Improved Ge wafer technology for multi-junction solar cells III

 
For the current and future solar cell technology developed in Europe, certain aspects of the Ge substrate require further improvement. This activity will also help to support UMICORE in maintaining its leading position and its competitiveness in a market which is becoming more and more aggressive and thus will help to guarantee Europe’s independence in this crucial component for high efficiency solar cells.

Objective(s)
To make the Ge-substrates cost effective; to increase the quality with a clear increase in the yield at solar cell manufacturer.

Achievements and status

• Increase in wafer strength: the round edge’s wheel has been optimized (reduced breakage); the surface grinding and the relief of the intrinsic stress are now more homogeneous, with a higher throughput and more cost effective (cheaper chemicals and recycling implemented).
• Improving of the wafer’s surface  was achieved by reducing the number of surface defects. The polishing technique was also improved, by using better suited chemicals and polishing pads; cleaning has increased by using optimized particle and metal cleaning and wafer drying based on surface tension gradient.

Benefits
Higher quality substrates with an increase in solar cell manufacturing yield. The increase in solar cell’s yield has implicit a cost reduction. This activity contributes to maintain the European independence in the manufacturing of solar cells.

Next steps
Some of the improvements achieved in this activity are already implemented in the production line. The rest will be gradually implemented before the end of 2016. The next step is to migrate all these improvements from 4 to 6’’, part of it covered in the activity Pegasus II - PErformance GuAranteed SUbStrates for 6“, ESA contract 4000117519/16/NL/GLC/tk). Some processes in this migration, such as the crystal pulling, will probably require additional effort.