https://pv-manufacturing.org/inline-quality-checks/
The most common in-line quality checks used in solar cell manufacturing are focus on the following process steps.
Diffusion
The phosphorus diffusion process is one of the most critical process steps in industrial silicon solar cell manufacturing. Small deviations in the process can have a severe impact on the final solar cell performance e.g. due to contacting issues or increased recombination losses. Consequently, there is a lot of interest to quantify the diffused wafers. Two common approaches used for the measurement of diffused layers in manufacturing are based on junction photovoltage and infrared transmission and reflection.
Another method relies on the difference in infrared reflection and transmission due to free carrier absorption due to the high doping density in the diffused layer. Free carrier absorption sharply increases in the infrared part of the solar cell and thus typically light in the 3-10 µm is used for this purpose. By combining reflection and transmission it even allows the measurement of a front and rear diffusion as is typical in bifacial n-type solar cells. More detail can be found at Aurora Solar Tech [3].
See other sources here: Semilab and ISRA Vision which were introduced by ACU last year.
BTI was never part of previous ACU investor deck. Why?
https://www.semiconductor-technology.com/contractors/optical/bt-imaging/
BT Imaging supplies the solar industry with the most comprehensive and flexible offline characterisation tool for R&D purposes, the LIS-R2, which measures silicon blocks, silicon wafers, solar cells and solar modules all within one tool.
It integrates PL, Electroluminescence (EL), series resistance (RS), QSSPC lifetime and calibrated PL measurement; it also uses the second generation PL technology developed by BT Imaging, which can be sped up to more than ten times the original in image acquisition.
It is the fastest PL tool in the world as it takes only two seconds to obtain PL images of as-cut wafers and has the highest resolution capability of 1MP, with a small tool footprint. BT Imaging has the widest installation base, with more than 30 tools used by leading silicon wafer and solar cell manufacturers, equipment vendors and material supplier
https://www.btimaging.com/products-c1g2d
Most of the PDF on the site are old and can use a refresh but BTI offering seems comprehensive.
https://patents.justia.com/assignee/bt-imaging-pty-ltd