Recycling of Compound Semiconductor Photovoltaics by Means of Ambipolar Electrolysis

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Inventors
Professor Donald Sadoway
Department of Materials Science and Engineering, MIT
External Link (sadoway.mit.edu)
Sebastian Osswald
Department of Materials Science and Engineering, MIT
David Bradwell
Department of Materials Science and Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Electrolytic recycling of compounds

US Patent Pending 2012-0034153
Publications
Recycling ZnTe, CdTe, and Other Compound Semiconductors by Ambipolar Electrolysis
Journal of the American Chemical Society, 133, no. 49 (December 14, 2011): 19971-19975.

Applications

The toxicity and scarcity of cadnium telluride (CdTe) have raised concerns over the use of CdTe in commercial products and have spurred a push towards finding a method to recycle those materials. This invention would be particularly useful in the photovoltaic industry where CdTe is a widely used solar material and for recycling companies focusing on compound semiconductors. 

Problem Addressed

The issues with the current technology are the toxic environmental impact of Cd and Te, which are widely used in solar cells, and the multiple steps required in  the present recycling methods. The concern of Cd and Te toxicity pressures manufacturers to recycle spent solar cells and manufacturing waste. The proposed AE recycling of CdTe solar cells selectively dissolves the compound semiconductor for the reclamation of Cd and Te that are suitable for reentry into the CdTe manufacturing stream. 

Technology

The invention provides a new method to recycle compound semiconductor materials used in the photovoltaic industry by employing ambipolar electrolysis (AE). The proposed process selectively dissolves the semiconductor material off of the solar cell into a molten salt bath, leaving behind the glass and metal wire contacts. AE can then be performed on the molten salt containing the dissolved compound, resulting in the simultaneous electro-deposition of the two metals onto separate electrodes. To recycle CdTe, the molten salt can be CdI2 or CdCl2-KCl, and the operating temperature is 500C. Given the high purity of the collected molten metals, Cd and Te products could be remixed under N2, producing CdTe, ready to be reintroduced into the manufacturing stream of new solar cells.

Advantages

  • Simple one-step process for the reclamation of Cd and Te
  • Continuous, closed-stream recycling where the products can be reintroduced into the manufacturing cycle
  • Shortens the recycling process
  • Recovers toxic materials