ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

Publications

Numerical modeling of the dislocation density of high quality cast silicon ingot material

D. Franke, I. Steinbach, W. Krumbe, J. Liebermann, W. Koch.

Proceedings of the 13th European Photovoltaic Solar Energy Conference, 458-460, (1995)

Abstract
The directional solidification of large ingots is an economic method for solar silicon production. Two quality criteria for high efficiency solar cells, which are produced from cast silicon ingots, are low residual casting stresses and low dislocation densities. Residual stresses can cause crackings during the sawing of the ingot into wafers. Dislocations are correlated to the carrier recombination probability. The prediction of stress and dislocation generation during the cooling stage from the melting point to room temperature allows an optimization of the process. This paper presents numerical calculations of dislocation densities by its dependence on the temperature and thermal induced stresses. Using a “Virtual Casting Furnace” (VCF), which calculates the temperature distribution during casting, the process control is optimized for the casting of high efficiency solar silicon. The model is applied to the SOPLIN- Process (SOlidification by PLanar INterface) of Bayer, Germany. Numerical calculations are presented, that demonstrate the principles of the process and the optimization strategy.


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