US20160312346A1 - Persulfate bath and method for chemically depositing a layer - Google Patents
Persulfate bath and method for chemically depositing a layer Download PDFInfo
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- US20160312346A1 US20160312346A1 US15/103,628 US201415103628A US2016312346A1 US 20160312346 A1 US20160312346 A1 US 20160312346A1 US 201415103628 A US201415103628 A US 201415103628A US 2016312346 A1 US2016312346 A1 US 2016312346A1
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- metal
- chemical bath
- deposition
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- 238000000151 deposition Methods 0.000 title claims abstract description 93
- 238000000034 method Methods 0.000 title claims abstract description 27
- JRKICGRDRMAZLK-UHFFFAOYSA-L peroxydisulfate Chemical compound [O-]S(=O)(=O)OOS([O-])(=O)=O JRKICGRDRMAZLK-UHFFFAOYSA-L 0.000 title claims description 27
- 229910052751 metal Inorganic materials 0.000 claims abstract description 64
- 239000002184 metal Substances 0.000 claims abstract description 64
- 239000000126 substance Substances 0.000 claims abstract description 55
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 40
- 150000003839 salts Chemical class 0.000 claims abstract description 20
- 239000002243 precursor Substances 0.000 claims abstract description 17
- -1 persulfate compound Chemical class 0.000 claims abstract description 10
- 230000000737 periodic effect Effects 0.000 claims abstract description 8
- 230000008021 deposition Effects 0.000 claims description 73
- 229910052717 sulfur Inorganic materials 0.000 claims description 39
- 239000011593 sulfur Substances 0.000 claims description 38
- 239000006096 absorbing agent Substances 0.000 claims description 28
- 239000011701 zinc Substances 0.000 claims description 28
- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 claims description 24
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Natural products NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 12
- 229910052725 zinc Inorganic materials 0.000 claims description 10
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 9
- 229910001870 ammonium persulfate Inorganic materials 0.000 claims description 9
- ROOXNKNUYICQNP-UHFFFAOYSA-N ammonium persulfate Chemical compound [NH4+].[NH4+].[O-]S(=O)(=O)OOS([O-])(=O)=O ROOXNKNUYICQNP-UHFFFAOYSA-N 0.000 claims description 8
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical compound S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 claims description 8
- 229910052718 tin Inorganic materials 0.000 claims description 8
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 claims description 8
- 229910000368 zinc sulfate Inorganic materials 0.000 claims description 8
- 239000010409 thin film Substances 0.000 claims description 7
- 229910052711 selenium Inorganic materials 0.000 claims description 6
- CHQMHPLRPQMAMX-UHFFFAOYSA-L sodium persulfate Substances [Na+].[Na+].[O-]S(=O)(=O)OOS([O-])(=O)=O CHQMHPLRPQMAMX-UHFFFAOYSA-L 0.000 claims description 6
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 claims description 6
- 229910052951 chalcopyrite Inorganic materials 0.000 claims description 4
- 229910052976 metal sulfide Inorganic materials 0.000 claims description 4
- 239000004246 zinc acetate Substances 0.000 claims description 4
- 229960001763 zinc sulfate Drugs 0.000 claims description 4
- LCPVQAHEFVXVKT-UHFFFAOYSA-N 2-(2,4-difluorophenoxy)pyridin-3-amine Chemical compound NC1=CC=CN=C1OC1=CC=C(F)C=C1F LCPVQAHEFVXVKT-UHFFFAOYSA-N 0.000 claims description 3
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims description 3
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 3
- 229910002567 K2S2O8 Inorganic materials 0.000 claims description 3
- 229910004882 Na2S2O8 Inorganic materials 0.000 claims description 3
- ZOIORXHNWRGPMV-UHFFFAOYSA-N acetic acid;zinc Chemical compound [Zn].CC(O)=O.CC(O)=O ZOIORXHNWRGPMV-UHFFFAOYSA-N 0.000 claims description 3
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 3
- 229910052733 gallium Inorganic materials 0.000 claims description 3
- USHAGKDGDHPEEY-UHFFFAOYSA-L potassium persulfate Chemical compound [K+].[K+].[O-]S(=O)(=O)OOS([O-])(=O)=O USHAGKDGDHPEEY-UHFFFAOYSA-L 0.000 claims description 3
- 239000011592 zinc chloride Substances 0.000 claims description 3
- 235000005074 zinc chloride Nutrition 0.000 claims description 3
- 239000005864 Sulphur Substances 0.000 abstract 2
- 238000000224 chemical solution deposition Methods 0.000 description 26
- 229910052984 zinc sulfide Inorganic materials 0.000 description 26
- 239000000243 solution Substances 0.000 description 21
- 229910052760 oxygen Inorganic materials 0.000 description 17
- 239000003153 chemical reaction reagent Substances 0.000 description 16
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 15
- 239000000654 additive Substances 0.000 description 12
- 239000011541 reaction mixture Substances 0.000 description 12
- 230000000996 additive effect Effects 0.000 description 11
- 150000001875 compounds Chemical class 0.000 description 11
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 10
- 238000004519 manufacturing process Methods 0.000 description 8
- 229910045601 alloy Inorganic materials 0.000 description 7
- 239000000956 alloy Substances 0.000 description 7
- 229910021529 ammonia Inorganic materials 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 6
- 238000005234 chemical deposition Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 239000005083 Zinc sulfide Substances 0.000 description 5
- 230000003287 optical effect Effects 0.000 description 5
- 239000011787 zinc oxide Substances 0.000 description 5
- DRDVZXDWVBGGMH-UHFFFAOYSA-N zinc;sulfide Chemical compound [S-2].[Zn+2] DRDVZXDWVBGGMH-UHFFFAOYSA-N 0.000 description 5
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 229910052793 cadmium Inorganic materials 0.000 description 4
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 239000011686 zinc sulphate Substances 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- 229910052738 indium Inorganic materials 0.000 description 3
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 239000012429 reaction media Substances 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- 150000003464 sulfur compounds Chemical class 0.000 description 3
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 2
- 229910017612 Cu(In,Ga)Se2 Inorganic materials 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 231100000252 nontoxic Toxicity 0.000 description 2
- 230000003000 nontoxic effect Effects 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- YUKQRDCYNOVPGJ-UHFFFAOYSA-N thioacetamide Chemical compound CC(N)=S YUKQRDCYNOVPGJ-UHFFFAOYSA-N 0.000 description 2
- DLFVBJFMPXGRIB-UHFFFAOYSA-N thioacetamide Natural products CC(N)=O DLFVBJFMPXGRIB-UHFFFAOYSA-N 0.000 description 2
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 1
- 229910000925 Cd alloy Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 229910003363 ZnMgO Inorganic materials 0.000 description 1
- MGTYKZBWBMDCNO-UHFFFAOYSA-N [In].O=S Chemical compound [In].O=S MGTYKZBWBMDCNO-UHFFFAOYSA-N 0.000 description 1
- 235000019395 ammonium persulphate Nutrition 0.000 description 1
- 239000012736 aqueous medium Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- CJOBVZJTOIVNNF-UHFFFAOYSA-N cadmium sulfide Chemical compound [Cd]=S CJOBVZJTOIVNNF-UHFFFAOYSA-N 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000008139 complexing agent Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000002609 medium Substances 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 231100000956 nontoxicity Toxicity 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005546 reactive sputtering Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000007847 structural defect Effects 0.000 description 1
- YOXKVLXOLWOQBK-UHFFFAOYSA-N sulfur monoxide zinc Chemical compound [Zn].S=O YOXKVLXOLWOQBK-UHFFFAOYSA-N 0.000 description 1
- 231100000167 toxic agent Toxicity 0.000 description 1
- 239000003440 toxic substance Substances 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
- C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
- C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
- C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
- C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
- C23C18/1208—Oxides, e.g. ceramics
- C23C18/1216—Metal oxides
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1828—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/543—Solar cells from Group II-VI materials
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the invention relates to the field of chemical deposition baths for the deposition of layers based on sulfur and metal. It also relates to methods for chemically depositing a layer based on metal and sulfur.
- CBD Chemical Bath Deposition
- Chemical bath deposition can thus be considered in the fabrication of certain thin layers of photosensitive devices. More particularly, the absorber layers in some photosensitive devices are generally covered by a so-called “buffer” layer made of an alloy comprising metal and sulfur. Generally, this buffer layer consists of an alloy of cadmium sulfur CdS.
- the toxicity of cadmium prompts us to look for alternative materials for the buffer layer, such as zinc sulfide ZnS and its derivatives.
- the deposition rate of these alloys on any surface, and particularly on other thin layers such as light absorbers is not optimal. Obtaining a chemical deposition that meets industry requirements can involve times considered to be long, exceeding 15 minutes or even an hour. Such lengthening of the deposition time adds to manufacturing costs and penalizes the entire chain of production of a device.
- the present invention provides a chemical bath for depositing a layer based on at least metal and sulfur.
- This bath comprises, in solution:
- This bath further comprises a persulfate compound.
- a bath for the chemical deposition of a layer comprising sulfur and a metal from groups IIB or IIIA of the periodic table is thus optimized by adding a persulfate-type compound into the bath solution mixture.
- the applicant has found that the addition of persulfate produces in the mixture an effect comparable to that of a reaction accelerator.
- the persulfate appears to interact with the sulfur precursor and accelerates the formation of the sulfur- and metal-based alloy on the deposition surface. This effect seems to be particularly pronounced when the metal belongs to groups IIIA or IIB, such as zinc Zn or indium In for example.
- persulfate allows obtaining homogeneous metal- and sulfur-based layers on large surfaces.
- the addition of persulfate to the chemical bath thus allows obtaining more homogeneous depositions over a large surface area compared to CBD depositions involving baths without this additive.
- Another advantageous effect obtained by the addition of persulfate lies in the fact that the deposition can be done without preheating the bath reagents. By eliminating a prior preheating step, it is possible to increase the production rate at the industrial scale. However, it is also possible to preheat the reagents, enabling the bath described above to easily be prepared in existing production lines.
- the optimized bath described above allows for example making deposits on glass, metal substrates, or semiconductors, as well as on compounds having photovoltaic properties such as absorbers.
- the compound may be chosen from the group consisting of ammonium persulfate of chemical formula (NH 4 ) 2 S 2 O 8 , sodium persulfate of chemical formula Na 2 S 2 O 8 , and potassium persulfate of chemical formula K 2 S 2 O 8 .
- These compounds may advantageously be in a solution that is miscible with the other reagents of the chemical bath. It has been noted that the deposition rate and the homogeneity of the obtained layer can be optimized in a particularly visible manner when at least one of these additives is used. However, the active component of the inorganic additive seems to be found in persulfate, and other persulfate-based compounds could therefore be envisaged.
- a concentration between 10 ⁇ 5 mol.L ⁇ 1 and 1 mol/L of persulfate may be provided in the bath, for a concentration between 0.05 mol/L and 1 mol/L of sulfur compound.
- Such a reaction mixture in the bath corresponds to a compromise between quantity of reagents used and rapidity of deposition.
- the solution containing the metal salt may be a solution selected from among: zinc sulfate, zinc acetate, and zinc chloride, at a concentration between 0.01 mol/L and 1 mol/L.
- the metal salt may include other metals from groups IIB and IIIA of the periodic table.
- a zinc metal salt in the bath provided a particularly pronounced reduction of the deposition time.
- the invention achieves a deposition rate which is up to eight times higher.
- a concentration between 0.01 mol/L and 1 mol/L of metal salt allows reducing the amount of raw material used to deposit the layer.
- the bath may further comprise an ammonia solution at a concentration of between 0.1 mol/L and 10 mol/L.
- ammonia solution gives a basic pH to the chemical bath, in order to initiate hydrolysis of the sulfur precursor so that it reacts with the metal salt.
- the solution containing the sulfur compound may be a solution of thiourea CS(NH 2 ) 2 .
- Thiourea is a sulfur precursor that is particularly suitable for the deposition of layers comprising sulfide. It is commonly used in the photosensitive devices industry, for example.
- Thiourea enables particularly rapid deposition in the presence of persulfate and of a metal salt.
- the deposition rates obtained when thiourea is used can thus be less than 5 minutes for a layer of metal sulfide or metal oxysulfide that is 20 nm thick.
- the metal may be an element from column IIB.
- Metals of column IIB are of particular interest to the photosensitive devices industry. In these devices, metals such as cadmium or zinc may be present in the buffer layer between the absorber and the front electrical contact of a photosensitive cell. Elements of column IIB are therefore particularly suitable for a chemical bath intended for the creation of buffer layers.
- the metal may be zinc.
- Deposition of a zinc sulfide or oxysulfide layer by CBD is of interest for example in the photosensitive devices industry due to its optical properties and non-toxicity.
- a layer made of such an alloy is an effective and non-toxic alternative to buffer layers of CdS, while allowing the transmission of more radiation of wavelengths below 500 nm.
- a layer of zinc sulfide or oxysulfide has a higher energy band gap than a CdS layer, therefore transmitting more light at wavelengths below 500 nm than a CdS layer.
- a layer of zinc sulfide or oxysulfide has optical transmission properties equivalent to those of layers of zinc oxide ZnO, which are often used to form the front electrical contacts of photosensitive devices.
- the invention also relates to a method for chemically depositing a layer based on at least metal and sulfur, in a bath comprising, in solution:
- a persulfate compound is provided in the bath.
- CBD deposition of a layer based on at least metal and sulfur with the addition of persulfate in the chemical bath offers several advantages, described above.
- the addition of persulfate in the bath increases the deposition rate, allows achieving more homogeneous layers, and can save preparation time due to the possibility of eliminating an earlier step of preheating the chemical bath reagents.
- the layer may be based on a metal sulfide.
- the metal sulfide for example ZnS, may be an alloy particularly suitable for applications in photosensitive devices. For example, it may be used as a buffer layer on absorbers of photosensitive devices.
- the layer may be based on a metal oxysulfide.
- Metal oxysulfides for example Zn(S,O), Zn(S,O,OH), or In x (S,O) y , In x (S,O,OH) y , where 0 ⁇ x ⁇ 2 and 0 ⁇ y ⁇ 3, have optical properties that are particularly suitable for the requirements of the photosensitive devices industry. They may also be suitable for use as buffer layers on a photosensitive layer.
- the bath temperature during deposition may be between 40° C. and 100° C.
- a deposition temperature below 100° C. and in particular below 70° C. allows a work environment that is less damaging to devices comprising alloys having a low melting point, without being penalized by an increase in the deposition duration.
- by reducing the temperature of the reaction medium it is possible to save energy due to less heating of the CBD deposition bath. These savings increase with the size of the bath, which can reach several square meters at the industrial scale.
- the layer based on metal and sulfur can represent a buffer layer deposited on an absorber of a thin-film photovoltaic cell, to interface the absorber with a front electrical contact.
- the quality of the interface between the absorber of a photosensitive cell and the buffer layer is crucial to achieving high conversion efficiency in the resulting device.
- persulfate as an additive in a chemical bath for the deposition of a buffer layer on a photovoltaic cell absorber is counterintuitive.
- Persulfate in particular ammonium persulfate, is generally used in industry as a cleaning and etching agent due to its highly oxidizing character.
- the applicant has noted that the addition of persulfate to a chemical bath as described above does not give the bath corrosive properties, which protects the surface on which the deposition takes place from chemical attack.
- the absorber may be based on a chalcopyrite compound among Cu(In,Ga)(S,Se) 2 , Cu 2 (Zn,Sn)(S,Se) 4 , and their derivatives.
- the solar cell absorbers listed above correspond to absorbers of thin-film cells of CIGS and CZTS type and their derivatives having conversion efficiencies that can exceed 20%. Making use of the method described above for depositing a buffer layer on these absorbers is particularly advantageous given the performance gains this provides. For example, by thus depositing a buffer layer of ZnS, Zn(S,O), or Zn(S,O,OH) on an absorber based on a chalcopyrite compound, it is possible to obtain a conversion efficiency exceeding 14% and an open circuit voltage and short-circuit current of the end device that are greater than those observed in devices obtained by other deposition methods.
- FIG. 2 is a schematic representation of the procedure for preparing a chemical bath
- FIG. 4 is a schematic representation of a photosensitive device
- FIG. 1 illustrates an example of an initial sample 100 , comprising a substrate 101 , a rear metal contact 102 , and an absorber layer 103 .
- the initial sample 100 shown therefore represents an unfinished portion of a thin-film photosensitive device.
- the absorber 103 intended to convert radiation into current may be a chalcopyrite compound such as one of the compounds among Cu(In,Ga)(S,Se) 2 , Cu 2 (Zn,Sn)(S,Se) 4 , and their derivatives. These derivatives may include, for example,
- the invention proposes a chamber 200 for the chemical bath, schematically represented in FIG. 2 .
- the chamber 200 may be closed by a cover 220 .
- This chamber 200 contains a solution 50 consisting of a mixture of reagents in the chosen concentrations.
- the sample 100 rests in this solution 50 .
- Means for heating this reaction medium may be provided.
- such a means is represented by a water bath 210 surrounding the chamber containing the reaction medium.
- a motor 230 may also be used to drive a stirring mechanism that stirs the solution 50 .
- FIG. 2 also shows a summary of the steps for obtaining the solution forming the reaction mixture 50 .
- the chemical bath is configured for deposition of a buffer layer of a photovoltaic device. For this reason, it is prepared from a first aqueous solution comprising a metal salt 10 , represented as being zinc sulfate ZnSO 4 .
- a second aqueous solution comprising a sulfur precursor 20 is also provided. This second solution is represented as being thiourea, of chemical formula CS(NH 2 ) 2 .
- Ammonia 30 to give the reaction mixture a basic pH, may also be provided.
- a medium that is basic due to the presence of ammonia promotes the reaction of the precursor with the metal salt.
- a fourth aqueous solution comprising a persulfate-based inorganic additive 40 is prepared. This fourth solution 40 is represented as comprising ammonium peroxydisulfate of chemical formula (NH 4 ) 2 S 2 O 8 .
- reaction mixture 50 is the solution into which the sample 100 is dipped.
- the addition of peroxydisulfate significantly reduces the time required to achieve deposition of ZnS on the absorber.
- the graph of FIG. 3 compares the rates of deposition of a thin layer by CBD, measured under three different conditions.
- the deposited ZnS layer may include oxygen and form a layer of Zn(S,O) or Zn(S,O,OH) type.
- ZnS layer will be used hereinafter to refer to a layer of pure ZnS as well as to a layer of Zn(S,O) or Zn(S,O,OH).
- Curve 301 shows the time required to deposit ZnS layers of different thicknesses, when the reaction mixture 50 is in a conventional configuration.
- “Conventional” is understood to mean a thiourea concentration of 0.65 mol/L, a ZnSO 4 concentration of 0.15 mol/L, and an ammonia concentration of 2 mol/L.
- the reagents were all preheated to a temperature of 80° C. before being placed in a chamber brought to the same temperature of 80° C.
- Curve 302 represents the time required to deposit ZnS layers of different thicknesses, when the reaction mixture 50 comprises a laboratory-tested configuration corresponding to a particularly advantageous embodiment. It is characterized by a thiourea concentration of 0.4 mol/L, a ZnSO 4 concentration of 0.1 mol/L, and an ammonia concentration of 2 mol/L. No preheating of the reagents is provided and the deposition temperature is 70° C.
- Curve 303 represents the time required to deposit ZnS layers of different thicknesses, when the reaction mixture 50 comprises the same characteristics as those associated with curve 302 , but with the addition of a concentration of 0.001 mol/L peroxydisulfate. Table 1 below summarizes the three configurations described above.
- the bath optimized according to the invention divides the deposition time by 2.5 compared to conventional techniques, and by more than 5 compared to a deposition conducted under the same conditions without the additive.
- the deposition conditions in the applicant's chemical bath are more efficient in materials saving and energy saving. This results from the lower concentrations of reagents, lower deposition temperature, and no preheating of the reagents.
- the example described above can advantageously result in the creation of a complete photovoltaic device as shown in FIG. 4 .
- FIG. 4 schematically illustrates a thin-film solar cell comprising the same structural elements as those of FIG. 1 .
- the represented device 400 further comprises a buffer layer 104 deposited on the absorber by CBD, as described above.
- a first window layer 105 for example of intrinsic zinc oxide or ZnMgO, can be deposited by known techniques such as reactive sputtering, chemical vapor deposition, electrodeposition, CBD deposition, or ILGAR® deposition.
- a front electrical contact 106 can then be deposited. For example, it may be a layer of aluminum-doped zinc oxide ZnO.
- Table 2 compares technical characteristics of solar cells such as the solar cell of FIG. 4 , comprising a chalcopyrite-type CIGS absorber.
- a first cell comprises a ZnS buffer layer obtained under conventional deposition conditions as described above in relation to curve 301 of FIG. 3 .
- a second cell comprises a ZnS buffer layer obtained by a CBD deposition process involving the bath of the invention, under conditions identical to those described in relation to curve 303 of FIG. 3 .
- a third cell comprises a CdS buffer layer obtained by CBD under conventional deposition conditions.
- Each cell of Table 2 has a surface area of 5 ⁇ 5 cm 2 and a buffer layer 20 nm thick.
- the cell having a ZnS buffer layer formed by the CBD deposition method developed in the context of the invention has a homogeneity that is superior to the other cells. In particular, it has a higher homogeneity than the cell having a ZnS layer formed by conventional CBD deposition.
- the form factor of the cell obtained by the method of the invention is comparable to that of cells having a CdS buffer layer. Nevertheless, the overall homogeneity of the cell created by CBD deposition with the addition of persulfate is better. Therefore the deposition method with the addition of persulfate is well suited to the creation of photosensitive cells of large surface area, or more generally to the creation of layers comprising metal and sulfur in industrial settings.
- the chemical bath developed, and the method that uses it to create a buffer layer allow obtaining under adapted deposition conditions a buffer layer of a non-toxic material, for example cadmium-free.
- FIG. 5 shows a graph comparing the quantum efficiency between 300 nm and 1100 nm of a ZnS buffer layer, represented by curve 502 , with that of a CdS buffer layer, represented by curve 501 .
- Quantum efficiency is a parameter that represents the ratio between the amount of electrons produced and the amount of photons received by the photosensitive device.
- the present invention is not limited to the embodiments described above by way of example; it also extends to other variants. Indeed, the bath described above and the method using this bath to produce a thin layer comprising metal and sulfur can be implemented in different configurations which all benefit from the gains in deposition rate and in quality of the obtained layer that are described above.
- the compromise between deposition rate and concentration of the reagents can be considered to be satisfactory for a concentration of metal salt between 0.01 mol/L and 1 mol/L, a concentration of sulfur precursor between 0.05 mol/L and 1 mol/L, a persulfate concentration between 10 -5 mol/L and 1 mol/L, and an ammonia concentration between 0.1 mol/L and 10 mol/L.
- the bath and the method that uses it can be envisaged without the addition of ammonia. It is possible, for example, to substitute another compound of basic pH, or a compound of pKa greater than 7.
- the ammonia can be eliminated for example by using potassium hydroxide KOH with a citrate-type complexing agent.
- the reaction mixture of the chemical bath may contain only persulfate, sulfur precursor, and a metal salt. Beyond these basic components, the composition of the reaction mixture may differ from what is detailed above.
- persulfate-based compounds such as sodium persulfate of chemical formula Na 2 S 2 O 8 or potassium persulfate of chemical formula K 2 S 2 O 8 , with equivalent performance.
- the thiourea may also be replaced by other sulfur precursors, preferably having equivalent chemical properties.
- the metal salt may be replaced by zinc chloride or acetate for the same applications as those described above.
- the zinc acetate may be anhydrous or hydrated, for example of formula Zn[CH 3 COOH] 2 .
- An indium- or cadmium-based salt may also be suitable for the metal salt when creating buffer layers on photosensitive devices.
- oxygen may be incorporated into the deposited layers to form a zinc oxysulfide of Zn(S,O) or Zn(S,O,OH) type.
- oxygen may be incorporated into a layer comprising another metal element such as indium, to form an indium oxysulfide of In x (S,O) y or In x (S,O,OH) y type.
- Other elements of groups IIB and IIIA of the periodic table may also be considered for the metal, however, due to their chemical properties similar to those of zinc, indium, or cadmium.
- the invention has also been tested successfully on other deposition surfaces such as glass, a semiconductor substrate, and a metal.
- the invention described above optimizes a chemical bath for the deposition of a thin layer comprising sulfur and a metal. This optimization increases the deposition rate while improving the structural quality of the layer obtained, and saves materials and energy.
- the invention has the advantage of being compatible with existing chemical baths for CBD chemical deposition, and offers an advantageous solution for industrial scale CBD deposition on large surface areas.
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Abstract
Description
- The invention relates to the field of chemical deposition baths for the deposition of layers based on sulfur and metal. It also relates to methods for chemically depositing a layer based on metal and sulfur.
- Methods for Chemical Bath Deposition (CBD) are commonly used in industry, for example to fabricate alloys in thin layers (“thin films”). These methods are particularly suitable for large-scale deposition to cover large areas exceeding 60×30 cm2. In addition, this technique is widely used in industry due to its low cost and its technical simplicity.
- Chemical bath deposition can thus be considered in the fabrication of certain thin layers of photosensitive devices. More particularly, the absorber layers in some photosensitive devices are generally covered by a so-called “buffer” layer made of an alloy comprising metal and sulfur. Generally, this buffer layer consists of an alloy of cadmium sulfur CdS.
- The toxicity of cadmium prompts us to look for alternative materials for the buffer layer, such as zinc sulfide ZnS and its derivatives. However, the deposition rate of these alloys on any surface, and particularly on other thin layers such as light absorbers, is not optimal. Obtaining a chemical deposition that meets industry requirements can involve times considered to be long, exceeding 15 minutes or even an hour. Such lengthening of the deposition time adds to manufacturing costs and penalizes the entire chain of production of a device.
- For this reason, special attention is being paid to finding technical means for achieving the deposition of a layer based on at least sulfur and a metal, by CBD.
- To reduce the deposition time of such a layer, it is known to increase either the concentration of reagents in the chemical bath or the temperature, or to preheat the reagents. However, these three means have the disadvantage of causing an increase in the consumption of materials and energy. They may also present the risk of damage to the deposition surface, or may involve additional steps in the chain of production of a type that incurs additional costs.
- Another solution for accelerating the deposition rate is to use a specific sulfur precursor in a chemical bath. Generally, the chemical baths for depositing a layer of metal and sulfur make use of a thiourea solution as sulfur precursor. Document US2013/0084401 proposes replacing thiourea by thioacetamide. This alternative, however, has the disadvantage that thioacetamide is a highly toxic compound and is therefore not very suitable for an industrial application.
- Another alternative suggested in document DE102009015063A1 consists in adding hydrogen peroxide H2O2 to a chemical bath provided for deposition of a thin layer based on sulfur and metal. This solution is not suitable for industrial applications where the deposition surface is fragile, given the corrosive nature of the H2O2 additive.
- For these reasons, we seek a means for increasing the deposition rate in a chemical bath of a layer comprising at least sulfur and a metal, and which is compatible with a wide range of industrial applications.
- To address the problems described above, the present invention provides a chemical bath for depositing a layer based on at least metal and sulfur. This bath comprises, in solution:
-
- a metal salt comprising a metal selected from among at least one of the elements of groups JIB and IIIA of the periodic table; and
- a sulfur precursor.
- This bath further comprises a persulfate compound.
- A bath for the chemical deposition of a layer comprising sulfur and a metal from groups IIB or IIIA of the periodic table is thus optimized by adding a persulfate-type compound into the bath solution mixture. The applicant has found that the addition of persulfate produces in the mixture an effect comparable to that of a reaction accelerator. The persulfate appears to interact with the sulfur precursor and accelerates the formation of the sulfur- and metal-based alloy on the deposition surface. This effect seems to be particularly pronounced when the metal belongs to groups IIIA or IIB, such as zinc Zn or indium In for example.
- In addition to increasing the deposition rate, the applicant has found that the addition of persulfate allows obtaining homogeneous metal- and sulfur-based layers on large surfaces. The addition of persulfate to the chemical bath thus allows obtaining more homogeneous depositions over a large surface area compared to CBD depositions involving baths without this additive.
- Another advantageous effect obtained by the addition of persulfate lies in the fact that the deposition can be done without preheating the bath reagents. By eliminating a prior preheating step, it is possible to increase the production rate at the industrial scale. However, it is also possible to preheat the reagents, enabling the bath described above to easily be prepared in existing production lines.
- These different effects are independent of the surface on which the deposit is made. In particular, the optimized bath described above allows for example making deposits on glass, metal substrates, or semiconductors, as well as on compounds having photovoltaic properties such as absorbers.
- These effects have been observed in different experimental configurations, and seem to occur regardless of the concentration of reagents in the chemical bath or the temperature of the bath.
- According to one advantageous embodiment, the compound may be chosen from the group consisting of ammonium persulfate of chemical formula (NH4)2S2O8, sodium persulfate of chemical formula Na2S2O8, and potassium persulfate of chemical formula K2S2O8.
- These compounds may advantageously be in a solution that is miscible with the other reagents of the chemical bath. It has been noted that the deposition rate and the homogeneity of the obtained layer can be optimized in a particularly visible manner when at least one of these additives is used. However, the active component of the inorganic additive seems to be found in persulfate, and other persulfate-based compounds could therefore be envisaged.
- According to one embodiment, a concentration between 10−5 mol.L−1 and 1 mol/L of persulfate may be provided in the bath, for a concentration between 0.05 mol/L and 1 mol/L of sulfur compound.
- Such a reaction mixture in the bath corresponds to a compromise between quantity of reagents used and rapidity of deposition. By keeping the amount of additive and of sulfur compound low, it is possible to achieve significant savings during production at an industrial scale. This is due to less waste of reagents.
- Advantageously, the solution containing the metal salt may be a solution selected from among: zinc sulfate, zinc acetate, and zinc chloride, at a concentration between 0.01 mol/L and 1 mol/L.
- The metal salt may include other metals from groups IIB and IIIA of the periodic table. However, a zinc metal salt in the bath provided a particularly pronounced reduction of the deposition time. In comparison to CBD deposition in a bath without persulfate and using a zinc metal salt, the invention achieves a deposition rate which is up to eight times higher.
- A concentration between 0.01 mol/L and 1 mol/L of metal salt allows reducing the amount of raw material used to deposit the layer.
- Advantageously, the bath may further comprise an ammonia solution at a concentration of between 0.1 mol/L and 10 mol/L.
- The use of an ammonia solution gives a basic pH to the chemical bath, in order to initiate hydrolysis of the sulfur precursor so that it reacts with the metal salt.
- According to one embodiment, the solution containing the sulfur compound may be a solution of thiourea CS(NH2)2.
- Thiourea is a sulfur precursor that is particularly suitable for the deposition of layers comprising sulfide. It is commonly used in the photosensitive devices industry, for example.
- Thiourea enables particularly rapid deposition in the presence of persulfate and of a metal salt. The deposition rates obtained when thiourea is used can thus be less than 5 minutes for a layer of metal sulfide or metal oxysulfide that is 20 nm thick.
- More particularly, the metal may be an element from column IIB.
- Metals of column IIB are of particular interest to the photosensitive devices industry. In these devices, metals such as cadmium or zinc may be present in the buffer layer between the absorber and the front electrical contact of a photosensitive cell. Elements of column IIB are therefore particularly suitable for a chemical bath intended for the creation of buffer layers.
- In one particular embodiment, the metal may be zinc.
- Deposition of a zinc sulfide or oxysulfide layer by CBD is of interest for example in the photosensitive devices industry due to its optical properties and non-toxicity. A layer made of such an alloy is an effective and non-toxic alternative to buffer layers of CdS, while allowing the transmission of more radiation of wavelengths below 500 nm.
- A layer of zinc sulfide or oxysulfide has a higher energy band gap than a CdS layer, therefore transmitting more light at wavelengths below 500 nm than a CdS layer.
- In addition, a layer of zinc sulfide or oxysulfide has optical transmission properties equivalent to those of layers of zinc oxide ZnO, which are often used to form the front electrical contacts of photosensitive devices.
- The invention also relates to a method for chemically depositing a layer based on at least metal and sulfur, in a bath comprising, in solution:
-
- a metal salt comprising a metal selected from among at least one of the elements of groups IIB and IIIA of the periodic table; and
- a sulfur precursor.
- In addition, a persulfate compound is provided in the bath.
- CBD deposition of a layer based on at least metal and sulfur with the addition of persulfate in the chemical bath offers several advantages, described above. The addition of persulfate in the bath increases the deposition rate, allows achieving more homogeneous layers, and can save preparation time due to the possibility of eliminating an earlier step of preheating the chemical bath reagents.
- In one particular embodiment, the layer may be based on a metal sulfide.
- The metal sulfide, for example ZnS, may be an alloy particularly suitable for applications in photosensitive devices. For example, it may be used as a buffer layer on absorbers of photosensitive devices.
- In another embodiment, the layer may be based on a metal oxysulfide.
- Metal oxysulfides, for example Zn(S,O), Zn(S,O,OH), or Inx(S,O)y, Inx(S,O,OH)y, where 0<x<2 and 0<y<3, have optical properties that are particularly suitable for the requirements of the photosensitive devices industry. They may also be suitable for use as buffer layers on a photosensitive layer.
- Advantageously, the bath temperature during deposition may be between 40° C. and 100° C.
- A deposition temperature below 100° C. and in particular below 70° C. allows a work environment that is less damaging to devices comprising alloys having a low melting point, without being penalized by an increase in the deposition duration. In addition, by reducing the temperature of the reaction medium, it is possible to save energy due to less heating of the CBD deposition bath. These savings increase with the size of the bath, which can reach several square meters at the industrial scale.
- According to one embodiment, the layer based on metal and sulfur may be deposited on a layer having photovoltaic properties, said layer having photovoltaic properties forming the absorber of a thin-film solar cell.
- In this manner, the layer based on metal and sulfur can represent a buffer layer deposited on an absorber of a thin-film photovoltaic cell, to interface the absorber with a front electrical contact. The quality of the interface between the absorber of a photosensitive cell and the buffer layer is crucial to achieving high conversion efficiency in the resulting device. Applying the chemical deposition method described above to the deposition of a buffer layer on an absorber yields homogeneous layers, having half as many defects as buffer layers deposited in a bath containing no persulfate, deposited in less than 10 minutes and without damaging the absorber itself.
- Due to the quality of the buffer layer obtained by implementing the method, the resulting photovoltaic device can have a conversion efficiency exceeding 14%.
- It should be noted that using persulfate as an additive in a chemical bath for the deposition of a buffer layer on a photovoltaic cell absorber is counterintuitive. Persulfate, in particular ammonium persulfate, is generally used in industry as a cleaning and etching agent due to its highly oxidizing character. The applicant has noted that the addition of persulfate to a chemical bath as described above does not give the bath corrosive properties, which protects the surface on which the deposition takes place from chemical attack.
- The absorber may be based on a chalcopyrite compound among Cu(In,Ga)(S,Se)2, Cu2(Zn,Sn)(S,Se)4, and their derivatives.
- These compounds may include, for example, Cu(In,Ga)Se2, CuInSe2, CuInS2, CuGaSe2, Cu2(Zn,Sn)S4, and Cu2(Zn,Sn)Se4. When these absorbers contain zinc and tin, these compounds are sometimes called CZTS.
- The solar cell absorbers listed above correspond to absorbers of thin-film cells of CIGS and CZTS type and their derivatives having conversion efficiencies that can exceed 20%. Making use of the method described above for depositing a buffer layer on these absorbers is particularly advantageous given the performance gains this provides. For example, by thus depositing a buffer layer of ZnS, Zn(S,O), or Zn(S,O,OH) on an absorber based on a chalcopyrite compound, it is possible to obtain a conversion efficiency exceeding 14% and an open circuit voltage and short-circuit current of the end device that are greater than those observed in devices obtained by other deposition methods.
- The method of the invention will be better understood by reading the following description of some exemplary embodiments presented for illustrative purposes but in no way limiting, and from observing the following drawings in which:
-
FIG. 1 is a schematic representation of a sample that is to receive the deposition of a layer of metal and sulfur; and -
FIG. 2 is a schematic representation of the procedure for preparing a chemical bath; and -
FIG. 3 is a graph comparing the measured deposition times to obtain different layer thicknesses by three different processes; and -
FIG. 4 is a schematic representation of a photosensitive device; and -
FIG. 5 is a graph comparing the quantum efficiencies of two layers made of different materials, as a function of the wavelength received. - For the sake of clarity, the dimensions of the various elements represented in these figures are not necessarily in proportion to their actual dimensions. In the figures, identical references correspond to identical elements.
- The invention relates to an improved chemical deposition bath and an improved CBD deposition method. The improvement aims in particular to significantly increase the deposition rate. Other advantageous effects have also been obtained in the context of the invention, such as increased deposition quality for example.
- In the embodiments described below by way of example, the particular case of deposition by CBD of a buffer layer on a photovoltaic cell absorber will be described. However, the invention can also be applied to deposition on any other type of surface, as will be restated further below.
- In the context of depositing a thin layer comprising at least sulfur and a metal,
FIG. 1 illustrates an example of aninitial sample 100, comprising asubstrate 101, arear metal contact 102, and anabsorber layer 103. Theinitial sample 100 shown therefore represents an unfinished portion of a thin-film photosensitive device. As an example, theabsorber 103 intended to convert radiation into current may be a chalcopyrite compound such as one of the compounds among Cu(In,Ga)(S,Se)2, Cu2(Zn,Sn)(S,Se)4, and their derivatives. These derivatives may include, for example, - Cu(In,Ga)Se2, CuInSe2, CuInS2, CuGaSe2, Cu2(Zn,Sn)S4, or Cu2(Zn,Sn)Se4, more commonly called CIGS and CZTS.
- In order to complete the fabrication of this photosensitive device, the invention proposes a
chamber 200 for the chemical bath, schematically represented inFIG. 2 . As in most chemical baths for CBD deposition, thechamber 200 may be closed by acover 220. Thischamber 200 contains asolution 50 consisting of a mixture of reagents in the chosen concentrations. Thesample 100 rests in thissolution 50. Means for heating this reaction medium may be provided. InFIG. 2 , such a means is represented by awater bath 210 surrounding the chamber containing the reaction medium. Amotor 230 may also be used to drive a stirring mechanism that stirs thesolution 50.FIG. 2 also shows a summary of the steps for obtaining the solution forming thereaction mixture 50. - In the example illustrated in
FIG. 2 , the chemical bath is configured for deposition of a buffer layer of a photovoltaic device. For this reason, it is prepared from a first aqueous solution comprising ametal salt 10, represented as being zinc sulfate ZnSO4. A second aqueous solution comprising asulfur precursor 20 is also provided. This second solution is represented as being thiourea, of chemical formula CS(NH2)2.Ammonia 30, to give the reaction mixture a basic pH, may also be provided. A medium that is basic due to the presence of ammonia promotes the reaction of the precursor with the metal salt. Finally, a fourth aqueous solution comprising a persulfate-basedinorganic additive 40 is prepared. Thisfourth solution 40 is represented as comprising ammonium peroxydisulfate of chemical formula (NH4)2S2O8. - Alternatives to the first three solutions can be envisaged, as will be described below.
- These four
solutions reaction mixture 50. Thereaction mixture 50 is the solution into which thesample 100 is dipped. - Advantageously, the addition of peroxydisulfate significantly reduces the time required to achieve deposition of ZnS on the absorber. To illustrate the time saved, the graph of
FIG. 3 compares the rates of deposition of a thin layer by CBD, measured under three different conditions. - The deposited ZnS layer may include oxygen and form a layer of Zn(S,O) or Zn(S,O,OH) type. “ZnS layer” will be used hereinafter to refer to a layer of pure ZnS as well as to a layer of Zn(S,O) or Zn(S,O,OH).
-
Curve 301 shows the time required to deposit ZnS layers of different thicknesses, when thereaction mixture 50 is in a conventional configuration. “Conventional” is understood to mean a thiourea concentration of 0.65 mol/L, a ZnSO4 concentration of 0.15 mol/L, and an ammonia concentration of 2 mol/L. The reagents were all preheated to a temperature of 80° C. before being placed in a chamber brought to the same temperature of 80° C. -
Curve 302 represents the time required to deposit ZnS layers of different thicknesses, when thereaction mixture 50 comprises a laboratory-tested configuration corresponding to a particularly advantageous embodiment. It is characterized by a thiourea concentration of 0.4 mol/L, a ZnSO4 concentration of 0.1 mol/L, and an ammonia concentration of 2 mol/L. No preheating of the reagents is provided and the deposition temperature is 70° C. -
Curve 303 represents the time required to deposit ZnS layers of different thicknesses, when thereaction mixture 50 comprises the same characteristics as those associated withcurve 302, but with the addition of a concentration of 0.001 mol/L peroxydisulfate. Table 1 below summarizes the three configurations described above. -
TABLE 1 Summary of the three deposition configurations represented in FIG. 3 Thiourea ZnSO4 NH3 (NH4)2S2O8 Deposition ZnS layer (mol/L) (mol/L) (mol/L) (mol/L) T (° C.) Conventional 0.65 0.15 2 80 deposition With 0.4 0.1 2 0.001 70 additive Without 0.4 0.1 2 70 additive - It is apparent from the evolution of the three
curves FIG. 3 , that the addition of (NH4)2S2O8 in a chemical bath significantly increases the rate of deposition of a ZnS layer. In particular, to obtain alayer 20 nm thick, the bath optimized according to the invention divides the deposition time by 2.5 compared to conventional techniques, and by more than 5 compared to a deposition conducted under the same conditions without the additive. - In addition, it should be noted that the deposition conditions in the applicant's chemical bath are more efficient in materials saving and energy saving. This results from the lower concentrations of reagents, lower deposition temperature, and no preheating of the reagents.
- The example described above can advantageously result in the creation of a complete photovoltaic device as shown in
FIG. 4 . -
FIG. 4 schematically illustrates a thin-film solar cell comprising the same structural elements as those ofFIG. 1 . The representeddevice 400 further comprises abuffer layer 104 deposited on the absorber by CBD, as described above. Over the buffer layer 104 afirst window layer 105, for example of intrinsic zinc oxide or ZnMgO, can be deposited by known techniques such as reactive sputtering, chemical vapor deposition, electrodeposition, CBD deposition, or ILGAR® deposition. A frontelectrical contact 106 can then be deposited. For example, it may be a layer of aluminum-doped zinc oxide ZnO. - Other advantages inherent to using the chemical bath described above for depositing a buffer layer are reflected in the performance of the photovoltaic devices obtained.
- Table 2 compares technical characteristics of solar cells such as the solar cell of
FIG. 4 , comprising a chalcopyrite-type CIGS absorber. A first cell comprises a ZnS buffer layer obtained under conventional deposition conditions as described above in relation tocurve 301 ofFIG. 3 . A second cell comprises a ZnS buffer layer obtained by a CBD deposition process involving the bath of the invention, under conditions identical to those described in relation tocurve 303 ofFIG. 3 . A third cell comprises a CdS buffer layer obtained by CBD under conventional deposition conditions. -
TABLE 2 Performance comparison of three solar cells. Efficiency Form factor Voc Buffer layer (%) (%) (mV) Jsc (mA/cm2) ZnS 13.7 71.8 611 31.3 Conventional CBD Standard deviation +/−0.41 +/−1.9 +/−3.3 +/−0.52 ZnS 14.2 73.7 622 31.4 CBD with additive Standard deviation +/−0.18 +/−0.99 +/−1.5 +/−0.18 CdS 13.8 73.7 619 30.1 Conventional CBD Standard deviation +/−0.13 +/−0.36 +/−4.6 +/−0.15 - Each cell of Table 2 has a surface area of 5×5 cm2 and a
buffer layer 20 nm thick. - The columns in Table 2 represent four parameters for each of the three solar cells. The first column represents the conversion efficiency of the solar cell. The second column represents the form factor of each cell, providing an indication of the quality of the interface between buffer layer and absorber. The third column represents an open circuit voltage Voc. The higher this voltage, the better the electrical properties of the cell. The fourth column represents the short-circuit current Jsc. The higher this current, the better the electrical properties of the cell.
- For each cell of Table 2, and for each parameter, the standard deviation of the corresponding value is indicated. This information provides an estimate of the homogeneity of the cell. The more a parameter varies within the cell, the higher the associated standard deviation. Such instability is indicative of structural defects in the cell, and all the more so in the buffer layer which is the only layer presenting substantial differences between the three compared cells.
- It is apparent from the values of Table 2 that the cell having a ZnS buffer layer formed by the CBD deposition method developed in the context of the invention has a homogeneity that is superior to the other cells. In particular, it has a higher homogeneity than the cell having a ZnS layer formed by conventional CBD deposition.
- Moreover, the cell produced by the method of the invention has a conversion efficiency that is greater than that of the other cells, as well as improved electrical properties.
- The form factor of the cell obtained by the method of the invention is comparable to that of cells having a CdS buffer layer. Nevertheless, the overall homogeneity of the cell created by CBD deposition with the addition of persulfate is better. Therefore the deposition method with the addition of persulfate is well suited to the creation of photosensitive cells of large surface area, or more generally to the creation of layers comprising metal and sulfur in industrial settings.
- Observation by electron microscope has confirmed these observations concerning the structural quality of the deposition obtained by implementing the method of the invention.
- The chemical bath developed, and the method that uses it to create a buffer layer, allow obtaining under adapted deposition conditions a buffer layer of a non-toxic material, for example cadmium-free.
- The improved electrical and optical properties of the zinc sulfide and oxysulfide buffer layers were analyzed by calculating the quantum efficiency of the layer, in comparison to that of a CdS buffer layer.
-
FIG. 5 shows a graph comparing the quantum efficiency between 300 nm and 1100 nm of a ZnS buffer layer, represented bycurve 502, with that of a CdS buffer layer, represented bycurve 501. Quantum efficiency is a parameter that represents the ratio between the amount of electrons produced and the amount of photons received by the photosensitive device. - It is apparent in
FIG. 5 that a ZnS buffer layer allows better light conversion at wavelengths below 500 nm. This gain in current can be explained by a greater light transmission coefficient in ZnS at these wavelengths in comparison to CdS. This optical property is itself the result of the band structure of the material, which has a higher energy band gap than CdS. - The present invention is not limited to the embodiments described above by way of example; it also extends to other variants. Indeed, the bath described above and the method using this bath to produce a thin layer comprising metal and sulfur can be implemented in different configurations which all benefit from the gains in deposition rate and in quality of the obtained layer that are described above.
- The concentrations of the various components of the
reaction mixture 50 are therefore adjustable. For the sake of economy, it is preferable to reduce the concentration of reagents. However, reduced concentrations tend to increase the time required to produce a thin layer of a given thickness. The examples described above correspond to a compromise between concentration and reaction rate. It is possible to use other concentrations and other temperatures to meet different specifications. It may be of interest, for example, to adjust the concentrations and temperatures to deposit a thin layer of a given thickness within a fixed time constraint. Indeed, due to the generally increased deposition rate, it is possible to use CBD deposition with persulfate as an additive to achieve layers more than 150 nm thick within a reasonable time, for example under an hour. - By increasing the deposition rate, it is possible to have the reaction mixture at a low temperature. Compared to conventional deposition techniques which generally involve temperatures of around 70° C., the invention allows obtaining a deposit in less than 15 minutes even when the temperature is below 60° C., for example down to 40° C.
- The compromise between deposition rate and concentration of the reagents can be considered to be satisfactory for a concentration of metal salt between 0.01 mol/L and 1 mol/L, a concentration of sulfur precursor between 0.05 mol/L and 1 mol/L, a persulfate concentration between 10-5 mol/L and 1 mol/L, and an ammonia concentration between 0.1 mol/L and 10 mol/L.
- However, the bath and the method that uses it can be envisaged without the addition of ammonia. It is possible, for example, to substitute another compound of basic pH, or a compound of pKa greater than 7. The ammonia can be eliminated for example by using potassium hydroxide KOH with a citrate-type complexing agent. At a minimum, the reaction mixture of the chemical bath may contain only persulfate, sulfur precursor, and a metal salt. Beyond these basic components, the composition of the reaction mixture may differ from what is detailed above.
- In particular, it is possible to use other persulfate-based compounds such as sodium persulfate of chemical formula Na2S2O8 or potassium persulfate of chemical formula K2S2O8, with equivalent performance.
- The thiourea may also be replaced by other sulfur precursors, preferably having equivalent chemical properties. Aside from zinc sulfate, the metal salt may be replaced by zinc chloride or acetate for the same applications as those described above. The zinc acetate may be anhydrous or hydrated, for example of formula Zn[CH3COOH]2. An indium- or cadmium-based salt may also be suitable for the metal salt when creating buffer layers on photosensitive devices.
- Furthermore, as the deposition of a layer of sulfur and zinc occurs in an aqueous medium, oxygen may be incorporated into the deposited layers to form a zinc oxysulfide of Zn(S,O) or Zn(S,O,OH) type. Similarly, it is possible to incorporate oxygen into a layer comprising another metal element such as indium, to form an indium oxysulfide of Inx(S,O)y or Inx(S,O,OH)y type. Other elements of groups IIB and IIIA of the periodic table may also be considered for the metal, however, due to their chemical properties similar to those of zinc, indium, or cadmium.
- As mentioned above, it is possible to apply the method described above in contexts other than deposition of a buffer layer on a photosensitive cell absorber.
- Indeed, the invention has also been tested successfully on other deposition surfaces such as glass, a semiconductor substrate, and a metal.
- More generally, the invention described above optimizes a chemical bath for the deposition of a thin layer comprising sulfur and a metal. This optimization increases the deposition rate while improving the structural quality of the layer obtained, and saves materials and energy. In addition, the invention has the advantage of being compatible with existing chemical baths for CBD chemical deposition, and offers an advantageous solution for industrial scale CBD deposition on large surface areas.
Claims (14)
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FR1362537 | 2013-12-12 | ||
FR1362537A FR3014908B1 (en) | 2013-12-12 | 2013-12-12 | PERSULFATE BATH AND METHOD FOR CHEMICAL DEPOSITION OF A LAYER. |
PCT/FR2014/053248 WO2015086987A1 (en) | 2013-12-12 | 2014-12-09 | Persulfate bath and method for chemically depositing a layer |
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US20160312346A1 true US20160312346A1 (en) | 2016-10-27 |
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US15/103,628 Abandoned US20160312346A1 (en) | 2013-12-12 | 2014-12-09 | Persulfate bath and method for chemically depositing a layer |
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US (1) | US20160312346A1 (en) |
EP (1) | EP3080332B1 (en) |
JP (1) | JP6184602B2 (en) |
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JPH10273783A (en) * | 1997-03-31 | 1998-10-13 | Yazaki Corp | Production of chalcopyrite light absorption film |
DE102009015063A1 (en) * | 2009-03-26 | 2010-09-30 | Helmholtz-Zentrum Berlin Für Materialien Und Energie Gmbh | Method for applying a Zn (S, O) buffer layer to a semiconductor substrate by means of chemical bath deposition |
DE102010006499A1 (en) * | 2010-01-28 | 2011-08-18 | Würth Solar GmbH & Co. KG, 74523 | Bath separation solution for the wet-chemical deposition of a metal sulfide layer and associated production methods |
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JP2017503073A (en) | 2017-01-26 |
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