Final Report Summary - FOXY (Development of solar-grade silicon feedstock for crystalline wafers and cells by purification and crystallisation)
FOXY was a 36-monthly EC-funded R&D project which has developed refining and crystallisation processes for metallurgical SoG-Si feedstock, has optimised associated cell and module processes, and has set parameters for these types of feedstock. The FOXY partnership originally aimed at:
1. further developing and optimising refining, purification, and crystallisation processes for metallurgical SoG-Si feedstock, as well as for recycled n-type electronic grade Si;
2. optimising associated cell and module processes;
3. setting input criteria for metallurgical and electronic n-type silicon to be used as raw materials for SoG-Si feedstock;
4. transferring the technology from laboratory to industrial pilot tests.
The project was organised into the following work packages (WPs):
- WP1 has developed versatile refining techniques that are able to produce SoG-Si from the direct route but also for refining / recycling of scrap material such as ingot off-cuts and broken wafers as well as dust from the wafering process.
- WP2 aimed at purifying available contaminated feedstock and testing it by ingot growing and wafer cutting. Focus was on optimising parameters for purification and crystallisation of N-type material. To realise this aim, N-doped silicon feedstock was purchased, ingots were produced and the directional solidification process was optimised.
- WP3 has worked on developing methods for electro-refining of metallurgical grade silicon to produce solar grade quality silicon after subsequent re-melting. Electrochemical studies showed that silicon can be anodically dissolved and cathodically deposited from molten CaCl2 based electrolytes. Rough calculations to estimate the energy consumption for electro-refining of metallurgical silicon showed that only about 3 kWh/kg Si is needed.
- WP4 has supported the other work packages by characterisation of the samples and giving feedback to WP1, WP2, WP3 for optimisation of ingot growth processes, and to WP5 in order to choose the best solar cell processes according to the quality of the materials. The characterisation results indicate that most of the material grown in WP1 and WP2 is suitable for solar cells. Some important properties, like lifetime and resistivity, have been measured using different techniques by more than one partner.
-WP5 has worked on large area solar cells (150 x 150 mm2) and achieved 16.7 % on SoG-Si p-type feedstock Cz-Si cells from 10 % blend; with texturisation the efficiency increased to above 17 %. Furthermore, with industrial n-type process after optimisation of individual processes: 16.4 % on mc-Si and 18.3 % on Cz-Si was achieved. These are the highest efficiencies ever reported for a screen printing process on n-type mc- and Cz-Si material.
- WP6 has evaluated and tested modules made from FOXY cells, resulting in a FOXY module with comparable efficiency as the reference.
- WP7 has integrated the feedback loops and parameter discussion, to ensure the exploitation and dissemination of the results outside the project. Furthermore, it provided a starting point for discussions on a solar grade silicon standard that are now continued outside the project.
1. further developing and optimising refining, purification, and crystallisation processes for metallurgical SoG-Si feedstock, as well as for recycled n-type electronic grade Si;
2. optimising associated cell and module processes;
3. setting input criteria for metallurgical and electronic n-type silicon to be used as raw materials for SoG-Si feedstock;
4. transferring the technology from laboratory to industrial pilot tests.
The project was organised into the following work packages (WPs):
- WP1 has developed versatile refining techniques that are able to produce SoG-Si from the direct route but also for refining / recycling of scrap material such as ingot off-cuts and broken wafers as well as dust from the wafering process.
- WP2 aimed at purifying available contaminated feedstock and testing it by ingot growing and wafer cutting. Focus was on optimising parameters for purification and crystallisation of N-type material. To realise this aim, N-doped silicon feedstock was purchased, ingots were produced and the directional solidification process was optimised.
- WP3 has worked on developing methods for electro-refining of metallurgical grade silicon to produce solar grade quality silicon after subsequent re-melting. Electrochemical studies showed that silicon can be anodically dissolved and cathodically deposited from molten CaCl2 based electrolytes. Rough calculations to estimate the energy consumption for electro-refining of metallurgical silicon showed that only about 3 kWh/kg Si is needed.
- WP4 has supported the other work packages by characterisation of the samples and giving feedback to WP1, WP2, WP3 for optimisation of ingot growth processes, and to WP5 in order to choose the best solar cell processes according to the quality of the materials. The characterisation results indicate that most of the material grown in WP1 and WP2 is suitable for solar cells. Some important properties, like lifetime and resistivity, have been measured using different techniques by more than one partner.
-WP5 has worked on large area solar cells (150 x 150 mm2) and achieved 16.7 % on SoG-Si p-type feedstock Cz-Si cells from 10 % blend; with texturisation the efficiency increased to above 17 %. Furthermore, with industrial n-type process after optimisation of individual processes: 16.4 % on mc-Si and 18.3 % on Cz-Si was achieved. These are the highest efficiencies ever reported for a screen printing process on n-type mc- and Cz-Si material.
- WP6 has evaluated and tested modules made from FOXY cells, resulting in a FOXY module with comparable efficiency as the reference.
- WP7 has integrated the feedback loops and parameter discussion, to ensure the exploitation and dissemination of the results outside the project. Furthermore, it provided a starting point for discussions on a solar grade silicon standard that are now continued outside the project.
