JP5311984B2 - Thin film solar cell manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a thin film solar cell having a light absorption layer between a pair of electrode layers.

  FIG. 1 shows a basic structure of a general thin film solar cell. As shown in FIG. 1, the thin-film solar cell has a first electrode layer 2 made of, for example, Mo formed on a substrate 1 made of soda lime glass, for example, and is formed on the first electrode layer 2. A light absorption layer 3 made of a compound semiconductor thin film is formed, and a transparent second electrode layer 5 made of ZnO or the like is formed on the light absorption layer 3 through a buffer layer 4 made of ZnS, CdS, or the like. .

As the light absorption layer 3 made of a compound semiconductor, a compound semiconductor thin film made of Cu (In, Ga) Se ₂ is used so as to obtain high energy conversion efficiency.

Cu (In, Ga) as preparation of Se ₂ is large in the production process used and the method of using a vacuum process such as vapor deposition or sputtering, a non-vacuum process for deposition by solid or liquid phase material coating or electrodeposition Separated.

Among these methods, Cu (In, Ga) Se ₂ is produced by applying a non-vacuum process raw material by dissolving individual metal salts of Cu, In, Ga, and Se in an organic solvent, drying and thermally decomposing them. There are a production method of baking, and a production method of applying an organic compound or complex containing elements of Cu, In, Ga, and Se into a solution, applying thermal decomposition, and baking.

The former production method using individual metal salts has a problem in that the solubility differs depending on each metal salt, so that the composition is easily separated and deposited at the time of drying, and the composition of the entire thin film tends to be nonuniform. On the other hand, in the production method using an organic compound or complex, if an ideal organic compound can be produced, the composition does not separate during drying, and theoretically, a Cu (In, Ga) Se ₂ thin film having a uniform composition is formed. It is possible to form.

For example, conventionally, a single precursor method (single source precursor method) is known, and in this method, Cu, Se, In, or Ga is present in one organic compound, and the organic compound is used as an organic solvent. It is a manufacturing method in which a Cu (In, Ga) Se ₂ thin film is formed by dissolving, coating, pyrolysis, and baking (see Patent Document 1).

The production method of Patent Document 1 will be specifically described. A metal salt such as Cu (CH ₃ CN) ₄ .PF ₆ and a Lewis base such as P (C ₆ H ₅ ) ₃ are reacted to produce {P (C ₆ A complex ion having a form such as H ₅ ) ₃ } ₂ Cu (CH ₃ CN) ₂ ⁺ is prepared, and this complex ion is reacted with a complex ion containing In or Ga and Se, whereby Cu and In or A single precursor containing Ga and Se is produced.
US Pat. No. 6,992,202

However, according to experiments by the present inventors, a metal salt such as Cu (CH ₃ CN) ₄ .PF ₆ and a Lewis base such as P (C ₆ H ₅ ) ₃ are reacted to produce {P (C ₆ H ₅ ) ₃ } ₂ Cu (CH ₃ CN) ₂ ^{+ in} the form of a complex ion, and this complex ion is reacted with a complex ion containing In or Ga and Se to form Cu and In or Ga and Se. Is prepared by dissolving the single precursor in an organic solvent and applying it to the first electrode layer of the substrate, followed by thermal decomposition and heat treatment in an inert atmosphere. When the Ga) Se ₂ thin film is formed, there is a problem that the adhesion between the Cu (In, Ga) Se ₂ thin film and the first electrode layer is low, and it is easy to peel off during handling.

  An object of this invention is to provide the manufacturing method of the thin film solar cell which can improve the joint strength of a light absorption layer and a 1st electrode layer.

  The present inventors heated a single precursor into an organic component and a metal component by heating a light absorption coating film formed by applying a light absorption layer solution in which a single precursor is dissolved in an organic solvent. In the thermal decomposition step of decomposing and removing organic components, the single precursor is thermally decomposed by heat treatment in an inert gas atmosphere having an oxygen concentration of 20 to 150 ppm, whereby the light absorption layer and the first electrode layer It has been found that the bonding strength can be improved and has led to the present invention.

That is, the method for producing a thin film solar cell of the present invention is a method for producing a thin film solar cell having a light absorption layer between a first electrode layer and a second electrode layer, and includes P (C ₆ H in one organic compound. ₅ ) A light absorbing layer solution in which a single precursor containing a Lewis base of ₃ and at least one of Cu, S and Se and at least one of In and Ga is dissolved in an organic solvent is used as the first electrode. A light-absorbing coating film forming step of forming a light-absorbing coating film on the layer, and heat-treating the light-absorbing coating film in an inert gas atmosphere having an oxygen concentration of 20 to 150 ppm to form the single precursor A thermal decomposition step of thermally decomposing into an organic component and a metal component and removing the organic component; and heat-treating the metal component at a temperature higher than a heat treatment temperature of the thermal decomposition step, so that at least of Cu, S, and Se 1 type and In And a light absorption layer forming step of forming a light absorption layer containing at least one of Ga on the first electrode layer, and a second electrode layer formation step of forming the second electrode layer on the light absorption layer It is characterized by comprising.

  According to the method for producing a thin film solar cell of the present invention, the oxygen concentration in the thermal decomposition step of thermally decomposing a single precursor into an organic component and a metal component is set to 20 to 150 ppm. The bonding strength between the layer and the first electrode layer can be improved.

  As a result of examining the above reasons, the present inventors set the oxygen concentration in the inert gas atmosphere of the thermal decomposition step to 20 to 150 ppm, so that oxygen enters the interface between the light absorption layer and the first electrode layer, Since the light absorption layer and the first electrode layer are chemically bonded via oxygen, it is considered that the adhesion between the light absorption layer and the first electrode layer is improved and the bonding strength can be improved. On the other hand, since the amount of oxygen in the inert gas atmosphere is very small, a compound containing at least one of Cu, S, and Se and at least one of In and Ga is not oxidized. It is considered that the oxidation of selenium is suppressed and Se deficiency does not occur.

  According to the method for manufacturing a thin film solar cell of the present invention, the oxygen concentration in the thermal decomposition step of thermally decomposing a single precursor into an organic component and a metal component is set to 20 to 150 ppm, whereby the light absorption layer and the first electrode layer The joint strength can be improved.

  The thin film solar cell produced by the manufacturing method of the present invention is a thin film solar cell having a light absorption layer between a pair of electrode layers. For example, as shown in FIG. A layer 2 is formed, a light absorption layer 3 made of a compound semiconductor thin film is formed on the first electrode layer 2, and a transparent second electrode layer 5 is formed on the light absorption layer 3 via a buffer layer 4. ing.

  As the substrate 1, for example, a soda lime glass substrate, a metal substrate such as Mo or SUS, a resin substrate such as polyimide, or the like can be used. A first electrode layer 2 is formed on the substrate 1, and a light absorption layer 3 is formed on the first electrode layer 2. A second electrode layer 5 is formed on the light absorption layer 3 via the buffer layer 4, and the light absorption layer 3 is sandwiched between the first electrode layer 2 and the second electrode layer 5. 1, a thin film solar cell having a light absorption layer 3 between the second electrode layers 2 and 5 is configured.

  In addition, although the example which laminated | stacked the board | substrate 1, the 1st electrode layer 2, the light absorption layer 3, the buffer layer 4, and the 2nd electrode layer 5 was demonstrated sequentially, in this invention, a pair of 1st, 2nd electrode layer 2, As long as the light absorption layer 3 is provided between the layers 5, various intermediate layers may be formed between the layers. Further, the present invention may be of a type that does not have the substrate 1, in other words, a type in which the first electrode layer 2 functions as a substrate.

As the light absorption layer 3 made of a compound semiconductor, CuInSe ₂ , CuGaSe ₂ , Cu (In, Ga) Se ₂ , CuInS ₂ , CuGaS, which are compound semiconductors made of a chalcopyrite structure, can be used to obtain high energy conversion efficiency. ₂ , Cu (In, Ga) S ₂ is used.

The manufacturing method of the thin film solar cell of this invention is demonstrated. First, for example, a substrate 1 made of soda lime glass is prepared. A first electrode layer 2 is formed on the substrate 1. The first electrode layer 2 is made of any electrode material selected from molybdenum (Mo), tungsten (W), chromium (Cr), polysilicon (SiO ₂ ), metal silicide, aluminum (Al), and the like. desirable. The first electrode layer 2 can be formed by a vapor deposition method, a sputtering method, a coating method, or the like.

Next, the light absorption layer 3 is formed on the first electrode layer 2. First, a light absorption layer solution for forming the light absorption layer 3 is prepared. This light absorption layer solution is a solution in which a single precursor containing Cu, In, Ga, and Se is dissolved. This single precursor can be produced by reacting the first complex ion obtained in the first complex ion solution production step with the second complex ion obtained in the second complex ion solution production step.
(First complex ion solution preparation process)
First, a Lewis base L composed of P (C ₆ H ₅ ) ₃ is reacted with an organic metal salt of Cu such as Cu (CH ₃ CN) ₄ .PF _{6 in} an organic solvent such as acetonitrile to obtain {P (C _A first complex ion solution in which a first complex ion having a shape such as ₆ H ₅ ) ₃ } ₂ Cu (CH ₃ CN) ₂ ⁺ is present is prepared (first complex ion solution preparation step).

Examples of the organic metal salts of _Cu, CuCl, CuCl 2, CuBr, may be used halides such as CuI. In addition to acetonitrile, acetone, methanol, ethanol, isopropanol, or the like can be used as an organic solvent for dissolving the Lewis base L and the organometallic salt of Cu.

The first complex ion solution is composed of a Lewis base L and an organometallic salt of Cu so that the molar ratio (Cu / L) is 1/3 or less. It is desirable to mix and dissolve this mixture in an organic solvent. In particular, the molar ratio (Cu / L) is preferably 0.1 or more from the viewpoint of improving the reaction yield.
(Second complex ion solution preparation process)
A second complex ion containing an organic compound containing S or Se and a halide of In or Ga is prepared.

For example, an organic compound and NaOCH ₃ and an organic selenium compound or an organic sulfur compound reacts with the InCl ₃ or GaCl ₃ are reacted in a solvent consisting of methanol, In _{{SeR} 4} ^- or Ga _{{SeR} 4} ^- To form a second complex ion. Here, R is a kind selected from acrylic, allyl, alkyl, vinyl, perfluoro, and carbamate.

For example, HSeC ₆ H ₅ is used as the organic selenium compound, and HSC ₆ H ₅ is used as the organic sulfur compound. Further, a solvent such as ethanol or propanol can be used instead of methanol. Note that the first complex ion and the second complex ion may be produced in any order.
(Single precursor production process)
Next, the first complex ion and the second complex ion are reacted to produce a single precursor containing Cu, S or Se, In or Ga, and the Lewis base L. That is, by mixing a first complex ion solution containing Cu, a second complex ion solution containing In or Ga, and Se, and reacting the first complex ion and the second complex ion, Cu and A single precursor can be prepared by separating a precipitate containing S or Se, In or Ga, and a Lewis base L and a solution above the precipitate, discharging the solution portion, and drying.

The temperature when the first complex ion and the second complex ion are reacted is preferably 0 to 30 ° C., and the reaction time is preferably 1 to 5 hours. In order to remove impurities such as Na and Cl, the portion precipitated by the reaction is desirably washed using a technique such as centrifugation or filtration.
(Light absorption coating film forming process)
A light absorption layer solution in which a single precursor is dissolved in an organic solvent is applied onto the first electrode layer to form a light absorption coating film.

  That is, the light-absorbing layer solution is prepared by dissolving the single precursor in an organic solvent such as toluene, pyridine, xylene, and acetone. And this light absorption layer solution is apply | coated on the above-mentioned 1st electrode 2 of the board | substrate 1, and a light absorption coating film is formed.

The application of the light absorption layer solution onto the first electrode layer 2 is desirably performed using a spin coater, screen printing, dipping, spraying, a die coater, or the like .

(Pyrolysis process)
The light absorbing coating film is dried. The drying is desirably performed in an inert atmosphere having an oxygen concentration of 20 to 150 ppm. In particular, a nitrogen atmosphere is desirable. It is desirable to maintain the temperature at the time of drying at 100 to 150 ° C. for 5 to 20 minutes. The light absorption coating film after drying may be formed by repeating the application and drying of the light absorption layer solution a plurality of times.
Continuously after the drying step, the light absorption coating film is heat-treated in an inert gas atmosphere having an oxygen concentration of 20 to 150 ppm. As a result, the single precursor is thermally decomposed into an organic component and a metal component, and the organic component is removed.
That is, generally, a light-absorbing coating film is heat-treated at 200 to 500 ° C. in an inert gas atmosphere such as a nitrogen atmosphere (oxygen concentration is about 10 ppm), and a single precursor is thermally decomposed into an organic component and a metal component, Although the component is removed, in the present invention, the oxygen concentration in the inert gas atmosphere in such a pyrolysis step is controlled to 20 to 150 ppm.

  As described above, the oxygen concentration in the inert gas atmosphere in the thermal decomposition step is set to 20 to 150 ppm because when the oxygen concentration in the inert gas atmosphere is lower than 20 ppm, the light absorption layer and the first electrode layer are joined. This is because the strength cannot be improved, and on the other hand, if the oxygen concentration is higher than 150 ppm, the oxidation of the light absorption layer proceeds remarkably, the Se composition fluctuates, and the power generation efficiency is lowered. In particular, the oxygen concentration is desirably 50 to 100 ppm.

The temperature at which the single precursor is thermally decomposed into the organic component and the metal component is in the range of 200 to 500 ° C., and the oxygen concentration is preferably 20 to 150 ppm, particularly at the temperature at which the thermal decomposition proceeds. This is kept at 200 to 500 ° C. for about 2 to 30 minutes, and then naturally cooled to room temperature.
(Light absorption layer forming process)
Then, the light absorption layer containing at least one of Cu, S, and Se and at least one of In and Ga is heated from room temperature to a temperature higher than the heating temperature of the thermal decomposition step and heat-treated. Form. The thickness of the light absorption layer 3 is, for example, 1.0 to 2.5 μm.

  The heat treatment is desirably performed in a reducing atmosphere. In particular, any one of a nitrogen atmosphere, a forming gas atmosphere, and a hydrogen atmosphere is desirable. The oxygen concentration in such a reducing atmosphere is desirably 1 ppm or less from the viewpoint of promoting grain growth of particles in the light absorption layer.

  The reducing atmosphere during the heat treatment is preferably a reducing atmosphere in which moisture is removed through a hygroscopic agent. The absorbent is not particularly limited as long as it can remove water, but molecular sieve (trade name) and the like are preferably used. The firing temperature is, for example, 500 ° C to 600 ° C.

After the formation of the light absorption layer 3, it is desirable to remove the high resistance layer made of Cu ₂ Se or the like on the surface by etching with a KCN aqueous solution.
(Buffer layer, second electrode layer forming step)
Thereafter, an n-type buffer layer 4 for heterojunction is formed on the light absorption layer 3. CdS, ZnS, ZnSe, ZnMgO, ZnS / ZnMgO, ZnO, InS, InSe, In (OH) ₃ , ZnInSe, ZnInS, ZnSSe, CuI, Mg Materials such as OH) ₂ are used. These can be formed by immersing a substrate formed up to the light absorption layer by a dip coating method, a CBD method (solution growth method) or the like in an aqueous solution to deposit fine particles.

  Next, a transparent second electrode layer 5 made of ITO or ZnO is formed on the buffer layer 4. It can be formed by sputtering, spraying or coating. The thickness of the buffer layer 4 is, for example, 10 to 200 nm, and the thickness of the second electrode layer 5 is, for example, 0.5 to 3.0 μm.

  In the method for producing a thin film solar cell of the present invention, the oxygen concentration in the pyrolysis step in which a single precursor is pyrolyzed into an organic component and a metal component is set to 20 to 150 ppm. By setting the concentration to 20 to 150 ppm, oxygen enters the interface between the light absorption layer and the first electrode layer, and the light absorption layer and the first electrode layer are chemically bonded via the oxygen. Adhesion with the electrode layer is improved, the bonding strength can be improved, and the amount of oxygen in the inert gas atmosphere is very small, so at least one of Cu, S, and Se and at least one of In and Ga Is not oxidized, Se oxidation is suppressed, and Se deficiency does not occur.

In addition, when producing a single precursor as a raw material for the light absorption layer solution, an almost pure single precursor can be obtained without going through an extraction process using a toxic substance such as CH ₂ Cl _2. In addition, the composition ratio such as Cu / In / Ga / Se can be controlled.

That is, when an organic metal salt of Lewis base L and Cu is dissolved in an organic solvent to prepare a solution containing a first complex ion containing Cu and Lewis base L, an organic salt of Lewis base L and Cu Is blended so that the molar ratio (Cu / L) is 1/3 or less, and more Lewis base L is blended than usual and dissolved in an organic solvent, such as a compound of Cu and Se. By suppressing the formation of by-products, the first complex ions such as {P (C ₆ H ₅ ) ₃ } ₂ Cu (CH ₃ CN) ₂ ⁺ can be easily and in large quantities, and thus, In Alternatively, complex ionization of Ga can be suppressed, and formation of complex ions containing Cu and S or Se and In or Ga and Lewis base L can be promoted, and the ratio of Cu and (In + Ga) in the single precursor can be 1: 1. The composition can be controlled so as to be close to.

Accordingly, the first complex ion and the second complex ion are allowed to react and precipitate, the precipitate is dried to produce a single precursor, and a light absorbing layer solution in which this single precursor is dissolved in an organic solvent is prepared. When the light absorption layer is formed by pyrolysis and baking, the production of Cu (In, Ga) Se ₂ can be promoted by suppressing the production of a compound having low conductivity such as Cu ₂ Se, and the energy conversion efficiency is improved. it can.

  Hereinafter, although the example and the comparative example are given and the manufacturing method of the thin film solar cell of this invention is demonstrated in detail, this invention is not limited only to a following example.

1 mmol of Cu (CH ₃ CN) ₄ .PF ₆ as the organometallic salt of copper and 10 mmol, 3 mmol and 2 mmol of P (C ₆ H ₅ ) ₃ as the Lewis base L were dissolved in 10 ml of acetonitrile, respectively. CH ₃ CN) ₄ .PF ₆ / P (C ₆ H ₅ ) ₃ molar ratios (Cu / L) were prepared as shown in Table 1, and 1/10, 1/3, and 1/2 solutions were prepared. . After confirming that these solutions were uniformly dissolved, the solution was stirred for 5 hours at room temperature with a magnetic stirrer to prepare a first complex ion solution containing the first complex ions (first complex ion solution preparation step). .

On the other hand, 4 mmol of NaOCH ₃ and 4 mmol of HSeC ₆ H ₅ were dissolved in 30 ml of methanol, and then InCl ₃ and / or GaCl ₃ was dissolved to a total of 1 mmol. After confirming complete dissolution, the mixture was stirred with a magnetic stirrer at room temperature for 5 hours to prepare a second complex ion solution containing the second complex ions (second complex ion solution preparation step). Table 1 shows the charged compositions of Cu, Se, In, and Ga.

  Next, the second complex ion solution was dropped into the first complex ion solution at a rate of 10 ml per minute. Thereby, it was confirmed that a white precipitate was generated during the dropping. After completion of the dropwise addition, the mixture was stirred at room temperature for 1 hour with a magnetic stirrer. As a result, a precipitate was precipitated.

  In order to take out only this precipitate, the operation of separating the solvent with a centrifuge, dispersing it in 50 ml of methanol, and centrifuging it was repeated twice.

The precipitate was dried in vacuum at room temperature to remove the solvent to make a single precursor.
Composition analysis of a single precursor was performed by emission spectroscopy (ICP) and listed in Table 1.

  Pyridine was added to this single precursor to produce a light absorption layer solution with a single precursor of 50% by mass in the total amount. This light absorption layer solution was formed into a thin film on the first electrode layer made of Mo of the soda lime glass substrate by the doctor blade method. In the glove box, the thin film was coated with the light absorption layer solution using nitrogen gas as a carrier gas, and applied to the first electrode layer to form a light absorption coating film (light absorption coating film forming step).

  After forming the light absorbing coating film, the soda lime glass substrate was dried for 5 minutes while being heated to 110 ° C. with a hot plate in a nitrogen atmosphere having an oxygen concentration of 100 ppm.

  After drying, continuously (nitrogen atmosphere with an oxygen concentration of 100 ppm), the temperature was raised from 200 to 400 ° C. at a rate of 90 ° C./min, held at 400 ° C. for 5 minutes, and the single precursor was pyrolyzed. Then, it was naturally cooled (pyrolysis process). Thereafter, as a firing step, the temperature was raised from room temperature to 530 ° C. at a temperature rising rate of 250 ° C./hr in a hydrogen atmosphere (oxygen concentration of 1 ppm or less), held at 530 ° C. for 1 hour, then naturally cooled to a thickness of 1 A light absorption layer made of a compound semiconductor thin film of .5 μm was formed (light absorption layer forming step).

  Thereafter, the adhesion (bonding strength) between the light absorption layer and the first electrode layer was evaluated by the SAICAS method. That is, a cutting tool having a blade width of 0.3 mm is brought into contact with the light-absorbing layer, and the cutting force is applied to the cutting tool at a vertical speed of 25 nm / sec and 250 nm / sec. It described in Table 2.

  Thereafter, cadmium acetate and thiourea were dissolved in ammonia, and the substrate was immersed therein to form a buffer layer made of CdS having a thickness of 0.05 μm on the compound semiconductor thin film. Furthermore, an Al-doped zinc oxide film (second electrode layer) was formed on the buffer layer by sputtering. Finally, an aluminum electrode (extraction electrode) was formed by vapor deposition to produce a thin film solar cell.

  In addition, the present inventors have determined the bonding strength for the case where a thin film solar cell was produced in the same manner as described above except that the oxygen concentration in the drying step and the thermal decomposition step was changed to 1, 20, 50, 150, and 300 ppm. It was evaluated and listed in Table 2.

  From Tables 1 and 2, it can be seen that in the thermal decomposition step, the sample of the present invention in which the oxygen concentration of the inert gas composed of nitrogen is 20 to 150 ppm has high bonding strength between the light absorption layer and the first electrode layer. On the other hand, the sample No. of the comparative example whose oxygen concentration of the inert gas consisting of nitrogen of the thermal decomposition process is 1 ppm. No. 13 shows that the bonding strength between the light absorption layer and the first electrode layer is low. Moreover, sample No. of the comparative example whose oxygen concentration of an inert gas is 300 ppm. 14 shows that the light absorption layer is oxidized and Se in the light absorption layer becomes 1.55 mol, and the energy conversion efficiency is low.

In the first complex ion preparation step, when the molar ratio (Cu / L) of Cu (CH ₃ CN) ₄ .PF ₆ / P (C ₆ H ₅ ) ₃ is 1/3 or less, A single precursor having a close composition is obtained, and it can be seen that the formation of Cu (In, Ga) Se ₂ can be promoted even after the heat treatment, and the energy conversion efficiency can be improved.

It is sectional drawing which shows an example of a thin film solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... 1st electrode layer 3 ... Light absorption layer 4 ... Buffer layer 5 ... 2nd electrode layer

Claims (1)

A method for producing a thin-film solar cell having a light absorption layer between a first electrode layer and a second electrode layer, wherein a Lewis base composed of P (C ₆ H ₅ ) ₃ in one organic compound , Cu and S, and A light absorbing layer solution in which a single precursor containing at least one of Se and at least one of In and Ga is dissolved in an organic solvent is applied onto the first electrode layer to form a light absorbing coating film. A light-absorbing coating film forming step, and thermally treating the light-absorbing coating film in an inert gas atmosphere having an oxygen concentration of 20 to 150 ppm to thermally decompose the single precursor into an organic component and a metal component, A thermal decomposition step of removing components, and heat-treating the metal component at a temperature higher than a heat treatment temperature of the thermal decomposition step, thereby at least one of Cu, S, and Se and at least one of In and Ga; Including light A thin film solar comprising: a light absorbing layer forming step of forming a light collecting layer on the first electrode layer; and a second electrode layer forming step of forming the second electrode layer on the light absorbing layer. Battery manufacturing method.

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