JP5564688B2 - CBD solution for CZTS semiconductor, method for producing buffer layer for CZTS semiconductor, and photoelectric device - Google Patents

Description

  The present invention relates to a CBD solution for a CZTS-based semiconductor, a method for producing a buffer layer for a CZTS-based semiconductor, and a photoelectric device. CZTS semiconductor buffer layer manufacturing method used in manufacturing thin film solar cells (eg, thin film solar cells, photoconductive cells, photodiodes, phototransistors, sensitized solar cells, etc.), and CZTS systems used in such methods The present invention relates to a CBD solution for a semiconductor and a photoelectric device including a buffer layer obtained by such a method.

  A photoelectric element refers to an element that can convert photon energy into an electrical signal (photoelectric conversion) through some physical phenomenon. A solar cell is a kind of photoelectric element, and can efficiently convert light energy of sunlight into electric energy.

The semiconductor used in solar cells, monocrystalline Si, polycrystalline Si, amorphous Si, GaAs, InP, CdTe, CuIn 1-x Ga x Se 2 (CIGS), Cu 2 ZnSnS 4 (CZTS) such as is known Yes.
Among these, chalcogenite-based compounds represented by CIGS and CZTS have a large light absorption coefficient, so that a thin film advantageous for cost reduction is possible. In particular, a solar cell using CIGS as a light absorption layer has high conversion efficiency in a thin film solar cell, and conversion efficiency exceeding that of a solar cell using polycrystalline Si is also obtained. However, CIGS has a problem that it contains an environmental load element and a rare element.
On the other hand, CZTS has a band gap energy (1.4 to 1.5 eV) suitable for a solar cell and is characterized by not containing an environmental load element or a rare element.

  In a solar cell using CIGS or CZTS as a light absorption layer, a buffer layer is essential. The buffer layer is formed between the light absorption layer and the window layer, and is presumed to be necessary for adjusting the band profile and the heterointerface. In order to form a buffer layer, a solution growth (Chemical Bath Deposition, CBD) method is often used, and CdS is often used in this system.

CdS itself is known as an optical sensor material, and there are many reports on the formation of CdS on a Si substrate or a glass substrate by a chemical method.
For example, Non-Patent Document 1 discloses a raw material (CBD solution) and a method for forming a CdS thin film on a glass substrate using the CBD method.
In the same document,
(1) When cadmium acetate is used, a single-phase CdS film can be formed,
(2) When cadmium sulfate is used, a film in which cadmium sulfate is mixed is formed.
(3) When cadmium chloride is used, it becomes a mixture of hexagonal crystals and cubic crystals, and
(4) Use of cadmium acetate improves translucency,
Is described.

Non-Patent Document 2 discloses a raw material and a method for forming a CdS thin film on a glass substrate using the CBD method.
In the same document,
(1) Compared with cadmium chloride, when cadmium acetate is used, a dense and translucent film can be formed; and
(2) It is disclosed that a high-quality film can be formed by adding an ammonium salt to a solution.

  Further, Non-Patent Documents 3 and 4 disclose raw materials and methods for forming a CdS film on the CIGS thin film surface using the CBD method.

E.Pentia et al., "The influence of cadmiumu salt anion on the growth mechanism and the physical property of CdS thin films," J. Optoelectronics & Advanced Mater., 2 (2000) 593-601 X.B.Xu et al., "Influence of cadmium salts on a modified chemical bath deposition of cadmium sulfide thin films," Surface Review & Letters, 15 (2008) 265-270 D. Abou-Ras et al., "Structural and chemical research of CBD- and PVD-CdS buffer layers and interface in Cu (in, Ga) Se2-based thin film solar cells," Thin Solid Films, 480-481 (2005 118-123 A. Kylner et al., "Impurity in chemical bath deposited CdS films for Cu (In, Ga) Se2 solar cells and their stability," J. Electrochem. Soc., 143 (1996) 2662-2669

  The problem to be solved by the present invention is for a CZTS semiconductor capable of forming a CdS buffer layer having good characteristics on a light absorption layer made of a CZTS semiconductor and thereby improving the characteristics of the photoelectric element. It is providing the manufacturing method of a buffer layer, the CBD solution for CZTS type semiconductors used for such a method, and a photoelectric element provided with the buffer layer obtained by such a method.

In order to solve the above problems, a CBD solution for a CZTS semiconductor according to the present invention comprises an aqueous solution containing cadmium acetate, a sulfur source, and a sulfide synthesis aid .
The concentration of the cadmium acetate is 0.001M or more and 0.05M or less,
The concentration of the sulfur source is 0.05M or more and 3.0M or less,
The concentration of the sulfide synthesis aid is 1.7M or more and 5.5M or less.
The manufacturing method of the buffer layer for CZTS semiconductor according to the present invention
A CBD step of immersing the substrate on which the CZTS semiconductor layer is formed in the CBD solution for CZTS semiconductor according to the present invention to form a CdS film on the surface of the CZTS semiconductor layer;
And a heat treatment step of heat treating the CdS film at 200 ° C. or lower.
The photoelectric device according to the present invention includes a buffer layer obtained by the method according to the present invention.

  When a CdS layer is formed on a CZTS semiconductor layer using the CBD method, the use of cadmium acetate as the Cd source improves the characteristics of the CZTS semiconductor layer. This is presumably because the presence of acetate ions derived from cadmium acetate in the CBD solution changes the heterointerface between the buffer layer and the CZTS layer into a good state.

4 is a TEM photograph of a CdS film (Comparative Example 2) formed using a CBD solution using cadmium chloride as a Cd source and not containing ammonium chloride. It is an EDS analysis result of the CdS film | membrane (comparative example 2) shown in FIG. It is a TEM photograph of a CdS film (comparative example 4) formed using a CBD solution using cadmium chloride as a Cd source and 0.4 g of ammonium chloride added. It is an EDS analysis result of the CdS film | membrane (comparative example 4) shown in FIG.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Method for producing buffer layer for CZTS semiconductor and CBD solution for CZTS semiconductor]
The method for producing a CZTS semiconductor buffer layer according to the present invention includes a CBD process and a heat treatment process.

[1.1. CBD process]
In the CBD step, the substrate on which the CZTS-based semiconductor layer is formed is immersed in a CBD solution containing cadmium acetate, a sulfur source, and a sulfide synthesis aid, and a CBD step is formed on the surface of the CZTS-based semiconductor layer. It has.

[1.1.1. Light absorption layer]
The CdS film is formed on the light absorption layer. In the present invention, the light absorption layer is made of a CZTS (Cu ₂ ZnSnS ₄ ) -based semiconductor layer.
In the present invention, “CZTS-based semiconductor” includes not only stoichiometric compounds but also all non-stoichiometric compounds, or all compounds containing Cu, Zn, Sn, and S as a main component. .
The CZTS-based semiconductor may be composed of only Cu, Zn, Sn, and S, or may further contain other chalcogen elements, various dopants, unavoidable impurities, and the like in addition to these.

[1.1.2. substrate]
The processing target is a substrate on which a light absorption layer is formed. Another layer may be formed between the substrate and the light absorption layer.
For example, a thin film solar cell using a CZTS semiconductor generally has a structure in which a substrate, a lower electrode, a light absorption layer, a buffer layer, a window layer, and an upper electrode are stacked in this order. Additional layers (for example, an adhesive layer, a light scattering layer, an antireflection layer, etc.) may be formed between the layers. A CZTS-based semiconductor is used for the light absorption layer. In the present invention, the material of each layer other than the light absorption layer and the buffer layer is not particularly limited, and various materials can be used according to the purpose.

[1.1.3. CBD solution for CZTS semiconductor]
A treatment solution for forming a CdS film (CBD solution for a CZTS-based semiconductor; hereinafter simply referred to as “CBD solution”) is composed of an aqueous solution containing cadmium acetate, a sulfur source, and a sulfide synthesis aid.

[A. Cadmium acetate]
In the present invention, cadmium acetate is used as the Cd source. When cadmium acetate is used as the Cd source, a high-quality CdS film can be formed on the CZTS-based semiconductor layer, although details are unknown.

[B. Sulfur source]
The “sulfur source” refers to a water-soluble compound containing S and capable of releasing S in an aqueous solution.
Specifically, as a sulfur source,
(A) A sulfur source comprising an organic compound such as thiourea (SC (NH ₂ ) ₂ ), thioacetamide (CH ₃ CSNH ₂ ), thioacetic acid (CH ₃ COSH), thiobenzamide (C ₆ H ₅ CSNH ₂ ) ,
(B) Sodium thiosulfate (Na ₂ S ₂ O ₃ ), potassium thiosulfate (K ₂ S ₂ O ₃ ), sodium sulfite (Na ₂ SO ₃ ), sodium hydrogen sulfite (NaHSO ₃ ), sodium disulfite (Na ₂ S ₂ O ₅ ), a sulfur source comprising an inorganic compound such as sodium sulfide (Na ₂ S),
and so on.
Any one of these may be included in the CBD solution, or two or more thereof may be included.

[C. Sulfide synthesis aid]
“Sulfide synthesis aid” refers to an agent capable of forming a complex of Cd ions and making an aqueous solution alkaline. The aqueous solution is made alkaline in order to decompose the sulfur source and generate S ²⁻ ions.
As a sulfide synthesis aid, specifically,
(A) ammonia water,
(B) cyanic acid compounds such as NaCN and KCN,
(C) thiocyanic acid compounds such as NaSCN and KSCN,
(D) a mixture of any two or more of (a) to (c),
and so on.

[D. CBD solution composition]
The composition of the CBD solution affects the characteristics of the CdS film.
When the concentration of cadmium acetate in the CBD solution is too low, the characteristics of the light absorption layer are deteriorated. Therefore, the concentration of cadmium acetate is preferably 0.001M or more. The concentration of cadmium acetate is more preferably 0.0015M or more.
On the other hand, when the concentration of cadmium acetate is too high, the characteristics of the light absorption layer are degraded. Therefore, the concentration of cadmium acetate is preferably 0.05M or less. The concentration of cadmium acetate is more preferably 0.01M or less.

When the concentration of the sulfur source in the CBD solution is too low, the characteristics of the light absorption layer are deteriorated. Therefore, the concentration of the sulfur source is preferably 0.05M or more. The concentration of the sulfur source is more preferably 0.1M or more.
On the other hand, if the concentration of the sulfur source is too high, the characteristics of the light absorption layer are degraded. Therefore, the concentration of the sulfur source is preferably 3.0M or less. The concentration of the sulfur source is more preferably 1.0M or less, and further preferably 0.6M or less.

If the concentration of the sulfide synthesis aid in the CBD solution is too low, the characteristics of the light absorption layer will deteriorate. The concentration of the sulfide synthesis aid is preferably 1.7M or more. The concentration of the sulfide synthesis aid is more preferably 2.0M or more.
On the other hand, if the concentration of the sulfide synthesis aid is too high, the characteristics of the light absorption layer are degraded. The concentration of the sulfide synthesis aid is preferably 5.5M or less. The concentration of the sulfide synthesis aid is more preferably 5.0M or less.

  The CBD solution is preferably an aqueous solution containing only the above-mentioned cadmium acetate, a sulfur source, and a sulfide synthesis aid. In particular, when an ammonium salt such as ammonium acetate is contained, the characteristics of the light absorption layer are deteriorated. In order to improve the characteristics of the light absorption layer, the concentration of the ammonium salt contained in the CBD solution is preferably 0.1 M or less. The concentration of the ammonium salt is more preferably 0.01M or less. The lower the ammonium salt concentration in the CBD solution, the better.

[1.1.4. Film formation conditions]
The CdS film is formed by immersing the substrate on which the light absorption layer is formed in a CBD solution and heating it at a predetermined temperature. Heating is performed to promote the reaction. The heating temperature is usually 30 to 80 ° C.
The film thickness of the CdS film can be controlled by the reaction time. Although reaction time is based also on a film thickness, it is 5 to 60 minutes normally.

[1.2. Heat treatment process]
The heat treatment step is a step of heat-treating the CdS film formed on the light absorption layer at 200 ° C. or less.
If the CdS film produced by the CBD method is left as it is, the CdS film is likely to be deteriorated due to the remaining moisture and reaction solution components. Therefore, after forming the CdS film by the CBD method, heat treatment is performed to remove the remaining water. The heat treatment temperature may be a temperature (200 ° C. or less) at which remaining moisture can be removed.
The atmosphere during the heat treatment is not particularly limited, and may be any of an oxidizing atmosphere, a reducing atmosphere, and an inert atmosphere.

[2. Photoelectric element]
The photoelectric device according to the present invention includes a substrate, a light absorption layer made of a CZTS semiconductor formed on the substrate, and a buffer layer formed on the light absorption layer. The buffer layer is obtained by the method according to the present invention. Another layer may be formed between the substrate and the light absorption layer.
For example, a thin film solar cell using a CZTS semiconductor generally has a structure in which a substrate, a lower electrode, a light absorption layer, a buffer layer, a window layer, and an upper electrode are stacked in this order. Additional layers (for example, an adhesive layer, a light scattering layer, an antireflection layer, etc.) may be formed between the layers. In the present invention, the material of each layer other than the buffer layer and the light absorption layer is not particularly limited, and various materials can be used according to the purpose.

For example, when the photoelectric element is a thin film solar cell, the thin film solar cell can be manufactured as follows. That is, first, a lower electrode and a light absorption layer are formed in this order on a substrate. Next, a CdS buffer layer is formed on the light absorption layer using the method according to the present invention. Further, a window layer and an upper electrode are formed in this order on the CdS buffer layer.
The formation method of layers other than a buffer layer is not specifically limited, A various method can be used. Specific methods for forming each member include sputtering, vacuum deposition, pulsed laser deposition (PLD), plating, electrophoretic deposition (EPD), and chemical vapor deposition (CVD). , Spray pyrolysis film formation (SPD), screen printing, spin coating, and fine particle deposition.

[3. Method of manufacturing buffer layer for CZTS semiconductor and operation of photoelectric element]
When a CdS layer is formed on a CZTS semiconductor layer using the CBD method, the use of cadmium acetate as the Cd source improves the characteristics of the CZTS semiconductor layer. This is considered due to the following reasons.

That is, when a CdS film is formed using the CBD method, a CdS film is formed on the substrate by the reaction between Cd ²⁺ dissociated from the cadmium salt and S ²⁻ dissociated from the sulfur source in an alkaline aqueous solution. Is done. When a CdS film is used as an optical sensor material, the CdS film is directly formed on a Si substrate or a glass substrate. In this case, since the Si substrate and the glass substrate are chemically inactive, the reaction between the substrate during film formation and the CBD solution hardly occurs. Therefore, it is not necessary to consider the reaction with the substrate when determining the film formation conditions.
On the other hand, when the CdS film is formed on the CZTS-based semiconductor layer, the CZTS-based semiconductor layer contains S, so that the CZTS-based semiconductor layer reacts with the CBD solution. Therefore, even if the conventional method is applied to a CZTS semiconductor as it is, a good quality CdS film cannot be obtained. In addition, there has never been an example in which a CBD solution considering such a reaction has been proposed.

It can be presumed that the open-circuit voltage (V _oc ) and the fill factor (FF) value are affected by the state of the heterointerface between the buffer layer and the CZTS-based semiconductor layer. In an alkaline aqueous solution, it is considered that corrosion and etching of the CZTS-based semiconductor layer occur simultaneously with the formation of the CdS film. Furthermore, it is conceivable that the constituent elements of the CZTS-based semiconductor layer once dissolved are again deposited on the CZTS-based semiconductor layer in the form of being taken into the CdS film.
At this time, it can be estimated that the pH of the aqueous solution or the presence of an anion derived from a ligand (ammonia, CN) or a Cd source affects the corrosion of the CZTS-based semiconductor layer simultaneously with the CdS film formation. Although details are unknown in the present invention, the presence of acetate ions derived from cadmium acetate affects the corrosion and re-deposition of the CZTS-based semiconductor layer. As a result, the heterointerface between the buffer layer and the CZTS-based semiconductor layer is affected. It is thought that it changed to a favorable state. Moreover, it is thought that _Voc and FF value improved by this.

In a solar cell, the parallel resistance (the slope of V = 0 of the IV curve) is an index that represents the degree of current leakage. The larger the parallel resistance, the better. The series resistance (I = 0 slope of the IV curve) is an index representing the amount of current that can be extracted. The smaller the series resistance, the better.
In the case of forming a CdS film using the CBD method, when cadmium acetate is used as the Cd salt, the parallel resistance is improved and the series resistance is lowered. It can be inferred that the improvement in parallel resistance and the reduction in series resistance mean improvement in the uniformity of the CdS buffer layer.
In the case of the present invention, it is considered that the presence of acetate anion derived from cadmium acetate has some influence on the formation of Cd complex and the reaction between Cd ion and S ion. As a result, it is considered that a good quality CdS film was formed.

(Example 1, Comparative Examples 1-2)
[1. Preparation of sample]
A solar cell was produced according to the following procedure.
(1) A Mo back electrode layer (layer thickness: ˜1 μm) was formed on a soda lime glass (SLG) substrate by a sputtering method.
(2) A Cu—Zn—Sn—S precursor film was formed on the Mo back electrode layer by sputtering. Subsequently, the precursor film was formed into a CZTS light absorption layer (layer thickness: ˜1.4 μm) by sulfuration treatment at 550 to 580 ° C. for 3 hours in an atmospheric pressure, 5% H ₂ S + N ₂ gas atmosphere.
(3) A CdS buffer layer (layer thickness: ˜70 nm) was formed on the CZTS film using the CBD method.
(4) An Al: ZnO window layer (layer thickness: ˜400 nm) and a comb-shaped Al surface electrode layer (layer thickness: ˜0.6 μm) were formed in this order on the CdS buffer layer by sputtering.
(5) The effective light receiving area of the produced solar cell was about 0.16 cm ² .

The CdS buffer layer was formed under the following conditions. First, in a 500 mL beaker, Cd salt: 0.004M equivalent, thiourea: 10.1 g (0.3 M), 28% aqueous ammonia: 90 mL (3.0 M), ion-exchanged water: 360 mL are placed at room temperature. Dissolved. As the Cd salt, cadmium iodide: 0.58 g (Comparative Example 1), cadmium chloride: 0.36 g (Comparative Example 2), or cadmium acetate: 0.43 g (Example 1) was used.
The substrate on which the CZTS film was formed was immersed in this reaction solution. After soaking, the beaker was placed in a water bath at 70 ° C. and heated. The solution temperature in the beaker gradually increased and reached about 60 ° C. after 20 minutes. After 20 minutes, the substrate was quickly taken out. The substrate was washed with ion exchange water and dried by blowing air. The dried substrate was heat-treated in nitrogen at 200 ° C. for 30 minutes in a tubular furnace. Thereafter, the window layer and the surface electrode layer were formed in accordance with the procedure described above.

[2. Test method]
Using the fabricated solar cell, short circuit current density (J _SC ), open circuit voltage (V _OC ), form factor (FF), conversion efficiency (E _ff ), parallel resistance, and series resistance are evaluated. did. A solar simulator was used for the measurement. In the measurement, artificial solar light of air mass 1.5 (AM1.5) was applied to the solar cell, the measurement was started without taking time, and the measurement was completed within several tens of seconds.
The following equation (1) is established for the conversion efficiency (E _ff ), open-circuit voltage (V _OC ), short-circuit current density (J _SC ), and form factor (FF).
E _ff = V _OC × J _SC × F.F. (1)

[3. result]
Table 1 shows the results. From Table 1, it can be seen that by using cadmium acetate, V _oc is increased by about 0.15 V and E _ff is also improved by about 2.4 times. It can also be seen that the parallel resistance is improved and the series resistance is reduced. This is presumably because cadmium acetate was used as the Cd source, the CdS / CZTS heterointerface state was improved, or the uniformity of the CdS buffer layer was improved.

(Example 2, Comparative Examples 3-6)
[1. Preparation of sample]
A solar cell was produced in the same manner as in Example 1 except that NH ₄ COOCH ₃ : 0.58 g (0.017 M) was added to the CBD solution (Example 2).
Moreover, NH ₄ Cl in CBD solution: except for adding 0.23~7.00g (0.01~0.29M) is to prepare the solar cell in the same manner as in Comparative Example 2 (Comparative Example 3-6) .

[2. Test method]
[2.1. Solar cell characteristics]
The solar cell characteristics were evaluated in the same manner as in Example 1.
[2.2. Evaluation of CdS film]
TEM observation and EDS analysis of the CdS film were performed.

[3. result]
Tables 2 and 3 show the results. Tables 2 and 3 also show the results of Example 1 and Comparative Example 2, respectively.
From Table 2, it can be seen that when ammonium acetate is added to the cadmium acetate-based CBD solution, the solar cell characteristics are rapidly deteriorated by slight addition. Similarly, it can be seen from Table 3 that when ammonium chloride is added to a cadmium chloride-based CBD solution, the solar cell characteristics are rapidly deteriorated by slight addition. This is because when a CdS film is formed on a CZTS-based semiconductor layer by the CBD method, if an ammonium salt is added to the CBD solution, the state of the heterointerface between the buffer layer and the CZTS-based semiconductor layer deteriorates, or the CdS film This is thought to be due to a decrease in uniformity.

1 and 2, respectively, a TEM photograph and an EDS analysis result of a CdS film (Comparative Example 2) formed by using cadmium chloride as a Cd source and using a CBD solution without addition of ammonium chloride. Indicates. 3 and 4 show a TEM photograph and an EDS analysis result of a CdS film (Comparative Example 4) formed using a CBD solution using cadmium chloride as a Cd source and 0.4 g of ammonium chloride added. Indicates.
1 to 4, it can be seen that when ammonium chloride is added to the cadmium chloride-based CBD solution, a relatively large amount of Zn and Cu are mixed in the CdS film. Non-Patent Document 2 describes that when a CdS film is formed on a glass substrate, a good-quality CdS film can be formed by adding an ammonium salt. This result is in contrast to Non-Patent Document 2. Is.
The reason that the solar cell characteristics were deteriorated by the addition of ammonium chloride is considered to be that ammonium chloride promoted corrosion of the CZTS-based semiconductor layer. Therefore, when a CdS film is formed on a CZTS-based semiconductor layer using the CBD method, the CBD solution preferably contains only a Cd salt, a sulfur source, and a sulfide synthesis aid.

(Examples 3 to 7)
[1. Preparation of sample]
The amount of cadmium acetate is 0.0086 to 1.29 g (0.0008 to 0.012 M), the amount of thiourea is 1.01 to 0.33 g (0.03 to 0.9 M), and the amount of 28% aqueous ammonia is A solar cell was produced in the same manner as in Example 1 except that 45 to 180 mL (1.5 to 6.0 M) and the amount of ion-exchanged water were 270 to 360 mL.

[2. Evaluation]
The solar cell characteristics were evaluated under the same conditions as in Example 1.

[3. result]
Table 4 shows the results. Table 4 also shows the results of Example 1.
From Table 4,
(1) J _sc , V _oc , and FF values decrease in both cases where the amount of aqueous ammonia is excessive and too small (see Examples 1, 3, and 5).
(2) If the amount of thiourea is too small, the J _sc , V _oc , and FF values decrease (see Examples 1 and 4),
(3) Increasing both the cadmium acetate and thiourea concentrations in the CBD solution improves J _sc but decreases V _oc and FF (see Examples 1 and 6),
(4) When both the concentrations of cadmium acetate and thiourea in the CBD solution are decreased, J _sc is improved, but V _oc and FF are extremely decreased (see Examples 1 and 7).
(5) In order to obtain high conversion efficiency, the concentration of cadmium acetate is 0.001 to 0.05M, the concentration of thiourea is 0.05 to 1.0M, and the concentration of aqueous ammonia is 1.7 to 5.5M. preferable,
I understand that.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  The method for producing a buffer layer for CZTS semiconductor according to the present invention includes various photoelectric elements using a CZTS semiconductor layer as a light absorbing layer of a thin film solar cell, photoconductive cell, photodiode, phototransistor, sensitized solar cell, etc. Can be used in the manufacture of

Claims (6)

Consists of an aqueous solution containing cadmium acetate, a sulfur source, and a sulfide synthesis aid ,
The concentration of the cadmium acetate is 0.001M or more and 0.05M or less,
The concentration of the sulfur source is 0.05M or more and 3.0M or less,
The concentration of the sulfide synthesis aid is 1.7M or more and 5.5M or less.
CBD solution for CZ TS-based semiconductors. The sulfur source is
(A) thiourea (SC (NH ₂ ) ₂ ), thioacetamide (CH ₃ CSNH ₂ ), thioacetic acid (CH ₃ COSH), and thiobenzamide (C ₆ H ₅ CSNH ₂ ), and
(B) Sodium thiosulfate (Na ₂ S ₂ O ₃ ), potassium thiosulfate (K ₂ S ₂ O ₃ ), sodium sulfite (Na ₂ SO ₃ ), sodium hydrogen sulfite (NaHSO ₃ ), sodium disulfite (Na ₂ S ₂ O ₅ ) and sodium sulfide (Na ₂ S)
The CBD solution for a CZTS-based semiconductor according to claim 1, which is any one or more selected from the group consisting of: The sulfide synthesis aid is
(A) ammonia water,
(B) a cyanic acid compound,
(C) a thiocyanic acid compound, or
(D) a mixture of any two or more of (a) to (c),
The CBD solution for CZTS semiconductors according to claim 1 or 2. The CBD solution for a CZTS semiconductor according to any one of claims 1 to 3 , wherein the concentration of the ammonium salt is 0.1 M or less. A CBD step of immersing a substrate on which a CZTS-based semiconductor layer is formed in the CBD solution for CZTS-based semiconductor according to any one of claims 1 to 4 to form a CdS film on a surface of the CZTS-based semiconductor layer;
A method of manufacturing a buffer layer for a CZTS semiconductor, comprising a heat treatment step of heat treating the CdS film at 200 ° C. or lower. The photoelectric element provided with the buffer layer obtained by the method of Claim 5 .

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