The objective of the project is to remove dependence of the photovoltaic industry on limited supplies of solar grade silicon feedstock, available as reject material from the microelectronics industry and replace it with the virtually unlimited supplies of metallurgical grade silicon. To realise this a low cost method of producing wafers in mg-Si must be found and must be coupled with a method of growing a thin film of silicon onto the substrate which can give a solar cell of good efficiency to enable a cost effective solar cell to be produced.
Emphasis will be placed on making use of the already available grades of mg-Si. These will be used to develop a low cost casting process for multicrystalline ingots for subsequent wafering. This should be possible as the substrate is not electrically active whereas in normal multicrystalline ingot fabrication particular attention is paid to maximising minority carrier diffusion length by slow solidification rates and the use of high purity crucibles. Wire sawing techniques and wafers cleaning techniques will be developed to utilise ingots which may have significant SiC inclusions. The thin film of silicon will be deposited by conventional epitaxial techniques with the importance of a buffer layer between the substrate and the film being evaluated. The design of a high throughput epitaxial reactor is essential to achieving low final product costs. A range of solar cell processes will be used to determine the most appropriate to achieve the necessary solar cell efficiency and process economics. Characterisation of the materials and solar cells will be undertaken as will a full economic evaluation of the preferred process.
EXPECTED ACHIEVEMENTS AND EXPLOITATION
The project is aimed at achieving a process which uses metallurgical grade silicon feedstock to produce a photovoltaic module at a cost equivalent to or lower than present silicon module technologies where solar grade silicon feedstock is used. The demonstration of a solar cell of 12% efficiency on a area of 100 cm2 is a major stepping stone in achieving this objective. The benefit of this project is that the PV industry will no longer be limited to the supply of silicon feedstock from the microelectronics industry thus allowing the implementation of photovoltaic generating systems to proceed without supply constraints. The industrial partners in material supply, equipment production, silicon wafer supply and photovoltaic manufacture will each seek to implement a successful outcome of the project.
Funding SchemeCSC - Cost-sharing contracts
OX12 9AJ Wantage - Oxforshire
79110 Freiburg (In Breisgau)