The manufacturing companies who produce silicon wafers for PV use with ingot technologies, such as Directional Solidification (DS) and Czochralski (CZ) pulling, have a strong need for technical innovations with the aim to reduce manufacturing costs and to increase production volumes, yields, process stability and wafer quality for more efficient solar energy conversion.
This project is a common research effort by the European industries and specifically refers to the introduction of new innovative technologies for realizing crystalline silicon substrates. Its aim is to decrease the present production cost of photovoltaic silicon wafers by approximately 45%. The consortium includes Bayer, Eurosolare and Siemens, who are the most important European industrial PV silicon material producers.
Research approach and methodologies:
1. A more rational management of the raw material: Studies will be carried out to establish the effect of compensation on the conversion efficiency of solar cells manufactured on substrates originated from mixtures of p-type and n-type electron grade (EG) silicon scraps and recycled production silicon.
2. Crystal Growth: The current Si crystal growth procedures employ DS and CZ technologies. For DS technology the goal is to improve the duty of the furnace by introducing a new technology based on variable thermal insulation during the different steps of the thermal cycle.
For CZ technology the goals are to increase the pulling rate by growing multi-grain crystalline structures (3-grain crystals) and to improve the material performance by heat treatments during and after the growth cycle.
3. Wafering technology: An automatic system for wafering, cleaning and collecting silicon wafers must be set up in order to produce thin (< 250 um) and large (> 225 cm2) wafers with a production yield > 95%.
4. Post-growth wafer treatments: These treatments are particu-larly suitable for multi-crystalline wafers. The goal is to recover wafers affected by impurity contamination by industrial POCl3 gettering and hydrogen passivation processes.
Expected Achievements and Exploitation
Reduction of the cost of active PV material will lead to a lower cost of the PV installed power. Partners involved in the fabrication of substrates will become more competitive. In particular this can be achieved by a wider use of existing silicon feedstock, improving the material quality by a better design and implementation of the crystal growth process and by introducing post-growth treatments, in analogy with the EG silicon process. Partners involved in solar cells and module fabrication will benefit from improved material performance and cost for final products. Crucible and equipment manufacturers will be able to supply higher quality products to the market. Results of the project are intended to be used at first between the partners and, subsequently, on the market.
Funding SchemeCSC - Cost-sharing contracts
OX12 9AJ Wantage - Oxforshire