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Silicon for solar cells at low costs on an intermediate scale

Final Report Summary - SISI (Silicon for solar cells at low costs on an intermediate scale)

The SISI project aimed at alleviating the photovoltaic (PV) industry dependence on the limited and expensive supply of silicon from the electronics industry. The consortium was convinced that the most promising option to provide the very large quantities of high-purity silicon required was the direct carbothermic reduction of quartz. In SISI, major European industry and institutes were included with expertise in ultra-high-purity quartz, silicon production and purification, and solar cell-processing. The project's goal was to demonstrate on an intermediate scale an integral direct carbothermic route for solar grade silicon (SoG-Si) production that could be industrialised.

In the SISI project, the combination of technologies was integrally scaled up with the following innovations:
- optimized raw material preparation and furnace operation for a stable and high-yield Si-production, suitable quartz purification and pelletising techniques;
- transfer of the purification techniques to intermediate scale, including new steps such as filtering.

The SISI project was organised in six work packages following the value chain and production steps: raw materials, Si-production, purification, wafer and cell process, technology implementation and consortium management.

The SISI project was very successful in achieving the goals that were set. The most important results of the project are listed below:
- With a 'quartz for solar cells' programme, the separation and refining methods were adopted and the form of the quartz was assessed in order to reduce or improve the pelletising step.
- A study was made on possible optimisation of carbon black supply. The production of SiC and silicon were done with selected high purity qualities from commercial producers, and proved to be satisfactory.
- To obtain a high quality SiC material as feed to the smelting furnace, a special designed pilot production unit was developed.
- During the smelting tests in year I, a well operating furnace design for high purity silicon smelting was developed. Also the new reaction concept was proved and a stable and predictable Si production was established. However, problems were encountered with the physical behaviour of the charge during long term operation. The main work during year II was devoted to the development of the pellets.
- Models and calculations of settling and filtration were carried out, and the results were verified by small scale testing. Design and construction of a filter unit for removal f SiC in intermediate and pilot scale were finished, and implemented, according to the objective of the project.
- A suitable method for reclaiming silicon from spent sawing sludge was tested and promising results were obtained.
- From three different ingots, wafers were produced and cells were processed using industry standard cell processing techniques. The efficiency levels were compared with other SoG-Si feedstock sources. The measured efficiency of the SISI cells was 1 % below reference for n-type material and 4 % below reference for p-type material. Based on these result, it was estimated that p-type wafers need to be 98 % cleaner for the 2 % limit that was set as a goal for the SISI project. N-type wafer were significantly more tolerant to impurities.
- To enable the exploitation of the knowledge developed in SISI, the SISI consortium partners established an IPR company called SOLSILC Development Company (SDC). Together with the establishment of this company an IPR agreement between the SISI partners was signed to organise exploitation of IPR from the SISI project.
- Several possible partners were evaluated. SDC granted a license with a investment company and signed a long lasting R&D contract to scale up the SOLSILC concept through a large scale pilot phase into industrial scale production.
- A plan was made for the development and realisation of a pilot facility, aiming at a start of pilot production in 2007 / 2008.The SiSi results have been evaluated and assessed with several market parties.
- Several companies expressed interest in the SoG-Si to be produced and requested quotations to supply SoG-Si. Market parties expressed interest for intermediate products and even asked for participation in the SOLSILC concept.
- For scientific purposes and for marketing purposes the RTD partners ECN and Sintef published information concerning the project several times in different bodies.
- All foreground information that was judged by the project partners to belong to the public domain was presented at international conferences and published in journals dedicated to photovoltaics issues. This was done after a careful selection of the information to be published and on the basis of a mutual consent prior to making it available to the public.

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