Tin-Aluminium Metal Contact for Silicon Based Solar Cells

In this work we demonstrate that the tin plating performed on screen-printed Al contact is able both to produce suitable contact with Al-Si and to replace the silver from the back contact in the cell manufacturing process thus reducing the solar cell cost. To this aim we have developed an innovative technique based on dynamic liquid meniscus able to touch the cell back contact in specific defined positions and perform wet processing such as Tin plating. We have used high resolution Scanning Electron Microscopy (SEM) and compositional microanalysis with Energy Dispersive X-Ray microanalysis (EDX) to evaluate the tin dispersion within aluminum-silicon interdiffused region and Transfer Length Method and current-voltage measurements to estimate the specific contact resistivity of the Sn-Al/c-Si metal contact and series resistance of the overall solar cell device. Several commercial aluminum screen printable pastes have been experimented also having different distribution of sphere particles dimensions. We have found that the interconnection ribbon soldered on tin contacts plated on screen printed aluminum back contact shows adhesion higher (> 1N/mm) than that verified on screen printed silver over silicon.