JP2017069454A - Ink for light absorption layer formation, compound film solar battery, and manufacturing method for compound film solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an ink for light absorption layer formation, which enables the formation of a light absorption layer arranged to be able to increase a photoelectric conversion efficiency; a compound film solar battery which enables the rise in photoelectric conversion efficiency; and a manufacturing method therefor.SOLUTION: An ink for light absorption layer formation comprises microparticles of a compound. As to the composition of the microparticles on the whole, the microparticles include at least one element of S and Se, and three elements, Cu, Zn and Sn, meeting the following relations: 0.80≤Cu/(Zn+Sn)≤0.88; and 0.95≤Zn/Sn≤1.05.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an ink for forming a light absorption layer made of a CZTS compound semiconductor, a compound thin-film solar cell including the light absorption layer, and a method for manufacturing the same.

A compound thin film solar cell having a layer composed of a CZTS-based p-type semiconductor (Cu ₂ ZnSnS ₄ , Cu ₂ ZnSnSe ₄ , Cu ₂ ZnSn (S, Se) _4, etc.) as a light absorption layer is known (for example, , See Patent Document 1). Since a CZTS-based compound semiconductor is a direct transition type semiconductor, a CZTS-based compound thin film solar cell is lighter than a Si-based solar cell including a light absorption layer made of Si, which is an indirect transition type semiconductor. It has a large absorption coefficient and a band gap energy suitable for a light absorption layer of a single connection solar cell.

Furthermore, in the CZTS-based compound thin film solar cell, the band gap energy of the compound semiconductor constituting the light absorption layer can be controlled by controlling the composition ratio of the elements constituting the light absorption layer. For example, when the composition ratio of the light absorption layer is Cu ₂ ZnSnSe ₄ , the band gap energy is 1.04 eV, and when the composition ratio of the light absorption layer is Cu ₂ ZnSnS ₄ , the band gap energy is 1. 53 eV.

In addition, the CZTS-based compound thin film solar cell has less environmental impact than other compound thin film solar cells such as CuInSe ₂ (CIS) thin film solar cells and CdTe thin film solar cells, and rare metals such as In It is preferable at the point which does not contain. For these reasons, CZTS-based compound thin film solar cells are attracting attention as next-generation solar cells.

  It is known that the photoelectric conversion efficiency of the compound thin film solar cell is higher, and the composition ratio of the light absorption layer is known to be one of the factors affecting the photoelectric conversion efficiency. For example, in Non-Patent Documents 1 and 2, a layer that is a precursor of a light absorption layer is formed by a vacuum process such as vapor deposition or sputtering, and the precursor layer is formed by heat treatment in a hydrogen sulfide atmosphere. About the light absorption layer made, the composition ratio with which high photoelectric conversion efficiency is obtained is disclosed. That is, such a light absorption layer has a stoichiometric ratio, that is, Cu / (Zn + Sn) = 1.0 and a ratio of Cu lower than that of the composition in which Zn / Sn = 1.0, and Zn It has been reported that the photoelectric conversion efficiency can be improved when the composition has a high ratio. Specifically, high photoelectric conversion efficiency can be obtained when the Cu / (Zn + Sn) ratio of the light absorption layer is about 0.85 and the Zn / Sn ratio is about 1.1 to 1.3. It has been reported.

US Patent Application Publication No. 2011/0097496

H. Katagiri, J. Vac. Soc. Jpn., Vol. 55, No. 12 (2012), 548-555 H.Katagiri.et al., Mater.Res.Soc.Symp.Proc., 1165 (2009) M04-01

  By the way, it replaces with a vacuum process and the method of forming a light absorption layer using a non-vacuum process is proposed. Since the formation method using the non-vacuum process is a manufacturing method that does not require an expensive vacuum apparatus, the manufacturing cost can be suppressed lower than the formation method using the vacuum process. Among these, a nanoparticle coating method using nanosized fine particles made of a CZTS compound semiconductor is preferable because a light absorption layer can be formed without using a highly dangerous substance such as hydrazine. The nanoparticle coating method is a method of forming a light absorption layer by forming a precursor layer by applying ink containing fine particles, and performing heat treatment on the precursor layer to sinter the fine particles.

  Of course, even in a compound thin film solar cell including a light absorption layer formed by a nanoparticle coating method, improvement in photoelectric conversion efficiency is desired. However, the range of the composition ratio disclosed in Non-Patent Documents 1 and 2 is a range in which high photoelectric conversion efficiency can be obtained in a compound thin film solar cell including a light absorption layer formed using a vacuum process. Therefore, even if the composition ratio is applied to the light absorption layer formed by the nanoparticle coating method, high photoelectric conversion efficiency is not always obtained. Therefore, the knowledge about the relationship between the composition of the light absorption layer formed by the nanoparticle application | coating method and photoelectric conversion efficiency is calculated | required.

  The present invention provides a light absorbing layer forming ink capable of forming a light absorbing layer capable of increasing photoelectric conversion efficiency, a compound thin film solar cell capable of increasing photoelectric conversion efficiency, and a method for producing the same. For the purpose.

The ink for forming a light absorbing layer that solves the above problems is a plurality of fine particles made of a compound, and the composition of the plurality of fine particles as a whole is at least one element of S and Se, Cu, Zn, And a plurality of the fine particles that include three elements of Sn and satisfy 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05.
According to the said structure, a photoelectric conversion efficiency can be improved in a compound thin film solar cell provided with the light absorption layer formed using the ink for light absorption layer formation.

In the light absorbing layer forming ink, the composition of the fine particles as a whole satisfies 0.85 ≦ Cu / (Zn + Sn) ≦ 0.88 and 1.01 ≦ Zn / Sn ≦ 1.05.
According to the said structure, a photoelectric conversion efficiency can be improved especially in a compound thin film solar cell provided with the light absorption layer formed using the ink for light absorption layer formation.

The compound thin film solar cell that solves the above problem is a compound thin film solar cell including a light absorption layer, and the composition of the light absorption layer is at least one element of S and Se, Cu, Zn, and 3 elements including Sn and satisfying 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05.
According to the said structure, the photoelectric conversion efficiency of a compound thin film solar cell can be improved.

In the method of manufacturing a compound thin film solar cell that solves the above-described problem, the total composition of a plurality of fine particles made of a compound includes at least one element of S and Se, and three elements of Cu, Zn, and Sn. And 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05, and the precursor of the light-absorbing layer is formed by applying an ink containing the plurality of fine particles. A coating step of forming a body layer, and a heating step of heating the precursor layer to form a light absorption layer.
According to the said manufacturing method, the compound thin film solar cell with improved photoelectric conversion efficiency can be manufactured.

In the manufacturing method, in the heating step, heating is started in a state where solid sulfur and solid selenium are present together with the precursor layer, and at the start of the heating, the molar ratio of the selenium to the sulfur is 1.
According to the manufacturing method, a light absorption layer which is a polycrystalline body having a large crystal and less segregation can be formed.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric conversion efficiency in a CZTS type compound thin film solar cell can be improved.

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. It is a figure which shows the relationship between the composition ratio of the ink for light absorption layer formation, and photoelectric conversion efficiency about each Example and each comparative example.

  With reference to FIG. 1, one Embodiment of the manufacturing method of the ink for light absorption layer formation, a compound thin film solar cell, and a compound thin film solar cell is described.

[Configuration of Compound Thin Film Solar Cell]
As shown in FIG. 1, the compound thin film solar cell 10 includes a substrate 11, and in order from a position close to the substrate 11, a back electrode 12, a light absorption layer 13, a buffer layer 14, a semi-insulating layer 15, a window layer 16, and The surface electrode 17 is located on the substrate 11.
The substrate 11 is, for example, one of a glass substrate, a metal plate, and a plastic film.

  The material for forming the back electrode 12 is, for example, Mo (molybdenum), Ni (nickel), Cu (copper), Ti (titanium), Fe (iron), Al (aluminum), titania, and stainless steel. Alternatively, the material for forming the back electrode 12 may be a material composed of carbon and carbon such as graphene, or transparent metal oxide having conductivity such as ITO (Indium Tin Oxide) and ZnO. It may be a thing.

The light absorption layer 13 is composed of a CZTS-based compound semiconductor that is one of p-type compound semiconductors, that is, a CZTS semiconductor. The CZTS compound semiconductor includes at least one element of group VIB (group 16) S (sulfur) and group VIB (group 16) Se (selenium), group IB (group 11) Cu, group IIB (12 Group) Zn (zinc) and group IVB (group 14) Sn (tin). That, _{CZTS-semiconductors,} IB 2 - is (IIB-IVB) -VIB ₄ group compound semiconductor.

  The light absorption layer 13 has a composition satisfying 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05. Furthermore, the light absorption layer 13 preferably has a composition satisfying 0.85 ≦ Cu / (Zn + Sn) ≦ 0.88 and 1.01 ≦ Zn / Sn ≦ 1.05. When the composition ratio of the light absorption layer 13 is within the above range, the photoelectric conversion efficiency of the compound thin film solar cell 10 is increased.

  In the above structure, the Cu / (Zn + Sn) ratio and the Zn / Sn ratio are both atomic ratios, and the ratio of the atomic% of Cu to the total of atomic% of Zn and atomic% of Sn is Cu / Let (Zn + Sn) be the ratio of Zn atomic% to Sn atomic% Zn / Sn.

The buffer layer 14 is made of an n-type compound semiconductor. The material for forming the buffer layer 14 is, for example, CdS, Zn (S, O, OH), ZnS, ZnSe, and In ₂ S ₃ . The semi-insulating layer 15 is made of an i-type compound semiconductor. The material for forming the semi-insulating layer 15 is, for example, a metal oxide such as ZnO. The window layer 16 is composed of an n-type compound semiconductor. The material for forming the window layer 16 is, for example, ZnO to which Al, Ga (gallium), B (boron), or the like is added, ITO, or the like.

  The surface electrode 17 is located on a part of the upper surface of the window layer 16. The material for forming the surface electrode 17 is, for example, a metal such as Al and Ag (silver). Alternatively, the material for forming the surface electrode 17 may be a material composed of carbon and carbon such as graphene, or may be a transparent metal oxide having conductivity such as ITO and ZnO. Good.

In addition, the compound thin film solar cell 10 may have layers other than each layer mentioned above. When the compound thin film solar cell 10 has another layer, the other layer is, for example, an antireflection film positioned on the window layer 16. The material for forming the antireflection film is, for example, MgF ₂ , and the thickness of the antireflection film is preferably about 100 nm. Since the antireflection film suppresses reflection of light incident on the compound thin film solar cell 10, the compound thin film solar cell 10 has the antireflection film, so that the light absorption layer 13 can absorb more light. . The other layer may be an intermediate layer located between the back electrode 12 and the light absorption layer 13 and having a composition for increasing the photoelectric conversion efficiency of the compound thin film solar cell 10.

[Method for producing compound thin-film solar cell]
A method for manufacturing the above-described compound thin film solar cell 10 using the nanoparticle coating method and an ink used for forming the light absorption layer 13 in this manufacturing method will be described.

  The compound thin film solar cell 10 is formed by laminating a back electrode 12, a light absorption layer 13, a buffer layer 14, a semi-insulating layer 15, a window layer 16, and a surface electrode 17 on a substrate 11 in this order. Is done.

  That is, the method for manufacturing the compound thin-film solar cell 10 includes a step of forming each of the layers described above, and the step of forming the light absorption layer 13 forms a precursor layer of the light absorption layer 13 on one surface of the back electrode 12. And a heating step of heating the precursor layer to form the light absorption layer 13.

  The back electrode 12 is formed on the upper surface of the substrate 11 by using, for example, sputtering, vapor deposition, and CVD (Chemical Vapor Deposition).

  In the coating process for forming the precursor layer, the light-absorbing layer forming ink is applied to the upper surface, which is one surface of the back electrode 12, so that a film containing fine particles is formed. Then, by drying the film containing fine particles, the solvent contained in the coated film is removed. Thereby, the coating film as a precursor layer is formed.

  The light absorbing layer forming ink includes a plurality of fine particles composed of the constituent elements of the light absorbing layer 13. 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.

Examples of the metal salt or metal complex include CuI, CuSO ₄ , Cu (NO ₃ ) ₂ , Cu (CH ₃ COO) ₂ , ZnI ₂ , ZnSO ₄ , Zn (NO ₃ ) ₂ , Zn (CH ₃ COO) _2. SnI ₂ , SnSO ₄ , Sn (CH ₃ COO) _2, or the like can be used. The metal salt preferably contains a halogen atom, and among the above compounds, at least one selected from the group consisting of CuI, ZnI ₂ and SnI ₂ is preferably used.

As the chalcogenide salt, K ₂ Se, Na ₂ Se, K ₂ S, Na ₂ S, and a mixture thereof can be used. Among these, it is preferable to use at least one of Na ₂ Se and Na ₂ S. Since NaI, which is a byproduct of the reaction between these compounds and metal iodide, has high solubility in an organic solvent, fine particles can be easily separated from the reaction solution by a method such as centrifugation.

  The reaction for producing the fine particles is preferably performed at a temperature of −67 ° C. or more and 25 ° C. or less, and more preferably performed at a temperature of −5 ° C. or more and 5 ° C. or less. If the temperature is equal to or higher than the lower limit of the above range, the reaction rate does not become too slow, so that the time required for generating fine particles can be shortened. In addition, when the temperature is equal to or lower than the upper limit of the above range, the reaction rate does not become too fast, and the particle size of the generated fine particles can be easily controlled.

The fine particles generated in this way are, for example, compounds 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). It is the particle which consists of. In addition to the above-mentioned compounds, the ink for forming the 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 consisting of: 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 described above may be included.

  The average particle size of the fine particles is preferably 1 nm or more and 200 nm or less, and more preferably 1 nm or more and 100 nm or less. When the average particle size of the fine particles is equal to or more than the lower limit of the above range, the fine particles are less likely to aggregate, so that the light absorbing layer forming ink can be easily prepared. On the other hand, when the average particle size is not more than the upper limit of the above range, the formation of cavities in the light absorption layer 13 after being formed by heating can be suppressed. The average particle diameter of the fine particles is an average value of the shortest diameters of the fine particles existing in a predetermined area in the cured product of the light absorbing layer forming ink, and is obtained using a scanning electron microscope (SEM). Measured.

  The fine particles are preferably amorphous fine particles. Since crystalline particles are in a stable state with respect to energy, each atom contained in the particles is likely to be fixed at a certain position, that is, difficult to diffuse. Easy to diffuse. For this reason, the use of amorphous particles increases the density of the light absorption layer 13. In addition, the amorphous in this embodiment includes an amorphous.

  The composition ratio of each element in the fine particle component obtained by collecting all the fine particles contained in the light absorbing layer forming ink, that is, the composition ratio of the whole fine particles is 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.8. 95 ≦ Zn / Sn ≦ 1.05 is satisfied. Furthermore, the composition ratio of the entire fine particles preferably satisfies 0.85 ≦ Cu / (Zn + Sn) ≦ 0.88 and 1.01 ≦ Zn / Sn ≦ 1.05. The composition ratio of the whole fine particles is the number of moles of each atom relative to the total number of moles of Cu, Zn, Sn contained in the compound used for the production of fine particles, that is, the number of moles of each metal salt or each metal complex used for the production of fine particles The ratio can be controlled by adjusting the ratio.

  In the light absorbing layer forming ink, the solution in which the fine particles are dispersed may be an organic solvent, and the type of the organic solvent is not particularly limited. The organic solvent is, for example, any of alcohol, ether, ester, aliphatic hydrocarbon, alicyclic hydrocarbon, and aromatic hydrocarbon. The organic solvent is preferably any of alcohol, pyridine, diethyl ether, pentane, hexane, cyclohexane, and toluene having a carbon number of less than 10, such as methanol, ethanol, and butanol, and methanol, pyridine, toluene And hexane is more preferable.

  The light absorbing layer forming ink preferably contains a binder in order to enhance leveling properties when the ink is applied. The binder content in the light absorption layer forming ink is preferably 5% by mass or more and 70% by mass or less, and preferably 20% by mass or more and 60% by mass or less, based on the mass of the fine particles included in the light absorption layer forming ink. More preferably. When the binder content in the ink is not less than the lower limit of the above range, the formation of cavities in the light absorption layer 13 after being formed by heating can be suppressed. Further, when the binder content in the ink is not more than the upper limit of the above range, the surface roughness of the light absorption layer 13 after being formed by heating can be suppressed.

  Examples of the binder include thiol organic substances, selenol organic substances, and alcohols having 10 or more carbon atoms. The binder may be Se particles, S particles, Se compounds, and S compounds, or may be sodium sulfide, sodium selenide, potassium selenide, sodium selenate, thiosulfate, and the like. Also good. Among these, the binder is preferably a thiol organic substance, and more preferably thiourea. When an organic compound is used as the binder, the light absorption layer 13 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 13. Of carbon remains.

  The coating method of the light absorbing layer forming ink may be a coating method or a printing method. Examples of the application method include a doctor method, a spin coating method, a slit coating method, and a spray method. Examples of the printing method include a gravure printing method, a screen printing method, a reverse offset printing method, and a relief printing method.

  In the heating step of heating the precursor layer, crystallization of a large number of fine particles contained in the precursor layer proceeds and the fine particles are sintered by applying heat to the precursor layer. Thereby, the light absorption layer 13 is formed.

The heat treatment of the precursor layer is performed by annealing using a heating furnace or rapid thermal annealing (RTA). The atmosphere of the heat treatment is a group composed of H ₂ S gas, H ₂ Se gas, N ₂ gas, Se vapor, S vapor, hydrogen gas, and a mixed gas of hydrogen and an inert gas such as N ₂ gas. It is preferable that at least one selected from is included. Since the explosion lower limit value of hydrogen gas is 4.1%, when the precursor layer is heated in an atmosphere containing hydrogen and an inert gas, the proportion of hydrogen contained in the atmosphere is 4% or less. Is preferred. When the proportion of hydrogen contained in the atmosphere is 4% or less, a crisis such as ignition or explosion can be avoided.

  In order to add Se vapor or S vapor to the atmosphere of the heat treatment, for example, solid sulfur or solid state is contained in a container for heat treatment that accommodates the substrate 11, the back electrode 12, and the laminate of the precursor layers. Heat treatment may be performed in a state where selenium is added. In the heat treatment, powdery tin, SnSe, or SnS as a sintering aid may be put in the heat treatment container.

  The maximum temperature of the heat treatment is preferably a predetermined temperature included in the range of 480 ° C. or more and 660 ° C. or less. From the viewpoint of promoting crystal growth, the maximum temperature of the heat treatment is preferably 550 ° C. or more. And it is preferable that the time heated at the maximum temperature is 5 minutes or more and 180 minutes or less.

  Here, it is preferable that the heating of the precursor layer is started in a state where the precursor layer is placed in an environment where solid sulfur and solid selenium exist. The molar ratio of solid selenium to solid sulfur at the start of heating is preferably 1.

  Since the temperature at which sulfur becomes vapor is lower than the temperature at which selenium becomes vapor, when heating is started in a state where the precursor layer coexists with solid sulfur and solid selenium, in the precursor layer, First, the crystal grows in an atmosphere mainly containing S vapor, and then the crystal grows in an atmosphere mainly containing Se vapor. Sulfur and selenium have different crystallization mechanisms, and crystallization with sulfur tends to proceed with nucleation, but crystals do not easily grow. On the other hand, crystallization with selenium tends to increase the crystal size, while segregation of ZnSe or the like in the formed light absorption layer 13 increases. The heating rate up to the maximum temperature in the heat treatment is appropriately set, that is, the heating rate is set so that the crystallization in S vapor and the crystallization in Se vapor proceed in this order successively. Thus, the light absorption layer 13 which is a polycrystalline body having a large crystal and less segregation can be formed. For example, even when the temperature rising rate is constant, the crystal growth as described above is possible. And, when the S: Se molar ratio is 1: 1 at the start of heating, such crystal growth suitably proceeds.

In the compound thin-film solar cell 10 including such a light absorption layer 13, since a wavelength region where high quantum efficiency is obtained is widened, it is possible to generate efficient power and to suppress a decrease in photoelectric conversion efficiency due to segregation. .
In addition, it is preferable that the film thickness of the light absorption layer 13 after a heating is 0.6 micrometer or more and 3 micrometers or less.

  The buffer layer 14 is formed on the upper surface of the light absorption layer 13 using, for example, a CBD (chemical bath deposition) method, a MOCVD (Metal Organic Chemical Vapor Deposition) method, an ALD (Atomic Layer Deposition) method, or the like.

The semi-insulating layer 15 is formed on the upper surface of the buffer layer 14 by, for example, MOCVD or sputtering, and the window layer 16 is formed on the upper surface of the semi-insulating layer 15 by using, for example, MOCVD or sputtering.
The surface electrode 17 is formed on the upper surface of the window layer 16 by using, for example, sputtering, vapor deposition, and CVD.

[Example]
The compound thin film solar cell and the manufacturing method thereof will be described using specific examples.
<Example 1>
[Formation of back electrode]
A back electrode made of Mo was formed on the upper surface of a soda lime glass substrate having a thickness of 2.0 mm using RF magnetron sputtering (RF: Radio-Frequency). The thickness of the back electrode is 600 nm.

[Adjustment of light absorbing layer forming ink]
A first solution of Example 1 was prepared by dissolving CuI, ZnI ₂ and SnI ₄ in pyridine. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Example 1. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Example 1 were set so that the following ratios were satisfied.
Cu: Zn: Sn = 1.74: 1.05: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Example 1. Cu—Zn—Sn—Se fine particles were generated by reacting the mixed solution in an inert gas atmosphere at 0 ° C. The mixed solution after the reaction was filtered to take out Cu—Zn—Sn—Se fine particles, and the Cu—Zn—Sn—Se fine particles were washed with methanol by centrifuging them. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Example 1 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.74: 1.05: 1.00: 3.92

  The Cu—Zn—Sn—Se fine particles and thiourea after washing were mixed so that the mass ratio of the Cu—Zn—Sn—Se fine particles and thiourea was 3: 2. Then, pyridine and methanol were added to the mixture to prepare a light absorption layer forming ink of Example 1 containing Cu—Zn—Sn—Se fine particles. The solid content in the light absorbing layer forming ink was 6.5% by mass.

  Based on the molar ratio of the compounds contained in the mixed solution, the composition ratio of the entire fine particles contained in the light absorption layer forming layer ink of Example 1 was calculated. In the light absorbing layer forming layer ink of Example 1, the Cu / (Zn + Sn) ratio is 0.850, and the Zn / Sn ratio is 1.05.

[Formation of light absorption layer]
A light absorbing layer forming ink was applied to the upper surface of the back electrode using a spray method, and the solvent contained in the light absorbing layer forming ink was evaporated in an oven at 260 ° C. to form a coating film as a precursor layer. . And the laminated body comprised from a board | substrate, a back surface electrode, and a precursor layer is put into the quartz case containing 40 mg of selenium, 16 mg of sulfur, and 10 mg of tin, and the atmosphere where nitrogen gas was introduce | transduced The temperature was raised to 600 ° C. and heated at 600 ° C. for 20 minutes. That is, for the solid sulfur and selenium present in the quartz case at the start of heating, the molar ratio of S: Se was 1: 1.

[Formation of buffer layer]
A buffer layer made of Cds was formed on the upper surface of the light absorption layer using the CBD method. Specifically, a mixed solution containing 0.0015 M cadmium sulfate (CdSO ₄ ), 0.0075 M thiourea (NH ₂ CSNH ₂ ), and 1.5 M ammonia water (NH ₄ OH) is heated to 65 ° C. Heated. And the buffer layer which has a film thickness of 100 nm was formed in the upper surface of the light absorption layer by immersing the laminated body provided with the light absorption layer mentioned above in a liquid mixture.
[Formation of semi-insulating layer]
A semi-insulating layer made of ZnO was formed on the upper surface of the buffer layer by MOCVD. The thickness of the semi-insulating layer is 50 nm.
[Formation of window layer]
A window layer made of B-ZnO (boron-doped zinc oxide) was formed on the upper surface of the semi-insulating layer by MOCVD. The thickness of the window layer is 1 μm.
[Formation of surface electrode]
A surface electrode made of Al was formed on a part of the upper surface of the window layer using a vacuum deposition method. Thereby, the compound thin film solar cell of Example 1 was obtained.

<Example 2>
In preparing the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Example 2 were prepared by the same steps as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

A first solution of Example 2 was prepared by dissolving CuI, ZnI ₂ and SnI ₄ in pyridine. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Example 2. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Example 2 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.72: 1.01: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Example 2. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Example 2 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.72: 1.01: 1.00: 3.87
In the light absorption layer forming layer ink of Example 2, the Cu / (Zn + Sn) ratio is 0.860, and the Zn / Sn ratio is 1.01.

<Example 3>
In preparing the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Example 3 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ , and SnI ₄ were dissolved in pyridine to prepare a first solution of Example 3. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Example 3. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Example 3 were set so that the following ratios were satisfied.
Cu: Zn: Sn = 1.758: 1.010: 1.000

The 1st solution and the 2nd solution were mixed and the liquid mixture of Example 3 was obtained. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Example 3 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.758: 1.010: 1.000: 3.889
In the light absorption layer forming layer ink of Example 3, the Cu / (Zn + Sn) ratio is 0.875, and the Zn / Sn ratio is 0.95.

<Example 4>
When adjusting the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Example 4 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

A first solution of Example 4 was prepared by dissolving CuI, ZnI ₂ and SnI ₄ in pyridine. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Example 4. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Example 4 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.576: 0.97: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Example 4. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed solution of Example 4 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.576: 0.97: 1.00: 3.758
In the light absorption layer forming layer ink of Example 4, the Cu / (Zn + Sn) ratio is 0.800, and the Zn / Sn ratio is 0.97.

<Example 5>
In preparing the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Example 5 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

A first solution of Example 5 was prepared by dissolving CuI, ZnI ₂ and SnI ₄ in pyridine. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Example 5. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Example 5 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.64: 1.05: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Example 5. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed solution of Example 5 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.64: 1.05: 1.00: 3.87
In the light absorption layer forming layer ink of Example 5, the Cu / (Zn + Sn) ratio is 0.800, and the Zn / Sn ratio is 1.05.

<Comparative Example 1>
In preparing the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin-film solar cell of Comparative Example 1 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

A first solution of Comparative Example 1 was prepared by dissolving CuI, ZnI ₂ and SnI ₄ in pyridine. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 1. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 1 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 2.00: 1.00: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Comparative Example 1. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Comparative Example 1 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 2.00: 1.00: 1.00: 4.00
In the light absorption layer forming layer ink of Comparative Example 1, the Cu / (Zn + Sn) ratio is 1.000, and the Zn / Sn ratio is 1.00.

<Comparative example 2>
In preparing the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin-film solar cell of Comparative Example 2 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ and SnI ₄ were dissolved in pyridine to prepare a first solution of Comparative Example 2. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 2. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 2 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.84: 1.05: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Comparative Example 2. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Comparative Example 2 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.84: 1.05: 1.00: 3.97
In the light absorption layer forming layer ink of Comparative Example 2, the Cu / (Zn + Sn) ratio is 0.900, and the Zn / Sn ratio is 1.05.

<Comparative Example 3>
When adjusting the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Comparative Example 3 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ , and SnI ₄ were dissolved in pyridine to prepare a first solution of Comparative Example 3. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 3. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 3 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.235: 0.90: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Comparative Example 3. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed solution of Comparative Example 3 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.235: 0.90: 1.00: 3.518
In the light absorption layer forming layer ink of Comparative Example 3, the Cu / (Zn + Sn) ratio is 0.650, and the Zn / Sn ratio is 0.90.

<Comparative example 4>
In preparing the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Comparative Example 4 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ , and SnI ₄ were dissolved in pyridine to prepare a first solution of Comparative Example 4. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 4. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 4 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.94: 1.05: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Comparative Example 4. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed solution of Comparative Example 4 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.94: 1.05: 1.00: 3.92
In the light absorption layer forming layer ink of Comparative Example 4, the Cu / (Zn + Sn) ratio is 0.950, and the Zn / Sn ratio is 1.05.

<Comparative Example 5>
When adjusting the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Comparative Example 5 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ , and SnI ₄ were dissolved in pyridine to prepare a first solution of Comparative Example 5. In addition, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 5. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 5 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.54: 1.05: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Comparative Example 5. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Comparative Example 5 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.54: 1.05: 1.00: 3.82
In the light absorption layer forming layer ink of Comparative Example 5, the Cu / (Zn + Sn) ratio is 0.750, and the Zn / Sn ratio is 1.05.

<Comparative Example 6>
In preparing the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Comparative Example 6 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ and SnI ₄ were dissolved in pyridine to prepare a first solution of Comparative Example 6. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 6. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 6 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.61: 0.90: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Comparative Example 6. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Comparative Example 6 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.61: 0.90: 1.00: 3.71
In the light absorption layer forming layer ink of Comparative Example 6, the Cu / (Zn + Sn) ratio is 0.850, and the Zn / Sn ratio is 0.90.

<Comparative Example 7>
When adjusting the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin-film solar cell of Comparative Example 7 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ , and SnI ₄ were dissolved in pyridine to prepare a first solution of Comparative Example 7. In addition, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 7. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 7 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.46: 1.09: 1.00

The 1st solution and the 2nd solution were mixed and the liquid mixture of comparative example 7 was obtained. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Comparative Example 7 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.46: 1.09: 1.00: 3.82
In the light absorption layer forming layer ink of Comparative Example 7, the Cu / (Zn + Sn) ratio is 0.700, and the Zn / Sn ratio is 1.09.

<Comparative Example 8>
In the adjustment of the light absorbing layer forming ink, the light absorbing layer forming ink and the compound thin film solar cell of Comparative Example 8 were prepared in the same manner as in Example 1 except that the amount of the compound used for adjusting the mixed liquid was changed. Formed.

CuI, ZnI ₂ , and SnI ₄ were dissolved in pyridine to prepare a first solution of Comparative Example 8. Further, Na ₂ Se was dissolved in methanol to prepare a second solution of Comparative Example 8. At this time, the number of moles of Cu, the number of moles of Zn, and the number of moles of Sn in the first solution of Comparative Example 8 were set so as to satisfy the following ratio.
Cu: Zn: Sn = 1.78: 1.09: 1.00

The first solution and the second solution were mixed to obtain a mixed solution of Comparative Example 8. At this time, the number of moles of Cu, the number of moles of Zn, the number of moles of Sn, and the number of moles of Se in the mixed liquid of Comparative Example 8 were set so as to satisfy the following ratio.
Cu: Zn: Sn: Se = 1.78: 1.09: 1.00: 3.99
In the light absorption layer forming layer ink of Comparative Example 8, the Cu / (Zn + Sn) ratio is 0.850, and the Zn / Sn ratio is 1.09.

<Evaluation method>
(Photoelectric conversion efficiency)
About the compound thin film solar cell of each Example and each comparative example, the IV characteristic by a standard sunlight simulator (light intensity: 100 mW / cm < ² >, air mass: 1.5) was measured, and the photoelectric conversion efficiency was computed.

<Result>
Table 1 shows the composition ratio of the entire fine particles in the light-absorbing layer forming layer ink of each example and each comparative example, and the calculated photoelectric conversion efficiency. FIG. 2 shows the relationship between the composition ratio and the photoelectric conversion efficiency using a two-dimensional orthogonal coordinate system in which the horizontal axis is the Cu / (Zn + Sn) ratio and the vertical axis is the Zn / Sn ratio. In Table 1, “<1” indicates less than 1.

  As shown in FIG. 2, the light-absorbing layer forming ink having a composition in which the entire fine particles satisfy 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05. In the compound thin-film solar cell of each example provided with the light absorption layer formed from the above, it is confirmed that a high photoelectric conversion efficiency of 7.5% or more is obtained, and the photoelectric conversion efficiency is increased as compared with each comparative example. It was shown that. In particular, in Examples 1 and 2 where the composition ratio of the entire fine particles satisfies 0.85 ≦ Cu / (Zn + Sn) ≦ 0.88 and 1.01 ≦ Zn / Sn ≦ 1.05, 8.5% It was shown that the above extremely high photoelectric conversion efficiency can be obtained.

  In addition, when the composition of the light absorption layer after passing through the heating step was analyzed using ICP-AES (ICP emission spectroscopic analysis), the composition ratio of each of the Cu / (Zn + Sn) ratio and the Zn / Sn ratio was measured. It has been confirmed that the composition ratio of the entire fine particles in the ink for forming the absorption layer coincides with the composition ratio in the light absorption layer formed using the ink for forming the light absorption layer.

A light absorption layer composed of a CZTS-based compound semiconductor has conductivity as a p-type semiconductor due to defects in the crystal. As in Comparative Examples 1, 2, and 4, the light absorption layer having a composition close to the stoichiometric ratio of Cu / (Zn + Sn) = 1 and Zn / Sn = 1 has few defects. A short circuit or a state close to that occurs, and it is difficult to output power. On the other hand, the farther the composition ratio of the light absorption layer is from the stoichiometric ratio, the more defects in the crystal. On the other hand, the precipitation of segregated substances increases, so the photoelectric conversion efficiency decreases.
The inventors of the present application have studied the range of the composition ratio of the light absorption layer that can reduce segregation while appropriately securing defects in the crystal, and have found the above range.

  The range of the above composition ratio found by the inventors of the present application is reported as the composition ratio of the light absorption layer formed by using a vacuum process, which can improve the photoelectric conversion efficiency in Non-Patent Documents 1 and 2. The Zn / Sn ratio is lower than the range of the composition ratio.

  The precursor layer formed by a vacuum process such as sputtering and the precursor layer formed by applying ink containing fine particles as in the above-described embodiment differ in the crystallization process of the precursor layer during heat treatment. . That is, when sputtering is used, first, a layer for each metal constituting the light absorption layer or one layer containing these metals is formed as the precursor layer. In the heating step, these metals react with elements contained in the atmosphere of the heat treatment after forming an alloy of these metals, and crystallization proceeds. On the other hand, in the precursor layer formed by application of ink containing fine particles, crystallization proceeds with almost no formation of such an alloy.

  Due to the difference in the progress of crystallization, a light absorption layer formed by sputtering and a light absorption layer formed from a coating film of ink containing fine particles, each composition component in the light absorption layer The trend of distribution is different. This is because the light absorption layer formed using sputtering and the light absorption layer formed from the ink coating containing fine particles have different composition ratio ranges that can increase the photoelectric conversion efficiency. Inferred to be one.

  Conventionally, it has been reported that when the light absorption layer has a composition in which the proportion of Cu is lower than that of the stoichiometric ratio and the proportion of Zn is high, the photoelectric conversion efficiency can be improved. However, no knowledge has been obtained about the difference in the optimum composition ratio depending on the manufacturing method of the light absorption layer. On the other hand, the inventors of the present application based on the above inference, the range of the above composition ratio that can increase the photoelectric conversion efficiency as a range specific to the light absorption layer formed from the coating film of the ink containing fine particles. I found.

As described above, according to the embodiment, the effects listed below can be obtained as described with reference to the examples.
(1) The entire fine particles contained in the light absorbing layer forming ink used for forming the light absorbing layer are 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1. .05. The light absorption layer 13 has a composition satisfying 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05. According to such a configuration, photoelectric conversion efficiency can be increased in the compound thin film solar cell 10.

  (2) The entire fine particles contained in the light absorbing layer forming ink have a composition satisfying 0.85 ≦ Cu / (Zn + Sn) ≦ 0.88 and 1.01 ≦ Zn / Sn ≦ 1.05. The light absorption layer 13 has a composition satisfying 0.85 ≦ Cu / (Zn + Sn) ≦ 0.88 and 1.01 ≦ Zn / Sn ≦ 1.05. According to such a configuration, in the compound thin film solar cell 10, in particular, the photoelectric conversion efficiency can be increased.

  (3) In the heating step, heating is started in a state where solid sulfur and solid selenium are present together with the precursor layer, and the molar ratio of selenium to sulfur is 1 at the start of heating. According to such a manufacturing method, the light absorption layer 13 which is a polycrystalline body having a large crystal and less segregation can be formed. In the compound thin-film solar cell 10 including such a light absorption layer 13, since a wavelength region where high quantum efficiency is obtained is widened, it is possible to generate efficient power and to suppress a decrease in photoelectric conversion efficiency due to segregation. .

  DESCRIPTION OF SYMBOLS 10 ... Compound thin film solar cell, 11 ... Substrate, 12 ... Back electrode, 13 ... Light absorption layer, 14 ... Buffer layer, 15 ... Semi-insulating layer, 16 ... Window layer, 17 ... Surface electrode

Claims (5)

  A plurality of fine particles comprising a compound, wherein the total composition of the plurality of fine particles includes at least one element of S and Se and three elements of Cu, Zn, and Sn; A light absorbing layer forming ink containing the plurality of fine particles satisfying 80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05. The ink for forming a light absorption layer according to claim 1, wherein the composition of the fine particles as a whole satisfies 0.85 ≦ Cu / (Zn + Sn) ≦ 0.88 and 1.01 ≦ Zn / Sn ≦ 1.05. . A compound thin film solar cell comprising a light absorption layer,
The composition of the light absorption layer includes at least one element of S and Se, and three elements of Cu, Zn, and Sn, and 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88, and , 0.95 ≦ Zn / Sn ≦ 1.05 A compound thin film solar cell. The total composition of the plurality of fine particles composed of the compound includes at least one element of S and Se and three elements of Cu, Zn, and Sn, and 0.80 ≦ Cu / (Zn + Sn) ≦ 0.88 and 0.95 ≦ Zn / Sn ≦ 1.05 are satisfied,
A coating step of forming a precursor layer of a light absorption layer by coating an ink containing the plurality of fine particles;
A heating step of heating the precursor layer to form a light absorption layer;
The manufacturing method of the compound thin film solar cell containing this. In the heating step, heating is started in a state where solid sulfur and solid selenium exist together with the precursor layer, and a molar ratio of the selenium to the sulfur is 1 at the start of the heating. 4. A method for producing a compound thin film solar cell according to 4.