SOLAR CELL EFFICIENCY FEATURE
photovoltaic sector, explains the manufacturing difficulties with regards to wafer processing: ‘They [the wafers] are moved from station to station during which damage can occur, not just in the processing stage, but also while being manipulated. There’s a lot of machine vision used between these steps to make sure only complete and undamaged wafers pass to the next processing point. ‘These wafers are very thin and each and every step makes them more expensive,’ he continues. ‘It’s always advisable to inspect between each step to ensure the wafer is still viable.’ Wafers are also classified
according to the surface colour and the electrical connections are inspected to check for broken links.
A very important step in solar
cell production is edge isolation, that is isolating the front and back contacts to generate voltage. ‘The thinner the scribe and the closer it is to the edge of the cell, the more active area the cell will have,’ explains Keppler. Vision systems are used to control the scribing machine to ensure it is positioned correctly. Machine vision plays a role in all the high- end mounting processes as well, for positioning the cells to form a panel.
‘Machine vision is used to
increase the efficiency of the cell itself, through optimising the edge isolation or making sure that bus bars and fingers are printed correctly or inspecting for micro-cracks in the wafer, all of which leads to a more efficient solar cell,’ Keppler comments. ‘Also, though, machine vision has a role in making the production of solar cells more efficient. Defective wafers can be sorted out of the line or reworked, or vision can reduce the numbers of wafers damaged during handling. It’s raising the efficiency on both sides, through the production process and also the product itself.’
A premium for quality While at the moment the photovoltaic industry remains in a consolidation phase, Hoex feels that there’s hope for the future for improving QC procedures in solar cell production with luminescence imaging. ‘When quality becomes more important to end-users and high-quality
solar cells can be sold at a premium, this could further drive the use of PL imaging. ‘There is a push by certification
organisations like VDE to use EL as part of going beyond the standard testing for PV modules,’ he continues, (the testing at the moment is laid down according to IEC or UL standards). ‘You
can pick up certain performance- limiting defects like cracks with EL very easily, while these defects cannot be detected by the standard tests. SERIS has a strong focus on quality and feels it is essential for the market. We try and push quality, but we also understand that companies need to make a profit.’ l
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PHOTOVOLTAICS 2012
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