Early Detection of Cracks in Wafers Increases Productivity and Reduces Costs in Solar Cell Production
The solar wafer is at the heart of the solar cell. But before it can be transformed into a cell, and later into a module, it receives a number of demanding treatments. This begins with sawing the silicon brick into wafers, which are only 100 to 200 μm thick, and is followed by mechanical influences in handling, processing and transportation. Small cracks in the core or on the edge of the wafer will grow due to the impact of these processes and during diffusion or firing due to thermal or mechanical stress. What started out as a micro defect can cause a final wafer to break – resulting in sunk costs for invested time, material and efforts.
Even though cracks in wafers can expand greatly in size, they often are quite hard to detect. This holds true especially in the early stages of processing, before they extend through thermal treatments or mechanical handling. In addition, on multicrystalline wafers, cracks don’t differ much from grain boundaries. Common optical inspection systems will not increase the contrasting of these defects, despite using infra-red transmission or bright field illumination.
