Characterisation of silver thick-film contact formation on textured monocrystalline silicon solar cells

The investigations presented in this paper help to clarify the firing temperature dependence of the microstructure at the interface of Ag thick-film contacts on textured silicon solar cells. Textured silicon wafers were chosen to put the investigations in a more relevant environment of a real solar cell. Scanning Electron Microscope (SEM) pictures were taken from silicon wafer surfaces beneath the contact where we found bright and dark regions. We identified them as the SiN layer deposited as an antireflection coating before printing and pure silicon originating from the raw wafer where the SiN layer was completely etched by the glass frit. The percentage of the surface area of the dark regions was quantified and brought into relation with the measured electrical properties and the recorded specific contact resistance. A clear correlation could be shown. The results are discussed referring to models of charge carrier transport in thick-film contacts.