Characterization of aluminium screen-printed local contacts

The formation of a Back Surface Field (BSF) during the alloying of a screen-printed aluminium paste with the silicon substrate is a critical step for the performance of solar cells. In this study, wafers with a locally contacted structure at the back side are investigated with Scanning Electron Microscope (SEM). An industrially feasible contacting technique is considered and a variation of the contact structure has been investigated. Moreover, a variation in the amount of screen-printed paste is proposed. Additionally, the effect of the crystallographic orientation of the grains on the electrical contacts is evaluated by investigating both mc and FZ samples. In conclusion, a model of the local contact formation is proposed. The understanding of the alloying dynamics allows the adaptation of the process in order to control the formation of the BSF layer.