Pinhole Detection in Si Wafer and Solar Cells

Pinhole Detection using RUV-AS System

Ultrasonic Technologies developed a new method to identify silicon wafers and solar cells with small, sub-millimeter “pinhole” defects and cracks. “Pinhole” represents a seed point anomaly which dramatically reduces wafer and cell strength and ultimately leads to breakage and yield reduction. UST developed and designed an Activating Station add-on which once integrated with the RUV system allows successful detection of “pinhole” cracks.

Ultrasonic Technologies has a proven record of detecting small to medium size ( > 1 mm) cracks and defects in solar cells and wafers. It was recently indicated by our customers that other mechanical problems pose a high probability of wafer/cell breakage in production. A sub-millimeter diameter “pinhole” represents a seed point defect which dramatically reduces the cell strength. Illustrative example of this defect in production grade silicon cell is presented here. A 3.6 x 3.6 mm map of a silicon cell using high-resolution Scanning Acoustic Microscope (SAM) with sub-millimeter pinhole. Note, that unopened cross cracks provide directions when the cell is broken.

To address this production problem, Ultrasonic Technologies developed a proprietary protocol to identify the wafers and cells with pinholes quoted here as an “Activation Station” (AS).

Activation Station concept: prior to RUV testing the cell is passing through the AS with settings defined by the operator. After activation the cell is transferred to the RUV system and analyzed using a new RUV statistical algorithm. Some heavily damaged cells are broken during the activation step and automatically removed by the hardware. Our tests show that the cells with pinholes located at the central area are captured with 100% accuracy.

This delivers a turn-key solution to solar cell and module manufacturers.

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Source: Ultrasonic Technologies

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