Effect of Al content on the performance of Ag/Al screen printed N-type Si solar cells

In this paper, the role of Al content in Ag/Al paste used for making screen printed contacts to B emitter is investigated. Five different Ag/Al pastes with varying Al content below <;5% Al were formulated. It is found that contact resistance decreased monotonically with the increase in Al content. In addition, a slight decrease in effective sheet resistance of boron emitter was observed for higher Al content paste, possibly due to some Al incorporation underneath the grid during contact formation. These two effects resulted in an increase in fill factor for higher Al content paste. However, increased Al content also resulted in wider grid line and lower aspect ratio, resulting in a slight decrease in Jsc and increase in grid line resistance. In addition, higher Al tends to increase emitter saturation current density (J_0e) and degrade junction quality. The competition between the fill factor and J_sc led to an optimum Al content, which produced basic n-type front junction cells with an average cell efficiency of 19.8% in this study.