JP2015198126A - Compound thin film solar cell, and method of manufacturing compound thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound thin film solar cell including a light absorption layer formed of a coating film of an ink containing fine particles, and capable of enhancing the photoelectric conversion efficiency, and to provide a method of manufacturing the same.SOLUTION: In a Cartesian coordinate system where the Cu/(Zn+Sn) ratio (atomic ratio) is x-axis, the Zn/Sn ratio (atomic ratio) is y-axis, the coordinate (x, y) indicating the Cu/(Zn+Sn) ratio and the Zn/Sn ratio of a light absorption layer included in a compound thin film solar cell is located on 7 straight lines connecting the coordinate A(0.71, 0.82), coordinate B(0.90, 0.82), coordinate C(0.94, 0.87), coordinate D(0.89, 1.00), coordinate E(0.84, 1.07), coordinate F(0.75, 1.08), coordinate G(0.71, 1.05) in the order of the coordinate A, coordinate B, coordinate C, coordinate D, coordinate E, coordinate F, and coordinate G, or in a region surrounded by 7 straight lines.

Description

  The present invention relates to a compound thin-film solar cell including a CZTS-based compound semiconductor layer and a method for manufacturing the same.

The CZTS-based compound thin film solar cell includes a CZTS-based compound semiconductor layer (Cu ₂ ZnSnS ₄ , Cu ₂ ZnSnSe ₄ , Cu ₂ ZnSn (S, Se) _4, etc.) as a light absorption layer. In such a compound thin film solar cell, the composition ratio of the light absorption layer is one of the factors affecting the photoelectric conversion efficiency. For example, Patent Document 1 discloses that in a light absorption layer, a Cu / (Zn + Sn) ratio is 0.78 to 0.90 and a Zn / Sn ratio is 1.18 to 1.32. It is disclosed that conversion efficiency can be obtained.

JP 2010-215497 A

  However, the range of the composition ratio disclosed in Patent Document 1 is a range obtained from the result of a test performed on a light absorption layer formed by sputtering. Therefore, even when the above composition ratio is applied to a light absorption layer formed by a method different from sputtering, high photoelectric conversion efficiency is not always obtained.

  For example, a method for forming a light absorption layer from a coating film of ink containing fine particles is a method that can form a light absorption layer at a lower cost than sputtering, and thus a light absorption layer formed by such a method. In a compound thin film solar cell including the above, it is required to increase the photoelectric conversion efficiency.

  The present invention provides a compound thin film solar cell capable of increasing the photoelectric conversion efficiency and a method for producing the compound thin film solar cell in a compound thin film solar cell including a light absorption layer formed from a coating film of ink containing fine particles. The purpose is to do.

A compound thin-film solar cell that solves the above-described problem includes a light absorption layer formed through application of ink containing fine particles of a compound, and the light absorption layer is composed of S and Se as elements derived from the fine particles. A compound thin film solar cell including at least one element and three elements of Cu, Zn, and Sn, wherein the Cu / (Zn + Sn) ratio (atomic ratio) is x-axis and the Zn / Sn ratio (atomic ratio) In the orthogonal coordinate system with y as the y-axis, the coordinates (x, y) indicating the Cu / (Zn + Sn) ratio and the Zn / Sn ratio of the light absorption layer are coordinates A (0.71, 0.82). , Coordinates B (0.90, 0.82), coordinates C (0.94, 0.87), coordinates D (0.89, 1.00), coordinates E (0.84, 1.07), coordinates F (0.75, 1.08) and coordinates G (0.71, 1.05) A, coordinates B, coordinates C, the coordinates D, coordinates E, coordinates F, the coordinates G, on the seven straight lines connecting sequentially the coordinates A, or, located inside the region surrounded by the seven straight lines.
According to the said structure, the photoelectric conversion efficiency in a compound thin film solar cell is improved.

In the compound thin film solar cell, the light absorption layer is located between the front electrode and the back electrode, and the Zn / Sn ratio of the portion near the front electrode in the light absorption layer is the back electrode. It is preferable that it is lower than the said Zn / Sn ratio of the part close | similar to.
According to the said structure, the photoelectric conversion efficiency in a compound thin film solar cell is further improved.
In the compound thin film solar cell, the light absorption layer preferably contains carbon.
According to the said structure, the ink containing the organic binder can be used for coating.

A method of manufacturing a compound thin film solar cell that solves the above problems includes a step of forming a coating film by applying an ink containing fine particles of a compound, a step of heat-treating the coating film to form a light absorption layer, The element derived from the fine particles in the ink includes at least one element of S and Se, and three elements of Cu, Zn, and Sn. , Cu / (Zn + Sn) ratio (atomic ratio) is x-axis and Zn / Sn ratio (atomic ratio) is y-axis, the Cu / (Zn + Sn) ratio and Zn / Sn The coordinates (x, y) indicating the ratio are coordinates A (0.71, 0.82), coordinates B (0.90, 0.82), coordinates C (0.94, 0.87), coordinates D (0.89, 1.00), coordinate E (0.84, 1.07) , Coordinates F (0.75, 1.08) and coordinates G (0.71, 1.05) are coordinate A, coordinate B, coordinate C, coordinate D, coordinate E, coordinate F, coordinate G, coordinate It is located on the seven straight lines connecting in the order of A or inside the region surrounded by the seven straight lines.
According to the said manufacturing method, the compound thin film solar cell with improved photoelectric conversion efficiency can be manufactured.
In the method for manufacturing a compound thin film solar cell, the fine particles are preferably amorphous particles.
According to the manufacturing method, the denseness of the formed light absorption layer is improved.

In the method for producing the compound thin film solar cell, the average particle diameter of the fine particles is preferably 1 nm or more and 200 nm or less.
According to the above manufacturing method, when the average particle size is 200 nm or less, formation of a gap in the film is suppressed in the heat treatment step when forming the light absorption layer. On the other hand, when the average particle diameter is 1 nm or more, the fine particles are less likely to aggregate, and thus the light-absorbing layer forming ink can be easily prepared.
In the method for manufacturing a compound thin film solar cell, the ink preferably contains a thiol organic substance.
According to the above production method, the thiol organic substance functions as a binder, and the leveling property of the film at the time of ink application is improved.

  ADVANTAGE OF THE INVENTION According to this invention, a photoelectric conversion efficiency can be improved in a compound thin film solar cell provided with the light absorption layer formed from the coating film of the ink containing microparticles | fine-particles.

It is sectional drawing which shows the whole structure of a compound thin film solar cell about one Embodiment which actualized the compound thin film solar cell of this invention. It is a figure which shows the test result about a composition and photoelectric conversion efficiency of a light absorption layer.

  With reference to FIG. 1, one Embodiment of a compound thin film solar cell and its manufacturing method is described.

[Configuration of Compound Thin Film Solar Cell]
As shown in FIG. 1, the compound thin-film solar cell includes a substrate 10 on which a back electrode 11, a light absorption layer 12, a buffer layer 13, a semi-insulating layer 14, a window layer 15, and The surface electrode 16 is located in this order.
For example, a glass plate, a metal plate, or a resin film such as plastic is used as the substrate 10.

  As a material for forming the back electrode 11, for example, a metal such as Mo, Ni, Cu, Ti, Fe, Al, titania, and stainless steel is used. Alternatively, a carbon-based electrode such as carbon or graphene, or a transparent conductive film such as ITO or ZnO may be used as the back electrode 11.

The light absorption layer 12 is a p-type compound semiconductor and is made of a CZTS-based compound semiconductor. The CZTS-based compound semiconductor is a so-called I _2- (II-IV) -VI ₄ group ₄ compound semiconductor containing at least one element of S and Se and three elements of Cu, Zn, and Sn. It is.

In a two-dimensional orthogonal coordinate system in which the Cu / (Zn + Sn) ratio is the x axis and the Zn / Sn ratio is the y axis, the Cu / (Zn + Sn) ratio in the light absorption layer 12 and the Zn / Sn ratio in the light absorption layer 12 are The coordinates (x, y) shown are in the following range. That is, the coordinates (x, y) indicated by the light absorption layer 12 with respect to the composition ratio are seven straight lines connecting the following coordinates A, coordinates B, coordinates C, coordinates D, coordinates E, coordinates F, coordinates G, and coordinates A in this order. Located above or inside the region surrounded by seven straight lines. The seven straight lines are a straight line connecting coordinates A and B, a straight line connecting coordinates B and C, a straight line connecting coordinates C and D, and a straight line connecting coordinates D and E. , A straight line connecting coordinates E and F, a straight line connecting coordinates F and G, and a straight line connecting coordinates G and A.
・ Coordinate A (0.71, 0.82)
・ Coordinate B (0.90, 0.82)
・ Coordinate C (0.94, 0.87)
-Coordinate D (0.89, 1.00)
・ Coordinate E (0.84, 1.07)
・ Coordinate F (0.75, 1.08)
・ Coordinate G (0.71, 1.05)

  The Cu / (Zn + Sn) ratio and the Zn / Sn ratio are both atomic ratios. If the coordinates (x, y) indicated by the light absorption layer 12 in the composition ratio are within the above range, the photoelectric conversion efficiency of the compound thin-film solar cell is increased.

  In the light absorption layer 12, the Zn / Sn ratio in the portion close to the front electrode 16 is preferably lower than the Zn / Sn ratio in the portion close to the back electrode 11. According to such a configuration, the photoelectric conversion efficiency is further increased. The thickness of the light absorption layer 12 is preferably 0.3 μm or more and 10 μm or less, and preferably 2 μm, for example.

The buffer layer 13 is an n-type compound semiconductor. As the buffer layer 13, for example, CdS, Zn (S, O, OH), ZnS, ZnSe, In ₂ S ₃ or the like is used. The semi-insulating layer 14 is an i-type compound semiconductor. As the semi-insulating layer 14, for example, a metal oxide such as ZnO is used. The window layer 15 is an n-type compound semiconductor. As the window layer 15, for example, ZnO or ITO to which Al, Ga, B, or the like is added is used.

  The surface electrode 16 is laminated on a part of the upper surface of the window layer 15. As a material of the surface electrode 16, for example, a metal such as Al or Ag is used. Alternatively, as the surface electrode 16, a carbon-based electrode such as carbon or graphene, or a transparent conductive film such as ITO or ZnO may be used.

Note that at least one of the buffer layer 13, the semi-insulating layer 14, and the window layer 15 may be omitted, and the compound thin-film solar cell may have other layers other than the above-described layers. For example, an antireflection film may be laminated on the window layer 15. Since the antireflection film has a function of suppressing light reflection, the light absorption layer 12 can absorb more light by providing the antireflection film. The antireflection film is formed to a thickness of about 100 nm using, for example, MgF ₂ .
Further, for example, an intermediate layer having a composition for increasing the photoelectric conversion efficiency may be provided between the back electrode 11 and the light absorption layer 12.

[Method for producing compound thin-film solar cell]
The compound thin film solar cell is formed by laminating a back electrode 11, a light absorption layer 12, a buffer layer 13, a semi-insulating layer 14, a window layer 15, and a surface electrode 16 in this order on a substrate 10.
The back electrode 11 is formed on the upper surface of the substrate 10 by using, for example, sputtering, vapor deposition, CVD, or the like.
The light absorption layer 12 is formed using a light absorption layer forming ink containing fine particles composed of the constituent elements of the light absorption layer 12.

The fine particles are nano-sized particles, and are generated by a reaction between a solution containing a metal salt or a metal complex and a solution containing a chalcogenide salt. The fine particles are, for example, particles made of a compound represented by a composition formula of Cu _2−x Zn _{1 + y} SnS _z Se _4−Z (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 4). In addition to the above-mentioned compounds, the ink for forming a light absorption layer includes Cu _2−x S _y Se _2−y (0 ≦ x ≦ 1, 0 ≦ y ≦ 2), Zn _2−x S _y Se as fine particles. _2-y (0 ≦ x ≦ 1, 0 ≦ y ≦ 2), Sn _2-x S _y Se _2-y (0 ≦ x ≦ 1, 0 ≦ y ≦ 2) It may contain particles of at least one compound selected from the group. Alternatively, the light absorption layer forming ink is represented by a composition formula of Cu _2−x Zn _{1 + y} SnS _z Se _4−Z (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 4) as fine particles. Instead of the compound particles, three kinds of compound particles included in the group may be included.

Regarding the composition ratio of the light absorbing layer forming ink, the coordinates (x, y) indicated by the light absorbing layer forming ink are coordinates (x, y) derived from all the fine particles contained in the light absorbing layer forming ink. . And the said coordinates (x, y) which the ink for light absorption layer formation shows about a composition ratio is the following ranges. That is, the coordinates (x, y) indicated by the light absorbing layer forming ink are the seven straight lines connecting the following coordinates A, coordinates B, coordinates C, coordinates D, coordinates E, coordinates F, coordinates G, and coordinates A in this order. Located above or inside the region surrounded by seven straight lines. The seven straight lines are a straight line connecting coordinates A and B, a straight line connecting coordinates B and C, a straight line connecting coordinates C and D, and a straight line connecting coordinates D and E. , A straight line connecting coordinates E and F, a straight line connecting coordinates F and G, and a straight line connecting coordinates G and A.
・ Coordinate A (0.71, 0.82)
・ Coordinate B (0.90, 0.82)
・ Coordinate C (0.94, 0.87)
-Coordinate D (0.89, 1.00)
・ Coordinate E (0.84, 1.07)
・ Coordinate F (0.75, 1.08)
・ Coordinate G (0.71, 1.05)

  If the coordinates (x, y) indicated by the light absorbing layer forming ink in the composition ratio are within the above range, the light absorbing layer 12 capable of increasing the photoelectric conversion efficiency can be formed. In the light absorbing layer forming ink, the coordinates (x, y) for the composition ratio of each of the fine particles contained in the light absorbing layer forming ink may be included in the above range, or the light absorbing layer forming ink. May include fine particles having coordinates (x, y) outside the above range.

  As the fine particles, it is preferable to use amorphous particles. Crystalline particles are stable in terms of energy, and thus each molecule is easily fixed at a certain position. However, in amorphous particles, each composition component is easily diffused by heat treatment. Improves the density.

  The average particle diameter of the fine particles is preferably 1 nm or more and 200 nm or less. When the average particle size is 200 nm or less, formation of a gap in the film is suppressed in the heat treatment step when forming the light absorption layer 12. Therefore, an increase in surface roughness in the light absorption layer 12 and a decrease in photoelectric conversion efficiency can be suppressed. On the other hand, when the average particle size of the fine particles is 1 nm or more, the fine particles are less likely to aggregate, and thus the light-absorbing layer forming ink can be easily prepared. The average particle diameter of the fine particles is obtained from observation using a scanning electron microscope (SEM) for the cured product of the light absorbing layer forming ink, and is obtained by measuring five observation regions each having a 1 μm square region. It is the average value of the shortest diameter in each fine particle measured in each.

  The solvent for dispersing the fine particles in the light absorbing layer forming ink is not particularly limited as long as it is an organic solvent. The organic solvent can be selected from, for example, alcohols, ethers, esters, aliphatic hydrocarbons, alicyclic hydrocarbons, or aromatic hydrocarbons. As the organic solvent, alcohols having less than 10 carbon atoms such as methanol, ethanol, and butanol, diethyl ether, pentane, hexane, cyclohexane, and toluene are preferable, and methanol, pyridine, toluene, and hexane are particularly preferable.

  The light absorbing layer forming ink preferably contains a binder in order to improve leveling properties during coating. The content of the binder is preferably 5% by mass or more and 70% by mass or less, and more preferably 20% by mass or more and 60% by mass or less of the fine particles contained in the light absorbing layer forming ink. When the binder content is 5% by mass or more, formation of cavities in the thin film after heat treatment is suppressed. When the binder content is 70% by mass or less, the surface roughness of the thin film after heat treatment is suppressed from increasing.

  As the binder, a thiol organic substance, a selenol organic substance, an alcohol having 10 or more carbon atoms, or the like can be used. Further, Se particles, S particles, Se compounds, S compounds, or the like may be used as the binder. Furthermore, sodium sulfide, sodium selenide, potassium selenide, sodium selenate, thiosulfate, or the like may be used as the binder. Among these substances, it is preferable to use a thiol organic substance as the binder, and it is more preferable to use thiourea. When an organic compound is used as the binder, the light absorption layer 12 formed from the light absorption layer forming ink has a trace amount of about 0.3 atomic% to 0.5 atomic% with respect to the entire light absorption layer 12. Of carbon remains.

  In the step of forming the light absorption layer 12, first, the light absorption layer forming ink is applied to the upper surface of the back electrode 11 to form a film containing fine particles. And the solvent contained in a film | membrane is removed by drying the coated film | membrane, and the coating film which is a precursor of the light absorption layer 12 is formed. By the heat treatment of the coating film, the sintering and crystallization of the fine particles proceed, and the light absorption layer 12 is formed. The light absorption layer 12 includes at least one element of S and Se and three elements of Cu, Zn, and Sn as elements derived from the fine particles.

  Examples of the coating method of the light absorbing layer forming ink include a doctor blade method, a spin coating method, a slit coating method, a coating method such as a spray method, a gravure printing method, a screen printing method, a reverse offset printing method, Or printing methods, such as a relief printing method, are mentioned.

The heat treatment is performed, for example, by annealing with a heating furnace or rapid thermal annealing (RTA). The atmosphere of the heat treatment is at least selected from the group consisting of H ₂ S gas, H ₂ Se gas, nitrogen gas, Ar gas, Se vapor, S vapor, hydrogen gas, and a mixed gas of hydrogen and an inert gas. Preferably one is included. The heat treatment temperature is preferably 250 ° C. or higher. When glass is used as the substrate 10, the temperature of the heat treatment is a temperature that the glass can withstand, specifically, 650 ° C. or less is preferable, and 600 ° C. or less is more preferable.

The heat treatment is preferably performed in the presence of an alkali metal such as sodium. For example, a layer containing an alkali metal is formed on the upper surface of the back electrode 11, and a light absorbing layer forming ink is applied on the layer containing the alkali metal, and heat treatment is performed. Specifically, for example, a layer containing an alkali metal can be formed by depositing a NaNbO ₃ compound, a KNbO ₃ compound, or a LiNbO ₃ compound on the upper surface of the back electrode 11 by sputtering. The layer containing an alkali metal can also be formed by depositing a compound such as Na ₂ S, Na ₂ Se, NaCl, or NaF on the upper surface of the back electrode 11 by vapor deposition or coating.

The light absorption layer 12 formed from the light absorption layer forming ink is preferably subjected to treatment with an acid such as hydrochloric acid. As a result, Zn atoms in the vicinity of the upper surface of the light absorption layer 12 are dissolved, so that the Zn / Sn ratio in the portion near the front electrode 16 in the light absorption layer 12 is higher than the Zn / Sn ratio in the portion near the back electrode 11. Can also be actively lowered. In addition, as an acid, a well-known inorganic acid and organic acid can be used.
The buffer layer 13 is formed on the upper surface of the light absorption layer 12 by using, for example, the CBD method, the MOCVD method, the ALD method, or the like.

The semi-insulating layer 14 is formed on the upper surface of the buffer layer 13 using, for example, MOCVD or sputtering, and the window layer 15 is formed on the upper surface of the semi-insulating layer 14 using, for example, MOCVD or sputtering. .
The surface electrode 16 is formed on a part of the upper surface of the window layer 15 by using, for example, sputtering, vapor deposition, CVD, or the like.

(Example)
The compound thin film solar cell and the manufacturing method thereof will be described using specific examples.
<Production of compound thin film solar cell>
(Adjustment of light absorbing layer forming ink)
CuI, ZnI ₂ and SnI ₄ were dissolved in pyridine to prepare a first solution. In addition, a _second solution was prepared by dissolving Na ₂ Se in methanol. At this time, by adjusting the amount of each of CuI, ZnI ₂ , and SnI ₄ added to the first solution, the coordinates (x, y) indicated by the light-absorbing layer forming ink and the light absorption of the composition ratio are adjusted. The coordinates (x, y) indicated by the layer can be changed.

The first solution and the second solution were mixed, and this mixed solution was reacted at 0 ° C. in an inert gas atmosphere to produce Cu—Zn—Sn—Se fine particles. As a result of measuring the average particle diameter of the fine particles thus obtained using a SEM (scanning electron microscope), the average particle diameter was 50 nm. The reaction solution is filtered and washed with methanol, and then the washed Cu—Zn—Sn—Se fine particles and thiourea are mixed so that the mass ratio of the fine particles to thiourea is 3: 2, and this mixture is mixed. Further, pyridine and methanol were further added to prepare a light absorption layer forming ink containing Cu—Zn—Sn—Se fine particles. The solid content contained in the light absorbing layer forming ink is 2% by mass.
(Formation of back electrode)
Using soda lime glass as a substrate, a back electrode composed of Mo was formed by sputtering.

(Formation of light absorption layer)
A light absorbing layer forming ink was applied to the upper surface of the back electrode by spraying, the solvent was evaporated in an oven at 250 ° C., and then a selenization treatment was performed at 550 ° C. for 60 minutes as a heat treatment. Thereby, the light absorption layer comprised from the CZTS thin film with a film thickness of 2 micrometers was obtained.
(Formation of buffer layer)
A mixture containing 0.0015 M cadmium sulfate (CdSO ₄ ), 0.0075 M thiourea (NH ₂ CSNH ₂ ), and 1.5 M aqueous ammonia (NH ₄ OH) was heated to 67 ° C. A buffer layer made of CdS having a film thickness of 100 nm was formed on the light absorption layer by immersing the structure in which the above light absorption layer was formed in this mixed solution.

(Formation of semi-insulating layer)
A semi-insulating layer made of ZnO having a thickness of 50 nm was formed on the buffer layer by MOCVD using diethyl zinc and water as raw materials.
(Formation of window layer)
A window layer made of ZnO: B having a thickness of 1 μm was formed on the semi-insulating layer by MOCVD using diethyl zinc, water, and diborane as raw materials.
(Formation of surface electrode)
A surface electrode made of Al having a film thickness of 0.3 μm was formed on the window layer by vapor deposition. Thereby, a compound thin film solar cell was obtained.

In the above method, when adjusting the light absorbing layer forming ink, the Cu / (Zn + Sn) ratio and the Zn / Sn ratio are different from each other by adjusting the addition amounts of CuI, ZnI ₂ , and SnI _4. 1-22 compound thin film solar cells were obtained.

<Evaluation method>
(Photoelectric conversion efficiency)
About the compound thin film solar cell of each test example, evaluation by a standard sunlight simulator (light intensity: 100 mW / cm < ² >, air mass: 1.5) was performed, and the photoelectric conversion efficiency was computed.
(Composition ratio)
About the compound thin film solar cell of each test example, after polishing the cross section of the light absorption layer flatly with Ar ions, evaluation by TEM-EDS (energy dispersive X-ray analysis for transmission electron microscope) was performed, and the atomic ratio was measured. Cu / (Zn + Sn) ratio and Zn / Sn ratio were calculated.

<Result>
About the compound thin film solar cell of each test example, the evaluation result of a composition ratio and photoelectric conversion efficiency is shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 2, a two-dimensional orthogonal coordinate system having a Cu / (Zn + Sn) ratio (atomic ratio) as the x-axis and a Zn / Sn ratio (atomic ratio) as the y-axis includes coordinates A to A region surrounded by the coordinates G is formed. The coordinate A (0.71, 0.82) is Test Example 10, and the coordinate B (0.90, 0.82) is Test Example 22. The coordinates C (0.94, 0.87) is Test Example 12, and the coordinates D (0.89, 1.00) is Test Example 19. Further, the coordinate E (0.84, 1.07) is Test Example 13, and the coordinate F (0.75, 1.08) is Test Example 14. Coordinate G (0.71, 1.05) is Test Example 15. The coordinates (x, y) indicated by the light absorption layer are the straight lines connecting the coordinates A to G in the order of coordinates A → coordinate B → coordinate C → coordinate D → coordinate E → coordinate F → coordinate G → coordinate A. In all the test examples located above or inside the region surrounded by these straight lines, a high photoelectric conversion efficiency of 4.0% or more was obtained.

  In addition, when the composition ratio disclosed in Patent Document 1 is applied to the light absorption layer formed from the ink film containing fine particles as described above, a large amount of ZnS is segregated in the light absorption layer, and photoelectric conversion is performed. The efficiency was low. For example, in Test Example 2 included in the composition ratio range disclosed in Patent Document 1 and Test Example 1 and Test Example 3 having a composition ratio close to Test Example 2, the photoelectric conversion efficiency is extremely low. According to the evaluation results of Test Examples 1 to 22, it was confirmed that high photoelectric conversion efficiency was obtained in a range lower than the composition ratio disclosed in Patent Document 1, particularly regarding the Zn / Sn ratio. As described in Patent Document 1, a light absorption layer formed by heat-treating a film formed by sputtering, and a coating film of ink containing fine particles as in the above embodiment is heat-treated. The formed light absorption layer is different in the manner of crystallization during heat treatment. Since the difference in the progress of crystallization is considered to be a factor that greatly affects the photoelectric conversion efficiency, the range surrounded by the coordinates A to G is a range unique to a manufacturing method using ink containing fine particles. Therefore, it is also a range derived from the viewpoint of the difference in the progress of crystallization and the research by the manufacturing method.

As described above, according to the embodiment, the effects listed below can be obtained as described with reference to the examples.
(1) When the Cu / (Zn + Sn) ratio and the Zn / Sn ratio of the light absorption layer 12 are in a range surrounded by the coordinates A to G, the photoelectric conversion efficiency in the compound thin film solar cell is increased.

(2) In the light absorption layer 12, when the Zn / Sn ratio near the front electrode 16 is lower than the Zn / Sn ratio near the back electrode 11, the photoelectric conversion efficiency in the compound thin film solar cell is further increased. Enhanced.
(3) When the light absorption layer 12 contains carbon, the light absorption layer forming ink containing the organic binder can be used for coating.

(4) When the Cu / (Zn + Sn) ratio and the Zn / Sn ratio in the fine particle component in the light-absorbing layer forming ink are in a range surrounded by the coordinates A to G, the composition has an enhanced photoelectric conversion efficiency. The light absorption layer 12 can be formed.
(5) If the fine particles contained in the light absorbing layer forming ink are amorphous particles, the denseness of the formed light absorbing layer 12 is improved.

(6) When the average particle size of the fine particles contained in the light absorbing layer forming ink is 200 nm or less, formation of a gap in the film is suppressed in the heat treatment step when forming the light absorbing layer 12. On the other hand, when the average particle diameter is 1 nm or more, the fine particles are less likely to aggregate, and thus the light-absorbing layer forming ink can be easily prepared.
(7) When the light absorption layer forming ink contains a thiol organic substance, the thiol organic substance functions as a binder, and the leveling property of the film at the time of applying the ink is improved.

  DESCRIPTION OF SYMBOLS 10 ... Board | substrate, 11 ... Back electrode, 12 ... Light absorption layer, 13 ... Buffer layer, 14 ... Semi-insulating layer, 15 ... Window layer, 16 ... Surface electrode.

Claims (7)

A light-absorbing layer formed by applying an ink containing fine particles of a compound, wherein the light-absorbing layer is S as an element derived from the fine particles, and at least one element of Se, Cu, Zn, and , A compound thin film solar cell containing three elements of Sn,
In an orthogonal coordinate system in which the Cu / (Zn + Sn) ratio (atomic ratio) is the x axis and the Zn / Sn ratio (atomic ratio) is the y axis, the Cu / (Zn + Sn) ratio and the Zn / Sn ratio of the light absorption layer The coordinates (x, y) indicating the coordinates are coordinates A (0.71, 0.82), coordinates B (0.90, 0.82), coordinates C (0.94, 0.87), coordinates D ( 0.89, 1.00), coordinate E (0.84, 1.07), coordinate F (0.75, 1.08), coordinate G (0.71, 1.05) , Coordinates B, coordinates C, coordinates D, coordinates E, coordinates F, coordinates G, coordinates A on the seven straight lines connecting in this order, or inside the area surrounded by the seven straight lines. Compound thin film solar cell. The light absorption layer is located between the front electrode and the back electrode,
The compound thin film solar cell according to claim 1, wherein the Zn / Sn ratio in a portion near the front electrode in the light absorption layer is lower than the Zn / Sn ratio in a portion close to the back electrode. The compound thin-film solar cell according to claim 1, wherein the light absorption layer includes carbon. Forming a coating film by applying an ink containing fine particles of a compound;
Heat-treating the coating film to form a light absorption layer;
A method for producing a compound thin film solar cell comprising:
The element derived from the fine particles in the ink includes at least one element of S and Se, and three elements of Cu, Zn, and Sn,
In an orthogonal coordinate system in which the Cu / (Zn + Sn) ratio (atomic ratio) is the x axis and the Zn / Sn ratio (atomic ratio) is the y axis, the Cu / (Zn + Sn) ratio and the Zn / Sn ratio of the light absorption layer The coordinates (x, y) indicating the coordinates are coordinates A (0.71, 0.82), coordinates B (0.90, 0.82), coordinates C (0.94, 0.87), coordinates D ( 0.89, 1.00), coordinate E (0.84, 1.07), coordinate F (0.75, 1.08), coordinate G (0.71, 1.05) , Coordinates B, coordinates C, coordinates D, coordinates E, coordinates F, coordinates G, coordinates A on the seven straight lines connecting in this order, or inside the area surrounded by the seven straight lines. A method of manufacturing a compound thin film solar cell. The method for producing a compound thin-film solar cell according to claim 4, wherein the fine particles are amorphous particles. The method for producing a compound thin-film solar cell according to claim 4 or 5, wherein the average particle size of the fine particles is 1 nm or more and 200 nm or less. The said ink contains thiol organic substance. The manufacturing method of the compound thin film solar cell as described in any one of Claims 4-6.

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