Case 13019

Reduction of dislocation density in silicon solar cell material for enhanced solar cell performance

Keywords:

Dislocation density, multicrystalline silicon wafers, dislocation density etching, dislocation density imaging, solar cells, solar cell wafers, bulk defects, edge dislocation, efficiency enhancement, crystal defects

Applications:

Polycrystalline silicon ingots, wafers and cells

Problem:

    Increasing energy conversion efficiency for pc-Si solar cells

Technology:

This invention describes a method to significantly reduce dislocation density in pc-Si bricks or wafers, consisting of the following three steps: 1) a high temperature anneal to eliminate dislocations, 2) a diffusion barrier to slow the entry of impurities, 3) a controlled cool to room temperature. Although dislocation density minimization is commonly attempted during ingot crystallization by a high-temperature “holding step” before cool-down, there are significant advantages to performing this at the brick or wafer level: greater surface area to volume ratio facilitates better dislocation out-diffusion and more linear time-temperature profiles, hence avoiding thermal stresses that generate new dislocations. The inventors have successfully demonstrated substantial reductions in pc-Si dislocations.

Advantages:
  • Industrial solar cell efficiencies (using standard screen-printing metallization) can be expected to improve by 1-1.5%, or a net improvement of >6% for a 15% efficient cell.

Inventors:
  • Professor Tonio Buonassisi (Department of Mechanical Engineering, MIT)
  • Katherine Hartman (Department of Materials Science and Engineering, MIT)
  • James Serdy (Laboratory for Manufacturing and Productivity, MIT)

Intellectual Property:

U.S. Patent filed January 23, 2009

Publications:

Katy Hartman, Mariana Bertoni, James Serdy, and Tonio Buonassisi. Dislocation density reduction in multicrystalline silicon solar cell material by high temperature annealing Applied Physics Letters 93, 122108 (2008). DOI: 10.1063/1.2909644

Related Cases:

14086: Dislocation Reduction in Silicon by Application of Cyclic Thermal Stress

Last revised: November 8, 2010

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