (1) a method of forming a metal precursor film of a group I element, a group II element, and a group IV element, and forming a compound of a metal precursor film and a group VI element; (2) A method of forming a film containing a group I element, a group II element, a group IV element, and a group VI element by vapor deposition is used.

  The thickness of the compound light absorption layer 13 can be set to 1 to 3 μm, for example.

  Next, as shown in FIG. 4, a buffer layer 14 having n-type conductivity is formed on the compound light absorption layer 13 to obtain a substrate composite 16.

The buffer layer 14 having n-type high resistance is, for example, a thin film of a compound containing Cd, Zn, and In, and is typically CdS, ZnO, ZnS, Zn (OH) ₂ or a mixed crystal of these. (O, S, OH), InS, InO, In (OH) or a mixed crystal thereof such as In (O, S, OH). This layer is generally formed by a solution growth method (Chemical Bath Deposition method: CBD method), but as a dry process, a metal organic chemical vapor deposition method (Metal Organic Chemical Vapor Deposition method: MOCVD method), a sputtering method is used. An atomic layer deposition method (ALD method) can also be used. In the CBD method, a thin film is deposited on a base material by immersing the base material in a solution containing a chemical species that serves as a precursor and causing a heterogeneous reaction between the solution and the base material surface.

  The thickness of the buffer layer 14 can be set to several nm to 200 nm, for example.

  In the case where the buffer layer 14 is formed using the CBD method, after the buffer layer 14 is formed, the substrate composite 16 is washed to remove residues such as particles adhering to the surface. Is preferred. Examples of the cleaning method include immersing the substrate composite 16 in a tank filled with pure water, or quick dump cleaning.

  Next, as shown in FIG. 5, the substrate composite 16 is immersed in a tank 20 filled with an aqueous solution 21 of at least potassium tetroxide, so that the surface of the buffer layer 14 contains at least four potassium. Oxidizing compounds are deposited.

  In the present specification, attaching a tetraoxide compound containing at least potassium to the surface of the buffer layer 14 means attaching a tetraoxide compound containing at least potassium to the surface or inside of the buffer layer 14. In the step shown in FIG. 5, a tetraoxide compound containing at least potassium may adhere to the first electrode layer 12 or the compound-based light absorption layer 13.

  In addition, in this specification, the attachment of a tetraoxide compound containing at least potassium to the surface of the buffer layer 14 means that ions of a tetraoxide compound containing at least potassium are attached to the surface of the buffer layer 14. It is.

Claim 2
The tetraoxide compound containing at least potassium is represented by a composition formula K ₂ MO ₄ , where K is potassium, O is oxygen, and M is a metal element or a Group 16 element.

  When the element M is a metal element, the element M is specifically preferably molybdenum (Mo).

  Further, when the element M is a Group 16 element, the element M is specifically preferably sulfur (S).

  The concentration of at least potassium tetroxide compound in the aqueous solution 21 is preferably in the range of 1 to 300 mmol / L, preferably 1 to 50 mmol / L. When the concentration is lower than 1 mmol / L, the amount of tetraoxide compound containing at least potassium on the surface of the buffer layer 14 decreases. Even if the concentration is higher than 50 mmol / L, it is considered that the effect of improving the conversion efficiency is exhibited.

  When the buffer layer 14 is formed using the CBD method, instead of the step shown in FIG. 5, an aqueous solution of a tetraoxide compound containing at least potassium is used as cleaning water for cleaning the substrate composite 16. While cleaning the substrate composite 16, a tetraoxide compound containing at least potassium may be attached to the surface of the buffer layer 14.

  Before forming the buffer layer 14, it is conceivable that a tetraoxide compound containing at least potassium is added to the compound light absorption layer 13 or the first electrode layer 12 and taken into the solar cell 10. When the buffer layer 14 is formed by use, there is a possibility that a tetroxide compound containing at least potassium elutes in the solution for growing the buffer layer 14. Therefore, in this embodiment, after the buffer layer 14 is formed, a tetraoxide compound containing at least potassium is attached to the surface of the buffer layer 14.

  Next, the 2nd electrode layer 15 is formed on the buffer layer 14, and the solar cell 10 shown in FIG. 1 is obtained.

  The second electrode layer 15 is formed of a material having n-type conductivity, a wide forbidden band width, transparent, and low resistance. Specifically, the second electrode layer 15 includes a zinc oxide-based thin film (ZnO) or an ITO thin film. In the case of a ZnO film, the resistivity can be reduced by adding a group III element (for example, Al, Ga, B) as a dopant. The second electrode layer 15 can also be formed by sputtering (DC, RF) or the like other than MOCVD.

  The thickness of the 2nd electrode layer 15 can be 1-3 micrometers, for example.

  Further, before forming the second electrode layer 15 on the buffer layer 14, an intrinsic zinc oxide film (i-ZnO) to which a dopant is not substantially added is formed, and on the intrinsic zinc oxide film, The second electrode layer 15 may be formed.

  Hereinafter, the manufacturing method of the solar cell disclosed in this specification will be further described using examples. However, the scope of the present invention is not limited to such examples.

Example 1
The solar cell of Example 1 was manufactured as follows.

First, the 1st electrode layer 12 was formed on the board | substrate 11 which is a glass plate using DC sputtering method by using Mo as a material. Next, a precursor film made of Cu, In, and Ga is formed as the compound-based light absorption layer 13 on the first electrode layer 12 by using a DC sputtering method, and this precursor film is subjected to heat treatment (selenization) in an atmosphere containing selenium. Then, heat treatment (sulfurization) was performed in a sulfur-containing atmosphere to form a ternary CIS compound semiconductor layer made of Cu (In, Ga) (Se, S) ₂ . Next, as the buffer layer 14, a Zn (O, S, OH) film that is a mixed crystal of ZnO, ZnS, Zn (OH) ₂ is formed on the compound light absorption layer 13 using the CBD method. A substrate composite 16 was obtained. Next, in the step shown in FIG. 5, the substrate composite 16 is immersed in a tank 20 filled with an aqueous solution 21 of K ₂ MoO ₄ as a tetraoxide compound containing at least potassium, and is then deposited on the surface of the buffer layer 14. K ₂ MoO ₄ was deposited. The concentration of K ₂ MoO _{4 in} the aqueous solution was set to four levels of 1, 5, 25, and 50 mmol / L. Next, as the second electrode layer 15, a zinc oxide-based thin film (ZnO) to which B was added was formed on the buffer layer 14 using the MOCVD method, and the solar cell of Example 1 was obtained. In the first embodiment, when the second electrode layer 15 is formed on the substrate composite 16 using the MOCVD method, the substrate composite 16 is heated to a temperature of 100 ° C. or higher as a pre-process of the MOCVD method. A preheating step is provided.

(Example 2)
In the step shown in FIG. 5, the substrate composite 16 is immersed in a bath 20 filled with an aqueous solution 21 of K ₂ SO ₄ as a tetraoxide compound containing at least potassium, and the surface of the buffer layer is filled with K ₂ SO _4. Was attached. The concentration of K ₂ SO _{4 in} the aqueous solution was 1 level of 1 mmol / L. Other steps were the same as in Example 1 described above, and a solar cell of Example 2 was obtained.

(Comparative Example 1)
A solar cell of Comparative Example 1 was obtained in the same manner as in Example 1 except that the step shown in FIG.

(Comparative Example 2)
In a process shown in FIG. 5, the substrate composite _16, is immersed in the of Na ₂ S 2 _{O 3} aqueous solution 21 is filled bath 20 and the surface of the buffer layer 14 is deposited a _Na 2 _S 2 _{O 3} . The concentration of Na ₂ S ₂ O _{3 in} the aqueous solution was set at two levels of 25 and 50 mmol / L. Other steps were the same as in Example 1 described above, and a solar cell of Comparative Example 2 was obtained.

(Comparative Example 3)
In the step shown in FIG. 5, the substrate composite 16 was immersed in a bath 20 filled with an aqueous solution 21 of NaBr, and NaBr was adhered to the surface of the buffer layer 14. The concentration of NaBr in the aqueous solution was set at two levels of 25 and 50 mmol / L. Other steps were the same as in Example 1 described above, and a solar cell of Comparative Example 3 was obtained.

(Comparative Example 4)
In a process shown in FIG. 5, the substrate composite _16, is immersed in a bath 20 of aqueous solution 21 of Na 2 MoO ₄ is satisfied, was deposited _Na 2 MoO ₄ on the surface of the buffer layer 14. The concentration of Na ₂ MoO _{4 in} the aqueous solution was set at two levels of 25 and 50 mmol / L. Other steps were the same as in Example 1 described above, and a solar cell of Comparative Example 4 was obtained.

(Comparative Example 5)
In the step shown in FIG. 5, the substrate composite 16 was immersed in a tank 20 filled with an aqueous solution 21 of KF, and KF was adhered to the surface of the buffer layer 14. The concentration of KF in the aqueous solution was one level of 50 mmol / L. Other steps were the same as in Example 1 described above, and a solar cell of Comparative Example 5 was obtained.

(Comparative Example 6)
In the process shown in FIG. 5, the substrate composite 16 was immersed in a tank 20 filled with an aqueous solution 21 of KCl, and KCl was adhered to the surface of the buffer layer 14. The concentration of KCl in the aqueous solution was set at three levels of 1, 5, and 50 mmol / L. Other steps were the same as in Example 1 described above, and a solar cell of Comparative Example 6 was obtained.

(Comparative Example 7)
In a process shown in FIG. 5, the substrate composite _16, an aqueous solution 21 of K ₂ S _{2 O 3} is immersed in filled tank 20, and the surface of the buffer layer 14 to adhere the _K 2 _S 2 _{O 3} . The concentration of K ₂ S ₂ O _{3 in} the aqueous solution was set at two levels of 25 and 50 mmol / L. Other steps were the same as in Example 1 described above, and a solar cell of Comparative Example 7 was obtained.

  FIG. 6 shows the results of evaluating the photoelectric conversion efficiency with respect to Example 1 and Example 2 and Comparative Examples 1 to 7 described above. The photoelectric conversion efficiency of other solar cells is shown with the photoelectric conversion efficiency of Comparative Example 1 as 100% of the reference.

In Example 1 and Example 2, the photoelectric conversion efficiency is improved as compared with Comparative Example 1. In Example 1, the photoelectric conversion efficiency is improved with respect to Comparative Example 1 over a range of K ₂ MoO ₄ concentration of 1 to 50 mmol / L.

  Comparative Examples 2 to 4 are solar cells formed using a compound containing Na, which is an alkali metal element. Comparative Example 4 is a solar cell formed using a tetraoxide compound containing Na. Comparative Examples 2 to 4 showed lower photoelectric conversion efficiencies than Examples 1 and 2 and Comparative Example 1.

  Comparative Examples 5 to 7 are solar cells formed using a compound containing potassium but not a tetraoxide compound. Comparative Examples 5 to 7 show lower photoelectric conversion efficiencies than Example 1, Example 2, and Comparative Example 1.

  The following reasons are estimated as a reason why Example 1 and Example 2 show high photoelectric conversion efficiency with respect to Comparative Examples 1-7.

  The K element, which is an alkali metal element, is considered to move from the surface of the buffer layer 14 to the compound light absorption layer 13 by the preheating treatment before forming the second electrode layer 15. It is considered that the K element is located at the interface or inside of the compound-based light absorption layer 13 and suppresses disappearance of carriers due to defects or the like, thereby improving the photoelectric conversion efficiency. The inventors of the present application do not exclude the existence of other reasons that the photoelectric conversion efficiencies of Examples 1 and 2 are improved with respect to Comparative Examples 1 to 7.

  When Example 1 and Example 2 and Comparative Examples 2-7 are compared, it turns out that photoelectric conversion efficiency changes with kinds of compound containing an alkali metal element.

  Moreover, when Example 1 and Example 2 are compared with Comparative Examples 2-7, as a tetraoxide compound containing an alkali metal element, K is better than Na, and as a compound containing K, K It was found that a tetraoxide compound containing

  In this invention, the manufacturing method of the solar cell of embodiment mentioned above can be suitably changed unless it deviates from the meaning of this invention.

  For example, in the embodiment described above, an aqueous solution of at least potassium-containing tetraoxide compound is used to attach a tetraoxide compound containing at least potassium to the surface of the buffer layer. However, at least potassium is added to the surface of the buffer layer. Other methods may be used as the method for attaching the tetraoxide compound to be contained.

  Specifically, a method of applying or spraying a solution containing a tetraoxide compound containing potassium on the surface of the buffer layer can be mentioned. Furthermore, when depositing a tetraoxide compound containing potassium on the buffer layer, it may be realized by a vacuum process such as sputtering or vapor deposition.

DESCRIPTION OF SYMBOLS 10 Solar cell 11 Substrate 12 1st electrode layer 13 System light absorption layer 14 Buffer layer 15 2nd electrode layer 16 Substrate composite 20 Tank 21 Aqueous solution

Claims (7)

A first step of forming a first electrode layer on the substrate;
A second step of forming a compound-based light absorption layer having p-type conductivity on the first electrode layer;
A third step of forming an n-type conductive buffer layer on the compound light absorption layer;
A fourth step of attaching a tetraoxide compound containing at least potassium to the surface of the buffer layer;
A fifth step of forming a second electrode layer on the buffer layer;
A method for manufacturing a solar cell comprising: 2. The compound according to claim 1, wherein the at least potassium-containing tetraoxide compound is represented by a composition formula K ₂ MO ₄ , wherein K is potassium, O is oxygen, and M is a metal element or a Group 16 element. Solar cell manufacturing method.   The method for manufacturing a solar cell according to claim 2, wherein M is a metal element Mo.   The method for manufacturing a solar cell according to claim 2, wherein M is S of a Group 16 element. The said 4th process WHEREIN: Using the aqueous solution of the tetraoxide compound which contains the said at least potassium, the tetraoxide compound containing the said at least potassium is made to adhere to the surface of the said buffer layer. Solar cell manufacturing method.   The method for producing a solar cell according to claim 5, wherein the concentration of the tetraoxide compound containing at least potassium in the aqueous solution is in the range of 1 to 300 mmol / L.   In the said 2nd process, the said compound type light absorption layer containing a chalcogen element is formed on the said 1st electrode layer, The manufacturing method of the solar cell as described in any one of Claims 1-6.

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