Solar Grade Silicon

Thermo-Calc can be used to predict the thermodynamics and phase equilibria of Si-based systems required for producing and refining Solar Grade Silicon to an ultra-high purity.

Solutions for Solar Grade Silicon

The fabrication of low cost solar cell grade silicon (SOG-Si) is important to the growth of the photovoltaic industry. However, the material properties of SOG-Si are highly sensitive to impurities of other elements, which can be detrimental to the cell efficiency. 

Understanding of the thermodynamics and phase equilibria of Si-based systems is required for producing and refining SOG-Si to an ultra-high purity, and Thermo-Calc can be used to generate such data for relevant Si-based systems.

Calculate the following based on your actual alloy chemistry:

  • Thermophysical properties:
    • Specific heat, enthalpy, latent heat
    • Phase-based properties, such as:
      • Critical transformation temperatures such as solvus temperatures of precipitates, amounts and compositions of phases, solubility limits, activities, phase diagrams, and more
      • Equilibrium and non-equilibrium solidification:
        • Liquidus, solidus, incipient melt temperatures, freezing range, fraction solid curves, solidification path, fraction eutectic, microsegregation, partition coefficients, latent heat, and more

Application Examples

Thermo-Calc has many applications to Solar Grade Silicon. Below is one such example.

Calculating Impurity Solubility for Solar Grade Silicon

Impurities in metallurgical grade silicon can drastically modify the material properties relevant for solar cells. For example, transition metal impurities such as iron, copper, and chromium can shorten the lifetime of excited carriers in the silicon solar cell and are thus detrimental to the cell efficiency. Their removal from silicon is therefore an important issue in silicon solar cell fabrication. Solvent refining has been investigated as a potential cost effective purification process that relies on preferential segregation of impurities to a liquid, from which high purity solid silicon crystals can be grown, as discussed in a paper by Yoshikawa and Morita, JOM, vol. 64, no. 8, pp. 946–951, 2012.

Thermo-Calc can be used to predict the solubility of impurity elements in pure Si as a function of temperature and composition as shown in the figure here. The software can also be used to predict the segregation coefficient between the solid and liquid phase, which is relevant to the solvent refining process.

A plot showing the the calculated impurity solubility in Si-containing binaries.

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