Silicon
Silicon is the base and reference material for the Photovoltaic Industry, from its advent in the 80’s. Countless R&D efforts have been carried out from that time on to find it an as efficient and available successor, reduced its hold on the market to 85% of the world supply today.
Apollon Solar is still convinced that Silicon will remain for a number of years the reference solar material, and the one which will enable a significant and reliable cost reduction of photovoltaic products.
In the field of Silicon, the most important projects of Apollon Solar are::
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Partners of the PHOTOSIL project are:
Innovative Crystallisation Technology for Multi-Crystalline Silicon Ingots
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Doping engineering
- Photosil - Production of Solar Silicon from metallurgical grade Silicon
- Innovative Crystallisation Technology for Multi-Crystalline Silicon Ingots
- ASTERICS – (Apollon Solar TEchnology for RIbbon growth of Crystalline Silicon)
- Doping engineering
PHOTOSIL – Production of Solar Silicon from metallurgical grade Silicon
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This French R&D Project was initiated by Apollon Solar in 2002 with the overall objective to provide an industrially viable source of Solar grade Silicon for the PV industry at low costs and sufficient purity.
This Solar grade Silicon presents an alternative to Electronic grade Silicon of very high purity and high varying costs and prices depending on the market situation.
The underlying technology of the PHOTOSIL project is a combination of refinement steps to upgrade widely available metallurgical Silicon, including:
- Metallurgical segregation process
- Plasma purification with electromagnetic stirring of silicon melt
- Ingot-Crystallization and associated segregation
The technological and economical goals for the PHOTOSIL Solar Silicon have been defined as:
- Solar cell efficiencies >15% on multi-crystalline Silicon wafers from PHOTOSIL Silicon
- Material yield > 85% after crystallisation of PHOTOSIL Silicon
- Costs of 15€/kg on feedstock and 35€/kg on multi-crystalline ingot level
Apart from providing its general PV expertise and assuring the project coordination, Apollon Solar’s technical involvement in the project concerns the crystalline silicon chain (from feedstock to ingots). In particular Apollon Solar is in charge of the cristallisation of multi-cristalline Silicon ingots.
- FerroPEM, former Silicon activities of the Pechiney group and now part of the Ferro Atlantica Group, world’s largest producer of metallurgical Silicon
- CNRS EPM-SiMAP, laboratory specialized on electromagnetic processing techniques for metals including inductive plasma purification of Silicon
- CEA- INES (National Institute for Solar Energy), laboratory with expertise on each step of the PV value chain
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2002 – 2005: Fundamental R&D work on laboratory scale on different purification techniques by the different PHOTOSIL partners, based on preliminary results on the EU ARTIST project.
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2005 – 2008: PHOTOSIL R&D project itself, funded by the project partners and public entities (Rhone Alpes Region, Savoie Department, ADEME). Realization of an industrial pilot line for all refinement steps, allowing batch sizes of up to 120kg to be processed. Further process development was carried out to upscale all purification techniques. -
From 2008 on: Continuation of PHOTOSIL project work in the frame of the French SNC R&D project
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2009: Proof-of-concept: Average Solar cell efficiencies >15% obtained on several p-type multi-crystalline Silicon ingots from 100% PHOTOSIL Silicon and with a crystallisation material yield >85%
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2009: Creation of PHOTOSIL Industries, a joint venture between FerroPEM and Apollon Solar’s shareholder EDF EN to industrially exploit the PHOTOSIL technology as soon as the process is techno-economically qualified by the partners.
Innovative Crystallisation Technology for Multi-Crystalline Silicon Ingots
For a variety of technological and historic reasons, crystalline Silicon continues to be the most widely used material for PV cells and modules in industry. One key element of the Silicon based PV value chain is the crystallisation of Silicon feedstock to produce ingots which are cut into wafers.
In close collaboration with the Grenoble based crystallisation furnace manufacturer CYBERSTAR, a new innovative crystallisation technology for multi-crystalline Silicon ingots has been developed. This technology is characterized by a simple and effective thermal set up with the objective to obtain high crystalline quality, high material yields, shorter cycle times and thus reduced overall costs for this important manufacturing step.
Principle
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Two independently powered inductive heating elements above and below the crystallisation crucible and an efficient lateral thermal insulation allow for strong and unidirectional, vertical temperature gradients to be established during crystal growth, but also for a gradient free annealing during cool down once the ingot is crystallized.
The entire thermal setup of the CYBERSTAR furnace therefore enables a very precise temperature control during all parts of the process. The lower induction heating coil serves also as heat exchanger which is important for an efficient heat extraction from the bottom of the crucible. The unidirection.
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Avantages
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Thermally anisotropic quartz crucible
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A new hybrid quartz crucible with thermally anisotropic behavior has been developed together with CYBERSTAR. As shown in the schematic view the crucible is composed of opaque quartz side walls and a transparent quartz bottom plate. This set up allows to preferentially extracting heat by infrared radiation through the bottom of the crucible, while the opaque side walls support lateral thermal insulation. At the same time, the high purity of the quartz avoids contamination of the Silicon.
Up to now this crucible has been regularly used and validated for ingots up to 60kg with dimensions of 350x350x250 mm3. First tests on a larger scale 500x500x250 mm3 for 120kg have been carried out successfully end of 2009.
In close collaboration with the Grenoble based crystallisation furnace manufacturer CYBERSTAR, a new innovative crystallisation technology for multi-crystalline Silicon ingots has been developed. This technology is characterized by a simple and effective thermal set up with the objective to obtain high crystalline quality, high material yields, shorter cycle times and thus reduced overall costs for this important manufacturing step.
Principle
Two independently powered inductive heating elements above and below the crystallisation crucible and an efficient lateral thermal insulation allow for strong and unidirectional, vertical temperature gradients to be established during crystal growth, but also for a gradient free annealing during cool down once the ingot is crystallized.
The entire thermal setup of the CYBERSTAR furnace therefore enables a very precise temperature control during all parts of the process. The lower induction heating coil serves also as heat exchanger which is important for an efficient heat extraction from the bottom of the crucible. The unidirection.
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Avantages
- Excellent crystal quality of obtained ingots
- Excellent segregation of remaining impurities in lower quality feedstock
- No crucible overheating and less ingot contamination from crucible
- High Silicon yield
- Reduced process times due to shorter melting times and increased crystallization speed
- Small footprint requirements
- Possibility to crystallize simultaneously 4 or 9 different ingots in smaller crucibles
- Possibility to use different sizes of crucibles in the same furnace
- 2002 – 2006: Process development and validation on laboratory scale (10kg ingots)
- 2007 – 2008: Upscale of ingot size to 60kg and 100kg as part of the PHOTOSIL project
- 2008: Begin of commercialisation of industrial furnaces by CYBERSTAR having a capacity up to 250kg ingots
- 2009: Opening of new CYBERSTAR development center for industrial furnace assembly with 3 furnaces of different capacity available (10kg, 60kg, and 250kg)
Thermally anisotropic quartz crucible
A new hybrid quartz crucible with thermally anisotropic behavior has been developed together with CYBERSTAR. As shown in the schematic view the crucible is composed of opaque quartz side walls and a transparent quartz bottom plate. This set up allows to preferentially extracting heat by infrared radiation through the bottom of the crucible, while the opaque side walls support lateral thermal insulation. At the same time, the high purity of the quartz avoids contamination of the Silicon.
Up to now this crucible has been regularly used and validated for ingots up to 60kg with dimensions of 350x350x250 mm3. First tests on a larger scale 500x500x250 mm3 for 120kg have been carried out successfully end of 2009.
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ASTERICS – (Apollon Solar TEchnology for RIbbon growth of Crystalline Silicon)
This technology aims at crystallizing Silicon ribbons of comparable thickness and dimensions to classical wafers directly from the liquid melt, thus avoiding the important material losses and cost associated with the cutting of ingots.
One important feature of this technology is a crucible with a lateral opening through which a solidified silicon ribbon is extracted while at the same time the molten Silicon is retained inside the crucible by electromagnetic forces. The electromagnetic retention of the liquid Silicon has been demonstrated at laboratory scale as well as the crystallisation of a Silicon layer.
Partners in this ongoing project are the CNRS laboratory EPM SiMAP and CYBERSTAR.
One important feature of this technology is a crucible with a lateral opening through which a solidified silicon ribbon is extracted while at the same time the molten Silicon is retained inside the crucible by electromagnetic forces. The electromagnetic retention of the liquid Silicon has been demonstrated at laboratory scale as well as the crystallisation of a Silicon layer.
Partners in this ongoing project are the CNRS laboratory EPM SiMAP and CYBERSTAR.
Doping engineering
This new field of activities aims at increasing the material yield and electrical performance of multi-crystalline Silicon ingots, produced from purified metallurgical Silicon. Often this type of Upgraded Metallurgical Grade (UMG) Silicon feedstock still contains a certain concentration of dopant atoms, in particular Boron and Phosphorous, which are the most difficult to remove impurities during the purification processes.
Principle
During crystallisation of UMG Silicon and due to the different segregation coefficient of the major two dopants Boron and Phosphorous, the net dopant concentration (difference between the acceptor or P-type dopant and the donor or N-type dopant concentrations) strongly varies along the ingot height and often leads to a dopant type inversion, typically from P-type in the bottom to N-type towards the top of the ingot, which drastically reduces the material yield.
Doping engineering consists in deliberately adding dopant atoms to the Silicon feedstock before crystallization. For example, the addition of Gallium, an acceptor dopant which presents a much smaller segregation coefficient than Boron, allows to keep the net dopant concentration constant and to obtain a fully P-type silicon along the whole ingot height.
This work is in R&D stage and subject of a PhD thesis.
Principle
During crystallisation of UMG Silicon and due to the different segregation coefficient of the major two dopants Boron and Phosphorous, the net dopant concentration (difference between the acceptor or P-type dopant and the donor or N-type dopant concentrations) strongly varies along the ingot height and often leads to a dopant type inversion, typically from P-type in the bottom to N-type towards the top of the ingot, which drastically reduces the material yield.
Doping engineering consists in deliberately adding dopant atoms to the Silicon feedstock before crystallization. For example, the addition of Gallium, an acceptor dopant which presents a much smaller segregation coefficient than Boron, allows to keep the net dopant concentration constant and to obtain a fully P-type silicon along the whole ingot height.
This work is in R&D stage and subject of a PhD thesis.