WO2012022476A1 - Chemical solutions for texturing microcrystalline silicon wafers for solar cell manufacturing - Google Patents
Chemical solutions for texturing microcrystalline silicon wafers for solar cell manufacturing Download PDFInfo
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- WO2012022476A1 WO2012022476A1 PCT/EP2011/004138 EP2011004138W WO2012022476A1 WO 2012022476 A1 WO2012022476 A1 WO 2012022476A1 EP 2011004138 W EP2011004138 W EP 2011004138W WO 2012022476 A1 WO2012022476 A1 WO 2012022476A1
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- acetic acid
- polyalkylene glycol
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 20
- 239000000126 substance Substances 0.000 title claims abstract description 10
- 235000012431 wafers Nutrition 0.000 title description 43
- 229910021424 microcrystalline silicon Inorganic materials 0.000 title 1
- 239000000203 mixture Substances 0.000 claims abstract description 85
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims abstract description 77
- 238000000034 method Methods 0.000 claims abstract description 36
- 239000002736 nonionic surfactant Substances 0.000 claims abstract description 22
- 229920001515 polyalkylene glycol Polymers 0.000 claims abstract description 20
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 19
- 229910021420 polycrystalline silicon Inorganic materials 0.000 claims abstract description 19
- 229910017604 nitric acid Inorganic materials 0.000 claims abstract description 18
- 229910001868 water Inorganic materials 0.000 claims abstract description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 11
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 10
- 229920000642 polymer Polymers 0.000 claims abstract description 10
- 238000002310 reflectometry Methods 0.000 claims abstract description 10
- 230000003247 decreasing effect Effects 0.000 claims abstract 3
- 239000004094 surface-active agent Substances 0.000 claims description 33
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims description 10
- 150000001298 alcohols Chemical class 0.000 claims description 10
- 150000002191 fatty alcohols Chemical class 0.000 claims description 5
- 239000010695 polyglycol Substances 0.000 claims description 5
- 229920000151 polyglycol Polymers 0.000 claims description 5
- 229960000583 acetic acid Drugs 0.000 description 15
- 238000009472 formulation Methods 0.000 description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 7
- 239000012362 glacial acetic acid Substances 0.000 description 7
- 229910052710 silicon Inorganic materials 0.000 description 7
- 239000010703 silicon Substances 0.000 description 7
- 230000007547 defect Effects 0.000 description 4
- 229910021419 crystalline silicon Inorganic materials 0.000 description 3
- 238000005530 etching Methods 0.000 description 3
- 229910021421 monocrystalline silicon Inorganic materials 0.000 description 3
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000005187 foaming Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000006798 recombination Effects 0.000 description 2
- 238000005215 recombination Methods 0.000 description 2
- 239000002253 acid Substances 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- -1 alkyl diphenyl oxide Chemical compound 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000002800 charge carrier Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000010587 phase diagram Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K13/00—Etching, surface-brightening or pickling compositions
- C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
- C09K13/08—Etching, surface-brightening or pickling compositions containing an inorganic acid containing a fluorine compound
-
- 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
- H01L31/02—Details
- H01L31/0236—Special surface textures
- H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
-
- 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
Definitions
- This invention relates to a process of employing a chemical solutions for texturing multicrystalline silicon wafers for use in manufacturing solar cells and to the chemical compositions for texturing multicrystalline silicon wafers for use in manufacturing solar cells and to.
- renewable energy sources are considered to be green or clean energy sources having a much lower environmental impact than conventional fossil based energy sources.
- solar energy is the most abundant energy resource on earth.
- PV photovoltaic
- PV is commercially available and a reliable technology with a significant potential for long-term growth in nearly all world regions.
- the most used material for the manufacturing of solar cells is crystalline silicon.
- Multi- crystalline silicon is most commonly used in the photovoltaic industry, due to the lower material costs.
- the different grain orientations in multicrystalline silicon wafers make the effective bulk lifetime of the minority charge carriers lower than for mono-crystalline silicon wafers.
- anisotropic alkaline texturing techniques to texturize monocrystalline silicon wafers are largely ineffective on multi-crystalline wafers due to the different crystal grain orientations of the grains. Therefore, an isotropic acidic etch is most frequently used in the texturization of multi-crystalline silicon wafers.
- the invention comprises a process for chemically texturing multicrystalline silicon wafers for use in manufacturing solar cells and to chemical compositions for accomplishing said texturization.
- the texturizing composition used in the process of the invention comprises, consists essentially of, or consists of a HF/HNO 3 mixture, water, acetic acid, and at least one nonionic surfactant having a molecular weight of from about 200 g/mol to about 10,000 g/mol and being selected from polyalkylene glycols or alkoxylated, preferably ethoxylated or propoxylated, alcohol polymers.
- the process of this invention comprises contacting the multicrystalline silicon wafers to be used in solar cell manufacturing with the texturizing composition of this invention for a time and at a temperature sufficient to accomplish the desired texturization of the silicon wafer surface.
- a composition of this invention and its use for texturing multicrystalline silicon wafers for use in manufacturing solar cells comprises, consists essentially of, or consists of a HF/HNO3 mixture, water, acetic acid, and at least one nonionic surfactant having a molecular weight of from about 200 g/mol to about 10,000 g/mol, preferably from about 200 g/mol to about 6000 g/mol, and more preferably from about 400 g/mol to about 4000 g/mol and being selected from polyalkylene glycols or alkoxylated, preferably ethoxylated or propoxylated, alcohol polymers.
- the surfactant component is pre-mixed with acetic acid before being combined with the other components of the composition to improve the dissolution of the surfactant in the HF/HNO3.
- the acetic acid is glacial acetic acid.
- the concentration of HNO3/HF acids in the texturizing compositions of this invention is different than that of the afore-mentioned prior art UKON process, as the addition of acetic acid and surfactants changes the phase diagram of the etching reaction.
- the HF/ HNO3 ratio (v/v%) for the composition of this invention should be between about 20:1 to about 40:1, preferably from about 25:1 to 35: 1, and more preferably from about 26:1 to 33:1.
- nonionic surfactants include, but are not limited to, TergitolTM L81E- an alcohol alkoxylate polymer of MW about 2750, TergitolTM L61E- a polyalkylene glycol of MW about 2000, TergitolTM L62E- a polyalkylene glycol of MW about 2500, TergitolTM L64E a polyalkylene glycol of MW about 2700, TritonTM DF-16- C 8 -Ci 0 alcohols alkoxylated of MW about 570, TritonTM DF-12 a modified polyethoxylated alcohol of MW 570, and DehyponTM O 054-a modified fatty alcohol polyglycol ether, and mixtures thereof.
- the nonionic surfactant component be low foaming.
- the amount of the surfactant component employed in the texturizing composition of this invention will be dependent upon the particular nonionic surfactant employed and the particular ratio of HF/HNO3 components employed in the composition.
- the amount of surfactant component will generally be from about 0.5 to about 10 wt%, preferably from about 1 to about 5 wt%, and still more preferably from about 1 to about 4 wt% based on the total weight of the texturizing composition.
- the non-ionic surfactant employed in the compositions of this invention can be mixed with the acetic acid component before it is mixed with the other components of the composition.
- the weight ratio of surfactant/ acetic acid employed will vary with the particular surfactant employed but will generally be in the range of from about 1 :2 to about 1 : 15, preferably from about 1 :3 to about 1 :10, and more preferably from about 1 :3 to about 1 :7
- the volume ratio of the combined surfactant+acetic acid components mixture to the remainder of the components of the composition (HF+HN0 3 +water) wall generally be from about 1 :8 to about 1 : 13, preferably from about 1 :9.8 to 1 : 13, and more preferably 1 :9.8 to 1 : 1 1.4.
- the amount of water added to the components of the texturizing composition of this invention will generally be from about 0 wt% to about 5 wt%, preferably from about 2 wt% to about 4 wt%, and more preferably from about 3 wt% to about 4 wt%, based on the total weight of the composition.
- the amount of water employed will be such that the weight ratio of water to combined HF7HN0 3 components (based on weight) will be from about 1 :45, preferably from about 1 : 40, and more preferably about 1 :30.
- the wafer is brought into contact with the texturizing composition of this invention in any suitable manner, generally by dipping the wafers in a bath of the texturizing composition.
- the wafers are contacted with the texturizing composition of this invention for a time and at a temperature to effect the texturization of the wafer surface.
- the process is generally conducted at a temperature of from about 2 °C to about 55 °C, more preferably at about from about 12 °C to about 21 °C, generally at room temperature, for a period of up to about 5 minutes, preferably for about 1 to 2 minutes, and more preferably about 1 minute.
- the aforementioned prior art UKON process is conducted at 4-15 °C, requiring massive amounts of cooling.
- nonionic surfactants of this invention also decreases etch defects leading, in principle, to higher wafer yields and less charge recombination on the wafer surface. This can be observed by simple optical inspection of the textured wafers for black etch pits on the wafers. As wafers get thinner and thinner, as has been the industry trend, preventing the formation of such etch pits becomes more crucial as such etch pits means more wafer breakage and lower production line yields.
- Inventive formulation 72.8 g of glacial acetic acid was mixed with 2.0 wt% Tergitol L61 surfactant component, wherein the weight of the surfactant is based on the total weight of the texturizing composition, and then the pre-mixed surfactant/ glacial acetic acid mixture was added to a formulation of 984 g 49% HF, 37.4 g 65% HN0 3 , and 32.2 g H 2 0.
- Comparative formulation 72.8 g of glacial acetic acid was mixed with 1.7 wt% TergitolTM L61 surfactant component, wherein the weight of the surfactant is based on the total weight of the texturizing composition, and then the pre-mixed surfactant/glacial acetic acid mixture was added to a formulation of 146.4 g 49% HF, and 1126.3 g 65% HN0 3 .
- Boron doped multicrystalline silicon wafers for use in manufacturing solar cells were dipped in each of the above texturizing compositions for about 1 minute at room temperature and the reflectance of the texturized wafer was determined with a refiectometer at 700 nm. The percentages of reflectivity were as follows where an untreated wafer was set at 100% reflectivity.
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Abstract
A process for chemical texturing a surface of a multicrystalline silicon wafer to be used in the manufacture of solar cells, the process by contacting the surface of said multicrystalline silicon wafer with a composition for a time and at a temperature sufficient to texturized the wafer surface for decreasing the reflectivity of the surface. The composition used for the textunzation is one of a HF/HNO3 mixture, water, acetic acid and at least one nonionic surfactant having a molecular weight of from about 200 g/mol to about 10000 g/mol and being selected from the group consisting of polyalkylene glycols and alkoxylated alcohol polymers.
Description
CHEMICAL SOLUTIONS FOR TEXTURING MULTICRYSTALLINE
SILICON WAFERS FOR SOLAR CELL MANUFACTURING
FIELD OF THE INVENTION
[0001] This invention relates to a process of employing a chemical solutions for texturing multicrystalline silicon wafers for use in manufacturing solar cells and to the chemical compositions for texturing multicrystalline silicon wafers for use in manufacturing solar cells and to.
BACKGROUND TO THE INVENTION
[0002] Renewable energy sources are considered to be green or clean energy sources having a much lower environmental impact than conventional fossil based energy sources. Out of several renewable energy resources, solar energy is the most abundant energy resource on earth. Currently, photovoltaic (PV) provides 0.1% of the total electricity generation however, due to dramatic cost reductions, PV is expanding very rapidly. In addition, PV is commercially available and a reliable technology with a significant potential for long-term growth in nearly all world regions. Currently, the most used material for the manufacturing of solar cells is crystalline silicon.
[0003]. Optical losses due to the reflectance of incident solar radiation is one of the most significant factors that limit solar cell efficiency. Therefore, lowering the surface reflection of silicon wafers by texturization is one of the main processes to improve a solar cell's efficiency Increased light absorption from a better-textured silicon surface will result in higher currents from the cell, which can result in up to several tenths of a percent higher efficiency. Consequently, texturing remains one of the key issues in the industrial fabrication of crystalline silicon solar cells, and suitable texturing methods that result in optimal cell performance are still being developed.
[0004] Currently, there are two main types of crystalline silicon that can be used for the manufacturing of solar cells, being mono-crystalline and multi-crystalline silicon. Multi- crystalline silicon is most commonly used in the photovoltaic industry, due to the lower material costs. However, the different grain orientations in multicrystalline silicon wafers, make the effective bulk lifetime of the minority charge carriers lower than for mono-crystalline silicon wafers. Furthermore, anisotropic alkaline texturing techniques to texturize monocrystalline silicon wafers, are largely ineffective on multi-crystalline wafers due to the different crystal grain orientations of the grains. Therefore, an isotropic acidic etch is most
frequently used in the texturization of multi-crystalline silicon wafers.
[0005] One of the commonly employed methods for texturing multicrystalline wafers is an acidic process known as the UKON etch, developed by the University of Konstanz, which consists of an HF/HNO3/H2O mixture. In this process, HN03 oxidizes the silicon surface and HF strips the oxide. This texturing solution, albeit very simple, results in significant defect etching and has high usage of the two acids. Many defects on the wafer surface can result in undesired charge recombination and the wafer becomes more brittle and breaks more easily, so that the average yield of the process decreases. .
[0006] Recently, several alternatives were reported that aim to reduce defect etching and increase production yield. This is achieved by adding a surfactant, such as in a proprietary process know as the ECN isotex process. Known problems associated with these additives is that they show a high degree of foaming causing a stable HF/HNO3 foam forcing line shutdowns and limiting throughput and, additionally, the surfactant sticks to the silicon wafer, contaminating it and necessitating further cleaning.
[0007] There is therefore a need for improved chemical texturization process for improved texturing of multicrystalline silicon wafers used in the manufacturing of solar cells in the photovoltaic industry and for suitable chemical compositions for accomplishing the texturization process that does not suffer from the problems associated with the prior art surfactants.
SUMMARY OF THE INVENTION
[0008] The invention comprises a process for chemically texturing multicrystalline silicon wafers for use in manufacturing solar cells and to chemical compositions for accomplishing said texturization. The texturizing composition used in the process of the invention comprises, consists essentially of, or consists of a HF/HNO3 mixture, water, acetic acid, and at least one nonionic surfactant having a molecular weight of from about 200 g/mol to about 10,000 g/mol and being selected from polyalkylene glycols or alkoxylated, preferably ethoxylated or propoxylated, alcohol polymers. The process of this invention comprises contacting the multicrystalline silicon wafers to be used in solar cell manufacturing with the texturizing composition of this invention for a time and at a temperature sufficient to accomplish the desired texturization of the silicon wafer surface.
DETAILED DESCRIPTION OF THE INVENTION
[0009] A composition of this invention and its use for texturing multicrystalline silicon wafers
for use in manufacturing solar cells comprises, consists essentially of, or consists of a HF/HNO3 mixture, water, acetic acid, and at least one nonionic surfactant having a molecular weight of from about 200 g/mol to about 10,000 g/mol, preferably from about 200 g/mol to about 6000 g/mol, and more preferably from about 400 g/mol to about 4000 g/mol and being selected from polyalkylene glycols or alkoxylated, preferably ethoxylated or propoxylated, alcohol polymers. In a preferred embodiment of the invention the surfactant component is pre-mixed with acetic acid before being combined with the other components of the composition to improve the dissolution of the surfactant in the HF/HNO3. In another embodiment the acetic acid is glacial acetic acid. The process of this invention comprises contacting the multicrystalline silicon wafers to be used in solar cell manufacturing with the texturizing composition of this invention for a time and at a temperature sufficient to accomplish the desired texturization of the silicon wafer surface.
[0010] The concentration of HNO3/HF acids in the texturizing compositions of this invention is different than that of the afore-mentioned prior art UKON process, as the addition of acetic acid and surfactants changes the phase diagram of the etching reaction. The HF/ HNO3 ratio (v/v%) for the composition of this invention should be between about 20:1 to about 40:1, preferably from about 25:1 to 35: 1, and more preferably from about 26:1 to 33:1.
[0011] Examples of such suitable nonionic surfactants include, but are not limited to, Tergitol™ L81E- an alcohol alkoxylate polymer of MW about 2750, Tergitol™ L61E- a polyalkylene glycol of MW about 2000, Tergitol™ L62E- a polyalkylene glycol of MW about 2500, Tergitol™ L64E a polyalkylene glycol of MW about 2700, Triton™ DF-16- C8-Ci0 alcohols alkoxylated of MW about 570, Triton™ DF-12 a modified polyethoxylated alcohol of MW 570, and Dehypon™ O 054-a modified fatty alcohol polyglycol ether, and mixtures thereof. It is desired that the nonionic surfactant component be low foaming. The amount of the surfactant component employed in the texturizing composition of this invention will be dependent upon the particular nonionic surfactant employed and the particular ratio of HF/HNO3 components employed in the composition. The amount of surfactant component will generally be from about 0.5 to about 10 wt%, preferably from about 1 to about 5 wt%, and still more preferably from about 1 to about 4 wt% based on the total weight of the texturizing composition.
[0012] The non-ionic surfactant employed in the compositions of this invention can be mixed with the acetic acid component before it is mixed with the other components of the composition. The weight ratio of surfactant/ acetic acid employed will vary with the particular surfactant employed but will generally be in the range of from about 1 :2 to about 1 : 15, preferably from
about 1 :3 to about 1 :10, and more preferably from about 1 :3 to about 1 :7
[0013] The volume ratio of the combined surfactant+acetic acid components mixture to the remainder of the components of the composition (HF+HN03+water) wall generally be from about 1 :8 to about 1 : 13, preferably from about 1 :9.8 to 1 : 13, and more preferably 1 :9.8 to 1 : 1 1.4.
[0014] The amount of water added to the components of the texturizing composition of this invention will generally be from about 0 wt% to about 5 wt%, preferably from about 2 wt% to about 4 wt%, and more preferably from about 3 wt% to about 4 wt%, based on the total weight of the composition. In general the amount of water employed will be such that the weight ratio of water to combined HF7HN03 components (based on weight) will be from about 1 :45, preferably from about 1 : 40, and more preferably about 1 :30.
[0015] For texturizing the surface of the multicrystalline silicon wafer to be used in the manufacture of solar cells the wafer is brought into contact with the texturizing composition of this invention in any suitable manner, generally by dipping the wafers in a bath of the texturizing composition. The wafers are contacted with the texturizing composition of this invention for a time and at a temperature to effect the texturization of the wafer surface. The process is generally conducted at a temperature of from about 2 °C to about 55 °C, more preferably at about from about 12 °C to about 21 °C, generally at room temperature, for a period of up to about 5 minutes, preferably for about 1 to 2 minutes, and more preferably about 1 minute. In contrast the aforementioned prior art UKON process is conducted at 4-15 °C, requiring massive amounts of cooling.
[0016] As examples of texturizing compositions of this invention there may be mentioned the following non-limiting examples. 69.3 mL (72.8 g) of glacial acetic acid was mixed with each of the following surfactant components, wherein the weight of the surfactant is based on the total weight of the texturizing composition, and then the pre-mixed surfactant/ glacial acetic acid mixture was added to a formulation of 848.6 mL (984 g) 49% HF, 26.7 mL (37.4 g) 65% HN03, and 32.2 ml (32.2 g) H20.
E Tergitol™ L61 2.3
F Tergitol™-L62 2.3
G Dehypon™ 0 054 0.1
Tergitol™ L64 0.9
H Tergitol™ L64 0.5
Triton™ DF-16 0.5
I Tergitol™ L64 0.5
Tergitol™ L81 0.5
J Dehypon™ 0 054 0.1
Tergitol™ L 81 0.4
K Tergitol™ L81 0.5
Triton™ DF-16 0.5
L Dehypon™ 0 054 0.1
Triton™ DF-16 0.9
[0017] Boron doped multicrystalline silicon wafers for use in manufacturing solar cells were dipped in each of the above texturizing compositions for about 1 minute at room temperature and the reflectance of the texturized wafer was determined with a reflectometer at 700 nm. Compared to an untreated wafer standard (reflectance set at 100%) the textured wafers produced wafers with the following lowered reflectance. Such lowered reflectivity of the wafers results in an increase in short circuit current of the resulting solar cell.
E 70.50
F 73.87
G 66.91
H 51.78
I 78.98
J 71.94
K 67.16
L 61.16
[0018] The use of the nonionic surfactants of this invention also decreases etch defects leading, in principle, to higher wafer yields and less charge recombination on the wafer surface. This can be observed by simple optical inspection of the textured wafers for black etch pits on the wafers. As wafers get thinner and thinner, as has been the industry trend, preventing the formation of such etch pits becomes more crucial as such etch pits means more wafer breakage and lower production line yields.
[0019] When the proprietary composition of the afore-mentioned ECN isotex process was substituted for the nonionic surfactant containing composition of the present invention in the above described texturization process the resulting percentage reflectivity was 86.65.
[0020] When 2.3 wt% Dowfax™ 2A1, an alkyl diphenyl oxide surfactant, was substituted for the nonionic surfactants of the present invention in similar compositions the resulting percentage reflectivity was 85.88.
[0021] As stated previously it is necessary to have a high ratio of HF/HN03 in favor of HF for the purposes of obtaining the desired texturization of this invention. When the ratio of HF/HNO3 is changed to favor a ratio high in HNO3 one is unable to obtain a reflectivity below 80 percent and the resulting wafers are significantly more polished in nature than wafers processed according to this invention. For example when the high HF/HNO3 ratio formulation of this invention was compared to a similar formulation but wherein there was a high HNO3/HF ratio, as shown in the following comparison, the percentages reflectivity obtained were as set forth in the following table. The formulations comprised the following.
Inventive formulation: 72.8 g of glacial acetic acid was mixed with 2.0 wt% Tergitol L61 surfactant component, wherein the weight of the surfactant is based on the total weight of the texturizing composition, and then the pre-mixed surfactant/ glacial acetic acid mixture was added to a formulation of 984 g 49% HF, 37.4 g 65% HN03, and 32.2 g H20.
Comparative formulation: 72.8 g of glacial acetic acid was mixed with 1.7 wt% Tergitol™ L61 surfactant component, wherein the weight of the surfactant is based on the total weight of the texturizing composition, and then the pre-mixed surfactant/glacial acetic acid mixture was added to a formulation of 146.4 g 49% HF, and 1126.3 g 65% HN03.
Boron doped multicrystalline silicon wafers for use in manufacturing solar cells were dipped in each of the above texturizing compositions for about 1 minute at room temperature and the reflectance of the texturized wafer was determined with a refiectometer at 700 nm. The percentages of reflectivity were as follows where an untreated wafer was set at 100% reflectivity.
[0022] While the invention has been described herein with reference to the specific embodiments thereof, it will be appreciated that changes, modification and variations can be made without departing from the spirit and scope of the inventive concept disclosed herein. Accordingly, it is intended to embrace all such changes, modification and variations that fall with the spirit and scope of the appended claims.
Claims
A process for chemical texturing a surface of a multicrystalline silicon wafer to be used in the manufacture of solar cells, the process comprising contacting the surface of said multicrystalline silicon wafer with a composition for a time and at a temperature sufficient to texturize the wafer surface for decreasing the reflectivity of the surface, said composition comprising a HF/HNO3 mixture, water, acetic acid and at least one nonionic surfactant having a molecular weight of from about 200 g/mol to about 10000 g/mol and being selected from the group consisting of polyalkylene glycols and alkoxylated alcohol polymers.
A process according to claim 1 wherein the surface of the wafer is contacted with the composition at a temperature of about 2° C to about 55° C for a period of up to about 5 minutes.
The process according to claim 2 wherein the surface of the wafer is contacted with the composition at room temperature for a period of about 1 minute.
A process according to claim 1 wherein the at least one nonionic surfactant is a surfactant having a molecular weight of from about 400 g/mol to about 4000 g/mol.
A process according to claim 1 wherein the surfactant component is pre-mixed with acetic acid before being combined with the other components of the composition.
A process according to claim 1 wherein the nonionic surfactant has been mixed with the acetic acid in a weight ratio of acetic acid/surfactant of from about 1 :3 to about 1 :69.
A process according to claim 1 wherein the v/v% ratio of HF to HNO3 in the composition is from about 20:1 to about 40:1.
A process according to claim 1 wherein the v/v% ratio of HF to HNO3 in the
composition is from about 26:1 to about 33:1.
9 . A process according to any one of claims 1 to 8 wherein the amount of surfactant is from about 0.5 to 10 wt % based on the total weight of the composition.
10. A process according to any one of claims 1 to 9 wherein the non-ionic surfactant is selected from the group consisting of an alcohol alkoxylate polymer of MW about 2750, a polyalkylene glycol of MW about 2000, a polyalkylene glycol of MW about 2500, a polyalkylene glycol of MW about 2700, a C8-C10 alcohols alkoxylated of MW about 570, a modified polyethoxylated alcohol of MW about 570, a modified fatty alcohol polyglycol ether, and mixtures thereof.
11. A process according to claim 1 wherein v/v% ratio of HF to HN03 in the composition is from about 26:1 to about 33:1; the amount of surfactant is from about 1 to 5 % based on the total weight of the composition, the non-ionic surfactant is selected from the group consisting of an alcohol alkoxylate polymer of MW about 2750, a polyalkylene glycol of MW about 2000, a polyalkylene glycol of MW about 2500, a polyalkylene glycol of MW about 2700, a C8-Ci0 alcohols alkoxylated of MW about 570, a modified polyethoxylated alcohol of MW about 570, a modified fatty alcohol polyglycol ether, and mixtures thereof; the nonionic surfactant has been premixed with the acetic acid in a weight ratio of acetic acid/surfactant of from about 1 :3 to about 1 :10 before being mixed with the other components of the composition, and the amount of water is from about 1 to about 4% based on the total weight of the composition.
12. A process according to any one of claims 1 to 11 wherein the texturization of the wafer results in a decreased reflectivity of the wafer such that when employed in a solar cell the short circuit current increases compared to an untexturized wafer.
13. A composition for chemical texturing a surface of a multi crystalline silicon wafer to be used in the manufacture of solar cells, said composition comprising a HF/HNO3 mixture, water, acetic acid and at least one nonionic surfactant having a molecular weight of from about 200 g/mol to about 10000 g/mol and being selected from the group consisting of polyalkylene glycols and alkoxylated alcohol polymers.
14. A composition according to claim 13 wherein the at least one nonionic surfactant is a surfactant having a molecular weight of from about 400 g/mol to about 4000 g/mol.
15. A composition according to claim 13 wherein the surfactant component is pre-mixed with acetic acid before being combined with the other components of the composition.
16. A composition according to claim 15 wherein the nonionic surfactant has been mixed with the acetic acid in a weight ratio of acetic acid/surfactant of from about 1:3 to about 1 :69.
17. A composition according to claim 13 wherein the v/v% ratio of HF to HNO3 in the composition is from about 20:1 to about 40:1.
18. A composition according to claim 13 wherein the v/v% ratio of HF to FFN03 in the composition is from about 26:1 to about 33:1.
19. A composition according to any one of claims 13 to 18 wherein the amount of surfactant is from about 0.5 to 10 wt % based on the total weight of the composition.
20. A composition according to any one of claims 13 to 19 wherein the non-ionic surfactant is selected from the group consisting of an alcohol alkoxylate polymer of MW about 2750, a polyalkylene glycol of MW about 2000, a polyalkylene glycol of MW about 2500, a polyalkylene glycol of MW about 2700, a C8-C10 alcohols alkoxylated of MW about 570, a modified polyethoxylated alcohol of MW about 570, a modified fatty alcohol polyglycol ether, and mixtures thereof.
21. A composition according to claim 13 wherein v/v% ratio of HF to HNO3 in the composition is from about 26:1 to about 33:1; the amount of surfactant is from about 1 to 5 % based on the total weight of the composition, the non-ionic surfactant is selected from the group consisting of an alcohol alkoxylate polymer of MW about 2750, a polyalkylene glycol of MW about 2000, a polyalkylene glycol of MW about 2500, a polyalkylene glycol of MW about 2700, a Cg-C10 alcohols alkoxylated of MW about 570,
a modified polyethoxylated alcohol of MW about 570, a modified fatty alcohol polyglycol ether, and mixtures thereof; the nonionic surfactant has been premixed with the acetic acid in a weight ratio of acetic acid/surfactant of from about 1 :3 to about 1 :10 before being mixed with the other components of the composition, and the amount of water is from about 1 to about 4% based on the total weight of the composition.
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|---|---|---|---|---|
| CN104073883A (en) * | 2014-06-11 | 2014-10-01 | 邬时伟 | Texturing process for polycrystalline silicon solar cell slice |
| CN112813501A (en) * | 2020-12-29 | 2021-05-18 | 广东省科学院化工研究所 | Monocrystalline silicon piece texturing additive and application thereof |
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| WO2015038340A1 (en) * | 2013-09-10 | 2015-03-19 | Bandgap Engineering, Inc. | Metal assisted etch combined with regularizing etch |
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| JP2004063744A (en) * | 2002-07-29 | 2004-02-26 | Shinryo Corp | Etching method of silicon substrate |
| US20070151944A1 (en) * | 2004-12-31 | 2007-07-05 | Industrial Technology Research Institute | Method for making solar cell |
| KR20090007127A (en) * | 2007-07-13 | 2009-01-16 | 주식회사 케이피이 | Method of manufacture of tri-crystalline si solar cell with surfactant and acid texture |
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| JP2004063744A (en) * | 2002-07-29 | 2004-02-26 | Shinryo Corp | Etching method of silicon substrate |
| US20070151944A1 (en) * | 2004-12-31 | 2007-07-05 | Industrial Technology Research Institute | Method for making solar cell |
| KR20090007127A (en) * | 2007-07-13 | 2009-01-16 | 주식회사 케이피이 | Method of manufacture of tri-crystalline si solar cell with surfactant and acid texture |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104073883A (en) * | 2014-06-11 | 2014-10-01 | 邬时伟 | Texturing process for polycrystalline silicon solar cell slice |
| CN112813501A (en) * | 2020-12-29 | 2021-05-18 | 广东省科学院化工研究所 | Monocrystalline silicon piece texturing additive and application thereof |
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| TWI558791B (en) | 2016-11-21 |
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