Reduced screen printed aluminum laydown for low cost silicon solar cells

The majority of PV market is covered by p-type c-Si based solar cells, having metal contacts produced by screen printing. Common screen printable Aluminum pastes, due to their chemical properties are able to form deep and effective Back Surface Filed (BSF), providing also low surface recombination velocity. According to the actual industrial state of the art the wet laydown of screen printable Al paste is in the range of 1.4-1.6g per cell, nearly 6-7 mg per printed cm2. This reflects in a cost per cell of 0.02-0.035€. In the roadmap to reduce the solar cell manufacturing costs, a lower laydown is a goal, which also could reflect in lower cell bowing after firing process. However it is not immediate to obtain the same electric performances reducing the Al available to form the BSF. In this paper we investigate the possibility to produce a lower laydown of Al paste which ensures the same electrical performances of a standard Al paste thickness, through the understanding of BSF formation mechanism and electrical properties of the paste in correlation with its formulation. To optimize the effect of the available metal, we have produced several Al pastes by screening different Al powder granulometry mix and frits to obtain good values of Voc, FF and BSF homogeneity comparable to those produced by standard screen printable Al pastes.