JP4783908B2 - Photoelectric element - Google Patents

Description

The present invention relates to an optical Denmoto child, more particularly, solar cells, photoconductive cell, relates to a photodiode, light Denmoto child that can be used, such as the phototransistor.

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

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

In order to solve this problem, various proposals have heretofore been made.
For example, in Non-Patent Document 1, an electron beam evaporation method is used to form a Sn / Cu / ZnS laminated precursor on SLG (soda lime glass), and the precursor is sulfided in a 5% H ₂ S + N ₂ atmosphere. A method for producing CZTS is disclosed.
In this document, a CZTS film having a Cu / (Zn + Sn) ratio of 0.8 to 0.9 is suitable as a light absorption layer, and a conversion efficiency of 4.53% is obtained by sulfidation at 520 ° C. Points are listed.

In Non-Patent Document 2, a Cu / Sn / ZnS stack precursor or a Sn / Cu / ZnS stack precursor is formed on a Mo-coated SLG substrate using an electron beam evaporation method, and the precursor is 5% H _2. A method for producing CZTS that is sulfided in an S + N ₂ atmosphere is disclosed.
According to this document, when a Cu / Sn / ZnS stack precursor is formed on a substrate, the surface of the thin film after sulfidation is rough and there are many voids, whereas an Sn / Cu / ZnS stack precursor is formed on the substrate. Then, the point that a big void is not seen on the thin film surface after sulfidation is described.

Patent Document 1 discloses a solar cell that is not CZTS, but has SLG formed on the surface of non-alkali glass, Mo thin film formed on the surface of SLG, and CIGS thin film formed on the surface of Mo thin film. ing.
This document describes that the substrate can be prevented from warping when a thin film is formed by disposing a high melting point material under the SLG.

Further, Patent Document 2 discloses a chalcopyrite thin film solar cell using InAlS as a buffer layer, although it is not CZTS.
This document describes that the use of InAlS as a buffer layer makes it difficult for band mismatching to occur and suppresses a decrease in photoelectric conversion efficiency due to bandgap unmatching.

Takeshi Kobayashi et al., "Investigation of Cu2ZnSnS4-Based Thin Film Solar Cells Using Abundant Materials", Japanese Journal of Applied Physics, vol.44, No.1B, 2005, pp.783-787 Hironori Katagiri, "Cu2ZnSnS4 thin film solar cells", Thin Solid Films 480-481 (2005) 426-432 JP 11-312817 A JP 2006-196771 A

In a thin film solar cell using a chalcopyrite compound, SLG is generally used as a substrate. This is considered to be because Na contained in SLG promotes grain growth of CIGS, particularly in the case of CIGS. In general, Mo is used for the lower electrode. This is because the adhesion between SLG and Mo is high, and thin film peeling is suppressed.
However, if the method used in CIGS is applied to a large-area CZTS as it is, in-plane conversion efficiency varies, and high conversion efficiency cannot be obtained as a whole.

An object of the present invention is to provide, in the photoelectric device using the CZTS compound as a light absorbing layer, Ru near possible to reduce variations in the conversion efficiency.

First light Denmoto element according to the present invention in order to solve the above problems,
In a photoelectric device including a light absorption layer made of a sulfide compound semiconductor containing Cu, Zn, Sn, and S,
The light absorbing layer is
The maximum concentration of Na in the region where Na and O are concentrated (the concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.49% by weight or less, and
The maximum concentration of O in the region where Na and O are concentrated (concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.57% by weight or less,
The members other than the light absorption layer constituting the photoelectric element are made of a material not containing Na whose Na content is 0.1% by weight or less (except that the substrate is made of quartz glass). Is the gist.
Furthermore, the second of the photoelectric elements according to the present invention is :
In a photoelectric device including a light absorption layer made of a sulfide compound semiconductor containing Cu, Zn, Sn, and S,
The light absorbing layer is
The maximum concentration of Na in the region where Na and O are concentrated (the concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.49% by weight or less, and
The maximum concentration of O in the region where Na and O are concentrated (concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.57% by weight or less,
At least one member other than the light absorption layer constituting the photoelectric element is made of a material containing Na with a Na content exceeding 0.1 wt% ,
The gist of the invention is that it further comprises a diffusion blocking layer for blocking diffusion of Na from the material containing Na into the light absorption layer.

Sulfurization using a H ₂ S + N ₂ mixed gas has a relatively high heat treatment temperature. Therefore, when a material containing Na is used for members other than the light absorption layer, Na diffuses to the light absorption layer, and a substance containing Na and O is generated in the light absorption layer. When a substance containing Na and O is generated in the light absorption layer, the portion is not CZTS, or the Cu concentration and the Zn concentration in the region including the portion are reduced, and a region with low conversion efficiency is generated.
On the other hand, in the case where a material other than the light absorbing layer is made of a material that does not contain Na (or a material that contains a very small amount of Na) , or a material that contains Na is used, when a diffusion blocking layer is further provided, It is possible to suppress the diffusion of Na into the light absorption layer, the generation of a substance containing Na and O due to this, and the fluctuation of the Cu concentration and / or the Zn concentration. Therefore, even when a large-area CZTS-based thin film is formed, in-plane conversion efficiency variation is reduced, and the overall efficiency is improved.

Hereinafter, an embodiment of the present invention will be described in detail.
First, the sulfide-based compound semiconductor according to the present invention and the photoelectric element according to the first embodiment of the present invention will be described. The sulfide-based compound semiconductor according to the present invention includes Cu, Zn, Sn, and S, and does not include a substance including Na and O. The photoelectric device according to the first embodiment of the present invention is characterized in that the sulfide-based compound semiconductor according to the present invention is used as a light absorption layer.

The “sulfide-based compound semiconductor containing Cu, Zn, Sn, and S” refers to a Cu ₂ ZnSnS ₄ (CZTS) -based compound. CZTS is a semiconductor having a band gap of about 1.5 eV and a light absorption coefficient of 10 ⁴ cm ⁻¹ or more. CZTS has low power generation efficiency in the stoichiometric composition, but shows relatively high conversion efficiency when Cu is slightly reduced compared to the stoichiometric composition. In the present invention, CZTS includes not only a compound having a stoichiometric composition, but also all non-stoichiometric compounds exhibiting relatively high conversion efficiency, or all compounds containing Cu, Zn, Sn, and S as a main component. Is included.
In order to obtain high conversion efficiency, the sulfide compound semiconductor preferably has an atomic ratio of Cu / (Zn + Sn) ratio of 0.69 or more and 0.99 or less. The Cu / (Zn + S) ratio is more preferably 0.8 to 0.9.

“Sulfide-based compound semiconductors that do not contain substances containing Na and O” means that when they are analyzed by an electron beam microprobe analyzer (EPMA), they do not include regions where Na and O are concentrated. This refers to a CZTS compound that does not include a region in which Na and O are concentrated in a size of about 1 μm or more, which is an approximate surface resolution with respect to a sulfide continuum.
In order to obtain high conversion efficiency, the maximum concentration of Na in the region where Na and O are concentrated is such that the concentration with respect to the entire analysis region is about 0.1 μm when the analysis region in the depth direction of the light absorption layer is about 1 μm. It is preferably 49% by weight or less. The maximum concentration of Na is more preferably 0.32% by weight or less.
Similarly, the maximum concentration of O in the region where Na and O are concentrated is preferably 0.57% by weight or less with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm. . The maximum concentration of O is more preferably 0.38% by weight or less.

Here, the “yield” is formed on the same substrate with respect to the number of small elements (n ₀ ) on the same substrate by dividing a large-area device formed on the same substrate into 10 or more small devices. It is defined as the ratio (= n × 100 / n ₀ ) of the number (n) of small elements exhibiting a conversion efficiency of 80% or more of the maximum conversion efficiency in the small elements. When the sulfide-based compound semiconductor according to the present invention is used as the light absorption layer, a photoelectric device having a yield of 80% or more or 90% or more can be obtained.

Next, a photoelectric element according to the second embodiment of the present invention will be described.
The photoelectric element according to this embodiment includes a light absorption layer, and members other than the light absorption layer are made of a material that does not contain Na.
In the present embodiment, the light absorption layer is made of a sulfide-based compound semiconductor (so-called CZTS) containing Cu, Zn, Sn, and S. Since the details of the sulfide-based compound semiconductor are as described above, the description thereof is omitted.

Photoelectric elements generally have a structure in which a number of members are stacked on a substrate. The “member other than the light absorbing layer” refers to a substrate and a film-like member other than the light absorbing layer laminated on the substrate.
The “material that does not contain Na” refers to a material that does not contain Na as a significant component. In other words, it refers to a material that does not diffuse Na into the light absorption layer at a limit amount or more that does not deteriorate the uniformity of the conversion efficiency of the light absorption layer during sulfurization. In order to obtain high conversion efficiency, a material that does not contain Na preferably has a Na content of 0.1% by weight or less.
For example, when soda lime glass (SLG) is used for the substrate, Na in the SLG diffuses to the light absorption layer at the time of sulfidation, and the uniformity of power generation efficiency is lowered. Therefore, SLG does not correspond to “a material that does not contain Na”.
On the other hand, when low alkali glass (LAG) is used for the substrate, there is no reduction in the uniformity of conversion efficiency even after sulfidation. Therefore, LAG corresponds to “a material that does not contain Na”. For example, in the case of Corning 1737 glass which is a kind of LAG, the total alkali (mainly Na) content is 0.1% by weight in the catalog value.
Specific examples of “materials not containing Na” other than LAG include quartz glass, non-alkali glass, metal, semiconductor, carbon, oxide, nitride, silicide, carbide, and compounds or mixtures thereof. There is.

  FIG. 1 shows a schematic diagram of a solar cell which is a kind of photoelectric element. In FIG. 1, a solar cell (photoelectric element) 10 is formed by laminating at least a lower electrode 14, a light absorption layer 16, a buffer layer 18, a window layer 20, and an upper electrode 22 in this order on a substrate 12. . Additional layers may be formed between the layers.

The substrate 12 is for supporting various thin films formed thereon. The substrate 12 may be a conductor or an insulator.
Specifically, as the substrate 12,
(1) Quartz glass, non-alkali glass, low alkali glass,
(2) metal, semiconductor, oxide, sulfide, nitride, carbide, silicide, carbon, or a compound or mixture thereof,
Etc. are preferably used.

The lower electrode 14 is for taking out the current generated in the light absorption layer 16. For the lower electrode 14, a material having high electrical conductivity and good adhesion to the substrate 12 is used. When a glass substrate is used as the substrate 12, for example, Mo having high adhesion with glass is used for the lower electrode 14. Examples of the material of the lower electrode 14 other than Mo include In—Sn—O, In—Zn—O, ZnO: Al, ZnO: B, SnO ₂ : F, SnO ₂ : Sb, and TiO ₂ : Nb. .

The light absorption layer 16 is for absorbing light and generating carriers, and CZTS is used in the present invention. Since CZTS has a large light absorption coefficient, its thickness can be extremely reduced.
The light absorption layer 16 is generally used in a thin film state, but may be used in the form of particles.

The buffer layer 18 is for improving the connection between the light absorption layer 16 and the window layer 20 and improving the conversion efficiency. For the buffer layer 18, a semiconductor that has high resistance and transmits most of visible light to near infrared light is used. For example, CdS is used for the buffer layer 18. Examples of the material for the buffer layer 18 other than CdS include ZnO, Zn (O, OH), Zn (O, S), Zn (O, S, OH) _x , Zn _1-x Mg _x O, and In ₂ S. There are ₃ etc.

The window layer 20 is for extracting light and reaching the light absorption layer 16 at the same time. The window layer 20 is made of a semiconductor having a low resistance and transmitting most of visible light to near infrared. When the light absorption layer 16 is made of CZTS, for example, ZnO: Al that is an n-type semiconductor is used for the window layer 20. Examples of the material of the window layer 20 other than ZnO: Al include ZnO: B, In—Sn—O, In—Zn—O, SnO ₂ : Sb, and TiO ₂ : Nb.

  The upper electrode 22 is for efficiently extracting the current collected by the window layer 20 to the outside. For example, Al is used for the upper electrode 22. The upper electrode 22 is usually formed in a comb shape because it is necessary to allow light to reach the light absorption layer 16. Examples of the material of the upper electrode 22 other than Al include Cu, Ag, and Au. Further, the upper electrode 22 may be an alloy containing one or more of Al, Cu, Ag, and Au. Specific examples of such alloys include Al-Ti alloys, Al-Mg alloys, Al-Ni alloys, Cu-Ti alloys, Cu-Sn alloys, Cu-Zn alloys, Cu-Au alloys, and Ag-Ti. There are alloys, Ag-Sn alloys, Ag-Zn alloys, Ag-Au alloys, and the like.

  The elements constituting the photoelectric element, and as additional layers other than the above-described substrate, lower electrode, light absorption layer, buffer layer, window layer, and upper electrode, specifically, an adhesive layer, a light scattering layer And antireflection layers.

  The adhesive layer is for enhancing the adhesion between the substrate 12 and the lower electrode 14. For example, when a glass substrate is used as the substrate 12 and Mo is used as the lower electrode 14, it is preferable to use Ti, Cr, Ni, W, or an alloy containing any one or more of these for the adhesive layer.

The light scattering layer is for reflecting incident light and enhancing the light absorption efficiency in the light absorption layer 16. There are a light scattering layer provided on the upper electrode 22 side from the light absorption layer 16 and a light scattering layer provided on the substrate 12 side from the light absorption layer 16.
The light scattering layer provided on the upper electrode 22 side with respect to the light absorption layer 16 includes an aggregate composed of transparent particles, an aggregate composed of two or more kinds of particles having different refractive indexes, a surface with irregularities, It is preferable to use one having a space. Specifically, the light scattering layer provided above the light absorption layer 16 allows most of visible light to near infrared light such as oxides such as SiO ₂ and TiO ₂ and nitrides such as Si ₃ N ₄ to pass through. It is preferable to use materials.
On the other hand, for the light scattering layer provided on the substrate 12 side with respect to the light absorption layer 16, for example, it is preferable to use a surface with irregularities on the surface. The light scattering layer provided below the light absorption layer 16 does not necessarily need to be a material that transmits light.
A similar light scattering function can be provided by processing the surface of the substrate 12 or the like.

The antireflection layer is for reducing the amount of reflection of incident light at the window layer 20 and increasing the light absorption efficiency at the light absorption layer 16. For the antireflection layer, for example, a transparent body having a refractive index smaller than that of the window layer 20, an aggregate composed of transparent particles having a diameter sufficiently smaller than the wavelength of sunlight, and the inside is sufficiently larger than the wavelength of sunlight It is preferable to use one having a space with a small diameter. Specifically, for the antireflection layer,
(1) A thin film made of MgF ₂ , SiO ₂ or the like,
(2) multilayer films of oxides, sulfides, fluorides, nitrides, etc.
(3) Fine particles made of an oxide such as SiO ₂ ,
Etc. are preferably used.

  When a material that does not contain Na is used for a member other than the light absorption layer, a photoelectric element having a yield of 80% or more or 90% or more can be obtained.

Next, a photoelectric element according to the third embodiment of the present invention will be described.
The photoelectric element according to the present embodiment includes at least a member other than the light absorption layer constituting the photoelectric element in the photoelectric element including a light absorption layer made of a sulfide-based compound semiconductor containing Cu, Zn, Sn, and S. One is characterized in that it is made of a material containing Na, and further comprises a diffusion blocking layer for blocking diffusion of Na from the material containing Na into the light absorption layer. Among these, the sulfide-based compound semiconductor is as described above, and thus the description thereof is omitted.

Specifically, as a diffusion blocking layer,
(1) Glass such as quartz glass, non-alkali glass, low alkali glass,
(2) oxides such as silica, alumina, titania, zirconia, bismuth oxide,
(3) metals such as Cr-Mo alloys,
(4) Semiconductors such as silicon,
(5) Sulfides such as zinc sulfide,
(6) Nitride such as silicon nitride, titanium nitride, boron nitride,
(7) Carbide such as silicon carbide,
(8) Silicides such as iron silicide and barium silicide,
(9) Carbon such as diamond and glassy carbon,
and so on.

In this embodiment, the photoelectric element is formed by laminating at least a lower electrode, a light absorption layer, a buffer layer, a window layer, and an upper electrode in this order on a substrate. The diffusion blocking layer may be inserted in any portion as long as it is between the material containing Na and the light absorption layer.
Here, the “material containing Na” refers to a material containing Na as a significant component. In other words, it refers to a material that diffuses Na exceeding the limit amount that does not reduce the uniformity of the conversion efficiency of the light absorption layer into the light absorption layer during sulfidation. An example of the material containing Na is SLG.

For example, when the substrate is made of a material containing Na, such as SLG, the diffusion blocking layer can be provided between the substrate and the lower electrode. In this case, the diffusion blocking layer may be an insulator or a conductor. Further, the diffusion blocking layer in this case is specifically selected from quartz glass, non-alkali glass, low alkali glass, metal, semiconductor, oxide, sulfide, nitride, carbide, silicide, and carbon. Any one or more is preferable.
Note that whether or not Na can be diffused depends not only on the material but also on the state of the film. For example, Mo originally has a very small diffusion coefficient of Na in a bulk state, but has a property of easily diffusing Na in a thin film state. On the other hand, for example, silica has a large diffusion coefficient of Na in the bulk state, but under the heat treatment conditions during the sulfidation treatment, it is not possible to diffuse Na to such an extent that the in-plane conversion efficiency of the light absorption layer varies. Absent.

  For example, when the substrate is made of a material containing Na such as SLG, the diffusion blocking layer can be provided between the lower electrode and the light absorption layer. In this case, the diffusion blocking layer needs to be a conductor. In addition, the diffusion blocking layer in this case is preferably one or more selected from metals, semiconductors, oxides, sulfides, nitrides, carbides, silicides, and carbons having electronic conductivity. .

  In the case where at least one member other than the light absorption layer constituting the photoelectric element is made of a material containing Na, if a diffusion blocking layer is provided in any part of the element, the yield is 80% or more, or 90% or more. A certain photoelectric element is obtained.

Next, a method for manufacturing a photoelectric element according to the present invention will be described.
The photoelectric element according to the present invention can be manufactured by forming a predetermined thin film on a substrate in a predetermined order. The method for forming the thin film is not particularly limited, and various methods can be used.
For example, the light absorption layer 16 made of CZTS is formed by using a precursor in which Cu, Sn, and ZnS are stacked in a predetermined order on a substrate by using a sputtering method, a vacuum evaporation method, a pulse laser deposition (PLD) method, or the like. And can be produced by sulfiding the precursor in an atmosphere containing H ₂ S (for example, in an atmosphere of 5 to 20% H ₂ S + N ₂ ). The temperature during sulfidation is about 500 to 600 ° C. In the case of producing the precursor, various CZTSs having different compositions can be produced by changing the thickness of Cu, Sn, or ZnS. Similarly, the lower electrode 14, the buffer layer 18, the window layer 20, and the upper electrode 22 can be manufactured using a sputtering method, a vacuum evaporation method, a PLD method, or the like.

Examples of methods for forming various thin films other than sputtering, vacuum evaporation, and PLD include:
(1) A solution in which an organic metal or the like is dissolved is coated on the substrate 12 and dried in air to cause hydrolysis and degeneracy to form a metal oxide thin film. The metal oxide thin film is in a hydrogen sulfide atmosphere. Sol-gel + sulfurization method for forming the light absorption layer 16 by heat treatment with
(2) Chemical bath film formation (CBD) method in which the buffer layer 18 is formed by dissolving thiourea or the like in an aqueous solution in which metal ions are dissolved, and immersing the substrate in the solution and heating the substrate.
and so on.

Next, the operation of the photoelectric element according to the present invention will be described.
Sulfurization using a 20% H ₂ S + N ₂ mixed gas has a relatively high heat treatment temperature. Therefore, when a material containing Na is used for members other than the light absorption layer, Na diffuses to the light absorption layer, and a substance containing Na and O may be generated in the light absorption layer. Na is said to promote the grain growth of chalcopyrite compounds and increase the conversion efficiency. However, in the case of CZTS, which is one of chalcopyrite compounds, when a material containing Na is used for a member other than the light absorption layer, a substance containing Na and O is partially generated in the light absorption layer. A portion that is not a semiconductor, or a region where the Cu concentration or the Zn concentration is reduced appears, and a region with low conversion efficiency is formed. As a result, the overall efficiency is reduced in a large-area element.
In contrast, when a material having a Na concentration of a certain level or less is used for a member other than the light absorption layer, a substance containing Na and O is not generated in CZTS. As a result, a non-semiconductor portion or a region having a reduced Cu concentration or Zn concentration is not generated, and variation in in-plane conversion efficiency is reduced even when a large-area CZTS-based thin film is formed. , Improve overall efficiency.

Further, as disclosed in Non-Patent Document 1, in CZTS, sub-phase crystals exist both when the Cu / (Zn + Sn) ratio is larger than 1.09 and smaller than 0.69. It is known. On the other hand, when the Cu / (Zn + Sn) ratio is set to 0.69 to 0.99, generation of a subphase can be avoided. However, when SLG is used for the substrate, when the Cu / (Zn + Sn) ratio is less than 1, a substance containing Na and O is easily generated in the CZTS film, and the in-plane variation in conversion efficiency increases.
On the other hand, if a material other than the light absorption layer is made of a material that does not contain Na, or if a diffusion blocking layer is provided in any part of the photoelectric element, even if the Cu / (Zn + Sn) ratio is less than 1, Generation of a substance containing Na and O can be suppressed.
Further, in addition to using a material that does not contain Na for the members other than the light absorption layer, or in addition to providing a diffusion blocking layer in any part of the photoelectric element, the Cu / (Zn + Sn) ratio is 0.8-0. If it is 9, the maximum conversion efficiency of the photoelectric element is increased, and the in-plane variation of the conversion efficiency can be reduced.

(Reference Example 1, Comparative Example 1)
[1. Preparation of sample]
A solar cell (Reference Example 1) 10 ′ having the structure shown in FIG. 2 was produced according to the following procedure.
(1) A Mo film (lower electrode 14) was formed on a quartz glass (QZG) substrate 12 by sputtering.
(2) A Cu—Zn—Sn—S precursor film was formed on the Mo film 14 by sputtering.
(3) The precursor film was converted into a CZTS film (light absorption layer 16) by sulfiding treatment at 550 to 580 ° C. for 3 hours in an atmospheric pressure, 20% H ₂ S + N ₂ gas atmosphere.
(4) A CdS film (buffer layer 18) was formed on the CZTS film 16 by the CBD method.
(5) A ZnO: Al film (window layer 20) was formed on the CdS film 18 by sputtering.
(6) A total of twelve comb-shaped electrodes (upper electrodes 22, 22...) Made of an Al film were formed on the ZnO: Al film 20 by sputtering.
(7) As shown in FIG. 2, the window layer 20, the buffer layer 18, and the light absorption layer 16, leaving a 4 mm × 5 mm grid (12 in total) in which the comb-shaped electrodes 22, 22. The Mo film 14 was exposed.
(8) A silver paste 24 was applied to the exposed surface of the Mo film 14.
In addition, a solar cell (Comparative Example 1) was produced according to the same procedure as in Reference Example 1 except that an SLG substrate was used as the substrate.

[2. Test method]
[2.1. Yield]
The conversion efficiency was measured for each of the 12 small elements formed on the substrate. The yield was calculated using the highest conversion efficiency in the small element.
[2.2. Composition analysis]
After forming the Mo film and the CZTS film on the substrate and before forming the CdS film, the in-plane composition distribution of the CZTS film was examined by an electron beam microprobe analyzer (EPMA). The measurement conditions were acceleration voltage = 15 kV, irradiation current = 0.1 μA, and probe beam diameter = about 0.5 μm. Under these measurement conditions, the analysis area per measurement point for CZTS is estimated to be depth direction = about 1 μm and in-plane direction = 1 to 2 μm.

[3. result]
Figure 3 shows the surface image by SEM of CZTS film obtained in Reference Example 1及 beauty Comparative Example 1, and EPMA by composition distribution of the SEM image and the same observation region. In FIG. 3, in Comparative Example 1, for example, a substance containing Na and O is formed in a region indicated by an arrow, thereby generating a non-semiconductor portion or a region where the Cu concentration or the Zn concentration is reduced. I understand that.
In addition, in FIG. 3, when judged by the scale bar (numbers are% by weight) relative to Na and O of Comparative Example 1, the region where the substance containing Na and O is thinly formed has a Na concentration of 0.32. It can be seen that it is present in the region of ˜0.65% by weight and O concentration of 0.38 to 0.75% by weight.
In contrast, in the reference example 1, Na concentration and O concentration are both below the detection limit, the formation of substances containing Na and O were observed.

In Comparative Example 1 using an SLG substrate as the substrate, the maximum conversion efficiency was 5.0%, and the yield was 58%. On the other hand, in Reference Example 1 using a quartz glass substrate as the substrate, the maximum conversion efficiency was 5.0% and the yield was 92%. As described above, these differences depend on the quality of CZTS, specifically, whether or not a substance containing Na and O exists. In other words, the reason for the low yield in Comparative Example 1 is that the substrate in contact with the CZTS film through the Mo film contains Na, and this Na diffuses into the CZTS film during the heat treatment and disturbs the composition distribution. It is done.

(Example 2)
[1. Preparation of sample]
A sample for composition analysis was prepared according to the following procedure.
(1) A SiO ₂ film was formed on the SLG substrate by sputtering.
(2) A Mo film was formed on the SiO ₂ film by sputtering.
(3) A Cu—Zn—Sn—S precursor film was formed on the Mo film by sputtering.
(4) The precursor film was converted into a CZTS film (light absorption layer) by sulfiding treatment at 550 to 580 ° C. for 3 hours in an atmospheric pressure, 20% H ₂ S + N ₂ gas atmosphere.

[2. Test method]
In-plane composition distribution of the CZTS film was measured by EPMA. The measurement conditions were the same as in Reference Example 1 .
[3. result]
FIG. 4 shows a SEM surface image of the CZTS film obtained in Example 2 and a composition distribution by EPMA in the same observation region as the SEM image. FIG. 4 shows that the formation of the substance containing Na and O is suppressed by forming the SiO ₂ film on the SLG substrate.

(Example 3)
[1. Preparation of sample]
A solar cell for yield evaluation was produced according to the same procedure as in Reference Example 1 except that a low alkali glass (LAG) substrate (Corning 1737 substrate) was used instead of the quartz glass substrate. The total alkali concentration of the 1737 substrate is about 0.1% by weight as a catalog value.
[2. Test method]
According to the same procedure as in Reference Example 1 , the yield was evaluated.
[3. result]
In the case of Example 3, the maximum conversion efficiency was 5.0% and the yield was 89%.

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

  The photoelectric element according to the present invention can be used for solar cells, photoconductive cells, photodiodes, phototransistors and the like.

It is a schematic block diagram of the solar cell using CZTS as a light absorption layer. It is the top view (upper figure) of the solar cell for yield evaluation, and its A-A 'line sectional drawing. SEM images of CZTS film obtained in Reference Example 1及 beauty Comparative Example 1, and a composition analysis result by EPMA of the same observation area and SEM images. It is a SEM image of the CZTS film obtained in Example 2, and a composition analysis result by EPMA in the same observation region as the SEM image.

Explanation of symbols

10 Photoelectric elements (solar cells)
12 Substrate 14 Lower electrode 16 Light absorption layer 18 Buffer layer 20 Window layer 22 Upper electrode

Claims (13)

In a photoelectric device including a light absorption layer made of a sulfide compound semiconductor containing Cu, Zn, Sn, and S,
The light absorbing layer is
The maximum concentration of Na in the region where Na and O are concentrated (the concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.49% by weight or less, and
The maximum concentration of O in the region where Na and O are concentrated (concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.57% by weight or less,
Members other than the light-absorbing layer constituting the photoelectric element, light Denmoto element which content is a material that does not contain N a 0.1 wt% or less of Na (provided that those substrate is made of quartz glass Except) . The photoelectric device is, on the substrate, at least a lower electrode, the light absorption layer, a buffer layer, a window layer, and an upper electrode photoelectric device according to claim 1 ing from those stacked in this order. The substrate, Roh emissions alkali glass, low alkali glass, metals, semiconductors, oxides, sulfides, nitrides, carbides, silicides, or a photoelectric device according to claim 2 ing carbon. The lower electrode, Mo, In-SnO, In -ZnO, ZnO: Al, ZnO: B, SnO 2: F, SnO 2: Sb, or TiO _2: Nb Tona Ru claim 2 or 3 The photoelectric device described in 1. The buffer layer, CdS, ZnO, Zn (O , OH), Zn (O, S), Zn (O, S, OH) x, Zn 1-x Mg x O, or an In ₂ S ₃ Tona Ru claims Item 5. The photoelectric device according to any one of Items 2 to 4 . The window layer, ZnO: Al, ZnO: B , In-SnO, In-ZnO, SnO 2: Sb, or TiO _2: from Nb Tona Ru claim 2 of any one of up to 5 Photoelectric element. The upper electrode, Al, Cu, Ag, or Au, or a photoelectric device according to any one of claims 2 ing an alloy containing one or more of any of these to 6. The photoelectric element is composed of 10 or more small elements formed on the same substrate,
The number of small elements (n ) exhibiting a conversion efficiency of 80% or more of the maximum conversion efficiency of the small elements formed on the same substrate with respect to the number of small elements (n ₀ ) on the same substrate. percentage photoelectric device according to any one of _{(= n × 100 / n 0} ) according to claim 1 step remains is Ru der 80% or more expressed as to 7. In a photoelectric device including a light absorption layer made of a sulfide compound semiconductor containing Cu, Zn, Sn, and S,
The light absorbing layer is
The maximum concentration of Na in the region where Na and O are concentrated (the concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.49% by weight or less, and
The maximum concentration of O in the region where Na and O are concentrated (concentration with respect to the entire analysis region when the analysis region in the depth direction of the light absorption layer is about 1 μm) is 0.57% by weight or less,
At least one member other than the light absorption layer constituting the photoelectric element is made of a material containing Na with a Na content exceeding 0.1 wt% ,
A photoelectric device further comprising a diffusion blocking layer for blocking diffusion of Na from the material containing Na into the light absorption layer. The photoelectric device is, on the substrate, at least a lower electrode, the light absorption layer, a buffer layer, a window layer, and a photoelectric element according to claim 9 in which the upper electrode consisting of those which are stacked in this order. The substrate is made of a material containing Na with a Na content exceeding 0.1% by weight ;
The diffusion blocking layer is provided between the substrate and the lower electrode;
The diffusion blocking layer, a quartz glass, non-alkali glass, low alkali glass, metals, semiconductors, oxides, sulfides, nitrides, carbides, silicides, and to claim 10 comprising any one or more selected from carbon The photoelectric element as described. The substrate is made of a material containing Na with a Na content exceeding 0.1% by weight ,
The diffusion blocking layer is provided between the lower electrode and the light absorption layer;
11. The photoelectric device according to claim 10, wherein the diffusion blocking layer is made of any one or more selected from metals, semiconductors, oxides, sulfides, nitrides, carbides, silicides, and carbon having electronic conductivity. The photoelectric element is composed of 10 or more small elements formed on the same substrate,
The number of small elements (n ) exhibiting a conversion efficiency of 80% or more of the maximum conversion efficiency of the small elements formed on the same substrate with respect to the number of small elements (n ₀ ) on the same substrate. the photoelectric element according to any one of claims 9 to 12 remain walking expressed as a percentage _{(= n × 100 / n 0} ) of not less than 80%.

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