Error diagnosis and optimisation of c-Si solar cell processing using contact resistances determined with the Corescanner

The screen-printing metallisation process used for 90% of industrially produced solar cells is sensitive to process conditions. The best way to monitor this contacting process is to measure contact resistance. The standard technique used is the transmission line method. However, this only measures contact resistance locally.In this paper, contact resistance over the whole cell surface is measured with the newly developed ‘Corescanner’. Using this instrument, the relation between processing parameters and solar cell contact resistance distribution is investigated. Our most important finding is that poor contacting results in large inhomogeneities in contact resistance. Even for cells with very low fill factors, regions of low contact resistance can be found.To conclude, the Corescanner provides us with a technique to monitor contact resistance. This instrument is an invaluable tool for fault detection, error diagnosis and process optimisation.