CA2616405A1 - Crystalline si solar cells made from upgraded metallurgical silicon - Google Patents
Crystalline si solar cells made from upgraded metallurgical silicon Download PDFInfo
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- CA2616405A1 CA2616405A1 CA002616405A CA2616405A CA2616405A1 CA 2616405 A1 CA2616405 A1 CA 2616405A1 CA 002616405 A CA002616405 A CA 002616405A CA 2616405 A CA2616405 A CA 2616405A CA 2616405 A1 CA2616405 A1 CA 2616405A1
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- phosphorus
- ppma
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- 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
- Y02E10/547—Monocrystalline silicon PV cells
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Description
CRYSTALLINE SI SOLAR CELLS MADE FROM UPGRADED
METALLURGICAL SILICON
BACKGROUND OF THE INVENTION
The shortage of available polysilicon for the production of ingots, wafers and solar cells has resulted in the last two years in the development of upgraded metallurgical silicon (UMG-Si). The lower production cost and energy usage of UMG-Si, lower capital requirements and shorter time to completion are major advantages compared to polysilicon. However, UMG-Si contains impurities, in particular boron and phosphorous, that lower efficiency and yield if not compensated. This invention describes how to compensate UMG-Si (silicon containing both boron and phosphorus ) with dopants to increase the yield in the production of ingots.
SUMMARY OF THE INVENTION
The invention describes how to adjust boron and phosphorus concentration in feedstock made of upgraded metallurgical silicon to get the largest amount of p-type silicon in the 0.5 0-cm (ohm-cm) to 3 SZ-cm resistivity range. This can be achieved by diluting UMG-Si with poly-silicon and/or by adding p-type dopant to the UMG-Si.
Upgraded metallurgical silicon (UMG-Si) is silicon obtained from the direct purification of metallurgical silicon to a high purity level (generally >99.99 %Si).
UMG-Si contains boron and phosphorus, two chemical elements that are generally used in the doping of silicon to make solar cells.
Boron and phosphorus level in UMG-Si:
0.1 ppmw < Boron (ppmw) < 3 ppmw 0.1 ppmw < Phosphorus (ppmw) < 10 ppmw
METALLURGICAL SILICON
BACKGROUND OF THE INVENTION
The shortage of available polysilicon for the production of ingots, wafers and solar cells has resulted in the last two years in the development of upgraded metallurgical silicon (UMG-Si). The lower production cost and energy usage of UMG-Si, lower capital requirements and shorter time to completion are major advantages compared to polysilicon. However, UMG-Si contains impurities, in particular boron and phosphorous, that lower efficiency and yield if not compensated. This invention describes how to compensate UMG-Si (silicon containing both boron and phosphorus ) with dopants to increase the yield in the production of ingots.
SUMMARY OF THE INVENTION
The invention describes how to adjust boron and phosphorus concentration in feedstock made of upgraded metallurgical silicon to get the largest amount of p-type silicon in the 0.5 0-cm (ohm-cm) to 3 SZ-cm resistivity range. This can be achieved by diluting UMG-Si with poly-silicon and/or by adding p-type dopant to the UMG-Si.
Upgraded metallurgical silicon (UMG-Si) is silicon obtained from the direct purification of metallurgical silicon to a high purity level (generally >99.99 %Si).
UMG-Si contains boron and phosphorus, two chemical elements that are generally used in the doping of silicon to make solar cells.
Boron and phosphorus level in UMG-Si:
0.1 ppmw < Boron (ppmw) < 3 ppmw 0.1 ppmw < Phosphorus (ppmw) < 10 ppmw
2 Conversion of ppmw to ppma Definition:
ppma: part(s) per million atomic ppmw: part(s) per million by weight 28.0855 [Pl ppma -[P]ppmw x 30.97376 = [P]ppmw x 0.91 [B]ppma = [B]ppmw x 28.0855 10.811 - [B]ppmw x 2.60 Dopant concentration in polysilicon ingot (Scheil's equation) C, =k=Ca -(1- fy.~k 1 where:
CS: Concentration of the solute in the solid;
Co: Initial concentration of the solute in the liquid;
k: Distribution coefficient;
f: Solid fraction.
Phosphorus Boron kP = 0.35 kB = 0.80 [P]ppma,s = 0.35 = [P]ppma,o . (I - f ~0.35-1 [B]ppma,s = 0.80. [B]ppma,a . (1-f )0.80-1 s r Proportion of p-type silicon in the polysilicon ingot Condition: [P]ppma,s = [B]ppma,s (p-n junction) [I']ppmw - 30.974 0.80 = (1- fs) 0.80-1 [B]ppmw 10.811 0.35 = (1- 0. fs)o.35-1 Quantity of p-type [P]/[8] ratio % of the in ot mw/ mw 0 6.55 80 3.17 90 2.32 95 1.70 99 0.82
ppma: part(s) per million atomic ppmw: part(s) per million by weight 28.0855 [Pl ppma -[P]ppmw x 30.97376 = [P]ppmw x 0.91 [B]ppma = [B]ppmw x 28.0855 10.811 - [B]ppmw x 2.60 Dopant concentration in polysilicon ingot (Scheil's equation) C, =k=Ca -(1- fy.~k 1 where:
CS: Concentration of the solute in the solid;
Co: Initial concentration of the solute in the liquid;
k: Distribution coefficient;
f: Solid fraction.
Phosphorus Boron kP = 0.35 kB = 0.80 [P]ppma,s = 0.35 = [P]ppma,o . (I - f ~0.35-1 [B]ppma,s = 0.80. [B]ppma,a . (1-f )0.80-1 s r Proportion of p-type silicon in the polysilicon ingot Condition: [P]ppma,s = [B]ppma,s (p-n junction) [I']ppmw - 30.974 0.80 = (1- fs) 0.80-1 [B]ppmw 10.811 0.35 = (1- 0. fs)o.35-1 Quantity of p-type [P]/[8] ratio % of the in ot mw/ mw 0 6.55 80 3.17 90 2.32 95 1.70 99 0.82
3 Dopant concentrations in usable compensated of p-type silicon Resistivity criteria : 0.5 0=cm to 30=cm NCC (Net current carrier) NCC = [B]ppma,.r - [P]pp,na,s To obtain 0.5 Q=cm min., NCC <_ 3.3 x 1016a1cm3 To obtain 30=cm max., NCC>_4.6x1015a1cm3 16 a lcm3 28.0855g NCC _ 3.3 x 10 3 13 = 1000000 = 0.66 ppma cm 2.33g 6.02 x 10 a a lcm3 28.0855g NCC _ 4.6 x 10 3 23 = 1000000 = 0.09 ppma cm 2.33g 6.02 x 10 a 15 10.09ppma ? NCC >_ 0.66ppma From these calculations, we are able to see that the more interesting range of boron and phosphorus to make solar cells is:
0.1 ppmw < Boron (ppmw) < 1 ppmw 0.1 ppmw < Phosphorus (ppmw) < 2.5 ppmw The complete results are shown in Graph 2. So, starting with a known level in boron and phosphorus, we can adjust the average chemistry of the melt of silicon by adding boron or phosphorus and/or diluting with poly-silicon (silicon at 99.9999999%
Si purity) to get the most quantity of p-type material having a resistivity of 0.5 to 30=cm in the ingot.
The upgraded metallurgical silicon may be diluted at different ratios with poly-silicon (silicon produced by Siemens process) to be in the best area of the graph.
This action does not change the phosphorus to boron ratio. This ratio can be modified by adding small amounts of phosphorus or boron.
0.1 ppmw < Boron (ppmw) < 1 ppmw 0.1 ppmw < Phosphorus (ppmw) < 2.5 ppmw The complete results are shown in Graph 2. So, starting with a known level in boron and phosphorus, we can adjust the average chemistry of the melt of silicon by adding boron or phosphorus and/or diluting with poly-silicon (silicon at 99.9999999%
Si purity) to get the most quantity of p-type material having a resistivity of 0.5 to 30=cm in the ingot.
The upgraded metallurgical silicon may be diluted at different ratios with poly-silicon (silicon produced by Siemens process) to be in the best area of the graph.
This action does not change the phosphorus to boron ratio. This ratio can be modified by adding small amounts of phosphorus or boron.
4 Producers of solar cells do not like to add boron because a phenomenon called "boron degradation": the initial rapid light-induced degradation of cell performance.
The quantity of usable p-type silicon can be increased by adding other p-type dopant (other than boron):
p-type dopant Distribution coefficient Atomic weight Al 2x10" 26.98 Zn 1 x10" 65.37 Ga 8x10" 69.72 I n 4x 0-4 114.82 These p-type dopants are able to increase the proportion of usable p-type silicon after the multi-crystalline solidification of the ingot. Gallium (Ga) and Aluminum (AI) are very interesting because of their high value of distribution coefficient:
they have a very good compensation effect at the end of the crystallization to compensate for the rapid increase in the phosphorus concentration.
The amount of aluminum (Al) or gallium (Ga) to add to the silicon melt is preferably:
0 ppmw < Gallium (ppmw) < 250 ppmw 0 ppmw < Aluminum (ppmw) < 100 ppmw NCC = [B]PPma,e. + [Ga]PPma,.c - [r ]ppma,s [Ga]ppma = [Ga]PPmw x 28=0855 69.723 = [Ga] Pm'" x 0.403 kUa = 0.008 [Ga]pPma,s = 0.008 - [Ga]PPma,o . (1 - fs)o.oos-1 Gallium is also known to have a better stability than boron. So, in the case of a silicon feedstock having a high phosphorus to boron ratio, it would be beneficial to add p-type dopant, like gallium, to increase the proportion of usable ingot in the production of solar cells instead of boron.
DESCRIPTION OF THE BEST MODE OF REALISATION
Example 1:
The quantity of usable p-type silicon can be increased by adding other p-type dopant (other than boron):
p-type dopant Distribution coefficient Atomic weight Al 2x10" 26.98 Zn 1 x10" 65.37 Ga 8x10" 69.72 I n 4x 0-4 114.82 These p-type dopants are able to increase the proportion of usable p-type silicon after the multi-crystalline solidification of the ingot. Gallium (Ga) and Aluminum (AI) are very interesting because of their high value of distribution coefficient:
they have a very good compensation effect at the end of the crystallization to compensate for the rapid increase in the phosphorus concentration.
The amount of aluminum (Al) or gallium (Ga) to add to the silicon melt is preferably:
0 ppmw < Gallium (ppmw) < 250 ppmw 0 ppmw < Aluminum (ppmw) < 100 ppmw NCC = [B]PPma,e. + [Ga]PPma,.c - [r ]ppma,s [Ga]ppma = [Ga]PPmw x 28=0855 69.723 = [Ga] Pm'" x 0.403 kUa = 0.008 [Ga]pPma,s = 0.008 - [Ga]PPma,o . (1 - fs)o.oos-1 Gallium is also known to have a better stability than boron. So, in the case of a silicon feedstock having a high phosphorus to boron ratio, it would be beneficial to add p-type dopant, like gallium, to increase the proportion of usable ingot in the production of solar cells instead of boron.
DESCRIPTION OF THE BEST MODE OF REALISATION
Example 1:
5 Upgraded metallurgical silicon with initial dopant concentration of 1.5 ppmw of boron and 4.5 ppmw of phosphorus is melted in a crystallization furnace. The amount of p-type silicon having a resistivity in between 0.5 0=cm and 30=cm is approximately 7.7% of the ingot.
Example 2:
Upgraded metallurgical silicon with initial dopant concentration of 1.5 ppmw of boron and 4.5 ppmw of phosphorus is melted with poly-silicon in a crystallization furnace.
The ratio of UMG-Si to poly-Si is 1:2. The amount of p-type silicon having a resistivity in between 0.5 0=cm and 3 0=cm is approximately 79.5% of the ingot, an increase of 72% of ingot usage (vs example 1).
Example 3:
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 1.5 ppmw of phosphorus is melted in a crystallization furnace. The amount of p-2 0 type silicon having a resistivity in between 0.5 f2=cm and 3Q=cm is approximately 79.5% of the ingot.
Example 4:
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 1.5 ppmw of phosphorus is melted in a crystallization furnace. The equivalent of approximately 25 ppmw of gallium is added to the melt and crystallization is carried out. The amount of p-type silicon having a resistivity in between 0.5 f2=cm and 3 0=cm is approximately 97.5% of the ingot, an increase of 18% of ingot usage (vs example 3).
Example 2:
Upgraded metallurgical silicon with initial dopant concentration of 1.5 ppmw of boron and 4.5 ppmw of phosphorus is melted with poly-silicon in a crystallization furnace.
The ratio of UMG-Si to poly-Si is 1:2. The amount of p-type silicon having a resistivity in between 0.5 0=cm and 3 0=cm is approximately 79.5% of the ingot, an increase of 72% of ingot usage (vs example 1).
Example 3:
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 1.5 ppmw of phosphorus is melted in a crystallization furnace. The amount of p-2 0 type silicon having a resistivity in between 0.5 f2=cm and 3Q=cm is approximately 79.5% of the ingot.
Example 4:
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 1.5 ppmw of phosphorus is melted in a crystallization furnace. The equivalent of approximately 25 ppmw of gallium is added to the melt and crystallization is carried out. The amount of p-type silicon having a resistivity in between 0.5 f2=cm and 3 0=cm is approximately 97.5% of the ingot, an increase of 18% of ingot usage (vs example 3).
6 Example 5:
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 2.5 ppmw of phosphorus is melted in a crystallization furnace. The amount of p-type silicon having a resistivity in between 0.5 0=cm and 3 0-cm is approximately 33.7% of the ingot.
Example 6:
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 2.5 ppmw of phosphorus is melted in a crystallization furnace. The equivalent of approximately 65 ppmw of gallium is added to the melt and crystallization is carried out. The amount of p-type silicon having a resistivity in between 0.5 0=cm and 3 0=cm is approximately 96.1% of the ingot, an increase of 62% of ingot usage (vs example 5).
It should be understood that the values quoted above are approximate. By "approximate", it is meant that the value can vary within a certain range, for example the value can vary from 0% to 5%, 0% to 10%, or 0% to 25%.
Of course, these examples are given by way of illustrating the invention and are in no way to be deemed as limitative.
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 2.5 ppmw of phosphorus is melted in a crystallization furnace. The amount of p-type silicon having a resistivity in between 0.5 0=cm and 3 0-cm is approximately 33.7% of the ingot.
Example 6:
Upgraded metallurgical silicon with initial dopant concentration of 0.5 ppmw of boron and 2.5 ppmw of phosphorus is melted in a crystallization furnace. The equivalent of approximately 65 ppmw of gallium is added to the melt and crystallization is carried out. The amount of p-type silicon having a resistivity in between 0.5 0=cm and 3 0=cm is approximately 96.1% of the ingot, an increase of 62% of ingot usage (vs example 5).
It should be understood that the values quoted above are approximate. By "approximate", it is meant that the value can vary within a certain range, for example the value can vary from 0% to 5%, 0% to 10%, or 0% to 25%.
Of course, these examples are given by way of illustrating the invention and are in no way to be deemed as limitative.
Claims
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1604907P | 2007-12-21 | 2007-12-21 | |
| US61/016,049 | 2007-12-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2616405A1 true CA2616405A1 (en) | 2008-04-09 |
Family
ID=39277259
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002616405A Abandoned CA2616405A1 (en) | 2007-12-21 | 2007-12-24 | Crystalline si solar cells made from upgraded metallurgical silicon |
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| CA (1) | CA2616405A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010080777A1 (en) * | 2009-01-08 | 2010-07-15 | Bp Corporation North America Inc. | Impurity reducing process for silicon and purified silicon material |
| DE102009034317A1 (en) | 2009-07-23 | 2011-02-03 | Q-Cells Se | Producing an ingot made of upgraded metallurgical-grade silicon for penetration-resistant p-type solar cells, where the ingot has a height originating from a bottom with p-type silicon to a head with n-type silicon |
-
2007
- 2007-12-24 CA CA002616405A patent/CA2616405A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010080777A1 (en) * | 2009-01-08 | 2010-07-15 | Bp Corporation North America Inc. | Impurity reducing process for silicon and purified silicon material |
| DE102009034317A1 (en) | 2009-07-23 | 2011-02-03 | Q-Cells Se | Producing an ingot made of upgraded metallurgical-grade silicon for penetration-resistant p-type solar cells, where the ingot has a height originating from a bottom with p-type silicon to a head with n-type silicon |
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| Date | Code | Title | Description |
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