Enhancing the solar cell efficiency with optimized metal paste

Aluminum (Al) back conductor paste plays an important role in the performance of the solar cells. The conversion efficiency of the solar cell depends on the properties of the Al paste. To increase the cell efficiency, the back surface field (BSF) properties should be carefully controlled by changing the thickness or the composition of Al conductor layer. As the thickness is to be thicker, BSF thickness is improved. Al powder, glass transition temperature (Tg) of glass frit, and inorganic additives are also affected the BSF properties. However, for a thin wafer, Al paste should be developed due to the bow (or sintering stress), which is generated with increasing the amount of Al. In this work, the correlation between the Si wafer bow and the amount of Al has been investigated experimentally and theoretically. The composition of back Al conductor paste was carefully controlled by changing the glass frits and adding the inorganic additives. The surface morphology and BSF uniformity were characterized by scanning electron microscopy (SEM). Although the amount of Al was increased, the bow of a thin Si wafer still remained lower than a commercial requirement, and same cell efficiency was obtained.