ECN publication
Contact resistances measured using the Corescanner : relations with cell processing
Published by: Publication date:
ECN Solar Energy 1-10-2001
ECN report number: Document type:
ECN-RX--01-018 Conference Paper
Number of pages: Full text:
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Presented at: 17th European Photovoltaic Solar Energy Conference, Munich, Germany, 22-26 oktober 2001.

To obtain screen printed grid lines on solar cells with a low contact resistance is a difficult task, since the contact formation is very sensitive to many parameters. For optimisation of the metallisation processing, information about the spatial distribution of the contact resistance on a cell is extremely valuable. A technique to measure this distribution has been foundand patented recently; it is based on potential mapping on a short-circuited cell under illumination. By now, this technique is incorporated in an instrument available for the PV industry, called the Corescan. In addition to contact resistance scanning, the Corescan can locate shunts when operating the cell under forward bias in the dark. As an example of the use of the instrument, Corescans were made on cells printed with different pastes and fired at different conditions. The scans show that cells with different pastes can be distinguished by their typical Corescans. One of the pastes produces no acceptable fill factor for any firing condition, but the Corescan shows that at least a part of the cell is contacted well for all conditions, which means that the paste has potential. For the other paste, with which a FF of 77 % was reached, the Corescan pattern indicates wether the firing temperature is too low or too high. Noting that good contact is still possible on a part of the cells with low FF, it should be possible to create a larger firing window, by enlarging these good contact regions. To conclude, by the development of the Corescan, the PV industry is now provided with a technique to map contact resistance. This instrument is a valuable tool for fault detection, error diagnosis and process optimisation.

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